Bioactivity of Fe2O3-CaO-SiO2 glass ceramics modified through the addition of P2O5 and TiO2

The bioactivity of ferromagnetic glass ceramics is one key factor affecting the success of hyperthermia treatments. In order to investigate the effect of the addition of a nucleating agent on the bioactivity of the resulting glass ceramics, two different nucleating agents were used for the fabrication of Fe₂O₃-CaO-SiO₂ glass ceramics, and their short-term and long-term effects on the cytotoxicity of human fetal normal colonic mucosa cells were evaluated. The results show that P₂O₅ promotes the formation of an apatite-like phase on the surface of Fe₂O₃-CaO-SiO₂ glass ceramics immersed in simulated body fluid. While TiO₂ had some adverse effect on the cell viability, P₂O₅ had little effect on the cell viability over a certain concentration range. In this paper, the prepared Fe₂O₃-CaO-SiO₂ glass ceramics with P₂O₅ added as nucleating agent are demonstrated to exhibit a good bioactivity and low cytotoxicity, which suggests good application prospects in the field of hyperthermia.     

Influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene and elastomer blends

The influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene (iPP), in their blends with poly(styrene-b-ethylene butylene-b-styrene) (SEBS), and a metallocenic ethylene-octene copolymer (EO) was investigated by DSC, optical microscopy and real-time small and wide angle X-ray scattering (SAXS and WAXS) experiments using synchrotron radiation. In non-nucleated iPP/SEBS blends, the crystallization of the iPP matrix occurred in the presence of the styrenic domains which induced a nucleating effect on the process, as observed in the synchrotron experiments. The metallocenic elastomer did not affect the crystallization behaviour of iPP in the iPP/EO blends in non-isothermal experiments, however, the development of crystallinity in the elastomer was restricted. In the nucleated isotactic polypropylene/elastomer blends a significant increase in the crystallinity and the crystallization rate of the iPP matrix was observed due to the presence of the nucleating agent. However, the nucleating efficiency of the additive was strongly affected by the nature and content of the elastomeric component. The nucleating agent efficiency was higher in the presence of the ethylene-octene component than the styrenic elastomer.     

Rheologically determined negative influence of increasing nucleating agent content on the crystallization of isotactic polypropylene

Dibenzylidene sorbitol (DBS) exists in the form of fibril and usually acts as an effective nucleating agent to facilitate crystallization of polyolefin during manufacturing. In this research, the isothermal crystallization of isotactic polypropylene (iPP) containing different amounts of DBS was followed by dynamic rheometry, and described upon a viewpoint of viscoelastic property evolution. Since the adopted temperatures within the entire sample preparation and characterization process were below the melting point of DBS, the DBS additives played a role of only solid nucleating agent, thus the possible effect of a changed miscibility between iPP and DBS on the viscoelastic properties as change of temperature could be ignored. Although saturation of nucleating iPP was observed at 0.1% DBS concentration, a negative influence with further increasing DBS content on the crystallization of iPP was determined for the first time via time sweep of G′ upon a single angular frequency and application of “inverse quenching” protocol within a wide range of angular frequency. Even more, a largely increased G′ and viscosity were observed in the melt as decreasing the temperature of iPP containing 0.1% DBS, suggesting a strong quasi-solid like behavior before iPP crystallization. A complement for well understanding the crystallization of iPP containing nucleating agent was discussed based on the formation of the DBS fibrils' network, the interfacial tension between crystalline/amorphous phase, and the consistency of crystallizing lamellae. Our study demonstrates clearly that the crystalline characteristic upon saturation of heterogeneous nucleating is difficult to be detected by traditional means, but could be followed reasonably by rheological measurements which is much sensitive to the microstructural changes.     

