Preceramic Polymer‐Derived SiAlON as Sintering Aid for Silicon Nitride

Abstract

Two kinds of sintering additives based on the polysiloxanes or polysilazanes filled with nano-sized powders as SiAlON precursors were tested for the densification of Si3N4-based ceramics. The results showed that both systems can be successfully used as additives for the preparation of Si3N4 ceramics with favorable mechanical characteristics. The ceramics were sintered with 18 wt% of preceramic polymer-based mixture, and good fracture resistance and high hardness values were obtained after sintering in optimized conditions (temperature, dwell time, nitrogen pressure). Higher densification temperatures and longer holding times were required for sintering of samples with polysilazane-based precursors. The best toughness values were approximately 5 MPa·m0.5, while the highest hardness was about 19 GPa. The differences in mechanical properties of the prepared composites can be related to the phase composition, microstructure and different chemical bonds present in the ceramic residue generated upon pyrolysis and final densification

HYDROTHERMAL CORROSION RESISTANCE OF SILICON NITRIDE WITH O'-Si Al ON GRAIN BOUNDARY PHASE

“…Two types of sintering aids have been used, both were composed of preceramic polymers combined with very fine inorganic fillers ( Table 1). The preparation of sintering aids is described in details elsewhere [19]. Briefly, the sintering additive A was prepared from the mixture of polysiloxane (Silres H44, Wacker-Chemie GmbH, Müchen, Germany), γ-…”

“…Linck et al has reported a very good hydrothermal corrosion resistance of polymer-derived silicon oxycarbide-based ceramics (SiOC, SiZrOC and SiHfOC) [18]. In our earlier work we have used the preceramic SiAlOC polymer-derived ceramic (PDC) material as a sintering aid for the densification of Si 3 N 4 and the material showed good mechanical proper-ties with a hardness of 19 GPa and fracture toughness 5 MPa•m 1/2 [19].…”

Low temperature fabrication of highly dense α‐Si3N4 ceramics

“…Ultrafine nano-sized Si 3 N 4 powders and amorphous Si 3 N 4 powders were used to increase the sintering activity and lower the sintering temperature. [12][13][14][15][16][17] As for the sintering additives, oxides and non-oxides, like silicide and fluoride, with low eutectic temperature were developed to lower the sintering temperature. [18][19][20][21] However, the ultrafine Si 3 N 4 powders and the sintering additives are unstable and not environmentally friendly.…”

“…On the one hand, the selection of the raw materials mainly focused on the Si 3 N 4 powder and the sintering additive. Ultrafine nano‐sized Si 3 N 4 powders and amorphous Si 3 N 4 powders were used to increase the sintering activity and lower the sintering temperature 12–17 . As for the sintering additives, oxides and non‐oxides, like silicide and fluoride, with low eutectic temperature were developed to lower the sintering temperature 18–21 .…”

EVA-PVA binder system for polymer derived mullite made by material extrusion based additive manufacturing

“…Polymer derived ceramics (PDCs), introduced in the early 1960s, are obtained as a result of pyrolysis of preceramic polymers (PCPs), usually in non-oxidative atmospheres [1,2]. Organosilicon precursors with a Si backbone and O, C, N, B or H atoms [3], known as Si-based preceramic polymers, have remained a hot topic since then and there have been a lot of studies on synthesis of oxide and non-oxide ceramics like mullite [4], wollastonite [5], cordierite [6], SiAlON [7,8], SiOC [9,10], SiC [11] and so on. These polymeric compounds release gas byproducts while crosslinking followed by pyrolysis at higher temperatures to obtain an amorphous ceramic residue [12].…”