硅酸镁胶凝材料体积稳定性及水化特性EI北大核心CSCD

用硅灰(SF)和不同温度煅烧后MgO制备水化硅酸镁(MgO-SiO2-H2O,M-S-H)胶凝材料,研究其流动度、凝结时间、pH值与M-S-H胶凝材料强度及膨胀特性的相互关系。采用X射线衍射和热重分析等测试手段分析了不同温度煅烧的MgO对MgO-SF净浆水化产物和M-S-H结构的影响。结果表明:随着煅烧温度增加,MgO衍射峰强度增加,峰宽变窄,晶粒尺寸增加,活性降低。1150℃煅烧MgO制备的净浆中Mg(OH)2和M-S-H物相含量高,且M-S-H硅氧四面体聚合程度最大。1150℃煅烧MgO制备的MgO-SF流动度适中易成型(净浆和砂浆流动度分别为129 mm和206 mm),净浆pH值和凝结时间适中,砂浆强度高、自由膨胀率(εt)最小。εt与Mg(OH)2的含量变化幅度正相关。     

水化硅酸镁胶凝材料研究进展

可溶性SiO_2与MgO反应可形成水化硅酸镁凝胶[(MgO)_x–SiO_2–(H_2O)_y,M-S-H]。M-S-H凝胶的组成可变,结晶度差,硅氧四面体呈层状结构,对体系抗压强度起主要作用。M-S-H凝胶形成速率依赖于反应物的活性,活性MgO和硅灰是常见的反应物,该混合物遇水放热,放热速率与MgO活性密切相关,浆体溶液呈弱碱性,被认为在建筑材料领域有潜在应用价值。系统总结了M-S-H反应机理、组成特点、孔溶液化学、水化热、工作性和强度演化规律及其影响因素,同时分析了Mg~(2+)对C-S-H和Ca~(2+)对M-S-H的作用机理,展望了水化硅酸镁胶凝材料发展前景。     

MgO活性和养护温度对MgO-SiO2-H2O胶凝材料性能的影响

研究了不同温度煅烧MgO(MO)与硅灰(SF)混合物的流动性、抗压强度和pH值。借助X射线衍射、热重分析、Fourier红外光谱和固态核磁共振等测试手段分析了不同养护温度对MO-SF浆体水化产物和水化硅酸镁(MgO-SiO_2-H_2O, M-S-H)结构的影响。结果表明:随着煅烧温度增加,MO衍射强度增加,峰宽变窄,晶粒尺寸增加,活性降低。低活性MO制备的MO-SF混合物净浆和砂浆流动性更高,最大抗压强度出现时间越晚。提高养护温度有助于MO水化。28 d时,养护温度提高到50℃能加速M-S-H的形成,但80℃养护抑制了Mg(OH)_2水解和M-S-H的形成。高温养护有助于M-S-H硅氧四面体聚合程度提高。50℃是形成M-S-H较为适宜的养护温度。     

硅酸镁胶凝材料体积稳定性及水化特性

用硅灰(SF)和不同温度煅烧后MgO制备水化硅酸镁(MgO-SiO_2-H_2O,M-S-H)胶凝材料,研究其流动度、凝结时间、pH值与M-S-H胶凝材料强度及膨胀特性的相互关系。采用X射线衍射和热重分析等测试手段分析了不同温度煅烧的MgO对MgO-SF净浆水化产物和M-S-H结构的影响。结果表明:随着煅烧温度增加,MgO衍射峰强度增加,峰宽变窄,晶粒尺寸增加,活性降低。1 150℃煅烧MgO制备的净浆中Mg(OH)_2和M-S-H物相含量高,且M-S-H硅氧四面体聚合程度最大。1 150℃煅烧MgO制备的MgO-SF流动度适中易成型(净浆和砂浆流动度分别为129 mm和206 mm),净浆pH值和凝结时间适中,砂浆强度高、自由膨胀率(ε_t)最小。ε_t与Mg(OH)_2的含量变化幅度正相关。     

