LCD-SLA 3D printing of BaTiO3 piezoelectric ceramics

Stereolithography-based 3D printing is a promising method to produce complex shapes from piezoceramic materials. In this study, LCD-SLA 3D printing was used to create lead-free piezoceramics based on barium titanate (BaTiO₃, BT). Three types of BT powders (micron, submicron and nanoscale) were tested in LCD-SLA 3D printing, and a technique for the preparation of a ceramic slurry suitable for LCD-SLA printing has been developed. Using TGA-DSC analysis, the thermal debinding parameters to obtain crack-free samples were determined, followed by further sintering and the study of the piezoelectric properties (ε_r = 1965, d₃₃ = 200 pC/N, tan = 1,7 %). The results of the study demonstrate high potential for the production of complex piezoceramic elements that can be used in aviation, in particular, aviation radio equipment; in the marine industry for transceiver modules of hydroacoustic antennas; and in the nuclear industry for pressure control sensors in the steam–water path.     

Additive manufacturing of borosilicate glass via stereolithography

Recent surge in additive manufacturing efforts demonstrate stereolithography as a promising technique for fabricating glass materials due to the high speed and scalability of the process. However, little efforts have been devoted to manufacture borosilicate glass by the stereolithographic process. One of the challenges is that its relatively low softening temperatures could interfere with the thermal post-printing process and introduce poor fidelity and structure instability. Here, we report on the first demonstration of stereolithographic manufacturing of cerium-doped (Ce-doped) (<10%) and undoped borosilicate glass which was enabled by a multi-step post thermal processing. The optical properties of the printed glass depend on thermal processing parameters (temperature, time, and environment) and can be readily tuned and optimized for a wide range of applications. The printed amorphous glass shows good structural stability with band gap of 3 eV, Urbach energy of 0.75 eV and refractive index of 2.14 for 8% Ce-doped glass, respectively. These results indicate Ce-doped glass fabricated by stereolithography is suitable for scintillator applications and that additive manufacturing could be promising for borosilicate glass fabrication.     

Influence of irradiation parameters on the polymerization of ceramic reactive suspensions for stereolithography

Stereolithography is an additive manufacturing process which makes it possible to fabricate useful complex 3D ceramic parts, with a high dimensional resolution and a good surface finish. Stereolithography is based on the selective UV polymerization of a reactive system consisting in a dispersion of ceramic particles in a curable monomer/oligomer resin. In order to reach a homogeneous polymerization in the green part, and to limit the risk of cracking and/or deformation during subsequent stages of debinding and sintering due to internal stresses, the influence of various fabrication parameters (laser power, scanning speed, number of irradiations) on the degree of polymerization was investigated. In addition, the impact of the irradiation of the subsequent upper layers onto the previously deposited and irradiated layers was evaluated. The degree of conversion was determined by Fourier Transform Infrared Spectroscopy (FTIR). Raman spectroscopy was also used and a brief comparison between these two methods is given.     

Fabrication of bioactive glass scaffolds by stereolithography: Influence of particle size and surfactant concentration

For decades, bioactive glass (BAG) has been utilized as a competent bone substitute owing to its intrinsic properties, such as outstanding biocompatibility and bioresorbability. Stereolithography (SL) is an additive manufacturing technology used to produce highly accurate three-dimensional BAG-based bone substitutes. However, the preparation of BAG-based SL resin is always a challenge, especially because of the inevitable sedimentation of BAG particles. In this study, BAG particles with different sizes were prepared by dry grinding (BAG_dry, greater particle size) and wet grinding (BAG_wet, finer particle size). Then, BAG_dry or BAG_wet SL resins with various amounts of surfactant were analyzed. The sedimentation rate for BAG powder increased with increasing particle size but decreased with increasing amounts of surfactant added to the resin. BAG_wet SL resins had a longer shelf life, so printing could still be finished after 14 days, whereas BAG_dry SL resins were no longer useable after 5 days. However, the BAG particle size did not affect the printing accuracy or scaffold strength. According to our results, BAG-based SL resin fabricated with BAG_wet (particle size <1.6 μm) and 5 wt% surfactant exhibited better resistance to sedimentation.     

