Hot corrosion behavior of TiO2 doped,Yb2O3 stabilized zirconia exposed to V2O5 + Na2SO4 molten salt at 700–1000 °C

3.5 mol% Yb₂O₃ stabilized zirconia (YbSZ) doped with 10 mol% TiO₂ (Ti-YbSZ) was produced, and its hot corrosion behavior exposed to Na₂SO₄ + V₂O₅ molten salt was investigated. The as-fabricated ceramic mainly consists of metastable tetragonal (t′) phase. When exposed to the molten salt at 700 °C, 800 °C, 900 °C and 1000 °C for 2 h and 10 h, YbVO₄ and m-ZrO₂ formed as corrosion products due to chemical reactions between the ceramics and the salt. Ti⁴⁺ in Ti-YbSZ solid solution keeps stable during the hot corrosion tests, which acts as a stabilizer for ZrO₂, preventing total decomposition of the t′ phase. After the hot corrosion tests, Ti-YbSZ has an apparently lower m phase content than Y₂O₃ doped Zirconia and YbSZ, indicative of better corrosion resistance. The hot corrosion mechanism of Ti-YbSZ is proposed based on Lewis acid-base rule, phase diagrams and thermodynamics.     

Synthesis and characterization of MgAl2O4–ZrO2 composites

Different types of dense 5–97% ZrO₂–MgAl₂O₄ composites have been prepared using a MgAl₂O₄ spinel obtained by calcining a stoichiometric mixture of aluminium tri-hydroxide and caustic MgO at 1300 °C for 1 h, and a commercial yttria partially stabilized zirconia (YPSZ) powder as starting raw materials by sintering at various temperatures ranging from 1500 to 1650 °C for 2 h. The characteristics of the MgAl₂O₄ spinel, the YPSZ powder and the various sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area, particle size analysis, Archimedes principle, and Vickers indentation method. Characterization results revealed that the YPSZ addition increases the sintering ability, fracture toughness and hardness of MgAl₂O₄ spinel, whereas, the MgAl₂O₄ spinel hampered the sintering ability of YPSZ when sintered at elevated temperatures. A 20-wt.% YPSZ was found to be sufficient to increase the hardness and fracture toughness of MgAl₂O₄ spinel from 406 to 1314 Hv and 2.5 to 3.45 MPa m^1/2, respectively, when sintered at 1600 °C for 2 h.     

Gd掺杂La2(Zr0.7Ce0.3)2O7陶瓷材料抗V2O5+Na2SO4熔盐腐蚀行为

优异的抗熔融V₂O₅+Na₂SO₄腐蚀能力是热障涂层面层材料选择的关键性能指标。通过Gd掺杂实现了1250℃下La₂(Zr_0.7Ce_0.3)₂O₇陶瓷材料抗熔融V₂O₅+Na₂SO₄腐蚀性能的提升,采用固相反应法制备了(La_1–x Gd_x)₂(Zr_0.7Ce_0.3)₂O₇ （x=0、0.5）陶瓷材料,并评估了其在900～1250℃的抗熔融V₂O₅+Na₂SO₄腐蚀性能。结果表明：Gd₂O₃掺杂后La₂(Zr_0.7Ce_0.3)₂O₇陶瓷材料各温度腐蚀深度分别下降约24%、16%、7%、7%,表现出优异的抗腐蚀性能。(La_0.5Gd_0.5)₂(Zr_0.7Ce_0.3)₂O₇陶瓷材料优异的抗V₂O₅+Na₂SO₄腐蚀性能主要归因于晶格畸变增加引起的缓慢扩散及化学碱性的协同作用。     

The influence of SrSO4 on the tribological properties of NiCr–Al2O3 cermet at elevated temperatures

The tribological properties of NiCr–40 wt%Al₂O₃ (NC40A) cermet-based self-lubricating composites containing 10 wt%–30 wt% SrSO₄ against alumina ball were investigated at elevated temperatures. The results indicated that the friction coefficients and wear rates were significantly reduced by adding different amounts of SrSO₄ above 200 °C. NC40A–10SrSO₄ composite exhibited satisfactory tribological properties above 200 °C due to the formation of synergistic lubricating films SrAl₄O₇ and NiCr₂O₄ on the contact surface, while low friction coefficient and wear rate of NC40A–30SrSO₄ composite at 400 °C were attributed to the synergistic lubricating effect of Sr₄Al₂O₇, SrAl₂O₄ and NiCr₂O₄.     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

