Synthesising solid state materials Flashcards
(25 cards)
Which products will form from high temperatures?
Thermodynamic product
Which products will form from low temperatures?
Kinetic product
What is the ceramic method?
Grind up and heat materials until they react
What are some of the disadvantages to the ceramic method?
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
What is a chimie douce method?
Initial low temp reactions followed by firing at high temps
What are the advantages of chimie douce reactions?
Higher purity as less time being heated, mixing at the atomic level leads to more homogeneous product
What are some disadvantages to chimie douce methods?
Expensive reagents, must be optimised between reactions
What is the process of a sol gel reaction?
Condensation to form sol, gelation to form gel and then supercritical drying/ageing
What are two examples of sol-gel reactions?
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
What are hydrothermal reactions?
Heat to temperatures greater than the BP of solvent using a teflon lined cylinder and controlling pressure
What are the advantages of using hydrothermal reactions?
Can use lower temps that other methods, use reactants that don’t typically dissolve in water
What are zeolites?
Microporous aluminosilicate framework structures
What are zeolites used for?
Catalysts and molecular separation
What is the process for producing zeolites?
using silica and alumina reagents under hydrothermal conditions at high pH, gel forms from copolymerisation between silica and aluminate ions
What does topotaxy mean?
When a solid state reaction occurs with a 3D orientational and structural resemblance between the reagent and product
What does epitaxy mean?
When a crystal grows on a crystaline substrate with a 2D correspondence
What are the different heating methods?
Electric furnaces, CO2 lasers, microwave heating, combustion heating
What are the advatanges and disadvantages of electric furnaces?
Cheap but issues with environment sensitivity
What are the advantages and disadvantages of microwave heating?
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)
What are the advantages and disadvantages of combustion heating?
Extreme temps with no external source but can be dangerous and difficult to control
What is the method of chemical vapour deposition?
Reactants are delivered in gas phase and product phase is deposited as a thin film on a substrate
What are the advantages of CVD?
Crystal and substrate have epitaxial relationship and so the orientation can be controlled.
What is the method for producing large single crystals?
Czochralski process
What is the Czochralski process?
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
