3D printing of fine alumina powders by binder jetting

Additive manufacturing of ceramics is still at an early-development stage; however, the huge interest in custom production of these materials has led to the development of different techniques that could provide highly performing devices. In this work, alumina (α-Al₂O₃) components were produced by binder jetting 3D printing (BJ), a powder-based technique that enables the ex-situ thermal treatment of the printed parts. The employment of fine particles has led to high green relative density values (>60 %), as predicted by Lubachevsky-Stillinger algorithm and DEM modelling. Then, extended sintering has been observed on samples treated at 1750 °C that have reached a final density of 75.4 %. Finally, the mechanical properties of the sintered material have been assessed through bending test for flexural resistance and micro-indentation for Vickers hardness evaluation.     

Effect of layer printing delay on mechanical properties and dimensional accuracy of 3D printed porous prototypes in bone tissue engineering

Recent advancements in computational design and additive manufacturing have enabled the fabrication of 3D prototypes with controlled architecture resembling the natural bone. Powder-based three-dimensional printing (3DP) is a versatile method for production of synthetic scaffolds using sequential layering process. The quality of 3D printed products by this method is controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The X-direction printed scaffolds with a pore size of 0.8 mm and a layer thickness of 0.1125 mm were subjected to the depowdering step. The effects of four layer printing delays of 50, 100, 300 and 500 ms on the physical and mechanical properties of printed scaffolds were investigated. The compressive strength, toughness and tangent modulus of samples printed with a delay of 300 ms were observed to be higher than other samples. Furthermore, the results of SEM and μCT analyses showed that samples printed with a delay of 300 ms have higher dimensional accuracy and are significantly closer to CAD software based designs with predefined 0.8 mm macro-pore and 0.6 mm strut size.     

3D printing of porcelain by layerwise slurry deposition

The Layerwise Slurry Deposition is a technology for the deposition of highly packed powder layers. A powder bed is achieved by depositing and drying layers of a ceramic suspension by means of a doctor blade. This deposition technique was combined with the binder jetting technology to develop a novel Additive Manufacturing technology, named LSD-print. The LSD-print was applied to a porcelain ceramic. It is shown that it was possible to produce parts with high definition, good surface finish and at the same time having physical and mechanical properties close to those of traditionally processed porcelain, e.g. by slip casting.This technology shows high future potential for being integrated alongside traditional production of porcelain, as it is easily scalable to large areas while maintaining a good definition. Both the Layerwise Slurry Deposition method and the binder jetting technologies are readily scalable to areas as large as >1?m².     

3D printing structure -based Cu&Bi2O3 anode toward high-performance rechargeable alkaline battery and photodetector

As an energy storage device, the aqueous alkaline battery holds great potential, particularly for applications requiring high energy density and high power density. Anode materials with excellent performance are indispensable to producing stable and high-energy aqueous rechargeable batteries. In this study, 3D-printed porous and planar substrates were employed as growth vehicles for Bi₂O₃. As a result, rapid charge transfer and ion diffusion are successfully achieved by utilizing porous structure channels. A remarkable specific capacity of 2.63 mAh cm^?2 is attained for the porous structure-based Bi₂O₃, which can attribute to the formed p-type homojunction between CuO/Cu₂O and Bi₂O₃. Additionally, the cycle stability of Bi₂O₃ deposited on the porous structure substrate is enhanced dramatically due to this structure enables less bismuth-based salt ions, oxide, and hydroxide deposition. Consequently, the harmful accumulation of bismuth-based mixture deposition on the anode surface was prevented, resulting in the mitigation of electrode passivation. Besides, a favorable photoresponse rate is displayed for the porous structure Bi₂O₃ anode, proving the practicable Cu&Bi₂O₃ combination and the reasonable structural design.     

Effect of particle size on three dimensional printed mesh structures

Three dimensional printing is a unique technique that can print complex 3D structures that cannot be produced by other means, especially for rapid prototyping purpose. In this study, 3D mesh structures are created by three dimensional printing with four different TiNiHf powder sizes. Mesh structure green strength and surface smoothness are characterized in order to produce high quality 3D structures. Binder spreading time and spreading rate in the TiNiHf powders are measured in order to understand binder penetration difference in the mesh structures. The study shows that smaller TiNiHf particle size produces higher mesh structure green strength and surface smoothness, consistent with the observation that binder spreading is slower for smaller TiNiHf particles.     

