炭纳米管的提纯重铬酸钾氧化法

介绍了一种新的、不同于常用的气相氧化法的炭纳米管纯化方法。采用 Ｋ２ Ｃｒ２ Ｏ７ 作为氧化剂将炭纳米颗粒氧化,并从热力学和动力学的角度对反应的可行性进行了分析,考察了硫酸用量、硫酸浓度、反应时间等因素反应的影响,确定了最佳工艺条件：硫酸浓度１∶１ （ Ｖ） Ｈ２ Ｓ Ｏ４∶ Ｋ２ Ｃｒ２ Ｏ７＝ ６∶１（ｍ ｏｌ）、反应时间２ ｈ、反应温度１４０℃,同时对纯化机理进行了解释。     

炭纳米管的提纯-重铬酸钾氧化法

介绍了一种新的、不同于常用的气相氧化法的炭纳米管纯化方法。采用Ｋ２Ｃｒ２Ｏ７作为氧化剂将炭纳米颗粒氧化,并从热力学和动力学的角度对反应的可行性进行了分析,考察了硫酸用量、硫酸浓度、反应时间等因素反应的影响,确定了最佳工艺条件：硫酸浓度１：１（Ｖ）Ｈ２ＳＯ４：Ｋ２Ｃｒ２Ｏ＝６：１（ｍｏｌ）、反应时间２ｈ、反应温度１４０℃,同时对纯化机理进行了解释。     

Nucleation studies in supersaturated aqueous solutions of KH2PO4 doped with KBr and K2Cr2O7

Induction periods were measured for various supersaturated aqueous solutions of potassium dihydrogen orthophosphate doped separately with potassium bromide and potassium dichromate by the direct vision method. Various critical nucleation parameters were calculated based on the classical theory for homogeneous crystal nucleation and the results are reported and discussed. The critical nucleation parameters increased with increase in doping concentration for both the dopants considered.     

A new etchant system,K2Cr2O7-H2SO4-HCl,for GaAs and InP

A new K₂Cr₂O₇-H₂SO₄-HCl system has been developed that is particularly suitable for use in etching solutions of GaAs and InP. This system provides high quality etched surfaces without any undesirable roughness or etch pits. It has been found that the etching rate can be controlled by changing the etchant component proportions. This is especially the case with HCl. This leads to no change of surface quality. Vertical walls, and mesa-shaped structures have been formed on etching profiles of (001) GaAs by stripes parallel to the [110], and [¯110] directions, respectively. The mesa-shaped profiles have been formed for (001) InP in both the [110] and [¯110] directions. The solution does not erode photoresist masks and is thereby attractive for a variety of device applications.     

Creep of Cr2O3 and yttrium doped Cr2O3

Abstract

Compressive creep tests of pure and Y doped Cr₂O₃ from 1217 to 1417°C have shown that the presence of Y substantially increases diffusional flow rates. It is suggested that this increase in deformation rate may account, in part, for the empirical evidence that improved adherence to the underlying metal is provided by Y containing scales compared with pure scales.

MST/819     

Hydrothermal Synthesis of K2ZrSi6O15 , K2ZrSi3O9 , K2ZrSi2O7, and ZrSiO4 in the System KOH–ZrO2–SiO2–H2O

The phase relations in the KOH–ZrSiO₄–H₂O, KOH–ZrO₂(cr)–SiO₂–H₂O, and KOH–ZrO₂(nanocr)–SiO₂–H₂O systems were studied at 400°C, 0.1 GPa, and KOH concentrations from 2 to 46 wt %. The crystallization fields of K₂ZrSi₆O₁₅, K₂ZrSi₃O₉, K₂ZrSi₂O₇, and ZrSiO₄ were located. The potassium zirconosilicates have open-framework structures made up of corner-shared ZrO₆ octahedra and SiO₄ tetrahedra. The composition of the crystallizing silicates is shown to depend on the nature of the starting Zr- and Si-containing materials.     

