Papers by Keyword: Thermal Stability

Abstract: Materials used for microelectronic devices need to have more multifunctional properties, such as excellent mechanical, thermal, and dielectric properties at the same time. In this paper, copper phthalocyanine/polyimide (CuPc/PI) composite films with high dielectric permittivity (k=9.9 with the volume fraction of CuPc is 28% at 100Hz) and high thermal stability are prepared by an in-situ polymerization process. The composite films show good dielectric properties and is almost independent of frequency in the measured frequency range up to 104 Hz. Notablely, The composites remain stable until the temperature reaches 500oC. In addition, the inclusion of CuPc slow down the composite degradation rate when the temperature is higher than 550oC. The resultant high performance of such polymer composites makes them attractive for technological applications in flexible high-k components.

Abstract: To provide reference for choosing technological parameters of subsequent powder densification, thermal stability of 3 h-milled 3 wt% graphite/copper nanocrystalline composite powders were investigated with such analytical methods as scanning electron microscopy (SEM), back-scattered electron images and X-ray diffraction (XRD). The results show that diffraction peak of graphite in XRD pattern is absent because of too small graphite particle. No major variation of grain size of Cu with annealing temperature is observed. Accumulation and growth of graphite phase aren’t seen. The microhardness is nearly constant for the annealed powders. Therefore, 3 h-milled 3 wt% graphite/copper nanocrystalline composite powders possess good thermal stability.

Abstract: The preparation, mechanical properties, grain size and thermal property of bulk nanocrystalline Cu (BNC-Cu) were investigated in this paper. BNC-Cu can be produced by in situ consolidation of pure Cu powder with high-energy ball milling at room temperature; the average grain sizes of Cu samples decreased with the increasing of ball milling time before 9 h because the grain refining velocity was bigger than the grain growing velocity in this stage. When the ball milling time was beyond 9 h, the average grain size reached a steady minimum value about 27.5 nm. The microhardness of BNC-Cu samples increased with the extending of ball milling time in the first 9 h because the dominating factor was the hardening effect caused by grain refinement and work hardening rather than softening in this stage. BNC-Cu gained its highest microhardness about 1.59GPa when the ball milling time reached 9 h. Subsequently, the microhardness of BNC-Cu slightly fluctuated around this value. Because there were numerous triple grain boundaries and the interaction among different crystal defects in BNC-Cu, BNC-Cu showed outstanding thermal stability when it was annealed in the range of 100°C to 400°C.

Abstract: Intrinsically conductive polymer-Polyaniline had high conductivity and many other properties, such as environmental stability and rather simple synthesis. In addition, doping with organic acids could enhance its processing, so it had wide range of applications, such as solar cells, antistatic and electromagnetic interference shielding. In this study, the organic amine 1-Dodecylamine (DOA) modification of sodium montmorillonite (NA+-MMT), and conducting polymer / layered silicate salt nanocomposites (PANI-PTSA/DOA-MMT) had been prepared by doping aniline with organic acid (PTSA), then added organic clay. The thermal, electrical properties and EMI effects of nanocomposites had discussed by XRD, TEM, EMI, TGA analysis, conduction measure and EMI tested. The results indicated the organo-clay interlayer distance expanded from 1.29 to 1.8 nm, and DOA-MMT dispersed in the material, that formed an exfoliated nanocomposite. The thermal stability of nanocomposites depended on content of DOA-MMT, material had the better thermal stability when DOA-MMT load was 5 wt. %. The nanocomposites had the best conductivity when DOA-MMT load was 1 wt. % as well as the electromagnetic shielding effectiveness was increase with increase in conductivity. In addition, the electromagnetic shielding of nanocomposites also depended on thickness and frequency of electromagnetic wave, the electromagnetic shielding was increased with increase in thickness and frequency.

Abstract: Na₂Ni(SO₄)₂·4H₂O crystal (NNSH) size up to 12mm×10mm×8mm have been grown by heating the solution gradually. The structure of crystal was determined by X-ray diffraction method. The transmission spectra with strong absortpion band at visible and infrared region were measured by using UV-VIS ultraviolet spectrophotometer. Absorption cross-sections of crystal at 344nm and 640nm were evaluated as 4.380×10^-18cm² and 3.63×10^-18cm^-2,respectively. NNSH was stable at high temperature, for the dehydration temperature of the crystal was determined to be 132.6 °C by thermogravimetric measurement. It was shown that NNSH had strong absorption at visible or infrared region and high thermal stability that may render it to be a filter material as to obtain more pure ultra-violet spectrograph and be accessible in high temperature environment.

