Metallic Calcium as a Precursor for Sol-Gel Synthesis of CaCO3-SiO2 and CaO-SiO2 Systems

A series of binary oxide systems with Ca/Si molar ratios of 0.05, 0.1, 0.25, 0.5 and 1.0 have been synthesized by the sol-gel technique from tetraethyl orthosilicate (TEOS) and metallic calcium powder. Upon calcination, a side effect of wollastonite formation as a result of the reaction between the components of the material has been observed in the two calcium-richest systems. The increase in calcium content produces an effect of porosity promotion. At high calcium contents, the homogeneity of the systems is limited by the ability of silica to disperse the calcium component. The properties of these systems are determined by the silica surface coverage with a large amount of the scattered CaCO3 fine microcrystallites (calcite), resulting from the phase segregation. The gels were characterized by X-ray powder diffraction, low temperature nitrogen adsorption, transmission and scanning electron microscopy (TEM, SEM and SEM/EDS), thermogravimetric analysis (TGA), and FT-IR spectra, to describe the parameters important from the point of view of their application as a support for metal-based catalysts.

Calciothermal reduction of tantalate iron and manganese

Processes of calciothermal reduction of metals from iron (FeTa2O6) and manganese (MnTa2O6) tantalates as well as tantalum oxide (Ta2O5) were studied in this work. According to the results of thermodynamic analysis performed in the temperature range 373 – 2773 К, the interaction of FeTa2O6 and MnTa2O6 with calcium proceeds with complete reduction of metals. By the calculation and comparison of the lgK equilibrium constants for the reactions of alumino- and calciothermal reduction of iron and manganese tantalates were showed the thermodynamic advantage of using metallic calcium as a reducing agent. Experimental investigations of calciothermal reduction on samples of synthesized oxides were carried out by the method of combined thermogravimetry and differential thermal analysis in the mode of non-isothermal heating to 1473 K in an argon flow. X-ray powder diffraction was used to determine the phase composition of the initial samples and interaction products. It was shown that the calciothermal reduction of metals from the synthesized manganese tantalate proceeds actively at temperatures above 1196 K, while iron tantalate and tantalum oxide with the appearance of molten calcium. Tantalum and its solid solutions with iron or manganese, corresponding to the structural type Ta7Fe6, were included in the main metal components of the products of the interaction of FeTa2O6 and MnTa2O6 with calcium.

Preparation of rare earth - transition metal (RE: Y, Tm: Co) intermetallic compounds by calciothermic reduction diffusion process

Rare earth cobalt alloys have many special magnetic properties and can be used to prepare magnetic and magneto-optical components. The yttrium – cobalt intermetallic compounds are prepared by calciothermic reduction – diffusion (CRD) process at temperature of 1000ºC, under argon atmosphere. Yttrium oxide, metallic cobalt powder, metallic calcium are used as raw materials in this process. Calcium acts as the reductant, which is used to prepare the YCo5 magnetic material. XRD, SEM, EDAX and some thermodynamic valuation have been carried out on the products. The chemical reactions controlled by unreacted core model theory were studied.

The possibilities of obtaining metallic calcium from Serbian carbonate mineral raw materials

The experimental investigations defined both the technological scheme of the calcium production from limestone by aluminothermic process and the basic operating parameters of the particular technological phases. The limestone with high content of Mg, Na and K was used in the paper. X-ray analysis reveals that the samples contain mainly calcite with small amount of dolomite. At first, the influence of temperature, time and granulometry on the calcium carbonate calcination was examined. The dissociation process was completed in 10-15 min at 1200?C, and dissociation rate increases with decreasing of particle size up to 5 mm. Afterwards, the aluminothermic reduction process of calcium oxide was investigated. At the temperature 1200?C, and vacuum of at least 3 kPa, the reduction process completed within 2 hours. The chemical composition of calcium oxide and calcium showed increased content of magnesium oxide and alkaline oxides (especially sodium).