【作者】 邓德华；

【导师】 曾庆元； 冯乃谦；

【作者基本信息】 中南大学 ， 道路与铁道工程， 2005， 博士

【摘要】 本文运用XRD相分析、扫描电镜观测、化学分析、常规性能测试等方法和生产实践,就如何提高镁质碱式盐水泥及其制品的性能,进行了理论与应用技术方面的研究。 理论上,首次提出主要形成碱式盐水化物而凝结硬化的水泥为碱式盐水泥的概念,讨论了它们的凝胶反应机理和形成条件。依据这一理论,指出氯氧镁水泥和硫氧镁水泥是三元胶凝体系的镁质碱式盐水泥,其碱式盐水化物的组成是Mg_q（OH）_p（2q-p）X·nH₂O,剖析了氯氧镁水泥组成原理、各物相的形成机理、水泥石的微结构与强度特征和耐水性及其改善机理等本质问题。 认为氯氧镁水泥的主要碱式盐水化物5相[Mg₃（OH）₅Cl·4H₂O]和3相[Mg₂（OH）₃Cl·4H₂O]是通过多核水羟合镁离子[Mg_p（OH）_q（H₂O）_r]^2p-q和OH^-、Cl^-等离子形成的,其形成过程经历了溶胶—凝胶—结晶三个阶段。试验结果表明:镁质碱式盐水泥石中物相的组成和含量受到三组份配比、MgO活性和一些添加物的影响;随三组份配比的变化,水泥石的微结构呈现A、B、C三种构型。指出其高强度得益于由有极性且非常细腻的水化物晶体构成的、有较强的结合力和较大界面能的水泥石微结构。 证明了氯氧镁水泥耐水性差的原因是其水化物不稳定。首次提出并论证了一个新观点,认为磷酸及其可溶性盐在掺量很少（<1%）的条件下能显著地改善氯氧镁水泥的耐水性,是因为它们在水中离解产生的各级磷酸根离子与Mg²⁺离子的络合作用,降低了碱式盐水化物形成并稳定存在所需的最低Mg²⁺离子浓度。这不但提高了5相和3相晶体的稳定性,而且减少了游离氯化镁。用此原理研发了比磷酸及其可溶性盐更好的X型和S型外加剂。X型外加剂使氯氧镁水泥的不良性能得到了大大改善;S型外加剂通过改变硫氧镁水泥的水化物组成,使之强度和稳定性成倍提高。由此指出,通过阴离子更多还原

【Abstract】 The theories and the practical techniques how to improve the properties of MgO-based basic salt cement and their articles are creatively investigated by the methods such as XRD, SEM and chemical analysis, etc.Here, the theory about basic salt （BS） cement is advanced for the first time. The cement whose setting and hardening occur mainly through the formation of some basic salt hydrates is defined as a BS cement. Also, the gelation in BS cements and some requirements to form BS cements are discussed. Thus, magnesium oxychloride cement （MOC） and magnesium oxysulfate cement （MOS） are MgO-based BS cements. Based on this theory, the formation mechanism of the phases in MOC pastes, the microstructures and the strengths of MOC stones, the reason for the poor water resistance of MOC stones and the mechanism to improve the water resistance are studied in detail.By the hydrolysis tests of Mg²⁺ ions, it had been proved that there were some stable multinuclear complexes[Mg_X（OH）_Y（H₂O）_Z]^2X-Y , yielded by the hydrolyzing—bridging reactions of Mg²⁺ ions ,in the system Mg²⁺ — OH^- — H₂O. In the setting and hardening of MOC pastes, the formation of 5 phase[Mg₃（OH）₅Cl·4H₂O] and 3 phase[Mg₂（OH）₃Cl·4H₂O] occurs through the multinuclear complexes [Mg_X（OH）_Y（H₂O）_Z]^2X-Y and the ions such as Cl^-, OH^- etc, in which involves three steps of sol—gel —crystallites. It was proved that the composition of the phases in MOC or MOS stones was related to the molar ratios of three components, the activity of MgO powder and some additives. Based on the different molar ratios of three components in MOC pastes, the microstructures of the MOC stones can be divided into three types such as A type, B type and C type. It is considered that the high strengths of MOC stones could be attributed to the strong bonds and great intersurface energy in the dense microstructure built by very fine crystallite grains of the BS hydrates with the strong polarity.The poor water resistance of MOC stones is due to the instability of the BS hydrates i.e. 5 phase or 3 phase in water. When adding small amount of the phosphoric acid or a soluble phosphate, the water resistance of MOC stones are greatly improved. A new idea is reachedfor the first time that the key factor being responsible for the great improvement of the water resistance of MOC stones, with the small amount of the phosphoric acid or a soluble phosphates, is the coordination between Mg2+ ions and the various anions such as H2PO4^, HPO42 , PO43 yielded by the ionizations of the acid or the phosphates in the solutions of MOC pastes. The coordination affects the hydrolyzing — bridging reactions of Mg2+ ions in the solutions, which not only enhances the stability of 5 phase and 3 phase in water, but also reduces the content of the free chlorides in MOC stones. X type and S type additives were developed and invented. X type additive can enhance the properties of MOC and its articles, while S type can change the hydrates in MOS pastes and greatly increase the strengths and stabilities under thermal and water conditions. Therefore, it is concluded that the addition of the additives containing some anions into BS cement pastes could affects the hydrolyzing — bridging reactions of metal ions and their products by the coordination, which is the most efficient way that can be used to change the compositions of BS hydrates in a BS cement and improve its properties.Based on these theorical researches and much more tests in the industrial production, the techniques are developed that can be used to produce the high quality articles of MgO-based BS cements.更多还原