共查询到19条相似文献,搜索用时 109 毫秒
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测定了25℃下,添加不同浓度的EDTA后,不同过饱和比下ZTS溶液的诱导期,研究了掺杂浓度及过饱和比对ZTS溶液成核的影响.研究显示,当溶液处于较高过饱和比时(S>1.13),均匀成核占主导;而在较低过饱和比时(S< 1.11),则以非均匀成核为主.利用经典成核理论对实验所得数据进行分析,计算得到了界面张力、临界核形成功、临界核半径等成核特性,发现了溶液过饱和比及掺杂浓度对成核速度的影响,解释了添加EDTA能提高溶液稳定性的原因.利用界面张力的值计算得到了表面熵因子. 相似文献
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对苯二甲酸十八酯(OTO)晶体在过饱和溶液中的成核过程 总被引:2,自引:0,他引:2
本文研究了对苯二甲酸十八酯在甲苯为溶剂的过饱和溶液中的成核过程。测定了以诱导时间表示的成核速率。通过经典成核理论计算了固-液表面张力,成核自由能和临界成核半径。指出OTO晶体在甲苯为溶剂的过饱和溶液部的成核速率随着温度和过饱和度的提高而增大,溶剂的性质将改变成核速率的大小。 相似文献
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利用全程摄像的方法测定了不同情况下ADP过饱和溶液的诱导期,研究了不同pH值、不同温度的ADP过饱和溶液的成核过程,讨论了pH值、温度和过饱和度S等因素对诱导期的影响.结果表明:改变pH值后,在同一过饱和度下,溶液的稳定性在不同温度间差异较小,更利于晶体在较高的温度下稳定快速的生长;改变pH值后,溶液在整个过饱和度范围内更趋向于均匀成核.根据经典均匀成核理论,针对ADP溶液均匀成核的状况计算出了不同pH值和温度下的固-液界面张力、临界成核功等成核参数,并从上述参数的相互比较中得到了改变pH值后溶液稳定性变强的微观原因.最后通过对表面熵因子的计算,确定了ADP晶体的微观生长机制为连续生长模式. 相似文献
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N. Teodossiev 《Crystal Research and Technology》1986,21(9):1167-1175
Secondary nucleation of ammonium alum has been investigated in seeded batch crystallization from aqueous solutions. The presence of a time lag is established during which the nucleation rate increases up to a constant value. The duration of the time lag increases with increasing supersaturation. The effect of fine heteroparticles of alumina and silica on the rate of secondary nucleation is studied. The heteroparticles slightly increase the nucleation rate but cause the appearance of a considerable number of new nuclei when introduced some time after the process beginning. An assumption is made that the heteroparticles mainly affect the surviving of non-growing nuclei without changing the actual rate of secondary nucleation. 相似文献
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Rates of nucleation of supersaturated aqueous solutions of Triglycine sulphate are measured by the induction period over the temperature range 30–50 °C. The effects of temperature and supersaturation on the induction period are reported. The interfacial tension, energy of formation and radius of the critical nuclei of the crystal are calculated in accordance with classical nucleation theory. Nucleation rate increases with increase in supersaturation and temperature, while interfacial tension decreases with increase in temperature. 相似文献
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The metastable zone width of pure ammonium oxalate aqueous solutions, as represented by maximum supercooling ΔTmax, is investigated as functions of cooling rate R and saturation temperature T0 by the polythermal method. The experimental results are discussed by using two recently advanced approaches: (1) self‐consistent Nývlt‐like approach based on a power‐law relationship between nucleation rate J and maximum supersaturation lnSmax, and (2) a novel approach based on the relationship between J and lnSmax described by the classical three‐dimensional nucleation theory. Analysis of the experimental data revealed that both approaches describe the experimental data on metastable zone width by the polythermal method reliably and provide useful information about the physical processes and parameters involved in nucleation kinetics. The values of various physical quantities predicted by both of these approaches are reasonable for a fairly‐soluble compound. A careful examination of the data on ΔTmax as a function of T0 obtained by polythermal method and from density measurements showed that ΔTmax has a slight tendency to decrease with increasing saturation temperature T0. The values of lnSmax at saturation temperature 303 K suggest that the metastable zone width of ammonium oxalate aqueous solutions is determined by primary nucleation in the polythermal method and by secondary nucleation during density measurements. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Calcium sulphate dihydrate (gypsum) crystallization was studied under conditions, of supersaturation and temperature, simulating a brackish water desalination unit using solar energy. The effect of an commercial sodium salt of poly(acrylic acid), based compound known as RPI, on homogeneous nucleation and growth of gypsum was also examined. Gypsum was precipitated by mixing aqueous CaCl2 and Na2SO4 solutions. It was found that, with increasing temperature or supersaturation, the induction time decreases and the growth rate increases. By using classical nucleation theory, the interfacial tension and the nucleation rate values were estimated. It was shown that the interfacial tension is temperature dependent. The addition of increasing quantities of RPI, in the same conditions of temperature and supersaturation, prolongs the induction time, decreases the nucleation rate and increases the interfacial tension. The addition mode of RPI (in calcium or in sulphate solution) was found as an important parameter in controlling the inhibition process of gypsum crystallization. XRD and SEM analysis showed that RPI antiscalant strongly affected the texture and the morphology of the deposit gypsum. