Antimony hydride, decomposition

Figure 6.4 shows the change in the sensor conductivity as a function of temperature. Curve / shows the dependence of sensor resistivity with temperature when the sensor is positioned in evacuated installation. The introduction of antimony hydride was made at temperature - 75°C bringing about no change in resistivity. When the temperature of the sensor was increased up to - 20 C there were no effects detected on its resistivity caused by antimony hydride. Only at higher temperatures one can observe deviation of dependence RiT) from curve 1 which is caused by decomposition of SbHa on ZnO. These results led to experiments on emission of H-atoms in a special vial when Sb-film treated by H-atoms was kept at a room temperature and sensors were kept at the temperature of - 80 C. Under these conditions, as is shown by above reasoning. 

The kinetics of the thermally induced homogeneous decomposition of phosphine (PH3) have not yet been studied. The species PH2, PH and P2 are formed on flash photolysis of PH3 and could be identified by their absorption spectra63. There are proposals as to the mechanism of the consecutive process after the photochemical primary step, but nothing is known about the kinetic parameters of these reactions. With arsine and antimony hydride only the heterogeneous decomposition has been studied64,65. 

The second is the form of equation which Stock and Bodenstein found to express the rate of decomposition of antimony hydride at 25° C. The value used for n was 0-6. 

The hydrides of phosphorus, arsenic, and antimony thus form an interesting transition series. On similar sorts of surface antimony hydride is the least stable, decomposing with measurable speed at ordinary temperatures, and phosphine is the most stable, not decomposing at an appreciable rate below a red heat. Arsine occupies an intermediate position. At low temperatures the adsorption is considerable, and, as a result, the stibine decomposition requires the pn equation, while the more stable hydrides, which only decompose rapidly at higher temperatures where the adsorption is smaller, obey the unimolecular law. It is interesting, moreover, that with stibine itself the exponent n increases towards unity as the temperature at which the reaction takes place is raised. 

Antimony hydride is endothermic. Berthelot and Petit have determined that 84 5 calories of heat will be set free from the decomposition of one of its molecules. From this it can be deduced that ite decomposition may be accompanied by explosion. 

At ordinary temperatures the rapidity of its decomposition depends Upon the nature of the vessel containing it. In antimony hydride we have an instance of what is known as uuto-katalysis. The decomposition of liquefied SbHj at room temperature is very rapid while in a gaseous state its decomposition at such temperature is slow. 

SAFETY PROFILE Poison by ingestion and intraperitoneal routes. A trace mineral added to animal feeds. Potentially explosive reaction with charcoal + ozone, metals (e.g., powdered aluminum, copper), arsenic carbon, phosphoms, sulfur, alkali metal hydrides, alkaline earth metal hydrides, antimony sulfide, arsenic sulfide, copper sulfide, tin sulfide, metal cyanides, metal thiocyanates, manganese dioxide, phosphorus. Violent reaction with organic matter. When heated to decomposition it emits very toxic fumes of I and K2O. See also lODATES. 

SAFETY PROFILE Poison by inhalation. Potentially explosive decomposition at 200°C. Flammable when exposed to heat or flame. Explosive reaction with ammonia + heat, chlorine, concentrated nitric acid, ozone. Incompatible with oxidants. The decomposition products are hydrogen and metallic antimony. When heated to decomposition it emits toxic fumes of Sb. Used as a fumigating agent. See also ANTIMONY COMPOUNDS and HYDRIDES. 

The ability to monitor trace levels of a number of heavy metals in a variety of samples is an important feature of modern environmental chemistry. Hence, sensitive analytical methods are required. When faced with the task of analyzing very low concentrations of antimony, bismuth and tin the hydride generation method is the first choice because of the improved sensitivity and lower detection limits as compared to many other techniques. The hydride generation technique includes the use of a reductant, such as a NaBH4 solution, to separate the volatile metal hydrides from the sample solution and the subsequent determination with atomic absorption after decomposition of the hydrides in a heated quartz cell. 

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