Handbookof AluminumV o l u m e 7P h y s i c a l Me ta l l u rgy a n d P ro c e s s e sedited byGeorge E . T ot t enG. E. To tte n & As s o c i a te s , In c .Se a ttl e , Wa s h i n gto n , U.S.AD. S c o t t Mac KenzieHo u gh to n In te rn a ti o n a l In c o rpo ra te dV a l l e y Fo rge , P e n n s y l va n i a , U.S.A.M A R C E L D E K K E R , I N C . N E W Y O R K B A S E LLibrary of Congress Cataloging-in-Publication DataA catalog record for this book is available from the Library of Congress.ISBN: 0-8247-0494-0This book is printed on acid-free paper.HeadquartersMarcel Dekker, Inc.270 Madison Avenue, New York, NY 10016tel: 212-696-9000; fax: 212-685-4540Eastern Hemisphere DistributionMarcel Dekker AGHutgasse 4, Postfach 812, CH-4001 Basel, Switzerlandtel: 41-61-260-6300; fax: 41-61-260-6333World Wide Webhttp:==www.dekker.comThe publisher offers discounts on this book when ordered in bulk quantities. For moreinformation, write to Special Sales=Professional Marketing at the headquarters address above.Copyright # 2003 by Marcel Dekker, Inc. All Rights Reserved.Neither this book nor any part may be reproduced or transmitted in any form or by anymeans, electronic or mechanical, including photocopying, microlming, and recording, orby any information storage and retrieval system, without permission in writing from thepublisher.Current printing (last digit):10 9 8 7 6 5 4 3 2 1PRINTED IN THE UNITED STATES OF AMERICAPrefaceAlthough there are a limited number of reference books on aluminum metallurgy,there is a signicant and continuing need for a text that also addresses the physicalmetallurgy of aluminum and its alloys and the processing of those alloys that will beof long-term value to metallurgical engineers and designers. In addition, a number ofvitally important technologies are often covered in a cursory manner or not at all,such as quenching, property prediction, residual stresses (sources and measurement),heat treating, superplastic forming, chemical milling, and surface engineering.We have enlisted the top researchers in the world to write in their areas of spe-cialty and discuss critically important subjects pertaining to aluminum physicalmetallurgy and thermal processing of aluminum alloys. The result is an outstandingand unique text that will be an invaluable reference in the eld of aluminum physicalmetallurgy and processing.This is the rst of two volumes on aluminum metallurgy and some of the topicsinclude: Pure aluminum and its properties. An extensive discussion of the physical metallurgy of aluminum, includingeffect of alloying elements, recrystallization and grain growth, hardening,annealing, and aging. Sources and measurement of residual stress and distortion. An overview of aluminum rolling, including hot rolling, cold rolling, foilproduction, basic rolling mechanisms, and control of thickness and shape. A detailed discussion of extrusion design. A thorough overview of aluminum welding metallurgy and practice.iii Casting, including design, modeling, foundry practices, and a subject oftennot covered in aluminum metallurgy bookscasting in a microgravityenvironment. Molten metal processing and the use of the Stepanov continuous castingmethod. Forging design and foundry practice. Sheet forming. An overview of equipment requirements and a detailed discussion of heattreating practices. An in-depth discussion of aluminum quenching. An overview of machining metallurgy and practices, including materialproperty dependence, machining performance process parameters, anddesign. An extensive, detailed, and well-referenced overview of superplasticforming. A thorough discussion of aluminum chemical milling, including pre-maskcleaning, maskant applications, and scribing, etching, and demasking. Powder metallurgy including: applications, powder production, part pro-duction technologies, and other processes.The preparation of this book was a tremendous task and we are deeplyindebted to all our contributors. We would like to express special thanks to AliceTotten and Patricia MacKenzie for their assistance and patience throughout the pro-cess of putting this book together. We would also like to acknowledge The BoeingCorporation and Houghton International for their continued support.George E. TottenD. Scott MacKenzieiv PrefaceContentsPreface iiiContributors ixPart One ALUMINUM PHYSICAL METALLURGYAND ANALYTICAL TECHNIQUES1. Introduction to Aluminum 1Alexey Sverdlin2. Properties of Pure Aluminum 33Alexey Sverdlin3. Physical Metallurgy and the Effect of Alloying Additionsin Aluminum Alloys 81Murat Tiryakio gglu and James T. Staley4. Recrystallization and Grain Growth 211Weimin Mao5. Hardening, Annealing, and Aging 259Laurens Katgerman and D. Eskin6. Residual Stress and Distortion 305Shuvra Das and Umesh ChandravPart Two PROCESSING OF ALUMINUM7. Rolling of Aluminum 351Kai F. Karhausen and Antti S. Korhonen8. Extrusion 385Sigurd Stren and Per Thomas Moe9. Aluminum Welding 481Carl E. Cross, David L. Olson, and Stephen Liu10. Casting Design 533Henry W. Stoll11. Modeling of the Filling, Solidication, and Cooling ofShaped Aluminum Castings 573John T. Berry and Jeffrey R. Shenefelt12. Castings 591Rafael Colas, Eulogio Velasco, and Salvador Valtierra13. Molten Metal Processing 643Riyotatsu Otsuka14. Shaping by Pulling from the Melt 695Stanislav Prochorovich Nikanorov and Vsevolod Vladimirovich Peller15. Low-g Crystallization for High-Tech Castings 737Hans M. Tensi16. Designing for Aluminum Forging 775Howard A. Kuhn17. Forging 809Kichitaro Shinozaki and Kazuho Miyamoto18. Sheet Forming of Aluminum Alloys 837William J. Thomas, Taylan Altan, and Serhat Kaya19. Heat Treating Processes and Equipment 881Robert Howard, Neils Bogh, and D. Scott MacKenzie20. Quenching 971George E. Totten, Charles E. Bates, and Glenn M. Webster21. Machining 1063I. S. Jawahir and A. K. Balajivi Contents22. Superplastic Forming 1105Norman Ridley23. Aluminum Chemical Milling 1159Bruce M. Grifn24. Powder Metallurgy 1251Joseph W. NewkirkAppendixes1. Water Quenching Data: 7075T73 Aluminum Bar Probes 12832. Type I Polymer Quench Data: 2024T851 Aluminum Sheet Probes 12853. Type I Polymer Quench Data: 7075T73 Aluminum Sheet Probes 12864. Type I Polymer Quenchant Data: 7075T73 Aluminum Bar Probes 1287Index 1289Contents viiContributorsTaylan Altan, Ph.D. Ohio State University, Columbus, Ohio, U.S.A.A. K. Balaji, Ph.D. The University of Utah, Salt Lake City, Utah, U.S.A.Charles E. Bates, Ph.D., F.A.S.M. The University of Alabama at Birmingham,Birmingham, Alabama, U.S.A.John T. Berry, Ph.D. Mississippi State University, Mississippi State, Mississippi,U.S.A.Niels Bogh, B.Sc. International Thermal Systems, Puyallup, Washington, U.S.A.Umesh Chandra, Ph.D. Modern Computational Technologies, Inc., Cincinnati,Ohio, U.S.A.Rafael Cola s, Ph.D. Universidad Auto noma de Nuevo Leo n, San Nicola s de losGarza, MexicoCarl E. Cross, Ph.D. The University of Montana, Butte, Montana, U.S.A.Shuvra Das, Ph.D. University of Detroit Mercy, Detroit, Michigan, U.S.A.D. Eskin, Ph.D. Netherlands Institute for Metals Research, Delft, The NetherlandsixBruce M. Griffin, B.S.M.E.T., M.S.M.E. The Boeing Company, St. Louis,Missouri, U.S.A.Robert Howard, B.Sc. Consolidated Engineering Company, Kennesaw, Georgia,U.S.A.I. S. Jawahir, Ph.D. University of Kentucky, Lexington, Kentucky, U.S.A.Kai F. Karhausen, Ph.D. VAW Aluminium AG, Bonn, GermanyLaurens Katgerman, Ph.D. Netherlands Institute for Metals Research, Delft, TheNetherlandsSerhat Kaya, M.Sc. Ohio State University, Columbus, Ohio, U.S.A.Antti S. Korhonen, D.Tech. Helsinki University of Technology, Espoo, FinlandHoward A. Kuhn, Ph.D. Scienda Building Sciences, Orangeburg, South Carolina,U.S.A.Stephen Liu, Ph.D. Colorado School of Mines, Golden, Colorado, U.S.A.D. Scott MacKenzie, Ph.D. Houghton International Incorporated, Valley Forge,Pennsylvania, U.S.A.Weimin Mao, Ph.D. University of Science and Technology Beijing, Beijing, ChinaKazuho Miyamoto, Dr.Eng. Miyamoto Industry Co. Ltd., Tokyo, JapanPer Thomas Moe, M.Sc.-Eng. Norwegian University of Science and Technology,Trondheim, NorwayJoseph W. Newkirk, Ph.D. University of MissouriRolla, Rolla, Missouri, U.S.A.Stanislav Prochorovich Nikanorov, Dr.Sc. A.F. Ioffe Physical Technical Institute ofRussian Academy of Sciences, Saint Petersburg, RussiaDavid L. Olson, Ph.D. Colorado School of Mines, Golden, Colorado, U.S.A.Ryotatsu Otsuka, Dr.Eng. Showa Aluminum Corporation, Osaka, JapanVsevolod Vladimirovich Peller A.F. Ioffe Physical Technical Institute of RussianAcademy of Sciences, Saint Petersburg, RussiaNorman Ridley, B.Sc., Ph.D., D.Sc., C.Eng., F.I.M. University of Manchester,Manchester, Englandx ContributorsJeffrey R. Shenefelt, Ph.D. Mississippi State University, Mississippi State,Mississippi, U.S.A.Kichitaro Shinozaki National Institute of Advanced Industrial Science andTechnology, Tsukuba, JapanJames T. Staley, Ph.D.* Alcoa Technical Center, Alcoa Center, Pennsylvania,U.S.A.Henry W. Stoll, Ph.D. Northwestern University, Evanston, Illinois, U.S.A.Sigurd Stren, Ph.D. Norwegian University of Science and Technology, Trondheim,NorwayAlexey Sverdlin, Ph.D. Bradley University, Peoria, Illinois, U.S.A.Hans M. Tensi, Ph.D. Technical University of Munich, Munich, GermanyWilliam J. Thomas, Ph.D. General Motors, Troy, Michigan, U.S.A.Murat Tiryakiog lu, Ph.D. Robert Morris University, Moon Township,Pennsylvania, U.S.A.George E. Totten, Ph.D., F.A.S.M. G.E. Totten & Associates, Inc., Seattle,Washington, U.S.A.Salvador Valtierra, Ph.D. Nemak Corporation, Monterrey, MexicoEulogio Velasco, Ph.D. Nemak Corporation, Monterrey, MexicoGlenn M. Webster, A.A.S. G.E. Totten & Associates, Inc., Seattle, Washington,U.S.A.