Fast heating

Unlike for synchrotron radiation, the maximum iatensity of x-rays from an x-ray tube is limited by how fast heat can be removed from the target to prevent its melting. In a conventional sealed tube, the target is stationary, relatively small, and must be continually cooled with water. In a rotating anode tube, the target is larger and is continually rotated so that the heat can be distributed over a larger surface. With such a tube the amount of heat, and hence. 

When crystais grow they give out iatent heat. If this is not removed from the interface then the interface wiii warm up to T, and soiidification wiii stop. In practice, latent heat will be removed from the interface by conduction through the solid and convection in the liquid and the extent to which the interface warms up will depend on how fast heat is generated there, and how fast that heat is removed. 

One of the interesting properties of PBPCP [187] was its fast heat dissipation characteristics and so it was tested by the well-known oxy-acetylene panel test (ASTM 285-70) for ablative materials. Figure 13 shows the survival of a flower for 100 s. kept on the 6.35-mm asbestos fiber-reinforced hexamine-cured panel. The ablation rate value of this material was 3.2 x 10 in/s in comparison with 3.6 x 10 in/s for asbestos-phenolic. As the char content of PBPCP was only 27% compared with 60% for conventional phenolics, mechanisms involving transpiration processes rather than heat blocking by char formation might be playing a greater role in this case [188]. 

Production molds are usually made from steel for pressure molding that requires heating or cooling channels, strength to resist the forming forces, and/or wear resistance to withstand the wear due to plastic melts, particularly that which has glass and other abrasive fillers. However most blow molds are cast or machined from aluminum, beryllium copper, zinc, or Kirksite due to their fast heat transfer characteristics. But where they require extra performances steel is used. 

Needles+H20 (from aq eth), anhydr crysts (from abs eth), mp 23°. Can be prepd by adding Na azide to a soln of 4-nitro-mesityIene-diazonium chloride-(2) (Ref 2). Expls on fast heating in all org solvs. Loses 2/3 of its N content in coned sulfuric acid... 

The electrostatic interactions in the complexes 19 were obviously sufficient to favor the zwitterionic structure in a manner that formation of the usual o-QM was suspended, so that all reactions typical of o-QMs in their quinoid form (such as [4 + 2]-cycloadditions) were suppressed or at least slowed down. Decomposition of the complex of a-tocopherol was immediate by fast heating to 40 °C or above. This caused disintegration of the complex 19, immediate rotation of the methylene group into the ring plane, and thus formation of the o-QM, which then showed the classical chemistry of such compounds. 

Fast pyrolysis is a high temperature, fast heating process in which vapor is produced, that is, subsequently condensed as a dark brownish liquid, bio-oil, with some coproduction from char and permanent gases. High yields of pyrolysis vapors/bio-oil can be achieved... 

Table I presents the results of "isothermal" simultaneous thermoanalytical (STA) runs, at 573 K and 773 K, for all three products. Similar data, at a fixed heating rate is shown in Table II. One of the crucial parameters is the temperature of maximum weight loss rate, corresponding to the time when dehydrochlorination of PVC starts becoming important. This temperature is close to 573 K in all cases. In fact, at a relatively fast heating rate, almost no decomposition occurs at temperatures under 563 K. If the materials are heated at 573 K for a prolonged period, complete dehydrochlorination takes place, but no further stages of PVC decomposition occur. None of the three materials investigated decomposes completely until a temperature of ca. 773 K is attained. Even then only a certain fraction of the entire mass of the samples is volatilised, due to the presence of inorganic fillers in their composition.

Thermochemical data obtained from experiments in which only a fast heat deposition is detected is more reliable than those in which two or more heat depositions are observed. This is due in part to the necessity for deconvolution of the experimental data. With conventional transducers and low pulses energies,... 

The rate of heating is variable. The slower this rate the better, because fast heating will shift temperatures higher and cause the size of the peak to increase. The rate of heating during calibration should equal the rate of heating during sample analysis. 

The rate at which the sample is heated up is very important, especially in the case of slow or complex reactions. Fast heating rates shift the reactions to higher temperatures and decrease the resolution when several reactions follow each other closely. 

Fig. 12.1 An ultra-fast heating of a cluster containing both N2 and 02 molecules upon impact at a surface. [9] Shown is the instantaneous configuration of 14 N atoms (dark) and 14 O atoms (light) 50 fsec after a cluster of 7 N2 and 7 02 molecules embedded in 97 Ne atoms impacts a surface at a velocity of 20 Mach. The potential used allows for alii 25 atoms of the cluster to interact with one another and with the atoms of the surface. In addition, each atom-atom chemical interaction is influenced by the presence or absence of other open-shell atoms nearby.

Our examples above demonstrated this quantitatively. For this reason, it is vital to design a reactor control system with very fast measurement dynamics and very fast heat-removal dynamics. If the thermal lags in the temperature sensor and in the cooling jacket are not small, it may not be possible to stabilize the reactor with feedback control. 

Compounds on Slow and Fast Heating, Propellants, Explosives, Pyrotechnics, Vol. 25, 2000, pp. 241-246. 

Apart from displaying the desired physical properties, such as light and weather fastness, heat fasmess, solvent resistance etc., there is a prime requirement that the pigment be readily and evenly dispersible in the application medium. Most pigments are sold as solids and the ease of dispersion in the medium to be used in the application is very dependent on the size of the particles in these solids. 

The same transformation was reported to follow treatment of 17 with excess sodium hydroxide (Sequiv), in aqueous acetone. In this case, the product yield was lower. With a reduced amount of alkali, 0.5 equiv KOH, both the hydroxy derivative 140 and the difurazanyl ether-linked bis(triazolooxadiazole) 37 resulted (Scheme 21) <1999RJ01525>. As a precaution it should be noted that the strongly acidic nature of hydroxyfurazans means they readily form stable salts with amines and alkali or alkaline earth metals, and such salts show a tendency to decompose with explosion on shock, friction, or fast heating, and so should be handled with care <1999RJ01525>. 

Hexamethylenetetramine Styphnate or Hexamine Styphnate. Probably C12H15N 08 (struct formula unknown) mw 385.34, N 25.45% crysts [from NM], mp 197-198° by fast heating Richmond et al (Ref 2) prepd it by adding one equivalent of hexamine to a satd aq soln of Styphnic Acid. The pptn of hexamine mono-styphnate was quantitative if the Styphnic Acid was saturated into ethanol instead of water, the loss by solubility in 1 1 water-ethanol was only 0.25 g per 10Q cc of soln. 

The West rod atomizers were marketed for a while, but their production has also ceased. These atomizers had the advantages of simplicity, low power requirements (less than half that required by a furnace) and fast heating rate (2000 K S l)- They were, however, considered to be extremely prone to interferences. This was attributed to the rapid cooling of the atoms once they had left the filament. This was partially overcome by setting the light beam so that it grazed the surface of the rod. 

The rate g in a linear heating program AT = q At should be carefully considered. Usually, a compromise between fast heating (for signal-to-noise ratio to be improved) and uniform heating of the sample is chosen. The temperature difference between the back (heated) and front surface of a flat sample for a given heating rate q may be estimated from... 

The capillary melting point of tetrahydrocarbazole ranges from 113° to 114° with slow heating and from 116° to 118° with fast heating. 

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