Effect of biobased and biodegradable nucleating agent on the isothermal crystallization of poly(lactic acid)

The effect of chemically modified thermoplastic starch (CMPS) on the thermal properties and isothermal crystallization kinetics of poly(lactic acid) (PLA) was studied by differential scanning calorimetry (DSC) and compared to that of granular starch and an inorganic nucleating agent, talc. Nucleated PLA showed an additional crystallization of PLA, which affected the melting temperature. The crystallinity and crystallization rate of PLA were considerably enhanced by addition of CMPS, even at 0.1% content, and the amount of the CMPS had little effect on the thermal properties and isothermal crystallization kinetics of PLA. The effect of CMPS as a nucleating agent was comparable to that of granular starch but slightly less than that of talc. However, CMPS can offer a fully biodegradable nucleating agent with no residues remaining for the biobased and biodegradable polymers.     

Effect of Cr2O3 on the crystallization behavior of synthetic diopside and characterization of Cr-doped diopside glass ceramics

Diopside is the main crystalline phase in silicate materials such as ceramics and glass-ceramics. Herein, the effect of Cr₂O₃ on the microstructure and crystallization behavior of synthetic diopside, as well as the solubility of Cr₂O₃ in diopside is discussed. Samples were prepared by the melting method and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and confocal laser scanning microscopy. Results show that the maximum achievable solubility of Cr₂O₃ in diopside is between 1% and 3% by weight, and that the magnesiachrome spinel formed by Cr₂O₃ can act as a nucleating agent for the diopside phase. Glass ceramics was prepared by synthesis slag which simulates the chromium-containing waste. The activation energy of crystallization is 274 KJ/mol and Avrami parameter is 3.23. The leaching behavior of glass ceramics was studied. Additionally, the effect of Cr₂O₃ on the mechanisms of phase change were discussed. The study provides a theoretical basis for the preparation of chromium containing waste-based silicate materials with diopside as the main crystalline phase.     

Influence of a particulate nucleating agent on the quiescent and flow-induced crystallization of isotactic polypropylene

Flow induced crystallization of commercial isotactic polypropylene (iPP) and its blends with sodium 2,2′-methylene bis-(4,6-di-tert-butylphenyl) phosphate (also known as NA11) is studied by means of in-situ time resolved small-angle X-ray scattering (SAXS). The isothermal crystallization at 145 °C (i.e. well below melting temperature of polymer) is performed after the application of steady shear to probe the anisotropic structure formation. In order to separate the influence of shear rate and shear time on polymer crystallization, four different shear conditions (60 s⁻¹ for 1 s, 30 s⁻¹ for 2 s, 15 s⁻¹ for 4 s and 6 s⁻¹ for 10 s) are applied while maintaining the same imposed strain in the polymer melt. Further the effect of different concentration of nucleating agent on the crystallization kinetics of iPP is examined both under quiescent and shear flow conditions. For instance, under quiescent condition, the crystallization half-time (τ_1/2) decreases with the increasing concentration of nucleating agent in the polymer. Under shear flow conditions, our observations are as follows: In the case of neat iPP, τ_1/2 decreases significantly at higher shear rates (≥30 s⁻¹). Compared to the neat iPP, for the same concentration of NA11 in the NA11/iPP blends differences in τ_1/2 with the increase in applied shear rates are significantly smaller. In other words, the crystallization kinetics is dominated by the amount of nucleating agent in the NA11/iPP blends as opposed to shear rates in the neat iPP. The present study shows that the critical value of shear rate required for chain orientation in the molten polymer is lower in the presence of the nucleating agent compared to neat iPP. The self-nucleation process investigated with the aid of differential scanning calorimetry (DSC), indicates that the nucleating efficiency of NA11 on iPP is around 60%.     

