Effects of nucleating agents on diopside crystallization in new glass-ceramics for tile-glaze application

The effect of crystallization produced by addition of TiO₂, ZrO₂ and P₂O₅ oxides to glass-ceramic of the system CaO-MgO-SiO₂ was studied using structural and thermal techniques. The devitrification process was independent of thermal treatment. X-ray diffraction studies performed on the glass-ceramic system indicated that diopside crystalline phase was more thermodynamically favourable than other phases. The effect of the nucleating agent depends on its nature: TiO₂ decreased the activation energy while P₂O₅ and ZrO₂ did not. SEM analysis of the doped glass-ceramics showed randomly distributed crystals with significant dimensional variations from those of the undoped system. All these formulations, showing a high crystallization rate, and a fast heating rate, can be used as tile glazes and/or tile-glaze components.     

锰锌铁氧体制备工艺及其对磁性玻璃陶瓷性能的影响

采用氧化物煅烧法、共沉淀法和溶胶-凝胶法制备锰锌铁氧体前驱体,并将其与生物玻璃陶瓷复合,制备磁性玻璃陶瓷。研究了不同工艺制备的铁氧体对材料磁性、生物活性和细胞亲和性的影响。结果表明,充磁至7.96×105 A/m,材料的饱和磁化强度在7.49～6.46A.m2/kg之间,矫顽力在9.95×103～1.60×104 A/m之间。其中使用共沉淀法制备铁氧体前驱体使复合材料磁滞回线包围面积最大,预期有最好的生热能力。而各铁氧体的掺入均导致材料生物活性下降,但在浸泡入模拟体液21d后,各材料表面均能生成类磷灰石层。将ROS17/2.8细胞与共沉淀法制备的铁氧体复合材料共同培养7d,材料显示出良好的细胞亲和性。     

成核剂与增稠剂对甘露醇相变特性的影响

糖醇是一种用于储热的相变材料,具有较高的潜热,然而,糖醇的高过冷度阻碍了其应用。D-甘露醇作为一种糖醇,在中温储热方面具有广阔的应用前景。选用氧化铝和碳化硅作为成核剂,海藻酸钠和羧甲基纤维素作为增稠剂,观察了纯甘露醇、成核剂、增稠剂以及单独或联合添加成核剂和增稠剂的甘露醇的形貌。采用差示扫描量热法研究了成核剂和增稠剂对甘露醇相变特性的影响。实验结果表明,氧化铝、碳化硅和适量的海藻酸钠促进了甘露醇的成核结晶,当氧化铝、碳化硅、海藻酸钠的质量分数分别为7.0%、9.0%、0.5%时达到最低过冷度,样品相比纯甘露醇过冷度分别降低了17.4、12.2和17.3℃。联合添加相比单独添加成核剂和增稠剂改善了甘露醇的成核结晶;当联合添加氧化铝和海藻酸钠的质量分数分别为5.0%和1.0%,而碳化硅和海藻酸钠的质量分数分别为3.0%和1.0%时,样品相比纯甘露醇过冷度分别降低了19.7℃、16.5℃。探讨了成核剂和增稠剂对甘露醇相变特性的影响机理,发现增稠剂提高了成核剂在甘露醇样品中的分散性,因而提高了成核剂的诱导成核作用。     

晶核剂的选择对可切削玻璃陶瓷析晶性能的影响

对可切削玻璃陶瓷材料来讲,其内部云母微晶相的含量及云母晶体间交错程度的大小直接影响材料的性能.本文采用添加不同的晶核剂的方法,通过差热分析(DTA)、扫描电镜(SEM)及X射线衍射(XRD)测试分析,研究了晶核剂对可切削玻璃陶瓷析晶性能的影响.研究表明同时采用F和Ti作为晶核剂时,材料内部的晶相含量明显提高,并且材料的可切削性能也得到了改善.     

