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In this study, we explored the consolidation, solid‐solution formation and high‐temperature properties of tantalum hafnium carbide with the 1 TaC:4 HfC ratio, that is, Ta0.2Hf0.8C. Tantalum hafnium carbide bulks can be consolidated using spark‐plasma sintering only at temperatures exceeding 2200°C. The bulks prepared using a 40‐min dwell at 2200°C had the lattice parameter a = 4.571(9) Å. Based on the three‐point flexural tests, it was observed that the toughness and strength of Ta0.2Hf0.8C remained high at 2000°C (3.4 ± 0.4 MPa m1/2, 500 ± 20 MPa). At 2000°C, majority of carbides show a plastic behavior, but the strain‐stress curves of the SPSed Ta0.2Hf0.8C ceramic were linear. Using the shrinkage rate data during the SPS and the strain‐stress data from the high‐temperature flexure, we estimated the activation energies for the densification and flexure as 820 ± 20 kJ/mol and 1180 ± 120 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Translucent AlN ceramics with 0‐2 wt.% MgF2 additive were prepared by spark plasma sintering. AlN powder was heated temporarily up to 2000°C, before holding at 1850°C for 20 minutes in N2 gas. The sintered ceramics consisted of a single phase of hexagonal AlN, and showed a transgranular fracture mode. The total transmittance was improved remarkably by the additive, to reach 74% at a wavelength of 800 nm for 1 wt.% MgF2. For 2 wt.% MgF2, the transmittance was slightly lower than that for 1 wt.% MgF2, and an absorption band was observed apparently at around 400 nm. The addition of MgF2 along with the temporary heating at higher temperatures than the sintering temperature contributed to improve the transmittance remarkably. [ABSTRACT FROM AUTHOR]

The effect of starting powders on the sintering of nanostructured tetragonal zirconia was evaluated. Suspensions were prepared with a concentration of 10 vol.% by mixing a bicomponent mixture of commercial powders (97 mol.% monoclinic zirconia with 3 mol.% yttria) and by dispersing commercially available tetragonal zirconia (3YTZ, Tosoh). The preparation of the slurry by bead-milling was optimized. Colloidal processing using 50μm zirconia beads at 4000 rpm generated a fully deagglomerated suspension leading to the formation of high-density consolidated compacts (62% of the theoretical density (TD) for the bicomponent suspension). Optimum colloidal processing of the bicomponent suspension followed by the sintering of yttria and zirconia allowed us to obtain nanostructured tetragonal zirconia. Three different sintering techniques were investigated: normal sintering, two-step sintering and spark plasma sintering. The inhibition of grain growth in the bicomponent mixed powders in comparison with 3YTZ was demonstrated. The inhibition of the grain growth may have been caused by inter-diffusion of cations during the sintering. [ABSTRACT FROM AUTHOR]

This paper has clarified the anelasticity of 8Y-FSZ/α-alumina composites wherein the 8Y-FSZ phases are dispersed like islands. The amount of anelastic strain generated and the manner of anelastic deformation were compared to those of monolithic 8Y-FSZ. The anelastic strains of six kinds of 8Y-FSZ/α-alumina, as well as of monolithic 8Y-FSZ and monolithic α-alumina, were measured. The results showed that the anelastic strain was produced even in the composite where 8Y-FSZ phases existed as islands, and that the more the anelastic strain produced, the higher the volume fraction of 8Y-FSZ. In addition, the composition with a fully densified alumina phase had the effect of inhibiting anelastic strain in the 8Y-FSZ phase. [ABSTRACT FROM AUTHOR]

Uniform coating and line patterning of a conductive polypyrrole (Ppy) film on nonconductive ceramic materials were performed for use as substrates in the electrophoretic deposition (EPD) process. The Ppy was synthesized by chemical oxidation in the pyrrole solution. Direct shaping or line patterning of alumina or zirconia particles by EPD was carried out using the Ppy films as cathodes. [ABSTRACT FROM AUTHOR]

Abstract: Recently to improve properties, highly microstructure controlled ceramics such as fine-grained, textured and laminated structures are required. We have demonstrated a new processing of textured ceramics with a feeble magnetic susceptibility by colloidal processing in a high-magnetic field and subsequent heating. As colloidal processing, slip casting and electrophoretic deposition (EPD) have been conducted successfully. Colloidal processing is known to be a powerful method for consolidating fine particles with a high density and homogeneous microstructure. Crystalline-textured controlled laminated alumina can be fabricated using EPD by varying the angle between the vectors of electric field and magnetic field. Also textured ceramics with complicated structure such as β-alumina and alumina-based nanocomposite can be fabricated by reaction sintering. The textured alumina-related compounds showed anisotropic properties depending on the crystal plane. The colloidal processing in a high-magnetic field confers several advantages and can be applied to many non-cubic ceramics. [Copyright &y& Elsevier]

