Grain microcrystal

To confirm that the matrix is amorphous following primary solidification, isothermal dsc experiments can be performed. The character of the isothermal transformation kinetics makes it possible to distinguish a microcrystalline stmcture from an amorphous stmcture assuming that the rate of heat released, dH/dt in an exothermic transformation is proportional to the transformation rate, dxjdt where H is the enthalpy and x(t) is the transformed volume fraction at time t. If microcrystals do exist in a grain growth process, the isothermal calorimetric signal dUldt s proportional to, where ris... 

Fig. 5. Silver haUde grain morphologies for (a) cubic, precipitated in an environment having a silver ion concentration, [Ag" ], of ca 2.5 x 10 mol/L (b) octahedral, ca 6.0 x 10 mol/L and (c) tabular microcrystals, ca 1.0 x 10 ° mol/L. A cross section of a tabular grain revealing double parallel twin planes...

Chemical Sensitization. After the photographic microcrystals are precipitated but before they are coated on a support, the crystals are treated to enhance their sensitivity to light. Chemical sensitization is a process which improves that abiUty of the emulsion grains to use the absorbed photons, independent of the wavelength. Various methods of post-precipitation chemical sensitization have been developed to reduce the number of photons required to produce a developable latent-image center. 

Discussion. The turbidity of a dilute barium sulphate suspension is difficult to reproduce it is therefore essential to adhere rigidly to the experimental procedure detailed below. The velocity of the precipitation, as well as the concentration of the reactants, must be controlled by adding (after all the other components are present) pure solid barium chloride of definite grain size. The rate of solution of the barium chloride controls the velocity of the reaction. Sodium chloride and hydrochloric acid are added before the precipitation in order to inhibit the growth of microcrystals of barium sulphate the optimum pH is maintained and minimises the effect of variable amounts of other electrolytes present in the sample upon the size of the suspended barium sulphate particles. A glycerol-ethanol solution helps to stabilise the turbidity. The reaction vessel is shaken gently in order to obtain a uniform particle size each vessel should be shaken at the same rate and the same number of times. The unknown must be treated exactly like the standard solution. The interval between the time of precipitation and measurement must be kept constant. 

Massive barite crystals (type C) are also composed of very fine grain-sized (several xm) microcrystals and have rough surfaces. Very fine barite particles are found on outer rims of the Hanaoka Kuroko chimney, while polyhedral well-formed barite is in the inner side of the chimney (type D). Type D barite is rarely observed in black ore. These scanning electron microscopic observations suggest that barite precipitation was controlled by a surface reaction mechanism (probably surface nucleation, but not spiral growth mechanism) rather than by a bulk diffusion mechanism. 

The heavy elements carry clear excesses in a s-process component as can be seen from Figure 7. This has been demonstrated for Kr, Sr, Xe, Ba, Nd, Sm (Ott and Begemann 1990 Prombo et al. 1993 Lewis et al. 1994 Richter 1995 Hoppe and Ott 1997). The models can be made to fit very precisely the measured data (Lattanzio and Boothroyd 1997 Busso et al. 1999). Mo and Zr can occur as microcrystals of Mo-Zr-C within graphite grains. Typical s-process patterns are observed, with isotopic variations of about a factor of more than 5 (Nicolussi et al. 1997 Nicolussi et al. 1998a). 

Many compounds, including clay minerals, form needle- or plateshaped crystals. With finely dispersed minerals, the electron diffraction method can give a special kind of diffraction pattern, the texture pattern, which contains a two dimensional distribution of a regularly arranged set of 3D reflections [2], Specimens of fine-grained lamellar or fiber minerals, prepared by sedimentation from suspensions onto supporting surfaces or films, form textures in which the component microcrystals have a preferred orientation. Texture patterns of lamellar crystals tilted with respect to the electron beam are called oblique texture electron diffraction patterns [1]. 

Tann — 350 K (3). The conduction barrier energy can be obtained from the Arrhenius plot — 296.8 and 295.4 K for the nominally identical samples la and lb (grown in different experiments) and 273.7 K for sample 3. Earlier reported Ea values for oriented thin TTF-TCNQ films lie between 170 and 580 K (Reinhardt et al., 1980 de Caro et al., 2000a). The decrease of E upon increase of T uh is in line with the increase in size of the microcrystals, which reduces the number of grain boundaries. The obtained ctrt values (2 < ctrt < 10 cm ) are comparable... 

The photographic emulsion is essentially a dispersion of microcrystals of AgBr in an organic substrate called gelatin . The emulsion therefore consists of microscopic grains which have a specific size distribution. This distribution is important in determining the sensitivity and the resolution of the emulsion. 

Since there is an enormous density of such equivalent sites on the surface of a silver halide microcrystal, it would be surprising if a single speck of Ag2S were formed on each grain even under optimum conditions of sulfur sensitization. The sensitizer forms an adsorption silver complex which reacts to form an adsorbed molecule of Ag2S. 

Multiplex CARS microspectroscopy, in conjunction with appropriate spectral analysis tools, was successfully applied to the study of phospholipid bilayer model systems [120, 121, 142, 70, 143], lipids within cells [144, 127, 145-147, 141], a single pollen grain [148], a single bacterial endophore [140], a molecular J-aggregate microcrystal [149], silicon components on a wafer [130], separated phases in polymer blends [123, 135], and concentration profiles in a microreactor [150]. 

InN single crystals of a size suitable for thermal conductivity measurements have not been obtained. The only measurement of the thermal conductivity has been made using InN ceramics [20], InN microcrystals obtained by microwave plasma were sintered under a pressure of 70 kbar at 700°C. The room temperature thermal conductivity was measured by the laser-flash method giving k = 0.45 W/(cm K) [20], This value is much below the estimate by Slack which gives k = 0.8 W/(cm K). This result indicates that the InN ceramic has a high impurity content and consists of small size grains. 

Related to these matters has been the question whether two-component electrode metals (dual-site model) could lead to an electrocatalyst surface that exhibited catalytic properties better than either of its components. Qualitative ideas about electron spillover between one component and another at microcrystal grain boundaries, or transfer of the chemisorbed intermediate from one site to another, could suggest the possibility of such an effect. However, a quantitative theoretical analysis of this question by Parsons (149), based on his treatment of chemisorption effects at single metals (23) having various AG ,, h values, showed that, for practical applications, almost no... 

The SKes of the elementary crystals are very small, of the order of micrometers and carmot be singled out to be characterized in the same way as single crystals. We will see how, nonetheless, they can be studied, using certain experimental techniques. In other works, these techniques are often called powder techniques , the word powder simply referring to polycrystals in this case. The microcrystals in question should not be eonfused with the more general term grain of powder, since a grain of powder can be either poly- or monocrystalline. 

Fig. 2. Excitation profiles of the v, Raman lines of all-tra s-(3-carotene for the (a) isopentane solution at 160 K, (b) spin-coated film at 11 K, and (c) randomly oriented crystals (grain size < I mm) at 11 K (bar graphs) as well as their optical absorption spectra (broken lines). The optical absorption spectrum in (c) is taken from that of microcrystals dispersed in a KBr disk.

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