Study on the properties of a novel shape-stable epoxy resin sealed expanded graphite/paraffin composite PCM and its application in buildings

In this study, a novel phase change material (PCM) of epoxy resin sealed expanded graphite/paraffin composite was developed as an independent attachment for building applications. A relatively high thermal energy storage density and a high thermal conductivity (2.141?W/(m·K)) were obtained in the composite PCM. The mass fraction of paraffin in the composite PCM could reach 94% without leakage of liquid paraffin when being heated at 50°C for more than 3 h, and the thermal cycle stability was good. Moreover, the thermal storage and release properties of this composite PCM with different thicknesses were studied by numerical simulation. The results showed that the thermal storage and release time are proportional to the thickness of the composite PCM, and there was almost no temperature gradient during the thermal storage and release process, which indicated that the thermal conductivity of this kind of composite PCM was high enough for building applications.     

A New Silicon-Containing Arylacetylene Resin With Amine Groups as Precursor to Si−C−N Ceramic

A new preceramic precursor was prepared by chlorination and ammoniation reaction of poly(methylsilyleneethynylenephenyleneethynylene) (MSEPE), [?SiH(CH₃)? C≡C?C₆H₄?C≡C?]_n. The obtained amine-modified silicon-containing arylacetylene resin (MSEPE-An) was a liquid polymer at room temperature and could be thermally cross-linked at temperatures lower than 200°C. The chemical structure of MSEPE-An was characterized by FTIR, ¹H NMR, and GPC. The pyrolysis of the cured MSEPE-An was carried out in N₂ atmosphere up to 1450°C to produce a Si?C?N ceramic composite. The ceramic composite was analyzed by FTIR and X-ray diffraction techniques. The electromagnetic wave absorption properties of a paraffin sample with 10 vol% Si?C?N ceramic powders were characterized in a frequency range of 2–18 GHz, according to a conventional reflection/transmission technique. Experimental results demonstrated that the Si?C?N ceramic composite provided good electromagnetic wave absorption performance.     

Thermal energy storage behaviour of nanoparticle enhanced PCM during freezing and melting

The present research work aimed to investigate the melting and solidification characteristics of NPCM. The NPCM was prepared using paraffin as the PCM and high conductive MWCNT as the nanomaterial without using any dispersant. The NPCM was prepared by dispersing MWCNTs with volume fractions of 0.3%, 0.6% and 0.9% in PCM as the base PCM. SEM morphology showed the uniform dispersion of MWCNTs in the paraffin wax. The MWCNT nano-additives PCMs showed two peaks in the heating curve by DSC measurement. Lessening in melting and solidification time of 30% and 43% was attained in the case of NPCM with 0.3% and 0.9%, respectively. It is observed from the DSC analysis that the latent heat of pure paraffin during freezing and melting cycle was 139.2 J/g (at 56.61 °C) and 131.8 J/g (at 57.55 °C), respectively. Whereas, the latent heat of NPCM with 0.9% of nanofluid was 150.7 J/g (at 56.36 °C) and 148.3 J/g (58.35 °C). It is construed that a maximum change in latent heat of 7.6% and 11% was observed between pure PCM and NPCM during freezing and melting cycle. For the lesser nanoparticle concentration (0.3% and 0.6%), the percentage change in latent heat was lesser than 0.9%.     

Structural and H2 sorption properties of MgH2�C10?wt%ZrCrM (M?=?Cu, Ni) nano-composites

Magnesium and its hydride MgH₂ are widely regarded as promising candidates for hydrogen storage materials due to its benefits of high gravimetric and volumetric capacity, excellent reversibility, abundance in the earth and a low cost. Much attention has been paid to improve its absorption/desorption kinetics, trying to make it useful for practical applications. To make composite of MgH₂ with other hydrogen storage compounds is an effective method to improve the hydrogen storage properties. In this study nano-composite of MgH₂ with ZrCrCu alloy was prepared using high energy ball-milling for 5 h under Ar atmosphere. Microstructure and morphology of the composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM). XRD patterns show that no alloy formation between MgH₂ and elements of the alloys takes place during milling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure?Ccomposition isotherms of these composites have been obtained in the pressure range 0.1?C10 bar at 275 and 300 °C. The absorption/desorption kinetics data have been analyzed using pressure 0.1?C5.0 bar at 275 and 300 °C to understand the mechanism of the hydriding/dehydriding reaction processes. A comparison of these results has been attempted with our previous published results of MgH₂?C10 wt%ZrCrNi in order to find the better composite for storage applications. It is observed by DSC curves that the onset temperature of hydrogen desorption is decreased for MgH₂?C10%ZrCrNi in comparison to MgH₂ which further decreased for MgH₂?C10%ZrCrCu. However, little loss in hydrogen absorption/desorption capacity is also observed for ZrCrCu composite in comparison to that of ZrCrNi composite.     

