Hydraulic setting Mg 3 (PO 4 ) 2 powders for 3D printing technology

Abstract

Three-dimensional powder printing was used in this study to fabricate custom made magnesium phosphate based structures. In a first step, farringtonite [Mg₃(PO₄)₂] powders were synthesised by sintering and subsequent grinding. Optimised powders suitable for printing were obtained after 60 min of grinding, which resulted in a medium particle size of 16 μm. These powders were reacted with binder liquids consisting of 2M K₂HPO₄, 0·5M (NH₄)₂HPO₄or 20%H₃PO₄ to form a matrix of either struvite-(K) (MgKPO₄.6H₂O), struvite (MgNH₄PO₄.6H₂O) or newberyite (MgHPO₄.3H₂O) by a hydraulic setting reaction. While printing of struvite-(K) was not possible due to the long setting time of this cement system, both newberyite and struvite samples could be processed with good dimensional accuracy. Strength was initially low after printing, namely in the range of 1·3–2·8 MPa; however, additional post-hardening in the binders increased the compressive strength to a maximum of 10 MPa for struvite and 36 MPa for newberyite. This was accompanied by a higher degree of conversion to the setting products, as evidenced by X-ray diffraction analysis. Magnesium phosphate based structures prepared by three-dimensional printing may find an application as biodegradable bone substitutes or can be used for the rapid manufacturing of moulds for metal casting, as demonstrated in this study.