Effects of powder properties on the 3D printing of BaTiO3 ceramic resins by stereolithography

Stereolithography is a layer-by-layer building fabrication technique enabling production of advanced ceramic 3D shapes that are not achievable by other methods. Critical parameters of stereolithography are associated with the preparation of a ceramic resin exhibiting suitable rheological and optical properties, as well as tunable curing property to achieve the desired level of resolution of complex 3D parts. However, tailoring the cure depth for each layer is challenging for functional ceramics due to their high refractive index giving increased light scattering. Here, the stereolithography 3D printing of BaTiO3 ceramic resins is investigated by employing a desktop 3D printer (λ = 405 nm) and a commercial base resin. The effects of two BaTiO3 powders with different size distributions (one micro-sized powder with grains in the range 1–20 μm, and one agglomerated nano-sized powder in the range 60–100 nm), on the viscosity and curing characteristics of the ceramic resins were investigated. It is shown that the nano-sized powder resulted in increased viscosity, increased scattering, and reduced cure depth compared to the micro-sized BaTiO3 ceramic resin. In general, the cure depth decreased with increasing ceramic loading. Successful prints were obtained for an overcuring of at least 40% between layers to assure good adherence between the layers. The printing properties of the ceramic resins from both powders were suitable for printing green parts with 50 μm layer thickness.publishedVersio

High-Rate Epitaxial Growth of Silicon Using Electron Beam Evaporation at High Temperatures

This paper describes the high-rate (~1.5 μm/min) growth of Si films on Si supporting substrates with (100) crystallographic orientation at 600 °C, 800 °C, and 1000 °C in a vacuum environment of ~1 × 10−5 mbar using electron beam (e-beam) evaporation. The microstructure, crystallinity, and conductivity of such films were investigated. It was established that fully crystalline (Raman spectroscopy, EBSD) and stress-free epi-Si layers with a thickness of approximately 50 µm can be fabricated at 1000 °C, while at 600 °C and 800 °C, some poly-Si inclusions were observed using Raman spectroscopy. Hall effect measurements showed that epi-Si layers deposited at 1000 °C had resistivity, carrier concentration, and mobility comparable to those obtained for c-Si wafers fabricated through ingot growth and wafering using the same solar grade Si feedstock used for the e-beam depositions. The dislocation densities were determined to be ∼2 × 107 cm−2 and ∼5 × 106 cm−2 at 800 and 1000 °C, respectively, using Secco etch. The results highlight the potential of e-beam evaporation as a promising and cost-effective alternative to conventional CVD for the growth of epi-Si layers and, potentially, epi-Si wafers. Some of the remaining technical challenges of this deposition technology are briefly indicated and discussed.publishedVersio

Aqueous sol-gel processing of transparent conducting rare earth doped indium tin oxide

