High-temperature Ceramics Research Articles

Hot Pressing and Characterization of ZrB<sub>2</sub>-SiC-MoSi<sub>2</sub> Composite

Transition metal diborides, especially zirconium and hafnium diboride are potential ceramic material for ultra high temperature applications above 1800°C. These borides are characterized by high melting point, formation of high melting point oxides, good oxidation resistance and excellent thermo-mechanical properties. In this present exploration, zirconium diboride (ZrB2) has been selected for its moderate density (6.09 gm/cc) and better oxidation resistance compared to high density hafnium diboride (11.2 gm/cc). The developed ZrB2 composite in the present study contains 10 wt. % SiC and 10 wt. % MoSi2 as sintering additives. SiC and MoSi2 were added to improve the thermal shock resistance and sinterability of the ultra high temperature ceramics (UHTCs). Vacuum hot pressing was carried out at 1800°C for a holding period of 30 minutes and applied pressure of 30 MPa. Attractive feature of this ZrB2 composite is good machinability due to better electrical conductivity and complicated shapes can be realized easily through electro discharge machining (EDM) process. Detailed XRD phase analysis and microstructural investigation of the polished and fractured composites was carried out using SEM. Mechanical and thermal properties tests have been carried out for the optimized ZrB2 composite material.

Thermomechanical properties and performance of ceramic resonators for wireless pressure reading at high temperatures

This paper reports on the design, fabrication, and thermomechanical study of ceramic LC resonators for wireless pressure reading, verified at room temperature, at 500 °C and at 1000 °C for pressures up to 2.5 bar. Five different devices were fabricated from high-temperature co-fired ceramics (HTCC) and characterized. Alumina green tape sheets were screen printed with platinum paste, micromachined, laminated, and fired. The resulting samples were 21 mm × 19 mm with different thicknesses. An embedded communicator part was integrated with either a passive backing part or with a pressure-sensing element, including an 80 µm thick and 6 mm diameter diaphragm. The study includes measuring thermally and mechanically induced resonance frequency shifts, and thermally induced deformations. For the pressure sensor device, contributions from changes in the relative permittivity and from expanding air trapped in the cavity were extracted. The devices exhibited thermomechanical robustness during heating, regardless of the thickness of the backing. The pressure sensitivity decreased with increasing temperature from 15050 ppm bar−1 at room temperature to 2400 ppm bar−1 at 1000 °C, due to the decreasing pressure difference between the external pressure and the air pressure inside the cavity.

Strengthening of ultra high-temperature ceramics by shot peening and multiple crack healing

A new method for improving the strength and reliability of ceramics is proposed that combines shot peening with multiple crack-healing. Composite ceramics with high crack-healing ability (ZrB2–SiC) were subjected to shot peening and multiple crack-healing. To determine the effect of the method, the mechanical properties of specimens subjected to different process parameters were evaluated. It was also found that the shot peening and multiple crack-healing process was effective for increasing both the apparent fracture resistance and flexural strength of the specimens, and is therefore also a promising technique for repairing dilapidated structural ceramics.

Collapse criteria for high temperature ceramic lattice truss materials

Based on the temperature dependent behaviors of the Young's modulus and the strength of high temperature ceramics, temperature dependent failure characteristics of high temperature ceramic lattice truss materials were analyzed to build temperature-dependent failure theory. In compression, compression fracture and buckling are the competing failure modes. In shearing, tensile fracture and buckling are the competing failure modes. High temperature softening of the ceramic strut induces fatal buckling collapse for the lightweight lattice truss structure at ultra-high temperature. Collapse criteria under different planar stress states were built and are supported by high temperature experiments. Instructed by the criteria, collapse surfaces consisting of fracture surface and buckling surface were plotted and give helpful suggestions to design high temperature resistant as well as lightweight lattice truss ceramic composites.

Pressureless Sintering of ZrB<sub>2</sub> with β-SiC Addition

Zirconium diboride (ZrB2) is a covalent compound that leads the category of ultra high temperature ceramics materials owing to its unique properties. In this work, the effect of addition of beta-silicon carbide (β-SiC) in pressureless sintering of ZrB2 was investigated. Four compositions were prepared with 0, 10, 20 e 30 vol% of SiC. ZrB2 powder and mixtures were prepared in by planetary milling with SiC spheres at 4 h. Two sintering temperatures were used, one at 2050 oC/1h and other at 2150 °C/1h. The addition of SiC has promoted an increasing in densification with the increasing of SiC content. The total densification of sample sintered at 2050 oC was 90% of theoretical density for sample with 30 vol% of SiC, while the maximum densification for temperature of 2150 oC was 91,0 %TD.

