Formation of CaSO4(aq) and CaSeO4(aq) studied as a function of ionic strength and temperature by CE

Ca²⁺ complexation by both sulfate and selenate ligands was studied by CE. The species were observed to give a unique retention peak as a result of a fast equilibrium between the free ions and the complexes. The change in the corresponding retention time was interpreted with respect to the equilibrium constant of the complexation reaction. The results confirmed the formation of CaSO₄(aq) and CaSeO₄(aq) under our experimental conditions. The formation data were derived from the series of measurements carried out at about 15, 25, 35, 45 and 55°C in 0.1 mol/L NaNO₃ ionic strength solutions, and in 0.5 and 1.0 mol/L NaNO₃ ionic strength solutions at 25°C. Using a constant enthalpy of reaction enabled to fit all the experimental data in a 0.1 mol/L medium, leading to the thermodynamic parameters: Δ_rG^0.1M(25°C)=?(7.59±0.23) kJ/mol, Δ_rH^{0.1 M}=5.57±0.80 kJ/mol, and Δ_rS^{0.1 M}(25°C)=44.0±3.0 J mol^?1 K^?1 for CaSO₄(aq) and Δ_rG^{0.1 M}(25°C)=?(6.66±0.23) kJ/mol, Δ_rH^{0.1 M}=6.45±0.73 kJ/mol, and Δ_rS^{0.1 M}(25°C)=44.0±3.0 J mol^?1 K^?1 for CaSeO₄(aq). Both formation reactions were found to be endothermic and entropy driven. CaSO₄(aq) appears to be more stable than CaSeO₄(aq) by 0.93 kJ/mol under these experimental conditions, which correlates with the difference of acidity of the anions as expected for interactions between hard acids and hard bases according to the hard and soft acids and bases theory. The effect of the ionic medium on the formation constants was successfully treated using the Specific ion Interaction Theory, leading to significantly different binary coefficients mol/kg^?1 and mol/kg^?1     

A structural study of the perovskite series Ca1−xNaxTi1−xTaxO3

Compounds in the solid solution series Ca_1−xNa_xTi_1−xTa_xO₃ were synthesized at 1300 °C, followed by annealing at 850 °C or 800 °C with quenching and/or slow cooling to room temperature. Rietveld refinement of their powder X-ray diffraction patterns show that all compounds are single-phase ternary perovskites which adopt the space group Pbnm (a≈b≈√2a_p; c≈2a_p; Z=4) at ambient conditions. The unit cell parameters and cell volumes of the compounds increase regularly with increasing values of x. The coordination of the A-site cations changes throughout the series from eight for CaTiO₃ to nine for NaTaO₃. Compounds with 0?x ?0.4 have A-site cations in eight fold coordination, whereas the coordination of those with 0.4<x<0.9 is ambiguous. Analysis of the crystal chemistry of the compounds shows that the change in coordination at x=0.4 is related to the departure of the B-site cations from the second coordination sphere of the A-site cations, as in compounds with x>0.4 the A-^IIO distances become less than the A-B intercation distances. Contemporaneous with these coordination changes, the tilt angles of the BO₆ polyhedra decrease with increasing values of x. This solid solution series is unusual in that these structural and coordination changes occur regardless that Goldschmidt tolerance factors remain essentially constant at approximately 0.89, and observed tolerance factors, assuming eight fold coordination of the A-site cations, range only from 0.91 to 0.93 (0?x?0.8).     

Ion-selective electrodes in potentiometric titrations; a new method for processing and evaluating titration data

A new method to convert the potential of an ion-selective electrode to concentration or activity in potentiometric titration is proposed. The advantage of this method is that the electrode standard potential and the slope of the calibration curve do not have to be known. Instead two activities on the titration curve have to be estimated e.g. the starting activity before the titration begins and the activity at the end of the titration in the presence of large excess of titrant. This new method is beneficial when the analyte is in a complexed matrix or in a harsh environment which affects the properties of the electrode and the traditional calibration procedure with standard solutions cannot be used. The new method was implemented both in a method of linearization based on the Grans's plot and in determination of the stability constant of a complex and the concentration of the complexing ligand in the sample. The new method gave accurate results when using titrations data from experiments with samples of known composition and with real industrial harsh black liquor sample. A complexometric titration model was also developed.     

