Definition
The branch of chemistry which deals with properties of matter and
their application in various areas of science and engineering is
called as materials science. The domain of materials science in
which we is related to the studies of the physical and chemical
behaviour of metallic elements and their mixtures is known as
‘METALLURGY’
 In any metallurgy process of any metal involves
some common steps:-
Metals can be classified:1) According to Noble metals:which have high resistance to
oxidation, corrosion, dissolution in organic acids; are 8 in
numbers: Au, Pt, Os, Ag, Pd, Rh, Ru. Out of these, silver has
low corrosion resistance in oral conditions and is not
considered as noble metal in dentistry. However, alloys of
silver and palladium have excellent corrosion resistance and
are some times known as semiprecious metals.
2) According to Base metals: Large number of metals, which
occur more abundantly and undergo oxidation and
corrosion easily, are base metals.
3) According to Metalloids: Few elements carbon, boron,
germanium, silicon, sometimes non metals. These and their
alloys have found their immense use due to their ability to
conduct electricity in selective directions in semiconductor
devices, communication and industries
 Metals also can be classified according
to their physical properties:
1)Metallic bonding:
These have crystalline structure due to long strange electrostatic
attractive forces and form metallic bonds. The valence electrons in
the outermost shells, get easily debonded at low temperatures by
thermal energies, leaving behind, the atoms as positive ions in their
lattice positions.
2) Form positive ions in solution :
Eg:-H in HCl, Na in NaCl, K in KCl etc. in solutions.
3)Good conductors of heat and electricity: free
electron gas density is responsible for this conduction. Gold,
silver, platinum, copper etc; are very good conductors due to
their high electron gas – densities. Ceramics, polymer resins etc.
lack free electrons and therefore are insulators.
4)ductile and malleable: Eg:- Gold, Platinum, Silver,
Copper, Tin etc.
5)Opaque due to absorption of electromagnetic radiations by
the free electrons.
6)Most of the metal surfaces appear white, except few, like
gold, copper etc as the free electrons can re-emit light of all
wavelengths.
EXTRACTIVE METALLURGY
• it is the study of the processes used in the separation and
concentration (benefication) of raw materials.
• The field is an applied science, covering all aspects of the physical
and chemical processes used to produce mineral-containing and
metallic materials, sometimes for direct use as a finished product,
but more often in a form that requires further physical processing
• Extractive metallurgy is the practice of removing valuable metals
from an ore and refining the extracted raw metals into a purer
form.
.
In order to convert a metal oxide or sulfide to a purer metal, the
ore must be reduced physically, chemically, or electrolytically.
• Extractive metallurgists are interested in three primary streams:
feed, concentrate (valuable metal oxide/sulfide), and tailings
(waste).
• After mining, large pieces of the ore feed are broken through
crushing and/or grinding in order to obtain particles small
enough where each particle is either mostly valuable or mostly
waste.
• Concentrating the particles of value in a form supporting
separation enables the desired metal to be removed from
waste products.
The sub disciplines are mineral processing,
pyrometallurgy, and hydrometallurgy
electrometallurgy.
PYROMETALLURGY : involves high temperature processes where
