Ceramic Suspensions Research Articles

Effect of monomers with different functionalities on stability, rheology, and curing behavior of ceramic suspensions

Vat photopolymerization (VP) technology is a popular manufacturing technology for ceramic parts with complex shapes and high dimensional accuracy. However, there is still a lack of systematic research on how to design suitable monomer formulations for ceramic powder with different characteristics. In this study, the effect of monomers with different functionalities on the stability, rheology, and curing behavior of different ceramic suspensions was investigated intensively. The results showed that the high-functionality monomer facilitates improved stability and cure depth. Whereas, it has a negative impact on viscosity and excess width. For ceramic powders with a low refractive index and light absorbance, a relatively high cure depth can be obtained by using a monomer with low functionality. Moreover, the cure depth and viscosity of aluminum nitride (AlN) suspensions with different monomer combinations were also studied. Finally, the alumina (Al2O3), zirconia (ZrO2), AlN, and silicon nitride (Si3N4) parts were successfully fabricated.

AC electric field-assisted fabrication of ice-templated alumina materials and remarkable enhancement of compressive strength

A novel methodology was developed that uniquely employs alternating current (AC) electric field to fabricate ice-templated ceramics. In the methodology, AC field was applied to an aqueous ceramic suspension, and then ice-templating was performed. Field application to an aqueous ceramic suspension resulted in a net motion of ceramic particles due to DC voltage generation. Suspension concentration increased near one of the electrodes, which was controllable through AC frequency and field duration. Density of the very bottommost regions in sintered materials increased with field duration, attributed to increased local suspension concentration. In sintered materials, the thickness of non-templated region increased with field duration, whereas templated microstructure turned increasingly dendritic with field duration, suggesting a strong influence of AC field on the growth characteristics of ice crystals. AC-field assisted materials exhibited remarkably enhanced compressive strength without any change in porosity. This work contributes to advancing the ice-templating technology using externally energized fields.

Piezoelectric Drop‐On‐Demand Inkjet Printing of High‐Viscosity Inks

Drop‐on‐demand inkjet printing of highly viscous fluids represents a highly attractive emerging technology for advanced material deposition. The jetting of viscous inks, such as concentrated polymer solutions and nanoparticle suspensions, is a key enabling technology for many industrial applications, ranging from microelectronics to biomedicine and ceramics manufacturing. Currently available standard inkjet printers typically operate in a relatively narrow viscosity range (up to 16 mPa s), and alternative drop‐on‐demand printing techniques (such as laser‐induced forward transfer) present limited industrial applicability. In this context, the development of a piezoelectric‐driven printhead capable of jetting high‐viscosity fluids is of great interest. Herein, a prototype of such a device is presented and its performance is evaluated using model fluids at increasing viscosities. Specifically, the dependence of emitted droplets’ properties on jetting parameters is evaluated and linked to the physical characteristics of the system. In optimal conditions, piezoelectric jetting of solutions characterized by viscosities in excess of 200 cP is achieved. Finally, as an applicative example, the jetting of functional inks is attempted. A ZnO suspension and a poly(3,4‐ethylenedioxythiophene) (PEDOT) based solution are successfully jetted to demonstrate the applicability of the developed printhead to the deposition of ceramic suspensions and concentrated polymer solutions.

Fabrication of porous PZT ceramics using micro-stereolithography technology

Based on micro-stereolithography (μSL) additive manufacturing (AM) followed by the use of the burnable plastic sphere (BURPS) technique, we present the fabrication of porous lead zirconate titanate (PZT) ceramics. A printing slurry was prepared by mixing photocurable ceramic suspensions with various contents of polymethylmethacrylate (PMMA) as a pore-forming agent (PFA). We found that the cure depth increased gradually with increasing PMMA content. The sintered PZT ceramics exhibited a porous microstructure of predominantly spherical pores formed by PMMA, with sizes ranging from ~15 to 35 μm. The porosity of the PZT ceramics increased from 11.3% to 21.9%, corresponding to a decrease in the density from 6.92 to 6.09 g/cm3 due to the increasing PMMA content. As the porosity increased, the acoustic impedance decreased from 24.4 to 12.6 MRayls (106 kg/m2 s). The porous PZT ceramic with 5 wt% PMMA exhibited superior dielectric and piezoelectric properties (d33 = 525 pC/N, εr = 2417, tanδ = 0.04) that were comparable to those of ceramics fabricated by conventional methods. These results suggest that μSL technology is a viable alternative for fabricating porous PZT ceramic components, especially pieces with complex geometric structures.

