Search

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The coupled effects of heat and frequency in very-high-cycle fatigue are known under ultrasonic testing, while the heat dissipation behavior of welded joints is less investigated. In this work, the specimen surface temperature of a low-strength-steel welded joint and its base metal were monitored by infrared thermal imaging technique under ultrasonic fatigue loading. Results showed that the surface temperature distribution of both welded and base metal exhibited a parabola shape, and the temperature evolved with three stages. The location of the highest temperature within the weld metal correlated well with fatigue failure location. The inhomogeneity and asymmetry of temperature distribution implied a dominant role for heat transfer mode and insignificant influence of microstructure heterogeneity or specimen type. The nature of heat dissipation in low-strength steel in ultrasonic fatigue was thermal–mechanical coupling effect, which should be paid close attention in the standardization of ultrasonic fatigue testing. [ABSTRACT FROM AUTHOR]

A new amidoxime-functionalized ultrahigh molecular weight polyethylene fibrous adsorbent (UHMWPE-g-PAO) was used for the recovery of Au(III) from acid aqueous solution. The maximum experimental absorption capacity of UHMWPE-g-PAO fiber was found to be approximately 220.0 mg·g−1. Au adsorption on UHMWPE-g-PAO was characterized by synchrotron radiation-based microcomputed tomography (SR-μ-CT), transmission electron microscopy (TEM), X-ray absorption near-edge structure spectroscopy (XANES) and synchrotron radiation-based Fourier transform infrared microspectroscopy (SR-FTIR). The SR-μ-CT and TEM results showed the distribution features of gold particles on the fiber. The mechanism of Au(III) recovery from aqueous solutions by UHMWPE-g-PAO was based on the adsorbed Au(III) ions, which were reduced to metallic zero-valent gold (Au(0)) by amino groups (–NH2) in the amidoxime (AO) groups during the adsorption process, as confirmed by high-resolution TEM (HRTEM) and XANES analyses. X-ray diffraction (XRD) results indicated that the incineration ashes contained metallic zero-valent gold. In conclusion, this amidoxime-functionalized fibrous adsorbent is a promising material for recovering gold from aqueous solution. [ABSTRACT FROM AUTHOR]

Combined heat and moisture transportation in an enclosure has been numerically investigated, which could benefit the sustainable building energy conservations and electronic cooling designs. An adiabatic and impermeable partition of finite thickness is considered, placed in the enclosure following an ordered arrangement. Effects of length and location of the partition, buoyancy ratio and thermal Rayleigh number on convective heat and moisture transfer rates in the enclosure are discussed. Firstly, this situation of the partition placed in the horizontal wall is studied, where inhibition effect of partition is observed. It is seen that the location of partition put relatively weaker influences on the heat and mass transfer in the regime of thermal-driven flow, when its length exceeds the critical value. Additionally, inhibition effect is more pronounced as the partition is fixed in center of vertical wall. Furthermore, local heat and mass transfer rates could be suppressed when the buoyancy ratio becomes negative. Finally, thermal Rayleigh number greatly affects the transport structures of fluid, heat and moisture, whatever aiding flow or opposing flow situations. Heat and mass transfer potentials could be promoted with increasing thermal Rayleigh numbers. Present work could be adopted to optimize the enclosure flows simultaneously with heat and moisture transport. [ABSTRACT FROM AUTHOR]

A novel quaternary ammonium polyethylene nonwoven fabric for removing chromium ions from water was prepared via radiation-induced grafting of glycidyl methacrylate and further modification with N,N′-dimethylethylenediamine. The structural and morphological characteristics of the adsorbent were analyzed using Fourier transform infrared spectroscopy (FTIR), thermogravimetry and differential thermogravimetry (TG/DTG), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The influences of several principal factors, including pH value, initial Cr(VI) concentration, contact time, and coexisting anions (including SO42−, CO32−, NO3−, PO43−, and Cl−), on adsorption performance were investigated via batch tests. The results showed that the optimum removal efficiency was 99.2% at pH 3 and the maximum adsorption quantity for Cr(VI) at 25 °C was 336 mg/g. The adsorption kinetic parameters were better fitted with the pseudo-second-order kinetic model, and the equilibrium data were described very well by the Freundlich isotherm model. Furthermore, the as-synthesized adsorbent exhibited excellent regeneration and recyclability while maintaining high adsorption performance after five adsorption/desorption cycles. [ABSTRACT FROM AUTHOR]