chemical reactions take place among gases, solids, and molten
materials.
HYDROMETALLURGY : is concerned with processes involving aqueous
solutions to extract metals from ores.
* The most common hydrometallurgical process is leaching, which
involves dissolution of the valuable metals into the aqueous solution.
* After the solution is separated from the ore solids, the solution is often
subjected to various processes of purification and concentration before
the valuable metal is recovered either in its metallic state or as a
chemical compound.
ELECTROMETALLURGY : involves metallurgical processes that take
place in some form of electrolytic cell.The most common types of
electrometallurgical processes are electrowinning and electro-
refining.
CARBONYL METALLURGY : is used to manufacture products of iron,
nickel, steel, and other metals.
*
Coatings are produced by vapor plating using metal carbonyl
vapors.
*
Carbonyl metallurgy is useful as a low temperature metal coating
technique that may well find many applications in the future.
SOLID
SOLUTIONS
Content:i.
Definition of solvent ,solute and solid solution.
ii.
Types of solid solution
iii.
iv.
v.
vi.
vii.
1.Substitution solid solution
-Disordered (b)
-Ordered (c)
2.Interstitial solid solution
3.Eutectic solid solution
viii. Hume Rothery’s Rules
ix.
Crystal Structure Factor
2. Relative Size Factor
x.
xi.
xii.
xiii.
xiv.
Chemical-affinity Factor
Properties of solid solutions
Coring
Homogenization
Solidification of alloys
4.Relative Valence Factor
What is solvent and solute?
Solvent definition :-the component of a solution
that is present in the greatest amount .it is the
substance in which the solute is dissolved.
Ex:- the solvent for seawater is water.
the solvent for air is nitrogen.
Solute definition :-the substance that is dissolved in
a solution .for solution of fluid the solvent is present I
greater then solute.
Example:-salt in water
What is solid solution ?
Any homogenous crystalline solid,
consisting of more than one type of
molecule or atom randomly dispersed, in
which the structure is independent of its
composition
Ex.:-brass is a solid solution
(copper 64% & zinc 36% )
Types of solid solution
1.Substitution solid solution (brass)
1. Disordered (b)
ii. Ordered (c)
2.Interstitutional solid solution
3.Eutectic solid solutions
1.Substitutional solid solution
One type of atom for another so that solute(cu)
enter the crystal to take positions normally
occupied by solvent atoms (nickel)
The great majority of the solid solution are
substitutional type
Example:-Cu-Ni,Cd-mg.
Disordered substitutional solid solution
Solvant atom do not occupy any
specific position Random in the lattice
structure of
the solvent.
example :- alloy
Ordered substitutional solid solution
The alloy in the disordered condition, If in I cooled
slowly, under-goes a re-arrange mentof the atoms
because of the diffusion that takes place during
cooling.
INTERSTITIAL SOLID SOLUTION
•
•
•
•
•
Small solute vs. large solvent
More common for C, N, O, and H as solutes
More easily dissolved in transition metal solvent
Solubility is limited
Solute diffuses easily via interstitial diffusion route.
The C is still too large for the interstitial sites so the Fe
lattice is badly strained.
Eutectic
 Different
solid solution
solutions of limited solutions of
limited solubilities,precipitate as
alternate layers of alpha and beta solid
solutions at certain eutectic
compositions whch has single lowest
melting point lik 779 degree celsius in
ag-cu eutectic alloy with ag= 72%
,cu=28%
Conditions (factors)for solid solubility
 It

