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Two hafnium diboride based composites, respectively, containing 20 vol%SiC and 20 vol%SiC–10 vol%AlN, were hot-pressed. Microstructures and mechanical properties were investigated and the thermal stability over 2000 °C was evaluated by oxyacetylene torch. Results indicated that the addition of AlN greatly improved the powder sinterability by eliminating the oxygen contamination. The mechanical properties for HfB2–SiC–AlN composite, especially the flexural strength were enhanced remarkably through the improvement in density and the formation of AlN–SiC solid solution. Oxyacetylene ablation results indicated that the addition of AlN also improved the thermal stability of composite under severe oxidation conditions. The ablation behavior was investigated and the ablation mechanism was discussed.

Thermal shock behavior of ZrB 2 –10 vol%SiC ultra-high temperature ceramics with addition of ZrO 2 was investigated by means of water-quenching as well as the finite element analysis. Optimal residual strength and critical temperature difference were obtained from ZrB 2 –10 vol%SiC ceramic added by 10vol%ZrO 2 . Simulated results revealed that ZrB 2 –10 vol%SiC–10 vol%ZrO 2 provided the lowest thermal stress and stress intensity factor during thermal shock, which confirmed the experimental data. Such improvement in thermal shock resistance compared with ZrB 2 –10 vol%SiC was primarily ascribed to the improved toughness by the addition of ZrO 2 . Besides, appropriate phase transformation of ZrO 2 during quenching was further beneficial to resist the thermal shock.

ZrB 2 –20 vol.%SiC–5 vol.%AlN ceramic composites (ZSA) were fabricated by hot pressing sintering under inert gas protected, which mechanical properties were improved obviously by introducing AlN as sintering aid. Ablation tests of ZSA were conducted with different heat flux parameters in high frequency plasma wind tunnel. The results showed that ZSA exhibited excellent ablation resistance at 2000 °C for 300 s in oxidation environment and a dense coherent scale was formed after ablation, whereas a strong degradation and mass loss were observed at 2600 °C for 300 s. The ablation behavior, microstructures evolvement and the effect of AlN were analyzed.

ZrB2-based ceramics containing 20 vol.% SiC and 10 vol.% AlN were prepared by hot pressing two different ZrB2 precursor powders with average particle sizes of 5 μm in ZSA (ZrB2–20 vol.% SiC–10 vol.% AlN) and 2 μm in GZSA (ZrB2–20 vol.% SiC–10 vol.% AlN) ceramics. The microstructures and mechanical properties were investigated. The thermal shock behavior was studied through the methods of retained flexural strength after quenching into water of 20 °C with the temperature differences between 0 and 800 °C. GZSA showed a better resistance to thermal shock in terms of the increased critical temperature difference (ΔTC of GZSA was 408 °C, about 40 °C higher than that of ZSA), since the finer grain size enhanced fracture toughness by promoting crack bridging, which inhibited the propagation of cracks due to thermal stresses. The influence of quenching temperature difference on the fracture toughness was not significant. Comparing with ZSA, the thermal stress fracture resistance parameter, R, and thermal stress damage resistance parameter, R⁗, of GZSA were all increased.

Ultra-high-porosity zirconia ceramics with interconnected pores were prepared by freezing zirconia/camphene slurries with solid loading ranging from 10 to 20 vol.%, followed by freeze-drying in air and subsequent heat treatment at 1500 °C for 2 h. All of the fabricated samples showed highly porous microstructures with moderate pores ranging from 20 to 50 μm in size. The porosity varied between 82% and 67%, while the compressive strength was significantly improved from 41 to 63 MPa.

The fully dense HfB 2 –SiC composites with B 4 C addition were hot-pressed at 1850 °C. The effects of B 4 C on densification behavior and thermo-mechanical properties were investigated and compared with B 4 C free composite. Results indicated that B 4 C greatly enhanced the sinterability and refined grains. The highest increase on flexural strength and fracture toughness at room temperature were about 62% and 64%, respectively and the thermal conductivity slightly decreased by the addition of B 4 C.

