Effect of vacuum impregnation on the performance of Co/SiO_2 Fischer-Tropsch catalyst

Two silica-supported cobalt catalysts were prepared by incipient wetness impregnation under atmospheric and vacuum conditions.N2 ph- ysisorption,H2 chemisorption,XRD,SEM,TEM,XPS and H2-TPR were used to characterize the catalysts.The results showed that the impregnation methods had an effect on the size,dispersion and reducibility of cobalt particles.Under vacuum conditions,cobalt-containing steeping liquor could penetrate into the inner pores of silica support and more bivalent cobalt oxides were formed in the Co3O4 crystallites.Furthermore,cobalt precursors were rarely inclined to agglomerate and the smaller cobalt particles were uniform on the support,which led to the higher activity of the Co/SiO2（B）catalyst than the normal one under the reaction conditions of 483- 523 K,1 - 2 MPa,gas hourly space velocity of 500–1000 h-1 and molar ratio of H2/CO=0.5 - 2.0.

Assessing efficacy of standard impregnation techniques on die-cast aluminum alloys using X-ray micro-CT

Utilizing lightweight Al alloys in various industrial applications requires achieving precise pressure tightness and leak requirements.Vacuum pressure impregnation(VPI)with thermosetting polymers is commonly used to address leakage defects in die-cast Al alloys.In this study,the efficacy of the VPI technique in sealing alloy parts was investigated using a combination of nondestructive micro X-ray computed tomography(micro XCT)and a standard leak test.The results demonstrate that the commonly used water leak test is insufficient for determining the sealing performance.Instead,micro XCT shows distinct advantages by enabling more comprehensive analysis.It reveals the presence of a low atomic number impregnates sealant within casting defects,which has low grey contrast and allows for visualizing primary leakage paths in 3D.The effective atomic number of impregnated resin is 6.75 and that of Al alloy is 13.69 by dual-energy X-ray CT.This research findings will contribute to enhancing the standard VPI process parameters and the properties of impregnating sealants to improve quality assurance for impregnation in industrial metals.

Self-Lubricating PEO Coating on an Al Alloy Produced by Vacuum Impregnation Post-treatment

The objective of this research was to develop a novel self-lubricating coating on an AA6061 aluminum alloy.Three coatings were prepared by the plasma electrolytic oxidation（PEO） process using 50-, 500-, and 1000-Hz pulsed direct current, respectively. The as-deposited coatings were then post-treated using two different methods, viz., ultrasonic vibration-aided vacuum oil impregnation（UVOI） and oil impregnation under ambient pressure（OIAP）. After posttreatment, an oil-containing, self-lubricating top layer was formed on the coatings. The effects of the coatings＇ surface morphologies and structures on their oil-holding capabilities were discussed. The results revealed that coatings prepared with higher frequency had a greater oil-holding capacity using OIAP post-treatment, while those prepared with lower frequency had a greater oil-containing capability using UVOI post-treatment. These phenomena are related to the morphologies of the coatings produced with various current modes. The tribological properties of the coatings before and after post-treatments were investigated by pin-on-disc sliding wear tests. Due to the formation of a lubricant-containing top layer, the post-treatment coatings had a lower friction coefficient and improved wear resistance compared with the asdeposited coatings. In addition, the coatings after UVOI treatment had better wear performance than those post-treated using the OIAP process. Among all coatings, the coating produced with a 50-Hz pulsed current followed by UVOI posttreatment achieved the lowest friction coefficient（0.03） and best wear resistance when sliding against a Si3N4 ceramic counterface. This study indicates that a novel self-lubricating coating can be prepared by a PEO process combined with vacuum oil impregnation post-treatment.

Shape-stablized EP/Paraffin Composite for Latent Heat Storage

620# and 56# paraffin mixtures were impregnated into expanded perlite （EP） by vacuuming method. Effects of impregnation with/without vacuum, vacuuming time, and thermal cycles were discussed. The appropriate mass fraction of paraffin mixture in the composite and vacuuming time were found respectively to be 80% and 20 min. Fourier transform infrared spectrometer （FT-IR） analysis shows that it has a good compatibility between paraffin mixture and EP. From differential scanning calorimetry （DSC） analysis, the latent heat of EP/Paraffin mixture composite is almost linearly related with the mass fraction of paraffin mixture in the composite. After 100 thermal cycles, the deviation of phase change temperatures is acceptable, but more deviation of latent heat appears. The calcium stearate dispersing granule coated by epoxy resin can effectively lower leakage during thermal cycles.

Slag Resistance of Magnesite-chrome Brick Impregnated with Chrome-bearing Sols

Cr2O3 has eminent slag corrosion resistance. So, the magnesite -chrome brick is thought as an important refractory material used in RH refining furnace in the process of steel-making around the world. After chromebearing sols being prepared by sol-gel method, single sol （ Cr（ OH）3） and mixed sol （ Mg（ OH）2 - Cr（ OH）3） were impregnated into magnesite - chrome bricks by vacuum impregnation. The corrosion resistance of the impregnated bricks to silicon steel slag was studied by porosimetric analysis and fractal dimension calculation. The results showed that the corrosion resistance of impregnated magnesite -chrome brick was better than that of the unimpregnated brick and the brick impregnated by MgSO4 solution, and the one which has surface-treated by Mg（ OH）2 -Cr（OH）3 sol was the best, mainly because of lower apparent porosity, smaller pores diameter and their smoother inner sarface.

Fabrication and Properties of Aluminabased Reticulated Porous Ceramics

The primary impregnation slurry was prepared using active alumina(56.25 mass%),kaolin(15 mass%),zirconia(3.75 mass%),deionized water(25 mass%),and extra adding FS(0.2 mass%)and CMC(0.4 mass%).The effects of the active alumina particle size(d50=5.043,2.934,and 1.629μm)on the rheology and the thixotropy of the slurry were researched.It was found that the bimodal activeα-Al2O3(AMA-10)with d50=1.629μm was optimum.The secondary impregnation slurry was prepared using AMA-10,kaolin and zirconia as the main raw materials.Then the alumina-based reticulated porous ceramics were fabricated by the organic foam impregnation method combined with a secondary vacuum impregnation process.The influence of the AMA-10 content on the properties of the ceramics was studied.The residual stress of the specimens was analyzed by finite element analysis.The results show that the smaller alumina particle size and multimodal distribution are beneficial to the thixotropy of the primary impregnation slurry.The secondary vacuum impregnation technique can significantly improve the mechanical properties,the thermal shock resistance and the residual strength of the alumina-based reticulated porous ceramics.With the decrease of alumina content in the secondary impregnation slurry,the residual stress of the external layer of ceramic reinforcement gradually changes from tensile stress to compressive stress,which effectively inhibits the expansion of the surface crack,and remarkably improves the crushing strength retention ratio of alumina reticulated porous ceramics.

New Development of VPI Process for Large Superconducting Coils

High vacuum is required for Vacuum Pressure Impregnation (VPI) process of large coils used in cryogenic. The defects such as dry spots and over rich resins should be minimized in large superconducting coils used. Both sealing problems associated with the mold and over rich resin problems are eliminated by using vacuum bag mold method with which we can simplify the design of vacuum mold.