A new functionalized ultrahigh molecular weight polyethylene-based chelating fiber (UHMWPE-AM) for trace uranium extraction from wastewater was synthesized by preirradiation grafting modification. Adsorption behavior of adsorbent was examined under varying conditions like solution pH, contact time, initial ion concentration and adsorbent dose. The results showed the maximum removal of U(VI) was 99.7% at pH 4. Adsorption isotherm was in agreement with Langmuir isotherm equation with the maximum monolayer adsorption capacity of 16.56 mg/g, and the pseudo-second-order model can well describe the kinetics process. The dominant coordination mechanism of U(VI) on the UHMWPE-AM fibers was ascribed to inner-sphere surface complexation. [ABSTRACT FROM AUTHOR]

A new hyperbranched polysiloxane containing maleimide (HPMA) was synthesized through the reaction between N-(4-hydroxyphenyl) maleimide and 3-glycidoxypropyltrimethoxysilane, which was then used to prepare cyanate ester (CE) resin-based hybrids (coded as HPMA x/CE, where x is the weight fraction of HPMA in the hybrid). The curing behavior of uncured hybrids and the typical properties (impact strength and dielectric properties) of cured hybrids were systemically investigated. Results show that the performance of hybrids is greatly related with the content of HPMA. Hybrids have obviously lower curing temperature than CE, overcoming the poor curing characteristics (higher curing temperature and longer curing time) of neat CE, for example, the curing peak temperature of HPMA20/CE is about 65°C lower than that of CE. In the case of cured resin and hybrids, the hybrids exhibit decreased dielectric constant and loss than CE resin; moreover, the former also exhibits lower water absorption than the latter. Specifically, the dielectric loss of HPMA15/CE hybrid is only about 27% of that of neat CE resin. In addition, the hybrids with suitable contents of HPMA have significantly improved impact strengths. The overall improved properties suggest that HPMA x/CE hybrids have great potential in applications needing harsh requirements of curing feature, dielectric properties, and toughness. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

An improved method is developed to synthesize octavinylsilsesquioxanes (VPOSS) with shorter time and higher yield, and then VPOSS is used to prepare new hybrids based on bismaleimide-triazine (BD/CE) resin, coded as VPOSS/BD/CE. The effect of the content of VPOSS on the key properties including curing behavior, thermal, mechanical, and dielectric properties as well as water resistance of VPOSS/BD/CE hybrids were systematically discussed. Compared with BD/CE resin, hybrids show similar curing behavior but different chemical structures and thus macro-performance. These key properties of hybrids are dependent on the content of VPOSS, all hybrids show significantly improved dielectric properties, water resistance, and dimensional stability; moreover, the hybrids with suitable content of VPOSS have bigger impact strengths. Specifically, with the addition of 7 wt% VPOSS to BD/CE resin, the dielectric constant decreases from 3.7 to 3.2, the dielectric loss decreases 55%, and the coefficient of thermal expansion reduces 23%; moreover, the glass transition temperature and initial decomposition temperature increase about 15°C. The attractive integrated properties suggest that VPOSS/BD/CE hybrids have great potential to be used as structural and functional materials for many cutting-edge fields. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The correlation between microstructure and dielectric properties of cyanate ester (CE)/hollow silicate tube (HST) hybrids was investigated by positron annihilation lifetime spectroscopy, coincidence Doppler-broadening spectroscopy, Fourier transform infrared spectra, and dynamic mechanical analyses. The addition of HST to CE resin brings a multi-aspect influence (cross-linked structure and density, free volume, and interfacial action) on the structure of the cross-linked network and thus results in significantly varied dielectric properties. There is an optimum content of HST in hybrids to get the lowest dielectric constant and loss. When the content of HST is smaller than the percolation threshold, the hybrid has decreased dielectric constant and loss; this mainly results in the reduced size of free volume and orthopositronium intensity ( I3), although when the content of HST is larger than the threshold, the increased I3 and the size of free volume as well as the interfacial polarization are responsible for the significantly enlarged dielectric constant and loss. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

