Rhodium explosive

Pellistors are used to detect flammable gases like CO, NH3, CH4 or natural gas. Some flammable gases, their upper and lower explosion limits and the corresponding self-ignition temperatures are listed in Tab. 5.1. This kind of gas sensor uses the exothermicity of gas combustion on a catalytic surface. As the combustion process is activated at higher temperatures, a pellistor is equipped with a heater coil which heats up the active catalytic surface to an operative temperature of about 500 °C. Usually a Platinum coil is used as heater, embedded in an inert support structure which itself is covered by the active catalyst (see Fig. 5.33). The most frequently used catalysts are platinum, palladium, iridium and rhodium. 

There is much current excitement and activity in the field of homogeneous hydrogenation using ruthenium catalysts. This is reflected in the recent, explosive increase in the number of research publications in this area, now rivaling those for rhodium catalysts (Fig. 3.1). Meanwhile, the price of rhodium metal has risen dramatically, becoming about ten times that of ruthenium, on a molar basis. The number of reports on the use of osmium catalysts has remained low, partly because of the higher price of osmium compounds - about ten times that of ruthenium - and partly because the activity of osmium catalysts is often lower. 

A series of 12 complexes of Co(III) with both ionic and covalent azide groups was prepared and most were easily detonable as dry salts, especially at elevated temperatures [1]. Polarography is an accurate and safe method of analysis for azides [2], Hexaammine-cobalt, -chromium and -rhodium hexaazidocobaltates are explosive, particularly in the dry state [3],... 

The first reaction is run over platinum-rhodium catalysts at around 900°C (1,652°F). In the second and third stages, a mixture of nitric oxide and air circulates through condensers, where it is partially oxidized. The nitrogen dioxide is absorbed in a tower, and nitric acid sinks to the bottom. Nitric acid is mainly used to make ammonium nitrate, most of it for fertilizer although it also goes into the production of explosives. Nitration is used to manufacture explosives such as nitroglycerine and trinitrotoluene (TNT) as well as many important chemical intermediates used in the pharmaceutical and dyestuff industries. 

Ruthenium, rhodium, iridium and platinum are characterised by yielding, upon reduction of their salts, highly explosive powders. Osmium and palladium do not appear to share this property.3... 

Explosive Ruthenium is obtained by dissolving an alloy of the metal with excess of zinc in hydrochloric acid. The zinc passes into solution, leaving metallic ruthenium as a finely divided, explosive residue. Unlike rhodium and iridium, ruthenium is explosive even when prepared in the entire absence of air. It seems hardly possible, therefore, that the same explanation for the explosivity can apply as for the first two metals (see pp. 156, 239). Perhaps Bunsen s original explanation is the correct one, namely, that an unstable modification or allotrope is first formed, and that this is converted into the stable variety with considerable heat evolution.7... 

Explosive Rhodium.—In 1868 Bunsen8 accidentally discovered that several of the platinum metals can be obtained in an explosive form. Rhodium is a case in point. If alloyed with excess of zinc or cadmium, and the product treated with hydrochloric acid, the zinc (or cadmium) passes into solution, leaving an insoluble residue of finely divided explosive rhodium. 

Bunsen explained the explosive property of the metal on the assumption that an unstable modification or allotrope results from the above method of preparation, and that its conversion into the stable variety is accompanied by explosive violence. This view, however, is open to question. When explosive rhodium is kept at 100° to 200° C. for several days it ceases to be explosive. Furthermore, if the metal is obtained by the foregoing method in entire absence of air, it is not explosive. 

A very dangerous fire and moderate explosion hazard when exposed to heat or flame can react vigorously with oxidizing materials. Warning pyrophoric in air. Mixtures with nitrogen oxide explode above 50°C. Violent reaction with zinc + transition metal halides (e.g., cobalt halides, rhodium halides, ruthenium halides). Mixtures with acetic acid + water produce a pyrophoric powder. To fight fire, use water, foam, CO2, dr " chemical. See also CARBONYLS and IRON COMPOUNDS. 

The preparation of N-phenylhydroxylamine in high yields from nitrobenzene under catalytic transfer hydrogenation conditions is also possible utilizing wet 5% rhodium on carbon and hydrazine hydrate. Unfortunately, the transition metal catalysts tend to be expensive and the high temperatures required can be detrimental, particularly when the resulting hydroxylamines are explosive in nature. ... 

Nitric acid is one of the most important inorganic acids. It is used in the production of fertilizers, dyes, drugs, and explosives. The major industrial method of producing nitric acid is the Ostwald process. The starting materials, ammonia and molecular oxygen, are heated in the presence of a platinum-rhodium catalyst (Figure 13.22) to about 800°C ... 

The rhodium and iridium complexes (121) and (122) are formed when LiN C(CF3)2 reacts with RhCl(PPh3)3 and ft-aHs-IrCl(CO)(PPh3)2, but are more conveniently prepared using the stable liquid reagent MesSn-N C(CF3)2 [LiN C(CF3)2 is explosively unstable above 20— 25 In toluene at reflux (122)... 

Bunsen worked out a method for the separation of platinum metals (preparation of pure rhodium). He determined the composition, NIg,NH3, of nitrogen iodide, developed a volumetric method of iodimetry, using a solution of sulphurous acid, and worked on water analysis. Bunsen and L. Schischkoff investigated the chemical reactions in the explosion of gunpowder. Bunsen discovered arsenic pentasulphide, and measured the adsorption of carbon dioxide on glass. ... 

Catalysts are often used in the laboratory for hydrogenations. These catalysts are often pyrophoric—they catch on fire in the air. If they are loaded with hydrogen, they can explode. The two most common kinds of hydrogenation catalysts encountered in the laboratory are finely divided metal catalysts, such as Raney nickel, and precious metal catalysts, including platinum, palladium, rhodium, and ruthenium, especially on carbon powder. Both kinds of catalysts have been involved in fires and explosions. Palladium on carbon, a very common hydrogenation catalyst, is quite pyrophoric and has earned such a notorious reputation that it was listed as one of the Dirty Dozen by the National Research Council." ... 

Autocatalysis can lead to explosive behavior. This has been observed in the reaction between NO and CO on the surfaces of platinum and rhodium. The overall reaction is... 

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