1

The position of lead in a challenging world ofmodern technology

M. N. PARTHASARATHI

THE old appellations of lead-- `enduring metal' and'indestructible metal'- were originally meant tosignify its excellent corrosion resistance and the

endless cycles in which the metal was used, scrappedand re-used. These attributes appear to be eyen moreappropriate in the present day challenging world ofmodern technology, With the advent of modern metalsand synthetic materials, it was feared that lead mightgo gradually out of usage. On the contrary, the con-sumption of lead has been steadily increasing fromancient times and does not show any sign of levellingoff. However, its growth rate has not been so specta-cular as, for instance, the modern metal aluminium.There have also been numerous inroads into many ofthe applications of lead , nevertheless, not only thetraditional and relatively old and established uses oflead are being continued, several new and modern usesof lead have been invented so that lead will continueto be used in ever increasing tonnages in the future.

The success of lead has been due to its relativelylow price (it is the cheapest non-ferrous metal) andthe unique combination of mechanical and chemicalproperties and no other metal is used in so manydiverse applications. Lead seems to have an inexhaus-tible range of versatile properties. Some of theseapparently latent properties are being continuouslyunearthed and appreciated, with the result that themetal is being put to new uses and applications in theever changing and demanding conditions of moderntechnology. For instance, lead has always had the pro-perty of sound attenuation and shielding for radio-active rays. But these properties came to the fore onlyrecently in the twentieth century. Likewise, there areever so mane properties of lead that lie hidden in itsmany compounds and these are being discovered slowlyand steadily, finding newer and more exotic applica-tions for the ancient metal.

The story ol' lead has been remarkable in severalrespects. At a time when it had practically no com-petition from modern metals and synthetic materials,its growth rate wa,, relatively slow. For example, duringthe whole of the 19th century, lead consumption wasonly of the same order of magnitude as that consumed

Dr M. N. Parthasarathi. Indian Lead Zinc Information Centre,Calcutta.

38

I

SYNOPSIS

The old appellations of lead such as 'enduring metal',`indestructible metal', etc. appear to be even moreappropriate in the present day challenging world of moderntechnology. The unique combination of diverse propertiesof lead has helped in the steady growth and usage ofthis ancient metal in spite of severe competition fromnewer metals and materials. The paper describes thetraditional uses of lead. the change in pattern of con-sumption due to the changes in the modern world andthe advent of other materials. It also describes the moremodern uses of the metal and predicts a steady increasein the consumption of lead Jronewer and betterapplications.

during the whole 20-year period between the greatwars. Subsequent growth rate was much faster and inthe last ten years the world has used more lead thanthat used during the entire twenty-year period betweenthe wars. The growth in consumption of lead in thepast decade has been showing a steady upward trend.This has been possible by not only the world usingmore tonnages of lead in the established applications ofthe metal, but also due to new uses and applications.

Changing patterns of use

Lead has been in use for well over 2 000 years. Itwas used in plumbing by the Egyptians, and someof these fixtures are preserved in good condition eventoday, Lead continues to be used in plumbing evenin modern times and the traditional uses of lead inbuilding are still being continued. There has, however,been marked changes in consumption over the centuryand particularly in recent times. Before the secondworld war, the main use of lead was cable sheathing,with sheet and pipe occupying the second place follo-wed by pigments and then batteries. In the 50s, withthe coming in of the automobile age, batteries movedto the second place, cable sheathing still maintainingthe first place. Later, batteries became the biggestoutlet, the cables being pushed down to a secondaryplace. The change in the pattern of world consumptionof lead during 1954-67 is depicted in Fig. 1 which

Parthasarathi : The position of lead in a challenging world of modern technology

BATTERIES31.67

h

M

0

OTHER USES

21.27

PIGMENTS ACHEMICALS

1 End-use pattern o

CABLES

14.37

0r

0.0

YEAR 1954

nN-

N

N

In I

O NU

UU O a 0 N

0a N W

0

aF W

m<

Z

i

f

IV

I-

II

W

m U < a 0

YEAR 1967

world lead consumption in 1954 and 1967 ; figures are in ' 000 tonnes

shows that there has been a considerable increase inthe total tonnages of lead used in all its applicationswhile the use of lead in batteries and anti-knock com-pounds has registered a significant rise.

