Opaque solid

Boiling an egg causes the transparent and gelatinous albumen ( egg white ) to modify chemically, causing it to become a white, opaque solid. Like all chemical reactions,... 

The DASPE nanoparticles have been synthesized by the ion association reaction between the dye cation (note that the native compound is an iodide salt DASPE-I) and the hydrophobic borate anion (TPB or TFPB-) in the presence of neutral polymer stabilizer polyvinylpyrrolidone (PVP) in aqueous solution [38, 39]. In the absence of PVP, mixing of aqueous TPB- (or TFPB-) and DASPE+ solutions at the same molar fraction yielded the orange opaque solid dispersion composed of the anion-exchanged dye species, DASPE-TPB (or... 

Aqueous soap solutions can be obtained in three distinct forms, the sol form containing the ionic micelle, a clear gel, and a white opaque solid the curd. The sol and gel forms of various soaps have been examined by McBain and his co-workers and shown to differ only in elasticity and rigidity, whilst the electrical conductivity, refractive index, concentration of metallic ion and lowering of the vapour pressure are all identical, results to be anticipated on the fibrillar theory. The gel as we have seen is fibrillar in nature and the conversion of a gel into a curd is brought about by the removal of soap fi om solutions in the form of relatively coarse fibres, a process similar to crystallisation. The experiments of Laing and McBain... 

The resulting reaction mixture, a clear yellow liquid containing a white opaque solid, is protected from atmospheric moisture by means of a calcium chloride drying tube and is set aside at room temperature for 1.5-2 hours. During this time slight effervescence continues (Note 3) and the white opaque suspended material gradually disintegrates to a finely divided translucent deposit. 

The first report of the polymerization of tetrafluoroethylene was by Plunkett in 1941, who had a cylinder of tetrafluoroethylene cut open to see why the expected amount of gas was not released when the valve was opened. His perspicacity led to the discovery of an inert, white, opaque solid with a waxy feel. Various methods of polymerization were tried after the adventitious discovery and the preferred methods for polymerization now involve aqueous media and super-atmospheric pressures. Suitable initiators (Hanford and Joyce) include ammonium, sodium, or potassium persulfate, hydrogen peroxide, oxygen, and some organic peroxy compounds. Oxidation-reduction initiation systems involving the use of persulfate with either ferrous ion or bisulfite or the use of bisulfite with ferric ion are also useful and have been discussed by Berry and Peterson. 

Optical microscopy is often the first step in surface analysis, since it is fast and easy to perform. It can be an aid in selecting the area of interest on a sample for further analysis with more complex methods. The application of classical optical microscopy to surface science is, however, limited because the maximum lateral resolution is in the order of the optical wavelength ( 500 nm). For opaque solids, the light penetrates into the material, giving optical microscopy a poor surface sensitivity. In addition, the depth of field is limited which calls for flat, polished surfaces or allows only plane sections of the sample to be viewed. 

The final cement is an opaque solid that consists of excess zinc oxide coated and bonded by possibly aluminum phosphate and zinc phosphate gels. The cement is porous and permeable to dyes [10]. 

VVe mentioned that there are three mechanisms of heat transfer, but not all three can exist simultaneously in a medium. For example, lieat transfer is only by conduction in opaque solids, but by conduction and radiation in semitransparent solids. Thus, a solid may involve conduction and radiation but not convection. However, a solid may involve heal transfer by convection and/or radiation on its surfaces exposed to a fluid or other surfaces. For example, the outer surfaces of a cold piece of rock will wannup in a warmer environment as a result of heat gain by convection (from the air) and radiation (from the sun or the warmer surrounding surfaces). But the inner parts of the rock will warm up as this heat is transferred to the inner region of the rock by conduction. 

FIGURE 12-6 Radiation in opaque solids is considered a surface phenomenon since the radiation emitted only by the molecules at the surface can escape the solid. 

The physical properties and thermal stability of SPEs are comparable with those of conventional fats and oils with the same fatty acid prohles. The physical characteristics of SPEs, similar to those of TAGs, are determined by the properties of the fatty acid side chains (38). Eor instance, SPEs produced from predominantly highly unsaturated fatty acids are clear liquids resembling conventional vegetable oils. On the other hand, SPEs made with more saturated fatty acids are opaque solids, resembling solid fats with a higher melting point (41). 

The following procedure is recommended for the small-scale preparatiai of anhydrous cerium chloride. Cerium chloride heptahydrate (ca. 20 g) is placed in a round-bottomed flask connected to a dry ice trap. The flask is evacuated and heated to lOO C for 2 h. The resulting opaque solid is quickly pulverized in a mortar and is heated again, in vacuo at the same temperature, for 2 h with intermittent shaking. A stirrer is then placed in the flask, which is subsequently evacuated, and the bath temperature is raised to 135-140 C. Drying is complete after 2-3 h of stirring. 

The fact that most flash pyrolysis studies have used radiant heating suggests solar heat as a natural means for effecting flash pyrolysis of biomass feedstocks. Since solar radiation has a characteristic temperature of almost 6000°K, it can be used to achieve very rapid heating of opaque, solid particles. Earlier studies (2) have shown that the quantity of heat required for biomass gasification is small less than 1 Gj per Mg of dry solid... 

The complex subject of thermal radiation transfer has received much study in recent years and is covered in a number of texts. The following introductory treatment discusses the following topics emission of radiation, absorption by opaque solids, radiation between surfaces, radiation to and from semitransparent materials, and combined heat transfer by conduction-convection and radiation. 

When radiation falls on a solid body, a definite fraction p may be reflected and the remaining fraction 1 — p enters the solid to be either transmitted or absorbed. Most solids (other than glasses, certain plastics, quartz, and some minerals) absorb radiation of all wavelengths so readily that, except in thin sheets, the transmissivity T is zero, and all nonreflected radiation is completely absorbed in a thin surface layer of the solid. The absorption of radiation by an opaque solid is therefore a surface phenomenon, not a volume phenomenon, and the interior of the solid is not of interest in the absorption of radiation. The heat generated by the absorption can flow into or through the mass of an opaque solid only by conduction. 

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