Papers by Keyword: CaF₂

Abstract: Evaluation the corrosivity of CaF₂ in hot water and 10mol%HF solution was studies.Theprepared powder and sintered ceramic was characterized by XRD and SEM technologies. we could conclude that impurities (such as CaO and CaCO₃) effected the porperties of CaF₂, the grain size is smaller, the corrosion resistance is lower. The CaF₂ of corrosion resistance was stronger in HF solution than hot water.

Abstract: Glass-ceramic was precipitated on the oxyfluoride glass surface by thermal annealing with a CO₂ laser and a heat gun. Micro x-ray diffraction showed the formation of CaF₂ ain the exposed region to the laser. Dopant distribution in glass ceramics was probed by confocal fluorescence microscope by observing much strong emission from Eu ions than the glassy area under 405 nm excitation. Much enhanced visible emissions under 365 nm excitation also showed well incorporation of Eu³⁺ ions into a crystalline environment.

Abstract: The external desulphurization of molten iron has become an important step in the production of steel and iron. The melting temperatures of high calcium desulfurization slag, which were taken from Shougang Shuicheng Iron and Steel (Group) Co. Limited, were investigated on basis of the method of hemisphaerium temperature. The contents of CaO, Al₂O₃ and CaF₂ in the slag were adjusted in 47%-53%, 14%-20% and 2%-10% respectively by adding analytical reagent Ca (OH)₂, Al₂O₃ and CaF₂ using orthogonal design. The results show that the melting temperature of desulfurization slag decreases obviously with the increase of the content of Al₂O₃ between 14% and 20%, and decreased markedly with the increase of the content of CaF₂ lower than 8%. The impact to the melting temperature of the high calcium slag is as follows: Al₂O₃ > CaF₂ > CaO.

Abstract: This paper studies the formation dynamics of belite-calcium barium sulphoaluminate cement clinker with and without CaF₂. The results suggest that, under the condition of the experimental preparation process, the formation process of belite-calcium barium sulphoaluminate cement clinker is controlled by diffusion mechanism in the temperature range of 1250-1380¡æ and the formation dynamics fits nicely with D₄̍́˽̂ځ˿̃˽˸́˽ځ˹^2/3=kt. Apparent activation energy was calculated to be 250 kJ·mol^-1and 195 kJ·mol^-1 for sample clinker without and with 0.6% CaF₂ content. It is concluded that CaF₂ contributes a lot to the reduction in energy consumption during the process of sintering belite-calcium barium sulphoaluminate cement clinker.

Abstract: t is of great importance to find ways to lubricate ZrO₂ceramic. In this paper, a kind of ZrO₂ matrix high temperature self-lubricating compositewith addition of CaF₂ and graphite as lubricants was prepared by hot-pressing. It was found that the tribological properties of ZrO₂(Y₂O₃)-CaF₂-graphiteshow a good tribological behavior both at low temperature and high temperatures. The low friction coefficients of ZrO₂ (Y₂O₃)-Mo-CaF₂-graphite at high temperatures were due to the perfect lubricity of CaMoO₄ which was formed on the worn surface at high temperatures.

Abstract: Er3+, Na+-co-doped CaF2 transparent ceramics with Er3+ dopant concentration of 5at% and Na+ of 0, 0.5, 1.0 and 1.5at% were fabricated by the vacuum hot pressing method. Absorption spectra, emission spectra and fluorescence lifetimes were measured at room temperature to study the effects of Na+ on the spectral properties of Er3+: CaF2 transparent ceramic. The results showed that after introducing Na ion into Er3+: CaF2 transparent ceramics, charge-neutralized Er3+-Na+ structure formed which prevented Er3+ from clustering, the absorption intensity of ceramics decreased with the increase of Na+ concentration, but the spectroscopy and photoluminescence properties of Er3+ in CaF2 transparent ceramic could be modulated by adjusting the concentration of Na+. Co-doping Na+ to increase fluorescence lifetime should have an optimal value.

Abstract: The hierarchical approach of multi-scale modelling was adopted to study the nanometric cutting process of calcium fluoride. Then fly cutting experiments of CaF₂ were performed to analyze the influence of cutting speed upon the surface roughness of CaF₂. The results of FEM simulations show that larger negative rake angle and larger cutting edge radius lead to lower tensile stress in the cutting region. Tangential cutting force will first increase with an increase of negative rake angle and cutting edge radius, and then start to decrease with them. The tensile stress in the cutting region will increase with cutting depth at first, and then become stable when it reaches a certain extent. The specific cutting force increases rapidly with decrease of cutting depth, showing an obvious size effect. Within the range of cutting speeds adopted in the simulations, cutting speed has little influence on the tensile stress in the cutting region. And the results of fly cutting experiments show that cutting speed has little influence on the surface roughness of a machined surface under the cutting speeds adopted. This verifies the validity of the simulation result to some extent.

Abstract: Through testing the amount of the free lime and the Loss ignition, the clinker formation rate, the reaction-rate constant (K) and the activation energy (Ea) were calculated according to the Gentling equation and Arrhenius equation. The effects of CaF₂ on the formation kinetics of Portland cement clinker were investigated by analyzing the K and Ea. X-ray diffraction (XRD) and scanning electron Microscope (SEM) were used to characterize the phase composition and the morphology of the resulting samples. The results show that the silicate minerals formation is promoted when a proper amount of CaF₂ is doped into the raw meal. The K increased from 0.7450 ×10^-5s^-1 to 7.1588 ×10^-5s^-1 and the Ea decreased from 386 kJ/mol to 122 kJ/mol when the amount of CaF₂ increased from 0.0% to 2.0% in mass. However, the results were reversed at the amount of CaF₂ exceeding 2%.

Abstract: Four micro-holes were made using micro-EDM on the rake face of the cemented carbide (WC/TiC/Co) tools. CaF₂ solid lubricants were embedded into the microholes to form self-lubricating tool (SLT-1). Dry machining tests on hardened steel were carried out with the SLT-1 self-lubricating tool and conventional tool (SLT-2). The cutting forces, tool wear and friction coefficient were measured and compared. It was shown that the cutting performance of SLT-1 self-lubricating tool was greatly improved compared with that of the SLT-2 conventional tool. Through the analysis of cutting force theory and test results, the mechanism of cutting performance improvement was considered to be the formation of a self-lubricating film on the rake face which decreases the shear stress and the reduction of contact length between chip and tool.

Abstract: The experiment studied the influence of slag system on nitrogen content in high nitrogen steels which refined by the method of high-pressure and bottom-blowing nitrogen under the conditions of 1.0Mpa. The results shows that nitrogen content are up to 1.0% without the over of slag, and after adding slag, nitrogen content are up to 1.39%; Alkalinity of protecting slag has little effect on the nitrogen content, however, there are very effective to increase nitrogen after using CaF2 instead of SiO2 ,and its nitrogen content are as high as 1.48%; the effect of increasing nitrogen are clear by adding no more than 0.5% pure aluminum, but when aluminum content are more than 0.5%, the nitrogen content in steel are not change significantly, meanwhile, if adding CaF2 slag system, it will be more effective increase nitrogen than only adding pure aluminum.