活性MgO含量对碱式硫酸镁水泥强度及水化产物的影响

为了研究活性MgO含量对碱式硫酸镁水泥强度及水化产物的影响,采用不同活性MgO含量的轻烧氧化镁制备水泥试样,进行抗压强度和抗折强度试验,并对水泥水化产物进行X射线衍射分析.结果表明,当改性剂掺量为活性MgO质量的1％时,活性MgO含量为60％的轻烧氧化镁制备的水泥试样在室温条件下养护28 d的抗压强度最高,水化产物的主要物相为5·1·7相和少量Mg(OH)2相;活性MgO含量为70％的轻烧氧化镁配制的水泥试样在同等条件下的抗压强度仅为活性MgO含量为60％时的60％,水化产物的主要物相为Mg(OH)2相和少量5·1·7相;活性MgO含量为43.2％的轻烧氧化镁制备的水泥试样强度最低,水化产物中以Mg(OH)2相为主,5·1·7相含量较少,以及剩余MgO相和未分解的MgCO3相.采用活性MgO含量为70％的轻烧氧化镁制备水泥试样时,增加改性剂掺量为活性MgO质量的2％时,试样各龄期强度有较大提高.     

基于水氯镁石合成水合硅酸镁及其在镁质浇注料的应用

水氯镁石是一种非常具有应用前景的镁盐资源,其储量丰富,成本低廉。以青海盐湖水氯镁石和水玻璃合成不同MgO/SiO₂摩尔比(0.5:1,1:1,1.5:1)的水合硅酸镁(M-S-H)凝胶,采用XRD、SEM、红外和核磁共振等测试手段研究M-S-H的合成机理和结构特征,进而将合成的M-S-H与硅微粉复合制备镁质浇注料,探究M-S-H结构对浇注料结合特性的影响规律。结果表明:不同MgO/SiO₂摩尔比的M-S-H呈层状堆叠结构,MgO/SiO₂摩尔比为1:1时M-S-H的层间自由水少,结晶度最高;M-S-H替代部分硅微粉制备镁质浇注料能显著提高1 550 ℃热处理后浇注料的力学性能,其中MgO/SiO₂摩尔比为1:1的M-S-H复合硅微粉制备的镁质浇注料综合性能最佳,与添加6%(质量分数)硅微粉制备的镁质浇注料相比,其常温抗折强度和高温抗折强度分别提高75%和8%。     

纳米SiO2对氧化镁激发矿渣材料性能的影响试验研究

为改善MgO-激发矿渣材料(MASM)力学性能,利用纳米SiO₂(NS)促进MASM的强度发展,研究了不同NS掺量对MASM凝结时间、抗压强度、水化历程、水化产物和微观形貌的影响,分析并揭示了NS的作用机理。研究结果表明:随着NS掺量的增大,MASM凝结时间逐渐缩短,流动度逐渐减小;NS掺量越大,矿渣水化越快,主要水化峰出现越早,峰值越高。NS不仅促进了MgO的反应和C-(A)-S-H的形成,还提高了MASM的结构密实性。掺入1%~2%(质量分数)的NS,可将MASM的抗压强度分别提高7.12%~33.37%(3 d)、12.44%~26.29%(7 d)、12.49%~31.09%(28 d)。     

钢渣-矿渣复合矿粉对水泥水化的影响

为了促进钢渣的资源化利用,克服纯钢渣粉活性低的缺点,将钢渣粉与矿渣粉按不同比例进行复配,并取代30%的水泥制备净浆。测试各试验组的抗压强度、水化放热速率和放热量,并对硬化浆体进行XRD、SEM和MIP测试。结果表明,当钢渣粉与矿渣粉的质量比例为1∶1时,最有利于提升水泥的抗压强度,而单掺30%钢渣粉的抗压强度最低。水化热测试发现,掺入30%纯钢渣粉的试验组具有最大的水化放热速率和水化放热量。XRD、SEM和MIP测试发现,掺入复合矿粉后生成新的水化产物Al₂Mg₄(OH)₁₂(CO₃)(H₂O)₃,硬化体更为致密,并且孔隙率和平均孔径均降低。     

