Ceramic Suspensions Research Articles

Influence of bivalent ions on the dispersion and gelation of ceramics suspensions

Influence of bivalent ions on the dispersion and gelation of ceramics suspensions

AC electric field-induced changes in viscosity of aqueous ceramic suspensions and tuning of freeze-cast microstructure and compressive strength

A systematic parametric study was conducted on alternating current (AC) electric field-assisted freeze-casting to enable a comprehensive understanding of tuning freeze-cast microstructure and compressive strength and provide insights into the role of AC field. A novel finding was that the AC field increased the viscosity of aqueous ceramic suspensions, where the viscosity increase was dependent on the ceramic loading of suspensions, dispersant concentration, and field duration. Viscosity increased with field duration for a fixed solid loading and dispersant concentration. It was suggested that AC field-induced dielectrophoretic (DEP) forces decreased interparticle distances and increased interparticle interactions in ceramic suspensions, hence viscosity. It was revealed that the increase in viscosity of ceramic suspensions due to the AC field could be reversed. It was demonstrated that simple magnetic stirring of the suspensions previously subjected to an AC field (which increased viscosity) reduced viscosity to the level of the as-prepared suspensions. For materials fabrication, an AC electric field was applied to aqueous ceramic suspensions for the desired duration, then turned OFF, followed by freeze-casting, which remarkably influenced freeze-cast sintered microstructure. The impact of the field on microstructure increased with solid loading, dispersant concentration, and field duration, and microstructure changes were associated with viscosity of suspensions prior to freeze-casting. With increasing viscosity, freeze-cast microstructure became increasingly dendritic, i.e., bridge density increased. A positive correlation was observed between bridge density and compressive strength for all the materials. Depending on the solid loading, dispersant concentration, and field duration, about 5- to 8-fold increase in strength was achieved.

Debinding and sintering optimization of stereolithography based silicon nitride parts for attaining centimetric wall-thickness shapes

Stereolithography of UV-curable ceramic suspensions is an additive manufacturing technique with high precision and great resolution to fabricate complex ceramic parts. While it widens the possibilities of applications, one of the drawback of this method is the low wall-thickness of the parts. The polymers forming the network structure upon cross-linking undergo pyrolysis in a step called debinding. During debinding, the gaseous compounds going through evacuation channels create internal pressures, often resulting in crack formation. So far, the critical wall-thickness where crackfree parts are obtained is located around 4 millimeters for silicon nitride. This paper reports the successful debinding of silicon nitride parts obtained by stereolithography. Thanks to an optimization of the debinding relying on TGA analysis, defectless parts with a wall-thickness of up to 11 mm were obtained, yielding parts of 9 mm after sintering. The mechanical properties were measured, showing values equivalent to silicon nitride obtained through conventional methods.

The new rheological model for zirconia suspensions with long-term kinetic stability

For successful 3D printing based on stereolithography technologies, one of the most important factors influencing the success of printing is the dynamic viscosity of the prepared suspension. For the purposes of viscosity prediction at different volume fillings, two ZrO2 powders with different yttrium content (CY3Z-RS and CY8Z-RS) with volume filling 0–40 % in two different dispersing mediums at two temperatures were investigated in this paper. The dependence of relative viscosity on volumetric filling was fitted by existing models and a new semi-empirical model based on experimental data was proposed and successfully plotted. Fitted data for all zirconia photosensitive suspensions showed a high correlation to the proposed model (R2 from 97.02 % to 99.61 %). The model in addition to the possibilities of mathematical generalization of his prescription, introduces a fitting parameter C, which is thought to be thermodynamically influenceable and predictable. Furthermore, another key characteristic that is often neglected in rheological characterization, the stability of prepared ceramic suspensions, was verified either by rheological measurements but also by employing prospective technology based on analytical centrifuge. It was confirmed that all prepared suspensions were highly stable, and all instability indexes reached values less than 0.05.

