Synthesising solid state materials

Question 1

Which products will form from high temperatures?

Answer 1

Thermodynamic product

Question 2

Which products will form from low temperatures?

Answer 2

Kinetic product

Question 3

What is the ceramic method?

Answer 3

Grind up and heat materials until they react

Question 4

What are some of the disadvantages to the ceramic method?

Answer 4

High heats are needed to overcome lattice energy which may cause product to decompose, may give incomplete reaction, compositionally inhomogeneous products, starting materials need to be really pure as purification afterwards is difficult

Question 5

What is a chimie douce method?

Answer 5

Initial low temp reactions followed by firing at high temps

Question 6

What are the advantages of chimie douce reactions?

Answer 6

Higher purity as less time being heated, mixing at the atomic level leads to more homogeneous product

Question 7

What are some disadvantages to chimie douce methods?

Answer 7

Expensive reagents, must be optimised between reactions

Question 8

What is the process of a sol gel reaction?

Answer 8

Condensation to form sol, gelation to form gel and then supercritical drying/ageing

Question 9

What are two examples of sol-gel reactions?

Answer 9

Silica - ensures purity of silica to be used in further reactions such as optical fibers, formation of not naturally occuring mesoporous solids using templating technique

Question 10

What are hydrothermal reactions?

Answer 10

Heat to temperatures greater than the BP of solvent using a teflon lined cylinder and controlling pressure

Question 11

What are the advantages of using hydrothermal reactions?

Answer 11

Can use lower temps that other methods, use reactants that don’t typically dissolve in water

Question 12

What are zeolites?

Answer 12

Microporous aluminosilicate framework structures

Question 13

What are zeolites used for?

Answer 13

Catalysts and molecular separation

Question 14

What is the process for producing zeolites?

Answer 14

using silica and alumina reagents under hydrothermal conditions at high pH, gel forms from copolymerisation between silica and aluminate ions

Question 15

What does topotaxy mean?

Answer 15

When a solid state reaction occurs with a 3D orientational and structural resemblance between the reagent and product

Question 16

What does epitaxy mean?

Answer 16

When a crystal grows on a crystaline substrate with a 2D correspondence

Question 17

What are the different heating methods?

Answer 17

Electric furnaces, CO2 lasers, microwave heating, combustion heating

Question 18

What are the advatanges and disadvantages of electric furnaces?

Answer 18

Cheap but issues with environment sensitivity

Question 19

What are the advantages and disadvantages of microwave heating?

Answer 19

Faster reactions because of more even heating, can be used dry or in solution, but is more expensive and difficult to know which compounds will be compatible (absorb microwave radiation)

Question 20

What are the advantages and disadvantages of combustion heating?

Answer 20

Extreme temps with no external source but can be dangerous and difficult to control

Question 21

What is the method of chemical vapour deposition?

Answer 21

Reactants are delivered in gas phase and product phase is deposited as a thin film on a substrate

Question 22

What are the advantages of CVD?

Answer 22

Crystal and substrate have epitaxial relationship and so the orientation can be controlled.

Question 23

What is the method for producing large single crystals?

Answer 23

Czochralski process

Question 24

What is the Czochralski process?

Answer 24

Under an inert atmosphere/chamber where silicon is melted and a rod containing a single crystal of silicon is placed and acts as a seed to grow larger crystal

Question 25

What is the Czochralski method used for?

Answer 25

To produce large crystals for semiconductors