Aqueous Slips Research Articles

Research of the dispersing and strengthening additives’ influence on the properties of slips and alumina ceramics samples from active alumina

The effect of dispersing and strengthening additives on the rheological properties of aqueous slips made from new brands of alumina produced by a German company was studied. The optimal quantities of dispersing additive for slips from all researched new brands of alumina were determined: for less dispersed alumina — 0.3 % and more dispersed alumina — 0.4 %, the introduction of which reduces the dynamic viscosity of slips to minimum values of — 30 mPa·s, 70 mPa·s and 110 mPa·s, respectively. It has been established that slips made from all researched new brands of alumina with the optimal dispersing additive quantity are characterized by high sedimentation stability and in combination with 0.2 % strengthening additive the sedimentation stability of slips increases.
 The main properties indexes of the samples from new brands of alumina before and after firing at a temperature of 1580 °C were determined. It was established that green samples from new brands of alumina are characterized by apparent density 2.23 g/cm3, 2.19 g/cm3, 2.18 g/cm3 and cold crushing strength 1.1 N/mm2, 1.0 N/mm2, 0.8 N/mm2, respectively, and samples after firing at 1580 °C by apparent density 3.75 g/cm3, 3.90 g/cm3, and 3.86 g/cm3, open porosity 3.3 %, 0.5 %, 0.4 % and bending strength 150 N/mm2, 180 N/mm2, 200 N/mm2, respectively.
 As a result of the performed research, it was established that new brands of more dispersed alumina are suitable for the production by the slip casting method in plaster molds of alumina ceramics with open porosity up to 0.5 % and bending strength ~ 180—200 N/mm2.
 According to the performed research results the technology of alumina ceramics by slip casting in plaster molds method was improved and the raw material base for its production was expanded.

Dense m-Li2ZrO3 formed by aqueous slip casting technique: Colloidal and rheological characterization

An aqueous colloidal processing method was proposed to prepare m-Li2ZrO3 bodies, with high green density and a homogenous microstructure, employing a pressureless forming technique. For this purpose, the preparation conditions of m-Li2ZrO3 aqueous suspensions were optimized considering colloidal processing variables, such as milling time (0–40 min), dispersant concentration (1–10 wt% of the solids content) and maximum solid loading (41–74 wt%). Particle size distributions and steady-state flow curves of the slips were analyzed, together with phase composition and microstructure of the ceramic bodies. The results show that after planetary ball milling for 30 min, the aqueous suspension with 63.1 wt% of m-Li2ZrO3, and a dispersant content equal to 10 wt% of the solid loading, yielded green bodies with bulk densities close to 66% TD by slip casting. Then, after the heat treatment process at 1100 °C for 12 h, bulk densities close to 88% TD were achieved. It was found that density values and microstructure of the green and sintered products bear a direct relationship to the particle size and the consistency of the slips.

Fabrication of highly transparent AlON ceramics by fast formed direct aqueous slip casting green body

By using a copolymer of isobutylene and maleic anhydride (Isobam-104) as dispersant to prepare slurries of high solid loading, aluminum oxynitride (AlON) green bodies were fast formed by direct aqueous slip casting. Based on the experiments on solid loading and dispersant amount, the optimal sample pressureless sintered at 1880[Formula: see text]C for 2.5 h showed the highest transmittance of 80.1%. The slurry drying time in mold was effectively reduced to only 2 h by increasing solid loading, which is more adaptive to fabricate complex-shaped and/or large-sized AlON components of high transparency.

