Dr Salamat Ali NCP Phase Transitions Seminar Final
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Phase Transitions in NanoPhase Transitions in Nano--
Structured MaterialsStructured MaterialsDr. Salamat AliDr. Salamat Ali
Govt. College University, LahoreGovt. College University, Lahore
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Outline
Introduction Phase Transformation Phase Diagram of a Simple System
Classification of Phase Transitions Some Tools to detect Phase Transition Other forms of Phase Transitions
Melting Temperature Some Results from Literature/GCUL Conclusion References
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Introduction
Phase: It is a region of material that is chemically uniform, physically
distinct, and (often) mechanically separable.
In thermodynamics,phase transition orphase change is the transformation of a
thermodynamic system from one phase to another.
Crystallisation is a condensation process involving the creation of a crystalline
daughter phase from a parent phase.
The formation of any new phase from a bulk parent phase requires the creation
of an interface between the two phases.
The creation of this interface requires an amount of work, dependant upon the
surface/interfacial tension of the interface.
http://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Phase_%28matter%29http://en.wikipedia.org/wiki/Phase_%28matter%29http://en.wikipedia.org/wiki/Thermodynamics -
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Phase Transformation
The nomenclature for the different phase transitions.
The distinguishing characteristicof a phase transition is an
abrupt sudden change in one ormore physical properties, inparticular the heat capacity, witha small change in a
thermodynamic variable such asthe temperature.
http://en.wikipedia.org/wiki/Heat_capacityhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Heat_capacity -
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Phase Diagram of a Simple System
The crystal phase is stable at high P and low T.
The liquid phase is stable at high P and high T.
The vapour phase is stable at low P and low/high T.
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Other Forms of Phase Transitions
The transition between the ferromagnetic(Anti-ferromagnetic)andparamagneticphases ofmagneticmaterials at the Curie
point(Neels Temperature).
The emergence ofsuperconductivityin certain metals whencooled below a critical temperature.
Changes in the crystallographicstructure such as betweenferrite (bcc) andaustenite (fcc) ofiron.
Order-disorder transitions such as in alpha-titaniumaluminides.
Quantum condensation ofbosonic fluids, such as Bose-Einstein
condensation and the superfluid transition in liquid helium.
The martensitic transformation which occurs as one of the manyphase transformations in carbon steel and stands as a model for
displacive phase transformations.
http://en.wikipedia.org/wiki/Paramagnetismhttp://en.wikipedia.org/wiki/Ferromagnetismhttp://en.wikipedia.org/wiki/Magnethttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Magnethttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Ferrite_%28iron%29http://en.wikipedia.org/wiki/Crystallographichttp://en.wikipedia.org/wiki/Austenitehttp://en.wikipedia.org/wiki/Crystallographichttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Ferrite_%28iron%29http://en.wikipedia.org/wiki/Austenitehttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Displacive_phase_transformationshttp://en.wikipedia.org/wiki/Displacive_phase_transformationshttp://en.wikipedia.org/wiki/Displacive_phase_transformationshttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Bose-Einstein_condensatehttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Titanium_aluminidehttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Austenitehttp://en.wikipedia.org/wiki/Ferrite_%28iron%29http://en.wikipedia.org/wiki/Crystallographichttp://en.wikipedia.org/wiki/Metalhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Curie_pointhttp://en.wikipedia.org/wiki/Magnethttp://en.wikipedia.org/wiki/Paramagnetismhttp://en.wikipedia.org/wiki/Ferromagnetism -
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First Order and Second Order Phase Transitions
First-order phase transitions exhibit a discontinuity in thefirst derivative of the free energywith a thermodynamic
variable.i.e.
(dG/dX (where X is any thermodynamic variable)
Second-order phase transitions have a discontinuity in asecond derivative of the free energy.
Modern Classification is basd upon latent heat first order involes latent heat while 2nd order does not).