Transparent conducting oxides (TCOs) demonstrate optical transparency in the visible region of the electromagnetic spectrum combined with near-metallic electrical conductivity. Owing to this unique combination of properties, TCOs have found numerous technological applications. Among the TCOs, indium tin oxide (ITO) is widely recognised as having the best combination of transparency and conductivity. The aim of this work was to develop an aqueous sol-gel process to prepare ITO and also doped ITO materials. The motivation was to make a simple, inexpensive and environmentally friendly process, while retaining the ability to prepare excellent materials. Wet chemical deposition techniques have many advantages compared to commercial physical deposition techniques, like sputtering, such as cost, simplicity and readily control of homogeneity and composition. Moreover, by using water instead of organic solvents, the process has the potential to be environmentally friendly and less expensive and thereby more relevant for up-scaling to industrial levels. The challenges related to the frequently used In- or Sn-chloride precursors in soft chemistry synthesis were circumvented by using indium nitrate and tin acetate as precursors. The aqueous sol-gel process developed in this work was demonstrated to give phase-pure In2O3 and ITO thin films as well as nano-crystalline powders. A gel was formed after evaporation of the solvent, and the amorphous nature of the gel demonstrated homogeneous cation distribution. Calcination of the gel caused decomposition and crystallisation to the desired oxide material. The chemistry of the sol-gel process was investigated by varying the initial cation concentration and the organic complexing agents. These parameters were demonstrated to influence on the decomposition/crystallisation of the gel during thermal treatment and the phase purity of the final oxide materials. The presence of hydroxyl groups appeared to be important regarding complexing and immobilisation of the cations, and the possible formation of the metastable rhombohedral polymorph of In2O3 could be controlled by the choice of the organic additives. ITO thin films were successfully deposited on substrates by spin coating using the aqueous sol-gel route. The ITO thin films were demonstrated to have excellent optical properties, such as a high transmittance in the visible region and band gap similar to reported values. The electrical properties of the as-deposited films were also quite promising. Particularly after heat treatment at high temperatures and annealing in reducing atmospheres, the specific resistance was excellent compared to ITO thin films prepared by other sol-gel methods and comparable to the best reported values for ITO. In situ conductivity measurements confirmed the effect of the annealing atmosphere on the conductivity of the films. It has been known for decades that it is difficult to fabricate polycrystalline In2O3 and ITO with high density. Nevertheless, the sintering of ITO is industrially important due to an industrial demand for dense ITO-targets used in sputtering. A comprehensive sintering study of the nano-crystalline, phase-pure powders of In2O3 and ITO was performed. Particularly the phase purity of the powder was important with respect to previous similar sintering studies. The mechanisms governing the sintering, with particular focus on the mass transport mechanisms, the effect of the tin doping and the sintering atmosphere were investigated. Mass transport below 1200 °C was given particular consideration since this temperature region has received very little attention in the literature. Hence, the present findings are also relevant for mass transport during heat treatment of ITO thin films, which is performed at significantly lower temperatures than the sintering of sputtering targets. One of the main motivations for working with ITO was the possibility to dope ITO with rare earth elements (REEs), thereby enabling the combination of the excellent properties of the ITO host with the characteristic luminescence of the REEs. A thorough investigation of the equilibrium phase composition and solid solubility of neodymium, europium and terbium in In2O3 and ITO at 1400 °C was performed. It was confirmed that the cubic In2O3 crystal structure is a promising host for REEs, as expected from the crystal structure of the pure rare earth oxides. The solubility was shown to decrease with increasing size mismatch between the ionic size of the dopant and the host. Phase-pure materials of In2O3 and ITO doped with REEs were successfully prepared in form of nano-crystalline powders and thin films. In this form the solubility limit for the REEs could be circumvented by synthesis of metastable materials. The effect of the REE-doping on the optical and electrical properties of the two host materials was investigated by various spectroscopic techniques and electrical conductivity and thermopower measurements. Neither the conductivity nor the transparency of ITO thin films was significantly deteriorated by the REE-doping. Finally, strong emissions at around 611 nm were observed for Eu-doped In2O3, demonstrating the possibility of obtaining photoluminescence in a TCO host material

Modified Pechini Synthesis of Oxide Powders and Thin Films

The modified Pechini method has become one of the most popular synthesis methods for complex oxide materials due to its simplicity and versatility. The method can be applied to synthesize nanocrystalline powders, bulk materials, as well as oxide thin films. Here, we present a comprehensive review of the method with focus on the chemistry through the three stages of the process: preparation of stable aqueous solution, polyesterification to form a solid polymeric resin, and finally decomposition/combustion of the resin to form an amorphous oxide followed by crystallization of the desired oxide phase. The review include several examples of important technical oxide materials where the method has been successfully been applied to prepare oxide powders and bulk or thin films.acceptedVersio

Modified Pechini Synthesis of Oxide Powders and Thin Films

The modified Pechini method has become one of the most popular synthesis methods for complex oxide materials due to its simplicity and versatility. The method can be applied to synthesize nanocrystalline powders, bulk materials, as well as oxide thin films. Here, we present a comprehensive review of the method with focus on the chemistry through the three stages of the process: preparation of stable aqueous solution, polyesterification to form a solid polymeric resin, and finally decomposition/combustion of the resin to form an amorphous oxide followed by crystallization of the desired oxide phase. The review include several examples of important technical oxide materials where the method has been successfully been applied to prepare oxide powders and bulk or thin films

