6 Metallurgy Flashcards
Basis of differentiation for Metals and Non metals are?
Atomic Structure
What are physical differences depended on?
What are chemical differences depende on?
- Arrangement of Atoms
- a. Number of valence shell
b. Their behaviour during chemical reaction (ability to redox)
Quality of the metals can be improved by?
- Alloying (mixing with other metals)
2. Protecting by electroplating
What is Metallurgy?
The large scale process of involved in extraction of pure metals from their respective ores.
Give the properties of metals and their exceptions for each.
- Exist in solid state: Mercury
- MP and BP: Na, K, Hg
- Density: Na, K, Ca
- Ductility: Hg, Zn
- Malleability: Zn
- Amphoteric oxides: ZAP
Give the properties of Non-metals and exception for each:
- Non Lustruous: Iodine and Graphite
- MP and BP: Carbon and Silicon
- Density: Diamond
- Ductility: Carbon Fibre
- Malleability: Carbon Fibre
- Acidic or Neutral oxides (CO, N2O, NO, H2O)
Occurance of metals can be:
- Free or Naitive
2. Combined
What is free or Native state?
- Occuring in freee metallic form
- Not acted upon by natural elements
- Like constituents of air and Water
- Example Gold and Platinum
What is Combined state?
Metals occuring in the form of Compounds.
What is a mineral?
- Compounds of various metals
- Found in nature
- Assosciated with their earthly impurities
What is an Ore?
- Naturally occuring mineral
- From which metals can be extracted
- Profitably and Conveniently
What is Metallurgy?
- Large scale process
- Involved in the extraction of pure metals
- From their respective ores
What is a matrix?
- Rocking impurities (including silica, mud)
- Assosciated with the ore
- Also called Gangue
What is a Flux?
- Substance added to the ore
- To get rid of matrix
- Resulting in the formation of a fusible compound -> SLAG
What are the steps involved in the extraction of Aluminium?
- Dressing of the ore (Concentration of the ore and seperating ore from Gangue) -> Baeyer’s Process.
- Conversion of Ore to Oxide Ore (not necesary)
- Reduction of metallic oxide to metal (Hall Heroult’s Process)
- Electrorefining -> Hoope’s Process
What is the most abundant metal in the earth’s crust? Give its %
Which is the 2nd most abundant metal in the earth’s crust? Give its %
Aluminium (7.4%)
Iron(4.7%)
Why doesnt aluminium occur in free state?
Because it is a reactive metal
What is the main ore of Aluminium?
What kind of oxide is it?
Bauxite (Al2O3.2H2O)
It is an amphoteric Oxide.
Give the three equation of Dressing of the ore.1
- Converting impure bauxite to Sodium Aluminate:
Al2O3. 2H2O + 2NaOH —> (150 to 200*) NaAlO2 + 3H2O - Converting Sodium Aluminate to Aluminium Hydroxide:
NaAlO2 + 2H2O —> (50 to 60*) Al(OH)3 + NaOH - Converting of Al(OH)3 to Pure Alumina:
Al(OH)3 —->(1100*) Al2O3 + 3H2O
Give the points of first step of the first step in extraction of aluminium:
- Bauxite (amphoteric) reacted with conc. Soln. of NaOH (base)(FOR 2 HRS UNDER PRESSURE) —> Gives salt and water.
- Impurities dont react -> Not amphoteric
- Impurities are seperated out AS RESIDUE
What are the two main impuries assoscitated with the bauxite ore?
- Fe2O3 and SiO2
Give the points of fsecond step of the dressing in extraction of aluminium:
- NaAlO2 diluted with water + Crystals of Al(OH)3 —> Further precipitates Al(OH)3. This is called Seeding
- After Agitation insoluble Al(OH)3 is filtered out and dried.
THIS IS HYDROLYSIS
Give the points of third step of the dressing in extraction of aluminium:
- Precipitated Al(OH)3 is ignited (1100) to give pure alumina.
What is the second step in extraction of aluminium?
Concentrated ore to its oxide.
Not Necessary. Ore is already oxide.
What is the 3rd step in extraction of Aluminium?
Hall Heroult’s Process.
Conversion of Pure Alumina to Pure Al
Give the constituents and ratio of the electrolytes used?
Fused Alumina: Cryolite (Na3AlF6) : Fluoraspar (CaF2) :: 1: 3: 1
By weight
What is the cathode and Anode of the electrolytic cell in hearoult’s process?
