Solid-state phase transformation

Driving forces for solid-state phase transformations are about one-third of those for solidification. This is just what we would expect the difference in order between two crystalline phases will be less than the difference in order between a liquid and a crystal the entropy change in the solid-state transformation will be less than in solidification and AH/T will be less than AH/T . 

Many metals and metallic alloys show martensitic transformations at temperatures below the melting point. Martensitic transformations are structural phase changes of first order which belong to the broader class of diffusion js solid-state phase transformations. These are structural transformations of the crystal lattice, which do not involve long-range atomic movements. A recent review of the properties and the classification of diffusionless transformations has been given by Delayed... 

Balema, V.P., K.W. Dennis, V.K. Pecharsky, V.P. Balema, V.K. Pecharsky, and K.W. Dennis, Solid state phase transformations in LiAlH4 during high-energy ball-milling, /. Alloys Compd., 313, 69,2000. 

Raghavan, V., and Cohen, M. (1975). "Solid-State Phase Transformations," Chapter 2, in N. B. Hannay, Ed., Treatise on Solid State Chemistry Changes in State, Vol. 5. Plenum Press, New York. A mathematical treatment of the subject including a good treatment of the kinetics of phase transitions. 

Another example of pressure-induced polymorphism is seen in the case of amiloride hydrochloride, where ball-milling Form-B causes a solid-state phase transformation into Form-A [43]. These workers deduced the phase relationship between two different pressure-induced polymorphs of the dihydrate, as well as the alternative route to one of those dihydrate forms that used the anhydrous form as the source material and effected the phase transformation through storage at high degrees of relative humidity storage. 

It is commonplace to assume a form of the Gibbs energy function which excludes the pressure variable for solid-state phase transformations, as the magnitude of the PAV term is small at atmospheric pressures. This is of course not the case in geological systems, or if laboratory experiments are deliberately geared to high-pressure environments. Klement and Jayaraman (1966) provide a good review of the data available at the time when some of the earliest CALPHAD-type calculations were made (Kaufman and Bernstein 1970, Kaufman 1974). Much work was also carried out on specific alloy systems such as Fe-C (Hilliard 1963) and the Tl-In system (Meyerhoff and Smith 1963). 

Airaksinen S, Kaijalainen M, Kivikero N, Westrmarck S, Shevchenko A, Rantanen J, Yliruusi J. 2005. Excipient selection can significantly affect solid-state phase transformation in formulation during wet granulation. AAPS PharmSciTech. 6(2) Article 41. 

Nucleation and growth kinetics — Nucleation-and-growth is the principal mechanism of phase transformation in electrochemical systems, widely seen in gas evolution, metal deposition, anodic film formation reactions, and polymer film deposition, etc. It is also seen in solid-state phase transformations (e.g., battery materials). It is characterized by the complex coupling of two processes (nucleation and phase growth of the new phase, typically a crystal), and may also involve a third process (diffusion) at high rates of reaction. In the absence of diffusion, the observed electric current due to the nucleation and growth of a large number of independent crystals is [i]... 

Anatase, brookite and rutile are three polymorphs of titanium dioxide. Anatase is a kind of thermodynamically metastable form while rutile is a kind of stable one. Anatase can transform irreversibly to rutile at elevated temperatures ranged from 400 to 1200 °C according to particle size, morphology and additives. The solid-state phase transformation behavior has been widely investigated while the phase evolution between anatase and rutile under hydrothermal condition has been little paid attention to so far [5]. In this work, the structural evolution from anatase to rutile under milder hydrothermal conditions is proposed as well [7, 10]. 

Hydrothermal conditions are frequently used to synthesize (e g., Yang et al. 2000 Wang and Ying 1999 Yanagisawa and Ovenstone 1999) and treat (Penn and Banfield 1998, 1999a,b) nanocrystalline titania samples. The surrounding phase now is water or an aqueous solution. Experiments are normally conducted between 100-300° C and at relatively low pressures (at 300°C the saturated vapor pressure of water is only 8.5 MPa (CPC book), far less than pressures applied in many solid state phase transformation experiments). 

Raghaven V, Cohen M (1975) Solid-state phase transformations. In Hannay NB (ed) Treatise on Solid State Chemistry 5 67-128... 

Figure 10.14 The DSC curve of carbon tetrachloride exhibits three solid-state phase transformations before melting. (Reproduced with kind permission of Springer Science and Business Media from M. Brown, Introduction to Thermal Analysis, Kluwer Academic Publishers, Dordrecht. 2001 Springer Science.)...

Pure barium is a silvery-white metal, although contamination with nitrogen produces a yellowish color. The metal is relatively soft and ductile and may be worked readily. It is fairly volatile (though less so than magnesium), and this property is used to advantage in commercial production. Barium has a bcc crystal structure at atmospheric pressure, but undergoes solid-state phase transformations at high pressures (2,3). Because of such transformations, barium exhibits pressure-induced superconductivity at sufficiendy low temperatures (4,5). 

The kinetics of solid-state phase transformations are often summarized in time-temperature-transformation (TTT) diagrams. The ITT diagram shows... 

Arrhenius Law. A logarithmic relationship between reaction rate and temperature which applies to creep, diffusion and solid state phase transformations (among many other chemical and physical reactions), log V = A - q/kT... 

In addition to reaction non-uniqueness, the occurrence of non-unique phase transformations during reaction is a possible origin of gross structural defects in pol)nnerized phases. A solid-state phase transformation will be nonunique unless the symmetry elements of the parent lattice are included in the symmetry elements of the product lattice. If this condition is not satisfied, the product phase will be statistically disordered so as to produce an overall symmetry which is a sum of the symmetries of parent and product phases. 

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