【作者】 郑广俭；

【导师】 童张法； 崔学民；

【作者基本信息】 广西大学 ， 化学工艺， 2011， 博士

【摘要】 地质聚合物(Geopolymer)是一种由[A104]和[Si04]四面体构成具有三维结构的铝硅酸盐无机聚合物,它具有很多优点,如强度高、耐腐蚀、耐火及寿命长等。因此,地质聚合物是近年来国际上研究非常活跃的一种新型无机高分子材料。地质聚合物的生产常以偏高岭土、粉煤灰、工业废渣或矿渣为主要原料。然而,不同产地的原料组成不同且很复杂,因而地质聚合物的应用受到很大的限制。溶胶-凝胶法是近年来发展起来的一种粉体制备的新型方法,当采用该方法合成地质聚合物材料的原料时,则可控制原料成分配比,即原料成分可任意调整,并且非常纯净。若应用该方法合成出的粉体具有碱激活性,则可人为设计粉体的成分与组成,这就有利于控制地质聚合物材料制品的纯度和性能。因此,地质聚合物的应用会有更加广阔的前景。本文参照偏高岭土的主要组成,采用化学合成方法,以正硅酸乙酯(TEOS)和水合硝酸铝(ANN)为主要原料,制备了纯净的Al2O3-2SiO2粉体,对其碱激活性及其结构特点以及制备工艺参数优化等进行了系统研究,主要研究结果如下：采用溶胶-凝胶法,合成了具有碱激活性的Al2O3-2SiO2粉体,采用该粉体制备的胶凝材料符合地质聚合物的主要标志性特征。同时,采用该法也制备了具有碱激活性的不同硅铝比粉体。由于溶胶-凝胶法合成地质聚合物材料粉体可控制原料配比,且原料成分纯净,这不仅有利于控制地质聚合物材料制品的纯度和性能,还为理论设计地质聚合物的组成和性能提供了可能。以地质聚合物材料的机械性能(抗压强度)为优化目标,研究了粉体制备过程中合成温度、乙醇用量、水用量、陈化时间、干燥时间、煅烧时间、煅烧温度等工艺因素对粉体碱激活性的影响。确定了制备高活性粉体的适宜工艺参数如下：合成温度,70℃；乙醇用量n(EtOH)/n(TEOS)一般控制在6左右。水用量n(H2O)/n(TEOS)一般控制在9左右；陈化时间,12h；干燥时间,10h左右；煅烧温度一般700℃～800℃；煅烧时间,4 h。以地质聚合物材料的机械性能(抗压强度)为优化目标,研究了地质聚合物制备过程中硅含量、钠含量、铝含量、水含量、养护时间和养护温度等工艺因素对抗压强度的影响。确定了制备地质聚合物材料的适宜工艺参数如下：地质聚合物材料的原料配比,n(SiO2)/n(Al2O3)为3.0～3.5、n(H2O)/n(A1203)约为10左右、n(Na2O)/n(Al2O3)约为1左右；养护温度不超过70℃。通过XRD、FTIR、27Al和29Si NMR等测试手段对本研究制备的Al2O3-2SiO2粉体以及地质聚合物的结构进行了表征,该粉体的结构特征与偏高岭土相似；而且,该粉体碱激后制得的地质聚合物与偏高岭土碱激后制得的地质聚合物其结构特征相似。然而,该粉体开始具有碱激活性的煅烧温度(300℃)低于高岭土开始转变为偏高岭土的煅烧温度(500℃)。通过DTS、TEM、SEM、BET低温液氮吸附等分析手段研究了溶胶—凝胶体系中水用量、乙醇用量、水解温度、陈化时间、干燥方式等工艺因素对Al2O3-2SiO2粉体的粒度、比表面和结构的影响。确定了制备低团聚的Al2O3-2SiO2纳米粉体的优化工艺参数为：水及乙醇对硝酸铝的摩尔比分别为0：1和16：1、合成温度为40℃、凝胶陈化时间为36小时、共沸蒸馏脱水结合微波加热干燥。实验中制得粉体的平均粒径为70～80nm,最大比表面积可达669 m2/g。采用共沉淀法,以正硅酸乙酯(TEOS)和水合硝酸铝(ANN)为主要原料,采用不同沉淀方式合成了具有碱激活性的Al2O3-2SiO2粉体。结果表明：滴加方式制备的粉体的碱激活性高于一次性加入方式。利用XRD.ICP.SEM.FTIR、27A1和29Si NMR等测试手段,研究了制品在固化过程中的反应机理。首先,粉体在碱性条件下发生溶解,其中Si-O-Si、Al-O-Si键发生断裂,生成[Al(OH)4]-、[SiO(OH)3]-和[SiO2(OH)2]-单聚体或其它低聚体,溶解过程中,铝的溶出速率快于硅的溶出速率；然后,生成的这些组分或低聚体之间发生聚合作用,脱水形成非晶质物相的地质聚合物,聚合过程中,铝酸盐基团与硅酸盐基团反应较快,而硅酸盐基团之间反应较慢。如果反应物系中名义化学式相同,在碱激液模数较低的范围内,碱激液中的硅占总硅比率增加时,有利于地质聚合反应的进行。通过粉体中Al的溶出活性研究表明,粉体在NaOH溶液中Al的溶出活性并不能完全反映粉体的碱激活性。高碱激活性的Al2O3-2SiO2粉体具有高含量的5配位Al；溶胶凝胶法制备粉体的碱激活性高于共沉淀法制备粉体的碱激活性。更多还原