The thermal shock behavior of hot-pressed ZrB 2- SiC composite containing 15vol.% graphite flake ( ZrB 2- SiC - G ) was investigated. The thermal shock testing was carried out by means of quenching into water from high temperatures (Δ T in the range of 200-1000°C). The damage introduced by the thermal shock was characterized by the degradation of bending strength. The residual strength exhibited a complex evolution and could be divided into three zones according to the variation of the temperature difference: (i) no damage zone (200-300°C), (ii) strength degradation zone (300-400°C), and (iii) low stable strength zone (400-1000°C). The minimum residual strength of 160 MPa, higher than 40% of the initial strength of 396 MPa, was obtained in the third zone of temperature difference. The surface feature of ZrB 2- SiC - G composite after the thermal shock tests was also investigated.

HfB 2 -SiC-based ultra-high-temperature ceramics with aluminum nitride (AlN) as a sintering aid were hot pressed at 1850°C. The sinterability and mechanical properties were investigated and compared with the composite without a sintering aid. It was shown that the addition of AlN greatly improved the powder sinterability and enabled the production of a nearly full-dense composite. The mechanical properties, especially the flexural strength, were enhanced remarkably through the improvement in the sinterability and microstructure. The oxidation resistance of a composite doped with 10 vol% AlN was evaluated by a plasma arc heater and the ablation mechanism was discussed.

ZrB2–SiC ceramic composites were prepared from commercially available powders by hot-pressing, and aluminum nitride (AlN) was added as a sintering aid. Sinterability, microstructure and mechanical properties were investigated and compared to the composite without AlN. It was shown that the addition of AlN greatly improved the powder sinterability and enabled the production of nearly full dense composite. The flexure strength, hardness and fracture toughness were improved with a small amount (5 vol.%) of AlN due to the improvement in densification and inhibition of grain growth. Meanwhile the sinterability and mechanical properties were greatly enhanced with the introduction of finer starting powders. However, the flexural strength and fracture toughness were not improved much when more AlN was added.

ZrO2-doped ZrB2–20 vol.% MoSi2 composites were prepared by hot-pressing. Compared with ZrB2–MoSi2 composite, the addition of ZrO2 caused an obvious improvement in microstructure as well as in mechanical properties. Due to the phase transformation toughening of ZrO2, the toughness of ZrB2–MoSi2 composites was clearly advanced by 50% from ∼4.3 to ∼6.3 MPa m1/2 regardless of the method of testing. Such enhancement, especially in toughness, indicates that it is an effective way to design ZrB2–MoSi2 composites with phase transformation toughening of ZrO2.

Hot-pressed zirconium diboride (ZrB 2 ) matrix composites containing 0–30 vol% silicon carbide (SiC) whiskers have been investigated to determine the effect of composition (i.e. amount of SiC whiskers) on the microstructure, mechanical properties and thermal properties. With increasing SiC whisker volume contents, the flexural strength and fracture toughness of the composites were improved compared to those of monolithic ZrB 2 . Flexural strength increased from 629 MPa for pure ZrB 2 to 767 MPa for ZrB 2 –30 vol%SiCw. Likewise, fracture toughness ranged from 5.4 to 7.1 MPa m 1/2 over the same composition range. Specific heat capacity increased with SiC whisker addition, while thermal diffusivity and thermal conductivity decreased slightly with the increase of SiC whisker content.

Structural ceramics, including ultrahigh-temperature ceramics such as zirconium diboride (ZrB2) and hafnium diboride (HfB2), are brittle and sensitive to flaws. As a result, the structural integrity of this ceramic component may be affected seriously. In this paper, a novelty technique namely preoxidation was proposed to overcome this problem. A ZrB2-based composite containing 20 vol% SiC whisker was produced by hot pressing. The composite was preoxidized at temperatures of 800° and 1200°C for various times ranging from 10 to 180 min in air. The flexural strength and microstructure of specimens were investigated systematically under each preoxidation condition. The strength was improved after preoxidation, with a maximum increase of strength (15%) for samples after preoxidizing at 800°C for 180 min. Microstructure analysis suggested that the increase in strength was due to the self-crack-healing behavior of the composite by surface oxide glass, such as B2O3-, SiO2-rich liquids, and borosilicate glass. However, oxide evaporation and formation of gas (i.e., B2O3 and CO) were found to be detrimental to for the crack-healing ability. Oxidation behavior during the preoxidation process followed parabolic-law kinetics.