High Performance Dental Zirconia Ceramics Fabricated by Vat Photopolymerization Based on Aqueous Suspension

Currently, a significant challenge in the fabrication of ceramic dental prostheses via vat photopolymerization lies in the utilization of slurries composed of organic monomers, which compromises environmental sustainability and impedes commercial viability. In this research, we successfully develop a low-viscosity aqueous zirconia ceramic suspension with a solid loading of 40 vol% and 20 vol% deionized waters, incorporating 3 wt% dispersant and 0.5 wt% photoinitiator for printing dental crowns using vat photopolymerization. The resulting green bodies require only water washing to remove unreacted material. The printed ceramics demonstrate an average flexural strength of 708 MPa, a relative density of 98.3 %, and a Vickers hardness of 14.7 GPa. A dental crown is ultimately fabricated with an accuracy of 92.8 %. This study demonstrates that zirconia ceramics fabricated by vat photopolymerization with aqueous suspension exhibit excellent mechanical properties and accuracy, highlighting their potential for broad applications in dental restorations through an environmentally sustainable approach.

Development of Processing Additive Compositions for Ceramic Suspension Based on the Study of the Physico-Chemical Properties of the Components

Development of Processing Additive Compositions for Ceramic Suspension Based on the Study of the Physico-Chemical Properties of the Components

Towards a debinding-free additive manufacturing of ceramics: A development perspective of water-based LSD and LIS technologies

Ceramic additive manufacturing (AM) requires a complex process chain with various post-processing steps that require expensive machines and special expertise. The key to further market penetration is AM that makes it possible to integrate into an already established ceramic process chain. Most successful AM technologies for ceramics are, however, based on processes that initially have been developed for polymeric materials. For ceramics AM, polymers or precursors are loaded with ceramic particles. This strategy facilitates the entry into AM, however the introduction of organic additives into the ceramic process chain represents a considerable technological challenge to ultimately obtain a ceramic component after additive shaping. In the present communication, two technologies based on ceramic suspensions will be introduced, the “layerwise slurry deposition” (LSD) and “laser induced slip casting” (LIS) technology. Both technologies take advantage of the high packing densities reached by conventional slip casting and moreover enable the processing of fines, even nanoparticles.

Vat photopolymerization of biomimetic bone scaffolds based on Mg, Sr, Zn-substituted hydroxyapatite: Effect of sintering temperature

In response to the urgent demand for innovative bone regeneration solutions, the focus of this study is to develop and characterize Mg, Sr, Zn-substituted calcium phosphate scaffolds that replicate the trabecular architecture of cancellous bone. Ion substitution represents a promising approach to improve the biological effectiveness of calcium phosphates and composite materials used in bone tissue engineering applications. Porous scaffolds mimicking the natural bone structure were additively manufactured from the photosensitive ceramic suspensions for vat photopolymerization using digital light processing. The impact of the selected trace elements (0, 1 and 5 mol.% substitution) and the sintering temperature (900, 1000, 1100, 1200, and 1300 °C) was investigated in relation to the obtained crystalline phase content, microstructure, elemental distribution, thermal stability, and mechanical properties. After sintering, in addition to hydroxyapatite, β-tricalcium phosphate was detected as a result of the added trace elements in the calcium-deficient hydroxyapatite used as a starting powder. The obtained scaffolds exhibited uniform distribution of the trace elements, and they feature 3D-designed porosity predominantly ranged from 10 to 900 μm in diameter, with an average pore size of 546.25 ± 10.95 μm. The total porosity of scaffolds was 76.24 ± 1.32 vol% and an average wall thickness of 217.03 ± 8.98 μm, closely resembling the morphology of cancellous bone tissue. The mechanical properties of the scaffolds sintered at 1100 °C, 1200 °C, and 1300 °C were in line with those typically observed in trabecular bone. The study demonstrates the feasibility of using custom made bioactive hydroxyapatite powders together with vat photopolymerization to design the porosity and properties of the bone scaffolds on demand, based on the requirements of individual bone defects.

Vat photopolymerization of silicon carbide strengthened alumina ceramic composites with honeycomb structure for heat insulation and oil/water separation

In this study, the effects of different silicon carbide (SiC) particle sizes on the viscosity and curing behavior of alumina (Al2O3) ceramic suspensions were thoroughly investigated. The findings revealed that increasing the size of SiC particles led to a noticeable decrease in the viscosity of the suspension. The Al2O3 ceramic suspension with 0.6 μm SiC powder demonstrated a shallower cure depth and wider excess width compared to the suspension with 1.0 μm SiC powder. Sintering tests demonstrated that the properties of the SiC–Al2O3 ceramics improved at higher sintering temperatures. Moreover, a high-performance honeycomb ceramic was successfully designed and fabricated with a porosity and compressive strength of 30.8 % and 188 MPa, respectively. Finally, the SiC–Al2O3 honeycomb ceramics were effectively applied in heat insulation and oil-water separation applications, demonstrating their remarkable capabilities.

