Papers by Keyword: Slip Casting

Abstract: Hybrid composite for drinking water filter aids were prepared by slip casting method. The slip was prepared from the mixture of 17.41% of zeolite Na-A, 17.41% of activated carbon, 0.35% of ZnO nanoparticles, 8.7% of phenolic resin, 0.54% carboxymethyl cellulose and 55.59% of reversed osmosis water. The slip was mixed in a high speed ball mill for 15, 30, 45 and 60 minutes and was then poured into plaster molds for 3 hours in order to maintain hollow casting. The green body was dried and fired at several of firing temperature of 600, 650, 700 and 750 °C. The major characteristics of the composite filter were characterized as: mechanical strength, morphology, pore diameter and ion exchange ability by three points bending, scanning electron microscopy (SEM), mercury porosimetry and inductive coupled plasma-optical emission spectroscopy (ICP-OES), respectively.

Abstract: The ability of zirconia ceramics to develop a bioactive surface is of great importance for biomedical applications. For that, it is also required to control phase stability (i.e. to avoid the tetragonal to monoclinic phase transformation) of zirconia surfaces in order to impart a high mechanical resistance. In this work, the phase stability of dense 3 mol% yttria stabilized-zirconia (3Y-TSZ) ceramics after acid and hydrothermal treatments was examined. Ceramic discs were prepared by slip casting from well dispersed 52 vol% suspensions, and subsequently sintered to 1300-1500 °C. The effect of various synthesis parameters and 0.25 wt% alumina doping on the phase transformation after acid and hydrothermal treatments was semi-quantitatively evaluated by XRD. The 3Y-TSZ sintered to 1500°C exhibited higher t→m transformation than samples sintered at lower temperatures. The phase transformation up to10h of hydrothermal treatment occurred by nucleation and growth mechanisms in which the nucleation process predominated. The presence of 0.25 wt% alumina in 3Y-TSZ sintered at 1500°C slightly enhanced the resistance to acid treatment.

Abstract: In this paper, composite Al₂O₃–t-ZrO₂ ceramics (composition: 95 wt. % Al₂O₃ – 5 wt. % t-ZrO₂ and 90 wt. % Al₂O₃ – 10 wt. % t-ZrO₂) was formed by slip casting in plaster mould. After drying, green bodies were sintered in laboratory electric kiln under air environment at a temperature of 1650 °C.Erosive wear resistance of sintered monolithic Al₂O₃ and composite Al₂O₃–t-ZrO₂ ceramics was determined by SEM analysis of the sample surface morphology before and after erosion at impact angle of 90° and SiC as erodent particles. Surface morphology analysis after erosion showed that wear scars were significantly larger on Al₂O₃ than on Al₂O₃–t-ZrO₂ samples. All conducted tests showed that tribological properties of monolithic Al₂O₃ can be improved with the addition of t-ZrO₂.

Abstract: Several methods for processing tubular anodes for solid oxide fuel cells have been developed, but many of them are expensive and sophisticated, therefore, there is a great interest in researching the use of a simple process to produce them. In this paper, the results of using slip casting for processing minitubes of NiO-8YSZ with the dimensions of 100x5x1 mm are presented. This is a versatile method for obtaining complex geometries with a suitable surface finish and dimensional precision at low cost compared with ceramic processing which uses high energy consumption and/or has high startup costs. In order to carry out this study, an aqueous slurry of an oxide mixture of NiO-8YSZ with poly-etilenglycol as a dispersant agent was used. The modification of the ratio of water:ceramic powders, the composition NiO:x8YSZ (30, 50 and 70 in wt.) and the casting time (3 to 30 min) were also applied. The minitubes obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopy of dispersive energy (EDS). The results show that slip casting is an appropriate method to obtain NiO-8YSZ minitubes. Minitubes of varying composition (30, 50 and 70% in wt. of NiO) with dimensions of 100x5x1 mm were obtained showing an excellent porosity (higher than 96% in v/v) and a homogeneous distribution of NiO and 8YSZ particles. XRD analysis confirms the presence of starting oxides before and after the casting process.

Abstract: In the present work, the characterization of monolithic materials formulated at different weight concentrations was conducted; employing two of the ceramic materials most used in the refractory industry, zircon and alumina. These monolithic materials were fabricated using colloidal techniques, specifically plaster casting mold, in order to obtain pieces with a higher particle consolidation and density, reducing porosity to lower values than the obtained using traditional shaping process of these materials. The monoliths were obtained employing two ceramic powders with different average particle size and morphology to achieve better packing in the green body. This characterization was carried out, firstly, determining the particle size of the raw materials by laser diffraction and the evaluation of particle morphology by scanning electron microscopy. Aqueous suspensions were formulated by containing both ceramic materials, which were dispersed with Tamol 963, and analyzed by rheometric techniques. Subsequently, bars were manufactured having the following dimensions; 4 mm wide, 3 mm thick and 45 mm in length, according to ASTM C1161-02cc, to be characterized microstructural and mechanically, also was observed the fracture habit after the mechanical test. As a final result, the materials formulated at higher alumina content showed higher density values, reaching 94.95% of the theoretical density, also showed a higher thermal expansion coefficient and high rupture modulus, reaching up to 600 MPa and Young modulus of 230 GPa. From the microstructure characterization it was observed that alumina matrix shows a transgranular fracture across the grains and zircon particles exhibited intergranular fracture among the grain boundaries.

