Papers by Keyword: Precipitation

Abstract: Carbonate hydroxylapatite (CHAP) with different carbon content synthesized by precipitation, As raw material to calcium nitrate、potassium phosphate、potassium carbonate, by changing the incorporation of potassium carbonate.The CHAP was characterized by XRD、TEM and FTIR. And through analysis compared structure and morphology of carbon hydroxyapatite with different carbon content.

Abstract: The relation between isotopic compositions of precipitation and surface air temperature provides an unique tool for paleoclimate studies. Ananysis was conducted of monthly and annual mean d¹⁸O content of precipitation and surface air temperature for spatial and a fixed location by using the the data of China (1985~2002) in Global Network of Isotopes in Precipitation (GNIP) Database.This study shows that there is a positive correlation between d¹⁸O of precipitation and surface air temperature for those stations whose latitude is higher than 34°~36°N. The seasonal d¹⁸O-temperature gradient derived from the monthly data of 12 stations in northern China is about 0.34‰°C^-1. The d¹⁸O-temperature gradient, however, derived from the longterm annual mean data of 13 stations,, is about 0.52‰°C ^-1 which is substantially larger than the seasonal gradient. This longterm annual d¹⁸O-temperature gradient could be used as the isotope thermometer for palaeoclimate reconstruction in mid- and high-latitude regions in China.

Abstract: The effect of heat treatment on phase transformation, precipitation behavior and micro-hardness response of Cu40Zn-1.0Ti brass was investigated via powder metallurgy method. The volume fraction of α phase increased with elevated temperature, equaled to that of β phase at 400 °C, and reached to a maximum value of 55.9% at 500 °C. The solid solubility of Ti in Cu40Zn brass matrix decreased with elevated heat treatment temperature, showed high chemical potential for precipitates reaction in Cu40Zn brass. The micro-hardness of the BS40-1.0Ti brass was primarily dependent on the solid solubility of Ti, but also dependent on the phase ratio of α and β phase.

Abstract: Researches on precipitation of calcium from seawater have been carried out using CO₂. The effect of pH value on calcium removals from seawater was investigated. It was found that it is easier to remove calcium from seawater at a higher pH value, and the removal rate of calcium can reach 60% to 90% when the pH value is from pH 8.0 to pH 9.0. The precipitated solids were characterized using X-ray diffraction (XRD) analysis. The results show that they consist of CaCO₃·H₂O at pH 8.0 to pH 8.7, of CaCO₃·H₂O and MgCO₃·3H₂O at more than pH 9.0.

Abstract: Magnesium carbonate precipitation by the reaction of MgCl₂ with Na₂CO₃, using sodium tartrate as an additive was studied. The effects of sodium tartrate concentration, reaction temperature, and stirring speed on the precipitation were investigated comprehensively. Scanning electron microscopy (SEM) and X-ray powder diffraction methods were used to characterize the carbonate precipitate products. Sodium tartrate concentration, reaction temperature, and stirring speed have significant effects on the morphology of the carbonate products. Sodium tartrate has an inhibitive effect on the precipitation. The product weight decreases with the increase in the amount of sodium tartrate added, and with the increase in reaction temperature, but is almost irrelevant to the stirring speed. The products obtained at 25 and 50°C were all identified as nesquehonite. The experimental results show that the use of an additive would be an effective method to adjust the morphology of magnesium carbonate.

Abstract: 0.3%Er is added to Al-5.6Zn-1.9Mg-1.6Cu-1.0Li alloy (in wt.%) to investigate the effect of erbium on microstructure of the alloy. Most of erbium exists in the primary Al₃Er phases which are incoherent with the alloy matrix unevenly. A few of fine Al₃Er phases, precipitated from supersaturated solid solution, are coherent with the matrix. η′-MgZn₂ precipitates in the single-aged alloy are sparser than that in the double-aged alloy. A few of fine Al₃Er phases act as the heterogeneous sites of η phases. There exist some precipitation free zones in the matrix around fine Al₃Er precipitates. Erbium is segregated to grain boundary seriously. A few of Al₃Er phases are present in grain boundary. The grain boundary precipitates are not continuous about the Al₃Er phases.

