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Basics of magnesium biodegradation
Published in Yoshinobu Onuma, Patrick W.J.C. Serruys, Bioresorbable Scaffolds, 2017
Michael Haude, Daniel Lootz, Hubertus Degen, Matthias Epple
In this chapter we provide fundamental information on the corrosion of magnesium, mostly from the perspective relevant for coronary scaffolds, currently the most advanced clinical application of magnesium implants. After implantation, magnesium is converted into magnesium hydroxide, which reacts with phosphate ions into magnesium phosphate, and, with calcium ions, into amorphous calcium phosphate with high water content. As a result, magnesium ions diffuse from the matrix and are excreted in urine. Only a minor portion of the scaffold strut areas is degraded to magnesium hydroxide after 90 days. After 360 days, the elution of magnesium from the metallic backbone is largely completed, and the strut areas are replaced by amorphous calcium phosphate with high water content. The scaffold resorption may allow uncaging of the treated coronary artery segment and restoration of the vessel wall physiology and vasomotion.
Evaluation of phosphate adsorption on zirconium/magnesium-modified bentonite
Published in Environmental Technology, 2020
Jianwei Lin, Siqi He, Yanhui Zhan, Honghua Zhang
The regeneration of the spent adsorbent is of the utmost importance for understanding the mechanism of adsorption. In this study, a 1.0 mol/L NaOH solution was selected as the desorbing solution to regenerate the phosphate-adsorbed ZrBT (P-ZrBT) and phosphate-adsorbed ZrMgBT (P-ZrMgBT). The desorption efficiencies of phosphate from P-ZrBT and P-ZrMgBT were determined to be 92.2 and 94.7%, respectively. This indicates that the phosphate adsorbed by ZrBT and ZrMgBT can be well desorbed by the NaOH solution. Similar desorption results have also be found for other zirconium-containing adsorbents such as hydrous zirconium oxide [15], amorphous zirconium hydroxide [57], silica-free superparamagnetic ZrO2@Fe3O4 [58] and magnetite core/zirconia shell nanocomposite [59]. When ZrBT and ZrMgBT are contacted with KH2PO4 solution, magnesium ion is expected to be released from these adsorbent materials into the solution. Under certain condition, magnesium ion can react with phosphate to form magnesium phosphate precipitates such as MgHPO4 and Mg3(PO4)2 [60]. High solution pH is favourable for the formation of magnesium phosphate precipitate [60]. Therefore, if the adsorbed phosphate exists in the form of magnesium phosphate precipitate, the desorption efficiency should be very low. The very high desorption efficiencies of ZrBT and ZrMgBT by 1.0 mol/L NaOH solution suggest that adsorption rather than surface precipitation plays the key role in the removal of phosphate by ZrBT and ZrMgBT.
Reaction mechanisms of slowly cooled and quickly cooled copper slag in magnesium phosphate cement
Published in Journal of Sustainable Cement-Based Materials, 2023
Though the mole ratio of MgO and KH2PO4 (or NH4H2PO4) in the equation is 1, the MgO/H2PO- 4 (M/P) mole ratio in actual application is higher than 1 [6, 7]. Redundant MgO particles fill in the hardened paste as aggregates [4, 8]. Compared with conventional OPC, magnesium phosphate cement has advantages of rapid setting and hardening, as well as high early strength [1, 9]. The compressive strength of magnesium phosphate cement could achieve more than 20 MPa at 1 h [10, 11]. Meanwhile, magnesium phosphate cement could build a strong bonding with the Portland cement-based material [12–14]. Magnesium phosphate cement also has advantages of low chemical shrinkage, low drying shrinkage, low permeability, good compatibility with impurities and contaminants, etc. [4, 11, 15]. Owing to these advantages and approximate color with old concrete, magnesium phosphate cement has been widely used in the rapid repairing of airport, bridge runways, grounds of industrial plants, slab in ballast-free railway, and shotcrete applications in recent years [16–18]. Besides, magnesium phosphate cement was also used in the solidification of hazardous waste, cement coating, fiber reinforced concrete structure, magnesia-based refractory concrete, etc. [2, 19–21]. However, due to the rapid setting of magnesium phosphate cement, time for on-site construction may be insufficient. Meanwhile, the water resistance of magnesium phosphate cement is poor [6]. Costly raw materials also hinder the marketing of magnesium phosphate cement. These problems restrict the engineering application of magnesium phosphate cement to a certain extent.