Established uses of lead

The established uses of lead are in batteries, cables,pigments and sheet and pipes. These will be dealt withbriefly, outlining the recent modern developments.

Lead-acid batteries

Batteries comprise the major outlet for lead and, withno chance of any competition in this field, consumptionof lead through this application is bound to show asignificant upward trend in proportion to the increasein the number of vehicles manufactured. The varietiesof batteries in use today consist of three categories :SLI batteries for starting, lighting and ignition and

similar small batteries used in aircraft and trains ;traction batteries for industrial trucks and commercialroad vehicles ; and, stationary batteries to provideemergency or auxiliary power in hospitals, theatres,telephone exchanges and power stations. In addition,there are other minor uses, such as for portable appli-ances, television sets, etc. A steady growth is expectedin all of these applications. In the last couple of yearsor so, considerable interest has been shown in therevival of battery powered passenger cars. Already,traction batteries are used in delivery trucks and otherindustrial vehicles and railcars, as for instance, inGermany. Although the battery-operated passenger carshave a drawback in a limited mileage range, there arenumerous advantages such as absence of noise and smoke,lower running and operating costs, safety and reliability.These, together with a change in the living conditionsof the modern world, make the battery vehiclesattractive in spite of their handicap of limited range.

Although the lead-acid battery has hid no serious

39

Parthasarathi : The position of lead in a challenging world of modern technology

competitor, the battery manufacturers have neverbeen complacent and have spared no pains for theimprovement of their product. The modern versionof the battery is a great improvement on the earlierproduct. Batteries are much lighter today, pack morepower and give longer lives. Most of the improvementsin the battery can be attributed to the rapid advancesmade in automobile technology and the exactingdemands made by the automobile manufacturers. Withthe battery powered passenger car on the thresholdof development, there is a demand for even lighter

and more powerful batteries. Battery manufacturers

are relentlessly trying to improve their products. Onthe metallurgical side, they are trying to develop dis-persion-strengthened lead which holds promise as amaterial for battery plates. Similar research is goingon for developing lighter containers, better separatorsand so on.

Cable sheathing

Lead is the most preferred sheathing material for powercables in the medium voltage range. There is no likeli-hood of changes in the position of lead and this isindicated by the installation of a large number ofnew continuous lead extruders throughout the worldin recent years.

In the lower range of voltages up to I KVA, therehas been extensive substitution by plastics and in thehigher ranges (gas and oil-filled) there has been somesubstitution by aluminium. Lead is still preferredwhere utmost reliability is required and, wherever subs-titution has taken place, it has been predominantlyfor economic rather than technical reasons. No furtherlarge scale substitution of lead is likely to take placein the near future. Furthermore, research and develop-ment work in progress for thinner and stronger lead-sheathing may counteract the trend for substitution.The ultimate solution perhaps may lie in the jointuse of materials such as lead and plastics. As of now,dispersion strengthened lead seems to be a promisingmaterial.

Sheet and pipes

About 300 000 tons of lead are being used for themanufacture of sheet and pipes for the building andchemical industry. Although the gross tonnage usedin this application is much more now than it was adecade ago. lead is facing stiff competition from othermetals, notably from plastics. Lead laminates mayfind increasing use in the chemical industry if the testsnow in progress to assess the effectiveness of the adhe-sion bonding techniques (to replace older methodsof lead burning) for lining steel acid tanks, etc. provesuccessful. Dispersion strengthened lead is now usedin chemical plant with considerable success.

its own as heavy duty structural primer. The maincompetitors to lead pigments in primers for iron andsteel are iron oxide, zinc dust and zinc chromate, butpaints based on them require a much more thoroughsurface preparation, though they may have some com-pensating advantages.

Lead alloys are extensively used in solders, printingmetals and bearings. There are different kinds of solders,depending on the industry. The automobile industrytoday uses solders to connect the contours of pressingsand other type of solders for radiator manufacture.There seems to be no threat of substitution of lead in

both these applications, although there is an indirectthreat to this outlet in the development of aluminiumradiators. The use of solder in making cans fromtinplate is nowadays confined to the side seams, theend seams being sealed with `lining compounds'. Thereis a trend towards reducing the amount of solder percan and the tin content of the solder. Unalloyed leadhas, in fact, given satisfactory results. However, thereis also a move to dispense altogether with side-seamsoldering, although it is doubtful if the use of sealingcompounds and other techniques can cope with thehigh speed of manufacture of the order of 500 cansper minute.