Fabrication of Cordierite Ceramic Foam Filter by Replication Method

Ceramic foam filter (CFF) is widely used to improve the quality of molten metal prior to casting. Cordierite is one of the most commonly used materials for making CFF. In this research, the fabrication of cordierite-based CFF by a replication method using a polyurethane template has been studied. Waterglass and polymethacrylic acid (PMAA) were used as defloculants to synthesize ceramic suspensions. CFF was made from kaolin, talc, alumina with a defloculant concentration of 0.3% which is sintered at a temperature of 1300 - 1350 oC. The experimental results showed that the porosity obtained for all CFF samples were above 70%. The best shape of CFF was obtained by using PMAA as defloculant. However, CFF did not reach the maximum strength yet so it is necessary to carry out further research on the CFF body composition.

Effect of Kaolin Particle Size Towards Preparation of Kaolin Ceramic Membrane

The purpose of this work is to study the effect of kaolin particle size for the preparation of low cost ceramic membrane suspension and ceramic membrane structure. Kaolin particle size is categorized into two categories; i) ≤ 1µm and ii) ≥ 1 µm. The suspension is prepared via stirring technique under 1000 rpm at 60°C. The particle size of kaolin is characterized using field emission scanning electron microscope (FESEM) and the prepared suspension is characterized in term of its viscosity. Results indicate that the particle size gave significant effect to the viscosity of ceramic membrane suspension. Preliminary data showed that kaolin with particle size ≤ 1µm resulted ceramic membrane with dense structure.

Effect of binder system on the thermophysical properties of 3D-printed zirconia ceramics.

Fabrication of 3D‐printed ceramic parts with high complexity and high spatial resolution often demands low wall thickness as well as high stiffness at the green state, whereas printing simpler geometries may tolerate thicker, more compliant walls with the advantage of a rapid binder‐burn‐out and sintering process. In this work, the influence of the binder system on the thermophysical properties of 3D‐printed stabilized zirconia ceramics was investigated. Samples were fabricated with the lithography‐based ceramic manufacturing (LCM) technology using two different photosensitive ceramic suspensions (LithaCon 3Y230 and LithaCon 3Y210), with the same ZrO2 powder. A significant difference in stiffness in the green state (~3 MPa vs. ~32 MPa for LithaCon 3Y230 and LithaCon 3Y210, respectively) was measured, associated with a rather loose or a linked network formed in the binder due to photopolymerization. Both materials reached high relative densities, that is, >99%, exhibiting a homogeneous fine‐grained microstructure. No significant differences on the coefficient of thermal expansion (11.18 ppm/K vs. 11.17 ppm/K) or Young's modulus (207 GPa vs. 205 GPa) were measured, thus demonstrating the potential of tailoring binder systems to achieve the required accuracy in 3D‐printed parts, without detrimental effects on material's microstructure and thermophysical properties at the sintered state.

Theoretical modeling based on stress wave propagation and experimental verification of residual stress in stereolithography printed ZrO2 ceramic suspensions

Zirconia ceramics are widely used in medical and dental industry due to their excellent biocompatibility and aesthetics. In this respect, stereolithography apparatus (SLA) is popular method for 3D printing of ceramic suspensions. However, deformation and cracking of SLA-printed ceramics caused by residual stress seriously limit their application in clinical dentistry. In this investigation, 75 wt. % ZrO2 suspensions were successfully prepared, and ZrO2 ceramic composites were produced via SLA 3D printing. Special attention was paid to the establishment of theoretical model of residual stress in SLA. According to results, the development of residual stress in SLA-printed ceramics depended on various parameters such as laser power, scanning speed, and radius of curvature, as well as linear shrinkage, stress wave, and pure bending stress. The variations of surface residual stress at different laser beam powers, scan speeds, and radii of curvature were found to be consistent with that predicted theoretically. The errors between the theoretical and experimental value were 2.8%, 1.4%, 4.3%, 5.3%, and 4.2%, respectively, when the laser beam powers increased in turn. The errors between the theoretical and the experimental value were 2.5%, 3.9%, 2.8%,2.4%, and 3.8%, respectively, when the scan speeds increased in turn. Thus, theoretical model established was proved high accuracy and conformity to 3D printing standards.

