Initial exotherm temperature

Cronin, J. L., and P. F. Nolan, "The Comparative Sensitivity of Test Methods for Determining Initial Exotherm Temperatures in Thermal Decompositions of Single Substances," J. Haz. Mat., 14 (1987). 

The recorded initial exotherm temperature is affected by a number of factors unrelated to the inherent chemical stability of the test material. These... 

The initial exotherm temperature is the temperature at which a self-sustaining exothermic reaction is detected in the sample under the specific experimental conditions. An exotherm is indicated by a sustained increase in the differential... 

Jhu et al. VSP Full cells VSP2 was used to meastrre the thermal hazard and runaway characteristics of commercial 18650 lithirrm-ion batteries. The tests evaluated the thramal hazard characteristics, such as initial exothermic temperature (TO), seU-heating rate (dT dt ), pressure-rise rate (dP dt ), pressirre tempraature profiles, maximum [41]... 

Test method Experimental conditions Sample mass Initial exotherm detected, K Adiabatic temperature increase, K Heat of reaction, J/g... 

Delays in working up the crude product caused violent explosions during attempted vacuum distillation. An alternative method of crystallisation is described [1]. There is a very high rate of pressure increase in exothermic decomposition [2], Energy of decomposition (in range 180-420°C) measured as 2.19 kJ/g by DSC, and Taj,24 was determined as 147°C by adiabatic Dewar tests, with an apparent energy of activation of 168 kJ/mol [3], The initial decomposition temperature by ARC was 166°C. 

The checkers observed a significant induction period prior to onset of the exothermic reaction. Care must be taken to avoid addition of the nickel acetylacetonate too rapidly initially or temperature control becomes difficult. 

This test can be used to give early detection of the initial exothermicity. It is possible to estimate thermokinetic parameters (e.g., the activation energy and the adiabatic self-heat rate) and to estimate how the initial temperature for self-sustaining reactions will vary with the quantity of material present. 

A series of 11 nitrobenzaldehydes was examined by TGA, DSC and ARC techniques. Only 5-hydroxy-2-nitrobenzaldehyde decomposed exothermally in an unsealed container, but all did so in sealed capsules, under dynamic, isothermal or adiabatic conditions, with evolution of much gas. Initial decomposition temperatures in °C (compound, ARC value, and DSC value at lOVmin, respectively, followed by ARC energy of decomposition in kJ/g) were - 2-nitro-, 176, 220, 1.44 3-nitro-, 166, 218, 1.94 4-nitro-, 226, 260, 1.27 2-chloro-5-nitro-, 156, 226, 697 2-chloro-6-nitro-, 146, 220,. 832 4-chloro-3-nitro-, 116, 165, 1.42 5-chloro-2-nitro-, 240, 3-hydroxy-4-nitro-, 200, 4-hydroxy-3-nitro-, 200, 5-hydroxy-2-nitro-, 175, 3-methoxy-4-nitrobenzaldehyde, 245°C, -. 4-Nitrobenzaldehyde showed by... 

Method 4 Na2S.9H20 (2.65 g, 11 mmol) in H20 (10 ml) is added the dibromoalkane (5 mmol) and Aliquat or TEBA-C1 (0.5 mmol) in PhH (10 ml). The initially exothermic reaction is stirred for ca. 1 h at room temperature and the organic phase is then separated, washed with H20 (2 x 20 ml), dried (MgS04), and evaporated to yield the alkene. Gaseous alkenes are collected using a gas burette ( the solvent can be omitted with liquid dihaloalkanes). 

Graetz et al. [188-190] studied the decomposition of two other polymorphs P-and y-AlHj in comparison to the a-polymorph, aU of which were freshly made by the organometaUic method developed by Brower et al. [180], Table 2.21 compiles thermodynamic and kinetic data extracted from their papers. It was found that at temperatures >1(X)°C, decomposition of P- and y-Aftf occurs with the initial exothermic phase transformation of P- and y-AUf — a-Aftf, which subsequently decomposes in the... 

