Showing papers in "International Journal of Applied Ceramic Technology in 2011"

Integrally Cored Ceramic Mold Fabricated by Ceramic Stereolithography

Abstract: Ceramic stereolithography (SLA) was used to fabricate a ceramic investment casting mold with the integral core within a ceramic mold shell, produced in a single patternless construction from refractory-grade fused silica. The SLA build material was a photopolymerizable suspension of 60vol% fused silica dispersed in a monomer solution based on 1,6-hexanediol diacrylate. The mold had 1047 layers, each 100mm thick. Green body dimensions before sintering were approximately 0.7% smaller than the design within the plane of the layers, and approximately 0.3% larger than the design perpendicular to the layers. The sintering shrinkage was 10.770.2% in both directions.

Grain Size‐Dependent Hardness of Transparent Magnesium Aluminate Spinel

Abstract: Most different transparent grades of sintered and single crystalline spinel were investigated by Vickers and Knoop tests with loads of 1 kg (HK1, HV1) and of 10 kg (HV10). The hardness ranking of all samples was HK1

Studies of Rare‐Earth‐Doped BiFeO3 Ceramics

Abstract: Rare-earth (RE) (Eu3+, Gd3+, Tb3+, and Dy3+)-doped BiFeO3 (BFO) ceramics were prepared by a modified solid-state reaction method, which adopted higher heating as well as cooling rates during sintering process. All the fabricated samples showed ferroelectric hysteresis loops with a remnant polarization of 21–35 μC/cm2. A piezoelectric coefficient (d33) of ∼48 pC/N was obtained and this value was showed to be composition independent. The pyroelectric properties of our samples were studied as a function of temperature. Generally, the pyroelectric coefficient slightly decreased with temperature, and this is attributed to the increase of electrical conduction at higher temperatures. Among the different doped BFO ceramics, Gd-doped samples exhibited the largest pyroelectric coefficient of 146 μC/m2K at room temperature. For the magnetic properties, slim hysteresis loop with remnant magnetizations of 0.016–0.044 emu/g were obtained in all the doped samples. Our results revealed that the RE-doped BFO ceramics posses an improvement in both the electrical and magnetic properties. On the basis of our studies, we demonstrate that RE-doped BFO is a potential candidate for magnetoelectric device applications.

Regenerative Performance of the NASA Symmetrical Solid Oxide Fuel Cell Design

Abstract: The NASA Glenn Research Center is developing both a novel cell design (BSC) and a novel ceramic fabrication technique to produce fuel cells predicted to exceed a specific power density of 1.0 kW/kg. The NASA Glenn cell design has taken a completely different approach among planar designs by removing the metal interconnect and returning to the use of a thin, doped LaCrO3 interconnect. The cell is structurally symmetrical. Both electrodes support the thin electrolyte and contain micro-channels for gas flow-- a geometry referred to as a bi-electrode supported cell or BSC. The cell characteristics have been demonstrated under both SOFC and SOE conditions. Electrolysis tests verify that this cell design operates at very high electrochemical voltage efficiencies (EVE) and high H2O conversion percentages, even at the low flow rates predicted for closed loop systems encountered in unmanned aerial vehicle (UAV) applications. For UAVs the volume, weight and the efficiency are critical as they determine the size of the water tank, the solar panel size, and other system requirements. For UAVs, regenerative solid oxide fuel cell stacks (RSOFC) use solar panels during daylight to generate power for electrolysis and then operate in fuel cell mode during the night to power the UAV and electronics. Recent studies, performed by NASA for a more electric commercial aircraft, evaluated SOFCs for auxiliary power units (APUs). System studies were also conducted for regenerative RSOFC systems. One common requirement for aerospace SOFCs and RSOFCs, determined independently in each application study, was the need for high specific power density and volume density, on the order of 1.0 kW/kg and greater than 1.0 kW/L. Until recently the best reported performance for SOFCs was 0.2 kW/kg or less for stacks. NASA Glenn is working to prototype the light weight, low volume BSC design for such high specific power aerospace applications.

Influence of Residual Monomer on Cracking in Ceramics Fabricated by Stereolithography

Abstract: The conventional build methods for polymeric stereolithography intentionally leave small regions of uncured monomer. We show that for ceramic stereolithography, these regions of uncured monomer are associated with macrocracking during heating. The cracking is caused by strains arising from the thermal polymerization of residual monomer while heating. Cracking can be avoided by changing the build style to eliminate the residual monomer.

