Relation between oxidation microstructure and the maximum energy product loss of a Sm2Co17 magnet oxidized at 500 ℃

The oxidation microstructure and maximum energy product (BH)_max loss of a Sm(Co_0.76, Fe_0.1, Cu_0.1, Zr_0.04)₇ magnet oxidized at 500 ℃ were systematically investigated. Three different oxidation regions were formed in the oxidized magnet: a continuous external oxide scale, an internal reaction layer, and a diffusion zone. Both room-temperature and high-temperature (BH)_max losses exhibited the same parabolic increase with oxidation time. An oxygen diffusion model was proposed to simulate the dependence of (BH)_max loss on oxidation time. It is found that the external oxide scale has little effect on the (BH)_max loss, and both the internal reaction layer and diffusion zone result in the (BH)_max loss. Moreover, the diffusion zone leads to more (BH)_max loss than the internal reaction layer. The values of the oxidation rate constant k for internal reaction layer and oxygen diffusion coefficient D for diffusion zone were obtained, which are about 1.91 × 10^-10 cm²/s and 6.54 × 10^-11 cm²/s, respectively.     

Spectroscopic properties in Er Er3+/Yb3+Co-doped fluorophosphate glass

Using the technique of high-temperature melting, a new Er³⁺/Yb³⁺ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er³⁺ and Yb³⁺ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd-Ofelt theory, the oscillator strength was computed. The lifetime of ⁴I_13/2 level (τ_m) of Er³⁺ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 τ_m. The large stimulated emission cross section of the Er³⁺ was calculated by the McCumber theory. The spectroscopic properties of Er³⁺ ion were compared with those in different glasses. The full width at half maximum and σ_e are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.     

利用二氧化碳的缓慢释放控制聚丙烯酰胺在含柠檬酸铬水溶液中的粘度

Partially hydrolyzed polyacrylamide (HPAM) has been widely used for water shut-off and profile control to enhance oil recovery. Herein, we reported a novel technique by which the crosslinking between HPAM and Cr³⁺ in aqueous solutions at 60 ℃ can be delayed effectively. Citric acid was selected as an organic complexing agent of Cr³⁺ so that the crosslinking between HPAM and Cr³⁺ can be prevented completely. Due to the decomposition of the bicarbonate (HCO₃^-) embedded in solution, CO₂ released from solution and the pH value of solution increased gradually. The degree of ionization of HPAM and its ability to complex with Cr³⁺ increased accordingly. When the complexation of Cr³⁺ with HPAM is stronger than that with citric acid, the viscosity of the HPAM solution increased significantly. Under the closed condition, together with the existence of potassium dihydrogen phosphate (KH₂PO₄), the release of CO₂ was very slow and the condition was highly controlled so that the ionization of HPAM was prevented initially. Furthermore, the hydrogen bonding interactions between HPAM and melamine embedded in solution previously also postponed the ionization of HPAM. As a result, the crosslinking between HPAM and Cr³⁺ can be delayed for almost one month, completely meeting the requirements for deep water shut-off and profile control to enhance oil recovery.     

活化气氛对钼基合成醇催化剂的结构和性能的影响

Activated carbon supported Mo-based catalysts were prepared and reduced under different activation atmospheres, including pure H₂, syngas (H₂/CO=2/1), and pure CO. The catalysts structures were characterized by X-ray diffraction, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The catalytic performance for the higher alcohol synthesis from syngas was tested. The pure H₂ treatment showed a high reduction capacity. The presence of a large amount of metallic Co⁰. and low valence state Mo^φ+ (0<φ<2) on the surface suggested a super activity for the CO dissociation and hydrogenation, which promoted hydrocarbons formation and reduced the alcohol selectivity. In contrast, the pure CO-reduced catalyst had a low reduction degree. The Mo and Co species at the catalyst mainly existed in the form of Mo⁴⁺ and Co²⁺. The syngas-reduced catalyst showed the highest activity and selectivity for the higher alcohols synthesis. We suggest that the syngas treatment had an appropriate reduction capacity that is between those of pure H₂ and pure CO and led to the coexistence of multivalent Co species as well as the enrichment of Mo^δ+ on the catalyst''s surface. The synergistic effects between these active species provided a better cooperativity and equilibrium between the CO dissociation, hydrogenation and CO insertion and thus contributed beneficially to the formation of higher alcohols.     

