7 Solid State Synthesis

Question 1

4 types of SS syn

Answer 1

• ceramic
• mechanochemical
• combustion
• low temperature

Question 2

What is Ceramic method?
- advantages/disadvantage

Answer 2

• rxn solid components at high T, solid percussors mixed and heated
• adv: readily available percussors, Inexpensive powder production
• dis: time consuming, power intensive

Question 3

Steps in ceramic

Answer 3

Grind/mix, press into pellet, in boat/furnace, heat, anneal, cool

Question 4

why slow heating in ceramic method

Answer 4

avoid vigorous rxn

Question 5

types of boats for cermaic

Answer 5

Quarts, Alumina

Question 6

What is annealing

Answer 6

• extended process at high T, ~50% rxn temp
• passivates defects

Question 7

Why grind reagents

Answer 7

Increase SA

Question 8

Why press into pellet

Answer 8

decrease path lenth

Question 9

In __________ atoms/ions _______ through lattice to passivate defects

Answer 9

annealing, migrate

Question 10

rule of thumb what T rxns occur

Answer 10

2/3 MP of one component , provides high mobility w/o melting material

Question 11

Rxn rate _______ as rxn progresses, equation?

Answer 11

decreases
rate= kx^-1 x=[prod]

Question 12

Factors that affect kinetics of SS rxns

Answer 12

1) contact area b/w surface
2) rates of diffusion ion through various phases
3) rate nucleation of product phases

Question 13

Where does the new compound form? defects?

Answer 13

In middle,
more defects as progresses

Question 14

Experimental considerations (4)

Answer 14

1) use salt to decompose high T
2) rxns start at structural defects (extended defects: grain bound, dislocations ect)
3) Need inert boat (silica, alumina, graphite)
4) precursors volatile/air sen use ampule

Question 15

how to increase SA (5)

Answer 15

grind, use ball mill, pellets, periodic cooling/grinding

when possible (usually not) do rxn in melt

Question 16

Disadvantages of ceramic (5)

Answer 16

• make undesirable phases
• inhomogeneous distribution of dopants
• can’t do in-situ monitoring
• difficult to separate prod mixtures
• reactants need to have sim decomposition T

Question 17

Molecular mixing: Coprecipitation
- challenges

Answer 17

• salts 2 metals ppt from solution to allow for molecular mixing
• need sim solubilities/ppt rates

Question 18

Molecular Mixing: Precursor
- challenges

Answer 18

• uses precursors that incorporate the atoms/ions wanted in prod with correct stoich ratios
• need to be able to remove impurities, not everything has a precursor

Question 19

Affecting Kinetics: Nucleation

Answer 19

• crystal structure prod diff then react/ lattice parameters largely diff maybe no nuc

Question 20

Oriented rxns

Answer 20

Epitactic: structure sim interface b/w prod and reac

Topotactic: structure sim bulk b/w prod and reac

Question 21

Mechanical methods

Answer 21

• reactive surfaces form when reagents place with hardon steal/ WC (tungston carbide)
• lots of defects , anneal but be carful not to make new pdt
• high diffusion even at RT, some localize heating but does not affect

Question 22

most defects of all methods

Answer 22

mechanical

Question 23

rank path lenths

Answer 23

mechanical> co-ppt > single precursor

Question 24

Combustion

Answer 24

• Fast, started using: electric arc, laser pulse, spark, chemical reaction
• less E, short rxn time, low operating/processing cost, vigorous, make not at eq pdt
• very exo

Question 25

2 types combustion: self propagation vs simultaneous combustion

Answer 25

self propagation (SHS): rxn progress through waves simultaneous combustion (SCM): throughout solid once ignition T reached

Question 26

Low T rxns - Intercalation rxn:

Answer 26

- layered structures with weak intermolecular interactions

Question 27

intercalation vs insertion rxn

Answer 27

intercalation: layered material insertion: 3D units

Question 28

low T: Insertion rxn

Answer 28

- have large lattice - cations inserted

Question 29

Low T: Ion exchange

Answer 29

exchange weakly bond with stronger

Question 30

Solid from gas phase

Answer 30

- non volatile reacts with gas to make stuff -exo if sink hotter source -endo is sink cooler source

Question 31

light bulbs

Answer 31

W (halogen( better, has lower vapour P then C (incandescent) and bigger MP - halogen in inter gas to reduc eveaperation - transort to gas phase and undergo reations in gas phase (CVT)

Question 32

Chemical vapour deposition (cvd)

Answer 32

make films - don't want gas phase rxn - 1+ precusor in vapor phase deposide on heated substrate chamber -

Question 33

General Aspects – CVD

Answer 33

1. Reagent transport in gas phase 2. Diffusion of precursors to the substrate 3. Adsorption of precursors onto growth surface 4. Diffusion to growth sites 5. Surface chemical reactions leading to film deposition 6. Desorption of byproducts 7. Transport of byproducts

Question 34

Precursor characteristics

Answer 34

Volatile liquid. – High thermal stability (evaporation/ transport). – Clean decomposition make stable by products readily removed from the reaction zone. – High purity, readily available, low cost. – Non-toxic and non-pyrophoric

Question 35

Percussor for CVD

Answer 35

multiple and single source