Decomposition Of Magnesium Carbonate Research Articles

Microwave sintering of IR-transparent Y2O3–MgO composite ceramics

A method for preparation of dense Y2O3–MgO composite ceramics by the microwave sintering was developed. The initial powders were obtained by glycine-nitrate self-propagating high-temperature synthesis (SHS) with different oxidant-to-fuel ratio. Density and IR-transmission of microwave sintered Y2O3–MgO ceramics increase with respect to dispersity of the SHS-powders and reach its maximum values for the powder prepared in a 20% fuel excess. The sintering behavior of Y2O3–MgO compacts was investigated by optical dilatometry and measuring an electric conductivity upon heating. Significant microwave radiation power surges at temperatures of 900–1000 °C, caused by the decomposition of magnesium carbonate, have been found. As a result of matching the conditions for the synthesis of powders and sintering modes, a transmission of composite ceramics of 78% at a wavelength of 6 μm was achieved at a maximum processing temperature of 1500 °C.

Features of determination of native carbon in carbon-containing rocks on the analyzer of carbon and water

The largest deposits of graphite in the Russian Federation are located in the Middle and South Urals. However, several manifestations, e.g., «Opytnyi» sector, which have not yet been placed under production, require substantiation of the strategies for their integrated development, which, in turn, requires gaining the reliable data on the content of graphite in carbon-containing rocks. A method for simultaneous determination of organic and native carbon in carbon-containing rocks using an ELTRA CW MULTIPHASE carbon and water analyzer is proposed. The method is based on the combustion of organic carbon (coal, shale) in a stream of oxygen at 550°C and native carbon (graphite) in the temperature range 550 – 1000°C with subsequent IR-spectroscopic determination of the content of gaseous carbon dioxide. The interfering effect of magnesium carbonate and calcium carbonate on the determination of organic and native carbon was taken into account in the calculations. The carbonate content was determined using a separate sample in a nitrogen flow by decomposition of magnesium carbonate at 550°C and calcium carbonate within a temperature range of 550 – 1000°C. The content of chemically bound water in the composition of the minerals of carbon-containing rocks, was determined simultaneously with carbon. The only one type of carbon — graphite — was observed in the studied samples of the carbon-containing rock from «Opytnyi». The different combustion capacity of graphite was revealed: some of the crystals almost completely burn out at a temperature below 800°C and others above 800°C, which suggests the presence of cryptocrystalline and explicit crystalline graphite in the rocks. The developed method is rapid and corresponds in accuracy to the method for native carbon determination ±0.27 C % – 0.01 C % developed and approved by the Research Council for Analytical Methods of Research (NSAM).

Dynamic Analysis of the Temperature and the Concentration Profiles of an Industrial Rotary Kiln Used in Clinker Production.

Cement is one of the most used building materials in the world. The process of cement production involves numerous and complex reactions that occur under different temperatures. Thus, there is great interest in the optimization of cement manufacturing. Clinker production is one of the main steps of cement production and it occurs inside the kiln. In this paper, the dry process of clinker production is analysed in a rotary kiln that operates in counter flow. The main phenomena involved in clinker production is as follows: free residual water evaporation of raw material, decomposition of magnesium carbonate, decarbonation, formation of C3A and C4AF, formation of dicalcium silicate, and formation of tricalcium silicate. The main objective of this study was to propose a mathematical model that realistically describes the temperature profile and the concentration of clinker components in a real rotary kiln. In addition, the influence of different speeds of inlet gas and solids in the system was analysed. The mathematical model is composed of partial differential equations. The model was implemented in Mathcad (available at CCA/UFES) and solved using industrial input data. The proposal model is satisfactory to describe the temperature and concentration profiles of a real rotary kiln.

Modelagem matemática dos perfis de temperatura do gás, do sólido e da parede do forno e dos perfis de concentração das principais espécies químicas presentes no interior do forno rotativo empregado na produção de clínquer

Resumo O cimento é um dos materiais de construção mais utilizados no mundo, sendo o tipo mais comum conhecido como cimento Portland. O processo de fabricação do cimento envolve numerosas e complexas reações endotérmicas e exotérmicas que ocorrem a diferentes temperaturas, o que o torna não trivial. Dessa forma, há um grande interesse na otimização do processo de produção de cimento. A clinquerização é uma das principais etapas da fabricação de cimento e ocorre dentro de forno rotativo. Neste estudo, o processo de produção de clínquer é analisado em um forno rotativo de via seca que atua em contracorrente. Os principais fenômenos envolvidos na obtenção do clínquer são: evaporação da água livre residual da matéria-prima; decomposição do carbonato de magnésio; descarbonatação; formação da fase líquida composta por C3A e C4AF; formação do silicato dicálcico e silicato tricálcico. O principal objetivo deste estudo é a proposta de um modelo matemático que descreve de forma realística o perfil de temperatura e de concentração dos componentes do clínquer ao longo do forno rotativo, desenvolvido a partir de mudanças propostas a um trabalho da literatura. O modelo, composto por equações diferenciais parciais, foi adaptado e implementado em linguagem computacional no programa Mathcad. O modelo proposto foi satisfatório para a descrição do perfil de temperatura e concentração dos componentes do clínquer ao longo de um forno rotativo.

