Papers by Author: Dong Liang Jiang

Abstract: In the present work, porous HA scaffolds with well controlled pore size, porosity and high compressive strength were prepared by aqueous gelcasting. PMMA beads with different size were used as the pore forming agent. The compositions, microstructure and properties of porous HA bioceramics were analyzed by XRD, SEM, Hg porosimetry etc. The mechanical properties were also tested. For scaffolds with the porosity as 70%, the average compressive strength was 11.9±1.7 MPa. Results showed that glecasting process can be used for the preparation of porous HA biomaterials with well controlled pore size and improved mechanical properties.

Abstract: Active researches have been conducted to seek the application of ceramics as structural components. However, the lack of damage tolerance ability has been a critical problem. Laminated composites as one of the main way for improving the brittleness of ceramics are getting more and more attention from the biomimetic point of view. In the present paper, three laminated composites, SiC/TiC, Al2O3/Ni and ZrB2-SiC/ZrB2 with intentionally introduced surface compressive stress were presented. The finite element method (FEM) was used to simulation the stress distribution and to optimize the layered structure for the development of more reliable materials. Based on FEM analysis, the laminated structure was realized by aqueous tape casting and hot pressing. The dependence of mechanical properties (fracture strength and toughness) on the structural parameter (the composition of layers, the thickness ratio between layers, number of layers) was investigated. The calculated mechanical properties were in agreement with the tested ones to some extent.

Abstract: In situ bonding porous silicon nitride (Si3N4) ceramics were fabricated in air using a conventional ceramic process using Si3N4, Al2O3 and MgO as the starting materials. The effects of additives content, sintering temperature and holding time on phase composition, microstructure, dielectric properties and porosity were studied. The porous Si3N4 ceramics were composed of α- Si3N4, SiO2 (cristobalite) and cordierite. Porous Si3N4 ceramics with porosities of 34.12~50.22%, dielectric constant of 2.95~4.45 and dielectric loss of ~0.0025 were obtained.

Abstract: Ultra-high temperature ceramic composites of ZrB2-SiC were densified by pressureless sintering. Ultra-fine ZrB2-SiC composite powders synthesized by sol-gel method were mixed with commercial ZrB2 and SiC powders. The sintered body of hybrid powders (combined commercial and synthesized composite powders) showed excellent properties not only in the relative density but also the flexure strength. Dry-pressed compacts using 4wt% Mo as a sintering aid were sintered to nearly full density at 2200°C/2h. The average strength was ~560MPa and the maximum was ~632MPa. SEM and TEM showed that SiC particles were distributed homogenously in the ZrB2 matrix and the average particle size was ~5μm. From HRTEM observations, the grain boundaries were apparently free of glassy phases and no intermediate phases existed.

Abstract: In this paper, the aqueous gelcasting of carbide ceramics (SiC, TiC, and B4C) were studied systematically. N, N-dimethyl acrylamide (DMAA) and N, N’-methylenebisacrylamide (MBAM) are used as organic monomer and cross-linker respectively. The initiator was selected from ammonium persulfate (APS) and 2, 2’-azobis[2-(imidazolin-2-yl) propane]dihydrochloride (AZIP2HCl) in accordance with the dispersant used. After gelcasting and drying, SiC samples can be densified by pressureless sintered at 2000°C. The gelcasted TiC green samples can be densified at 1530°C in vacuum with the strength as high as 1062.7749.81. The gelcasted B4C samples can be easily densified at 2250°C by pressureless sintering with the relative density around 96.2%. Results showed that it was possible to prepare carbide ceramics with complex shape and satisfied mechanical properties by gelcasting.

Abstract: The present study was performed to determine the suitable processing conditions to obtain boron carbide slurries for gelcasting. We examined how dispersant, pH and other factors function in boron carbide slurries. The optimum conditions for the preparation of stable slurries with high solid content were determined. The effect of monomers on the slurry properties was studied. The properties of gelcasted green and sintered B4C samples were also investigated.

Abstract: Stable ZrB2-based ultra-high temperature ceramic slurries were prepared and characterized with a solid content 40 vol% by aqueous gelcasting which was suitable to form high quality and complexshaped ceramic parts. In the present work, Ammonium Citrate Tribasic (ACT) was used as the dispersant. The properties of ZrB2 slurry, and the influencing factors were investigated by conventional techniques such as sedimentation tests, particle size distribution measurements, electrokinetic measurements and rheological analysis. High solids loading and low viscosity slurry was obtained by controlling the optimal conditions for the ZrB2-based ceramic powders.

Abstract: The effects of high-energy ball milling on SiC powders were studied using a planetary apparatus. Conditions to obtain nanostructured SiC powders with an average crystallite size of 4 nm were determined and powders were characterized by XRD, SEM and TEM analyses. This process was applied to prepare fine powders leading to dense SiC ceramics by sintering at 1900oC for 30 minutes under 30 MPa in argon.

Abstract: (Al2O3+Ni) and (Al2O3+Ni)/Ni laminated materials were prepared by tape casting and hot pressing sintering. The mechanical properties of (Al2O3+20wt%Ni) laminated composites were higher than those of (Al2O3+50wt%Ni) composites and Al2O3 sample. The strengthening in the (Al2O3+Ni) composites mainly results from microstructure refinement of the alumina grain size, cracks bridging and crack deflection by the Ni particles. Results showed that the strength and fracture toughness of (Al2O3+Ni)/Ni laminated materials were higher than those of Al2O3/Ni laminated materials with the same layer numbers and thickness ratio. The good mechanical properties of (Al2O3+Ni) and (Al2O3+Ni)/Ni laminated materials result from the second phase of Ni particles in Al2O3 layers.