Calcining temperature

Light or heavy magnesium carbonate is exposed to a red heat, and carbon dioxide and water are expelled leaving light or heavy magnesium oxide. The density is also influenced by the calcining temperature higher temperatures yield more compact forms. 

Luminescence. Limestone possesses only limited luminescent qualities, ranging from very faint or none with the impure types. However, quicklime is very luminescent at calcining temperatures, hence the term limelight. 

Stability. AH calcitic and dolomitic limestones are extremely stable compounds, decomposing only in fairly concentrated strong acids or at calcining temperatures of 898°C for high calcium and about 725°C for dolomitic stones at 101.3 kPa (1 atm). A very mild destabilizing effect is caused by C02-saturated water, as described in the preceding section on solubihty. Aragonite, however, is not as stable as calcite. In sustained contact with moisture,... 

Magnesia Calcination temperature, °C Surface area, m /g CrystaUite size, p.m Porosity, %... 

Calcium Pyrophosphate. Calcium pyrophosphate, Ca2P20y, is manufactured by high temperature calcination of DCP in a rotary calciner. Temperature is carefiiUy controlled to adjust the proper ratio of P- and y-forms. 

During calcination, water is removed at temperatures between 200 and 300°C sulfur trioxide is removed at temperatures between 480 and 800°C. At about 480°C the crystals of Ti02 are being formed and continue to grow with increasing temperature. To prepare the anatase pigment, the final calcination temperature of the hydrolysate prepared in the presence of anatase seeds should reach about 800—850°C. 

Anthracite is calcined at appreciably higher temperatures (1800—2000°C). The higher calcining temperatures for anthracite are necessary to complete most of the shrinkage and to increase the electrical conductivity of the product for use in either Soderberg or prebaked carbon electrodes for aluminum, siHcon, or phosphoms manufacture. 

Table 5, Effect of calcination temperature of Cera hydrate on the fired properties of p" -alumina...

Figure 2. Variation of crystallite size with calcination temperature...

Figure 5 depicts the effect of calcination temperature on subsequent catalyst activity after reduction at 300°C (572°F). Activity was measured in laboratory tubular reactors operating at 1 atm with an inlet gas composition of 0.40% CO, 25% N2, and 74.6% H2, and an inlet temperature of 300°C. Conversion of CO is measured and catalyst activity is expressed as the activity coefficient k in the first order equation ... 

Thermal analysis has been widely and usefully applied in the solution of technical problems concerned with the commercial exploitation of natural dolomite including, for example, the composition of material in different deposits, the influence of impurities on calcination temperatures, etc. This approach is not, however, suitable for the reliable determination of kinetic parameters for a reversible reaction (Chap. 3, Sect. 6). 

Figure 4.11. Typical Tafel plots for Pt catalyst-YSZ interfaces during C2H4 oxidation on Pt the large difference in I0 values between the two Pt films (labeled R1 and R2) is due to the higher calcination temperature of Pt film R2 vs Pt film Rl.4 Reprinted with permission from Academic Press.

CO conversions over Au/Ce02 catalyst were measured in the dry and wet condition as shown in Fig. 1. Similar to other supported gold catalysts, Au/Ce02 catalyst showed higher CO conversions in the presence of water vapor than in the absence of it at the same temperature. Catalytic activities for CO oxidation over Au/Ce02 catalysts prepared at different calcinations temperature were compared in the dry and wet condition as shown in Fig. 2. Au/Ce02 catalyst calcined at 473 K showed the highest initial CO conversion in the absence of water vapor. However, the CO conversion decreased steadily and reached a steady-state value over this catalyst. 

Fig. 2. CO conversions at 363 K in the dry condition (open points) and 353 K in the wet condition (filled points) over lOOmg and 50 mg of Aa/CeOi catal) containing 0.95 wt% Au prepared at different calcination temperatures (373 K (circle), 473 K(square), 573 K(triangle up), 673 K (triangle down), 773 K (diamond), 873 K (hexagon)). The reactants of 100 ml/min, 1 vol% CO and 1 vol% O2 in He, were fed to the catalyst.

In general, the increase of preparation or calcination temperature helps to increase the crystallite size of anatase titania. However, anatase phase is thennally unstable and is easily converted to rutile phase. Moreover, reactive surface area decreases with increasing the... 

Figure 6. Ion Intensity Ratios for 10% WO3/AI2O3 as a Function of Calcination Temperature.

In the following the samples are identified by a notation indicating atomic ratios and the calcination temperature e g. LalMnl-973 identifies perovskite LaMn03 calcined at 973 K. 

Extensive data on the charaaerization and the thermal evolution of the different catalysts have been reported elsewhere [9-14]. Phase composition, cell parameters and surface area of the final materials are summarized in Table 1. The XRD data indicate that for all the hexaaluminate-type samples the formation of the final phase begins at 1273 -1373 K and requires calcination temperatures of 1473-1573 K to be completed. 

PtWZ (Std) to obtain a reference catalyst. Prior to reaction, all samples were calcined for one hour at the chosen temperature (1096 K for WZ, Pt/Al203 and Pt/WZ (Std), and 773 K for Pt/WZ (acac)) and subsequently reduced for 1 h under a H2 flow of. 5 liter/ min g at 623 K. The choice of temperature for the second calcination cycle of the Pt/WZ (acac) sample is not in any way arbitrary. The idea is to use a non-aqueous scheme to keep the incorporation of moisture to a minimum, and a calcination temperature low enough to guarantee better metal dispersions. 

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