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.     

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.     

Stabilization of tricalcium phosphate slurries against sedimentation for stereolithographic additive manufacturing and influence on the final mechanical properties

Ceramic parts manufactured by lithography‐based ceramic manufacturing (LCM) excel in resolution and surface quality. The material for LCM is a photosensitive ceramic particle‐filled slurry which needs to have homogeneous properties over time and during each processing step. The goal of this study was to use “mechanical” stabilization for a tricalcium phosphate‐filled slurry done by increasing slurry viscosity, solids loading, or inducing thixotropic behavior. The modified slurries were compared with a nonstable reference slurry. While all methods lead to increased storage stability, only the stabilized slurry with 0.5 wt% fumed silica is stable during the printing process.     

Washcoating of Different Zeolites on Cordierite Monoliths

Cordierite monoliths were washcoated with slurries of different zeolites (ZSM5, β zeolite, mordenite, and Zeolite Y) in order to establish the relationship between washcoat characteristics and the powder and slurry properties. To achieve this objective, initially, the zeolite particle size was reduced to 2–3 μm by wet ball milling, and during this process the crystallinity and surface area of the powder were not significantly affected. The rheological behavior of the zeolite slurries is a function of the type of zeolite and solid content. The washcoat properties, such as loading, thickness, uniformity, and reproducibility, depend on the particle size of the powder, number of immersions, slurry concentration, slurry viscosity, and surface tension. The mechanical stability of the zeolite washcoat decreases with an increase in cumulative loading and slurry particle size. Addition of binder (colloidal silica) results in an improvement in zeolite loading and washcoat adherence.     

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].     

Photocurable ceramic slurry using solid camphor as novel diluent for conventional digital light processing (DLP) process

This study presents the utility of solid camphor as a novel type of diluent for the preparation of photocurable ceramic slurries with sufficiently low viscosity at high solid loading (48 vol%), which can be applicable for the conventional digital light processing (DLP) process. The camphor addition remarkably decreased the viscosity of calcium phosphate (CaP) ceramic slurries without affecting their photopolymerization behavior. This approach could effectively mitigate the clogging of pores with residual slurries, and thus the porous structure of porous CaP scaffolds with 3D channels could be tightly controlled. Furthermore, the high densification of CaP frameworks after sintering at 1250 °C for 3 h could be achieved owing to the use of the high solid loading in the CaP slurry. The porous CaP scaffolds produced displayed high compressive strength (˜ 23.8 MPa) and modulus (˜ 276 MPa) at a high porosity of ˜ 50.6 vol%.     

Fabrication of Stable Al2O3 Slurries and Dense Green Bodies Using Wet Jet Milling

A wet jet milling process was used as a novel method to prepare Al₂O₃ slurries. The wet jet-milled slurries showed very low viscosity compared with the ball-milled slurries. Moreover, the viscosity of the wet jet-milled slurries was constant for long times, whereas that of the ball-milled slurries increased rapidly with time. Al₂O₃ particles after wet jet milling retained initial surface conditions, although Al₂O₃ particles after ball milling yielded more OH groups on the surface. Casting rate was sensitive to the solid content and preparation method of slurry. The relative density of the green bodies prepared from the wet jet-milled slurries was about 65% or more and was independent of 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 and was higher than 60% at the solid content of 50% by volume. Linear shrinkage of the sintered bodies prepared from the wet jet-milled slurries was very low and independent of the solid content of the slurry whereas that of the sintered bodies prepared from the ball-milled slurries increased with decreasing solid content.     

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.     

Preparation of alumina by aqueous gelcasting

The alumina ceramic was prepared by aqueous gelcasting. The effects of zeta potentials, solid loading, dispersant content and milling time on the alumina suspension were studied systematically. The dispersant content has remarkable effects on the viscosity of the suspension. The appropriate dispersant concentration for alumina aqueous slurry with the solid loading of 55 vol.% is 0.6 wt.%. It can be seen that all suspensions (50–56 vol.% solid loading) exhibited a shear-thinning behavior and relatively low viscosity, which was suitable for casting. The degree of shear thinning and the viscosity at high shear rates increased with increasing volume fraction of solid. As the milling time prolongs, viscosity of the suspension decreases first, then the plateau appears and the average diameter keeps changeless. When the milling time was shorter than 20 h, the viscosity of slurries decreased gradually as the time of milling increased. After 20 h milling, the viscosity of the slurry tended to be consistent. Therefore, the ball milling time should be equal to or more than 20 h to obtain a stable suspension at equilibrium. The time available for casting the slurry (idle time) can be controlled by the amounts of initiator and catalyst added to the slurry as well as by the processing temperature. Micrograph of the gelcast green body was homogeneous.     

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.     

Defect and microstructural evolution during drying of soapnut-based alumina foams

The present study demonstrates the use of soapnut, a naturally occurring surfactant for producing alumina ceramic foams. A range of slurry compositions with soapnut amounts ranging from 2 to 20 wt% in water, alumina loading of 35–55 vol% were studied. Though all slurry compositions foamed when subjected to mechanical agitation the formation of green ceramic foams free of macroscopic defects was found to be strongly dependent on conditions during drying of foamed slurries. Addition of guar gum to the slurries was shown to enhance foam stability and thus produce defect-free foams from compositions that otherwise either collapsed or resulted in other macroscopic defects during drying. Drying conditions also had a strong effect on microstructural parameters such as cell size and cell connectivity. Soapnut-based foams appear to have a greater connectivity between cells than foams produced by other comparable processes.     

