Papers by Keyword: Slip Casting

Abstract: Pore size gradient hydroxyapatite scaffolds with interconnected pores were fabricated using a novel template with graded polymer beads and slip casting. The microstructure, phase, porosity, and compression strength of the fabricated pore size gradient HA scaffolds were characterized. The scaffolds were also examined for their cell compatibility in vitro using human osteosarcoma (HOS) cells. By using a polymer template with graded sizes, the scaffolds showed gradually increasing pore size of approximately 177-578 μm and interconnection size ranges from 71.5-290.7 μm along the cylindrical axis. The porosity of selected sections of the pore size gradient HA scaffolds ranged from 62.4-71.2%, while the compressive strength decreased from 8.1-3.72 MPa as the pore size and NaCl content increased. HOS cells showed best growth in sections of the scaffold with pore sizes of 480-578 μm.

Abstract: Conventional methods for preparing ceramic bodies, such as cold isostatic pressing, gypsum-mold slip casting, and filter pressing are not completely suitable for fabricating large and thick ceramic plates, because of disadvantages such as the high cost of equipment, formation of density gradient, and differential shrinkage during drying. These problems could be avoided by employing step pressure-vacuum hybrid slip casting in which consolidation occurs not only by the compression of the slip in casting room, but also by vacuum sucking of the dispersion medium (water) around the mold. This method enabled us to fabricate a 110 × 110 × 20 mm alumina plate without cracks and with homogenous density, and the possibility of extending the method to fabricate other ceramic products appears to be promising.

Abstract: To study the microstructure and mechanical properties of alumina nanocomposites, Al2O3/2.5 vol.% Ni and Al2O3/10 vol.% ZrO₂ nanocomposites were consolidated by pulsed electric current sintering (PECS). Fracture toughness was found to increase by 13 % and 16 % respectively compared to reference alumina. Hardness increased slightly in Al2O3/Ni because of a fraction of nickel particles under the critical size (2 following the rule of mixtures. By investigating the results, causes of improved mechanical properties were critically evaluated.

Abstract: Magnesium-aluminium spinel (MgAl₂O₄) in the form of transparent ceramics is applied in shields of infrared detectors or emitters, high-temperature widows and elements of military aircrafts and vehicles. Apart from high transparency for specific wave lengths, such materials should have good mechanical properties, especially hardness. It is the reason for production of the fine-grained materials. It seems that they can be produced from submicron powders consolidated by one of colloidal techniques. The work presents preliminary results of investigations on colloidal consolidation of two fine spinel powders with different particle size by pressure filtration and slip casting. The aim of the studies was consolidation of the fine powders leading to green samples with narrow pore size distribution. The samples were then sintered in isothermal conditions. Microstructure, Vickers hardness and transmission in infrared spectrum of the dense materials were examined.

Abstract: The aim of this work is to produce a stable suspension of iron oxide reinforced by different ceramic nanoparticles like SiO₂, TiO₂. Measurements of mean particle size, zeta potential and flow curves have been done. Additionally deflocculation curves and sedimentation were drawn to complement the study. The results showed that nanoparticles helped suspensions to maintain a deflocculated stable condition for longer periods of time.

Abstract: Previous works studied the colloidal processing of nickel-silica and nickel-titania nanocomposites fabricated via slip casting. A rheological approach was used to characterize and optimize a 30 vol.% nickel aqueous suspension with up to 10 vol.% SiO₂ and 5 vol.% TiO₂ nanoparticles. In this work, the effect of mechanical activation of Ni-SiO₂ and Ni-TiO₂ nanocomposites on microstructural and mechanical properties was studied. For this aim Ni-SiO₂ and Ni TiO₂ slip-cast compacts were attrition milled for up to 12 hours. Green bodies of the mechanical-alloyed powders were obtained by cold pressing (300 MPa). Next, those green bodies were annealed at 700°C for 1 h, repressed at 700 MPa and sintered at 900°C for 1 h in flowing Ar/5%H₂ atmosphere. Porous and dense materials were characterized by SEM/FESEM, Archimedes densities and Vickers microhardness measurements. Mechanical alloying produces a remarkable improvement on microstructure homogenization, sintering densification and hardness comparing with slip-cast composites.

Abstract: Various textured alumina ceramics were prepared by colloidal processing in high magnetic field and heating from alumina powder as raw material in this study. The effects of the magnetic field strength, heating time and heating temperature on the particle orientation were systematically examined for these samples with scanning electron microscope (SEM) and X-ray diffraction (XRD) etc. The experimental results showed that alumina grains are polyhedral ball shape of, no textured structure exists in the sintered bodies without magnetic field treatment; the alumina grains align with the c-axis parallel the magnetic field direction under high magnetic field, the grains present strip shape in the sintered alumina bodies with the magnetic field treatment; the particle orientation degree increases with increasing the heating time and heating temperature; when the sintering temperature achieves about 1823K, the textured microstructure can be obviously observed in the sintered alumina bodies.

Abstract: Fused silica micro-powders with D₅₀ of 1.8μm were firstly prepared by ball milling. Effects of milling time on particle size distribution and microstructures of the powders were discussed. Then, the green compacts with volume density of 1.86g/cm³ was obtained by slip casting with lactic acid as dispersant. Effects of lactic acid content on apparent viscosity of the slurry, thickness and density of the green compacts were investigated. Finally, fused silica ceramics with thermal expansion coefficient of 0.56∙10^-6/°C, bending strength of 64MPa and volume density of 1.94g/cm³ were prepared.

Abstract: With boron-rich slag, silica fume, bauxite chalmette and carbon black as starting materials, α-sialon/AlN/BN powder was prepared by carbothermal reduction-nitridation. The powder was attrition milled to submicron size and suspended in water. The effects of yttrium oxide as a sintering aid, pH, and addition of deflocculant on the suspensions were studied. Optimum slip casting properties, i.e. lowest viscosity values, the highest absolute zeta potential values, the smallest floc size and sediment volume were found at pH=10 for the powder. The suspensions were used to slip cast discs which were sintered in a high purity nitrogen atmosphere at 1700 °C for 2 h. The strength was about 230 MPa, the toughness 3.6 MPa•m1/2 and the hardness about 13.8 GPa.

Abstract: Co-deposition of silicon carbide particles and carbon (or carbon sources) particles is essential for preparation of reaction bonded silicon carbide (RBSC) products by slip casting. The way of co-depositing of silicon carbide particles and carbon particles during slip casting process, and the influence of composition of raw particles on particle co-depositing in green bodies were studied. The experiment results show: 1.Co-deposition of binary particles is greatly affected by particle size distribution, and large proportion of rigid SiC particles increases the difficulty in demoulding procedure because of small shrinkage; 2. Dispersants in deposited cake trend to enrich at the surface in contact with mould wall, while this enrichment of dispersant has little effect on mechanical performance of RBSC products; 3. Sharp edges on surface of raw particles could result to friction among particles, which afford strength to green bodies but prevent particles packing more closely.