Effect of calcination temperature on the properties of magnesium oxides for use in magnesium oxychloride cements

A comparison is made of the properties of magnesium oxides prepared from basic magnesium carbonates and Indian and Greek rock magnesites. the density increased with burning temperature and the reactivity decreased. the effect of this on the properties of oxychloride cements is shown. Iodine number is shown to be a good index of reactivity and specific surface (air permeability) to indicate the amount of chloride solution needed to make a workable mix with an oxide.     

Water-resistant blended oxychloride cements

Comprehensive studies into natural silicates led to an informative parameter that can be of help in assessing their usability in cement technology. This parameter is their hydraulic activity. The study reported here covered the manner in which cements based on natural silicates harden and how the silicate constituents affect the mechanism by which the hardened cement acquires high mechanical strength and water resistance.     

The influence of composition and temperature on hydrated phase assemblages in magnesium oxychloride cements

Due to their nonhydraulic nature, magnesium oxychloride cements (MOCs) are susceptible to degradation following contact with water. Improving the water resistance of these materials requires better understanding of hydrated phase relations and the sensitivity of hydrated phases to water. Toward this end, a series of targeted experiments and complementary thermodynamic calculations were carried out to assess hydrated phase assemblages in the system MgO‐MgCl₂‐H₂O across a range of compositions. Focus is placed on appraising the effects of composition and reaction temperature. In broad agreement with literature data, under ambient conditions, hydrated MOCs are noted to contain Phase 3 (P3), Phase 5 (P5), and brucite, but the mass partitioning of these phases is highly dependent on H₂O/MgCl₂ and MgO/MgCl₂ molar ratio as well as curing temperature and age. At room temperature, P3 is favored at lower water contents, however, P5 and/or brucite are favored to form as water availability increases. Thermodynamic calculations indicate that P3 is “more stable” than P5 at lower temperatures—an outcome which impacts the engineering properties, for example, strength and volume stability. The impacts of the accuracy and self‐consistency of currently available thermodynamic data and their implications on predicted phase assemblages are discussed.     

Strength development in magnesium oxysulfate cement

Modulus of elasticity and microhardness measurements were made on magnesium oxysulfate systems (paste and compacted) having a wide range of porosity. Three sets of compacts were made; each set was made with particles having a different size range (5 to 150 μm; 150 to 300 μm; 300 to 600 μm). The log mechanical property versus porosity curves for paste samples were linear. The curves for compacted samples had a change in slope at 7.5 per cent porosity. At porosities less than 7.5 per cent, the data for paste and compacted samples were on the same curve. Tat higher porosities microhardness values for compacted samples were greater than those for paste samples; modulus of elasticity values were less. Compacted samples made with finest particles had higher values for mechanical properties at a given porosity. The mechanical behaviour of these systems was explained on the basis of the relative contribution of porosity, pore size distribution, interparticular bonds and strength of the solid phase.     

适用于氯氧镁水泥混凝土减水剂的制备与表征

通过自由基聚合法,采用烯丙基聚氧乙烯醚(APEG2400)为主链,甲基丙烯磺酸钠为嵌段合成了一种适用于氯氧镁水泥的缓凝型聚羧酸减水剂。探讨了减水剂掺量对氯氧镁水泥浆体流动度与混凝土抗压强度的影响。结果表明,当合成条件为n(丙烯酸)∶n(烯丙基聚氧乙烯醚):n(甲基烯丙基聚氧乙烯醚):n(甲基丙烯磺酸钠)=24∶3∶1∶4,反应在85℃下进行,减水剂掺量为0.6%时,氯氧镁水泥浆体的流动度达到最佳,同时氯氧镁水泥的7 d与28 d抗压强度比未掺减水剂的混凝土分别提高了38%和33%。     

矿物掺合料对氯氧镁水泥早期水化行为的影响

研究了矿物改性氯氧镁水泥前期水化行为,绘制了各矿物掺合料氯氧镁水泥水化电阻率-时间曲线,测试终凝时间以及1 d抗弯与抗压强度。结果表明,矿物掺合料能够延缓氯氧镁水泥水化速度,并随着矿物掺合料掺量的提高,其水化速度逐渐变慢。同等掺量下硅灰延缓反应时间的作用最为明显,其次是石粉与粉煤灰。硅灰的掺入延缓氯氧镁水泥水化速度,大幅度提高其初终凝时间,降低早期强度,其掺量不宜超过20%。粉煤灰与石粉氯氧镁水泥初终凝时间均在规范要求以内,对早期抗弯拉强度与抗压强度影响幅度相对较小。添加粉煤灰与石粉试样晶体较掺硅灰试样结晶程度更高。     

