四元体系Rb+, Cs+, Mg2+ // SO42- - H2O 298.2 K相平衡研究

采用等温溶解平衡法研究了298.2 K下四元体系Rb⁺, Cs⁺, Mg²⁺ // SO₄^2- - H₂O的相平衡关系,测定了该体系的溶解度、密度以及折射率,并绘制了相应的稳定相图、水图、密度-组成图和折射率-组成图。研究表明：298.2 K下,该四元体系为复杂四元体系,有复盐Cs₂SO₄·MgSO₄·6H₂O和Rb₂SO₄·MgSO₄·6H₂O以及固溶体[(Rb, Cs）₂SO₄]生成。其稳定相图由4个四元共饱点、9条单变量曲线以及6个结晶区组成。四元共饱点中E₁、E₂、E₃为相称共饱点,E₄为不相称共饱点。6个结晶相区分别对应3种单盐Rb₂SO₄、MgSO₄·7H₂O、Cs₂SO₄,2种复盐Cs₂SO₄·MgSO₄·6H₂O、Rb₂SO₄·MgSO₄·6H₂O和1种固溶体[(Rb,Cs）₂SO₄]。其中,复盐Rb₂SO₄·MgSO₄·6H₂O结晶区最大,表明其在该体系中最易结晶析出;Cs₂SO₄结晶区最小。平衡液相的密度和折射率随着溶液中Cs₂SO₄含量变化呈规律性变化。该体系稳定相图将为硫酸镁亚型盐湖卤水中的铷、铯等资源开发利用提供理论依据。     

Proton glassy state of Rb1-x(NH4)xH2AsO4

We have presented the first experimental data of the temperature dependence of ε'_c and ε'_c for Rb_1-x (NH₄)_x H₂AsO₄. The results are demonstrated by the presence of a glassy state in Rb_1-x (NH₄)_x H₂AsO₄ for x = 0.31.     

Rb_2O掺杂对MnCe/ZrO_2催化燃烧碳烟的性能影响

采用柠檬酸溶胶-凝胶法制备掺杂不同Rb2O含量的MnCe/ZrO2复合氧化物催化剂,采用热重法考察其催化燃烧碳烟的活性,并借助XRD和H2-TPR手段探讨掺杂不同Rb2O含量对MnCe/ZrO2催化燃烧特性的影响。结果表明,适量Rb2O可以使催化剂与碳烟在高温下接触更为紧密,吸附空气中CO2,形成碳酸盐物质,提高催化剂的氧含量,并作为活性氧传输中心,提升MnCe/ZrO2催化燃烧性能。与未掺杂MnCe/ZrO2催化剂相比,完全燃烧温度下降31℃,碳烟在394℃内完全氧化。     

Effect of Sc substitution and pressure on phase transition in Rb2KGaF6 elpasolite

Solid solutions Rb₂KGa_xSc_1-xF₆ (x = 1.0; 0.95; 0.9; 0.8; 0.6) were studied by X-ray, neutron, calorimetric and DTA under hydrostatic pressure methods. Both heat capacity and entropy are strongly influenced by x concentration. According to (T vs. x) phase diagram suggested the phase transition temperatures of compounds with x from 1.0 to 0.8 belong to the same phase boundary.     

Ultrasonic investigations of incommensurate Rb2Zncl4

Elastic properties of Rb₂Zncl₄ were investigated by measuring the velocity and attenuation of both, transversal and longitudinal ultrasonic waves propagating along the crystallographic axes. At the lock-in phase transition temperature only v₄₄ shows a remarkable anomaly. This anomaly has been found to be asymmetric with respect to the interchange of oscillation and propagation direction of the transverse ultrasonic wave. The anomaly of v₄₄ at T_c is proportional to the contents of commensurate regions in the IC structure. From the temperature dependence of ultrasonic velocities at the phase transition from paraelectric to IC phase the critical behaviour of the order parameter should correspond rather to the (n = 2)-Heisenberg-model than to the Ising model.     

Acoustic behavior of the incommensurate state of Rb2Zncl4 by brillouin scattering?