No significant changes in lead consumption in theform of solders are expected in the electric and electronicindustries. The introduction of printed circuits has notbrought about a reduction in solder consumption, butthe current trend towards micro-miniaturisation (solidstate circuits) mayby the electronicfuture.

reduce the consumption of solderindustry at some time in the

With changes in printing methods leading to a pro-gressive replacement of hot metal techniques, the demandfor printing metal is likely to fall. Trends of lead con-sumption in bearing alloys are not very clear. Therehave been some substitutions in several types of bear-ings, but the overall demand is still good, althoughlikely to fall in the future.

Lead sheets, collapsible tubes, etc.

Lead sheets, collapsible tubes, etc. are minor outletsfor lead. The former is expected to grow steadily whilethe latter, which has lost a significant portion of itsmarket to aluminium, has regained some of the lostground in respect of fluoride toothpastes where alu-minium cannot be used.

Modern uses of lead and recentresearch and development

Having discussed the traditional and established usesof lead, an attempt will now be made to review brieflythe modern uses of lead and recent research anddevelopment.

Pigments and allovs Organolead compounds

While white l1ad has lost a significant portion of Tetraethyl lead and tetramethyl lead (the anti-knockits market toWiitanium dioxide , red lead is holding compounds) are the most well-known organolead com-

40

1"""77 + 1' If T I+ ili ilk 11

1 illlll 7 ,

m.^i^^^^+wle^lA^AnI^PRI^IIM1111^A1^ '^Il^l^^^w4 1wP"r I

Parthasarathi : The position of lead in a challenging norld of modern technology

pounds, accounting for about 250 000 tons of lead ayear. With the rising consumption of petrol and theincreasing use of automobiles, there will be a growingdemand for the lead anti-knock compounds. In recentyears, under the active research programme of Inter-national Lead Zinc Research Organization (ILZRO;,several new organolead compounds have been synthesisedon a semi-technical scale and are under assessment bythe industry in a number of potential uses. All thesewill develop new markets in such diverse applicationsas antifouling paints, wood preservatives, lubricantadditives, anti-bacterial agents , molluscides for the controlof bilharzia disease, rodent repellants, polyurethanefoam catalysts and rot- resistant textiles.

Noise and vibration control

Lead, both as sheet metal and as a component offabricated composite materials, is finding increasing usein sound and vibration control. The normally undesir-able properties of heavy weight and bulkiness causethe most ideally suitable combination of propertiesrequired for acting as a barrier to air-borne noise. Inspite of the heavy weight of lead, it is claimed thatfor an equally effective sound barrier condition, thepartition built of lead will be almost invariably lighter.Although lead partitions are not as cheap as conven-tional building materials, the savings effected in extrausable space and lighter structural requirements, thinnerfloors, etc. may make them a more economical pro-position, particularly where building space and weightare of importance.

Lead is' also used as a dispersed powder in vinylsheet, with or without fabric backings. Silicone andepoxy formulations loaded with powdered lead or leadore are also used. Many new materials, chiefly plasticsin vinyl epoxy and polyethylene-polypropylene families,have been used with lead and lead compounds toform new composites suited for special use. Leadlaminates with other metals such as aluminium areused as enclosures to noisy machines to lessen soundtransmission.

Lead and asbestos have been used in building toreduce the transmission of vibration. With the increasednumber of high speed and heavy vehicles, undergroundrailways, air-conditioning and other machinery, it isnecessary to employ anti-vibration or isolation materialsmore extensively. Lead by itself can be used for anti-vibration pads, since it has the blend of required pro-perties-massive but not rigid. However , a combinationof lead and asbestos has not only vastly superior anti-vibration properties ( than either material alone) buthas a number of other favourable characteristics, suchas easy workability, corrosion and chemical resistance,imperviousness (of lead) to water and, above all, veryhigh load bearing capacity. Lead- asbestos is usedextensively to reduce transmission of vibration due torailroad or sub-way traffic from the ground to adjoin-ing building structures. A recent trend has been theisolation of vibration from big and small machineswhich are located inside or on top of buildings, forexample , cooling towers.

