硅溶胶及在涂料中应用

综述了硅溶胶生产的原理及方法．指出离子交换法和单质硅粉溶解法是当前硅溶胶生产的主要方法．并且单质硅粉溶解法具有较大发展潜力；归纳了硅溶胶在涂料中的应用及其实现途径，并针对硅溶胶的特点进行了分析。就目前硅溶胶与高分子聚合物乳液复合材料的制备提出了建议。     

硅溶胶的生产技术进展及市场分析

概述了当前国内硅溶胶行业生产技术进展及市场需求分析,同时对离子交换法、溶胶—凝胶法、单质硅一步溶解法等硅溶胶生产工艺进行分析评述,以期为当前硅溶胶行业的发展提供帮助。     

硅溶胶制备方法评述

对制备硅溶胶的离子交换法，单质硅一步溶解法、电解电渗析法、酸中和法及胶溶法进行了述评，阐述了制备条件对硅溶胶产品性能的影响。     

硅溶胶的制备及在纺织品整理上的应用研究进展

硅溶胶的工业生产方法主要为离子交换法和单质硅溶解法。本文综述了硅溶胶在纺织品上的功能整理用途,以达到疏水、固色、增深、阻燃、结构生色等目的。最后对硅溶胶在纺织品上的发展前景进行了展望。     

硅晶片抛光用高纯度大粒径硅溶胶的研究

本文采用硅粉水解-胶粒整理法制备硅晶片抛光所用硅溶胶,考察了单质硅粉的加入量、反应时间、反应温度、硅溶胶底液浓度、催化剂种类及用量对硅溶胶胶粒平均粒径增长的影响,得到最佳工艺条件:单质硅粉的最佳加入量为25 g、反应时间7h、反应温度80℃、硅溶胶底液的质量浓度为8％、选稀氨水为催化剂、用量为12 mL,在此条件下可制备得到平均粒径为20 nm的硅溶胶产品.经过多次粒子生长可以制备得到适用于硅晶片抛光产业的高纯度大粒径硅溶胶.     

单质硅溶解法制备硅溶胶的研究

采用单质硅溶解法,以氢氧化钠作为催化剂,由硅粉和水反应了制备硅溶胶。研究了实验过程中不同工艺条件如反应温度,反应时间,以及硅粉和氢氧化钠用量对硅溶胶制备的影响,并对制备的硅溶胶的性能进行了研究。实验结果表明,硅溶胶制备的较佳工艺条件是：在200 mL去离子水中加入25 g硅粉和0.16 g氢氧化钠,并在温度为900℃下反应8 h。     

硅溶胶的制备及其性能指标分析

简要介绍了工业广泛应用的制备硅溶胶的离子交换工艺和单质硅溶解工艺,分析了与硅溶胶性能密切相关的钠含量、SiO2含量、pH值、黏度、粒径和稳定性等性能指标的重要性,并汇总了这些性能指标的常用测试方法,期望对企业和科研单位硅溶胶的生产和测试具有一定的指导意义。     

单质硅粉溶解法制备硅溶胶正交实验研究

研究了以单质硅粉为原料、水玻璃与氨水为复配催化剂制备硅溶胶的最佳工艺。通过正交实验设计,得出了硅溶胶的最佳制备条件:反应时间为7h,反应温度为80℃,水玻璃∶水∶硅粉=1∶20∶3(质量比)。     

硅溶胶的合成及其对陶瓷的防污性能研究

硅溶胶具有比表面积大、高分散性、良好的稳定性、绝缘性和粘结性以及亲水性和憎油性等优点,广泛应用在无机涂料、抛光液、耐火材料、催化剂、医学等行业。文中采用单质硅粉水解法制备了碱性硅溶胶,研究了硅粉用量、反应时间、反应温度、NaOH用量等因素对硅溶胶收率及其性能的影响。实验结果表明制备碱性硅溶胶的最佳工艺条件为:去离子水为200 mL,硅粉用量为25 g,反应温度85℃,反应时间为10 h, NaOH用量为0.7 g。用于抛光砖表面处理,能填补陶瓷表面凹凸不平的表面,具有持久的防污效果,并能提高瓷砖的光亮度。     

硅溶胶用作FCC催化剂粘结剂的研究现状

介绍了硅溶胶的性质,总结了单质溶解法、离子交换法、电解渗析法、胶溶法、分散法等制备方法,论述了pH值、溶胶粒子粒径、助剂及其他影响因素对硅溶胶稳定性的影响,并对粘结剂用硅溶胶的发展前景做了展望。     

