Development of Ceramic Inks for Direct Continuous Jet Printing

A ceramic ink that contains 30 vol% of zirconia in butyl acetate and 2 wt% of a commercial oligomeric dispersant is considered. The dispersion and viscosity of this ink was optimized in previous work; however, its conductivity is too low for continuous ink-jet printing. The conductivity has been improved by the addition of ethanol and ammonium nitrate, but this addition detrimentally affects the dispersion, viscosity, and surface tension of the ink. This problem has been largely overcome by reducing the amount of ceramic in the ink. The ceramic inks that have been developed are tested in a pressurized, continuous ink-jet printer, and, depending on their performance, the ink composition is modified further.     

Bimodal Ceramic Ink for Continuous Ink-Jet Printer Plasma Spraying

The issue of the low ceramic volume loading currently used in ceramic inks for direct jet-printing applications, such as plasma spraying, was addressed. Judicious additions of a second, finer zirconia powder were made to the submicrometer zirconia suspensions that are conventionally used in direct ceramic jet-printing applications. Various amounts of oligomeric dispersant were added to the ceramic suspensions. The sediment packing densities and the viscosities of the suspensions were recorded. The highest gravitational sediment-packing densities occurred when 2.5–3 wt% of dispersant was used. This corresponded well with the minimum ink viscosity of 8 mPa·s that occurs at the same level of dispersant. Bimodal ceramic ink was formulated based on these observations. The ceramic volume loading of the ink was increased by 250% (i.e., from 2 to 5 vol%) using a bimodal size distribution. This ink was injected into a plasma flame using a continuous ink-jet printer. The splats produced were comparable, although significantly smaller, to those produced by conventional plasma spraying.     

Optimization of Dispersion and Viscosity of a Ceramic Jet Printing Ink

Different amounts (0.5–10.0 wt%) of an oligomeric dispersant were added to a ceramic ink containing 30 vol% of zirconia in butyl acetate. The sediment packing densities of the resulting suspensions were measured. The viscosities of the suspensions were determined using a syringe that was adapted as a capillary viscometer suitable for the measurement of the low viscosities encountered (up to 400 mPas). The highest sediment-packing density coincided with the lowest viscosity and occurred when 1–2 wt% of dispersant, based on the ceramic, was added. Investigation of the supernatant of the suspensions by thermogravimetric analysis indicated that this amount corresponded to the highest level of adsorption of the dispersant on the ceramic. The sediment from this suspension yielded a high density on subsequent sintering.     

Microengineering of Ceramics by Direct Ink-Jet Printing

A modified piezoelectric drop-on-demand ink-jet printer was used to build 3-D ceramic structures with cavities and overhangs by direct ceramic deposition. Inks in the form of zirconia and carbon suspensions were prepared with suitable viscosities and surface tensions. The multinozzle printer was used to microengineer small components in which support structures were created from the carbon ink and the carbon was removed after pyrolysis of the organic vehicle but before sintering the zirconia. The viability of this process is discussed in terms of machine limitations and ink drying problems.     

Optimization of the ceramic ink used in Direct Ink Writing through rheological properties characterization of zirconia-based ceramic materials

Understanding and optimization the rheological properties characterization of zirconia (ZrO₂) based ceramics inks is critical for optimizing the production of Direct Ink Writing (DIW) components to achieve complex structures with similar properties as those obtained by using the traditional processing routes. In this work, ZrO₂ based ceramic materials with different yttrium contents (3 and 8 mol %) were designed and produced by DIW to determine the most suitable ceramic ink composition in terms of the rheological properties (e.g. flow curves, viscosity, loss modulus G′, storage modulus G″, etc.) to design new components. Different ceramic inks with charges up to 75 wt % were prepared and characterized. A systematic study of the feedstock, as well as the different ceramic inks, was performed to determine the optimal ceramic charge. This characterization evidences that rheological properties of zirconia based ceramic inks are influenced by the particle size and amount of ceramic content. Furthermore, the rheological study highlights that the ZrO₂ inks present a Non-Newtonian behavior depending on the ceramic content. Results revealed that the yttrium content affects the flow properties of ZrO₂ suspensions in such a way that, higher shear rate was required to make the suspensions flow at increasing the amount of powder. It was also found that the best rheological properties corresponded to 73 and 70% for the 3Y- and 8Y–ZrO₂ of ceramic charge, respectively.     