Development of Ceramic Supports Derived from Low-Cost Raw Materials for Membrane Applications and its Optimization Based on Sintering Temperature

Abstract: In this work, a macroporous ceramic support was fabricated using inexpensive clays available in India by uniaxial compaction technique. Green ceramic supports were developed by mixing of kaolin, pyrophyllite, feldspar, ballclay, quartz, and calcium carbonate of desired composition with polyvinyl alcohol as a binder and were sintered at different temperatures (850°C, 900°C, 950°C, and 1000°C). The raw materials and sintered supports were characterized using thermogravimetric analysis, particle size distribution (PSD), X-ray diffraction, and scanning electron micrograph analysis. The effect of sintering temperature on porosity, mean pore size, pore size distribution, shrinkage, flexural strength, and pure water permeability was investigated. Chemical stability tests for the sintered supports were conducted with 20 wt% of H2SO4, HCl, and NaOH solutions and the supports showed good chemical resistance. The porosity of the sintered supports was in the range of 41–46%. It was observed that the average pore diameter and flexural strength of the supports increases with increase in sintering temperature. Based on these results, the support sintered at 950°C (porosity=44%, mechanical strength=28 MPa, and average pore diameter=1.01 μm) was considered as the optimum support for membrane applications. Solvent permeation studies were conducted for 950°C sintered support and the results confirmed that the support was hydrophobic in nature.

Hexagonal Boron Nitride as a New Ultraviolet Luminescent Material and Its Application

Abstract: Hexagonal boron nitride (hBN), which is conventionally used as one of the best-known heat-resistant materials due to its high thermal and chemical stability, has recently been found as a highly luminous material in the far-ultraviolet (FUV) region. This paper reviews the recent studies of hBN growth, optical properties, and device application development. In the case of highly pure crystals of hBN grown by the solvent growth method, the electronic excitation states near the band gap are governed by optically allowed exciton effects, which originate from the Jahn–Teller effect on the exciton series. The excitonic luminescence bands are utilized for an FUV plane light-emitting device excited by field emitters to take advantage of the highly luminous character.

Low‐Temperature Sintering and Microwave Dielectric Properties of Li2ATi3O8 (A=Mg, Zn) Ceramics

Abstract: New temperature-stable low-loss ceramic–glass composites based on Li2ATi3O8 (A=Mg, Zn) ceramics have been prepared by the conventional solid-state ceramic route. The effect of lithium magnesium zinc borosilicate (LMZBS) glass addition on the sinterability, phase purity, microstructure, and microwave dielectric properties of Li2MgTi3O8 (LMT) and Li2ZnTi3O8 (LZT) dielectric ceramics has been investigated for low-temperature co-fired ceramic applications. The LMT+3 wt% of LMZBS glass sintered at 925°C/4 h has ɛr=24.5, Qu×f=44,000 GHz, and τf=(+)0.2 ppm/°C. Addition of LZT ceramics with 3 wt% of LMZBS glass sintered at 900°C/4 h has ɛr=23.2, Qu×f=31,300 GHz, and τf=(−)15.6 ppm/°C. The LMT and LZT ceramic–glass composites do not react with the commonly used silver electrode material.

Anisotropy of the Mechanical and Thermoelectric Properties of Hot‐Pressed Single‐Layer and Multilayer Thick Ca3Co4O9 Ceramics

Abstract: Ca3Co4O9 (349) thermoelectric (TE) ceramics were prepared by hot-pressing (HP) process under various stress levels up to 30 MPa. Microstructure investigations have revealed strong enhancements of the bulk density and the texture strength, and a remarkable decrease of the in-plane grain boundary density as the HP stress, σ, is increased. The mechanical properties obtained from nanoindentation and three-point bending tests, and the TE properties were correlated to the microstructure. The influence of the HP stress level on these properties was examined in the parallel (c) and perpendicular (ab) directions to the pressing axis. Hardness (Hab and Hc ) and elastic modulus (Eab and Ec ) values were shown to increase remarkably with the HP stress level and the anisotropy ratio between out-of-plane and in-plane resistivity values too. As ρab was considerably reduced and the Seebeck coefficient, Sab, remains constant when σ is raised, the power factor, PFab, was greatly improved for the higher stress values. and PFab900 K are 64 and 595 μW.m−1.K−2, respectively, for the HP samples processed under 30 MPa. Thick specimens usable in practical devices were obtained by HP stacked single layers. Their microstructure was investigated and correlated to the TE and mechanical properties.

