You are here:

Metallurgy/Metallurgy

Advertisement


Question
QUESTION: Hi, pls i need an explanation about factors affecting the solid solubity of one metal in another

ANSWER: Dear Musa,

In case of solid solubility, lattice structure of host plays a crucial and great role.Please study Hume-Rothery.
Rule1: Atomic Size Factor (the 15%) Rule1.Extensive substitutional solid solution occurs only if the relative difference between the atomic diameters (radii) of the two species is less than 15%. If the difference > 15%, the solubility is limited.Comparing the atomic radii of solids that form solid solutions

Crystal Structure Rule2 .
For appreciable solid solubility, the crystal structures of the two elements must be identical.
There distinguish three of alloys.

Rule 3: Valency Rule .
A metal will dissolve a metal of higher valency to a greater extent than one of lower valency. The solute and solvent atoms should typically have the same valence in order to achieve maximum
solubility.

The Electronegativity Rule .
Electronegativity difference close to 0 gives maximum solubility.The more electro positive one element and the more electronegative the other, the greater is the likelihood that they will form an intermetallic compound instead of a substitutional solid solution. The solute and the solvent should lie relatively close in the electrochemical series.


Substitutional: solute substitutes the solvent in the crystal lattice without structural changes.Some alloy systems exhibit complete solid solubility (e.g. Cu-Ni,Cd-Mg), others show only limited solubility at any temperature.
Interstitial: solute does not occupy the sites in the lattice of the solvent but resides in crystallographic pores.
Transformational: A completely new lattice is formed. Usually occurs as a result of inter-metallic compound formation.

Hope this meets your requirement.

Regards,

RP Sharma

---------- FOLLOW-UP ----------

QUESTION: Pls an explanation from ore to metal of copper and aluminium. Thanks

Answer
Dear Musa,

Copper rich ores are relatively rare, so very valuable, so production costs are quite high.
Copper ores are concentrated by a technique known as froth flotation.
The ores are roasted to drive off unwanted water and convert them to a more suitable chemical form for reduction to copper metal.
After reduction of the ore the liquid copper can be run off from the coke fired copper smelter (furnace).
Below are descriptions of the extraction of copper with balanced chemical equations.
The balanced equations quoted below, are a simplification of what can be quite complicated chemistry, BUT they do adequately describe and illustrate the chemical processes for extracting copper from its ores.
From copper carbonate ores* ...
The ore can be roasted to concentrate the copper as its oxide.
Water is driven off and the carbonate thermally decomposed.
copper(II) carbonate ==> copper oxide + carbon dioxide
CuCO3 ==> CuO + CO2   (a thermal decomposition)
CuCO3(s) ==> CuO(s) + CO2(g)
The oxide can be smelted by heating with carbon (coke, charcoal) to reduce the oxide to impure copper, though this method isn't really used much these days (the 'bronze age' method archaeologically!).
copper(II) oxide + carbon ==> copper + carbon dioxide
2CuO + C ==> 2Cu + CO2     (an oxide reduction reaction, O loss)
2CuO(s) + C(s) ==> 2Cu(s) + CO2(g)
The copper oxide is reduced to copper because of oxygen loss.
The carbon acts as the reducing agent the 'oxygen remover'.
REDOX definition reminders reduction is a process of oxygen loss (or electron gain) and oxidation is a process of oxygen gain (or electron loss).
From copper sulphide ores ...
These include chalcocite/chalcosine = copper(I) sulphide Cu2S and covellite = copper(II) sulphide CuS
and chalcopyrite CuFeS2. which is one of the most important ores for the extraction of copper.
This can be roasted in air to produce copper(I) sulfide which is roasted again in a controlled amount of air so as not to form a copper oxide (see below).
2CuFeS2 +  4O2 ==> Cu2S + 3SO2 + 2FeO
Copper sulphide ores can be rapidly roasted in heated air enriched with oxygen to form impure copper and this extraction process is called 'flash smelting'.
Nasty sulphur dioxide gas is formed, this must be collected to avoid pollution and can be used to make sulphuric acid to help the economy of the process.
copper(I) sulphide + oxygen ==> copper + sulphur dioxide
Cu2S + O2 ==> 2Cu + SO2
Cu2S(s) + O2(g) ==> 2Cu(s) + SO2(g)
The loss of sulfur from the copper sulfide is still a reduction change.
at the same time the sulfur gets oxidised to sulfur dioxide oxygen gain.
or
copper(II) sulphide + oxygen ==> copper + sulphur dioxide
CuS + O2 ==> Cu + SO2
CuS(s) + O2(g) ==> Cu(s) + SO2(g)

