共查询到20条相似文献,搜索用时 15 毫秒
1.
The amorphous phase obtained by rapid quenching with an hammer-anvil device of solar furnace melted binary mixture (1?x)Al2O3-xNd2O3 was investigated by thermal analysis and optical methods. By this way the domain of this amorphous phase obtention is determined. It is concluded that the amorphous phase is indeed a glass exhibiting no short range order which recristallizes circa 900°C in the two equilibrium phases βAl2O3 and NdAlO3. 相似文献
2.
Electrical conductivity and Seebeck coefficient of semiconducting EuB6 and YbB6 have been investigated and compared. The results are discussed in terms of a band model in which the conduction band is the 5d or 6s band of the rare-earth sublattice. 相似文献
3.
The hematite precipitation from zinc or cobalt-substituted defective spinels of type has been investigated using electrical conductivity and infrared spectrometry. The experimental data show that the temperature and kinetic of hematite precipitation depend of substitution extent x and might be closely associated with the cation vacancy in the spinel lattice. Stabilization of spinel solid solution by the cation is more pronounced for zinc than for cobalt and the effect of the cation is interpreted in terms of cation distribution in the spinel lattice. 相似文献
4.
M. Pluchery 《Materials Research Bulletin》1974,9(3):251-264
An X-ray diffraction technique for measuring the anisotropy factors of pyrocarbon coatings on fuel particles for high temperature reactors has been developed. The measurements yield directly absolute values of BAF averaged over about 100 particles, with an accuracy of ± 0.01. A modified procedure for measuring a single irradiated particle is considered. BAF-values obtained from discs and from particles coated in the same run do not exhibit any simple correlation. 相似文献
5.
The incorporation of phosphorus impurities from phosphoric acid baths into the dielectric films formed on aluminium and niobium by anodic polarisation have been studied by X-ray fluorescence analysis. Results are discussed in relation to the metallic substrate and electrochemical parameters such as acid concentration, apparent current density and limiting voltage of film formation. 相似文献
6.
Yvonne Repelin Elisabeth Husson Nguyen Quy Dao Henry Brusset 《Materials Research Bulletin》1980,15(7):985-993
The structural characteristics from X ray diffraction powder patterns and indexed according to the Pnma space group are given for SrTa2O6 isomorphous with SrNb2O6 and for a modification of BaTa2O6 isomorphous with CaTa2O6. Cell parameters are refined for each compound. The force field of different niobates and tantalates of “1×2 block” type structure calculated from a vibrational analysis is then compared and the relative stability of the two modifications of BaTa2O6 is shown. 相似文献
7.
The preparation of a new series of heptavalent rhenium compounds of Ln3ReO8 type (Ln = rare earths) is described. The crystals are orthorombic for Ln = La (space groups Ccmm, Ccm21 or Cc2m) and Ln = Pr, …, Gd (space group B2212), face centered cubic of fluorite type for Ln = Tb, …, Lu and Y. 相似文献
8.
《Materials Research Bulletin》1987,22(3):309-321
Precise X-ray powder diffraction investigations on pentasil type zeolites having respectively the H1.4B1.36Al0.02Si94.6O192 and H3.2B3.2Al0.02Si92.8O192 compositions reveal that the visual modifications observed on the step-scan profiles can be interpreted by localizing the centroid of the p-xylene molecule on the mirror plane of the 4c site in the Pnma space-group. Among the three possible orientations of the p-xylene molecule, the best fit is obtained for the solution where the line joining the methyl groups is parallel to the straight channel. Several trial and error calculations show that the organic molecule might present a statistical disorder with two simultaneous orientations in the channels. 相似文献
9.
The infrared study of water adsorbed on vanadium oxide xerogel (V2O5 1,6 H2O; V2O5 0,5 H2O) suggests two models for the structure of adsorbed water molecules. Water molecules of V2O5 1,6 H2O are involved in hydrogen bonds with the V = O groups. This arrangement would give an interlamellar spacing of 1,155 nm, as is found by X - ray studies. In the case of V2O5 0,5 H2O water molecules are not involved in hydrogen bonds and are this localized in the holes of the structure of vanadium oxide units. 相似文献
10.
We have tried to correlate the flat band potential of a semi-conductor with the electronegativity scales. From this correlation the value of the flat band potential for new compounds could be deduced. 相似文献
11.
