Structure and properties of nanostructured Fe(AlCr)2O4–Cr–(AlCr)2O3–Fe composite coating prepared by plasma spraying

In-situ nanostructured Fe(AlCr)₂O₄-based composite coating (FACr_52.5 coating) was prepared by reactive plasma spraying with micro-sized Al–Fe₂O₃–Cr₂O₃ powders. The microstructure, toughness and Vickers hardness, and adhesive strength of the coating were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and mechanical tests. The results indicated that the interlamellar spacing of the FACr_52.5 coating is only 1 μm. The coating exhibited nanostructured microstructure. The in-situ Cr (20 nm) and Fe (50–200 nm) particles were uniformly distributed in an Fe(AlCr)₂O₄ matrix, while the grain size of the Fe(AlCr)₂O₄ matrix is about 60 nm. The FACr_52.5 composite nano-coating exhibited much higher hardness, better wear resistance, stronger adhesive strength and toughness as compared to those of the composite nano-coating sprayed with Fe₂O₃–Al powders. Excellent mechanical properties of the FACr_52.5 coating were attributed to the uniform distribution of the in-situ nano-sized Cr particles in the coating matrix.     

Phase evolution and microstructural studies in CaZrTi2O7 (zirconolite)–Sm2Ti2O7 (pyrochlore) system

From the characterization of a series compositions with general stoichiometry as Ca_1−xZr_1−xSm_2xTi₂O₇ (0.00 ≤ x ≤ 1.00), the phase evolution between zirconolite (CaZrTi₂O₇) and pyrochlore type Sm₂Ti₂O₇ has been elucidated. All the compositions were prepared by high temperature solid state reaction and characterized by powder X-ray diffraction (XRD) and electron probe for microanalyses (EPMA). Three major phase fields, namely two layer (2-M) or four layer (4-M) monoclinic zirconolite and cubic pyrochlore structure types were observed in this system. In addition, a feeble amount of perovskite type phase is found to coexist with zirconolite phase. 4-M zirconolite phase is observed as single phase field at the composition with x = 0.30 and 0.35, while cubic pyrochlore phase is observed as single phase at the compositions with x ≥ 0.60. Further, the composition and microstructure of coexisting phases are verified by back scattered electron image and EPMA studies.     

25℃下K2SO4–(NH4)2SO4–CO(NH2)2–H2O四元体系的相平衡

测定了25℃下K2SO4–CO(NH2)2–H2O及(NH4)2SO4–CO(NH2)2–H2O 两个三元体系相平衡的数据，并依据Pitzer电解质溶液理论对实验测定值进行了关联，关联结果与实验测定值相吻合. 通过测定25℃下K2SO4–(NH4)2SO4–CO(NH2)2–H2O四元体系的相平衡数据可知尿素不能与硫酸钾或硫酸铵形成复盐，因此该四元体系的相平衡数据可近似由其所含三元体系的相互作用参数推算得出.     

Microstructure and electrical properties of ZnO–ZrO2–Bi2O3–M3O4 (MCo,Mn) varistors

Phase evolution, microstructure and the electrical properties of ZrO₂-added pyrochlore-free ZnO–Bi₂O₃–M₃O₄ (MCo, Mn) varistors have been studied as functions of ZrO₂ content up to 10 vol% and the sintering temperature between 900 and 1300 °C. Zirconia remained as intergranular second phase particles up to 1100 °C, which retarded densification and inhibited the grain growth of ZnO. At higher temperatures, on the contrary, ZrO₂ particles began to be entrapped in ZnO grains and irreversibly transform from monoclinic to stable cubic phase dissolving transition metal ions. The grain size of ZnO decreased with increasing ZrO₂ content, and increased with the increase of the sintering temperature. Accordingly breakdown voltage changed with both ZrO₂ content and the sintering temperature as was expected. Nonlinear coefficient (α) depended primarily on the sintering temperature: it increased to >40 up to 1000 °C, and significantly decreased to <30 at higher temperatures probably due to the volatilization of Bi₂O₃. While the specimens sintered at 1200 °C or above had relatively high leakage current (I_L) and large clamping ratio (C_R), those with ZrO₂ content of 0.5–5.0 vol% and sintered below 1200 °C revealed low I_L of ⩽20 μA/cm² and C_R well below 2.0. In spite that varistor characteristics of ZrO₂-added system could not match those of commercial ZnO varistors, its low temperature sinterability and ease of breakdown voltage control via ZrO₂ content without a serious loss of its figures of merit are worth noticing, particularly for multi-layered chip varistor (MLV) application.     