1,3-二烷基咪唑离子液体-水二元混合物的溶致显色参数和优先溶剂化行为

Binary mixtures of 1,3-dialkylimidazolium based ionic liquids (ILs) and water were selected as solvent systems to investigate the solute-solvent and solvent-solvent interactions on the preferential solvation of solvatochromic indicators at 25℃. Empirical solvatochromic parameters, dipolarity/polarizability (π^*), hydrogen-bond donor acidity (α), hydrogen-bond acceptor basicity (β), and Reichardt''s polarity parameters (E_T^N) were measured from the ultraviolet-visible spectral shifts of 4-nitroaniline, 4-nitroanisole, and Reichardt''s dye. The solvent properties of the IL-water mixtures were found to be influenced by IL type and IL mole fraction (x_IL). All these studied systems showed the non-ideal behavior. The maximum deviation to ideality for the solvatochromic parameters can be obtained in the xIL range from 0.1 to 0.3. For most of the binary mixtures, the π^* values showed the synergistic effects instead of the E_T^N, α and β values. The observed synergy extent was dependent on the studied systems, such as the dye indicator and IL type. A preferential solvation model was utilized to gather information on the molecular interactions in the mixtures. The dye indicator was preferentially solvated on the following trend: IL >IL-water complex >water.     

Structures and luminescence properties of Yb3＋ in the double perovskites Ba2YB＇O6 （B＇=Ta5＋, Nb5＋） phosphors

The Yb³⁺ doped Ba₂YB'O₆ (B'=Ta⁵⁺, Nb⁵⁺) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb³⁺:Ba₂YB'O₆ (B'=,Ta⁵⁺, Nb⁵⁺) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO₆ or NbO₆ centre with large Stokes shift. The Yb³⁺ doped into these hosts are situated at Y³⁺ sites of cubic symmetry (O_h). The experimental energy levels of Yb³⁺ in Ba₂YTaO₆ and Ba₂YNbO₆ were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg--Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb³⁺:Ba₂YB'O₆(B'=Ta⁵⁺, Nb⁵⁺) from (²F_5/2)Γ₈^- to the low-energy states were calculated.     

Local structure distortion and spin Hamiltonian parameters for Cr3＋-Vzn tetragonal defect centre in Cr3＋ doped KZnF3 crystal

The quantitative relationship between the spin Hamiltonian parameters (D, g_‖, Δg) and the crystal structure parameters for the Cr³⁺—V_Zn tetragonal defect centre in a Cr³⁺:KZnF₃ crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr³⁺—V_Zn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the V_Zn vacancy and the differences in mass, radius and charge between the Cr³⁺ and the Zn²⁺ ions induce the local lattice distortion of the Cr³⁺ centre ions in the KZnF₃ crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. We find that the ligand F^- ion along [001] and the other five F^- ions move towards the central Cr³⁺ by distances of Δ₁ = 0.0121 nm and Δ₂ = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr³⁺ ions in the Cr³⁺:KZnF₃ crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.     

Formation of high-T c phases of the system Bi-Pb-Sr-Ca-Cu-O in a fluxed KCl melt

The influence of the conditions of synthesis and annealing on the ratio of the volumes and the temperature T _c ⁿ at which transition to the superconducting state begins is investigated on the basis of diamagnetic susceptibility measurements and x-ray phase analysis for bismuth 2212 and 2223 phases obtained from solution in a KCl melt. It is found that the value of T _c ⁿ for the 2212 phase decreases as the temperature and the holding time are increased in synthesis. The 2212–2223 transition in the fluxed KCl melt takes place in the presence of an oxygen deficiency, and the width of the transition interval to the superconducting state of the 2223 phase depends on the cooling rate of the fluxed melt after isothermal holding and also on subsequent annealing in air. Temperatures T _c ⁿ =107 K, 90 K, and 20 K are observed for unannealed crystals of the 2223 phase with average dimensions 50×50 μm. Air annealing leads to oxygen saturation of their lattice, and T _c ⁿ =107 K throughout the entire structure of the crystal. Fiz. Tverd. Tela (St. Petersburg) 39, 1761–1763 (October 1997)     

Characteristics of pentacene organic thin film transistor with top gate and bottom contact

High performance pentacene organic thin film transistors (OTFT) were designed and fabricated using SiO₂ deposited by electron beam evaporation as gate dielectric material. Pentacene thin films were prepared on glass substrate with S--D electrode pattern made from ITO by means of thermal evaporation through self-organized process. The threshold voltage V_TH was --2.75± 0.1V in 0---50V range, and that subthreshold slopes were 0.42± 0.05V/dec. The field-effect mobility (μ_EF) of OTFT device increased with the increase of V_DS, but the μ_EF of OTFT device increased and then decreased with increased V_GS when V_DS was kept constant. When V_DS was --50V, on/off current ratio was 0.48× 10⁵ and subthreshold slope was 0.44V/dec. The μ_EF was 1.10cm²/(V.s), threshold voltage was --2.71V for the OTFT device.     

