Cementing mechanism of potassium phosphate based magnesium phosphate cement

Magnesium phosphate cements (MPCs) are materials that belong to chemically bonded ceramic materials. They have a wide range of potential applications, due to their superior performance. In this paper, the reaction products and cementing mechanism of magnesium phosphate bonded cement based on the dead burned magnesia and the mono-potassium phosphate (MPP) are investigated. Fine powder and grains of dead burned magnesia were used to prepare pure cement paste and bonding cluster samples, respectively. The cement reaction products and their micro-morphology in the both different samples are examined. The microstructure of specimens is analyzed by SEM, TEM, XDR, and optical microscopy. Struvite of potassium (MgKPO₄·6H₂O) is observed in the reaction products. According to the analysis, it is found that struvite exists in both crystalline and amorphous form. There is also residual magnesia in the hardened cement paste. By means of microscopy observation, it can be seen that reaction products form around the unreacted magnesia and can develop into a continuum structure, which further produces the hardened paste. Struvite can grow up to form the more perfect crystal in a long term curing age, if large enough space is available during the hydration process.     

Solubility controlling of the precursor powders of magnesium phosphate cement by changing the powder composition

One of the important factors to introduce a cement as an injectable one is to control the setting time of the cement. In this paper to control the setting time of magnesium phosphate cement, the effect of addition of calcium and sodium on phase composition and the solubility of its precursor powders was evaluated. Three phosphate precursor powders that contained only Mg, Mg–Na and Mg–Na–Ca were synthesised via an emulsion precipitation method. Phase composition, particle size distribution and solubility of the powders were determined by XRD, laser particle size analyser and ionic chromatographic methods, respectively. Addition of calcium and sodium decreased the mean size of the powder significantly from 114 to 12?µm. Furthermore, solubility of the powders decreased by the addition of calcium and sodium.     

Research progress on the properties and applications of magnesium phosphate cement

Magnesium phosphate cement (MPC) is a new cementing material with great development potential and excellent properties. In addition to traditional cement, MPC also has the characteristics of ceramics, refractory materials, and biological materials. The MPC materials can be applied especially in architecture and other fields such as wall spraying, structure repair, solid waste curing, biomedical engineering, and 3D printing. Nowadays, MPC materials are being used in more updated, cutting-edge applications. This paper mainly summarizes the research progress of MPC in terms of material properties and applications in various fields in recent years, analyzes the research results of various scholars, and discusses the future research direction and current problems to be solved.     

Fast setting tricalcium silicate/magnesium phosphate premixed cement for root canal filling

MTA-based root-end filling is a promising therapeutic approach for root repair, however, difficult handling characteristics, presence of toxic elements in the material composition and long setting time are main drawbacks for clinical applications. The purpose of this study was to develop a novel fast setting silicate based premixed cement for endodontic use. The premixed cement contained tricalcium silicate (C3S) as the main constituent for hydration, magnesium phosphate cement (MPC) as setting accelerators and glycerol as water-miscible liquid. The physicochemical properties and antibacterial property of the novel cements were evaluated. Moreover, biocompatible zirconium oxide (ZrO₂) was chosen as radiopacifying agent added into the premixed cement. The radiopacity, physicochemical properties, antibacterial property and cytotoxicity of the radiopaque premixed calcium silicate based cements were evaluated. The setting time of the premixed MPC/C3S cements could be modulated within the range from 70 min to 205 min by adjusting the content of MPC. Meanwhile, the premixed MPC/C3S cement displayed good flowability and injectability when the amount of MPC less than 20%. The addition of ZrO₂ provided the premixed MPC/C3S cement with excellent radiopacity while had no significant effects on the setting time, flowability, film thickness, injectability and washout resistance. Moreover, the premixed cement with or without ZrO₂ had good antibacterial property and cytotoxicity. Our results indicated that the premixed MPC/C3S/ZrO₂ cement could be considered as a promising candidate for application in endodontics owing to its desirable physicochemical properties, antibacterial activity and cytocompatibility, especially relatively short setting time and good sealing ability.     

