Thermodynamic properties of seven gaseous halogenated hydrocarbons from acoustic measurements: CHClFCF3, CHF2 CF3, CF3 CH3, CHF2CH3, CF3CHFCHF2, CF3CH2CF3, and CHF2CF2CH2F

Measurements of the speed of sound in seven halogenated hydrocarbons are presented. The compounds in this study are 1-chloro-1,2,2,2-tetrafluoroethane (CHClFCF₃ or HCFC-124), pentafluoroethane (CHF₂ CF₃ or HFC-125), 1,1,1-trifluoroethane (CF₃CH₃ or HFC-143a), 1,1-difluoroethane (CHF₂CH₃ or HFC-152a), 1,1,1,2,3,3-hexafluoropropane (CF₃CHFCHF₂ or HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (CF₃CH₂CF₃ or HFC-236fa), and 1,1,2,2,3-pentafluoropropane (CHF₂CF₂CH₂F or HFC-245ca). The measurements were performed with a cylindrical resonator at temperatures between 240 and 400 K and at pressures up to 1.0 MPa. Ideal-gas heat capacities and acoustic virial coefficients were directly deduced from the data. The ideal-gas heat capacity of HFC-125 from this work differs from spectroscopic calculations by less than 0.2% over the measurement range. The coefficients for virial equations of state were obtained from the acoustic data and hard-core square-well intermolecular potentials. Gas densities that were calculated from the virial equations of state for HCFC-124 and HFC-125 differ from independent density measurements by at most 0.15%, for the ranges of temperature and pressure over which both acoustic and Burnett data exist. The uncertainties in the derived properties for the other five compounds are comparable to those for HCFC-124 and HFC-125.     

PbZrO3含量对PZN-PZ-PT因溶体弥散性相变的影响

报道了相界附近ＰＺＮ－ＰＺ－ＰＴ三元系固溶体弥散性相变,并研究了ＰｂＺｒＯ３含量对ＰＺＮ－ＰＺ－ＰＴ固溶体弥散性相变的影响,发现随着ＰｂＺｒＯ３含量的增加,ＰＺＮ－ＰＺ－ＰＴ固溶体弥散程度有所增加。     

Fe2O3掺杂MgTiO3-CaTiO3微波陶瓷的介电性能研究

采用固相法制备0.93MgTiO3-0.07CaTiO3-xFe_2O_3(摩尔分数x=0.01~0.025)微波介质陶瓷材料,研究添加Fe_2O_3后,体系的晶体结构、显微结构和微波介电性能之间的变化规律。利用XRD、SEM、网络分析仪对样品的相组成、微观结构、介电性能进行测试分析。研究表明:该复合陶瓷样品的致密度、介电常数和Q·f值随Fe_2O_3含量的增加先增大后减小。当x(Fe_2O_3)为0.015,在1290℃烧结4h时,获得最优的介电性能:εr=21.32,Q·f=37448GHz,τf=0.577×10-6/℃。     

Preparation and Properties of Al2O3-doping LiNi1/3Co1/3Mn1/3O2 Cathode Materials

LiNi_1/3Co_1/3-xMn_1/3O₂ doped with Al₂O₃ (x = 0%, 2.5%, 5%, 10%) was synthesized by co-precipitation of Ni, Co, and Mn acetates. The influence of Al₂O₃ doping on structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ was studied using X-ray diffraction (XRD) analysis, scanning electron microscopy, charge/discharge tester, and electrochemical workstation. It was found that the materials achieved the best electrochemical properties when x was 5%. The first discharge capacity was 156.3 mAh · g^?1(0.1 C, 2.0–4.8 V), which was close to the un-doped sample (156.8 mAh · g^?1). After 20 cycles, the capacity retention ratios at the C-ratios of 0.1C, 0.2C, and 0.5 C were 96.1%, 94.9%, and 89.4%, respectively, while the capacity retention ratios of the un-doped samples were only 92.6% (0.1 C), 91.8% (0.2 C), and 88.7% (0.5C). The alternating current impedance shows that the charge transfer in the electrode interface was the easiest when x was 5%.     