正二十四烷烃石蜡/膨胀石墨（EG）复合相变材料分子动力学模拟

相变材料(PCMs)在相变时的恒温、高能量密度等特性,经常应用于设备的热管理,但是PCMs导热系数低的缺点影响了其使用范围.本文采用分子动力学方法,模拟了在正二十四烷烃石蜡PCMs中添加不同结构(层状、交叉状)的膨胀石墨(EG)之后构成的复合PCMs的物性.文章通过径向分布函数(RDF)、声子态密度(PDOS)、比热容和导热系数这四个指标,分析了夹角为0°的层状结构,夹角为45°、90°的交叉状EG添加物对于石蜡热物性的影响. EG(0°、45°、90°)添加使得石蜡的原子分布在不同程度上变得更加均匀、紧密,使得石蜡的比热容有所增加.同时,两种类型的添加物提高了石蜡的PDOS,提高了导热系数.其中,EG(90°)添加物对于石蜡导热系数的提升最为明显,石蜡/EG(0°、45°、90°)模型中EG的含量分别为33.63 wt%、30.86 wt%和23.20 wt%,相比于的石蜡的导热系数分别提升了417.1%、345.7%和522.9%. EG的添加能够提高石蜡的导热系数,不同结构的EG对石蜡导热系数的影响有着较大的区别.     

Synthesis and elevated temperature performance of a polypyrrole-sulfur-multi-walled carbon nanotube composite cathode for lithium sulfur batteries

A sulfur-multi-walled carbon nanotube composite (S/MWCNT) was prepared using a two-step procedure of liquid-phase infiltration and melt diffusion. Polypyrrole (PPy) conductive polymer was coated on the surface of the as-prepared S/MWCNT composite by in situ polymerization of pyrrole monomer to obtain PPy/S/MWCNT composite. The composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical performance of the as-prepared cathode material was investigated at 25, 40, and 70 °C at various rates. It was found that temperature has dual effects on the performance of Li/S cells. Increasing the temperature, on one hand, facilitates the lithium ion transport through the cathode and, on the other hand, leads to faster dissolution of active material into the electrolyte. The PPy coating can effectively trap polysulfides in its porous structure, even at elevated temperatures, leading to the improvement of the discharge capacity, the cycle stability, and the coulombic efficiency. The electrochemical impedance spectroscopy (EIS) results reveal that the PPy coating reduces the formation of passive layer on the cathode surface, even at high temperatures, resulting in a better elevated temperature performance. A high reversible capacity of 945 mAh g^?1 was maintained after 50 cycles for the PPy/S/MWCNT composite at 70 °C at a rate of 0.5 C.     

Performance prediction of an absorption heat pump for utilization in industry

Recently, an absorption heat pump has been put on the market for industrial utilization. It is a H₂O-LiBr absorption machine which heats up water to 90°C with a cold source at 40°C. The capacity and COP of the machine have been studied by a computer program as a function of cold source temperature and heated fluid temperature. Also, a comparison with a compression heat pump is reported.     

Electrochemical performance of methyl methacrylate graft-copolymerized composite separator based on radiation polymerization technique

The pre-irradiation method is introduced to prepare methyl methacrylate graft-copolymerized composite separators. The morphologies of the grafted membranes (GMs) were observed under a scanning electron microscope. The cyclic voltammetry and electrochemical impedance spectra results indicated that the obtained polymer electrolytes (PEs) based on GMs could hold the excellent performance of Li⁺ transportation and possess good affinity with Li metal electrode. The Li/PEs/LiCoO₂ cells demonstrated excellent cycling performance with little capacity loss after 80 cycles. These cells also showed a good rate property and could retain 70.2% (25 °C) and 81% (75 °C) of discharge capacity at 2C rate as compared to that at C/5 rate. The results of this paper suggest that the high-quality composite separators can be obtained by pre-irradiation technique, and this also offered a new and convenient way for the large-scale manufacture of Li-ion polymer battery.     