s defined by Hume rothery rules
common elements in gold and palladium alloys
metal
Crystal lattice
Atomic
diameters
Gold
Fcc
2.882
Platinum
Fcc
2.775
Palladium
Fcc
2.750
Silver
Fcc
2.888
Copper
fcc
2.556
Tin
Bct
3.016
Zinc
Hcp
2.665
silicon
cubic
2.351
Hume Rothery’s Rules

Types of Hume Rothery’s Rules :
1. Crystal Structure Factor
2. Relative Size Factor
3. Chemical-affinity Factor
4. Relative Valence Factor
William Hume-Rothery (18991968)
1. Crystal Structure Factor:The Crystal lattice structure of the two
elements should be same for complete solubility,
otherwise the two solution would not merge into
each other.
Also, for complete solid solubility the size
factor must usually be less than 8%
Example:-Al and Si
Al and Si is partially soluble. (phase diagram)
Si => diamond cube Structure
Al=>F.C.C. Structure
2. Relative Size Factor(the 15%):-
If two metals are to exhibit extensive solid
solubility in each other it is essential that their atomic
diameter shall be fairly similar, since atoms differing
greatly in size cannot be accommodated readily in the
same structure.
If the relative size factor is between 8% and 15%, the
alloy system usually shows a minimum and if this factor
is greater than 15%, substitutional solid solution
formation is very limited
Mismatch=
r(solute)-r(solvant)
r(solvant)
*100<=15%
EXAMPLE:- Al and Si
Radius of Aluminum is 0.0143nm
Radius of silicon is 0.117nm
%different =
*100
rAl - rsi *100
rAl
= 0.0143-0.117
0.0143
=18.2% >15%
3.Chemical-affinity Factor
The greater the chemical affinity of two
metals, the more restricted is their solid solubility.
When their chemical affinity is great, two
metals tend to form an intermediate phase rather
than a solid solution.
Generally, the farther apart the elements are
in the periodic table, the greater is their chemical
affinity.
EXAMPLE:- Al and Si
Al electro negativity is 1.6
, Si electro negativity is 1.9
4. Relative Valence Factor
Consider two atom ,one with large
valence electron and the other with
small number of valence electrons
EXAMPLE:- Al and Si
Al has a +3 charge
Si has a +4 charge
Another Example is :- in the Al-Ni
alloy system, both metals have f.c.c.
structure. The relative size factor is
approximately 14% . However, Ni is
lower in valance than Al and thus
solid nickel dissolves 5% aluminums,
but the higher valance Al dissolves
only 0.04% Ni.
Properties of solid solutions
 Corrosion
resistance- changes according to
noble metal contents
 Density Mechanical properties-small difference in
atomic sizes cause localised lattice
distortion-increasing slip resistance
 Thermal properties- alloys have ranges of
melting temperatures depend on
compositions .
 Coefficient of thermal expansion also can
be changed
Coring

From the silver- palladium phase it is evidence
that the composition of the grain is not uniform.
The first nucleus is rich in palladium, but as the
temperature decreases, the palladium content
decreases with an increase in the silver content
.

It can recognized therefore that cored
structure results with the core consisting of the
higher melting alloy constituents and the
matrix containing the lower melting
components. This is called coring. A cord
structure is undesirable particularly in relation
to the corrosion resistance of the alloy. A
cored structure is formed a) when the alloy is
rapidly cooled after solidifying. b) when the
rang between the liquidus line and the solidus
line is great
HOMOGENISATION
 It
is the process used to eliminate coring
through elimination of compositional
differences. This is done by heating the
cored structure below is melting
temperature to allow atomic diffusion to
take place
Solidification of alloys
 The
melting temperature of any pure material
(a one-component system) at constant
pressure is a single unique temperature. The
liquid and solid phases exist together in
equilibrium only at this temperature. When
cooled, the temperature of the molten
material will steadily decrease until the melting
point is reached.
 At
this point the material will start to crystallise,
leading to the evolution of latent heat at the
solid liquid interface, maintaining a constant
temperature across the material. Once
solidification is complete, steady cooling
resumes. The arrest in cooling during
solidification allows the melting point of the
material to be identified on a time-temperature
curve.
ALLOYS
CONDITIONS :
 HIGH
CORROSION RESISTANCE
 BY ALLOYING WITH NOBLE METALS LIKE
GOLD,PLATINUM OR PASSIVATING METALS
LIKE CHROMIUM,TITANIUM
 ADEQUATE MECHANICAL PROPERTIES
 BY
SOLUTION HARDENING ,GOLDCOPPER,SILVER,GOLD-PLATINUMPALLADIUM,CHROMIUM-COBALT OR
NICKEL,CARBON-STEEL ETC
 MECHANICAL PROPERTIES ALSO CAN BE
CHANGED BY HEAT
TREATMENTS,TEMPERING,ANNEALING,PREC
IPITATIONS OF PHASES ETC
 SUITABLE THERMAL PROPERTIES
 MELTING
TEMPERATURE RANGE CAN BE
INCREASED BY ADDING
PLATINUM,PALLADIUM,OR CAN BE
LOWERED (BY ADDING
SILVER,ZINC,COPPER,OR INDIUM),
 COEFFICIENT OF THERMAL EXPANSION
ALSO CAN BE INCREASED OR DECREASED