*RetiredContributors xi1Introduction to AluminumALEXEY SVERDLINBradley University, Peoria, Illinois, U.S.A.1 INTRODUCTION AND GENERAL OVERVIEWAluminum is the most heavily consumed non-ferrous metal in the world, with cur-rent annual consumption at 24 million tons. About 75% of this total volume, or18 million tons, is ``primary aluminum'' (that is, aluminum extracted from ore,as opposed to secondary aluminum which is derived from scrap metal processing).The ancient Greeks and Romans used alum in medicine as an astringent, and indyeing processes. In 1761 de Morveau proposed the name ``alumine'' for the base inalum. In 1807, Davy proposed the name aluminium for the metal, undiscoveredat that time, and later agreed to change it to aluminum. Shortly thereafter, the namealuminium was adopted by IUPAC to conrm with the ``ium'' ending of mostelements. Aluminium is the IUPAC spelling and therefore the internationalstandard. Aluminium was also the accepted spelling in the United States until 1925,at which time the American Chemical Society decided to revert back to aluminum,and to this day Americans still refer to aluminium as ``aluminum''.While the opportunities are growing, aluminum must continue to compete withvarious materials that offer lower cost or other competitive advantages. Aluminumcompanies must continue to innovate to provide customers with better enablingtechnologies and superior materials with unique properties. Aluminum manufac-turers must explore new process technologies to drive down production costsand make aluminum more competitive. Over the next two decades, investmentin research and technology development may likely be the most important factorin product competitiveness.The process of primary aluminum production can be divided into three inde-pendent stages which are, as a rule, carried out at different plants. These are:1. The actual mining of the necessary raw materials (bauxite and a variety ofother ores);. The processing of the ore and preparation of aluminum oxide (alumina);. Production of primary aluminum from alumina.World production of primary aluminum totaled 18.056 million metric tons in1991 [1]. In 1983, more than 70% of the world's bauxite was produced in Australia,Guinea, Jamaica, Brazil, and the former Soviet Union. Bauxite reserves in theUnited States are less than 1% of the world total (Table 1).Over the decade, 1983^1993, world production increased 20.3%, and annualgrowth rate of more than 2.0%. The United States accounted for 22.8% of theworld's 1993 production while the European Community accounted for 12.5%.The Republics of the former Soviet Union accounted for 21.0%. The others 43.6%include Asia (11.6%), Canada (10.1%), South America (9.9%), Oceania (8.5%),and Africa (3.4%). The total U.S. supply in 1991 was 8,020 thousand metric tons,with primary production representing about 51.3% of total supply, imports account-ing for 17.4%, and secondary recovery representing 31.2%.World primary aluminum production from 1981 through 1991 is shown in Fig.1. In 1995, U.S. primary aluminum smelters produced 3.375 million metric tons ofaluminum, 17.3% of the total world production of 19.442 million metric tons (Fig.2). Production of primary aluminum in 1996 in the United States was reportedto be 3.577 million metric tons, an increase of about 6% over 1995. Recycling isa critical component of the aluminum industry; in 1995, secondary reners recovered3.188 million metric tons of recycled aluminum, representing a little more thanone-third of the total U.S. aluminum supply of 9.265 million metric tons [2].The world aluminum industry is composed of six large integrated rms, theirsubsidiaries, or afliates Alcan Aluminum Ltd, Aluminum Company of America(Alcoa), Reynolds Metals Company, Kaiser Aluminum and Chemical Corporation,Pechiney, and Swiss Aluminum Limited (Alusuisse) and about 50 smaller publiclyFigure 1 World primary aluminum production from 1981 through 1991: 1. North America(a ^ United States; b ^ Canada); 2. South America; 3. Europe; 4. Africa; 5. Asia; 6. Oceania;7. World Total.2 SverdlinTable1WorldPrimaryAluminumProductionfrom1981through1991[1]YearsCountry19811982198319841985198619871988198919901991NorthAmerica56054339444453214782439248835478558556155951a.United44893274335340993500303733433944403040484121States11161065109112221282135515401534155515671830b.CanadaSouthAmerica78879593810481153138914861543169217831794Europe59985838601563306290647167166747681964456065Africa473500420410513554579591607616612Asia16821417139015951568148815771775199520122091Oceania53354469710011092111812561414150215421543WorldTotal1507913433139041570515398154121651717548182001801318056Introduction to Aluminum 3owned companies, and governments of centrally planned and market economycountries that control about 40%, 25%, 35% and of world aluminum productioncapacity, respectively [3]. U.S. primary aluminum metal production from 1893through 1990 is presented in Fig. 3 [4] and U.S. imports for consumption in Apriland 1999 year-to-date shown in Table 2 and Fig. 4. [5].Although the United States continues to be the leading producer of primaryaluminum metal in the world, its dominance in the industry has begun to wane.In 1960, the United States accounted for slightly more than 40% of the world'sproduction. In 1990, the U.S. share of world production had decreased to 23%. MostFigure 2 World primary aluminum production.Figure 3 U.S. primary aluminum production.4 Sverdlinof the restructuring of the world aluminum industry began in the late 1970s andcontinues to this day. Australia and Canada have emerged as major metal producers.Other countries entering the world market today are Brazil, China, Norway,Venezuela, and several countries in the Persian Gulf area [2].Another factor that should be considered in analyzing the domestic aluminumindustry is the growing importance of secondary aluminum to the domestic supplysituation. Secondary aluminum is dened as aluminum recovered from both newand old purchased scrap. New scrap generated by fabrication of aluminum productsFigure 4 U.S. imports for consumption of aluminum: April 1999 and Year-to-Datecross-section dimension not greater than 9.5 mm in coils. (a) Quantity, in Kilograms; (b)Customs Value, in Thousands of Dollars.Introduction to Aluminum 5may be either home scrap (sometimes called runaround scrap) or prompt industrialscrap. Home scrap is recycled within the company generating the scrap and conse-quently seldom enters the commercial secondary market. Prompt industrial scrap,however, is new scrap from a fabricator who does not choose to, or is not equippedto, recycle the scrap. This scrap then enters the secondary market. Old scrap isa product of obsolescence and becomes available to the secondary industry whenconsumer products have reached the end of their economic life and have been dis-carded. In 1960, 397,000 metric tons of aluminum was recovered from new andold scrap. In 1990, almost 2.4 million metric tons of aluminum was recovered frompurchased scrap. More than half of this secondary aluminum was recovered frompostconsumer, or old, scrap [1].By 2000, total U.S. aluminum demand, including primary metal, old scrap, andnonmetal uses, is expected to reach about 9.3 million metric tons, equivalent to anannual rate of growth of 3.2% from the 1983 level. The forecast range of domesticaluminum demand in 2000 is 6.4^13 million tons. Rest-of-the-world aluminumdemand in 2000 is expected to range from 29 to 56 million tons.The annual production of primary metal in the United States is expected todecline to about 4 million tons per year by 2000, and the remainder of the U.S.Table 2 U.S. Imports for Consumption of Aluminum: April 1999 and 1999 Year-to-Date(Customs Value, in Thousands of Dollars) (Units of Quantity: Kilograms)April 1999 1999 YTDCountry Quantity Value Quantity ValueWORLD TOTAL 200,237,195 249,906 528,455,522 699,432Australia 9,035,342 10,793 20,175,358 32,574Austria ^ ^ 2,489 5Bahrain 239,104 312 239,104 312Brazil 619,451 748 3,231,529 4,353Canada 57,287,283 73,741 200,313,608 267,738China ^ ^ 8,219,905 10,966Germany 238,594 310 274,266 1,091France 7,190 44 39,391 736India 1,517,506 1,839 1,792,797 2,342Ireland ^ ^ 3,074 6Japan ^ ^ 730 19Mexico 2,813 4 3,630 6Netherlands 20,504 28 21,978 31New Zealand 12,712,597 15,572 20,158,130 26,158Norway ^ ^ 18,5222 123Russia 101,602,508 124,494 225,620,083 292,072South Africa ^ ^ 7,278,263 9,080Tajikistan 2,252,476 3,379 15,124,748 18,040Turkey 21,000 21 21,000 21United Arab Emirates 222,333 289 421,234 564United Kingdom ^ ^ 85 6Venezuela 14,458,494 18,332 25,495,598 33,1916 Sverdlinmetal supply is expected to be obtained from other countries and the recycling of oldscrap.2 THE MAIN TYPES OF ALUMINUM ORESIn nature, aluminum does not exist as a metal because of the high chemical afnityfor oxygen. Aluminum compounds, primarily the oxide in forms of various purityand hydration, are widely distributed in nature. In these forms, aluminum is thesecond most plentiful metallic element on Earth silicon27.5%. It has been esti-mated that 8% of the Earth's crust is composed of aluminum. The elements are iron(approximately 5.0%), magnesium (approximately 2.0%), zinc and tin (0.004% each)[5^7], follow aluminum in content in the Earth's crust.Although aluminum is one of the most abundant materials in the Earth's crust(invariably as alumina or in some other combined oxide form) any usable ore depositmust be readily