Phase transitions, laboratory

The ability to control pressure in the laboratory environment is a powerful tool for investigating phase changes in materials. At high pressure, many solids will transfonn to denser crystal stmctures. The study of nanocrystals under high pressure, then, allows one to investigate the size dependence of the solid-solid phase transition pressures. Results from studies of both CdSe [219, 220, 221 and 222] and silicon nanocrystals [223] indicate that solid-solid phase transition pressures are elevated in smaller nanocrystals. 

It is of special interest for many applications to consider adsorption of fiuids in matrices in the framework of models which include electrostatic forces. These systems are relevant, for example, to colloidal chemistry. On the other hand, electrodes made of specially treated carbon particles and impregnated by electrolyte solutions are very promising devices for practical applications. Only a few attempts have been undertaken to solve models with electrostatic forces, those have been restricted, moreover, to ionic fiuids with Coulomb interactions. We would hke to mention in advance that it is clear, at present, how to obtain the structural properties of ionic fiuids adsorbed in disordered charged matrices. Other systems with higher-order multipole interactions have not been studied so far. Thermodynamics of these systems, and, in particular, peculiarities of phase transitions, is the issue which is practically unsolved, in spite of its great importance. This part of our chapter is based on recent works from our laboratory [37,38]. 

Goldwire, Jr., H. C., H. C. Rodean, R. T. Cederwall, E. J. Kansa, R. P. Koopman, J. W. McClure, T. G. McRae, L. K. Morris, L. Kamppiner, R. D. Kiefer, P. A. Urtiew and C. D. Lind. 1983. Coyote series data rejwrt LLNL/NWC 1981 LNG spill tests, dispersion, vapor bum, and rapid-phase-transition. Lawrence Livermore National Laboratory Report UCID-I9953. Vol. 2. 

The field of gas-phase transition metal cluster chemistry has expanded rapidly due to the development of the laser vaporization source and the fast flow chemical reactor. The work from the three major laboratories have been reviewed. Many additional laboratories are developing cluster chemistry programs and will soon certainly make significant contributions. 

The phase transition from amorphous to crystalline can sometimes be promoted by thermal treatment (annealing) [ 1.45]. In a laboratory scale, this can be done relatively simple. In a production scale the process must be proven as reproducible and reliable by a validation process, which is time consuming. It is therefore recommended, that a search for CPAs and process conditions, which would lead to crystallization be carried out, using methods such as DTA, DSC, ER and DRS (see Section 1.1.5) also see Yarwood [1.46. If this is not successful, time and temperature for TT should be chosen in such away, that the tolerances for time and temperature are not to narrow, e. g. -24.0 °C 0.5 °C and 18 min 1 min are difficult to operate, while -30 °C 1.5 °C and 40 min 2 min might be easier to control. 

Poly(N-isopropylacrylamide) (polyNIPAAM), formed by a free radical polymerization of N-isopropylacrylamide, is a water soluble, temperature sensitive polymer. In aqueous solution, it exhibits a lower critical solution temperature (LCST) in the range of 30-35 C depending on the concentration and the chain length of the polymer. Thus, as the solution temperature is raised above the LCST, the polymer undergoes a reversible phase transition characterized by the separation of a solid phase which redissolves when the solution temperature is lowered below the LCST. Its physicochemical properties have been investigated by several laboratories (1-3). 

DE - A Two-Dimensional Eulerian Hydro-dynamic Code for Computing One-Component Reactive Hydrodynamic Problems , Los Alamos Scientific Laboratory Report LA-3629-MS (1966) 23b) C.L. Mader, "FORTRAN-SIN - A One-Dimensional Hydrodynamic Code for Problems Which Include Chemical Reactions, Elastic-Plastic Flow, Spalling, and Phase Transitions , Los Alamos Scientific Laboratory Report LA-3720(1967) 24) R.C. Sprowls, "Com-... 

The heating curve of a substance shows how its temperature changes as energy is supplied as heat at a constant rate. The curve contains a lot of useful information about a substance, including the temperature and enthalpy of each phase transition and the heat capacity of each phase. Simple laboratory heaters can be used to obtain a crude estimate of a heating curve. However, for accuracy, one of two related techniques is normally used. 

I would like to dedicate this chapter to Professor Isaac Bersuker on the occasion of his 75 th birthday as an acknowledgement of his pioneering contributions to the field of vibronic crystal chemistry and structural phase transitions, and to the science of vibronic interactions in general. I had the advantage to work in the Laboratory... 

The exchange of NaBr and KBr with HC1 reaches an equilibrium in which, near to room temperature, a mixed Cl /Br surface is at equilibrium with a gaseous HCl/HBr mixture whose composition depends on the surface anion ratio, but which is typically about 1 mole % HBr. This equilibrium was discovered in the laboratory of one of us (LGH) about eighteen years ago [96], but the topic proved difficult to pursue because of the difficulty of quantitative analysis of the gas mixture. Eventually, a temperamental but workable gas chromatographic technique [97] having provided the key to this analysis, we were able to show that the equilibrium is highly non-ideal [98]. The bromide surface apparently undergoes a two-dimensional phase transition, induced by HC1 or HBr adsorption, close to room temperature, in which the halide ions become mobile,... 

With more beam time available in the laboratory, we were able to go through the phase transition in much smaller temperature steps. Before the measurements were taken, the system was kept at each temperature for at least half an hour to ensure that thermal equilibrium had been achieved. The diffraction patterns obtained from a sample with r = 0.1, c = 0.1 M (the same conditions as for the LAD experiment) are shown in Figure 10.3a at live temperatures between -2 and 2°C, in 1°C steps. 

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