Regarding aluminium extraction:
Aluminium is a light, conductive, corrosion resistant metal with a strong affinity for
oxygen. This combination of properties have made it a widely used material, with
applications in the aerospace, architectural construction and marine industries, as well as
many domestic uses. It is only over the last century, however, that it has been possible to
economically refine aluminium, due to the enormous amount of energy needed to
electrolyse its oxide.
Aluminium occurs naturally as the mineral bauxite (primarily a mixture of Al2O3
.
3H2O,
Fe2O3 and SiO2), and is purified in the following process.
Step 1 - Purification of raw materials
Bauxite is mined at Weipa, in Queensland, then crushed and washed to remove water
soluble impurities. The remaining material is dissoved in NaOH and heated. where Al2O3
is selectively dissolved by the reaction
Al2O3 + 6NaOH + 3H2O → 2Na3Al(OH)6
Some crystalline forms of SiO2 can also dissolve by the reaction
SiO2 + 4NaOH → Na4SiO4 + 2H2O
These two new species are soluble, but Fe2O3 is a basic oxide and hence it is insoluble in
this solution and can be filtered out. Over time the Na3Al(OH)6 decomposes to Al(OH)3
(an insoluble species), which is also filtered out.
Na3Al(OH)6 + 2H2O → 3NaOH + Al(OH)3
.
3H2O
This is then decomposed by heating to tempertures above 1000 o
C to give alumina, Al2O3.
2Al(OH)3
.
3H2O → Al2O3 + 9H2O
Step 2 - Reduction of the alumina
The resultant alumina (Al2O3) is dissolved in molten cryolite (Na3AlF6), forming an ionic
and electrically conductive solution. This is decomposed by electrolysis, using a
consumable carbon anode with two concurrent reactions proceding according to the
following equations:
Al2O3 + 3C → 2Al + 3CO
2Al2O3 + 3C → 4Al + 3CO2
The aluminium produced is subsequently alloyed depending on the required end-product.
Alloying reagents include Cu, Mg and Si and these are added in a metal treatment furnace
because of the importance of precise composition control in order to impart the desired
properties

Though your English was not accurate hence I guessed what you want.

Regards,
RP Sharma

Metallurgy

All Answers


Answers by Expert:


Ask Experts

Volunteer


RAJINDER PRASAD SHARMA

Expertise

Questions that i can answer:- 1-sand casting of cast iron,S.G. iron,steel and aluminium alloys 2-Gravity die casting of aluminium 3-Low pressure die casting of aluminium 4-High pressure die casting of aluminium 5-Failure analysis of ferrous and non-ferrous castings Questions that i can`t answer:- 1-testing of iron and steel 2-Problem related to welding 3-Problems related to corrosion 4-Amorphous metals,rubbers,nylon,plastics and plastic moulding

Experience

1-Sand casting and ferrous and non-ferrous alloys 2-Gravity die casting,low pressure die casting,high pressure die casting of aluminium alloys.With a specialisation in auto-mobile components castings. 3-Alloy steel making on arc furnace,AOD,VOD,Con-cast root of alloy steel making. I have been working as Foundry man since last 27 years.

Organizations
Hindustan motors Ltd.

Education/Credentials
I am a Metallurgical Engineer graduated from National institute of Technology,warangal(India) in 1984 and in 1991 i completed my masters degree in business administration(M.B.A.) from Institute of Management Technology,Ghaziabad(India).

©2016 About.com. All rights reserved.