Microstructure Contact Studies for Skutterudite Thermoelectric Devices

Abstract: The skutterudite/electrode thermoelectric joints were fabricated with the insertion of Ti foil by spark plasma sintering. The interfacial microstructure and reliability of joints were studied during thermal duration test. A multilayer structure, which was composed of intermetallic compounds, was observed at the CoSb3/Ti interface after thermal aging of 20 days. The interfacial reactions and diffusion path between CoSb3 and Ti were discussed. The contact resistance of CoSb3/electrode junction was measured through four-probe method and the thermal contact resistance was calculated based on multilayer mode measurement. Effects of the contact resistivity on the performance of CoSb3-based device were discussed.

Sputtering and Pulsed Laser Deposition for Near‐ and Mid‐Infrared Applications: A Comparative Study of Ge25Sb10S65 and Ge25Sb10Se65 Amorphous Thin Films

Abstract: The deposition of Ge25Sb10S65 and Ge25Sb10Se65 amorphous chalcogenide thin films was performed by radio-frequency magnetron sputtering and pulsed laser deposition technique. The deposited layers were characterized by studying their morphology, topography, chemical composition, structure, and optical functions permitting a direct comparison of two deposition methods for obtaining attractive amorphous chalcogenide films. Reactive ion etching was then used to pattern rib/ridge waveguides in sulfide and selenide films with low surface roughness, vertical sidewalls, and reasonable etching rate. Optical losses of fabricated waveguides were measured at 1550 nm with values better than 1 dB/cm obtained for sulfide/selenide films deposited by both techniques.

Laser Micromachining of Zirconia (Y-TZP) Ceramics in the Picosecond Regime and the Impact on Material Strength

Abstract: (accessed July 10, 2009).The capabilities of a high average power picosecond laser are assessed for micromachining yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in its hard state. Laser machining of this material presents an attractive alternative to conventional machining techniques when precision customized parts are required due to the difficulty in machining Y-TZP in its hard state. Compared with previous nanosecond work the picosecond laser enables similar micromachining to be carried out at the same rate but with a superior surface finish and with no evidence of surface cracking. Strength measurements have been carried out using a four-point bend test rig and confirm that the improvement in surface quality translates to higher strength in machined components.

Electrical Resistance as a Nondestructive Evaluation Technique for SiC/SiC Ceramic Matrix Composites Under Creep‐Rupture Loading

Abstract: SiC/SiC ceramic matrix composites under creep-rupture loading accumulate damage by means of local matrix cracks that typically form near a stress concentration, such as a 90° fiber tow or a large matrix pore, and grow over time. Such damage is difficult to detect through conventional techniques. This study demonstrates that electrical resistance is a viable method of monitoring and inspecting damage in SiC/SiC composites at high temperature. Both interrupted and uninterrupted creep-rupture experiments were performed at 1315°C and 110 MPa with in situ resistance measurements. A linear relationship was found between resistance and cumulative crack depth.

Microstructural Characterization of a Cf/ZrC Composite Manufactured by Reactive Melt Infiltration

Abstract: The microstructure of a carbon fiber-reinforced ZrC matrix composite, Cf/ZrC, manufactured by reactive melt infiltration (RMI) was characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, electron backscattering diffraction (EBSD), and transmission electron microscopy. Characterization results revealed a heterogeneous microstructure typical of composites processed by RMI. The major features that were observed include ZrC single crystals in the matrix, Zr–ZrC eutectic phase, and the fiber/matrix interface. The hardness and modulus of ZrC single crystals and the eutectic phase were determined through micro- and nanoindentation. EBSD studies proved that ZrC matrix grains distribute randomly. Fiber bundle areas were examined and revealed poor intrabundle infiltration. Closer inspection of the ZrC crystals revealed the presence of never-before reported inclusions. Analysis of the inclusions revealed their phase composition and a microstructural formation mechanism outlines their development during processing. The phase composition was proved to be nanosized α-Zr with round or needle-like shape. There are two plausible mechanisms for the formation of the inclusion. One is the trapping mechanism that some liquid zirconium from grain boundaries of ZrC grains may become trapped inside ZrC particles during their coalescence growth. The other is precipitation mechanism that α-Zr may precipitate inside some ZrC grains during formation of Zr–ZrC eutectic phase or ZrC grains with deficient carbon under cooling.