Abstract: The effect of the transformation of phase in nanopowders of transition alumina has showed to be detrimental for the final characteristics of the consolidated materials. It was found that the complete transformation from gamma (γ-Al₂O₃) to alpha (α-Al₂O₃) alumina generated larger grain sizes and lower relative densities. This work studies the effect of slip casting preformed on the transformation phase of alumina during microwave sintering of α-alumina nanopowders. The sintering of the samples was carried out in a typical unimodal microwave furnace with a 2.5 GHz frequency. Sintering was carried out under air atmosphere at temperatures vary between 1100 and 1500 °C with heating rate of 100 and 200 °C/min and with a sintering plateau of 5 minutes. Sample characterization was performed by XRD, SEM, and TEM. The phase quantification was calculated using the Rietveld software from the XRD patterns. To have a good heating control in the microwave system it is possible by using slip casting to preform compact. It was observed that the heating rate has a strong effect on the phase transformations. Secondary phases like θ, θ’(x, y) appeared in samples sintered with a heating rate of 200 °C/min no matter the sintering temperature. Meanwhile the complete alumina transformation was found when sample were heating at 100 °C/min.

Abstract: Consolidation of ceramic parts may be achieved by several techniques, including the slip casting and cold isostatic pressing (CIP) methods. In the present work, the performances of the two methods are compared in the fabrication of nanostructured zirconia compacts for dental crown applications. First, a zirconia suspension suitable for slip casting was prepared. The rheological properties of the zirconia suspension were optimized by adding a dispersant agent and controlling the pH. Zirconia slurries were then slip-cast into a pellet. Second, another group of zirconia pellets were fabricated using uniaxial pressing and were then cold-isostatically pressed. Both slip-cast and CIP samples were sintered at 1300 °C with a soaking time of 2 hrs. The mechanical properties of both samples were compared. The samples prepared by slip casting were denser compared with those prepared via CIP. Slip casting technique produced samples with 98.8% of the theoretical density, which resulted in the high Vickers hardness (11.4 GPa) of the slip-cast samples. Morphological studies revealed that the microstructures of the slip cast-sample were more homogeneous and contain no porosity. The formation of such a structure is due to the enhancement of the particle packing efficiency by slip casting as well as to the removal of larger agglomerates by colloidal processing prior to casting. As a consolidation stage, slip casting appears to be more suitable than the CIP technique in preparing reliable nanostructural ceramic parts.

Abstract: In this work suspensions containing natural amorphous silica fibers (NASF), amorphous silica gel and nanometric colloidal amorphous silica were prepared and rheologically analyzed. The suspensions were prepared by varying the volume percentage of solids between 22 and 32%, ammonium polyacrylate (APA), as dispersant, from 0 to 5% and polyvinyl alcohol (PVA), as binder, between 1 and 3.5%. The mixtures were obtained in a propeller mechanical mixer and formed by slip casting. The results of rheological characterization indicated that the suspensions with 30% solids, 4% dispersant and 3% binder were those that showed a stable rheological system and suitable for processing by slip casting.

Abstract: In this work aqueous ceramic suspensions were prepared from a parent glass-ceramic powder (3.8 μm) belonging to the LZSA (Li₂O-ZrO₂-SiO₂-Al₂O₃) system without or with additions of different volume fractions (1.0-7.5%) of TiO₂ nanoparticles (25 nm). The obtained suspensions were rheologically characterized so that stable suspensions were defined e formed by slip casting. The obtained compacts were sintered (850-950°C/60 min) and their green and sintered densities were determined and related to linear shrinkage measurements. The results showed that samples sintered at 950oC for 60 min with 1.0% TiO₂ addicted presented linear shrinkage of 12% and relative densities of 97%.

Abstract: In this study,the Zeta potential of original and modified SiC micropowder was researched,and the effects of surface modification on SiC slurry solid loading,rheologyh and density of slip casting body were studied.The structure of body was looked through SEM. The results indicated that the dispersion of modified SiC micropowder was greatly improved,the slip casting SiC slurry which had 73vol% solid loading,low viscosity and good fluidity was prepared,after slip casting,the density of body was 2.698[g·cm^-3],and the structure was uniform.