Experimental Investigations on Latent Heat Storage Unit using Paraffin Wax as Phase Change Material

Thermal performance of a latent heat storage unit is evaluated experimentally. The latent heat thermal energy storage system analyzed in this work is a shell-and-tube type of heat exchanger using paraffin wax (melting point between 58°C and 60°C) as the phase change material. The temperature distribution in the phase change material is measured with time. The influence of mass flow rate and inlet temperature of the heat transfer fluid on heat fraction is examined for both the melting and solidification processes. The mass flow rate of heat transfer fluid (water) is varied in the range of 0.0167 kg/s to 0.0833 kg/s (1 kg/min to 5 kg/min), and the fluid inlet temperature is varied between 75°C and 85°C. The experimental results indicate that the total melting time of the phase change material increases as the mass flow rate and inlet temperature of heat transfer fluid decrease. The fluid inlet temperature influences the heat fraction considerably as compared to the mass flow rate of heat transfer fluid during the melting process of the phase change material.     

Preparation of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials by electrospinning

LiNi_0.5Mn_1.5O₄ cathode material was prepared by electrospinning using lithium hydroxide, manganese acetate, nickel acetate, acetic acid, ethanol, and poly(vinyl pyrrolidone) as raw materials. The effect of calcination temperature on the structure, morphology, and electrochemical properties was investigated. XRD results indicate that the LiNi_0.5Mn_1.5O₄ composite is well crystallized as a spinel structure at calcination temperature of 650 °C for 3 h. SEM results reveal that this composite has a nanofiber shape with average size of about 300–500 nm. Electrochemical performance tests reveal that this composite shows the initial discharge capacity of 127.8 and 105 mAhg^?1 at 0.1 and 3 C rates, respectively, and exhibits good cycling performance.     

Physical and water aging of glass fiber-reinforced plastic pipes

Physical and water aging of glass/epoxy composite — GFRE — pipes used for oil transport were investigated with special emphasis on their effect on the flexural and impact behavior. Different aging conditions were selected in order to simulate in-service environments trying to obtain reliable results from accelerated laboratory tests. In water uptake experiments at 80°C, the mass increases continuously, suggesting that an irreversible process occurs. In addition, samples aged in air at 80°C exhibit a DSC endothermic peak that can be related to physical aging. The calorimetric curve for specimens water aged at 80°C shows combined effects of water absorption and physical aging. On the other hand, while the independent effect of temperature and water aging on the composites mechanical response is only moderate, their combined effect seems to be dramatic. This result is mostly attributed to the weakening of the fiber–matrix interface induced by the water ging at high temperature, which consequently affects flexural and impact properties. SEM observations confirm the irreversible damage observed in water uptake experiments. Good interfacial adhesion between fiber glass and epoxy resin is observed for unaged specimens, whereas completely clean fibers are seen for specimens water aged at 80°C, indicating that the fiber–matrix interface is completely removed as a result of this aging condition.     

Gas turbine waste heat driven multiple effect absorption system

In this article, two arrangements of the multiple effect absorption (MEA) type are presented. They are using LiBr-H₂O and are powered by the exhaust of gas turbines. The first arrangement (MEA-I) is used as a cooling device and is coupled to an engine that drives a VC cooling unit. The other one (MEA-II) is used as a solution concentration machine and is coupled to an engine that drives a RO unit.Thermodynamic analysis for MEA-I showed a COP_t of 1.31 and 2.18 for evaporation temperatures of 5°C and 14°C respectively. Relative to the VC, the MEA-I increased the cooling capacity by 65% and 77% with payback periods of 35 months and 29 months for evaporation temperatures of 5°C and 14°C respectively.The MEA-II is analyzed using sea water as an example for a water based solution. Relative to a gas turbine driven RO desalination unit the MEA-II increased the fresh water produced by 13.5%. As a solution concentration machine the MEA-II requires 28% of the heat of evaporation with a solution top temperature of 36°C which makes it equivalent to a machine with five evaporators, where the solution top temperature reaches 66°C. Based on selling the released solvent byproduct water alone, the MEA-II would have a payback period of 77 months.     