This paper reports the texturing behavior of β-sialon by strong magnetic field alignment (SMFA) during slip casting, followed by reaction pressureless sintering, using either α or β-Si3N4, Al2O3, and AlN as the starting materials. It is found that the β-Si3N4 crystal exhibits a substantially stronger orientation ability than the α-Si3N4 crystal regardless of the Si3N4 raw powders in the magnetic field of 12 T. The β-raw powder produces a highly a, b-axis-oriented β-Si3N4 green body with a Lotgering orientation factor of up to 0.97. During sintering, the β-raw powder allows the a, b-axis-oriented β-sialon to retain the Lotgering orientation factor similar to and even higher than that of β-Si3N4 in the green body. In contrast, the α-raw powder leads to a faster transformation rate of α/β-Si3N4 to β-sialon but a substantially lower texture in β-sialon. The results indicate that the use of the β-raw powder is more efficient for producing highly textured β-sialon via SMFA than that of the α-raw powder as well as the prolonged sintering. [ABSTRACT FROM AUTHOR]

Textured CaBi4Ti4O15 (CBT) ceramics were fabricated by slip casting in a high magnetic field of 12 T, and a layer structure was obtained by co-firing with the textured CBT ceramics and a metal internal electrode. The crystalline a( b)-axis of CBT was aligned parallel to the magnetic field, and highly a( b)-axis textured ceramics were obtained. The orientation degree of the textured ceramics was 0.82, and the electromechanical coupling coefficient of thickness extensional (TE) vibration was about 1.5 times larger than that of the randomly oriented ceramics. The second harmonic TE vibration was successfully generated in the layer structure specimens, which contained two layers of the textured ceramics and an internal electrode. Therefore, it was recognized that the layer structure was satisfactorily fabricated. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical properties of ceramics materials can be tailored by designing their microstructures. It had generally been difficult to utilize a magnetic field for controlling the texture of diamagnetic ceramics because of their extremely small susceptibility; however, the possibility of controlling the texture by a magnetic field occurred with the development of superconducting magnets. We demonstrate in this study that alumina/alumina laminar composites with alternate crystalline-oriented layers are produced by electrophoretic deposition in a strong magnetic field and that the bending strength of the laminar composite depended on the direction of the multilayered microstructure. [Copyright &y& Elsevier]

Abstract: Preparation of oriented AlN bulk ceramics was achieved by slip casting in a high magnetic field. The c-axis of AlN was perpendicular to the direction of a magnetic field. The mechanical properties and the thermal conductivity of the textured AlN depend on the direction of the crystallographic orientation. [Copyright &y& Elsevier]

Textured monolithic alumina ceramics were synthesized by electrophoretic deposition (EPD) in strong magnetic field of 10 T. Single crystalline, granular α-alumina particles in aqueous suspensions were rotated due to their anisotropic diamagnetic susceptibility and then deposited on substrate. A multilayered alumina composite of oriented and randomly oriented layers was also synthesized by the alternate EPD of alumina suspensions which were placed in and out of a superconducting magnet. It was demonstrated that the EPD in a strong magnetic field is a promising ceramic processing technique for fabricating sophisticated ceramic composites. [Copyright &y& Elsevier]

The texture of feeble magnetic ceramics can be controlled by a strong magnetic field. When the magnetic susceptibility of the c axis is smaller than that of the other axes, the c axis aligns perpendicular to the magnetic field; however, the direction is randomly oriented on the plane perpendicular to the magnetic field. The authors demonstrate in this letter that a highly controlled texture in bismuth titanate, which has a c-axis susceptibility smaller than the other axes, can be achieved using a two-step magnetic field procedure. This highly controlled orientation is effective for improving the electromechanical coupling coefficient. [ABSTRACT FROM AUTHOR]

Investigates the effect of ultrasonification on the microstructure and tensile elongation of zirconia-dispersed alumina ceramics. Use of colloidal processing; Effectiveness of ultrasonification; Improvement of the superlastic tensile ductility.

Abstract: Hydroxyapatite (HAP, Ca10(PO4)6(OH)2) is a main component in the human body and teeth, and a specific crystal orientation is required because of the different properties for each crystal plane. In this study, two types of hydroxyapatite powders were used for the fabrication of a textured HAP. The effects of the processing parameters on the orientation, such as de-agglomeration by ultrasonication and milling procedures, applied magnetic field and sintering temperatures, were examined. Using the de-agglomerated particle by a milling procedure, it is possible to control the particle orientation, but when using heavily agglomerated particles, it was impossible to control the particle orientation by applying a high magnetic field. Highly textured HAP can be fabricated by slip casting using a well-dispersed suspension in a high magnetic field followed by sintering above 1373K. [Copyright &y& Elsevier]

Abstract: Textured titania thick films were fabricated by applying external electrical and magnetic fields. X-ray diffraction (XRD) results and scanning electron microscopy (SEM) images revealed that the titania grains in the c-axis direction were orientated along the high magnetic field (10T) even though the anisotropic susceptibility of titania ceramic is quite weak. [Copyright &y& Elsevier]