Multi-scale characteristics of magnesium potassium phosphate cement modified by metakaolin

Workability and early-ages mechanical properties are important indicators of magnesium potassium phosphate cement (MKPC) as a repair material. The effect of metakaolin (MK) on the setting time, fluidity and early-ages strength of MKPC paste was studied, and its influence mechanism was analyzed through pore structure, microstructure and nanomechanical properties. The results show that 10% and 20% of MK prolong the setting time of MKPC paste, but excessive MK shortens the setting time of MKPC paste. Meanwhile, incorporating MK reduces the fluidity of MKPC paste, and the early-ages strength of MKPC specimens increases when the substitution ratio of MK is 10%. When 10% of MK is incorporated to the MKPC paste, the 30-d shrinkage of the sample is only 69% of the control group. Meanwhile, a proper amount of MK can improve the pore structure of the MKPC specimen and make its microstructure denser by generating amorphous aluminosilicate phosphate gel. It is observed from the nano-scale characteristics that incorporating 10% MK can reduce the content of pore phase and unreacted MgO phase, and increase the volume fraction of hydration products.     

Organic-inorganic composites based on magnesium phosphate cement and acrylic latexes: Role of functional groups

The role of carboxyl functional groups in acrylic latex employed to fabricate an organic-inorganic composite material based on magnesium phosphate cement has been investigated. The acidic nature of the latex aqueous medium enhanced the dissolution of the magnesium oxide in the first stages of the cement reaction. The following increase in pH promoted the deprotonation of the carboxyl groups, which became involved in surface adsorption effects. Adsorption processes were found to control the nucleation and growth of the reaction products. The resulting overall hindering effect slowed down the reaction rates and delayed the precipitation of the solid phosphates with beneficial consequences, namely, the retardation of setting time and the modulation of the heat released. Modification in the morphology of the formed crystals, with the prevalence of platelet-like over prismatic habit, along with a decrease in their average size, was obtained. The crystals formed in higher amounts with respect to the neat cement because the reaction proceeds closer to equilibrium. The obtained microstructure is strengthened because of a more effective intermingling between crystals and the amorphous phase. Furthermore, the synergistic combination of polymer and phosphate cement improved the elastic properties, and reduced the water absorption, impacting positively on the durability of the composite.     

超快硬磷酸镁水泥研究进展

概述了制备磷酸镁水泥所使用的原料和水泥的制备方法。探讨了磷酸镁水泥的水化机理和缓凝机理,并对主要水化产物磷酸镁铵（MgNH4PO4·6H2O）的晶体化学结构进行了分析。综述了磷酸镁水泥的研究进展和应用前景。指出：磷酸镁水泥基础性研究不够深入,特别是水化机理和水化产物等方面存在争议;在磷酸镁水泥中采用较多的化学原料时会造成成本偏高;磷酸镁水泥在水化反应过程中释放氨气会造成空气污染;中国对磷酸镁水泥的研究报道较少,应用领域也较有限。以上种种因素限制了磷酸镁水泥的规模化生产和应用。因此,在深入开展磷酸镁水泥基础理论研究的同时,仍需对其应用领域进行推广,特别是寻求廉价的矿物和岩石原料或工业废弃物作为替代原料（如菱镁矿替代轻质碳酸镁等镁盐）或填料,这是磷酸镁水泥大量规模化生产和应用的关键。     

Multi-scale characteristics of magnesium potassium phosphate cement enhanced by waste concrete powder

Using recycled concrete powder (RP) as an alternative binder can effectively reduce construction and demolition waste and contribute to developing eco-friendly repair materials. However, the effect of RP on magnesium potassium phosphate cement (MKPC) has not been sufficiently studied. In this study, MKPC pastes were prepared by replacing different contents of MgO with RP, and the evolution of the structural behavior was explained from nanoscale to microscale. The results show that incorporating an appropriate amount of RP can increase the fluidity and setting time of the MKPC mixture and improve its mechanical properties. The drying shrinkage and water resistance of MKPC specimens also improve with the increasing RP content. Incorporating an appropriate amount of RP can refine the pore structure of MKPC samples, while the generation of gel-like products can compensate for the adverse effects of reduced struvite-K content. The nanoscale characteristics of the MKPC samples also indicate that incorporating RP results in a decrease in the residual MgO and pore phase content, an increase in the content of the hydrated phase, and a decrease in the loss of the hydrated phase volume fraction due to water soaking. Upon optimizing the RP content, the MKPC mixture exhibits a lower cost and carbon footprint, with the 28-d compressive strength of the sample mixed with 10% RP increased by 7.36% relative to the plain sample, indicating that recycling RP is feasible in an eco-friendly MKPC system.     