Silica-sol-based spin-coating barrier layer against phosphorous diffusion for crystalline silicon solar cells

The phosphorus barrier layers at the doping procedure of silicon wafers were fabricated using a spin-coating method with a mixture of silica-sol and tetramethylammonium hydroxide, which can be formed at the rear surface prior to the front phosphorus spin-on-demand (SOD) diffusion and directly annealed simultaneously with the front phosphorus layer. The optimization of coating thickness was obtained by changing the applied spin-coating speed; from 2,000 to 8,000 rpm. The CZ-Si p-type silicon solar cells were fabricated with/without using the rear silica-sol layer after taking the sheet resistance measurements, SIMS analysis, and SEM measurements of the silica-sol material evaluations into consideration. For the fabrication of solar cells, a spin-coating phosphorus source was used to form the n⁺ emitter and was then diffused at 930°C for 35 min. The out-gas diffusion of phosphorus could be completely prevented by spin-coated silica-sol film placed on the rear side of the wafers coated prior to the diffusion process. A roughly 2% improvement in the conversion efficiency was observed when silica-sol was utilized during the phosphorus diffusion step. These results can suggest that the silica-sol material can be an attractive candidate for low-cost and easily applicable spin-coating barrier for any masking purpose involving phosphorus diffusion.     

Fabrication of Al2O3-SiO2 ceramics through combined selective laser sintering and SiO2-sol infiltration

In this study, different posttreatment methods, including silica-sol infiltration (SI), vacuum silica-sol infiltration (vSI), debinding (DB), and pressure-less sintering (PS), were combined with selective laser sintering (SLS) to fabricate Al₂O₃-SiO₂ ceramics. The macro-morphology and microstructure of sample fabricated under different laser processing parameters and posttreatment process were investigated. Results show that the geometric dimension accuracy and surface quality of the final samples can be effectively improved with appropriate SLS parameters and posttreatment. The optimal SLS processing parameters are determined to be 0.15 mm, 10 W, 0.1 mm, and 1500 mm/s for the hatch spacing, laser power, layer thickness, and scanning speed, respectively. The SLS/DB/vIN/FS samples have the smallest linear shrinkage ratio (<1%), the least warpage degree (<3%), and the best surface quality (surface altitude difference <170 μm). Mullite, quartz, corundum, and cristobalite composed the phases of the sample, of which cristobalite came largely from the infiltrated silica-sol. Since a higher amount of silica-sol infiltrated into the sample under SLS/DB/vIN/FS process, more cristobalite phase formed in the pore of the sample during sintering, which avoided excessive microstructure shrinkage during sintering and ensured the high geometric accuracy and surface quality of the final sample.     

Antireflecting coatings for glass based on monolayers of amorphous silica nanoparticles

The results of investigations into monolayered antireflective coatings based on silicon dioxide (silica) nanoparticles obtained according to the sol-gel technology using a simple and efficient technique of dipping into a sol of soda-lime glass are presented. The influence of silica-sol synthesis parameters and the size of the deposited nanoparticles on the structure and properties of the obtained coatings are revealed.     

Design and demonstration of an experimental membrane reactor set-up for oxidative coupling of methane

In this experimental research, the performance of the oxidative coupling of methane (OCM) reactions in a porous packed bed membrane reactor was investigated. A commercially available porous alpha-alumina membrane was modified to obtain the characteristics needed for a stable and catalytically inert OCM membrane reactor. The silica-sol impregnation–calcination method and a new silicon oxycarbide (SiOC) coating-calcination approach were applied to modify the membrane. The characteristics of the resulted membrane and its typical performance as OCM membrane reactor are reported.     

Design and realization of interface strengthening to GNPs/YSZ nanocomposite coating

Interfacial strengthening of ceramic coatings on metal surfaces is a goal that has been pursued by researchers in this field, but remains unsolved. In this work, the interface strengthening between ceramic coating and metal substrate was designed and successfully realized. GNPs were modified with silica-sol at the molecular scale to disperse in YSZ uniformly and the GNPs/YSZ nanocomposite coatings with high bonding strength were produced due to in-situ generation of interfacial carbides. Results show that the bonding strength of 9 wt% GNPs/YSZ nanocomposite coating increased by up to ∼54% compared to nanostructured YSZ coating without NiCrAlY bond-coat, and even 17% higher than that of nanostructured conventional type YSZ coating with NiCrAlY bond-coat. This technique could be applied to reinforce the interface between various materials, showing great application potential.     