The oxidation of Fe-20Cr-xAl (x=2, 4, 6) and Fe-20Cr-6Al-0.025 Ce alloys was studied in pure oxygen (1 bar), the temperature ranging between 800 and 1100°C. The parabolic law is obeyed when alloys containing 4 or 6 % Al are oxidised. An α-Al2O3 scale is formed. The oxidation rate does not depend on the composition. The reaction is more complex with the Fe-20Cr-2Al alloy. An iron and chromium oxide layer is formed at the beginning. Alumina precipitates in the metal. After a few hours a continuous α-Al2O3 barrier is formed. The lower oxidation rate (when compared with other alloys) is then justified and the reason why the parabolic law is not obeyed can be explained. 相似文献
12.
13.
The action of AsH3 on cupric ion solutions permits to precipitate the phases Cu5?xAs2 and β-Cu3?xAs, and also annother phase of composition near Cu3As. It is shown that the variation of the composition of these arsenides results from an oxydo-reduction reaction, dependent on the pH of the solution, with trivalent arsenic as second member of the couple. 相似文献
14.
B. Gillot 《Materials Chemistry and Physics》1984,10(4):375-384
The order-disorder phenomenon in defect γ-spinels of type and with M3+ = A13+, Cr3+ and M2+ = Zn2+, Co2+, Mn2+ obtained from ferrous spinels was investigated using IR spectrometry. These compounds possess a vacancy ordering on octahedral sites for substitution extents of less than 0.30 and no ordering has been observed for substitution extent > 0.40. The ordering process is also influenced by the nature and position of the trivalent or divalent cation, particle size, heating temperature and oxidation time. 相似文献
15.
Marcus Vlasse Michel Saux Patrick Echegut Gérard Villeneuve 《Materials Research Bulletin》1979,14(6):807-812
The structure and especially ordering between oxygen and fluorine has been determined by X-ray diffraction and NMR. ScOF has the baddeleyite type structure, where scandium is linked to three fluorines and to four oxygens. The cationic coordination of fluorine and oxygen is respectively triangular and tetrahedral. An ordered anionic distribution has been determined without any ambiguity by refining the structure for the various oxygen-fluorine configuration possibilities and by comparing calculated and observed second moments. 相似文献
16.
Inventory of a family of mixed chromium-erbiumsulfides (belonging to orthorhombic or monoclinic systems). Two of three parameters keep constant values, only the third (b) changes. The erbium atoms occupy octahedral regular and prismatic seven-coordinated sites. Chromium atoms are at the center of octahedral sites sometimes deformed by Jahn-Teller effect. We show how these structures are built from same basal pattern. An agreement between geometric pattern and chemical formula is laid down, it allows to confirm value of b parameter. 相似文献
17.
We have study the segregation coefficient k of selenium in gallium antimonide for slightly and heavily doped single crystals. We show that k is a function only of the growing rate. We compare there results to tellurium ones. We deduce the value of k when v is zero: this value is ko = 0,013. We show also that the variation of the number of free carriers is linear with Nd the number of donors, in n type as well as p type. 相似文献
18.
Chemical durability of glasses has been investigated in atmospheric moisture conditions. Corrosion of the melt by the vapor contaminates all the vitreous bulk. The corrosion of OH free glass until Tg is only a surface phenomenon depending on a diffusion process. 相似文献
19.
The kinetics of finely divided, (Fe2+Fe3+2?xAl3+x)O4 type (0 ? x ? 2), substitution magnetites oxidation into metastable phase γ(Fe3+1?yAl3+y)2O3 (x = 3y) has been accounted for by means of the law of diffusion, under variable working conditions, of the cationic vacancies generated at solid-gas interface with a diffusion coefficient that decreases when the stoichiometric difference is high. The crystallites size and the trivalent substituant percentage increases, in both cases, slow down the reaction rate. 相似文献
20.
Conditions for comparison between experimental data and the theoretical results obtained from Amelio's analytical model of secondary electron emission are defined. We show that the quantity numerically comparable is the yield δ0 due to the contribution to secondary electron formation by the primary electrons during their penetration into the target. The results show that the model presented leads to a choice of the mean free path which is unrealistic and inconsistent with the theory in terms of the Boltzmann transport equation. 相似文献