High-temperature Ceramics Research Articles

Dimethylaminoborane-modified copolysilazane as a novel precursor for high-temperature resistant SiBCN ceramics

A novel polyborosilazane (PBSZ) precursor was synthesized by the reaction of copolysilazane (CPSZ) with dimethylaminoborane (DMAB). The resultant PBSZs were characterized by FT-IR and NMR spectroscopy. It was found that both, BH and NH bonds of DMAB, react with CPSZ leading to boron containing copolysilazanes. The polyborosilazanes were pyrolyzed at 900 °C in argon and the precursor-to-ceramic transformation was studied by TG-MS and FT-IR spectroscopy. The modification of CPSZ with DMAB enhances the cross-linking of the resulting PBSZ, which increases the final ceramic yield from 57.8% to 77.5–80.0%. Finally, the ceramics obtained at 900 °C were subsequently annealed at different temperatures ranging from 1200 to 1800 °C. The heat-treated products were characterized by X-ray powder diffraction and electron microscopy. Accordingly, the resulting SiBCN ceramics exhibit significantly enhanced high-temperature-resistance with respect to decomposition and crystallization as compared with boron-free CPSZ-derived SiCN ceramics. TEM results support that the thermal stability is due to the segregation of a BN(C) phase as interlayer between Si3N4 nanocrystals formed during heat-treatment of SiBCN at T > 1500 °C.

Hydrogen extraction characteristics of high-temperature proton conductor ceramics for hydrogen isotopes purification and recovery

To develop high-efficiency and economical hydrogen isotope purification and recovery processes for a tritium extraction system in a fusion reactor, hydrogen extraction characteristics of an electrochemical hydrogen pump using high-temperature proton conductors were studied. The driving forces of hydrogen transportation in the proton conductors are electric potential difference, which can extract hydrogen isotopes selectively from a solid breeder blanket purge gas with low-pressure hydrogen isotope gas. In the experiments, a one-end closed tube made of proton-conducting ceramic CaZr0.9In0.1O3−α (effective electrode area: 160cm2) was developed because of its high chemical stability, mechanical strength, and durability in a series of perovskite-type proton conductors. The hydrogen pumping characteristics were evaluated over the temperature range from 923K to 1073K by extraction of 664–1200ppm H2 balanced with He, H2 was selectively extracted from and the mixture of He and H2 at the rate of Faraday's Law under an applied voltage of 3.5V DC. In the case of He with 0.12% H2 at 1023K and at 1.15V DC, the maximum hydrogen evolution rate was 0.12ml/min, the hydrogen recovery efficiency was more than 99%, suggesting the extraction of hydrogen could be operated with a current efficiency close to unity. The possible application of hydrogen pumps for the TES of CIPITISE at CIAE has been estimated.

Electromagnetic properties of Si–C–N based ceramics and composites

Besides the excellent high-temperature mechanical properties, Si3N4 and SiC based ceramics containing insulating or electrically conductive phase are attractive for their tunable dielectric properties, which may vary from electromagnetic (EM) wave transparent to absorption and shielding. Consequently, SiC, Si3N4, SiON, SiBN, SiBC, SiCN and SiBCN ceramics have attracted extensive interest in recent years. SiO2, Si3N4, Si3N4–SiO2, Si3N4–BN, and Si3N4–SiO2–BN are promising EM wave transparent materials for applications in microelectronic packaging, microwave transparent reaction chamber, radome and antenna window. C, SiC, SiC–C, Si3N4–C and Si3N4–SiC are potential EM wave shielding materials, which can be used as electronic packaging of highly integrated circuits, and be used in wireless communication system, telecommunication base stations and the other electronic devices. Si3N4–SiBC, Si3N4–SiCN and Si3N4–SiBCN are attractive EM wave absorbing materials for potential applications in amplifier, accelerator, microwave heating, anechoic chambers, stealth aircraft and ship. Other potential harsh environment or high-temperature applications will also benefit from the Si–C–N ceramic system. The concept of hybrid structure and EM metamaterials (MMS) opens up new avenues in developing EM wave absorption materials. The key developments and future challenges in this field are summarised. The main issues regarding permittivity of high-temperature structural ceramics are discussed, with an emphasis on the EM wave transparent, shielding and absorbing mechanisms that are responsible for the EM wave properties.

Machining of ZrB2-SiC Composites by Wire-EDM Technique

Wire-EDM has evolved as one of the latest machining techniques for fabrication of micro-components of advanced structural ultra high temperature ceramics. Hot-pressed zirconium diboride (ZrB2) based composites containing 5-20 wt% silicon carbide (SiC) have been sintered and investigated to determine the effect of the amount of SiC addition in ZrB2 on the electrical properties and machining parameters. Keeping the input parameters fixed, the machining performance in terms of material removal rate and surface roughness has been studied. As expected, it has been observed that with the increase in percentage weight of SiC, material removal rate decreases because the resistivity of the composite increases.