High-pressure synthesis,crystal structure,and magnetic properties of KSbO3-type 5d oxides K0.84OsO3 and Bi2.93Os3O11

5d Solid-state oxides K_0.84OsO₃ (Os^5.16+; 5d ^2.84) and Bi_2.93Os₃O₁₁ (Os^4.40+; 5d ^3.60) were synthesized under high-pressure and high-temperature conditions (6 GPa and 1500–1700 °C). Their crystal structures were determined by synchrotron x-ray diffraction and their 5d electronic properties and tunnel-like structure motifs were investigated. A KSbO₃-type structure with a space group of Im-3 and Pn-3 was determined for K_0.84OsO₃ and Bi_2.93Os₃O₁₁, respectively. The magnetic and electronic transport properties of the polycrystalline compounds were compared with those obtained theoretically. It was revealed that the 5d tunnel-like structures are paramagnetic with metallic charge conduction at temperatures above 2 K. This was similar to what was observed for structurally relevant 5d oxides, including Bi₃Re₃O₁₁ (Re^4.33+; 5d ^2.66) and Ba₂Ir₃O₉ (Ir^4.66+; 5d ^4.33). The absence of long-range magnetic order seems to be common among 5d KSbO₃-like oxides, regardless of the number of 5d electrons (between 2.6 and 4.3 per 5d atom).     

Formation and Annealing of BaTiO_3 and SrTiO_3 Nanoparticles in KOH Solution

Barium titanate (BaTiO3) and strontium titanate (SrTiO3) nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO2 particles and corresponding alkaline earth hydroxides, Ba(OH)2 and Sr(OH)2 respectively, in 50 mol·dm-3 KOH solution at 150℃. Each structural evolution of BaTiO3 and SrTiO3 during the hydrothermal treatment was investigated by X-ray diffraction (XRD), field emission scanning elec- tron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM...     

Effects of nano-Fe2O3 powder on thermal emission property of microarc oxidation coating on titanium alloy

Abstract

A ceramic coating was formed on the titanium alloy by microarc oxidation in an electrolyte containing nano-Fe₂O₃, emulsifier OP-10 and sodium phosphate. The composition, surface and cross-sectional morphology and the element compositions of the coatings were characterised by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis system. The spectral emissivity of the coatings was measured by a Fourier transform spectrometer apparatus. The bonding strength between the coating and the titanium alloy was studied by tensile strength test. The thermal shock resistance of the coatings was also evaluated. The results showed that nano-Fe₂O₃ was incorporated into the coating, and the coating had high emission at the wavelength range of 3–20 μm. The bonding strength was 33·2 MPa, and after being subjected to severe thermal shocking for 50 cycles, little peeling-off of the coating occurred.     

Cyclic oxidation of FeCrAlY/Al2O3 composites

Abstract

Three-ply composites consisting of a FeCrAlY matrix and continuous single crystal Al₂O₃ (sapphire) fibers were cyclically oxidized at 1,000° and 1,100°C for up to 1,000 1-h cycles. FeCrAlY matrix only samples were also fabricated and tested for comparison. Fiber ends were exposed at the ends of the composite samples. Following cyclic oxidation, cracks running parallel to and perpendicular to the fibers were observed on the large surface of the composite. In addition, there was evidence of increased scale damage and spallation around the exposed fiber ends, particularly around the middle ply fibers. This damage was more pronounced at the higher temperature. The exposed fiber ends showed cracking between fibers in the outer plies, occasionally with Fe and Cr-rich oxides growing out of the cracks. Large gaps developed at the fiber–matrix interface around many of the fibers, especially those in the outer plies. Oxygen penetrated many of these gaps resulting in significant oxide formation at the fiber–matrix interface far within the composite sample. Around several fibers, the matrix was also internally oxidized showing Al₂O₃ precipitates in a radial band around the fibers. The results show that these composites have poor cyclic oxidation resistance due to the CTE mismatch and inadequate fiber–matrix bond strength at temperatures of 1,000°C and above.     

Effect of Nb,Mo, V contents on oxidation resistance of Ti3Al based alloys

In the present paper, the effect of the contents of Nb, Mo, V on the oxidation properties (700°C, in air) of Ti₃Al based alloys has been studied. It has been shown that the alloys were oxidized rapidly as exposed at 700°C in the air. After 100 h exposure, oxygen-affected alloy surface layer of about 10 thickness has been formed on account of the poor protection of the oxide film. An addition of (11–13%)¹ Nb enhanced the oxidation resistance. The addition of Mo and V in the Ti₃Al–Nb system alloy reduced the oxidation resistance significantly.     

