Jinmei Dong

Effects of Material Ratio, Fly Ash, and Citric Acid on Magnesium Oxysulfate Cement

The effects of material ratio, fly ash, and citric acid on the compressive strength and phase composition of magnesium oxysulfate (MOS) cement have been studied. From these results, when the molar ratio of active MgO/MgSO₄ increases from 3 to 5, the compressive strength of magnesium oxysulfate cement increases. When the molar ratio of active MgO/MgSO₄ is 3, the main crystal phase contributing to the mechanical strength is 3Mg(OH)₂·Mg- SO₄·8H₂O; when the molar ratio increases to 5, the main crystal phase is a new magnesium subsulfate that can be expressed as yMg(OH)₂·MgSO₄·zH₂O (Y phase). The compressive strength of MOS cement by adding fly ash decreases from 56.89 to 33.75 MPa (8.251 to 4.895 ksi) by 39.29% when the dosage of fly ash increases to 40%, because SiO₂ in fly ash can form magnesium silicate hydrate gel, which can adsorb onto the surface of the Y phase nucleus and inhibit its growth. In the presence of 0.5% weight citric acid (CA), the compressive strength of MOS cement increases, because CA may facilitate the formation of yMg(OH)₂·MgSO₄·zH₂O (Y phase).

Effects of citric acid on hydration process and mechanical properties of thermal decomposed magnesium oxychloride cement

In order to make full use of salt lake magnesium resources and improve the strength of the thermal decomposed magnesium oxychloride cement (TDMOC), the effects of citric acid on the hydration process and mechanical properties of TDMOC was studied. The hydration heat release at initial 24 h and strengths at 3, 7, and 28 days of TDMOC specimens were conducted. The hydration products and paste microstructure were analyzed by XRD, FT-IR and SEM, respectively. The results showed that citric acid can not only reduce the 24 h hydration heat release and delay the occurring time of second peak of TDMOC, but also produce more 5Mg(OH)2·MgCl2·8H2O and less Mg(OH)2 in hydration process of TDMOC. More perfect and slender crystals were observed in the microstructure of the TDMOC pastes with citric acid. The results demonstrated that citric acid as an additive of TDMOC can decrease the hydration heat release and increase the compressive strength and flexural strength of TDMOC. The possible mechanism for the strength enhancement was discussed.

Effects of calcination temperature of boron-containing magnesium oxide raw materials on properties of magnesium phosphate cement as a biomaterial

A new magnesium phosphate bone cement (MPBC) was prepared as a byproduct of boroncontaining magnesium oxide (B-MgO) after extracting Li2CO3 from salt lakes. We analyzed the elementary composition of the B-MgO raw materials and the effects of calcination temperature on the performance of MPBC. The phase composition and microstructure of the B-MgO raw materials and the hydration products (KMgPO4·6H2O) of MPBC were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that ionic impurities and the levels of toxic elements were sufficiently low in B-MgO raw materials to meet the medical requirements for MgO (Chinese Pharmacopeia, 2010 Edition) and for hydroxyapatite surgical implants (GB23101.1-2008). The temperature of B-MgO calcination had a marked influence on the hydration and hardening of MPBC pastes. Increasing calcination temperature prolonged the time required for the MPBC slurry to set, significantly decreased the hydration temperature, and prolonged the time required to reach the highest hydration temperature. However, the compressive strength of hardened MPBC did not increase with higher calcination temperatures. In the 900-1 000 °C temperature range, the hardened MPBC had a higher compressive strength. Imaging analysis suggested that the setting time and the highest hydration temperature of MPBC pastes were dependent on the size and crystal morphology of the B-MgO materials. The production and microstructure compactness of KMgPO4·6H2O, the main hydration product, determined the compressive strength.

Study on the injectability of a novel glucose modified magnesium potassium phosphate chemically bonded ceramic

A novel magnesium potassium phosphate chemically bonded ceramic (MKPCBC) was prepared as a byproduct of boron-containing magnesium oxide (B-MgO) after extracting Li2CO3 from salt lakes. In this work, the influence of glucose on the properties of MKPCBC, such as the setting time, compressive strength and hydration heat, was investigated. In addition, we studied the effect of the magnesium-phosphate ratio (M/P) and liquid-solid ratio (L/S) on the injectability of MKPCBC. The pH change in glucose modified MKPCBC paste was also investigated. The phase composition and microstructure were studied in detail by using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). The results show that the optimal content of glucose is 6wt%. The optimum proportions of M/P and L/S for MKPCBC are 1.5 and 0.25, respectively. The properties of the novel MPCBC can meet the requirements of biomaterials. In addition, the retardation mechanism of glucose on MKPCBC and the hydration mechanism of novel MKPCBC were studied in detail through the continuous monitoring of the phase composition and microstructure.