Reaction threshold temperature

The test equipment shown in a schematic drawing in the method consists of a test flask, a furnace, a temperatiue controller, a syringe, a thermocouple and other auxiliary parts. The measurement is performed in a dark room for optimum visual detection of cool flames. The results are reported as ignition temperature, time lags (delay between sample insertion and material ignition), and reaction threshold temperature (the lowest flask temperature at which nonluminous pre-flame reactions (e.g., temperature rise) occur). 

D2883 Test Method for Reaction Threshold Temperature of Liquid and Solid Materials ... 

A hydrogen bomb, which uses nuclear fusion for its destructive power, is three bombs in one. A conventional explosive charge triggers a fission bomb, which in turn triggers a fusion reaction. Such bombs can be considerably more powerful than fission bombs because they can incorporate larger masses of nuclear fuel. In a fission bomb, no component of fissionable material can exceed the critical mass. In fusion, there is no critical mass because fusion begins at a threshold temperature and is independent of the amount of nuclear fuel present. Thus, there is no theoretical limit on how much nuclear fiiel can be squeezed into a fusion bomb. 

Industrial preparation of 4-cyano-3-nitrotoluene by heating the reaction components at around 170°C for 6 h led to an explosion in 1976. Subsequent investigation by DSC showed that the cyano compound in presence of the starting materials exhibited an exotherm at 180°C. After 6 h reaction, this threshold temperature fell to 170°C. Isothermal use of a safety calorimeter showed that a large exotherm occurred dining the first hour of reaction and that, in absence of strong cooling,... 

NFPA now normally refers to autoignition as the Hot Flame Ignition Temperature, as a more precise definition. Subsequently the following two additional terms are being adopted by NFPA to further refine the ignition properties of materials. The lowest temperatures at which cool flame ignitions are observed are named the Cool Flame Reaction Threshold (CFT). The lowest flame temperatures at which an exothermic gas phase reaction is noticed are named the Preflame Reaction Threshold (RTT). 

From everyday experience, we know that an egg will not denature at room temperature, however long it is left. We are not saying here that the egg denatures at an almost infinitesimal rate, so the lack of reaction at room temperature is not a kinetic phenomenon rather, we see that denaturation is energetically non-spontaneous at one temperature (25 °C), and only becomes spontaneous as the temperature is raised above a certain threshold temperature, which we will call T criticai) (about 70 °C for an egg). 

Low extract yields were obtained either by short reaction times at high temperatures or by more extended reaction at low temperatures. The designations of high and low temperature depend upon the individual coal and, more especially upon the coal rank. The evidence accrued in this research has shown that there exists a threshold temperature below which the potential for liquids formation is minimal and above which conversion can proceed at an appreciable rate. 

The preflame reactions include slow oxidation and cool flame reactions (110). Slow oxidation threshold temperatures and reaction rates have been considered important factors in controlling knock resistance (43, 75, 133). Knock ratings have been related to cool flame intensities and temperature limits (36, 43, 153). Recently, Barusch and Payne (9) have found striking correlations between octane number and the position of the cool flame in a tube (a parameter which should be a function of Ti). The heat evolved during cool flame reaction may also be a vital factor in determining the occurrence of knock (106,156,179). 

It has been observed that a definite threshold temperature exists below which the Swarts reaction will not proceed. The best results are obtained if the desired product is removed as fast as it is formed. More highly fluorinated products may be obtained if the reaction products are refluxed in the reactor. 

Aeq is known for most diatomic molecules (capable of participating in two-center chain reactions) from spectroscopic data, while ktx is known for Br2 and I2 for a variety of different third bodies M. This makes it possible to compute, for a number of systems which have been studied, the values of ta and Fa- Benson and Buss d have done so for a number of bromination systems. In addition they have calculated from Eq. (XIII.6.11), with the aid of some simplifying assumptions, threshold temperatures for different diatomic species X2. These are the temperatures at which 90 per cent... 

What is of special interest in Table XIII.2 is that the threshold temperatures are quite high for even such relatively weakly bonded species as I2 and F2 and the pre-stationary-state periods are quite long. If we compare them with the thermal systems studied, we come to the conclusion that for many of these systems, either the stationary state has not been attained until relatively late in the experiment or else that, if it has been attained, it must have been by other processes, presumably wall processes. (There is by now a large body of data to indicate that walls act as catalysts to initiate and terminate chains.) In that case, however, it is quite likely that there is also a considerable amount of reaction going on at the walls. It appears that only for the systems H2 + Br2 and CH4 + Bt2 have the thermal reactions been studied under conditions in which homogeneous reactions predominated. 

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