Fabrication of SiC ceramic architectures using stereolithography combined with precursor infiltration and pyrolysis

Stereolithography based additive manufacturing provides a new route to produce ceramic architectures with complex geometries. In this study, 3D structured SiC ceramic architectures were fabricated by stereolithography based additive manufacturing combined with precursor infiltration and pyrolysis (PIP). Firstly, photosensitive SiC slurry was prepared. Then, stereolithography was conducted to fabricate complex-shaped green SiC parts. Polymer burn-out was subsequently performed, and porous SiC preforms were produced. After that, precursor infiltration and pyrolysis was used to improve the density and strength. Finally, 3D-structured SiC ceramic architectures with high accuracy and quality were obtained. It is believed that this study can give some fundamental understanding for the additive manufacturing of SiC ceramic structures.     

Fabrication and properties of diatomite ceramics with hierarchical pores based on direct stereolithography

Porous diatomite ceramics with hierarchical pores and high apparent porosity (50.29–56%) were successfully fabricated via direct stereolithography. The pre-ball-milling time, dispersant type and dispersant concentration were systematically investigated to prepare diatomite pastes with high solid loading, low viscosity and a self-supporting effect. The results showed that a pre-ball-milling time of 24 h was more suitable to prepare diatomite pastes with high solid loading, and Span80 at 2 wt% was the optimal dispersant to obtain 40 vol% diatomite paste with a low viscosity and a self-supporting effect. To restrain the formation of defects, a heating rate as low as 0.2 °C/min was allowed to control the pyrolysis rate in the multistage debinding process. At sintering temperatures ranging from 900 °C to 1000 °C, porous diatomite ceramics exhibited a typical bimodal porosity, high apparent porosity and great flexural strength.     

Fabrication of bulk piezoelectric and dielectric BaTiO3 ceramics using paste extrusion 3D printing technique

A simple and facile method was developed to fabricate functional bulk barium titanate (BaTiO₃, BT) ceramics using the paste extrusion 3D printing technique. The BT ceramic is a lead-free ferroelectric material widely used for various applications in sensors, energy storage, and harvesting. There are several traditional methods (eg, tape casting) to process bulk BT ceramics but they have disadvantages such as difficult handing without shape deformation, demolding, complex geometric shapes, expansive molds, etc. In this research, we utilized the paste extrusion 3D printing technique to overcome the traditional issues and developed printable ceramic suspensions containing BT ceramic powder, polyvinylidene fluoride (PVDF), N,N-dimethylformamide (DMF) through simple mixing method and chemical formulation. This PVDF solution erformed multiple roles of binder, plasticizer, and dispersant for excellent manufacturability while providing high volume percent and density of the final bulk ceramic. Based on empirical data, it was found that the maximum binder ratio with good viscosity and retention for desired geometry is 1:8.8, while the maximum BT content is 35.45 vol% (77.01 wt%) in order to achieve maximum density of 3.93 g/cm³ (65.3%) for 3D printed BT ceramic. Among different sintering temperatures, it was observed that the sintered BT ceramic at 1400°C had highest grain growth and tetragonality which affected high performing piezoelectric and dielectric properties, 200 pC/N and 4730 at 10³ Hz respectively. This paste extrusion 3D printing technique and simple synthesis method for ceramic suspensions are expected to enable rapid massive production, customization, design flexibility of the bulk piezoelectric and dielectric devices for next generation technology.     

