Chemical methods of dispergation of metallic phases
作者:B. P. Tarasov、E. E. Fokina、V. N. Fokin
DOI:10.1007/s11172-011-0193-9
日期:2011.7
The results of a cycle of works on the chemical dispergation of intermetallic compounds and alloys were summarized and analyzed. The chemical dispergation occurs in a hydrogen or ammonia atmosphere in the temperature range from 20 to 500 °C and a pressure of 0.5–2.0 MPa. The phase transformations were studied. The conditions suitable for the production of polymetallic phase powders of various degrees of dispersity were determined.
The perovskite type oxonitridotantalates LnTaON2 with Ln=La, Ce, Pr, Nd, Sm, and Gd were synthesized by the ammonothermal method employing custom‐built autoclaves made of nickel‐based superalloy. Metal powders were reacted with NaOH and NaN3 as mineralizers under supercritical conditions with purified ammonia at temperature range of 870–1070 K and pressure values of 150–300 MPa. Crystal structures
SrCeN2 wurden durch Reaktion von Li2CeN2 mit Ca3N2 bzw. Sr2N in Stickstoffatmosphare bei 1020 K hergestellt. Wie Messungen der magnetischen Suszeptibilitaten zeigen, enthalten beide Verbindungen CeIV. Die Kristallstrukturen wurden mit der Rietveld-Methode anhand der Rontgenpulverdiffraktogramme verfeinert. CaCeN2 kristallisiert im NaCl-Strukturtyp mit statistischer Verteilung von Ca und Ce (Raumgruppe Fm3¯m;
CaCeN2 和 SrCeN2 是通过 Li2CeN2 与 Ca3N2 或 Sr2N 在氮气氛中在 1020K 下反应制备的。根据磁化率的测量,两种化合物都含有 CeIV。晶体结构由 X 射线粉末衍射图的全剖面 Rietveld 精修确定。CaCeN2 结晶为具有无序 Ca 和 Ce 的岩盐型结构(空间群 Fm3¯m,a = 499.21(1) pm,Rprofile = 0.061,RBragg = 0.034)。SrCeN2 的低温改性结晶为 α-NaFeO2 型结构(空间群 R3¯m,a = 362.18(4) pm,c = 1795.8(2) pm,Rprofile = 0.085,RBragg = 0.031)。在升高的温度下,有序-无序相变导致 HT-SrCeN2(空间群 Fm3¯m,a = 515.01(2) pm,从 1273 K 淬灭)具有立方晶胞和 Sr 和 Ce 的完全无序。Neue
Dissociative and Associative Concerted Mechanism for Ammonia Synthesis over Co-Based Catalyst
current catalytic reaction mechanism for ammoniasynthesis relies on either dissociative or associative routes, in which adsorbed N2 dissociates directly or is hydrogenated step-by-step until it is broken upon the release of NH3 through associative adsorption. Here, we propose a concerted mechanism of associative and dissociative routes for ammoniasynthesis over a cobalt-loaded nitridecatalyst. Isotope
目前氨合成的催化反应机制依赖于解离或缔合途径,其中吸附的 N 2直接离解或逐步氢化,直到通过缔合吸附释放 NH 3后被破坏。在这里,我们提出了在负载钴的氮化物催化剂上合成氨的缔合和解离路线的协同机制。同位素交换实验表明,吸附的 N 2可以在 Co 金属和氮化物载体上活化,从而导致优异的低温催化性能。表面低功函数 (2.6 eV) 特征与 CeN 载体上表面氮空位的形成共同作用产生了 N 2的双重途径与目前报道的 Co 基催化剂相比,活化能大大降低 (45 kJ·mol –1 ),这导致在温和条件下有效合成氨。
Rare-Earth Nickel Nitridoborates with (BN) Anions: CharacterizedRENi(BN) and AnticipatedREM(BN) Compounds
The compounds RENi(BN) with RE = Y, La, Ce, Pr, Tm and Yb were synthesized by solid state reactions from metal powders and α-BN at temperatures between 1000° and 1200 °C. In addition, the mixed phases (Ca,Yb)Ni(BN) and (Ca,Tm)Ni(BN) were synthesized. All products were characterized by powder XRD measurements and indexed isotypic with the structure of CaNi(BN), consistent with the tetragonal space group