Crystallization window

The specific value of the crossover depends on both the emulsion used and the conditions of exposure. For exposures made in air, the crossover occurs at a reduction potential that is less negative the lower the pAg.of the emulsion (248). Honda and associates (264) attribute this dependence to "anodic and cathodic shifts of the band edge of the silver halide, respectively." They support this explanation by experiments on the effects of silver ions and halide ions on the sensitized photocurrent in an electrochemical cell having an AgBr or AgCl sheet crystal window. 

Operating conditions. AAS device with background corrector, absorption cuvette open (15 cm length, 15 mm diameter) and closed system with crystal windows circulating pump, 2.51 min-1 pressure fusion vessel. Wavelength, 253.7 nm EDL, Hg (5 W) deuterium compensator. 

A few precautions should be observed when working with this cell. Under conditions of high humidity it might be necessary to place a mask over the front of the cooling block with an opening just wide enough for the i.r. beam to pass. Also, it should be remembered that most single crystal window materials are sensitive to thermal shock. The cell should therefore be allowed to warm at least to 0°C before it is cleaned. 

The use of infrared spectrophotometry in clinical chemical problems on an ultramicro scale has been described by Stewart et oZ. (S13, S14). Two drops of serum or other body fluids are spread out between the barium fluoride crystal windows of the sample cell. A light path of... 

Depending on the glass-transition temperamre of the added component, the crystallization window is widened or narrowed. 

Zinc Sulfide (ZnS, Irtran-2) 0.5-18 2.3 0,5 pm 2,0 18 pm ATR crystals, windows soluble in acids, slightly soluble in water... 

AMTIR-1 (Ge33Asi2Se55) 1-14 2.5 - 2.6 ATR crystals, windows high homogeneity, not soluble in water... 

Diamond (C) 0.2-20 2.4 ATR crystals, windows extremely hard, high resistance to acids and alkalis at temperatures up to 120 °C... 

Liquid samples are contained within a cell, which uses crystal windows such as NaCl, KBr, Cap2 and Bap2 and great care must be taken to avoid water, as it can readily etch the cell window. 

The window materials that can be used in the far-infrared region are limited (see Table 2.1). A practically useful material not listed in Table 2.1 is spectroscopic-grade polyethylene high-density polyethylene plates of a few millimeters thickness can be used as cell windows in the far-infrared region. Polyethylene has two weak bands in the vicinity of 100 cm but these bands do not seriously disturb measurements of far-infrared spectra. Quartz (z-cut) may be used as windows in the low-wavenumber region (below about 250 cm ). Synthetic diamond and sapphire crystal windows may also be used. 

For a binary miscible blend (A amorphous polymer, B crystalline polymer) the glass transition is intermediate between those of plain components (Tg, Tje) and thus the crystallization range—and the crystallization behavior— will depend on the glass transition of the amorphous component (Tja) (Fig. 10.2) [19]. In fact, if FgA is lower than T,b, the glass transition of the crystallizable polymer, the crystallization window of the blend (T°-Tg), where T° represents the equilibrium melting point of B in the blend, is larger than that of the neat crystallizable component (T b -TgB), and the ability to crystallize is enhanced. On the contrary, if TgA... 

At various times, the use and accuracy of infrared temperature measurement has been extolled. This is very far from the truth, and accuracy and consistency has not been seen to be any better than the conventional thermocouple. Because of the requirements for a crystal window , location of an infrared thermometer has to be in one of the less severe mixing zones, resulting in a system life which is usually extended compared to conventional thermocouples. An infrared probe only measures a surface temperature the readings are therefore susceptible to the variations which can occur due to frictional heating of the mixing rubber surface, or alternatively to the effects of the cooled metal on the rubber surface from which it may have just parted. 

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