Precipitation of oxide

Cavity. A fluid-filled cavity is sometimes present beneath the core (Fig. 3.3). The cavity may be huge as in Fig. 3.8 or small as in Fig. 3.9. The cavity may result, in part, from acidic conditions internally. Acid conditions may prevent precipitation of oxides and hydroxides inside the tubercle. 

Hydrolytic precipitation process is accomplished only by adding water, and the addition of this exclusive reagent usually causes the precipitation of oxides, hydrated oxides, hydroxides, or hydrated salts. For instance, the precipitation of hydroxides can be depicted as ... 

The 02(aq) reacted with the Mn11, forming a colloidal precipitate of oxidized manganese, likely composed of a mixture of Mnm and MnIv. We can write this reaction in a simple form as,... 

Oxyhydroxides Amorphous precipitates of oxides and hydroxides that form in alkaline solutions such as seawater. These precipitates usually contain a variety of caUons, such as trace metals. 

The presence of precipitates of oxidized, denatured hemoglobin (Heinz bodies) helps distinguish the hemolytic anemia caused by of G6PD deficiency from that caused by pyruvate kinase deficiency. 

However, copper alkoxides with longer chains appear to be more soluble in their parent alcohol. S. Shibata et al. (20) have used the n-butoxides of Y, Ba and Cu dissolved in n-butanol and hydrolyzed with water. They obtain a precipitate of oxides that is composed of a very fine submicron powder that readily sinters starting above 250°C. However, the different reaction rates for the hydrolysis and the precipitation of the three different cations lead to cationic segregation. 

An important problem in the speciation analysis of arsenic is the above-mentioned co-precipitation of oxidized forms of arsenic with sparingly soluble compounds of iron or manganese, or the formation of iron and calcium arsenates... 

Table 16.3 Summary of reactions for the precipitation of oxides from aqueous solution.

The origin of the hydride of methyl in the above gaseous mixture is readily perceived, when the volatility of zincmethylium and the method of collecting the gas are taken into consideration on opening the decomposition-tube beneath water, a copious effervescence was observed wherever the evolved gas came in contact with water and as this effervescence was accompanied by the formation of a flocculent precipitate of oxide of zinc, it could only be caused by the presence of the vapour of zincmethyliiun, which, on coming in contact with water, would be instantaneously decomposed into oxide of zinc and hydride of methyl. 

The formation of a slightly soluble oxide can be recognized from the potentiometric curve with a short section of non-saturated solution (Fig. 3.6.2, curve 3), i.e. in this case the concentration of oxygen-containing impurities in the pure melt is insufficient for precipitation of the oxide from the melt. However, the precipitation of oxide starts when even the first small weight of Lux base-titrant is added to the melt. 

Internal Oxidation - precipitation of oxides rich in A1 or Si within the intermetallic. Intergrannlar Oxidation - special case of internal oxidation in which oxides form along grain boundaries within the intermetallic. 

It is even possible to save the sulphurous acid in these exhausted mother-liquors, by saturating them with a milk of lime. This produces a precipitate of oxide of iron and of sulphite of lime, and leaves chloride of calcium only in the mother-liquors. The precipitate, mixed with sulphide of calcium, is transformed by sulphurous acid into the hyposulphites of lime and iron. And if the proportion of iron be too great, it may be precipitated by a slight excess of milk of lime. 

Dissolution of oxygen into the alloy may result in sub-surface precipitation of oxides of one or more alloying elements (internal oxidation). 

Passivation with Participation of the Electrolyte The high field model of oxide growth excludes a contribution from metal ions in the electrolyte. In some cases, however, a precipitation of oxide from the electrolyte can contribute to passivation. 

Corrosion mechanisms in molten sulfates consist of a sequence of chemical reactions and transport processes including oxide dissolution, transport of dissolved species through the salt film, and subsequent precipitation of oxide within the salt film in contact with the gas atmosphere. 

When alloyed with small percentages of certain metals (e.g., aluminum, beryllium, iron, silicon, manganese, tin, titanium, and zinc), copper oxidizes with precipitation of oxide particles within the body of the metal as well as forming an outer oxide scale. Oxidation within the metal is called subscale formation or internal oxidation. Similar behavior is found for many silver alloys, but without formation of an outer scale. Internal oxidation is not observed, in general, with cadmium-, lead-, tin-, or zinc-based alloys. A few exceptions have been noted, such as for alloys of sodium-lead, aluminum-tin, and magnesium-tin [44]. Internal oxidation is usually not pronounced for any of the iron alloys. 

The growth mechanism of the outer porous layer involves a dissolution reaction at the bottom of the pores followed by precipitation of oxide near the pore opening. As a consequence, its growth does not require a high electric field and it can reach a much greater thickness than the barrier layer, up to many micrometers. The ionic current passes across the outer film by diffusion and migration of dissolved ions in the electrolyte that fills the pores. The effective ionic conductivity of the outer layer therefore largely exceeds that of the barrier layer. 

Redox flow battery systems are promising devices, because the tendency is toward the development of low-cost systems, and future developments seem to be leaning toward choosing less toxic redox couples, more abundant materials, more stable membranes and effective recycling processes. Electrolytes can always be reused provided there is no precipitation of oxides - a phenomenon which occurs at low temperature. 

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