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1、1.Inmanycasesproductshavecomplexshapesmadebyuseofoneoranotherofsuchformingtechniquesasdryorisostaticpressing,plasticshaping,extrusion,injectionmolding.2.Twostructuralunitsareinvolvedinmostclayminerallattices.Oneisthesiliceous,andtheotheriscalcareous.3.Thevarioustypesofcrystalimperfectionscanbeg
2、roupedintothreeclasses:pointdefects,linedefects,surfacedefects.4.Basedprimarilyonchemicalmakeupandatomicstructure,solidmaterialshavebeenconvenientlygroupedintofourclassifications:metals,ceramics,polymers,andcomposites.5.Threetypesofgalvaniccouplescanstartanelectrochemicalattack:compositioncoupl
3、es,stresscouples,concentrationcouples.6.Welding:Weldingisthejoiningoftwoormorepiecesofmaterialbyapplyingheat,pressure,orboth,withorwithoutfillermaterial,toproducealocalizedunionthroughfusionorrecrystallizationacrosstheinterface.7.Casting:Acastingmaybedefinedas“ametalobjectobtainedbyallowingmolt
4、enmetaltosolidifyinamold",theshapeoftheobjectbeingdeterminedbytheshapeofthemoldcavity.8.Elasticdeformation:Whentheappliedloadisremoved,thelatticestrainisrelieved,andthecrystalregainsitsoriginalshape.Thisreversiblechangeofshapeiscalledelasticdeformation.9.Thepropertiesofthemolditselfinfluencethe
5、qualityofthecasting.Normally,plasterofparis,whichiseconomical,relativelyeasytofabricateintointricateshapes,andreusable,isusedasthemoldmaterial.10.Thereisanincreasinginterestinceramicitemsmadefromhighlyrefinednaturalorsyntheticcompositionsdesignedtoprovidespecialproperties.Theseobjectsaretermeda
6、dvancedceramic,andfinduseaskeycomponentsinsuchhigh-technologyfieldsascuttingtools,wear-resistantparts,high-temperaturereactors,andmanyotherspecialapplications.11.Formaterialshavingveryanisotropicthermalcoefficientsofexpansionandlargegrainsize,microcrackingdevelopswhentheceramiciscooledtoroomtem
7、peratureaftersintering.Thiscanbedetrimentaltostrength・12.Vacanciesfacilitatemasstransferinsolids,providinganaturalpathforatomsmovingfromonepointofthecrystaltoanother.Thisphenomenon,usuallyreferredtoasdiffusion,isaveryimportantmean
