A DENTAL MATERIALS SEMINAR ON SOLIDIFICATION OF METALS

1. SOLIDIFICATION OFSOLIDIFICATION OF
METALSMETALS
DR.SHAGUN AGARWALDR.SHAGUN AGARWAL
DEPARTMENT OF PEDIATRICSDEPARTMENT OF PEDIATRICS
AND PREVENTIVE DENTISTRYAND PREVENTIVE DENTISTRY

2. CONTENTSCONTENTS
• IntroductionIntroduction
• MetalsMetals
• History of metalsHistory of metals
• Properties of metalProperties of metal
• Classification of metalsClassification of metals
• Inter atomic bondsInter atomic bonds
• Solidification of metalsSolidification of metals
• Nucleation and growth of crystalsNucleation and growth of crystals

3. INTRODUCTIONINTRODUCTION
• Metals and alloys play an important role in dentistry.Metals and alloys play an important role in dentistry.
• These form one of the four possible groups of materials used inThese form one of the four possible groups of materials used in
dentistry which include Ceramics, Composites and Polymers.dentistry which include Ceramics, Composites and Polymers.
• These are used in almost all the aspects of dentistry including theThese are used in almost all the aspects of dentistry including the
dental laboratory , direct and indirect dental restorations anddental laboratory , direct and indirect dental restorations and
instruments used to prepare and manipulate teeth.instruments used to prepare and manipulate teeth.
• Although the latest trend is towards the “metal free” dentistry, theAlthough the latest trend is towards the “metal free” dentistry, the
metals remain the only clinically proven material for long termmetals remain the only clinically proven material for long term
dental applications.dental applications.

4. METALSMETALS
• Chemical elements in general can be classified asChemical elements in general can be classified as
• MetalsMetals
• Non- metalsNon- metals
• MetalloidsMetalloids

5. • Metalloids are those elements on the border line showing bothMetalloids are those elements on the border line showing both
metallic and non metallic properties, example: carbon and silica.metallic and non metallic properties, example: carbon and silica.
• They do not form free positive ions but their conductive andThey do not form free positive ions but their conductive and
electronic properties make them important.electronic properties make them important.
• Metals constitute about 2/3Metals constitute about 2/3rdrd
of the periodic table published byof the periodic table published by
DMITRI MEDELEYEV in 1868.DMITRI MEDELEYEV in 1868.
• Of the 103 elements which are categorized in the periodic tableOf the 103 elements which are categorized in the periodic table
according to chemical properties , 81 are metals.according to chemical properties , 81 are metals.
• According to metals handbook, they can be defined as “ AN OPAQUEAccording to metals handbook, they can be defined as “ AN OPAQUE
LUSTUROUS CHEMICAL SUBSTANCE , THAT IS GOOD CONDUCTORLUSTUROUS CHEMICAL SUBSTANCE , THAT IS GOOD CONDUCTOR
OF HEAT AND ELECTRICITY AND WHEN POLISHED IS A GOODOF HEAT AND ELECTRICITY AND WHEN POLISHED IS A GOOD
REFLECTOR OF LIGHT.”REFLECTOR OF LIGHT.”

6. HISTORY OF METALSHISTORY OF METALS
• Metals have been used by man ever since he first discoveredMetals have been used by man ever since he first discovered
them.them.
• In ancient and prehistoric times , only a few metals wereIn ancient and prehistoric times , only a few metals were
known and accordingly these periods were called as :known and accordingly these periods were called as :
“COPPER AGE”, “BRONZE AGE”, AND “ IRON AGE”.“COPPER AGE”, “BRONZE AGE”, AND “ IRON AGE”.
• Today more than 80 metallic elements and a large number ofToday more than 80 metallic elements and a large number of
alloys have been developed.alloys have been developed.
• Ore is a mineral containing one or more metals in a free orOre is a mineral containing one or more metals in a free or
combined state.combined state.

7. PROPERTIES OF METALSPROPERTIES OF METALS
• All metals are solid expect for mercury and gallium which areAll metals are solid expect for mercury and gallium which are
liquid at room temperature and hydrogen which is a gas.liquid at room temperature and hydrogen which is a gas.
• They have a metallic luster and mirror like surface.They have a metallic luster and mirror like surface.
• They make a metallic sound when struck.They make a metallic sound when struck.
• Are strong, hard and dense.Are strong, hard and dense.
• Ductile and Malleable.Ductile and Malleable.
• Conduct heat and electricity.Conduct heat and electricity.

8. • Have specific melting and boiling point.Have specific melting and boiling point.
• Form positive ions in solution and get deposited at theForm positive ions in solution and get deposited at the
cathode during electrolysis.cathode during electrolysis.
• Example- copper in copper plating.Example- copper in copper plating.
• Metals are tough and this is due to the fact that the atoms ofMetals are tough and this is due to the fact that the atoms of
metals are held together by means of metallic bonds.metals are held together by means of metallic bonds.
• The chemical properties are based upon the electromotiveThe chemical properties are based upon the electromotive
series.series.
• The higher the element in the series, the more metallic it is.The higher the element in the series, the more metallic it is.
• This tendency of metals to lose electrons is known asThis tendency of metals to lose electrons is known as
oxidation potential.oxidation potential.

