Thermal Shock Resistance of Laminated ZrB2–SiC Ceramic Evaluated by Indentation Technique

In this work, the thermal shock behavior of laminated ZrB₂–SiC ceramic has been evaluated using indentation‐quench method based on propagation of Vickers cracks and compared with the monolithic ZrB₂–SiC ceramic. The results showed that the laminated ZrB₂–SiC ceramic exhibited better resistance to crack propagation and thermal shock under water quenching condition, and the critical temperature difference (ΔT_c) of laminated ZrB₂–SiC ceramic (ΔT_c ≈ 590°C) was much higher than that of monolithic ceramic (ΔT_c ≈ 290°C). The significant improvement in thermal shock resistance was attributed to residual stresses enhancing the resistance to crack growth during thermal shock loading.     

Fabrication and functionalization of carbon nanotube films for high-performance flexible supercapacitors

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Carbon nanotube (CNT) films have shown many promising advantages in the development of high-performance flexible supercapacitors in terms of electrode specific area, mechanical reliability under bending and stretching, electron and ionic mobility tailored for high-rate performance etc. In this review, the recent progress in the design, preparation and functionalization of CNT film based electrodes for the fabrication of high-performance flexible supercapacitors are introduced in details, including the synthesis of conductive CNT films for the electrodes of supercapacitors, and the functionalizations of CNT film with other high-capacitance materials by both mixing and in situ growth strategies for high-performance composite electrodes. Furthermore, we also discussed the assembly strategies, prototypes and electrochemical performance of flexible supercapacitors based on CNT film composite electrodes. At last, the challenges and trends of the CNT film based flexible supercapacitors are prospected as well.     

Nanomechanical and tribological behavior of hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposites for biomedical applications

A hydroxyapatite (HA) particulate reinforced ultrahigh molecular weight polyethylene (UHMWPE) nanocomposite is fabricated by internal mixer at 180°C and using of paraffin oil as a processing aid to overcome the high viscosity of melted UHMWPE. The reinforcing effects of nano‐HA are investigated on nanomechanical properties of HA/UHMWPE nanocomposites by nanoindentation and nanoscratching methods. Results show that the nanocomposite with 50 wt % nano‐HA exhibits a Young's modulus and hardness of 362.5% and 200% higher, and a friction coefficient of 38.86% lower than that of pure UHMWPE, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42052.     

A new method for estimating the isothermal devitrification and crystallization of mold powder slags from non-isothermal DSC data

The rate of formation of crystalline phases from liquid and glassy mold powder slags is of foremost importance in the performance of molds used for continuous casting of steel. This study shows how the Induction Period (of Šimon and Kolman) and the Kissinger methods can be combined in a kinetic model to evaluate the isothermal rate of formation of crystalline phases from thermo-analytical data – onset temperature, T_i, peak maximum temperature, T_m, shape index, S, and conversion at peak maximum, x_m – collected at various linear heating and cooling rates. The diagram of the extent of isothermal transformation as a function of time calculated for a commercial mold powder, used for casting low carbon steels, shows good agreement with the degree of transformation observed in photomicrographs of glass disks devitrified isothermally, at several temperatures for different times. Additionally, qualitative and quantitative X-ray diffraction results obtained at room-temperature from glass powder samples treated isothermally and quenched also show good accord with the degree of transformation predicted with the kinetic model developed in this work.     

Preparation and thermal performance analysis of novel multilayer cladding structure composites

With regard to the adiabatic principle of insulation, a novel multilayer cladding structure composites (MCSC) with vacuum inside was put forward, which could be used in high temperature insulation field. In the composites, SiO₂ was used to fill the microcracks and protect the carbon matrix from oxidizing. This novel material was composed of two parts, one was the core material consisted of SiC foam ceramic, the other was the flawless outer shell consisted of carbon fiber reinforced composites with vacuum inside that produced by Chemical Vapor Infiltration (CVI) Pyrolytic Carbon (PyC) and silicasol-infiltration–sintering methods. Material density was 0.81 g/cm³. The effective thermal conductivity of MCSC ranged from 0.193 W/m · K to 0.721 W/m · K within the temperature from 303 K to 703 K, which was 13.5–23.3% lower than the value of SiC ceramic foam core materials. However, at 1473 K, the measured data of MCSC and SiC foam were 1.815 W/m · K and 1.911 W/m · K, respectively. It was only 5.02% lower than that of SiC foam.     

