Experimental Ammonia-free Phosphate-bonded Investments using Mg ( H_2PO_4 )_2 Solution

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In our previous study, we investigated ammonia-free phosphate-bonded investments using Mg (H_2PO_4)_2 powder. The purpose of the present study was to attempt usage of 50 wt% Mg (H_2PO_4)_2 solution instead of powder. Magnesium oxide (MgO) was prepared as a binder and cristobalite was selected as a refractory. After arranging six kinds of experimental investments (A-F) with different cristobalite/MgO ratios, the fundamental properties of the dental investments were examined. The properties of the molds were influenced by the amount of MgO. Decreases in MgO showed lower mold strengths, longer setting time and larger setting expansion. According to XRD analysis, the peaks of MgH(PO_4)_3 3H_2O newly formed, cristobalite and MgO were detected in the A set, but MgO peaks in F set were reduced. On the other hand, the surface of F was entirely covered by phosphorus. From these results, it was found that the usage of Mg(H_2PO_4)_2 solution was possible for ammonia-free investments.
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