卤水成分对氯氧镁水泥强度的影响

采用均匀实验设计考察KCl、MgSO4、NaCl以及制备镁水泥主要原料MgCl2对镁水泥强度的影响,并运用DPS软件对所得实验数据进行二次多项式回归,阐述了KCl、MgSO4、NaCl、MgCl2以及各因素交互项对镁水泥强度的影响。通过SEM和XRD从微观角度分析了镁水泥内部结构和主要成分,为甘肃高台苦盐池的苦卤资源晒制老卤生产镁水泥制品提供了必要的理论依据。     

纳米α-Ni(OH)_2膜的合成及其超级电容性质研究

采用化学沉淀法在室温下合成了一种α-Ni(OH)_2纳米薄膜,探讨了合成温度及表面活性剂的影响。采用XRD、SEM、TEM和BET对材料进行表征。结果表明,合成温度及表面活性剂的种类对产物组成和形貌有较大影响,室温下,样品为厚度约2 nm的薄膜,带有较多的褶皱,比表面积206.8 m²/g;50℃下合成的产物表面褶皱开始消失,且不均匀,有颗粒状物质生成,80℃下的产物褶皱状结构消失,主要为团聚在一起的颗粒组成。同时,将α-Ni(OH)_2纳米膜制成单电极,循环伏安和恒电流充放电测试表明,α-Ni(OH)_2纳米膜具有较好的电化学性质,当充放电电流密度为1 A/g时,电极材料的比容量达到539.6 F/g。     

Influence of molar ratios on properties of magnesium oxychloride cement

A parametric study has been conducted to investigate the influences of the molar ratios of MgO/MgCl₂ and H₂O/MgCl₂ on the properties of magnesium oxychloride (MOC) cement. By an integrated assessment of the experimental studies of strength development and X-ray diffractograms, together with application of the relevant phase diagram, it is recognized that the molar ratios of MgO/MgCl₂ and H₂O/MgCl₂ can significantly affect the properties of MOC cement. For a MOC cement paste possessing a dominance of 5MgO·MgCl₂·8H₂O (phase 5) crystals, the molar ratios of MgO/MgCl₂ of 11-17 and H₂O/MgCl₂ of 12-18 are found to be the most favorite ranges for design purpose. The choose of the molar ratio of H₂O/MgCl₂ is, however, largely depends on the molar ratio of MgO/MgCl₂ mainly for controlling workability of paste. Therefore, the most critical parameter to be selected in the design process is the molar ratio of MgO/MgCl₂, although the reactivity of the MgO powder is also important. Besides, the molar ratio can also be affected by the reactivity of the MgO powder to be employed. It is believed that a molar ratio of MgO/MgCl₂ of 13, the most suitable one shown in this study, can be used as a starting point in the normal practice.     

Exploring the self-cleaning and antimicrobial efficiency of the magnesium oxychloride cement composites

Composites of magnesium oxychloride cement (MOC) functionalized with TiO₂ nanoparticles are proposed here as an alternative technology to maintain clean building surfaces from airborne pollutants and microorganisms. The MOC composites were characterized by different techniques such as XRD, FTIR, SEM, EDS, UV–Vis, compressive strength, and nanoindentation tests. According to the results, phase 3 (3 Mg(OH)₂^.MgCl₂^.8H₂O) with needle-like morphology was the primary crystallized hydration product for the MOC composites. Also, the samples exhibited good mechanical properties and good light absorption, allowing them to activate under solar light irradiation. The self-cleaning efficiency of the MOC composites was evaluated by measuring the removal of three types of pollutants: methylene blue (MB), rhodamine B (RhB), and reactive black 5 (RB5), under two scenarios: natural sunlight and accelerated weathering conditions. The self-cleaning tests revealed outstanding efficiencies of the composites to remove MB (82%), RhB (88%), and RB5 (91%) under solar light and accelerated weathering tests. On the other hand, the antimicrobial activity was evaluated against E. coli (gram-negative) and S. aureus (gram-positive) under irradiation. The zone of inhibition (ZOI) showed diameters higher than 21 mm to E. coli for samples with 5% of TiO₂ or superior, revealing a high microbial inhibition of the gram-negative bacteria. Also, the structural and morphological stability of the MOC composites was confirmed after several cycles for the accelerating weathering tests, demonstrating their potential to be used outdoors to reduce environmental pollution.     