FE modeling of the compressive behavior of porous copper-matrix nanocomposites

Compressive mechanical test and numerical simulation via finite element modeling have been employed on closed-cell copper-matrix nanocomposite foams reinforced by alumina particles. The FE analysis' purpose was to model the foam deformation behavior under compressive loading and to investigate the correlation between material characteristics and the compressive mechanical behavior. Exploring this, several foam samples with different conditions were manufactured and compression test was carried out on the samples. Scanning electron microscopy and image analysis have been performed on the foam samples to obtain the required data for the numerical simulation. The stress–strain curves exhibited plateau stress between 18 and 112.5 MPa and energy absorption in the range of 20.03–51.20 MJ/m³ for the foams with different relative densities. The foams exhibited enhanced mechanical properties to an optimum value, as a consequence of increasing the reinforcing nanoparticles, through both experimental tests and numerical simulation data. Also, the validated model of copper-matrix nanocomposite foams has been used to probe stress distribution in the foams. In addition, the results obtained by numerical simulation via ABAQUS CAE finite element modeling provided support for experimental test results. This confirmed that FEM is a favorable technique for predicting mechanical properties of nanocomposite copper foams.     

Design of high sorbent pectin/CaCO3 composites tuned by pectin characteristics and carbonate source

Five pectin samples – which differ by the methylation degree and/or amide content – were used to prepare inorganic/organic composites by CaCO₃ mineralization from supersaturated solutions. The pectin chemical structure and concentration could control the composite superstructure by induction or orientation of crystal growth. The inorganic materials may also control CaCO₃ polymorphism and morphologies and therefore different carbonate sources, such as Na₂CO₃, diethylcarbonate or ammonium carbonates, were used as modulators for crystal growth. The morphology of the new CaCO₃/pectin composites was investigated by SEM and the polymorphs content by X-ray diffraction, as compared to bare CaCO₃ samples prepared in similar conditions. The composites were tested as sorbents for Cu(II) and Ni(II) ions.     

High piezoelectric response in the new coexistent phase boundary of 0.87BaTiO3–(0.13-x)BaZrO3–xCaTiO3

An investigation of the coexistent ferroelectric phase was carried out on the ternary system of 0.87BaTiO₃–(0.13-x)BaZrO₃–xCaTiO₃ [abbreviated as BT–BZ–xCT (where 0.00 ≤ x ≤ 0.13)]. Temperature-, frequency-dependent dielectric data, electric field-dependent strain and polarization as a function of composition are presented in order to understand the relationships of structure-properties and find the high piezoelectric response in this system. Results showed that ceramics in the composition range of 0.00 ≤ x < 0.04 were of a rhombohedral structure and transformed into a tetragonal structure at x > 0.06. The multiphase coexistence of the rhombohedral and tetragonal phase in this system was identified at x = 0.06. A large, virtually hysteresis-free electric field induced strain of 0.23% was achieved with the composition, x = 0.06, at 40 kV/cm on the boundary between rhombohedral and tetragonal phase. This relates to an extraordinarily high and normalized piezoelectric coefficient (S_max/E_max) of 1280 pm/V, which was reached at a low electric field applied at 10 kV/mm. These results indicated that a high piezoelectric response may stem primarily from the rhombohedral-tetragonal phase boundary, due to greater lattice softening and reduced energy barriers for polarized rotation.     

Fabrication and microstructure of porous SiC ceramics with Al2O3 and CeO2 as sintering additives

In the present study, porous silicon carbide ceramics were prepared via spark plasma sintering at relatively low temperatures using Al₂O₃ and CeO₂ as sintering additives. Sacrificial template was selected as the pore forming mechanism, and gelcasting was used to fix the slurry in a short time. The evolution process of the microstructures during different steps was observed by SEM. The influence of the sintering temperature and sintering additives on the shrinkage and porosity of the samples was studied. The microstructures of different samples were characterized, and the mechanical properties were also evaluated.     

Synchrotron X-ray tomographic characterization of CVI engineered 2D-woven and 3D-braided SiCf/SiC composites

The properties of ceramic matrix composites strongly depend upon their complex internal structures. To better understand and improve the properties of the silicon carbide fiber-reinforced silicon carbide matrix composites (SiC_f/SiC), we explored the microstructural properties of composites reinforced with either two-dimensional (2D) woven or three-dimensional (3D) braided preforms using synchrotron X-ray computed microtomography. Transects and volumetric images of the composites were reconstructed from objection images and the microstructures were investigated in three spatial directions. The network of void space in a composites was visualized in 3D and quantitative analysis of the porosity was performed to characterize the fiber-tissue structures. 2D-woven SiC_f/SiC composite exhibited important fluctuations of porosity in different directions and the stacking of plies had a significant effect on the porosity distribution. In contrast, 3D-braided SiC_f/SiC composites showed much less variation of porosity. We found the degree of densification of the composite also influenced the porosity distribution.