The Design and Simulation of Wide Range Pressure Sensor Based on HTCC for High-Temperature Applications

A wide range pressure sensor is designed based on the theoretical basis of LC series resonance circuit model to realize the wireless passive measurement in the harsh environment, such as high temperature and high pressure. The capacitive pressure sensitive device is devised by the technology of high-temperature co-fired ceramics (HTCC) to form nine density cavities in zirconia ceramic substrates, and thick film technology to print capacitance plates and planar spiral inductors. The theoretical calculation and simulation analysis of the designed sensor are made respectively under high pressure (10MPa) and temperature (600 °C), the results of which verify the feasibility of the design in a wide range of pressure for high-temperature applications, and provide the reliable theory basis for the fabrication of wide range pressure sensor.

Rapid synthesis of nanocrystalline magnesium chromite and ferrite ceramics with concentrated sunlight

Abstract High-temperature refractory ceramics and catalysts such as MgM2O4 (M = Cr, Fe) are produced conventionally via energy-intensive solid-state syntheses (using 0.44–10 GJ electricity for sintering per ton oxide, equivalent to combustion of 48–1088 kg coal per ton oxide). This article reports rapid production of 17 ± 2 mol% MgFe2O4 and 8.6 ± 0.9 mol% MgCr2O4 after 30 min at 1200 °C employing 0.82 kW m−2 sunlight concentrated at a geometric ratio of about 900 m2 m−2 using a Fresnel lens. Solar radiation promotes the diffusion-limited ferrite formation (42 ± 5 μmol MgFe2O4 per mol Fe2O3 s−1 vs. 26 ± 3 μmol mol−1 s−1 in absence of sunlight) while the transition metals promote the reduction of Mg2+. The nanocrystalline and macroporous spinel has a specific surface area of 9.7–11.9 m2 g−1 (in the order of sol–gel synthesis methods) and is stable under extreme conditions, i.e., high temperature, solar radiation, and reducing agents.

The ablation behavior of ZrB2/Cu composite irradiated by high-intensity continuous laser

Abstract Ultra high temperature ceramics (UHTCs) based composite ZrB 2 /20 vol.% Cu was prepared by spark plasma sintering (SPS) at 1650 C° for 3 min. The ablation behavior of composite irradiated for 2–20 s by 20 MW/m 2 high-intensity continuous laser was investigated. The phase and microstructure evolution of ZrB 2 /20 vol.% Cu during ablation was demonstrated by XRD and SEM, respectively. The results reveal that no macroscopic damage but only one ablated layer with 40 μm in thickness is observed even after being ablated for 20 s. It implies that ZrB 2 /20 vol.% Cu composite exhibits good ablation resistance against high-intensity continuous laser. The continuous Cu in composite evaporates preferentially, which impacts on the following ablation behavior. The generated ZrO 2 at the spot center shows different forms such as closely packed nano-ZrO 2 , micron ZrO 2 or melting ZrO 2 for different ablation time. The melting ZrO 2 is helpful to promote the ablation resistance of ZrB 2 /20 vol.% Cu.

Effect of Molding Process on Properties of Laminated ZrB2-SiC-Cg Ultra High Temperature Ceramics

Laminated ZrB2-SiC-Cg ceramics were successfully prepared by tape casting - dipping and tape casting - stacking respectively. The effect of different molding process on the mechanical properties of materials was investigated. The microstructure and fracture behavior were characterized as well. The flexural strength, fracture toughness and fracture work of laminated ZrB2-SiC-Cg ceramics prepared by tape casting-stacking were 427 MPa, 11.3 MPa·m1/2, 415 J/m2, respectively. The thickness of ZrB2-SiC layers was about 250 μm, and the thickness of graphite layers was about 25 μm. As a comparison, Laminated ZrB2-SiC-Cg ceramics prepared by tape casting - dipping showed non-uniform thickness of the ZrB2-SiC layers and graphite layers. And the flexural strength, fracture toughness and fracture work of laminated ZrB2-SiC-Cg ceramics prepared by tape casting-dipping were 252 MPa, 5.7 MPa·m1/2, 104 J/m2, respectively. The improvement on the mechanical properties of laminated ZrB2-SiC-Cg ceramics prepared by tape casting - stacking was attributed to the uniform graphite layer and ZrB2-SiC layer and the reducing amount of graphite infiltrated into ZrB2-SiC matrix layer.

