Papers by Keyword: Crystallization

Abstract: Different amounts of SiO2 were used to substitute P2O5 to prepare lithium-iron-phosphate glass melts. It was found that glass can only formed after annealing the melt cast sample if the sample contains SiO2 not more than 5 mol%. The addition of 5 mol% SiO2 into the lithium-iron-phosphate glass strengthens the phosphate glass network. The density, chemical durability, both the transition and crystallization temperatures increase with the addition of SiO2. In addition, the addition of SiO2 results in the decrease in the activation energy of lithium-iron-phosphate glass, making the glass easier to crystallize. However, both the lithium-iron-phosphate glass and the glass with SiO2 show surface crystallization with LiFeP2O7 as the crystalline phase.

Abstract: Crystallization behavior of melt aluminum on the surfaces of SiC whisker (SiCw) was analyzed based on the consideration to obtain the SiC-Al interfaces with the lowest energy in SiCw/Al composite. The interfacial structure was investigated to determine whether a specific orientation relationship exists between SiC and Al. Analysis results indicate that four kinds of orientation relationships possibly exist between SiC and Al when only the <110> crystal direction of the aluminum is considered as the firstly formed crystal direction along the concave joint line of <110> of the SiC whisker. Interfacial atom match bonding models were set up in theory and one kind of crystal orientation relationship has been proved by our previous experimental result.

Abstract: Formation behavior of nanovoids during the annealing of amorphous Al₂O₃ and WO₃ was studied by transmission electron microscopy. The density and size of the voids in Al₂O₃ and WO₃ increase with increasing annealing temperature from 973 to 1123 K and from 573 to 673 K, respectively. It is suggested that the formation of nanovoids during annealing is attributed to the large difference in density between as-deposited amorphous and crystalline oxides.

Abstract: The calcium carbonate crystallization was controlled by Ca²⁺ concentrations, under the system of lignin solution with concentration of 10 g / L. Its morphology, structure and thermal decomposition were characterized by FT-IR, SEM, XRD and TG. Results showed that in lignin solution system, concentration of Ca²⁺ had significant effects on the crystallized morphology, orientation and crystallinity of calcium carbonate. Calcium carbonate crystal under low Ca²⁺ concentration had more uniform size while under high Ca²⁺ concentration which tended to form various sizes with more complete crystallization. The calcium carbonate crystals were all calcite calcium carbonate, which formed under different Ca²⁺ concentrations.

Abstract: Needle-like apatite-leucite glass-ceramics were synthesized in the SiO2-Al2O3-Na2O-K2O-P2O5 CaO-CaF2 system. Four glass batches were prepared by varying SiO2/P2O5 ratio, then melted and quenched. Crystallization was studied in compacted powder samples at different temperatures. Glasses were characterized for chemical bonding by FT-IR, phases and crystal structure by XRD, microstructure by SEM and hardness and fracture toughness by Vickers microhardness.

Abstract: The high-pressure crystallized poly (ether ether ketone) (PEEK) samples were investigated using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that the thermal stability of PEEK could be improved through appropriate high-pressure treatment. Although the 10wt.-% loss temperature and maximum decomposition temperature of the PEEK samples decreased with the increase of crystallization temperature and crystallization time, the effect of the applied pressure on preventing them from further degradation was obviously observed. Furthermore, the amorphous region of certain PEEK samples was eroded off after high-temperature degradation, which made the details of the spherulitic structures revealed more clearly using traditional etching technique. PEEK spherulites with different characteristics were disclosed with SEM, including those with sheaf-like structures, quench haloes or interpenetrating fibrils. The study presented here may be instructive to the applications of the polymer under such ultimate environmental conditions as high pressure and high temperature.

Abstract: In this work, the carbon nanotubes(CNTs) were reinforced with polypropylene(PP)matrix resins to improve the electrical and thermal properties of PP/ CNTs composites in different contents of 0,1, 3,and 5 wt.%. The surface, volume resistivity and crystallization type of the composites were investigated. As a result, the maximum degradation rate temperature of the composite is improved 30 °C, the surface resistivity and volume resistivity of composite are 5 ×10⁶, 7 ×10⁵,respectively, for the optimum composition of composite (CNTs 3 wt.%). The integrated XRD pattern of the composites shows the typical α-form PP crystals.

Abstract: Fused quartz powder (size<0.04mm) was used as raw material, nano-Y₂O₃, nano-CeO₂ and nano-La₂O₃ (size<0.08μm) were dividedly used as additives with dosage of 2% each. Fused quartz ceramic materials were sintered in reduction atmosphere at 1300°C, 1350°C and 1400°C for 1h. The effect of rare earth nano-oxides on sintering and crystallization of the fused quartz ceramic were researched by measurements of apparent porosity, bending strength and thermal expansion rate, and analyses of XRD and SEM. The results showed that additives nano-Y₂O₃, nano-CeO₂ and nano-La₂O₃ had obvious effect of inhibiting crystallization of fused quartz, and the samples added nano-Y₂O₃ and nano-La₂O₃ were better. Sample added nano-Y₂O₃ had least thermal expansion rate. Sample added nano-La₂O₃ had higher bending strength, and it showed that nano-La₂O₃ had better effect on sintering of fused quartz ceramic. It can be deduced that nano-La₂O₃ plays the excellent role as the crystallization inhibitor of fused quartz materials.

Abstract: Structure, viscosity and crystallization behavior of CaO-MgO-SiO₂ ceramic fiber with Nd₂O₃ were investigated by DTA, XRD and FTIR techniques. The results show that the addition of Nd₂O₃ enhanced the fiberization by extending the viscosity curve of the glass melt to lower temperature and improved the melt fiberizability. With the reinforcement of silicate glass network by Nd³⁺, the precipitation of crystals in fibers was inhibited at high temperatures.

Abstract: Fused quartz granules (d₅₀=19 μm) were used as raw material, and B₄C-Yb₂O₃ (1:1, in mass) was used as additive with dosages of 1% (in mass, similarly hereinafter), 2% and 3%. Fused quartz ceramic materials were fabricated in reduction atmosphere at 1250 °C, 1300 °C, 1350 °C and 1400 °C for 1 h. The apparent porosity, bending strength and thermal expansion ratios of the samples were examined and they were analysed by means of XRD and SEM. The results showed that the sample sintered at each temperature with 3% B₄C-Yb₂O₃ had the lowest apparent porosity, the highest bending strength and more compact microstructure. This indicated that 3% B₄C-Yb₂O₃ was conducive to sintering of fused quartz ceramic materials. The results of XRD analysis and thermal expansion ratio analysis showed that 3% B₄C-Yb₂O₃ compound additive had obvious effect on inhibiting crystallization of the samples sintered at various temperatures. It can be deduced that the 3% B₄C-Yb₂O₃ compound additive plays the excellent role in inhibiting crystallization and facilitating sintering of fused quartz ceramic materials.