ZrO 2 (3Y)-BN composites were prepared by hot-pressing with different contents of BN ranging from 0 vol.% to 40 vol.%. The addition of BN was found to have a significant influence on the phase transformation, microstructure, mechanical properties and thermal shock resistance of the composites. With the increased content of BN, the Vickers’ hardness, flexural strength and fracture toughness of the ZrO 2 (3Y)-BN composites exhibited a gradual degradation, but the thermal shock resistance was obviously improved. Results showed that the critical thermal shock temperature (Δ T C ) of ZrO 2 (3Y) was only 280 °C; however, it was increased to be more than 430 °C and 530 °C for ZrO 2 (3Y)-20BN and ZrO 2 (3Y)-40BN, respectively. Improvement of thermal shock resistance for the ZrO 2 (3Y)-BN composites was mainly due to the lower α , E , k and higher ratio value of K IC / σ by adding BN particles.

The crack-healing behavior of zirconium diboride ceramic composite reinforced with silicon carbide whiskers has been investigated through pre-cracking, crack-healing and flexural strength testing processes. A Vickers indentation (∼70 μm in size) was introduced and the crack was healed under different conditions. Cracks could heal completely in air, but did not heal in a vacuum. This composite has good self crack-healing ability at temperatures ranging from 800 to 1200 °C, with 1000 °C being the optimum healing temperature.

The explanations for the bonding nature for ZrB 2 and HfB 2 from electronic structure calculations based on different approaches are inconsistent and even contradictory with each other. First principles pseudopotential calculations have been performed to investigate the bonding nature, elastic property and hardness for the two compounds. The nature of chemical bonding for ZrB 2 and HfB 2 can be recognized as a combination of covalent, ionic and metallic bonds from their electronic structures. Density of state, valence charge density and Mulliken population have also been explored to assess the origins of “pseudogap” and charge transfer. The calculated independent elastic constants using finite strain technique generate accurately elastic, bulk and shear modulus for polycrystalline aggregate compared with extrapolated experimental data. The calculated anisotropy factors indicate that ZrB 2 and HfB 2 are largely compression and shear isotropic. While the different bond strengths of boron–boron and boron-metal produces the significant XZ in-plane elastic anisotropy. The model for hardness calculation using Mulliken population is also proved to be effective in hardness prediction for the metal diborides.

ZrB2/ZrO2 functionally graded ceramics (FGCs), newly developed for ultrahigh-temperature application, were prepared by spark plasma sintering. Denser graded microstructure as well as a “strong” interface were achieved for ZrB2/ZrO2 FGC sintered at 1800 °C. Due to the phase transformation of ZrO2, the toughness of ZrB2/ZrO2 FGCs was increased from ∼5 MPa m1/2 for the ZrB2-rich layer to ∼10 MPa m1/2 for the ZrO2-rich layer. The effect of sintering temperature on the toughness of ZrB2/ZrO2 FGCs was further investigated.

HfB2—20vol% SiC composite was hot-pressed at 1900°C with silicon nitride (Si3N4) as sintering aid. Sinterability and mechanical properties were investigated and compared to the composite without the sintering aid. It was shown that the addition of Si3N 4 greatly improved the powder sinterability and enabled the production of nearly full dense composite. The flexural strength and fracture toughness were 590 MPa and 5.43 MPa m1/2, respectively. The oxidation resistance of composite doped with Si3N4 was evaluated by the oxyacetylene oxidation test and the oxidation mechanism was discussed.

ZrB 2 –10 vol%SiC–20 vol%YSZ composites were prepared by hot-pressed sintering with yttria content ranging from 2 mol% to 8 mol% in YSZ. The phase constitution, microstructure and mechanical properties of the composites were found to be strongly dependent on the yttria content. The average grain size became bigger for the composites with higher yttria content. When the yttria content was below 3 mol%, there is no cubic zirconia in the polished surface of composites, and the flexural strength of the composites was above 740 MPa. With the increase in yttria content, the fracture toughness fell down from 6.4 MPa m 1/2 to 5.6 MPa m 1/2 . Vickers’ hardness of the hot-pressed composites varied above 18 GPa without obvious effect of the yttria content.