Composite resins for 3D printing of corundum and corundum-kaolin based monoliths for catalytic applications

Several composite organic-inorganic resins dedicated to 3D printing using Digital Light Processing (DLP) technology containing nano- and micro-structured corundum as well as corundum/kaolin mixtures were prepared and characterised in terms of their rheology and stability. Using these resins, short monoliths were printed using the DLP technology at a resolution of x:y:z = 30/30/50 μm. After thermal pre-treatment, the printed materials were studied by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). Based on the selected monoliths, MnO_x- and Na₂WO₄-containing catalysts were prepared by two-step impregnation and tested in the oxidative coupling of methane (OCM) at 820 °C using a ratio of methane/oxygen of 3.8/1. The maximum conversion of methane (28%) and total conversion of oxygen (100%), as well as stable selectivity to ethane (22%) and ethylene (44%), were achieved using three short monoliths (GHSV = 7676 h^?1). A further enhancement of the number of monoliths influenced only the CO_x and C₃ selectivity. Moreover, a comparative study of monolithic and powder samples with identical compositions revealed that for the monolithic catalyst the yield of C₂–C₃ hydrocarbons is slightly lower (1–2%) but at a 3–4 times lower pressure drop.     

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 printed ceramic phosphor and the photoluminescence property under blue laser excitation

An Al₂O₃/YAG: Ce³⁺ ceramic phosphor was fabricated for high-flux laser lighting using the digital lighting process (DLP)-based 3D printing method for the first time. The photocurable ceramic suspension for 3D printing was prepared by blending well-treated Al₂O₃/YAG: Ce³⁺ composite powders with photosensitive resin monomers and photo-initiators. The printing parameters, debinding and sintering processes were designed delicately to fabricated the dense sub-millimeter-sized cylinder ceramic with high dimensional accuracy. The ceramic showed excellent luminescence property under blue laser excitation with a threshold of 20.7 W/mm², higher than that prepared via dry-pressing followed by vacuum sintering. The luminescence properties and the microstructures of both ceramics were further comparatively investigated to find the possible interpretations for improvement of laser flux for the 3D-printed ceramic. The present work indicated that the new developed 3D printing method was promising for preparing luminescent ceramics for high-flux laser lighting in a rapid, effective, low-cost and precision-controlled manner.     

3D printing of high-purity silicon carbide

A method for advanced manufacturing of silicon carbide offering complete freedom in geometric complexity in the three-dimensional space is described. The method combines binder jet printing and chemical vapor infiltration in a process capable of yielding a high-purity, fully crystalline ceramic—attributes essential for ideal performance in very high-temperature applications or in the presence of displacement damage. Thermal conductivity and characteristic equibiaxial flexural strength of the resulting monolithic SiC at room temperature are 37 W·(m·K)⁻¹ and 297 MPa, respectively.     

3D printing boehmite gel foams into lightweight porous ceramics with hierarchical pore structure

We herein report a novel hierarchically porous ceramic foams derived from boehmite gel foams, which possess both high porosity and superior strength. The gel foams show excellent printability due to its predominant stability, high yield stress and storage modulus, which endows such foam material ideal ink for 3D printing lightweight and complex-shape materials via direct ink writing approach. The 3D printed ceramic foams possess programmable architecture assembled by porous filaments, uniform macro-pores with tunable size in the range of 4∼70 μm, as well as nanoscale pores in cell wall, after sintering at relatively low temperature of 1200–1300 °C. In this way, ceramic foams with high strength were achieved, attributed to the tiny grains, large amount of grain boundaries, uniform pores and hierarchical pore structure. Notably, the foams sintered below 1200 °C have significant advantage on specific surface area, which could reach up to 300-400 m²/g.     

Multiple metals doped polymer-derived SiOC ceramics for 3D printing

Multiple metals doped polymer-derived SiOC ceramics with octet truss structure were prepared by employing a photosensitive methyl-silsesquioxane as preceramic polymer through sol-gel method and Digital Light Processing 3D printing. The physical and chemical properties of the preceramic polymers and printed octet truss structure SiOC ceramics were investigated. Results show that the organosilicon preceramic polymers have outstanding photocuring properties and could transform into amorphous SiOC ceramics at 800–1200?°C. It is illustrated that the excellent mechanical properties of SiOC ceramics with octet truss structure (after 3D printing and pyrolysis) are attributed to the metal elements pinning in the amorphous matrix on the atomic level. Doping other metal elements such as Fe, Ni, Co, Pt, etc, is thought to bring promising properties for the lattice structure SiOC ceramics and potentially further expand its applications in the future.     

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.     