Surface Treatment of Templates for Fabrication of Reticulated Porous Ceramics

Before impregnation of the organic templates with an aqueous ceramic slurry, the templates were treated using silica sol. The surface morphology, elasticity of the templates, and the solid loading were studied. After the treatment, the coherence between the template and the slurry was significantly optimized, and the surfaces of the templates were uniformly covered by slurry. The elasticity of the templates was also increased. Consequently, the loading content increased considerably.     

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.     

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.     

Influence of sewage sludge on the slurryability of coal-water slurry

In this study, the maximum solids loading, stability and rheological properties of coal-sludge slurries were investigated and compared with those of coal-water slurries. The maximum solids content of coal-sludge slurry was much lower than that of coal-water slurry because of the ∼82% water in sewage sludge. NaOH addition as a pre-treatment of sewage sludge improved the maximum solids content to 61% and 60% for dispersants A₁ and A₂, respectively, for a sludge-coal mass ratio of 22.1:100. Compared to coal-water slurries, the stability of coal-sludge slurries was better, with no solid deposition after 96 h. Coal particles and sewage sludge formed a stable medium and settlement of large coal particles was prevented. All the coal-sludge slurries exhibited pseudo-plastic behavior; this type of fluid is shear-thinning and is easy to transport.     

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。     

粉煤灰泡沫陶瓷浆料的稳定机制

通过不同组分浆料的沉降实验,研究了固含量、分散剂(淀粉、硅酸钠、柠檬酸三铵)对浆料稳定性能的影响。实验过程中测量了1#～12#浆料浑浊液和上清液的高度,进而得到浆料的相对沉降高度(RSH)值。通过测量10#、13#、14#浆料在沉降过程中上清液高度的变化,研究了13#、14#浆料的稳定性。实验结果分析发现,在含硅酸钠的悬浮浆料中,随着浆料中固含量的增加,淀粉作为分散剂对浆料的稳定性能的影响减小;在不含硅酸钠的浆料中,这一规律只在3#～6#的浆料中出现;淀粉、柠檬酸三铵作分散剂可显著提高浆料的稳定性。硅酸钠对浆料的分散效果较差,保证素坯在低温强度的状态下,应尽量减少硅酸钠的用量。     

粉煤灰泡沫陶瓷浆料的稳定机制

通过不同组分浆料的沉降实验,研究了固含量、分散剂（淀粉、硅酸钠、柠檬酸三铵）对浆料稳定性能的影响。实验过程中测量了1#～12#浆料浑浊液和上清液的高度,进而得到浆料的相对沉降高度（RSH）值。通过测量10#、13#、14#浆料在沉降过程中上清液高度的变化,研究了13#、14#浆料的稳定性。实验结果分析发现,在含硅酸钠的悬浮浆料中,随着浆料中固含量的增加,淀粉作为分散剂对浆料的稳定性能的影响减小;在不含硅酸钠的浆料中．这一规律只在3#～6#的浆料中出现;淀粉、柠檬酸三铵作分散剂可显著提高浆料的稳定性。硅酸钠对浆料的分散效果较差,保证素坯在低温强度的状态下,应尽量减少硅酸钠的用量。     

High solid loading,low viscosity photosensitive Al2O3 slurry for stereolithography based additive manufacturing

Photosensitive Al₂O₃-resin slurries with high solid loading, low viscosity used for stereolithography based additive manufacturing were prepared in this paper. The dispersion behavior and rheological behavior of the Al₂O₃-resin slurries were studied by rheology observation and sedimentation tests. The dispersant type, concentration and solid loading had significant effects on the rheological behavior and stability of the photosensitive Al₂O₃-resin slurries. A long term stability and homogeneity slurry was obtained when the dispersant and concentration were KOS110 and 5?wt%, respectively. The Al₂O₃ slurry prepared with a high solid loading up to 60?vol%, low viscosity of 15.4?Pa?s at 200?s^?1 was chosen for stereolithography based additive manufacturing.     

Mechanical behaviour and pore morphology of functionally graded alumina preforms and their composites

Functionally-graded ceramic composites were produced using a hot pour-and-set method via freeze casting of alumina slurries with solid loading between 40% and 20%, with gelatine as a binder. The slurry and additives were tailored for controlling the microstructure and mechanical properties, such as pore morphology, preform density and compressive strength. Varying the gelatine concentration between 2.5% and 9%, transformed the pore morphology from lamelllar to honeycomb and into closed cell. At 3% concentration, increasing the solid loading from 10% to 30% yielded higher compressive strength from 48 MPa to 317 MPa. The resultant compressive behaviour closely matched to Gibson-Ashby closed cell predictive model. Alumina/epoxy composite mechanical performance plateau as the solid loading increased; the 20% solid loading composite produced the best performance. The compressive strengths of the alumina/epoxy and alumina/aluminium composites were on average 300% and 1110% higher than their respective preform counterparts, across a solid loading range of 10–20%.