After subsidence of temperature following initial exotherm, the fiber bundle with the partially cured pot is removed from the mold for fiber end exposure. The mechanical integrity of the potted end in this green state must be sufficiently great to permit careful handling and insertion in the machine necessary for fiber-epoxy excision. 

The reaction of hexamine dinitrate (241) with 98% nitric acid at —30°C, followed by quenching with aqueous sodium nitrate, yields the nitrosamine (244). When the same reaction is cautiously quenched with ethanol the ethoxyether (245) is obtained. Treatment of the ethoxyether (245) with cold absolute nitric acid yields the bicyclic ether (246). ° Treatment of any of the cyclic nitramines (242)-(246) with nitric acid and ammonium nitrate in acetic anhydride yields RDX. ° Hexamine dinitrate is often used in low temperature nitrolysis experiments in order to avoid the initial exotherm observed on addition of hexamine to nitric acid. 

The temperature in the condensed phase increases from the initial propellant temperature, Tq, to the burning surface temperature, Tj, through conductive heat feedback from the burning surface. Then, the temperature increases in the gas phase because of the exothermic reaction above the burning surface and reaches the final combustion temperature, Tg. Since the physical structure of AP composite propellants is highly heterogeneous, the temperature fluctuates from time to time and also from location to location. The temperature profile shown in Fig. 7.2 thus illustrates a time-averaged profile. This is in a clear contrast to the combustion wave... 

Addition of the aqueous solution is exothermic and should, therefore, be carried out over the course of a few minutes. The checkers found that the initial internal temperature was S-O C which rose to 10°C upon addition of the first few mL of quench solution. 

Assumed, not rigorously established. c Parentheses indicate peak temperature of initial exotherm. d81% n-Ci2OH, remainder other primary C12 alcohols. 

Two methods are commonly used to obtain isothermal data from DSC. The first method involves insertion of the sample into the DSC previously equilibrated at the required temperature. In the second method the sample is placed in the DSC cell at ambient temperature and the temperature is then increased at a controlled rapid rate to the required temperature. Small samples are used to ensure the sample temperature remain close to the required value. In both methods there is an initial off-balance signal and the output finally reaches a value corresponding to completion of the reaction. The baseline is usually taken as this final steady state signal, and horizontal negative extrapolation to intersect with the initial exotherm is taken as zero time for the reaction, as shown in Fig. 4. 

Knock resistance has also been correlated with other preflame reaction properties such as the rate of pressure development during adiabatic compression (17), the temperature coefficient of preflame reactions (202), and the pressure developed prior to firing (34). Estrad re (59) made a correlation between the temperature of initial exothermic oxidation in a tube and knock. No quantitative connection exists between apparent activation energy (160) or the total heat (179) of the precombustion reactions and knock. 

The facts that the LCST of PNIPAAm is only 32 °C and the polymerization reaction is highly exothermic can also lead to problems with reproducibility of the gel synthesis. If the solution is deliberately warmed above the LCST during polymerization, an opaque gel with a permanently phase separated microstructure is formed [65]. Depending upon the initial solution temperature, initiator concentration and type, and heat transfer characteristics of the gel mold, the solution temperature can rise substantially during polymerization and alter the gel s properties. 

Hexanedinitrile (adiponitrile). Use 150 ml of dry dimethyl sulphoxide, 21.2 g (0.17mol) of 1,4-dichlorobutane (Expt 5.52) and 20g (0.41 mol) of dried sodium cyanide. Maintain the reaction temperature at 90 °C for a further 15 minutes after the initial exothermic reaction has subsided. Add 150 ml of dichloromethane to the cooled reaction mixture and pour into an excess of saturated sodium chloride solution in a separatory funnel. Add just sufficient water to dissolve precipitated salts and separate the dichloromethane layer. Extract the acqueous layer once with dichloromethane, wash the combined extracts twice with salt solution, dry over magnesium sulphate and remove the solvent using a rotary evaporator. Fractionally distil the residue under reduced pressure and collect the adiponitrile as a fraction of b.p. 140-141 °C/ 1.5mmHg. The yield is 14.6g (81%). Some dimethyl sulphoxide (b.p. 40-42°C/1.5mmHg) may be obtained as a forerun. 

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