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Chem 327 > 7 Solid State Synthesis > Flashcards

7 Solid State Synthesis Flashcards

1
Q

4 types of SS syn

A
  • ceramic
  • mechanochemical
  • combustion
  • low temperature
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2
Q

What is Ceramic method?
- advantages/disadvantage

A
  • rxn solid components at high T, solid percussors mixed and heated
  • adv: readily available percussors, Inexpensive powder production
  • dis: time consuming, power intensive
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3
Q

Steps in ceramic

A

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

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4
Q

why slow heating in ceramic method

A

avoid vigorous rxn

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5
Q

types of boats for cermaic

A

Quarts, Alumina

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6
Q

What is annealing

A
  • extended process at high T, ~50% rxn temp
  • passivates defects
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7
Q

Why grind reagents

A

Increase SA

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8
Q

Why press into pellet

A

decrease path lenth

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9
Q

In __________ atoms/ions _______ through lattice to passivate defects

A

annealing, migrate

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10
Q

rule of thumb what T rxns occur

A

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

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11
Q

Rxn rate _______ as rxn progresses, equation?

A

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

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12
Q

Factors that affect kinetics of SS rxns

A

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

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13
Q

Where does the new compound form? defects?

A

In middle,
more defects as progresses

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14
Q

Experimental considerations (4)

A

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

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15
Q

how to increase SA (5)

A

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

when possible (usually not) do rxn in melt

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16
Q

Disadvantages of ceramic (5)

A
  • 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
17
Q

Molecular mixing: Coprecipitation
- challenges

A
  • salts 2 metals ppt from solution to allow for molecular mixing
  • need sim solubilities/ppt rates
18
Q

Molecular Mixing: Precursor
- challenges

A
  • 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
19
Q

Affecting Kinetics: Nucleation

A
  • crystal structure prod diff then react/ lattice parameters largely diff maybe no nuc
20
Q

Oriented rxns

A

Epitactic: structure sim interface b/w prod and reac

Topotactic: structure sim bulk b/w prod and reac

21
Q

Mechanical methods

A
  • 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
22
Q

most defects of all methods

A

mechanical

23
Q

rank path lenths

A

mechanical> co-ppt > single precursor

24
Q

Combustion

A
  • 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
25
Q

2 types combustion: self propagation vs simultaneous combustion

A

self propagation (SHS): rxn progress through waves

simultaneous combustion (SCM): throughout solid once ignition T reached

26
Q

Low T rxns - Intercalation rxn:

A
  • layered structures with weak intermolecular interactions
27
Q

intercalation vs insertion rxn

A

intercalation: layered material
insertion: 3D units

28
Q

low T: Insertion rxn

A
  • have large lattice
  • cations inserted
29
Q

Low T: Ion exchange

A

exchange weakly bond with stronger

30
Q

Solid from gas phase

A
  • non volatile reacts with gas to make stuff

-exo if sink hotter source
-endo is sink cooler source

31
Q

light bulbs

A

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)
32
Q

Chemical vapour deposition (cvd)

A

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

33
Q

General Aspects – CVD

A
  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
34
Q

Precursor characteristics

A

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

35
Q

Percussor for CVD

A

multiple and single source

Chem 327 (18 decks)

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