Electrophoretic deposition for fabrication of ceramic microparts

Electrophoretic deposition (EPD) is mostly used for producing moulds and layers. The present work shows the fabrication of ceramic microparts by the use of structured electrodes. As electrode structures euro coins and spinning nozzles were used. Additionally a cost effective and simple method was developed, which allows preserving the original master mould by using microstructured silicone moulds as substrate. This was enabled by coating the silicone moulds with graphite to obtain an electrically conductive surface, required for electrophoretic deposition.     

Kneading and molding of ceramic microparts by precision powder injection molding (PIM)

This paper investigates the kneading and formability of microparts made using alumina in micro‐powder injection molding. In this study, quality feedstock with uniform powder dispersion was achieved when optimum kneading process was performed. In addition, the thin microplates were successfully manufactured using a custom‐made injection machine. Shrinkage was significantly reduced in microspecimens when the mold temperature was increased to 70°C. The results of flow visualization were conformed to that of experiments in this study. A very important result for flow visualization and experiment was molten polymer filled the cavity by shortest period producing a least shrinkage in microparts. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 892–899, 2006     

Innovative fabrication of PZT pillar arrays by a colloidal approach

An innovative approach for fabricating pillar arrays for ultrasonic transducer applications is disclosed. It involves the preparation of concentrated piezoelectric lead zirconate titanate (PZT) suspensions in aqueous solutions of epoxy resin and its polymerization upon adding a polyamine based hardener. Zeta potential and rheological measurements revealed that 1 wt.% dispersant, 20 wt.% of epoxy resin and a hardener/epoxy resin ratio of 0.275 mL g⁻¹, were the optimized contents to obtain strong PZT samples with high green strength (35.21 ± 0.39 MPa). Excellent ellipsoidal and semi-circle shaped pillar arrays presenting lateral dimensions lower than 10 μm and 100 μm height were successfully achieved. The organics burning off was conducted at 500 °C for 2 h at a heating rate of 1 °C min⁻¹. Sintering was then carried out in the same heating cycle at 1200 °C for 1 h. The microstructures of the green and sintered ceramics were homogeneous and no large defects could be detected.     

Processing of thin film ceramic membranes for oxygen separation

Processing of dense and thin ceramic membrane layers for high temperature selective oxygen separation is addressed in this study. Mixed oxygen-ionic and electronic conducting perovskite oxide system based on La_0.2Sr_0.8Fe_0.8Ta_0.2O_3−δ composition is employed for processing of structural and functional layers. Special focus is aimed at obtaining thin layer and final microstructure with particle size in the sub-micron range. Thin layer deposition is performed by dip coating technique using stable colloidal suspension of perovskite particles dispersed within ethanol media. Two polymer based surfactants were screened for their effect on particle agglomeration and rheological response. By using optimum quantity of 2.5 wt.% addition of selected surfactant it is possible to obtain dense 15-60 μm thick functional layers. The thermal cycle applied resulted in final particle sizes within sub-micron range. By employing suspension with pore former it was possible to significantly increase the surface area of the functional layer.     

Short fiber reinforced 3d printed ceramic composite with shear induced alignment

This paper accounts for utilization of shear induced alignment method during ceramic stereolithography. Lateral oscillation mechanism, combined with 3d printed wall pattern, was employed to generate necessary shear to align fiber in desired direction. First, semicircular channel pattern was printed to assess the effect of difference between wall direction and oscillation direction on the fiber alignment. Then, flexural strength of ceramic matrix was tested with nickel coated carbon fiber and ceramic fiber reinforcements. The results demonstrated that the shear induced alignment further improves the flexural strength compare to randomly distributed samples. Flexural strength of aligned samples with 1.0 wt% carbon fiber loading was improved by ~90% compared to randomly orientated samples and by ~333% compared to unreinforced samples. Finally, fracture surface morphology of the flexural strength test specimens was evaluated. The main fracture mechanism was observed as fiber pull-out.     

Synthesis of nanocrystalline ytterbium-doped yttria by citrate-gel combustion method and fabrication of ceramic materials

Nanosized ytterbium doped yttria powders were prepared by citrate-gel combustion techniques. As-synthesized precursor and calcined powders were characterized for their crystalline structure, particle size and morphologies. Nanocrystalline Yb³⁺:Y₂O₃ powders with pure cubic yttria crystal structure were obtained by calcination of as-prepared precursors at 1100 °C for 3 h. Powders obtained were well dispersed with an average particle size of 60 nm. By using the obtained powders, nearly full dense Yb³⁺:Y₂O₃ ceramics were produced by vacuum sintering at 1800 °C for 12 h. The emission spectrum of the sintered ceramics under the excitation wavelength of 905 nm illustrates that there are three fluorescence peaks locating at 976 nm, 1030 nm and 1075 nm respectively, all corresponding to the ²F_5/2 → ²F_7/2 transitions of ytterbium ion.     

