PowerPoint Presentation

DryingFiringSinteringAndZiad !A green body refers to a ceramic compound, usually clay or powder, after molding and before it has been fired or sintered, respectively.The evaporation of water from a green product board.Which in it the molecular of water Mechanically bondedThis process is used to protect ceramic from cracking during firing process Method of drying :DehydrationAir drying

DehydrationDehydration start from 350 degrees C (662 degrees F)Water in structure of clay which is combined together will dehydrated This drying is completed by about 500 degrees C (932 degrees F). After this point you could no longer mix the dried clay with water to make new wet clay. An irreversible chemical change has taken place.

Air dryingthis method of drying is used for clay contain large amount of water 25%When clay starts to dry, water evaporates from it. As this happens, the particles of clay are drawn closer together resulting in shrinkageMany problems with clay are formed by uneven rates of drying, which create stresses in the clay. Sometimes these stress show up right away as cracks Clays which have very fine particle sizes will shrink more than clays with larger particle sizesWhen the water has evaporated form between the clay particles, and all the remaining clay particles are in contact, drying shrinkage is complete

Flextural strengththe fracture strength of the green body at the end of the shrinkage phase. And it depend on many factors such as Drying Temp , Raw Denisty and Drying rate .

It is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas.ApplicationsPharmaceuticalIndustrialFoodMicrowaves Microwaves are simply high frequency radio waves generated by magnetrons at 2450 MHz. At this frequency the wavelength is 12.24cms . This frequency is controlled by international agreement.

Advantage 1- High Speed2- Save energy3- reduces scrap

DefectsCracking :- Due to rapidly Drying at high Temp , Bubbles of air.lamination :- May happen during this process this refer to the forming of the material . Distortion :- Its a product may have to supported by special setters during the process .

Is the second part of heat treatment processConsists of heating the articles to high temperatures > 800C Clay must be dry enough to enter firing processLeads to the strengthening of the unsintered molded article into their durable shapesWe start heating the dry clay to remove some more waterAt 500C the changes in it becomes irreversible and it cant be recycled to the workable stateClay at this point becomes fragile and crumbly[clay]-OH + HO-[clay] [clay]-O-[clay] + H2O(g) Hydrogen bonds are replaced by shorter oxygen ones so the clay shrinks a little bitIf we stop at 500c , linkages would be strong enough to prevent recycling but not enough to strengthen the piece

Crystal structure of kaolinite is lost and amorphous metakaolinite is formedthe pot is first fired to about 1000C to produce what is known as 'biscuit wareIt is quite strong and porous ; it readily absorbs water and dries again very easilyEarthenware : is fired at temperature from (1000-1150C)Stoneware : is fired at temperature higher than 1200CSome chemical changes happen in a temperature higher earthenware temperature but happens in stoneware temperature crosslinking of metakaolinite to give a three-dimensional network with the elimination of watermetakaolinite turns into mulite (3Al2O3.2SiO2) which forms needle-like crystals feldspar melts into a glassThat makes stoneware much more stronger and heat resistantGlazing is covering the article by a thin coating of glass. This can be for aesthetic or for practical reasons or usually bothGlazes are usually made of :silicon dioxidealuminium oxidefluxes, generally alkali or alkaline earth metal oxidesTransition metal oxides.

Its show time !

Electric Kilns Often made out of soft bricks, usually an oxidation or neutral atmosphere, heated by coils carrying electricity. Gas Kilns propane or natural gas, often used to achieve a reduction atmosphere. Wood Kilns most are larger than electric and gas kilns, heated by wood combustion. Saggars Raku

firing must also be carefully controlled, since the decomposition and combustion products are gases which can cause cracking.The firing atmosphere is particularly important in the case of white articles.Oxidizing atmosphereReducing atmosphere

DUNTING Cracking in the clay which often occurs from either heating or cooling the kiln too quickly. Opening the kiln too early should be avoided. EXPLODING Happens during the early stages of the firing and are often caused by the water being removed too fast. PEELING The contraction of a glaze, slip, engobe or underglaze during the firing which can cause it to flake off. PINHOLING Tiny holes in the fired glaze surface. Can be caused by incorrect firing, poor clay preparation or improper glaze application. Sintering processSintering is part of the firing process used in the manufacture of ceramic objectsThese objects are made from substances such as silica , lime , alumina , glass etc

How it worksMixing water,binder, deflocculant, and unfired ceramic powder to form aslurrySpray-dryingthe slurryPutting the spray dried powder into a mold and pressing it to form a green body (an unsintered ceramic item)Heating the green body at low temperature to burn off the binderSintering at a high temperature to fuse the ceramic particles togetherFactors affect itTemperature time durationgreen body densitypressureimpurities contentparticle sizeTypes of sinteringThere are two types of sintering: with pressure (also known ashot pressing), and without pressure. Pressurless sintering is possible with graded metal-ceramic composites, with a nanoparticle sintering aid and bulk molding technology.THE END