Barium chromate formation

Due to the large thermal expansion mismatch between barium chromate and the sealing glass or FSS (e.g., AISI446) [213], the extensive formation of barium chromate has been shown to result in crack initiation and growth between the sealing glass and alloy coupons. 

The formation of barium chromate often leads to the physical separation of the sealing glass and the metal alloy due to barium chromate s high thermal expansion. Along interfacial regions where oxygen or air access is blocked, chromium or chromia can react with barium-calcium-aluminosilicate (BCAS) glass-ceramic to form a chromium-rich solid solution and a series of pores. 

Chemical kinetics deductions are, in some circumstances, possible from a reaction system using a dispersed solid. If the solid is entirely insoluble, for example a supported catalyst, true surface kinetics can be obtained provided (i) it can be shown that the chemical reaction on the surface is much slower than the associated mass transfer, and (ii) the surface area of the solid can be obtained. These conditions applied in the case of the oxidation of an aqueous solution of hydrazine using a dispersion of insoluble barium chromate [16]. Another case is where it can be shown that an increase in the amount of the solid component does not increase the reaction rate. In this case, exemplified by the formation of benzyl acetate from benzyl bromide and solid sodium acetate in toluene solvent, it is likely that the reaction occurs in the solution phase and that the reaction is proceeding at the saturation concentration of the solid reactant in the liquid phase [17]. 

The rate of aging is strongly influenced by other solutes in solution and thus can be increased or decreased by the presence of excess lattice ions in solution. Barium sulfate ages more slowly in barium ion solution than in sulfate and more slowly in sulfate than in water. The aging of silver chloride is impeded by silver ion, but speeded by chloride ion a similar effect exists for silver bromide. For lead chromate no particular lattice ion effect was noticed. Apparently the rate of aging does not parallel solubility, which is decreased by the common ion effect. Kolthoff and others postulated that the solubility in the adsorbed water layer may be different from that in the bulk of the solution. For example, in the case of silver chloride in the presence of adsorbed chloride ion, the solubility may be increased owing to the formation (Section 7-7) of AgCl2 in the immediate vicinity of the surface. It appears likely that the adsorbed lattice ion also has a pronounced effect on the rate of recrystallization, which is not necessarily parallel with solubility even in the adsorbed water layer. 

AMMONIUM NITRATE (6484-52-2) A strong oxidizer. An ingredient in dynamite. Violent reaction and/or the formation of explosive mixtures with hot water, reducing agents, combustible materials, organic materials, ammonium dichromate, barium chloride, barium nitrate, charcoal, cyanoguanidine, phosphorus, potassium chromate, potassium dichromate, potassium nitrate, potassium permanganate, sodium chloride, finely divided metals. Forms explosive or heat- and shock-sensitive compounds with acetic acid, alkali metals (potassium, sodium, etc.), ammonia, nitric acid, sodium hypochlorite, sulfur, urea. At elevated temperatures, contained or confined material may explode violently. 

One driving force for a chemical reaction is the formation of a solid, a process called precipitation. The solid that forms is called a precipitate, and the reaction is known as a precipitation reaction. For example, when an aqueous (water) solution of potassium chromate, K CrO iaq), which is yellow, is added to a colorless aqueous solution containing barium nitrate, Ba(N03)2((T(j), a yellow solid forms (see Figure 8.1). The fact that a solid forms tells us that a reaction—a chemical change—has occurred. That is, we have a situation where... 

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