Fabrication and microstructure of Al2O3–ZrO2(3Y)–SiC nanocomposites

Al₂O₃–ZrO₂(3Y)–SiC composite powder was prepared by the heterogeneous precipitation method. Calcinating temperature of the powder was important to obtain dense sintered body. The nanocomposites were got by hot-pressing, and addition of ZrO₂ did not raise the sintering temperature. Some Al₂O₃ grain shape was elongated, and Al₂O₃ grain size was about μm. Nano SiC particles were observed uniformly distributing throughout the composites, and most of them were located within the matrix grains. Because SiC particles located within ZrO₂ grains influenced the phase transformation of ZrO₂, the sintering of nanocomposites, which controlled grain size and transformable ZrO₂ amount, become important to get high performance. The strength of 80 wt% Al₂O₃–15 wt% ZrO₂–5 wt% SiC nanocomposites was 555 MPa, and toughness was 3·8 MPa m^1/2, which were higher than those of monolithic Al₂O₃ ceramics. ©     

Dielectric behaviors of Nb2O5–Co2O3 doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics

Nb₂O₅ and Nb–Co doped 0.85BaTiO₃–0.15Bi(Mg_1/2Ti_1/2)O₃ (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb₂O₅/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb₂O₅ was found to possess a moderate dielectric constant (? ～ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from ?55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.     

Microwave dielectric characteristics of 0.75(Al1/2Ta1/2)O2–0.25(Ti1−xSnx)O2 ceramics

The microwave dielectric characteristics of 0.75(Al_1/2Ta_1/2)O₂–0.25(Ti_1−xSn_x)O₂ ceramics were investigated. The microwave dielectric properties of 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂ sintered at 1450 °C exhibited a dielectric constant (ϵ_r) of 31.2, a Q·f₀ of 54,590 GHz, and the temperature coefficient of resonant frequency (τ_f) of +12.8 ppm/°C. To control of the τ_f and enhance the Q·f₀ for 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂, Sn⁴⁺ was substituted for Ti⁴⁺. With an increase of Sn content from 5 to 50 mol%, the ε_r slightly decreased, the Q·f₀ increased and the τ_f shifted from positive to negative value. The τ_f within ±10 ppm/°C of zero was realized for the Sn content below 30 mol% and the microwave dielectric properties had the ε_r value of 31.2–26.3, the Q·f₀ of 54,600–70,700 GHz, and τ_f of +12.8–−9.3 ppm/°C for this compositions. The relationship between microstructure and microwave dielectric characteristics was investigated.     

Mechanism of the Formation of Ba2Ti9O20-Based Phases in the Course of Solid-Phase Interaction in the BaO–TiO2(ZrO2) and Cs2O–BaO–TiO2(ZrO2) Systems

The mechanism of solid-phase interaction in the BaO–TiO₂(ZrO₂) and Cs₂O–BaO–TiO₂(ZrO₂) systems is investigated. It is established that the formation of the Ba₂Ti₉O₂₀ compound and Ba₂Ti₉O₂₀-based solid solutions is a multistage process proceeding through the formation of intermediate phases. The solid-phase interaction in the BaO–TiO₂(ZrO₂) system occurs through the formation of the BaTi₄O₉ intermediate compound. The Ba₂Ti₉O₂₀ single-phase product is formed only in the presence of ZrO₂ (0.82 mol %) upon heat treatment at a temperature of 1250°C for 5 h. In the Cs₂O–BaO–TiO₂(ZrO₂) system, the BaTi₅O₁₁ metastable intermediate phase is formed at the first stage of the solid-phase interaction. The Cs _x Ba_{2 – x/2}Ti_{9 – y} Zr _y O₂₀ single-phase solid solutions are prepared upon heat treatment at 1100°C for 1 h. It is demonstrated that, in the Ba₂Ti₉O₂₀ structure, cesium can isomorphously substitute for barium with the formation of Cs _x Ba_{2 – x/2}Ti_{9 – y} Zr _y O₂₀ solid solutions (0 x 0.8, y = 0 and 0.09).     

Catalytic reactivity and surface chemistry of polyaniline(EB)–Pd–H2O systems

Catalytic reactivity and surface chemical effects induced by the presence of water in the molecular system polyaniline(EB)–Pd–H₂O were investigated. The polyaniline(EB) doped with palladium reveals its high activity and selectivity in the semihydrogenation: hexyne → hexenes (→ hexane). However, to demonstrate these effects, the specimen has to be submitted to a special treatment to lose most of its water. The XPS analysis allowed identification of the catalytically active sites of the studied system. They were ascribed to the [PdCl₄]²⁻ complex anions present at the surface of the dry specimens. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase Equilibria in the Sections of the Ca(NO3)2–CO(NH2)2–H2O System and Deicing Properties of Nitrate–Urea Mixtures

Theoretical Foundations of Chemical Engineering - Phase equilibria in the sections of the Ca(NO3)2–CO(NH2)2–H2O system and the deicing properties of calcium nitrate and carbamide...     

