Tianlong Deng

Valence properties of tellurium in different chemical systems and its determination in refractory environmental samples using hydride generation – Atomic fluorescence spectroscopy

Using HG - AFS as a powerful tool to study valence transformations of Te, we found that, in presence of HCl and at high temperature, Te can form volatile species and be lost during sample digestion and pre-reduction steps. It was also noticed that the chemical valences of Te can be modified under different chemical and digestion conditions and even by samples themselves with certain matrices. KBr can reduce Te(VI) to Te(IV) in 3.0xa0M HCl at 100xa0°C, but when HNO3 was >5% (v/v) in solution, Br2 was formed and caused serious interference to Te measurements. HCl alone can also pre-reduce Te(VI) to Te(IV), only when its concentration was ≥6.0xa0M (100xa0°C for 15min). Among 10 studied chemical elements, only Cu(2+) caused severe interference. Thiourea is an effective masking agent only when Cu(2+) concentration is equal or lower than 10xa0mg/L. Chemical reagents, chemical composition of sample, as well as the modes of digestion can greatly affect Te valences, reagent blanks and analytical precisions. A protocol of 2-step-digestion followed by an elimination of HF is proposed to minimize reagent blank and increase the signal/noise ratios. It is important to perform a preliminary test to confirm whether a pre-reduction step is necessary; this is especially true for samples with complex matrices such as those with high sulfide content. The analytical detection limits of this method in a pure solution and a solid sample were 100xa0ng/L and 0.10xa0±xa00.02xa0μg/g, respectively.

Interference of Lithium in Measuring Magnesium by Complexometry: Discussions of the Mechanism

There is usually a large concentration of magnesium in the brine of salt lakes and as a consequence it is difficult to measure Mg2

Arsenic species analysis in freshwater using liquid chromatography combined to hydride generation atomic fluorescence spectrometry

A novel pretreatment system and method for arsenic species continuous analysis of arsenite, arsenate, monomethylarsenate (MMA) and dimethylarsonate (DMA) in freshwater using liquid chromatography combined to hydride generation atomic fluorescence spectrometry (LC-HG-AFS) was designed. Arsenic species of As(III), As(V), MMA and DMA in freshwater samples can be well separated, and the analytical time using the developed method is shortened twice compared to the conventional analytical procedure. Besides, the signal of As(V) can be increased by about 50% and the sensitivity to As(V) has been enhanced. The common coexisting ions in freshwater samples have no interferences with arsenic speciation analysis. A sensitive, low cost and interference-free procedure was developed and successfully applied to arsenic speciation in freshwater with the recoveries of four arsenic species within 89.2–106.2%. LC-HG-AFS has good prospects for speciation analysis of trace and ultra trace elements allowing for hydride generation.

Thermal Characteristics of Room Temperature Inorganic Phase Change System Containing Calcium Chloride

A novel inorganic calcium-based phase change material(PCM-Ca) consisted of 47.1%(mass fraction) water, 47.7% calcium chloride, 2% potassium nitrate, 2% potassium bromide and 1.2% strontium chloride with a solid-liquid phase change temperature of 21.4 °C was investigated systematically. Among the components of PCM-Ca, calcium chloride and water act as the latent heat storage materials, and potassium nitrate, potassium bromide and strontium chloride work as the modifier, thickener and nucleating agent, respectively. Thermochemical properties including melting point, latent heat, density and thermal conductivity of the PCM-Ca were measured experimentally. The experimental results indicate that the melting latent heat, thermal conductivity at the melting point and density at room temperature for the PCM-Ca are 203.3 kJ/kg, 1.3637 W·m–1·K–1 and 1.55×103 kg/m3, respectively. Moreover, a thirty-run-cycling test showed that the PCM-Ca has a good thermal characteristic with no phase segregation or supercooling, and the maximum deviations of latent heat and phase change temperature are only 0.2% and 1.6%, respectively.

Thermodynamic Study of Solid–Liquid Equilibrium in NaCl–NaBr–H2O System at 288.15 K

The solubility data, composition of the solid solution and refractive indices of the NaCl–NaBr–H2O system at 288.15 K were studied with the isothermal equilibrium dissolution method. The solubility diagram and refractive index diagram of this system were plotted at 288.15 K. The solubility diagram consists of two crystallization zones for solid solution Na(Cl,Br) · 2H2O and Na(Cl,Br), one invariant points cosaturated with two solid solution and two univariant solubility isothermal curves. On the basis of Pitzer and Harvie-Weare (HW) chemical models, the composition equations and solubility equilibrium constant equations of the solid solutions at 288.15 K were acquired using the solubility data, the composition of solid solutions, and binary Pitzer parameters. The solubilities calculated using the new method combining the equations are in good agreement with the experimental data.

Phase and Physicochemical Properties Diagrams of Quaternary System Li 2 B 4 O 7 + Na 2 B 4 O 7 + Mg 2 B 6 O 11 + H 2 O

The phase and physicochemical properties diagrams of the quaternary system (Li2B4O7 + Na2B4O7 + Mg2B6O11) at 288.15 K and 0.1 MPa were constructed using the solubilities, densities, and refractive indices measured. In the phase diagrams of the system there are one invariant point, three univariant isothermic dissolution curves, and three crystallization regions corresponding to Li2B4O7 · 3H2O, Na2B4O7 · 10H2O, and Mg2B6O11 · 15H2O, respectively. The solution density, refractive index of the quaternary system changes regularly with the increasing of Li2B4O7 concentration. The calculated values of density and refractive index using empirical equations of the quaternary system are in good agreement with the experimental values.