煅烧磷石膏对蒸压硅酸盐制品水化过程的影响

磷石膏经高温煅烧改性后与粉煤灰、砂粉、石灰及水泥熟料等制备蒸压硅酸盐制品,研究了不同温度煅烧的磷石膏对蒸压硅酸盐制品水化过程的影响,用蒸压制品中未反应的Ca(OH)₂量及结合水量分析它们的反应速率,用XRD测定蒸压硅酸盐制品的水化产物,并结合SEM分析,结果表明,经煅烧的磷石膏对蒸压硅酸盐制品的水化有明显的促进作用,托勃莫来石与C-S-H(1)等水化产物的迅速生长而形成密实的水化产物结构是其增强蒸压硅酸盐制品的根本原因。     

钢渣粉对硫铝酸盐水泥水化过程的影响及热力学模拟

通过测试水泥浆体的凝结时间、抗压强度、电阻率,同时结合水化产物分析及热力学模拟,研究了不同掺量钢渣粉对硫铝酸盐水泥水化行为的影响规律。结果表明,随着钢渣粉质量掺量的增大,初凝时间呈先延长后缩短的趋势,且在掺量为20%时达到最大值。在28 d龄期内,掺入钢渣粉的水泥硬化浆体抗压强度均小于未掺入钢渣粉的硬化浆体,但在龄期达到60 d和90 d时,掺入40%钢渣粉试样的抗压强度均大于未掺入钢渣粉的试样。钢渣粉与硫铝酸盐水泥复合浆体的电阻率在水化初始阶段随着钢渣粉掺量的增大而增大,在水化后期(约3 h后)则随钢渣粉掺量的增大而减小。在1 d龄期内,钢渣粉掺量为40%的试样中的钢渣粉发生了水化反应,使得水泥浆体在减速期的水化速率最大。由热力学模拟结果可知：在钢渣粉掺量为40%的试样中,C₂S在10 h后开始进行水化反应,C₂ASH₈则在168 h后开始生成;当钢渣掺量大于15%时,随着钢渣粉掺量的增大,钙矾石和铝胶的生成量逐渐减少,C₂ASH₈的生成量逐渐增多。     

Development of low pH cement systems forming magnesium silicate hydrate (M-S-H)

This work aimed to develop novel cement systems for waste encapsulation that would form with a pH of around 10. The approach taken was to investigate the formation of brucite by hydration of a light burned periclase (MgO). Commercially available MgO powders often contain some CaO, and therefore silica fume was added to form C-S-H gel. Identification of the hydrated phases in MgO/silica fume samples showed that brucite formed in substantial quantities as expected. However, brucite reacted with the silica fume to produce a magnesium silicate hydrate (M-S-H) gel phase. After 28 days, the pH of systems rich in MgO tended towards the pH controlled by residual brucite (~ 10.5), whereas when all brucite reacts with silica fume a cement with an equilibrium pH just below 10 was achieved.     

Formation of magnesium silicate hydrate (M-S-H) cement pastes using sodium hexametaphosphate

Magnesium silicate hydrate (M-S-H) gel is formed by the reaction of brucite with amorphous silica during sulphate attack in concrete and M-S-H is therefore regarded as having limited cementing properties. The aim of this work was to form M-S-H pastes, characterise the hydration reactions and assess the resulting properties. It is shown that M-S-H pastes can be prepared by reacting magnesium oxide (MgO) and silica fume (SF) at low water to solid ratio using sodium hexametaphosphate (NaHMP) as a dispersant. Characterisation of the hydration reactions by x-ray diffraction and thermogravimetric analysis shows that brucite and M-S-H gel are formed and that for samples containing 60 wt.% SF and 40 wt.% MgO all of the brucites react with SF to form M-S-H gel. These M-S-H cement pastes were found to have compressive strengths in excess of 70 MPa.     