Microhardness studies on as-grown faces of NaClO3 and NaBrO3 crystals

Single crystals of NaClO₃ and NaBrO₃ are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO₃ whereas in addition to the cracks at the corners microcracks also appeared in NaBrO₃ crystals around the impressions. The impressions formed in NaBrO₃ are not very clear as in NaClO₃, a possible mechanism for it is discussed. The work hardening index number(n) for both these crystals is around 1.6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO₃ is harder than NaClO₃ (ΔH ≈ 100 kg/mm ²,this could be due to strong inter ionic forces acting between Na-Br in NaBrO₃ crystals. Using Gilman’s empirical relation, hardness values are calculated from the values of elastic constants (C ₄₄) and are found to be close to the experimental results.     

Some thermodynamic aspects of the high-temperature transition in doped V2O3

Measurements of the entropy change are reported for the high-temperature metal-insulator (MI) transitions in the (V_1–xCr_x)₂O₃ and (V_1–xAl_x)₂O₃ systems. It is emphasized that the entropy of the I phase exceeds that of the M phase. Evidence is presented to show that the M and I phases coexist over a narrow temperature range. The transformation is attended by enormous hysteresis effects; these indicate that the lattice plays an important role in the transition. The probable role of Cr³⁺ and Al³⁺ as a dopant in the V₂O₃ lattice is briefly discussed. A phase diagram for the dilute V₂O₃-Al₂O₃ alloy system is presented.     

Microstructural study of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 heteroepitaxial trilayer films grown on (100) SrTiO3 substrates

Detailed transmission electron microscopic study has been carried out on heteroepitaxial YBa₂Cu₃O₇/SrTiO₃/YBa₂Cu₃O₇ trilayer thin films grown on (100)SrTiO₃ substrates prepared by DC and RF magnetron sputtering. The microstructural results showed the existence of somea-axis-oriented YBCO grains 20–90 nm wide in thec-axis-oriented YBCO matrix. Some of thea-axis grains in the lower YBCO thin film layer have protruded into the above SrTiO₃ layer, which may cause short circuit between the two YBCO superconducting layers. This is unsuitable for the application of trilayer thin films for microelectronic devices. The defects on the surface of the substrates would also influence the growth quality of the YBCO thin films.     

YBa2Cu3O7 superconductor as a mild,deep oxidation catalyst

Several Y-Ba-Cu-O compositions including the superconducting YBa₂Cu₃O₇ are scanned for their oxygen uptake using low temperature oxygen chemisorption (LTOC) technique as the principal probe at 195 K. BET surface area and pore size distribution were also determined. The results indicate their potential for use as mild, deep oxidation catalysts even under ambient and sub-ambient conditions.     

Phase developments in the Pb(Zn1/2W1/2)O3-Pb(Zn1/3Ta2/3)O3-Pb(Zn1/3Nb2/3)O3 pseudo-ternary system

The phase stability ranges in the B-site precursor (Zn_1/2W_1/2)O₂-(Zn_1/3Ta_2/3)O₂-(Zn_1/3Nb_2/3)O₂ were determined by X-ray diffraction (XRD), where wolframite, tri-αPbO₂, and columbite phases were identified. Next attempts were carried out (with the addition of PbO) for the system Pb(Zn_1/2W_1/2)O₃-Pb(Zn_1/3Ta_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃, where the perovskite phase did not develop in the entire compositions investigated. Instead, only the Pb₂WO₅ and pyrochlore phases (along with ZnO) resulted.     

Decolourization of Methyl Orange using Fenton-like mesoporous Fe(2)O(3)-SiO(2) composite

Rapid decolourization of Methyl Orange by Fenton-like mesoporous Fe(2)O(3)-SiO(2) catalyst has been reported. The effect of various parameters such as initial pH, initial H(2)O(2) concentration, Fe content in the catalyst and initial dye concentration on decolourization process were studied. The results show that 20mg of mesoporous Fe(2)O(3)/SiO(2) composite (with Si/Fe=10) was sufficient to decolourize 0.6 mg/ml of Methyl Orange in presence of 2 ml of H(2)O(2) at an initial pH of 2.93 within 20 min. The pH range for effective decolourization (≥90%) was found to be 1-3. Leaching tests indicated that the activity of the catalyst was almost unaffected up to three consecutive cycles although ≤0.2 ppm of Fe ion was leached into treated water in each run.     