Cure behavior of colorful ZrO2 suspensions during Digital light processing (DLP) based stereolithography process

In this study, the light absorption of the pure ZrO₂ and three types of colorful ZrO₂ mixtures were investigated. It was found that the absorbance of colored ZrO₂ powder increases with the colorant content, and the yellow-colored powder has the strongest absorbance at the wavelength of 405 nm compared with the other two types of colored ZrO₂ powder. The cure behavior investigation on the ceramic suspensions of the above four types of ZrO₂ powders during DLP process shows that as the colorant content increases, the cure depth and excess cure width both decrease due to the ceramic absorbance. The cure depth of colored suspensions is linear with logarithm of incident energy, consistent with Beer-Lambert model, while the further research into the cure width shows that the excess cure width increases nonlinearly with logarithm of incident energy, which is inconsistent with Quasi-Beer-Lambert model. Additionally, colorful ZrO₂ accessories were successfully fabricated.     

Curing performance and print accuracy of oxidized SiC ceramic via vat photopolymerization

To improve the print quality of SiC ceramic, an amorphous SiO₂ layer is prepared on the surface of SiC by oxidation (SiC@SiO₂). The changes in curing depth and width direction of SiC@SiO₂ curing sheets with different degrees of oxidation were investigated. The results showed that curing depth increased while curing width decreased with an increasing degree of oxidation. The edge morphologies of SiC@SiO₂ curing sheets changed from serration to flat shape with increasing degree of oxidation, and uneven overcuring regions appear in the width direction. Additionally, 12% SiC@SiO₂ ceramic was fabricated via vat photopolymerization combined with reaction sintering. The dimensional deviation ratio of printed green bodies increased with decreasing printed line width and pore diameter. The minimum printed line width of 329 μm and pore diameter of 483 μm with good print quality were obtained. Furthermore, the flexural strength of 225.4 MPa and bulk density of 2.77 g cm⁻³ for sintered 12% SiC@SiO₂ parts were obtained.     

Inter-particle interactions of alumina powders in UV-curable suspensions for DLP stereolithography and its effect on rheology,solid loading,and self-leveling behavior

For the UV-curable alumina suspensions used in digital light processing (DLP) stereolithography, optimizing the dispersant type is important for achieving low viscosity, high solid loading, and remarkable self-leveling behavior. However, the inter-particle interactions in UV-curable alumina suspensions dispersed using different dispersants are overlooked. Herein, the effect of inter-particle interactions on rheology, solid loading, and self-leveling behavior of UV-curable alumina suspensions was systematically investigated. Three different commercial dispersants were used: oleic acid (OA), alkane-acrylic phosphate ester (PM1590), and copolymer dispersant (BYK111). After dispersing, BYK111 endowed alumina powders with thicker adsorption polymer layer to provide stronger steric repulsion force and facilitated better wetting of alumina powers in the photocurable resin, resulting in a reduced network structure degree, which decreased the viscosity (1.04 Pa s at 30 s^?1); homogeneous packing of alumina powders, which enhanced the maximum solid loading (55 vol%); and inhibition of particle flocculation, which facilitated the spontaneous spreading of suspension.     

Optical properties of multi-stacked BaTiO3/SrTiO3 thin films synthesized via chemical method

In this work, the BaTiO₃ and SrTiO₃ thin films as well as BaTiO₃/SrTiO₃ lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO₃, but cubic structure for SrTiO₃. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO₃ samples and from 4.13 eV to 3.80 eV for SrTiO₃ samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO₃, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO₃ and SrTiO₃. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO₃ sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied.     

Near-visible stereolithography of a low shrinkage cationic/free-radical photopolymer blend and its nanocomposite

In this work, a newly prepared cationic/free-radical photopolymer, which consists of two epoxies and a tetrafunctional acrylate, is presented for the first time for a visible light stereolithography (SL), showing the advantages of both cationic and free-radical resins. An onium salt, commonly used as a cationic UV initiator, and a photosensitizer make the blend suitable for a near-visible (405 nm) SL. An increase in the polymerization rate and a drop in the induction period are observed for the newly prepared cationic/free-radical blend, compared with either only cationic systems or free-radical resins. This suggests that the combination of cationic and free-radical polymerizations in a single resin has a positive synergistic effect. The addition of silica nanoparticles to the blend provides a reinforcing and toughening effect. Indeed, the resin loaded with silica shows a 31% increase in the elastic modulus, compared with the unfilled resin. Regarding the values of tensile strength and elongation at break, they, respectively, grow by 47 and 15%, when the nanocomposite resin is compared with the neat resin. A very low volumetric shrinkage of 0.7% and a remarkable printing quality of objects obtained with this new photopolymer will enable the 3D printing of microrobots, bioengineering microdevices, and sensors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48333.     