Kinetics and Activation Energy of Magnesium Oxide Hydration

The kinetics of hydration of magnesium oxide (MgO) powder to form magnesium hydroxide (Mg(OH)₂) were measured using isothermal calorimetry at different temperatures, and the morphology of the powders before and after hydration were examined. The hydration kinetics of light‐burned MgO exhibit a hydration rate peak similar to that of portland cement hydration, whereas the hydration kinetics of hard‐burned MgO are comparatively slower at the same temperature, and exhibit a continuously declining hydration rate after the first several minutes of reaction. The hydration kinetics of both light‐burned and hard‐burned MgO can be fit using a boundary nucleation and growth model that has previously been applied to the hydration of portland cement and tricalcium silicate. Activation energy values for MgO hydration were determined from the fitted rate constants and were also measured directly using small temperature excursions according to a recently proposed method. For light‐burned MgO the resulting values are in good agreement and indicate a value of 77 kJ/mol. For the hard‐burned MgO the activation energy values vary considerably depending on temperature and how the activation energy is measured, but are always lower than the value obtained for the light‐burned MgO.     

Role of sodium hexametaphosphate in MgO/SiO2 cement pastes

The extent of reaction between magnesium oxide (MgO) and silica fume (SiO₂) is normally limited and mixes require high water contents to give suitable rheology. The use of considerably lower water contents and the formation of magnesium silicate hydrate (M-S-H) gel as a binding phase is made possible by adding sodium hexametaphosphate (Na-HMP) to the mix water prior to the addition of MgO and SiO₂. This results in the formation of extensive reaction products and cured samples with high compressive strength and low porosity. In this work, the effect of Na-HMP on the hydration of MgO/SiO₂ mixes is investigated using high water to solids ratio samples to allow monitoring of pH and the solution chemistry during hydration. It is shown that a relatively small amount of Na-HMP inhibits the formation of Mg(OH)₂ when MgO is hydrolyzed. It is proposed that this is due to adsorption of phosphate species on the MgO which inhibits the nucleation of the Mg(OH)₂. This gives rise to high Mg^2 + species in solution and elevated pH (> 12) conditions relative to when Mg(OH)₂ forms. In contrast, the phosphate does not suppress formation of M-S-H gel. In combination with the enhanced dissolution rate of SiO₂ at high pH, M-S-H gel can form quickly without competition for Mg^2 + ions by Mg(OH)₂ precipitation. Incorporating the optimum concentration of Na-HMP into the mix water therefore transforms the properties of cement paste and mortar samples formed by reacting MgO and SiO₂.     

硫酸盐浸泡环境下CaO-Na2CO3激发矿渣砂浆性能退化及机理研究

以Na₂SO₄和MgSO₄溶液为侵蚀介质,研究了在浸泡环境下CaO-Na₂CO₃激发矿渣(CNS)砂浆和普通硅酸盐水泥(OPC)砂浆经硫酸盐侵蚀前后的抗折强度、抗压强度及不同深度处的SO^2-₄浓度,结合X射线衍射(XRD)、扫描电子显微镜(SEM)、压汞法(MIP)等测试方法分析了CNS砂浆和OPC砂浆的侵蚀产物及孔结构,对比讨论了Na₂SO₄和MgSO₄对CNS砂浆和OPC砂浆的侵蚀机理。结果表明:CNS砂浆的水化产物主要是低Ca/Si比的水化硅铝酸钙(C-A-S-H),不存在氢氧化钙,碳酸钙的填充作用使其孔结构优于OPC砂浆,并且在相同侵蚀环境下,CNS砂浆的抗硫酸盐侵蚀能力大于OPC砂浆;MgSO₄侵蚀环境下CNS砂浆的侵蚀产物主要是水镁石(腐蚀后期会带动试件表面的砂浆一起剥落)和无黏聚力的水化硅铝酸镁(M-A-S-H);与Na₂SO₄相比,MgSO₄对CNS砂浆的腐蚀性更强。     

