Preparation of high solid loading and low viscosity ceramic slurries for photopolymerization-based 3D printing

In this study, high solid loading and low viscosity cordierite slurries are successfully developed for the first time for photopolymerization-based additive manufacturing. The processability of the slurries is mainly determined by their rheological properties and photocuring parameters. The slurry preparation involves the orthogonal optimization of compositions in order to achieve suitable viscosity, stability and homogeneity. The photocuring parameters of the as-prepared slurries, including penetration depth D_p and critical exposure E_c, are also determined experimentally. Results show that viscosity increases with reduction in particle size. A higher solid-volume fraction also results in an exponential growth in viscosity. As for the dispersant amount, a concentration of 5?wt% leads to the lowest viscosity. Particle size also play an important role in the solid loading capacity of the slurries, as results suggest that smaller particles improve performance. In terms of the photocuring behaviors, the addition of 2?wt% photoinitiator generates an optimal curing process. 40?vol% solid loading leads to the thickest curing depth for all slurries with different types of particle sizes. Finally, a cordierite part with a complex hollow structure and a fine resolution is successfully fabricated. The present study offers a material basis for the polymerization-based 3D printing of porous cordierite structures.     

YAG ceramic processed by slip casting via aqueous slurries

Stable YAG (Y₃Al₅O₁₂) aqueous slurry with ammonium polyacrylate (NH₄PAA) polyelectrolytes as dispersant was prepared by ball mill method. The effects of polyelectrolyte concentration and pH value on the stability of the suspension is described here, and the stability maps are constructed at different pH value and polymer concentration. The rheological behavior of YAG slips of different solid loading (60–70%) has been studied by measuring their viscosity and shear stress as a function of shear rate and pH of the slurry. An optimal amount of dispersant and pH value for the suspension was found. YAG suspension displays a maximum in zeta potential values and a minimum viscosity in pH range of 9–11. Slips behaved as near Newtonian at the pH value up to a solid loading of 60 wt% and as non-Newtonian with thixotropic behaviors above this solid loading value. The density and the green as well as sintered microstructure of the cast products bear a direct relationship to the state of this slips induced by the alternation in the pH and the concentration of the dispersant as well as solid loading.     

Dispersion and stability of SiC ceramic slurry for stereolithography

Stereolithography based additive manufacturing provides an effective method to fabricate complex-shaped SiC ceramic components. The dispersion and stability of the ceramic slurry are very important for stereolithography. In this study, the dispersion and stability of SiC ceramic slurries were investigated systematically. The effects of resin monomers, dispersants, particle size, solid loading and ball milling time on the dispersion, rheological behavior and stability of SiC ceramic slurries were studied in detail. Finally, an optimal SiC ceramic slurry for stereolithography based additive manufacturing was obtained, and complex-shaped SiC ceramic architectures were fabricated.     

Stereolithography-based additive manufacturing of gray-colored SiC ceramic green body

The stereolithography-based additive manufacturing of white-colored Al₂O₃ and ZrO₂ ceramics has been widely reported, whereas the stereolithography-based additive manufacturing of gray-colored SiC ceramic is very difficult and challenged. In this paper, the reasons for the difficulty which SiC ceramic facing during stereolithography were discussed and compared to Al₂O₃ and ZrO₂ ceramics. The effects of particle size, solid loading, stereolithography parameters, and photoinitiator kind and concentration on the curing ability of SiC slurries were further studied in detail. Finally, complex-shaped SiC ceramic green parts with high accuracy and high quality were successfully fabricated. This study demonstrated that the stereolithography-based additive manufacturing had a great possibility for preparing gray-colored SiC ceramics.     

