Slip Casting Route Research Articles

Manufacture of carbon-bonded alumina based on a lactose-tannin binder system via slip casting

Binders play an important role in the manufacture of carbon-bonded alumina (Al2O3-C) refractory materials. To diminish the currently used coal tar pitch binder Carbores® P, which could release hazardous polycyclic aromatic hydrocarbons during operations, environmental-friendly lactose and tannin are applied as the main binders in this study. Compact cylinders of fine-grained Al2O3-C based on the lactose-tannin (16 wt%) binder system with significantly reduced pitch content (4 wt%) are successfully prepared via slip casting for the first time. The lactose to tannin mass ratio is systematically varied from 5:1 to 1:5 in the raw material formulation. The specimens based on the new binder system are less dense, more porous and contain less residual carbon than the pitch-based reference. Mechanical tests show that the specimens with lactose-tannin ratio of 5:1, 4:1 and 3:1 have considerable cold crushing strengths, although the splitting tensile strengths are low. In contrast to the well-established pressing route, the slip casting route for compact Al2O3-C is more comparable to the replica route for Al2O3-C foam filter due to the pressureless shaping process.

Synthesis of in-situ mullite foam using waste rice husk ash derived sol by slip-casting route

In this study, mullite foam ceramic is synthesized via a simple slip-casting method without using any pore producing additive or agent, in order to avoid the emission of greenhouse gases (mainly CO2) from the matrix. Waste rice husk ash (RHA) extracted sol (solid contain ~7.5 wt%) as an alternative of conventional silica sources along with active alumina is used for the preparation of slip-casting slurry. About 22 wt% solid containing slurry is casted in the plaster of paris (POP) mold. The casting mass is dried at 110 °C and fired at 1100 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, and 1400 °C. Several properties like phases, microstructure, porosity, density, mechanical strength, and thermal conductivity are comprehensively investigated with the foam samples. At 1250 °C fired sample is retained mullite dominating phase in the matrix. The single-phase mullite is formed at 1300 °C fired sample with 75.99% total porosity, 11.07 MPa compressive strength, and thermal conductivity of 0.153 W/m·k. Furthermore, the strength value and thermal conductivity are increased and porosity is reduced with the increasing firing temperature. The obtained results exhibit that the waste RHA derived sol is capable to produce low-temperature in-situ mullite foam through slip-casting route without generating the pollutants (mainly CO2↑).

Preparation and characterization of multilayer Gd2O2S:Tb phosphor screen for X‐ray detection application

AbstractGd2O2S:Tb (GOS) phosphor screen, generally with a multilayer structure, has been widely used in digital X‐ray imaging. GOS phosphor screen is fabricated via a slip casting route, which is an effective method to obtain multilayer composites with good strength. The GOS slurry was prepared using the menhaden oil, polyvinyl butyral and PEG‐400 as dispersant, binder and plasticizer, respectively, and slip casted on a support layer. After the GOS scintillation layer is formed, a transparent polyethylene terephthalate film is covered on it as a protective layer. The X‐ray excited emission spectra of the obtained GOS phosphor screen is well match to the spectral response of a‐Si:H photodiode, and the spatial resolution was close to 3.7 LP/mm, which could meet the request of the commercial application.

Effect of calcined colemanite additions on properties of hard porcelain body

Abstract Utilization of calcined colemanite as a sintering aid in hard porcelain body, prepared by slip casting route using aqueous suspension containing mixtures of kaolin, quartz and potassium feldspar, was investigated. After calcination, colemanite powders were added to the admixture of porcelain by partial substitution with potassium feldspars in the range of 0–5 wt% to discover its influences on the densification and technological properties of the final product. Through optimization of process parameters of ceramic suspensions by using appropriate dispersing agents and facilitating densification by calcined colemanite addition, hard porcelain possess high strength was obtained. When relationship between the additive concentration with temperature was established, it is found that porcelain formulations resulted in substantial reduction of firing temperature about 50 °C without compromising its quality by 1 wt% calcined colemanite addition.