Efficient composite dispersants for high solid content, low viscosity nano-zirconia slurries: An experimental and molecular dynamics simulation study

An effective dispersant is essential for creating a high-quality water-based ceramic suspension. When the solid content of the slurry is high, a single dispersant proves inadequate. This study proposes a strategy for producing nano-YSZ (yttria-stabilized zirconia) ceramic slurries with high solid content and low viscosity using compound dispersants ammonium polyacrylate (PAANH4) and fructose. The efficacy of dispersion is evaluated through rheological experiments and zeta potential analysis. The optimal dispersant effect is achieved when the compound dispersants are added in the following proportions: PAANH4 = 0.5 wt% and fructose = 5 wt%. Consequently, the viscosity of the nano-YSZ slurry, with a solid content of 50 vol%, is reduced to 696 mPa·s at a shear rate of 100 s−1. Both PAANH4 and fructose effectively lower the slurry’s viscosity via two separate mechanisms: electrostatic-steric stabilization and increasement of free water content. Molecular dynamics (MD) simulation was utilized to examine the nanoparticle dispersion process. The results show that after adding dispersants, the distance between two equilibrium particles is 4 nm, and the potential mean force curve displays a clear energy barrier. This provides a new method for investigating the dispersion effects of dispersants.

High-performance aluminum nitride made by Vat photopolymerization through optimization of resin refractive index and plasticizer content

In this study, we evaluated the effects of three resins with different refractive index on the viscosity and curing behavior of aluminum nitride (AlN) ceramic suspensions. Our findings indicate that the viscosity of the AlN suspensions increased with the concentration of polyethylene glycol o-phenylphenyl ether acrylate (OPPEA). Conversely, the viscosity decreased with increasing concentrations of cyclic trimethylolpropane formal acrylate (CTFA) and ethylene glycol phenyl ether acrylate (PHEA). Regarding the curing behavior, the AlN ceramic suspension prepared with OPPEA exhibited the largest cure depth and excess width, whereas the suspension prepared with CTFA had the lowest cure depth and excess width. Further analysis of the sensitivity and critical energy revealed that the suspension containing OPPEA demonstrated the highest sensitivity in the vertical direction and the lowest sensitivity in the horizontal direction. This implies that the smallest critical energy is in the vertical direction, and the largest critical energy is in the horizontal direction. Additionally, an increase in the content of the plasticizer dibutyl phthalate (DBP) was beneficial for reducing cracks in the AlN ceramic debinding bodies. Finally, high-performance AlN ceramics were produced, exhibiting a relative density exceeding 98 %, a bending strength of 470.39 ± 6.5 MPa, and a thermal conductivity of 163.45 W/m·K.

A new method for judging and predicting the stability of ceramic suspensions by rheological tests

In preparing stable ceramic suspensions, the interactions of particles and polymer chains should be emphatically considered, which depends on DLVO stabilization theory. However, DLVO stabilization theory are qualitative and lack quantitative methods for judging and predicting stability. The present study introduced a new method for directly judging and predicting suspension stability based on rheological tests and established a correlation between measured data and the state of ceramic suspensions. Among rheological properties, the dominance of the storage modulus G' is more conducive to the realization of steric stabilization, whereas the loss modulus G" exerts a more significant influence in bridging and depletion flocculation states. The stability of suspensions with a given particle size can be judged and predicted by comparing the value of tan δ (the ratio of G" and G') under identical measurement conditions. Lower values of tan δ indicate better stability of the ceramic suspensions. The new method has been verified by experiments of classical alumina suspensions. The results indicate that the alumina suspensions with 14, 17, 20, and 23 vol% of solid particles exhibit optimal stability when combined with PVA concentrations of 3.5, 3.0, 2.5, and 2.0 wt%. Meanwhile, this combination leads to the minimum values of tan δ within the linear viscoelastic region (0.71, 0.45, 0.33, and 0.31, respectively). The universality of the method has been further demonstrated in zirconia suspensions dispersed with Dolapix CE64 dispersant. The application of this method has demonstrated its significance in judging and predicting the stability of ceramic suspensions.