Oxidation of ZrB 2 -based ultrahigh-temperature ceramic composites containing 10, 20, and 30 vol% SiC was performed at 1900°C for 1 h in air. ZrB 2 -20 vol% SiC exhibited the highest oxidation resistance at this temperature and formed a dense coherent oxide scale after oxidation, whereas a strong degradation was observed for both ZrB 2 -10 vol% SiC and ZrB 2 -30 vol% SiC. In addition, cracks and spallation in the oxide scale were also detected for the latter materials. The oxidation behaviors of ZrB 2 -SiC composites were investigated. The effect of SiC content was analyzed and oxidation models were proposed to describe the observed microstructures.

Hot-pressed ZrB2–SiC ceramics was hot-pressed at a temperature of 1900 °C, and yttria (Y2O3) was added as a sintering aid. The amount of Y2O3 that was added had a significant influence on the sinterability and mechanical properties of the ZrB2–SiC ceramics. When a small amount (3 vol.%) of Y2O3 was added, the Y2O3 reacted with impurities oxides (ZrO2, B2O3 and SiO2) that were present on the surface of the starting powder. The elimination of impurities oxides suppressed the grain growth effectively, which led to an improvement in the densification of ZrB2–SiC ceramics. The mechanical properties, both the flexural strength and fracture toughness were enhanced through these improvements in the sinterability and microstructure. On the other hand, when a large amount (8 vol.%) of Y2O3 was added, the mechanical properties were not improved much, presumably because the extra additive made redundant liquid phase at the grain boundaries.

Zirconium diboride (ZrB 2 )-based ultra-high temperature ceramics reinforced by SiC whisker were prepared by spark plasma sintering (SPS) and conventional hot pressing (HP). Dense materials were fabricated at 1600 °C by SPS and 1800 °C by HP. The densification behavior was investigated through the analysis of the HP and SPS shrinkage curves. The microstructures and mechanical properties were analyzed and compared in order to understand the influence of the two sintering techniques. The mechanical properties took full advantage of the addition of SiC whisker. Both materials exhibit high flexural strength and fracture toughness of >700 MPa and >6 MPam 1/2 , respectively. The main outcome of the present work is that when the ZrB 2 –SiC W ceramics composite was densified either by SPS or HP, the mechanical properties especially fracture toughness was higher than that of analogous monolithic and composites materials.

ZrB 2 –SiC–ZrC composites were fabricated using ZrB 2 , SiC, ZrC as raw powders for hot pressing (HP) and Zr, B 4 C, Si for reactive hot pressing (RHP). The synthesis process played a critical role in determining the microstructural features of the composites. The ZrB 2 grains were equiaxed in the HP sample, while equiaxed and plate-like ZrB 2 grains were found in the RHP samples. Milled Si powders as reactant promoted the homogeneous distribution of SiC. The relationships between microstructural features and mechanical properties of the composites are discussed.

The present work reported the effect of addition of ZrO2 on the microstructure and mechanical properties of ZrB2-based ceramic composites by means of hot-pressed sintering. Observation of microstructure and systematic testing results of mechanical properties were carried out. Through X-ray diffraction analysis and calculation of the volume fraction of ZrO2 phase transformability, the toughening mechanism of the present composites was explored. The phase transformation toughening by ZrO2 additive played an important role in improving the fracture toughness of ZrB2-based composites.

The synthesis route, microstructure and properties of ZrB 2 –ZrC–SiC composites prepared from a mixture of Zr–B 4 C–Si powders by in situ reactive synthesis were investigated. The reactive path and synthesized mechanism of ZrB 2 –ZrC–SiC composite were studied through series of pressureless heat treatments ranging from 800 °C to 1700 °C in argon. The in situ ZrB 2 –ZrC–SiC composites were fabricated under different synthesis processing. The one with 88.4% relative density performed poorly in mechanical properties due to the occurring of self-propagating high-temperature synthesis (SHS). The fully dense ZrB 2 –ZrC–SiC composite was obtained under the optimized synthesis processing without SHS reactions. Its Vickers hardness, flexural strength and fracture toughness were 20.22 ± 0.56 GPa, 526 ± 9 MPa and 6.70 ± 0.20 MPa m 1/2 , respectively.