Effect of soluble Cr2O3 on the silicate network,crystallization kinetics,mineral phase,microstructure of CaO-MgO-SiO2-(Na2O) glass ceramics with different CaO/MgO ratio

Cr₂O₃ is often used as a glass additive to prepare glass ceramics. Chromium element exists mainly in two parts in the glass ceramics: chromium-containing spinel and soluble chromium in glass matrix. Herein, effect of soluble chromium on the CaO-MgO-SiO₂-(Na₂O) glass system is researched. Glass and glass ceramics were characterized by Raman spectrum, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry. It is found that the addition of Cr₂O₃ increased the Q²si structure unit in glass networks, especially in glass systems with high MgO content. The crystallization temperatures of the systems were increased with the addition of Cr₂O₃. Soluble chromium reduced the crystallization activation energy of the glass system slightly, but did not alter its crystallization behavior (surface crystallization). With the increase of MgO content, the mineral phases of the glass ceramics gradually changed from wollastonite to diopside. Cr₂O₃ reduced the lattice parameters of the mineral phases. The addition of Cr₂O₃ has a significant effect on grain refinement and structural compactness of the glass ceramics system with high MgO content.     

Growth behavior,morphology and properties of lithium aluminosilicate glass ceramics with different amount of CaO,MgO and TiO2 additive

Li₂O–Al₂O₃–SiO₂ glass with CaO, MgO and TiO₂ additive were investigated. With more CaO + MgO addition, the crystallization temperature (T_p) and the value of Avrami constant (n) decreased, the activation energy (E) increased. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. With more TiO₂ addition, the crystallization temperature decreased, E and n had a little change. The crystallization of the glass ceramics changed from surface crystallization to two-dimensional crystallization. Plate-like, high mechanical properties spodumene-diopside glass ceramics were obtained. The mechanical properties related with crystallization and morphology of glass ceramics.     

成核剂对聚丙烯力学性能与结晶行为的影响

研究了两种类型的成核剂对国产共聚聚丙烯的结晶形态以及拉伸强度、冲击强度的影响。结果表明:加入TMB-5型成核剂,聚丙烯的冲击强度有一定程度改善,w(TMB-5)为0.1%时,改性聚丙烯的缺口冲击强度达到最大;TMX-2型成核剂可改善聚丙烯的拉伸性能,但抗冲击性能降低较大;TMB-5型成核剂可显著地改变聚丙烯的结晶行为,诱导聚丙烯在结晶过程中主要形成β晶;TMX-2型成核剂可诱导聚丙烯在结晶过程中主要生成α晶,与纯PP相比,α晶的形成能力增强。     

Effect of nucleating agent addition on crystallization of isotactic polypropylene

The isothermal and nonisothermal crystallization kinetics of nonnucleated and nucleated isotactic polypropylene (iPP) were investigated by DSC and a polarized light microscope with a hot stage. Dibenzylidene sorbitol (DBS) was used as a nucleating agent. It was found that the crystallization rate increased with the addition of DBS. The influence of DBS on fold surface energy, σ_e, was examined by the Hoffman and Lauritzen nucleation theory. It showed that σ_e decreased with the addition of DBS, suggesting that DBS is an effective nucleating agent for iPP. Ozawa's theory was used to study the nonisothermal crystallization. It was found that the crystallization temperature for the nucleated iPP was higher than that for nonnucleated iPP. The addition of DBS reduced the Ozawa exponent, suggesting a change in spherulite morphology. The cooling crystallization function has a negative exponent on the crystallization temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2089–2095, 1998     

Effect of composition and sintering process on mechanical properties of glass ceramics from solid waste

Sintered diopside glass ceramics were successfully prepared from mixtures of blast furnace slag, fly ash and mining tailing. Results showed that sample C2 with relatively low iron oxides and mass ratio of CaO/SiO₂ possessed the highest bending strength value among samples. A low content of iron oxide enhanced densification degree because pores were developed by reduction of ferric oxide into ferrous oxide. Moreover, a low CaO/SiO₂ mass ratio also greatly promoted the densification process by prolonging the sintering time and delaying the crystallisation. In addition, sample C1 developed by one-stage sintering had a worse mechanical performance than that obtained by two-stage sintering although they had the same crystals. For all samples, despite of different compositions and sintering processes, the main crystal phases are augite and diopside ferrian.     