Abstract: When Permanent Magnet Synchronous Machines (PMSM) working with rated load or overload, stator iron loss and copper loss, bearings friction loss, permanent magnet (PM) eddy-current all will cause PM temperature rise. In this condition, the PM is affected by the temperature and the stator of the reverse magnetic field generated prone to arouse demagnetization phenomenon, it will directly affect the performance of permanent magnet machines. Previous calculation method which used magnetic circuit method to analyze PM demagnetization characteristics cannot reflect the actual working condition of PM. Firstly, the calculation formula of PM thermal stability is deduced in this paper. Secondly, demagnetization characteristics are analyzed based on FEM, which can reflect the actual working condition of PM more accurately. This paper providing reference basis for optimum electromagnetic design, PM selection and optimum PM design.

Abstract: A silicon-containing arylacetylene resin, poly[(dimethylsilyl)eneethynylene phenyleneethynylene] with methoxy silyl terminal group (abbreviated MSAR) was synthesized. The resin and tetraethoxysilane (abbreviated TEOS) were used to prepare silicon-containing arylacetylene resin (abbreviated SAR) /SiO₂ hybrid materials by a sol-gel method. Both the curing process of the xerogel and thermal properties of the hybrid materials were studied by FT-IR, DSC and TGA. The thermogravimetric analysis of the hybrid materials showed that Td₅ (temperature of 5% weight loss) was 696°C and char yield was 92.1% at 800°C in nitrogen. A Si-C-O ceramic residue was obtained in high yield(86.8%) by sintering up to 1450°C in nitrogen.

Abstract: Polyaniline(PANI) nanofibers were firstly prepared by rapid mixture method, EP/PANI nanocomposite was obtained by in-situ adding the PANI nanofibers to epoxy resin(EP). Thermal degradation behavior of PANI and kinetic analysis of thermal decomposition of EP/PANI nanocomposites were investigated in detail by using thermogravimetric analyser (TGA) in inert atmosphere. Typical three step decomposition profiles of PANI were obtained. On the basis of isoconversional analysis by the methods of Kissinger-Akahira-Sunose method(KAS method) and Flynn-Wall-Ozawa method(FWO method), it was found that the value of the activation energy of EP/PANI nanocomposites is higher than that of pure EP, which proves that PANI nanofibers obviously improve the thermal stability of pure EP.

Abstract: The potential of using cellulose to reinforce the thermal stability of kenaf derived cellulose (KDC)/polylactic acid (PLA) composite was investigated in this study. The cellulose was derived from kenaf bast fibre which was chemically treated via chlorination and mercerisation processes. The composites with various loadings of cellulose (dry weight basis) ranging from 0% to 60% were produced by melt mixing and compression moulding. Dynamic mechanical properties namely storage modulus (E’), loss modulus (E”) and tan δ of the KDC/PLA composites and the commercial PLA were analysed and compared as a function of temperature. ESEM micrographs demonstrated that the mercerisation of kenaf fibres have successfully removed the lignin and hemicellulose, thus producing cellulose which can be observed by its rougher surface and greater size reduction than the raw fibre. The DMA results demonstrated that the storage modulus of 60% KDC/PLA composite is twice higher than the commercial PLA and the rest of the composites within a high temperature range (above 80°C). The glass transition temperatures (Tg) generated from the loss modulus curves exhibit that the peak of the loss modulus was shifted to higher temperature as the percentage of the cellulose loading was increased. These results show a better thermal stability of the composites when incorporated with the cellulose.

Abstract: The objective of this work is to investigate the influence of LDH loading on the thermal stability and thermal degradation kinetics of the PP/Ni-Al LDH nanocomposites using thermogravimetric analysis (TGA) and to compare the results with that of the neat PP. For this, Ni-Al LDH was first prepared by co-precipitation method at constant pH using their nitrate salts and subsequently organically modified using sodium dodecyl sulphate (SDS) by regeneration method. A series of novel PP/Ni-Al LDH nanocomposites was then prepared with various amounts of LDH by melt intercalation method. The XRD results confirm the formation of exfoliated PP/LDH nanocomposites. PP/LDH nanocomposites exhibit enhanced thermal stability relative to the neat PP due to the presence of barrier effect of LDH lamellar layers and the thermal stability of the nanocomposites also increases with increase in the LDH loading. When 10% weight loss is selected as a point of comparison, the decomposition temperature of PP/LDH (5 wt %) nanocomposite is 15 oC higher than that of neat PP. The thermal degradation activation energy of the nanocomposites is determined via Coats-Redfern method and compared with that of neat PP. The improvement of thermal stability of PP nanocomposites is also confirmed by increasing the activation energies (Ea) and the integral procedural decomposition temperature (IPDT) compared with neat PP. Criado method is finally used to determine the degradation reaction mechanism of various samples.