Binder removal via a two-stage debinding process for ceramic injection molding parts

Debinding binders in two stages is critical to maintaining the shape of injected parts; the resulting decomposition affects the strength and rigidity of a structure. This study determines the optimal debinding process on the basis of a higher binder removal rate and the production of defect-free parts. The feedstock used was a combination of alumina–zirconia powder with a binder that consists of high-density polyethylene (HDPE), paraffin wax (PW), and stearic acid (SA). During the first stage, the injected parts were immersed in an n-heptane solution at 50 °C, 60 °C, 65 °C, and 70 °C to remove PW and SA. Binder weight loss was evaluated as a function of time. In the second stage, HDPE was removed by using thermal debinding. The results show that the optimum solvent debinding process runs for 16 h at 60 °C. The weight loss of the binder reaches 41.1% and results in the formation of defect-free parts. The binders are degraded at approximately 550 °C during thermal debinding. This degradation resulted in decomposition of nearly 96.9% of the binders. Low heating rates (1 °C/min to 2 °C/min) prevent defects from forming in the injected parts.     

Influence of tapes’ properties on the laser cutting process

Ceramic tapes are used to build 3-dimensional components and microsystems in layer manufacturing. The tapes are individually printed and structured before being stacked and laminated. The structuring process of the tapes affects the maximal resolution of fluidic channels, suspended bridges and beams, which in turn determines the scale of miniaturization of the produced components. The aim of this paper is to investigate if the tape composition can be optimized to improve the cutting resolution of laser cutting, which is a very flexible tool for micromachining. Using the Siemens star pattern, the laser cutting resolution was measured for alumina green tapes of different binder compositions with different laser settings. For all tapes the resolution was better the higher the laser beam velocity. At higher velocity though, a higher number of cutting cycles is necessary to cut the tape. The laser cutting resolution depends on the binder composition, but the laser parameters must also be optimized to achieve high cutting resolution.     

Fabrication of transparent neodymium-doped yttrium aluminum garnet ceramics by high solid loading suspensions

Dense neodymium-doped yttrium aluminum garnet (Nd:YAG) transparent ceramic was obtained by slip casting and solid-state reaction. The colloidal behavior of the aqueous suspensions of neodymia, yttria, and alumina mixed powders using Dispex A as dispersant was investigated. The variation in zeta potential due to pH alteration was studied. The isoelectric point (IEP) was at pH 4.5 and 4 for the specimens with and without Dispex A, respectively. The optimal dispersion conditions were achieved for the suspensions at pH 9.6 with 0.4 wt% Dispex A. The green body prepared by slip casting was vacuum sintered from 1200 °C to 1750 °C. The grain size of the sintered body increased, and the pore size decreased with increasing sintering temperature. Pore-free Nd:YAG transparent ceramic with a grain size of 5–10 μm was obtained by sintering at 1750 °C for 10 h. The in-line transmittance of the annealed specimen reached 80.8% at 1064 nm.     

One-step fabrication of nanowire-grid polarizers using liquid-bridge-mediated nanotransfer molding

Ag nanowire-grid polarizers (NWGPs) were prepared by a one-step fabrication method, called liquid-bridge-mediated nanotransfer molding (LB-nTM). LB-nTM is a new direct nano-patterning method based on the direct transfer of various materials from a mold to a substrate via liquid layer. We fabricated NWGPs with Ag nanowire arrays (81 nm parallel lines and 119 nm spaces) on 2.5 in. transparent substrates by LB-nTM using an Ag nanoparticle solution. The maximum and minimum transmittances of the Ag NWGP at 800 nm were 80% and 10%, respectively.     

Effects of fiber length and solid loading on the properties of lightweight elastic mullite fibrous ceramics

Mullite fibrous ceramics were successfully prepared by a TBA-based gel-casting with mullite fibers as the main matrix. The effects of the fiber length and the gel-casting solid loading on the composite properties and microstructure were investigated. The 3D structure of the composite was constructed by the randomly arranged mullite fibers with the fixed crossing point, and therefore the fiber length was the most important factor influencing the microstructure of the composition. Further analyses indicate that long fibers were more suitable for the fabrication of high porosity composite. Compared with controlling the fiber length, adjusting the gel-casting solid loading was an easy method of tailoring the properties of the composite. The composite fabricated with the low solid loading and long fibers exhibited a high porosity, a low thermal conductivity, and an excellent elastic property, and can be regarded as a potential high-temperature thermal insulator applied in the industrial or aerospace thermal protection system.     

Mullite-based cellular ceramics obtained by a combination of direct foaming and reaction bonding

Mullite-based cellular ceramics were prepared via the polymer precursor route using poly(silsesquioxane) in combination with particulate alumina or alumina/aluminum mixtures. The multi-functional preceramic polymer was used as pore-forming agent by employing a self-foaming process during the polymer cross-linking step, as well as a precursor for reactive silica, one of the reagents in mullite formation. The size of filler particulates was found to strongly affect foaming of the polymer/filler mixtures, with coarser particles facilitating an improved foaming performance. Thermal conversion in air at 1600 °C resulted in the formation of cellular ceramics with high mullite contents. The partial substitution of alumina with aluminum in the initial mixtures resulted in improved mechanical properties at comparable porosities, resulting in compressive strengths of 0.3 MPa at total porosities of 93%. A correlation between thermal analysis data and crystalline phase development during the thermal treatment allowed for the clarification of processes taking place during heat treatment, yielding information for a future process optimization approaches.     

