Nickel Boride–Mediated Cleavage of 1,3-Dithiolanes: A Convenient Approach to Reductive Desulfurization

1,3-Dithiolanes are rapidly cleaved by nickel boride, generating corresponding hydrocarbons in excellent yields. The hydrogenolysis is rapid at room temperature and does not require protection from the atmosphere. Mild reaction conditions, simple workup, and good yields of pure products are some of the major advantages of the procedure.     

Vibrational spectra and factor group analysis of rare-earth chromium borates,RCr3(BO3)4, with R = La–Ho

Anhydrous orthoborates RM₃(BO₃)₄, where R = Y, La–Lu, M = Al, Ga, Cr, Fe, with huntite structure type are considered as multifunctional laser materials. The crystal structure of these borates is either rhombohedral with space group R32 (D₃⁷) (Z = 3) or monoclinic with space group C2/c (C_2h⁶) (Z = 4) depending on the growth conditions. Both modifications have very close polytypic structures, and it is difficult to identify them by powder diffraction data. In this context, double borates of rare-earth cations and Cr³⁺ have been grown from high-temperature solutions and are characterized by Raman and infrared spectroscopy in a crystalline state in combination with factor group analysis of vibrational modes. The assignment for the stretching and bending vibrations of BO₃³⁻ groups and external modes has been made. Some external modes have been identified by study of mass effect (Al–Cr, La–Ho). Comparison of the Raman spectra of these borates shows redistribution of band intensities of two spectral modifications, related to different symmetry groups. As predicted by factor group analysis, the number of IR-active vibrational modes of stretching and bending vibrations of BO₃³⁻ units significantly increases in infrared spectra of monoclinic borates in comparison with rhombohedral ones. The dependence of the realized borate space group on the crystal growth conditions and the sort of rare-earth atom was revealed. Both GdCr₃(BO₃)₄ and EuCr₃(BO₃)₄ borates crystallize in space group R32 irrespective of growth conditions. The borates with the large rare-earth elements La–Nd always form the monoclinic structures, irrespective of crystallization temperature. The borates SmCr₃(BO₃)₄, TbCr₃(BO₃)₄ and DyCr₃(BO₃)₄ have been obtained in two modifications in dependence of crystalline borate substance/solvent ratio and related temperature of crystallization.     

Rare-earth Metal Borosilicides R9Si15–xB3 (R = Tb,Yb): New Ordered Structures Derived from the AlB2 Structure Type

Two novel ternary borosilicides R₉Si_15–xB₃ (R = Tb, x = 1.80, R = Yb, x = 1.17) were synthesized from the initial elements using tin flux method. Their crystal structures were determined by means of X-ray single crystal diffraction. Both refer to space group R32, Z = 1: a = 6.668(2) Å, c = 12.405(4) Å [R₁ = 0.027, wR₂ = 0.031 for 1832 reflections with I_o > 2σ (I_o)] for Tb₉Si_15–xB₃, and a = 6.5796(3) Å, c = 12.2599(5) Å [R_F = 0.052, wR = 0.090 for 1369 reflections with I_o > 2σ (I_o)] for Yb₉Si_15–xB₃. The structures represent a new structure type, derived from that of AlB₂, with ordering in the metalloid sublattice resulting in distorted [Si₅B] hexagons. The presence or absence of boron in this ordered structure is discussed on the basis of difference Fourier syntheses, interatomic distances, structural analysis, and theoretical calculations in relation with the parent structures of the binaries AlB₂ and Yb₃Si₅ (Th₃Pd₅ type of structure). Theoretical calculations show substantial covalent interactions between the metal and nonmetal elements. The small percentage of silicon atoms, which are missing in these nonstoichiometric compounds, probably allows strengthening boron-metal and boron-silicon bonding.     

Identifying a perovskite phase in rare-earth nickelates using X-ray photoelectron spectroscopy

We demonstrate a practical way to identify the presence of a perovskite phase in rare-earth nickelates (RNiO₃) using X-ray photoelectron spectroscopy (XPS). By varying the calcination temperature, we prepared RNiO₃ powders with different degrees of chemical reaction. We found that perovskite RNiO₃ becomes predominant after high-temperature calcination (≥1,000 °C) in X-ray diffraction and XPS (at Ni 3p and O 1s edges) measurements. While the observed spectra at the Ni 3p edge are similar for all powders, a sizable difference was observed in the O 1s-edge spectra depending on the calcination temperature. With the formation of a perovskite phase with a trivalent Ni³⁺ state, an XPS peak corresponding to oxygen ions in the perovskite lattice distinctly emerges. Our work shows that the Ni³⁺ state cannot be determined by analyzing the Ni 3p edge solely and rather, the O 1s edge should be simultaneously monitored for explicit identification.     

甘油氧化的光谱电化学傅里叶变换衰减全反射谱红外光谱薄膜流动池中硼酸镍层厚度的优化

在碱性甘油电氧化反应中,利用电化学傅里叶变换衰减全反射谱红外光谱法,研究了薄膜流动池中滴注硼酸镍催化剂负载量对玻碳电极性能的影响.连续操作的径向流动池包括一个位于内反射元件上方50μm的钻孔电极,可实现红外光谱分析.这是在确定条件下对电催化剂进行简便和可重复筛选的一个适合的方法,同时还提供了对复杂反应(如甘油氧化)产物选择性的检测.通过对泵送电解液进行更耗时的定量高效液相色谱分析,结果表明,衰减全反射红外光谱法可快速鉴定产物.在层流条件下,水中使用0.1 M甘油和1 M KOH,流速为5μL min-1时,甘油转化率较高.转化率和选择性取决于催化剂的负载量,负载量又决定了催化剂层的厚度和粗糙度.由于在更粗糙的膜中停留时间更长有利于再吸附和C-C键断裂,因此当负载量最高达210μg cm-2时,甘油转化率为73％且甲酸选择性接近80％.当最低负载量为13μg cm-2时,甘油转化率达到63％,甲酸选择性降至60％,相应地,C2物种(如乙醇酸盐)选择性较高,为8％.因此,只有催化剂负载量较低时才能形成几微米厚度范围内的薄膜,此时才适合进行优质催化剂的筛选.     

