Zhu Dachuan

Tribological Properties of Muscovite/La2O3 Composite Powders as Lubricant Additives

Muscovite/La2O3 composite powders were prepared by ball-milling solid-state chemical reaction at room temperature. The phase composition and micromorphology of the composite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The tribological properties of different samples were tested and compared using four-ball wear testing on an MMW-1A multifunctional friction and wear testing machine. The SEM micrography and energy spectrum of the composite powders illustrated that La2O3 particles were coated on the surface of muscovite particles. The results of the friction tests indicated that lubrication oil with muscovite/La2O3 composite powders presents better friction reducing and antiwear properties than that of the base oil, and the friction coefficients and diameters of wear scars decreased by 47.6 and 11.2% using 500SN base oil with 0.6g/L of muscovite/La2O3 composite powders as additives, respectively. The composite powders with 5 wt% La2O3 present the best comprehensive tribological properties. The micromorphology and chemical composition of the worn surface were analyzed by SEM and EDX, which confirm that the composite powders directly participate in the complicated physicochemical process of reactions on the worn surfaces, therefore improving the tribological properties of the base oil.

Preparation of a Core-Shell Structured Al2O3/YAG:Ce Phosphor by a Spray Drying Method and Formation Mechanism

Abstract The core-shell structured Al 2 O 3 /YAG:Ce phosphor was prepared by a spray drying method. The obtained samples show cubic Y 3 Al 5 O 12 structure, have a spherical shape with the size in the range of 1~8 μm and exhibit higher internal quantum yield compared to the samples prepared by co-precipitation. Based on the fact that the spray drying method can be employed to fabricate microencapsulate particles, the formation mechanism of the core-shell structured Al 2 O 3 /YAG:Ce phosphor was formulated. The slurry, which was mixed with micrometer Al 2 O 3 particles and polycations consisting of Y 3+ , Al 3+ and Ce 3+ , was atomized and shaped by the evaporation of droplets. In the process of solvent evaporation, the interparticle capillary forces make the self-assembly of polycations into the close-packed shell surrounding the Al 2 O 3 particles, because the polycations have a bigger diffusion rate than Al 2 O 3 particles. At last, the precursor was calcined at the temperature from 850 o C to 1250 o C for 2 h and then the core-shell structured phosphor was produced. Therefore, a novel idea for preparing core-shell structured phosphor is proposed.

Preparation and Tribological Properties of Cu-doped Muscovite Composite Particles as Lubricant Additive

Cu-doped muscovite(Mu) composite particles, abbreviated as Mu/Cu, were prepared via liquid phase reduction method. The morphologies, phase composition and elementary distribution of the as-prepared Mu/Cu and raw muscovite particles were characterized by means of scanning electron microscope(SEM), X-ray diffraction(XRD) and energy dispersive spectrometry(EDS). The tirbological properties of Mu/Cu and Mu as lubricant additives in lithium grease were evaluated on a block-ring tribomachine. The roughness, 2D and 3D morphologies and elementary distribution of block worn surface were analyzed to explore the tribogical mechanism. The results show that muscovite are evenly coated by the cubic Cu nanoparticles in composite particles. Both Mu/Cu and Mu can effectively improve the tirbological properties of lithium grease and Mu/Cu exhibits better tribological performance than Mu. The friction coefficient of Mu/Cu is decreased by 69.2% as compared to that of lithium grease. The layer structure of muscovite is synergistic with Cu nanoparticles in contribution to the formation of lubricant film mainly consisting of O, Si, Fe, Cu as well as Al elements on the block worn surface thereby further reducing the friction and wear.