Isothermal Sections in the (Fe,Ni)-Rich Part of the Fe-Ni-Al Phase Diagram

The ternary Fe-Ni-Al phase diagram below 50 at.% Al was investigated by a combination of powder x-ray diffraction (XRD) and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the respective equilibrium phases were determined within the partial isothermal sections at 900, 1000, 1100 and 1200 °C.     

Aging and environmental effects on YBa2Cu3O6.95 superconductor

The effect of aging and environmental degrading on a YBa₂Cu₃O_6.95 ceramic superconductor has been studied by x-ray diffraction, scanning electron microscopy, infrared spectroscopy, and electrical resistivity measurements. The superconductor prepared by solid state reaction was well characterized and then exposed to the normal laboratory environment for more than three years. The material showed substantial microstructural degradation with a small decrease in the transition temperature from normal to superconducting state (T _c). IR spectroscopy reveals the presence of water and carbonate. The damage in oxygen content can be restored by reannealing in oxygen for about six hours at 470 °C, but the restoration of exactly the same microstructural and electrical characteristics is not possible.     

Carboxymethylcellulose synthesis in organic media containing ethanol and/or acetone

A study of the carboxymethylation of wood pulp cellulose and cotton linters cellulose in different organic media, namely, ethanol, acetone, and ethanol-acetone mixtures, is performed. Previously, the ethanol-acetone 1 : 1 (w/w) mixture used as reaction medium was found to give a higher degree of substitution (DS) than the pure solvents separately. In the present work, the kinetic investigation of cellulose carboxymethylation was carried out in ethanol-acetone 3 : 7 (w/w) mixture, as well as in acetone as reaction media, and the same synergistic effect of the solvents mixture was observed. The data suggested a pseudo-first-order kinetic behavior satisfactorily described by the following equation: ln(1.11 − DS) = −kt. The two reaction steps observed are related to the transformations of less ordered regions with higher reaction rate and more ordered regions with smaller reaction rates, respectively. A possible explanation for this behaviour is given, taking into account the different structural changes of cellulose crystallinity and accessibility produced by ethanol-acetone 3 : 7 (w/w) mixture, ethanol, and acetone, as revealed by X-ray diffraction and calorimetry determinations. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 481–486, 1998     

Biased mutagenesis in the N-terminal region by degenerate oligonucleotide gene shuffling enhances secretory expression of barley alpha-amylase 2 in yeast

Recombinant barley alpha-amylase 1 (rAMY1) and 2 (rAMY2), despite 80% sequence identity, are produced in very different amounts of 1.1 and <0.05 mg/l, respectively, by Saccharomyces cerevisiae strain S150-2B. The low yield of AMY2 practically excludes mutational analysis of structure-function relationships and protein engineering. Since different secretion levels of AMY1/AMY2 chimeras were previously ascribed to the N-terminal sequence, AMY1 residues were combinatorially introduced at the 10 non-conserved positions in His14-Gln49 of AMY2 using degenerate oligonucleotide gene shuffling (DOGS) coupled with homologous recombination in S.cerevisiae strain INVSc1. Activity screening of a partial library of 843 clones selected six having a large halo size on starch plates. Three mutants, F21M/Q44H, A42P/A47S and A42P rAMY2, also gave higher activity than wild-type in liquid culture. Only A42P showed wild-type stability and enzymatic properties. The replacement is located to a beta-->alpha loop 2 that interacts with domain B (beta-->alpha loop 3) protruding from the catalytic (beta/alpha)(8)-barrel. Most remarkably Pichia pastoris strain GS115 secreted 60 mg/l A42P compared with 3 mg/l of wild-type rAMY2. The crystal structure of A42P rAMY2 was solved and found to differ marginally from the AMY2 structure, suggesting that the high A42P yield stems from stabilization of the mature and/or intermediate form owing to the introduced proline residue. Moreover, the G to C substitution for the A42P mutation might have a positive impact on protein translation.     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Activated carbon supported bimetallic CoMo carbides synthesized by carbothermal hydrogen reduction