Microstructural evolution of HfB2 based ceramics during oxidation at 1600–2000°C

HfB2–2 wt-%-La2O3, HfB2–20 vol.-%SiC and HfB2–20 vol.-%SiC–2 wt-%La2O3 were sintered by spark plasma sintering for 5 min between 1900 and 2000°C. Oxidation studies were carried out in static air on sintered ultra high temperature ceramics at 1600, 1800 and 2000°C, and the weight change and microstructure changes after oxidation were examined. LaBO3 formed on the surface after oxidation for 1 h above 1600°C in all La2O3 containing materials, and the cross-section microstructure shows growth of LaBO3 fibres from pores due to vapour phase reaction. Addition of La2O3 altered the oxidation kinetics of HfB2, significantly increasing the oxidation layer thickness above 1600°C. However, above 1800°C reaction has occurred between the sample and the zirconia crucible.

Soluble and meltable hyperbranched polyborosilazanes toward high-temperature stable SiBCN ceramics.

High-temperature stable siliconborocarbonitride (SiBCN) ceramics produced from single-source preceramic polymers have received increased attention in the last two decades. In this contribution, soluble and meltable polyborosilazanes with hyperbranched topology (hb-PBSZ) were synthesized via a convenient solvent-free, catalyst-free and one-pot A2 + B6 strategy, an aminolysis reaction of the A2 monomer of dichloromethylsilane and the B6 monomer of tris(dichloromethylsilylethyl)borane in the presence of hexamethyldisilazane. The amine transition reaction between the intermediates of dichlorotetramethyldisilazane and tri(trimethylsilylmethylchlorosilylethyl)borane led to the formation of dendritic units of aminedialkylborons rather than trialkylborons. The cross-linked hb-PBSZ precursors exhibited a ceramic yield higher 80%. The resultant SiBCN ceramics with a boron atomic composition of 6.0-8.5% and a representative formula of Si1B(0.19)C(1.21)N(0.39)O(0.08) showed high-temperature stability and retained their amorphous structure up to 1600 °C. These hyperbranched polyborosilazanes with soluble and meltable characteristics provide a new perspective for the design of preceramic polymers possessing advantages for high-temperature stable polymer-derived ceramics with complex structures/shapes.

ChemInform Abstract: Recent Progress on Synthesis, Multi‐Scale Structure, and Properties of Y—Si—O Oxides

AbstractReview: 179 refs.

A band enhanced metamaterial absorber based on E-shaped all-dielectric resonators

In this paper, we propose a band enhanced metamaterial absorber in microwave band, which is composed of high-permittivity E-shaped dielectric resonators and metallic ground plate. The E-shaped all-dielectric structure is made of high-temperature microwave ceramics with high permittivity and low loss. An absorption band with 1 GHz bandwidth for both TE and TM polarizations are observed. Moreover, the absorption property is stable under different incident angles. The band enhanced absorption is caused by different resonant modes which lie closely in the absorption band. Due to the enhanced localized electric/magnetic fields at the resonant frequencies, strong absorptions are produced. Our work provides a new method of designing high-temperature and high-power microwave absorbers with band enhanced absorption.

Progress of a novel amorphous and nanostructured Si-B-C-N ceramic and its matrix composites prepared by an inorganic processing route

The development of novel, high-temperature structural and multifunctional heat-resistant materials for service under high-temperature oxidation, severe thermal shock, ablation by combustion gas flow, and other harsh conditions has become one of the most pressing needs in the aerospace industry. Amorphous and nanocrystalline Si-B-C-N ceramic and its matrix composites have great potential applications in the fields of high-temperature structural and multifunctional heat-resistant ceramics because of their special structures and outstanding high-temperature properties. The preparation of dense Si-B-C-N ceramic bulks is greatly limited by the organic polymer precursor pyrolyzing method (organic processing route). Mechanical alloying and post-hot-pressing technologies (inorganic processing route) using inorganic powders as the raw materials were pioneered by researchers from the Institute of Advanced Ceramics at Harbin Institute of Technology about 10 years ago. The inorganic processing route, which is very simple and effective in the preparation of materials with uniform microstructures and excellent properties, has been used to obtain dense Si-B-C-N ceramic bulks and structural components resistant to high temperatures. The inorganic processing route has become an indispensable complement to the organic processing route and has resulted in improved and enriched experimental data and understanding of Si-B-C-N ceramics. Current research achievements in the field of SiBCN ceramics and their matrix composites obtained by the inorganic processing route (including microstructural characteristics, evolution laws, mechanical and thermophysical properties, the resistance to oxidation, thermal shock and ablation, and related mechanisms) are summarized and future trends are predicted.

Variation of Piezoelectric properties and mechanisms across the relaxor-like/Ferroelectric continuum in BiFeO3- (K0.5Bi0.5)TiO3-PbTiO3 ceramics.