Structural and magnetic properties of glass-ceramics containing silver and iron oxide

Glass-ceramics with a nominal composition of 25SiO₂–(50 − x)CaO–15P₂O₅–8Fe₂O₃–2ZnO–xAg (where x = 0, 2 and 4 mol%) have been prepared. Structural features of glass-ceramics have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Magnetic properties were studied using vibrating sample magnetometer and Mössbauer spectroscopy. Ca₃(PO₄)₂, hematite and magnetite are formed as major crystalline phases. The microstructure reveals the formation of 25–30 nm size particles. Mössbauer spectroscopy has shown the relaxation of magnetic particles. Saturation magnetization value is increased with an increase of Ag content up to 4 mol%, which has been attributed to the formation of magnetically ordered particles. The antibacterial response was found to depend on Ag ions concentration in the glass matrix and samples with 4 mol% Ag in glass matrix have shown effective antibacterial activity against Escherichia coli.     

成核剂对PLLA/PDLA共混纤维结构和性能的影响

将取代芳基磷酸酯盐类化合物(TMP-5)、多酰胺类化合物(TMC-328)、水滑石(HT)等不同类型的成核剂添加到聚L-乳酸(PLLA)与聚D-乳酸(PDLA)中共混熔融纺丝,初步研究了成核剂对纤维结构和性能的影响。结果表明,PDLA与PLLA共混熔融纺丝可以形成立构复合型PLA(sc-PLA)晶体,成核剂的加入,更加促进了聚乳酸纤维中sc-PLA晶体的形成;而且,成核剂TMP-5的加入,既可以改善纤维的耐热性能,又有助于纤维断裂强度和拉伸模量的增大,提高了纤维的力学性能。     

Microstructure characteristics for anorthite composite glass with nucleating agents of TiO2 under non-isothermal crystallization

The anorthite-based composite glass doped with TiO₂ and B₂O₃ was prepared by quenching of molten droplets. Phase development and crystals microstructure of glass were investigated under non-isothermal conditions. A glass transition temperature of 770°C and an exothermal peak around 870°C in the DTA trace was associated with anorthite crystallization (CaAl₂Si₂O₈). For glass specimens under nucleation and crystallization heat-treatment, the final predominant phase was identified as anorthite. Anorthite crystals show preferential nucleation at specific sites with rutile TiO₂ crystals precipitated from the glassy matrix and anorthite crystallization is governed by heterogeneous volume nucleation. The introduced TiO₂ plays the role of nucleating agents to reduce the crystallization temperature lower than 900°C for anorthite-based glass-ceramics. Chemical compositions could be related to the crystal microstructures on different characteristic regions. It was observed that the sintering aid of B₂O₃ neither reacted with nor dissolved in the anorthite or rutile TiO₂ crystals, and remained a glassy phase in the matrix. Occurrence of acicular precipitations was attributed to the orientation growth of TiO₂ crystals. Anorthite crystals were observed to grow with the forms of feathery-spherical particles, having a tendency to coalescence into a huge domain.     

Controlled crystallization and characterization of cordierite glass-ceramics for magnetic memory disk substrate

Glass-ceramics containing cordierite (2MgO-2Al₂O₃-5SiO₂) as a crystal phase based on the glasses in the system MgO-Al₂O₃-SiO₂ were investigated for the application to magnetic disk substrate for higher storage capacity. Parent glasses were prepared with CeO₂ addition as a flux and were crystallized by a controlled 2-step heat treatment The maximum nucleation and crystal growth rates were 2.4 × 10⁹/mm³ · hr at 800 °C and 0.3 m/hr at 915°C respectively. Only - cordierite was precipitated after heat-treatment. After nucleation at 800 °C for 5 hours prior to crystallization at 915 °C for 1 hour, the resulting crystal volume fraction and crystal size were 17.6% and 0.3 m, respectively. Heat-treated specimens through the above condition showed the optimum properties for magnetic memory disk substrates as follows.; Bending strength of 192 MPa, Vickers hardness of 642.1 kg/mm², thermal expansion coefficient of 39 × 10^–7/K and surface roughness of 27 Å.     

