3D-Printing of zirconia dental prostheses

Abstract in proceedings of the Fourth International Congress of CiiEM: Health, Well-Being and Ageing in the 21st Century, held at Egas Moniz’ University Campus in Monte de Caparica, Almada, from 3–5 June 2019.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.info:eu-repo/semantics/publishedVersio

Preparation of ceramic microlectromechanical systems (MEMS) using a gelcasting consolidation technique

The present work focuses the preparation and characterisation of suspensions withthree different powders, ferrite, PZT and alumina, for the fabrication of 3D-shapedceramic structures by gelcasting. The characterization of powders by particle size ispresented together with the preparation and characterization of the resultingsuspensions by rheological and zeta potential measurements. Using 1-wt% of DispexA-40 is possible to prepare concentrated PZT and ferrite suspensions to beconsolidated by gelcasting. The workability of gelcasting technique is demonstratedon a range of component geometries suitable for MEMS applications

Aqueous Flow Reactor and Vapour-Assisted Synthesis of Aluminium Dicarboxylate Metal-Organic Frameworks with Tuneable Water Sorption Properties

Energy-efficient indoors temperature and humidity control can be realised by using the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium-based metal-organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium-based MOFs: (1) in aqueous solutions using a continuous-flow reactor and (2) through the vapour-assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers to obtain polymorph materials with tuneable water sorption properties. The synthesis conditions determine the crystal structure and either the MIL-53 or MIL-68 type structure with square-grid or kagome-grid topology, respectively, is formed. Fine-tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation and room climatisation applications

Fostering the properties of Zr0.8Sn0.2TiO4 (ZST) ceramics via freeze granulation without sintering additives

The present paper reports the overall benefits of freeze granulation for enhancing the properties of zirconium tin titanate Zr0.8Sn0.2TiO4 (ZST) ceramics in the total absence of sintering additives. The ZST powder was synthesized by solid state reaction and attrition milled in ethanol for 10 h. This starting non-granulated powder (NG-ZST), without and with 1 wt% ZnO as sintering additive, was used to consolidate green bodies by dry pressing. The pure ZST powder was also dispersed in aqueous media to obtain stable suspensions with high solid loadings. Free flowing spherical homogeneous granules were prepared by freeze granulation and used to consolidate ZST green bodies by dry pressing (FG-ZST). The effects of processing variables and sintering temperature (1300-1450 degrees C) on densification and on the structural, mechanical and electrical properties of ZST ceramics were systematically investigated. Our study clearly reveals the superior properties of FG-ZST ceramics, which derive from an enhanced sintering behaviour associated with the absence of sintering additives

Fabrication of ceramic microneedles - The role of specific interactions between processing additives and the surface of oxide particles in Epoxy Gel Casting

Epoxy Gel Casting (EGC) was recently coined to designate a setting mechanism based on the in situ polymerization of epoxy resins dissolved in the aqueous dispersion media of ceramic powder suspensions upon adding suitable amine-based crosslinking agents. The specific interactions between the surface of the powder particles and the processing additives are likely to determine different partitions of the crosslinking species, dissolved in the bulk solution, or adsorbed at the surface of the particles, and affect the EGC process. The present work aims at evaluating the influence of surface chemistry on the extent of the specific interactions at the solid/liquid interface and how it affects the polymerization kinetics and the properties of ceramic green bodies consolidated by EGC. Three different ceramic oxides (alumina, zirconia and fused silica) having similar particle size distributions were used. Stable colloidal suspensions with 45 vol.% solids were prepared by dispersing the powders in aqueous solutions containing a fixed amount of a common dispersant and various dissolved amounts of an epoxy resin. Zeta potential, theological measurements and calorimetry were used to assess the specific interactions and their effects on the consolidation kinetics upon adding a polyamine hardener, and on the final properties of consolidated parts. With the isoelectric point of the naked particle surface decreasing, there were noticeable decreases in gelation time, shrinkage, green density, and flexural strength of the green ceramic body's properties. An interaction model is proposed to explain the observed differences. The potential of EGC to consolidate ceramic microneedles cast in soft rubber moulds was demonstrated. (C) 2016 Elsevier Ltd. All rights reserved

