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The influence of temperature, pH, acid type, and surface area on the kinetics of the acid dissolution of natural and synthetic
willemites and natural hemimorphites has been investigated. Specific rate constants, based upon areas determined by krypton
adsorption measurements, were estimated from the experimental data obtained. For both willemite and hemimorphite, the rates
of dissolution in different acids are shown to be related to the relative strengths of zinc-acid anion complexes. The reactivity
of willemite toward acids increases with increasing replacement of zinc by manganese. Mixed chemical/diffusion control is
responsible for the observed rates of willemite dissolution under the conditions studied (HNO3, HCl, HClO4, H3PO4, H2SO4, pH 0.31 to 3.00,T 21 to 94 °C). Estimates of the relative contributions of chemical and diffusional resistances to the overall rate have been
made for the dissolution of manganese-free willemite in sulfuric acid solutions. The experimentally measured rates have been
demonstrated to be in reasonable agreement with predicted overall dissolution rates. Proposals are made regarding the nature
of the diffusion and chemical steps involved in the dissolution process. Hemimorphite was found to be considerably more reactive
than willemite and its dissolution is primarily diffusion controlled under the conditions studied (T 20 to 76 °C, pH 2 to 3.5).
Formerly a Postgraduate Research Student, Department of Metallurgy and Materials Science, Royal School of Mines, Imperial
College, London 相似文献
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(ZrO2)0.96(Y2O3)0.03(Al2O3)0.01陶瓷的制备及性能研究 总被引:1,自引:0,他引:1
采用化学共沉淀法制备(ZrO2)0.96(Y2O3)0.03(Al2O3)0.01的粉末, 在不同的升温速率、不同的烧结时间和不同的烧结温度等烧结工艺下制备出(ZrO2)0.96(Y2O3)0.03(Al2O3)0.01三相体系复合陶瓷. 经研究发现, 在升温速率和降温速率均为5 ℃·min^-1 的烧结制度下, 1550 ℃烧结时, 可以得到抗弯强度达998 MPa, 抗热震次数达33次, 相对密度达96%和电性能较好的烧结体. 相似文献
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Binding properties of bovine colostral anti-dinitrophenyl (dnp) immunoglobulins g2 (igg2) 总被引:1,自引:0,他引:1
The number of combining sites per mole of bovine colostral anti-DNP IgG2 was found to be 2 and the total affinity constant was 0.81 X 10(4) M-1. Unlike bovine colostral IgG1, the nonspecific binding of H3-epsilon-DNP-1-lysine by IgG2 as a function of increased concentrations, did not show a negative, cooperative slope. Spectral measurements made with anti-DNP IgG2 in the reference cell vs. anti-DNP IgG2 plus hapten in the experimental cell revealed a hypochromic, red shift from 363 to 365 nm. If the reference cell contained hapten, a red shift from 280 to 283 nm and an enhancement in the extinction coefficient of IgG2 was observed. These spectral changes were not observed if nonspecific IgG2 was substituted for anti-DNP IgG2 in the experimental cell. The enhancement in the extinction coefficient was interpreted to be due to a possible exposure of previously buried tryosine and tryptophan residues. 相似文献
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A set of benzimidazole derivatives bearing on position 2 a tetrahydropyranyl or tetrahydrofuranyl residue was prepared and tested for antitumoral, anti HIV-1 and other pharmacological activities. While the anti-HIV activity was completely lacking, moderate antitumoral activity was found in a few compounds; particularly the 5,6-dichloro-2-(tetrahydropyran-2-yl)-benzimidazole (8) was able to inhibit the growth of 19 cell lines of humane tumors at near micromolar concentration. On the other hand compounds 4, 6-8 and 10 exhibited significant tracheal relaxant activity in vitro at concentration 3-10 micrograms/ml, thus resulting superior to theophylline and comparable to amrinone. 相似文献
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