Fabrication of mixed α/β-SiAlON powders via salt-assisted combustion synthesis

Abstract

High-quality Y-and Ca-α/β-SiAlON and α-SiAlON ceramics were synthesized via salt-assisted combustion synthesis from Si, Al, and metal oxide (Y 2 O 3 and CaO) with the addition of NaCl and MgCl 2 under a nitrogen pressure of 1 MPa. NaCl and MgCl 2 were employed as they act as excellent diluents that effectively absorb the reaction heat through melting and evaporation. We found that the type of metal chlorides employed significantly affected the α/β ratio and the morphology of the product, with the use of NaCl affording high α/β ratios and equiaxed morphologies, while the use of MgCl 2 resulting in low α/β ratios and elongated grains. The results of this work suggest that high-purity α/β-SiAlON composite products of intended α/β ratios can be successfully fabricated by controlling the initial metal chloride content.

Spark plasma sintering of α/β-SiAlON synthesized by salt-assisted combustion

“…In contrast, the Ca0.3M18 and Y0.2M18 samples obtained with the addition of 18 mass% MgCl 2 exhibit much lower α-phase SiAlON contents of 7% and 56%. These results are consistent with our previous work, which showed that NaCl is more efficient at promoting the formation of α-phase SiAlON [12]. It should be noted, however, that these values are only approximate, as any amorphous phase fractions cannot be determined precisely using this method.…”

“…In previous work, 12 mass% NaCl and 18 mass% MgCl 2 addition was needed to achieve complete nitridation of Si in the salt-assisted combustion synthesis of α/β-SiAlON [12]. Based on this, the same amounts of NaCl and MgCl 2 were added to the reactant powders in the present study.…”

“…Methods that have been used to produce α/β-SiAlON or α-SiAlON ceramics include hot-pressing (HP) [6], pressure-less sintering [7], reaction sintering [8], carbothermal reduction and nitridation (CRN) [9], and combustion synthesis (CS) [10][11][12][13]. Among these, combustion synthesis (CS) has proven to be particularly effective in terms of energy-and time-savings due to the simplicity of the equipment needed, short reaction time and high-purity product obtained.…”

“…In previous studies, we successfully synthesized high purity β-SiAlON and α/β-SiAlON powders by adding a small amount of NaCl or MgCl 2 to the reaction mixture for salt-assisted combustion synthesis instead of traditional SiAlON diluents [12,17]. These diluents were selected on the basis of their high latent and sensible heat; however, it was unclear the products synthesized by this new method could be sintered to form a dense product.…”

Fabrication of AlN particles and whiskers via salt-assisted combustion synthesis

“…In these studies, NaCl was shown to decrease the adiabatic temperature and wave velocity, stabilizing the combustion reaction, and thereby reducing the rate of aggregation and grain growth. Our previous work [22][23][24] on the combustion synthesis of SiAlON has shown that metal chlorides such as NaCl, KCl, and MgCl 2 are ideal diluents that absorb the reaction heat effectively via their sensible and latent heats, thereby lowering the combustion temperature. In addition, different morphologies were obtained in the products according to the type and amount of metal chloride used.…”