Lead in ceramics

The use of lead compounds in the ceramic industry isnot by any means new, but there have been remarkableachievements in this field in recent years . For instance,it has been possible to develop strongly adherent enamelcoatings capable of withstanding repeated blows andresistant to chipping and cracking . Both functional anddecorative effects can be achieved , such as in theenamel coating of aluminium which, in turn , has ledto the production of enamel cast aluminium and mag-nesiunm . Porcelain enamelled aluminium laminated onhardboard and masonite can be sawed , sheared ordrilled with simple tools and hence finds immense usein and around the home . The high lead content, lowfiring temperature enamel on steel may find increasinguse in window frames , kitchen cabinets, etc. becauseof the ease and versatility of application.

Lead in thermoelectricity and piezoelectricity

Although thermoelectric power is available at relativelylow conversion efficiencies, it has some unique advan-tages and great commercial potential. The possibilityof its use as a remote power source with relatively lightweight and no moving parts holds attraction in avariety of applications. In spite of every energeticresearch for newer and better materials, lead tellurideis the most efficient material for power generation inthe range of 260 to 650 C. Its scope of applicationis two-fold - firstly, as an auxiliary power from wasteheat sources : secondly, as independent power packagesfor areas remote from power lines. Lead-telluride isbeing used increasingly in thermocouples in someindustrial and home control systems because it pro-vides relatively greater power and has made it possibleto dispense with expensive amplifying mechanisms orsecondary power sources to drive controls. CalledPZT in the trade, a mixture of lead-zirconate andlead-titanate is an excellent piezoelectric material andhas great commercial potential. Its introduction inultrasonic cleaning and processing equipment may makethis process more widely accepted. It is used in `sparkpumps' (tiny gadgets accommodated in the palm of ahand and capable of generating a 20000 volt spark)which form part of the starter mechanism of lawnmowers and other machines.

Lead coatings

Terne plate is not really a modern material. But therehas been a revival of interest in this material, parti-cularly in the U.S.A., not so much due to any develop-ments in the process or product, but due to theavailability of the product in more suitable forms.Terne plate is currently used for roofing, automobileand other gasoline tanks, radio and television chassis,non-food cans and a variety of miscellaneous metalproducts in which corrosion resistance, deep drawingand solderability are important.

ILZRO has developed a high speed electroplatingtechnique for lead and lead alloys, ar.• electro-terne

41

Parthasararhi : The position of lead in a challenging world of modern technology

is now well on its way to acceptance on a commercialbasis . One important application will he in the auto-mobile industry. Other applications include non-food cans, metal house siding and roof drainageproducts.

D. M. Machine

In acoustical and roofing applications, although leadis an ideal material, it is still considered expensive,and the exclusive application of lead for this usagewill depend on the low cost of lead sheet. Significantachievements have been made in this direction by theinvention of the machine for continuous casting of leadsheet. It is claimed that the total cost of casting athin gauge sheet by this process is less than one fifth ofthe cost by conventional rolling techniques. This develop-ment will be an essential part of the ultimate success ofmany of the applications of metallic lead sheet.

Dispersion strengthened lead

Research and development work on the powder metal-

lurgy of lead promises to yield very high dividends inthe form of several new products which will be con-siderably superior to the lead and lead productsavailable at present. Rolled and extruded products oflead, obtained from powders, can be considerablystrengthened by the introduction on their surface of athin layer of oxide. The material has great potential

application in the manufacture of batter grids, roofingsand cable sheathing.

Conclusion

Lead is perhaps used in more diverse applications thanany other non-ferrous metal and, in a short article, itis not possible to do full justice to the numeroususes of lead and its compounds. Lead is a very ancientmetal but has not only survived the viscissitudes intechnology but also continues to perform importantfunctions in home and industry. Relentless research onlead for new products and improvement of old pro-ducts and processes are continually in progress, and itis predicted that lead will continue to be used in everincreasing tonnages in the future.

Discussions

Dr L. Wallace Coffer (Operation Hardrock, New Delhi) :Could you tell us a little more about the direct for-mation of sheet from molten lead ?