ZrB 2 –SiCw ultrahigh-temperature ceramics have been investigated by water quench testing over the temperature range 400–1200 °C. All specimens preserved integrity and retained most of their strength (more than 80%) after being shocked for one or five cycles. Obvious surface changes as a result of oxidation were observed when testing at temperatures higher than 800 °C. Surface oxidation plays an important role in the thermal shock behavior of SiC-whisker-reinforced diboride ultrahigh-temperature ceramics.

Oxidation resistance tests were carried out on hot-pressed ZrB 2 –20 vol%SiC using an oxyacetylene torch. The temperature of the oxidized specimens exceeded 2200 °C. The mass and linear oxidation rates of the ZrB 2 –20 vol%SiC composites for 10 min were −0.23 mg/s and 0.66 μm/s, respectively. The surface layer appeared dense and adherent with the exception of a few burst bubbles and craterlets. No macro-cracks or spallation were detected after oxidation, suggesting that these composites possess a super oxidation resistance. The microstructure of the surface and cross-section of the oxidized specimens were studied by scanning electron microscopy along with energy dispersive spectrometry and X-ray diffraction. The oxidation mechanism was also discussed.

The C/C/SiC composite was fabricated within several days by the method of precursor impregnation and pyrolysis (PIP) using hexamethyldisilazane (HMDS) as the precursor. The carbon fiber plates, woven and punctured with two-dimensional orthogonal continuous carbon bundle and short carbon fiber, were used as the reinforced preforms. The characters of the C/C/SiC composite were analyzed using XRD, EDS and SEM, and three-point-bending test. The results indicated that pyrolyzed substance of the precursor contained excessive carbon, followed by silicon, and a small amount of nitrogen. There were micro-cracks on the massive matrix. The phase composition was difficult to distinguish, primarily considered as the Si–C–N composite. The structure of C/C/SiC was dense and homogeneous with some pores whose sizes were less than 5 μm between fibers and less than 100 μm between the carbon fiber bundles, respectively. Fiber pull-out was observed on the bending fracture surface. The stress–strain curve of both at room temperature and 1300 °C appeared ascending zigzag. Flexural strength was 150 MPa at 1300 °C, higher than 121 MPa at room temperature.

Infrared temperature measurement technology is widely used in non-contact temperature measurement field. The designed system adopts infrared measuring temperature sensor of TN series to measure the target temperature and displays the data on the LCD screen with the STM32. At the same time, it combines with the LabVIEW programming to achieve the purpose of the remote control. Different from the non-contact temperature measurement technology, this system holds more advantages, which response fast, measure widely and so on. Meanwhile, convenience is also been provided for the daily life and industrial production.

Tape casting and hot-press sintering are used to fabricate an Al2O3/3Y-TZP laminated composite. The as-prepared material is deep drawn at high temperature to research its superplastic formability. It is found that the microstructure of the material sintered at 1550 °C is fine and no significant residual porosity was detected from SEM observations at the interfaces between the two types of layers. The superplastic forming experiment shows that, when the strain rate is constant, temperature has a great influence on the superplasticity of the Al2O3/3Y-TZP laminated composite. A hat-like part with the greatest deform height is obtained at 1500 °C. The processing will be less effective at higher or lower temperature.

In order to investigate the superplasticity of ceramic/ceramic laminated composite under tensile stress, the superplastic deep-drawing process was simulated by FEM. The results shown that, the strain and stress conditions of laminated composite, made by ceramic with different superplastic formability, are better than that of monolithic ceramic. Consequently, the material may exhibit high superplasticity. To testify this, some experiments were carried out. Tape casting and hot-press sintering are used to fabricate Al2O3/3Y-TZP laminated composite. As-received material is deep-drawing at high temperature to research its superplasticity. The results shown that, when suitable strain rate and forming temperature were used, the as-received material has excellent superplasticity.

We theoretically investigate an optical system, which consists of a waveguide side-coupled to a cascade of cavities, the filtering properties by the time domain coupled-mode theory. In such a system, the filter operating bandwidth and the width of transmission peaks are completely determined by the mutual coupling coefficients between the cavities. The characteristics are numerically demonstrated in photonic crystals by the finite-difference time-domain method.

