Effects of introducing silica particles on the rheological properties and crystallization behavior of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET)/silica composites were prepared by melt compounding, and their rheological properties and isothermal crystallization were discussed. Introduction of silica particles (0.5–2 wt.%) increased the storage modulus (G′) and decreased loss tangent (tanδ). However, the effect of the particles on rheological properties became negligible at a high frequency more than ca. 70 rad/s. In the Cole–Cole plot, the PET/silica composites showed little deviation from the master curve regardless of the presence of silica particles. The particles increased the relaxation time of PET at particularly low frequency. The isothermal crystallization kinetics of PET/silica was examined using a differential scanning calorimeter (DSC). The half-time of crystallization was decreased with increasing the silica content. The incorporation of silica particles decreased the equilibrium melting temperature by ca. 5.5 °C. In addition, the composites exhibited higher average value of Avrami exponent (2.7–2.9) in comparison with that of pure PET (2.2).     

聚对苯二甲酸乙二醇酯熔体等温结晶的焓松弛

利用微分扫描热分析（DSC）获得了聚对苯二甲酸乙二醇酯（PET）熔体等温结晶过程焓松弛速率曲线,并对结晶焓松弛速率曲线进行微分从而获得等温结晶焓松弛加速度曲线。文中通过定义相对结晶速率R和相对结晶加速度A,确定了相对结晶速率R和相对结晶加速度A与结晶焓松弛速率和结晶焓松弛加速度之间对应相差的一个常数值,然而其所对应的变...     

Modelling the effects of various contents of fillers on the relaxation rate of elastomers

This paper describes numerical investigations conducted on filled rubbers. Some experimental data on stress relaxation tests carried out on various filled elastomers evidenced that increasing the content of rigid particles such as fillers or changes in the crystallization index, result in higher values of the stress relaxation rate. This result seems to indicate that higher rigid particle contents promote macroscopic viscoelastic strain. To better understand this effect, finite element analyses were carried out on axi-symmetric unit cells as well as unit cell for numerical homogenization with periodic computations.     

Oscillatory-like relaxation behavior of light transmitted through ferrofluids

An oscillatory-like relaxation process in which there are two valleys in the T-t curve is observed when light is transmitted through binary ferrofluids composed of both ferrimagnetic CoFe(2)O(4) nanoparticles and paramagnetic p-MgFe(2)O(4) nanoparticles in the presence of a high magnetic field and through pure (single) CoFe(2)O(4) ferrofluids in a low magnetic field. This relaxation behavior is explained using a model of a bidispersed system based on both chained and unchained particles. In such a bidispersed system, the variation of the transmitted light results mainly from the motion of the chains, with the polarized unchained particles' gas producing the modulation effect. The oscillatory-like relaxation phenomenon depends on the features of both the chained and unchained particle systems. If either the particle volume fraction of chained particles or of unchained particles is very low, or the degree of polarization of the unchained particles gas is very weak, a simple nonlinear relaxation process, giving only a valley in the T-t curve, will appear for the transmitted light. For pure CoFe(2)O(4) ferrofluids, the number of chained and unchained particles does not remain constant under different values of the magnetic field. According to the analysis of the relaxation behavior of transmitted light, it is known that binary ferrofluids based on strong magnetic CoFe(2)O(4) particles and weak magnetic p-MgFe(2)O(4) particles can be much closer to the theoretical bidispersed system than single ferrofluids containing only strong magnetic particles.     

Crystallization behavior of nanodisperse phases

Extensive experimental work demonstrates that the crystallization leading to the formation of a nanocrystalline phase is characterized by the following specific features: particles of the solid phase nucleate in a small region of the system where a high supersaturation is produced (local character of the process); crystallization involves a few, kinetically self-similar stages (multistage character); several structural and morphological forms may develop concurrently during crystallization (multiple paths). The information accumulated to date provides the basis for quantitatively describing all the stages of crystallization and optimizing the synthesis of nanomaterials     

Study on the formation of Pt/C catalysts by non-oxidized active carbon support and a sulfur-based reducing agent