Solubilities, Densities, and Refractive Indices in the Quaternary System (Li 2 B 4 O 7 + Na 2 B 4 O 7 + Mg 2 B 6 O 11 + H 2 O) at 298.15 K

Solubilities, densities, and refractive indices in the quaternary system (Li2B4O7 + Na2B4O7 + Mg2B6O11 + H2O) at T = 298.15 K and p = 0.1 MPa were investigated experimentally with the method of isothermal dissolution equilibrium. According to the experimental data, the phase diagrams and the diagrams of densities and refractive indices versus lithium tetraborate composition in the solution were plotted, respectively. In the phase diagrams of the quaternary system at 298.15 K, there are one invariant point, three univariant isotherm dissolution curves, and three crystallization regions corresponding to Li2B4O7 · 3H2O, Na2B4O7 · 10H2O and Mg2B6O11 · 15H2O, respectively. The size of crystallization areas of salt is in the order Mg2B6O11 · 15H2O > Na2B4O7 · 10H2O > Li2B4O7 · 3H2O, which demonstrates Mg2B6O11 · 15H2O can be more easily separated from solution in this quaternary system. The solution density and refractive index of the quaternary system at 298.15 K change regularly with the increasing of Li2B4O7 concentration. The calculated values of density and refractive index using empirical equations of the quaternary system are in good agreement with the experimental values.

Synthesis and thermal energy storage properties of a calcium-based room temperature phase change material for energy storage

In order to obtain a low-cost, high latent heat and thermostable phase change material with a phase change temperature between 18 and 25xa0°C as a room temperature phase change material, a novel solid–liquid calcium-based composite named as PCM-Ca of 44.6% CaCl2, 6.9% Ca(NO3)2, 1.2% SrCl2 and 47.3% H2O with a phase change temperature of 21.8xa0°C and latent heat of 155.5xa0Jxa0g−1 was developed. The determination of thermal performances of PCM-Ca indicated that the thermal conductivities in liquid and solid state are of 0.6429 and 0.8256xa0Wxa0m−1xa0K−1, and the thermal conductivity in the phase change point is 1.2401xa0Wxa0m−1xa0K−1; the specific heat capacities at the temperature range of 5.5–26.5xa0°C and 31.5–38.5xa0°C were fitted as yu2009=u20090.0001x4xa0−xa00.0042x3u2009+u20090.0707x2xa0−xa00.4151xu2009+u20093.9526 (ru2009=u20090.9999) and yu2009=u2009−0.0001x4u2009+u20090.0208x3xa0−xa01.1155x2u2009+u200926.477xu2009+u2009231.57 (ru2009=u20090.9984), respectively. The stability analysis demonstrated that PCM-Ca is stable at the temperatures less than 130xa0°C, and no phase separation and the obvious supercooling phenomenon were presented after thirty times cycle use. This material PCM-Ca has a potential for energy storage application.

Apparent Molar Volumes of Aqueous Solutions of Magnesium Tetraborate from 283.15 to 363.15 K and 0.1 MPa

Densities for aqueous solutions of magnesium tetraborate MgB4O7(aq) at the molalities of (0.00556–0.03341) mol·kg−1 were measured with an Anton Paar Digital vibrating-tube densimeter at temperature intervals of 5xa0K from 283.15 to 363.15xa0K and 0.1xa0MPa. Apparent molar volumes were obtained based on the experimental density data, and the 3D diagrams of the apparent molar volume (Vϕ) of MgB4O7(aq) against temperature (T) and molality (m) were plotted. On the basis of the Vogel–Tamman–Fulcher equation, the coefficients of the correlation equation for densities of MgB4O7(aq) against temperature and molality were parameterized. According to the Pitzer ion-interaction model of the apparent molar volume, the temperature correlation equations of Pitzer single-salt parameters F(i,p,T)u2009=u2009a0u2009+u2009a1u2009×u2009Tu2009+u2009a2u2009×u2009T2u2009+u2009a3/Tu2009+u2009a4u2009×u2009ln(T)u2009+u2009a5u2009×u2009T3 (where T is temperature in Kelvin, ai are model parameters) for MgB4O7 were obtained for the first time.

Heat Capacity and Thermodynamic Property of Lithium Pentaborate Pentahydrate

In order to recover cesium tetraborate pentahydrate (Cs2O·2B2O3·5H2O) from the high concentration cesium-containing salt lake brines and geothermal water resources, the molar heat capacity of Cs2O·2B2O3·5H2O has been measured with a precision calorimeter at the temperature from 303 to 349u2009K. It was found that there is no phase transition and thermal anomalies. The molar heat capacity of cesium tetraborate pentahydrate is fitted as Cp,m (J·mol−1·K−1)u2009=u2009593.85705u2009+u200948.0694[Tu2009−u2009(Tmaxu2009+u2009Tmin)/2]/(Tmaxu2009−u2009Tmin)/2]u2009+u200924.86395[(Tu2009−u2009(Tmaxu2009+u2009Tmin)/2)/(Tmaxu2009−u2009Tmin)/2]2u2009+u20090.53077[(Tu2009−u2009(Tmaxu2009+u2009Tmin)/2)/(Tmaxu2009−u2009Tmin)/2]3, and the relevant thermodynamic functions of enthalpy, entropy, and Gibbs free energy of cesium tetraborate pentahydrate are also obtained at intervals of 2u2009K from 303 to 349u2009K.