Home > Uncategorized > Introduction to Solid State Chemistry Lecture 21: Glasses/Theft Prevention

Introduction to Solid State Chemistry Lecture 21: Glasses/Theft Prevention

Overview
Today’s lecture is 48 minutes. The class average for the test was 59+-16. He’s still drinking his fresca.

Details
Silicates form glasses. Glasses are disordered solids. Metallic glasses are 80% metal, 20% nonmetal like Ge80B20. Crystalline SiO2 is quartz. Amorphous SiO2 is glass.

Why does a liquid go to an amorphous solid? It’s like musical chairs. Atom mobility – high mobility promotes crystallization. Arrangement – complex formations promote amorphous. When does the music stop? The cooling rate; a high cooling rate favors glasses.

Glasses are used in fiber optic cables. Silicates are based on SiO2 oxide. Si is silicon the element. Si4 -4 is a silicate and is fully oxidzed. sp3 hydrization, 109.5. O forms bridges like O-Si-O-Si-O-
with the ability to rotate, thermal energy will be consumed.

The x ray spec of amorphous has one broad peak. Not sharp defined peaks. When things form bonds, it has more energy. The ordered crystal has tighter packing, more bonds per unit volume.

Glass formation: supercooled liquid – (glass transistion temp)-glassy solid
Crystallization: ctallization liquid melting temperature xtalline solid

The higher the rate of cooling, the more disorder we can quench in.

Bridging oxygens lead to glass formations.

OXide Glasses are chemically inert (covalent bonds), insulating (high bandgap), mechanically brittle (no opportunity for slippage), optically tranparent, high melting point. We can reduce processing temperature by changing its composition.

You can learn anything you want about polymers with pasta.

O-2 is the oxide ion. Attacks Si-O-Si bond, into Si-O(-1) (-1)O-Si. This is chain-scission. Oxide ion donors come from CaO.

CaO = Ca2+ + O2-. Bridging and terminal oxygen. Network formers like GeO2. Network modifiers like CaO, Li2O, MgO, La2O3, PbO. PbO has alot of electrons and a high index of refraction.

Cooling liquid metal very quickly, freeze the random orientations in. AuSi. Water cooled copper wheel. Disordered metallic glass. Not transparent, very small bandgap.

Magnetoelastic resonators: theft prevention. Resonator is a 39 Fe, 39 Ni, 2Mo, 20B metglass. Bias magnet of FeCoCr ductile alloy of the door thingy. Antenna/reciever of 58 kHz. If not demagnetized, it rings.

Breaking covalent bonds is a fracture.

E crystal < E glass

The higer the molar volume, the more the energy. Coefficient of thermal expansion=CTE. CTE of a liquid is much greater than CTE of a solid. On a graph, the slopes are different. V molar is a measure of disorder; more volume, more disorder. Vxs= Vxytl – V glass.

Review
MAC mobility, arrangement, cooling
aurophillic bonds 3A 10kcal/mole

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