amenable to benece, so that a pure aluminum oxide can beobtained. However, physical benece of the oxides has not been very successful.Consequently chemical processing has always been necessary to extract purealumina from the other ingredients associated with it in the deposit. This, therefore,restricts the practical range of materials. Any chemical benece must be basedon selective removal of either the aluminum oxide or the other ingredients. However,frequently the other oxides are chemically similar, and this problem is compoundedby the amphoteric behavior of aluminum which makes it extremely difcult toselectively remove the impurities (or ``gangue''). Therefore benece processes areusually based on selective dissolution of aluminum oxide. Kinetically, dissolutionin strong caustic is favored. Therefore, mineralogical deposits which contain silicain structural forms that will readily dissolve in concentrated caustics, are unsatis-factory [8].Bauxites contain hydrated forms of aluminum oxide, and are thus the mosteconomically amenable mineralogical sources for chemical benece to producealumina. They occur in several different structural forms, depending on the numberof molecules of water of hydration and also the crystalline form. The name``Bauxite'' is derived from the village Les Baux in the south of France, wherethe mineral was rst commercially exploited [8].Historically, the commercial production of primary aluminum has been basedalmost entirely on the use of bauxite, in which aluminum occurs largely a hydratesof alumina. However, deposits containing aluminum in the other mineral formsare widespread and virtually inexhaustible. The average aluminum content ofthe Earth's crust has been estimated at 15.7% on an Al2O3 basis, and deposits con-taining more than 13% aluminum (25.0% Al2O3) are common [3].Information on bauxite reserves and resources ranges from reports based onthorough exploration for some deposits to reports giving only a total quantity esti-mate based on unspecied eld work for other deposits. The reserve andreserve-based estimates in Table 3 are the result of evaluating data and informationobtained from many sources. Salient bauxite statistics from 1945 through 2000 pre-sented in Fig. 5.Major deposits of bauxite are located in countries remote from the main alumi-num producing and consuming centers in North America and Europe. Most of thehigh grade bauxite deposits suitable for extraction of alumina occur in tropicalIntroduction to Aluminum 7Table 3 World Bauxite Resources, January 1985 [3] (Million Metric Tons of Bauxite)Region Reserves Reserve base*North America and Caribbean IslandsUnited States 38 40Dominican Republic 30 45Haiti 10 15Jamaica 2,000 2,000South AmericaBrazil 2,250 2,300Guyana 700 900Suriname 575 600Venezuela 235 240EuropeFrance 30 40Germany 2 2Greece 600 650Hungary 300 300Italy 5 5Romania 50 50Spain 5 5Former Soviet Union 300 300Yugoslavia 350 400AfricaCameroon 680 800Ghana 450 560Guinea 5,600 5,900Mozambique 2 2Sierra Leone 140 160Zimbabwe 2 2AsiaChina 150 150India 1,000 1,200Indonesia 750 805Malaysia 15 15Pakistan 20 20Turkey 25 30OceaniaAustralia 4,440 4,600Other 200 200Total 21,000 23,000*The reserve base includes demonstrated resources that are currently economic (reserves), marginally eco-nomic (marginal reserves), and some of those that are currently sub-economic (sub-economic resources)8 Sverdlinor semitropical regions. In all these deposits, the hydrated aluminum oxide isinvariably associated with small amounts of compound of iron, silicon and titaniumand trace amounts of other elements. Most of the tropical deposits are of ablanket-type which can be over 7 m thick and mined by open-cast methods.Inter-layered deposits and small pocket deposits are also found. Some of themare also amenable to open-cut mining. In physical appearance, the various bauxitedeposits can differ considerably. This is due to prior weathering, basic variationsIn the crystalline form of the hydrated aluminum oxide, and variations in the natureof impurities associated with it [8].Bauxite is found within 30 million-year-old weathered rock, which has brokendown to leave a high proportion of aluminum bearing minerals. A combinationof rainfall and organic acids caused the weathering of the dolomite and granite rocksuntil most of the elements are dissolved, leaving a reddish soil known as lateritewhich is rich in aluminum oxides and iron. The developed bauxite deposits are com-mon throughout the world. Pure alumina (Al2O3) can be reduced comparativelycheaper and easier from bauxite. From alumina, the metallic aluminum can bereceived by electrolysis [8^12]. However, the comparative limitation of bauxitedeposits and complex mining operations at many bauxite deposits have resultedthe necessity of development of other types of raw materials to extract aluminumprotably.The major deposits in central Arkansas were formed by weathering, duringEocene time, or nepheline syenite intrusive of Late Cretaceous age. The predominantaluminum oxide mineral in the bauxite is the trihydrate form, gibbsite. SomeFigure 5 Salient bauxite statistics.Introduction to Aluminum 9deposits are residual on the igneous rock and clay, while others are the result oftransportation and accumulation of eroded deposits. The composition of the oremined in Arkansas varies widely within a range of 40% to 52% Al2O3, 7% to17% SiO2, and 6% to 12% Fe2O3.The bauxite deposits in the coastal plain of Alabama and Georgia are found aslenses within at-laying beds of kaoinitic clay, which are overlain by sand and claysof early Tertiary age. The grade of the bauxite is 48% to 56% Al2O3, 12% to16% SiO 2, and less than 2.5% Fe2O3. The low iron oxide content qualies thisore for use in refractories and chemicals [3].In Jamaica, the bauxite deposits ll sinkholes, channels, and blanket unevendepressions in the karst surface of limestone of middle Tertiary age. Jamaican baux-ite is largely gibbsitic, although mixture containing up to 20% monohydrate aluminaoccur. Ore grade is 45% to 49% Al2O3, 0.8% to 8% SiO2, 17% to 22% Fe2O3, and2.5% TiO2. The bauxite deposits in the Dominican Republic and Haiti are similarin grade, age and genesis, and are identied as ``Jamaican type'' bauxites.Bauxite deposits in Suriname and Guyana are scattered throughout a narrowbelt extending along the contact between the Precambrian crystalline rocks ofthe Guyana Shield and the sedimentary beds of Tertiary or later age that formthe coastal plain. The alumina mineral is gibbsite and the ore is high grade: typically55% to 60% Al2O3, 2% to 5% SiO2, and less than 3% Fe2O3.In the large deposits discovered in northern Brazil since 1967, the bauxiteoccurs as a residual capping on dissected plateaus several hundred feet abovethe Amazon or other nearby rivers. The ore has developed on unconsolidatedTertiary sediments and is convert by 12^30 of kaolinitic clay. The approximate gradeafter washing is 55% Al2O3, 3.5% SiO2, and 11% Fe2O3.The Weipa bauxite deposit in Queensland, Australia, occurs in the upperportion of a at-laying laterite that extends for more than a hundred miles alongthe West Coast of the Cape York Peninsula. The bauxite ranges in thickness froma few feet to 30 ft and is covered by a soil overburden 1^3 ft thick. The depositsare associated with Tertiary kaolinitic sands, from which they were probablyderived. The grade of the beneciated bauxite is 53% to 58% Al2O3, 4% to 7% SiO2,and 12% Fe2O3.In Guinea, the large Sangaredi bauxite deposits occurs as laterite caps oninland plateaus at elevations of 900 ft or more above sea level. Most of the bauxiteis believed to have formed through weathering of schists and sand-stones ofDevonian or Post-Devonia Age. Typical ore contains 57% to 60% Al2O3, less than1% SiO2, and 2% to 4% Fe2O3.Many of the European bauxite deposits are associated with pockets anddepressions in the karst weathering surface of Mexozoic limestone beds that havebeen buried, folded, and faulted subsequent to the development of the bauxite.European bauxites are composed predominantly of monohydrate alumina minerals,although some gibbsitic deposits are mined in Hungary and a few other countries [3].Bauxites represent mountain rocks, the main component of which is aluminumoxide. Bauxite contains a large number of impurities such as silica, iron and titaniumoxides, and various other elements mostly in minor or trace amounts [13]. Theamount of free aluminum oxide can vary. Typical economic bauxite ores containgreater than 45% alumina, less than 12% iron oxides and less than 8% of combinedsilica. The bulk density of most bauxites is between 1.3 and 1.9 g/cm3. The general10 Sverdlinclassication of bauxite rocks based on their chemical structure can be represented inTable 4 [14^16].In various types of ores, free aluminum oxide is presented as a trihydrate(Al2O33H2O) which is crystallized in monoclinic crystallographic system or amonohydrate (Al2O33H2O) which is crystallized in orthorhombic crystallographicsystem.Silicon dioxide is the main harmful impurity in bauxites. It is present at theform of free silica or as a compound with other elements. In addition, bauxites havethe iron in the various forms. Besides the main chemical elements, bauxites containTi, S, Li, Cu, Ag, Au, Be, Zn, Sr, Cd, Ba, Sc, rare-earth elements such as B,Ga, Ge, Zr, Sn, Hf, Pb, P, V, Nb, Bi, Cr, Mo, Mn, Co, Ni, and U.Free moisture in crude bauxite may range from 5% to 30% [5]. In dried bauxite,most of the free moisture has been removed by heating crude bauxite in rotary dryingkilns at about 600