Cathode: Carbon Lining (gas carbon) of the cell
Anode: Carbon Rods (Graphites) attached to copper clamps dipping into fused electrolyte
Temperature and Current needed for the electrolyte is?
950 degrees
100 amperes at 6 to 7 volts
The electrons involved in the balanced equation is?
Six Electrons
6
The products formed in anode and cathode are?
Cathode: Pure aluminium metal
Anode: Oxygen gas (CO and CO2)
Why is Aluminium Electrolytically reduced?
- Al2O3 is highly stable oxide. =>
- Aluminium has strong affinity for oxygen.
- Hence cant be reduced by reducing agents.
What are the difficulties faced during the electrolytic reduction of aluminium?
- High temperatures due to the MP (2050) of Alumina
a. Large amount of electrical energy required to liberate Al from Alumina.
b. Large amount of electrical energy to Mantain the electrolyte in the molten state.
c. Liberated Al (650) will volatize out and wasted. - Fused alumina is almost a non-electrolyte
What is the MP of alumina and Aluminium?
Alumina -> 2050 degrees
Aluminium -> 660 degrees
Why is Cryolite and Fluorspar added?
Addition of Cryolite (mainly in a higher ratio) and Fluorospar:
1. Lowers the Fusion point to 950 instead of 2050.
2. Enhanced the mobility by acting as a solvent for electrolytic mixture.
Cryolite:
1. Molten state of subdivision -> Dissolves Alumina
2. Enhances the conductivity of the mixture -> Pure alumina (non-conductor)
What are the elements present in the electrolyte?
Al2O3, Na3AlF6, CaF2
Who resolved the difficulties faced during the eelctrolytic reduction of copper and made it cheaper and Simpler and when?
Charles Hall in 1886.
Why is a layer of coke sprinkled over the electrolytic mixture?
- Prevents buring of carbon electrolodes in air (at the emergence point of the bath)
- Prevents heat loss by radiaiton
Why are graphite anodes continuously replaced?
- Oxygen is evolved
a. May escape as agas
b. React with carbon anode.
i. Oxidies to Carbon monoxide can escape through an outlet or
ii. Can further burn to CO2 - Carbon is consumed and renewed perioidcally.
why is it preferable to use a number of graphite electrodes as anode instead of single electrode?
This is because carbon anode is consumed after a certain period of usage.
Pure aluminium is ___ than the electrolyte.
It is periodically removed through the ___ or ___ at the ___
Heavier
Outlet or Tap hole at the base
Decrease in concentration of Al2O3, ___ the resistance and ___ on the control lamp.
Increases, GLOW
Unintuitive
Why is electrolytic reduction of aluminium said to be a continuous process?
- Pure aluminium settles down (heavier). Periodically removed thu outlet and tap hole at the base.
- When concentration falls (resistance increases and light bulb glows) then more alumina is added.
Then the process continues.
Al that is obtained is almost ___% pure
99.5% !!!
What is the step 4 of extraction of aluminium?
Electrorefining of the impure metal (already 99.5% pure -_-)
Tank contains, how many layers and what are they>O
In Hoope’s process
Upper Layer (Cathode), Molten Pure Al with carbon Electrodes Middle layer (electrolyte) -> Cryolite, CaF2, BaF2, AlF (*NOT AlF3*) Lower Layer (Anode) -> Impure Al with carbon lining at the anode.
How is Pure Al withdrawn in Hoope’s Process?
Tapping Hole
What are Alloys?
- Substance prepared by adding other metals (or non-metals)
- To a base metal
- In appropriate proportions
- Obtain certain desirable properties.
How are alloys made?
By melting components TOGETHER and solidifying the mixture.
Properties of Alloys:
- Its components must be miscible and not seperate on solidification
- Properties are intermediate between those of the metals composing them.
What is Amalgam?
An alloy in which base metal is mercuy.
What is Liquid amalgam and an amalgam used in voltain cells?
- Na/Hg
2. Zn/Hg
What are the ores of alluminium?
- Duralumin
2. Magnalium
Give the percentage composition and materials involved in Duralumin.
Al (95%)
Cu (4%)
Mg (0.5%)
Mn (0.5%)
Give the percentage composition of Magnalium?
- Al (95%)
2. Mg (5%)
Uses of the Al Alloys:
Duralumin -> Al (lightness) and Mg (Strength)
Aircrafts, Light tools and Cooker
Magnalium -> Light, Hard, Tough and Corrosion resistant
Aircrafts, Scientific tools