Influence of solid loading on the rheological,porosity distribution,optical and the microstructural properties of YAG transparent ceramic

Stable aqueous dispersed mixture of commercial Al₂O₃ and Y₂O₃ nano powders was prepared by ball mill. Ammonium poly meta acrylate (Dolapix CE64) and tetraethyl orthosilicate (TEOS) were added as dispersant and sintering aid, respectively. The effects of slurry solid loading on the fabrication of transparent polycrystalline YAG ceramics by slip casting method were investigated. The rheological properties of slurries with different solid loading (64, 70 and 76?wt%) were studied by measuring the viscosity and shear stress as a function of shear rate. The effect of solid loadings on the porosity distribution was examined. The specimens were vacuum-sintered at 1715?°C for 10?h. Slips with 64 and 70?wt% solid loading behaved as near-Newtonian and as non-Newtonian with thixotropic behavior at 76?wt% solid loading. The relative densities of the green bodies increased from 58.0?±?0.6% (SD?=?0.424) to 64.0?±?0.3% (SD?=?0.228) by increasing the solid loading from 64?wt% to 70?wt% and then decreased to 63.0?±?0.2% (SD?=?0.141) at 76?wt% solid loading. The results showed that the suitable solid loading for fabricating transparent YAG ceramics is 70?wt%. This sample had the narrowest pore size distribution (4–100?nm), homogenized surface fracture of green body, dense microstructure (99.990?±?0.005% final relative density, SD?=?0.003) and the average grain size of 6?µm. It had the highest in-line transmittance, which was approximately 77% at 1064?nm.     

The controllable microstructure of porous Al2O3 ceramics prepared via a novel freeze casting route

In traditional aqueous slurry freezing casting processing, the growth method of ice crystals is hard to control, resulting in the uncontrollable pore's morphologies of the porous ceramics. In the experimental, the pure Al₂O₃ sol was used to substitute water as a medium for preparing ceramic slurry. With Al₂O₃ sol addition, it becomes easy to control the microstructure and pore's morphologies of the porous Al₂O₃ ceramics via adjusting of the solid loading, composition of the ceramic slurries, as well as the cooling methods. The SEM micrographs showed that the sol-contained ceramic slurry combined with freeze casting processing can easily prepare the porous Al₂O₃ ceramics with different pore sizes and different morphologies. The porous Al₂O₃ ceramics prepared from 70 wt.% to 90 wt.% solid loading sol-contained Al₂O₃ slurries and sintered at 1500 °C for 2 h have open porosities from 81.7% to 64.6%.     

Effects of sintering additives on dispersion properties of Al2O3 slurry containing polyacrylic acid dispersant

The effects of sintering aid adsorption on the dispersion properties of aluminum oxide slurries were investigated. We considered Al₂O₃ slurry without additives and Al₂O₃ slurry with a Mg additive with 0.1 mass% in oxide equivalent as a sintering aid. In this study, we evaluated the adsorption isotherm of polyacrylic acid (PAA) onto Al₂O₃ and the dispersion degree of Al₂O₃ slurries in sedimentation tests under gravity. The adsorption isotherm featured a characteristic adsorption isothermal line with a maximum value when Mg additive was present in Al₂O₃. In addition, the packing fractions did not correspond to the apparent viscosity. However, in slurry that was allowed to settle for several days, both of them agreed.Therefore, the disagreement between the packing fraction and the apparent viscosity immediately after preparation arose from changes of the dispersion state, such as the decrease of the distance between particles with time.     

Preparation of dense 0.9Al2O3−0.1TiO2 ceramics with highly improved microwave dielectric properties by a noncontaminated DCC method

