Gas evolution tests

The evolution of carbon dioxide or methane from a substrate rqpresents a direct parameter for mineralisation. Therefore, gas evolution tests can be... 

Gas evolution tests are popular test methods because they are relatively simple, rapid (days to weeks) and sensitive. A direct measure for mineralisation is determined, and water-soluble or insoluble polymers can be tested as films, powders or objects. Furthermore, the test conditions and inoculum can be adjusted to fit the application or environment in which biodegradation should take place. Aquatic synthetic media are usually used, but also natural sea water or soil samples can be applied as biodegradation environments. A prerequisite for these media is that the backgroimd COa-evolution is limited, which excludes the application of real composting conditions. Biodegradation under composting conditions is therefore measured using an inoculum derived from matured compost with low respiration activity . ... 

The evolution of CO2 or CH4 from a substrate represents a direct parameter of mineralisation. Therefore, gas evolution tests can be important tools in the determination of the biodegradability of polymeric materials. A number of well-known test methods have been standardised for aerobic biodegradation, such as the (modified) Sturm test [70-75] and the laboratory controlled composting test [76-79] ... 

The results of the hazardous chemical evaluation are used to determine to what extent detailed thermal stability, runaway reaction, and gas evolution testing is needed. The evaluation may include reaction calorimetry, adiabatic calorimetry, and temperature ramp screening using accelerating rate calorimetry, a reactive system screening tool, isoperibolic calorimetry, isothermal storage tests, and adiabatic storage tests. 

Methylation with diazomethane may be carried out as follows (FUME CUPBOARD )-. Dissolve 2-3 g. of the compound (say, a phenol or a carboxylic acid) in a little anhydrous ether or absolute methanol, cool in ice, and add the ethereal solution of diazomethane in small portions until gas evolution ceases and the solution acquires a pale yellow colour. Test the coloured solution for the presence of excess of diazomethane by removing a few drops into a test-tube and introducing a glass rod moistened with glacial acetic acid immediate evolution of gas should... 

The evaluation of ehemieal reaetion hazards involves establishing exothermie aetivity and/or gas evolution that eould give rise to inei-dents. Flowever, sueh evaluation eannot be earried out in isolation or by some simple sequenee of testing. The teehniques employed and the results obtained need to simulate large-seale plant behavior. Adiabatie ealorimeters ean be used to measure the temperature time eurve of selfheating and the induetion time of thermal explosions. The pertinent experimental parameters, whieh allow the data to be determined under speeified eonditions, ean be used to simulate plant situations. 

An excess of sodium carbonate promotes foaming during the distillation, and is to be avoided. Since the neutral point is not easily recognized with test paper, the carbonate is added in decreasing amounts, until, a fresh portion is no longer decomposed with gas evolution. 

Vacuum stability. Gas evolution was 1.92 mg/g/40 hours (material recrystd twice from et chloride iso-Pr ale 9 1) 0.89-0.98ml/g/40 hours (sample dried at 40c in vacuum) (Ref 11, p 30). Another stability test, developed by W.C. 

MRH Aluminium 10.71/33, iron 4.35/50, magnesium 10.88/40, manganese 5.06/50, sodium 5.56/55, phosphorus 7.32/25, sulfur 4.27/20 Mixtures of the chlorate with ammonium salts, powdered metals, phosphorus, silicon, sulfur or sulfides are readily ignited and potentially explosive [1], Residues of ammonium thiosulfate in a bulk road tanker contaminated the consignment of dry sodium chlorate subsequently loaded, and exothermic reaction occurred with gas evolution during several hours. Laboratory tests showed that such a mixture could be made to decompose explosively. A reaction mechanism is suggested. 

Other types of equipment available to investigate the gas evolution are various autoclave tests (Section 2.3.3.2), isoperibolic autoclave tests (Section 2.3.1.2), and closed Dewar tests (Section 2.3.2.2). Mass flux data are also required in designing any vent facilities (Chapter 3). 

The equipment is quite adequate for screening purposes. In its simplest form (i.e., a glass tube in an oven), it is a relatively low cost technique that can be assembled with standard laboratory equipment. However, the simple test set-up provides no quantitative thermal data for scale-up purposes, but only T0 values. The more advanced instruments like the SEDEX and SIKAREX, which are also isoperibolic calorimetry equipment, acquire specific thermal stability data that can be used for scale-up. Furthermore, the small autoclave tests provide gas evolution data. 

The global rates of heat generation and gas evolution must be known quite accurately for inherently safe design.. These rates depend on reaction kinetics, which are functions of variables such as temperature, reactant concentrations, reaction order, addition rates, catalyst concentrations, and mass transfer. The kinetics are often determined at different scales, e.g., during product development in laboratory tests in combination with chemical analysis or during pilot plant trials. These tests provide relevant information regarding requirements... 