Influence of 3D printing process parameters on the tribological properties of acrylic resin

This article studied the mechanism of the influence of light-curing 3D forming parameters of acrylic resin on its tribological and mechanical properties. A three-factor hybrid orthogonal table was designed, that is, the three key process parameters of printing monolayer thickness (P), heat treatment (H), and ultraviolet curing treatment (U). The priority of three process parameters affecting tribological performance was studied based on Gray Correlation Theory. The results showed that the order of priority was P, U, and H. The tribological and mechanical properties of acrylic resin decreased with the increase of printing monolayer thickness, while the printing efficiency increased with the increase of the printing monolayer thickness. Based on Gray Correlation Theory, the “Wear Resistance Efficiency” (WRE) parameter was defined to comprehensively evaluate the wear resistance and printing efficiency of the samples. When the thickness of the printing monolayer was 30 μm, the comprehensive properties of the material reached the optimal value. The U increased the cross-linking degree of the acrylic interlayer molecules, and the H reduced the residual stress generated during the printing of the samples. The research results provided data support for the application of 3D printing acrylic resin and its nanocomposites in the field of tribology.     

3D打印用聚丙烯复合材料的制备及性能研究

将碳酸钙和滑石粉按质量比为1∶1混合,与聚丙烯(PP)共混,制备可用于熔融沉积法(FDM)打印的PP材料,研究填料用量对3D打印试样力学性能和微观结构的影响。结果表明,随着填料用量的增大,3D打印制品的力学性能下降,PP材料的收缩率显著降低,试样内部纤维之间无空隙。当碳酸钙和滑石粉质量各占配方总质量的20%时,3D打印的PP制品性能最好。     

Binder stabilization and rheology optimization for vat-photopolymerization 3D printing of silica-based ceramic mixtures

Enhancing inlet gas temperature in aero/gas turbines to reduce their carbon-footprint, has led to a strive for better performing inlet cooling mechanism of the turbine blades. The internal cooling of the blades is made by ceramic cores in their casting process, but conventional ceramic molding has long reached its maximum possible geometrical complexity, hence shedding light on 3D printing of these cores. The objective of this study is to develop low-viscous, fully stabilized, commercially viable ink for vat-photopolymerization of silica-based ceramics. This paper investigates the best dispersion type and amount for different formulated monomer mixtures, and explains the best correlation between viscosity, solid loading, binders, dispersants, peeling forces and mechanical properties, and offers an optimized mixture to avoid the common ceramic printing issue, namely crack propagation of cores during sintering. Among five dispersant agents, the SOL20, SOL24 and FA4611 exhibited better performance than other dispersion agents, and the optimum concentration level for each binder and dispersant agent was ensured through sedimentation test. Their dispersion capability and long-term stability were further investigated to designate the best dispersion agent for each binder system. Further verification was made by sedimentation study of the samples at 40 °C for 40 days and reducing the superficial area of the used powder mixture. According to the result of the rheology analysis, the best dispersions were achieved using SOL20 for the loaded binder mixtures of M1 and M4, SOL24 for M3and FA4611 for M2. The instability of M1 and M2 with their respective dispersant agent was coordinated through the thixotropic agent of TX/2, and complete stabilization and near-Newtonian behavior were achieved. However, the research showed that the addition of TX/2 to fully stabilized M4 and M2 suspensions negatively impacts the mixtures’ rheological behavior from near-Newtonian to shear-thickening. In the final stage of this study, peeling forces, sintering and three-point bending tests were conducted to determine the final formulated suspension to print ceramic core components. M4 and SOL20 combination was selected for SiO₂-ZrSiO₄ loading and dispersing, respectively. The impact of solid loading between the range of 58 and 65 vol% on the rheological behavior of the final suspension and the mechanical properties of sintered bodies were investigated to assign an optimum solid rate. The adequate strength on sintered and degree of viscosity for ceramic vat-polymerization processing was achieved at 58 vol%. Lastly, a validation study is conducted by printing a complex ceramic core model by a commercial LCD hobby printer. This validation shows the significance of this study to scale up the manufacturing of complex-shaped ceramic cores and to revolutionize the sector, by printing inexpensive and readily available irregular-shaped (non-atomized) ceramic powder, using the most cost-effective LCD printers (non-specialized expensive ceramic printers).     

