Calcium oxide

About: Calcium oxide is a research topic. Over the lifetime, 7600 publications have been published within this topic receiving 66104 citations. The topic is also known as: caustic lime & quicklime.

Yttria stabilized zirconia membrane stability in molten fluoride fluxes for low-carbon magnesium production by the SOM process

Abstract: The Solid Oxide Membrane (SOM) process for magnesium production involves the direct electrolysis of magnesium oxide for energy efficient and low-carbon magnesium production. In the SOM process, magnesium oxide is dissolved in a molten oxy-fluoride flux. An oxygen-ion-conducting SOM tube, made from yttria stabilized zirconia (YSZ), is submerged in the flux. The operating life of the electrolytic cell can be improved by understanding degradation processes in the YSZ, and one way the YSZ degrades is by yttria diffusion out of the YSZ. By adding small amounts of YF3 to the flux, yttria diffusion can be controlled. The diffusion of yttria into the flux was quantified by determining the yttria concentration profile as a function of immersion time in the flux and distance from the flux-YSZ interface. Yttria concentrations were determined using x-ray spectroscopy. The diffusion process was modeled using a numerical approach with an analytic solution to Fick’s second law. These modeling and experimental methods allowed for the determination of the optimum YF3 concentration in the flux to minimize yttria diffusion and improve membrane stability. Furthermore, the effects of common impurities in magnesium ores, such as calcium oxide, silica, and sodium oxide/sodium peroxide, on YSZ stability are being investigated.

Reactivity of lime and related oxides. III. Sorption of liquid water on calcium oxide (‘wet’ hydration)

Abstract: Calcium oxide samples differing widely in surface activity (5–100m.2 g.-1) have been ‘wet’ hydrated at room temperature using water, pure or diluted with acetone as an inert liquid. Rates of hydration and changes in surface area and lattice structure indicate that ‘wet’ hydration proceeds by a mechanism similar to that found earlier for ‘dry’ hydration by water vapour, i.e., hydration proceeds inwards from the outside of each calcium oxide particle by an advancing interface mechanism. In each case, the more active limes become aged (agglomerated) rapidly, but when the less active limes are ‘wet’ hydrated the number of crystallites generally increases much more than for ‘dry’ hydration; cleavage of the calcium hydroxide formed on the surface of the oxide is therefore more extensive, in keeping with the faster hydration. Slow ‘wet’ hydrations using 1% water more closely resemble ‘dry’ hydrations in that the number of crystallites increases only over their later stages. Ultimately, all the ‘wet’ hydrated samples age on prolonged contact with water, their crystallite growth showing some relationship to that of calcium hydroxide precipitated from solution by double decomposition.

Development and evaluation of materials for thermochemical heat storage based on the CaO/CaCO3 reaction couple

Abstract: The current work relates to the development of synthetic calcium oxide (CaO) based compositions as candidate materials for energy storage under a cyclic carbonation/decarbonation reaction scheme. Although under such a cyclic scheme the energy density of natural lime based CaO is high (∼ 3MJ/kg), the particular materials suffer from notable cycle-to-cycle deactivation. To this direction, pure CaO and CaO/Al2O3 composites have been prepared and preliminarily evaluated under the suggested cyclic carbonation/decarbonation scheme in the temperature range of 600-800°C. For the composite materials, Ca/Al molar ratios were in the range between 95/5 and 52/48 and upon calcination the formation of mixed Ca/Al phases was verified. The preliminary evaluation of materials studied was conducted under 3 carbonation/decarbonation cycles and the loss of activity for the case of natural CaO was obvious. Synthetic materials with superior stability/capture c.f. natural CaO were further subjected to multi-cyclic carbonation/decarbonation, via which the positive effect of alumina addition was made evident. Selected compositions exhibited adequately high CO2 capture capacity and stable performance during multi-cyclic operation. Moreover, this study contains preliminary experiments referring to proof-of-principle validation of a concept based on the utilization of a CaO-based honeycomb reactor/heat exchanger preliminary design. In particular, cordierite monolithic structures were coated with natural CaO and in total 11 cycles were conducted. Upon operation, clear signs of heat dissipation by the imposed flow in the duration of the exothermic reaction step were identified.