In this paper, dense 0.9Al₂O₃ ??0.1TiO₂ ceramics with highly improved microwave dielectric properties were prepared by a noncontaminated direct coagulation casting (DCC) method. The suspension was destabilized and coagulated by consumption of the dispersant without introducing impurity ions. The effect of dispersant content, pH value and solid loading on the rheological properties of 0.9Al₂O₃ ??0.1TiO₂ suspension was investigated. It was found that 0.9Al₂O₃ ??0.1TiO₂ suspension with a high solid loading of 50?vol% and low viscosity of 0.7?Pa?s could be prepared by adding 0.5?wt% TMAOH at the pH in the range of 10–12. The suspension was coagulated by adding 2?vol% GDA when it was treated at 60 ~ 80?°C for 40 ~ 60?min. Compared with dry pressing method, more homogeneous and denser microstructure could be obtained in 0.9A1₂O₃ ??0.1TiO₂ ceramics prepared by DCC via dispersant reaction which were sintered at 1550?°C for 3?h and annealed at 1100?°C for 5?h. The Al₂TiO₅ second phase in 0.9A1₂O₃ ??0.1TiO₂ ceramics prepared by DCC via dispersant reaction could be eliminated more easily by annealing treatment. After annealing treatment, only Al₂O₃ and TiO₂ phases could be detected. Therefore, higher density and much better microwave dielectric properties with ρ?=? 3.81?±?0.02?g/cm³, ε_r =?12.17?±?0.02, Q ×?f =?25,637?±?749?GHz, τ_f =?13.12?±?1.62?ppm/°C were obtained by DCC via dispersant reaction, and the Q ×?f value almost improved by 25%. Without introducing impurity ions, it provides a new insight into preparing complex shaped function ceramics with high properties.     

Effect of ball-milling parameters on the rheological properties of mold powder slurry

In this study, mold powder slurries with high solid loading and low viscosity were prepared during the ball-milling process for improving the homogeneity and mechanical properties of granules after spray-drying. The effect of ball-milling parameters, such as solid loading, binder/dispersant content, and ball-milling time, on the flowability, dispersibility, stability, and rheological behavior of mold powder slurries was systematically investigated by rheology observation and sedimentation tests. As these parameters varied, the slurry exhibited the shear-thinning behavior of a non-Newtonian fluid with a shear rate range of 0–50 s^?1, which was adequately described by the Herschel-Bulkley model. The optimal parameters that optimized the flowability, dispersibility, and stability of the slurry, along with its rheological behavior, were chosen as follows: solid loading, 60 wt%; modified sodium carboxymethyl cellulose binder content, 1.0 wt%; sodium tripolyphosphate dispersant content, 0.5 wt%; ball-milling time, 60 min.     

Improving cure performance of Si3N4 suspension with a high refractive index resin for stereolithography-based additive manufacturing

Silicon nitride (Si₃N₄) slurries with high solid loading, low viscosity and good stability is difficulty prepared, due to low intrinsic surface charge and a large refractive index (RI) difference between Si₃N₄ powder and resin. In this paper, the curing behavior of Si₃N₄ slurry with different functional group and RI of resin monomer were systematically researched, and then the kind and optimum content of dispersant were investigated. Subsequently, a high solid loading Si₃N₄ slurry (44 vol%) with good curing behavior, low viscosity and favorable stability was successfully prepared. Lastly, the dense Si₃N₄ ceramic parts were fabricated by the suitable Si₃N₄ slurry (44 vol%) via stereolithography. After debinding and sintering process, the relative density and flexural strength of Si₃N₄ ceramic were 98.28% and 800 ± 27.28 Mpa, respectively.     

Rheological behavior and curing deformation of paste containing 85 wt% Al2O3 ceramic during SLA-3D printing

The preparation of high solids loading Al₂O₃ paste is of great significance for improving the properties of ceramics formed by UV-curing. However, the solid contents of alumina slurry used by digital light processing (DLP) and traditional alumina paste for stereolithography (SLA) are both less than 80 wt%. With increase in solid content, the viscosity of paste increases sharply, and rheological property deteriorates. In this study, ceramic paste containing 85 wt% (62 vol%) Al₂O₃ was prepared for SLA-3D printing of ceramics, and more than 85 wt% solid content was achieved by dispersant and other additives. Effects of different dispersants on rheological and curing properties of Al₂O₃ ceramic paste were studied. At room temperature, the viscosity of 85 wt% Al₂O₃ ceramic paste was 51733 mPa s at shear rate of 30 s^?1. A novel method was proposed to control curing deformation of parts during printing. As-manufactured ceramic did not show any cracks by naked eye and exhibited excellent mechanical properties, with three-point bending strength of 540 MPa, fracture toughness of 4.19 MPa m^1/2, Vickers hardness of 16 GPa, surface roughness of 0.463 μm, and density of 3.86 g/cm³.     

