Isothermal and Non-Isothermal Crystallization Kinetics of PVDF and PVDF/PMMA Blends

Background: poly(vinylidene fluoride) PVDF and PVDF/PMMA blends have been investigated with a focus on the crystal structure, immiscibility and mechanical properties. However, few reports were found on the crystallization behaviors of PVDF and PVDF/PMMA blends, especially on crystallization kinetics. The article is to report the research on isothermal and nonisothermal crystallization kinetics for PVDF and PVDF/PMMA blends using differential scanning calorimetry (DSC). Results: Besides crystallization temperature and isothermal crystallization activation energy, the Avrami equation exponent of PVDF in blends decreased compared with pure PVDF. The nonisothermal crystallization kinetics of PVDF and PVDF/PMMA (70:30) blends were investigated by Ozawa equation, Jeziorny method and crystallization rate constant (CRC) in detail. The nonisothermal crystallization energy of pure PVDF and its blends were determined by the Kissinger and Vyazovkin’s method. Conclusion: The nucleation and growth mechanism of PVDF in blends changed compared with pure PVDF. The Ozawa equation is not applicable in nonisothermal crystallization kinetics of PVDF and PVDF/PMMA blends. The decreasing of crystallization ability of PVDF in blends were found and confirmed by CRC and the decline of crystallization rate constant in Jeziorny method. Such is opposite to the results of Kissinger’s and Vyazovkin’s method, chances are that these two methods were not used to calculate the nonisothermal crystallization activation energy where the nucleation process was influenced.

Design of Large Injection Mould for Car Dashboard

The dashboard is the most important part of the large inner decoration of cars; it should not only have enough strength and rigidity, but also have a harmonious body model which can unify the theme. Besides, it needs to reach the goal of lightweight. In order to achieve these three goals, the car dashboard is made by engineering-plastics and adopts the technology of injection moulding. This paper introduces the keys of design and the advanced technology of large injection moulding for car dashboard.

Research Advances of Typical Two Dimensional Layered Thermoelectric Materials

Thermoelectric technologies have caught our intense attention due to their ability of heat conversion into electricity. The considerable efforts have been taken to develop and enhance thermoelectric properties of materials over the past several decades. Recently, two-dimensional layered materials are making the promise for potential applications of thermoelectric devices because of the excellent physical and structural properties. Here, a comprehensive coverage about recent progresses in thermoelectric properties of typical two dimensional (2D) layered materials, including the theoretical and experimental results, is provided. Moreover, the potential applications of 2D thermoelectric materials are also involved. These results indicate that the development of 2D thermoelectric materials take a key role in the flexible electronic devices with thermoelectric technologies.

Effect of Carbides and γ/γ' Eutectic on Crack Initiation and Propagation in Ni-based Superalloy

The Ni-based Udemit720Li superalloy tends to form large γ/γ' eutectic on grain boundaries (GBs) during solidification due to the addition of excessive Al and Ti elements, which provides convenience to study the effect of carbide and γ/γ' eutectic on crack initiation and propagation during tensile process. In this paper, Udemit720Li superalloy samples were prepared by induction melting casting method, arc melting and suction casting method. The microstructure, tensile properties and mechanism of crack initiation and propagation in Ni-based superalloy fabricated by two methods are investigated. The results exhibit γ/γ' eutectic accelerates the stress concentration at GB and thus leads to premature fracture failure. The samples with grain-boundary eutectic have higher strain hardening rate, but their cumulative and local misorientations are lower. For samples without eutectic at GB, the primary crack initiates at grain-boundary carbide along GB and extends along GB or into grain matrix, and exhibits better deformation performance and dislocation storage capacity within grains.

Effect of Deformation Conditions on Mechanical Properties of Zr-based Metallic Glasses

In this paper, the effects of different strain rate(1×10-5 s-1, 5×10-5 s-1, 1×10-4 s-1, 5×10-4 s-1, 1×10-3 s-1) and aspect ratio(1:1, 1.5:1, 2:1, 2.5:1, 3:1) on mechanical properties of Zr-based metallic glasses at room temperature were investigated. The results indicate that as the strain rate increases, the plastic strain and compressive strength of the specimens gradually decrease. The specimen with the strain rate of 1×10-5 s-1 exhibits the higher plastic strain of 10.25 %, compressive strength of 2002 MPa and fracture strength of 1999 MPa. In addition, accompanied with the increase in aspect ratio, the plastic strain of the specimens declines from 25.42 % to 1.97 %, meanwhile, the compressive strength and fracture strength of the specimens also present declining trend.