Effect of alcohol leachable chloride on strength of magnesium oxychloride cement

The major crystalline phases in magnesium oxychloride cement (MOC) have been extensively studied, but the other phases have not been studied due to the difficulty in identifying them. In the current study, we focused on the effect of chlorine-containing phases other than crystalline oxychlorides on the strength of cured MOC materials. The alcohol leachable chloride (ALC) was proposed to characterize the other phases containing chlorine, and the absolute ethanol leaching test was developed to determine ACL content in a cured MOC paste. The results showed that either decreasing MgO/MgCl₂ molar ratio or increasing H₂O/MgCl₂ molar ratio led to an increase in ALC content in cured MOC slurry, but adding a small amount of phosphoric acid resulted in very little or almost no ALC in the modified MOC slurry. In addition, increasing ALC content has been shown to significantly reduce the compressive strength of hardened MOC pastes. Thus, the modified MOC pastes had high strength, compared with the corresponding common MOC pastes. According to the experimental results, the relationship between the ALC content and the compressive strength of cured MOC materials was established. Therefore, a low ALC content was proposed as a characteristic index of high-quality MOC materials.     

柔韧性丙烯酸酯乳液胶粘剂改性氯氧镁水泥研究

以软单体为主合成了一种丙烯酸酯乳液,将其用于氯氧镁水泥的改性,当乳液加入量为水泥量的15%时改性效果最佳.用改性的氯氧镁水泥和玻璃纤维布制成的无机玻璃钢耐水性提高,柔韧性增加,克服了制品的"返卤"及翘曲变形等缺点,扩展了氯氧镁水泥的应用范围.     

碳化作用对镁质胶凝材料微观结构演变过程的影响

为揭示碳化作用对镁质胶凝材料微观结构演变过程的影响,通过扫描电镜（SEM）、X射线衍射（XRD）和压力试验机,对室内养护5 a龄期的镁质胶凝材料净浆试样和30 a龄期的镁质胶凝材料房梁试样进行分析。结果表明,碳化作用对镁质胶凝材料的微观形貌和物相组成影响较大。空气中的二氧化碳由表及里渗入镁质胶凝材料中,在二氧化碳渗入的过程中引起镁质胶凝材料微观形貌和物相组成的变化。镁质胶凝材料的微观形貌主要由针棒状、多孔状向块状转变,物相由5·1·8［5Mg（OH）₂·MgCl₂·8H₂O］相经2·1·1·6［2MgCO₃·Mg（OH）₂·MgCl₂·6H₂O］相最终转化为稳定的水菱镁矿和菱镁矿。由于碳化作用,镁质胶凝材料5 a龄期的抗压强度相比1 a龄期下降了22.1 MPa。因此,需要采用隔离方法处理镁质胶凝材料,以减少其碳化作用,延长其使用年限。     

氧化钙对氯氧镁水泥低温凝结性能的影响

为了深入研究氯氧镁水泥低温凝结机理,进而改善和提高氯氧镁水泥在低温时的快硬性能,把氧化钙加入到氯氧镁水泥料浆中,通过搅拌、成型、恒温恒湿箱养护后测定其凝结时间及早期强度。结果表明：氧化钙加入后放出热量,引发氯氧镁水泥水化起始期反应的进行,有效缩短氯氧镁水泥的凝结时间。当氧化钙掺量为氧化镁质量的4%时,氧化镁活性为62.24%和72.01%时初凝时间分别由593 min缩短到146 min、由570 min缩短到126 min,终凝时间分别由673 min缩短到374 min、由641 min缩短到260 min,同时都提高了氯氧镁水泥的低温早期强度。     

Petrographic evidence of calcium oxychloride formation in mortars exposed to magnesium chloride solution

Many researchers have reported chemical interactions between CaCl₂ and MgCl₂ solutions and hardened Portland cement paste. One potentially destructive phase reported in the literature is calcium oxychloride (3CaO·CaCl₂·15H₂O). In the past, limited numbers of researchers have reported identification of this phase by X-ray diffraction. In this work, petrographic evidence of oxychloride formation is presented based on optical microscopy, scanning electron microscopy and microanalysis. This evidence indicates that calcium oxychloride does form in mortars exposed to MgCl₂ solutions.     

