Recycling of Used Commercial Phosphate-bonded Investments with Additional Mono-ammonium Phosphate

Abstract

Industrial waste is on the increase, resulting in severe environmental contamination. Against this background, this study sought to investigate the possibility of recycling used phosphate-bonded investments.Commercial phosphate-bonded investment was mixed and heated according to manufacturer's instructions, then powdered with a ball mill machine to be used as recycled investment (Code: R) . Mono-ammonium phosphate (NH4H2PO4) of 2, 5, 8, 11, and 14 g were added to 100 g of R because of residual MgO, and coded as Ra, Rb, Rc, Rd, and Re respectively.Investment properties were then examined. Particle size of R was 50.66 pm and close to the original investment.It was found that more NH4H2PO4 led to larger setting expansion, smaller thermal expansion, and lower fired strength.The data of Re in these three aspects were 1.42 ± 0.09%, 0.78 ± 0.21%, and 8.85 ±0.88 MPa respectively, and differences against the original investment were significant.Ra showed significantly longer setting time than other investments.Based on the results of this study, we concluded that it was possible to set used phosphate-bonded investments by adding NH4H2PO4; in particular, Rd showed suitable expansion and acceptable mechanical properties.

Experimental Binder-free Investments Reused to Cast Dental Precious Alloys

“…In terms of casting method, a heat-shock casting method was also investigated to reduce the operation time 5) . Of late, our research focus is on the reuse of dental investments 4) . However, there are difficulties in reusing commercial products.…”

“…However, there are difficulties in reusing commercial products. In our previous research 4) , all investments tested had to be disposed of after each experiment. This is neither rare nor unusual in the field of dentistry, despite the public concern that industrial waste is causing severe environmental contamination.…”

“…From the viewpoint of waste reduction, it is worthy to reuse the material with high frequency by routine laboratory use. In this connection, dental gypsum and/or dental investment should be target materials, but they are rarely examined [2][3][4] .…”

Soda-lime glass as a binder in reusable experimental investment for dental castings

“…We previously investigated reuse of mold materials, and found that phosphate-bonded investments could be recycled 1) . We also developed a new type of dental casting investment consisting of only refractory materials without binder, which could also be reused 5) .…”

“…The quantity of industrial waste produced increases each year, and this has become a major environmental issue 1) . Reuse of casting metal is common [2][3][4] in dental laboratory works.…”