排序方式: 共有59条查询结果,搜索用时 250 毫秒
51.
52.
The vaporization behavior of boron phosphate has been studied by using Knudsen effusion mass spectrometry. The vapor over BPO(4) consists of B(2)O(3), P(4)O(10), PO(2), BPO(4) (platinum cell) and B(2)O(3), PO, PO(2), BPO(3), BPO(4) (molybdenum cell). Standard enthalpies of formation and atomization (kJ/mol) were derived for BPO(4) (g) (-1000 +/- 15 and 2863 +/- 16) and for BPO(3) (g) (-731 +/- 15 and 2347 +/- 16), respectively. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
53.
54.
Microwave heating of ceramic composites 总被引:1,自引:0,他引:1
The microwave heating of a ceramic composite is modelled andanalysed. The composite consists of many small ceramic particlesembedded in a ceramic cement. The composite is assumed to bewell insulated, and each particle is assumed to be in imperfectthermal contact with the surrounding cement. Based on thesetwo assumptions an asymptotic theory exploiting the small Biotnumber and small non-dimensional contact conductance is developed.Our asymptotic theory yields a set of nonlinear partial differentialequations which govern the temperature in the composite. Theseare reduced to a set of coupled nonlinear ordinary differentialequations in which the surface area of each particle entersas a parameter. Recent experiments with such composites haveshown that the steady-state temperature of the composite isstrongly dependent upon the radii of the embedded particles.Our model captures this effect. In fact, our analysis showsthat the assumption of imperfect thermal contact between theparticles and the ceramic cement is essential for this trendto be established. 相似文献
55.
采用"grafting from"的方式在溶液聚合体系中将苯乙烯(St)接枝聚合在微米级硅胶表面,制备了接枝微粒PS/SiO2;使用新型氯甲基化试剂1,4-二氯甲氧基丁烷,对接枝的聚苯乙烯进行了氯甲基化反应,制得了接枝有氯甲基聚苯乙烯(CMPS)的接枝微粒CMPS/SiO2;使用叔胺试剂对CMPS大分子链上的苄氯基团实施了季铵化反应,最终制得了固载有季铵盐(Quaternary salt)的复合型功能微粒QPS/SiO2.用红外光谱(FTIR)与化学分析法对功能微粒QPS/SiO2的化学结构与组成进行了表征;研究了各种因素对CMPS/SiO2季铵化反应的影响规律;初步考察了QPS/SiO2对大肠杆菌的(E.coil)抗菌性能.研究结果表明,接枝微粒CMPS/SiO2的季铵化反应比较容易进行;溶剂性质、叔胺试剂的种类及温度对CMPS/SiO2的季铵化反应均有影响.使用CMPS的良溶剂和用位阻小的叔胺试剂,所得产物的季铵化度均较高.QPS/SiO2具有很强的抗菌活性.使用很小的剂量(10 g/L)、在很短的接触时间内(3 min)抗菌率即可达100%,是一种优良的水不溶抗菌材料;QPS/SiO2的季铵化度越高,其抗菌活性越高;使用碳氢链较长的三丁胺制备的QPS/SiO2,其抗菌性能明显优于使用三乙胺制备的QPS/SiO2. 相似文献
56.
Simple models of a reflection nebula in the form of a plane-parallel slab containing smooth spherical solid particles in submicron
size range have been considered. Single scattering has been assumed. The effect of varying the composition and size distribution
function of the grains have been brought out in the calculations using Mie theory of scattering. The analytical part of the
geometry of the problem has been treated quite rigorously and the resulting expression for nebular intensity has been presented
in a somewhat new form. In this paper, the case of the star behind the nebula has been examined.
A comparison of the theoretical results with the observations of the Merope nebula shows that the dirty ice grains with index
of refraction about 1·3–0·1i and size parametera
0 = 0·5μ give reasonable agreement with the colours. Simultaneously, the polarization in the visual and blue wavelength bands agree
approximately up to offset angle of 6 minutes of arc. The larger offset angles pose an intriguing problem. The general trends
of nebular colours and polarization with variation of real and imaginary parts of index of refraction and the size distribution
parameter have been tabulated to serve as a guide for further study of reflection nebulae with the star in the rear.
