Na2CrO4-NaOH-H2O体系中Na2CrO4 蒸发结晶工艺研究

以90 ℃的Na2CrO4-NaOH-H2O体系相图为依据,采用蒸发盐析结晶的方法从体系中分离铬酸钠晶体,研究了搅拌强度、蒸发速度、结晶温度、晶种添加等因素对工艺过程的影响规律,得到最优工艺操作条件：搅拌强度为能使晶体离底悬浮所需的最小转速;每1 050 g原料的蒸发速率约为140 mL/h;结晶温度为90 ℃;并添加一定量的晶种。在以上操作条件下制备出的铬酸钠晶体粒度较大,尺寸均一。同时研究了不同氢氧化钠浓度下体系压力与沸点间的关系,为铬酸钠结晶过程的温度控制提供了基础数据。     

Phosphonates Meet Metal−Organic Frameworks: Towards CO2 Adsorption

Here we report a new highly microporous zirconium phosphonate material synthesized under solvothemal conditions. The specific Brunauer-Emmett-Teller (BET) surface area of the “unconventional metal−organic framework” (UMOF) is measured to be ∼900 m²/g, after following an appropriate activation protocol. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows that the material bears a free −OH functionality on the phosphonate linker that may interact with CO₂. CO₂ adsorption isotherms were collected and a measured heat of adsorption of 31 kJ/mol was obtained. In addition, adsorption isotherms of CO₂, N₂, and CH₄ at 298 K combined with Ideal Adsorbed Solution Theory (IAST) show that the material can be expected to display high selectivities for uptake of CO₂ versus N₂ or CH₄.     

CrO2磁粉的进展

ＣｒＯ２磁粉独特的电磁特性使它在高密度磁记录的开发中起到重要作用。在开发新粒子和矫顽力方面取得巨大进步；开关场分布和粒子尺寸范围方面扩展到以前不可能达到的程度。这类新的ＣｒＯ２磁粉呈现的一系列特性对其它记录材料来说是达不到的。     

CrO3—H2SO4镀铬液中CrO3含量的快速测定的研究

本文用PZ-A-5型液体比重天平测定了标准CrO_3-H_2SO_4,镀铬溶液的比重,得出CrO_3,含量(G)与镀液比重(d)的关系,并导出G-d关系的经验公式。同时分别用化学法和比重法进行了测定,结果两者的准确度相当,当比重法操作简便,速度快又不耗化学试剂。如在生产中广泛使用,将缩短分析周期,降低分析费用、提高分析效率。     

Effect of Br− on the Adsorption Rate of Palladium(II) Ions onto Condensed-Tannin Gel in Chloride Media

Abstract

In chloride media, chloropalladium(II) species are adsorbed onto tannin gel particles through an inner-sphere redox reaction mechanism containing the intermediate step, formation of a ligand-substituted Pd(II)-tannin complex. In this Pd(II) adsorption process, it was observed that the adsorption rate can be increased by introducing Br^?, a softer ligand than Cl^?, into the aqueous chloride solution. The formation of mixed-ligand palladium(II) complexes accelerates the rate of ligand-substitution reactions with the hydroxyl groups of tannin gel by the trans effect. The adsorption condition can be optimized by controlling the [Br_tot]/[Cl_tot] ratio, in which the predominant Pd(II) species are bromo-chloro palladium(II) complexes, the favorable species for the trans effect.     

NaOH-NaAlO_2-Na_2CrO4-H_2O四元水盐体系相平衡

通过对相关的ＮａＯＨ－Ｎａ２ＣｒＯ４－Ｈ２Ｏ三元水盐体系和ＮａＯＨ－ＮａＡｌＯ２－Ｎａ２ＣｒＯ４－Ｈ２Ｏ四元水盐体系在不同温度下相平衡的研究和比较,找出各物质之间相平衡特性的差异,以作为碱－铬－铝盐结晶分离的依据之一．     

锌铁水滑石类及改性吸附剂吸附K2CrO4研究

采用共沉淀法制备锌铁水滑石类(LDH),并使用十二烷基硫酸钠(SDS)对其进行改性。利用比表面积与孔径分析、扫描电镜与透射扫描电镜、X射线衍射、傅立叶变换红外光谱和多功能电子能谱等手段分析材料,研究材料的改性机制,通过动力学和热力学实验,验证材料的吸附效果。结果表明,锌铁LDH材料孔隙结构发达,层状结构清晰,改性后的材料层间距扩大,吸附容量进一步提高,是更为优秀的吸附材料。对于Cr(Ⅳ)的质量分数30 mg/g的溶液,改性后的锌铁LDH吸附剂优化投加量为0.2～0.4 g/L;溶液pH对除铬效果影响较大,pH为4时吸附效果最好;反应温度较高时除铬效果较好。改性后的锌铁LDH吸附剂对Cr(Ⅳ)的最大吸附容量可达到117 mg/g。     