Influence research of temperature heat treatment on the microstructure of alumina ceramics

The JSC "URIR named after A. S. Berezhnoy" developed and introduced the technology of highly refractory alumina extra-dense ceramics. It is known that, the structure and properties of alumina ceramics in many cases depend on the temperature of its heat treatment, the holding time at the final temperature, the thermal unit, and a number of other factors. In order to study the processes of structure formation during of heat treatment the microstructure of alumina ceramic samples of two compositions (composition 1 with a moisture content of 30 %, as well as with dispersing and hardening additives, and composition 2 with a moisture content of 20 % only with dispersing additive) which were made by slip casting aqueous alumina slips based on reactive alumina α–from with Al2O3 content over 99 %, specific surface ~ 9 m2/g by electron microscopic analysis was studied. It was established that, after heat treatment at 1000 °C the beginning of sintering and recrystallization of corundum grains are observed, after heat treatment at 1200 °C take place packing of structure and recrystallization of α–Al2O3. After firing at 1400 °C the microstructure of samples composition 1 is represented to a large extent by crystals of tabular corundum with a particle size ~ 0.5—5.5 μm, predominant — ~ 2.5—3.0 μm. After firing at 1400 °C the microstructure of samples composition 2 is represented — by individual particles of a rounded and oval form with a size of ~ 0.5—3.5 μm, predominant — ~ 1.5—2.0 μm which are interconnected by intercrystalline layers. The microstructure of alumina ceramic samples of both compositions after firing at 1500 °C is similar and is composed of recrystallized corundum grains with a size of ~ 0.5—5.5 μm, predominant — ~ 1.5—2.0 μm, among which there are also larger α–Al2O3 grains, with a size of ~ 2—8 μm. After firing at 1580 °C the microstructure of samples is represented by a dense fine-grained structure of well-formed practically defect-free corundum grains, with a size of ~ 0.5—3.0 μm, among which grains of ~ 5—10 μm.

Direct coarse powder aqueous slip casting and pressureless sintering of highly transparent AlON ceramics

Direct coarse powder aqueous slip casting was proposed to prepare AlON green body for pressureless sintering of highly transparent AlON ceramics. It was reported that anti-hydrolysis treatment to AlON powder before aqueous slip casting was essential due to hydrolysis reaction between AlON and water. However, both XRD of hydrolyzed powder and pH value of aqueous slurry indicate that the hydrolyzate amount is positively correlating with hydrolysis reaction area, i.e., surface area of powder. Therefore, replacing fine particle with coarse one to reduce surface area of powder is an efficient hydrolyzates reduction scheme by lessening hydrolysis reaction sites. As a result, the hydrolyzate in green body of direct slip casting coarse AlON powder (91 vol% of particles have a size of >1.0 μm) was successfully reduced to an insignificant amount so that the sintered ceramics had a high transmittance (84.1% at ~3750 nm), which also verified the effectiveness of the proposed hydrolyzate-reduction scheme.

Separation of Halloysite Nano Tubes (HNTs) by Homogenization of Quartz Contaminated Kaolins

Natural halloysite kaolin contains a lot of impurities such as quartz phases and varies in morphology and size during their formation in the earth. So to utilize as a new type of natural nano material, removing quartz impurities from kaolin clays without scathe the tube morphologies are necessary. So to remove quartz impurities from kaolin by forming a well deflocculated aqueous slip without fracturing the morphology of tubes, the slip of homogenized halloysite clay was recovered by adding polyvalent metallic cations and anionic polyelectrolyte flocculants simultaneously to selectively flocculate the mixture of quartz and halloysite, whereby the halloysite particles form floes and the tubular halloysite remains in suspensions. Then, the uniform size and tubular shape of halloysite was obtained which could be suitably used as a container or a carrier to encapsulate nanomaterials.

Microstructure and mechanical properties study of slip-cast copper–alumina composites

Alumina matrix composites reinforced with metallic copper were produced and their microstructure and mechanical properties were studied. The composites were fabricated by aqueous slip casting technique, and sintered at 1500 °C in a hydrogen atmosphere. The samples showed low porosity and a core-skin structure with copper-free skin and a uniform spatial distribution of copper particles in the core. The addition of metallic Cu particles at low amounts in the Al2O3 matrix resulted in a small reduction in the stiffness and the hardness but augmented impact resistance. The mechanical properties of the composites were in good agreement with porosity-corrected predictions of the simple rule of mixtures, indicating that this fabrication method produces composites for which the enhanced toughness is not accompanied by a large reduction of their other mechanical properties.