1- x - y)BiFeO3-x(K0.5Bi0.5)TiO3-yPbTiO3 (BFKBT- PT) piezoelectric ceramics were investigated across the compositional space and contrasted against the xBiFeO3- (1-x)(K0.5Bi0.5)TiO3 (BF-KBT) system, whereby a range of relaxor-like/ferroelectric behavior was observed. Structural and piezoelectric properties were closely related to the PbTiO3 concentration; below a critical concentration, relaxor-like behavior was identified. The mechanisms governing the piezoelectric behavior were investigated with structural, electrical, and imaging techniques. X-ray diffraction established that longrange non-centrosymmetric crystallographic order was evident above a critical PbTiO3 concentration, y > 0.1125. Commensurate with the structural analysis, electric-field-induced strain responses showed electrostrictive behavior in the PbTiO3-reduced compositions, with increased piezoelectric switching in PbTiO3-rich compositions. Positive-up-negative-down (PUND) analysis was used to confirm electric-field-induced polarization measurements, elucidating that the addition of PbTiO3 increased the switchable polarization and ferroelectric ordering. Piezoresponse force microscopy (PFM) of the BF-KBT-PT system exhibited typical domain patterns above a critical PbTiO3 threshold, with no ferroelectric domains observed in the BF-KBT system in the pseudocubic region. Doping of BiFeO3-PbTiO3 has been unsuccessful in the search for hightemperature materials that offer satisfactory piezoelectric properties; however, this system demonstrates that the partial substitution of alternative end-members can be an effective method. The partial substitution of PbTiO3 into BF-KBT enables long-range non-centrosymmetric crystallographic order, resulting in increased polar order and TC, compared with the pseudocubic region. The search for novel high-temperature piezoelectric ceramics can therefore exploit the accommodating nature of the perovskite family, which allows significant variance in chemical and physical characters in the exploration of new solid-solutions.

Effect of Different Mn-doping Types on BLFG-PT High-temperature Piezoelectric Ceramics

Mn-doped 0.63(Bi0.94La0.06)(Fe0.95Ga0.05)-0.37PbTiO3 ceramics with exactly stoichiometric ratio in lattice for substituting Ti-site induced large microstructure distortion and internal stress. However, for the specimens of Mn introduction as sintering aids, distinct relaxation characteristic transforming from pure BLFG-PT can be obtained. Moreover, little difference could be classified according to the selected raw materials of MnCO3 and MnO2 on the properties of BLFG-PT ceramics. They both could effectively improve the density and make the high-temperature phase transition become more diffused, revealing relaxor ferroelectrics characteristic. In addition, all the Mn-doped samples, greatly decreased dielectric loss were observed which indicates the potential use of Mn-doping in high power piezoelectric device application and modification.

Critical roles of Mn-ions in enhancing the insulation, piezoelectricity and multiferroicity of BiFeO3-based lead-free high temperature ceramics

A lead-free multiferroic ceramic of BiFe0.96Sc0.04O3–BaTiO3 is a type of ABO3 perovskite structure, belonging to the R3c space group, but exhibiting poor insulation and weak multiferroicity.

Ultra high temperature ceramics: tantalum carbide (tac)

ÖzetUltra yüksek sıcaklık seramikleri(UHTC); sahip oldukları yüksek sertlik, aşınma direnci yanında çok yüksek sıcaklıklarda çalışma atmosferine olan dayanımları nedeniyle özellikle uzay ve havacılık sektörlerinde kullanım potansiyeli yüksek olan ileri teknolojik seramik esaslı malzeme sınıfıdır. UHTC genel olarak 4. ve 5. grup metal (M:Ta, Ti, Hf gibi) elementlerinin karbürlü(MC), nitrürlü(MN), oksitli (MO) ve borürlü (MB) bileşiklerinden oluşmaktadır. Tantalyum Karbür (TaC)esaslı seramikler, hem yüksek sıcaklık dirençleri ve kararlılıkları hem de yüksek sıcaklıklarda üstün mekanik özellikleri nedeniyle en fazla ilgiyi üzerine çeken refrakter asıllı bir seramik malzemelerden bir tanesidir. Bu çalışmada, Tantalyum Karbür esaslı seramik malzemelerin yüksek sıcaklık koşullarında faz ve kristal yapısı, Ta/C bileşim oranına bağlı olarak mekanik, elektriksel ve termal özelliklerin değişimi karşılaştırmalı olarak incelenmiştir. TaC esaslı seramiklerin uygulama potansiyeli araştırılmıştır..