A Novel Production Method for Porous Sound‐Absorbing Ceramic Material for High‐Temperature Applications

Abstract: A new processing technique combining the freeze gelation process with sacrificial templating is used to create self-supporting ceramic sound absorption structures for high-temperature applications. The process leads to near-net shape components with an open-pored structure. Expanded perlite, acting as melting filler, increases the porosity up to 74%. The resulting properties of the microstructure such as porosity and airflow resistance are presented. Acoustical measurements in an impedance tube show high sound absorption coefficients up to 0.7. The measured sound absorption is compared with a mathematical simulation. In summary, this process allows the fabrication of temperature-resistant ceramic sound absorbers.

Preparation and Application of High Near-Infrared Reflective Green Pigment for Ceramic Tile Roofs

Abstract: Complex inorganic green pigments having a high near-infrared (NIR) solar reflectance were synthesized. Chromium oxide (Cr2O3) was used as the host component with mixtures of TiO2, Al2O3, and V2O5 as the guest components. TiO2, Al2O3, and V2O5 were mixed into 39 different compositions. It was found that a sample, denoted by S9, with the composition of Cr2O3, TiO2, Al2O3, and V2O5 are 80, 4, 14, and 2 wt%, respectively, gives a maximum NIR solar reflectance of 82.8% compared with 69.6% of a commercially available cool pigment powder. The comparison study on the effectiveness of the synthesized pigment and a commercial pigment on ceramic glaze and sprayed on ceramic tile roofs show that the new powder has given a better result by keeping the tested room about 2°C cooler. It can be concluded that the new formulated green pigment is a highly thermal effective as an NIR reflective roof coating.

Molten Salt Synthesis and Characterization of Titanium Carbide-Coated Graphite Flakes for Refractory Castable Applications

Abstract: Titanium carbide (TiC)-coated graphite flakes were prepared using the low-temperature molten salt synthesis technique. Titanium (Ti) particles were mixed with graphite in a mass ratio (Ti/C) between 1/5 and 3/5, and reacted in alkali chloride salts at 650–950°C for 4–8 h. The TiC formation reaction was complete in KCl or the KCl–LiCl eutectic salt after 8 h at 850°C, but not in LiCl or NaCl, indicating that the former were more effective than the latter in accelerating the TiC coating formation. Although various Ti/C ratios were used, the TiC formation reaction was complete in all samples heated for 4 h at 950°C, indicating that the amounts/thickness of TiC coatings could be readily tailored for future castable applications. TiC coatings prepared in KCl or the KCl–LiCl eutectic salt (after 4 h at 950°C or 8 h at 850°C) were of high quality: crack free, homogeneous, and comprising nanosized TiC particles. The coating synthesis process is believed to be dominated by the “template-growth” mechanism.

Annealing of Thermally Sprayed Ti2AlC Coatings

Abstract: Phase transformations during annealing of coatings sprayed with the High Velocity Oxy-Fuel technique using Ti2AlC powder have been investigated by in-situ x-ray diffraction. The asdeposited coating ...

Solvent-Assisted Laser Drilling of Silicon Carbide

Abstract: Laser drilling of single crystalline silicon carbide (SiC) wafer in air, under water, and under methanol with a 355 nm wavelength laser is investigated and compared. Among these different media, laser drilling of SiC under a solvent, methanol, is found to produce holes with a relatively cleaner and smoother surface. Ablated particle redeposition at the entrance and exit of the holes is minimized. Minimum oxide (i.e., silicon dioxide) or heat-affected zones are observed and the surface finish inside the holes is much smoother and more uniform as compared with those drilled in air and under water. The improvement of drilling quality can be attributed to the relatively lower boiling temperature and better wettability of the solvents, which enhance the effects of cooling (thermal damage free) and ablated particle cleaning during laser drilling. It is found that the quality of laser drilling of SiC varied with the thickness of solvent layer, that is, water and methanol. A solvent layer of 500 μm is suggested to be used for the enhancement of laser ablation rate and quality.

Novel Low Loss, Low Permittivity Glass–Ceramic Composites for LTCC Applications

Abstract: New low-temperature sinterable dielectric materials based on Li2CaSiO4 (LCS) ceramic has been developed. The LCS ceramics were prepared by solid-state ceramic route. The calcination and sintering temperatures of LCS were optimized as 800°C/4 h and 1000°C/2 h, respectively, for the best density and dielectric properties. The dielectric properties of the ceramic were measured in the radio frequency by parallel plate capacitor method and in the microwave frequency range by cavity perturbation technique. The LCS sintered at 1000°C/2 h had ɛr=4.36 and tan δ=0.003 at 8 GHz. The sintering temperature of LCS is lowered from 1000°C to 850°C/2 h for low-temperature co-fired ceramic application by the addition of different borosilicate glasses with reasonably good microwave dielectric properties. The stability of the glass–ceramic composites with temperature was also investigated.