Monte Carlo simulation of photopolymerizable ceramic suspension curing profile in vat photopolymerization

Vat photopolymerization holds promise for intricate ceramic structures through additive manufacturing. However, the scattering of ceramic pastes during printing can result in inaccuracies and defects. To address this, we propose utilizing a Monte Carlo method to account for scattering in absorbing media, predicting the curing profile of photopolymerizable ceramic suspensions. This method considers factors like the reflective air-slurry interface and the impact of particle size distributions on the curing profiles, which have been relatively overlooked in prior research. Employing physical equations, we developed a Matlab simulation program, facilitating the study of various process parameters on curing performance. The simulations accurately predict solidification width and depth for slurries with distinct volume fractions and powder particle sizes. The calculated correlation coefficient score was 0.9530 regarding curing depth in all six cases, significantly supporting the proposed method. Overall, this study underscores the potential of the Monte Carlo method in enhancing the precision of vat photopolymerization 3D printing for ceramics.

Rate dependence in adhesive particle–particle contacts affect ceramic suspension bulk flow behavior

Particle–fluid mixtures are known for displaying a wide variety of interesting flow mechanisms, such as thickening and thinning under shear. It is now becoming increasingly evident that even molecular scale effects are relevant for this macroscopic flow behavior of suspensions. Here we show that even 50μm ceramic beads in a non-density matched solvent are affected by the pH of the solvent. We trace the origin of the pH dependence to the contact mechanics using colloidal probe atomic force microscopy (CP-AFM). The gel-like structure of the pH 3 samples suggests that adhesion effects play a major role, but which adhesion timescale competes with shear rate to affect the rheology is not obvious. We test here two time scales in the contact mechanics: total contact time tc and contact retraction speed vr. We observe that contact time is the most important variable to correlate with rheology. The ceramic particle suspension so serves as a model system to help understand which adhesive mechanism affects flow behavior in the suspension.

Карборундовые огнеупорные бетоны на основе искусственного керамического вяжущего

This work considers a method to increase the mechanical strength and corrosion resistance to glass and slag melts of aluminosilicate refractories. For this purpose, artificial ceramic binders (ACB) of mullite-carborundum composition were synthesized using the technology of highly concentrated ceramic binder suspensions (HCCBS). The morphological characteristics and grain size of ACB were analyzed, and the structure and physico-mechanical properties of the sintered products were investigated. It was found that nanodispersed particles are formed as a result of mechanochemical processes occurring during joint grinding. The average particle size was about 30 – 40 nm. Thermally treated samples based on high-alumina chamotte consist of crystalline phases of corundum, mullite, and SiC, which are uniformly distributed in the material. It is shown that with an increase in the annealing temperature, the physico-mechanical properties improve. The introduction of mullite-carborundum binder into the composition of high-alumina chamotte refractories has led to improved physico-mechanical properties and corrosion resistance to glass and slag melts. The results showed that refractories containing 50 % high-alumina chamotte possess the most favorable physico-mechanical properties. Compared to the factory sample, experimental samples demonstrated a significant improvement in corrosion resistance to glass and slag melts by 90 % and 94 %, respectively.

Microfabrication of Li4SiO4 pebbles with complex pore structure via digital light processing: Accuracy control and properties optimizing

Li4SiO4 ceramic pebble is deemed as the most attractive tritium breeder for fusion reactor blanket. In this work, we fabricated a novel Li4SiO4 pebble with micrometer-scale pore structure by digital light processing to verify the feasibility of complex pore structure manufacturing for future breeders. The effects of processing parameters on printing accuracy, microstructure and mechanical properties of Li4SiO4 pebbles were investigated. For synthesizing the pure Li4SiO4 phase, the optimal stoichiometric ratio of Li2SiO3 to Li2CO3 was 1:1.09 in the premixed powder. The photosensitivity of dual-phase ceramic suspension was investigated according to an attenuation model, and the overgrowth was reduced to ∼50 μm by using the dimension formula. After optimizing the post-processing, the radial pore structure Li4SiO4 pebbles with excellent crush load (50.3 N, standard deviation = 4.4 N) and suitable open porosity (18.3 %) can be yielded. This work provides a fresh solution to control the pore structure of tritium breeding pebbles in an unprecedented micrometer scale.