Experimental Study on the Thermal Damage Characteristics of Limestone and Underlying Mechanism

This work discusses an experimental investigation on the thermal damage characteristics of limestone and underlying mechanism. Cylindrical rock samples were heated to a specific temperature level of 25, 100, 200, 300, 400, 500, 600, 700, 800, and 900 °C. Then the thermal damage evolution equation was established based on the experimental results and the characteristics of thermal damage were analyzed. Last, possible mechanisms for the observed thermo-physical and mechanical response are discussed. The results show that with the increase of temperature in the tested range of temperature, the P-wave velocity, peak compressive strength and elastic modulus decrease, but the peak strain increases; the damage factors increase faster in 200–600 °C; the development of high-temperature-induced cracks conforms to the dislocation theory; the decomposition of magnesium carbonate and dolomite is the main reaction in the tested temperature range.

Modelagem matemática de um forno rotativo empregado na produção de clínquer

Uma das principais etapas do processo de obtenção do cimento é a etapa de clinquerização, que ocorre dentro do forno rotativo. Em pleno funcionamento, o forno rotativo empregado na produção de cimento é alimentado basicamente de matéria-prima, combustível e ar. As vazões de saída são, basicamente, o clínquer e aos gases de combustão. Neste estudo, o processo de produção de clínquer por via seca é analisado, sendo a alimentação composta por 80% a 95% de calcário, 5% a 20% de argila e por pequenas quantidades de minério de ferro. O combustível empregado neste estudo é o carvão mineral. Os principais fenômenos envolvidos na obtenção do clínquer são a evaporação da água livre residual da matéria-prima, a decomposição do carbonato de magnésio, a descarbonatação, a formação da fase líquida do C3A e do C4AF, a formação do silicato dicálcico e a formação do silicato tricálcico. O objetivo principal deste estudo é a proposta de um modelo matemático que descreve o processo de obtenção do clínquer no forno rotativo. O modelo, composto por equações algébricas, foi desenvolvido por meio de balanços de massa e energia do forno. A modelagem foi implementada em linguagem de programação, empregando-se um programa comercial. A condição operacional considerada representa uma condição média adotada na indústria. O modelo proposto se mostrou satisfatório para a descrição do processo de clinquerização, sendo especialmente útil na realização da análise da demanda energética do equipamento.

Influence of heating on various properties of six Mediterranean soils. A laboratory study

The influence of temperature between 25–500 °C on several physical and chemical properties was studied on samples collected from six typical Mediterranean soils. In all soil samples, an increase in the temperature of the soil heating was found to decrease organic matter content. Soil color was affected in several ways. In soil samples having high organic matter content, the Brightness values decreased in the 25–200 °C interval and increased between 200–500 °C. In contrast, the Chroma values increased mainly between 200 to 500 °C. The RR redness index values also increased between 200 and 500 °C because of the higher Chroma and the redder Hue. The pH decreased except in the samples from the high organic surface horizons where the pH increased at temperatures above 300 °C. The soil sample containing low amount of organic matter, but rich in clay and carbonates, showed similar changes; in this case, the decomposition of magnesium carbonate also was believed responsible for the increase in soil pH at temperatures greater than 300 °C. Soil texture changes associated with increasing temperature included an increase in sand and a decrease in clay content. Increasing soil temperatures up to 500 °C drastically reduced the amount of water-stable aggregates but at the same time increased the sand content. The electric conductivity increased with temperature in the 100 to 300 °C interval and decreased at 500 °C.

Investigation of solid-solid interactions between pure and Li2O-doped magnesium and ferric oxides

The results obtained showed that the addition of small amounts of LiNO3 to the reacting mixed solids, consisting of equimolar proportion of Fe2O3 and basic MgCO3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO3 (6 mol% Li2O) decreased the decomposition temperature of MgCO3 from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe2O4. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li2O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe2O4 phase at temperatures starting from 700°C. The addition of 6 mol% Li2O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe2O4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61 kJ mol−1 for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li2O, respectively.

The origin of the exothermic peak in the thermal decomposition of basic magnesium carbonate

The thermal analysis of basic magnesium carbonate has been investigated by thermogravimetry (TGA), derivative thermogravimetry (DTGA) and differential thermal analysis (DTA). The end product was magnesium oxide formed from the decomposition of magnesium carbonate. The composition of the samples studied varied, but the general formula that represented them was xMgCO 3· yMg(OH) 2· zH 2O. In the present study, the thermal analysis of such magnesium carbonates in nitrogen, carbon dioxide and air was carried out at different heating rates and the origin of the exothermic peak was studied. Generally, the decomposition peaks were endothermic, but a persistent exothermic peak was noted, always accompanied by a very sharp drop in the TG curve, and the weight loss in this region may be significant. The exothermic DTA peak was found to be strongly influenced by the rate at which the samples were heated, sample size and atmospheric conditions.