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排序方式: 共有314条查询结果,搜索用时 601 毫秒
1.
2.
A. Wajid C. Gogol C. Hurd M. Hetzel A. Spina R. Lum M. McDonald R. J. Capik 《Journal of Crystal Growth》1997,170(1-4):237-241
We describe a continuous wave resonant acoustic sensor that has been optimized as a very sensitive in-line monitor for measuring the composition of precursor gases used in MOCVD processes. The precursor/carrier gas mixtures flow through a compact stainless steel acoustic chamber that is isolated from the acoustic transducers by a set of metallic diaphragms. The sensor has been successfully operated at supply line pressures from atmosphere down to 50 Torr with gas flow rates of up to 1600 sccm. The accuracy of the speed of sound measurement for hydrogen gas is better than 0.005%, even in a high noise and low pressure environment. Hydrogen, as well as nitrogen or argon carrier gases, are accommodated within the instrument's 1–5 kHz working frequency range. The instrument's sensitivity and stability are demonstrated with the laboratory data. Measurements of the dynamic response characteristics of the metalorganic bubbler lines at low pressure are also be presented. Application of the cell is general, encompassing any of the metalorganic and hydride materials typically used in MOCVD processes. 相似文献
3.
Let R be a ring and d : R → R a derivation of R. In the present paper we investigate commutativity of R satisfying any one of the properties (i)d([x,y]) = [x,y], (ii)d(x o y) = xoy, (iii)d(x) o d(y) = 0, or (iv)d(x) o d(y) = x o y, for all x, y in some apropriate subset of R. 相似文献
4.
Imtiaz Ahmad M. Arsala Khan M. Shakirullah M. Ishaq Yousaf Iqbal Saeed ur Rehman 《中国化学会会志》2004,51(4):729-734
Influence of pretreatments, i.e., demineralization and pre‐soaking in some solvents on the yields of liquefied products obtained from hydro‐depolymerization of Pakistani coal in a pool of hydrogen has been discussed. Results of hydrogenation experiments demonstrated that demineralizing the coal sample prior to liquefaction caused the yields to decrease compared with the virgin coal samples. The contribution of mineral matter of coal has been evaluated by comparing the yields of liquid products of virgin and leached samples. Increase in the yields obtained from the hydrogenation experiments of swollen coal samples was not satisfactorily significant. 相似文献
5.
H.?Hussain H.?U.?Rehman Z.?AhmadEmail author 《Journal of Sol-Gel Science and Technology》2005,36(3):239-248
Nano-composites from aramid-silica system have been prepared via sol-gel process. Poly (phenyleneterephthalamide) copolymer
chains were prepared by reacting a mixture of p- and m-phenylenediamines with terephthaloyl chloride in dimethylacetamide used as solvent. The sol-gel process in the polymer
matrix was carried out through hydrolysis and condensation of a mixture of tetraethoxysilane and (3-glycidoxypropyl) trimethoxysilane.
The latter was used to develop linkage, on one hand with silica network structure using alkoxy groups and on the other hand
with aramid chains at its secondary amine groups through glycidal groups of silane. Mutual interaction between the two disparate
phases aramid and silica network was thus created. Thin films of the composites containing different proportions of silica
ranging from 5.0 to 25.0-wt% were cast by the solvent elution technique. The α-relaxation temperature associated with the
glass transition was measured by the dynamic mechanical thermal analysis. The results showed an increase in the glass transition
temperature from 328°C for the pure aramid to 352°C for the hybrid materials containing 25-wt% silica, an indicative of the
increased interfacial interaction between the two phases. Films having relatively low silica content were flexible and transparent,
but those with high silica content were opaque and brittle. These films were tested for their tensile strength, modulus and
toughness. The mechanical strength of the composites as compared to the pure aramid increased initially but with further addition
of silica the strength decreased. The initial increase can be explained due to increased interfacial interaction between the
two phases, however agglomeration of silica particles was responsible for decreasing strength at higher silica contents. 相似文献
6.
Darr JA Guo ZX Raman V Bououdina M Rehman IU 《Chemical communications (Cambridge, England)》2004,(6):696-697
For the first time, the MOCVD technique has been used to deposit carbonated hydroxyapatite onto Ti6AL4V substrates using volatile monomeric (liquid) complexes [Ca(beta-diketonate)(2)(L)] and P(OEt)(3). 相似文献
7.