Growth mechanism of NaClO3 and NaBrO3 crystals from aqueous solutions

A study of growth rates of NaClO₃ and NaBrO₃ has been carried out using a small growth cell by in situ observation. Normal growth rates of (100) faces of NaClO₃ and (111) faces of NaBrO₃ along 〈110〉 direction are measured under relatively high supersaturation ranging from 3–8%. In the initial stages of growth, (100), (110) and (111) faces develop in NaClO₃ and gradually all the faces are replaced by the (100) faces only. In the case of NaBrO₃, mostly (111) faces develop with occasional occurrence of small (100) faces at the intersection of (111) faces. The growth mechanisms are investigated from growth rate vs supersaturation plots and from the observations of surface features. In the present supersaturation range, the growth mechanism appears to be due to two-dimensional growth mechanism.     

La2O3、Nd2O3、Y2O3对高岭石高温相变动力学的影响

利用综合热分析技术、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和扫描电镜(SEM)研究了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温条件下转变成莫来石过程的作用,并采用Kissinger方程、Ozawa方程以及JMA修正方程(Ⅰ)和(Ⅱ)分析了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温相变动力学的影响。结果表明:3种稀土氧化物的掺入对高岭石的相变动力学参数产生了影响,相变活化能和频率因子与未掺入稀土氧化物的高岭石相比有所降低,析晶方式则未发生变化,均属于体积晶化。对比掺入3种稀土氧化物的高岭石相变活化能和频率因子可以看出,Y_2O_3对于高岭石高温条件下相变的促进作用最为明显,相变活化能最低。稀土氧化物对于高岭石高温相变产物影响不大,主晶相为莫来石相,次晶相为方石英相,但稀土氧化物的掺入使得方石英相的结晶度明显提高。     

羧甲基纤维素-Fe3O4复合纳米磁性材料的制备及其渗透性能

采用改进的氧化沉淀法在羧甲基纤维素(CMC)溶液中制备了以磁性纳米Fe3O4为核心,外包CMC的复合磁性纳米粒子。用透射电镜、X射线衍射、红外光谱、Zeta电位和震动样品磁强计对复合粒子进行了表面形貌、结构和磁学的表征。实验结果表明,CMC-Fe3O4复合纳米粒子为反尖晶石型,平均粒径约为40 nm;CMC在Fe3O4粒子表面是化学吸附;在相同pH值下,CMC-Fe3O4的表面Zeta电位低于纯相Fe3O4;CMC-Fe3O4的饱和磁化强度为36.74 emu.g-1;CMC-Fe3O4复合粒子在土壤介质中的过滤系数约为0.03 cm-1;在10 cm土柱渗透实验中,72%的CMC-Fe3O4复合粒子悬浊液穿过了土壤介质。     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.     

X-ray study of the air-oxidiseda-Ga2Se3 and Ga2Te3 powders

X-ray studies of the stoichiometrically prepareda-Ga₂Se₃ and Ga₂Te₃ are reported after various stages of air-oxidation in the temperature ranges 250 to 825° C and 250 to 650° C respectively. Diffractometric powder data of Ga₂Te₃ are also reported over the complete 2ϑ range with remarkable difference in the relative intensities of the (444) and (642) reflections. Ina-Ga₂Se₃ the oxidation proceeds by formation of the most stable phase, beta-gallium sesquioxide, complete oxidation occurring at 650° C. For Ga₂Te₃ a mixture of Ga₂TeO₆ and TeO₂ is obtained as the intermediate oxidation products in the range 500 to 600° C, while at 450° C some extra lines which could be indexed on the super-lattice cell of Ga₂Te₃, along with Te and unchanged Ga₂Te₃ lines, are observed. Oxidation at the higher temperature of 650° C led to the disappearance of TeO₂ lines leaving Ga₂TeO₆ as the final well-crystallised phase.