Tape casting of aqueous Al2O3 slurries

The well-dispersed aqueous Al₂O₃ slurries suitable for tape casting were prepared, the effects of the concentration of dispersant, of the pH value, of solid content etc. on the properties of slurries were investigated, and the results indicated that the rheological of slurries was effected greatly by pH value and organic additives. After cutting, laminating and binder removal, the laminated Al₂O₃ green bodies were sintered by hot-press in a vacuum furnace. SEM micrographs showed that the microstructure of the aqueous green-body and samples were different from that of non-aqueous, and the mechanical properties of aqueous Al₂O₃ samples were much high than that of non-aqueous Al₂O₃.     

Fabrication of stable Al2O3 slurries and dense green bodies using soft-energy milling process

Wet-jet milling and planetary homogenizing processes as soft-energy milling methods were employed as a novel method to prepare stable Al₂O₃ slurries. The viscosity of slurries prepared from the soft-energy milling was constant and stable for long time, as compared to ball-milled slurries. Though Al₂O₃ particles surface after ball milling yielded more hydroxyl groups, Al₂O₃ particles surface after the soft-energy milling was similar state to raw particles surface. Relative density of the green bodies prepared from the wet-milled slurries was about 67% and was independent on the slurry solid content. On the other hand, the relative density of the green bodies prepared from the ball-milled slurries increased with increasing solid content. Linear shrinkage of the sintered bodies prepared from the soft-energy milled slurries was independent of the slurry solid content, whereas that of the sintered bodies prepared from the ball-milled slurries increased with decreasing solid content.     

Dispersion and properties of zirconia suspensions for stereolithography

Stereolithography is an attractive technique for the fabrication of complex-shaped ceramic components with high dimensional accuracy. One of the challenges in this technology is the development of high solid loading, low viscosity photosensitive ceramic suspension. In this study, the dispersion of zirconia in photocurable resin and the slurry properties were intensively investigated. Rheological measurements showed that DISPERBYK-103 proved to be an effective dispersant. 42 vol% ZrO₂ suspension was successfully prepared using 3.5 wt% DISPERBYK-103 as the dispersant, with a suitable viscosity (4.88 Pa·s) below the maximum allowable viscosity value (5 Pa·s) for stereolithography applications. The adsorption behavior of DISPERBYK-103 on the surface of zirconia powders was characterized by TG and FT-IR, confirming the dispersion effect of dispersant. Contact angle measurements were also conducted to show that the adsorption of DISPERBYK-103 could help to improve the wettability between powder and photocurable resin. Results showed that DISPERBYK-103 was effective for the preparation of suitable slurries for the development of ZrO₂ ceramics through stereolithography.     

水基纳米SiC复合料浆的流变性能和稳定性

引言 纳米复相碳化硅陶瓷是在多相复合碳化硅陶瓷基础上发展起来的-种新型碳化硅陶瓷材料,通过引人第二或第三纳米增强相来同时实现细晶结构、梯度残余应力场、裂纹桥联、自增韧等增强增韧机理,从而获得多强韧化机理协同强化碳化硅陶瓷,已成为碳化硅陶瓷的研究方向之一[1-4].其中,纳米增强相在碳化硅基体(包括料浆、复合粉体、陶瓷)中的分布是制备纳米复相碳化硅陶瓷的关键和前提之一[5].     

Wet jet milling of Al2O3 slurries

A wet jet milling process was employed as a novel method to prepare ceramic slurries. The wet jet milling pulverized raw materials to primary particle size within a short time. The wet jet-milled slurries showed very low viscosity, as comparing to ball-milled slurries. Moreover, the viscosity of wet jet-milled slurries was stable for long times, whereas that of ball-milled slurries increased rapidly with increase in the time. Al₂O₃ particles after wet jet milling kept initial surface conditions, though Al₂O₃ particles after ball milling yielded more OH groups on the surface. The relative density of the green bodies prepared from the wet jet-milled slurries was about 65% or more without depending on the solid content of slurry. On the other hand, the relative density of the green bodies fabricated by the ball-milled slurries increased with the slurry solid content, and it reached more than 60% at 50 vol% of solid content.     

