The dimensional stability and dynamic mechanical properties on bamboo (non woven mat)/kenaf (woven mat) hybrid composites was carried out in this study. The hybridization effect of bamboo (B) and ...kenaf (K) fibers at different weight ratio were studied at B:K:70:30, and B:K:30:70 while maintaining total fiber loading of 40% by weight. The coefficient of thermal expansion (CTE) and dynamic mechanical properties of composites were analyzed by thermomechanical anlayzer (TMA), and dynamic mechanical analyzer (DMA), respectively. Positive hybridization effects were observed on B:K:50:50 hybrid composite with lowest CTE and highest dynamic mechanical properties among all composites. The dimensional stability were strongly influence by the fiber orientation where all composites shows prominent expansion in the transverse fibers direction but relatively low expansion in longitudinal fibers direction. Dynamic mechanical properties in term of complex modulus (E*), storage modulus (E′), loss modulus (E″), Tan delta and Cole-Cole plot were studied. DMA results reveal that B:K:50:50 hybrid composite possess the highest complex modulus due to the strong fiber/matrix interfacial bonding which supported by the coefficient of effectiveness and Cole-Cole plot. Hence, it is concluded that 50:50 weight ratio of bamboo and kenaf fibers is the optimum mixing ratio to enhance both dimensional and dynamic mechanical properties of hybrid composites, and it can be utilized for automotive or building materials applications which demand high dimensional stability and dynamic mechanical properties.
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Thermal therapy based on phase change materials (PCMs) has broad application prospects in the field of personal thermal care. Herein, a serious of EPDM/MXene/PW (EMP) based shape-stable phase change ...composites (SSPCCs) with excellent flexibility was prepared in large scale via water-assisted melt blending. The MXene nanosheets were dispersed well in the EPDM matrix during the melt blending processes with the assistance of water. With the introduction of a small amount of MXene nanosheets (only 0.8 wt%), the light-to-thermal conversion efficiency of SSPCCs were improved obviously. The melting phase change enthalpy and freezing phase change enthalpy of EMP-0.8 are about 120 J/g and 115 J/g, respectively. And after 200 times thermal cycles and 25 times light-thermal cycles, the phase change enthalpy of obtained EMP-0.8 SSPCC hardly changes. All the results show that the obtained EMP based SSPCCs can be fully utilized in the field of personal thermal therapy.
Authentic representative gum exudate samples from Acacia species namely Acacia senegal var. senegal (ASG), Acacia mellifera (AMF), Acacia seyal var. seyal (ASY), and Acacia tortilis var. raddiana ...(ATR), were physicochemically analyzed. The moisture, ash, nitrogen and protein content, pH, specific optical rotation, and number average molecular weight were found to be ranging from 9.76% to 8.35%, 3.40% to 2.05%, 0.243% to 1.549%, 1.610% to 10.378%, 4.45 to 4.94, −48.25 to +86.75 and 0.24×106 to 2.95×106 respectively. The 13C and 1H NMR spectra of gum samples showed similarity in individual sugar components, but characteristic patterns of each gum, were observed. FTIR spectra of the studied gums show the presence of the same functional groups in the four gums. DSC and TGA thermograms were characteristic for each gum. Evaluation of the functional properties of the four gums indicated that ATR gum bears the best emulsification characteristics in terms of emulsion’s stability and emulsification power.
Aiming at the development of thermal environmental barrier coatings (TEBCs) material, the factor of grain size is introduced into the high-entropy rare-earth disilicate for the first time. The ...(Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7 with smaller grain size was prepared by one-step pressureless sintering method. Results of thermal conductivity and coefficient of thermal expansion (CTE) reveal that thermal conductivity of (Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7 bulk material is lower than that all existing EBCs and even most TBCs and potential TEBCs material, which is 0.686 W m−1 °C−1 at 1300 °C. Excellent thermophysical properties indicate that designed (Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7 with small grain size can be used as a promising TEBCs material.