Surface preoxidation to improve dispersibility of zirconium diboride in aqueous medium

The dispersibility of ZrB2 particles in aqueous medium had a significant effect on colloidal forming processes of ZrB2 based ultra high temperature ceramics. To improve the dispersibility of ZrB2, surface preoxidation was developed. After preoxidation, a layer of oxides composed of ZrO2 and B2O3 formed on particle surfaces. The dispersibility of ZrB2 particles in aqueous medium was investigated using zeta potential measurements, sedimentation tests and viscosity measurements. The surface oxygen of ZrB2 particle preoxidised at 800°C was 2·66±0·12 wt-%. It was found that ZrB2 had the best dispersibility and the lowest viscosity after surface preoxidation at 800°C for 1 h.

Development and Characterization of Biphasic Hydroxyapatite/β-TCP Cements.

Biphasic calcium phosphate bioceramics composed of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) have relevant properties as synthetic bone grafts, such as tunable resorption, bioactivity, and intrinsic osteoinduction. However, they have some limitations associated to their condition of high-temperature ceramics. In this work self-setting Biphasic Calcium Phosphate Cements (BCPCs) with different HA/β-TCP ratios were obtained from self-setting α-TCP/β-TCP pastes. The strategy used allowed synthesizing BCPCs with modulated composition, compressive strength, and specific surface area. Due to its higher solubility, α-TCP was fully hydrolyzed to a calcium-deficient HA (CDHA), whereas β-TCP remained unreacted and completely embedded in the CDHA matrix. Increasing amounts of the non-reacting β-TCP phase resulted in a linear decrease of the compressive strength, in association to the decreasing amount of precipitated HA crystals, which are responsible for the mechanical consolidation of apatitic cements. Ca2+ release and degradation in acidic medium was similar in all the BCPCs within the timeframe studied, although differences might be expected in longer term studies once β-TCP, the more soluble phase was exposed to the surrounding media.

High thermally stable BiFeO3–PbTiO3–BaTiO3 ceramics with improved ferroelectric properties

High temperature (0.9-x)BiFeO3–(x)PbTiO3–0.1BaTiO3 (BF–PT–BT) ceramics at MPBs (x = 0.18, 0.20 and 0.22) were synthesized by solid-state reaction technique. Well-saturated P–E loops were obtained and an enhanced ferroelectric behavior of Pr ~60 μC/cm2 and Ec ~50 kV/cm was observed in 0.68BiFeO3–0.22PbTiO3–0.10BaTiO3 ceramics, which was much higher than those of reported BiFeO3–PbTiO3-based and BiFeO3–BaTiO3-based ceramics. The temperature stability of the ceramics was also investigated, showing a high resistivity to thermal depoling, with a degradation temperature Td of ~500 °C. Our results suggested that BF–PT–BT was a good lead-reduced high-temperature ferroelectric ceramics.

Investigation of Structural and Electrical Properties of B-Site Complex Ion (Mg1/3Nb2/3)4+-Modified High-Curie-Temperature BiFeO3-BaTiO3 Ceramics

B-site complex ion (Mg1/3Nb2/3)-modified high-temperature ceramics 0.71BiFeO3-0.29BaTi1−x(Mg1/3Nb2/3)xO3 (BF-BTMNx) have been fabricated by the conventional solid-state reaction method. The compositional dependence of the␣phase structure, electrical properties, and depolarization temperature of the ceramics was studied. The main phase structure of BF-BTMNx ceramics is perovskite phase with pseudocubic symmetry. The experimental results show that the dielectric and piezoelectric properties, and temperature stability strongly depend on the (Mg1/3Nb2/3)4+ content. The optimum (Mg1/3Nb2/3) content enhances the piezoelectric properties, Curie temperature, and depolarization temperature. The ceramic with x = 1% exhibited enhanced electrical properties of d33 = 158 pC/N and kp = 0.322, combined with high-temperature stability with Curie temperature of Tc = 453°C and depolarization temperature of Td = 400°C. These results show that the ceramic with x = 1% is a promising lead-free high-temperature piezoelectric material.

化学的・物理的修飾によるチタン酸アルミニウム系低熱膨張性高温材料の新展開

化学的・物理的修飾によるチタン酸アルミニウム系低熱膨張性高温材料の新展開

S0420204 UHTC複合材料の耐酸化性評価([S042-02]セラミックスおよびセラミックス系複合材料(2),機械材料・材料加工部門)

ZrB_2-SiC-ZrC (ZSZ), which is known as one of ultra high temperature ceramics (UHTCs) composite material, with four different compositions containing 16 vol.%SiC and ZrB_2-16 vol.%SiC were sintered by spark plasma sintering. These sintered compacts are oxidized at 1700 ℃ by IR image furnace in airflow. The result showed that all samples were covered with SiO_2 and ZrO_2. Moreover, oxide scale of ZSZs containing higher ZrC than ZrB_2 has been damaged. Observation of the cross-section of all samples revealed that oxide area was consist of five different layers: SiO_2 layer, SiO_2 with ZrO_2 layer, SiC-depleted layer and unoxidized area. Furthermore, the thickness of oxide layer of ZSZs containing more ZrB_2 than ZrC was thinner. Thus, it was expected that these samples have good resistance to oxidation.

