A review of 3D printed porous ceramics

Three-dimensional (3D) printing of ceramics has gained widespread attentions in recent years. Many excellent reviews have reported the printing of ceramics. However, most of them focus on printing of dense ceramics or general ceramic aspects, there is no systematical review about 3D printing of porous ceramics. In this review paper, the 3D printing technologies for fabricating of porous ceramic parts are introduced, including binder jetting, selective laser sintering, direct ink writing, stereolithography, laminated object manufacturing, and indirect 3D printing processes. The techniques to fabricate hierarchical porous ceramics by integrating 3D printing with one or more conventional porous ceramics fabrication approaches are reviewed. The main properties of porous ceramics such as pore size, porosity, and compressive strength are discussed. The emerging applications of 3D printed porous ceramics are presented with a focus on the booming application in bone tissue engineering. Finally, summary and a perspective on the future research directions for 3D printed porous ceramics are provided.     

Mechanical and biological evaluation of 3D printed 10CeTZP-Al2O3 structures

Three-dimensional structures were robocasted from a 10 mol% ceria-stabilized zirconia and alumina composite (10CeTZP-Al₂O₃). A hydrogel-based printable ink was developed using a unique non-ionic copolymer surfactant. Self-supporting and free-standing structures, including round lattices with interconnected pores (200–600 μm pores; 30–50% porosity), rectangular bars (95% density on average) and cones were successfully printed. The round lattices of 200 μm pores and 30% porosity showed compression strengths similar to those of cortical bone, reaching almost 200 MPa. The maximum flexural strength value attained for the rectangular bars was 575 MPa. In vitro biological studies demonstrated that the samples allow for practically 100% cell viability, confirming their non-cytotoxic nature. Cell differentiation tests were performed using osteoblasts incubated for 7 days in supplemented cell culture medium. Quantification of specific osseous differentiation genes showed that the robocasted structures induced a higher degree of osseous differentiation than tissue culture polystyrene.     

A comparative study of (Ce) and (Gd) doping influence on the superconducting properties of YBCO ceramics

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa_2-xRE_xCu₃O_7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature T_C and the critical current density J_C.The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa_2-xRE_xCu₃O_7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature T_C was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of T_C for YBa_2-xRE_xCu₃O_7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density J_C was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.     

（急）3D打印气凝胶的研究现状

气凝胶材料具有高比表面积、高孔隙率、低密度以及低热导率等诸多优良性能，被认为是21世纪的十大新材料之一。然而传统气凝胶由于其力学性能有限，难以经过后加工技术形成所需的复杂形状结构，满足实际应用的需求。因此，无需复杂后处理即定制化制备复杂形状结构材料的3D打印技术有望成为突破气凝胶材料应用瓶颈的先进制造技术。本文从3D打印气凝胶的技术种类和材料类型两个方面，综述了3D打印气凝胶材料的研究进展；归纳了3D打印气凝胶材料在阻燃隔热、介电和组织工程中的独特应用并展望了3D打印气凝胶的发展趋势。最后指出扩宽3D气凝胶材料的材料体系、开发更适应气凝胶打印的3D打印技术、提升打印精度与速度和深入研究3D打印气凝胶的可控孔隙结构对其性能的影响是未来的几个重要的研究方向。3D打印气凝胶材料的开发有望促进气凝胶材料的快速发展。     

3D printed millireactors for process intensification

The scope of the present research aims at demonstrating the 3D printing use in the manufacturing of microchannels for chemical process applications. A comparison among digital model processing applications for 3D print(slicers) and a print layer thickness analysis were performed. The 3D print fidelity was verified in several devices, including the microchannels' printing with and without micromixer zones. In order to highlight the 3D print potential in Chemical Engineering, the biodiesel synthesis was also carried out in a millireactor manufactured by 3D printing. The millireactor operated under laminar flow regime with a total flow rate of 75.25 ml ? min~(-1)(increment of about 130 times over traditional microdevices used for biodiesel production).The printed millireactor provided a maximum yield of Ethyl Esters of 73.51% at 40 °C, ethanol:oil molar ratio of7 and catalyst concentration of 1.25 wt% and residence time about 10 s. As a result of flow rate increment attained in the millireactor, the number of required units for scaling-up the chemical processes is reduced. Using the approach described in the present research, anyone could produce their own millireactor for chemical process in a simple way with the aid of a 3D printer.     

