Papers by Author: Tian Ma

Abstract: The microstructure of the inorganic fullerene-like WS2 was analyzed by scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM) in this work. The results indicate that the diameter of the WS2 particles is around 60~120 nm. The WS2 consists mainly of hollow polyhedral structures with quasi-spherical shape that is capable of sustaining much higher shock pressures due to a more uniform stress distribution on its surface. This characteristic made it a super shock wave absorbing material, which is great worth of bullet proof applications. This work is expected to develop a new type bullet-proof composite which can be used in the army.

Abstract: MWCNT/Ultrahigh-molecular-weight polyethylene (MWCNT/UHMWPE) composite was prepared by adding purified MWCNTs into the precursor solution of UHMWPE. Based on that, MWCNT/UHMWPE fibers were obtained using a gel spinning-molding technique. The thermal, mechanical and aggregation structure of MWCNT/UHMWPE fibers were characterized by TGA, mechanical property measurement and XRD, respectively. The results indicated the incorporation of MWCNTs into UHMWPE macromolecular chains have not change the aggregation structure of UHMWPE significantly, and the as-prepared MWCNT/UHMWPE fibers have evidently improved thermal stability and mechanical strength compared with the pristine UHMWPE fibers.

Abstract: In view of the unique porous structure of hemp stem, the comparison experiments were implemented on adsorption properties of hemp stem powder and Abies holophylla Maxim powder to formaldehyde, benzene and TVOC. In addition, on the basis of preliminary study on solid-gas adsorption kinetics of hemp stem, applicability of several adsorption theories was analyzed versus solid-gas adsorption. The results showed that the unique structure endowed hemp stem better adsorption properties than Abies holophylla Maxim’s. However, for different adsorbents, the adsorption kinetics characters differed obviously. Bangham and Langmuir adsorption rate equation fitted the gas-solid adsorption kinetics of hemp stem to some extent, and Langmuir’s could present its absorption to TVOC much better.

Abstract: Reaction-formed silicon carbide (RF-SiC) ceramics can be prepared by melt Si-infiltration of the carbon preform which fabricated by casting of carbon powder of hemp straw. In order to make clear the pore structure of the carbon powder of hemp straw which affect the mechanical property of RF-SiC ceramics, the morphology and inherent pore structure of carbon powder of hemp straw were characterized with powder X-ray diffraction, laser diffraction size analysis, scanning electron microscopy, transmission electron microscopy, mercury porosimetry and nitrogen adsorption. The results indicated that some parts of interconnected macroporous and mesoporous structures of hemp straw still remained after carbonization and the RF-SiC ceramics with outstanding performance can be fabricated with this carbon powder by melt Si-infiltration of the porous preform

Abstract: Micro-hardness is one of the most important mechanical properties for bullet-proof ceramics. The micro-hardness of typical and commercial available bullet-proof ceramics alumina, silicon carbide and boron carbide were studied in this paper. The result indicated that the high ballistic performance (protection coefficient) was mostly attributed to the high micro-hardness of the ceramics. The ballistic protection mechanics of the ceramics was analyzed based on the ceramics’ hardness, structures and protection coefficients.

Abstract: Two groups of silicon carbide ceramics were prepared by pressureless sintering processing with a small amount of boron and carbon as sintering additives. The flexural strength, Vickers hardness, fracture toughness and compressive strength of the samples were measured and compared. Sample A achieved much higher flexural strength (389.4MPa) than that of sample B (250.3MPa) due to the difference of additive dosage. However, the two groups of samples attained comparable values for the other three mechanical properties. SEM observation revealed that the stoichiometric ratio of the Si/C atom in the sintered body is an important factor to affect the mechanical performance of the silicon carbide. The ballistic performance of the samples was also evaluated in this study. The results showed that sample B exhibited more excellent ballistic property, which is probably related to the high flexural strength. The detailed influencing factors need to be studied further.

Abstract: Colloidal injection moulding of ceramics (CIMC), an innovative technique combining the advantages of conventional injection moulding and colloidal forming process, is applied to prepare thin-wall rutile tube for high capacity ozone generator. The forming process is studied detailed and the processing parameter of forming, drying and sintering schedule is determined in this research. The wall thickness of the sintered tube is 1.5~2mm and its inner diameter is about 26 mm, length is about 300 mm. The electric properties of the tube are also measured under different conditions. The above-mentioned tube is applied in ozone generator and the yield of ozone is about 55mg·L-1.

Abstract: The effects of solid volume fraction (SVF) on the gelation of alumina suspensions for gelcasting, debonding and sintering of the green body were studied. It was found that with SVF rising, the gelation of alumina suspension delayed; and the strength of green body decreased. On the other hand, high SVF resulted in that polymerized acrylamide split at a relative low temperature. These phenomena manifest that the fast polymerization of monomers in high SVF alumina suspension was inhibited, and the flexibility of the gelcasting was improved. However, Excessive solid volume fraction was prone to a bad rheological behavior of alumina suspension, and deteriorated the microstructure and properties of sintered body.

Abstract: Zirconia suspensions with coarse particles were prepared and the rheogical behavior and sediment stability of such suspensions with different dispersants were studied. It was found that ZrO2 suspension stabilized with TAC (tri-ammonium citrate) has an obvious shear-thinning behavior and rapid settlement; In contrast, the suspension stabilized with arabic gum shows a shear-thickening behavior and hardly any settlement. Considering both fluidity and settlement stability, APA (ammonium-polyacrylate) was chosen as the dispersant to increase the solid volume fraction of ZrO2 suspension. Utilizing the above suspension, a kind of refractory nozzle for precision casting of a Cu-Cr alloy was prepared by gelcasting. Such nozzle has a very good resistance to thermal shock and flux scouring.

Abstract: In this paper, a W/O microemulsion system composed of cyclohexane / water / TritonX-100 / hexyl alcohol is adopted to prepare ultrafine spherical zirconia powder via the reaction between the precipitant and zirconium salt solved in the nano reactors. Furthermore, the powder’s surface characteristics and aqueous dispersibility that strongly depends on the post-treatment process are investigated thoroughly.