Dependence on temperature and oxygen

The reaction involving HgO depends on temperature and oxygen pressure. 

Fig. 3-3 shows the phase diagrams for the cerium, praseodymium and terbium oxides. It reveals several phases in each of the systems with their compositions depending on temperature and oxygen partial pressure. The different phases have been named as i = MO1.714, C, = MOi.ysg, e = MOi.goo, 5 = MO1.8I8 and (3 = MO1.833. Electron diffraction patterns (see Fig. 3-21) revealed the unit cells of those phases and their relationship to the... 

In many cases drying goods require desiccants with predefined characteristics depending on temperature and oxygen sensitivity. 

Since those cathodes include the transition metal oxide, their valence state may change under polarization. This means that the interface stability depends on temperature and oxygen potential so that operation conditions should affect the interface stability. A most typical example is the LSM/YSZ interfaces. Since the tetravalent Mn ions are relatively stable in the perovskite lattice, this causes the formation of A-site deficiency in Lai yMn03. Since this is related with the valence stability, behaviors associated with the A-site deficiency is sensitively dependent on the Sr content in LSM, polarization directed and its magnitude, and temperature. 

Following the formation of dehydroascorbic acid, the reaction proceeds irreversibly the degradation process produces oxalates, formates, and carbon dioxide, depending on temperature and pH. As usual, the oxygen-scavenging reaction rate is increased by raising the pH and the temperature. 

Let us illustrate this phenomenon with a practical example, the variation of oxygen and of nitrogen equilibrium solubilities with depth in the ocean [1]. For seawater, the density p depends on temperature and salinity, and it could vary from 1.025 to 1.035 g cm. For dissolved oxygen, V2 = 0.97 cm g in seawater at a water temperarnre near 25°C. If d is expressed in meters, then at the lower limit of the water density. Equation (21.17) becomes... 

Oxygen self-diffusion in calcite dependence on temperature and water... 

Oxygen diffusion in quartz dependence on temperature and water fugacity. Chem. Geol. 90, 55-70. 

Petry C., Chakraborty S., and Palme H. (2004) Experimental detennination of Ni diffusion coefficients in olivine and their dependence on temperature, composition, oxygen fu-gacity, and crystallographic orientation. Geochim. Cosmochim. Acta 68, 4179-4188. 

Fritzsche, using the formula a- = A exp — E/kT) for the conductivity, A being slowly dependent on temperature and E an activation energy (which he assumed to be that for diffusion of oxygen), found in his investigations that E averages 3 e.v. We will attempt to show a correlation between Ei, the O energy level, and the value of E calculated by Fritzsche. 

The oxidation behaviour of Si3N4 ceramics strongly depends on impurities in the gas atmosphere. Impurities like alkaline or alkaline earth metals, S02, and vanadium drastically decrease oxidation [431, 433, 434]. The main influence of the different impurities is caused by a change of the viscosity or the destruction of the oxide scale, accelerating the diffusion of oxygen or water vapour into the ceramic and increasing the corrosion. Of coarse, the effect strongly depends on temperature and gas composition. 

Fig. 5.23 Speculative diagram describing the dependence of charge transport mechanisms in alumina on temperature and oxygen pressure.

Reaction with water vapor or humid air (60-95% relative humidity) in the temperature range 20-500 °C results in the formation of a WO3 layer. No lower oxides or hydrates could be found by ESCA. The thickness of the oxide layer increases with increasing humidity. The reaction rate depends on temperature and I20]/[H2] partial pressure ratio and is more rapid than with liquid water. Water molecules are adsorbed at the tungsten surface and dissociate. The oxygen atoms difiuse into the tungsten metal, forming at first a solid solution and then the oxide compound, while, hydrogen escapes as element. 

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