molybdenum-based additives on the properties of materials

Title: molybdenum-based additives on the properties of materials
　　Author: Liu Juntao
　　Degree-granting units: Shandong University
　　Keywords: molybdenum;; additives;; wear;; corrosion resistance;; cerium oxide
　　Summary:
　　Molybdenum has a strategic importance as a rare, high melting point, corrosion resistance and good thermal conductivity, but poor wear resistance, limiting the molybdenum application as structural materials. China's molybdenum resources, ranking first in the world, but China's molybdenum processed products compared with foreign countries has a Strong magnets large gap. Therefore, the use of resources, development of new materials has become necessary. Molybdenum metal and ceramic can be integrated with the characteristics of the preparation of metal and ceramic ceramic materials. While rare earth oxides can be used as stabilizer and grain growth inhibitors, can improve the microstructure of the material, so by adding rare earth oxides and ceramic materials, preparation of molybdenum-based material has practical significance. Therefore, this study in the molybdenum-based materials in the additive, its microstructure and wear resistance, corrosion resistance research.
　　In this paper, prepared by pressureless sintering of the way Mo-CeO2, Mo-Cr2O3, Mo-Al2O3-CeO2 composites, sintering properties were measured using X-ray diffraction (XRD), electron probe (EPMA), scanning electron microscopy (SEM ) on the sintering phase, microstructure analysis and the results show that: CeO2 can promote the sintering of Mo, Cr2O3 on Mo, CeO2 on Mo-Al2O3-CeO2 materials to promote burning is not obvious, CeO2, Cr2O3 were able to inhibit the Mo grain growth. Mo-Al2O3-CeO2 after CeAl11O18 phase sintering, and with increasing volume fraction of CeO2, CeAl11O18 gradually increased, Al2O3 reduced accordingly, when the volume fraction of CeO2 6%, Al2O3 completely CeAl11O18 replaced. Theory that when CeO2 and Al2O3 molar ratio of 0.182 when the material is just completely into CeAl11O18 Al2O3 phase. The formation mechanism is: 2CeO2 +11 Al2O3 → 2CeAl11O18 +1 / 2O2 materials Al2O3 + CeAl11O18, CeAl11O18 compared to point-like, or worm-like distribution of sheets in the matrix in Mo, Mo phase boundary showing blunt morphology.
　　MM200 type wear testing machine used on the Mo-Al2O3-CeO2 composite wear resistance test by scanning electron microscopy analysis of the wear morphology. The results showed that with increasing volume fraction of CeO2, low-load (50N, 70N), the material of the friction coefficient first decreased and then increased in the high load (90N), the friction coefficient increased gradually. The relative density is the main factor affecting wear resistance of materials, CeO2 only trace of wear resistance. Mo-Al2O3-CeO2 composite wear mainly as abrasive wear, adhesive wear and mechanical grinding, the wear process can be worn by the theoretical model to explain the delamination.
　　Room temperature, using the full immersion of the way Mo-Al2O3-CeO2 composite materials resistant to nitric acid, sulfuric acid and hydrochloric acid to study the performance. Studies have shown that materials resistant to hydrochloric acid, sulfuric acid corrosion is better, but poor corrosion resistance to nitric acid. With the increased volume fraction of CeO2, Mo-Al2O3-CeO2 composite materials resistant to nitric acid, sulfuric acid corrosion can be increased http://www.chinamagnets.biz/Neodymium/Ball-Neodymium-Magnets.php and then decreased 6% in the most corrosion-resistant; the material's corrosion resistance to hydrochloric acid after the first drop by, when the volume of CeO2 fraction of 6% of the most intolerant corrosion. Mo-Al2O3-CeO2 composite priority in nitric acid corrosion of Mo phase, the main corrosion mechanism of micro-chemical corrosion and electrochemical corrosion; in sulfuric acid corrosion in Mo and Al2O3 + CeAl11O18, CeAl11O18 phase boundary, the main corrosion mechanism for the electric chemical corrosion; in hydrochloric acid to pitting corrosion of the way.
　　Degree Year: 2010