Chemical solution deposition of functional ceramic coatings using ink-jet printing

This paper discusses the development of environmentally-friendly precursor inks suited for ink-jet printing of functional ceramic coatings. We synthesized superconducting materials, SrTiO3 thin films for coated conductor applications and transparent TiO2 photocatalytic coatings. Here, we discuss all aspects of ink formulation, including the stabilization of metal ions, nanoparticle inks or combination of both. This demands the investigation and determination of the inks rheological parameters. Ceramic nanoparticles are often incorporated in our inks to decrease thermal processing temperatures (e.g., TiO2 or YSZ coatings...) or enhance the properties of the functional ceramic coating (e.g., pinning centres in superconducting coatings). These ceramic nanoparticles (ZrO2, HfO2, TiO2...) are synthesized through methods based on microwave heating from aqueous and/or organic solutions. With that, we aim at developing smart and environmentally friendly processes that require lower energy input

Fast, microwave-assisted synthesis of monodisperse HfO₂ nanoparticles

A conventional solvothermal synthesis was compared to a microwave-assisted method for the synthesis of HfO2 nanoparticles. In a microwave, the reaction could be completed in 3 h, compared to 3 days in an autoclave. In the microwave synthesis, the ensemble of particles was found to have a better size dispersion and a smaller average size (4 nm). The reaction mechanism was investigated and proof for an ether elimination process was provided. Post-synthetic modification with dopamine or dodecanoic acid permitted the suspension of the synthesized particles in both polar and apolar solvents, which is an advantage for further processing

Digitally printed superconducting coatings and patterns

The most suitable way to implement superconducting materials in large scale applications is as wires. To overcome the brittle nature of ceramic high-temperature superconductors and to increase the overall performance of the wire, a coated conductor design was developed. In this thesis, we focus on the development of ink-jet processing as a new technique for chemical solution deposition of Y(Gd)Ba2Cu3O7-δ [Y(Gd)BCO] coatings and patterns. For this, cheap and fluorine-free metal salts are used as starting products, which were dissolved in water. The research is mainly focused on the precursor’s chemical stability and printability. The addition of complexing agents is necessary to increase the total metal concentration. Still, an optimisation of the pH value is obligatory for a long shelf life of the precursor solution. A 0.185 mol L-1 YBCO ink with a viscosity of 4.77 mPa s and a surface tension of 67.9 mN m-1 was finally obtained. The printability of the solution is predicted using the ratio: Oh-1= Re/We1/2. With a value of 7.37, the ink’s properties fall within the printing value: 1< Oh-1 <10. After tuning the driving waveform, proper ink-jetting behaviour was visualised using a strobe assisted camera. The optimised deposition parameters resulted in a 350 nm thick YBCO coating, grown on SrTiO3, showing preferential c-axis orientation. This layer exhibits a critical current of 0.67 MA cm-2 at 77 K in self-field. After changing the deposition parameter, high-resolution patterns could be deposited on several substrates. The shape and dimensions of printed YBCO tracks were determined using optical microscopy and noncontact profilometry, showing 100 to 500 nm thick and 40 to 220 µm wide YBCO tracks

Ink-jet printing of aqueous inks for single-layer deposition of Al-doped ZnO thin films

In this article, Al-doped ZnO thin films deposited by a one single-layer approach are studied. An aqueous precursor solution was prepared for the deposition of Al-doped ZnO thin film via ink-jet printing. The physical properties of the ink were studied in detail by rheology measurement and drop visualization. The wetting of the ink with the substrate was studied by the use of wetting envelopes. A single layer of the ink was deposited on the substrate and fully processed. The thin films were studied by X-ray diffraction, scanning electron microscopy, resistivity measurements, and optical transmission measurements. The optimal dopant concentration was set at 3 at.%, which resulted in thin films with a resistivity of 2.54 c cm and an optical transmission larger than 90% over the visible range of the electromagnetic spectrum

The Use of a Water-Based Sol Gel System for the Production of CeO2 and La2Zr2O7 Buffer Layers (in Coated Conductors)

Thin ceramic buffer layers of CeO2 and La2Zr2O7 were produced by a sol-gel process based on metal acetates, organic complexing agents and water. Thermal analysis and thermomicroscopy have learnt us something about the chemical characteristics of the precursor solution. Single or multiple layers of the ceramic buffer layer were deposited on Ni-5at%W textured tape using the dip-coating technique. The desired (001) orientation was obtained after a high temperature (1050°C) heat treatment under forming gas (Ar-5%H2). It was shown that changing the thickness of the layers from 10 nm to 100 nm by controlling the dip-coating parameters, plays a crucial role in obtaining the (00l) texture. In manufacturing high quality buffer layers for coated conductors, it is of major importance to create a strong texture throughout the layer. By means of XRD and pole figures, the bulk orientation was studied. Special attention was given to the texture of the top layer using RHEED. The microstructure of the films was further studied by SEM, AFM, FIB and HRTEM