Preparation and properties of the AEO9/alcohol/alkane/water reverse microemulsion ceramic inks

Reverse microemulsion method was applied and the AEO₉/alcohol/alkane/water system was chosen to prepare ceramic inks for forming by jet-printing. The ceramic inks were prepared by reaction after mixing the zirconium oxychloride and ammonia reverse microemulsions homogeneously through vigorous stirring. The physicochemical properties of the ZrO₂ ceramic inks were systematically determined and discussed based on the requirements of the ink-jet printers available. They generally met the requirements for the drop on demand printers and were adjusted and improved by adding a small amount of alcohol and inorganic electrolyte to meet the demands for continuous ink-jet printers. It was shown that the ceramic ink with viscosity below 18 mPa s and conductivity close to 100 mS m⁻¹ was obtained after modification. Transmission electron microscope observation showed that ZrO₂ nanoparticles in the reverse microemulsion were very well dispersed and the stability of the inks was excellent. Besides, several ceramic ink compositions with bicontinuous structure were specially designed based on the phase diagram, and the changes of water-dissolving amount into the system was investigated aiming to increase the concentration of ZrO₂ ceramic ink.     

Shear bond strength tests of zirconia veneering ceramics after chipping repair

All ceramic systems are replacing the classical metal–ceramic crowns in dental practice. Zirconium dioxide (zirconia) core associated with veneering ceramic provides both good mechanical and aesthetic properties of prosthetic restorations. However, such zirconia crowns may be affected by defects of adaptation, too tight contacts in the proximal area and fissures of the ceramic veneer. The latter produces chipping; this requires a reattachment, therefore a second burning of the zirconia–ceramic interface. Such an additional procedure may affect the mechanical resistance of the ceramic veneer and the bond between the zirconia core and the ceramic veneer. The aim of this study was to evaluate the alterations of this shear bond strength (SB) between the zirconia core and the ceramic veneer, as produced by the first set of complete burning procedures and by the second correction burning of the dental restorations. Thirty-three zirconia discs were veneered with ceramic material and the SB was evaluated for each sample. Each ceramic cylinder detached from the zirconia was bonded on the core through a new layer of dentin and another burning procedure; the SB was tested again. The results of the two SB tests were compared; the statistical analysis concluded that there is an approximately 10% decrease of the resistance after the second burning. Also, the spread of the values for each test showed the high impact of the human factor on such dental restorations. In all the tests, the weakest area proved to be the interface between the zirconia core and the layered ceramics.     

Cavitation wear of structural oxide ceramics and selected composite materials

The usage of ceramic materials in the applications endangered by intensive cavitation could limit erosion phenomena. In the presented work, cavitation erosion resistance of commonly used (in structural application), oxide phases (α-alumina, tetragonal zirconia) were investigated. Additionally, the behaviour under cavitation conditions of two composite materials, based on alumina and zirconia matrices, was tested.Significant difference in cavitation wear mechanisms for alumina and tetragonal zirconia materials was observed. Alumina was degraded by removing the whole grains from the large surface subjected to cavitation. Degradation of zirconia proceeded locally, along ribbon-like paths of removed grains. Cavitation wear of composites was strongly dependent on the residual stress state in the material. Alumina/zirconia composite with compressive stresses in the matrix showed a significant improvement of cavitation resistance. The zirconia/tungsten carbide composite with relatively high level of tensile stresses in the matrix was the worst of all investigated materials.     

Computer-Aided, Single-Specimen Controlled Bending Test for Fracture-Kinetics Measurement in Ceramics

Fracture testing of ceramics by using controlled crack growth is proposed to allow study of crack-kinetics behavior under a given loading history. A computer-aided, real-time data acquisition system improves the quality of crack-growth parameters obtained in a simple, single-specimen bend test. Several ceramic materials were tested in the present study: aluminum nitride as a linear-elastic material; and alumina and yttria-stabilized zirconia, both representative of ceramics with microstructure-dependent nonlinear fracture properties. Ambiguities in the crack-growth diagrams are discussed to show the importance of accounting for crack-growth history in correctly describing nonequilibrium fracture behavior.     