ALLOYS ARE PREPARED BY MELTING THE
INGREDIENTS WITH REQUIRED PROPORTIONS
AND SOLIDIFYING BY CASTING INTO SUITABLE
PREPARED MOULDS.THE COMPONENTS ARE
CAREFULLY SELECTED TO MINIMIZE TOXIC
MATERIALS LIKE MERCURY,BERYLLIUM,NICKEL
ETC..COMPOSITIONS ARE USUALLY EXPRESSED
BY WEIGHT PERCENTAGE .BUT IT IS MORE
USEFUL TO EXPRESS IN ATOMIC PERCENTAGE
AS THIS GIVES BETTER PICTURE OF THE PHASE
STRUCTURES.
 FOR
EXAMPLE:AuCu3 phase has Au and
Cu in 1:3 or 25 and 75 atomic
percentages , whereas 45:55 weight %.
 Similarly AuCu phase has 50:50 atomic%
and 70:30 weight% if gold and copper are
alloyed resp
 The
properties of alloys change
according to the compositions. Hence
various properties of the alloys of different
compositions are studied from 0% to
100%.The solidification temperature
changes determined from cooling curves
are represented graphically which is
known as constitution or equillibrium
phase diagrams
CLASSIFICATION OF DENTAL
CASTING ALLOYS
1.NOBILITY :
 NOBLE
METALS ARE Au,Pt,Ir,Os,Pd,Rh,Ru
HIGH NOBLE:Contain gold >=
40%,noble metals>=60%
 EX:-Au-Cu-Ag-Pd-Au-Pt etc……
NOBLE
 Contain
noble metals>=25%
 Ex:-Pd-Ag-Au
PREDOMINANTLY BASE
MATERIALS
 Noble
metals <=25%or 0-25%
 Ex:-Cr-Co,Cr-Ni,Cr-Co-N,Cr-Co-W,or
 Ni-Ti-,Ti-Al-V,FeC,Fe-Cr-Ni-C,Fe-Cr-Ni-
C(Stainless steel)
COMPOSITIONS

Mentioned according to decreasing order of
weight percentages

MAJOR ELEMENTS:gold alloys,palladium
alloys,silver alloys,titanium alloys……..

MAJOR TWO ELEMENTS:Au-Cu,Au-Ag,PdAg,Ag-Pd,Ni-Ti,CoCr,Ni-Cr,……

MAJOR THREE ELEMENTS:Au-Cu-Ag,Pd-AgCu,Co-Cr-W,Ni-Cr-Be,Ti-Al-V……
DOMINANT PHASES
 Single
isomorphic solid solution;AuCu,PdAg….
 Eutectic:Silver –
copper,eutectoid:pearlite,stainless steel
 Peritectic change ;Pt-Ag,Ag-Sn…..
 INTER-METALLIC:Au-Cu,AuCu3,Cu3Sn,Cu6Sn5,Ag3Sn….
APPLICATIONS
 All-metal
inlays,crowns,bridges
 Metal-ceramic prosthesis
 Removable and fixed cast partial
dentures
 Implants,post and cores
MECHANICAL PROPERTIES
 Soft-burnishable:YS<80MPA
 Medium-burnishable:YS=80-180MPa
 Hard-heat
hardenable YS=180-240MPa
 Extra hard-heat hardenable YS>300MPa
 NOTE
1:-If the alloys contain only
two,three,four metals they are called as
binary,ternery,quarternery etc..,alloys.
GOLD COPPER SYSTEM
INTRODUCTION
 Gold
and Copper have close melting points
1063℃and1083℃ .They are completely soluble in
each other forming solid solution at high
temperatures.These are disordered substitutional
alloy below the solidus.The equillibrium phase
diagram has a narrow regionin between the liquidus
and solidus,and meet each other at 911℃ when the
gold is about 80 wt %
 Below the solidus temperature when the atomic % of
gold is more than 50% disordered substitutional,solid
solution of Cu in Au phase is formed.when this α
phase is slowly cooled, below 375℃ or 410℃, the
attraction between Au and Au or Cu atoms, cause
intermetallic alloys 𝜶𝟏 and 𝜶𝟐 phases.
Au-Cuȝ phase :
 If the amount of copper atoms is large or
Au:Cu=25:75 at percentage solid state
reaction take place by ordering the
copper atoms in the middle of the faces
and gold atoms at the corners of f.c.c
unit cell.
Under these arrangement ,it can shown
that there are three copper atom
situated nearest to each gold atoms .This
gold copper phase has same f.c.c
structure and does not contribute to the
hardening of the alloy significantly
gold copper,fct phase:
 when the percentage of the gold is
more,the solid state reaction take
place by forming intermetallic alloy
gold copper equilibrium phase, with
copper atoms and gold atoms in
alternate layers.due to the small
difference in atomic size and
interatomic forces , between copper
atom, the super lattice formed has
one axis shorter, i.e. face centred
tetragonal fct. Structure.
This phase precipitates by slow cooling, in
different orientation at different sites.at each
site it cause distortion of disordered fcc lattice
or produce locallized elastic strains.
This method of hardening is known as
precipitation hardening.The formation of such
equilibrium super lattice phases can take
place only by very slow cooling
.
Softening or solution heat treatment