【Abstract】 A geopolymer is one type of aluminosilicate inorganic polymer materials composed by tetrahedral [AlO4] and [SiO4] units with three-dimensional structures. Because of its excellent property of high strength, anticorrosion, standing fire and long life, the research of the novel geopolymer has recently become a hot spot in the field of inorganic polymer material in the world. At present, materials such as metakaolin, fly ashes and blast furnace slag are often used to produce geopolymers. However, since the chemical composition of these materials is very complex and various with their sources, their application is limited to some extent. Sol-gel process is a novel method for preparation of powders and has received much attention in recent years, due to high purity, good homogeneity and high reactivity of materials prepared in this process.As the purity and Si/Al ratio of the powders for the geopolymer are easily adjusted in the sol-gel process, the properties and composition of the powders can be controlled with relative ease. If the powders prepared by this process are able to be alkali-activated, they will be useful because the composition of powders can be designed according to our requirement, which is beneficial to control of purity and performances of geopolymer products. Hence, the application of geopolymers would be more extensive in the future.In this study, pure Al2O3-2SiO2 powders for a geopolymer were prepared by a chemical synthesis methods with tetraethoxysilane (TEOS) and aluminum nitrate (ANN) as the starting material referring to the principal composition of metakaolinite, that is, Si/Al molar ratio of 1. At the same time, alkali-activation reactivity and structure of the powders and optimization of process parameters for preparing powders were systematically investigated. The principal results are as follows.The pure Al2O3-2SiO2 precursors (powders) for a geopolymer have been prepared by the sol-gel method. The alkali-activated products derived from the powders meet the general criteria for a geopolymer. At the same time, the powders with different Si/Al molar ratios have also been prepared. As the purity and Si/Al ratio of the powders for the geopolymer are easily adjusted in the sol-gel process, the properties and composition of the powders can be controlled with relative ease. Thus it is not only easy to control purity and performances of geopolymer products, but also possible to design theoretically their composition and performances.The optimum process parameters for preparing high-reactivity powders were determined considering the compressive strength of the geopolymer products as the main criterion. The optimum process parameters for preparing high-reactivity powders are as follows:synthetic temperature is 70℃,the mole ratio of ethanol to TEOS about 6, the mole ratio of water to TEOS about 9, aging time about 12 h, drying time about 10 h, calcination temperature 700℃-800℃, and calcination time 4 h.The optimum process parameters for preparing geopolymers were determined considering the compressive strength of the geopolymers products as the main criterion. The optimum process parameters for preparing geopolymers are as follows:the mole ratio of SiO2 to Al2O3 is 3.0～3.5, the mole ratio of H2O to Al2O3 about 10, the mole ratio of Na2O to Al2O3 is about 1, curing temperature more than room temperature and less than 70℃.By NMR, XRD and FTIR analysis, some microstructure characteristics of the as-prepared powders and their alkali-activation products are similar to those of metakaolin and its alkali-activation product, respectively. However, the heat-treated temperature at which the powders begin to be alkali-activated is lower than that at which kaolin begins to transform to metakaolin.Analytical methods such as DTS, TEM, SEM, BET were employed to study the effects of process parameters, such as quantities of water and ethanol, hydrolysis temperature, aging time and drying methods, on the size, specific surface area and structure of nanometer powders. The optimum process parameters for preparing low agglomerative Al2O3-2SiO2 nanometer powders are as follows:the mole ratio of water and ethanol to TEOS are 0:1 and 16:1 respectively, synthetic temperature is 40℃, aging time is 36 h and the drying way is azeotropic distillation with microwave drying. The powders possess uniform size, laminar structure and monodispersity. The average particle diameters of the powders were in the range of 70-80 nm and the largest BET specific surface area were up to 669m2/g.The pure Al2O3-2SiO2 powders for a geopolymer have been prepared by a coprecipitation method with tetraethoxysilane (TEOS) and aluminum nitrate (ANN) as the starting material. Results show that the reactivity of the powders prepared by drop addition is higher than by bulk addition.The mechanism of the geopolymerization was studied By NMR, SEM, ICP, XRD and FTIR analysis. In dissolution process, the Si-O-Si or Al-O-Si bonds in the particles were broken and monomers and oligomers such as [Al(OH)4]-, [SiO(OH)3]-,[SiO2(OH)2]- etc. were formed. The dissolution rate of Al is faster than that of Si. In condensation process, resultants in the dissolution process condense and geopolymers are formed. The condensation process in these systems occurs in two stages:(a) quick condensation between aluminate and silicate species; followed by (b) a slow condensation stage solely involving silicate species. For the reaction system with the same nominal formula, the increase of the molar ratio of Si in alkali activator solution to total Si favors the geopolymerization in the range of low alkali activator solution modulus. The alkali-dissolvability of the powders shows that the alkali-dissolvability of the powders in NaOH solution does not represent geopolymerization activity completely.The Al2O3-2SiO2 powders with the high alkali-activation reactivity are of high contents of 5-coordinated Al. The reactivity of the powders prepared by sol-gel method is higher than that by coprecipitation method.更多还原