Properties of Slip‐Cast and Pressureless‐Sintered ZrB2–SiC Composites

Abstract: In view of the perspective to produce near-net shapes of ultra-refractory ceramics, ZrB2–SiC composite were produced by slip casting on plaster mould and pressureless sintered at 2150°C with a holding time of 120 min, using silicon nitride as a sintering aid. After sintering, slip-cast samples reached a very high relative density over 98%, while for comparison, the density of cold isostatic pressed samples was about 94%. Traces of the formation of secondary phases such as B4C, graphite, and BN were found in all samples, while no grain boundary phases were revealed. RT flexural strength of as-sintered slip cast bars was affected by the presence of an external porous layer of coarse ZrB2 particles, while at 1500°C the flexural strength increased, as a glassy layer sealed the superficial defects. Because of the absence of softening grain boundary phases, subcritical crack growth did not occur during high-temperature strength tests.

Compositional Effects in Nanostructured Yttria Partially Stabilized Zirconia

Abstract: There is a considerable current interest in learning how to process genuinely nanostructured ceramics as they offer the potential for significantly enhanced properties; however, it is often difficult to make large enough components to allow more than the most basic of property measurements. In this work, densified components measuring up to 50 mm in size have been produced and a number of very interesting properties have been measured and demonstrated.

Microstructure and Properties of Porous Si3N4 Ceramics with a Dense Surface

Abstract: Porous Si3N4 ceramics with a dense surface are fabricated by a joint process of pressureless sintering and chemical vapor deposition (CVD). Before CVD, the Si3N4 ceramic shows a uniform microstructure with well-distributed pores. During CVD, the depositions of Si3N4 in the inner surface and on the external surface of the ceramics lead to a decrease of porosities and pore sizes. As a result, both the flexural strength and fracture toughness of the Si3N4 ceramic increase by >30%, the surface hardness increases more than five times, and the dielectric constant and loss increase slightly.

CoAl2O4 Nano Pigment Obtained by Combustion Synthesis

Abstract: The aim of this research was to study the influence of pH (2.5, 7, 10.5), molar ratio of fuel to nitrates (0.36, 0.56, 0.75), and calcination temperature (600, 800, 1000, 1200°C) on the characteristics of CoAl2O4 nano pigments synthesized using a solution-based combustion method. Gel formation, morphology, specific surface area, and color of the powder were characterized using TG–DTA (thermogravimetric and differential thermal analysis), XRD (X-ray diffraction), TEM (transmission electron microscopy), BET (Brunauer–Emmett–Teller), and UV–Vis. The results indicate that spinel CoAl2O4 was formed independently of the different variables studied and that higher temperature promotes crystallite size. According to the TEM micrographs, most of particles calcined at 800 and 1000°C have average particle sizes <30 and 75 nm, respectively. Consistent with BET results, maximum specific surface area was obtained at pH of 7. Colorability tests demonstrate that the mixtures of glaze and calcined nano pigments are still dark blue after heating up to 1200°C.

Electrophoretic Deposition of Ceramic Nanoparticles

Abstract: An electrophoretic deposition (EPD) method has been developed for the deposition of nanostructured zinc oxide (ZnO) and TiO2 films. It was shown that the stabilization and charging of the nanoparticles in suspensions can be achieved using organic molecules, such as dopamine and alizarin yellow (AY) dye, which were adsorbed on the oxide nanoparticles. Fourier-transform infrared spectroscopy investigations showed that the adsorption mechanism is based on the complexation of metal ions at the surfaces of oxide nanoparticles. Cationic dopamine additive was used for the formation of deposits by cathodic EPD. The adsorption of anionic AY on the oxide nanoparticles resulted in charge reversal and enabled the formation of anodic deposits. The method enabled the codeposition of ZnO and TiO2 and the formation of composite films. It was shown that the deposition yield and deposit composition can be controlled by the variation of deposition time and suspension composition. The deposits were studied using X-ray diffraction and electron microscopy. The deposition mechanism and kinetics of deposition are discussed.