Reviewed by G. Cohn, Edit in Expls Pyrots 6(4), 1973- (This compilation records compatibility testing at Pieatinny Arsenal. Compatibility indicator was the result of gas evolution determined in (he vacuum stability test. Reports present the information in two ways by generic name or trade name of the plastic and by explosive. The reader can quickly scan the information to see with what expls a plastic is compaticle and what plastics can be used safely with a particular explosive)... 

The vacuum stability test (VST) is considered the most acceptable test for measuring stability and compatibility of explosives, worldwide. This is an empirical test in which rate of gas evolution is measured under isothermal conditions and a limit of 01 cm3 of gas per gram of an explosive is set for explosives heated at 120°C (150°C for RDX) for 40h (25h for PETN). A similar test but at somewhat lower temperatures, is used to assess compatibility of an explosive with other explosives or with non-explosive materials such as binders (polymers), plasticizers etc. 

Stability This was ascertained by performing a vacuum stability test at 60 °C for 48 h, and gas evolution in the range of 2-10 cm3 g was reported by various researchers. Some researchers are of the opinion that excessive gas evolution from raw HNF is attributed to the presence of solvents and other impurities. However, high purity HNF or recrystallized HNF with controlled particle size is reported to evolve 0.1-0.5 cm3 g 1 and use of some stabilizer may further increase its stability. The order of stability of HNF among other oxidizers is HNF < ADN < NC < CL-20 < RDX < HMX, that is, it is a most unstable substance. Nevertheless, the stability of HNF is such that it may be stored at 25 °C for several years [83] until it reaches a mass loss of 1%. 

The peak gas evolution rate, QGmax, can be obtained from calorimetric measurements (see Annex 2 and equations (A2.3) and (A2.4)). It is important that such calorimetric tests are performed so as to minimise the amount of dissolved gas in the test. "Open" tests are therefore preferred to "closed" tests[2]. 

Qv and Qg should be evaluated at the same temperature and pressure, usually the relief pressure. QG, the volumetric rate of gas evolution, can be obtained from measurements in a calorimetric test by the use of equations (A2.3) or (A2.4) (see Annex 2). Qv is the volumetric rate of vapour generation and can be calculated, as follows, from the rate of temperature rise in a closed calorimetric test or in an open test with a high superimposed containment pressure (see Annex 2). 

The information required for relief sizing for gassy systems is the rate of gas evolution, Qg, (for the full-scale vessel), as a function of temperature. This can be calculated from the rate of pressure rise in the small-scale test by means of one of the following equations111,121. Equation (A2.3) is the more general equation and is best used for data from closed tests ... 

An alternative method of obtaining the gas evolution rate is to use an open test, venting to a constant pressure automated gas burette or to a thermal mass flowmeter111. However, these techniques have been developed to characterise the normal chemical reaction by measuring gas flow rates from a heat flow calorimeter... 

The open test method for tempered hybrid systems is the same as that given for vapour pressure systems in A2.4.3 above. However, in addition to measuring the test cell temperature, the rate of pressure rise in the closed containment vessel during tempering should also be measured. The rate of heat release per unit mass, q, can be obtained from measured dT/dt data, suitably corrected for thermal inertia (e.g. by using equation (A2.12)). Equation (A2.4) can be used to determine the rate of permanent gas evolution, QG. As the containment vessel provides a large heat sink, vapour is likely to condense, so that the rate of pressure rise is due only to the non-condensible gas., ... 

A similar test to that for gassy systems (see A2.5 above) should be used to determine the permanent gas evolution rate. The rate of temperature rise should also be measured so that the rate of vaporisation can be calculated using equation (A2.7) above. 

The action of light. Mercury fulminate is sensitive to sunlight. Farmer found that on exposure to the sun s rays for 5 weeks in summer a test sample of fulminate showed considerable decomposition with gas evolution. 

Fix the leak rate and thus p . Allow the ribbon to come to a steady state at any value of 7 c, i.e., 7 c..id. Determine 9 by the flash-off method. Call this 6, or steady-state 9. Again let 0 increase to 0 at T = 7. Now reduce the leak rate to a very low value and wait until the pressure in the system reaches a new low value of p . This will be determined by the rate of gas evolution from the glass walls and the pump speed. Now suddenly raise the ribbon temperature to 7 i, at which the evaporation rate E is to be determined. From a preliminary test this T, should be so chosen that p will rise to about 100p . Record p vs. time t. E at any time t can then be calculated from the following equation ... 

---