Aqueous Slip Casting of Transparent Aluminum Oxynitride

Highly transparent Aluminum oxynitride (AlON) body has been produced using aqueous slip casting technique. High‐purity alumina and AlN were used as raw materials for the synthesis of single‐phase AlON powder. As‐synthesized AlON powder was surface modified to enable the AlON powders resistant to hydrolysis in water during aqueous slip casting. High solid loaded aqueous AlON slip was prepared for casting followed by drying and sintering to produce transparent AlON. Phase formation and stability was characterized by XRD, pH, and viscosity measurements. AlON powders before and after surface treatments were characterized. Sintered transparent AlON samples were characterized for their mechanical, microstructural, and optical properties. Sintered and polished AlON produced in this study has shown inline transparency up to 80% between 0.22 and 6 μm wavelength region.

Processing of ZrO2 scaffolds coated by glass–ceramic derived from 45S5 bioglass

Three dimensional, highly porous, ZrO2 scaffolds coated by glass–ceramic derived from 45S5 bioglass were fabricated. The surface reactivity of 45S5 in aqueous solution was investigated as a function of the immersion time. The influence of the solid loading on the rheological behavior of 45S5 aqueous slips with ammonium polyacrylate (NH4PA) was studied; besides the effect of poly(vinyl)alcohol (PVA) on the relative viscosity was determined. The structure and microstructure of uncoated and coated ZrO2 scaffolds were characterized. The high ionic exchange capability of 45S5 was demonstrated by the pH rise, the significant weight loss and the amorphous calcium phosphate nucleation, upon its immersion in aqueous solution. The addition of PVA did not affect the dispersion properties of the 45S5 powder, which were basically controlled by its negative surface charge. 30wt% 45S5 slips with 4wt% PVA exhibited a yield stress and an adequate viscosity in the low shear rate range, to produce a bioglass coating into the ZrO2 scaffold. The glass-ceramic coating was distributed along the strut surfaces, forming a thin film without altering the porosity and the strut thickness of the original ZrO2 scaffold structure.

Some Features of Porous Permeable Ceramic Molding by Slip Casting

Preparation of porous filter ceramic by casting from aqueous slips into a gypsum mold is studied. The effect of different factors on casting porous filter ceramic and methods for controlling its properties are established. Test filter ceramic is prepared and operating parameters are determined.

Production Features of β-Spodumene Composition Glass Ceramic Synthesis. Part 2. Study of the Possibility of Using Production Waste in the Stage of Slip Preparation and Workpiece Formation

Results are given for a study of features of workpiece casting technology from aqueous lithium aluminum silicate glass slips. Production examples are developed reducing raw material loss to a minimum during slip preparation and workpiece molding.

가압-진공 하이브리드 주입 성형에 의한 알루미나의 성형에 미치는 다단 가압의 영향

Conventional cold isostatic pressing, slip casting, and filter pressing are not completely suitable for fabricating large plates because of disadvantages such as the high cost of equipment and formation of density gradient. These problems could be avoided by employing pressure-vacuum hybrid slip casting (PVHSC). In the PVHSC, the consolidation occurs not only by the compression of the slip in casting room, but also by vacuum sucking of the dispersion medium around the mold. We prepared the alumina bodies by the PVHSC in a static- or stepwise-pressure manner for loading up to 0.5 ㎫ using an aqueous slip. The green bodies were dried at 30℃ with 40 ~ 80% relative humidity. Under static pressure, casting induced a density gradient in the formed body, resulting in cracking and distortion after the firing. However, the stepwise pressure loading resulted in green bodies with homogeneous density, and the minimization of the appearance of those defects in final products. Desirable drying results were obtained from the cast bodies dried with 80% RH environment humidity. When sintered at 1650℃ for 4 h, the alumina plate made by stepwise-pressure casting reached full density (＞ 99.7% relative density).