Influence of thermal stress on the relative permittivity of the AlGaN barrier layer in an AlGaN/GaN heterostructure Schottky contacts

Ni Schottky contacts on AlGaN/GaN heterostructures were fabricated. Some samples were thermally treated in a furnace with N₂ ambience at 600 °C for different times (0.5 h, 4.5 h, 10.5 h, 18 h, 33 h, 48 h, and 72 h), the others were thermally treated for 0.5 h at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C). With the measured current—voltage (I—V) and capacitance—voltage (C—V) curves and by self-consistently solving Schrodinger's and Poisson's equations, we found that the relative permittivity of the AlGaN barrier layer was related to the piezoelectric and the spontaneous polarization of the AlGaN barrier layer. The relative permittivity was in proportion to the strain of the AlGaN barrier layer. The relative permittivity and the strain reduced with the increased thermal stress time until the AlGaN barrier totally relaxed (after 18 h at 600 °C in the current study), and then the relative permittivity was almost a constant with the increased thermal stress time. When the sample was treated at 800 °C for 0.5 h, the relative permittivity was less than the constant due to the huge diffusion of the contact metal atoms. Considering the relation between the relative permittivity of the AlGaN barrier layer and the converse piezoelectric effect, the conclusion can be made that a moderate thermal stress can restrain the converse piezoelectric effect and can improve the stability of AlGaN/GaN heterostructure devices.     

ICP-AES法测定金属硅中的Al、B、Ba、Ca、Cr、Cu、 Fe、Mg、Mn、Ni、Sr、Ti、V和Zn杂质元素

本文提供了一种测定金属硅中Ｂ,Ｆｅ,Ａｌ,Ｃａ,Ｍｎ等１４个杂质元素的ＩＣＰ－ＡＥＳ方法,在样品处理过程中,加入适量体积的甘露醇能够抑制Ｂ的挥发。用本方法测定了一个国家地球化学标准样（ＧＳＲ－４）,结果令人满意。     

发射光谱法测定高纯银中微量金、铂、钯、铑、铱、锑、铅、铋、铁、铜、镍、铬、铝和锌

本文研究了贵金属标准溶液除氯离子的有关问题，解决了高纯硝酸银中贵金属等杂质元素的标样配制，以硝酸银直接压样于普通电极中直流电弧激发，可测定９９．０～９９．９９％的高纯银，该方法简便、快速、准确。     

纯硒中杂质元素的ICP-AES测定

电感耦合等离子体-原子发射光谱同时测定纯硒中的碲、铅、铋、锑、铜、铁、镍、铝、锡、砷和硼12种元素的含量,优化出各元素的分析波长和分析条件;用基体匹配补偿基体效应,方法简单,快速可靠,样品回收率为94%-107%.     

ICP—AES法直接测定锡锭中的As,A1,Bi,Cd,Cu,Fe,Pb,Se,Sb,Zn

以电荷耦合器件为检测器的全谱直读等离子体光谱仪直接测定锡锭中Ａｓ、Ａ１、Ｂｉ、Ｃｄ、Ｃｕ、Ｆｅｄ、Ｐｂ、Ｓｅ、Ｓｂ、Ｚｎ十种杂质元素的含量。该方法简便、快速且具有比化学法更低的检出限,加标回收试验结果不明,回收率为９２％－１０５％,ＲＳＤ均小于１．５％。     

电感耦合等离子体原子发射光谱法测定高纯铼酸铵中Ca、Cd、Mn、Fe、Mg、Al、Cu、Co、Mo、Pb、Sn和Ni

本文介绍了电感耦合等离子体发射光谱法（ICP－AES）测定高纯铼酸铵中12个杂质元素的方法。采用挥发健康基体，探讨了高铼酸铵基体的干扰及其消除办法。ICP－AES测定结果的准确度和精密度均能满足分析要求。     

ICP—AES法测定铁矿中铝,钙,镁,锰,钴,铜,钠和钾

本文研究了ICP-AES法测定铁矿中铝,钙、镁、锰、钴、铜、钠和钾的方法。对仪器工作参数,共存元素的光谱干扰和基体效应干扰进行了探讨。采用向标准系列中加入铁基空白溶液建立工作曲线,试样经酸处理后即可直接测定。本方法获得了良好的回收率(95～103%)和变异系数(0.5～1.3%,n=11),同原子吸收法进行比对试验,结果一致。     

Surface energies of the solid solutions between Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W

The surface energy for different surface orientations of the solid solutions as a function of concentration formed by Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W is computed and analyzed using the BFS method for alloys. Similarities and differences among the different binary alloys are examined in terms of strain and chemical effects.     

ICP-AES法直接测定锡锭中的As、Al、Bi、Cd、Cu、Fe、Pb、Se、Sb、Zn

以电荷耦合器件为检测器的全谱直读等离子体光谱仪直接测定锡锭中As、Al、Bi、Cd、Cu、Fe、Pb、Se、Sb、Zn十种杂质元素的含量.该方法简便、快速且具有比化学法更低的检出限,加标回收试验结果表明,回收率为92%-105%,RSD均小于1.5%.     

X射线荧光光谱法测定不锈钢中的组分

用X射线荧光光谱法测定了不锈钢中Si、Mn、P、Cu、Ti、W、Mo、V、Ni、Cr、Nb等11种元素的含量。对磨样条件、准确度和精密度进行了实验,实验表明本方法与化学法所测结果相符。