Synthesis of rod-like ZrB2 powders

Rod-like ZrB2 powders were synthesised at 1500°C in vacuum by boro/carbothermal reduction using ZrO2, B4C and graphite as the starting materials. During the heating process, the ZrB2 grains primarily grow along the c axis to form a rod-like morphology without any heterogeneous catalyst. The final products are pure rod-like ZrB2 particles, which are thought to be promising starting powders to prepare high performance ultrahigh temperature ceramics with unique microstructures such as textured one through tape casting process.

Impact of the Mineral Composition and Sintering Temperature on the Synthesis of Anorthite Ceramics

Anorthite good sintering properties and strength, there promotion prospects in oil and gas fields in the ceramic proppant fracturing. In this experiment, fly ash, coal and limestone as raw materials by high-temperature reaction sintering ceramics, Explore mineral composition, the sintering temperature of the final preparation phase of the resulting composition and physical properties of the impact, better product performance obtained at 1250 °C.

Synthesis of high-temperature Mo5SiB2-based ceramics in the combustion mode

This study is devoted to the synthesis and investigation of the Mo5SiB2-based ceramic material (T 2 phase). The influence of the initial temperature on basic combustion parameters is shown. It is found that preheating the reaction mixture enables the initiation of the combustion in the self-oscillatory mode and the initial temperature dependences of the combustion temperature and rate have a linear character. The effective activation energy of the SHS process is calculated. Some variants of chemical reactions between Mo, Si, and B are proposed to explain the combustion mechanism in the investigated ternary system. Compacted samples are obtained using the forced SHS compaction. The phase composition, structure, and properties of synthesized ceramic materials, in which Mo5SiB2 grains are the main component with an average size of 10–20 μm, are studied. The lines of Mo3Si and Mo intermediate phases, the total fraction of which does not exceed 4%, are identified as well. The produced T 2 phase-based material has a high specific density and hardness.

CFD modeling and simulation of sulfur trioxide decomposition in ceramic plate-fin high temperature heat exchanger and decomposer

Abstract In this study numerical analysis was carried out for four different types of fins namely rectangular, triangular, inverted bolt fins and ripsaw fins and three different types of arrangements namely straight, staggered and top and bottom arrangement. The obtained results were compared with each other and the design with the highest decomposition percentage of sulfur trioxide was selected. The working fluids used in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. The operating pressure was 1.5 MPa and the operating temperature ranges from 973 K to 1223 K. From the results it was found that the ripsaw fin design with thickness of 0.05 mm gives the highest decomposition percentage of sulfur trioxide. The inverted bolt fins gives a good heat transfer rate but due to the fin arrangement and the flow disturbances caused by the arrangement the pressure drop was the highest compared to the other fins. The pressure drop and heat transfer obtained for the rectangular and triangular fins were similar to each other. The obtained decomposition percentage of sulfur trioxide for straight, staggered and top and bottom arrangement were 17.60%, 16.74% and 20.55%. The obtained decomposition percentage increased from 16.74% to 85.15% when the channel length of the heat exchanger was increased ten times.

Development of porous composite self-propagating high-temperature ceramics of the Ti-B-C system

The results of investigations into the porous composite ceramics produced from the Ti-B-C system by self-propagating high-temperature (SHS) synthesis are represented. The effect of the titanium amount in the charge and the billet density on the structure formation and strength characteristics of synthesized porous materials is studied. The results of their investigations using a JSM-6390A scanning electron microscope, an ARL X’TRA diffractometer, and an INSTRON 5988 universal testing machine are given.

Electrochemical Study of Corrosion in High Temperature Molten Salts

Concentrating solar power systems are projected to need to produce energy with a cost of $0.06 / kWh when implemented on a very large scale. It is generally believed that temperatures of the heat transfer fluids will need to be higher than 800oC to drive an advanced Brayton cycle or Rankine cycle with superheated steam to reach this target. However, current state-of knowledge of corrosion science indicates a lack of published data on the impact of molten salts at temperatures above 800°C on corrosion of molten salt contacting materials such as steels or high temperature alloys and ceramics. This work investigates the corrosion mechanism of selected alloys and ceramics in chloride and fluoride molten salts used for high operating temperature heat transfer fluids using a combination of electrochemical techniques, theoretical calculations, and thermodynamic predictions. The electrochemical characterizations included linear polarization resistance scans, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization. Results show that the Fe-Ni-Cr alloys tested have high general corrosion and require corrosion inhibition. Advanced materials, such as SiC-SiC and TZM, have been shown to have much lower corrosion and good passivation behavior. Experimental tests using coupon immersion in the molten salts support the mechanism determined from electrochemical testing that the main element being oxidized is Cr. Analysis of samples also indicates selective Cr oxidation creates porous layers in the sample. The electrochemical impedance tests suggest that the corrosion is diffusion controlled.