Lamellar-interpenetrated Al−Si−Mg/Al2O3−ZrO2 composites prepared by freeze casting and pressureless infiltration

Using freeze casting and pressureless infiltration methods, we prepared lamellar Al−Si−Mg/Al₂O₃−ZrO₂ composites with initial ceramic loading of 30 vol% and different Al₂O₃:ZrO₂ weight ratios (Al₂O₃:ZrO₂=1:9, 3:7, 5:5, 7:3 and 9:1). The resultant composites inherited the lamellar structure of the Al₂O₃−ZrO₂ scaffolds, and the thickness of both metal and ceramic layers showed a trend of first increase and then decrease with increasing Al₂O₃ content. During pressureless infiltration, multiple chemical reactions took place between ZrO₂ and the Al−12Si−10Mg alloy and the main reaction products were (Al_1−m, Si_m)₃Zr, Al₂O₃ and ZrSi₂ phases. The degree of the reaction depended on the ZrO₂ content in the ceramic composition. In general, the compressive strength of the composites decreased with increasing Al₂O₃ content, but three-point bending strength showed a first decrease and then increase. When Al₂O₃:ZrO₂=1:9, the compressive and bending strength of the composites reached about 997±60 MPa and 426±10 MPa, respectively. A simple model was proposed to illustrate the fracture mode and toughening mechanism of the composites.     

Magnetic and structural properties of CoCrxFe2−xO4 spinels prepared by solution self combustion method

In this study we report the synthesis of nano-sized CoCrxFe_2−xO₄ (0<x<1) by solution self combustion method. Citric acid is used as fuel. Self combustion method provided excellent control over the composition. Upon increased Cr substitution, saturation magnetization, remnant magnetization, and coercivity were all found to decrease. The compositional influence Cr upon the magnetic properties and the structural parameters is found to be nearly linear. The crystallite size of the nanoparticles decreases linearly from 17 nm to 5 nm with increase in Cr content. The increase in Cr content decreases the magnetic ordering of material and converts into a soft magnetic material.     

Electrical conductivities of aqueous ZnSO4−H2SO4 solutions

Conductivities of aqueous ZnSO₄–H₂SO₄ solutions are reported for a wide range of ZnSO₄ and H₂SO₄ concentrations (ZnSO₄ concentrations of 01.2 M and H₂SO₄ concentrations of 02 M) at 25°C, 40°C and 60°C. The results indicate that the solution conductivity at a given ZnSO₄ concentration is controlled by the H₂SO₄ (H⁺) concentration. The variation of the specific conductivity with ZnSO₄ concentration is complex, and depends on the H₂SO₄ concentration. At H₂SO₄ concentrations lower than about 0.25 M, the addition of ZnSO₄ increases the solution conductivity, likely because the added Zn²⁺ and SO ₄ ^2– ions increase the total number of conducting ions. However, at H₂SO₄ concentrations higher than about 0.25 M, the solution conductivity decreases upon the addition of ZnSO₄. This behaviour is attributed to decreases in the amount of free water (through solvation effects) upon the addition of ZnSO₄, which in turn lowers the Grotthus-type conduction of the H⁺ ions. At H₂SO₄ concentrations of about 0.25 M, the addition of ZnSO₄ does not appreciably affect the solution conductivity, possibly because the effects of increasing concentrations of Zn²⁺ and SO ₄ ^2– ions are balanced by decreases in Grotthus conduction.Nomenclature a ion size parameter (m) - a ^* Bjerrum distance of closest approach (m) - C stoichiometric concentration (mol m^–3 or mol L^–1) - I ionic strength (mol L^–1) - k constant in Kohlrausch's law - M molar concentration (mol L^–1) - T absolute temperature (K) - z _i electrochemical valence of speciesi (equiv. mol^–1) - z (z _–|z _–|)^1/2=2 for ZnSO₄ - z ₊ valence of cation in salt (=+2 for Zn²⁺) - z _– valence of anion in salt (=–2 for SO ₄ ^2– ) Greek letters fraction of ZnSO₄ dissociated - specific conductivity (^–1 m^–1) - ^expt measured specific conductivity (^–1 m^–1) - equivalent conductivity (^–1 m² equiv.^–1) - equivalent conductivity at infinite dilution (^–1 m² equiv.^–1) - ⁰ equivalent conductivity calculated using Equation 2 (^–1 m² equiv.^–1) - _cale measured equivalent conductivity (^–1 m² equiv.^–1) - _expt equivalent conductivity of ioni at infinite dilution (^–1 m² equiv.^–1) - reciprocal of radius of ionic cloud (m^–1) - viscosity of solvent (Pa s) - dielectric constant - ± mean molar activity coefficient - density (g cm^–3)     