Neutron Diffraction Study on the Magnetic Structure of 153EuMnO3-δ: One Way to Assess the Magnetic Structure of EuMnO3-δ

Owing to the strong neutron absorption of 151Eu, 151Eu free 153EuMnO3-δ has been synthesized to collect the neutron diffraction data for analyzing the magnetic structure of EuMnO3-δ. The obtained neutron diffraction data of 153EuMnO3-δ indicates that the magnetic diffraction peaks corresponding to cAAFM (canted A-type antiferromagnetic) phase can be observed, but the magnetic diffraction peaks corresponding to expected ICAFM (incommensurate antiferromagnetic) phase may be too weak to be observed.

Synthesis and Thermotropic of PAMEs Based on 1-Phenethyl-4-Piperidone Moiety

New poly(azomethine-ether)s PAMEs containing 1-phenethyl-4-piperidone moiety have been synthesized through a solution polymerization of various diformyl-a,w-diphenoxyalkanes, I-IV with 3,5-bis(p-aminobenzylidene)-1-Phenethyl-4-piperidone VI. The structures of these polymers were confirmed using spectroscopic techniques. The inherent viscosities of the resulting polymers were found to range from 0.65 to 0.95 dl/g. The solubility of the PAMEs was estimated, showing good solubility in aprotic solvents. The thermal properties of the PAMEs were also evaluated by DSC technique. Liquid crystalline state of the polymers was observed on polarizing microscope exhibiting nematic phase for most of the synthesized polymers.

High Temperature Flexural Deformation Properties of Engineered Cementitious Composites (ECC) with Hybrid Fiber Reinforcement

Engineered Cementitious Composites (ECC) is a class of high-performance fiber reinforced composites with ultra-ductility designed based on micromechanics, and it has been developed for increasing application in the construction industry during recent decades. The properties of ECC at room temperature have been tested and studied in depth, however, few studies focus on its performance after high temperature that is one of the worst conditions to ECC. To investigate the change tendency and mechanism for the high temperature flexural properties of hybrid fiber reinforced ECC and the feasibility of calcium carbonate whisker to reduce the cost of ECC materials, polyvinyl alcohol fiber (PVA) reinforced strain hardening cementitious composites (PVA-ECC), steel fiber + PVA fiber reinforced ECC (defined as HyFRECC-A) and steel fiber + PVA fiber + CaCO3 whisker reinforced ECC (defined as HyFRECC-B) subject to room temperature and 200 ℃, 400 ℃, 600 ℃, 800 ℃ elevated temperature exposure were experimentally compared. The results indicate that equally replacing PVA fibers by steel fibers degraded the flexural hardening ability of PVA-ECC at room temperature, while the addition of appropriate amount of CaCO3 whisker improved the flexural strength, toughness and flexural hardening behavior. The elevated temperature posed a significant effect on the flexural strength and toughness of the three types of ECCs. Flexural deflection hardening behavior of the three types of ECCs was eliminated after high temperature exposure. Flexural strength and toughness of PVA-ECC presented an exponential decay along with the increase of temperature. The addition of steel fiber slowed down the decay rate. Although the use of CaCO3 whisker increased the post-temperature flexural strength and toughness of HyFRECC-B, the decay rate was not further decreased.

Research Progress of Ceramic Metallization Technology

Due to the wide application of ceramics in electronic device packaging, the performance of ceramic metallization layer directly determines the performance of the whole package device. This paper introduces the main preparation methods of ceramic metallization, discusses the influence of Mo powder size, metallization formula, sintering temperature and other factors on the performance of ceramic metallization layer prepared by activated Mo-Mn method, and introduces several kinds of methods that can be tested to test the performance of ceramic metallized sealing samples. A new research direction of Ceramic Metallization Technology in the advanced field is put forward.

Effects of Si Content on Microstructure and Mechanical Properties of 8079 Aluminum Alloy

Because of high strength and low breaking rate, 8079 aluminum alloy has become the main material of double zero aluminum foil. However, there are still many problems in the manufacturing process, such as broken belt, pinhole and so on. As the main influencing element, Si has a great influence on the alloy. In this work, the influences of Si with various contents on microstructural evolution and mechanical properties of 8079 aluminum alloy were analyzed by energy dispersive spectrometer (EDS), optical microscope (OM), X-Ray diffraction analyzer (XRD), universal testing machine and Vickers hardness tester. The results showed that the primary Si phase was tiny and dispersed in the alloy when the content of Si is less than 1.3%. As the second phases dispersion strengthening, the Si phase can improve the strength of the alloy. However, when the Si content was too high, the Si phase increased and coarsened. Meanwhile, Fe-rich phase which increased by Si decreased the fine grain strengthening and the second phases strengthening mechanism. The coarse Si phase and the Fe-rich phase are brittle phase, which are easy to become the crack source in the process of material deformation and reduce the strength and toughness of the alloy. The mechanical property test shows that the performance of 8079 aluminum alloy is the best when the Si content is 1.3%.