3D printing of ceramics: A review

Along with extensive research on the three-dimensional (3D) printing of polymers and metals, 3D printing of ceramics is now the latest trend to come under the spotlight. The ability to fabricate ceramic components of arbitrarily complex shapes has been extremely challenging without 3D printing. This review focuses on the latest advances in the 3D printing of ceramics and presents the historical origins and evolution of each related technique. The main technical aspects, including feedstock properties, process control, post-treatments and energy source–material interactions, are also discussed. The technical challenges and advice about how to address these are presented. Comparisons are made between the techniques to facilitate the selection of the best ones in practical use. In addition, representative applications of the 3D printing of various types of ceramics are surveyed. Future directions are pointed out on the advancement on materials and forming mechanism for the fabrication of high-performance ceramic components.     

3D打印聚乳酸热塑挤压成型材料的研究及应用

对3D打印聚乳酸(PLA)热塑挤压成型材料的研究进展做了全面的综述。分析了PLA材料在3D打印材料中的优势,介绍了PLA材料的合成方法、结构与性能,以及3D打印PLA材料的改性方法、成型工艺与性能要求,并对3D打印PLA材料在生物医学中的应用做了详细描述;最后讨论了3D打印PLA材料未来的发展前景。     

3D printed carbon-ceramic structures for enhancing photocatalytic properties

3D printing creates structures from digitally designed models by bottom-up fabrication method, achieving excellent control of target structures from various materials. Compared with conventional manufacturing methods such as machining, chemical engineering and bio-template, 3D printing shows advantages in aspects of parameterization-designed structure, rapid preparation, high precision and low cost. Herein, 3D printed carbon-ceramic support with designed array patterns, square, circular and diamond, was fabricated in an inert atmosphere to obtain sophisticated pore structure with high surface area. The existence of pyrolyzed carbon from UV-curable resin suppressed the mass transfer process when sintering and was found to greatly increase pore area from 0.067 m²/g to 0.509 m²/g. Molybdenum disulfide (MoS₂) chosen as a typical catalyst was loaded on the sintered support. The photodegradation efficiency of as-printed carbon support with MoS₂ increased to 45.95% while that of pure MoS₂ was only 23.35%. The catalyst-support system showed significant stability and the efficiency decreased to 82.35% after five cycles. UV–Vis diffused reflectance spectra proved that pyrolyzed carbon increased the light adsorption efficiency at the whole range of visible light.     

3D打印成型陶瓷零件坯体及其致密化技术

3D打印技术在陶瓷零件成型方面具有较大应用潜力,被认为是近净尺寸成型高性能复杂结构陶瓷零件的一种新途径。本文比较了陶瓷零件或其坯体的激光选区熔化、薄材叠加制造、熔融沉积造型、光固化、三维打印和激光选区烧结等不同3D打印工艺及其致密化手段的优势和不足,认为较低的相对密度和强度是阻碍3D打印陶瓷零件实现产品应用的主要障碍。本团队近年来采用造粒混合法制备出具有良好流动性的3D打印复合陶瓷粉体,再通过激光选区烧结(SLS)和冷等静压(CIP)技术分别进行坯体成型及均匀致密化处理,制备出了高性能、复杂结构的Al_2O_3致密陶瓷零件。本文回顾了这些工作,并补充介绍了溶解沉淀和溶剂蒸发这两种制备复合陶瓷粉体的新方法,利用SLS/CIP复合工艺进一步制造了ZrO_2、SiC、高白土等其它材质的复杂陶瓷零件,为3D打印陶瓷用于航空航天、医疗、艺术等领域奠定了基础。     