The Enhanced Low‐Voltage Cathodoluminescent Properties of Spherical Y2O3:Eu3+ Phosphors Coated with In2O3 and its Application to Field‐Emission Displays

Abstract: Dispersed and spherical Y2O3:Eu3+ red phosphor particles were prepared by the urea homogeneous precipitation method. In2O3 nanoparticles were successfully coated on the surface of the phosphor. Phase compositions, morphologies, photoluminescence (PL) spectra, and cathodoluminescence (CL) properties of Y2O3:Eu3+ phosphors before and after In2O3 coating were examined. It was found that CL properties such as luminous efficiency, lifetime, and stability of In2O3-coated phosphor screen were improved significantly, even though its PL intensity decreased compared with that of the uncoated sample. The reason is attributed to the increase of the electrical conductivity and the decrease of the charge accumulating effect. The present results prove that Y2O3:Eu3+ phosphor coated with an appropriate amount of In2O3 is more suitable to the requirement for low-voltage field-emission displays.

Superhydrophobic Nanostructured Boehmite Coatings Prepared by AlN Powder Hydrolysis

Abstract: A simple method that exploits the hydrolysis of AlN powder was used to deposit a nanostructured boehmite coating onto a polished sintered alumina substrate. The coating consists of interconnected polycrystalline nanoporous lamellas and exhibits a large specific surface area. Heat treatment of the as-deposited coating at 500°C transformed it to γ-alumina, and then to δ-alumina at 900°C, with no substantial change in the morphology. However, the nanoporosity of the lamellas disappeared after the heat treatment at 900°C. After a subsequent chemical modification of the coatings with various low-energy-surface chemicals, that is, carboxylic acids, heptadecafluoro-1,1,2,2-tetrahydrodecyl trimethoxy-silane (FAS), the initially highly hydrophilic coatings were transformed into a hydrophobic ones. Carboxylic acids proved to be less-effective low-energy-surface chemicals because they produce hydrophobic surfaces with a water droplet contact angle of only 135°. A superhydrophobic surface, exhibiting a water-droplet contact angle of 155°, was prepared by modifying the boehmite or γ-alumina coating with FAS.

Combustion Synthesis and Luminescent Properties of Nano and Submicrometer‐Size Gd2O3:Dy3+ Phosphors for White LEDs

Abstract: Monoclinic phase Dy3+:Gd2O3 nanophosphors were synthesized by a combustion method using glycine followed by sintering to obtain submicrometer-size phosphors. The X-ray diffraction patterns confirmed the monoclinic structure of Gd2O3:Dy3+ phosphors. The phosphors were characterized by a transmission electron microscope, Raman, Fourier transform infrared, and fluoresence spectroscopy. The sizes of the phosphor particles are in the range from nearly 35 to 93 nm. It was observed that the emission intensities are varied with the excitation wavelength and concentration. The mechanism responsible for concentration quenching was discussed. The enhancement of emission intensities was observed while increasing the sintering temperature of the phosphor. Moreover, the CIE chromaticity coordinates of Dy3+-doped Gd2O3 phosphors fall in the white light domain of the chromaticity diagram. The above characteristics indicate that these phosphors may be potential candidates for the application of near-ultraviolet-based white-light-emitting diodes.

Effect of Excess MgO Mole Ratio in a Stoichiometric Cordierite (2MgO·2Al2O3·5SiO2) Composition on the Phase Transformation and Crystallization Behavior of Magnesium Aluminum Silicate Phases

Abstract: The effect of excess MgO, 2.0–4.0 mol ratios on the crystallization behavior and purity of μ-cordierite was investigated using X-ray diffraction (XRD), differential thermal analyzer, and TGA. Quantitative XRD, the Rietveld technique, was carried out using the HighScore Plus software. The glass crystallization process route was used with talc and kaolin as the main raw materials and compensated with MgO, Al2O3, and SiO2 accordingly. The crystallization temperature of the glasses decreased as a function of the MgO mole ratio. Less than 2.8 mol MgO increased the formation of α-cordierite up to 94 wt%. However, above 2.8 mol ratio, the forsterite phase started to appear, together with mullite, μ-cordierite, and spinel.

Influence of Stearic Acid Concentration on the Processing of ZrO2-Containing Feedstocks Suitable for Micropowder Injection Molding

Abstract: The influence of stearic acid concentration on the processability of polyethylene/wax-microsized zirconia feedstocks was investigated systematically. Regarding dense and warpage-free ceramic parts, the addition of stearic acid as a dispersant is crucial for feedstock preparation with at least 50 vol% solid loads. A stearic acid concentration of 2.2 mg/m2 (referring to the fillers specific surface area) yields the best feedstock flow properties and homogeneity. Filling studies showed that feedstocks containing 55 vol% of submicrometer-sized zirconia powder in a polyethylene–wax binder system with 2.2 mg/m2 stearic acid as a dispersant can be processed by micropowder injection molding.