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161.
The kinetic curves at infinite temperature for the solid-state reactions of the interface shrinkage type were drawn theoretically by taking account the particle size distribution in the sample mixture. The CRTA curves for the reactions with the particle size distribution can be drawn by utilizing the universal kinetic curves at infinite temperature. The proper kinetic treatment for the CRTA curves with the particle size distribution is discussed in connection with the property of the kinetic equation with respect to the particle size distribution. The present kinetic consideration is taken as a simulation for the reactions with a certain distribution in among the reactant particles, produced preferably by the mass and heat transfer phenomena during the thermoanalytical measurements. The merit of the rate jump method by a single cyclic CRTA curve is also discussed on the basis of the present results. 相似文献
162.
SiO2/α-FeOOH和SiO2/γ-Fe2O3微粒的界面研究 总被引:1,自引:0,他引:1
α-FeOOH微粒由于其表面高活性,在转变成γ-Fe2O3的热处理过程中容易烧结,一旦这种烧结现象发生,得到的γ-Fe2O3磁粉磁性能大大下降[1].为了克服这一困难,目前采用在α-FeOOH微粒表面包敷有机物[2]和无机物[3]来隔离颗粒,阻止其聚集.其中SiO2表面包敷处理是最令人感兴趣的研究课题之一[4,5].SiO2是一种难烙性的非磁性材料,它包敷在α-FeOOH微粒表面外,不仅可提高α-FeOOH转变成γ-Fe2O3的热处理温度,有利于得到外形完好、晶格完整的γ-Fe2O3磁粉,而且由包效层与内核之间的界面相互作用引起的表面各向异性常… 相似文献
163.
本文应用x-射线衍射(XRD)、X-射线光电子能谱(XPS)、俄歇电子能谱(AES)、扫描电子显微技术(SEM)研究了钼酸铵在石墨炉内石墨探针表面上的原子化机理。实验结果表明,在温度<1350K时,钼酸铵经历MoO_3和Mo_4O_(11)中间产物转变为MoO_2(s)。在更高温度下,MoO_2(s)首先还原为Mo_2C,而后进一步转变为MoC(s)。MoC再分解为Mo(s)。钼的原子化起源于Mo的升华。 相似文献
164.
165.
Hoebbel Dagobert Reinert Thomas Schmidt Helmut Arpac Ertugrul 《Journal of Sol-Gel Science and Technology》1997,10(2):115-126
The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated -diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and -ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and 13 C NMR spectroscopy and were found to be L:M 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H2O : OR) = 0.5–2.0 decreases with increasing H
166.
The effect of a weak convective heat transfer on the thermocapillary interaction of two bubbles with an arbitrary orientation relative to an externally imposed temperature gradient is examined. Asymptotic analysis of the case of large separation distances, Z, suggests that the corrections to the bubbles' velocities are of
(Pe/Z2), rather than
(Pe2) previously found for an isolated bubble. Equal-sized bubbles are known to move with the same velocities, as if they were isolated, when heat conduction is the only transport mechanism. However, the convective transport results in a relative motion of the bubbles. The tendency of equal bubbles to line up in a plane perpendicular to the applied thermal gradient is shown analytically in the weakly nonlinear limit of small Pe numbers, and an interesting interaction behavior in the case of unequal bubbles is discussed. 相似文献
167.
A supported liquid and a poly(vinyl chloride) (PVC)-based membrane selective for dodecylsulfate (DS−) ion are described. The active element is a membrane containing a dissolved ion association complex of DS− with cetylpyridinium (CP+) cation. The supported liquid membrane electrode (acetophenone as solvent) showed a Nernstian response towards the DS− anion over the concentration range of sodium dodecylsulfate (SDS) from 8.3×10−3 to 1.0×10−6 mol dm−3 at 25 °C. The proposed electrode also showed a super-Nernstian potential response (108±2 mV decade−1) at low concentrations (1.0×10−9 to 1.0×10−6 mol dm−3). Moreover, this electrode showed good selectivity and precision (R.S.D.?2.0%), and was usable within the pH range 4.0-6.8. The proposed electrode revealed a lower limit of detection of 6.3×10−7 mol dm−3 and improved selectivity in comparison with the some previously reported DS− ion selective electrodes. The isothermal temperature coefficient of this electrode amounted to −0.001 V °C−1. The liquid membrane electrode may find application in the direct determination of SDS by the standard addition method at pH 5.0, and in the physicochemical studies of surfactant solutions. 相似文献
168.
Graphite arc emission spectrometry has become possible as a result of the invention of novel types of optical spectrometers
with Echelle-optics and semiconductor array detectors, and by the application of electronically controlled, high current arc
generators. An optimization of the excitation parameters to boron carbide analysis is reported here, measuring background
corrected line intensities that were integrated for the time of total evaporation of 5 mg boron carbide sample with or without
added chemical modifiers. The following set of experimental conditions were compared with respect of analytical sensitivity
and precision: (A) no modifier, Ar + O2 (20%), 16 A; (B) sample + graphite powder (1 + 1), Ar + O2 (20%), 16 A; (C) sample + CaF2 (1 + 1), Ar, 25 A; (D) sample + CaF2 + graphite powder (1 + 1 + 1), Ar, 25 A. The graphite powder modifier resulted in improved precision in general, and the
CaF2 was effective as a plasma ionization buffer and fluorinating agent. The best compromise was found under conditions B, when
oxygen was present in the discharge atmosphere. This is likely due to the stepwise conversion of the boron carbide matrix
to the more volatile boron oxide. Under conditions B, detection limits in the ranges of 0.3–9 μg g−1 for Al, Ca, Cr, Cu, Fe, Mg, Mn and Si and that of 18–38 μg g−1 for Ti, W, and Zr were attained. Average RSDs of 10.2 and 9.7% were found, respectively, without and with internal referencing
to boron. 相似文献
169.
The effects of variant counterions with ionic strength of 0.05, 0.10, 0.20 and 0.25 mol·kg^-1 on the stability and particle size of silica sols have been studied using the traditional methods of Ubbelohde viscosity measurement, TEM and titration respectively, finding that the stability and particle size of the silica sols are all concerned with the acidic, positively electric properties and the sizes of the counterions, as well as the attraction between the counterions and surface silicon hydroxyl groups of the silica sols. The small positively charged counterions lead to the decrease in particle sizes, making the silica sol the most stable. But the larger weakly acidic counterions can restrict the particle sizes of the silica sols and easily make the sols coagulate. It was also found that there existed a linear relationship between log r and log η, which has not ever been reported. The effect of temperature on the stability and particle sizes was also discussed. 相似文献
170.
Oi-lian Song Guang-zhao Zhang Chi Wu 《高分子科学》2007,(5):441-445
Using a core(142 nm)made of linear polystyrene(PS)chains as a seed,we further polymerized a thin layer of cross-linked PS shell(7 nm)on it in water to form a core-shell particle.Such a particle swells in toluene,which enables linear PS chains inside the core to gradually diffuse out through the porous shell.Using a combination of static and dynamic laser light scattering,we examined the chain diffusion process by following the change of the scattering intensity(i.e.the average molar mass of the particles).For the first time,we have revealed that the diffusion exhibits three stages.In the first stage,the chain diffusion through the shell is even faster than their translational diffusion in a dilute solution.The three stages respectively correspond to the change of the solution in the core from concentrated to semidilute and then from semidilute to dilute. 相似文献