采用水热法,以丁二醇和水作为混合溶剂,研究了二氧化钛纳米晶体的生长机理。X射线衍射(XRD)结果显示产物为锐钛矿纳米TiO2。用透射电镜(TEM)、高分辨透射电镜(HRTEM)等对不同时间的晶体结构进行表征,发现晶体生长具有明显的奥斯特瓦尔...采用水热法,以丁二醇和水作为混合溶剂,研究了二氧化钛纳米晶体的生长机理。X射线衍射(XRD)结果显示产物为锐钛矿纳米TiO2。用透射电镜(TEM)、高分辨透射电镜(HRTEM)等对不同时间的晶体结构进行表征,发现晶体生长具有明显的奥斯特瓦尔德熟化(OR)特征。颗粒粒径均处于纳米级,其粒径数值随温度增加而变大。丁二醇作为溶剂兼表面活性剂对于纳米晶体的生长起到重要调节作用。采用OR方程,分别对220℃、180℃、140℃三个温度下纳米Ti O2的生长进行模拟,模拟曲线和实验结果吻合很好,并获得其生长活化能为15.0 k J/mol。展开更多
The coarsening of particles dispersed in a solution was found by Ostwald in 1900. Then, the following cubic law between mean radius (r-) and annealing time (t) was established by Lifshitz-Slyozov and Wagner in 1961. I...The coarsening of particles dispersed in a solution was found by Ostwald in 1900. Then, the following cubic law between mean radius (r-) and annealing time (t) was established by Lifshitz-Slyozov and Wagner in 1961. It should be noted,however,that the above equation is valid in the coarsening of B particles in A-B solution.Therefore,some modification is necessary in the case of multi-component materials.For instance,the coarsening of (Fe,Cr)aCb in γFe-M-C matrix is described s folows;According to Eq.(2),the coarsening rate of M23C6 in heat-resistant steel(9%Cr^1%W-0.1%C)depends on the diffusion rate of Cr,because.However,experimental data inform us that the rate-de-termining element is not Cr but W as shown in Fig.1The problem is solved by modifing the formula of M23C6 from (Fe,Cr,W)23C6to Fe4(Cr,W)19C6 in this case (Fig.2).Consequently,the coarsening equation is expressed as follows.展开更多
The microstructures and growth process characteristics precipitation-crystallization method were investigated by SEM, TEM of spherical Ni（OH）2 particles synthesized by the aqueous and XRD, and their growth mechanism...The microstructures and growth process characteristics precipitation-crystallization method were investigated by SEM, TEM of spherical Ni（OH）2 particles synthesized by the aqueous and XRD, and their growth mechanism was discussed. With the reaction beginning and continuing, amorphous Ni（OH）2 nano-crystallites grow up to spherical micron-particles with radially arranged crystallites. The nucleation, crystallization and re-crystallization led by Ostwald ripening simultaneously take place through the whole growth processes. With the course from reversible aggregation to irreversible agglomeration, the Ni（OH）2 particles tend to grow according to the template growth model： the growth on the crystallite templates stretching in the radius directions is free and quick, while the growth rate for crystallites in other directions is confined due to lower monomers concentration and tends to dissolve So it is only the radially arranged crystallites that predominate in the particle and lead to characteristic microstructures.展开更多
文摘采用水热法,以丁二醇和水作为混合溶剂,研究了二氧化钛纳米晶体的生长机理。X射线衍射(XRD)结果显示产物为锐钛矿纳米TiO2。用透射电镜(TEM)、高分辨透射电镜(HRTEM)等对不同时间的晶体结构进行表征,发现晶体生长具有明显的奥斯特瓦尔德熟化(OR)特征。颗粒粒径均处于纳米级,其粒径数值随温度增加而变大。丁二醇作为溶剂兼表面活性剂对于纳米晶体的生长起到重要调节作用。采用OR方程,分别对220℃、180℃、140℃三个温度下纳米Ti O2的生长进行模拟,模拟曲线和实验结果吻合很好,并获得其生长活化能为15.0 k J/mol。
文摘The coarsening of particles dispersed in a solution was found by Ostwald in 1900. Then, the following cubic law between mean radius (r-) and annealing time (t) was established by Lifshitz-Slyozov and Wagner in 1961. It should be noted,however,that the above equation is valid in the coarsening of B particles in A-B solution.Therefore,some modification is necessary in the case of multi-component materials.For instance,the coarsening of (Fe,Cr)aCb in γFe-M-C matrix is described s folows;According to Eq.(2),the coarsening rate of M23C6 in heat-resistant steel(9%Cr^1%W-0.1%C)depends on the diffusion rate of Cr,because.However,experimental data inform us that the rate-de-termining element is not Cr but W as shown in Fig.1The problem is solved by modifing the formula of M23C6 from (Fe,Cr,W)23C6to Fe4(Cr,W)19C6 in this case (Fig.2).Consequently,the coarsening equation is expressed as follows.
基金Project(50134020) supported by the National Natural Science Foundation of ChinaProject supported by Postdoctoral Fund of Central South University
文摘The microstructures and growth process characteristics precipitation-crystallization method were investigated by SEM, TEM of spherical Ni（OH）2 particles synthesized by the aqueous and XRD, and their growth mechanism was discussed. With the reaction beginning and continuing, amorphous Ni（OH）2 nano-crystallites grow up to spherical micron-particles with radially arranged crystallites. The nucleation, crystallization and re-crystallization led by Ostwald ripening simultaneously take place through the whole growth processes. With the course from reversible aggregation to irreversible agglomeration, the Ni（OH）2 particles tend to grow according to the template growth model： the growth on the crystallite templates stretching in the radius directions is free and quick, while the growth rate for crystallites in other directions is confined due to lower monomers concentration and tends to dissolve So it is only the radially arranged crystallites that predominate in the particle and lead to characteristic microstructures.
