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%。     

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。     

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。     

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.     

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.     

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。     

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.     

Aluminous cements containing magnesium aluminate spinel from Egyptian dolomite

Three mixes of calcium aluminate cements containing MA spinel were prepared using appropriate mixtures of Egyptian dolomite (MgO, 20.16% and CaO, 31.32%) with active alumina (99.50% A)¹. The cement mixes were prepared at 1600°C using the sintering method. The products were finely ground and their chemical and mineralogical compositions were investigated using the appropriate techniques. Also, their physicomechanical and refractory properties had been determined. The results indicated that their mineralogical compositions were refractory MA spinel, in addition to CA and/or CA₂ phases depending on the composition of the starting materials. The prepared cements exhibited a compromise between considerable strength and higher refractoriness. When 10% of such cements were added to refractory grade magnesia aggregate, in the presence of 0.1% Li₂CO₃ as a strength modifier, refractory castable bodies with improved hot-strength and thermal shock resistance had been achieved.     

Characteristics of magnesium polyphosphate cements derived from ammonium polyphosphate solutions

Magnesium polyphosphate cement pastes prepared by mixing MgO powder and ammonium polyphosphate (AmPP) solutions yielded early strengths of 2000 psi (13.78 MPa) at an age of 1 hr. The major reaction products responsible for the initial strength development at room temperature were found to be ternary phases of NH₄MgPO₄·6H₂O and Mg₃(PO₄)₂·4H₂O. The former exhibited morphological features resembling interlocking crystals composed of thin plates ～ 7 μm in length.The use of sodium tetraborate decahydrate (borax) as an additive to reduce the rate of reaction between MgO and AmPP was demonstrated. The inclusion of 20% borax by weight of AmPP extended the reaction time to 20 min, compared with a reaction time of <3 min for specimens without borax.     

The mechanism for soluble phosphates to improve the water resistance of magnesium oxychloride cement

This paper discusses the reasons why the addition of some soluble phosphates to magnesium oxychloride cement (MOC) can greatly improve its water resistance. With the XRD analysis and the determination of the strength retention coefficients (a judging index for the water resistance), it has been shown that the addition of small quantity of the soluble phosphates, such as H₃PO₄, NaH₂PO₄·2H₂O, and NH₄H₂PO₄, to MOC pastes does not influence the phases formed in the MOC pastes, but can result in the great increases of the strength retention coefficients of hardened MOC pastes, i.e., the great improvement of the water resistance of MOC. It was considered that the key components being responsible for the improvement of the water resistance could be the anions H₂PO₄⁻, HPO₄²⁻, and PO₄³⁻ yielded by the ionization of these phosphates in the solution of MOC pastes. These anions can decrease the lowest concentration of Mg²⁺ ions in the solution required by the formation of 5Mg(OH)₂·MgCl₂·8H₂O (5-phase) or 3Mg(OH)₂·MgCl₂·8H₂O (3-phase) in the MOC pastes and increase the stability of these phases in water. Thus, when the hardened MOC pastes with small quantity of the soluble phosphates are immersed in water, the 5-phase or 3-phase in them will not be decomposed by water, which makes the strength of the hardened MOC pastes remain unchanged in water.     

中国镁资源优势及镁质化工材料发展方向

镁质化工材料属于镁质材料的一种，包括镁盐中各类产品，广泛应用于国民经济中的各个领域。其原料来源广，储量丰富，主要包括含镁非金属矿、海水、卤水、盐湖苦卤，以及化工、冶金、轻工等行业副产物，可通过机械加工法或化学加工法制取不同规格、不同类型的镁质化工材料。重点介绍了活性氧化镁、电工级氧化镁、硅钢级氧化镁、高纯氧化镁等开发与生产现状；分析了中国具有丰富的镁资源和能源、多种工艺路线生产镁质化工材料，以及精细镁产品发展迅速的优势，建议建立万吨级骨干企业，发挥原料及生产方法多样、镁产品品种齐全的优势，采用先进设备，提升自控水平和精细化率，满足国内外市场的需求。     

Effects of magnesium oxychloride and silicon carbide additives on the foaming property during firing for porcelain ceramics and their microstructure

Porcelain green bodies that were prepared with a porcelain tile powder as a major raw material, and magnesium oxychloride (MO) and silicon carbide (SiC) as additives were fired at 1000–1200°C. Effect of the additives on the foaming property for porcelain ceramics and its microstructure was quantitatively investigated to clarify the foaming origin of polished porcelain waste during firing. The experimental results show that a small amount of the mixture of both MO and SiC added into the porcelain green body causes the body foaming during firing more significantly, compared to the addition of either SiC or MO. The foaming of porcelain green body with only SiC is more remarkable than that of the porcelain green body with only MO at the same content and firing conditions. The MO accelerates the foaming of porcelain green body with SiC during firing. In addition, the foaming mechanism was also discussed.