Alumina/MWCNTs composites by aqueous slip casting and pressureless sintering

Abstract Slip casting of stabilized aqueous suspensions followed by pressureless sintering was used for preparation of dense Al 2 O 3 /MWCNTs composites. The suspensions were stabilized by commercial polyelectrolyte dispersant Darvan C–N. In order to increase the stability, the pH value of the suspension was adjusted to ∼10. At this pH the highest ζ-potential values of the alumina powder and of the MWCNTs functionalised in boiling nitric acid were achieved. Two different agents, namely ammonium hydroxide and sodium hydroxide, were used for the pH adjustment. Their influence on the viscosity of suspensions and on consolidation and densification behaviour of the Al 2 O 3 /MWCNT composites was evaluated. The effect of ammonium hydroxide was more pronounced, as confirmed by lower viscosity of the suspension, higher sintered density, and fine-grained microstructure of the sintered composites. The Al 2 O 3 /t-MWCNTs composites with 0.1 wt% of the MWCNTs, with 99.9% relative density, the mean size of alumina grains ∼1 μm, and homogeneously distributed carbon nanotubes were prepared by the pressureless sintering at 1500 °C.

가압-진공 하이브리드 주입성형에 의한 알루미나의 균질 성형

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 owing to disadvantages of these processes, such as the high cost of the equipment, the formation of density gradients, and differential shrinkage during drying. These problems can be avoided by employing a pressure-vacuum hybrid slip casting approach that considers not only by the compression of the aqueous slip in the casting room (pressure slip casting) but also the vacuum sucking of the dispersion medium (water) around the mold (vacuum slip casting). We prepared the alumina formed bodies by means of pressure-vacuum hybrid slip casting with stepwise pressure loading up to 0.5 MPa using a slip consisting of 40 vol% solid, 0.6 wt% APC, 1 wt% PEG, and 1 wt% PVA. After drying the green body at 30℃ and 80% RH, the green density of the alumina bodies was about 56% RD. The sintered density of an alumina plate created by means of sintering at 1650℃ for 4 h exceeded 99.8%.This method enabled us to fabricate a 110 × 110 × 20 mm alumina plate without cracks and with a homogeneous density, thus demonstrating the possibility of extending the method to the fabrication of other ceramic products.

Hydrolysis-Induced Aqueous Gelcasting: The Latest Concept for Net-Shape Consolidation of Ceramics—A Review

This is a review article covering literature reported on consolidation of ceramic components out of aqueous-based Al2O3, MgAl2O4 spinel, β-Si4Al2O2N6, β-SiAlON-SiO2 composite, and zirconia toughened alumina (ZTA) slurries following hydrolysis induced aqueous gelcasting (henceforth referred to as GCHAS) route. GCHAS is a combination of aqueous gelcasting (GC) and hydrolysis assisted solidification (HAS) routes. The advantages of GCHAS over other net-shape forming techniques in the fabrication of certain important ceramic structures such as thin wall radomes have been reviewed in this article. Interestingly, among the various colloidal-based net shape forming techniques available, GCHAS has been found to be a most promising one for consolidating complex-shaped ceramic structures with significantly high green strength and high product yield. Sintered properties of ceramics consolidated by GCHAS are compared and discussed with those of similar ceramics consolidated by aqueous slip casting (SC), GC, HAS, and a conventional dry-powder pressing (DP) of freeze dried granules in this article.

Slip Casting of a Si3N4‐Based System

Silicon oxynitride ceramics were prepared by aqueous slip casting in plaster moulds. The colloidal behavior of slurries prepared with various dispersants was optimized through the electrokinetic sonic amplitude and rheological measurements. Samples with dimensions up to 5 × 10 × 2 cm were produced and the optimal processing and sintering conditions were determined. The flexural strength and dielectric constant of selected samples were similar to the values reported in literature for materials obtained with more expensive shaping techniques. The results showed that the preparation of large silicon oxynitride components by slip casting is feasible.