Development of a System for Additive Manufacturing of Ceramic Matrix Composite Structures Using Laser Technology.

Ceramic matrix composites (CMCs) are refractory ceramic materials with damage-tolerant behavior. Coming from the space industry, this class of materials is increasingly being used in other applications, such as automotive construction for high-performance brake discs, furnace technology, heat coatings for pipe systems and landing flaps on reusable rocket sections. In order to produce CMC faster and more cost-efficiently for the increasing demand, a new additive manufacturing process is being tested, which in the future should also be able to realize material joints and higher component wall thicknesses than conventional processes. The main features of the process are as follows. A ceramic fiber bundle is de-sized and infiltrated with ceramic suspension. The bundle infiltrated with matrix material is dried and then applied to a body form. During application, the matrix material is melted by laser radiation without damaging the fiber material. For the initial validation of the material system, samples are pressed and analyzed for their absorption properties using integrating sphere measurement. With the results, a suitable processing laser is selected, and initial melting tests of the matrix system are carried out. After the first validation of the process, a test system is set up, and the first test specimens are produced to determine the material parameters.

Roles of solid loading in stereolithography additive manufacturing of ZrO2 ceramic

The stereolithography additive manufacturing is reported to fabricate ZrO2 ceramic components with complex-shapes for various military and engineering applications recently. Investigations show that the solid loading of the ceramic suspension exhibits significant influence on the properties of stereolithography additive manufactured ZrO2 ceramic. However, the intrinsic relationships between the solid loading of the ZrO2 suspension and the relative density, microstructure, mechanical and other properties of the ZrO2 ceramic have not been investigated systematically. In this study, the roles of solid loading in stereolithography additive manufacturing of ZrO2 ceramic were discussed in detail. Firstly, the rheological property, curing behavior of the ZrO2 suspensions with different solid loading were studied, and the stereolithography additive manufacturing was subsequently conducted. After that, the effects of the solid loading on the phase composition, relative density, mechanical property, microstructure, coefficient of thermal expansion (CTE), and shrinkage of the as-prepared ZrO2 ceramic were studied in-depth. The relationship between the solid loading of the ZrO2 suspension and the properties of the ZrO2 ceramic were successfully revealed. At last, ZrO2 ceramic components with good shape stability, high precision, and high performance were obtained. It is believed that this paper can give a deep understanding of the stereolithography additive manufacturing of ceramics.

Optimization of part orientation and adapted supports for manufacturing of ceramic parts by stereolithography using finite element simulations

The manufacturing of ceramic green parts using the stereolithography process requires several steps, which can each influence the mechanical properties of the printed parts: dimensional precision, surface roughness and mechanical strength. The part orientation with respect to the working plan and adapted supports are key points to avoid the failure of the green part during its construction. Indeed, mechanical forces generated during the spreading of thin layers of ceramic suspension generate significant loads on the green part being printed and may displace it or lead to its rupture. It is then crucial to choose a part orientation that minimize these effects and to create adapted supports that can hold the scraping loads. In this respect, a finite element simulation of scraping is performed to analyze the best green part orientation and adapted supports during the stereolithography process. A specific and original experiment is developed to identify the scrapings loads, essential as input data for the simulation. Modellings confirms that the orientation of the support greatly influences the deformations of the green part and highlights the importance of the support stiffness that absorb the scraping forces.