Development and application of high strength ternary boride base cermets

Reaction boronizing sintering is a novel strategy to form a ternary boride coexisting with a metal matrix in a cermet during liquid phase sintering. This new sintering technique has successfully developed world first ternary boride base cermets with excellent mechanical properties such as Mo₂FeB₂, Mo₂NiB₂ and WCoB base ones.In these cermets Mo₂FeB₂ and Mo₂NiB₂ base ones consist of a tetragonal M₃B₂ (M: metal)-type complex boride as a hard phase and a transition metal base matrix. The cermets have already been applied to wear resistant applications such as injection molding machine parts, can making tools, and hot copper extruding dies, etc.This paper focuses on the characteristics, effects of the additional elements on the mechanical properties and structure, and practical applications of the ternary boride base cermets.     

稀土、2-羟基-3-萘甲酸、邻菲咯啉三元配合物合成及表征

在乙醇溶液中合成了稀土离子(RE=Tb,Eu,Sm,Nd)与2-羟基-3-萘甲酸(HL)、邻菲咯啉(phen)固体配合物。通过元素分析、红外光谱、紫外光谱、差热-热重分析,确定了配合物的组成为REL₄·phen₂·Na·H₂O。初步研究了这些配合物的谱学性质并推测出羧基(—COO—) 与稀土离子和钠离子属于桥式配位, 形成了链状结构的化合物。其中钠离子和稀土离子分别为六配位和八配位模式。     

Recovery of low temperature electron irradiation-induced damage in n-type gaas

Undoped n-type GaAa was irradiated near 5 and 77 °K with electrons having incident energies between 0.46 and 1.30 MeV. The recovery of the electrical resistivity and the Hall coefficient upon annealing from 4 to 520 °K was monitored. Changes which occurred upon annealing below 200 °K could be reversed by ionizing radiation. A small amount of irreversible ionization-induced recovery was observed after irradiation near 5 °K. Major irreversible recovery stages were centered near 235 (stage I), 280 (stage II) and 520 °K (stage III). Recovery in stage I and II obeyed first order kinetics. The activation energies of stages I and II were determined as 0.72 and 0.83 eV, respectively. The carrier concentration changes per unit irradiation dose corresponding to the three recovery stages differed in their energy dependence indicating that the defects which are removed in stage III have the lowest threshold energy. The carrier concentration changes per unit irradiation dose corresponding to stages I and III were higher for irradiation near 5 °K than for irradiation near 77 °K.     

Experimental Verification of the Theoretical Prediction of High‐Temperature Superconductivity in Phases of Titanium Borides TiB k

Theoretical predictions of hightemperature superconductivity (HTSC) in titanium borides, TiBk, have been experimentally verified. These predictions have been reported previously in the form of theoretical phase diagrams. They predicted the existence of HTSC in TiB _k (1.43 < k < 2.57) phases and in TiB_1.5–1.6. An abrupt decrease at 110 K was found on the temperature curve of conductivity R(T) for titanium samples whose surfaces were coated with diffuse layers of depthvariable boride compositions TiB _k . This indicates that the layers include phases possessing HTSC. This behavior of the R(T) curves is explained assuming that the inclusions of HTSC phases have a strong effect on the resistance of the composite materials at T_c. The composition of the boride layers has been investigated by mass spectrometry. Diffuse boride layers were applied to titanium surface by treating its surface with a B₂H₆ + H₂ gas mixture at 610–700°C followed by annealing in vacuum.     

EPR and optical measurements of weakly doped LiNbO3: Er

Optical spectroscopy measurements of the congruent LiNbO₃ (LN) single crystals, weakly doped with Er (0.1–0.3 wt%) and Er (0.3 wt%) and Yb (0.5 wt%), have been carried out. The shape of the optical absorption and additional absorption bands registered after γ-irradiation suggests the presence of Er³⁺ ion pairs. EPR investigations were performed for LN single crystal doped with Er (0.1 wt%). Unusual behaviour of the temperature dependence of the intensity and linewidth of the main EPR line—corresponding to the fine transition of ^evenEr³⁺—ions, is reported. The main EPR line appears to be a superposition of several paramagnetic centres originating from isolated ^evenEr³⁺ ions and ^evenEr³⁺–^evenEr³⁺ pairs of ions. In low temperature region (below 20 K), the main EPR signal is dominated by signals arising from ^evenEr³⁺–^evenEr³⁺ pairs of ions. The inverse intensity of the EPR line at low temperature region fulfils the Curie–Weiss law and enabled to determine the Curie–Weiss constant Θ=1.5±0.5 K. The positive sign of Θ suggests that the ferromagnetic interactions arise in the system of ^evenEr³⁺–^evenEr³⁺ ion pairs in LN. Our results suggest that the distribution of Er ions in congruent LN is not homogeneous and Er impurity ions can form clusters in host lattice even in the case of weak erbium doping.