The effects of acids (monochloroacetic, dichloracetic, trichloroacetic and sulfuric acids) and bases (diethanolamine, triethanolamine, piperidine) on electrophoretic mobility and electrophoretic ...deposition (EPD) of particles of amphoteric Al2O3 and ZrO2 in anhydrous 2-propanol were studied. It was found that the ζ-potential of Al2O3 and ZrO2 particles had in acidic and alkaline 2-propanol media opposite charge to that in aqueous medium. This phenomenon was explained by the low dissociation constants of acids and bases in 2-propanol. This enables electrosteric stabilization of Al2O3 and ZrO2 particles by acid anions and base cations. Similar electrophoretic behaviour of Al2O3 and ZrO2 particles in 2-propanolic dispersions stabilized by MCAA allowed the preparation of compact, regular layered laminates with high cohesion at the interface of layers.
The traditional method for shaping ceramics is by slip casting on gypsum molds; however, its application for near‐net shaping of ceramic components is limited due to contamination by calcium ions. ...The focus of this study is the modification of the mold to limit Ca2+ contamination and to maintain favorable sucking properties. Cement was added to a standard gypsum mold to suppress its erosion, and a decrease in the sucking rate was observed due to its reduced macroporosity. The highest values of green densities were obtained at gypsum/cement weight ratios of 90/10 and 70/30. The microstructure analysis showed that alumina blocks prepared from the molds containing higher quantities of cement (30 or 50 wt%) were resistant to abnormal grain growth caused by Ca2+ contamination from the gypsum. The gypsum/cement mixtures for making molds for slip casting significantly limit mold erosion due to a lower sucking rate and abnormal grain growth of the slip cast samples because of the decreased diffusivity of Ca2+ ions. Therefore, the present modification of the mold renders the slip casting method more suitable for the near‐net shaping of ceramics.
In the present work, the effect of an indifferent electrolyte (LiCl) on the electrical conductivity of dispersions for the electrophoretic deposition (EPD) of thick layers (>1mm) of hydroxyapatite ...(HA) with low surface roughness was studied. The indifferent electrolyte was added at concentrations of 0.10 and 0.25g/L into dispersions, which contained HA particles, 0–21.25wt% monochloroacetic acid (MCAA) and 2-propanol. The stability of the dispersions, which was determined by measuring the zeta potential, increased with the MCAA content in the dispersion (up to −31.4mV). An addition of LiCl slightly reduced the stability of the dispersions but significantly increased their electrical conductivity. The increase in electrical conductivity caused the decrease in deposition rate during the EPD, which affected the deposition yields and deposit thickness. The relative density of the HA deposits increased with the MCAA content in the dispersion and further increased when 0.10g/L of LiCl was added. Moreover, using a highly conductive dispersion, thick HA layers were deposited with low surface roughness and no surface cracks. An optimum content of indifferent electrolyte in the dispersion enables the preparation of relatively dense and thick (>2mm) HA deposits with a low surface roughness (~3µm) via EPD, which can be used in medical applications.
The positive effect of plasma mediated treatment of powder fraction in water-based dispersion is a rather well documented fact. Despite its importance for ceramic processing, the applicability of ...plasma treatment of ceramic particles in a non-aqueous dispersions remains unexplored. In the presented article, a specific planar type of dielectric barrier discharge - Diffuse Coplanar Surface Barrier Discharge (DCSBD), operated in atmospheric pressure air was used for the surface activation of sub-micron alumina particles. These were consequently dispersed in organic solvent of 2-propanol and evaluated for the performance during the process of electrophoretic deposition (EPD). The surface of ceramic particles and the dispersion behaviour were investigated using thermogravimetric analysis, XPS, measurement of zeta potential and particle size distribution. Plasma treatment of ceramic particles had a substantial effect on the deposition rate, which caused a significant reduction of surface roughness and slight improvement of the density and mean grain size of the fabricated coatings. Moreover, the plasma treatment resulted in a simultaneous anodic and cathodic EPD.
The ceramic dispersions were prepared using 0.85, 1.70, 4.25, 12.75 or 21.25wt.% of monochloroacetic, dichloroacetic or trichoroacetic acid, 15wt.% alumina and 2-propanol. The mechanism of anionic ...stabilization in 2-propanolic media was described. Alumina green bodies were prepared from the stable dispersion via electrophoretic deposition (EPD). It was found that increasing dispersion conductivity significantly influenced the EPD yields. The most effective electrophoretic depositions were performed from dispersions with conductivity in range 4.0–5.3×10−4Sm−1. Deposits with the highest green density were prepared from the dispersion stabilized by trichloroacetic acid. This behavior was explained by low voltage drop during deposition. The surface roughness was high at low dispersion conductivity and with increasing acid concentration in dispersion the surface of deposits was smoother. The mechanism of particle arrangement in deposit was discussed. Influence of stabilizer amount in the dispersion on the hardness and fracture toughness was described.