F. Calcined bauxite is heated in the kilns to 1700^1900

F toreduce 1 ton of calcined bauxite.Cell-grade alumina specications and typical specications for grades of baux-ite are presented in Table 5 and 6.The nepheline rocks are the second most important type of aluminum rawmaterial after bauxites. These rocks contain Na[AlSiO4] mineral. The theoreticalcomposition of nepheline is 35.7% Al2O3; 42.4% SiO2; 21.9% Na2O. There are manydifferent types of the nepheline rocks. They are rich with potassium only or withsodium and potassium. Nephelines crystallize in the hexagonal close-packed latticeof the pyramidal class. Normally they can be found as granular and solid mountainmass (massif). As crystals nepheline is seldom found. Usually nepheline has lightcoloring or it is colorless. Nepheline is rather easily dissolved in mineral acids withSiO2 forming a gel [17].In spite of that, aluminum in nepheline also contains silicon, the signicantcontents of alkalis in the composition of this mineral enables the opportunity toreduce from them an aluminum oxide and produce the by-products of sodiumTable 4 Minerals Commonly Found in BauxitesMinerals Chemical compositionGibbsite (hydragillite) o-Al2O3.3H2OBa ehmite o-Al2O3.H2ODiaspore [-Al2O3.H2OHematite o-Fe2O3Goethite o-FeOOHMagnetite Fe3O4Siderite FeCO3Ilmenite FeTiO3Anatase TiO2Rutile TiO2Brookite Al2O3.2SiO2.3H2OKaolinite Al2O3.2SiO2.2H2OQuartz SiO2Introduction to Aluminum 11carbonate and cement. Usually the nepheline rocks can be found as the mountainmasses in combination with alkaline rocks.Alunite is KAl3[SO4]2[OH]6 belongs to the group of the alkaline double sulfateof aluminum. It is also the important raw material for aluminum production. Thechemical composition of this ore can vary signicantly. Theoretical compositionof alunite is 37.0 wt% Al2O3; 11.4 wt% K2O; 38.6 wt% SO3; 13.0 wt% H2O. Inaddition to the compounds above, SiO2, CaO and Fe2O3 can be present.Alunite crystallizes in the tetragonal system. Usually it consists of smallcrystals with grayish, yellowish or reddish color. Due to the potassium and sulfurcontents, potassium fertilizers and sulfuric acid can be extracted.Disthene (kyanite) is a high quality raw material for electrothermal reductionof aluminum. The minerals of this group represent polymorphic modications ofTable 6 Typical Specications for Grades of Bauxite (Weight-percent, Maximum ContentUnless Otherwise Specied)Metal grade Refractory grade Abrasive gradeConstituent (dried Jamaican type) (calcined) (calcined)Al2O3 47.0* 86.5* 83.0*SiO 3.0 7.0 6.0Fe2O3 22.0 2.5 8.0TiO2 3.0 3.75 3.0^4.5**K2O + Na2O NS 0.2 0.7MgO + CaO NS 0.3 NSCaO NS NS 0.2MgO NS NS 0.4MnO2+Cr2O3+V2O5 2.0 1.0 1.0P2O5 1.5 NS 0.5Loss on ignition NS 0.5 1.0* Minimum** RangeNS No specicationTable 5 Cell-Grade Alumina Specications, in Weight-PercentImpurity Maximum content Impurity Maximum contentSiO2 0.015 B2O3 0.001Fe2O3 0.015 TiO2 0.002MnO 0.002 P2O5 0.001NiO 0.005 MgO 0.002Cr2O3 0.002 CaO 0.040CuO 0.010 Na2O 0.400V2O5 0.002 K2O 0.005ZnO 0.010 Chloride, residual 0.050Ga2O3 0.020 ^ ^12 Sverdlinthe substance with the chemical formula of AlOAl [SiO4]. Theoretical chemical com-position is 63.2% Al2O3 and 36.8% SiO2.Disthene crystallizes in the triclinic lattice. Most frequently disthene crystalshave light-blue, grayish-blue, least often yellow or brown color and glassy glance.Anisotropy of hardness and coloring were noticed on disthene crystals. So on a plane(100) in a direction hardness is equal 4.5 and along a direction !010) is 7.0.Coloring along the base plane is olive-green, and through lateral planes isredish-brown.Table 7 [8] summarizes the basic differences of the three fundamental forms ofbauxite which occur, namely gibbsite, ba hmite and diaspore. It is seen that the lattertwo are in the monohydrate form, whereas the former is a trihydrate. The twomonohydrate forms give rise to different structural forms of alumina on rapiddehydration, while they also exhibit different solubilities in caustic soda. Gibbsitedissolves much more readily. In caustic soda (having a higher solubility as wellas dissolving faster), but it has a lower intrinsic alumina content. The conditionsfor the dissolution of the alumina hydrate will vary for the different structural forms,and also depend on caustic soda concentration and temperature.Many of the deposits currently being mined have a dominance of gibbsite(trihydrate), but they often have a signicant proportion of a monohydratecrystalline form also. Therefore, the chemical processing must be a compromisebetween the optimum conditions for each of the two types. This is particularlyso for the extensive bauxites occurring in the northern area of Australiawhichis the main supplier for the present world market.As already mentioned, the main impurities are compounds of iron, silicon andtitanium. The iron compounds occur chiey in the form of haematite (Fe2O3),siderite (FeCO3) and goethite (FeOOHnH2O). The silicon compounds occurs inthe various structural forms of quartz as well as hydrated double salts with aluminasuch as kaolinite and halloycite (Al2O32SiO23H2O). Generally titanium occursin, the form of rutile (TiO2), but it can also be present in small amounts as ilmeniteor anatase. The compounds of iron and titanium are insoluble in caustic solutionsand therefore present no problem for the selective dissolution of the aluminum oxide.The silicon occurring as quartz does not present a serious problem either, since it hasTable 7 Comparison of Bauxites [8]GibbsiteBauxite type (Hydragillite) Ba hmite DiasporeComposition Al2O3.3H2O Al2O3.3H2O Al2O 3.3H2OMaximum alumina content, wt % 65.4 85 85Crystal system Monoclinic Orthorhombic OrthorhombicDensity, g/cm32.42 3.01 3.44Temp. for rapid dehydration (

C) 150 350 450Solubility of Al2O3 (g/l) in 100 g/lNa2O aqueous solution at 125

C105 45 VirtuallyinsolubleIntroduction to Aluminum 13only a limited solubility in the caustic soda solution used. This contrasts with thecombined forms (kaolinite and halloycite) which readily c solution. The dissolutionof silica leads to a reduction in the yield of the extracted alumina, and thereforethe soluble desirable. Consequently the silica content is usually referred to as reactiveor unreactive, depending on its tendency. Table 8 summarizes a range of compo-sitions predominantly containing gibbsite [8].3 REDUCTION OF ALUMINUMModern-day aluminum production involves two independent industrial processesfor the transition from the naturally occurring aluminum oxide ores to the extractedmetal (Fig. 6) [18]. The reduction of aluminum oxide to aluminum includes two mainstages:. production of an aluminum oxide (alumina) from aluminum ores. It can bedone by different chemical methods.. Production of aluminum from an aluminum oxide by electrolysis with fusedsodium aluminum uoride (Na3AlF6) commonly called cryolite[6,8,14,18^20].3.1 Production of Aluminum Oxide from Bauxites3.1.1 The Bayer ProcessAll commercially produced alumina from bauxite is obtained by a process patentedby Karl Bayer in 1888 (German Patent 43,977). The Bayer process involves a causticleach of the bauxite at elevated temperature and pressure, followed by separation ofthe resulting sodium aluminate solution and selective precipitation of the aluminumas the hydrated aluminum oxide (Al2O3 3H2O).Alumina (aluminum oxide) is white powder produced from bauxite ores bytreating them with caustic soda in the Bayer process (Fig. 7) [8]. The actualprocessing conditions such as the leach temperature, holding time, and caustic con-centration, as well as the costs, are inuenced by the type of bauxite to be processed.Table 8 Typical Compositions from Different Bauxite Deposits (in Weight %) [8]African Gold British Darling Ranges WeipaOxides* Coast Guyana (Western Australia) Greece (Australia)Al2O3 55.2 61.1 30^35 available 60.2 57.0SiO2 2.0 5.0 1^2 reactive SiO2 3.1 5.018^22 quartzFe2O3 11.5 1.5 20.0 21.7 7.5TiO2 2.1 2.5 ^ 3.0 2.5Ignition loss 29.3 30.0 20.0 11.7 27.0*Balance, minor impurities which include MgO,V2O5, P2O5, Ga2O3, CaO, ZrO2, MnO, Cr2O3, ZnO, organicmaterials, etc.14 SverdlinAs a result, a Bayer alumina plant is designed to treat a specic bauxite and cannotuse a bauxite that is too different from the one the plant was designed to use, withoutmajor plant modications [3].The Bayer process is initiated by mixing crude bauxite with preheated spentleach solution. Lime is added during this initial step to control the phosphorus con-tent and to increase the solubility of alumina. The resulting slurry, containing40% to 50% solids, is pumped with additional caustic leach solution to pressurizeddigesters where high-pressure steam is used to raise the temperature. Aluminaand some of the silica are dissolved during this step, soluble sodium aluminateis formed, and a complex sodium aluminum silicate is precipitated.The technological scheme of the Bayer bauxite processing method consists ofseveral operations. Bauxite coming from a mine is dried, and progressively crushed.Then it is placed into an autoclave with a NaOH solution at 230

C and higher thanatmospheric pressures.Digestion, in tanks 10^15 ft in diameter and up to 90 ft high, takes up to 5 hr.Leaching temperatures range form about 140

C to about 323

C, with correspondingpressures ranging from about 60 psi to over 1000 psi. The lower temperature rangesare used for bauxites in which nearly all of the available alumina is present asgibbsite. The higher temperature is needed to digest bauxite having a large percent-age of ba ehmite. Caustic concentration of the spent leach solution, expressed asFigure 6 Flow-sheet for aluminum production from alumina.Introduction to Aluminum 15grams per liter of sodium carbonate (Na2CO3), averages about 200 g/l for gibbsiticbauxite and about 300 g/l for bauxites with a high ba ehmite content.Bauxites arrive on chemical processing without the preliminary mechanicalenrichment. This process involves digesting bauxite at high temperatures withcaustic soda which dissolves the alumina leaving iron oxide and silicates as wasteproducts (red mud). This is accomplished by the following chemical reactionAl(OH)3(sol) aoH(liq)==aAlO2(liq) H2OThe resulting slurry of sodium aluminate solution and insoluble red mud from thedigesters is cooled to atmospheric boiling temperature, and a coarse sand wastefraction is removed by gravity separators or wet cyclones. The ne solids in thered mud are then separated by decantation of the overow in setting tanks measuringabout 15 ft in depth and 50^125 ft in diameter [3].2aAlO2 4H2O = 2 aOHAl2O3 3H2OFigure 7 The ow-sheet of the Bayer process.16 SverdlinThe claried sodium aluminate liquor is cooled until it becomes super-saturated, then seeded with ne crystals of alumina trihydrate. The alumina is pre-cipitated as the trihydrate, separated by sedimentation or ltration, and washed.The spent leach solution containing caustic soda is regenerated in the precipitationstep, and together with the alumina remaining in solution, is recycled to the digesters.The ltered and washed alumina trihydrate is calcined for use in making metal.Al2O3 3H2O = Al2 H2OTwo forms of calcined alumina are used to produce aluminum. EuropeanBayer plants have traditionally produced a ne-grained highly calcined, ouryalumina while North American Bayer plants have always produced a coarsergrained, porous, sandy alumina that has not been totally calcined to the alphaalumina. The red mud contains Fe2O3, TiO2, the sodium aluminosilicate, and a smallquantities of other metal oxides. Because the complex represents a loss of bothalumina and soda a low reactive silica content in the bauxite is desirable. The lossof soda is made up by adding caustic soda or soda ash and lime to the spent leachsolution to bring it up to the appropriate caustic concentration before it is recycled.The liquor is washed out and is separated from the red mud. The liquor isltered and then a small amount of aluminum hydroxide is introduced and slowlymixed. As a result, aluminum oxide is precipitated, from the aluminate solution.The precipitated trihydrate (aluminum hydroxide) is ltered and is thencalcined in a rotary kiln at 1200^1300

