Precipitate Slurry Research Articles

Facile Low Temperature Hydrothermal Synthesis of BaTiO3 Nanoparticles Studied by In Situ X-ray Diffraction

Ferroelectric materials are crucial for today’s technological society and nanostructured ferroelectric materials are important for the downscaling of devices. Controlled and reproducible synthesis of these materials are, therefore, of immense importance. Hydrothermal synthesis is a well-established synthesis route, with a large parameter space for optimization, but a better understanding of nucleation and growth mechanisms is needed for full utilization and control. Here we use in situ X-ray diffraction to follow the nucleation and growth of BaTiO3 formed by hydrothermal synthesis using two different titanium precursors, an amorphous titania precipitate slurry and a Ti-citric acid complex solution. Sequential Rietveld refinement was used to extract the time dependency of lattice parameters, crystallite size, strain, and atomic displacement parameters. Phase pure BaTiO3 nanoparticles, 10–15 nm in size, were successfully synthesized at different temperatures (100, 125, and 150 °C) from both precursors after reaction times, ranging from a few seconds to several hours. The two precursors resulted in phase pure BaTiO3 with similar final crystallite size. Finally, two different growth mechanisms were revealed, where the effect of surfactants present during hydrothermal synthesis is discussed as one of the key parameters.

Influence of pH Value on the Properties of NH4Fe2(OH)- (PO4)2·2H2O Precursor and LiFePO4/C Composite

With the aim of investigating the influence of pH value on the properties of NH4Fe2(OH)(PO4)2·2H2O precursor and LiFePO4/C composite, we prepared a series of (NH4)Fe2(OH)(PO4)2·2H2O by adjusting the pH value in the chemical precipitation process. In addition, the LiFePO4/C composite was fabricated by using (NH4)Fe2(OH)(PO4)2·2H2O as precursor. The images of scanning electron microscopy demonstrate that the precursor particle size increases as the pH value increases, which facilitates the tuning of the properties of the LiFePO4/C composite. A further investigation indicates that an increase of viscosity of the precipitate slurry in the chemical precipitation process is responsible for the change of precursor particle size. In addition, the electrochemical performance of the LiFePO4/C composite is also governed by pH value. LiFePO4/C composite prepared at the pH value of 4.0 delivers a discharge capacity of 91 mAh g−1 and 114 mAh cm−3 at 10 C, showing a capacity retention of 99.48% after 100 cycles, which confirms the excellent rate capability and cycling stability.

Aluminum Removal from Leach Liquor of Nitric Acid Pressure Leaching Laterite Ores

In this paper, the removal of aluminum in leach liquor of nitric acid pressure leaching laterite was investigated, and a new method of aluminum removal by precipitation with calcium sulphide was presented. The effect of reaction temperature, pH value before ageing and ageing time on the removal of aluminum were examined in details. The optimum conditions were determined as follows: reaction temperature 40 °C, pH 3.9~4.1 (before aging) and aging time 30 min. Compared with the traditional precipitation method, the loss of nickel and cobalt was less than 1% in the obtained aluminum precipitate slag, which is 3% lower than that by the traditional method; the filtration rate of aluminum precipitate slurry was faster than the traditional method, when the filtration press was controlled at -0.04 MPa, the filtration rate of aluminum precipitate slurry could reach 0.109 m3/(h•m2), which is 6.5 times higher than that obtained by the traditional method.

Spatial distributions of 137Cs and 239+240Pu in surface seawater within the Exclusive Economic Zone of East Coast Peninsular Malaysia

The studies of (137)Cs and (239+240)Pu distributions in surface seawater at South China Sea within the Exclusive Economic Zone (EEZ) of Peninsular Malaysia were carried out in June 2008. The analysis results will serve as additional information to the expanded baseline data for Malaysia's marine environment. Thirty locations from extended study area were identified in the EEZ from which large volumes of surface seawater samples were collected. Different co-precipitation techniques were employed to concentrate cesium and plutonium separately. A known amount of (134)Cs and (242)Pu tracers were used as yield determinant. The precipitate slurry was collected and oven dried at 60(o)C for 1-2 days. Cesium precipitate was fine-ground and counted using gamma-ray spectrometry system at 661.62keV, while plutonium was separated from other radionuclides using anion exchange, electrodeposited and counted using alpha spectrometry. The activity concentrations of (137)Cs and (239+240)Pu were in the range of 3.40-5.89Bq/m(3) and 2.3-7.9mBq/m(3), respectively. The (239+240)Pu/(137)Cs ratios indicate that there are no new inputs of these radionuclides into the area.