Cr2O3 doping in ZnO–0.5 mol% V2O5 varistor ceramics

The effects of the amount of Cr₂O₃ (0.5–4 mol%) on the microstructure and the electrical properties have been studied in a binary ZnO–0.5 mol% V₂O₅ system. The microstructure of the samples consists mainly of ZnO grains with ZnCr₂O₄ and α-Zn₃(VO₄)₂ as the minority secondary phases. The addition of Cr₂O₃ is found to be effective in controlling the abnormal ZnO grain growth often found in V₂O₅-doped ZnO ceramic system, and a more uniform microstructure can be obtained. The varistor performance is also improved as observed from the increase in the non-linear coefficient α of the Cr₂O₃-doped ZnO–V₂O₅ samples. The α value is found to increase with the amount of Cr₂O₃ for up to 3 mol% Cr₂O₃ content. Further increase in Cr₂O₃ is found to cause a decrease in the α value. The highest α value of 28.9 is obtained for the ZnO–0.5 mol% V₂O₅–3 mol% Cr₂O₃ sample.     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

Multiferroic ceramics in BaO–Y₂O₃–Fe₂O₃–Nb₂O₅ system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba₂YFeNb₄O₁₅, and minor phases of monoclinic YNbO₄ and hexagonal Ba₃Fe₂Nb₆O₂₁. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe³⁺ and Nb⁵⁺ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics.     

Investigation of the effect of ZrO2 and ZrO2/Al2O3 additions on the hot-pressing and properties of equimolecular mixtures of α- and β-Si3N4

In this work, hot-pressing of equimolecular mixtures of α- and β-Si₃N₄ was performed with addition of different amounts of sintering additives selected in the ZrO₂–Al₂O₃ system. Phase composition and microstructure of the hot-pressed samples was investigated. Densification behavior, mechanical and thermal properties were studied and explained based on the microstructure and phase composition. The optimum mixture from the ZrO₂–Al₂O₃ system for hot-pressing of silicon nitride to give high density materials was determined. Near fully dense silicon nitride materials were obtained only with the additions of zirconia and alumina. The liquid phase formed in the zirconia and alumina mixtures is important for effective hot-pressing. Based on these results, we conclude that pure zirconia is not an effective sintering additive. Selected mechanical and thermal properties of these materials are also presented. Hot-pressed Si₃N₄ ceramics, using mixtures from of ZrO₂/Al₂O₃ as additives, gave fracture toughness, K_IC, in the range of 3.7–6.2 MPa m^1/2 and Vicker hardness values in the range of 6–12 GPa. These properties compare well with currently available high performance silicon nitride ceramics. We also report on interesting thermal expansion behavior of these materials including negative thermal expansion coefficients for a few compositions.     

亚/超临界水中典型硫酸盐Na2SO4和K2SO4的溶解特性及机理

超临界水氧化是一种能够高效无害化处理有毒和复杂有机废物的前沿技术。然而,无机盐溶解度在水临界点附近急剧降低而发生盐沉积,导致反应器堵塞,已成为了该技术大规模推广应用的基础性瓶颈问题。因此,本文对亚/超临界水中典型硫酸盐Na₂SO₄和K₂SO₄的溶解特性及机理进行了研究。获得了更宽温度和压力范围内Na₂SO₄和K₂SO₄在水中的溶解度数据。在84.13～540.46kg/m³水密度范围内Na₂SO₄和K₂SO₄溶解度分别增加了约8931倍和36211倍,相同条件下K₂SO₄溶解度高于Na₂SO₄。溶解度并非严格随水密度增加而增加,Na₂SO₄在25MPa和663.15K的高密度（215.18kg/m³）下溶解度（64.375mg/L）明显低于在21MPa和643.15K的低密度（195.73kg/m³）下溶解度（906.141mg/L）,近似水密度下溶解度相差了约13倍,因为前者处于超临界态而后者处于亚临界态。溶解度在643.15～663.15K范围内下降速率远高于663.15～723.15K,与水密度和介电常数随温度的变化趋势一致。通过分子动力学揭示了Na₂SO₄和K₂SO₄二元盐水体系中的离子成核特性等微观机理。Cl^-的电荷/半径比低于SO₄^2-并且多原子离子结构的SO₄^2-的配位层比单原子离子结构的Cl^-多,所以氯盐溶解度高于硫酸盐。常温常压下会形成水合Na⁺、K⁺和SO₄^2-离子,水分子对盐离子的静电屏蔽作用较强。超临界条件下水分子的静电屏蔽效应减弱,离子碰撞聚集形成团簇,从而产生盐晶体。研究结果能够为超临界水技术的进一步发展提供指导。     