The article summarises optimisation of electrophoretic deposition of alumina and zirconia from concentrated isopropanolic suspensions stabilised by monochloracetic acid. Method for in situ monitoring ...of deposited mass was developed and experimentally checked. Prediction of electrophoretic deposition kinetics was based on the voltage drop measurement and electrophoretic mobility estimation from experimental kinetics data. It was shown that voltage change during electrophoretic deposition did not affect relative density of the deposited layers in the laminates prepared. For this purpose a method of the relative density measurement using the microscopic measurement of relative shrinkage of individual layers was developed. Accuracy of the method was confirmed by comparison with shrinkage measurement using high temperature dilatometry. Adopting obtained results the alumina/zirconia laminate with precise control of layers thicknesses and final densities was prepared.
Presented article summarises preparation of fibre reinforced alumina and alumina laminates containing zirconia micro-fibres. Electrophoretic deposition was performed from concentrated isopropanolic ...suspensions stabilised by monochloracetic acid containing mixture of alumina powder and certain amount of zirconia micro-fibres. A method for in-situ monitoring the deposition of alumina and zirconia micro-fibres mass was applied to control deposition kinetics. Two different approaches for composite deposition were applied: (i) electrophoretic deposition of powders mixture and (ii) electrophoretic co-deposition from sonicated suspension containing stabilization aid. Applying the optimised procedure the alumina laminates reinforced with zirconia fibres were prepared. The co-deposition of ceramic micro-fibres and powder led to the preparation of microstructures having unique orthogonal fracture properties. Developed laminate with layers created by zirconia micro-fibres in the alumina matrix seems to be the most promising. This type of material exhibited potential of the crack trapping and deflection even when very small amount of micro-fibres was used.
Internal residual stresses can enhance the fracture resistance and mechanical reliability of layered ceramics. The magnitude of the stresses depends on the elastic and thermal properties of the ...layers and the typically assumed reference (stress-free) temperature, below which internal stresses develop. A novel combined experimental and numerical simulation approach has been developed to determine the reference temperature and experimentally proved in alumina–zirconia ceramic laminates. Dilatometric data of monolithic phases are input for the numerical simulation and experimental data on the laminate properties are used for the stress-free temperature determination. In contrast to typical assumptions, reference temperature very near the sintering temperature (i.e. approx. Tref≈1470°C) was found, which should be considered for the estimation of internal (residual) stresses in alumina/zirconia-based layered ceramics.
The electrophoretic deposition of alumina and zirconia powders from isopropanolic suspension in the presence of monochloroacetic acid was studied in the constant-current regime. The different levels ...of electric current during deposition from 250μA to 48mA were used. The green density of the deposit depends on the current density and then on the particle velocity during deposition, reaching values from 58% to 61% according to the electric current used. It was found that the lower the green density of the green deposit, the larger the pores. The low green density led to low final fired density and subsequently to the low Vickers hardness HV5 ranging from 2000 to 1650 depending on electric current used. Based on these findings microlaminates having various thickness ratios to achieve different residual stress levels were prepared consisting of alternating layers of alumina and zirconia.
The present study deals with ballistic performance of corundum and silicon carbide ceramics against 7.62 mm calibre projectile. In particular, ceramic samples of dimension 100 x 100 mm with various ...thickness in the range of 6.94 - 6.96 mm and 7.77 - 7.79 mm were glued to Al plate with thickness of 8 mm and tested against 7.62 mm calibre projectiles, namely 30.06 M2 AP, 7.62 mm x 51 AP (WC) and 7.62 mm x 54 R B32. The conducted tests have provided the V sub(50) value for tested materials composed of 8 mm Al plate and ceramic.Furthermore, applying linear approximation the value V sub(50) for normalized ceramic areal density of 26 kg/m super(2) was calculated. From the given V sub(50) values, the energy of projectile absorbed in ceramic and in Al plate was also calculated. Finally, the results showed that corundum ceramic exhibited significantly lower ballistic efficiency probably due to lower thickness (26 kg/m super(2) corresponds to thickness of 6.61 mm) in comparison with SSiC ceramic (26 kg/m super(2) corresponds to thickness of 8.33 mm). The highest efficiency showed 7.62 mm x 51 AP (WC) with a hard core against both ceramics. An unexplained point remains similar V sub(50) value for 30.06 M2 AP and 7.62 mm x 54 R B32 projectile for corundum ceramic and significantly different for SSiC ceramic.