Dr M. N. Parthasarathi (Author) : The process of con-tinuous casting of lead sheets is popularly known asthe DM (Direct Manufacturing) process. A water-cooleddrum or roll just dips in a bath of molten lead andis rotated at a pre-determined speed. As the moltenmetal comes in contact with the drum, it solidifiesin the form of a sheet and is carried forward bythe rotating drum. The sheet is then stripped by meansof a blade known as the doctor blade and thentrimmed and coiled on to a reel. Figure shows aschematic diagram of the DM machine. The sheetthickness would depend on such factors as tempera-ture of the molten lead, rate of heat extraction fromthe drum, speed of rotation of the drum, depth ofimmersion of the drum in the bath, etc. The machinefor this l)M )rocess is relatively simple in construc-tion and pr es a fully integrated production unit

with low cost of installation and operation. At presentthe DM process is suited to pure lead or lead alloyshaving a narrow solidification range and research workis being directed towards further development of theprocess to increase its range of applicability.

Mr G. Rama Rao, (Barauni Oil Refinery) : Lead is usednowadays for the storage of radioactive isotopes ;what property of lead has been taken into accountin this case ? Is it density alone or some other aspect ?

Dr M. N. Parthasarathi (Author) : While the majorreason for using lead as a radiation shielding materialis its high density or massiveness, there are certainother factors which also favour the use of lead forthis application. Lead has the important advantagein that it does not become a source of secondaryradiation. Lead radiation shields almost invariablyresult in saving in weight and space. There are ins-tances where the use of lead instead of iron forgamma radiation attenuation has resulted in a weight

42

I

1 III 1 EIII T

Parthasarathi ; The position of lead in a challenging world of modern technology

1 A schematic diagram of the direct manufacturing lead sheetcasting machine

IJ

(CASTINGTANK

REEL

carrying out homogeneous lead lining, as little tin aspossible should be used. Of particular importance arehomogeneous lead coatings which are exposed to highchemical or thermal strains. Experience has shownthat tinless lead coatings perform satisfactorily at hightemperatures and high acid concentrations.

While it is acknowledged that the use of tin resultsin a very strong bond between lead and steel, it mustbe however kept in mind that to ensure a safetymargin, tin soldered homogeneous lead coatings shouldnot he employed at a temperature higher than 180-C.On the other hand, tin-free coatings can be heated upto 220 C with no danger of the lead coating gettingdetached.

Mr S. W. K. Morgan , Imperial Smelting Process Ltd.,England) : What are the uses of dispersion strengthenedlead in batteries ?

saving of at least 30%. This corresponds to a shieldingthickness reduction of more than 50",,. In general,lead radiation shields are also easier to handle andinstall.

11r Sunil Dey (Chemical and Metallurgical Design Co.(P) Limited, New Delhi) : Will the author commenton the advantages and disadvantages of homogeneouslead lining with/without tinning ?

Dr \1. N. Parthasarathi : Homogeneous lead coating is,from the technical point of view, the most perfectof the lead coating processes because it combines thestrength of the steel with the corrosion resistance ofthe lead. Generally a tin solder is used as a bondingmaterial between lead and steel. The tin solder meltson deposition of the lead and diffuses into it. Whiletinning gives rise to a very strong bond between leadand steel, there is however a disadvantage in that athigher temperatures and higher acid concentrations,corrosion might result due to the diffusion of tininto lead. Corrosion tests with various types of leadcoatings of varying tin contents in the presence ofsulphuric acid showed that the attack was propor-tional to the tin content. Tests have shown that in

Mr U. K. C'hatterjee, (Indian Institute of Technology,Kharagpur) : What may be the specific uses of dis-persion strengthened lead '!

Dr M. N. Parthasarathi (Author) : Dispersion strengthe-ned lead has shown promise as an excellent materialfor fabricating battery grids. While the antimonial leadalloys which are being presently used have better strengththan pure lead, they however have inferior electro-chemical and corrosion properties. DSL, on the otherhand, combines the excellent corrosion resistance ofpure lead with the high mechanical strength of leadalloys. It, therefore, constitutes an ideal material forbattery grids.

Dispersion strengthened lead can replace pure leadand lead alloys in all the traditional applications ofthis metal, and at the same time, it can be used in anumber of new applications.

DSL has so far been tried out in such fields ofapplication as lead acid batteries, cable sheathing,radiation shielding, sound attenuation, chemical plantconstruction and architecture.

Widespread application of DSL is possible on accountof its good mechanical properties, excellent corrosionresistance and satisfactory electrical and electrochemi-cal properties.

43