Temperature dependence of elastic stiffness constant C₁₁ was studied from 60 to -100°C by Brillouin scattering and refractive index measurements. It is found that C₁₁ decreases with decreasing temperature over the incommensurate phase and its temperature gradient becomes more or less flat at several degrees above the incommensurate-commensurate transition point T_c, where the dis-commensurate structure appears. This unusual temperature dependence of C₁₁ seems to be attributable to the incommensurately modulated structure of Rb₂ZnC1₄.     

Monte carlo study of a model for the mixed crystal Rb1-x, (NH4)xH22PO4

A microscopic model for the mixed crystal Rb_1-x(NH₄)_xH₂PO₄ is introduced which takes into account the acid protons as well as the NH₄ groups. Using Monte Carlo simulation, the topology of the experimentally determined phase diagram is reproduced rather well, including the onset of freezing into a glasslike state.     

异山梨醇与碳酸二甲酯两步法合成聚碳酸酯的工艺

研究了以碳酸铷（Rb₂CO₃）和乙酰丙酮锂（LiAcac）为催化剂,异山梨醇（IS）和碳酸二甲酯（DMC）为原料合成聚碳酸酯（PC）的工艺过程。优化了酯交换反应催化剂用量、原料配比、缩聚反应催化剂用量、缩聚反应温度以及缩聚反应停留时间,并对酯交换产物和聚碳酸酯产品进行了红外光谱、核磁氢谱、核磁碳谱和热重分析,得到较优工艺条件为：Rb₂CO₃用量1×10^-3mol/mol_IS、原料配比n(DMC)/n(IS)=14、LiAcac用量2×10^-3mol/mol_IS、缩聚温度225℃、缩聚停留时间4h,所得的PC产品特性黏数可达36.55mL/g,数均分子量（M_n）为30659,重均分子量（M_w）为42551,M_w/M_n为1.39,色差为6.92,玻璃化转变温度（T_g）为155.6℃。     

Room-Temperature Strength and Fracture of ZrO2-Y2O3 Single Crystals

Strength and fracture toughness results are presented for ZrO₂ single crystals stabilized with Y₂O₃. The crystals (2 cm in diameter by 5 cm long) were prepared by skull melting. The partially stabilized compositions with 4 to 6 wt% Y₂O₃ showed a dramatic improvement in mechanical properties over the fully stabilized samples containing 20 wt% Y₂O₃, i.e. a strength exceeding 1000 MPa and a fracture toughness of 8 Mpa,.m ^1/2 were achieved compared to 200 MPa and 2 Mpa.m^1/2, respectively, for fully stabilized ZrO₂ single crystals.     

Phase Equilibria in the KNbO3-SrNb2O6 and KNbO3-BaNb2O6 Systems

Phase equilibrium studies of the KnbO₂-SrNb₂O₆ system revealed that tetragonal tungsten bronze-type solid solutions extend from 59 to 87 mol% SrNb₂O₆. The solid solution field has a relatively flat liquidus peaking at 1486°C and 78 mol% SrNb₂O₆. In contrast, solid solutions are limited to 67 to 75 mol% BaNb₂O₆ in the KnbO₃-BaNb₂O₆ system, with peritectic decomposition occurring at the 75 mol% solid-solution limit. The diagrams establish conditions for perfecting the growth and stoichiometry of potassium-strontium and potassium-barium niobate electrooptic crystals. Dielectric and crystallographic properties of crystals grown in these systems are presented, and the phase relations are compared to previous work in the sodium-barium niobate system.     

Piezoelectric Properties of Sn2P2S6 Ceramics

Piezoelectric ceramics Sn₂P₂S₆ was prepared and investigated as potential candidate for hydrophone applications. Their structural and morphological properties were checked by X-ray diffraction and scanning electron microscopy. The set of electromechanical properties was determined using resonance technique. The hydrostatic charge piezoelectric coefficient d_h and hydrostatic voltage coefficient g_h were measured at the frequency of 100 Hz in an acoustic coupler (pistonphone). It was found that g_h and d_h*g_h coefficients, which are the most important figures of merit for piezoelectrics operating in the hydrostatic regime, in the ceramics studied take values comparable to that of the composites on the basis of Sn₂P₂S₆ and the PZT piezoelectric ceramis. The disadvantage of Sn₂P₂S₆ ceramics is rather high level of the low frequency dielectric losses caused by the hopping conductivity along the grain boundaries.