The casting is heated to a high temp about 700℃ , just
below the solidus and held at that temp for about 10
min.for the atomic diffusion to take place. It is then
quenched. The soft ductile nature is again recovered.
This annealing heat treatment, removes the works
hardening effects.
Gold-disorder heat
 Type 3 and type 4 casting gold alloys fall in
this in composition range, suitable for
precipitation hardening heat treatments.
 The as –cast solution hardened, gold alloy –
casting is soft and ductile and can easily be
trimmed and polished. During these
procedures, the alloy also gets work
hardened and strained
 The finished alloy, also can be cooled
from 400℃ to 250℃ and then quenched.
 The most common and easier method of
hardening is placing the finished article
like a crown, in an electric furnace at
about 350℃ to 400℃, for about 10 to 20
min and then quenching. subjecting this
heat treatment for longer time makes the
casting brittle.
Hardening heat treatments
methods

If the alloy is heated to 700℃ and cooled
very slowly, the equillibrium superlattice
phases precipitate, when temp falls below
410℃ .it can quenched, when it cools
below 250℃, as atomic diffusions are very
slow below this temp and become
effective.
BINARY ALLOYS
The properties of the casting alloys depend
upon the constituent elements and the
compositions, specially those of main
ingradients.the equilibrium phase diagrams help
to analyse and study the properties alloys.the
constitution equilibrium phase diagram become
very complicated for analysis of ternary,
quadranary etc. alloys.
 Fe-C system shows the eutectoid transformation
from Austenite →ferrite+cementite phases by
solid state reaction at 723℃ when the alloy
containig C< 𝟐.% is cooled slowly. If cooled
suddenly or quenched, very hard martensitic
steel precipitates increasing hardeness to very
high value.

 Noble metal binary alloys used in dentristry are
Au-Cu, Au-Ag, Au-Pd, Au-Pt, Pd-Cu and Pd-Ag.

Au-Cu system shows complete solid solubility
at high temp and form intermetallic ordered
phases Au-Cu and Au-Cuȝ below about 400℃ .