Synthesis and characterization of magnetic bioactive glass-ceramics containing Mg ferrite for hyperthermia

Novel magnetic bioactive glass-ceramics (M GC) were synthesized by doping Mg ferrite to wollastonite–fluorapatite-containing glass-ceramics. The phase composition was investigated by XRD. The magnetic property was measured by VSM. The in vitro bioactivity was investigated by simulated body fluid (SBF) soaking experiment. Cell growth on the surface of the material was evaluated by co-culturing osteoblast-like ROS17/2.8 cells with M GC. The results showed that CaSiO₃, Ca₂MgSi₂O₇, Ca₅(PO₄)₃F and Fe₂MgO₄ were the main phases of M GC. Under a magnetic field of 10,000 Oe, the saturation magnetization and coercive force of M GC were 7.2 emu/g and 175 Oe, respectively. After soaking in SBF for 14 days, a lot of hydroxyapatite containing CO₃^2? was observed on the surface of M GC. The experiment of co-culturing cells with M GC showed that osteoblast-like ROS17/2.8 cells could attach well on the surface of M GC. The material has the potential to be used as thermoseeds for hyperthermia.     

Properties of sintered glass-ceramics prepared from plasma vitrified air pollution control residues

Air pollution control (APC) residues, obtained from a major UK energy from waste (EfW) plant, processing municipal solid waste, have been blended with silica and alumina and melted using DC plasma arc technology. The glass produced was crushed, milled, uni-axially pressed and sintered at temperatures between 750 and 1150 °C, and the glass-ceramics formed were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties assessed included Vickers's hardness, flexural strength, Young's modulus and thermal shock resistance. The optimum sintering temperature was found to be 950 °C. This produced a glass-ceramic with high density (～2.58 g/cm³), minimum water absorption (～2%) and relatively high mechanical strength (～81 ± 4 MPa). Thermal shock testing showed that 950 °C sintered samples could withstand a 700 °C quench in water without micro-cracking. The research demonstrates that glass-ceramics can be readily formed from DC plasma treated APC residues and that these have comparable properties to marble and porcelain. This novel approach represents a technically and commercially viable treatment option for APC residues that allow the beneficial reuse of this problematic waste.     

The influence of modified zeolites as nucleating agents on crystallization behavior and mechanical properties of polypropylene

Polypropylene (PP) composites with unmodified and modified zeolites were prepared by melt blending in single-screw extruder. The modified zeolites, diethoxy (distearoyl) silane (DDS)–zeolite 13X (DDS-13X) and diethoxy (distearoyl) silane–zeolite 5A (DDS-5A), were obtained by grafting diethoxy (distearoyl) silane onto zeolite 13X and 5A, respectively. The influence of the unmodified and modified zeolites as nucleating agents on properties of polypropylene was investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC), polarized light microscopy (PLM), Vicat softening temperature (VST) and mechanical properties test. The XRD results revealed that zeolite 13X and DDS-13X had a great influence on nucleation of PP compared to zeolite 5A and DDS-5A. The DSC results showed that the addition of small amount of modified zeolites lead to increase in crystallization temperature (T_c), initial crystallization temperature (T_onset) and crystallinity (X_c) of PP composites compared to unmodified zeolites, especially, DDS-13X was more effective than DDS-5A, and the highest crystallinity X_c (50.48%) was observed in PP/0.3 wt.% DDS-13X, which was responsible to the higher tensile strength and flexural strength of PP/DDS-13X. The PP/DDS-5A, however, exhibited evident increase in flexural strength and a little change in tensile strength compared to pure PP. Moreover, as the addition amount of DDS-5A or DDS-13X up to 1 wt.%, the impact strength of both PP/DDS-5A and PP/DDS-13X reached 43 kJ/m², which was about 2.8 times greater than that of the pure PP (11.3 kJ/m²). These results were in good agreement with the spherulite morphology observed from PLM micrographs.     