Influence of nucleation agents on crystallization and machinability of mica glass–ceramics

Effects of ZrO₂, La₂O₃, CeO₂, Yb₂O₃ and V₂O₅ on the crystallization kinetics, microstructure and mechanical properties of mica glass–ceramics were investigated by the differential scanning calorimetry (DSC), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness tester. Results show that bulk crystallization can be obtained by introducing proper nucleation agents into the glass. Both Ozawa method and Kissinger method are suitable for analyzing the crystallization kinetics of mica glass–ceramic. The addition of nucleation agents has little influence on the value of n, keeping two-dimensional crystal growth mechanism. ZrO₂ and V₂O₅ are best nucleation agents in mica system. The increase of crystallization temperature is helpful for the increase of aspect ratio, and the microstructure of the glass–ceramics becomes interconnected, which contributes the improvement of the machinability of the glass–ceramics. Microhardness (H_v), cutting energy (μ¹) and machinability parameter (m) can be used for estimating the machinability of mica glass–ceramics.     

加入物对石英陶瓷烧结和析晶的影响

研究了加入物Ｈ_３ＢＯ_３和Ｈ_３ＰＯ_４对石英陶瓷的烧结和析晶的影响。结果表明，加入适量的Ｈ_３ＢＯ_３或Ｈ_３ＰＯ_４有助于试样的烧结，随着烧成温度的提高，加入物可抑制石英玻璃的析晶。     

Effects of nucleating agent on nonisothermal crystallization of syndiotactic polystyrene

The effects of nucleating agent on nonisothermal crystallization were examined for syndiotactic polystyrene (SPS) using Differential Scanning Calorimetry (DSC). The crystallization peak temperature T_c, the crystallization rate parameter (CRP), the enthalpy of crystallization and melting, and the recrystallization behavior were compared between organic (DMBS, 1,3,2,4-dis-5-(3,4-dimethyl benzylidene) sorbitol) and inorganic (talc) nucleating agents. Both of the nucleation agents promoted the crystallization rate of SPS until some critical concentration of about 3,000 ppm. DMBS worked more effectively as a nucleating agent than talc, although the T_c showed lower level in SPS/DMBS than SPS/talc.     

Enhancing mechanical performance of polylactide by tailoring crystal morphology and lamellae orientation with the aid of nucleating agent

The performance of semicrystalline polymers is significantly dependent on the crystal morphology and lamellae orientation. In this work, the crystal superstructure and mechanical properties of polylactide (PLA) with different amounts of nucleating agent (tetramethylene-dicarboxylic dibenzoyl-hydrazide, TMC-306) were investigated. It was found that TMC-306 can be dissolved in PLA melt and re-crystallize into fibrils upon cooling. These fibrils can serve as nucleation templates to induce the crystallization of PLA on their surface, resulting in a large enhancement in crystallization rate. More importantly, PLA lamellae can grow perpendicular to the long axis of TMC-306 fibrils, inducing the formation of shish-calabash, shish-kebab and needle-like structures, depending on the concentration of TMC-306 used. Taking advantage of shear flow experienced in injection molding, TMC-306 fibrils tend to align in PLA melt along the shear flow direction, inducing the formation of highly orientated PLA lamellae in injection-molded articles. In this way, a simultaneous improvement in impact toughness, tensile strength and elongation at break is achieved. This work provides a good example of using a fibrous nucleating agent as a template to tailor the crystal morphology and lamellae orientation, thus achieving greatly enhanced properties for PLA.     