Modified calcium magnesium phosphate bone cement with improved microenvironment

Calcium magnesium phosphate bone cement (MCPC) has been widely used in bone defects restoration and attracted much attention due to excellent mechanical properties and biodegradability. However, excessive MgO tends to cause a local alkaline microenvironment which is adverse for cell growth and differentiation. In this work, we constructed the MCPC composites with improved microenvironment, enhanced osteogenic differentiation and biomineralization by introducing various concentrations of gelatin solutions. Gelatin played important roles in the improvement of physicochemical property, biodegradability, biocompatibility, osteogenic differentiation activity and biomineralization of MCPC. When incorporated with 1% and 5% of gelatin, the MCPC composites exhibited higher compressive strength and osteogenic differentiation ability of BMSCs in vitro. In conclusion, the modified MCPC composite is a potential candidate for bone defects repair and regenerate.     

磷酸镁水泥性能试验研究

采用过烧镁砂与磷酸镁二氢钾为主要原料,按照一定配比制备出可工业化生产的磷酸镁水泥。研究了磷酸镁水泥的凝结硬化时间、不同龄期的强度、干缩率、耐腐蚀性及粉煤灰对其性能的改性,并采用X射线衍射分析和扫描电镜等手段对其水化产物进行了分析。研究结果表明,磷酸镁水泥凝结时间受水灰比、成型温度影响较大,早期强度发展迅速,干缩率较小,耐腐蚀性好,掺加适量的粉煤灰可有效地提高其后期强度。该体系水化产物主要是六水磷酸镁钾晶体和一些无定形物质。     

Properties enhancement of magnesium phosphate cement by cross-linked polyvinyl alcohol

A novel ceramic composite has been obtained by introducing polyvinyl alcohol in magnesium-based chemically-bonded ceramics and exploiting the cross-link reaction with glutaraldehyde during setting. The properties of the obtained material and the interaction of the polymer with the cement reaction have been investigated. Several beneficial effects were observed. Namely, an extension of the working time, a reduction in the water sensitivity, a decrease in the rate of the heat evolution during hardening. The latter has been ascribed to the intervention of surface adsorption processes, which hindered the dissolution of MgO, as well as the nucleation and growth of the magnesium phosphate products, in concert with the film forming ability of the polymer. Thanks to the complementarity of their mechanical properties, the cement and the additive operated in a synergistic fashion, allowing for the obtainment of a material possessing higher strength and better elastic properties. Three-dimensional quantitative image analysis from synchrotron X-ray microcomputed tomography evidenced the development of a more compact microstructure, comprising a higher number of crystals of smaller size. As a consequence, the pore network exhibited a higher fraction of small pores and lower pore connectivity. These characteristics contributed to hinder the water absorption, as confirmed by the fluid transport simulations within the volume. The observed correlation between the solution pH and the polymer cross-link density offers the way to effectively modulate the material performance by acting on the chemical environment thanks to its compatibility with the cross-link reaction.     

Preparation and characterization of a novel magnesium phosphate cement-based emulsified asphalt mortar

To improve the efficiency of repairing asphalt pavements, a rapid-hardening magnesium-based cement emulsified asphalt (MCEA) mortar was developed. The effect of mix parameters on the properties of MCEA sample was systematically discussed, including asphalt to cement (A/C) ratio, asphalt and cement (S/(A+C)) ratio, water to cement (W/C) ratio, and MgO to phosphate (M/P) ratio, as well as the fresh properties, mechanical behavior and microstructure of MCEA sample were investigated. The results show that the initial setting time of MCEA paste is within 30 min, and the fluidity is 60–180 mm, which can effectively improve the efficiency of pavement repair engineering. Meanwhile, by adjusting the mix proportion parameters, the setting time and fluidity can be adjusted according to engineering needs. The compressive and flexural strengths of plain magnesium phosphate cement mortar reach 46.45 and 7.7 MPa, respectively, and they decrease with the increase of A/C, W/C, and M/P ratios. With the increase of S/(A+C) ratio, the area of emulsified asphalt encapsulated particles decreases, which improves the mechanical properties of MCEA mortar. Increasing the A/C ratio results in an increase in the residual MgO content and a decrease in the struvite content in the MCEA paste. Meanwhile, the residual MgO content in the MCEA paste prepared by the S-type emulsified asphalt is significantly lower than that of the N-type MCEA paste, which is related to the water content of the emulsified asphalt. In addition, the incorporation of emulsified asphalt also increases the porosity of the MCEA sample, but the N-type emulsified asphalt can play a role in refining the pore structure of the sample.     