Communicated by Prof. Jan Patzelt     

Pyroelectric properties of the ferroelectric single crystal series (KxNa1-x)0.4 (SryBa1-y)0.8 Nb2O6

A ferroelectric single crystal series (K_xNa_1-x)0.4(Sr_y Ba_1-y)_0.8 Nb₂O₆(0.50≤x≤0.75, 0.30≤y≤0.90), with tungsten-bronze type structure in by the Czochralski technique. The changes of the dielectric behavior and the pyroelectric coefficient with different chemical compositions have been measured. The results of measurement show that some of the crystals (such as x=0.50, y=0.75) have good pyroelectric figures of merit FM_RN=10.2×10^-13 C·m/J and FM_RN=1.6×10^-11 C·m/J. These crystals should be useful as pyroelectric detector materials.     

Dielectric and piezoelectric properties of Pb1-xBaxNb2O6 ferroelectric tungsten bronze crystals

Tungsten bronze single crystals in the Pb_1-xBa_xNb₂O₆ system were grown from a melt using the Czochralski technique. The dielectric, piezoelectric and pyroelectric properties were determined. The dielectric constant Ka and piezoelectric coefficient dI5 showed a strong enhancement upon approaching the tetragonal:orthorhombic morphotropic phase boundary as predicted by thermodynamic phenomenology. It is clear that crystals with a composition in the tetragonal phase field near this boundary will be of major interest for various piezoelectric device applications.     

Bi2MoO6@CQDs/TiO2纳米管阵列的制备与光电催化性能

为提高TiO₂的可见光光电催化活性,本文用Bi₂MoO₆和碳量子点(CQDs)对TiO₂纳米管阵列(TNA)进行了改性。以CQDs、Bi(NO₃)₃·5H₂O和Na₂MoO₄为原料,通过简单的溶剂热法,在TNA中沉积了CQDs和Bi₂MoO₆,成功制备了新型Bi₂MoO₆@CQDs/TNA。扫描电镜(SEM)和元素mapping分析结果表明,CQDs和Bi₂MoO₆成功涂覆在TNA管壁上。通过在可见光下降解甲基橙(MO)溶液,评价了所制备的光催化剂的光电催化性能。结果显示,经3 h的光电催化降解,Bi₂MoO₆@CQDs/TNA对MO的去除率比Bi₂MoO₆/TNA高32%。CQDs优异的上转换光致发光(UCPL)性能促进了TiO₂在可见光下被激发产生光生载流子,同时Bi₂MoO₆与TiO₂的耦合抑制了光生载流子的复合,从而提高了Bi₂MoO₆@CQDs/TNA的光电催化活性。     

Na2O-Al2O3-SiO2-P2O5玻璃的结构和析晶性能研究

采用熔融-淬冷法制备了不同(Al₂O₃+P₂O₅)含量的碱铝硅酸盐玻璃,通过拉曼光谱、X射线衍射光谱、扫描电镜研究了其结构特征和析晶性能。发现随着(Al₂O₃+P₂O₅)含量减少,玻璃中Na₂O含量增加,玻璃化转变温度从685 ℃降低到622 ℃,当减少至摩尔分数为22%时,出现析晶峰且起始析晶温度降低。拉曼光谱表明Q⁴_P对应的拉曼峰强度变低且逐渐向低波数方向移动,说明Na₂O作为网络修饰体使硅酸盐玻璃结构逐步解聚,玻璃的析晶能力逐渐增强。结果表明:当(Al₂O₃+P₂O₅)摩尔分数为22%时热处理后的样品存在晶型转变,700 ℃热处理时以NaAlSiO₄霞石晶体为主,900 ℃时转变为以Na_6.8Al_6.3Si_9.7O₃₂霞石晶体为主。当(Al₂O₃+P₂O₅)的摩尔分数为21%和20%时,热处理后的样品能稳定析出Na₃PO₄和Na_6.8Al_6.3Si_9.7O₃₂晶体。热处理后的样品析出了耐酸侵蚀性较差的富磷相和Na₃PO₄晶体,导致化学稳定性变差。     