How to Classify Phase Transitions
http://en.wikipedia.org/wiki/Thermodynamic_free_energyhttp://en.wikipedia.org/wiki/Thermodynamic_free_energy -
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Some Tools to detect Phase Transitions
XRD (For Structure)
Resistivity ()
Susceptibility () Specific Heat (Cp)
Pressure
Volume
(Should be a function of Temperature)
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Phase Transition in Nanostructures
The same thermodynamic and kinetic principles that controlphase transitions in bulk materials can be applied to
nanostructuredmaterials. However, oftentimes common simplifications that are used in
these two fields are not appropriate for use with nanophase
materials. Therefore, there are a number of noteworthy phasetransition phenomena that occur in nanomaterials. SayMelting Point.
The melting point of a solid is size dependent. In the nanoregime, this dependence becomes significant.
Why?
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Melting Temperature Environmental effects
Pressure of the system Contaminants or Impurities
Structural effects Grain size
Phases present
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Unruh, Patterson, and Shah
Studied the effects of particle size onthe melting behavior of Bix(SiO2)100-xfilms
Amorphous SiO2 substrate created byvapor deposition
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X-ray Diffraction and DSC (Unruh et. al.)
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Thermodynamics Pressure in the solid does not equal the pressure in
the liquid: Ps = P l +2/r
d = -SdT + VdP
SmdT = 2V dr/r2 Bulk melting temperature: Tm=Hm/Sm Simplifying and combining all the above Eqs. Thefinal
result is:
T = (2VTm) / (rHm)
(which means that change in M.P. is inverselyproportional to the radius of the sphere).
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Calculated Melting Point of Gold(Ichimose et al.)
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Observed Melting point of Bi (Unruh et. al)
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Observed Melting Temperature of CuO
Nano-Particles
0 5 10 15 20 25 30
870
875
880
885
890
895
900
905
MeltingTemperat
ure(0C)
Particle size (nm)
Melting Temperature of Bulk CuO ~ 12000C
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The Crystallization of Metallic
GlassesMainly two factors are important:
Nucleation
Critical radius requirement causes anucleation energy barrier G*
Crystal (Grain) Growth
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Grain Growth
G =H -TS
Initially reduced the free energy of thesystem due to the reduction in surface tovolume ratio
Ultimately slows due to entropyrequirements
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Grain Growth Kinetics Driving force for grain growth:
v 2M/D dD / dt
Where: v = the driving force for grain growth
M = Mobility
= surface energy
D = Mean grain diameter t = time of reaction
Mean grain diameter: D = Ktn
(K is proportionality constant that increases withtemperature, n is the fractional constant)
Composition and temperature dependent
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DSC and X-ray Diffraction (Baricco et.al.)
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Crystallization of Ceramic Glasses
Spassov and Meinhardt studied Co33Zr67 Unable to experimentally conclude whether nanophase
was due to polymorphic transformation or primarycrystallization
Kinetic analysis showed it to be a time dependentprimary crystallization
Hi h P Ph
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High Pressure Phase
Stabilization
Unexpected metastable phases arepresent in some nano-structured ceramics
Trend seems to be that these phases aretypically seen under high-pressureconditions
Some are observed in doped materials ofthe same chemical composition
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Solid-state Diffusion
Solid-state diffusion does not control nano-
materials in the same manner as it does inbulk materials
Mathematically the same, but occurs
relatively quickly due to the finite size ofthe particle
Temperature, but not pressure, dependent
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SnO2 Used in oxygen sensors
Normal annealing results in a tetragonalphase
Under high pressure conditions,
orthorhombic crystal structure can form Not stable under ambient conditions
(cannot generally be forced throughdoping)
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Nanophase SnO2
Shows evidence of a post-anneal
orthorhombic phase when heat treated inO2 deficient environment
Evidence suggests the material is not
stoichiometric SnO2 Overall stress of the system is reduced by
the formation of orthorhombic structure
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ZrO2
Used in oxygen sensors, and the
fabrication of fuel cells Microcrystalline material is tetragonal
High temperature or high pressures cancause a reversible martensitictransformation to monoclinic
Dopants can be used to stabilizemonoclinic at ambient conditions
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Nanocrystalline ZrO2
Monoclinic phase is stable at ambient
conditions Produced by sol-gel method Appears to be the result of preparation pH
Transformation is neither martensitic or reversible
OH- ions coupled with Zr vacanciesprovide the required stress on the system
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Grain size Stability
Grain size stability in nanocrystalline materials
has been found to be closely related to the: structural characteristics of the material, such as
grain size and its distribution,
grain morphologies,
triple junctions,
porosity in the sample, and so on.
