Decomposition temperature points

Another consequence of the suggested chemical interaction between maleated polymers and zinc stearate is that the WPC material starts to decompose at lower temperatures (at about 300°C compared to 350°C) compared to that compounded without the metal-containing lubricant [25]. However, knowing that metal-containing compounds serve as catalysts of oxidation of plastics (see Chapter 15), the earlier plastic degradation could have occurred without any coupling agents, just due to the presence of zinc stearate. A simple test in that case would be to increase an amount of an antioxidant in the system, and the earlier decomposition temperature point would have predictably returned back to normal. Hence, the above experiment... 

Ammonium nitrate decomposes into nitrous oxide and water. In the solid phase, decomposition begins at about I50°C (302°F) but becomes extensive only above the melting point (I70°C) (338°F). The reaction is first-order, with activation energy about 40 kcal/g mol (72,000 Btii/lb mol). Traces of moisture and Cr lower the decomposition temperature thoroughly dried material has been kept at 300°C (572°F). All oxides of nitrogen, as well as oxygen and nitrogen, have been detected in decompositions of nitrates. 

The decomposition temperature is extremely variable and depends upon the rate of heating. The temperatures reported here were obtained by immersing the melting-point tube in a bath preheated to 200°, and then heating rapidly. 

Fire Hazards - Flash Point Not flammable Flammable Limits in Air (%) Not flammable Fire Extinguishing Agents Not pertinent Fire Extinguishing Agents Not To Be Used Not pertinent Special Hazards of Combustion Products Produces toxic and irritating vapors when heated to its decomposition temperature Behavior in Fire Not pertinent Ignition Tenqterature Not flammable Electrical Hazard Not pertinent Burning Rate Not pertinent. 

The decomposition point is obtained in a sealed capillary tube and is not corrected. As the solid is heated, it first changes from yellow to brownish red and then decomposes to a dark red liquid. The decomposition temperature of this compound has been reported to be 208.5°,4 224-225°,5 and 225-230°. ... 

If the polymer is hard, insoluble, and infusible without decomposition, and if it refuses to swell greatly in any solvent, it may be assumed either that it is highly crystalline, with a melting point above its decomposition temperature, or that it possesses a closely interconnected network structure (e.g., as in a highly reacted glyceryl phthalate or a phenol-formaldehyde polymer). Differentiation between these possibilities is feasible on the basis of X-ray diffraction. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

In the iodide refining process described above, several conditions are implicit. Van Arkel has listed them as (i) the metals form volatile iodides (ii) the melting points of the metals are higher than the dissociation temperatures of the corresponding iodides (iii) the volatile iodides are formed at manageable temperatures (iv) the iodides easily decompose at elevated temperatures and (v) the vapor pressures of the metals are very low at the decomposition temperatures of the iodides. 

Decomposition temperature Decomposes before boiling point is reached. 

The decomposition temperature is that at which a chemical breaks down into two or more substances. This temperature can be used to evaluate candidate chemical agents. A low decomposition temperature (one that is markedly lower than the boiling point) will usually mean that dissemination of the chemical agent will cause excessive decomposition. 

In some cases a material decomposes at a given temperature. If this decomposition is to be avoided, the temperature at which processing occurs must be kept below that point. When distillation is used, the hottest point is in the reboiler. The only way to be absolutely sure that no point in the reboiler exceeds the decomposition temperature is to make certain the temperature of the heating medium does not exceed it. The temperature of the heating medium sets the temperature at the bottom of the column, and from this the pressures and temperatures within the column may be estimated (see Chapter 8). Under these circumstances, the column may have to operate at below-atmospheric pressure. 

The water of crystallization may be removed by heating the dihydrate at 120-150° under reduced pressure for two hours. The melting points reported in the literature vary considerably. The anhydrous material turns yellow at about 225-230° and decomposes at temperatures ranging from 238-242° to 253-255°, depending on the rate of heating. The instantaneous decomposition temperatures determined on the Maquenne block were 270-275°. 

A typical measurement was performed as follows. The feeder was lowered into the crucible and the sample solution (seawater) was allowed to flow under an inert atmosphere with the suction on. A constant current was applied for a predetermined time. When the pre-electrolysis was over, the flow was changed from the sample to the ammonium acetate washing solution, while the deposited metals were maintained under cathodic protection. Ammonium acetate was selected for its low decomposition temperature, and a 0.2 ml 1 1 concentration was used to ensure sufficient conductivity. At this point the feeder tip was raised to the highest position and the usual steps for an electrothermal atomic absorption spectrometry measurement were followed drying for 30 s at 900 C, ashing for 30 s at 700 °C, and atomization for 8 s at 1700 °C, with measurement at 283.3 nm. The baseline increases smoothly with time as a consequence of an upward lift of the crucible caused by thermal expansion of the material. 

Case histories regarding reactive chemicals teach the importance of understanding the reactive properties of chemicals before working with them. The best source of data is the open literature. If data are not available, experimental testing is necessary. Data of special interest include decomposition temperatures, rate of reaction or activation energy, impact shock sensitivity, and flash point. 

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