Fabrication of zirconia all-ceramic crown via DLP-based stereolithography

Zirconia ceramics have shown a wide applicable prospect in dental prosthetics because it possesses excellent mechanical performance and biocompatibility. The rheological behavior and curing properties of zirconia stereolithography slurry were studied, as well as the microstructure of the green, pyrolyzed, and sintered body. Variquat CC-42 NS was proved to be effective for zirconia powder dispersing in photocurable resin (SP-RC700). The curing characteristic of slurry showed that the depth of penetration tended to increase with the solid loading. Finally, the zirconia all-ceramic crowns were fabricated via DLP-based stereolithography printer. Results showed that the particles were evenly distributed in the cured resin matrix without obvious agglomeration, and the interlayered structure disappeared after binder burnout. The sample with a major crystalline phase of tetragonal zirconia and a porosity of 10(1)% were obtained after sintering at 1550°C.     

Properties regulation of SiC ceramics prepared via stereolithography combined with reactive melt infiltration techniques

Stereolithography(SLA) combined with reactive melt infiltration (RMI) is an effective way to fabricate silicon carbide(SiC) ceramic components with complex shapes and high precision. The purpose of this paper is to increase the content of SiC in the sintered body and improve the properties of SiC ceramics prepared by SLA/RMI technologies by the impregnation of the precursor of carbon source after debinding. The effects of the concentration of phenolic resin solution on the strength of sintered body were studied. The results show that this method can reduce the coefficient of thermal expansion and improve the thermal conductivity of the final body. At the same time, when the concentration of phenolic resin solution is 40 wt%, the final body obtained the best comprehensive properties. The value of bulk density, flexural strength and elastic modulus were 2.89 g/cm³, 244.17 ± 5.13 MPa and 402.39 GPa, respectively. This strategy provides a promising prospect for the preparation of space optical mirrors with complex shapes and high strength by the SLA/RMI method.     

Grain size effect on piezoelectric and ferroelectric properties of BaTiO3 ceramics

A series of dense barium titanate (BaTiO₃, BTO) ceramics with different grain sizes (GS) were prepared by two-step sintering method. The effect of GS on piezoelectric coefficient (d₃₃) and planar electromechanical coupling factor (k_p) displayed a trend similar to that on relative permittivity (ɛ′). The values of d₃₃, k_p, and ɛ′ increased significantly with decreasing GS, reaching maximum values (ɛ′ = 6079, d₃₃ = 519 pC/N and k_p = 39.5%) at approximately 1 μm, and then decreased rapidly with further decreasing GS. The results revealed that high-performance BTO ceramics could be effectively prepared by controlling GS. Polarization–electric field hysteresis loops and temperature dependence of ɛ′ were also investigated.     

Enhancement in magnetic,piezoelectric and ferroelectric properties on substitution of titanium by iron in barium calcium titanate ceramics

Lead free polycrystalline ceramics with compositional formula Ba_0.90Ca_0.10Ti_1–3x/4Fe_xO₃ (BCT), (x=0.000, 0.005, 0.010, 0.015 and 0.020) were prepared by the solid state reaction method. The effect of substitution of Fe³⁺ ion at Ti-site on the ferroelectric and piezoelectric properties of BCT ceramics was studied. Remanant polarisation (P_r) and saturation polarisation (P_s) show an increasing trend while the reverse trend was observed for coercive field (E_c) with Fe³⁺ substitution. The values of the piezoelectric charge coefficient (d₃₃) and piezoelectric coupling coefficient (k_p) was found to increase with increase in Fe content. Ceramic sample with x=0.02 was found to have a maximum value of d₃₃ (130 pC/N) and k_p (29%). The prepared ceramic samples show magnetic properties as confirmed by recorded MH loops. On substitution of Fe³⁺ ions, the ferroelectric BCT ceramics show clear transformation of the diamagnetic nature of BCT ceramics to weak ferromagnetism.     