The formation mechanism of Pt/C catalysts using non-oxidized active carbon support and the weak reducing agent Na₂S₂O₄ was investigated. Platinum on carbon catalysts were fabricated by an impregnation/reduction process of the Pt-precursor H₂PtCl₆ on carbon support. The effect of thermal treatment in argon up to 700°C on the structural characteristics of these catalysts was studied by XRD and TEM analyses. The importance of carbon support properties on Pt/C formation was recognized. Before thermal treatment a very weak internal organization (a very small particle size and amorphous structure) in the metal was obtained. Thermal treatment at relatively low temperatures leads to the growth and then to the crystallization of platinum particles in the well-known face centered cubic structure. The sintering of Pt particles occurs through the migration of Pt atoms on the carbon support, likely by a bridge-bonding mechanism on sulfur atoms. A fast growth of Pt particles occurred in the temperature range 300—400°C. Thermal crystallization, instead, occurred mostly going from 400 to 550°C. Following annealing at 550°C, the formation of platinum sulfide was revealed. The sample thermally treated at 700°C showed an anomalous XRD pattern with Pt reflexions shifted towards high angles and an increase of Pt[111]/Pt[220] peak intensity ratio.     

Structure and Magnetic Properties of BaCoTiFe10O19 Thin Films with an Easy-Axis In-Plane Orientation

BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.     

Influence of crystallization time on microstructures and dielectric properties of tungsten–bronze glass–ceramics

A glass with a composition of 22.5SrO–22.5BaO–15Nb₂O₅–40SiO₂ (mol %) was prepared by a melt-quenching method and then heat-treated at 950 °C for different crystallization time. Microstructure observations were carried out using scanning electron microscope and dielectric properties were measured by a LCR meter. The experimental results show that volume fraction of the crystalline phase increased, dielectric constant maximum enhanced, and Curie temperature shifted as the crystallization time is prolonged. The decrease in the Curie temperature for the sample crystallized at 950 °C for 1 h is considered to be caused by the clamping effect from the glass matrix or small compositional fluctuation. Impedance spectroscopy has been employed to study the polarization contributions arising from the glass and crystalline phases in the glass–ceramics for different crystallization time. With the increase in crystallization time, the magnitudes of impedance and modulus as well as the relaxation frequency changed significantly. The activation energy calculated from the relaxation frequency increased for the glass phase due to a denser network structure, while the crystalline phase showed a slight decrease implying there is no change in its polarization mechanism.     

Heat relaxation phenomena at low temperature in amorphous LaZn

An anomalous heat relaxation with a very long time constant (about 60 h) has been observed in amorphous La_0.78Zn_0.22. The total heat release is about 1.5 mJ per gram of sample. This phenomenon can be attributed to the ortho-para transformation of hydrogen trapped in the sample. This behavior disappears after crystallization.     

Influences of crystallization time,batch molar ratios Al2O3/SiO2 and Na2O/SiO2 on particulate properties of sodalite crystals prepared under room-temperature conditions

Sodalite crystals were prepared by the hydrothermal method under room-temperature conditions. The influences of crystallization time, batch molar ratios Al₂O₃/SiO₂ and Na₂O/SiO₂ on the crystalline end products were investigated. For comparison, an experiment was also carried out in which sodalite was synthesized at 90 °C for 10 h. The results revealed that with the prolongation of crystallization time from 1 h to 14 days, the crystallization followed a sequence of phase transformations from an amorphous phase to zeolite NaA, and finally to sodalite. Spherical sodalite crystals composed of very small crystallites were obtained after 10 h of room-temperature crystallization. Whereas, with the same gel composition, the sodalite synthesized at 90 °C for 10 h was large lepispherical particles. High Al₂O₃/SiO₂ molar ratio favored the generation of smaller individual sodalite nanocrystals, which resulted in the formation of larger steady congregated agglomerates. Moreover, alkalinity circumstance determined whether or not sodalite was formed. Well-developed cubic zeolite NaA particles were obtained at Na₂O/SiO₂ = 1.4; when the Na₂O/SiO₂ was increased to 8.0, zeolite NaZ-21 crystals were generated, meanwhile, the decomposition of wool ball-like sodalite particles into nanorods was also observed.     

