ENGR_4341_Lecture_18_and_19_R_New - Engineering Materials ENGR 4341 Lectures#18 and#19 1 Ceramics and glasses Ceramics and Glasses Most environmentally

ENGR_4341_Lecture_18_and_19_R_New - Engineering Materials...

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1 Engineering Materials ENGR 4341 – Lectures #18 and #19 Ceramics and glasses
2 Ceramics and Glasses Most environmentally durable engineering materials Application Structure – Property Relationship Classification Ceramics and Glasses Crystalline Ceramics Glasses Glass-eramics Silicates non crystalline solids Oxide compounds Non oxide compounds SiO 2 , MgO, ZnS, MgAl 2 O 4 silicates non-silicates glass Controlled Crystalline process Li 2 O – Al 2 O 3 -SiO 2 }
Application 3
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6 Ceramic --Crystalline Silicates: most common---abundance in earth’s crust Si = 26% O = 50% Pottery—since 4000 B.C. Clay—brick, tile, sewer pipe Refractories—high temp resistant, used in furnaces Non-silicate oxide ceramics Biological ceramic—primary bone structure is hydropoxyapatite: Ca 10 (HPO 4 ) 6 (OH) 2 Non-oxide ceramics
7 Ceramic –Crystalline Silicates Furnaces & other high temp Electrical insulation
8 Ceramic –Crystalline Non-silicates
9 Ceramic –Crystalline Non-oxides
10 Glasses—Non-Crystalline
11 Glasses—Non-Crystalline •Network formers: can connect with network of SiO 4 4- tetrahedra. Forms the basic network that provides structure in absence of crystal Intermediates: these cations can substitute for Si ion Network modifiers: breaking of silicate network. Makes the material easier to form, but can also make it more susceptible to chemical attack. •Borosilicate w/ lower Na 2 O or CaO used for laboratory glassware •Borosilicate w/ higher Na 2 O or CaO used for common glass
12 Glasses—Non-Crystalline
13 Glasses—Non-Crystalline GLASSES: Vitreous silica (amorphous or noncrystalline): high purity SiO 2 •Borosilicate glasses: soda-lime-silica 15% Na 2 O, 10% CaO, 70% SiO 2 (soda refers to Na, lime refers to Ca) This is what window and container glass is made from Fiber Glazes on ceramics: more impervious surface Enamels (not paint) on metals: protection against corrosion
14 Glass - Ceramics Most sophisticated ceramic materials Trade names: Pyroceram Cer-Vit Hercuvit Corning Ware Ceran Glass – Ceramics has fine crystalline phase to strengthen the glass. High resistance to thermal shock, due to very low thermal expansion coefficients Formed from chemical family of Li 2 O-Al 2 O 3 -SiO 2 Inorganic glasses fine-grained glass ceramics (80 - 90% crystals) Nucleating agent Titanium oxide Controlled high temperature heat treatment (devitrification process)
15 Characteristics of Glass-Ceramics Low coefficient of thermal expansion High thermal shock resistance High mechanical strength High thermal conductivity Ovenware, tableware, dinnerware Insulators and substrates for printed circuit boards Applications
16 Glass - Ceramics Formation of glass first, followed by careful reheating and crystallization with a nucleating agent (TiO 2 )
17 Glass - Ceramics
18 Processing of Ceramics and Glasses
19 Thermal Properties Mechanical Properties Optical Properties (Chap 16) Melting temperature Thermal expansion

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