Accelerating rate calorimetry

Consumption of magnetite can be followed by this procedure whether the products of reaction remain in true solution or reprecipitate as separate solid phases. 

50 (170, 171). The logic to search for and follow an exotherm is programmed to permit use of a selection of run parameters and to provide an on-line display of critical variables such as time, temperature, and pressure. A search for a reaction exotherm is accomplished by elevating the sample temperature by a fixed increment (step-heat) and then checking to see if the sample self-heat rate exceeds a user-selected threshold. Once an exotherm is detected, automatic collection of time, temperature, and pressure data is carried out until the reaction has finished and the self-heat rate has dropped back below the threshold value. All operations are controlled by a microprocessor system with final data presentation presented via a built-in line printer. 

51 (168). The ARC is first heated to a desired starting temperature and held a period of time for thermal equilibrium to be achieved before a rate search is performed. If the rate is less than the preset rate, the ARC will proceed automatically to the preselected temperature step heat-wait-search sequence until a self-heat rate greater than the preset rate is detected. 

The calorimeter will be maintained at adiabatic conditions until the completion of the experiment. The stepwise heating is accomplished with a radiant heater located at the bottom of the jacket. 

The performance of the ARC, as evaluated by the use of di-t-butyl peroxide, is shown in Table 11.10. Using a sample mass of 2g, the thermai intertia. p, was 7.0. Literature values of E for di-f-buty peroxide in various solvents range from 34.0-39.1 kcal/mol (168). Thus, the ARC values are somewhat lower. In order to evaluate the solvent effect, a 14.6 weight-% di-t-butyl peroxide in mineral oil was run in the ARC and an E of 38-9 kcal/ mole was found. 

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Reactivity (instability) information Acceleration rate calorimetry Differential thermal analysis (DTA) Impact test Thermal stability Lead block test Explosion propagation with detonation Drop weight test Thermal decomposition test Influence test Self-acceleration temperature Card gap test (under confinement) JANAE Critical diameter Pyrophoricity... 

ABAQUS, description, 123 Accelerating-rate calorimetry advantages and disadvantages, 428-429 experimental procedure, 429-430 hazard evaluation on MDl, 43lr isothermal decomposition studies, 431-432,433/ use in assessment of hamrds of chemicals, 428... 

Reactivity (instabiiity) information Acceleration rate calorimetry Differential thermal analysis (DTA) Impact test Thermal stability Lead block test... 

Accelerating Rate Calorimetry. This is a heat-wait-search technique (see Fig. 5.4-62). A sample is heated by a pre-selected temperature step of, typically, 5 C, and then the temperature of the sample is recorded for some time. If the self-heating rate is less than the calorimeter detectability (typically 0.02 "C) the ARC will proceed automatically to the next step. If the change of the sample temj)erature is greater than 0.02 °C, the sample is no longer heated from outside and an adiabatic process starts. The adiabatic run is continued until the process has been completed. ARC is usually carried out at elevated pressure. 

Townsend, D., "Accelerating Rate Calorimetry," I. Chem. Eng. Symp. Series, 68 (1981). 

Snee, T. J., "Incident Investigation and Hazard Evaluation Using Differential Scanning Calorimetry and Accelerating Rate Calorimetry," J. Occupational Accidents, 8 (1987). 

ARC Accelerating Rate Calorimeter Accelerating Rate Calorimetry... 

Chemical reactivity test data produced by employers or obtained from other sources (e.g., differential scanning calorimetry, thermogravimetric analysis, accelerating rate calorimetry). 

The PSI element of both the OSHA PSM Standard and the EPA RMP regulation can be improved by requiring the inclusion of all existing information on chemical reactivity. Examples of such information are chemical reactivity test data, such as DSC, thermogravimetric analysis (TGA), or accelerating rate calorimetry and relevant incident reports from the plant, the corporation, industry, and government. OSHA and EPA should require the facility to consult such resources as Bretherick s Handbook of Reactive Chemical Hazards,Sax s Dangerous Properties of Industrial Materials, and computerized tools (e g., CHETAH, The Chemical Reactivity Work Sheet). 

Testing includes screening (e.g., literature research, mixing calorimetiy, thermodynamic calculations, estimation of heats of reaction, DSC, flash point calculations), quantitative assessment (e g., accelerated rate calorimetry, specialized calorimetry), and scaleup (vent size packaging [VSP], modeling, reaction calorimetry). 

See ACCELERATING RATE CALORIMETRY, ASSESSMENT OF REACTIVE CHEMICAL HAZARDS, CALORIMETRY, HEAT FLOW CALORIMETRY... 

See also ACCELERATING RATE CALORIMETRY, SELF-ACCELERATING DECOMPOSITION TEMPERATURE... 

In early research efforts, attention was concentrated on carbonaceous anodes because of the earlier experiences with metallic lithium. Dahn and coworkers studied the thermal response of carbonaceous materials in the presence of electrolytes in an adiabatic environment created in a thermal analysis technique known as accelerating rate calorimetry (ARC). By choosing an arbitrary threshold value for... 

See also accelerating rate calorimetry, sele-accelerating decomposition... 

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