Abstract: Disclosed are a silicon nitride ceramic sintered body and preparation method thereof. The silicon nitride ceramic sintered body includes a sintered bulk and a hard surface layer having a thickness of 10-1000 ?m, formed on a surface of the sintered bulk, wherein the sintered bulk comprises a first silicon nitride crystalline phase and a first grain boundary phase; the hard surface layer comprises a second silicon nitride crystalline phase and a second grain boundary phase; the first grain boundary phase comprises a metal tungsten phase being tungsten elementary substance and/or a tungsten alloy; the second grain boundary phase comprises tungsten carbide particles; tungsten element in the metal tungsten phase accounts for 80-100 wt % of total tungsten element in the first grain boundary phase; and tungsten element in the tungsten carbide particles accounts for 60-100 wt % of total tungsten element in the second grain boundary phase.

Abstract: Disclosed are a silicon nitride ceramic sintered body and a-preparation method thereof. The silicon nitride ceramic sintered body includes a sintered bulk and a hard surface layer having a thickness of 10-1000 ?m, formed on a surface of the sintered bulk, wherein the sintered bulk comprises a first silicon nitride crystalline phase and a first grain boundary phase; the hard surface layer comprises a second silicon nitride crystalline phase and a second grain boundary phase; the first grain boundary phase comprises a metal tungsten phase being tungsten elementary substance and/or a tungsten alloy; the second grain boundary phase comprises tungsten carbide particles; tungsten element in the metal tungsten phase accounts for 80-100 wt % of total tungsten element in the first grain boundary phase; and tungsten element in the tungsten carbide particles accounts for 60-100 wt % of total tungsten element in the second grain boundary phase.

Abstract: Disclosed are a silicon nitride ceramic sintered body and a preparation method thereof. The silicon nitride ceramic sintered body has a content of a silicon nitride crystalline phase of not less than 98 wt %, a relative density of not less than 99%, a porosity of not larger than 1%, a grain boundary phase including Li, O, N, and Si elements, and a total content of C, F, Al, Mg, K, Ca, Na and rare-earth metals elements of less than 0.1 wt %.

Abstract: The present disclosure discloses a preparation method of a multi-functional marine engineering alloy. Through the coupling of a multi-principal alloy structure, structural entropy, and temperature and powder metallurgy and heat treatment, mutual solubility between elements and free energy of an alloy system are regulated, Cu grain boundary segregation is eliminated, and uniform and dispersed nano-precipitation of the anti-fouling element Cu in corrosion-resistant and high-plasticity multi-principal alloys is realized. The preparation method is simple and controllable to operate, and the prepared material has plasticity higher than 75%, high yield strength, excellent corrosion resistance and anti-fouling property, and has important application prospects in the field of marine engineering.

Abstract: The present disclosure discloses a preparation method of a multi-functional marine engineering alloy. Through the coupling of a multi-principal alloy structure, structural entropy, and temperature and powder metallurgy and heat treatment, mutual solubility between elements and free energy of an alloy system are regulated, Cu grain boundary segregation is eliminated, and uniform and dispersed nano-precipitation of the anti-fouling element Cu in corrosion-resistant and high-plasticity multi-principal alloys is realized. The preparation method is simple and controllable to operate, and the prepared material has plasticity higher than 75%, high yield strength, excellent corrosion resistance and anti-fouling property, and has important application prospects in the field of marine engineering.

Abstract: A method of preparing a composite catalyst for polyester synthesis includes the steps of: 1) sequentially dissolving a titanium compound, a silicon compound and a tin compound in an organic solvent; 2) adding a water solution of an acidic compound or of an alkaline compound in the compound from step 1) to cause hydrolysis thereof and collecting a precipitate, and washing the hydrolysis precipitate with a deionized water to obtain the composite catalyst. The catalyst is not only effective in polyester production polycondensation, but also has significant catalytic activity in esterification. The produced polyester chips all have a desirable hue.