Tungsten Bronze Field and Melt Growth of Crystals in the Na2O-BaO-Nb2O5 System

The extents of the liquidus and solidus fields were determined for tungsten bronze-type solid solutions in the Na₂O-BaO-Nb₂O₅ system by DTA and melt crystal growth experiments. Bronze-type solid solutions exist to 7.1Na₂O-34.9BaO-58Nb₂O₅ in the Nb₂O₅-rich region and from 12Na₂O-38BaO-50Nb₂O₅ to 4.6Na₂O-45.4BaO-50Nb₂O₅ along the NaNbO₂-BaNb₂O₆ join, which includes NaBa₂Nb₅O₁₅=10Na₂O-40BaO-50Nb₂O₆. There is little, if any, solid solubility of compositions with a deficiency of Nb₂O₅. Curie temperatures decline rapidly and dielectric constant peaks broaden with Nb₂O₅ substitution because the Nb:O ratio becomes greater than the octahedral 1:3 ratio. Useful ferroelectrics exist along the NaNbO₃-BaNb₂O₆ join where the Nb:O ratio is 1:3. Large striae-free crystals, with less optical scattering than Czochralski-grown crystals, were grown from unseeded Na₂O-rich melts (e.g. 15Na₂O-37.5BaO-47.5Nb₂O₅) cooled from 1520° to 1300°C at 2°C/h. Annealing effects on these crystals whose compositions lie on the NaNbO₃-BaNb₂O₆ join are discussed.     

Formation Mechanism and Synthesis of Apatite-Type Structure Ba2+xLa8−x(SiO4)6O2−δ

The formation process of Ba₂La₈(SiO₄)₆O₂ was clarified using thermogravimetry–differential thermal analysis (TG-DTA) and a high-temperature powder X-ray diffraction (HT-XRD) method. Phase changes identified from the HT-XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG-DTA curves. Raw material with the composition Ba₂La₈(SiO₄)₆O₂ was completely reacted at 1400°C and produced only an apatite-type compound without a secondary phase. Moreover, the synthesis of Ba_{2+ x} La_{8− x} (SiO₄)₆O_2−δ crystals with x = 0–2 was attempted using a solid-state reaction.     

Transformational Superplasticity of Bi2WO6 and Bi2MoO6

Transformational Superplasticity was studied in the compounds Bi₂WO₆ and Bi₂MoO₆. The magnitudes of transitional strain are related to the ( T_t/T_mP ), s of the phase transitions and are proportional to the externally applied stresses. Strain-rate sensitivities were similar, 0.85 and 0.86; however, the Bi₂WO₆ exhibited a strain-axis intercept and the Bi₂MoO₆ a stress-axis intercept. The grain-size effect present in the Bi₂WO₆ supports an accommodated grain-boundary sliding mechanism for the superplastic deformation process.     

Precipitation in LiF-MgF2 Solid Solutions

Precipitation was studied for LiF single crystals containing up to 4 wt% MgF₂. Replica electron microscopy observations, combined with hardness and lattice parameter measurements, showed that, irrespective of the level of MgF₂, precipitation consistently occurs during quenching. Rapidly cooled crystals with lower MgF₂ concentrations (<1 wt%) develop large cruciform particles of a metastable phase with approximate composition MgF₂-6LiF. Lower cooling rates or higher MgF₂ contents caused transformation of these metastable particles to rod-shaped stable MgF₂ phase. This occurs via nucleation on the metastable crosses. The large misfit between the LiF matrix and the MgF₂ phase causes development of an incoherent interface and an associated disturbance of a propagating crack was observed near each MgF₂ particle.     

二氧化硅负载磷钨钼酸催化合成环己酮1,2-丙二醇缩酮

以二氧化硅负载磷钨钼酸（H_3PW_6Mo_6O_（40）/SiO_2）为催化剂,环己酮和1,2-丙二醇为原料合成环己酮1,2-丙二醇缩酮。探讨了H_3PW_6Mo_6O_（40）/SiO_2对缩酮反应的催化活性,研究了酮醇物质的量比、催化剂用量、反应时间等因素对产物收率的影响。实验结果表明：H_3PW_6Mo_6O_（40）/SiO_2是合成环己酮1,2-丙二醇缩酮的良好催化剂。在固定环己酮用量为0.20mol的情况下,n（环己酮）：n（1,2-丙二醇）=1.0：1.3,催化剂用量占反应物料总质量的0.8%,带水剂环己烷的用量为12mL,反应时间45min的条件下,产品收率可达83.95%。