Surface and catalytic properties of CuO/MgO system doped with K2O and Cr2O3

The effects of doping of CuO/MgO system with K₂O or Cr₂O₃ (1–6 wt.%) on its surface and catalytic properties were investigated. The analytical techniques employed were XRD, nitrogen adsorption at −196 °C and decomposition of H₂O₂ at 30–50 °C. The results revealed that K₂O-treatment of the system investigated, followed by calcinations at 400 °C resulted in the conversion of some of the surface copper oxide into potassium coprate K₃Cu₅O₄ phase whose diffraction lines disappeared upon heating at 500 °C. Chromium oxide-doping did not lead to the formation of any copper oxide-Cr₂O₃ compound(s) in the treated sarples calcined at 400 and 500 °C. Also, K₂O-doping conducted at 400 °C increased the degree of crystallinity and particle size of MgO phase and exerted opposite effects in the crystallinity and particle size of CuO phase. The doping process either with K₂O or Cr₂O₃ effected a measurable progressive decrease (42–53%) in the specific surface area of the investigated system subjected to heat treatment at 400 and 500 °C. However, the opposite effect was observed upon doping with 1 and 2 wt.% Cr₂O₃ followed by heating at 500 °C. The catalytic activity of the investigated system decreased by doping with K₂O. The addition of 6 wt.% effected a decrease of 78% and 68% in the value of the reaction rate constant per unit surface area for the catalytic reaction carried out at 30 °C (k_{30 °C}⁻) over the doped catalysts calcined at 400 and 500 °C, respectively. Cr₂O₃-doping on the other hand, much increased the catalytic activity of the treated samples and an increase of 106% and 80% in the value of k_{30 °C} was observed upon doping with 6 wt.% Cr₂O₃ for the solids calcined at 400 and 500 °C, respectively. The results were discussed in terms of creation of new in pairs and conversion of some active sites (surface CuO) into less active site (K₃Cu₅O₄).     

Excited state characteristics of the Li2B4O7 and KLiB4O7 glasses activated by Cr3+ ions

The excited state characteristics by means of the excited state absorption (ESA), optical gain and bleaching spectra have been measured for prototype glasses with Li₂B₄O₇ (LBO) and KLiB₄O₇ (KLBO) compositions activated by Cr³⁺ ions. The work addressed to search for novel attractive media for broadband lasers and amplifiers, is a completion of detailed spectroscopic evaluation described in earlier papers. One of the examined materials (KLBO), in accordance with optimistic comments given in previous work, reveals a very broad gain spectrum in the near IR, which itself is interesting in view of very few reports on glasses showing optical gain for Cr³⁺ ions in the low-field local environment. The ESA/gain/bleaching spectra, registered with equipment of improved sensitivity, have been reproduced by calculations, and detailed single configuration coordinate diagram, based on experimental data, has been created for interpretation.     

Real structure of Cd2Nb2O7 pyrochlore single crystals

X-ray topography and diffractometry are used to study the crystal structure of cadmium pyroniobate Cd₂Nb₂O₇ at room temperature. Structural quality parameters were determined for crystals grown with different degrees of impurity doping. The nature of the crystal lattice damage is analyzed as a function of the type and concentration of impurities. Pis’ma Zh. Tekh. Fiz. 25, 26–33 (July 26, 1999)     

Cr/Cr2O3多层膜的研究

用真空蒸镀及自然氧化方法在玻璃基底上制备纳米量级的4、5、6、7对层的Cr／Cr2O3多层膜。采用称重法测定薄膜的厚度；在常温和低温下使用三点法测定多层膜的电特性；用扫描电镜（SEM）观察薄膜的表面和截面的形貌及成分；用X射线衍射仪检测相结构。结果表明：制备的是纳米量级非晶态的Cr／Cr2O3多层膜，在常温和低温（77K）下均具有类似负阻的特性。     

SiO2-Al2O3-MgO-K2O-(F,Cr2O3)玻璃陶瓷的析晶

为了研究形核剂氟化物、氧化铬及其复合作用对SiO2-Al2O3-MgO-K2O系玻璃陶瓷形核和析晶的影响,采用高温熔融法制备了不同氟化物和氧化铬含量的基础玻璃,并对该基础玻璃进行了差热分析、显微分析和X射线衍射分析.结果表明:在所研究的玻璃体系中,氟化物或氧化铬的加入,都不同程度地削弱了玻璃体的结构,降低了玻璃的转变温度;当基础玻璃只含有氟化物时,玻璃在表面析出云母晶体,内部发生分相现象,而玻璃中仅含有氧化铬时,玻璃中发生整体析晶;没有氟化物的存在,不能析出云母晶体;当同时加入两种元素的物质后,对玻璃体析晶的影响不是简单的加合,复合的作用更为突出,进一步降低了玻璃的转变温度和析晶温度,整体均匀析出云母晶体.     