Temperature dependence of the stress transfer for thermal resistance polymer composites by X-ray diffraction

Temperature dependence of the stress transfer from the matrix resin to the incorporated fiber has been measured for poly(p-phenylene benzobisoxazole) (PBO) fiber/bismaleimide (BMI) resin composite by a novel X-ray diffraction method. At 120°C, stress transfer and tensile strength of the PBO/BMI composite are superior to that of the PBO/epoxy composite, due to the excellent thermal resistance and good mechanical property of BMI resins. The PBO/BMI composite possesses good adhesion and excellent mechanical properties at high temperature, which are suitable for thermal resistance applications.     

Structural phase transitions in langmuir liquid crystal films

The isotherms of water molecule absorption on hyperfine Langmuir films made based on liquid crystals are investigated. A sharp increase in the adsorption capacity of the films at temperatures of 75°C (for a film with a thickness of ten monolayers) and 102°C (for a film with a thickness of five monolayers) has been revealed. This behavior is explained by structural phase transitions that take place at these temperatures.     

Shelf Life and Controlled Cure of Epoxies by Loaded Zeolite

Epoxy formulations based on the multi-functional amine hardener, dicyandiamide (Dicy), regularly contain a free accelerator for reducing the curing temperature and the time needed to complete the network formation. Unfortunately, all accelerators reduce the shelf life of these adhesives at 25°C. In order to solve this problem, accelerator-loaded zeolites fillers were developed, optimised with respect to host–guest interactions and characterised by Fraunhofer IFAM (Bremen, Germany) with regard to the release and curing behaviour in epoxy adhesive formulations. They are added to an epoxy adhesive (diglycidylether of bisphenol A (EP) and dicyandiamide (Dicy), mass ratio 100:6.7), stored at 25°C in regular air or cured (heated with β = 10 K/min to 170°C subsequent isothermal curing for 45 min). That shelf life and curing behaviour are investigated by FT-IR spectroscopy and modulated DSC. Compared to the EP containing free accelerator, the zeolite-filled EP possesses a threefold increase in shelf life at 25°C due to the immobilization of the accelerator in the pores of the zeolites. While the free accelerator acts steadily during heating, it is shown that the loaded zeolite releases the accelerator at about 76°C. Surprisingly, the released accelerator is not only involved in the chemical formation of the epoxy network but it accelerates the dissolution of Dicy considerably. As the result, network formation at 170°C finishes after not more than 19 min and the starting temperature for curing could be reduced to 140°C.     

Structural and magnetic properties of Co-C composite films and Co/C multilayer films

CoC composite films and Co/C multilayer films have been prepared by a method incorporating ion beam sputtering and plasma chemical vapor deposition. It has been found that the structure and magnetic properties of both the Co-C composite and the Co/C multilayer films depend strongly on the substrate temperature during deposition. The Co-C composite film deposited at room temperature is amorphous, with relatively low saturation magnetization and coercivity. On the other hand, the film deposited at 250 °C is composed of fine Co crystallites separated by amorphous C or Co-C phase. As a result, both the saturation magnetization and coercivity are increased compared with the film deposited at room temperature. When deposited at room temperature, the Co/C multilayer film exhibits good periodicity, with a period of 70 nm (Co: 40 nm, C: 30 nm) and sharp and flat Co-C interfaces. High magnetization (602 emu/cm³) and low coercivity (1.6 Oe) are obtained for such a film. However, increasing the substrate temperature to 250 °C was found to be detrimental to the magnetic properties due to the formation of cobalt carbide at the Co-C interface. Received: 11 July 2000 / Accepted: 13 July 2000 / Published online: 30 November 2000     

Preparation and Characterization of 2,2-bis[4-(3-Aminophenoxy)phenyl]propane/4,4′-Oxydianiline/4,4′-Oxydiphthalic Anhydride (3-BAPOPP/44ODA/ODPA) Polyimide Films with Various Co-monomer Ratios

A new diamine monomer 2,2-bis[4-(3-aminophenoxy)phenyl]propane (3-BAPOPP) was synthesized through two steps and its melting point was determined by differential scanning calorimetry (DSC). It was then copolymerized with 4,4′-oxydianiline (44ODA) and 4,4′-oxydiphthalic anhydride (ODPA) to obtain a series of aromatic polyimide(3-BAPOPP/44ODA/ODPA-PI) films. Fourier transform infrared (FT-IR) was used to characterize the structures of the monomer and the polyimide films. Water absorption, ultraviolet-visible (UV-Vis) spectroscopy, contact angle, DSC, and thermo-gravimetric analysis (TGA) were used to characterize the properties of 3-BAPOPP/44ODA/ODPA-P films. The results showed that the PI films had low water absorption in the range of 1.5%～1.9%, low surface energy in the range of 43.3 ～43.5 mJ/m², glass transition temperature (T_g) in the range of 192.5°C～226.1°C, and dielectric constant in the range of 2.79～3.02 at 1 MHz. The films also exhibited good thermal properties and good optical properties, with the ultra violet cut-off wavelength being in the range of 346～364 nm.     

