Papers by Keyword: Thermal Stability

Abstract: By means of the establishment of thermal stability evaluation model and simulating in Huafeng factory residential building ,the relationship between the D value and building thermal stability and the optimal distribution ratio are obtained.The results show that:at the shape coefficient≤0.40, the most optimal matching relation is :heat transfer coefficient is 1.0, thermal inertia index is 2.0;at the shape coefficient >0.40, the most optimal matching relation is :heat transfer coefficient is 0.8, thermal inertia index is 2.0.

Abstract: The effects of synthesized silver nanoparticles on electrospun PHBV ultrafine fibers were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Addition of silver nanoparticles increased from 0.1% to 2.0%, the sooth ultrafine fiber with an average diameter of about 2 μm formed a non-woven mat was obtained. DSC showed the efficient heterogeneous nucleation by the silver nanoparticles for facilitating PHBV crystallization.The thermal stability of the PHBV/Ag ultrafine fibers improved with the increase in the content of the silver nanoparticles.

Abstract: The addition of nanoparticles has been proven to a high potential application for improving polymer thermal stability properties. In this paper, the nanocomposites based on epoxy matrix modified with different mass ratio of silica nanoparticles were investigated. In order to disperse and incorporate silica nanoparticles into epoxy matrix, silica nanoparticles were modified with coupling agent (Gamma-glycidoxy propyl trimethoxy silan, KH-560). FTIR spectra showed that KH-560 was absorbed on the surface of SiO₂ nanoparticles. The thermo gravimetric traces indicated that the addition of silica nanoparticles has improved the thermal stability properties of epoxy matrix significantly. The decomposition temperature of nanocomposite increased with the addition of nanoSiO₂, and the temperatures of the maximum rate of degradation of the unmodified nanocomposite with 0wt%, 1wt%, 3wt%, 5wt% nanoSiO₂ were 401^oC, 405^oC, 411^oC, 421^oC, respectively. The temperatures for 50% weight loose of the modified nanocomposite with 1wt% and 3wt% nanoSiO₂ were 389^oC and 405^oC, respectively.

Abstract: The W48.5Ni34Fe14.6B2.9 (wt.%) amorphous ribbons were prepared using melt spinning method. The crystallization kinetics of amorphous ribbons was investigated by differential scanning calorimeter (DSC) at different heating rates from 10 to 40 K/min. The activation energy of amorphous ribbons was simulated by Kissinger and Ozawa equations, respectively. The precipitated phases at different annealing temperatures were analyzed by X-ray diffraction (XRD). The results showed that the glass transition temperature (T_g), the crystallization temperature (T_x) and the peak temperature (T_p) were found to increase during enhancing heating rate, indicating the obvious kinetic effects of glass transition and crystallization. The consistency of values of the activation energy calculated by Kissinger and Ozawa equations suggested the good accuracy about experiment results. The specific temperatures of T_x and T_p detected by DSC and the deduced crystallization activation energy are generally higher than these of other amorphous alloys, which suggests a higher resistance to crystallization. The W48.5Ni34Fe14.6B2.9 alloy substantially remained at amorphous structure when annealed at 923K for 60 min, showing that the alloy possessed a higher thermal stability.

Abstract: Nanostructured apatite has been widely used as a bone substitute material due to its close resemblance to human bone mineral. To further mimic biological apatites, multiple ions doped non-stoichiometric nanoapatite has been studied. A nanosized apatite (NAp-2) containing Mg (1.09 wt%), Na (0.15 wt%), K (0.008 wt%) and CO₃^2- (5.18 wt%) was synthesized by a wet precipitation technique. The presence of these ions in NAp-2 was detected using ICP. Broad diffraction peaks of XRD results indicated the presence of nanocrystalline phase pure NAp-2. The primary particle size of the resulted powder was ~ 20 nm, typical of bone crystal size, estimated using Scherrers equation. Based on CHN results, the NAp-2 powders showed a total loss of 51 and 78% of carbonate ions when heat-treated at 900°C in both CO₂ and air atmospheres, respectively. This indicates that the heat-treatment in CO₂ flux has reduced the carbonate ions lost from the NAp-2. A highly crystalline HA phase was formed in the ionic doped NAp-2 without secondary phases, indicating a thermal stability of this powder at 900°C in CO₂ and air atmospheres. Thus, this study demonstrated that a phase pure multiple ions doped nanoapatite was synthesized using a wet precipitation technique.

Abstract: Magnetic properties, thermal stability and structure of the alloys - (Fe_0.6Co_0.4)₈₆Hf₇B₆Cu₁ (1), (Fe_0.7Co_0.3)₈₈Hf₇B₄Cu₁ (2) and (Fe_0.7Co_0.3)₈₈Hf₄Mo₂Zr₁B₄Cu₁ (3) obtained in the form of ribbons quenched from the melt were investigated after their nanocrystallization in the course of the thermal (TA) and stress (SA) annealings in the air at different temperatures. In all three alloys SA resulted in the induction of magnetic anisotropy with an easy axis along the direction of the ribbon. It is established that the alloy 3 after SA at 620°C for 20 min has the best thermal stability of magnetic properties, which remained practically unchanged after the subsequent annealing at 550°C for 26 hours. Magnetic properties of the alloys 1 and 2 subjected to SA under the same conditions did not change after annealing at 500°C.

Abstract: The evolution of structure of high-strength heavily deformed Cu-Nb composites processed by two different methods (melt-and-deform and bundle-and-deform) is briefly reviewed based on the authors’ (with their coauthors) original studies and the available publications. Specific features of their texture are considered. In particular, it is demonstrated that the ribbon-like Nb filaments possess not only the sharp fiber texture but the limited texture with components characteristic of cold-drawn Nb. The semi-coherent and amorphous state of Cu/Nb interfaces is discussed. The thermal stability of single-core and multi-core wires is considered. The effect of Zr and Ti doping on the structure and mechanical properties is demonstrated.

Abstract: The research on the mechanical properties and thermal stability of the natural rubber filled with different dosage of Zinc oxide (ZnO). The results showed that with the increase of the content of the ZnO, the tensile strength first increased, then decreased the, but the tear strength showed a trend of increase,the thermal stability had improved; When the amount of ZnO added was 9, damping performance was better.

Abstract: Combination of centrifugal melt spraying and hot die-forging of a rapidly solidified semi-product was presented as a promising and inexpensive method for processing of aluminium based alloys of unconventional chemical compositions, e.g., those containing high concentrations of thermally stabilizing transition metals. In our study, the use of this processing method is illustrated for the Al–23Si–8Fe–5Mn (wt. %) alloy. Structure was examined by LM, SEM, EDS and XRD. Mechanical properties were determined by hardness and compressive tests. Thermal stability was assessed by measuring the hardness development during long-term annealing, elevated temperature compressive tests and creep tests. The research showed that the investigated alloy exhibits excellent thermal stability as compared with commercial thermally stable aluminium alloys currently used in automotive and aerospace industry.

Abstract: The conventional magnetic recording has approached its physical limits. Further growth of the areal density is limited by the superparamagnetic effect and by the limited possibilities to further improve write heads design and pole materials in order to enhance the writing field. A new technology proposed to surpass these limits is the heat assisted magnetic recording (HAMR). The principle of HAMR and the structure of a HAMR system are discussed, as well as the processes characterizing the writing process and the requirements for the materials needed for this type of recording. Some important challenges of the HAMR technology are summarized.