Photoresponse and AC impedance characterization of TiO2–SiO2 mixed oxide for photocatalytic water decomposition

TiO₂–SiO₂ mixed oxides were prepared by sol–gel processes with one-stage (mix up fully hydrolyzed titania- and silica-sol), two-stage (with pre-hydrolysis) and modified two-stage synthesis routes. The photoresponse and AC impedance characterization of the derived catalysts are studied and correlated for the first time with the photocatalytic activities in water decomposition under UV illumination. Synergistic effects in terms of photocatalytic activity and electronic properties including band-gap energy, flat band potential and doping density were observed on atomically mixing TiO₂ and SiO₂ by the two-stage synthesis route. Meanwhile, the decline of photocurrent density were found on TiO₂–SiO₂ relative to bare TiO₂, which could be attributed to low quality crystalline structure of the former compared to that of the latter. The superior photocatalytic performance of TiO₂–SiO₂ is ascribed to the higher flat band potential, band-gap energy, and doping density than those of bare TiO₂.     

Microscopic regulation of plant morphological pores on mechanical properties of porous mullite materials

Generally, a multilayer structure is present inside a walnut shell, and the residual structure of the walnut shell is retained after impregnation and firing. When the walnut shell is used as a pore-forming agent, this structure helps in improving the mechanical and thermal insulation properties of the lightweight porous materials. In this study, porous mullite materials (PMMs) with plant morphological structure pores were prepared using a-Al₂O₃ and silica powder as the raw materials with addition of sol-impregnated walnut shell powder (WSP). The influence of sol type and firing temperature on the pore structure of the PMMs was analyzed, which affected the compressive strength and thermal conductivity. The plant morphological porous structure was observed in the samples after sol impregnation. After firing at different temperatures, the porous structure gradually contracted and supported the pores, improving the mechanical properties, while the complex porous structure increased the heat conduction path, thereby improving the insulation performance. Using WSP impregnated with silica-sol and zirconia-sol as pore-forming agents, PMMs with higher compressive strength and relatively low thermal conductivity (TC) were prepared.     

Improvement in heat resistivity of alkaline earth silicate fiber boards by Al4SiC4 coating

Alkaline earth silicate (AES) fiber ceramic board was immersed in a novel coating slurry consisting of Al₄SiC₄ particles and silica-sol, forming a 500-μm coating layer on the AES fiber board. Linear shrinkage of the uncoated AES fiber board was over 3.0% after heating at 1100°C or higher for 8 hours, whereas the linear shrinkage of the AES fiber board with an Al₄SiC₄ coating was below 2.0%. The coating layer of Al₄SiC₄ changed to a hard shell structure consisting of cristobalite, alumina, and mullite after heating. When AES fiber board with an Al₄SiC₄ coating layer was heated at 1200°C for 8 hours, the compressive strength of the board reached 0.45 MPa, 2.5 times greater than that of the original uncoated board.     

Effect of silica sol on phase transition of alumina-mullite fibers

Duplex oxide ceramic fibers have excellent high temperature properties. However, controlling the microstructure of duplex oxide ceramic fibers is difficult and complexed. In this work, the effect of silica sols affecting the interaction of precursor sol-gel particles on the high-temperature phase transition and microstructure of alumina-mullite fibers was investigated. The results show that the silica sol affects the particle interactions and distribution in the mixed sol. Alumina-mullite fibers prepared from non-homogeneous precursor sols generated α-Al₂O₃ at 1400 °C, while fibers prepared from homogeneous precursor sols required higher temperatures. In addition, mullite (3Al₂O₃:2SiO₂) with an orthogonal structure is more likely to be generated in the non-homogeneous Al₂O₃-SiO₂ precursor sol. The prepared alumina-mullite fibers have a tensile strength of up to 1.68 GPa. Finally, the mechanism of the influence of silica-sol properties on the final organization of the alumina-mullite fiber was further discussed.     

牙膏级磷酸氢钙生产方法综述

介绍了牙膏级磷酸氢钙的主要生产方法及特点,并就每一种生产工艺的优点及不足作了评价;通过对不同生产条件进行比较,提出了适宜的工艺路线;在分析国内牙膏生产现状的基础上,对牙膏级磷酸氢钙的发展及市场前景进行了展望。