Phenylacetylene chemisorbed on Pt (111), reactivity and molecular orientation as probed by NEXAFS Comparison with condensed multilayer and polyphenylacetylene

Near-edge X-ray absorption spectroscopy (NEXAFS) has been used to investigate the reactivity of phenylacetylene (PA) towards a Pt(111) surface and its molecular orientation. Spectra have been taken in the photon energy region 280–320 eV at both grazing and normal X-ray beam incidence angles with respect to the sample surface. NEXAFS K-edge spectra have been recorded for PA adsorbed in the monolayer as well as in the multilayer regime and, for comparison, the spectrum of the PA related polymer, polyphenylacetylene (PPA), has also been measured. The assignment of the π* and σ* resonances has been made on the basis of the chemical structure and interpreted with the help of ab initio calculations. Both the ionisation potentials for the C 1s electrons and the theoretical C K-edge absorption spectra have been calculated for all the six inequivalent carbon atoms of PA and of phenylethylene (PE) which is a model molecule for PPA. From the analysis of the data we have indication for an interaction involving mainly the CC triple bond of the acetylenic functional group of PA that undergoes opening and leads to the formation of a di-sigma bond with Pt, while the benzene CC bonds seem not affected. A polarization dependence has been evidenced for the π* resonances of PA adsorbed in monolayer condition indicating a molecular orientation of the phenyl ring π* orbitals between 37° and 34° relative to the normal to the crystal surface.     

Swelling Properties and Environmental Responsiveness of Superabsorbent Composite Based on Starch-G-Poly Acrylic Acid/Organo-Zeolite

Star-g-poly (acrylic acid)/organo-zeolite 4A (S-g-PAA/OZ) superabsorbent composite was prepared by grafting partially neutralized acrylic acid onto starch in the presence of organo-zeolite 4A (OZ) as an inorganic component. The morphology was characterized with scanning electron microscopy (SEM). Energy dispersive spectrometer (EDS) analysis revealed the fine distribution of OZ in superabsorbent composite. The swelling kinetics of the composites were characterized by means of a Schott's second-order model. The effect of OZ concentration in the composite on the water absorbency and swelling behavior were tested. The swelling properties of the composites were evaluated in various environments; pH, salinity, temperature, urea solution, and solvent-water mixtures. The activation energy (ΔE) for water during the swelling process was also determined through Arrhenius plots. The results showed that the proper amount of OZ was beneficial for improvement of the water absorbent capacity and the initial swelling rate in distilled water. The optimum prepared composite with 10 wt % OZ, possessed the maximum water absorption (511g/g) in distilled water and (521 g/g) in 0.1 wt % urea solution. The results inferred that S-g-PAA/OZ superabsorbent composite can be exploited for agriculture and medical applications.     

An Efficient Co/C Microwave Absorber with Tunable Co Nanoparticles Derived from a ZnCo Bimetallic Zeolitic Imidazolate Framework

A facile strategy is developed to modulate the content, particle size, and dispersity of magnetic metal nanoparticles (NPs) in porous carbon composite derived from Co/Zn bimetallic zeolitic imidazolate framework (ZIF). By adjusting the Co/Zn mole ratio in ZIF structure, porous carbon embedded with controllable Co NPs is synthesized through pyrolysis of CoZn‐based ZIF during which Zn is selectively evaporated away at 900 °C. The Co/C composite derived from ZIF with Co/Zn ratio of 1/1 (Co50/C composite) displays well‐dispersed Co NPs uniformly embedded in porous carbon. Meanwhile, the impedance matching of the composite is significantly improved due to the appropriate amount of Co NPs. Benefiting from the synergistic effect between Co NPs with magnetic loss and carbon with dielectric loss, the Co50/C composite exhibits excellent microwave absorbing properties with strong absorption, thin thickness, and lightweight, which is superior to previous metal–organic framework‐derived absorbers. When the filler loading of Co50/C composite in paraffin matrix is only 20 wt%, a minimum reflection loss of −51.6 dB is achieved at a very thin layer thickness of 1.6 mm.