Mechanical reinforcement and crystallization behavior of poly(ethylene 2,6-naphthalate) nanocomposites induced by modified carbon nanotube

Poly(ethylene 2,6-naphthalate) (PEN) nanocomposites reinforced with a very small quantity of carbon nanotube (CNT) were prepared by melt compounding using a twin-screw extruder. Morphological observations revealed that the modified CNT was uniformly dispersed in the PEN matrix and increased interfacial adhesion between the nanotubes and the polymer matrix, as compared to the untreated CNT. Furthermore, a very small quantity of the modified CNT can improve the mechanical and thermal properties of the PEN nanocomposites. This study also demonstrates that the non-isothermal crystallization behaviors of the PEN nanocomposites are strongly dependent on the presence of the modified CNT and cooling rate. The variations of the nucleation activity and activation energy for crystallization reflected the enhancement of crystallization of the PEN nanocomposites induced by the modified CNT. Combined Avrami and Ozawa analysis was found to be effective in describing the non-isothermal crystallization of the PEN nanocomposites in the presence of the modified CNT.     

Toughening modification of polycarbonate/poly(butylene terephthalate) blends achieved by simultaneous addition of elastomer particles and carbon nanotubes

Small quantities of maleic anhydride grafted styrene-ethylene-butylene-styrene (SEBS-g-MAH) copolymer and carbon nanotubes (CNTs) were introduced into polycarbonate (PC)/poly(butylene terephthalate) (PBT) blends. The results demonstrated that simultaneously adding SEBS-g-MAH and CNTs greatly enhanced the fracture toughness of the samples and the impact strength increased with increasing CNT content. The morphologies, the dispersion of CNTs, the relaxation behaviors and the crystallization behaviors of samples were systematically investigated. SEBS-g-MAH formed the dispersed particles in the system. The particle diameter was decreased in the blend composites. CNTs exhibited homogeneous dispersion in the blend composites and they also formed a percolated network structure at relatively high content. The transesterification between PC and PBT components was suppressed by SEBS-g-MAH, and the crystallization ability of the PBT component was greatly enhanced. The toughening mechanisms were mainly related to the suppressed transesterification, the decreased elastomer particle size, and the formation of a CNT network structure.     

Periodically Laser Patterned Fe?B?Si Amorphous Ribbons: Phase Evolution and Mechanical Behavior

The properties of amorphous alloys are significantly influenced by structural relaxation and partial/full crystallization induced by thermal annealing of the alloy. In this paper, the phase evolution and mechanical behavior of laser‐patterned Fe? B? Si amorphous alloys are reported. The laser patterning was employed to cause localized thermal effects on the surface of amorphous ribbons. The laser irradiation with a lower fluence (12 J · cm^?2) caused significant embrittlement of the alloy due to the structural relaxation. The partial crystallization of an amorphous alloy into α‐Fe(Si) was also observed with laser irradiation using higher laser fluences (15 and 17 J · cm^?2). The embrittlement effect due to laser‐irradiation‐induced crystallization was more severe than that due to structural relaxation.     

Nuclear magnetic resonance in small superconducting particles. II

The effects of superconducting fluctuations are investigated in a small metallic particle with spin-orbit scattering at the surface and impurity sites. The spin susceptibility and the nuclear spin relaxation time are calculated, using the Green's function method developed in a preceding paper. At low temperatures the spin susceptibility takes a value closer to that of Pauli paramagnetism than in the case without spin-orbit scattering. The effect of the Zeeman energy on the relaxation time is reduced. It decreases the enhancement of the relaxation time. These results are in good agreement with NMR experiments for tin particles.     