Formulation and characterization of black ceramic ink for a digital ink-jet printing

Formulation of black ceramic ink and its ink-jet printability on a glass substrate were investigated. The thermal and chemical stabilities of CoFe_2-xCr_xO₄ and Ni_0.925Mn_0.075Fe_1.875-xCr_xMn_0.125O₄ black inorganic pigments were analyzed with various amounts of Cr substitutions. The ceramic ink was prepared using the pigment composition that demonstrated color stability during the high temperature glazing process with a minimal Cr substitutional amount. After the dispersion stability and rheological property were optimized, the ceramic ink was suitably jetted from a print head as a single sphere-shaped droplet without satellite droplets. To improve the printability of the ceramic ink, the glass substrate was treated with a perfluorooctyl trichlorosilane (PFTS) solution. As a result, the PFTS surface treatment increased the contact angle of the ceramic ink droplets on the glass substrate and effectively minimized the ink spreading phenomena.     

Preparation and characterization of waterborne ceramic ink with submicron-sized praseodymium-doped zirconium silicate pigment by water-based diblock polymer dispersants

Two diblock polymer dispersants (i.e., PMAA-b-AMPS and PSSS-b-GMA) were synthesized and used as water-based dispersants for dispersion and stabilization of waterborne ceramic ink with submicron-sized praseodymium-doped zirconium silicate (Pr-ZrSiO₄) pigment. The color property, dispersion, and stability of the pigment particles in aqueous suspension were determined by colorimetry, laser particle size analysis, and sedimentation test. The adsorption mechanism of carbon chains of dispersants on the particle surface was analyzed by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and electrokinetic potential measurement. Also, the viscosity, surface tension and stability of waterborne ceramic ink with the pigment particles were measured by rheometry, surface tension analysis and standing settlement. The results show that the submicron-sized pigment particles in waterborne ceramic ink show optimum dispersibility and stability at 5 wt% addition of diblock polymer dispersants PMAA-b-AMPS and PSSS-b-GMA mixed in a mass ratio of 9:1. This could be since the mixed dispersants provide the more interparticle electrostatic repulsion and steric hindrance energies due to the proper adsorption on the particle surfaces. It is indicated that adding 20 wt% of diethylene glycol monobutyl ether into the waterborne ceramic ink can effectively enhance the viscosity and reduce the surface tension, thus satisfying the applied requirements in inkjet printing. In addition, the jettability of waterborne ceramic ink on a simulated ceramic green body was also evaluated based on semi-empirical analysis.     

反相微乳液法制备陶瓷装饰用彩喷墨水

根据多种方法综合判断不同配比下Span80一Tween60／正己醇／环己烷／FeCl3水溶液的反相微乳液的相变情况，绘出反相微乳液区的拟三元相图，从而得出乳化剂／正己醇／环己烷／FeCl3水溶液的质量百分数之比为20．7：5．2：63．7：10．4是最佳组分配比。在该体系中制备出适合陶瓷装饰用彩色喷墨打印用的FeCl3红色陶瓷墨水。考察了固含量与电导率的关系，分析了影响固含量的因素。     

Zirconia microbial hollow fibre bioreactor for Escherichia coli culture

Porous ceramic hollow fibre membranes can be used as bioreactors for microbe immobilization and growth. In this work, zirconia ceramic hollow fibre membranes were synthesised from 80 nm zirconia particles using a combined phase inversion and sintering technique The resulting membranes were characterised using SEM and XRD and tested for Escherichia coli immobilization. The membrane structural evolution with controlled E. coli growth was investigated. The well-maintained E. coli growth clearly shows that not only the hollow fibre lumen but also these micro-channels inside the fibre wall can be used as micro-bioreactors. Due to the unique structure properties, the prepared ZrO₂ hollow fibre membranes can find wide applications in microbe immobilization system.     

Extrusion-based additive manufacturing of functionally graded ceramics

The Ceramic On-Demand Extrusion (CODE) process has been recently proposed for additive manufacturing of dense, strong ceramic components via extrusion with uniform layered drying. This study focuses on enabling CODE to fabricate functionally graded ceramics. A controlled volumetric flowrate for each ceramic paste was used to achieve a gradient between alumina and zirconia. A dynamic mixer was built to mix constituent ceramic pastes homogeneously. Functionally graded alumina/zirconia samples were printed, sintered, and tested to examine the capability of CODE in fabricating functionally graded components. The desired and actual material compositions were compared using energy dispersive spectroscopy. Dimensions of sintered samples were evaluated to study the deformation of functionally graded components during drying and sintering. Vickers hardness was also measured at different locations, corresponding to different material compositions. Finally, a case study was conducted to demonstrate the capability of the proposed method to build functionally graded ceramics with complex geometries.     