自由基–阳离子混杂固化型3D打印光敏树脂研究

选择丙烯酸酯作为自由基型预聚物,3,4–环氧环己基甲基–3,4环氧环己基甲酸酯作为阳离子型预聚物,三丙二醇二丙烯酸酯为活性稀释剂,2,2–二甲基–α–羟基苯乙酮和三芳基硫鎓盐为光引发剂来制备一种混杂固化光敏树脂。将聚氨酯丙烯酸酯(PUA)加入到上述制备的光敏树脂中,探究PUA作为辅助预聚物对光敏树脂性能的影响,用超声分散法制备了纳米氧化石墨烯(GO)改性光敏树脂复合材料。当PUA的质量分数为20%时,力学性能最优;GO对光敏树脂的力学性能有改善的作用,拉伸强度从17.84 MPa最大增强至27.84 MPa,提高了56%;且该混合体系的体积收缩率在3%左右,线收缩率也很小。     

Fabrication of bone tissue engineering scaffolds with a hierarchical structure using combination of 3D printing/gas foaming techniques

The goal of this research was to study and optimize the structure and geometric features of scaffolds made using a combined method of 3D printing and gas foaming. This endeavor aimed to produce scaffolds with a hierarchical structure that closely resemble bone tissue. The study examined the effects of saturation pressure, foam temperature, and foam time on the scaffolds using response surface methodology (RSM). RSM is statistical technique used for optimizing and analyzing processes by modeling relationship between input variables and output responses. The results of multi-objective optimization showed that highest pressure (55 MPa), the shortest time (40 s), and the temperature of 68°C were the optimal conditions. RSM was also used to develop mathematical models of structural properties, dimensional accuracy, and mechanical strength, focusing on different foam parameters, which could be used to predict desired properties. Subsequently, the designed scaffold underwent MTT assay testing to assess cell toxicity indicating its biocompatibility. The results demonstrate that by using the correct foam parameters in combination with 3D printing, it is possible to achieve polymer scaffolds with proportional dimensions, geometry, and mechanical strength suitable for cell growth to use inside the human body.     

A review: 3D printing of microwave absorption ceramics

Along with extensive research on the 3D printing and microwave absorption ceramics, 3D printing technology provides a great possibility for microwave absorption ceramics with arbitrary shapes in a faster, cheaper and more flexible way. This review focuses on the latest evolution in the raw materials, the structure design and the advanced additive manufacturing technologies of 3D printing microwave absorption ceramics. Firstly, the representative raw materials are divided into three categories, including ceramic powder, cermet powder and precursor resin. In addition, additives give rise to improvement of microwave absorption properties of ceramics. Secondly, based on two attenuation theories, structure design makes further efforts to enhance the microwave absorption performance of ceramics. Finally, comparisons are made between diversified manufacturing technologies to facilitate the selection of the best ones for different application in practical use. This study presents a summary of research that has been conducted to produce microwave absorption ceramics by additive manufacturing.     

DLP 3D printing of scandia-stabilized zirconia ceramics

The present article aims to explore the printability of scandia-stabilized zirconia ceramic parts using desktop and low-cost DLP 3D printer. The acrylate-based homogeneous slurries with zirconia powder stabilized by 6 mol.% of Sc₂O₃ (6ScSZ) and 10 mol.% of Sc₂O₃ and 1 mol.% of Y₂O₃ (10Sc1YSZ) were prepared with appropriate rheological and UV-curing properties. In comparison with yttria-stabilized zirconia, slurries filled with 6ScSZ and 10Sc1YSZ powders reviled lower viscosity at the same solid content. The cure depth of the suspensions was suitable to print the objects with 50 μm of layer thickness, good interlayers connection, and surface finishing. No critical defects in ceramics such as cracks or delamination were observed. Both ceramics have the Vickers microhardness value of 11 GPa and the high ionic conductivity up to 0.2 S/сm at 900 °C demonstrating that the DLP is a promising method of fabricating scandia-stabilized zirconia parts as electrolyte material for SOFC application.     

Development of a 3D model to predict curing dimensions and conversion rates of curable ceramic systems during stereolithography 3D printing process

To meet industry’s expectations for manufacturing ceramic parts by stereolithography, a better comprehension of the process, in particular laser scattering through the ceramic slurry is mandatory. This knowledge makes it possible to define adapted printing conditions to control the dimensions, homogeneity of the conversion and mechanical properties of the green parts, in order to achieve better resolutions and optimize the properties of sintered parts. This approach is focused on the development of a 3D polymerization modeling for stereolithography process able to predict curing and associated thermal phenomena. First, a design of experiments is carried out to identify material-dependent parameters, calibrate and validate the model, then able to predict monomer conversion rates and dimensions after curing depending on manufacturing parameters. Finally, temperature variation and exposure homogeneity have been evaluated. These results will allow, in future studies, to interpret the differences of deformations and mechanical properties of green parts.