The synthesis, superplastic deep drawing and cavitation behavior of a fine-grained alumina–zirconia ceramic composite have been investigated. The results show that dense Al2O3/ZrO2 samples with average grain diameter of 230 nm can be elongated to a dome height of at least 12 mm at the punch rate of 0.6 mm·min−1 at 1400 °C. Deformed microstructure of the material indicates that not only the nucleation and growth of internal cavities are effectively suppressed but also the intragranular dislocation structures and sub-boundaries are observed around the nano-particles in alumina grains, which proves that intragranular dislocation creep is playing an important role in deformation. While the research on the deep drawing of the materials with the initial average grain size of 450 nm conforms that a plasticity controlled cavity growth process takes place during deformation.

We theoretically investigate the transmission properties of a cascade of cavities coupled to waveguide by the time domain coupled-mode theory. Based on the theoretical analysis, broad bandwidth optical waveguide intersections in photonic crystals are modeled and optimized. The transmission properties are simulated by finite-difference time-domain method and transmission coefficients higher than 98% for a wide frequency range between 0.360 (2 πc / a ) and 0.364 (2 πc / a ) are obtained.

2070 Background: Because detecting tumor-derived cell free DNA (cfDNA) in the blood of patients with primary or metastatic brain tumors is challenging, here we studied whether cerebrospinal fluid (CSF) could be serve as an alternative “liquid biopsy” by enabling measurement of circulating DNA within CSF to characterize tumor specific mutations. Methods: The paired cfDNA in CSF and plasma were collected from 20 patients with brain tumors and was subjected to enrichment for a 1.15M size panel cover exon regions from 1,086 genes. Followed by next generation sequencing on an Illumina X10 platform, the captured sequencing data was further processed using bioinformatics analysis to identify somatic mutations, including single nucleotide variants (SNV) and short insertions/deletions (indels). Results: The mutation profiles of 48 tumor associated genes in cfDNA were compared between the CSF and plasma. Our results showed that both average somatic mutation number and frequency identified in the cerebrospinal fluid was much higher than that in the corresponding plasma samples (25 vs. 18 & 1.39% vs. 0.55%). Among the twenty cases, one more potential actionable mutation, EGFR exon 19 deletion mutation with a 25.38% allele frequency variation, was only detected in the CSF cfDNA of a patient with brain metastasis lung cancer. Conclusions: Tumor mutations were detectable in CSF cfDNA of patients with different primary and metastatic brain tumors. Thus cerebrospinal fluid cell free DNA analysis could be a potential alternative analysis for patients with primary or metastatic brain tumors.

The high relative density of the ZrB2-based composite toughened by 25 vol.%Nb (ZN) was hot-pressed at reduced temperatures with low pressure of 30 MPa. Compared with the toughness of 2.3–3.5 MPa m1/2 and strength of 350 MPa of the monolithic ZrB2, the toughness and strength of the ZN composite were improved to 6.7 MPa m1/2 and 773 MPa, respectively, due to the addition of ductile Nb. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. Furthermore, the densification mechanism was analyzed and discussed. The results here pointed to a potential method for improving fracture toughness and strength of ZrB2-based ceramics.

A ZrB2–SiC nanocomposite ceramic in which 20 vol.% nanosized SiC powder was introduced into a ZrB2 matrix was fabricated by hot-pressing at 1900 °C for 60 min under a 30 MPa uniaxed load. The composite microstructure showed intragranular nanostructures that were peculiar to this material. Investigation of the mechanical properties revealed a flexural strength of 930 ± 28 MPa and a fracture toughness of 6.5 ± 0.3 MPa m1/2. These improved mechanical properties were strongly dependent on the formation of the unusual intragranular nanostructures.

Graphite containing nominally 40 vol.% ZrC (graphite–ZrC) was prepared from commercially available ZrO2 and graphite powders by hot pressing at 2000 °C in a vacuum. The oxidation behavior of the graphite–ZrC composite was carried out in dry stagnant air at the temperatures of 1200 and 2200 °C. Compared with the pure graphite, the graphite–ZrC composite exhibited good oxidation resistance because the mass loss of the composite powder was significantly lower than that of the pure graphite. The mass loss of graphite–ZrC at 2200 °C was lower than pure graphite at 1200 °C. Furthermore, the introduction of ZrC also improved the strength of the graphite–ZrC composite.

