1 2 Amorphous materials like glass are fundamentally di erent than crystalline ceramics and metals 3 Glass viscosity depends on temperature and changes gradually with temperature In contrast consider how the viscosity of H2O varies from 1 C to 1 C 4 The building block for glass structures is the SiO44 tetrahedron 5 Quartz crystalline Fused Silica amorphous 6 AddiQves like Na2O break up the 3 D network of SiO44 tetrahedron thereby lowering the viscosity at a given temperature 7 8 9 Unlike cast metals glass has a much larger viscosity and needs to be molded e g you need to push it around since it does not ow by gravity very well 10 Centrifugal CasQng of Glass 11 If you place an empty glass container directly on a heat source it oYen breaks Why does glass have poor thermal shock resistance 12 13 Tempered Glass 14 Ceramics are Processing from Powders metals are someQmes as well Why not cast them as we do metals Typical Cast Microstructure 15 Powder Processing Shape Forming Uniaxial Pressing dry Slip CasQng wet 16 Once the powders are formed into a shape they sQll have porosity in between the parQcles Powder compacts are a two phase mixture of the powder and air Good thermal insulator but lacking in strength 17 One reason to get rid of porosity opQcal properQes 18 19 Sintering reducQon in interfacial energy by parQcles fusing together below their melQng temperature 20 21 Sintering of Copper Wire Wound on a Spool 22 Densi caQon of a ZrO2 Y2O3 Powder Compact 23 24 Agglomerates from CalcinaQon During Powder Synthesis 25 High Grade ZrO2 Powder Primary ParQcles Surface Area 16 m2 g Granules for easier handling 26 27
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