the base metal binary alloy phase diagrams
considered frequently are Ag-Cu, Ag-Sn and FeC eutectoid transformation. These arise due to
partial solid solubility, and solid state reactions.
INTERMETALLIC COMPOUNDS
One of the conditions to form substitutional types of a
single phase-disordered solid solutions is,that the
alloying metals should not have chemical
affinities.However many metal show slight chemical
affinities when the solid solution is cooled below
certain temperatures.In such cases , the atoms of the
metals occupy definite positions in the lattice
temperatures.
These intermetallic compound have different
properties than their constituent metal .
Examples
Certain critical composition in Ag-Sn alloy system
with Ag – 73.2% and Sn= 26.8%.During solidification
at 480 ℃ ordered.Dring amalgamation the
intermetallic 𝜸₁(Ag₂Hg₃) , 𝜸₂(Sn ₇Hg) phases formed
have different properties than Ag or Sn or Hg
Intermetallic compound like Au –Cu and AuCu₃ phases
are formed by solid state reactions of disordered Au-Cu alloy
below about 400℃ the precipitation of the Au-Cu
superlattice increases hardness.
The precipitation of many intermetallic phases like
PtAu₃. AgAu , Pd – Cu are some examples.
Applications equilibrium phase diagrams
 During the solidificatins of alloys,sometimes many equilibrium
phases are formed different proportions.These may be
disordered substitutional or ordered substitutional , intermetallic
ect.
Examples:
 Ag-Cu alloys : With different compositions it is possible to form , 𝜶₁
, 𝜷 , solid solutions, hypoeutectic , eutectic , and hyper eutectic
alloys.
 Au – Cu : alloys solution hardening can be controled by adjusting
the composition.
 Hardness of carbon steel , depends on the amount of carbon
present and martensite formation.
 Silver amalgam alloy phases can be adjusted by varying the
composition and clinical procedures to avail its required best
properties.
Equilibrium phase diagarams of some binary alloys
SILVER-COPPER
SYSTEM
____SILVER AND COPPER___
*Belong to f.c.c structures
*M.P—Silver:961ºC…..
Copper:1083ºC…
Features of Equilibrium phase
diagrams:
1.Alpha phase
When the amount of copper is less
than 8.8% soldification takes place
along forming substitutional,cored
alpha phase in liquid which soldifies
around 860ºC into silver rich – alpha
solid phase.
2. Beta phase
*Amount of silver-less than 8.0%
*Soldification takes place along
forming substitutional Ag in Cu
i.e.copper rich beta terminal phase.
3.Eutectic phase
*Silver-72%
*Copper-28%
*Lowest temperature
*Rn:
Liquid−−−−−→
𝐚𝐥𝐩𝐡𝐚 𝐬𝐨𝐥𝐢𝐝 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧 +
𝐛𝐞𝐭𝐚 𝐬𝐨𝐥𝐢𝐝 𝐬𝐨𝐥𝐮𝐭𝐢𝐨𝐧.(at 779ºC)
4.Hypoeutectic phase
*amount of copper in alloy more
than 8.8%,crystalisation begins at
about 875ºC with 5% copper.
*has alpha crystals embedded in
eutectic phase.
5.Hypereutectic phase:
*Liquid having silver 8-72% is cooled along
the primary cored crystals of copper rich
beta phase are formed
Constitution
diagram of AgCu system
EUTECTIC ALLOYS
 For
partially solid soluble alloys,for a
definite composition,it has a single
lowest melting temperature
 E.g.Alloys like Cu-Ag
 Eutectic composition:
Cu-28%
Ag-72%
 Has alternate layers of Ag rich and a
Cu rich beta phases.
 Hypoeutectic
phase – alpha cored
silver rich primary crystals in the
eutectic matrix
 Hypereutectic phase – beta coed
copper rich primary crystals in
eutectic matrix
PROPERTIES:
 Very
hard and brittle
 Ductile and malleable
 Hypo- and hypereutectic alloys are
also brttle and hard.
 Age-hardening further increases
strength in all cases
 Silver rich alpha phase has
excellent corrosion resistance
APPLICATIONS



In paediatric dentistry
-silver rich alpha phase
-for temporary crowns
Disperse or admix , high copper silver amalgam
alloys
Grain refinement of gold alloys
-small amount of ruthenium or
iridium is added
-depress melting temperature
-causes more nucleation and grain
refinement
Any Question????