Spontaneous thermal dispersion

However, the temperature, at which the maximum of the initial scattered light occurs, seems to be related to the scattering angle 9S and thus to the period Ag , respectively. Figure 9.14(b) shows the correspondence between the temperature Tm of maximum intensity Ig and the spatial period Agn. A spatial disorder of the smallest polar structures occurs at Tm = 45 °C, while the spatial orientation of the largest structures remains stable up to Tm = 60 °C. Such big dispersion of the thermal decay of polar structures over Agn unambiguously illustrates the relaxor behavior of sbn. At the same time it is a key point to understand the bandwidth in the determination of the phase transition temperature Tm in sbn from different methods. For example, in sbn doped with 0.66 mol% Cerium, Tm detected from the maximum of the dielectric permittivity e at 100 Hz (e-method) equals Tm = 67 °C [20], Determination of Tm from the inflection point of the spontaneous electric polarization P3... 

Thermolysis of mixtures of Ba and Sr chromates and oxalates has been studied by thermal analyses and e.s.r. Relatively dispersed Cr species can be obtained by thermal treatment in the temperature range 723—773 K. At 1123K the final product is M3(Cr04)j (M = Ba or Sr). The alkaline earth carbonates, produced in situ by decomposition of the corresponding oxalates, play a major role in the reduction of Cr to Cr, which occurs at > 873 K. An analogous study on Mg chromate-oxalate mixtures reveals spontaneous reductions of Cr to Cr , and Cr to Cr at 873 K and 523 K, respectively, under vacuum. No effect of MgCOj was observed for this system. ... 

According to Rehbinder and Shchukin the above condition has a simple physical meaning if the particles are of colloidal dimensions, and the interfacial tension is low, the spontaneous separation of particles from a macroscopic phase becomes possible, since the work required to form a new surface is compensated by the gain in energy upon the involvement of the newly formed particles in thermal motion. There is a critical value of the specific surface free energy, ocr, below which the spontaneous dispersion process becomes possible. This critical value is given by... 

The necessary condition for spontaneous formation of disperse system and condition of its equilibrium with a macroscopic phase can be also obtained by utilizing the concepts of theory of fluctuations. This may be conveniently illustrated by the example of a highly mobile interface, such as liquid - liquid or liquid-vapor. The surface of liquid is not completely flat thermal fluctuations result in the appearance of capillary waves. It was shown by L. Mandelshtam (1914) that in the vicinity of critical point, e.g. around the temperature corresponding to a complete mixing of two liquids, the interface acquires substantial... 

HYDROLIN (7775-14-6) Combustible solid. Finely dispersed dust or powder forms explosive mixture with air. Contact with water, moist air, or steam, emitting sulfur dioxide and heat, with risk of spontaneous combustion. Contact with acids produces sulfur dioxide. A strong reducing agent. Violent reaction, ignition, or explosion on contact with oxidizers, sodium chlorite. Elevated temperatures above 122°F/50°C may cause violent thermal decomposition, producing sodium sulfate and sulfur dioxide. When dissolving, always slowly add this material to water. 

The light-scattering spectrum which is related to 7 (q, /) by Eq. (3.3.3) consequently probes how a density fluctuation <5/ (q) spontaneously arises and decays due to the thermal motion of the molecules. Density disturbances in macroscopic systems can propagate in the form of sound waves. It follows that light scattering in pure fluids and mixtures will eventually require the use of thermodynamic and hydrodynamic models. In this chapter we do not deal with these complicated theories (see Chapters 9-13) but rather with the simplest possible systems that do not require these theories. Examples of such systems are dilute macromolecular solutions, ideal gases, and bacterial dispersions. ... 

The ease of emulsion formation increases and the droplet size achievable decreases as the interfacial tension falls. Systems in which the interfacial tension falls to near zero j<10-3 mNm (dyne cm-1)] may emulsify spontaneously under the influence of thermal energy and produce droplets so small (<10 nm diameter) that they scatter little light and give rise to clear dispersions. The micro emulsions so formed occupy a place between coarse emulsions and micelles. They are usually effectively monodispersc and unlike coarse emulsions are thermodynamically stable. Microemulsion droplets have sometimes been classified as swollen micelles. In fact, there probably exists an essentially continuous sequence of states from association colloids to coarse emulsions,... 

Duplex Ceramics. Spherical pressure zones 10-50pm diameter are homogenously dispersed in a ceramic matrix, to toughen it and to enhance its thermal shock resistance. The zones contain a high proportion of unstabilized zirconia. Spontaneous or stress-induced tetragonal/monoclinic transformation of the zirconia produces compressive stresses in the zones, and radial compressive and tensile hoop stresses in the nearby matrix. (H.E. Lutz and N. Claussen, J. Ear. Ceram. Soc. 7 (1991) 209)... 

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