•It is the first time to introduce the grain size into the thermal conductivity of high-entropy rare earth silicate materials.•The prepared (Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7 has very low thermal conductivity than all existing EBCs materials.•(Yb0.2Tm0.2Lu0.2Sc0.2Er0.2)2Si2O7 with small grain size has excellent thermophysical properties and is a candidate for TEBCs.
Ultra High Molecular Weight Polyethylene with a reduced number of entanglements can be stretched in the solid state both uni- or biaxially to produce highly oriented tapes and films. The chain ...orientation, in combination with the reduced number of chain ends, is responsible for the high tensile modulus and tensile strength of the drawn materials, and, as we report here, also for the high thermal conductivity achieved through lattice movements. A property such as thermal conductivity in an electrical insulator makes UHMWPE tapes and films of great applicative interest. In-plane laser-flash thermal analysis has been applied to measure the thermal diffusivity of samples of different molecular weights stretched both uni- and biaxially, and a strong correlation has been found between the drawing ratio and the resulting in-plane thermal conductivity. Values of at least 40 W/m K have been achieved for UHMWPE having Mw comprised between 2 and 10 million, while higher values of 65 W/m K are observed for the higher Mw samples having relatively lesser number of chain ends. Surprisingly the biaxially stretched samples also show in-plane conductivity, with the highest value reaching 18 W/m K, comparable to stainless steel.
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•‘Disentangled’ UHMWPE can be stretched in the solid state to produce highly oriented tapes and films.•The chain orientation is responsible for the high tensile modulus/strength of the drawn materials.•High thermal conductivity is also observed, through lattice movements.•Uni-axially oriented tapes reach thermal conductivities up to 65 W/m K.•Bi-axially oriented films show thermal conductivities up to 18 W/m K.
A flavor precursor of 4-methyloxybenzyl-2, 3, 4, 6-tetra-O-acetyl-β-D-glucopyranoside (MBGL) was synthesized via a modified Koenigs-Knorr reaction. The thermal decomposition behaviour and pyrolysis ...intermediate products of the glycoside were studied by simultaneous thermogravimetric/differential thermal analysis (TG/DTA) and synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS). TG/DTA results showed that the largest mass loss rate appeared at a T
of 246.7 °C. PIMS was used to identify the pyrolysis products of MBGL at 300 °C, 500 °C and 700 °C, respectively. The experimental apparatus had some advantages in real-time analysis and fewer secondary reactions. Some important pyrolysis intermediates, such as the ions of the 4-methyloxybenzyl group at m/z 121 and the glycone moiety at m/z 347, were detected by PIMS. The results indicate that the MBGL was probably showed a different pyrolysis way compared with the other glycosides. This work reports a useful application of synchrotron VUV PIMS in a thermal decomposition study of glycoside flavor precursors.
Exothermicity is a key parameter for evaluating coal spontaneous combustion (CSC). A suitable oxygen concentration is essential for CSC. Ionic liquids (ILs), which are a popular type of fire ...prevention material, inhibit coal oxidation. 1-Butyl-3-methyl imidazole tetrafluoroborate (BMIMBF4) was used at various mass ratios (0, 2, 5, and 10 mass%) to treat coal to inhibit CSC. Through simultaneous thermal analysis tests, coal samples were investigated in atmospheres with oxygen concentrations of 5, 10, 15, and 21 vol%. The results indicated that the mass loss decreased with increasing IL content. However, the mass loss did not decrease indefinitely with increasing IL content. The lowest mass loss was observed at an IL concentration of approximately 7.5 mass%. The inhibition increased with decreasing oxygen concentrations. Moreover, the inhibiting effect first increased slowly until the IL concentration exceeded 10 mass%, after which the inhibiting effect increased rapidly. The relationship between the exothermic rate and the mass loss rate of the coal at Stage 2 of the reaction was comparatively analysed. The reaction rate between oxygen and coal was the key factor influencing the exothermic rate. In the oxidation of coal, both the oxygen concentration and inhibitor content affected the comprehensive combustion index of coal.
•The relationship between the amount of IL added and the mass loss/CAIT was defined.•Fitted curves of the mass loss (y3) and oxygen concentration (x2) were obtained.•A high mass loss or heat accumulation led to an easy occurrence of CSC.•Comprehensive index parameters under different conditions were explored and elucidated.
