Effect of ethanol on the crystallization and phase transformation of MgCO3·3H2O in a MgCl2–CO2–NH3·H2O system

Formation and Phase Transformation of MgCO3·3H2O Whiskers in the Presence of Sodium Dodecyl Sulfate

Huge amounts of MgCl₂·6H₂O are produced annually as a byproduct or waste from KCl production in the Qinghai province of China. An ecological and economic way to solve this problem is transforming the abandoned MgCl₂·6H₂O to valuable MgCO₃·3H₂O whiskers. The formation and phase transformation of MgCO₃·3H₂O whiskers were studied in the crystallization process, in which MgCl₂ and NH₄HCO₃ were precipitated in the presence of sodium dodecyl sulfate (SDS) at 50 °C. Results showed that porous spherical MgCO₃·3H₂O, MgCO₃·3H₂O whiskers, and flocculent rod-like 4MgCO₃·Mg(OH)₂·4H₂O were formed with decreasing concentration of SDS as the crystallization proceeded. When the concentration of SDS was lower than the critical micellar concentration (6.5 mmol·L^-1) at 60 min, SDS was beneficial for the growth in the [010] direction to form one-dimensional MgCO₃·3H₂O whiskers with a high aspect ratio, good uniformity, and a smooth surface (length, 60-70 μm; aspect ratio, 110-140).

Characterization and Biocompatibility of Insoluble Corrosion Products of AZ91 Mg Alloys

Biodegradable Mg alloys have good bioactivity and suitable mechanical properties, which is desirable for application in the clinical fields. However, the biocompatibility of Mg alloys during the degradation process has always been a concern. In this paper, the corrosion behavior of AZ91 alloys in a simulated cell culture environment was studied, especially the insoluble corrosion product during the degradation was characterized, and the biocompatibility of the insoluble corrosion products was evaluated. The results of immersion test showed that the corrosion rate of the AZ91 alloy was low under the condition of high CO2 and humidity, especially in phosphate-buffered saline. Moreover, the insoluble corrosion product was MgCO3·3H2O, which showed a needle-like, circular aggregated, and square-radial feature. Meanwhile, MgCO3·3H2O showed poor cell biocompatibility by increasing the pH and Mg2+ content of the culture solution, which may affect the biocompatibility of Mg alloys.