High-performance insulating materials have been increasingly demanded by many cutting-edge fields. A new kind of high-performance composites with high thermal conductivity, low coefficient of thermal expansion (CTE), and low dielectric loss was successfully developed, consisting of hexagonal boron nitride (hBN) and 2,2′-diallylbisphenol A (DBA)-modified 4,4′-bismaleimidodiphenylmethane (BDM) resin. The effects of hBN and its content on the integrated properties, including curing behavior of uncured system, the CTE, thermal conductivity, dielectric properties, and thermal resistance of cured composites, are systematically investigated and discussed. Results show that there are amino groups on the surface of hBN, which supply desirable interfacial adhesion between hBN and BDM/DBA resin and a good dispersion of hBN in the resin. With the increase of the hBN content, the thermal conductivity increases linearly, whereas the CTE value decreases linearly; in addition, dielectric loss gradually decreases and becomes more stable over the whole frequency from 10 to 109 Hz. In the case of the composite with 35 wt% hBN, its thermal conductivity, CTE in glassy state, and dielectric loss are about 3.3, 0.63, and 0.5 times of the corresponding value of BDM/DBA resin, respectively. These attractive integrated properties suggest that hBN/BDM/DBA composites are high-performance insulating materials, which show great potential in applications, especially for electronics and aerospace industries. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel kind of incompletely condensed polyhedral oligomeric silsesquioxane (TAP-POSS) containing allyl groups was successfully synthesized, and its structure was characterized by fourier transform infrared, nuclear magnetic resonance (H-NMR and Si-NMR) and X-ray diffraction. In addition, TAP-POSS was hybridized with 2,2′-diallylbisphenol A (DBA)-modified 4,4′-bismaleimidodiphenylmethane (BDM) resin to develop a new kind of hybrids with simultaneously improved thermal stability and dielectric properties. Compared with BDM/DBA resin, the BDM/DBA/TAP-POSS hybrids have obviously increased thermal resistance reflected by the increased glass transition temperature ( T) and char yield at high temperature. For example, the T of modified BDM/DBA resin with only 3.0 wt% TAP-POSS is 330 °C, which is 36 °C higher than that of pure BDM/DBA resin. On the other hand, the dielectric properties over wide frequency and temperature ranges are thoroughly investigated, and results show that the dielectric constant and loss of all hybrids are not only lower than those of BDM/DBA resin over the whole frequency and temperature ranges tested, but also exhibit smaller dependence on temperature and frequency. These phenomena can be explained from the variety of cross-linked structure induced by the presence of TAP-POSS. The outstanding integrated properties of BDM/DBA/TAP-POSS hybrids suggest that TAP-POSS has advantages over conventional POSS, thus the method proposed herein is a new approach to develop high performance structural/functional materials for cutting-edge industries. [ABSTRACT FROM AUTHOR]

A novel method is proposed to synthesize new mesoporous silica containing amine groups (MPSA), and it was further employed to modify bismaleimide-dialllyl bisphenol (BD)/cyanate ester (CE) resin to form novel MPSA/BD/CE hybrids; in addition, the typical properties of MPSA/BD/CE were systematically investigated. Results show that these hybrids have very low dielectric constant and loss as well as good thermal properties. Compared with BD/CE resin, all hybrids have not only decreased dielectric constant and loss but also similar dependence of dielectric properties on frequency over the whole frequency from 10 to 106 Hz. Specifically, with the addition of MPSA to BD/CE resin, the dielectric constant reduces from 3.5 to 3.0, and the dielectric loss is only 85% of that of BD/CE resin. Note that all hybrids show better thermal resistance (reflected by higher glass transition temperature, decreased maximum degradation rate, and higher char yield at 800°C) than BD/CE resin. All these differences in macro-properties are attributed to the different structure between MPSA/BD/CE hybrids and BD/CE resin. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A new addition curable silicone resin (ASiR) system with excellent dielectric and thermal properties was developed, which consists of only two components: poly(methylphenylvinylsiloxane) (PMPVSi) and an end-capped hydrogen-functionalized hyperbranched polysiloxane (EHFHPSi). PMPVSi is synthesized by a green and controllable process; EHFHPSi is first synthesized via A2 + B3 approach, and then end-capped by hexamethyldisiloxane (HMDS). Three formulations were designed to investigate the optimum stoichiometry. Results show that cured ASiR resins have greatly different dielectric and thermal properties because of the different chemical structure of cured networks resulting from the different stoichiometries. The resin with a suitable stoichiometry has not only excellent dielectric properties including extremely low dielectric constant (2.96 at 1 Hz) and loss (0.0003 at 1 Hz) as well as good stability on frequency, but also outstanding thermal resistance, exhibiting great potential to be used as a new kind of high-performance resins for many cutting-edge industries, especially the microelectronic and insulation fields. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Novel high performance hybrids (N-PPSQ/BDM/DBA) with very good flame retardancy, thermal, and dimensional stability as well as low dielectric constant and loss were developed, which consist of 4,4′-bismaleimidodiphenyl methane/2,2′-diallyl bisphenol A (BDM/DBA) resin and a novel functionalized ladderlike polyphenylsilsesquioxane (N-PPSQ). N-PPSQ was synthesized through the hydrolysis and condensation between phenyltrimethoxysilane and γ-aminopropyl triethoxysilane, and its structure was characterized by X-ray diffraction, nuclear magnetic resonance, gel permeation chromatography, and Fourier transform infrared. Compared with BDM/DBA resin, N-PPSQ/BDM/DBA hybrids show significantly improved integrated performances including remarkably reduced dielectric constant and loss, significantly improved flame retardancy, thermal, and dimensional stability, showing great potential for applications having harsh requirements in integrated performances. For example, in the case of the hybrid with 15 wt% N-PPSQ, its coefficient of thermal expansion in glassy and rubbery state are only about 49 and 42% of that of BDM/DBA resin, respectively; its limiting oxygen index increases from about 26.1-42.1%; while its dielectric loss is only about 87% of that of BDM/DBA resin at 1 kHz. These attractive improved properties are attributed to the variety in the cross-linked structure induced by the presence of N-PPSQ. [ABSTRACT FROM AUTHOR]

