Reactivity, strength, cost, ductility all important Ca) Ceramic refractories (crucibles and boats ta)Factors influencing choice of temperature include Tamman's rule and potential for volatilization Zb recio z Metals (ru cibles colts and tubes) Tamman's Rule: Extensive reaction will not occur until the -Pt 1770 C 10 ml crucibles $500 or more of the reactants Au 1063 C 10 ml crucibles $340 ab)Initial heating cyele to lower temperature can help to prevent spillage and volatilization 2450C 10 ml crucibles $930 Ce)Atmosphere is also critical Steel: 1400 C (under inert gas 1Pt-1600C PtOT -Oxides(Oxidizing Conditions)-Air, O Low Temps Mo:~2000°C oXides(Reducing Conditions)-H/Ar, CO/COz High T Ta:~2500°C .Nitrides -NH. or Inert(N. Ar, etc. Sulfides-HS Pyrex: borosilicate glass(76%SiO,, 16% B,O Bao.. sEaled tube reactions, Vacuum furnaces 7. Grind product and analyze (x-ray powder diffraction) Quartz Pure SiO2, Tmax 1 100C 8. If reaction incomplete return to step 4 and repeat. Possible reaction paths between Sulfurization method Two Solid grains BaCo, +(1-xNiO+xCoo->BaNi,- Co,S, A B gas phase diffusion interface diffusion urface diffusion Solid solid reaction Atom movement in materials odel for a classical solid-solid reacti (below melting point ! Diffusion; is required for the heat treatment of metals, he solidification Planar interface between two crystals manufacture of transistors and solar cells nd the electrical conductivity of many ceramic materials MgO+ Al O3, MgAl,O, (SpineD Stability of Atoms Atoms possess thermal energy can move from orman reeds a)anormal lattice d another normal lattice(sel Diffusion) O pALO Mgo AL,O3 )) a normal lattice a vacancy(Vacancy Diffusion) (Interstitial Di (d) one side of bor e other side of boundary2 5. Select sample container Reactivity, strength, cost, ductility all important a) Ceramic refractories (crucibles and boats) -Al2O3 1950°C 10 ml crucibles $30 -ZrO2 /Y2O3 2000°C 10 ml crucibles $94 b) Precious Metals (crucibles, boats and tubes) -Pt 1770°C 10 ml crucibles $500 -Au 1063°C 10 ml crucibles $340 -Ag 960°C 10 ml crucibles $43 -Ir 2450°C 10 ml crucibles $930 -Steel: ~ 1400°C (under inert gas) -Pt: ~ 1600°C (PtO­) -Mo: ~ 2000°C -Ta: ~ 2500°C c) Glass Tubes Pyrex : borosilicate glass (76% SiO2 , 16% B2O3 , BaO ...) Tmax. ~ 400°C Quartz Pure SiO2 , Tmax. ~ 1100°C 6. Heat a)Factors influencing choice of temperature include Tamman’s rule and potential for volatilization Tamman’s Rule: Extensive reaction will not occur until the temperature reaches at least 2/3 of the melting point of one or more of the reactants. b)Initial heating cycle to lower temperature can help to prevent spillage and volatilization c)Atmosphere is also critical Oxides(Oxidizing Conditions) –Air, O2 , Low Temps Oxides(Reducing Conditions) –H2 /Ar, CO/CO2 , High T Nitrides –NH3 or Inert (N2 , Ar, etc.) Sulfides – H2S Sealed tube reactions, Vacuum furnaces 7. Grind product and analyze (x-ray powder diffraction) 8. If reaction incomplete return to step 4 and repeat. Sulfurization Method 1 x x 2 CS / Ar BaCO3 +(1- x)NiO+ xCoO¾¾2 ¾®BaNi - Co S Possible Reaction Paths Between Two Solid Grains A and B A B gas phase diffusion volume diffusion interface diffusion surface diffusion Model for a classical solid-solid reaction (below melting point !): Planar interface between two crystals MgO + Al2O3 ® MgAl2O4 (Spinel) Phase 1: formation of seeds Phase 2: growth of seeds MgO Al2O3 Al MgO 2O3 Solid Solid Reaction Atom Movement in Materials Diffusion: is required for the heat treatment of metals, the manufacture of ceramics, the solidification of materials, the manufacture of transistors and solar cells, and the electrical conductivity of many ceramic materials. Stability of Atoms Atoms possess thermal energy can move from (a) a normal lattice Ë another normal lattice (Self￾Diffusion) (b) a normal lattice Ë a vacancy (Vacancy Diffusion) (c) a interstitial site Ë another interstitial site ( Interstitial Diffusion) (d) one side of boundary Ë the other side of boundary