C to remove the water of hydration andto leave the alumina in a form suitable for use in the electrolytic production ofaluminum.Invariably, the alumina prepared by the Bayer process has small amounts ofimpurities associated with it and typical impurity levels are summarized in Table9 [8].Variations in impurity levels will occur with different ore types, but the valuesshow that a fairly high quality material is produced in the Bayer process. Someof the sodium oxide will be as sodium aluminate, and the small amounts of calciumoxide are present by virtue of the technology used to reconstitute the sodiumhydroxide liquor for the extraction stage. This method is used for processing of highquality bauxites only.Table 9. Typical Impurities in Commercial Hydrated and Calcined Alumina [8]Percentage impurityImpurity Dried alumina trihydrate Normal calcined aluminaSiO2 0.020 0.03Fe2O3 0.015 0.02Na2O 0.250 0.50CaO 0.030 0.05Loss on ignition 34.700 0.80Moisture (free) 0.400 ^Introduction to Aluminum 173.1.2 The Production of Alumina from Bauxites with the Higher SiliconContentThe production of alumina (aluminum oxide) from bauxites with the higher siliconcontent (from 8% to 15% silica) and other inclusions from aluminum raw materialsis carried out by the agglomeration [14,18]. This combination process has been devel-oped by Alcoa. In this process, the bauxite is mixed with the limestone and thesodium carbonate. The mixture agglomerates in rotary furnaces at 1200^1300

C.In the agglomeration process the sodium carbonate reacts with aluminum oxide for-ming the sodium aluminate:Al2O3 a2CO3 = 2aAlO2 CO2.The received aluminum oxide is crushed and leached by water or a soda solution. Asa result aluminum passes into a solution. The non-soluble red mud is separated fromit. Then a solution free from silicon dioxide is produced by heating with a lime in anautoclave at 160

C. The silicon dioxide precipitates out as non-soluble calciumsilicate (white mud). The calcium silicate is separated from the liquor by ltration.The resulting liquor precipitates aluminum hydroxide by passing carbon dioxidethough the liquor:2aAlO2 3H2OCO2 = 2Al(OH)3 a2CO3.Formed aluminum hydroxide has been separated by ltration, then washed outand calcined for alumina production. Extraction alumina by an agglomerationmethod accounts for 90% of total alumina products. A portion of the washedalumina may be left in the trihydrate form for chemical uses or it may be furtherprocessed under controlled conditions to produce a variety of chemical alumina,such as activated or tabular alumina for uses other than metal production.3.1.3 The Combine Method (Bayer Process with Agglomeration)For processing high silicon content bauxites sometimes, it is expedient to apply acombination of a Bayer process with the method of agglomeration [8]. The combi-nation of the Bayer process and agglomeration process improves the technologicalcycle of processing bauxite and enables the use of low quality bauxites.In the former Soviet Union, alumina is extract from nepheline [(Na, K)AlSiO4]otation concentrates and other non-bauxitic materials containing about 30%alumina. Nepheline syenite has been mined at Belogorsk in Siberia and obtainedas a byproduct of apatite recovery from syenite deposits in the Kola Peninsula.3.1.4 Processing Method for Alumina from NephelineThe processing method for alumina from nepheline ores consists in the agglomer-ation of a charge comprised of nepheline concentrate and limestone into the rotatingfurnaces at the temperature of 1280^1310

C [8,18]. Calcium oxide of limestonereacts with nepheline. A cake consisted of bicalcium silicate and sodium aluminateis formed. A cake is leached by the sodium-alkali-aluminate solution which sodium18 Sverdlinand potassium aluminates pass into. Formed at the carbonization, aluminumhydroxide drops out into a deposit, and sodium carbonate and potash remain ina solution.2aAlO2 3H2OCO2 = 2Al(OH)3 a2CO3.Filtered and calcined aluminum hydroxide is a nal product from which pure alumi-num is extracted from. The process of extraction makes about 80% of Al2O3.Historically, a small tonnage of alumina has been extracted commercially inNorway from high-iron bauxites by the Pedersen process. In this process, bauxite,limestone, coke, and iron ore are smelted in an electric furnace to produce pig ironand calcium aluminate slag containing 30% to 50% alumina. The slag is leachedwith sodium carbonate solution, and alumina trihydrate was precipitated by carbondioxide. During World War II, the process was also used at a Swedish plant to treatandalusite (Al2SiO5).3.1.5 The Pechiney H-Plus ProcessIn Europe, the major development has been the process called the Pechiney H-Plusprocess. Developed by Pechiney in France the process consists of sulfuric acid leach-ing of the raw material, hydrocholric acid addition to the leach liquor andcrystallization of AlCl36H2O by saturation of the leach liquor with gaseousHCl [21]. The aluminum trichlorid precipitate is puried by dissolution andreprecipitation. The nal product is calcined to form alumina and to produceHCl for recycle. Successful laboratory scale development has been followed by apilot plant operation at 15^20 tons Al2O3 per day scale at Marseilles. Accordingto Cohen and Mercier [22], the alumina so produced has a higher purity than aluminaproduced from bauxite by the Bayer process. The process ow-sheet is shown in Fig.8. An analysis of the potential economics of the process indicated that, with heatrecovery, the total operating cost to produce alumina from coal shale would prob-ably be 1.15^1.4 times the cost of production from bauxite at 1978 bauxite andenergy prices.3.1.6 Technology for the Recovery of Metallurgical-Grade Alumina fromCoal AshLarge quantities of coal ash are produced in the United States every year bycoal-burning power-plants. In 1975, this amounted to 60 million tons, of which 42.4million tons was boiler slag [23]. (Fly ash is the ne material that is carried out of theboiler with the stack gases and is collected by precipitators. Bottom ash is coarsermaterial that falls through the grate, and boiler slag is the molten as that collectsat the bottom of slag tap boilers.)Fly ash, bottom ash, and boiler slag all contain signicant amounts of Al2O3and therefore can be considered as potential sources for the production ofmetallurgical-grade Al2O3. Typically, y ash contains from 15% to 30% SiO2,50% Fe2O3, up to 20% Al2O3, with the remainder containing alkali andalkaline-earth oxides plus some unburned carbon [24]. Fly ash cannot be considereda high-grade potential source of metallurgical-grade Al2O3 when compared with thelarge reserves of kaolinitic clays (35^40% Al2O3) and anorthosite (25^30% Al2O3)[25].Introduction to Aluminum 19Considerable economic benet would result if y ash could be physically ben-eciated to upgrade its Al2O3 content before being processed by extractivemetallurgical technique. A form of beneciation that has been studied is magneticseparation. Scientists in the former Soviet Union have applied this technique tothe ashes from a coal-gasication plant to produce a nonmagnetic fraction con-taining greater than 30% Al2O3 [26].Table 10 shows the calculated costs in the United States as of late 1976 toproduce 1 ton of Al2O3.Figure 8 Flow-sheet of the Pechiney H-Plus process.20 SverdlinOf the three general methods (alkaline-sinter process, acid-leach process,chlorination processes) examined for recovering metallurgical-grade Al2O3 fromcoal ash, sintering (lime or lime-soda) offers the most short-term potential. Ithas been demonstrated that Al2O3 can be produced by this procedure, and the incor-poration of a desilication step would possibly produce a grade of Al2O3 acceptable tothe aluminum industry. The major unresolved problem with lime sintering iseconomic. Coal ash is basically a low-grade source of Al2O3, and the reagentsand operating costs to conduct a high-temperature sintering operation are high.To be economically viable, the production of Al2O3 from coal ash by a sinteringprocess should be integrated with cement production.Direct acid treatment of coal ash does not appear promising. Some form ofpretreatment of the ash, such as reaction with limestone during power generation,may provide a means to improve the yield of Al2O3 during acid leaching.Dry chlorination of coal ash at high temperature is interesting because of theeffective conversion of the aluminum values of AlCl3. Dry chlorination expensivein money and energy to decompose [27].3.2 Production of Commercial Purity AluminumPrimary aluminum is produced by the reduction of alumina by electrolysis in amolten bath of natural or synthetic cryolite (Na3AlF6), which serves as an electrolyteand a solvent for the alumina.3.2.1 Electrolytic Reduction (Smelting)Commercial purity aluminum is manufactured mainly by electrolysis [28^32]. Theprocess used for the electrolytic reduction of alumina to the metal does not differfundamentally from the original process devised in 1889 by He r Uult and Hall.The main change being an increase in the size of each electrolytic cell [33].Table 10 Calculated Costs in the U.S. to Produce 1 Ton of Alumina [27]Process cost,Cost per ton,U.S. DollarsMaterial U.S. Dollars Fly ash BauxiteBauxite 16.00 ^ 41.32Fly ash ^ ^ ^Soda ash 55.00 11.55 4.12Limestone 5.00 58.50 0.38Lime 25.00 ^ ^Starch 220.00 ^ 1.10Coal 20.00 40.00 ^Oil 133.00 21.28 10.30Steam ^ 13.80 11.81Electricity (*) 16.50 1.08TOTAL 167.38 70.11*Cost of electricity was $0.015 per kilowatt-hourIntroduction to Aluminum 21Primary aluminum production is electricity-intensive. The current U.S. aver-age energy consumption for aluminum reduction is estimated to be 15.18 kWh/kgof aluminum. The lowest energy consumption that can be achieved today is about13.0 kWh/kg of aluminum for a line of modern, high-amperage reduction cells. Pro-duction cells normally have current efciencies ranging from 85% to 95%. Large,modern reduction cells operate with current efciencies of 94^96% [34].Figure 9 is a diagrammatic section of a multi-anode furnace from which themain points of construction can be seen. The outer casing consists of a brick-linedrectangular steel box which acts as container and support. Inside this box thecathode is constructed of baked carbon or graphite blocks, cemented together witha paste of ground coke and pitch, and of such a shape as to contain the bath ofelectrolyte. The electrolyte is largely molten cryolite or with additions of calciumuoride and aluminum uoride are made and alumina. A typical composition ofthis solution consists of cryolite 75^90%, alumina 2^8%, aluminum uoride upto 10%, calcium uoride 5%.The anode consists either of a number (as many as twenty) or pre-baked carbonblocks dipping into the molten electrolyte, or of a single massive Sa derberg electrode.Although there are two fundamental designs of anodes used in industrial aluminumelectrowinning, they are both formulated form similar materials and undergothe same type of reactions within the operating cell. For environmental reasons,there has been an increasing tendency to move to the ``pre-baked'' anodes, and there-fore the presentation of data and discussion of reactions will be biased towards thisform of anode. The Sa derberg type of electrode uses the waste heat of the furnaceto bake the anode paste in situ instead of this being done as a separate operationas with the pre-baked anodes.Figure 9 Schematic diagram of an electrolytic cell tted with a ``So//derberg'' anode.22 SverdlinElectrolysis of Aluminum Oxide (Figure 9)Aluminum oxide Al2O3 dissolves in molten cryolite Na3AlF6 at the temperature of950^970