Synergistically reinforcement of a self-setting calcium phosphate cement with bioactive glass fibers

Calcium phosphate cements (CPCs) are highly promising for clinical uses due to their in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits their uses to non-load-bearing applications. In the present research, first, bioactive glass fibers (BGFs) in the ternary SiO₂-CaO-P₂O₅ system were prepared, and then the fiber composites with compositions based on CPC and BGFs were prepared and characterized. Then, the effect of structure and amount of BGF incorporation into the CPC system, and the effect of mechanical compaction on the fiber-modified system were investigated. The results showed that the compressive strength of the set cements without any BGFs was 0.635 MPa which was optimally increased to 3.69 MPa by applying 15% BGF and then decreased by further addition of it. In addition, both the work-of-fracture and elastic modulus of the cement were considerably increased after applying the fibers in the cement composition. Also, the setting time slightly decreased by applying the fibers. In summary, processing parameters were tailored to achieve optimum mechanical properties and strength. The prepared composite may be useful in surgical sites that are not freely accessible by open surgery or when using minimally invasive techniques.     

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.     

矿物掺合料改性磷酸镁水泥研究进展

在总结磷酸镁水泥水化产物、水化速度、孔结构、流动性和物理力学性能等的基础上,综述了粉煤灰、矿渣、硅灰、赤泥和偏高岭土等矿物掺合料对磷酸镁水泥的改性效果和作用机理。矿物掺合料改性磷酸镁水泥具有优异的物理力学性能和经济性,耐水性、严苛条件下耐久性、负温下水化硬化特征和矿物掺合料改性机制等课题尚待深入研究,以期为促进磷酸镁水泥及其修补砂浆在重点工程中的应用提供参考。     

Study on the improvement of compressive strength and fracture toughness of calcium phosphate cement

Calcium phosphate cement (CPC) has superior properties, such as excellent bioactivity, biocompatibility, osteoconductivity and degradability, since its hydration product is hydroxyapatite (HA). As a novel cement material, CPC also shows injectable and self-setting properties. However, the compressive strength (CS) and fracture toughness of most CPCs are far lower than that of human weight-bearing bones, which largely limit their applications in the repairment of weight-bearing bones. To improve the CS and fracture toughness of CPC, several methods, including in-situ reinforcement by Ca4(PO4)2O (TTCP) ceramic particles, suitable nanofibers are introduced in this study. The maximal CS of CPC prepared with TTCP (average particle size of 22.3 ± 0.4 μm) reached to 98.4 MPa, which is close to the strength of human long bones. The enhanced CS of CPC was attributed to the in-situ reinforcing effect of residual TTCP particles. Tendon collagen slices and HA nanofibers were used to improve the fracture toughness of CPC. The flexural strength (FS) and the work of facture (WOF) of CPC were slightly increased by adding HA nanofibers but was significantly increased by the addition of tendon collagen slices. With 1.000 wt% tendon collagen slices, the FS and WOF of CPC were increased by 61.3% and 22.6 times, respectively.     

矿物掺合料对磷酸镁水泥性能影响及机理研究现状

磷酸镁水泥(MPC),具有快硬、早强等优点,应用于道路抢修、重金属固化等领域,但其存在凝结时间过快、耐久性差等缺陷.通过矿物掺合料对MPC进行改性,延缓其凝结时间、改善其耐久性的同时,实现了工业废渣的循环再利用.本工作综述了粉煤灰、矿渣、偏高岭土、硅灰等矿物掺合料对MPC流动度、凝结时间、力学性能、耐久性的影响,并对矿...     

快速固化型磷酸钙骨水泥的研究

用模拟体液(simulated body fluid,SBF)作为固化液,对磷酸四钙(TTCP)+一水磷酸二氢钙(MCPM)+β-磷酸三钙(β -TCP)系骨水泥理化性质进行研究.结果表明,随液固比增大,抗压强度先增加后降低,当液固比为0.445时,抗压强度达到最大值15.23 MPa;骨水泥固化较快,液固比为0.594时,t_f为12 min;随着浸泡时间的增加抗压强度逐渐减小;X射线(XRD)和扫描电镜(SEM)分析结果显示,随液固比改变,固化反应结晶物均有羟基磷灰石(HA)相出现;浸泡后的骨水泥没有新物相产生.     

陶瓷过滤机在磷精矿生产中的应用

介绍TC系列陶瓷过滤机的工作原理;描述陶瓷过滤机的结构;研究陶瓷过滤机在贵州川恒化工有限责任公司磷精矿脱水中的实际运行情况,并将陶瓷过滤机与带式过滤机的性能进行了比较。结果表明,陶瓷过滤机具有自动化程度高、真空度高、生产效率高、滤饼水分低、节能显著等优点;陶瓷过滤机用于磷精矿脱水,滤饼水分稳定在10%～13%(质量分数),比带式过滤机低10%;陶瓷过滤机是磷精矿脱水设备中较为理想的一种设备。