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The corrosion resistance of slag α-Sialon ceramics, preparedviapressure-less sintering and hot-pressing from slag α-Sialon powder, to NaOH and HNO3was studied in this work. The result shows that slag α-Sialon ceramics have exellent corrosion resistance to NaOH and good resistance to HNO3. The corrosion mechanism and corrosion mode of acid and alkali to slag α-Sialon ceramics was investigated by means of scanning electron microscopy (SEM), and the results indicate that the corrosion of acid and alkali to hot-pressing ceramic is the slow surface corrosion, not only on the crystal grains, but also on the grain boundary phase, while the fast pitting is the dominant corrosion mode for pressure-less ceramic. The corrosion of NaOH solution to ceramics mainly occurred the grain boundary phase, while not only the grain boundary phase, but also crystal phase are corroded by HNO3.

The pressure-less sintering of slag α-Sialon powder, derived from slag wastes by self-propagating high-temperature synthesis technology, was carried out and the phase assemblages of slag α-Sialon sintered at different temperatures were studied. The results showed that the formation of β-Sialon phase did occur during the pressure-less sintering and was restrained to some extent via mass diffusion of Ca2+/Mg2+ added in embedded powder in samples. α-Sialon phase with two different unit cells was detected in samples sintered at 1700°C and above, and the formation mechanism was also discussed.

Different ratios of Ce to Y were selected to stabilize (Ce,Y) α-sialon during self-propagating high-temperature synthesis (SHS). The phase assemblages were then studied for both SHS-ed (Ce,Y) α-sialon powders and sintered ceramics. The results showed that the amount of α-sialon phase increased as a main crystalline phase in SHS-ed powders when 20 at.% of Ce was replaced by Y in the composition, and further increase in the substitution of Y for Ce did not obviously increase the α-sialon content, whereas β-sialon was the major phase in the SHS-ed powders without the introduction of Y in the composition. The transformation of α-sialon to β-sialon did occur when the SHS-ed powders were hot-pressed for the compositions without Y and substitution of Y for Ce less than 40 at.%. The 50 at.% replacement of Ce by Y was enough to stabilize (Ce,Y) α-sialon structure as the (Ce,Y) α-sialon phase was kept in the sample with similar amount to that in the SHS-ed powders.

In the present work, the mechanical properties and erosion-resistance ability of hot-pressed and pressureless sintered slag α-sialon ceramics, which were started from slag α-sialon powders prepared by SHS technique based on slag powders, [J. Mater. Chem. 12 (2002) 1199] were measured. The hardness and toughness of pressureless sintered slag α-sialon samples reached 15.53 GPa and 4.72 MPam 1/2 respectively. The strength of hot-pressed slag α-sialon ceramics reached 599 MPa as well. In comparison with Al 2 O 3 and ZrO 2 ceramics, as-sintered slag α-sialon ceramics showed much higher erosion-resistance ability. These properties are very close to that of normal α-sialon ceramics prepared by expensive chemical agents as raw materials.

(Ca,Mg)-α-sialon powders were previously [J. Mater. Chem. 12 (2002) 1199] prepared by Self-propagating high-temperature synthesis (SHS) technology using slag as a raw material (abbreviated as Slag α-sialon powder). In this study, phase assemblages of the Slag α-sialon samples hot-pressed from 1450 to 1700 °C were investigated. Results indicated that α-sialon was the main crystalline phase in the whole sintering process, however, a small amount of β-sialon appeared in the samples sintered at 1500 °C and above. In addition, the SHS technique was also used to prepare α-sialon powders using chemical agents as raw materials (named Chem α-sialon). Samples made from the Chem α-sialon powder were hot-pressed under the same conditions for a comparison. Similar phase assemblages were obtained for the samples starting from Chem α-sialon powders, except for even more amount of βsialon phase contained. Material with a single α-sialon phase could be got in both samples when 10 wt.% additional slag and CaCO 3 were introduced into the Slag α-sialon and Chem α-sialon starting powders respectively.