C [7] and break down electrochemically by discharging aluminum cationson the cathode (the molten aluminum), and the acid-containing ions (oxygenions)on the graphite-carbonic anode. The molten cryolite dissociate on ionsNa and AlF36 :a3Al6==3a Al!36 and aluminum oxide----on complexions AlO2 ano AlO :Al2O3==AlO2 AlO. which are in balance with the simple ions:AlO2 ==Al3 2O2 . AlO==Al3 O2 .The reduction of trivalent aluminum is the predominant process occurring at thecathode:Al3 3e AlIn addition the incomplete discharge of the trivalent aluminum with the formation ofunivalent ions can take place: Al3 + 2e Al and discharge univalent ions withsettling of the metal:Al e Al.At the graphite anode there is the discharge of oxygen ions. The oxygenoxidizes carbon of the anode and is released as a mixture of CO2 + CO.The primary aluminum (raw aluminum) taken from an electrolyser containsthree groups of impurities: a non-metallic (uorine salts), such as a- and g-aluminumoxide, aluminum carbide and aluminum nitride, and graphite particles; metallicssuch as iron and silicon passing from raw materials, coal materials and structuralelectrolyzer elements; and gaseousmainly hydrogen formed as a result of electro-litic water dissociation.For simultaneous aluminum purication from non-metallic impurities andhydrogen, the ltration through a uxing lter with the adding blowing nitrogenis applied. As a result of such purication the contents of hydrogen in aluminumis reduced from 0.22 down to 0.16 cm3on 100 g of metal.The most effective method of simultaneous purication of aluminum fromsodium, hydrogen and non-metallic impurities, is by bubbling a gas mixture of nitro-gen with 2^10% Cl through the molten metal. This method of purication permits alower sodium content of 0.0003^0.001% at the total consumption of a gas mixturefrom 0.8 up to 1.5 m3/g of the metal [32].Future Developments in Hall^Heroult CellsWith the gains in productivity and cost reductions achieved over the past decadeallowing aluminum to remain a competitive commodity metal and meet the growthin world demand of 2^3% per year, the primary aluminum industry has becomecomplacent in searching for alternative processes. Intellectual energy has beenfocused on cost cutting and environmental concerns [43].Introduction to Aluminum 23Inert anodes have been the dream of aluminum producers from the beginning,and numerous materials have been tried. But there are no really inert materialsso far. In the cathode, prolonged cell life, a lower cathode voltage drop, stabilityover time, and more resistant sidewalls are needed. While a 1300 day life was accept-able 50 years ago, and 2000 day lives are acceptable today, cathode lives of more than3000 days will be demanded in the future. With the rise in use of graphitic blocks todecrease the cathode voltage drop, improved abrasion resistance is a necessarychallenge. One solution is a coating with TiB2 [43].There are signicant efforts to develop transition stable wetted cathodes andnonconsumable anodes. It looks as if aspects of designs for retrotted cells andadvances in material science will be resolved in industrial tests by 2005. In 1997,the Aluminum Association and the U.S. Department of Energy joined forces to fundfurther the search for materials for the inert anodes. From the present perspectives,meaningful pilot bipolar cells for liquid aluminum could be in progress by 2010at the earliest [43].There are challenges remaining in the section and management of the lining ofthe reactor. Even when the pure CO evolved in this process is reconverted to elec-trical energy, there is twice as much CO2 evolved as for the electrolytic process,although the unit energy is lower.Perhaps an alternative approach in extracting aluminum in the liquid statecould derive from what is being discovered about slurry electrolytes. In this method,solid aluminum, even if dendritic, could be electrodeposited on a rotating disccathode form a low melting (540^600

C) all-uoride electrolyte using anonconsumable anode. The solid aluminum would be removed within the fullyenclosed cell and transported to a melting furnace above 660

C where the solidaluminum and entrapped bath would be separated. In this concept, the bath isrecycled to the cell, and the now-liquid aluminum processed conventionally [43].3.2.2 The ALCOA Chloride ProcessIn January 1973 ALCOA [35] announced the development of a new aluminum elec-trolysis process. The process employs electrolysis of aluminum chloride dissolvedin alkali and alkaline earth chloride melts. Among the most favorable aspects ofthe process are reduced electrical energy consumption (*30%), less pollutionand more exible operation.The rst step of the ALCOA process is the production of very pure alumina bythe Bayer process. The two succeeding steps are the chlorination of alumina and theelectrolysis of the dissolved molten aluminum chloride. The resulting aluminumchloride is puried by passage through a special lter before resublimation in aninert gas. The alumina is then transported to a tank where it is stored in thecrystalline state. The cell used for the electrolysis consists of a steel mantle linedwith a thermally insulating, non-conducting refractory material which is notcorroded by the electrolyte.The total energy consumption of the process depends on the raw materialsused, e.g. bauxite versus pure alumina and petroleum coke versus carbon coke.While the Hall^He roult process has its uoride emission problem, the chlori-nation steps in the ALCOA process may result in chlorinated hydrocarbons beingformed. The economic potential for this process is strongly dependent on the costof producing AlCl3 in the chlorination step.24 SverdlinThe advantages of the ALCOA method is compared with electrolysis of thekryolite^aluminum oxide melt (Al2O3 dissolved in cryolite Na3AlF6) are: energysaving up to 30%; an opportunity of application Al2O3 with the higher silicon con-tent; substitution of cryolite by cheaper salts; reducing or completely eliminatingthe problem of uorine liberation.3.2.3 The Toth ProcessThis process is based on reduction of AlCl3 by Mn and bears the name of its inventorCharles Toth. Since 1968 the process has been described in several patents [24] andalso has received considerable publicity in the nancial and engineering press.The Toth process comprises four major steps:Step 1: at the temperature of 925

CAl2O3(in clay) 3C 3Cl2 = 2AlCl3 3COStep 2: at the temperature of 230

C2AlCl3 3Mn = 2Al 3MnCl2Step 3: at the temperature of 600

C2MnCl2 O2 = 2MnO2Cl2Step 4: at the temperature of 1750

CMnOC = Mn COThe total reduction considered being2Al2O3(in clay) 3O2 12C = 4Al 12COToth process is an indirect carbothermal reduction of alumina. Several types ofcheap minerals with Al2O3 contents as low as 30^40 wt%, for instance kaolinelabradorite and bauxite, are potential raw materials.Beside the potential use of low grade ore, the really favorable aspect of the Tothprocess is its presumably low demand of electrical energy, i.e. 5% of theHall^He roult process according to the inventor. It must be recognized, however,that the appreciable reduction in electrical energy is largely compensated by anincreased carbon consumption.A successful large-scale operation of the Toth process still remains to be dem-onstrated and considerable work has to be done before the nal answer to its poten-tial can be given.3.2.4 Aluminum Extraction from Anorthosite by Leaching withHydrochloric Acid and FluorideThe United States is more than 90% dependent on imported bauxite as a source foraluminum, but it has vast non bauxitic aluminum resources, such as kaolinite,anorthosite, alunite, etc. To reduce this dependence, the Bureau of Mines conceiveda raw materials-process technologies matrix as a means of systematicallyIntroduction to Aluminum 25investigating the technology options available for processing domestic aluminumresources [36]. Resources considered were clay, anorthosite, alunite, dawsonite con-tained in oil shale, and coal as and coal shale [25,37].Most of the research on alumina recovery from anorthosite was concentratedon the lime-soda-sinter process [38]. Anorthosite is sintered with soda ash andlimestone. Leaching, desilication, and precipitation steps are performed beforealumina is recovered as the trihydrate. The lime-soda-sinter process has two majordrawbacks:. In addition to mining anorthosite, large amounts of limestone and soda ashare required.. Sintering is performed at 1300

C, which consumes appreciable amounts ofenergy.Another method for recovering alumina from anorthosite is the melt-quenchtechnique [39] in which a charge of anorthosite is arc melted at approximately1650

C and then rapidly cooled. The resulting amorphous product is amenableto alumina extraction by acid. Because of their crystalline structure, aluminumsilicates, such as anorthosite, are not readily attacked by a mineral acid unlessthe crystalline structure is altered. Acid in conjunction with the uoride ion disruptsthe silicate structure sufciently so that acid leaching is effective in extracting thealuminum content.Anorthosite is a rock composed mainly of calcium-rich plagioclase. Anortho-site resources of the United States are estimated at 599 billion tons averaging27% Al2O3 [25]. Large anorthosite deposits are located in Minnesota, New York,Wyoming, and California. Chemical analysis of the anorthosite is the following:29.3% Al2O3, 2.0% Fe2O3, 11.5% CaO, 0.15% TiO2, 51.4% SiO2, 5.1% Na2O, 0.29%K2O, 0.26% MgO.Excellent aluminum extractions were obtained from Wyoming anorthosite bycountercurrent leaching with hydrochloric acid and uoride ion. The model (Fig.10) schematically illustrates simulated three-stage countercurrent leaching by aseries of batch tests. Fresh HCl leachant moves downwards; anorthosite ore movesto the right. The two upper rows prepare leaching acid for use in the bottom row,where ore is contacted by acid of increasing strength. Since the spent liquors fromthe initial rst and second rows are not utilized in the stages immediately below,they are discarded. Fluoride was added to the fresh leaching acid. H2SiF6, Na2SiF6,and CaF2 were used as sources of uoride, and at equivalent amounts of uorideaddition no difference was noted in their effect. Retention time for each stagewas 2 h, or a total leach time of 6 h.The leaching process eliminates the energy-intensive step of high-temperaturecalcination. Countercurrent leaching resulted in a more efcient use of acid anduoride than single-stage leaching. Ninety percent of the aluminum values wereextracted with 95% of stichiometric HCl requirement and a F/Al ratio of 0.27.If acid concentration is increased, the uoride addition can be decreased.3.2.5 Alternative Methods of ProductionDespite several disadvantages, the electrolytic method for the production of alumi-num is still the only process practiced on an industrial scale. The main drawbacksare:26 Sverdlin. the very large size of the economic unit. the employment of low voltage D.C. as a source of energy. the additional capital investment in the alumina factoriesContinued efforts have been made to devise a process that would be free fromthese problems, and recently a certain amount of progress has been made. It is com-paratively simple to reduce crude bauxite in an electric furnace with carbon, butthe result is an alloy of aluminum with iron and silicon, which must be puried.Two methods are available: in one the aluminum is dissolved in a suitable solvent,e.g. Zn, Mg, or Hg, the impurities ltered off, and the solvent recovered bydistillation, in the other, which has been operated on a pilot scale in Canada,the aluminum is volatilized as a sub-halide. The Al-Fe-Si alloy is treated with alumi-num chloride at 1000^1200

