溶胶-凝胶法制备Ti(C,N)-Mo_2C-Ni复合粉末的研究

本文采用溶胶-凝胶法在较低温度(1 400℃)下制备了Ti(C,N)-Mo2C-Ni金属陶瓷复合粉末。通过红外光谱(FTIR)、X-ray衍射(XRD)、热重分析(TG-DTA),扫描电镜(SEM)、能谱(EDS)、比表面积分析(BET)、氮/氧含量测定等分析检测方法 ,对该粉末的制备过程进行了初步的研究与分析。结果表明:在1 400℃,真空条件下,以钛酸四丁酯为钛源,以蔗糖为碳源,乙二醇为溶剂,采用溶胶-凝胶法结合碳热还原法所制得的Ti(C,N)-Mo2C-Ni金属陶瓷复合粉末晶粒小,纯度较高;其制备机理为:原料通过水解、缩聚、裂解/分解等反应,经过干燥后首先得到TiO2混合先驱体粉末,再经过碳热还原及一系列化学反应最后生成了Ti(C,N)-Mo2C-Ni金属陶瓷复合粉末。     

Phase stability and electronic structures of YbAl3−xMx (M = Mg, Cu, Zn, In and Sn) studied by first-principles calculations

YbAl₃ is a potential thermoelectric (TE) material to be used in TE power generator utilizing waste heat sources. This work systematically investigated the alloying behavior of M in YbAl_3−xM_x (M = Mg, Cu, Zn, In and Sn) and their electronic structures by first-principles calculations. The solubility of alloying elements M and phase stability of YbAl_3−xM_x were studied by analyzing the elastic constants, formation and cohesive energies. The results show that Mg, In and Sn are the effective alloying elements for preparing YbAl_3−xM_x solid solutions, which are helpful for improving TE properties of YbAl₃.     

Deposition of titanium oxide films by reactive High Power Impulse Magnetron Sputtering (HiPIMS): Influence of the peak current value on the transition from metallic to poisoned regimes

In this study, reactive High Power Impulse Magnetron Sputtering (HiPIMS) experiments were carried out to synthesize titanium oxide films, using a 45 × 15 cm² titanium target in Ar/O₂ gas mixtures. The deposition process was studied as a function of the peak current (i_peak) at constant voltage during the pulse (1 kV) and constant average power (P_av). As the oxygen flow was increased, i_peak was kept constant (160, 300 or 400A) by adjusting the pulse duration and the average power (2 or 4 kW) by adjusting the pulse repetition frequency. For all experimental conditions, an abrupt transition from metallic towards poisoned regimes was observed. The transition curves exhibit hysteresis. As i_peak is increased from 160 A to 450 A, for P_av = 4 kW, the oxygen content (Ω) in the Ar/O₂ mixture needed to poison the target surface was reduced from Ω = 11.5% to Ω = 8.5%. These values are much smaller than those recorded for DC magnetron sputtering (DCMS) (Ω = 42%) and pulsed DCMS (Ω = 36%) experiments carried out at the same power. These results are explained by the enhancement of the ionization and dissociation rates of oxygen molecules with the increase of i_peak.     

Preparation and structural characterization of perovskite-type LaxLn1−x″CoO3 by the thermal decomposition of heteronuclear complexes, LaxLn1−x″| Co(CN)6| · nH2O (Ln″ = Sm and Ho)

Perovskite-type La_xLn_1−x″CoO₃ oxides are prepared by the thermal decomposition of La_xLn_1−x″ [Co(CN)₆] · nH₂O hetero-nuclear complexes. Except for LaCoO₃ (hexagonal), the structures observed for La_xSm_1−xCoO₃ are othorhombic. While the perovskite-type oxide HoCoO₃ is not formed by decomposition at 1000°C of the corresponding hexacyano complex, the partial replacing of Ho with La is effective in forming the pervoskite-type oxide having an orthorhombic structure containing Ho even at 800°C. A monotonous correlation (quasi-linear relationship) was found between the b- and c-lattice constants of the orthorhombic structures of the perovskite-type oxides and the effective radii of Ln ions, defined as r_eff = xr_1.a + (1 − x)r_1.0″. The distortion parameter for the orthorhombie cell (3″a/b−1) increaseswith decrease in r_eff and is expected to be 0.270 for perovskite-type HoCoO₃. The crystal structure of the La_xLn_1−x″, CoO₃ oxides is mainly controlled by the effective radii of Ln ions.