Jain S, Fotou GP, Kodas TT
Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, 87131
J Colloid Interface Sci. 1997 Jan 1;185(1):26-38. doi: 10.1006/jcis.1996.4558.
In situ coating of aerosol particles by gas-phase and surface reaction in a flow reactor is modeled accounting for scavenging (capture of small particles by large particles) and simultaneous surface reaction along with the finite sintering rate of the scavenged particles. A log-normal size distribution is assumed for the host and coating particles to describe coagulation and a monodisperse size distribution is used for the coating particles to describe sintering. As an example, coating of titania particles with silica in a continuous flow hot-wall reactor was modeled. High temperatures, low reactant concentrations, and large host particle surface areas favored smoother coatings in the parameter range: temperature 1700-1800 K, host particle number concentration 1 x 10(5)-1 x 10(7) #/cm3, average host particle size 1 &mgr;m, inlet coating reactant concentration (SiCl4) 2 x 10(-7)-2 x 10(-10) mol/cm3, and various surface reaction rates. The fraction of silica deposited on the TiO2 particles decreased by more than seven times with a hundredfold increase in SiCl4 inlet concentration because of the resulted increase in the average SiO2 particle size under the assumed coating conditions. Increasing the TiO2 particle number concentration resulted in higher scavenging efficiency of SiO2. In the TiO2/SiO2 system it is likely that surface reaction as well as scavenging play important roles in the coating process. The results agree qualitatively with experimental observations of TiO2 particles coated in situ with silica.
在流动反应器中，通过气相和表面反应对气溶胶颗粒进行原位包覆的过程进行了建模，该模型考虑了清除作用（大颗粒捕获小颗粒）、同时发生的表面反应以及被清除颗粒的有限烧结速率。假设主体颗粒和包覆颗粒的尺寸分布为对数正态分布以描述凝聚过程，而对于包覆颗粒则使用单分散尺寸分布来描述烧结过程。作为一个例子，对在连续流动热壁反应器中用二氧化硅包覆二氧化钛颗粒的过程进行了建模。在以下参数范围内，高温、低反应物浓度和大的主体颗粒表面积有利于形成更光滑的包覆层：温度1700 - 1800 K，主体颗粒数浓度1×10⁵ - 1×10⁷个/cm³，主体颗粒平均尺寸1μm，入口包覆反应物浓度（SiCl₄）2×10⁻⁷ - 2×10⁻¹⁰ mol/cm³，以及各种表面反应速率。在假定的包覆条件下，由于平均SiO₂颗粒尺寸增大，SiCl₄入口浓度增加一百倍时，沉积在TiO₂颗粒上的二氧化硅分数下降了七倍多。增加TiO₂颗粒数浓度会导致SiO₂的清除效率更高。在TiO₂/SiO₂体系中，表面反应以及清除作用在包覆过程中可能都起着重要作用。结果与二氧化钛颗粒原位包覆二氧化硅的实验观察结果在定性上是一致的。