C at atmospheric pressure. The resulting sub-chloride,AlCl, is passed to a condenser where the aluminum is deposited according tothe reaction:3AlCl ==2Al AlCl3The aluminum chloride is recycled.Another method which has reached pilot plant stage in France depends on thereduction of pure alumina with carbon, and instead of capturing the aluminum vaporin another metal and so obtaining an alloy, the vapor is captured, and re-oxidationprevented, with aluminum carbide. The two reactions:Al2O3 3C = 2Al 3COand2Al2O3 9C = C3Al4 6COFigure 10 Diagram of simulated, three-stage countercurrent leaching.Introduction to Aluminum 27proceed simultaneously, and under the right conditions at 2400

C an alloy of alumi-num and the carbide is obtained which may contain as much as 80% aluminum. This,on cooling, deposits the carbide, which can be separated by uxing with fusedchlorides. The carbide is recycled.None of these methods saves energy in comparison to the electrolytic method,but they do open up the possibility of working smaller units, with lower capitalinvestment.4 PRODUCTION OF SUPER PURITY ALUMINUM (REFINEMENT)The production of superpurity aluminum, 99.99+% purity, requires special pro-cedures, such as a continuous electrorening of commercially pure aluminum ina Hoopes cell.The electrolitic renement of aluminum carries out by the three-layer method[7,19,40]. For this purpose there are three layers available into the electrolizer (Fig.11). The bottom layer serves as the anode. It represents a rened (puried) aluminumalloy with copper. Copper is introduced to increase the density of a layer. An averagedensity layer is the molten electrolyte. Its density is less than the density of an anodealloy and higher than one of puried (cathode) aluminum which is above an elec-trolyte (a molten top layer).At anode dissolution more electropositive impurities than aluminum such asFe, Si, Ti, Cu, and other, remain in an anode alloy. Aluminum is dissolved onlyat the anode. It goes into electrolyte in the form of metal ions Al3:Al 3e Al3Figure 11 Super-purity rening furnace.28 SverdlinDuring the electrolysis, ions of aluminum are transferred to the cathode:Al3 3e Al.As a result, a layer of the molten puried aluminum is accumulated on the cathode.More electronegative impurities than aluminum such as Ba, Na, Mg, Ca can bedissolved electrochemically on the anode. These ions report to the electrolyte.Because of the small amount of electronegative impurities in the raw aluminumthey have not accumulated to a great extent in the electrolyte. The discharge of theseions on the cathode does not practically occur because their electrode potential ismore electronegative than aluminum.The uoride^chlorine electrolyte is more common for this process The chemi-cal composition of it is 55^60% BaCl2, 35^40% AlF4 + NaF and up to 4.0% NaCl.Mole ratio NaF/Al3 is 1.5^2.0; The melting point of the electrolyte is 720^730

C.The temperature of the electrolysis is approximately 800

C. The electrolyte densityis 2.7 g/cm3.The anode alloy is prepared from the primary aluminum and pure copper(99.90^99.95% Cu) which is introduced into the metal in quantity of 30^40% [7].The density of a liquid anode alloy of such composition is 3.0^3.5 g/cm3. Densityof pure molten cathode aluminum is 2.3 g/cm3. Purity of aluminum rened bythe three-layer method is 99.95%. Purity is determined based on the quantity of vemain impurities such as Fe, Si, Cu, Zn, Ti.On evidence derived from [6] rened aluminumhas the following composition:Fe ^ 0.0005^0.002%; Si ^ 0.002^0.005%; Cu ^ 0.0005^0.002%; Zn ^ 0.0005^0.002%;Mg ^ traces; Al ^ other. Rened aluminum usually processes into a semi-nishedproduct of the specied above composition or alloyed by magnesium.4.1 Production Extreme Purity Aluminum4.1.1 Zone MeltingThe principle of zone melting consists of repeated passing of a melted zone along analuminum ingot [7]. The impurities decreasing the melting point aluminum atthe zone melting are concentrated in the molten zone and are transferred to theend as an ingot. These impurities are Ga, Sn, Be, Sb, Ca, Th, Fe, Co, Ni, Ce,Te, Ba, Pt, Au, Bi, Pb, Cd, In, Na, Mg, Cu, Si, Ge, Zn. The impurities increasingthe melting point are concentrated in a solid (initial) part of an ingot. Theseimpurities are Nb, Ta, Cr, Ti, Mo, V. The impurities such as Mn and Sc do notchange the melting temperature of aluminum and are not removed at the zonemelting.Aluminumhas signicant chemical activity. Therefore, zone melting should becarried out in a vacuum or in an atmosphere of inert gas (argon or helium). Duringthe zone melting in a vacuum, extreme purity of aluminum can be achieved becausesome impurities ``volatilize.'' Typical elements that volatilize are Mg, Zn, Cd, alka-line and alkaline-earth metals.Introduction to Aluminum 29By zone melting with several consecutive cycles, it is possible to achieve verypure aluminum [41]. The initial material of each new cycle is the purest part ofan ingot received at the previous cycle. The purity of received aluminum is deter-mined based on the difference of the main impurities such as Si, Fe, Mg, Mn,Ti, Cu, Cr, Zn, Na, V making up more than 99.9999%.Another method of achieving extreme purity aluminum is rened electrolysis ofpure or commercial pure aluminum [6]. Complex aluminorganic aluminum com-pounds are applied as the electrolyte. Electrolysis does at 100