A part of this work was presented at the first scientific meeting of the Astronomical Society of India, held on 27 and 28
February 1974 at Hyderabad.
An erratum to this article is available at . 相似文献
57.
用本实验室合成的Ca0.80Zn0.20Te多晶料为原料,采用改进的布里奇曼法在镀碳和未镀碳的石英安瓿中生长出Ca0.80Zn0.20Te晶锭。使用X射线衍射仪对合成产物及晶锭进行了分析,生长晶体的X射线衍射峰尖锐,摇摆谱对称,表明晶锭的结晶性能较好;用IRPrestige-21红外光谱仪分析了晶体的红外透射光谱,测试结果表明安瓿镀碳后生长的晶体位错密度小,均匀性较好,电阻率优于未镀碳安瓿生长的晶体;晶体的蚀坑密度在10^3-10^4cm^-2之间,比未镀碳安瓿生长的晶体低1个数量级。 相似文献
58.
J. A. Anastasopoulos A. Soto Beobide L. Sygellou S. N. Yannopoulos G. A. Voyiatzis 《Journal of Raman spectroscopy : JRS》2014,45(6):424-430
Carbon nanotubes (CNTs) have attracted great attention for their potential use in many applications because of their intrinsic properties. The importance other than the impact of the application of CNT‐embedded membranes in the area of water technology development is immense. In this context, the identification and quantification of CNTs in aqueous resources during relevant water purification processes can be proven of high significance. Surface‐enhanced Raman scattering (SERS) potentially has the sensitivity required for trace analysis and has been previously used for CNT identification on solid substrates. A thorough study for the identification and quantification of small concentrations of multi‐walled CNTs (MWCNTs) in water suspensions via SERS has been performed. The functionalization of MWCNTs with pyridine groups seems to favor the surface enhancement of relevant Raman signal. This study constitutes the first step of a work in progress for the characterization of CNTs at quite low concentration range by SERS in any water suspension. It is based on an ex ante functionalization of the CNTs by pyridine, demonstrating the potential of the method. Our long‐term aim is its general application built, however, in an ex post relevant functionalization of the CNTs in any aqueous solution. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
59.
Kaliva M Gabriel C Raptopoulou CP Terzis A Voyiatzis G Zervou M Mateescu C Salifoglou A 《Inorganic chemistry》2011,50(22):11423-11436
Diverse vanadium biological activities entail complex interactions with physiological target ligands in aqueous media and constitute the crux of the undertaken investigation at the synthetic level. Facile aqueous redox reactions, as well as nonredox reactions, of V(III) and V(V) with physiological citric acid and hydrogen peroxide, under pH-specific conditions, led to the synthesis and isolation of a well-formed crystalline material upon the addition of ethanol as the precipitating solvent. Elemental analysis pointed to the molecular formulation (NH4)4[(VO2){VO(O2)}(C6H5O7)2]·1.5H2O (1). Complex 1 was further characterized by Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), Raman spectroscopy, cyclic voltammetry, and X-ray crystallography. The crystallographic structure of 1 reveals the presence of the first dinuclear V(V)-citrate complex with non-peroxo- and peroxo-containing V(V) ions, concurrently present within the basic VV2O2 core. The nonperoxo unit VO2+ and the peroxo unit VO(O2)+ are each coordinated to a triply deprotonated citrate ligand in a distinct coordination mode and coordination geometry around the V(V) ions. These units are similar to those in homodinuclear complexes bearing oxo or peroxo groups. The unique assembly of both units in the anion of 1 renders the latter as a potential intermediate in the peroxidation process, from [V2O4(C6H5O7)2]4– to [V2O2(O2)2(C6H6O7)2]2–. The transformation reactions of 1 establish its connection with several V(V) and V(IV) dinuclear species present in the aqueous distribution of the V(IV,V)-citrate systems. The shown position of 1 as an intermediate in the mechanism of H2O2 addition to dinuclear V(V)-citrate species portends its role in the complex aqueous distribution of species in the ternary V(V)-peroxo-citrate system and its potential reactivity in (bio)chemically relevant media. 相似文献