FEM simulations of microstructure effects on thermoelastic properties of sintered ceramics

A model was developed to simulate macroscopic material properties of polycrystalline ceramics from the material properties of the constituting phases and the microstructure. Cubic and random structures were included. The model allows a variation of volume fractions of the phases, grain size and grain boundary areas. Representative for a large number of material properties, elastic tensor, thermal conductivity, coefficient of thermal expansion and thermal stress are calculated for individual microstructures using finite element methods (FEM). Simulations focus on two types of bi-continuous ceramic composites: zirconia toughened alumina (ZTA) and a porous zirconia ceramic which was infiltrated by a spinel-glass. Microstructure of experimental samples is represented by two different model structures: a Voronoi type structure for the ZTA ceramic and a cubic structure of cubes interconnected by cylinders for the infiltrated zirconia system. A substantial impact of microstructure on macroscopic material properties and internal stress distribution is obtained. A good agreement between measured and simulated material properties was found.     

Robocasting of dense 8Y zirconia parts: Rheology,printing, and mechanical properties

Advanced ceramics with complex geometry have become indispensable in engineering applications. Due to limitations of traditional ceramic fabrication processes, additive manufacturing represents a revolution for shaping and consolidation because of its unique capabilities for increasing shape complexity and reducing waste material. Among the additive manufacturing techniques, robocasting is often considered to yield fine and dense ceramic structures with geometrically complex morphology and high strength. Within this context, it is the objective to attain dense 8 mol% yttria-stabilized zirconia (8Y-ZrO₂) by evaluating the influence of solid loading and filament orientation on the physical and mechanical properties of sintered parts. In doing so, a printable ink was developed using an inverse-thermoresponsive hydrogel. Results revealed that ceramic charges of 67.5 and 70 wt% achieved the best balance regarding density, hardness, and compression strength. Furthermore, rectilinear geometry with a filament orientation at 45º displayed higher mechanical response than 0/90º and cylindrical ones.     

陶瓷装饰用彩喷墨水研究进展

介绍了陶瓷装饰用喷墨打印技术的概念、特点及陶瓷墨水的性能要求,分析了彩色陶瓷墨水组成和制备技术的研究进展。     

Ceramic dies selection for electrical resistance sintering of metallic materials

Processing metallic powders by electrical resistance sintering requires the use of insulating ceramics dies. Selecting the appropriate ceramic material according to the electrical, thermal and mechanical properties is a need. Dies produced with several ceramic materials have been tested during the production of cemented carbide in order to check their behaviour in the process and final product properties. Tialite/mullite, zircon/mullite, zirconium phosphate based ceramic, yttria-stabilized zirconia and sialon, in most cases with modified compositions and shaping processes in order to achieve a high density, have been tested. Dry powder processing by cold isostatic pressing and furnace sintering resulted to be the better process for dies production. The effect of die properties on the produced cemented carbide, and the behaviour and life of the die during the production have been analysed. Very smooth die surface increases the number of cycles withstood during metallic parts production, because of lower extraction stresses, as checked for sialon dies. Zirconium phosphate based dies, with low thermal conductivity, show the most densified hard metal parts surface.     

Experimental Study of the Fracture Toughness of a Ceramic/Ceramic-Matrix Composite Sandwich Structure

A hybrid experimental–numerical approach has been used to measure the fracture resistance of a sandwich structure consisting of a 304 stainless steel/partially stabilized zirconia ceramic-matrix composite crack-arresting layer embedded in a partially stabilized zirconia ceramic specimen. The mode I fracture toughness increases significantly when the crack propagates from the ceramic into the ceramic-matrix composite region. The increased toughening due to the stainless steel particles is explained reasonably well by a toughening model based on processing-induced thermal residual stresses. In addition, several experimental modifications were made to the chevron-notch wedge-loaded double cantilever beam specimen to overcome numerous problems encountered in generating a precrack in the small, brittle specimens used in this study.     

红色陶瓷墨水的制备与性能研究

采用金属盐溶解法制备出一种呈色良好并能满足喷墨打印机各项理化性能要求的红色陶瓷墨水.研究墨水组成和基础釉配方两种因素对该红色陶瓷墨水呈色性能的影响;并对喷墨陶瓷片烧成后的表面进行分析,探讨其呈色机理.结果表明:制得的陶瓷墨水表面张力、粘度、pH值等理化性能均符合喷墨打印机要求,且铬锡比为0.04∶1的陶瓷墨水施于高钙透明基础釉上烧成时呈色效果最佳.