Magnetite-based glass-ceramics prepared by controlled crystallization of borosilicate glasses: Effect of nucleating agents on magnetic properties and relaxation

The specific magnetic structure and magnetic relaxation phenomena in magnetite nanoentities grown in a glassy matrix by controlled crystallization of Fe-containing borosilicate and boroaluminosilicate glasses in the presence of two types of nucleating agents, Cr₂O₃ and P₂O₅, were investigated. The structure, morphology and magnetic properties are strongly influenced by the nucleating agents. Cr₂O₃ generates magnetite-based glass ceramics with magnetite configurations showing an upward relaxation of magnetization at low and high temperatures but downward at intermediate temperatures. The magnetite grown with P₂O₅ displays only downward relaxation but with different signs of the temperature derivative of the relaxation rate S in different temperature ranges. The observed effects are discussed with respect to the following factors: i) the existence of a multimodal size distribution of the magnetite (nano)particles as revealed by high resolution electron microscopy; ii) the degree of occupation of different sublattices of the magnetite structure with Fe³⁺ and Fe²⁺ ions; and iii) the interplay between the relaxation mechanisms in different temperature ranges.     

一种成核剂对聚乳酸结晶行为的影响

通过示差扫描量热法研究了一种新型成核剂对聚乳酸结晶行为的影响,并通过Avrami方程对其结晶动力学进行分析。结果显示,当聚乳酸中加入0.3%质量分数的成核剂,即可使其半结晶时间由61.4 min缩短至9.2 min。通过偏光显微镜对聚乳酸及含成核剂的聚乳酸的晶体形貌观察,发现成核剂可以显著的提高聚乳酸的结晶速率,相同时间内,球晶数量显著增多,晶粒尺寸明显减小。     

加入不同种类成核剂抗冲击共聚PP的非等温结晶动力学

采用差示扫描量热仪研究了加入羧酸盐类成核剂和有机磷酸盐类成核剂的抗冲击共聚聚丙烯2500H的熔融、结晶和非等温结晶行为。结果表明:加入质量分数为0.02%的成核剂后,2500H的结晶度和所有结晶特征温度均提高,其中,结晶度提高0.3%~3.0%,结晶温度提高4.4~11.0℃,结晶起始温度提高4.4~12.2℃,结晶终止温度提高6.3~11.6℃。与加入有机磷酸盐类成核剂的2500H相比,加入羧酸盐类成核剂的2500H具有更低的结晶过冷度,成核能力相对较高;但加入有机磷酸盐类成核剂的2500H表现出更快的结晶速率,而加入羧酸盐类成核剂的2500H虽然在高温条件下能促使2500H较快形成晶核,但并不利于结晶速率的提高。     

成核剂对聚丙烯结晶形态及力学性能的影响

研究了有机磷酸盐成核剂对聚丙烯(PP)结晶行为及力学性能的影响．采用差示扫描量热法和偏光显微镜分析比较了3种成核剂。结果表明：添加质量分数为0.2％的成核剂,可使PP的结晶峰温度提高15．6～17．8℃。结晶度增加2．5％～10．5％,同时提高了结晶速率,球晶尺寸大幅度降低;试样的拉伸强度、弯曲模量均有提高。弯曲模量提高15．5％～44．9％。     

Effect of atmosphere control on magnetic properties of CaO-Al2O3-SiO2-Fe3O4 glass ceramics

The influences of atmosphere during processes of melting and heat treatment, heat treatment temperature, Fe₃O₄ content and basicity on the magnetic properties of magnetite-based glass ceramics were investigated. For sample containing 20 % Fe₃O₄ melted in different atmospheres, the highest saturation magnetisation was realized in 20vol% air + 80 vol% Ar, due to the fact that ratio of Fe³⁺ to Fe²⁺ in melt obtained in this atmosphere was close to 2. However, it was found that the coercivity of glass ceramics was not affected by the melting atmosphere. A high sintering temperature led to the decrease of saturation magnetisation and the increase of coercivity. As increasing Fe₃O₄ content, the main crystal phase transformed from CaSiO₃ to CaFe_0.6Al_1.3Si_1.08O₆ and finally to magnetite phase, accompanied by the increase of saturation magnetisation and coercivity. In addition, the increase of basicity caused the decrease of saturation magnetisation and the increase of coercivity.