Novel modified cyanate ester (CE) resins with decreased dielectric loss, improved thermal stability, and flame retardancy were developed by copolymerizing CE with hyperbranched phenyl polysiloxane (HBPPSi). HBPPSi was synthesized through the hydrolysis of phenyltrimethoxysilane, and its structure was characterized by 1H-NMR, 29Si-NMR, and Fourier transform infrared spectra. The effect of the incorporation of HBPPSi into CE resin on the curing behavior, chemical structure of cured networks, and typical performance of HBPPSi/CE resins were systemically evaluated. It is found that the incorporation of HBPPSi into CE network obviously not only catalyzes the curing of CE, but also changes the chemical structure of resultant networks, and thus results in significantly decreased dielectric loss, improved thermal stability, and flame retardancy as well as water absorption resistance. For example, in the case of the modified CE resin with 10 wt% HBPPSi, its limited oxygen index is about 36.0, about 1.3 times of that of neat CE resin, its char yield at 800°C increases from 31.6 to 35.4 wt%; in addition, its dielectric loss is only about 61% of that of neat CE resin at 1 kHz. All these changes of properties are discussed from the view of the structure-property relationship. The significantly improved integrated properties of CE resin provide a great potential to be used as structural and functional materials for many cutting-edges fields. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel kind of solventless silicone hybrids (SSiH) containing branched poly(methylphenylvinylsiloxane) (PMPVSi), end-capped hydrogen-functionalized hyperbranched polysiloxane (EHFHPSi), and octavinyl-polyhedral oligomeric silsesquioxane (OVPOS) was developed through a hydrosilylation reaction. Each of the three basic components was synthesized by harmless and recyclable methods. The new hybrids are considerably suitable for vacuum pressure impregnation process, and can serve as an excellent class C insulating material. The effect of differing stoichiometries of OVPOS and EHFHPSi on the performance of cured hybrids is discussed. Results show that SSiH hybrids possess excellent dielectric and thermal properties as well as low viscosity. The reduction in the dielectric constant and the improvement of thermal property of SSiH hybrids can be explained by the unique structure and morphology of hybrids resulting from the presence of OVPOS and EHFHPSi. The novel silicone hybrids exhibit great potential to be used for many cutting-edge industries, especially the microelectronic and insulation fields. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

High-performance thermosetting resins should have good toughness and stiffness, so simultaneously toughening and stiffening is the main target in developing high-performance resins. A novel modified cyanate ester resin with improved toughness and stiffness was developed by copolymerizing 2,2′-bis(4-cyanatophenyl)isopropylidene (CE) with hyperbranched polyphenylsilsesquioxane (HBPPSi). The mechanical properties and their nature were systematically investigated from the viewpoint of structure-property relations using positron annihilation lifetime spectroscopy and spectral analyses. It is found that a suitable content of HBPPSi in CE resin can effectively improve toughness and stiffness. In the case of the CE resin modified with 10 wt% HBPPSi, its impact and flexural strengths are 21 kJ m−2 and 148 MPa, respectively, about 2.6 and 1.4 times of those of neat CE resin. The flexural modulus increases from 3.0 (for neat CE resin) to 3.4 GPa. The results of dynamic mechanical analyses also corroborate the static mechanical properties. The improved toughness and stiffness of CE resin can be attributed to the synergistic effect resulting from changes of both polymer chain structure and aggregation state structure. These attractive features of HBPPSi/CE resins suggest that the method proposed herein may be a new approach for the development of high-performance resins for cutting-edge industries. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]