Concentration of 137Cs in seawater surrounding East Malaysia

Studies of 137Cs distribution in East Malaysia were carried out as part of a marine coastal environment project. The results of measurements will serve as baseline data and background reference level for Malaysia coastline. Twenty-one locations were identified along the coastline of East Malaysia, and from each location water samples were collected at the surface of the seawater. Ten near-shore locations were also selected and seawater was collected at three different depths. Large volumes of seawater were collected and the co-precipitation technique was employed to concentrate cesium. A known amount of 134Cs tracer was added as yield determinant, followed by addition of copper(II) nitrate salt and a solution of potassium hexacyanoferrate(II) trihydrate, to precipitate the total cesium. The precipitate slurry was oven dried at 60 °C for 1–2 days, finely ground and counted using gamma-ray spectrometry. The activity of 137Cs was determined by measuring the peak area under the photopeak of the gamma-spectrum at 661 keV, which is equivalent to gamma-intensity corrected for detection efficiency, percentage of gamma-ray abundance of the radionuclide and recovery of 134Cs tracer. There were no significant differences of 137Cs activities both in surface and bottom water samples at 95% confidence level. The activity of 137Cs (for all samples) was found to be in the range of 1.47 to 3.36 Bq/m3 and 1.69 to 3.32 Bq/m3 for Sabah and Sarawak, respectively.

Organic Analyses of Highly Radioactive Solutions Requiring Pretreatment by 137Cs Removal

The beta-emitting radionuclide 137Cs is precipitated from the Savannah River Site (SRS) high-level waste by adding sodium tetraphenylborate (TPB). The concentrated and washed precipitate slurry containing CsTPB is transferred to Defense Waste Processing Facility (DWPF) Salt Processing Cell and hydrolyzed to yield an aqueous product (PHA) free of benzene. The PHA is highly radioactive (1E+11 dpm) and contains some water-soluble organic compounds that need to be analyzed for process control and process history. High performance liquid chromatography (HPLC) methods were developed to analyze these compounds with instruments contained in unshielded fume hoods. Removing 137Cs from PHA in a shielded cell prior to HPLC analyses is essential to minimize personnel radiation exposure. In this study ammonium molybdophosphate (Bio-Rad AMP-1) was used for removing 137Cs in PHA (pH 3.8). With a two-step application of AMP slurry, a decontamination factor of 1E+4 was achieved for Cs removal. Two separate HPLC methods were used to analyze four polar organic compounds. The recovery of all the organic compounds were above 85%.

Doped aluminas as hydrorefining catalyst supports

The influence of the addition of boron, calcium, magnesium, zirconium and zinc compounds on the physicochemical properties of alumina supports has been studied. Dopants were introduced during aluminium hydroxide precipitation. It was concluded that the effect of dopant incorporation depends on the type of additive and its concentration in the precipitated slurry. Aluminas doped with boron and magnesium showed the best physicochemical properties as hydrorefining catalyst supports. The obtained results are discussed on the basis of the open literature results.

Precipitation of Strontium Sulphate

AbstractPrecipitation of unseeded supersaturated aqueous solutions of SrSO4 and growth of SrSO4 crystals at the size of approximately 20 μm were studied. Within the examined range of supersaturations, i.e. Sa < 16, the nucleation in aqueous solutions is controlled by the heterogeneous nucleation mechanism. The induction period of precipitation depends on the rates of both the nucleation and growth of the formed nuclei. The growth of SrSO4 crystals in supersaturated solutions at S ⪅ 5.6 is of the 2nd order with respect to the concentration and at temperatures 25 ÷ 45°C the process is controlled by the surface reaction mechanism. The number of crystals in the precipitated slurry is decreasing rapidly as a result of the Ostwald maturing.