Designing texture is one possible way for improving the electrical, chemical, mechanical and other properties of ceramics. We have reported that oriented α-alumina was obtained by slip casting in a high magnetic field followed by sintering. β-Alumina is well known as sodium ion conductor used in a sodium-sulfur battery. β-Alumina consists of spinel blocks and ion conductive planes. Since the direction of the ion conductive plane of polycrystalline β-alumina is random, the ionic conductivity of the polycrystal is lower than that of the single crystal. The purpose of this study is to prepare oriented β-alumina to enhance the sodium ion conductivity. Oriented β-alumina was prepared by the following method: (1) oriented α-alumina green bodies were prepared by colloidal processing in a high magnetic field, (2) the oriented α-alumina green bodies were infiltrated with Na2O and MgO, and (3) the oriented β-alumina bodies were synthesized by reaction sintering at 1600 and 1700 °C. The reaction product and orientation of the β-alumina were confirmed by XRD. [Copyright &y& Elsevier]

Conventional superplastic ceramics have been established at temperatures over 1400 °C with a slower deformation velocity of about 10−4 (s−1). For the application of superplasticity to the manufacturing process, however, high-strain rate deformation velocity of around 10−2/s−1 is necessary. We have reported that alumina addition to 3YTZ (3 mol.%Y2O3 doped ZrO2) is effective in the enhanced ductility. The purpose of this study is to fabricate high-strain rate superplastic 3YTZ by adding manganese and aluminium oxides. Dense and fine-grained 3YTZ systems were obtained by slip casting and low temperature sintering. Manganese and alminium oxides added 3YTZ showed a maximum tensile ductility of about 600% at 1450 °C at a strain rate of 1.2×10−2 s−1. [Copyright &y& Elsevier]

Highly structure-controlled B 4 C ceramics were prepared via strong magnetic field-assisted slip casting of a slurry, containing B 4 C base particles and pore-forming agents with a fiber shape. To achieve gas release at a lower porosity for maintaining its mechanical strength, these B 4 C ceramics had a structure in which a large number of oriented tubal pores were dispersed in a crystallographically-aligned and dense B 4 C matrix phase. The B 4 C microstructure, such as structuration and orientation degree distributions of the B 4 C grains and tubal pores, was characterized by SEM observation, EBSD analysis, and X-ray CT. Among the investigations, it was found that the oxidic impurities, as an inhibitor of sintering, which existed on the B 4 C surface, can be removed by ethylation and azeotropy due to an ethanol treatment followed by vacuum drying. Thus, an ethanol treatment of a green compact before sintering was significantly effective for the fabrication of the B 4 C ceramics, including the microstructure that coexisted with a dense matrix phase with tubal pores. The resultant ceramic specimens showed the remarkable three-point bending strength of 459−554 MPa, which is two times higher when compared to conventional B 4 C pellets with a similar porosity. [ABSTRACT FROM AUTHOR]

The use of large-sized, highly transparent polycrystalline strontium fluorapatite (S-FAP) ceramics could be a breakthrough in the high-power laser field due to its excellent laser gain properties. However, its hexagonal crystal structure makes it difficult to obtain laser quality in polycrystalline ceramics owing to birefringence. In this study, fully densified transparent Nd- and Yb-doped S-FAP ceramics with an average grain size of ∼100 nm can successfully be fabricated via liquid-phase nano-powder synthesis followed by spark plasma sintering, thereby achieving laser oscillation of the Nd:S-FAP ceramics for the first time. Furthermore, we elucidated the discrepancy in the emission properties between single-crystal and ceramics with randomly oriented crystal grains. We believe that these findings can provide important insights into the design and development for efficient non-cubic ceramic laser systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Transparent polycrystalline alumina was developed over many years because its attractive properties are expected to find applications in many fields. Crystallographic orientation is one of the effective ways to improve transparency in birefringent ceramics such as alumina, because birefringence at grain boundaries can be suppressed by the alignment of optical axis. Fabrication of high-transparency alumina with an oriented c-axis and fine microstructure can be attained by slip casting in a strong magnetic field, followed by spark plasma sintering at 1150 °C for 20 min. The real in-line transmittance of the textured alumina with a thickness of 0.80 mm was 70% at λ = 640 nm, which was higher than that of randomly-oriented alumina. The c-axis orientation reduced the actual difference of the refractive index and suppressed remarkably the birefringence. [ABSTRACT FROM AUTHOR]

Abstract: Binderless WC ceramics were prepared by reactive spark plasma sintering, using tungsten trioxide, tungsten and carbon black as the starting materials. Phase assemblages and microstructure of the as-sintered ceramics were investigated. It was found that graphite existed as an impurity phase due to the volatilization of WO3, and W could compensate for the WO3 loss to form WC with a single phase. Benefiting from the enhanced sinterability, WC ceramics with high relative density and good hardness could be obtained at temperature as low as 1500°C. [Copyright &y& Elsevier]