Spray freeze granulation of submicrometre alpha-alumina using ultrasonication

Granulation is a key factor towards improvement of the flowability of fine ceramic powders to make them suitable for industrial dry pressing. Controlled granulation of fine alumina particles with a primary particle size of ∼ 150 nm was carried out using spray-freeze drying, which led to the production of flowable granules with high crushability. The fracture surface of uniaxially die-pressed green bodies made from granules with density values of ≥ 50%of theoretical showed a uniform microstructure. Sintering experiments were performed using conventional single- and two-stage radiant heating methods followed by density and grain size measurement and characterisation of the final dense compacts to study the efficiency of two-stage sintering in grain growth elimination. The results have been compared with those of alumina bodies prepared using similar suspension by the slip-casting route.

Synthesis and Characterization of Bone & Teeth Ash and Analysis of Their Influence on the Properties of Bone China

The work was done to understand the effects of naturally occurred bone and teeth ash on the physical as well as mechanical properties of bone china products. Both bone and teeth ash was prepared following conventional thermal decomposition method. Locally found cattle bones and tooth was utilized for this purpose. Three different routes of powder or ash preparation i.e. boiling-wood firing, excavating-calcination and boiling-calcination were followed. The calcination temperature was fixed at 950°C-2 hours. After that, density and phase identification of ash was carried out. Finally, bone china product was manufactured using powder compaction and slip casting route. Firing was done at a constant temperature (1150°C-2 hours). Further characterizations (density, percent firing shrinkage, percent water absorption and modulus of rupture measurement) of the sintered samples were evaluated. Boiling-calcination route was found to be the most superlative route. However, enhanced properties of bone china were obtained by the addition of teeth ash.

Fabrication of alumina porous scaffolds with aligned oriented pores for bone tissue engineering applications

In the present study, porous alumina scaffolds with specific orientation and anisotropic properties are fabricated for application in bone tissue repair. The scaffolds with double shape pores, tubular oriented and isotropic rounded pores, were prepared using alumina and silica as starting materials by the slip casting route. Milled polyurethane foam and silk fibers were applied as replica materials as well. The effect of fiber types and diameter and number of fibers on the microstructure and pore size was studied. Moreover, different characteristics such as porosity, density, orientation, flexural strength and compressive strength of the samples were investigated. Results showed that various fibers with different diameters and numbers led to forming the pores with different pore sizes, microstructure and consequently changes in the physical and mechanical properties. In addition, the simultaneous presence of fibers and particles led to more porous scaffolds. The oriented tiny micro-tube and rounded pores were observed in all porous ceramic scaffolds. Mechanical testing showed an anisotropy in the mechanical behaviors such that higher strengths were observed in the oriented pore direction than that of transverse. With increasing the number and diameter of silk fibers, the scaffolds with a high porosity up to 68 vol% and proper flexural strength were obtained.

Investigation of calcium zirconate ceramic synthesized by slip casting and calcination

Abstract In order to provide large scale bodies composed of synthesized calcium zirconate ceramic, the slip casting technology as well as calcination was applied. Optimized suspensions with high solid content and low viscosity were obtained by adding a dispersant agent and subsequently slip cast into plaster moulds to produce bars. Densification as well as material properties were studied at temperatures ranging from 1200 to 1500 °C. Due to their good properties, bars sintered at 1500 °C were selected for crushing to get coarse and fine grains for calcium zirconate rich refractory materials. To evaluate the applicability of the slip casting route, the mechanical properties of the obtained coarse grains were compared with commercial fused-cast product.

Hot corrosion behavior of slip‐cast alumina‐chrome refractory crucible against molten glass

Alumina‐chrome bodies were prepared by slip casting route. Slip casted bodies were sintered in the temperature range of 1550–1650 °C in reducing atmosphere with 2 h soaking time at peak temperature. Highly dense alumina‐chrome body with bulk density 4.24 g/cc and almost zero apparent porosity were obtained at 1650 °C. The hot corrosion test of alumina‐chrome crucible against borosilicate glass was carried out in static condition at 1200 °C for 4 h. The study of the glass–refractory interface after static corrosion test was done by scanning electron microscopy, energy dispersive X‐ray spectroscopy analysis and X‐ray diffraction (XRD) analysis. The XRD pattern of glass–refractory interface does not show formation of any new phases. Elemental mapping of glass–refractory interface indicates corrosion up to a depth of 70 µm has taken place in the form of ion migration.