Drawing of Piezoceramic Fibers and Ribbons Using a Novel Alginate Gelation Method and Properties of Fiber and Ribbon-Based Piezodevices

Piezoceramics are usually shaped into three dimensional bulk form using dry pressing or slip casting methods. However, certain applications require piezoceramics to be shaped in one dimensional fiber or two dimensional ribbon form. In this study, piezoceramic fibers and curved piezoceramic ribbons were fabricated using a novel alginate gelation method. Alginate is a natural linear polymer that is obtained from brown kelp. In the presence of multivalent cations, it forms ionic cross-links and gels in a three dimensional network form. In our study, gelation conditions of alginate containing aqueous slips of lead zirconate titanate based piezoelectric ceramic powders were investigated. Piezoelectric ceramic fibers and ceramic ribbons were prepared by sintering of gelled powders for transducer applications. Structural characteristics of these ceramics and electrical characteristics of piezodevices prepared from these ceramics were investigated and reported.

Drawing of Piezoceramic Fibers and Ribbons Using a Novel Alginate Gelation Method and Properties of Fiber and Ribbon-Based Piezodevices

Piezoceramics are usually shaped into three dimensional bulk form using dry pressing or slip casting methods. However, certain applications require piezoceramics to be shaped in one dimensional fiber or two dimensional ribbon form. In this study, piezoceramic fibers and curved piezoceramic ribbons were fabricated using a novel alginate gelation method. Alginate is a natural linear polymer that is obtained from brown kelp. In the presence of multivalent cations, it forms ionic cross-links and gels in a three dimensional network form. In our study, gelation conditions of alginate containing aqueous slips of lead zirconate titanate based piezoelectric ceramic powders were investigated. Piezoelectric ceramic fibers and ceramic ribbons were prepared by sintering of gelled powders for transducer applications. Structural characteristics of these ceramics and electrical characteristics of piezodevices prepared from these ceramics were investigated and reported.

Rheological properties of aqueous alumina–alumina-doped Y-PSZ suspensions

The effect of the substitution of alumina (Al2O3) by 0.3wt% Al2O3-doped 3mol% yttria-partially stabilized zirconia (Y-PSZ) on the rheological properties of concentrated aqueous slips was studied. Al2O3–Al2O3-doped Y-PSZ aqueous suspensions with different Al2O3-doped Y-PSZ contents: 0, 22 and 50vol% were prepared using ammonium polyacrylate (NH4PA) as dispersant. The particle size distributions of Al2O3 and Al2O3-doped Y-PSZ powders were similar; however, the particle shape and the surface coating of alumina conferred a markedly higher specific surface area to the Al2O3-doped Y-PSZ powder. The substitution of Al2O3 by Al2O3-doped Y-PSZ in the mixtures decreased the negative surface charge of the powders at pH 9, thereby increasing the amount of NH4PA adsorbed and consequently the electrosteric repulsion between particles. However, the viscosity and yield stress values increased with increasing Al2O3-doped Y-PSZ content for all the solid loading studied. This could be explained by a larger interaction size of the Al2O3-doped Y-PSZ particles which resulted in a higher effective volume solid fraction and a lower amount of free-liquid available for flow.

Spherical indentation damage in TiC–Ni 3Al composites

Advanced cermets based on titanium carbide (TiC), with a ductile nickel aluminide (Ni 3Al) binder, have shown significant promise for use in a variety of demanding wear environments, due to a combination of high strength and good corrosion behaviour. In the present study, TiC–Ni 3Al composites were produced by melt infiltration, using aqueous slip cast TiC preforms, and Ni 3Al binder contents from 10 to 50 vol. %. These samples were subjected to spherical indentation testing, with applied loads from 250 to 2000 N, using WC–Co spheres ranging in diameter from 1.19 to 2.38 mm. Indentation stress-strain curves were determined and compared to the calculated elastic (i.e. Hertzian) response. The bonded interface method was used to examine the subsurface damage of the cermets after indentation. Significant deformation of the binder and the eventual fracture of TiC grains were observed. The nature of the quasi-plasticity of TiC–Ni 3Al, and the affect of binder content on surface and subsurface deformation, are discussed.