3D Ceramic Structures Research Articles

Additive Manufacturing of SiOC, SiC, and Si3N4 Ceramic 3D Microstructures

Herein, the fabrication of hard ceramic SiOC 3D microstructures by precursor synthesis, laser lithography, and pyrolysis combination is proposed. Precursors are hybrid organosilicon materials prepared via sol–gel method using trimethoxymethylsilane and 3‐(trimethoxysilyl)propyl methacrylate, which has an acrylate functional group enabling laser photopolymerization process. Hard 3D ceramic structures (hardness up to ≈15 GPa, reduced elastic modulus ≈105 GPa) from soft organometallic derivatives are obtained after high‐temperature pyrolysis under nitrogen atmosphere. The advantage of the proposed method is the absence of shrinkage defects leading to a uniform repetitive decrease in the volume of printed microstructures. In contrast to slurry‐based printing technology, the proposed method is focused on homogeneous monolithic molecular resins resulting in visual smooth surfaces of prepared microstructures. Moreover, the printing resolution of the proposed method is substantially improved through the absence of predispersed ceramic microparticles in mixtures, which is a necessary element in a slurry‐based technology.

Particle-free compositions for printing dense 3D ceramic structures by digital light processing

ABSTRACT UV-curable particle-free ceramic compositions for stereolithography-based 3D printing technologies present a promising alternative to the commonly used particle-based compositions. So far, such compositions were mainly based on solutions of pre-ceramic polymers which limit their applications to silicon-containing materials. However, the application of particle-free inks for the fabrication of other ceramic materials, in particular dense polycrystalline ones, is very little explored. We present a new and general fabrication approach based on all-solution compositions, by combining sol–gel chemistry and photopolymerization, for obtaining dense 3D ceramic structures by DLP printing. The process is demonstrated here for the fabrication of barium titanate (BaTiO3). By using chelating solvent and monomer, a stable UV-curable solution is obtained. An aging period of 8–14 days was crucial for obtaining dense ceramic objects without any secondary phases. The heat treatment was found to affect the microstructure, density and hardness of the resulting ceramics. The presented process enables obtaining objects free of carbon materials, having a density as high as 98% of the theoretical value, and a hardness of 4.3 GPa.

Mechano-Plastic Pyrolysis of Dynamic Covalent Polymer Network toward Hierarchical 3D Ceramics.

Shaping ceramics into complex 3D geometries is desirable yet challenging, particularly those with structural hierarchy spanning different length scales. A mechano-plastic pyrolysis process that overcomes this limitation is reported. In addition to taking advantage of the moldability of organic polymers, the process uniquely incorporates mechano-plasticity via dynamic covalent bond exchange for reconfiguring the shape of a preceramic polymer. The combined steps result in simultaneous shape control at both micro- and macro-scales. Further pyrolysis leads to complex ceramic structures that are otherwise difficult to produce. To enable this process, rational design of the polymer network is required to satisfy an unusual combination of mechano-plasticity and pyrolysis. Overall, the process offers an avenue for efficient fabrication of hierarchical 3D ceramic structures suitable for engineering applications.

Graphene Oxide: An All-in-One Processing Additive for 3D Printing.

Many 3D printing technologies are based on the development of inks and pastes to build objects through droplet or filament deposition (the latter also known as continuous extrusion, robocasting, or direct ink writing). Controlling and tuning rheological behavior is key for successful manufacturing using these techniques. Different formulations have been proposed, but the search continues for approaches that are clean, flexible, robust and that can be adapted to a wide range of materials. Here, we show how graphene oxide (GO) enables the formulation of water-based pastes to print a wide variety of materials (polymers, ceramics, and steel) using robocasting. This work combines flow and oscillatory rheology to provide further insights into the rheological behavior of suspensions combining GO with other materials. Graphene oxide can be used to manipulate the viscoelastic response, enabling the formulation of pastes with excellent printing behavior that combine shear thinning flow and a fast recovery of their elastic properties. These inks do not contain other additives, only GO and the material of interest. As a proof of concept, we demonstrate the 3D printing of additive-free graphene oxide structures as well as polymers, ceramics, and steel. Due to its amphiphilic nature and 2D structure, graphene oxide plays multiple roles, behaving as a dispersant, viscosifier, and binder. It stabilizes suspensions of different powders, modifies the flow and viscoelasticity of materials with different chemistries, particle sizes and shapes, and binds the particles together, providing green strength for manual handling. This approach enables printing complex 3D ceramic structures using robocasting with similar properties to alternative formulations, thus demonstrating the potential of using 2D colloids in materials manufacturing.

Stereolithography process: Influence of the rheology of silica suspensions and of the medium on polymerization kinetics – Cured depth and width

Abstract UV laser stereolithography is a rather new shaping technique that makes it possible the fabrication of complex 3D ceramic structures with a high dimensional accuracy. The green part is built through layer by layer photopolymerization of a light sensitive suspension. Polymerization is thus a critical step to control in this shaping technique. Photopolymerization, with the initiation, propagation and termination reactions, involves the mobility of reactive species and is then sensible to the rheology of the media. This study investigated the influence of the rheology of suspensions of silica particles in an acrylate oligomer and of the intergranular curable organic phase on the UV polymerization. In this respect, the effects of the powder concentration, the state of dispersion and of the dilution of the reactive oligomer on polymerization, are measured. In addition, the influence of the powder loading on the cure depth and cure width, which are respectively pertinent indicators of the reactivity of the suspension and of the dimensional accuracy of the green part, is evaluated.

Design and Fabrication of a Complex LTCC-Based Reactor for the Production of Hydrogen for Portable PEM Fuel Cells

The development process for complex 3D ceramic structures in the integrated evaporator, mixer, reformer and combustor (EMRC) system for the production of hydrogen needed in portable polymer-electrolyte membrane (PEM) fuel cells is presented. Low-temperature co-fired ceramic (LTCC) technology was used to fabricate the ceramic structures of the system. The process started with the design and fabrication of each separate (stand-alone) component, which was developed and tested, and then optimized to fulfill the requirements for the integrated EMRC system. The final 3D ceramic structure consists of 45 LTCC tapes (Du Pont 951PX). The dimensions of the structure are 75 × 41 × 9 mm3 and the weight is about 73 g.

Direct Ink Writing of Three‐Dimensional Ceramic Structures

The ability to pattern ceramic materials in three dimensions (3D) is critical for structural, functional, and biomedical applications. One facile approach is direct ink writing (DIW), in which 3D structures are built layer‐by‐layer through the deposition of colloidal‐ or polymer‐based inks. This approach allows one to design and rapidly fabricate ceramic materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. In this feature article, we present both droplet‐ and filament‐based DIW techniques. We focus on the various ink designs and their corresponding rheological behavior, ink deposition mechanics, potential shapes and the toolpaths required, and representative examples of 3D ceramic structures assembled by each technique. The opportunities and challenges associated with DIW are also highlighted.