Combustion, heat Metallic impurities

Although Sir Humphry Davy felt certain that silica is not an element, he was unable to decompose it with his powerful voltaic pile, and was also unsuccessful in his attempts to isolate silicon by passing potassium vapor over red-hot silica. Gay-Lussac and Thenard observed that silicon tetrafluoride and potassium react violently when the metal is heated, and that a reddish brown, combustible solid is obtained. This was probably very impure amorphous silicon (37, 39). 

The open hearth furnace uses the Siemens regenerative principle to raise maximum combustion temperatures to about 1,650°C and possesses a heating capability independent of the heat content or impurity burning reactions of the iron charge. These features enable the charge placed in the furnace to be any ratio of scrap to hot metal up to 100% scrap, since the furnace can melt this. Usual practice, however, is to use a roughly 50 50 mix of scrap to melt [17]. 

AMMONIUM PERCHLORATE (7790-98-9) A powerful oxidizer. An explosion hazard sensitive to friction, impact, shock, and heat. Often contains the highly sensitive and explosive nitryl perchlorate as an impurity. Likewise, small amounts of potassium periodate will increase impact sensitivity. Violent reaction with reducing agents, combustible materials. Shock-sensitive materials formed on contact with ferrocene S, organic matter, metal powders, potassium permanganate, sulfur. At elevated temperatures, contained or confined material may explode violently. Contact with many materials in the presence of heat can cause a violent reaction, including explosion. 

It is a primary explosive. It explodes violently upon thermal and mechanical shock. It requires lesser energy for initiation than lead azide and also fires with a shorter time delay. The heats of combustion and detonation are 1037 and 454 cal/g, respectively (i.e., 156 and 68 kcal/mol, respectively). The detonation velocity is 6.8 km/sec (at the crystal density 5.1 g/cm ). The pure compound explodes at 340°C (644°F) (Mellor 1967). The detonation can occur at much lower temperatures in an electric field when initiated by irradiation. Also, the presence of impurities can lower down the temperamre of detonation. Such impurities include oxides, sulfides, and selenides of copper and other metals. 

Busch et al. (1971) purified Eu by a fractionating column arrangement. The baffles of the column were at different temperatures due to their distance from the high frequency induction coil which heated the crucible containing the crude metal. The temperature of the various baffles was not reported. Eu with total impurities less than 0.02 at.% was obtained as determined by mass spectroscopy. The reason for the higher purity of this Eu compared to the Eu purified by sublimation (see table 2.5) is not clear but could be due to differences in analytical techniques, since the purification methods are essentially the same. The mass spectrometer method used by Busch et al. (1971) to analyze the Eu was not checked against standard methods such as vacuum fusion for H, Kjeldahl for N, combustion for C and neutron activation for O. As explained in ch. 37C, the mass spectrometric results for these impurities could be in error by a factor of 10. 

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