•Appling ECB to recoil machine of artillery.•The analytical electromagnetic model is established by multilayer theory to derive the heat source of this ECB.•The 2D-numerous model is established by FD ...method and coupled with source method.•The working characteristic of this ECB under intense impact load considering temperature is analyzed.
With the increasing requirements for safety and reliability, it is now necessary to analyze the thermal characteristics to the same extent as the electromagnetic design for eddy current brakes(ECB), because the working characteristic will be greatly influenced by temperature. In this paper, the transient thermal-magnetic coupling analysis of permanent magnet cylindrical eddy current brake, which is used as the recoil mechanism in artillery, is presented. First, the structure and working principle of this ECB are described in detail. Second, the analytical electromagnetic model is established by multilayer theory to derive the heat source of this ECB. Thirdly, the thermal-magnetic coupling model is established to calculate the dynamic inhomogeneous temperature field of the ECB. The heat conduction equation is solved in different regions with inhomogeneous internal heat source by Finite Difference method(FDM) in two-dimensional cylindrical coordinate. Finally, the validity of the proposed model is verified by commercial Finite Element software. The thermal characteristic and its effects on braking force is analyzed during working. The maximum value of temperature approximately rises by 16℃ in each firing. The braking force will decline by 8% considering temperature.
Spontaneous combustion of secondary oxidation coal seriously affects the safety of goaf in coal mine. To investigate the effect of nitrogen on secondary oxidation coal, thermal analysis and ...temperature-programmed methods were adopted to explore the thermal behavior and extinguishing ability. The combustion process was divided into the heating process and extinguishing process. Simultaneous thermal analyses performing connected with a Fourier transform infrared spectroscopy analyzer, were applied to the heating process. A temperature-programmed system was employed for extinguishing process. The results demonstrated that nitrogen concentration inhibited the oxidized decomposition and solid-phase reaction. As the nitrogen concentration increased, characteristic temperatures were delayed, and the activation energy of the secondary oxidation coal combustion stage elevated from 138.6 to 158.6 kJ/mol. The nitrogen concentration had little effect on the product H2O, CO, and CO2, while change of the nitrogen concentration mainly inhibited the generation of oxygen-containing functional groups and decomposition of aliphatic hydrocarbons. When the nitrogen concentration increased to 50% during the extinguishing process, the time required for the temperature to decrease from 400 to 30 °C was 39.0% shorter than that during natural extinction, and CO disappeared 42.1% faster. Reaction kinetics were used to analyze the fire extinguishing process of secondary oxidation coal and its spontaneous combustion. The heating process is conducive to determining the combustion characteristics of secondary oxidation coal. The extinguishing process experiments can monitor the changes after extinguishing the spontaneous combustion of coal in a closed fire zone.
A concept for stabilizing highly sensitive and explosive copper(II) azide with 1‐N‐substituted tetrazoles is described. It was possible to stabilize the system by the use of highly endothermic, ...nitrogen‐rich ligands. The sensitivities of the resulting energetic copper coordination compounds can be tuned further by variation of the alkyl chain of the ligands and by phlegmatization of the complexes with classical additives during the synthesis. It is demonstrated, using the compound based on 1‐methyl‐5H‐tetrazole (Cu(N3)2(MTZ), 1) that this class of complexes can be applied as a potential replacement for both lead azide (LA) and lead styphnate (LS). The complex was extensively investigated according to its chemical (elemental analysis, single‐crystal and powder X‐ray diffraction, IR spectroscopy, scanning electron microscopy) and physico‐chemical properties (differential thermal analysis, sensitivities towards impact, friction, and electrostatic discharge) compared to pure copper(II) azide.
Tuning the boom: Volatile copper(II) azide is stabilized by the addition of both tetrazole ligands and phlegmatizing agents. The resulting complexes can be tuned in terms of their sensitivity and serve to replace lead azide as well as lead styphnate, thus reducing the release of toxic lead into the environment.
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