Optimisation of chemical solution deposition of Indium Tin Oxide thin films

An environmentally friendly aqueous sol–gel process has been optimised to deposit indium tin oxide (ITO) thin films, aiming to improve the film properties and reduce the deposition costs. It was demonstrated how parameters such as cation concentration and viscosity could be applied to modify the physical properties of the sol and thereby reduce the need for multiple coatings to yield films with sufficient conductivity. The conductivity of the thin films was enhanced by adjusting the heat treatment temperature and atmosphere. Both increasing the heat treatment temperature of the films from 530 to 800 °C and annealing in reducing atmosphere significantly improved the electrical conductivity, and conductivities close to the state of the art sputtered ITO films were obtained. A pronounced decreased conductivity was observed after exposing the thin films to air and the thermal reduction and ageing of the film was studied by in situ conductivity measurements

Solid solubility of rare earth elements (Nd, Eu, Tb) in In2−xSnxO3 – effect on electrical conductivity and optical properties

Wide band-gap semiconductors doped with luminescent rare earth elements (REEs) have attracted recent interest due to their unique optical properties. Here we report on the synthesis of the transparent conducting oxides (TCOs) indium oxide and indium tin oxide (ITO) doped with neodymium, europium and terbium. The solid solubility in the systems was investigated and isothermal phase diagrams at 1400 °C were proposed. The solubility of the REEs in In2O3 is mainly determined by the size of the rare earth dopant, while in ITO the solid solubility was reduced due to a strong tendency of the tin and REE co-dopants to form a pyrochlore phase. The effect of the REE-doping on the conductivity of the host was determined and optical activity of the REE dopants were investigated in selected host materials. The conductivity of sintered materials of REE-doped In2O3 was significantly reduced, even at small doping concentrations, due to a decrease in carrier mobility. The same decrease in mobility was not observed in thin films of the material processed at lower temperatures. Strong emissions at around 611 nm were observed for Eu-doped In2O3, demonstrating the possibility of obtaining photoluminescence in a TCO host, while no emissions was observed for Nd- and Tb-doping

Palladium (Pd) membranes as key enabling technology for precombustion CO2 capture and hydrogen production

Palladium (Pd) membranes are a promising enabling technology for power generation and hydrogen production with CO2 capture. SINTEF has developed and patented a flexible technology to produce Pd-alloy membranes that significantly improves flux and thereby reduces material costs. Reinertsen AS and SINTEF aim to demonstrate the Pd membrane technology for H2 separation on a side stream of the Statoil Methanol Plant at Tjeldbergodden, Norway. In the present article, we present the upscaling of the membrane manufacturing process, together with the membrane module and skid design and construction.publishedVersio

Palladium (Pd) membranes as key enabling technology for precombustion CO2 capture and hydrogen production

Palladium (Pd) membranes are a promising enabling technology for power generation and hydrogen production with CO2 capture. SINTEF has developed and patented a flexible technology to produce Pd-alloy membranes that significantly improves flux and thereby reduces material costs. Reinertsen AS and SINTEF aim to demonstrate the Pd membrane technology for H2 separation on a side stream of the Statoil Methanol Plant at Tjeldbergodden, Norway. In the present article, we present the upscaling of the membrane manufacturing process, together with the membrane module and skid design and construction.publishedVersio

Palladium (Pd) membranes as key enabling technology for precombustion CO2 capture and hydrogen production

Palladium (Pd) membranes are a promising enabling technology for power generation and hydrogen production with CO2 capture. SINTEF has developed and patented a flexible technology to produce Pd-alloy membranes that significantly improves flux and thereby reduces material costs. Reinertsen AS and SINTEF aim to demonstrate the Pd membrane technology for H2 separation on a side stream of the Statoil Methanol Plant at Tjeldbergodden, Norway. In the present article, we present the upscaling of the membrane manufacturing process, together with the membrane module and skid design and construction