Effect of light attenuation on polymerization of ceramic suspensions for stereolithography

Weak bonding strength between interlayers can seriously affect the quality of ceramic parts manufactured by stereolithography. Therefore, the possibility of using chemical bonds to strengthen the adhesion within these parts and the extent to which may be effective are of interest. Thus, a multi-exposure model was built to illustrate the state of this interface. The secondary conversion of a cured layer defined as conversion rate increment caused by decayed ultraviolet (UV) light in a subsequent exposure was selected to represent the extent of a chemical bond. The level of UV light attenuation occurred when travelling through a suspension layer was determined using the Attenuation Law. When decayed light illuminated a cured layer, it underwent further photopolymerization, which was detected by temperature change. The secondary conversion was affected by parameters including the incident energy dose and the propagating length. Optimization of these parameters helped to achieve higher chemical bond ratio.     

Preparation and characterization of single-crystalline barium strontium titanate nanocubes via solvothermal method

Single-crystalline barium strontium titanate nanocubes were synthesized via the solvothermal synthesis using TiCl₄-BaCl₂ as precursors in the mixed solvent of water-ethanol-ethylene glycol monomethyl ether. The products were characterized by XRD, TEM and XRF. The well-dispersed barium strontium titanate nanocubes with narrow particle size distribution may be attained by this simple solvothermal method and the particle morphology and size of powders are dependent on Sr/(Sr + Ba) mole ratio in reactants.     

Rheological behaviour of BaZrO3 suspensions in non-aqueous media

The colloidal behaviour of concentrated non-aqueous suspensions of barium zirconate is investigated. Optimum dispersing conditions are investigated for organic suspensions prepared with different solvent systems: methylethylketone (MEK)/ethanol, trichloroethylene (TCE)/ethanol, a methylisobutylketone (MIBK)/methylethylketone/cyclohexanone (CHN) and pure ethanol. Stabilisation of the suspensions is achieved by using two different dispersants: ester phosphate (EPH) and Hypermer KD-6. Rheological studies have been made in order to determine the optimum of each dispersant concentration as a function of the solvent systems. The best stabilisation of 30 vol.% suspensions is obtained by using EtOH with 3 wt.% KD-6 and TCE/EtOH with 1 wt.% EPH. Zeta potential studies show that the use of dispersants increases the positive surface potential on the particles. The zeta potential values increasing from +10 mV in the absence of EPH to +42 mV with 1.0 wt.% EPH and to +33 mV with KD-6. These results suggest that electrostatic repulsion plays an important role on the stability of these organic suspensions. Stabilised suspensions were slip cast in plaster molds and green densities higher than 55% of the theoretical density was obtained.     

Fabrication strategy of complicated Al2O3-Si3N4 functionally graded materials by stereolithography 3D printing

For multi-ceramic materials based on the stereolithography (SL) principle, a 3D printing strategy was developed, and then an Al₂O₃-Si₃N₄ functionally graded material (FGM) ceramic part was fabricated using this strategy. Six groups of mixtures, with a Si₃N₄ content gradient of 20 vol% and a certain bimodal particle size distribution, were prepared using UV-curable pastes. A modified formula was proposed to evaluate the relationship between the actual minimum voidage of mixtures and the viscosities of their corresponding pastes. The viscosity of each paste was controlled using the prediction formula and optimization of dispersants. To design theprinting layer thickness, a mathematical relationship was established between Si₃N₄ content and curing depth of paste. The Al₂O₃-Si₃N₄ green body without deformation was printed using optimized parameters such as a layer thickness of 40 μm and a paste viscosity of ∼13,000 mPa·s. Finally, using debinding and sintering, denseparts having a complicated shape were obtained.