On reducing anisotropy in 3D printed polymers via ionizing radiation

The mechanical properties of materials printed using fused filament fabrication (FFF) 3D printers typically rely only on adhesion among melt processed thermoplastic polymer strands. This dramatically limits the utility of FFF systems today for a host of manufacturing and consumer products and severely limits the toughness in 3D printed shape memory polymers. To improve the interlayer adhesion in 3D printed parts, we introduce crosslinks among the polymer chains by exposing 3D printed copolymer blends to ionizing radiation to strengthen the parts and reduce anisotropy. A series polymers blended with specific radiation sensitizers, such as trimethylolpropane triacrylate (TMPTA) and triallyisocyanurate (TAIC), were prepared and irradiated by gamma rays. Differential scanning calorimetry (DSC), tensile testing, dynamic mechanical analysis (DMA) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were employed to characterize the thermomechanical properties and the chemical structure of the various polymers. TAIC was shown to be a very effective radiation sensitizer for 3D printed sensitized polylactic acid (PLA). The results further revealed that crosslinks induced by radiation temperatures near T_g of shape memory systems have prominently enhanced the thermomechanical properties of the 3D printed polymers, as well as the solvent resistance. This enables us to deliver a new generation of inexpensive 3D printable, crosslinked parts with robust thermomechanical properties.     

Experimental study on mix proportion and fresh properties of fly ash based geopolymer for 3D concrete printing

This paper presents the material design and fresh properties of geopolymer mortar developed for 3D concrete printing application. Unlike traditional casting, in 3D printing, extruded materials are deposited layer-by-layer to build complex architectural and structural components without the need of any formwork and human intervention. Extrudability, shape retention, buildability and thixotropic open time (TOT) are identified as critical early-age properties to characterize the 3D printable geopolymer material. Five different mix designs of geopolymer are tested in a systematic experimental approach to obtain a best printable mix and later it is used to print a 60-centimeter-tall freeform structure using a concrete gantry printer to validate the formulation.     

Sol-gel infiltration of complex cellular indirect 3D printed alumina

Gelled aqueous solutions containing the soluble precursor aluminum chlorohydrate were developed for the infiltration of porous indirect 3D printed alumina. Viscosity and amplitude sweep tests confirmed the gel formation and sheer thinning behavior beneficial for the subsequent coating and infiltration process. High temperature XRD confirmed the formation of corundum at a temperature of 1000?°C. Complex alumina structures with high surface area and isotropic pore channels were achieved by indirect 3D printing. Coating and infiltration of the pre sintered alumina with a subsequent sintering step transformed the precursor to corundum and partially filled the residual porosity and decreased surface defects after 3D printing. With the gel coating a pronounced improvement up to a maximum value of Δσ_compr?=?61.9?MPa was observed and with the gel infiltration a maximum improvement of ΔE?=?136.2?GPa. The results show the possibility to infiltrate even complex alumina structures with aqueous alumina precursors without the need to disperse ceramic particles.     

Effect of dispersants on structural integrity of 3D printed ceramics

Ceramic 3D printing based on stereolithography is an excellent alternative to overcome drawbacks of conventional subtractive manufacturing for 3D shape control. Optimization of photocurable ceramic slurry is one of the most essential conditions to achieve favorable 3D printed structures using SL. Homogeneity of ceramic particle dispersion in photocurable resin is particularly important to optimize ceramic suspension. Dispersant plays a significant role in increasing homogeneity. Dispersant in photocurable ceramic resin has an additional effect on photocurability and integrity of 3D printed green body. We herein discuss how dispersants influence 3D printing conditions based on stereolithography using various commercially available dispersants of BYK series such as BYK103, BYK111, BYK180, BYK182, and BYK2001. Both BYK111 and BYK180 showed better performances than others because of their lower volatilities under general temperature condition during a printing process. Both solubility and decomposition temperature of dispersants largely influenced the structural quality after washing and debinding processes. This study provides worthy information to design photocurable ceramic suspension for various types of ceramic materials.     

