Oxygen reaction with calcium

DOT CLASSIFICATION 4.3 Label Dangerous When Wet, Poison SAFETY PROFILE Highly toxic due to phosphide, which in presence of moisture emits phosphine. The phosphine may ignite spontaneously in air. Incandescent reaction with oxygen at 300°C. Incompatible with dichlorine oxide. When heated to decomposition it emits toxic fumes of POx. See also CALCIUM COMPOUNDS and PHOSPHIDES. 

Originally, the term oxidation referred only to reactions with oxygen. It now is used to describe any process in which the oxidation number of a species increases, even if oxygen is not involved in the reaction. When calcium combines with chlorine to form calcium chloride. 

The presence of sodium sulfate and sodium chloride is principally the result of secondary absorption reactions. Sodium sulfate is formed by the oxidation of sodium sulfite via reaction with oxygen absorbed from the flue gas. Oxidation also occurs in other parts of the system where process solutions are exposed to air however, the amount of oxidation is small relative to the oxidation which occurs in the absorber. At steady state, the sulfate must leave the system either as calcium sulfate or as a purge of sodium sulfate at the rate at which it is being formed in the system. Although a practical limit for the level of oxidation that can be tolerated by the limestone dual alkali system has not yet been established, it appears that oxidation rates equivalent to 15 to 20% of the S02 removed might be accommodated without intentional purges of sodium sulfate. 

Direct corrosion can occur when a gas in the environment reacts directly with a metal. The discussion that follows applies to all gases, but reaction with oxygen will be used to illustrate this phenomenon. For example, both aluminium and calcium react rapidly with oxygen to form the appropriate oxide ... 

The term oxidation is used because the first reactions of this sort to be studied thoroughly were reactions with oxygen. Many metals react directly wifli O2 in air to form metal oxides. In these reactions the metal loses electrons to oxygen, forming an ionic compound of the metal ion and oxide ion. For example, when calcium metal is exposed to air, the bright metallic surface of the metal tarnishes as CaO forms ... 

Formerly, the term oxidation meant reaction with oxygen. The current definition greatly enlarges the meaning of this term. Consider the reaction of calcium metal with chlorine gas (Figure 4.13) the reaction looks similar to the burning of calcium in oxygen. The chemical equation is... 

Formation of emissions from fluidised-bed combustion is considerably different from that associated with grate-fired systems. Flyash generation is a design parameter, and typically >90% of all soHds are removed from the system as flyash. SO2 and HCl are controlled by reactions with calcium in the bed, where the lime-stone fed to the bed first calcines to CaO and CO2, and then the lime reacts with sulfur dioxide and oxygen, or with hydrogen chloride, to form calcium sulfate and calcium chloride, respectively. SO2 and HCl capture rates of 70—90% are readily achieved with fluidi2ed beds. The limestone in the bed plus the very low combustion temperatures inhibit conversion of fuel N to NO. ... 

Beryllium, calcium, boron, and aluminum act in a similar manner. Malonic acid is made from monochloroacetic acid by reaction with potassium cyanide followed by hydrolysis. The acid and the intermediate cyanoacetic acid are used for the synthesis of polymethine dyes, synthetic caffeine, and for the manufacture of diethyl malonate, which is used in the synthesis of barbiturates. Most metals dissolve in aqueous potassium cyanide solutions in the presence of oxygen to form complex cyanides (see Coordination compounds). 

It has been shown that the activity of NO synthases is regulated by cofactors calcium binding protein calmodulin and tetrahydrobiopterin (H4B). Abu-Soud et al. [149] have studied the effect of H4B on the activity of neuronal nNOS I, using the isolated heme-containing oxygenase domain nNOSoxy. It was found that nNOSoxy rapidly formed an oxygenated complex in the reaction with dioxygen, which dissociated to produce superoxide (Reaction (6)) ... 

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