C between solid alumi-num electrodes. The composition of electrolyte can differ. For example, in [42],electrolysis of 50% solution of NaF 2Al(C2H5)3 in toluene is applied. Using thismethod, the metal purity of 99.999^99.9999% can be achieved.REFERENCES1. J. R. Devis, Ed. Aluminum and Aluminum Alloys, ASM International, 1993.2. Aluminum Industry Technology Roadmap, May 1997, The Aluminum Association, Inc.,in conjunction with the U.S. Department of Energy. A report.3. F. X. McCawley and L. H. Baumgardner, ``Aluminum'', Mineral Facts and Problems,1985 Edition, United States Department of the Interior.4. http://minerals.usgs.gov/minerals/pubs/commodity/aluminum/stat/tb12.txt.5. Aluminium properties, physical metallurgy and phase diagrams. American Society forMetals, Metals Park, Ohio, 1967, p. 530.6. Aluminium-Tashcenbuch, Aluminium-verlag GMBH, Dusseldorf, 1974, p. 663.7. I.N. Fridlyander, Physical Metallurgy of Aluminium and Its Alloys, Moscow, 1983, p.287 (in Russian).8. K. Grjotheim and B. J. Welch, Aluminum Smelter Technology, A Pure and AppliedApproach, Aluminium-Verlag GMBH, Dsseldorf, 1997.9. A. S. Russell, ``Developments in Aluminum Smelting, Alum. and Suppl.'' June 1981,57(6), pp. 105^109.10. A. I. Belyaev, M. B. Rapoport, and L. A. Firsanova, Electrometallurgia Aluminia,Moscow-Leningrad, 1938 (in Russian).11. V. P. Mashovets, Electrometallurgia Aluminia, Moscow, 1953 (in Russian).12. J. D. Edwards, F. C. Frary, and Z. Jeffries, New York and London, 1930.13. F. Schmid, ``Geology of Recent/Potential Bauxite Producing Areas in Sierra Leone andin the People's Revolutionary Republic of Guinea (West Africa),'' Bauxite-Proceedingsof the 1984 Bauxite Symposium, Los Angeles, CA, February 27^March 1, 1984, pp.486^499.14. ``Industry Requirements to Ores Quality,'' Aluminum, Handbook for Geologists,Moscow, 1962, p. 60 (in Russian).15. Yu. K., Goretskiy, ``Trends in Bauxites Distribution and Conditions of TheirFormation, Bauxite and Their Mineralogy,'' Genesis, Academy of Science of the USSR,1958 (in Russian).16. A. P. Vinogradov, ``Trends in Elements Distribution in Earth Crust, GeoKhimia,'' No.1, Academy of Science of the USSR, 1956 (in Russian).17. V. Smirnov, ``Alumina Production in Russia Part I: Historical Background,'' JOM,1996, 48(8), pp. 24^26.18. A. I. Lainer, Aluminum Oxide Production, Moscow, Metallurgiszdat, 1961 (in Russian).19. V. A. Mazel, Aluminum Oxide Production, Moscow, Metallurgiszdat, 1955 (in Russian).20. Prof. D. Altenpohl, Aluminum Viewed from Within, An Introduction into the Metallurgyof Aluminum Fabrication, 1st Edn, Aluminium-Verlag GMBH, Dsseldorf, 1982.30 Sverdlin21. D. S. Flett, ``Aluminum fromindigenous resources: present position in Aluminum and itsfuture patterns of use in Great Britain,'' ASM, 1982.22. J. Cohen and H. Mercier, ``Recovery of alumina from non-bauxitic aluminum-bearingraw materials,'' AIME Annual Meeting, Las Vegas, 1976.23. J. A. Eisele and D. J. Bauer, ``Evaluation Technology for the Recovery ofMetallurgical-grade Alumina from Coal Ash,'' U.S. Department of the Interior, Bureauof Mines, 1979.24. D. C. Cavin, W. A. Klemn, and G. Burnet, ``Analytical Methods for Characterization ofFly Ash,'' Proc. Iowa Acad. Sci., 1974, 81(3).25. U.S. Bureau of Mines, Potential Sources of Aluminum, BuMines IC 8335, 1967, p. 148.26. S. A. ``Ash as a Source of Iron Production,'' Nauch. Tr. Mosk. Gorn. Inst, 1959, 27, pp.137^43; In Chem. Abst., 1961, 55, 1632h.27. F. A. Peters, Private Communication, 1977. Available for consultation from J. A., Eisele,and D. J. Bauer, Bureau of Mines, Reno Metallurgy Research Center, Reno, Nev.28. R. Zimmerman, and K. Gunter, Metallurgy and Materials Science, Handbook,Metallurgiszdat, Moscow, 1982, p. 480 (in Russian).29. A. I. Belyaev, Metallurgy of Light Non-Ferrous Alloys, Metallurgia, Moscow, 1970, p.366 (in Russian).30. World Metal Statistics, 1981, 7, p. 36.31. Yu. V., Baimakov, and M. M. Vetukov, Electrolisis of Metaled Salts, Metallurgia,Moscow, 1966, p. 560 (in Russian).32. Yu. I., Barsukov, A. M. Voroshenkov, et al. In: Scientic Research and Experience ofDesign in Metallurgy of Light Metals, Metallurgia, Moscow, 1981, pp. 110^116 (inRussian).33. P. C. Varley, The Technology of Aluminum and Its Alloys, CRC Press, 1970.34. Nolan Richards, ``Strategies for Decreasing the Unit Energy and Environmental Impactof Hall^Heroult Cells,'' Light Metals, 1994.35. K. Grjotheim, C. Krohn, and H. A. ye, Aluminum, 1975, 8(4).36. P. R. Bremner, J. A. Eisele, and D. J. Bauer, ``Aluminum Extraction from Anorthositeby Leaching with Hydrochloric acid and Fluoride,'' Report of investigations, UnitedStates Department of the Interior, Bureau of Mines, 8694, 1982.37. ``Mineral Facts and Problems,'' Bulletin 671, 1980, p. 17.38. R. A. Brown, F. J. Cservenyak, R. G. Anderberg, H. J. Kandiner, and F. J. Frattali,``Recovery of Alumina From Wyoming Anorthosite by the Lime-Soda-Sinter Process,''BuMines RI 4132, 1947, p. 127.39. H. Leitch, H. Iverson, and J. B. Clemmer, ``Extraction of Alumina by Leaching Metledand Quenched Anorthosite in Sulfuric Acid,'' BuMines RI 6744, 1965, p. 32.40. A. A. Kostukov, I. T. Kil, V. P. Nikiforov, et al., Non-Ferrous Alloys Handbook, Alumi-num Production, Metallurgia, Moscow, 1971, p. 560 (in Russian).41. S. E. Maraev, Yu. I., Belyakov, et al., ``Casting and Machining of Aluminum and ItsAlloys,'' Transactions of VAMI, 1979, 105, pp. 76^85 (in Russian).42. Metal, 1973, 3, pp. 203^211.43. H. A. ye, N. Mason, R. D. Peterson, N. E. Richards, E. L. Rooy, F. J. StevensMcFadden, and R. D. Zabreznik, ``Aluminum: Approaching the New Millennium,''JOM, February, 1999, pp. 29^42.Introduction to Aluminum 312Properties of Pure AluminumALEXEY SVERDLINBradley University, Peoria, Illinois, U.S.A.1 INTRODUCTIONAluminum's unique properties ^ its light weight, high strength, and resistance tocorrosion ^ make it an ideal material for use in conventional and novel applications.Aluminum has become increasingly important in the production of automobiles andtrucks, packaging of food and beverages, construction of buildings, transmission ofelectricity, development of transportation infrastructures, production of defenseand aerospace equipment, manufacture of machinery and tools, and productionof durable consumer products. As demand for more technologically complexand ecologically sustainable products increases, opportunities for aluminum willcontinue to expand [1].Aluminum is the third most abundant element in the Earth's crust. Aluminumis the chemical element of the 3rd group in the periodic table of the elements.The atomic number of aluminum is 13, values for the atomic weight are 26.9815based on 12C, and 26.98974 based on 16O [2]. Aluminum has a silver-white color.It does not have any natural isotopes. Its articial isotopes are radioactive isotopes^ 26Al and 26Al. The isotope 26Al has a half-life of 106years and isotope 27Al isstable and consists of 14 neutrons and 13 protons. Table 1 lists the propertiesand characteristics of some isotopes found in aluminum.The nuclear properties of aluminum are of practical interest. The naturallyoccurring isotope Al27has a cross section for thermal neutrons of 0.21 barn (1 barn= 10 24cm2). This low cross section combined with the short half-life of the radio-active product from the irradiation of aluminum an especially attractive materialfor use within nuclear reactors. In the early nuclear reactors, aluminum was usedalmost exclusively for protective sheaths around uranium fuel elements and as tubeand ttings for conducting coolant through the pile.33Aluminum may possess a coordination number for oxygen of either 4 or 6. Theprocess of recrystallization of aluminum oxide is normally slow. Thus, there are agreat many crystal structures for aluminum oxide. The corundum structure has only6 coordinate Al in hexagonal crystals. It can probably be viewed as a distorted hex-agonal closest packed structure of oxide ions, with some of the octahedral holesoccupied by Al3 ions. Beta alumina has spinal structure with extra cation vacanciesto bring the stoichiometry to M2O3 from the ideal spinal formula of MM2O4.2 GRADES OF ALUMINUMDepending on amount of impurities, aluminum is classied into extreme purityaluminum and commercial purity aluminum (primary aluminum).In Russia there are four grades of extreme purity metal with the content ofaluminum no less than 99.996%; 99.99%; 99.97%, 99.93%, other elements presentare iron, silicon, copper [4]. The chemical composition of primary aluminum is pre-sented in Table 2 (Russian Standard GOST 11069^74) [4].Table 3 shows nomenclature for the various degrees of purity of aluminumaccepted in the USA [5]. Aluminum exceeding 99.99% in purity, produced bythe Hoopes [6] electrolytic process, was rst available early in 1920. In 1925,Edwards [7] reported some of the physical and mechanical properties of this gradeof aluminum. Taylor, Willey, Smith, and Edwards [8] published a paper in 1938that gave several properties for 99.996% Al that was produced in France by a modi-ed Hoopes process.Table 1 Isotopes of Aluminum [3]Energy of Some typicalParticles Type of radiation, modes ofIsotope Half-life absorbed decay ev* formationAl230.13 sec ^ ^ ^ ^Al242.7 sec Neutron [+ 8.5 Mg24(p, n), 1.38^7.1 ^Al257.5 sec Neutron [+ 3.2 Mg25(p, n)Al26m7.0 sec Neutron [+ 3.2 Mg25(d, n)Al26106years Neutron ec (**) ^ Mg25(d, n)[ 1.16 Mg26(p, n), 1.83, 1.14 Al27(n, 2n)Al27100% ^ ^ ^ ^abundance,stableAl28144 sec 2 protons [- 2.86 Al27(n, ,)1 proton , 1.78, 1.27 Al27(n, ,)Al29396 sec Proton [- 2.5, 1.4 Al (o, 2p)Proton , 1.28, 2.43 Mg (o, p)* Electron-volts** Electron capture34 SverdlinBased on ISO standards the classication of aluminum is shown in the Table 4[9].The chemical composition of the extreme purity and primary aluminumaccording to the DIN1712 is shown in Table 5 [4].Table 6 lists the AA wrought alloys that are covered by standards as used inGreat Britain, Germany, France, Japan, Russia, and in the Recommendationsof the International Organization for Standardization (ISO). The list includes onlythose alloys that are essentially in agreement composition-wise with the compositionof the AA alloy. Standards are subject to change and the actual issue of the speci-cation or standard currently in effect should be consulted for full information.Table 2 Russian Classication of AluminumImpurities, %, not more thanTotal ofcontrolledGrade Al, % Fe Si Cu Zn Ti Others impuritiesExtreme purity aluminumA999 99.9999 ^ ^ ^ ^ ^ ^ 0.001Super purity aluminumA995 99.995 0.0015 0.0015 0.001 0.001 0.001 0.001 0.005A99 99.99 0.003 0.003 0.003 0.003 0.002 0.001 0.010A97 99.97 0.015 0.015 0.005 0.004 0.002 0.002 0.030A95 99.95 0.030 0.030 0.005 0.002 0.005 0.005 0.050Commercial aluminumA85 99.85 0.08 0.06 0.01 0.02 0.010 0.02 0.15A8 99.80 0.12 0.10 0.01 0.04 0.020 0.02 0.20A7 99.70 0.16 0.16 0.01 0.04 0.020 0.02 0.30A7E 99.70 0.20 0.08 0.01 0.04 0.010 0.02 0.30A6 99.60 0.25 0.20 0.01 0.06 0.030 0.03 0.40A5 99.50 0.30 0.30 0.02 0.06 0.030 0.03 0.50A5E 99.50 0.35 0.12 0.02 0.04 0.015 0.02 0.50A0 99.0 0.50 0.50 0.02 0.08 0.030 0.03 1.00Table 3 The Various Degrees of Purity of Pure Aluminum(the USA Standard) [5]Aluminum, % Designation99.5000 to 99.7900 Commercial purity99.8000 to 99.9490 High purity99.9500 to 99.9959 Super purity99.9960 to 99.9990 Extreme purity>99.9990 Ultra purityProperties of Pure Aluminum 353 PHYSICAL PROPERTIESThe properties of aluminum depend to some extent on purity. This may vary fromthe ordinary aluminum of commercial purity to super-purity aluminum. For specialpurposes, aluminum may be further puried by zone rening to give a purity ofabout 99.99995%. Aluminum is well known for its low density, 2.7 g/cm3, highreectivity and high electrical and thermal conductivity. It is very resistant to atmos-pheric corrosion, due to instantaneous formation of an adherent oxide lm, whichprotects the metal against further attack. The more important physical propertiesare shown in Table 7, which also indicates how these properties are affected by purity[11]. It will be seen that the main effects of purity are upon electrical resistivity (theelectrical resistance offered by a material to the ow of current, times thecross-sectional area of current ow and per unit length of current path; the reciprocalof the conductivity) and thermal conductivity.Table 4 Classication of Aluminum Based on International Standard (ISO)Purity of aluminum DesignationExtreme purity A199.99R; A199.95R; A199.9R; A199.8; A199.7Commercial purity A199.8; A199.7; A199.5For electric