粉煤灰掺量对氯氧镁水泥混凝土物理力学性能的影响

为了拓展氯氧镁水泥(MOC)材料的应用领域,以盐湖提钾肥副产物水氯镁石、轻烧氧化镁和粉煤灰为胶凝材料,制备了不同粉煤灰掺量的氯氧镁水泥混凝土(MOCC)。研究了粉煤灰掺量对MOCC抗压强度、物相组成、微观形貌和孔结构的影响。结果表明:随着粉煤灰掺量的增加,MOCC的抗压强度逐渐降低,当粉煤灰掺量为40%(质量分数)时,其300 d抗压强度降低至39.99 MPa,降低了22.52%。MOCC的主要水化产物为5Mg(OH)₂·MgCl₂·8H₂O(5·1·8)和Mg(OH)₂,掺加粉煤灰并没有产生新的晶相。掺入粉煤灰增加了MOCC的孔隙率和有害孔体积,从而降低了其抗压强度。采用相同水灰比制备了普通硅酸盐水泥混凝土,抗压强度对比测试结果表明:掺40%的粉煤灰MOCC的抗压强度虽然比未掺粉煤灰MOCC抗压强度低,但仍比普通硅酸盐水泥混凝土300 d龄期的抗压强度(33.42 MPa)高出19.66%,说明MOCC比普通硅酸盐水泥混凝土具有较高的抗压强度。     

重金属在水泥窑协同处置的净浆硬化体中的分布及形态

通过欧共体标准物质局（European Community Bureau of Reference）提出的一种三级4步提取法（BCR）,分析了垃圾焚烧飞灰和经水泥窑协同处置的净浆硬化体中重金属的分布和形态。探究了随水化反应的进行,其重金属形态转化的趋势。结果表明,重金属主要分布在氢氧化钙、水化硅酸钙（C-S-H）、钙矾石（AFt）和未水化的水泥熟料中。随着水化反应的进行,Zn、Cu、Cr、Cd和Mn皆有向迁移能力较强的形态转化的趋势,其中Cr和Cd的转化趋势较为明显。与垃圾焚烧飞灰相比,重金属通过水泥窑高温煅烧和水化反应,其迁移能力较强的形态占比明显减少。     

The magnesia-silica gel phase in slag cements: alkali (K, Cs) sorption potential of synthetic gels

Blends of Portland cement with blast furnace slag hydrate to yield two gel phases, one essentially a calcium silicate hydrate (C-S-H) composition, the other a magnesium silicate hydrate (M-S-H) composition: the two gel phases are essentially immiscible. Together, the gel phases comprise an important source of sorption potential for the alkalis present in ordinary cement and blending agents. M-S-H gels have been synthesised and their sorption potential measured for postassium (K) and cesium (Cs) at 25 °C by using fresh gels as well as gels previously aged at 85 °C for 6 months. The ability of slag-cement blends to lower pore fluid alkalinity generally, and in nuclear waste technology to incorporate Cs, is interpreted in terms of the sorption data.     

MgO源对纳米η-Al2O3制备镁铝尖晶石的影响

分别以轻烧氧化镁粉、碳酸镁、分析纯氢氧化镁为MgO源,纳米η-Al₂O₃为原料(其摩尔比为1∶1),采用固相反应法制备镁铝尖晶石。研究不同MgO源对纳米η-Al₂O₃制备镁铝尖晶石的显气孔率、体积密度、物相组成、晶胞参数以及微观结构的影响。结果表明,随着烧结温度升高,三种MgO源与纳米η-Al₂O₃制得镁铝尖晶石试样的致密性逐渐升高。在1 600 ℃下,以氢氧化镁为MgO源与纳米η-Al₂O₃制得尖晶石试样的体积密度最大为3.296 g/cm³,显气孔率最低为1.9%,晶粒发育最好,晶粒尺寸约为3~5 μm。1 300 ℃时,三种MgO源与纳米η-Al₂O₃全部生成镁铝尖晶石,与以α-Al₂O₃为Al₂O₃源制备镁铝尖晶石的传统固相法相比,镁铝尖晶石的合成温度降低了100 ℃,可以降低镁铝尖晶石的成本,对镁铝尖晶石的应用具有实际意义。