Summary The paper describes tests for liquid chromatographs to assess the autosampler and pump flow rate precision; suitability of
the instrument for normal phase chromatography; UV detector performance; and external band broadening characteristics. Tests
for mixing and proportioning characteristics of solvent pumps and performance of diode array detectors are also considered.
These tests are designed to evaluate the performance of both newly released liquid chromatography equipment and equipment
already in operation. Data from evaluations carried out by instrument manufacturer’s and suppliers is reported and discussed.
This data offers specifications to a common format for initial selection of instruments prior to purchase. 相似文献
8.
Habib-ur- Rehman Akbar Ali Jamil Anwar Wasim Yawar 《Journal of Radioanalytical and Nuclear Chemistry》2006,267(2):421-425
Summary The synergistic mixture comprising picrolonic acid (HPA) and benzo-15-crown-5 (B15C5) in chloroform has been used for the
extraction of Ce(III), Eu(III) and Tm(III) as representatives of lanthanide(III) ions from pH 1-2 solutions having ionic strength
of 0.1 mol. dm-3(K+/H+, Cl-). The composition of the extracted species has been determined as M(PA)3. nB15C5 where M is Ce, Eu and Tm and n=1 or 2. The influence of various anions and cations on the extraction of these ions has also been studied and only oxalate,
cyanide and tartrate have some deleterious effect. The extraction equilibrium constants have been evaluated and discussed. 相似文献
9.
Jie Feng Hongyang Zhao Wajid Ali Dandan Yin Xinyang Li Nawab Ali Khan Prof. Shujiang Ding 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(71):17818-17823
Coordination polymers are promising cathode materials for rechargeable alkaline batteries. Therefore, the precise modulation of these cathodes by chemical structure and in-depth structure transform study is necessary. Here, two model coordination polymer battery cathodes were designed to demonstrate the dynamic structure–performance relationship. We studied the electrochemical performance of two kinds of nickel-based coordination polymer, comprising a planar 2D cyanide-bridged network and a 3D cyanide-bridged network pillared by pyrazine molecules. The 2D coordination polymer showed serious voltage degradation with poor rate capability, whereas the 3D coordination polymer exhibited stable voltage output coupled with high rate at various current densities. The investigation revealed the underlining relationship of plateau voltage degradation and hydrolysis process of electrodes. It was revealed that the pyrazine pillar molecules in the 3D coordination polymer could suppress the hydrolysis and lead to the in situ formation of partially hydrolyzed structure with excellent electrochemical kinetics; this exhibited obvious smaller peak separation (27 mV compared with 149 mV) and hence an almost twofold increase in capacity retention (31.9 to 50.0 %) and energy density retention (18.2 to 35.9 %) at 10 A g−1. 相似文献
10.
Khalid Mujasam Batoo Khalid Mehmood Ur Rehman 《Chinese Journal of Physics (Taipei)》2018,56(1):108-116
A series of Sm-CoMn substituted hexagonal ferrites with chemical composition of Sr0.85-xCa0.15SmxFe12-y(Co0.5Mn0.5)yO19 (0.00?≤?x?≤?0.60, (0.00?≤?y?≤?0.50) were synthesized by the solid-state reaction method. Microstructure and magnetic properties of the hexaferrites have been investigated by the X-ray diffraction, field emission scanning electron microscopy and a permanent magnetic measuring system. A single magnetoplumbite phase is exhibited in the hexaferrites with the substitutiom of Sm (0.00?≤?x?≤?0.12) and CoMn (0.00?≤?y?≤?0.10) contents. For the hexaferrites containing Sm (x?≥?0.24) and CoMn (y?≥?0.20), impurity phases are observed in the structure. The FESEM micrographs exhibit that the hexaferrites with different Sm-CoMn contents have formed hexagonal structures and the grain size of the hexaferrites remains unchanged with increasing Sm-CoMn content. The remanence (Br), Hk/Hcj ratios, and maximum energy product [(BH)max] decrease with increasing Sm-CoMn content (0.00?≤?x?≤?0.60, (0.00?≤?y?≤?0.50). Instrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) increase with increasing Sm-CoMn content (0.00?≤?x?≤?0.12, 0.00?≤?y?≤?0.10), and then decrease with increasing Sm-CoMn content (0.12?≤?x?≤?0.36, 0.10?≤?y?≤?0.30), while for the hexaferrites with Sm (x?≥?0.36) and CoMn (y?≥?0.30), with increasing Sm-CoMn content, Hcj increases and Hcb decreases. 相似文献