Integrity of Structural and Thermo-structural Materials for Indian Space Programme

As stakes are very high, a space programme places one of the highest priorities on the integrity of structural materials and Indian space programme is no exception to this. Starting from design of process, an exhaustive series of structural simulations, mechanical and structural tests and inspection-steps at room, elevated and cryogenic temperatures are followed during qualification and acceptance of structural materials for space applications. A continuous effort of space material-scientists is to adopt the emerging advanced destructive and non-destructive testing methods in order to enhance the reliability of structures. In the second phase of Indian space programme, high temperature materials are poised to play increasingly more important role. This in turn, calls upon the scientists to develop a variety of thermo-structural materials based on dispersion strengthened alloys, ceramic matrix composites, intermetallics, ultra high temperature ceramics etc. Keeping pace with these developments, a host of characterization techniques are being evolved and facilities are being established to ensure the thermo-structural integrity of high temperature materials. The paper presents the whole gamut of important structural and thermo-structural materials that are presently in use or under development for the future missions of ISRO. It also includes the testing methodologies being adopted at VSSC/ISRO for qualifying these materials from the structural integrity point of view.

413 溶融含浸法による炭素繊維/超耐熱セラミックス複合材の試作(OS4-(3),OS4 オーガナイズドセッション《材料・組織と加工》)

413 溶融含浸法による炭素繊維/超耐熱セラミックス複合材の試作(OS4-(3),OS4 オーガナイズドセッション《材料・組織と加工》)

Qualitative analysis of hafnium diboride based ultra high temperature ceramics under oxyacetylene torch testing at temperatures above 2100°C

Oxidation tests were carried out on HfB2–SiC, HfB2–HfC, HfB2–WC–SiC, and HfB2–WSi2 ceramics using an oxyacetylene torch. The samples were oxidized between 2100 and 2300 °C. From cross-sectional images, scale non-adherence was noted as a limiting factor in oxidation resistance. The sample with the best scale adherence was HfB2–WSi2. Factors involving scale non-adherence such as vapor pressure, coefficient of thermal expansion mismatch and phase transformations were considered. In comparing the scale adherence of the samples it was hypothesized that vapor pressure buildup is the principal contributing factor in the scale adherence differences observed among the tested samples. However, the coefficient of thermal expansion mismatch and HfO2 phase transformation cannot be neglected as contributing factors to scale non-adherence in all samples.

Study on Experimental System for High Temperature Ceramic Filter

High temperature ceramic filter is designed and implemented for purification of hot coal gas, and then an experimental system is build in order to test its filtration performance. The reverse-pulse-jet-cleaning is introduced in detail. Finally, field experiment has been carried out and the results show that the ceramic filter keeps a high dust control efficiency and long on-line stability.

MnO2-modified 0.98(K0.5Na0.5)NbO3–0.02LaFeO3 ceramics with low dielectric loss for high temperature ceramics capacitors applications

The MnO2-doped 0.98(K0.5Na0.5)NbO3–0.02LaFeO3 [0.98KNN–0.02LF-x] lead-free ceramics were prepared by the conventional solid-state sintering method. The effects of MnO2 doping on the phase structure, microstructure, and electrical properties of the ceramics were investigated. The results reveal that MnO2 is an excellent sintering aid for the 0.98KNN–0.02LF-x ceramics to improve the densification and decrease the sintering temperature. Additionally, the MnO2 doping significantly increases the dielectric permittivity and decreases the dielectric loss of the 0.98KNN–0.02LF ceramics. The 0.98KNN–0.02LF-1.5mol% ceramics show excellent high temperature dielectric properties: the dielectric permittivity εr is approximately 2000 and dielectric loss tgδ is smaller than 3% at a broad temperature range from 100 to 400°C.

Preparation and Research of High-Temperature Foam Ceramic

High-temperature foam ceramics were produced from sludge, Zhongxiang porcelain sand, shale and sand, with addition of SiC 0.15%~0.40% as foaming agent, respectively, sintered at 1130°C~1160°C. The phase composition and micro structure of sintered samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and density, compressive strength and thermal conductivity were evaluated. The results showed that the main phase of amorphous phase plagioclase in sintered samples and interior of samples with a large number of uniformly distributed closed pores, rose sintering temperature and increased SiC addition leading to pores size enlarged and density, compressive strength and thermal conductivity diminished.