Faqiang Shi,Limeng Liu,Jiandong Wu,Junfeng Hou,Yujin Wang
TaC x (x = 0.5, 0.55, 0.6 and 0.7) ceramics with 20 mol% Al addition were prepared by hot pressing TaC, Ta and Al powder mixtures. Effects of the overall C:Ta ratios and the Al addition on constituent phases, microstructures and mechanical properties of the consolidated materials were examined. Results showed that O impurity contained in the starting powders was collected in form of Al 2 O 3 due to strong affinity of O with Al. The TaC x -Al composites were easy to densify due to presence of molten Al at its melting point ( T m = 660 °C) and a transient Al–Ta eutectic liquid at higher temperatures. After densification, the metallic liquids were eliminated ultimately by formation of refractory Ta 4 AlC 3 via reaction of Al, Ta and TaC. Reactions between the remnant Ta and TaC after Ta 4 AlC 3 formation resulted in ζ-Ta 4 C 3-z or h-Ta 2 C depending on the initial C:Ta ratio. The Ta 4 AlC 3 compound was compatible with the tantalum carbides. Microstructures of the TaC x -Al (x = 0.5–0.7) composites were consisted of ζ-Ta 4 C 3-z and Ta 4 AlC 3 fine lamellar grains to benefit the mechanical properties of the composites. The TaC 0.7 –20mol% Al composition had satisfying mechanical properties (flexural strength 613 ± 28 MPa and fracture toughness 11.2 ± 0.8 MPa m 1/2 ). TG-DSC evidenced an increase in oxidation resistance of the TaC x ceramics by the addition of 20 mol% Al.
Jiaxin Li,Yuhong Chen,Yongquan Li,Zhangjun Bai,Kang Wang
Alloys with composition of Ta-10 wt.% W and Ta-10 wt.% W-6 wt.% Al, respectively, were prepared by the hot-press sintering process. The oxidation behaviour at 900°C and 1000°C was studied. The oxidation weight gain curves of the Ta–10%W alloy followed the linear law and the final oxidation product was Ta2O5 solid solution. Meanwhile, due to the addition of Al, the oxidation weight gain curves of the Ta–10%W–6%Al alloy followed the parabolic law. The final oxidation products at 900°C formed a dense outer layer Al2O3 and an inner layer. However, after being oxidised at 1000°C, the oxidation products included Al2O3, AlTaO4 and Ta22W4O67. Since the dense Al2O3 oxide film was consumed by the generation of AlTaO4, the inward diffusion of oxygen cannot be prevented. The oxidation resistance degraded at 1000°C. The addition of Al significantly improved the oxidation resistance of the Ta-W-based alloy system.
Recent advances in torrefaction pretreatment technologies have the potential to improve biomass storage, transportation, and combustion. Torrefaction pretreatment, on the other hand, does not address the issue of high alkali metal content in biomass, which can easily lead to ash deposition, slagging, and corrosion on the boiler heating surface. NH 4 H 2 PO 4 , Ca 3 (PO 4 ) 2 , diatomite (primarily SiO 2 ), and calcined kaolin (Al 2 O 3 ·2SiO 2 ) were added to torrefied wheat straw to control the release and transformation of potassium in the process of biomass combustion, and the effects of additives on K precipitation and migration were explored. The results demonstrated that all four additives might limit the release of K from torrefied wheat straw during combustion. Phosphoric acid additives had a better effect than silicon-aluminum additives, with the best result being Ca 3 (PO 4 ) 2 , followed by calcined kaolin. The amount of phosphoric acid additives should be controlled at 10wt%, and the amount of silicon aluminum additives should be maintained at 5wt%, based on the economy and retention impact of K. XRD and chemical fractionation analysis revealed that phosphoric acid additives primarily control the K transformation by forming K–Ca–P salt and ammonium acetate state K, silica-aluminum additives primarily control it by forming K silicates and aluminosilicates, and diatomite also improved the retention of water-soluble K through physical adsorption. Graphical abstract
危险品化学品经营许可证（带存储）