V2O5、NiO、Fe2O3和钒渣对Al2O3/MgAl2O4的腐蚀机理

研究了V2O5、NiO、Fe2O3和钒渣对Al2O3和MgAl2O4尖晶石的腐蚀。把Al2O3和MgAl2O4试样分别同上述氧化物一起从室温加热到1 400℃、1 450℃和1 500℃,加热速率为10℃.min-1。用XRD和SEM对每个系统的腐蚀机理进行了分析。结果显示,所研究的氧化物对Al2O3的影响弱于对MgAl2O4的影响。氧化铝被NiO侵蚀形成NiAl2O4尖晶石,MgAl2O4尖晶石被V2O5侵蚀形成MgV2O6。本文还观察到钒渣中的成分Fe2O3、Mg、Ni、V和Fe分散到了Al2O3结构中。另一方面,Fe2O3、Ca、S、Si、Na、Mg、V和Fe分散到了MgAl2O4结构中。最后,把得到的结果与FactSage软件的预测结果进行了对比。     

(NH4)2SO4和Na2SO4混合溶液中(NH4)2SO4结晶动力学及铁/铝/锰/铬等离子对(NH4)2SO4结晶的影响规律

湿法冶金、三元前体制备等过程均会产生含硫酸钠与硫酸铵的高盐废水。研究高盐废水中硫酸铵的结晶动力学,并考察常见金属离子的影响规律对高盐废水处理具有重要意义。本文以含硫酸钠与硫酸铵混合溶液中硫酸铵的结晶过程为例,系统考察了硫酸铵的结晶动力学及铁、铝、锰、铬对硫酸铵结晶的影响规律。含硫酸钠与硫酸铵混合溶液硫酸铵结晶动力学研究结果表明,硫酸铵生长速率和成核速率方程分别为为B=1.303×10^-16G^1.069M_T^1.801,G=15.708σ^1.387;在硫酸钠与硫酸铵混合体系中,溶液过饱和度影响硫酸铵成核及生长速率,溶液过饱和度减小,晶体的成核及生长速率都会减小,与单体系硫酸铵结晶动力学结果相比,动力学参数均有所下降。铁、铝、锰、铬对硫酸铵结晶的影响规律研究结果表明,铁、铝抑制了硫酸铵晶面生长,结晶粒度减小;锰、铬对硫酸铵结晶有一定的促进作用,结晶粒度增大。金属离子改变了硫酸铵晶习,锰使结晶呈现三棱柱状,铁、铝使硫酸铵结晶片状生长。不同金属离子条件下的结晶动力学方程表明,铁和铝对结晶...     

电化学Ta2O5薄膜漏电流机理的研究进展

介绍了阳极Ta2O5薄膜的电化学形成机理,并重点分析了电化学形成的Ta2O5薄膜漏电流机理的研究进展。描述了影响电化学Ta2O5薄膜生长的关键因素,包括氧含量、杂质缺陷和薄膜晶化等;分析了Ta2O5薄膜漏电流机理,如空间电荷限制电流(SCLC)、Fowler-Nordheim(F-N)导电机理、Pool-Frenkel(PF)发射、Schottky(S)发射等。最后展望了降低电化学Ta2O5薄膜材料的漏电流的理论及技术发展前景,Ta2O5薄膜后期的热处理、高分子增强塑性和复合薄膜技术等方面的新技术的应用将值得期待。     

高纯V2O5制备钒电池用VOSO4的工艺研究

对以高纯V2O5为原料、SO2还原V2O5法制备VOSO4的工艺及其反应机理进行了研究,计算了制备VOSO4的反应焓变和吉布斯自由能变化,并用制备的VOSO4作为钒电池的活性材料进行了充放电性能测试。结果表明:该法生产工艺简单,V2O5∶SO2∶H2SO4的最佳摩尔比为1∶1.10~1.15∶1.10~1.15。制备出的VOSO4中V4+的含量占总钒量的99.71%、V5+含量仅占0.29%,具有良好的充放电性能,可以作为钒电池电解液的活性材料。     

反相微乳法制备纳米V2O5

采用十六烷基三甲基溴化铵(CTAB)/正丁醇/正辛烷/水溶液微乳体系成功制备了纳米V2O5。先采用反相微乳法分别制备碱性偏钒酸铵微乳液和稀硫酸单相微乳液,再将两种微乳液混合得到V2O5前驱物,经陈化、洗涤、干燥、焙烧得到纳米V2O5。通过测定电导率分析了微乳体系的稳定性,采用FTIR、XRD、TEM对纳米V2O5的结构、成分、晶形、粒径等进行了表征。结果表明,采用反相微乳法制备的纳米V2O5为球形、分散性较好、颗粒粒径为6～20nm。     