Synthesis and crystal structure of a uranyl bichromate, [CH6N3]2[(UO2)(CrO4)(Cr2O7)](H2O)

Crystals of the first uranyl bichromate, [CH₆N₃]₂[(UO₂)(CrO₄)(Cr₂O₇)](H₂O), were obtained by evaporation from aqueous solutions. The compound crystallizes in the triclinic system, space group $P\bar 1$ , a = 7.1829(17), b = 9.304(3), c = 14.884(4) Å, α = 102.43(2)°, β = 97.98(2)°, γ = 101.07(2)°, V = 936.3(5) ų, Z = 2. The structure was solved by direct methods and refined by the full-matrix least-squares method to R ₁ = 0.064 (wR ₂ = 0.138) for 2225 reflections with |F _hkl | ≥ 4σ(|F _hkl |). The structure is based on infinite [(UO₂)(CrO₄)(Cr₂O₇)]^2? chains where [UO₇]^8? pentagonal bipyramids are linked by tridentate [Cr(1)O₄]^2? groups and [Cr₂O₇]^2? groups; these chains run along x axis and are oriented parallel to $(0\bar 11)$ . Trigonal [CH₆N₃]⁺ cations and water molecules are arranged between the chains.     

YBa2Cu3O7 − x 240 K Phase Transition

YBa₂Cu₃O_{7 ? x} ceramic samples have been investigated simultaneously by the thermal expansion and the acoustic emission methods during thermocycling through 200–300 K into liquid nitrogen steam. No jumps in the dilatation curves but change in the slope of one has been found at 228 and 234 K on heating and cooling respectively. These points are accompanied by the acoustic emission signals, a small value testifying for oxygen atoms displacement into the crystal lattice. On the basis of these measured experimental data, a thermal expansion coefficient α and a specific capacity c _m have been calculated. By this c _m value an oxygen atom activation energy ΔE = 0.15 eV has been calculated. It is shown that an isostructural oxygen-displacement second-order phase transition takes place between certain orthorhombic phases in YBa₂Cu₃O_{7 ? x} near 240 K.     

Electronic structure of YBa2Cu3O7 and YBa2Cu3O6—charge-self-consistent band structure calculations

Charge self-consistent LCAO band structure (CSCBS) calculations are reported for orthorhombic YBa₂Cu₃O₇ and tetragonal YBa₂Cu₃O₆ assuming ordered vacancy models. The effective atomic charges are used to study the charge transfer. In YBa₂Cu(1)₁Cu(2)₂O₇, the two types of copper atoms have their energy bands almost overlapping with effective valency of each copper as 7/3 (or effective valency of each oxygen as approximately — 13/7), so that electron hopping can take place without any loss or gain of energy while in YBa₂Cu(1)₁Cu(2)₂O₆, Cu(1)₁ is monovalent and Cu(2)₂ are divalent with significant difference in their bands. Therefore, YBa₂Cu₃O₇ should conduct much better compared to YBa₂Cu₃O₆. This corroborates the experimental observations that YBa₂Cu₃O₇ is a (super)conductor while YBa₂Cu₃O₆ is not. The calculated effective charges and DOS support the above view.     

紫外倍频晶体K2Al2B2O7的生长与性能

研究了溶液配比和降温速率对K2Al2B2O7(KABO)晶体生长的影响,发现NaF与KABO的适宜比例为2:1,晶体生长的合适降温速率为(0.1~5)℃/d,NaF为合适助熔剂.籽晶的取向也影响晶体的质量,[110]方向是KABO晶体生长的最佳生长方向;采用顶部籽晶技术,以NaF为助熔剂可生长出尺寸为50 mm×20 mm×17mm、重30 g的高光学质量KABO透明单晶.晶体对波长2500nm以上的光表现出各向异性吸收,紫外截止边为180nm.用V型棱镜法测出的KABO晶体折射率拟合出了Sellmeier方程,计算了SHG相位匹配范围,一类相位匹配最短倍频波长为225.5 nm.KABO晶体的266 nm SHG相位匹配角为58.1°.长度为3.6 mm的晶体Nd:YAG激光器四倍频输出能量转换效率为12.3％.     

ReP2O7: A new isomorph of ZrP2O7

Synthesis of ReP₂O₇, a new compound isomorphic with ZrP₂O₇, is reported along with unsuccessful attempts to synthesize MnP₂O₇. The lattice parameter of ReP₂O₇ was found to be $\text{a}{}_0\text{= 7.94 ± 0.02}\text{A}\text{?}$, and an indication of a “triple cell” superlattice sismilar to that of ZrP₂O₇ was found.     

Structure and Thermodynamic Properties of the DyGaTi2O7 and EuGaTi2O7 Titanates

Inorganic Materials - The DyGaTi2O7 and EuGaTi2O7 titanates have been prepared by solid-state reactions in a starting mixture of Dy2O3 (Eu2O3), Ga2O3, and TiO2 via firing in air at temperatures of...