Experimental Determination and Modeling of the Radiative Properties of Silica Nanoporous Matrices
Experimental Determination and Modeling of the Radiative Properties of Silica Nanoporous Matrices
复制标题
DOI：
10.1115/1.3109999
复制
发表时间：
2009-08-01
影响因子：
--
通讯作者：
Baillis, Dominique
中科院分区：
文献类型：
--
作者：
Lallich, Sylvain;Enguehard, Franck;Baillis, Dominique
超绝缘材料目前受到关注，因为房屋和办公室的加热和冷却是二氧化碳排放的重要组成部分。在这项研究中，我们的目标是在纳米多孔二氧化硅矩阵，是纳米多孔超绝缘材料的主要组成部分的辐射传输建模。我们首先从不同的热解无定形二氧化硅粉末中精心制作样品，这些粉末在比表面积、纳米颗粒直径和组成方面彼此略有不同。各种样品的光学特性，使用两个光谱仪上的波长范围（250 nm; 20 μ m）。一旦半球形的透射率和反射率光谱测量，我们推导出的辐射特性，使用参数识别技术。然后，由于所考虑的介质是由包装准球形纳米粒子，我们试图使用原来的米氏理论来模拟它们的辐射特性。为了在大部分波长范围内获得实验和理论之间的良好一致性，我们必须考虑比初级纳米颗粒大五倍的散射体;这归因于散射体不是纳米颗粒而是在粉末制造过程中构成的纳米颗粒的聚集体。然而，在小的波长范围内（λ小于1 μ m），我们永远不能得到一个令人满意的协议使用米氏理论。这种分歧归因于这样一个事实，即原来的米氏理论没有考虑到聚集体的纳米结构。因此，我们开发了一个基于离散偶极子近似的代码，该代码改善了小波长范围内的建模结果，基于我们的计算，使用扩散限制的簇-簇聚集算法生成的聚集体，以确保分形维数接近通常发现的二氧化硅纳米颗粒聚集体。
Superinsulating materials are currently of interest because the heating and cooling of houses and offices are responsible for an important part of CO2 emissions. In this study, we aim at modeling the radiative transfer in nanoporous silica matrices that are the principal components of nanoporous superinsulating materials. We first elaborate samples from different pyrogenic amorphous silica powders that slightly differ one from another in terms of specific surface, nanoparticle diameter, and composition. The various samples are optically characterized using two spectrometers operating on the wavelength range (250 nm; 20 mu m). Once the hemispherical transmittance and reflectance spectra are measured, we deduce the radiative properties using a parameter identification technique. Then, as the considered media are made of packed quasispherical nanoparticles, we try to model their radiative properties using the original Mie theory. To obtain a good agreement between experiment and theory on a large part of the wavelength range, we have to consider scatterers that are up to five times larger than the primary nanoparticles; this is attributed to the fact that the scatterers are not the nanoparticles but aggregates of nanoparticles that are constituted during the fabrication process of the powders. Nevertheless, in the small wavelength range (lambda smaller than 1 mu m), we can never get a satisfactory agreement using the Mie theory. This disagreement is attributed to the fact that the original Mie theory does not take into account the nanostructure of the aggregates. So we have developed a code based on the discrete dipole approximation that improves the modeling results in the small wavelength range, basing our computations on aggregates generated using the diffusion-limited cluster-cluster aggregation algorithm in order to ensure a fractal dimension close to what is usually found with aggregates of silica nanoparticles.