9. CLASSIFICATION OF METALSCLASSIFICATION OF METALS
• Pure metals and Mixture of metalsPure metals and Mixture of metals
• Noble metals and Base metalsNoble metals and Base metals
• Cast metal and Wrought metalCast metal and Wrought metal
• Light metal and Heavy metalLight metal and Heavy metal
• High melting metal and Low melting metalHigh melting metal and Low melting metal
• Highly malleable and ductile metalsHighly malleable and ductile metals

12. SOLIDIFICATION OF METALSSOLIDIFICATION OF METALS
• During solidification ,the liquid changes in to solid duringDuring solidification ,the liquid changes in to solid during
cooling.cooling.
• The energy of liquid is less than that of the solid above theThe energy of liquid is less than that of the solid above the
melting point. Hence liquid is stable above the meltingmelting point. Hence liquid is stable above the melting
point.point.
• Below the melting point, the energy of liquid becomesBelow the melting point, the energy of liquid becomes
more than that of the solid.more than that of the solid.
• Hence below the melting point, the solid becomes moreHence below the melting point, the solid becomes more
stable than than the liquid.stable than than the liquid.
• Therefore at the melting point, liquid gets converted intoTherefore at the melting point, liquid gets converted into
solid during cooling.solid during cooling.

14. • This transformation of liquid into solid below meltingThis transformation of liquid into solid below melting
point is known as solidification.point is known as solidification.

15. SOLIDIFICATION OF PURESOLIDIFICATION OF PURE
METALSMETALS
Figure :Temperature as a function of time for the solidification of pure metals. Note that the
freezing takes place at a constant temperature. (b) Density as a function of time

16. • Thermodynamically , both liquid and solid have equal energy atThermodynamically , both liquid and solid have equal energy at
melting point and therefore both are equally stable at meltingmelting point and therefore both are equally stable at melting
point.point.
• Therefore ,no solidification or melting will take place at the meltingTherefore ,no solidification or melting will take place at the melting
pointpoint
• Liquid will remain liquid and solid will remain solid.Liquid will remain liquid and solid will remain solid.
• Some under-cooling will be essential for solidification.Some under-cooling will be essential for solidification.
• This transformation occurs by nucleation and growth.This transformation occurs by nucleation and growth.

18. SOLIDIFIED SKIN ON A STEELSOLIDIFIED SKIN ON A STEEL
CASTINGCASTING
Figure 10.11 Solidified skin on a steel casting. The remaining molten metal is poured out
at the times indicated in the figure. Hollow ornamental and decorative objects are made by
a process called slush casting, which is based on this principle. Source: After H. F. Taylor,
J. Wulff, and M. C. Flemings

21. SOLIDIFICATION OF IRON ANDSOLIDIFICATION OF IRON AND
CARBON STEELSCARBON STEELS
Figure 10.5 (a) Solidification patterns for gray cast iron in a 180-mm (7-in.) square casting.
Note that after 11 minutes of cooling, dendrites reach each other, but the casting is still mushy
throughout. It takes about two hours for this casting to solidify completely. (b) Solidification of
carbon steels in sand and chill (metal) molds. Note the difference in solidification patterns as
the carbon content increases. Source: After H. F. Bishop and W. S. Pellini

25. NUCLEATION AND GROWTH OFNUCLEATION AND GROWTH OF
CRYSTALSCRYSTALS
• At the solidification temperature, atoms from the liquid,At the solidification temperature, atoms from the liquid,
such as molten metal, begin to bond together and start tosuch as molten metal, begin to bond together and start to
form crystals.form crystals.
• The moment a crystal begins to grow is know as nucleusThe moment a crystal begins to grow is know as nucleus
and the point where it occurs is the nucleation point.and the point where it occurs is the nucleation point.
• When a metal begins to solidify, multiple crystals begin toWhen a metal begins to solidify, multiple crystals begin to
grow in the liquid.grow in the liquid.

26. • The final sizes of the individual crystals depend on theThe final sizes of the individual crystals depend on the
number of nucleation points.number of nucleation points.
• The crystals increase in size by the progressive additionThe crystals increase in size by the progressive addition
of atoms and grow until they impinge upon adjacentof atoms and grow until they impinge upon adjacent
growing crystalgrowing crystal

37. Segregation
The non-uniform distribution of impurities or
alloying elements. The degree of segregation
depends not only on the chemical composition
of the alloy, but also on the rate of cooling,
both of the ingot as a whole, and of each
individual point within the mass. For example,
near the surface, where the rate of cooling is
rapid, the segregated impurities are trapped in
the rapidly growing crystals. Fur- their inside
the ingot, where the cooling is slower, the
segregates will collect together and produce
the so-called ghosts, or they may tend to rise
to the surface and collect in the scrapped
ingot head. In normal segregation, the
constituents with the lowest melting points
concentrate in the last portions to solidify, but
in inverse segregation this is reversed. The
segregation tends to form in bands sloping
inwards to the top of the ingot (A segregate)
and at the same time, due to shrinkage, it
takes a V shape (V segregate) along the
upper part of the ingot axis.

38. MICROSEGREGATIONMICROSEGREGATION

41. CAST STRUCTURES OF SOLIDIFIEDCAST STRUCTURES OF SOLIDIFIED
METALSMETALS
Figure Schematic illustration of three cast
structures of metals solidified in a square mold:
(a) pure metals; (b) solid-solution alloys; and
(c) structure obtained by using nucleating
agents. Source: After G. W. Form, J. F.
Wallace, J. L. Walker, and A. Cibula
Figure Development of a preferred
texture at a cool mold wall. Note
that only favorably oriented grains
grow away from the surface of the
mold

42. SOLIDIFICATION CONTRACTION ORSOLIDIFICATION CONTRACTION OR
EXPANSIONEXPANSION

43.  REFERENCES
 DENTAL MATERIALS CLINICAL
APPLICATIONS
Pankaj Datta
 BASIC DENTAL MATERIALS
John J.Manappallil
 PHILLIPS’ SCIENCE OF DENTAL
MATERIALS
Kenneth J. Anusavice