Papers by Keyword: Crystallization

Abstract: The blends of poly(trimethylene terephthalate) (PTT) with maleated styrene-butylene-co-ethylene-styrene copolymer (SEBS-g-MA) were prepared by melt blending. Their morphologies and crystallization behavior were investigated. Morphology observation shows the well-dispersed phase of SEBS-g-MA in PTT matrix and the partical size of SEBS-g-MA increased as the content of SEBS-g-MA increasing. Differential scanning colorimetry(DSC) experiments showed that the melting point of pure PTT and their blends was almost constant. Addition of 5-30wt% SEBS-g-MA in blends increased crystallization points of PTT phase and the crystallinity of the blends were higher than that of PTT.

Abstract: Fused quartz granule was used as raw material, and La2O3 nanopowder was used as additive with dosages of 1wt %, 2 wt % and 3 wt %. Fused quartz ceramic materials were fabricated in reduction atmosphere at 1300 °C, 1350 °C and 1400 °C for 1 h, respectively. The properties of samples including apparent porosity, bending strength and thermal expansion ratio were measured. The results show that the sample with 2 wt % La₂O₃ nanopowder has the lowest apparent porosity and the highest bending strength, and sample added 1% nano-La₂O₃ has the best inhibiting effect on crystallization of fused quartz. The samples with La₂O₃ nanopowder adding have lower thermal expansion ratio than blank sample. The XRD and SEM results show that the diffraction peak intensity of quartz phase decrease and the microstructure of the samples become more compact, after the La₂O₃ nanopowder was added into fused quartz ceramics. It indicated that La₂O₃ nanopowder has excellent inhibiting effect on crystallization of fused quartz and facilitating effect on sintering of fused quartz ceramics.

Abstract: Fused quartz granule was used as raw material, and CeO₂ nanopowder was used as additive with dosages of 1wt %, 2 wt % and 3 wt %. Fused quartz ceramic materials were fabricated in reduction atmosphere at 1300 °C, 1350 °C and 1400 °C for 1 h, respectively. The properties of samples including apparent porosity, bending strength and thermal expansion ratio were measured. The results show that the sample with 1 wt % CeO₂ nanopowder has the lowest apparent porosity, the highest bending strength and the lowest thermal expansion ratio. The XRD and SEM results show that through the CeO₂ nanopowder adding, the diffraction peak intensity of quartz phase in the fused quartz ceramics decrease, and the microstructure of the samples become more compact. It can be deduced that CeO₂ nanopowder plays the excellent role as the crystallization inhibitor and sintering assistant to fused quartz materials sintered at various temperatures.

Abstract: Steady increase of requirements to quality an axial zone continuously cast blooms stimulated in last time development of principles of its deformation at the end of solidifications with the purpose of suppression of axial porosity and segregation: soft reduction or mechanical soft reduction. The technology of soft reduction is one of the most effective ways of improvement quality of internal layers continuously cast blooms. In this case the central part of section of continuously cast blooms is in liquid or liquid-solid condition (mushy zone). At the same time, in practice now there are, at least, some original technical decisions for realization of this method.

Abstract: Lithium carbonate, zinc oxide and silica as the main raw materials, potassium oxide and sodium as flux, phosphorus pentoxide as nucleating agent, the glass in Li₂O-ZnO-SiO₂ was synthesized by conventional melt cooling method and then converted to glass-ceramics. The crystallization behavior, microstructure and thermal expansion coefficient of the resulting glass-ceramics were investigated by XRD, SEM and thermal performance test. The results show that the Tg of the matrix glass is about 508°C, initial crystallization temperature is about 620°C. When the crystallization temperature ranges from 650°C to 750°C, the main crystal phase is Li₂ZnSiO₄. Increasing crystallization temperature to 850°C, much cristobalite crystals is formed. Owing to the high TEC of the cristobalite, the glass-ceramics with TEC of 12.27×10^-6°C^-1 were obtained, which is matched with the TEC of stainless steel SAE 1010.

Abstract: The crystallization behavior of potassium vanadate from highly concentrated potassium hydroxide aqueous solution was investigated. The effect of various parameters including KOH concentration, V₂O₅ concentration, final crystallization temperature, cooling rate, stirring speed and additive amount of seed were examined. The optimal experimental conditions for K₃VO₄ crystallization were obtained as follows: KOH concentration 800850 g/L, KOH-to-V₂O₅ mass ratio 8~9, stirring speed 200 r/min, crystallization temperature from 80°C to 40°C with natural cooling, and seed addition 2% wt. Under optimal conditions, the K₃VO₄ crystallization yield of 87% was obtained, and the purity of crystals was about 90%.

Abstract: Both poly(L-lactide) (PLLA) and poly(ethylene succinate) (PES) are biodegradable synthetic aliphatic polyesters with excellent biocompatibility. They are semicrystalline thermoplastic polymers processed by most conventional processing methods. In view of their complementary properties, blending PLLA with PES becomes a promising approach to improve the properties of PLLA without compromising its biodegradability. In the present work, fully biodegradable PLLA/PES blend(the weight ratio 90/10) was melt-blended in stainless steel chamber. The crystallization morphology was investigated using a polarized optical microscope (POM), showing more clear spherulites with typical crosslink extinction patterns and faster crystallization rate of PLLA in blend at the lower heating rate. It clearly showed that the addition of PES largely increased the crystallization rate of PLLA and improved the crystallinity of PLLA in blends.

Abstract: A series of poly(trimethylene terephthalate)/maleinized poly(octene-ethylene) copolymer blends are prepared and their melting, crystallization and dynamic mechanical propwerties were studied by using differential scanning calorimetry (DSC) and dynamic mechanical analyzer (DMA) respectively. The results suggest that the glass transition temperature of the blends shift to higher temperature because of the interaction between PTT and POE components. POE-MAH serves as a nucleating agent for the crystallization of PTT, and it increases the crystallizaiton rate of the blend and the start crystallizaiton temperature, but reduces the degree of crystallinity. Proper content of POE, e.g.1-2%, can improve the elastic modulus of the blend, but too much POE will depress the modulus.

Abstract: The phase morphology, rheology, and crystallization properties of the PA6/PP-g-MAH/POE blends prepared by melt-blending method were studied by scanning electron microscopy (SEM), capillary rheometer and differential scanning calorimetry (DSC), respectively. The results suggest that the compatibility of PA6 and POE can be improved by the compatibilizer of PP-g-MAH and the 10% of PP-g-MAH is preferred. PP-g-MAH and PA6 can both serve as nucleating agents for each other, and improve their crystallization behaviors. All melts of PA6/PP-g-MAH/POE blends are pseudo-plastic fluids, and PP-g-MAH components can increase the melt apparent viscosity due to its inherent higher viscosity, and so the processing property of the blend will be controlled in much wider temperature range.

Abstract: Nano- crystallization of Fe₅₅Cr₁₈Mo₇B₁₆C₄ bulk amorphous alloy has been analyzed by X- ray diffraction, differential scanning calorimetric test, and TEM observations in this research. In practice, crystallization and growth mechanism were evaluated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models. A two -step crystallization process was observed in the alloy in which α – Fe, Fe23B6, and Fe3C phases were crystallized in the structure after annealing process. In addition, activation energy for the first step of crystallization process (i.e. α – Fe phase) was measured to be 276 (kj/mol) and 290 (kj/mol) according to Kissinger and Ozawa models respectively. Avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. Further, it is known from the TEM observations that crystalline α – Fe phase nucleated in structure of the alloy in an average size of 10 nm and completely mottled morphology.