Experimental techniques exotherm measurements

On the basis of the previous work, Polanyi, Skinner and I decided to use hexane as solvent and TiCl4 as catalyst (what we now call initiator). The experimental technique was crude, but its essential feature, retained thereafter, was to use the temperature rise of the reaction mixture, due to the exothermicity of the polymerisations, to measure the rate and the extent (yield Y) of the reactions. 

Polymerization thermodynamics has been reviewed by Allen and Patrick,323 lvin,JM [vin and Busfield,325 Sawada326 and Busfield/27 In most radical polymerizations, the propagation steps are facile (kp typically > 102 M 1 s l -Section 4.5.2) and highly exothermic. Heats of polymerization (A//,) for addition polymerizations may be measured by analyzing the equilibrium between monomer and polymer or from calorimetric data using standard thermochemical techniques. Data for polymerization of some common monomers are collected in Table 4.10. Entropy of polymerization ( SP) data are more scarce. The scatter in experimental numbers for AHp obtained by different methods appears quite large and direct comparisons are often complicated by effects of the physical state of the monomei-and polymers (i.e whether for solid, liquid or solution, degree of crystallinity of the polymer). 

The evaluation of chemical reaction hazards involves establishing exothermic activity and/or gas evolution that could give rise to incidents. However, such evaluation cannot be carried out in isolation or by some simple sequence of testing. The techniques employed and the results obtained need to simulate large-scale plant behavior. Adiabatic calorimeters can be used to measure the temperature time curve of selfheating and the induction time of thermal explosions. The pertinent experimental parameters, which allow the data to be determined under specified conditions, can be used to simulate plant situations. 

The diffusion cloud (flame) technique developed by Hartel and Polanyi in the 1930s is one of the early methods of studying rapid bimolecular chemical reactions imder pseudo-first-order, steady-state conditions. This method is the source of most measured rates for reactions of alkali metals with halogenated compounds and still serves as a basis for experimental and theoretical studies. In most applications of the technique, sodium metal is heated in an oven, mixed with an inert carrier gas, and allowed to diffuse into a backgroimd of a reactant gas. In very exothermic reactions the sodium flame is chemiluminescent otherwise the cloud is illuminated with a sodium resonance lamp. The reaction rate can be measured either by determining the distance the sodium diffuses until it all reacts or by spectroscopically measuring the total amount of sodium in the cloud. ... 

The calorimetric application of thermal hazards analysis for energetic LIBs has proven to be a useful alternative technique because of the requirement of temperature measurements. The ARC experimental results of the thermal runaway test showed that the temperature of the exothermic reaction was near 100 °C. As the exothermic reaction progressed beyond 150 °C, the reaction rate accelerated, and the battery disintegrated. At this point, the battery components were ejected from the casing, which could lead to bums or even explosions [9, 23]. 

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