| 题名 | SiO2空心球结构与隔热性能的关联研究 |
| 作者 | 廖玉超 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-01 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 陈运法 |
| 关键词 | 空心球 有限元模拟 导热系数 空腔半径 壁厚 |
| 其他题名 | The relationship between structure and thermal insulation performance of SiO2 hollow spheres |
| 学位专业 | 化学工程 |
| 中文摘要 | 由于空心球独有的特点，在隔热方面的应用逐步引起了人们的关注，普遍认为其隔热性能与空腔大小紧密关联，即与Knudsen效应一致，但对其影响因素的认识尚不完善。因此，寻求预测空心结构导热性能的合理模型、探索其结构与隔热性能之间的相互作用机制具有重要的意义。本文以SiO2空心球为例，从材料制备到导热性能检测，到模型提出和计算，再到材料的应用，较为系统地研究了结构参数与隔热性能之间的关系，主要研究内容与结果包括：（1）基于普遍认同的Knudsen效应，探索了一种新的纳米SiO2空心球的制备方法：以Zn2+与氨水生成的沉淀物为临时模板，并以微乳液滴作为微反应器控制产物尺寸。具体而言，将分别含有Zn2+与氨水的两种微乳液混合，产生临时模板；随着第三份含有浓氨水的微乳液的加入，临时模板在导向形成SiO2壳层的同时逐步被浓氨水侵蚀，最终得到纳米SiO2空心球。该方法操作简便、能耗低、颗粒尺寸小、无需后处理。然而，利用3ω法测定的导热系数结果表明，纳米SiO2空心球的隔热效果并不理想，这与Knudsen效应存有偏差。由此推测，降低空心球空腔尺寸并不是调控其导热系数的唯一有效方法。（2）基于有限元理论，提出了空心球的导热模型。以微乳法得到的纳米SiO2空心球为分析对象，发现导热系数模拟值与3ω法测定值接近，说明模型具有合理性。通过改变模型颗粒的空腔半径Ri、壁厚h和球壁材料导热系数λshell，在纳米、亚微米范围内，可计算得到一系列单个空心球颗粒的导热系数。数据表明： a) 单个空心球颗粒的导热系数与h/Ri值紧密相关，且当h/Ri ≈ 0.2时降至最低值；b) 在h/Ri值相等的情况下，Ri越小则导热系数越低；c) 球壁的种类和微结构也是重要影响因素。该模型为进一步优化空心球材料的制备工艺和结构设计提供了依据。（3）以正硅酸乙酯（TEOS）为原料，聚苯乙烯球为模板，制备了三种亚微米尺寸的SiO2空心球，由3ω法测定的导热系数均小于0.02 W·m-1·K-1，同时发现堆积密度是影响粉体空心球材料导热性能的关键因素之一，最低导热系数对应的堆积密度约为单个空心球颗粒密度的7 %，此时隔热性能最佳。采用本文提出的模型和气凝胶理论对空心球导热系数进一步计算，结果均与实验测定值接近，说明亚微米SiO2空心球的确是一种性能优异的隔热材料。与纳米空心球相比，亚微米空心球的壳层厚度达几十纳米，球壳强度显著提高，有利于实际应用。 (4）以制备得到的亚微米SiO2空心球为原料，采用表面接枝技术，将空心球与聚氨酯基体复合，制备得到了透光性能良好的隔热薄膜。研究结果发现，KH550与盐酸能使SiO2空心球表面的官能团和电荷与聚氨酯基体匹配，因此空心球在聚氨酯基体中能良好分散，所得的复合薄膜导热系数低至0.05 W·m-1·K-1，且透明性并未明显降低。采用本文提出的模型计算复合薄膜的导热系数，发现模拟值与实验值接近，但复合薄膜的导热系数变化规律与单个空心球不一致，可能是由于界面热阻造成的，关于其定量计算有待进一步深入研究。 |
| 英文摘要 | Due to the typical structure of hollow spheres, their thermal insulation applications have been attracted by many researchers in recent years. Commonly, their thermal insulation is associated with the hollow size, which is consistent with Knudsen effect. But the research on the other factors of hollow spheres is not enough. Therefore, it is necessary to develop the reasonable model predicting the thermal conductivity and find out the relationship between structure and thermal insulation. Taking SiO2 hollow spheres for example in this paper, we do the researches including material preparation, thermal conductivity test, model proposal and material application, and then explore the relationship between structure parameters and thermal insulation. The main research progress and results are as follows: (1) Based on the Knudsen effect widely accepted, a novel synthesis method for nano-size SiO2 hollow spheres is developed. Zn2+ reacts with ammonia to produce precipitates, which are used as temporary templates. The microemulsion droplet as micro reactor controls the size of products. Firstly, the mixture of two microemulsions containing Zn2+ and ammonia respectively produce temporary templates. After the addition of the third microemulsion containing concentrated ammonia, the temporary templates can be coated with SiO2 shells derived from TEOS and synchronously etched gradually by ammonia. Then the nano-size SiO2 hollow spheres can be obtained. The advantages for this method lie in easy operation, low energy consumption, small size for products and no need of post-treatment. However, the thermal conductivity values by 3ω method show that nano-size SiO2 hollow spheres are not excellent insulation materials, which is inconsistent to the Knudsen effect. Therefore, the reduction of hollow size is not the only way for the thermal conductivity adjustment of hollow spheres. (2) Based on the finite element theory, a heat transfer model is proposed. The simulated thermal conductivity value of SiO2 hollow sphere produced by microemulsion method is close to the one determined by 3ω method, which confirms the reasonability of the model. In the size range from nanometer to submircometer, the thermal conductivity values can be obtained through adjusting the hollow radius Ri, shell thickness h and shell material’s λshell. It can be concluded that a) the thermal conductivity is related with h/Ri value and reaches minimum when h/Ri ≈ 0.2; b) in the case of equal of h/Ri value, the smaller Ri the smaller thermal conductivity; c) the specie and micro structure are the important factors affecting thermal conductivity. The model provides the basis for the optimization of preparation technique and structure design of hollow sphere. (3) Three submicrometer SiO2 hollow spheres are prepared using tetraethoxysilane (TEOS) as raw material, polystyrene as template. Their thermal conductivity values tested by 3ω method are smaller than 0.02 W·m-1·K-1. It is found that the bulk density is one of the key factors influencing the thermal conductivity. The material shows the best insulation performance under its optimal bulk density, which is 7 percentage of single hollow sphere particle density. Moreover, the proposed model and the aerogel theory are adopted to calculate the thermal conductivity. The simulated and calculated values are close to the experimental ones, which indicate the submicrometer SiO2 hollow spheres possessing super thermal insulation. Compared with nano hollow spheres, submicrometer SiO2 hollow spheres are promising in practical applications due to enough shell thickness. (4) Polyurethane (PU) and submicrometer SiO2 hollow spheres are combined to form transparent and thermal insulated thin film, wherein SiO2 hollow spheres are modified by steps with KH550 and hydrochloric acid. Because of the modifications of function group and charge, hollow spheres can be distributed uniformly in PU matrix. The thermal conductivity values of the resulted composite thin films are as low as 0.05 W·m-1·K-1, and their transparency change little. The simulated value from the finite element model is close to the experimental one. However, changing regularity of thermal conductivity of the composite thin film differs from that of single hollow sphere particle. The differences between them may be caused by the interface thermal resistance, the quantitative calculation of which needs further investigation. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1801]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 廖玉超. SiO2空心球结构与隔热性能的关联研究[D]. 中国科学院研究生院. 2012. |
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