Physico-chemical and NMR relaxometric characterization of gadolinium hydroxide and dysprosium oxide nanoparticles

Gadolinium hydroxide and dysprosium oxide nanoparticles, which constitute a new interesting class of magnetic nanoparticles, are characterized by different methods, using x-ray diffraction, magnetometry and NMR relaxometry at multiple fields. The rod-like particles are first shown to have a simple paramagnetic behavior, like the bulk compound, without any influence of the nanometric size of the particles. Because of their paramagnetic moment, these particles considerably shorten water relaxation times, especially the transverse relaxation time at high fields. The relaxation induced by gadolinium hydroxide particles is due to a proton exchange between the particle surface and bulk water, while the transverse relaxation caused by dysprosium oxide particles is governed by the diffusion of water protons around the magnetized particles. 1/T(2) increases linearly with the magnetic field for gadolinium hydroxide particles while a quadratic increase is observed for dysprosium oxide nanoparticles. The relaxation results are compared with those from previous studies and interpreted using different theories for the relaxation induced by magnetic particles.     

非晶态合金Fe16Ni60Cr4B16Si4的结构弛豫和晶化

用差热分析法（ＤＴＡ）研究了Ｆｅ１６Ｎｉ６０Ｃｒ４Ｂ１６Ｓｉ４，非晶态合金升温过程结构驰豫和晶化特征，根据结构驰豫和晶化激活能的计算结果分析两个过程的原子运动行为，用ＴＥＭ研究了结构驰豫，讨论了ＤＴＡ与显微维氏硬度两曲线间的关系，提出结构驰豫是以调幅分解和形核两种方式进行，纳米晶成核温度ＴＭ。     

Crystallization and structure of high boron content iron-boron ultrafine amorphous alloy particles

Amorphous to crystalline transformation of chemically prepared Fe₆₄B₃₆ ultrafine amorphous alloy particles has been investigated by Mössbauer spectroscopy, Brunauer-Emmett-Teller surface area measurements and transmission electron microscopy. Structural relaxation was observed below 350°C, which resulted in narrowing the full width at half maximum for the hyperfine field distribution from 13.0 to 10.6 T, while the average hyperfine field kept unchanged, to be about 20.3 T. Crystallization started on the surface at about 300°C and proceeded into the bulk at about 400°C. Partial crystallization between 400 and 450°C resulted in increasing the average hyperfine field for the remaining Fe-B amorphous matrix to 21.6 T. -Fe and Fe₂B were the only iron containing phases related to bulk crystallization, with the latter as a predominant component, accompanied by the segregation of about 19% boron atoms. Above 500°C, sintering of the particles became very remarkable and a solid state reaction between diffusing iron and boron atoms to form Fe₂B took place making the spectral area ratio for Fe₂B to -Fe components increase accordingly. A locally distorted non-stoichiometric Fe₂B quausicrystalline structure for the high boron content sample was proposed.     

Crystallization of sol-gel-derived glass ceramic powders in the CaO-MgO-Al2O3-SiO2 system

Samples in the anorthite primary crystallization field were prepared in the CaO-MgO-Al₂O₃-SiO₂ quaternary system by sol-gel techniques. The homogeneous dried gels were characterized by infrared spectroscopy, thermal analysis and electron microscopy. The crystallization of gel-like glass as a function of temperature was followed by X-ray diffraction. Anorthite was detected as the only crystalline phase. Thermal analysis results indicated a mechanism of crystal growth dominated by surface nucleation. This fact could be related to the small size of the primary particles observed by electron microscopy.     

不同端基及分子量聚氧乙烯的结晶行为研究

通过偏光显微镜和DSC技术，较为详细地研究了不同端基及分子量PEO的结晶行为，当PEO的分子量大于6000g/mol时，分子量对其结晶行为的影响逐渐变得很小，当分子量介于6000g/mol-2000g/mol时，为一临界分子量区，分子量变化对其结晶能力有很大的影响。氯乙基酯端基PEO链的折叠结晶受限较大，结晶度损失较大，而且，当分子量降至临界分子量区时，PEO结晶受限对端基体积更加敏感，结晶能力大大降低，羟基端基对结晶熔融焓（ΔHf)的影响与分子量的大小有强烈的关系，Tm仅随着端基体积的变大而下降。