氯化钡(BaCl_2·2H_2O)

正1)性质。无色单斜晶系结晶。冷结晶为扁平菱形,热结晶为无定形。工业品为白色片状或粉状结晶。结晶水在空气中稳定,加热到113℃时失去结晶水。易溶于水,溶解度随温度的升高而增大。有乙醇及氯离子(如氯化钙)存在时,溶解度显著降低。在乙醇及酸中的溶解度比在水中的溶解度小。在无水乙醇中失去结晶水,但并不溶解。不溶于丙酮。氯化钡的水溶液具苦咸味,并且因含氯离子而具有较强的腐蚀性。工业氯化钡有毒、不易燃、不易爆。     

Modeling of Liquid-Liquid Extraction (LLE) Equilibria Using Gibbs Energy Minimization (GEM) for the System TBP–HNO3–UO2–H2O–Diluent

Liquid-liquid extraction (LLE) is a widely used separation method for an extensive range of metals including actinides. The Gibbs energy minimization (GEM) method is used to compute the complex chemical equilibria for the LLE system HNO₃–H₂O–UO₂(NO₃)₂–TBP plus diluent at 25°C. The nonelectrolyte phase is treated as an ideal mixture defined by eight tri-n-butyl phosphate (TBP) complexes plus the inert diluent. The Pitzer method is used to capture nonidealities in the concentrated electrolyte phase. The generated extraction isotherms are in very good agreement with reported experimental data for various TBP loadings and electrolyte concentrations demonstrating the adequacy of this approach to analyze complex multiphase multicomponent systems. The model is robust and yet flexible allowing for expansion to other LLE systems and coupling with computational tools for parameter analysis and optimization.     

CaO–MgO–Al2O3–SiO2 (CMAS) corrosion behaviour of LaMgAl11O19/GdPO4 thermal barrier coating materials

CaO–MgO–Al₂O₃–SiO₂ (CMAS) corrosion poses serious hidden dangers for the application of thermal barrier coatings (TBCs). In this study, LaMgAl₁₁O₁₉ (LMA) and GdPO₄ were mixed at molar ratios of 2:1, 1:1 and 1:2 to prepare LMA/GdPO₄ materials, and the CMAS corrosion behaviours of these materials were investigated at 1300°C–1500 °C for 20 h and 40 h. It was demonstrated that temperature was the main factor influencing the corrosion behaviours and products. The materials were damaged at 1300 °C by the crystallization of CMAS melts to form CaAl₂Si₂O₈. In contrast, the materials were corroded by CMAS melts via the reaction between CMAS and GdPO₄ at 1500 °C. These results indicate that the addition of GdPO₄ to LMA can improve the resistance of the LMA material to CMAS corrosion.     

Stability in the system CaO–Al2O3–H2O

The solubility of AH₃, CAH₁₀, C₂AH_7.5, and C₃AH₆ was determined experimentally at 7 to 40 °C and up to 570 days. During the reaction of CA, at 20 °C and above initially C₂AH_7.5 formed which was unstable in the long-term. The solubility products calculated indicate that the solubilities of CAH₁₀, C₂AH_7.5 and C₄AH₁₉ increase with temperature while the solubility of C₃AH₆ decreases. Thus at temperatures above 20 °C, C₃AH₆ is stable, while at lower temperature also CAH₁₀ and C₄AH₁₉ are stable, depending on the C/A ratio.At early hydration times, CAH₁₀ can be stable initially at 30 °C and above, as the formation of amorphous AH₃ stabilises CAH₁₀ with respect to C₃AH₆ + 2AH₃. With time, as the solubility AH₃ decreases due to the formation of microcrystalline AH₃, CAH₁₀ becomes unstable at 20 °C and above.     

Tribological properties of NiCr–ZrO2(Y2O3)–SrSO4 composites at elevated temperatures

The effect of SrSO₄ content on the tribological properties of NiCr–30wt%ZrO₂(Y₂O₃) (NC30Z) cermet was evaluated over a wide temperature range from room temperature to 1000 °C. The results indicated that the inclusion of SrSO₄ effectively improved the friction coefficients and wear rates of NC30Z cermet above 400 °C. NC30Z–5SrSO₄ composite against alumina ball exhibited satisfactory tribological performance, which was attributed to synergistic lubrication of pseudocubic-SrZrO₃ and NiCr₂O₄ between 400 °C and 800 °C and cubic-SrZrO₃, NiCr₂O₄, NiO and Cr₂O₃ at 1000 °C.