用Na2SO4提高牛眼透明质酸回收率的研究

通过NaCl和Na     

V2O5制备VN的还原氮化机理

以V₂O₅粉末为原料,C粉末为还原剂,对碳热还原氮化法制备VN的机理进行研究,重点讨论了配碳量和温度对产物的影响.结果表明,V₂O₅为逐级还原,存在直接和间接还原;配碳量（C/V₂O₅）为28%（ω）时,产物氮含量最高;800¹ 000℃发生碳化反应生成VC_1-x,1000¹200℃同时发生碳化和氮化反应,主要生成V（C,N）;温度超过1 300℃,V（C,N）向VC_1-x转化.随温度升高,产物氮含量逐渐降低,钒含量逐渐升高,产物之间发生团聚甚至熔蚀形成球状,大部分颗粒粒径约为1μm.采用本工艺进行实际生产,产品氮含量>17%,钒含量为79%,碳含量<2%,表观密度约为3.5 g/cm³,符合国家标准.     

CaO对MgAl2O4材料和ZrO2-MgAl2O4材料侵蚀机制研究

为了研究CaO对MgAl₂O₄材料和ZrO₂-MgAl₂O₄材料的侵蚀机制,以MgAl₂O₄微粉、脱硅锆微粉和分析纯碳酸钙为原料,将碳酸钙煅烧、粉碎后得CaO微粉,以MgAl₂O₄粉和CaO粉质量比为4∶1制备了MgAl₂O₄材料,以脱硅锆粉、MgAl₂O₄粉、CaO粉质量比为3∶4∶1制备了ZrO₂-MgAl₂O₄材料,并分别于1 500、1 600、1 700℃保温3 h煅烧。利用相图和热力学计算分析了体系中可能发生的反应,利用XRD和SEM分析了烧后试样的物相组成和显微结构。结果表明：对于MgAl₂O₄材料,CaO与MgAl₂O₄会反应生成低熔点CaO·Al₂O₃和12CaO·7Al₂O₃。对于ZrO₂-MgAl₂O₄材料,大量CaO与ZrO₂反应生成高熔点c-ZrO₂和CaZrO₃,而剩余少量CaO与MgAl₂O₄反应生成CaO·Al₂O₃,减少了低熔点相的生成。     

In vitro behavior of bioactive phosphate glass–ceramics from the system P2O5–Na2O–CaO containing titania

Soda lime phosphate bioglass–ceramics with incorporation of small additions of TiO₂ were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the soda lime phosphate glasses were performed using X-ray diffraction analysis. Calcium pyrophosphate (β-Ca₂P₂O₇), sodium metaphosphate (NaPO₃), calcium metaphosphate (β-Ca(PO₃)₂), sodium pyrophosphate (Na₄P₂O₇), sodium calcium phosphate (Na₄Ca(PO₃)₆) and sodium titanium phosphate (Na₅Ti(PO₄)₃) phases were detected in the prepared glass–ceramics. The degradation of the prepared glass–ceramics was carried out for different periods of time in simulated body fluid at 37 °C using granules in the range 0.300–0.600 mm. The released ions were estimated by atomic absorption spectroscopy and the surface textures were measured by scanning electron microscopy. Investigation of in vitro bioactivity of the prepared glass–ceramics was done by the measurement of the infrared reflection spectra for the samples after immersion in the simulated body fluid for different periods at 37 °C. The result showed that no apatite layer was formed on the surface of the samples and the dominant phase remained on the surface was β-Ca₂P₂O₇, which is known for its bioactivity.     

Phase equilibria and liquidus surface of CaO-SiO2–5 wt%MgO-Al2O3-TiO2 slag system

The lack of phase equilibria relations and liquidus surface thermodynamic information for CaO-SiO₂–5?wt%MgO-Al₂O₃-TiO₂ system has seriously restricted the comprehensive utilization of the titanium resources. In present study, the phase equilibrium relationships were investigated for CaO-SiO₂–5?wt%MgO-Al₂O₃-TiO₂ phase diagram system at 1300?°C and 1400?°C using the high temperature equilibrium technique followed by X-Ray Fluoroscopy (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscope (EDX) analysis. In the composition range studied, the liquid phase, melilite solid solution phase and CaO·TiO₂ phase were found. The two-phase equilibrium of liquid coexisting with CaO·TiO₂ phase was intensively dicussed, and the spatial liquidus surfaces at 1300?°C, 1400?°C and 1450?°C (data from literatures only) for liquid coexisting with CaO·TiO₂ phase were first constructed in CaO-SiO₂–5?wt%MgO-Al₂O₃-TiO₂ tetrahedral phase diagram, which can realize a visual understanding of the phase relation change trendency in 3-dimensional space.