Development and optimization of PZT suspensions with high solid loading and low viscosity for stereolithography-based additive manufacturing

Achieving synergy between high solid loading and low viscosity for ceramic suspensions a critical issue in the field of stereolithography. In this work, we successfully obtained a well-dispersed PZT suspension with high solid loading (55 vol%) and low viscosity (3047.5 mPa s at 60 rpm) by adding appropriate amounts of dispersant (1 wt% KOS110) and thickening agent (2 wt% PEG300), providing a foundation for crack-free photosensitive lead zirconate titanate (PZT) samples. This work presented a simple approach for achieving synergy between the high solid loading and low viscosity of ceramic suspensions for stereolithography-based additive manufacturing.

A model for predicting the stability of ceramic suspensions

The prediction of the stability of ceramic suspensions with multiple particles is limited depend on classical DLVO theory or Stokes equation. The mechanical effect of particles settling in suspension was studied, and a simplified mechanical equilibrium model of particles was proposed, shown as follows: u=Δρgd218η−τyd36η. The sedimentation of particles is mainly influenced by the density difference between particles and fluid Δρ, particle size d, suspension viscosity η, as well as shear yield stress τy. For a given suspension, Δρ, d and η are constants, and τy can be directly measured through rheological methods. When calculated settling velocity of particles approaches infinitely small values, the suspensions can be considered stable. The expression derived in this work had been verified by the experimental data. In addition, correlation between the results from improved settlement height method and the calculated settling velocity was established.To further investigate the impact of additives on suspensions stability, the Kelvin-Voigt rheological model was employed to characterize viscoelastic properties during oscillation, and a coefficient K (K=τy−G'γcτy) was proposed to quantitatively determine the contribution of the “dashpot” component in influencing the yield stress τy. The regulation strategy for additives in suspensions was established based on experiments: a K value exceeding 0.274 indicates excessive additives concentration and necessitates reduction, whereas a K value below 0.274 suggests an insufficient additives concentration and requires additional dosage. In summary, the above model is helpful to predict the stability of ceramic suspensions.

Large aspect ratio microscale 1–3 piezoelectric arrays prepared by soft mold combined with UV curing

1-3 piezoelectric composites, as materials with integrated structural/functional characteristics, are typically used to manufacture ultrasonic transducers. As a core sensitive element, the structural dimensions as well as the molding quality of the 1–3 piezoelectric array, will directly affect the transducer's operating performance. In this paper, an improved soft mold process is proposed to prepare lead zirconate titanate (PZT) microscale 1–3 piezoelectric arrays by a soft mold combined with UV curing process. Firstly, the rheological behavior of PZT ceramic suspension and the preparation process of polydimethylsiloxane (PDMS) soft mold were studied. The surface contact angle of the Si master mold modified by trimethylchlorosilane (TMCS) was significantly increased, facilitating the peeling of the PDMS soft mold from the Si master mold surface, thus improving the surface quality of the PDMS soft mold. Then, the sintering process, microstructure, and electrical properties of microscale 1–3 piezoelectric arrays were systematically investigated. The perpendicularity and integrity of the piezoelectric arrays were improved by an optimized sintering process, and the arrays had micropillar diameters as small as 8 μm and aspect ratios over 7.5. The electrical properties of the piezoelectric composites with thicknesses of 55 μm and 42 μm were analyzed to obtain their resonant frequencies fs of 33.8 MHz and 41.3 MHz, respectively. The developed novel soft mold process can realize the preparation of microscale 1–3 piezoelectric arrays with fine structure and large aspect ratios, which are expected to fabricate high-frequency ultrasonic transducers.

Effect of particle size on rheology, curing kinetics, and corresponding mechanical and thermal properties of aluminum nitride (AlN) ceramic by digital light processing (DLP)-based vat photopolymerization

In this work, the influence of AlN particle size (250 nm, 1.2 µm, and 5 µm) on the curing behavior, stability and viscosity of ceramic suspensions was evaluated. It was revealed that an increase in the particle size of AlN powders reduced the stability and viscosity of the suspension. For curing behavior, the ceramic suspension prepared with 250 nm AlN powder exhibited the smallest curing depth and excess width, whereas the 5-μm ceramic suspension had the largest curing depth. The analysis of the scattering length revealed that a decrease in AlN powder particle size reduced the scattering length. After sintering, both the 250-nm and 1.2-μm samples could be sintered densely at temperatures more than 1800 °C with the relative density greater than 99%. Finally, following a 5 h sintering at 1850 °C, the 250-nm and 1.2-μm samples obtained thermal conductivities of 171 and 174 W/mK, respectively.