Solid solution of MgO

The physico-chemical properties of Co ions in solid solutions of MgO have received much attention. In particular, the species formed upon interaction of CO have been intensively studied by i.r. " The observed bands are very similar in all cases, but the interpretation of the valence state of the Co in the surface carbonylic species is debated. Extensive surface reduction is infact hypothesized with formation of low-valent Co complexes, while the Co centre is still considered to be in its original divalent state. ... 

The ranges of solid solutions of MgO and AI2O3 remained unchanged and are 2 % and 1 % respectively. The solubihty limit of AJ2O3 does not depend on temperature whereas for MgO is highly increasing with temperature (1.5% at 1420 °C). 

Simultaneously it displace Fe from the silicate phases increasing its content in interstitial matter [31], Kawashima et al. [33] found that in the industrial clinkers, produced in the conditions far from the equilibrium, the solid solutions of MgO and Fc203 in silicates lower the whiteness. 

The phase diagram of the Zr02-Mg0 system shows, on the Zr02 side, the three polymorphic phases that exist in Zr02 (here, the solid solution of MgO in Zr02 is shown, indicating the three polymorphs of Zr02 at 0 % MgO). 

So, in the latter case the apparent activation energy is increased by the heat of adsorption of CO, amounting to about 40-60 kJ/mol as calculated from the IR experiments. Hence, for both the Co and the Cu samples E is slightly larger than 2 (table 2) while for iron ai is considerably lower. All these values are compatible with values reported in the literature for Fe-zeolites [6,7,10,11] or dilute solid solutions of Co in MgO [31]. The kinetic and IR results with NO indicate that, like CO, it can remove the oxygen from the... 

Evaluating the results a clear kinetic picture of the catalysts has been obtained. In the steady state the active sites in Fe- and Cu-ZSM-5 are nearly fully oxidized, while for Co only -50% of the sites are oxidized. The former catalysts oporate in an oxidation reduction cycle, Fe /Fe and CuVCu. Coi in zeolites is hardly oxidized or reduced, but ESR studies on diluted solid solutions of Co in MgO indicate that Co -0 formation is possible, rapidly followed by a migration of the deposited oxygen to lattice oxygen and reduction back to Co [36]. For Fe-ZSM-5 such a migration has been observed, so a similar model can be proposed for the zeolitic systems. Furthermore, it is obvious that application of these catalysts strongly depends on the composition of the gas that has to be treated. 

In 1989, Gadalla and Sommer (252) reported that a solid-solution NiO/MgO (1 1.35) catalyst prepared by precipitation can inhibit the carbon deposition in the CO2 reforming of methane however, they obtained a low CO2 conversion (66%), a low H2 selectivity (79%), and a low CO selectivity (77%), even at the very low WHSV of 3714 cm3 (g catalyst)-1 h-1 with a CH4/CO2 (1/1, molar) feed gas and the high temperature of 1200 K. Their relatively high CH4 conversion was partly a consequence of homogeneous gas-phase reactions that occurred under their conditions. Indeed, the authors found extensive carbon deposits plugging the reactor upstream and downstream of the reaction zone. 

Stabilized zirconia refers to a solid solution of zirconium oxide with one or more of a number of stabilizing oxides (CaO, MgO, 20, or others) to form a cubic fluorite structure. This... 

AI2O3 will form a limited solid solution in MgO. At a specific temperature called the eutectic temperature (1995°C), approximately 18 wt% of AI2O3 is soluble in MgO. Predict the change in density on the basis of (a) interstitial Al + ions and (b) substitutional Al + ions. 

Figure 4.31 Thermal conductivity in the solid solution system MgO-NiO. Multiply by 418.7 to obtain k in units of W/m K. From W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, Introduction to Ceramics. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Second, replacement at the interface of an ionocovalent oxide by a metallic one. A typical example of this is provided by the Ti/MgO system. Liquid Ti can react to dissolve several at.% O and form metal-like oxides such as TiO or even solid solutions of Ti with high oxygen contents. The perfect wetting observed for this system (Figure 6.2) can be explained by the double in-situ modification of the interface the adsorption of oxygen at the liquid-side and the formation of a metallic phase at the solid-side. 

As in the case of MgO, the powder is precalcined at temperatures of 1000-1350°C to reduce the surface area of the particles [22]. The surface area is reduced by partial elimination of porosity of individual grains and by grain growth resulting from consolidation of amorphous content. The presence of MgO and silica in zinc oxide promotes densification by forming a solid solution of ZnO with these oxides [7,23]. In addition to this densification, compounds of lower solubility formed by the solid solutions, such as zinc silicates, are likely to reduce the overall solubility of zinc oxide. 

MgFj solid electrolytes have also been used to measure activities of MgO in both compounds (Magnesium Titanates - Shah et al, 1970) and solid solutions involving MgO. In the latter category, MgO-ZnO, MgO-CoO and MgO-NiO have been studies by Raghavan et al. (1975) and Prasad (1971). Seetharaman (1970) has rechecked some of the results. He found very good agreement in results obtained from the different techniques. 

Comment on each of the following observations, (a) Li2Ti03 forms a continuous range of solid solutions with MgO. (b) When TiCl3 is heated with concentrated aqueous NaOH, H2 is evolved. 

The activities of FeO in solid solutions of FeO and MgO were obtained at 1100 ° and 1300 °C by Hahn and Muan (1962). The method was similar to that for the pyroxene solid solutions described above. Solid solutions of FeO and... 

The solid solution KCl-RbCl differs basically from the solid solution NiO-MgO in two ways. Firstly, the system KCl-RbCl exhibits purely ionic conduction. The transport numbers of electronic charge carriers are negligibly small. Secondly, a finite transport of anions occurs. Because of these facts, the atomic mechanism of the solid state reaction between KCl and RbCl is essentially of a different sort than that between NiO and MgO. Once again, the diffusion profile exhibits an asymmetry (see Fig. 6-1). However, in this case the asymmetry arises not so much because of the variation of the defect concentration with composition, but rather because of the different mobilities of the ions at given concentration. Were the transport number of the chloride ions negligible, then the diffusion potential (which would be set up because of the different diffusion velocities of potassium and rubidium) would ensure that the motion of the two cations is coupled. If, on the contrary, the transference number of the chloride ions is one, then there is no diffusion potential, and the motion of the two cations is decoupled. 

If Cr-Si-N crystals which have dissolved Si atoms into the B1 lattice can be prepared, the improvement of hardness can be expected with the distortion of the crystal lattice such as Cr(N,0) . It has been reported that CrN is epitaxially grown on MgO (001) substrates . Pulsed laser deposition (PLD) is a good method to control the composition of thin films, which is ideal to deposit Cr-Si-N with precise Si content control. However, there are no reports that Cr-Si-N was prepared by PLD. In addition, the solubility of Si atoms into CrN lattice has not been investigated. In this work, we prepared Cr-Si-N thin films on Si(lOO) and MgO(lOO) substrates by PLD and investigated the solid solution of Si atoms into CrN lattice for improvement of the hardness. 

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