大血藤药材及不同提取物FTIR的比对分析

采用红外光谱法(FTIR)、二阶导数红外光谱法和二维相关光谱分析技术(Two-Dimensional Correlation Spectroscopy) 对江西和安徽大血藤药材、水提物、蒽醌类提取物和残渣进行了快速无损比对分析研究,从中发现两产地大血藤药材的谱图中均出现1 400～1 620 cm-1和1 000～1 200 cm-1两个强峰带,说明药材含有大量的药效成分蒽醌类和糖类物质;蒽醌提取物的谱图中也有上述2个谱带,但1 400～1 620 cm-1谱带明显强于1 000～1 200 cm-1谱峰,说明该提取工艺适宜提取蒽醌类物质;而水提物中2个谱峰带则是后者明显强于前者,证实该提取工艺适宜提取糖类物质;另外通过红外谱图和二阶导数红外谱图的对比发现在药材残渣中含有大量的草酸钙晶体。证明红外光谱技术不仅能对原药材及提取物的药效基团进行分析和指认,还能区分不同产地药材的提取物含量的高低,成功地建立了大血藤及其不同提取物药效成分比对分析的新方法。     

悬浮液进样-火焰原子吸收光谱法直接测定高乐高中的钙和铁

将悬浮液进样技术应用于火焰原子吸收光谱法,样品不经消解直接测定了高乐高中的钙和铁含量.将高乐高悬浮于琼脂胶体中制成悬浮液,直接喷入空气-乙炔火焰,用标准加入法测定,平均加标回收率钙为96.3％,相对标准偏差(RSD)≤3.4％;铁为95.2％,RSD≤6.3％,方法简便,快速,准确.     

Fixation of bioactive calcium alkali phosphate on Ti6Al4V implant material with femtosecond laser pulses

Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790 nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4 J/cm²) the 30 fs laser pulses penetrate the partly transparent ceramic layer of 20-40 μm thickness. The remaining laser fluence at the ceramic-metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15 J/cm²) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4 J/cm², only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants.     

Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes

The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl₂) and sodium carbonate (Na₂CO₃) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals.     

Imaging of stroke: a comparison between X-ray fluorescence and magnetic resonance imaging methods

A dual imaging approach, combining magnetic resonance imaging to localize lesions and synchrotron rapid scanning X-ray fluorescence (XRF) mapping to localize and quantify calcium, iron and zinc was used to examine one case of recent stroke with hemorrhage and two cases of ischemia 3 and 7 years before death with the latter showing superficial necrosis. In hemorrhagic lesions, more Fe is found accompanied with less Zn. In chronic ischemic lesions, Fe, Zn and Ca are lower indicating that these elements are removed as the normal tissue dies and scar tissue forms. Both susceptibility and T2* maps were calculated to visualize iron in hemorrhages and validated by XRF Ca and Fe maps. The former was superior for imaging iron in hemorrhagic transformation and necrosis but did not capture ischemic lesions. In contrast, T2* could not differentiate Ca from Fe in necrotic tissue but did capture ischemic lesions, complementing the susceptibility mapping. The spatial localization, accurate quantitative data and elemental differentiation shown here could also be valuable for imaging other brain tissue damage with abnormal Ca and Fe content.     

火焰原子吸收光谱法测定粤东第一温泉中钾、钠、钙、锰和锌

用火焰原子吸收光谱法测定粤东第一温泉源头水中的钾、钠、钙、锰和锌。测定结果为 :钾 2 .5 5 4mg/ L、钠 2 4 2 .0 mg/ L、钙 74 .4 0 mg/ L、锰 1 .0 78mg/ L、锌 0 .96 0 0 mg/ L,RSD1 .2 1 %— 2 .5 6 %,回收率 98.3%— 1 0 1 .1 %。     

Effects of Ca and Na acetates on nitrogen transformation during sewage sludge pyrolysis

The study reports the effects of Ca and Na acetates on the transformation of nitrogen species during sewage sludge pyrolysis. Sludge samples, with or without acetates, were pyrolysed in a fix-bed reactor at 150–550 °C, and the nitrogen species in the pyrolysis products (char, tar, and gas) were characterised and quantified. Ca and Na acetates distinctly affect nitrogen transformation during sludge pyrolysis, which is ascribable to their different catalytic activities for the decomposition of nitrogen species in sludge. The addition of Ca acetate is found to increase nitrogen retention in char and reduce the formation of nitrogen species in tar, which is mainly due to the suppressed decomposition of protein-N as well as the promoted formation of stable nitrogen species in char. On the other hand, the addition of Na acetate enhances the decomposition of nitrogen species in sludge, such as protein- and inorganic-N. The levels of both Ca and Na acetates are significantly reduced in the nitrogen-containing gas emissions because acetone is produced when acetates are heated, and acetone readily reacts with NH₃ to produce binary clusters or amines. Our results show that acetate addition is an important strategy for the reduction of NH₃ emission during sludge pyrolysis.