光固化ZrO2陶瓷料浆的流变性能研究

围绕陶瓷粉体在光敏树脂中的分散,研究了粉体性质、分散剂种类及其掺加量、固含量对光固化ZrO₂陶瓷料浆流变性能的影响。结果表明:粉体性质对料浆的流变性能有着显著影响,比表面积小、球形度高的ZrO₂陶瓷粉体更有利于配制低粘度、高固含量的料浆;料浆的流变性能以及稳定性主要受分散剂种类及其掺加量的控制,以相对粉体质量4%的X-100分散剂制备的陶瓷料浆的流变性及稳定性更佳;固含量与粘度之间的关系满足Krieger-Dougherty模型。本文对分散剂的作用机理进行了分析探讨,为光固化ZrO₂陶瓷料浆高精度固化成型提供了试验基础。     

影响氧化铝水基料浆流变学特性的关键因素

用流变学的方法在RV-20型流变仪上研究不同条件,如:固含量、分散剂加入量、烧结助剂、增塑剂等对碱性氧化铝悬浮体的流变性的影响.结果表明:氧化铝陶瓷碱性料浆(pH＞7)在低的剪切速率(＜100 s-1)时,表现为剪切变稀.在水基料浆中添加MgO时,会发生强烈的水合反应,导致料浆失去流动性.增塑剂甘油的加入导致料浆粘度升高的幅度是有限的,不会对料浆固含量和浇铸工艺造成显著不利的影响.加入水溶性丙烯酸乳液后,在低的剪切速率下,料浆仍然呈现剪切变稀行为,随着乳液含量的增加,料浆的静态粘度逐渐增大.分散剂聚丙烯酸氨的加入量对料浆的稳定性具有显著的影响.在分散剂的加入量为固相质量的0.8%左右时,分散剂在陶瓷颗粒表面形成饱和吸附,此时料浆的稳定性达到了最佳状态.     

Fabrication of transparent yttria ceramics by alcoholic slip-casting

Y₂O₃ transparent ceramics were prepared from alcoholic slurries of Y₂O₃ nanopowders via a slip-casting method to avoid the hydrolysis issue. Polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG) and polyethylenimine (PEI) were used as dispersants to improve the rheological properties of the slurries. It was found that PEI is the most effective dispersant in ethanol. The adsorbed amount of PEI was evaluated by infrared absorption and rheology measurements. Y₂O₃ slurry with a solid loading of 20.8 vol% and a viscosity of <0.1 Pa s at the shear rate of 10 s⁻¹ was obtained using 1.5 wt% PEI. The slurry yielded a homogeneous green body, and finally resulted in a high-quality Y₂O₃ ceramic with the in-line transmittance of 80% at 800 nm.     

Preparation and characterization of Ce-ZrO2/Al2O3 composites by DLP-based stereolithography

This work investigates the printability of Ce-ZrO₂/Al₂O₃ composites through a Digital Light Processing (DLP) technology. Commercially available 10 mol% CeO₂ and 12 mol% CeO₂-stabilized zirconia were mixed with alumina powders, to provide 11 mol% CeO₂-stabilized ZrO₂/16 vol% Al₂O₃ (Ce-ZA₁₆) composite materials. The powders were dispersed under wet conditions, and the homogeneous nanometric dispersion was maintained once added into the liquid monomer. Slurries at several solid loadings were explored, with and without dispersant addition. First, the key role of the dispersant to significantly enhance the solid loading and thus the sintered density was demonstrated. Second, among different dispersant-added slurries at various solid loadings, ranging from 65 to 80 wt%, the best compromise between rheological behavior and curing depth was established. The best formulations, comprised between 70 and 80 wt%, successfully provided fully dense and completely homogeneous composites.