Heat dissipation in 3D printed cellular aluminum nitride structures

The improvement of heat dissipation in electronic and energy devices is a challenge that can be addressed through the use of highly porous materials. Presently, the additive manufacturing of 3D aluminum nitride is described, and different lattice patterns with porosities in the range 45–64 % are achieved by direct ink writing. All the structures are robust and the effective thermal conductivity (k_eff) for cuboid structures decreases by 50–75 % with the filament separation and shows anisotropic characteristics, since k_eff along the longitudinal axis of the scaffold is up to six times greater than for the transversal one. Heat transfer during free cooling experiments for cuboid and cylinder scaffolds, after rapid heating at temperatures above 1000 °C, takes place by radiation for temperatures >500 °C and by convection through the complete cooling process. The heat dissipation time constants of both processes decrease almost linearly with the designed scaffold parameters of porosity and rod separation.     

Interfacial microdroplet evaporative crystallization on 3D printed regular matrix platform

Droplet evaporative crystallization on microscale heterogeneous surface is a vivid topic in chemical engineering, bioengineering, nanomaterials, and so on. Here, 3D printed interfacial matrix platform with regular pillar convexity and tunnel structure is fabricated to reveal the mechanism of the interfacial micro droplet crystallization. Element-based rotation volume model is established to simulate the concentration and nucleation barrier distribution during the microscale process. Sodium urate monohydrate and NaCl crystallization on the pillar convex structure both confirm that confined capillary flow in the micro droplet and initial nucleation condition dominate the nucleation, growth control and particle distribution. Droplet crystallization stretches over the tunnel structure reveal an interesting phenomenon that two regions possessing distinct-different nucleation barriers can isolated obtain the crystal particles from nanoscale to even millimeter scale. The fabricated platform and the capillary circulation transfer theory unfold a potential approach to harvest high value-added crystals with specific morphology and desire sizes distribution.     

Tensile properties and corrosion resistance of PCL-based 3D printed composites

The practicality of implantable biomedical materials depends on the design of size and function to meet the needs of personal customization. This paper used fused deposition modeling 3D printing process to make composite materials, and studied the performance of 3D printed samples through different matrix molecular weights, print filling settings, additives, and their contents. Mechanical properties, thermal analysis, structural characterization, surface hydrophilicity, and functional verification of PCL-based 3D printed composites were discussed. We found that 80% print filling and 10% SA addition could greatly improve the work of fracture of the tensile sample. Furthermore, the efficacy and content of CS was also verified and analyzed. These resulting information are helpful for structural design and functional matching of medical composites.     

Anisotropy management on microstructure and mechanical property in 3D printing of silica-based ceramic cores

Ceramic core is an essential component in the precise casting of hollow turbine blades, and the investigation on 3D printing of silica-based ceramic cores is crucial to the development of aviation industry; however, they are suffered from difficulty in high-temperature strength and structural anisotropy. In present work, silica-based ceramic cores were prepared via DLP stereolithography 3D printing, and the anisotropy management on microstructures and properties were explored based on the particle size of fused silica powders. In 3D printed ceramic cores with coarse powders, significant anisotropy was displayed exhibiting multilayer structure with large gaps in horizontal printing and uniform porous microstructure in the vertical direction, which was further explained by the particle deposition in printing. With finer silica powders, the uniformity in the microstructures was highly improved, attributed to the enhanced particle dispersion in ceramic slurries and promoted interlayer particle rearrangement during sintering. To evaluate the anisotropy in mechanical property, the ratio of vertical strength to horizontal strength (σ_V/σ_H) was proposed, which rose from 0.48 to 0.86 as the particle size decreased from 35 µm to 5 µm, suggesting enhanced mechanical uniformity. While the average particle size of silica powders was 5 µm, the flexure strengths of ceramic cores in different directions were up to 18.5 MPa and 16.3 MPa at 1540 °C with σ_V/σ_H ratio of 0.88, which well satisfied the demands for the casting of turbine blades. This work inspires new guidance on the anisotropy management in ceramic cores prepared by 3D printing, and provides new technology for fabrication of silica-based ceramic cores with superior high temperature mechanical properties.