Equilibrium and Kinetic Studies on Lithium Adsorption from Geothermal Water by λ-MnO2

The adsorption equilibria of lithium from geothermal water were investigated by using both powdery and granulated forms of λ-MnO₂ derived from spinel-type lithium manganese dioxide. Optimum amounts of adsorbents were 1.0 g adsorbent/L-geothermal water for powdery λ-MnO₂ and 6.0 g adsorbent/L-geothermal water for granulated λ-MnO₂. The adsorbents exhibited the promising adsorption capacities and their adsorption equilibria of lithium agreed well with the Langmuir adsorption isotherm model. The kinetic data of lithium adsorption have been evaluated using pseudo-first-order, pseudo-second-order kinetics models, as well as Elovich kinetic model. In addition, intra-particle diffusion model has been used for evaluating the kinetic data to evaluate the adsorption mechanism. The adsorption kinetic process was attributed to the gradual adsorption stage where intra-particle diffusion was found as the rate-controlling step.     

Phosphate glasses containing monodisperse Fe3−δO4@SiO2 stellate nanoparticles obtained by melt-quenching process

The challenge to obtain stable glasses containing monodisperse magnetic nanoparticles with controlled size and shape is an exciting and almost unexplored field of research. Such new materials can be used in magneto-photonics or ultra-sensitive magnetic sensors. In this work, for the first time, colorless and transparent bulk glasses containing monodisperse 20 nm Fe_3−δO₄ nanoparticles were prepared by a melt-quenching route. Magnetic nanoparticles were synthesized by thermal decomposition and covered with a stellate mesoporous silica shell in order to protect them against dissolution during the glass melting process. The incorporation of nanoparticles into glasses and the ideal parameters obtained for this system are discussed. The new nanocomposite materials were characterized in order to investigate the structure, thermal, and magnetic properties. Such an original approach is a very promising way to incorporate a wide panel of nanoparticles, including metallic, bimetallic and metal oxide nanoparticles, into a variety of glasses providing new properties to these materials.     

Ni0.4Co x Cd0.6 − x Fe2O4 ferrites as prepared by autocombustion synthesis

Ni_0.4Co _x Cd_0.6?x Fe₂O₄ ferrites (x = 0.0, 0.2, 0.4, and 0.6) were prepared by autocombustion synthesis and characterized by XRD, SEM, and other physical methods. XRD reveals the formation of spinel structure without any impurity phase. With increasing x, the lattice parameter was found to decrease from 8.60 to 8.37 Å. The FTIR spectra show the presence of tetrahedral site (at 571.12 cm^?1) and octahedral site (at 407.07 cm^?1). SEM images indicated the formation of agglomerated grains with a size of about 4.3 μm. The resistivity of the ferrites was found to decrease from 24.53 to 10.02 × 10⁸ Ω cm while the drift mobility to increase from 2.30 to 4.41 × 10⁸ cm² V^?1 s^?1 with increasing x.     

Blue pigments based on CoxZn1−xAl2O4 spinels synthesized by the polymeric precursor method

The Co_xZn_1?xAl₂O₄ system (x = 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1) was synthesized by the polymeric precursor method and characterized by the techniques XRD, TG-DTA, IR, UV–vis and colorimetry. The XRD patterns displayed the characteristic peaks of the spinel structure and a good crystallinity. The DTA curves showed an exothermic peak corresponding to the enthalpy of the transition taking place at about 700 °C. The infrared spectra displayed vibrations at about 650, 550, 540, 520, 500, 490 cm^?1, which were ascribed to the spinel structure. The UV–vis spectra presented three bands at 550, 580 and 620 nm attributed to the Co²⁺ spin transitions in tetrahedral sites. The colorimetric data point out the formation of blue pigments, corresponding to highly negative values of b¹. The lightness, coordinate L¹, increases with the heat treatment temperature. These facts reveal that Co_xZn_1?xAl₂O₄ is a promising system that can be employed to obtain ceramic blue pigments.     