Experimental characterization of polydisperse particle‐loaded flow for linear resin transfer molding injections

AbstractThis study investigates the experimental filtration of micron‐scale particles of a wide granulometry through fibrous media. The method used examines a key parameter in the resin transfer molding process which is the spatial evolution of particulate filler concentration. Tests were carried out with three grades of ceramic microparticle suspensions dispersed in glycerol/water blends, injected into a quasi‐unidirectional fibrous medium. The influence of process parameters was extensively studied through a series of experiments by varying initial concentrations of suspension, injection pressures, pure liquid viscosities, fiber volume fractions, and particle size distributions. A non‐destructive, simple, economical, and rapid characterization method was used, which consisted of taking samples of suspensions at different points through the preform length and obtaining concentrations through density measurements. The evolution of granulometry from the inlet to the outlet was studied and the size range of retained particles was deduced. Tests revealed that the particle concentration decreased with increased sampling distance. Fiber content and particle size distribution were the most influential factors on filtration behavior. The analysis showed that the smaller‐sized particles are largely deposited at the fiber's surface, while the average‐ to large‐sized ones were either blocked at the inlet, transported to the outlet, or settled under gravitational forces.

Volume shrinkage and conversion rate of Al2O3 ceramic stereolithography suspension polymerised by ultraviolet light

The volume shrinkage and conversion rate are important factors determining the defect generation and accuracy control of green parts in ceramic stereolithography. In this study, a specific laser reflection method with coverslips and real-time Fourier-transform infrared (RT-FTIR) spectroscopy were used to determine the effects of the double-bond concentration, monomer ratio, photoinitiator, and incident light intensity on the real-time volume shrinkage and conversion rate. A slurry with a lower double-bond concentration obtained by using a solvent exhibited a smaller shrinkage. The shrinkage law for pure resin wasn't applicable owing to the ceramic particles. The mixing of ethoxylated pentaerythritol tetraacrylate (PPTTA) and 1,6-hexanediol diacrylate in suitable ratios promoted the conversion. In addition, the PPTTA could regulate the overall shrinkage. The photoinitiator had a small effect on the shrinkage. A high light intensity increased shrinkage significantly, while the conversion rate determined the shrinkage at a low light intensity.

Investigation of the influence of softening modifiers on the knockout of investment castings

The paper considers the problem of laboriousness of cleaning and knocking out investment casting castings from ceramic molds material. The influence of softening modifiers on the structure and residual strength of ceramic samples was analyzed. A magnesium sulfide and copper chloride were selected for the study because of their temperature of destruction, which is in the range of the calcination temperature of the ceramic shells and the temperature of pouring the mold with liquid metal. For comparative studies of particle size distribution after exposure to shock loading the samples were formed from ceramic suspension with introduction of 1.5 and 3 wt.% of softening modifiers. Fractures of ceramics were examined using a two-beam electron scanning microscope “Versa 3D”. It was shown that the use of copper chloride as a softening modifier in the composition of ceramics is facilitate the process of knockout the mold of investment casting.

Environmental footprint as a criterion in the ZTA composites forming process via centrifugal slip casting

The main goal of this study was to optimize the technological process of forming and sintering Zirconia Toughened Alumina (ZTA) composites in terms of reducing energy demand. Based on the results of Life Cycle Assessment carried out according to ISO 14044 and EN 15805 standards, the elimination of preliminary homogenization of ceramic suspension in the planetary mill, allowed to reduce energy consumption by over 25%. The method of forming ZTA materials by CSC method, allowed to obtain finished tube-shaped products, which did not require any mechanical treatment after sintering. Such an approach may be an alternative solution for production of ZTA pipes that can be used in transport of aggressive substances, even in extreme corrosive or temperatures conditions.

Ceramic Composition Binder Suspensions in the Al2O3–SiO2–SiC System and Ceramic Concretes Based Upon Them

Ceramic Composition Binder Suspensions in the Al2O3–SiO2–SiC System and Ceramic Concretes Based Upon Them

Stability, rheological behaviors, and curing properties of 3Y–ZrO2 and 3Y–ZrO2/GO ceramic suspensions in stereolithography applied for dental implants