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The article describes the effect of degree of supersaturation, σ, on the crystallization of specific polymorphs of phenylbutazone from its methanolic solution at 20 °C. At low initial supersaturation, σ ≤ 2.0, the fraction of the metastable α polymorph in the crystallized product exceeds that of the δ polymorph, while at σ ≥ 5.0, the fraction of the stable δ polymorph increases in the crystallized product. The results are explained by the effect of supersaturation on the relative rates of nucleation and crystal growth of the polymorphs. Furthermore, the mechanism of nucleation and crystal growth also change with supersaturation. Supersaturated methanolic solutions of phenylbutazone exhibit a critical temperature at which the nucleation rates of the polymorphs decrease drastically. This effect is partly explained by the decreased mobility of phenylbutazone molecules at lower temperatures. Nucleation is most rapid when the crystallization temperature is close to the transition temperature, Tt(α ⟷ δ), between the polymorphs, α and δ. The nucleation rate decreases as the temperature difference between Tt(α ⟷ δ) and the crystallization temperature increases. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Wenpeng Li Ning Liao Xiaohui Duan Chonghua Pei Xiaoqing Zhou 《Crystal Research and Technology》2015,50(7):505-515
The nucleation kinetics of HMX (cyclotetramethylene tetranitramine, C4H8N8O8) in γ‐butyrolactone was studied in cooling process by induction time method. The laser scattering method was used to measure the solubility data and metastable region of HMX in γ‐butyrolactone. The induction time was measured over a range of supersaturation at different temperatures. Then, the nucleation mechanism of HMX in γ‐butyrolactone was investigated by analysis the relationships between induction time and supersaturation. The results indicated homogeneous nucleation dominated at high supersaturation of S >1.35, while the heterogeneous nucleation dominated at low supersaturation of S < 1.35. The values of interfacial tension at different final temperatures were calculated to indicate the ability of HMX to be crystallized. The growth mechanism of HMX was investigated by the data fitting applying different growth mechanism models and identified as two‐dimensional nucleation‐mediated (2D) growth. Finally, the effects of supersaturation and temperature on the crystal defects were analyzed based on the nucleation kinetics. When the temperature is below 303.15K, homogeneous nucleation dominated the nucleation process at higher supersaturation. Fine HMX crystals with more defects were produced. On the contrary, heterogeneous nucleation mechanism dominated at lower supersaturation. large regular HMX crystals with fewer defects were formed when the temperature is above 318.15K. 相似文献
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《Journal of Crystal Growth》1999,196(2-4):220-225
We have applied the Johnson–Mehl–Avrami–Kolomogorov (JMAK) theory of crystal nucleation and growth to the problem of protein crystallization in the batch method. Without integrating the JMAK equation explicitly, we use dimensional analysis to derive a general formula for the half-life for decay of the protein supersaturation. This formula includes a dimensioned group and an arbitrary dimensionless function. We integrate the JMAK equation exactly for the special case where the growth rate is independent of the supersaturation and the nucleation rate is proportional to its square. This gives an equation for the time decay of the supersaturation and a formula for the half-life in which all arbitrary dimensionless functions are evaluated. The results are consistent not only with Von Weimarn's rule, which asserts that the average size of a crystal increases as the supersaturation decreases, but also with our experimental results for crystallization of lysozyme, in which the half-life at fixed pH decreases with increasing ionic strength and decreasing temperature. 相似文献
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The effects of temperature, supersaturation, excess of reacting component salts and method of precipitation on the batchwise precipitation of potash alum crystals, by mixing aqueous solutions of potassium sulphate and aluminium sulphate, have been investigated. From the primary characteristics of the process (crystal size, size distribution and yield) relative crystal growth rates and relative nucleation rates are calculated and interrelation of these rates with the corresponding supersaturation leads to a value of the nucleation order. It is concluded that secondary nucleation plays an important role in the batch precipitation of potash alum crystals. 相似文献
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Jun‐Woo Kim Jungwook Kim Keun‐Deuk Lee Kee‐Kahb Koo 《Crystal Research and Technology》2013,48(12):1097-1105
Nucleation kinetics in the cooling crystallization of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) from γ‐butyrolactone was studied by converting total counts/s measured by in situ focused beam reflectance measurement (FBRM) into number of crystals. The classical nucleation rate model, which is derived exclusively from the thermodynamic state for the nucleation and molecular collision frequency, was found to be inadequate to describe the experimentally measured nucleation rates. However, the nucleation rates predicted by the modified classical nucleation rate model, inclusive of an additional temperature term, were found to be in good agreement with those measured in the present work. Furthermore, the metastable zone widths are also found to be more accurately predicted by the modified classical nucleation rate model than the classical approach, which assumes that the mass‐based nucleation rate is an exponential function of supersaturation and is equal to the supersaturation rate. 相似文献