Zeta potential and rheological behaviour of aqueous kaolin suspensions dispersed with sodium hexametaphosphate

Deflocculants adsorb on particles' surfaces, increase the repulsive forces among them, reducing viscosity, while the soluble salts have an opposite effect on viscosity. This work studies the influence of deflocculant and salt concentration on zeta potential and correlates the results with rheological measurements

Influence of chemical composition on sintering ability of ZTA ceramics consolidated from freeze dried granules

Dense zirconia-toughened alumina (ZTA) ceramic composites with ZrO2 = 0, 5, 10, 15, 20, 30, 60 and 100 wt.% have been prepared by sintering green compacts obtained by dry powder pressing of freeze dried granules consisting of α-alumina and a yttria partially stabilized zirconia (YPSZ) at various temperatures ranging from 1450 to 1650 °C for 1-2 h. The characteristics of sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes principle, Vickers indentation method and by 3-point bend test. Characterization results revealed that adding YPSZ increased the 3-point bend (flexural) strength, fracture toughness and homogeneity of the microstructure, but slightly decreased the hardness and the sintering ability of alumina. A 20 wt.% YPSZ was sufficient to increase the fracture toughness and flexural strength of specimens sintered for 2 h at 1600 °C from 2.5 to 4.6 MPa m1/2 and 150 to 400 MPa, respectively. The XRD results revealed that there is no solid-solution formation between zirconia and alumina constituents of ZTA ceramic composites upon sintering

Microfabrication of high aspect ratio BST pillar arrays by epoxy gel casting from aqueous suspensions with added water soluble epoxy resin

The present paper reports on the successful fabrication of micro-sized pillar arrays of Ba0.6Sr0.4TiO3 (BST) electroceramics via cost effective epoxy gel casting (EGC) consolidation method based on the in situ polymerization of aqueous suspensions with added water soluble epoxy resin. The synthesized BST solid solution powder was fine milled and surface protected against hydrolysis to avoid its degradation in the aqueous environment. The micro patterning process was divided in the following steps: (i) production of high quality SU-8 master moulds by photolithography and of the respective negative replicas in PDMS (soft mould); (ii) casting of stable high solid loading BST suspensions in the soft moulds with added setting agents followed by de-moulding, drying and sintering. Patterned array of hexagonal shaped pillars with 320 mu m of height and side length similar to 40 mu m were obtained with smooth side wall features along height. Various structural, mechanical and electrical properties of BST material after sintering were also measured to demonstrate the feasibility of the proposed aqueous processing route. (C) 2014 Elsevier Ltd. All rights reserved

Structural, mechanical and dielectric properties of Ba0.6Sr0.4TiO3—The benefits of a colloidal processing approach

This paper reports on the benefits gathered from a proper colloidal dispersion/deagglomeration of a Ba0.6Sr0.4TiO3 (BST) powder in water followed by spraying the aqueous suspension against liquid nitrogen to obtain homogeneous granules. The density of green compacts derived from the freeze granulated (FG) powder was compared with that of compacts prepared from the same starting BST powder but non-granulated (NG). The sintering ability of the greens and the density, mechanical and functional properties of the obtained ceramics sintered at various temperatures properties were shown to be strongly enhanced by the freeze granulation step. Freeze granulation enabled decreasing the optimal sintering temperature for 50 °C, and enhanced all the relevant measured properties, which showed a good correlation with sintered density. Maximum values of dielectric constant (εrmax=5087) and dielectric loss (tan δ = 0.009) were measured at the phase transition temperature (Tc = −3 °C) and at a constant frequency of 10 kHz for the FG BST ceramics sintered at 1250 °C, which also showed a flatter temperature-dependent dielectric profile