The combination of yttria-zirconia (3Y–ZrO2) and stereolithography (SLA) is essential for forming alternative bioceramics for complex, custom-designed dental implants. In addition, suitable bioceramic suspensions are preconditions for such fabrication using SLA technology. In this study, 3Y–ZrO2 and 3Y–ZrO2/graphene oxide (GO) powders dispersed in ultraviolet curable acrylic-based resins are developed. A sedimentation experiment is performed to evaluate various ratios of monomers and dispersants to ensure good stability and dispersion of the suspensions. The hydrophobic structures of KH560 are introduced on the surfaces of ceramic powders, representing better wettability performances with 40 vol% NPG2PODA and 60 vol% Di-TMPTA. Moreover, the effects of premixed solvents and solid contents on the rheological behaviors of suspensions are investigated to confirm shear thinning and pseudo plasticity, with the experimental results fitting the Krieger–Dougherty curves. Further, the cure depth and width of the ceramic suspensions are studied, the results of which show that the penetration depth and critical exposure of the 3Y–ZrO2 (3Y–ZrO2/GO) pastes are 17.2 ± 0.50 μm and 4.80 ± 0.62 mJ/cm2 (11.8 ± 1.20 μm and 22.80 ± 9.34 mJ/cm2), respectively. The addition of GO results in a sharp increase in critical exposure, which intensifies the light scattering and hinders the curing of the ceramic paste. The research is expected to serve as a technical guide for the fabrication of ceramic suspensions for dental implants using SLA technology.

A review on the rheological behavior and formulations of ceramic suspensions for vat photopolymerization

Vat photopolymerization is an additive manufacturing process that produces high-performance ceramic parts. A critical step in the process is the preparation of a suspension that meets the requirements of high ceramic loading and proper rheological behavior, since an increase in solid loading might compromise the suspension rheology, resulting in non-uniform layer recoating. This review examines the rheological behavior of ceramic suspensions for vat photopolymerization, discussing the influence of the suspension formulation (solid loading, ceramic particle size and size distribution, monomers, diluents, and dispersants) on rheological aspects such as viscosity, shear-thinning/thickening behavior, critical shear rate, yield stress, and thixotropy. It provides a summary of the best formulations, which achieved low viscosity (<3 Pa.s) and high solid loading (>40 vol%), and reports the main trends and challenges of ceramic vat photopolymerization, suggesting general guidelines for the preparation of highly loaded photocurable ceramic suspensions with low viscosity.

Cement-Free Refractory Concretes. Part 6. Comparative Evaluation of Natural (Clay) and Artificial Ceramic Binders (HCBS)

Comparative assessment of artificial (based on highly concentrated ceramic binders suspensions - HCBS) and natural (based on clay and kaolin) ceramic binders of similar composition is conducted. Analysis of their properties and characteristics shows both their significant similarity and significant difference. As with HCBS, the binding (strength) properties of clay and kaolin are determined by the colloidal particle content and nanoparticles within them. In contrast to HCBS, clay and kaolin have a significant content of chemically bonded water, a high water requirement for molding systems, and clearly different (by an order of magnitude and greater) shrinkage during drying. If binders based on clays are considered from the point of HCBS classification, then according to their chemical composition they may be classified as acid-amphoteric (similar to materials based on chamotte). However, in terms of chemically bonded water and volume concentration of a suspension, they are closer to HCBS of amphoteric and basic compositions. Addition of refractory clay and kaolin is very effective in ceramic concrete production.

Dual-scale porous biphasic calcium phosphate gyroid scaffolds using ceramic suspensions containing polymer microsphere porogen for digital light processing

This study demonstrates a novel type of biphasic calcium phosphate (BCP) gyroid scaffolds featuring of gyroid macroporous structure and micropous BCP walls using poly(methyl methacrylate) (PMMA) microspheres as the porogen for ceramic digital light processing (DLP) technique. To tailor the microporosity of the BCP walls and the overall porosity of the dual-scale porous BCP scaffolds, the PMMA content with regard to the BCP powder was controlled in the range of 40 vol% to 70 vol%. After debinding at 600 °C and sintering at 1200 °C for 3 h, micropores were uniformly created throughout each BCP framework, while preserving 3−dimensional gyroid macroporous structures. As the PMMA content increased from 40 vol% to 70 vol%, the microporosity remarkably increased from 31.9 (±2.5) vol% to 55.2 (±1.4) vol%. This approach allowed the achievement of very high overall porosities (82.2–89.7 vol%) for the dual-scale porous scaffolds. However, all the scaffolds showed reasonable compressive strengths (0.8 MPa −2.1 MPa), which are comparable to those of cancellous bones.