Micro‐Raman spectroscopy of indentation induced phase transformation in nanozirconia ceramics

Micro‐Raman spectroscopy has been employed as an effective technique to determine the phase transformations in nanostructured yttria stabilised zirconia (YSZ) ceramics with different yttria contents. Samples have been prepared with varying mean grain sizes by a slip casting route followed by a microwave assisted two‐step sintering cycle starting with aqueous nanozirconia suspensions. Indents were generated using a Vickers pyramidal indenter at different loads, and the resulting phase transformations were mapped using micro‐Raman spectroscopy. The results were compared to those of a commercial submicrometre 3 mol.% YSZ. The amount of transformation was found to be much lower for nanozirconia compared to the submicrometre zirconia with similar yttria content.

Slip casting of nanozirconia/MWCNT composites using a heterocoagulation process

The addition of carbon nanotubes (CNTs) is expected to increase the fracture toughness of ceramic matrix composites, but an uniform dispersion of the nanotubes in the matrix is essential. This is a complex issue in aqueous medium because of the nanotubes hydrophobicity. In this work, the stability and rheological behaviour of nanozirconia concentrated suspensions, from 20 to 33 vol% solids, with and without multiwall carbon nanotubes (MWCNTs) was optimised in order to obtain homogeneous green samples by slip casting. The manufacture of nanozirconia/MWCNTs composites was performed using a heterocoagulation process in which the CNTs were homogeneously coated by the ceramic particles through strong electrostatic attractive forces between the two phases and further consolidation by a slip casting route. After sintering, the effect of the MWCNT on the hardness and fracture toughness of the nanostructured zirconia samples was evaluated.

Effect of suction force and starting powders on microstructure of Bi4Ti3O12 ceramics prepared by magnetic alignment via slip casting

The microstructures of Bi 4 Ti 3 O 12 (BIT) ceramics made in a vertical magnetic field via a slip casting route are investigated. Two kinds of BIT powders, with equiaxial and plate-like particles, are used. Magnetic force aligns the BIT particles successfully, but the samples are not homogenous. In the top zone, BIT grains in both samples have a – b -plane orientation due to the strong magnetic force. In the bottom zone, the sample using equiaxial particles shows a random microstructure, and the sample using plate-like particles shows c -plane orientation. This is because of the suction force of slip casting.

Comparative study of different routes of particulate processing on the characteristics of alumina functionally graded microfilter/membrane supports

This work investigates the preparation and characterization of flat functionally graded alumina microfilters/membrane supports employing different preparation routes of particulate processing, i.e., slip-casting (different rates), sedimentation and centrifugal casting using a similar slip of highly dispersed α-alumina particles. A powder with a cut off diameter of 1.2 μm but comprehending a sub-micron particle size range has been used in order to increase the permeability of the whole body. Permeability, average permeable pore diameter and tortuosity, curvature and top layer characteristics (defects, surface porosity, pore diameter) as a function of sintering temperature and processing routes have been investigated. Reasonable membrane characteristics are obtained at an optimum temperature of 1525 °C for the centrifuge and slow rate slip-casting routes while the sedimentation route results in severe surface macro cracks. At this temperature, the slip-casting route suffers from relatively low surface porosity (2.5%) when compared with the centrifuge samples (10.7%). This is while the surface pore diameter is about 0.1 μm smaller for the latter (0.28 μm).

Preparation and characterisation of porous hydroxyapatite bioceramic via a slip-casting route

Porous hydroxyapatite bioceramic was fabricated using a casting method by mixing a polymeric powder with a slip containing fine hydroxyapatite powders. The rheology of the ceramic slip was examined. After sintering, the resultant porous hydroxyapatite bioceramic was characterised in terms of the porous microstructure and mechanical properties. The experimental results demonstrated that the resultant porous ceramic with a successful control of pore size and porosity characters can be obtained. The flexural strength (σf) of the porous hydroxyapatite ceramic decreased with increased macropore size and correlated well with the porosity (p) by an exponential function: σf = 115 exp (−4.5 p) MPa. The Young's modulus ( E) of the porous bioceramic can also be adequately described by E = 140 exp (−4.2p).