Abstract: Climate change is emerging as one of the most miscellaneous expressions of the global change nowadays. It potentially affects ecosystems including water resources. The change of climate also has significant impacts on the availability of water, as well as the quality and quantity of water that is available and accessible. Aiming at studying the effect of climate change on water resources, 25 years collected secondary data of both climatic and hydro-meteorological stations were used and Statistical analysis was performed using ORIGIN PRO 8.0 Software. The study linked the surface elevation of Lake Kivu variation with respect to climate change where the level of the lake matches to pluviometric and anomalies values. Finally, the statistical analysis could not directly link the temperature variation with that of surface water level in the lake. Climate change is real and happening now and surely affects water resources among others making an urgent need to control anthropogenic inputs into the atmosphere, one of the factors forcing climate change.

Abstract: ZnO nanoparticles were synthesized in the method of precipitation, and they were characterized by the means of the transmission electron microscopy (TEM), the X-ray powder diffraction (XRD), the thermogravimetric analysis and differential thermal analysis (TG-DTA), and the Fourier transform infrared spectroscopy (FT-IR). Also their photocatalytic and degradation performance for the methyl orange aqueous solution were studied. The research results showed as-prepared ZnO nanoparticles were spherical crystals in hexagonal crystal system, and their size distribution was mainly in the range of 20-30 nm. The annealing temperature was about 390 °C, and a few organics remained, which may be helpful for the formation of ZnO particles. They had integrated crystal form, high crystallinity and thermal stability. Moreover, the obtained ZnO nanoparticles had excellent photocatalytic and degradation performance for the methyl orange aqueous solution. When reacted for 3.5 h, the degradation rate of the methyl orange aqueous solution was up to about 97%.

Abstract: Nitriding is a well-established thermochemical surface treatment of carbon micro-alloyed steels aiming enhancing surface properties such as fatigue, wear and corrosion resistances. The idea is taking benefits from the high hardening level due to a fine nitride precipitation and also the compressive residual stress state. Due to some complex interactions of phenomena during nitriding, the last has not been completely explained yet. When interest is focused on stress depth gradient and time evolution, difficulties find origins in pronounced heterogeneities whether it is the chemical gradient due to nitrogen diffusion, the resulting gradient of microstructure or the gradient of volumetric misfits. Relaxation of residual stresses is so usually described using a thermally controlled creep phenomenon due to the couple of diffusion and stress, but depend on phenomenological descriptions. A key point is also disregard that is the diffusion of carbon and its redistribution across the nitrided surface during the treatment. Based on experimental characterizations of model carbon iron-based alloys, the role of phase transformations, especially carbides, is explored in order to give better understandings of the residual stress development during nitriding.

Abstract: A novel synthesis route for the production of Sr3MgSi2O8:Eu2+,Dy3+ sub-micron quasisphere phosphor powder is reported. Both the host and activator cations were co-precipitated in water-ethanol mixed solutions and precipitation was performed with analytical grade ammonium citratetribasic. As the dispersion media, optimum concentration for PEG in the precursor solution is determined to be 0.08 g/mL. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and fluorescence spectrophotometer were employed to characterize the phosphor. The effect of the calcining temperature on the crystalline particle and luminescence properties of Sr3MgSi2O8:Eu2+,Dy3+ is systematically discussed. Sr3MgSi2O8:Eu2+,Dy3+ single phased quasi-sphere phosphor was achieved by calcining the asprecipitated precursor at 1100°C. Sr2SiO4 was identified as the intermediate phase during the calcination process. Despite the small particle size, the emission intensities were higher by the present method. However, the afterglow characteristic was not better than that prepared by solidstate reaction in the comparable condition.