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A kind of multiscale β-sialon grain-reinforced Al2O3 matrix composite ceramic tool material, named ASN, was prepared and studied. For the ASN, β-sialon (molecular formula: Si4Al2O2N6) was synthesized in situ by a hot-pressing and solid-solution reaction process. A total of six samples were prepared at varying sintering temperatures and holding times under vacuum conditions. The solid solution reaction mechanism of β-sialon, the phase composition, mechanical properties, microstructure, and strengthening and toughening mechanisms of the composite ASN were investigated. As a result, within the experimental parameters, an optimal ASN tool material was obtained under a pressure of 32 MPa and at a temperature of 1550 °C for 20 min. The tested mechanical properties of the optimal sample were as follows: flexural strength 997 ± 59 MPa, fracture toughness 6.4 ± 0.3 MPa·m1/2, Vickers hardness 18.2 ± 0.4 GPa, and relative density 98.1 ± 0.2%. According to crystal defect theory, the solid solution reaction mechanism of in-situ-synthesized β-sialon in an Al2O3 matrix involves a double mechanism of unequivalence (or hetero-valence) and interstitial filling. The multiscale β-sialon grains mainly consisted of four grains, which were elongated β-sialon grains with a diameter of 0.3–0.4 μm and an aspect ratio of 6–9, elongated β-sialon grains with a diameter of 70 nm and an aspect ratio of 10, β-sialon whiskers with a diameter of 0.2 μm and an aspect ratio of 12–15, and intragranular β-sialon whiskers with a diameter of 70 nm. The mechanical properties were improved due to strengthening and toughening mechanisms, such as mixed structure mode (intergranular and transgranular), elongated grain pullout, interface bonding, crack reflection, pinning, and bridging. [ABSTRACT FROM AUTHOR]

To investigate the nucleation behavior of ammonium sulphate, commonly used as a fertilizer, during cooling crystallization, polythermal methods have been used to determine the metastable zone widths (MSZWs) of ammonium sulphate in aqueous solution from the saturation temperature at 288.15 to 317.15 K under cooling rates of 6.0 to 30.0 K per hour. MSZWs increased with the increasing cooling rate and the saturation temperature. Based on classical nucleation theory, the nucleation potential model linked the MSZWs to the critical nucleation potential and pre-exponential factor. The MSZWs from one saturation temperature or with one cooling rate were used to predict the MSZWs with other saturation temperatures or with other cooling rates, by the nucleation potential model. The estimated MSZWs were compared with the experimental values. Further, according to the characteristics of the electrolyte solution, the supersaturation term in the nucleation potential model was modified by the activity coefficient. The estimated MSZWs showed improved accuracies and a tendency to be positively correlated with both the supersaturation temperature and cooling rate, which was consistent with the experimentally measured MSZWs. [ABSTRACT FROM AUTHOR]