Adsorption and coalescence in mixed surfactant systems: Water−hydrocarbon interface

Major commercial uses of surfactants involve a mixture of these compounds. The properties of the monolayer formed at the water?hydrocarbon interface depend upon the interaction between the surfactant molecules. The presence of salt influences the interactions between the surfactants in the monolayer and in the micelle. In this work, these interactions in presence and in absence of a 1:1 salt were studied and the results were analyzed using the nonideal solution theory. An anionic, a cationic and a nonionic surfactant were used. The stability of emulsions is significantly affected by the interaction between the surfactants. To study this effect, coalescence of cyclohexane drops at a flat water?cyclohexane interface was studied in the mixed surfactant systems, and the results were compared with single surfactant systems. The effect of salt on coalescence time was studied. The results were analyzed using the film drainage and stochastic theories of coalescence. Seven film drainage models were used to predict the coalescence time, and the values predicted by these models were compared with the experimental data. The parameters of the stochastic model were analyzed based on the properties of the systems.     

Synthesis and Surface Modification of Mesoporous Silicate SBA‐15 for the Adsorption of Metal Ions

Abstract

In this study surface modified SBA‐15, coated with octadecyltrichlorosilane (C18), is considered as an alternative adsorbent for metal ions in water. The SBA‐C18 was loaded with Bis(2,4,4-trimethylpentyl) phosphinic acid (cyanex 272) as the metal ion extractant. The adsorption characteristics of phosphinic acid loaded SBA‐C18 were evaluated for Cu(II) and Zn(II) ions in aqueous solution. Adsorption tests indicated that a contact time of 1 hour was sufficient for adsorption equilibrium to occur. The pH_1/2 values of Zn(II) and Cu(II) onto SBA‐C18, were found to be similar to published data for levextrel ion exchange resins and around 1 pH unit lower than published solvent extraction data for cyanex 272 in xylene.     

Hydrothermal synthesis and characterization of nanorods “LixV2−δO4−δ·H2O”

Nanorods “Li_xV_2−δO_4−δ·H₂O” were hydrothermally synthesized with starting agents LiOH·H₂O and V₂O₅, and reducing agent hydrazine monohydrate (NH₂NH₂·H₂O) under alkaline condition at 160 °C. The samples were characterizated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The nanorods obtained have diameters from 80 to 100 nm with length up to several micrometers. Molecular coordination and assembly mechanism can be assumed to explain the formation of one-dimensional nanorods.     

Antiferromagnetism and heat capacity of NaCo2−xCuxO4 ceramics

Polycrystalline samples of NaCo_2−xCu_xO₄ (x=0, 0.01, 0.03 and 0.05) were synthesized in two different ways: 1) by a mechanochemically assisted solid-state reaction method (MASSR) and 2) by a citric acid complex method (CAC). In this work we examined the influence of these synthesis routes and small Cu concentrations on magnetic properties and the heat capacity of sintered samples. The magnetic susceptibility (χ) of all samples followed the Curie-Weiss law in the temperature range between 50 K and 300 K, while a negative Weiss constant (θ) implied an antiferromagnetic interaction. According to the magnetic susceptibility data, a peak around 30 K indicating the presence of Co₃O₄ as a secondary phase appeared for all MASSR samples and CAC samples with Cu content above 1%. The effective magnetic moment (μ_eff) of CAC samples was lower than the theoretical, spin only value obtained for the Co⁴⁺ ion in the low spin state indicating the presence of low spin Co³⁺(S =0). These values were also lower compared to the values obtained for MASSR samples. The highest μ_eff of 1.75 μ_B/atom Co was obtained for the undoped MASSR sample. The heat capacity of CAC samples at 2 K decreased with Cu concentration due to lowering of the electronic specific heat coefficient (γ). The highest γ of 63.9 mJ/molK² was obtained for the undoped CAC sample. This reduction in γ values was the result of the decrease of the density of state and/or mass enhancement factor.     

Optimization and statistical modeling of catalytic oxidation of 2-propanol over CuMnmCo2−mO4 nano spinels by unreplicated split design methodology

Optimization of 2-propanol oxidation over CuMn_mCo_2?mO₄ nanospinels was carried out by a split design method. 15-term model was proposed to fit the experimental data. The model revealed that both whole plot and subplot variables have significant effects on conversion of 2-propanol. The model predicted the interaction of subplot and whole plot variables as well as their importance. The maximum conversion of 2-propanol was observed over CuMn₂O₄ (x₁ = 0.33, x₂ = 0, x₃ = 0.67) at calcination and reaction temperatures of 800 °C (z₁ = 1) and 300 °C (z₂ = 1), respectively. The predicted response and the response obtained from experiment for optimum conditions were 93.36 and 96, respectively.