Effects of solid loading on stereolithographic additive manufactured ZrO2 ceramic: A quantitative defect study by X-ray computed tomography

In this study, the effects of solid loading on the defects and mechanical performance of stereolithographic additive manufactured ZrO₂ ceramic were studied by X-ray computed tomography (X-CT). ZrO₂ ceramics were fabricated by stereolithographic additive manufacturing from suspensions with different solid loading. The geometrical features and distribution of the defects within the ceramic were quantitatively characterized, classified, and analyzed, the formation mechanism were discussed. The correlations between the defects and mechanical properties were also investigated, and the effects of solid loading on the performance of ZrO₂ ceramic were revealed. The authors want to give a method, X-CT, for the defect characterization among stereolithographic additive manufactured ceramic.     

Reaction-bonded SiC derived from resin precursors by Stereolithography

A photo-curable resin with a high carbon yield after pyrolysis was developed in the present research. It consisted of phenolic epoxy acrylate resin, phenolic resin, triethylene glycol as pore forming agent and benzoin dimethyl ether as photoinitiator. The well-prepared mixed resin was used by Stereolithograpy to form resin prototypes. The influence of mixed resin composition on the process parameters was studied to meet the requirement for the cured thickness. Carbon preforms with open porosity of 27% and bending strength of 4.48 MPa were obtained after pyrolyzing the resin prototypes. After molten silicon infiltration at the temperature 2300 ?C, the carbon preform converted to reaction-bonded SiC. The maximum bending strength of the produced SiC samples was 127.8 ± 0.5 MPa as the pore forming agent content was 40 wt.%. Neither residual carbon nor silicon remained in the reaction-bonded SiC sample according to the XRD analysis.     

Impulse Excitation Technique IET as a non-destructive method for determining changes during the gelcasting process

Gelcasting is a good method for obtaining ceramic components with a pre-defined shape. From the point of view of the course of the ceramic casting process, a very important issue is the so-called idle time or gelation time whose measurement is usually based on determining changes in ceramic slurry viscosity by means of rheometers. However, searches are being continued to find methods which would have the least impact on the interactions between ceramic powder particles and the forming polymeric structure and would allow more time range to observe changes in gelcasting process compared to classic measurements of viscosity.In the article, based on measurements on Al₂O₃, ZrO₂ and SiC-based gelcasting systems with various water-soluble acrylic monomers, it has been demonstrated that such requirements may be fulfilled by IET (Impulse Excitation Technique).     

Fe-doped YSZ electrolyte for the fabrication of metal supported-SOFC by co-sintering

Considering Fe as sintering aid for Yttria Stabilized Zirconia (YSZ), studies have been conducted under conditions necessary for the fabrication of MS-SOFC by co-sintering. Pure and Fe doped YSZ was sintered at 1350 °C in air and in argon atmosphere and a comparative study has been performed. Structural characterizations were carried out using X-ray diffraction (XRD) techniques, while ionic conductivity was measured in air using four-probe impedance spectroscopy. It is found that Fe enhances the sintering rate of YSZ in both air and argon atmosphere. All samples sintered in argon atmosphere are characterized by better ‘sinterability’, larger lattice parameter, higher density, larger grain size and lower conductivity, as compared to samples sintered in air. Ionic conductivity is found to decrease with increase in Fe concentration for all sintered samples.     

景德镇陶瓷雕塑艺术的成型工艺初探

目前,景德镇陶艺泰斗周国桢在接受陶城报记者采访是,发出了＂在景德镇从事陶瓷雕塑艺术很难啊!＂这样的慨叹。笔者特感同身受。我国是世界雕塑艺术的大国。我国雕塑艺术渊源深厚,它作为中国工艺美术的一朵奇葩,一直绽放着耀眼的光芒。针对当今瓷都景德镇重画轻塑的有关现状,将陶瓷雕塑艺术的成型工艺进行一个重新的整理和发掘,重新探讨考量,旨在明晰史料,去伪存真,一来为继承传统精华做好初步的资料存储。二来是在兼容并蓄前人智慧的基础上发挥自身特点,在进一步启迪陶瓷雕塑艺术的更新与发展上做一些自己的思考。     

Advantages of soft X-ray absorption over TEM-EELS for solid carbon studies--a comparative study on diesel soot with EELS and NEXAFS

Diesel soot was investigated with electron energy loss spectroscopy (EELS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The EELS spectra were obtained in connection with transmission electron microscopy studies, whereas the NEXAFS were obtained from a scanning transmission X-ray microscope (STXM) and from a conventional NEXAFS beamline at two synchrotron facilities. The X-ray absorption spectra show molecular species, aliphatics, such as carboxyl, and C-H bonds, which are not visible in EELS spectra of the same material. In particular, EELS fails to detect surface-functional groups, which can be detected with NEXAFS. Since numerous works on molecular carbon structure determined with TEM-EELS have been published, it is possible that these results have to be reassessed.