Petrographic and thermal evaluation of dolomites for the manufacture of magnesium oxychloride cement

In the preparation of magnesium oxychloride cement from MgO and MgCl₂.6H₂O solution, MgO is sometimes replaced by partially calcined dolomite, MgO.CaCO₃. In this paper, the suitability of dolomites for this purpose was studied by use of petrographic, d.t.a. and X-ray diffraction techniques. It is shown that for making good oxychloride cement, the dolomite should be compact and microcrystalline. Impurities such as siderite, haematite, magnetite and clayey matter which are generally present in dolomites, form a coating over the MgO particles during partial calcination at 750° and make the fired material less reactive and generally unsuitable for making oxychloride cement.     

氯氧镁水泥返卤成因及其改进的研究

本文从氯氧镁水泥的原料活性MgO含量,配方,相转变,养护等方面分析和研究了氯氧镁水泥返卤成因,指出其根本原因是制品中存在的过量MgCl2,并研究了改进的方法。     

Strontium-loaded magnesium phosphate bone cements and effect of polymeric additives

Magnesium phosphate-based cements (MPCs) are nowadays regarded as promising materials in the field of bone repair. The inclusion of Sr ions in the formulations may represent a valuable strategy to improve their bone regeneration performances, but the effect that such ion exerts on the physico-chemical properties of the material have not been investigated so far. In this work we describe the development of Sr-MPCs obtained including Sr ions in different forms, i.e., using Sr-substituted tri-magnesium phosphate precursor powder or including in the formulation Sr-based salts (SrCl₂ and SrHPO₄). The materials were characterized both in the form of pastes and hardened cements, finding that according to the type of Sr precursor used we can tune the setting time, the amount of binding phases in the cements, their morphology and thermal behavior. The dissolution behavior and the release kinetics of Mg²⁺ and Sr²⁺ can as well be modulated, and in particular the use of SrCl₂ in the formulation leads to a higher dissolution and a faster release of a significant amount of both Mg²⁺ and Sr²⁺, compared to the other samples. Given the unsatisfying performances obtained during the injectability and anti-washout tests, we also included two polymeric additives, namely poly(N-isopropylacrylamide) and mucin, in the Sr-MPCs formulations. The results demonstrate that it is possible to obtain Sr-MPCs with promising properties for applications as bone cements, that can be tuned according to the form under which Sr is included in the formulation. In addition, mucin markedly improves the cohesion and injectability of the Sr-MPC pastes, providing a simple but effective strategy to develop materials of interest in the orthopedic field.     

Experimental study on urban refuse/magnesium oxychloride cement compound floor tile

This article is a study on the production technology of urban refuse magnesium oxychloride cement compound floor tile by taking urban refuse and magnesium oxychloride cement as main raw materials. We experimentally studied the influence of the concentration of magnesium chloride solution and the fineness of magnesium oxychloride cement on the property of the product by means of experiments and analyzed the microstructure of hydration product using SEM.     

Effect of magnesium chloride concentrations on the properties of magnesium oxychloride cement for nano SiC composite purposes

Different magnesium oxychloride cements (MOCs) were studied with a fixed 13 moles of magnesite and 12 moles of water with different moles of magnesium chloride, MgCl₂·6H₂O from 0.5 to 1.9. Cold crushing strength, initial and final setting times, and dissolution in water were all increased with an increase in magnesium chloride. 1.5 moles of magnesium chloride showed the highest compressive strength. X-ray diffraction analysis (XRD) studies showed a gradual decrease in hydrated magnesia, Mg (OH)₂ and a gradual increase in phase 5, 5Mg(OH)₂·MgCl₂·6H₂O. Scanning electron microscopy (SEM) studies indicated that needle shaped crystals of phase 5 are responsible for the reinforcement of the matrix of these Sorel cements. The highest strength sample was used to develop a nano composite with nano particles of SiC. This composite does not require melting or firing for sintering, and there is no risk of grain growth. High content of needle shaped reinforcing crystals of phase 5 in the matrix with an increase in magnesium chloride, together with nano sizes aggregate particles of SiC provided a promising nano composite.