A ZrB2 ceramic containing 20 vol.% SiC and 10 vol.% graphite flake (ZrB2–SiC–G) was fabricated by hot pressing. It was shown that the fracture toughness was improved due to the introduction of graphite flake, whereas the flexure strength and hardness decreased slightly. The fracture toughness of ZrB2–SiC–G composite was 6.1 ± 0.3 MPa·m1/2, which was much higher than that of monolithic ZrB2, ZrB2–SiC composite and similar ZrB2–SiC–C composite. The toughening mechanisms are crack deflection and branching as well as stress relaxation near the crack tip. The results here pointed to a potential method for improving fracture toughness of ZrB2-based ceramics.

The present paper investigated the microstructure and mechanical properties of ZrB 2 -10 vol.%SiC p -10 vol.%ZrO 2 composites hot pressed at three temperatures. Phase transformability from t-ZrO 2 to m-ZrO 2 during fracture was analyzed through calculating the volume fractions of m-ZrO 2 and t-ZrO 2 on polished and fracture surfaces. The densification temperature was found to have a significant effect on the microstructure, phase transformation and the properties of the composites. When the composite was hot pressed at 1950 °C, the average grain size was 9.5 µm, and the fracture toughness was 4.5 MPa·m 1/2 . Comparatively, when the composite was hot pressed at 1750 °C, the average grain size was 3.4 µm, and the fracture toughness increased by ~ 50% to 6.8 MPa·m 1/2 .

A new oxidation method, high frequency induction heating, was introduced to investigate the rapid oxidation characteristics of ZrB 2 -SiC at 1800 °C up to 50 min. A high temperature was achieved within 30 s by adjusting the current or voltage. According to the isothermal test at 1800 °C, the oxidation kinetics for the composite followed a para-linear law. The specific weight gains increased from 4.86 to 12.89 mg/cm 2 when the exposure time increased from 10 to 50 min. When exposure for 30 min, a thin outmost layer of SiO 2 , a ZrO 2 layer and a thick SiC-depleted layer formed on the surface of specimens. The structural characteristic of oxidation layer obtained by high frequency induction heating was similar to those formed by standard oxidation furnace.

We present an optical structure, which consists of metal nanoparticles embedded in Fabry-Perot (F-P) cavity, to investigate the Fano resonance, which originates from the interaction between F-P mode and the plasmon modes supported by the nanoparticles. The coupling system is modeled theoretically by coupled-mode theory in time domain and the transmission properties are demonstrated numerically by the finite-difference time-domain method. The charge distribution features of the nanoparticle plasmon modes are further characterized by using boundary integral equation technology. Results show that the F-P modes can be used to active the optical inactive surface plasmon modes by breaking the mode symmetry.

We present an optical coupling system, which consists of waveguide, cavity and waveguide resonator, to investigate coupled-resonator-induced transparency effect. The transmission properties are analyzed theoretically by using coupled-mode theory in time domain. We also numerically demonstrate the effect by simulating the propagation of electromagnetic waves in photonic crystals by finite-difference time-domain method.

Carbon-bonded carbon fiber composites (CBCFs) containing SiC particles with uniform microstructure were produced using an innovative dispersion and flocculent approach. The mixed phenolic (Pf), SiC particles and chopped carbon fibers (Cf) were blended uniformly using polyethyleneimine (PEI) as a dispersant and polyacrylamide (PAM) as a flocculating agent. A homogeneous distribution of SiC particles coated CBCFs was obtained with the addition of 0.6 wt% PEI and 0.8 wt% PAM. The effect of PEI and PAM content on the microstructure, slurry dispersibility and stability of SiC-modified CBCFs was investigated. The compressive strength and compression modulus of the SiC-modified CBCFs were improved compared with unmodified CBCFs. This simple and versatile approach can be used to prepare large-scale and modified CBCFs.

In accordance with the structural characteristic and the form- and-position error demand of spline axis, a kind of measuring means is put forward in this paper to solve bouncing error of centering diameter on spline axis. Considering the noncontact laser measuring head, which uses the principle of laser optical triangle, the basic working principle of laser measuring head and the structure of measuring system are described in detail, and they are verified in the experiment.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.