Carbothermal formation of β′-sialon from kaolinite and halloysite studied by 29Si and 27Al solid state MAS NMR

Early‐Stage Thermal Oxidation of Carbothermal β‐Sialon Powder

“…5 XRD showed it to be predominately monophasic with z ‫ס‬ 2.45. The particle distribution and typical impurity levels were also reported; the average particle size was around 2 m and the only impurity phase detectable by XRD was a trace of x-phase sialon.…”

Synthesis of β-SiAlON powder by carbothermal reduction–nitridation of zeolites with different compositions

“…On the other hand, for sample z-3 (the highest Si/Al ratio of the three raw zeolites), no mullite was observed after being fired under the same conditions (1300 • C for 0 min). Previous reports have shown that mullite is formed when crystalline aluminosilicates such as kaolinite 24 and zeolite are fired over 1000 • C. 25 It seems that the formation of mullite is highly dependent on the Si/Al ratio, where zeolites with a lower Si/Al ratio (sample z-1 < sample z-2 < sample z-3) form greater quantities of mullite. Since the Si/Al ratio in mullite (=1/3) is lower than in all the raw zeolites used in this study, it is thought that a Si-rich amorphous phase and Al-rich mullite phase are formed in each of these samples by way of firing.…”

Carbothermal synthesis of β-sialon from mechanochemically activated precursors

“…5 The small peak at −18 ppm indicates the formation of a small amount of SiC, an intermediate in the CRN process in halloysite which is generally not detected by XRD. 4 Heating to 1400 • C (Fig. 5D) produces a broad spectral feature extending from the position of uncombined silica Heating the precursor ground for 12 h at 1200 • C indicates that the reaction sequence is already more advanced than in the unground control, the 29 Si NMR spectrum (Fig.…”

“…Since mechanochemical processing is known to facilitate the formation of mullite from mixtures containing kaolinite by the formation of new Si O Al bonds, 3 and since mullite formation is an initial stage in the carbothermal reaction sequence, 4 it was anticipated that the combination of mechanochemical activation with CRN may have a beneficial effect. To avoid possible complications arising from atmospheric oxidation of particle surfaces freshly exposed by grinding, the mechanochemical activation was carried out under a continuously replenished atmosphere of purified nitrogen.…”

“…The ␤-sialon produced thus from kaolinite has an expected z-value of 3, but compounds with other z-values can readily be obtained by adjusting the composition of the reaction mixture with additional alumina or silica. Carbothermal synthesis of ␤-sialon (z = 3) from kaolinite clay can be represented by the overall equation: 3Al 2 Si 2 O 5 (OH) 4 …”