A carbothermal hydrogen reduction method was employed for the preparation of activated carbon supported bimetallic carbide. The resultant samples were characterized by BET surface area measurement, X-ray diffraction, and temperature-programmed reduction-mass spectroscopy. The results showed that nanostructured β-Mo₂C can be formed on the activated carbon by carbothermal hydrogen reduction above 700 °C. The particle sizes of β-Mo₂C increase with increasing reaction temperatures and Mo loading. The bimetallic CoMo carbide can be synthesized by the carbothermal hydrogen reduction even around 600 °C. The bimetallic CoMo carbide is from carbothermal hydrogen reduction of CoMoO₄ precursor and is easily formed when the Co/Mo molar ratio is 1.0. Separation of the bimetallic CoMo carbide phase into Mo carbide and Co metal occurs when the temperature of the reduction is above 700 °C. The addition of a second metal such as Co and Ni, decreases the formation temperature of carbide because the second metal promotes formation of CHx species from reactive carbon atoms or groups on carbon material and hydrogen, which further carburizes oxide precursors.     

The complementary nature of x-ray photoelectron spectroscopy and angle-resolved x-ray diffraction Part I: Background and theory

X-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) are often used to analyze the surface of complex oxide materials. When XRD is used in an atypical angle resolved x-ray diffraction (ARXRD) mode, crystalline composition as a function of depth can be obtained. Similarly, when XPS is used in conjunction with argon depth profiling, composition as a function of depth can also be obtained. A review of the two techniques is included, comparing and contrasting their ability to obtain chemical information as a function of depth for heterogeneous oxide layers. The novel, simultaneous implementation of these two techniques is a unique combination of procedures that can provide substantial amounts of information about the composition of complex oxides.     

粉末X射线衍射法测定氢气还原的气相醛加氢催化剂

采用粉末X射线衍射鉴定氢气还原的气相醛加氢催化剂中晶体物相并应用Scherrer法定量测定铜的晶粒尺寸。其晶体物相鉴定结果为:石墨、氧化锌、铜。采用化学计量学峰形拟合的方法计算铜(111)晶面晶粒尺寸约为10.3 nm,测定数据能够满足气相醛加氢催化剂研发的要求。     

Structural properties and morphology of Zn(1 − x)CdxO solid solution grown on ZnO and C-plane sapphire substrate

Zn_(1 − x)Cd_xO solid solutions with a composition ranging from pure ZnO up to x = 0.062 have been grown on ZnO and c-plane sapphire substrates by using metal organic chemical vapor deposition. The optical transmission spectra were used to estimate the cadmium mole fraction of the solid solutions. The lattice deformation and morphology of these films were examined in detail using high resolution X-ray diffraction and atomic force microscopy as Cd incorporation and used substrate. Our study reveals significant lattice deformation from x ≥ 0.7%. The atomic force microscopy images show facetted grains for films grown on ZnO substrate but rather round for c-plane sapphire substrate. The grain shape is controlled by the presence of the ionic charges on the polar surface of ZnO which is disturbed by cadmium incorporation and also the employed substrate material.     

High-temperature resistivity and thermoelectric properties of coupled substituted Ca3Co2O6

Abstract

Polycrystalline samples of Ca_3?xNa_xCo_2?xMn_xO₆ (x=0.0–0.5) have been prepared by the sol-gel cum combustion method using sucrose in order to investigate the effects of the coupled substitution of Na and Mn on Ca and Co sites on the transport properties of Ca₃Co₂O₆(Co326). The products were characterized by Fourier transform infrared spectroscopy, powder x-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis and scanning electron microscopy. XRD patterns reveal the formation of single-phase products up to x=0.5. Coupled substitution increases the solubility of both Na and Mn on Ca and Co sites, respectively, in contrast to the limited solubility of Na and Mn (x=0.2) when separately substituted. TGA confirms the formation of the Ca₃Co₂O₆ phase at temperatures ～720 °C. The grain size of the parent and substituted products is in the range 150–250 nm. Electrical resistivity and Seebeck coefficient were measured in the temperature range 300–800 K. Resistivity shows semiconducting behavior for all the compositions, particularly in the low-temperature regime. The Seebeck coefficient increases with temperature throughout the measured temperature range for all compositions. The maximum Seebeck coefficient (200 μV K^?1) is observed for x=0.5 at 825 K, and this composition may be optimal for high-temperature thermoelectric applications.