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Conclusions
Thermodynamics and kinetics both playan important role in phasetransformations.
The phase transformations andstabilizations are particle size dependent.
This dependence is critical in the nanoregime.
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References
Baricco, M. et al. Formation of Nanophases by Crystalization of
Amorphous AlloysMaterial Science Forum vol. 195 Trans TechPublications, 1995.
Bokhimi, X. et al. Tetragonal Nanophase Stabilization in NondopedSol-Gel Zirconia Prepared with Different Hydrolysis CatalystsJournalof Solid State Chemistry, vol 135 p. 28-35, 1998.
Gaskell, David R. Introduction to the Thermodynamics of Materials, 3rded. Taylor and Francis, Washington, DC. 1995.
Hampel, G. et al. Structure Investigations on Annealed Fe(CuNb)SiBAlloys with Different Si-B ContentsPhysica Status Solidi A, vol. 149
no. 1 p. 515-33, J une 16, 1995. Ichimose, N. et al. Superfine Particle TechnologySpringer-VerlagLondon, 1992.
Porter, D. A. and Easterling K. E. Phase Transformations in Metals andAlloys 2nd ed. Chapman and Hall, London, 1992.
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References (cont.)
Potter, Mark C., ed. Fundamentals of Engineering, 5th ed. Great LakesPress, Okemos, MI 1996.
Ragone, David V. Thermaodynamics of Materials Vol. IIJ ohn Wiley &Sons. Inc. New York, 1995.
Shek, C. H. et al. Nanomicrostructure, Chemical Stability, andAbnormal Transformation in Ultrafine Particles of Oxidized TinJournal
of Physics and Chemistry of Solids, vol. 58 no. 1 p.13-17, J an 1997.
Sheng, P and M. Zhou Melting and Thermal Characteristics of SmallGranular ParticlesMaterials Research Society SymposiumProceedings, vol. 195. Materials Research Society, Apr 16-20 1990.
Spassov, T. et al. Nanocrystalization of Co33Zr67 GlassesJournal ofMaterials Science, vol 32 p. 1483-6, Mar 15, 1997.
Unruh, K. M. et al. Melting Behavior in Granular Metal Thin FilmsMaterials Research Society Symposium Proceedings, vol. 195.
Materials Research Society, Apr 16-20 1990.
Our Group
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Our GroupMaterial Science/Nano-Technology Research Laboratory
Department of PhysicsGCU, LahoreThe Group stepped into the field of Nano-science in 2005
Running ProjectsColossal Magneto-resis tant (CMR) Nanomaterials
Metal Oxide Nanomaterials
Doped Metal Oxide NanomaterialsDoped Sulfide Nanomaterials
Transparent Conducting Oxides for Solar cells
Carbon Nano-tubes
Nanotechno logy for Cancer Treatment
Facilities Available:Fabrication of Nano-Materials:
Include Two State of the Art Furnaces
1). RT to 14000C (Muffle)
2). Tube Furnace (RT to 18000C) with controlled environment
3). PVD Set-up (under construct ion)
Characterization Techniques
Structural and Phase Analysis using XRDThermal Properties by DSC/TGA (RT to 15000C) and a DSC for low temperature down to 90 K
Magnetic Properties by AC Susceptibi lity Measurement (77-300K)
Electrical Properties using Resist ivity Measurement (77- 300K)
Open to Collaborate