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This study aims to enhance the mechanical properties of additively manufactured polymer parts by incorporating ceramic particles (SiO2) into diluted urethane methacrylate (UDMA) photopolymer resin using digital light processing (DLP) technology. The resulting PUMA/SiO2 composites, featuring varying SiO2 contents (16.7, 28.5, and 37.5 wt%) and processed under different conditions, underwent a comprehensive series of mechanical, thermal, and chemical tests. Hardness tests showed that composites with 37.5 wt% SiO2 demonstrated superior hardness with low sensitivity to processing conditions. Bending tests indicated that elevated vat temperatures tended to degrade flexural properties, yet this degradation was mitigated in the case of the 37.5 wt% SiO2 composition. Tensile tests revealed a transition from viscoelastic to linear elastic behaviors with increasing SiO2 content, with high tensile strength sustained at low vat temperatures (<35 °C) when the SiO2 content exceeded 28.5 wt%. Thermogravimetric analysis supported these findings, indicating that increased SiO2 content ensured a more uniform dispersion, enhancing mechanical properties consequently. Thermal tests showed augmented thermal conductivity and diffusivity with reduced specific heat in SiO2-inclusive composites. This study provides guidelines for optimal PUMA/SiO2 composite utilization that emphasizes high SiO2 content and low vat temperature, offering comprehensive insights for high-performance ceramic composite fabrication in functional applications.
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Due to the high hardness and brittleness of ceramic materials, conventional cutting methods result in poor quality and machining difficulties. Additive manufacturing has also been tried in various ways, but it has many limitations. This study aims to propose a system to monitor surface defects that occur during the printing process based on high-viscosity composite resin that maximizes ceramic powder content in real time using image processing and convolutional neural network (CNN) algorithms. To do so, defects mainly observed on the surface were classified into four types by form: pore, minor, critical, and error, and the effect of each defect on the printed structure was tested. In order to improve the classification efficiency and accuracy of normal and defective states, preprocessing of images obtained based on cropping, dimensionality reduction, and RGB pixel standardization was performed. After training and testing the preprocessed images based on the DenseNet algorithm, a high classification accuracy of 98% was obtained. Additionally, for pore and minor defects, experiments confirmed that the defect surfaces can be improved through the reblading process. Therefore, this study presented a defect detection system as well as a feedback system for process modifications based on classified defects.
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Photopolymerization-based ceramic 3D printing shows unmatched superiority in fabricating high-performance ceramic parts compared with the conventional preparation technology. Nevertheless, it remains challenging to achieve efficient 3D printing due to the light scattering in photosensitive ceramic slurries, increasing the width of solidification and reducing the curing depth during photocuring. Herein, we report an efficient ceramic 3D printing approach based on curcuminoid dye-sensitized photopolymerization under green light-emitting diode (LED). For deep penetration and minimal light scattering, ceramic bodies with good performance can be produced from a ceramic slurry with curcuminoid dye by using a green LED-digital light processing (DLP) 3D printer. Curcuminoid dye was found to provide the ability to transfer electrons to photoinitiator and play a role in improving the accuracy of the entire 3D printing process. The proposed approach here provides a viable solution toward efficient ceramic additive manufacturing by green LED-DLP-3D printing.
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Hydrogen is expected to play an important role in the near future in the transition to a net-zero economy. Therefore, the development of new in situ and real-time analytical tools able to quantify hydrogen at high temperatures is required for future applications. Potentiometric sensors based on perovskite-structured solid-state electrolytes can be a good option for H2 monitoring. Nevertheless, the geometry of the sensor should be designed according to the specific necessities of each technological field. Conventional shaping processes need several iterations of green shaping and machining to achieve a good result. In contrast, 3D printing methods stand out from conventional ones since they simplify the creation of prototypes, reducing the cost and the number of iterations needed for the obtainment of the final design. In the present work, BaCe0.6Zr0.3Y0.1O3-α (BCZY) was used as a proton-conducting electrolyte for potentiometric sensors construction. Two different shapes were tested for the sensors' electrolyte: pellets (BCZY-Pellet) and crucibles (BCZY-Crucible). Ceramics were shaped using extrusion-based 3D printing. Finally, parameters, such as sensitivity, response time, recovery time and the limit of detection and accuracy, were evaluated for both types of sensors (BCZY-Pellet and BCZY-Crucible) at 500 °C.
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Ceramic polymer composite slurries were prepared using nano- and micro-sized Al2O3 in order to analyze rheological properties, sedimentation, and curing behavior. Slurries with different Al2O3 particle sizes were prepared with varying concentrations of photoinitiator, and subjected to different exposure times to prepare a printing object. All slurries exhibit shear-thinning behavior, and the viscosity increases with decreasing Al2O3 particle size. The 100 nm Al2O3 slurry is confirmed to be more sol-like, while the 500 nm and 2 µm Al2O3 slurries have a gel-like structure. As the Al2O3 particle size increases, a thick sedimentation layer forms due to rapid settling, but as the distance between particles increases, the UV light scattering reduces, and the curing rate increases. The exposure time range viable for printing, and the dimension conformity of the printed specimen with the design file, is improved by increasing the Al2O3 particle size. In the case of 500 nm and 2 µm Al2O3 slurries, the maximum heat flow, curing enthalpy, and conversion rate are high with respect to photoinitiator concentration, in the order of 1.0 > 0.1 > 3.0 wt.%. When the photoinitiator concentration exceeds 1 wt.%, it appears to affect the reactivity of the slurry.
