Resolidification temperatures

The results are shown in Fig. 2, where the QI yield was adopted as a measure of liquefaction extent. Because the solubility of decacyclene in quinoline was rather limitted, the QI contained a considerable amount of decacyclene. Liquefaction of this coal proceeded scarcely below 420°C of the softening temperature with this solvent as well as pyrene. Above this temperature, the QI yield decreased sharply with the increasing liquefaction temperature until the resolidification temperature of the coal. The maximum LY observed at this temperature was estimated 67%, decacyclene being assumed uncharged under the conditions. Above the resolidification temperature, the QI yield increased sharply. The carbonization may start. Decacyclene was known unreacted at 470°C in its single heat-treatment (10), and in its cocarbonization with some coals(11), although it is fusible. Cocarbonization of fusible... 

As discussed earlier, the Plastofrost estimate of the resolidification temperature (semicoke formation) is incorrect for MVB and LVB coals. Thus, that technique does not give the "real plastic range. The best estimate seems to come from using the Plastofrost measurement of the initial fusion temperature and the dilatometer reading of the temperature of maximum dilatation. 

A Microscopic Study of the Optical Anisotropy of Some Cokes Near Their Resolidification Temperatures... 

A comparative study has been made by optical and electron microscopy of the anisotropic texture of several cokes from caking coals and pitches carbonized near their resolidification temperature. A simple technique made it possible to examine, by both methods, the same area of each sample and to identify the corresponding zones of the two very similar images. The anisotropy observed in polarized light appears in electron microscopy as differences in contrast resulting not from inequalities in electron absorption, but, as revealed by microdiffraction and dark Reid examinations, from diffraction phenomena depending on the general orientation of the carbon layers within each anisotropic area. 

The coals and pitches or their mixtures were carbonized up to temperatures around the resolidification temperature, the test being stopped as the temperature reaches its maximum value the rate of heating adopted was 3°C. min. 1 for coals and 0.5°C. min.-1 for pitches only in order to avoid, in the latter case, an excessive foaming in the product. 

Thus, measurements of solidified sessile drops can be and are used to derive estimated values of contact angles, but these estimates are less precise than those derived from direct observation of liquid drop profiles except for very well wetting systems. The estimates for solidified drops tend to be smaller, typically by up to 5°, and more variable than those derived from observation of liquid profiles. Larger differences can be observed when, during cooling, dewetting of the liquid drop occurs before the resolidification temperature is reached. In this case, traces of the location of the triple line before dewetting are easily seen on the substrate surface. 

Over the temperature range 623 K to 773 K, caking coals begin to soften, coalesce, swell and then re-solidify into a porous structure which, at temperatures just above the resolidification temperature, is green coke. 

Spectra of semicokes made from Pittsburgh No 8 coal at various temperatures are shown in Figure 7 Increasing the heat-treatment temperature from 300 C causes little change in a given spectrum until 400 C At this temperature, corresponding to the onset of fluidity, the peaks become sharper At 450 C, corresponding to maximum fluidity, the peaks become their sharpest. Beyond the resolidification temperature of 470 C, spectral definition is lost, and by 525 C the spectrum is essentially featureless ... 

Both forms sublime very readily, even at room temperature a small sample on exposure to the air will completely volatilise in a short time, particularly on a warm day or if the sample is exposed to a gentle current of air. Hence the above method for rapid drying. A sample confined in an atmospheric desiccator over calcium chloride rapidly disappears as the vapour is adsorbed by the calcium chloride. A sample of the hexahydrate similarly confined over sodium hydroxide undergoes steady dehydration with initial liquefaction, for the m.p. of the hydrated-anhydrous mixture is below room temperature as the dehydration proceeds to completion, complete resolidification occurs. 

Physical Properties.—Arsenic tribromide is a solid at ordinary temperatures, crystallising in beautiful colourless rhombic prisms6 which possess a feebly aromatic odour 7 and are stable in dry air. In the presence of moisture slight fuming occurs. The crystals melt sharply at 31° C.8 The density 9 at 15° C. is 3-66 after fusion and resolidification, the product has density 3-54 at 25° C.10 The density of the liquid at various temperatures may be obtained from the expression 11... 

Expansion, contraction, and volume change on resolidification measured as a function of temperature when heated. 

Coal ground to <4.75 mm was placed in the plastometer equilibrated at 300 C. The coal was then heated at a standard rate of 3 C/min to the desired temperature without stirring and allowed to cool. Heat-treatment temperatures ranged in 25 increments between 300 and 550 C for the Pittsburgh No. 8 coal, between 300 and 500 C for the Illinois No. 6 coal, and between 400 and 550 C for the Lower Kittanning coal Other samples of these coals were subjected to the standard Bethlehem plastometer test to measure the temperatures of onset of fluidity, maximum fluidity, and resolidification. 

Figure 5 shows rod-shaped features in the 500 C Lower Kittanning semicoke seen in the transmitted electron mode. Although 500 C is beyond the temperature of resolidification measured in the plastometer, the temperatures reported for low-fluidity coals are not as meaningful as those for high-fluidity coals. In addition, fluid properties of many samples of low-fluidity coals cannot be measured in the plastometer. Accordingly, the temperatures measured for one sample may not be applicable to other samples of the same low-fluidity coal. 

As the temperature is raised after the resoUdification stage, the solid usually undergoes contraction, but at a rate that is determined by the rate of devolatilization, and will vary from coal to coal. In fact, two temperature ranges of decomposition have been identified the first occurs shortly after resolidification at ca. 500°C (ca. 930°F) and the second stage occurs at approximately 750°C (approximately 1380°F). 

In general, hot-melt adhesives are solid below 80 °C. Ideally, as the temperature is increased beyond this point, the material rapidly melts to a low-viscosity fluid that can be easily applied. Upon cooling, the adhesive sets rapidly. Because these adhesives are thermoplastics, the melting/resolidification process is repeatable. Typical application temperatures of hot-melt adhesives are 150-190 °C with melt viscosities in the range of 500-3000 mPas. 

Fabrication involves impregnating the fibres with the matrix, consolidating the two and transforming the matrix to a continuous solid of the required shape by cross-linking (for a thermoset) or melting and resolidification (for a thermoplastic). Thermosets, depending on their type, react from room temperature upwards and may require a post cure at a temperature related to the heat distortion temperature (HDT) of the... 

Several informations are obtained by the solution of Eq.l with the appropriate boundary conditions temperature distribution inside the sample and time dependence, melt propagation and penetration, velocity of the resolidification front. As an example the dynamic of the melt penetration and its dependence on the energy density is shown in Fig.2 for 30 nsec ruby laser pulse ir- ... 

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