Preparation of transparent MgO·1.8Al2O3 spinel ceramics by aqueous gelcasting, presintering and hot isostatic pressing

Highly transparent Mg0.27Al2.58O3.73N0.27 ceramic fabricated by aqueous gelcasting, pressureless sintering, and post‐HIP

“…All the peaks match very well with those of the cubic spinel structure (PDF#8-0340). 19 This phenomenon implied that these two powders exhibit different surface chemical properties. Then the pH value of MgAlON slurry was nearly kept constant even after 24 hours.…”

“…21 To overcome this difficulty, a lot of work so far has been focused on introducing surfactants to prevent hydrolysis of powders. 17,19,23,24 However, it is quite difficult to exclude the phosphate layer in the following binder burnout process and some of the added organic compounds are toxic. 17,19,23,24 However, it is quite difficult to exclude the phosphate layer in the following binder burnout process and some of the added organic compounds are toxic.…”

“…30 During aqueous gelcasting, one of the most important effects on the strength of green body is the gel network generated by the in-situ polymerization of organic monomers. 18 In contrast, MAM-MBAM has much lower toxicity than AM-MBAM, 32 and the green body possesses sufficient strength (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) to permit machining. [16][17][18][19] In these systems, since the main component of AM-MBAM is a neurotoxin, the application of the acrylamide system is limited.…”

“…Aqueous gelcasting is a well-established and environmentally friendly colloidal processing technology for making ceramic green bodies with high quality and complicated shape, [8][9][10] which has been applied to the shaping of various transparent ceramics, such as alumina, MgAl 2 O 4 , and AlON. [11][12][13][14][15][16][17][18][19] During the aqueous gelcasting process, one of the critical steps is to prepare stable ceramic slurry with high solid loading and low viscosity. Unfortunately, it is reported that the ceramic powders of the spinel-type materials are always hydrolyzed in aqueous medium due to their basic nature, 16,20 which makes it difficult to obtain stable and homogenous aqueous suspension with high solid loading.…”

“…For instance, orthophosphoric acid (H 3 PO 4 ) and stearic acid (C 18 H 36 O 2 ) have been used to control the hydrolysis of MgAl 2 O 4 and AlON spinel powders. 17,19,23,24 However, it is quite difficult to exclude the phosphate layer in the following binder burnout process and some of the added organic compounds are toxic. Hence, it is imperative to find a method to inhibit the hydrolysis of spinel powders without the surface treatment of powders.…”