2.4 Solid state synthesis methods

Question 1

Problems in material synthesis

Answer 1

1) Reactions intrinsically slow
2) High temperatures requireed
3) Purity difficult to control

Question 2

what is method used- dependant on?

Answer 2

WHAT material and FORM of that material

Question 3

Methods

Answer 3

Solid state reactions
Combustion (SSM and SHS)
Mechano synthesis
Sol gel synthesis
Hydrothermal 
Czochralski method
CVD

Question 4

Solid state reactions

Answer 4

Precursors stoichiometric ratios
Grind up precusor mix and heat 500-2000C
Slowish 12-24

Heat resistance cruciblee and grind throughout
High purity
BaTiO3

Question 5

Combustion 2 types

Answer 5

SHS
Self-propagating High-T synthesis
SM’s reacto exotherm and once initiated generate a high T
SSM solid state metathesis
exothermic nature comes from a high lattice energy product
better controlled

Both initiation t varies reaction to reaction
SSM generally better controlled
silica crucible

Question 6

Mechanosynthesis general

Answer 6

aka (Ball milling or liq assisted grinding)

Providing continual mechanical stress to a system

Provides non conventional reactivity and exotic intermediates or many steps to one

Contamination risk from BM media LOWERS PURITY
Greener/low cost- no high T required
EG ZEOLITES

Question 7

Sol-gel

Answer 7

Wide range of forms produced
ceramic fibres, nanoparticles, aerogel, ceramic
(M) alkoxide and others
SOL: colloidal suspension of nanoparticles
GEL:interconnected network of pores and chains

AMORPHOUS product

Question 8

mechanosynthesis method

Answer 8

Method:
ball milling media and reactants in a vessel which is shaken or rotated continuously
ball milling media = zirconica, steel or ceramic

Question 9

sol gel method

Answer 9

1. Prepare solution of cationic precursors
2. Gradually dry until a sol forms
3. continue to mature until amorphous gel forms
4. Calcine gel to form oxide product

Question 10

Hydrothermal synthesis

Answer 10

Heating reactants in water/steam at high p and T

Water is both solvent and pres transmitting medium

seal in hydrothermal bomb and then calcine
t=100C-500C

solvothermal=other solvant than water
eq quartz-piezoelectric

Question 11

Czochralski method

Answer 11

eg si semiconductor
Melt precursors (v high T)
add dopants
dip a rod mounted with a seed- a single crystal with specific desired orientantion into the molt
slowly pull up rod- whilst rotating one large crystal with right orientation willl form

v slow but v useful and v pure

Question 12

CVD

Answer 12

Chemical Vapour deposition

• high purity films and coatings
• volatile precursors

A(v)->B(s) +C(g)

Question 13

CVD step by step method

Answer 13

1) Precursor in gas phase
2) PRecursor transported to surface
3) adsorb onto surface
4) diffuse across surface
5) reaction/growth (island or step
6) desorbtion of any volatile products