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Fabrication of 3D-printed ceramic parts with high complexity and high spatial resolution often demands low wall thickness as well as high stiffness at the green state, whereas printing simpler geometries may tolerate thicker, more compliant walls with the advantage of a rapid binder-burn-out and sintering process. In this work, the influence of the binder system on the thermophysical properties of 3D-printed stabilized zirconia ceramics was investigated. Samples were fabricated with the lithography-based ceramic manufacturing (LCM) technology using two different photosensitive ceramic suspensions (LithaCon 3Y230 and LithaCon 3Y210), with the same ZrO2 powder. A significant difference in stiffness in the green state (~3 MPa vs. ~32 MPa for LithaCon 3Y230 and LithaCon 3Y210, respectively) was measured, associated with a rather loose or a linked network formed in the binder due to photopolymerization. Both materials reached high relative densities, that is, >99%, exhibiting a homogeneous fine-grained microstructure. No significant differences on the coefficient of thermal expansion (11.18 ppm/K vs. 11.17 ppm/K) or Young's modulus (207 GPa vs. 205 GPa) were measured, thus demonstrating the potential of tailoring binder systems to achieve the required accuracy in 3D-printed parts, without detrimental effects on material's microstructure and thermophysical properties at the sintered state.
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Osteochondral regeneration remains a vital problem in clinical situations affecting both bone and cartilage tissues due to the low regeneration ability of cartilage tissue. Additionally, the simultaneous regeneration of bone and cartilage is difficult to attain due to their dissimilar nature. Thus, fabricating a single scaffold for both bone and cartilage regeneration remains challenging. Biomaterials are frequently employed to promote tissue restoration, but they still cannot replicate the structure of native tissue. This study aims to create a single biomaterial that could be used to regenerate both bone and cartilage. This study focuses on synthesizing calcium-deficient apatite (CDA) with the gradual addition of manganese. The phase stability and the effect of heat treatment on manganese-doped CDA were studied using X-ray diffraction (XRD) and Rietveld refinement. The obtained powders were tested for their 3-dimensional (3D) printing ability by fabricating cuboidal 3D structures. The 3D printed scaffolds were examined for external topography using field-emission scanning electron microscopy (FE-SEM) and were subjected to compression testing. In vitro biocompatibility and differentiation studies were performed to access their biocompatibility and differentiation capabilities. Reverse transcription-quantitative PCR (RT-qPCR) analysis was done to determine the gene expression of bone- and cartilage-specific markers. Mn helps in stabilizing the ß-TCP phase beyond its sintering temperature without being degraded to α-TCP. Mn addition in CDA improves the compressive strength of the fabricated scaffolds while keeping them biocompatible. The concentrations of Mn in the CDA ceramic were found to influence the differentiation behavior of MSCs in the fabricated scaffolds. Mn-doped CDA is a promising candidate to be used as a substitute material for bone, cartilage, and osteochondral defects to facilitate repair and regeneration via endochondral differentiation. 3D printing can assist in the fabrication of a multifunctional single-unit scaffold with varied Mn concentrations, which might be able to generate the two tissues in situ in an osteochondral defect.
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Achieving a viable process for three-dimensional (3D) printing of ceramics is a sought-after goal in a wide range of fields including electronics and sensors for harsh environments, microelectromechanical devices, energy storage materials, and structural materials, among others. Low laser absorption of ceramic powders renders available additive manufacturing (AM) technologies for metals not suitable for ceramics. Polymer solutions that can be converted to ceramics (preceramic polymers) offer a unique opportunity to 3D-print ceramics; however, due to the low viscosity of these polymers, so far, their 3D printing has only been possible by combining them with specialized light-sensitive agents and subsequently cross-linking them layer by layer by rastering an optical beam. The slow rate, lack of scalability to large specimens, and specialized chemistry requirements of this optical process are fundamental limitations. Here, we demonstrate 3D printing of ceramics enabled by dispensing the preceramic polymer at the tip of a moving nozzle into a gel that can reversibly switch between fluid and solid states, and subsequently thermally cross-linking the entire printed part "at-once" while still inside the same gel. The solid gel, which is composed of mineral oil and silica nanoparticles, converts to fluid at the tip of the moving nozzle, allows the polymer solution to be dispensed, and quickly returns to a solid state to maintain the geometry of the printed polymer both during printing and the subsequent high-temperature (160 °C) cross-linking. We retrieve the cross-linked part from the gel and convert it to ceramic by high-temperature pyrolysis. This scalable process opens up new opportunities for low-cost and high-speed production of complex three-dimensional ceramic parts and will be widely used for high temperature and corrosive environment applications, including electronics and sensors, microelectromechanical systems, energy and structural applications.