Synthesis of a soluble preceramic polymer for ZrC using 2-hydroxybenzyl alcohol as carbon source

A preceramic polymer for ZrC was successfully synthesised by chemical reaction between zirconium oxychloride (ZrOCl₂·8H₂O) and 2-Hydroxybenzyl alcohol via a one-pot route. The molecular structure, thermal properties and pyrolysis behaviour of the precursor were investigated. The results indicated that the precursor might be Zr–O–Zr chain polymer with 2-Hydroxybenzyl alcohol as ligand. The precursor was air-stable and exhibited excellent solubility in common organic solvents. The conversions from precursor to ZrC powders were investigated by TG-DTA, X-ray diffraction, Scanning electron microscope, TEM and Raman spectrum. The precursor underwent a thermal decomposition in four steps, and ZrC powders were formed at 1300°C via carbothermal reduction reaction of ZrO₂ and carbon in argon with ceramic yield of 63.0%. The ZrC particles were fine and exhibited irregular polyhedron morphology with average size in the range of 100–300?nm.     

Optimization of the n-hexane isomerization process using response surface methodology

Isomerization reactions on commercial zirconium sulfate catalyst are investigated in order to determine influence of hydrogen/feed ratio, space velocity and temperature on n-hexane conversion. Investigated range of inlet parameters includes values that are applied in the industrial practice of the isomerization process. Box–Behnken experimental design was carried out in order to optimize n-hexane isomerization process. Statistical analysis of experimental data was performed to obtain second order polynomial model and the optimum conditions were determined: hydrogen/feed ratio of 6, space velocity of 2 h⁻¹ and temperature of 170 °C. At optimum conditions conversion of n-hexane was 70 wt.%. In addition, temperature dependency of product composition was investigated at optimum values of hydrogen/feed ratio and space velocity. Obtained results show that methylpentanes greatly depend on temperature, unlike dimethylbutanes, in the studied range from 130 to 170 °C. Isomer that was produced in highest quantities was 2-methylpentane, while 3-methylpentane forms in somewhat smaller amounts. 2,2- and 2,3-dimethylbutanes, which contribute the most to the octane number value, are formed in relatively small quantities, amounting to less than 10 wt.% of the total amount of isomers formed.     

Adsorption and diffusion of cesium ions in zirconium(IV) iodomolybdate exchanger

Tetravalent metal acid (TMA) salt zirconium(IV) iodomolybdate ion exchanger was chemically synthesized under different conditions and subjected into batch reactor for cesium removal investigation. The properties of synthesized exchangers were characterized using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Data revealed that the prepared beads are amorphous in nature and thermally stable up to 350 °C. The influences of contact time, pH, ionic strength, and organic acids were investigated. Results illustrated that cesium uptake reached equilibrium within 2 h and it is strongly dependent on ionic strength and nearly independent of pH values. Speciation of cesium ions and their ability to form ternary complexes less adhered to the applied exchangers predominate their adsorption behavior. The prepared exchangers had a good ion-exchange capacity ranged from 7.94 to 9.62 mmol g⁻¹.     

Influence of zirconium salt precursors on the crystal structures of zirconia

Procedures have been developed for preparing zirconia to yield either tetragonal or monoclinic phases following low (400–600 °C) temperature calcination. The data in this note emphasize the need for paying attention to the precursor zirconium salt in preparing the monoclinic or tetragonal phases. A salt precursor obtained from a supplier at different times may produce different results. Generally, it is more difficult to obtain a precursor that will produce the monoclinic phase than the one that will produce the tetragonal form.     

EXTRACTION OF COPPER SALTS WITH A MIXED EXTRACTANT (III): AGGREGATION AND MOLECULAR STRUCTURE

A study of the extraction of copper salts from aqueous solutions into an equimolar solution of a long-chain amine and a long-chain carboxylic acid in toluene has shown that a cationic copper aggregate is formed in the organic phase. A mechanism of the extraction process and a model structure of the aggregate are proposed based on UV-visible, and NMR spectra, water solubilization, and computer-aided model design (CAMD).     

Processing and mechanical properties of hot-pressed zirconium diboride – zirconium carbide ceramics

ZrB₂ was mixed with 0.5 wt% carbon and up to 10 vol% ZrC and densified by hot-pressing at 2000 °C. All compositions were > 99.8% dense following hot-pressing. The dense ceramics contained 1–1.5 vol% less ZrC than the nominal ZrC addition and had between 0.5 and 1 vol% residual carbon. Grain sizes for the ZrB₂ phase decreased from 10.1 µm for 2.5 vol% ZrC to 4.2 µm for 10 vol% ZrC, while the ZrC cluster size increased from 1.3 µm to 2.2 µm over the same composition range. Elastic modulus was ~505 GPa and toughness was ~2.6 MPa·m^½ for all compositions. Vickers hardness increased from 14.1 to 15.3 GPa as ZrC increased from 2.5 to 10 vol%. Flexure strength increased from 395 MPa for 2.5 vol% ZrC to 615 MPa for 10 vol% ZrC. Griffith-type analysis suggests ZrB₂ grain pullout from machining as the strength limiting flaw for all compositions.     

Al_2TiO_5粒径对Al_2TiO_5-ZrO_2复合材料性能的影响

分别将平均粒径为2、6、10μm的Al2TiO5粉分散在Zr4+浓度为0.06 m01·L-1的氧氯化锆溶液中,滴加0.2 mol·L-1的氨水至溶液的pH值为9.1～9.3,使ZrO2沉淀于Al2TiO5颗粒表面,过滤,干燥,于650℃焙烧,制成ZrO2质量分数为5%的AL2TiO5-ZrO2复合粉体,然后以PVA为结合剂成型为53 mm×10 mm×10 mm的试样,经干燥和1 500℃保温2 h烧成后,检测烧后试样的显气孔率、常温抗折强度、热膨胀率、抗热震性并观察其显微结构.结果表明,用平均粒径为6 μm的Al2TiO5粉制备的Al2TiO5-ZrO2复合材料的综合性能最好:显气孔率最低(5%),抗折强度最大(35 MPa),热膨胀率最小,抗热震性最好,结构较致密.     

复合细化超细晶纯锆动态再结晶模型研究

采用Gleeble-3800热模拟试验机对晶粒尺寸为200～250 nm的复合细化超细晶纯锆在变形温度为300～450℃,应变速率为0.001～0.05s-1的范围内进行单向热压缩实验.结果表明:热加工参数对超细晶纯锆流动应力影响很大.通过实验数据以及显微组织分析可知,在较高的变形温度和较低的应变速率下更容易发生动态再...