Apatite-forming ability and magnetic properties of glass-ceramics containing zinc ferrite and calcium sodium phosphate phases

Fine particles of zinc ferrite (ZnFe₂O₄) and calcium sodium phosphate [NaCaPO₄] were crystallized in bulk x(ZnO, Fe₂O₃)(65?x)SiO₂20(CaO, P₂O₅)15Na₂O (6 ≤ x ≤ 21 mol %) glassy matrix by heat treatment. Initial magnetization curves reveal that samples with x = 6 and 9 mol % zinc–iron oxide exhibit both ferrimagnetic and paramagnetic contributions, whereas, samples with x > 9 mol % zinc–iron oxide exhibit only ferrimagnetic contribution. This observation is supported by the disappearance of the electron paramagnetic resonance (EPR) absorption line centered at g ≈ 4.3 in samples with x > 9 mol % zinc–iron oxide. Apatite-forming ability of the glass-ceramic samples was investigated by examining apatite formation on the surface of the samples treated in simulated body fluid (SBF). Increase in apatite-forming ability was observed with an increase in zinc–iron oxide content. The results obtained have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass-ceramic composition. A good correlation has also been observed between the magnetic nature of the samples and their apatite-forming ability. These materials are expected to find application as thermo-seeds in hyperthermia treatment of bone cancer.     

Properties of magnetic fluid particles

Very fine particles of magnetite, nickel ferrite, and cobalt ferrite were produced by grinding coarser powders in a ball mill with a carrier fluid and a surfactant. The particles were examined by means of chemical analysis, electron microscopy, x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. Properties were determined before and after removing the surfactant coating. The most significant observation was that in some systems a large fraction of the spins was pinned in extremely high anisotropy fields as a result of bonding to the surfactant molecules. Anomalous magnetic hysteresis behavior was also noted when the surfactant coating was present.     

不同组分PZT压电薄膜的性能

采用sol-gel工艺在Pt/Ti/SiO2/Si衬底上制备了不同条件的锆钛酸铅（PZT）薄膜.分析了不同的前烘温度、不同锆钛比例对PZT薄膜的微观结构和电特性所产生的影响.SEM分析结果显示,铁电薄膜的晶化较完善,薄膜表面均匀致密.用X射线衍射分析了不同条件制备的PZT薄膜,表明薄膜的微观结构和取向不仅对热处理的条件非常敏感,而且也深受薄膜组分的影响.铁电测试表明对PZT（锆/钛=30/70）,300℃热处理的薄膜具有最大的自发极化值.而对于不同锆钛比的薄膜,在准同型相界附近的53/47配比的PZT薄膜表现出最好的铁电性、介电性和最高的体电阻率.     

Effect of nucleating agents and cooling rate on the microstructure and properties of a rotational moulding grade of polypropylene

Rotational moulding consists of coating the inside surface of a metal mould with a layer of plastic by rotating the mould, firstly in an oven and then in a cooling bay to induce solidification to the desired part shape. As the rotational speeds are slow (typically about 10 rev/min), the resulting hollow articles are practically stress free. The primary material used for rotationally moulded parts is polyethylene but there is an increasing interest in using polypropylene to provide stiffer, higher temperature products. Unfortunately the slow cooling combined with the slow crystallisation rate of polypropylene results in brittle mouldings with coarse spherulites. Since the inner surface of the plastic is in contact with air during moulding, degradation is also likely to occur. In order to improve the mechanical properties of the rotationally moulded polypropylene, and nucleating additives were added. The effect of using faster cooling rates was also studied. It was found that heterogeneous nucleation, both of and spherulites, did not improve the ductility of the samples. However, when fast cooling was used, the impact strength of the polypropylene improved markedly, independent of the presence of nucleating additives. In the rotationally moulded polypropylene parts, the fast cooling could only be applied to the outer surface of the mould, which led to asymmetric cooling. This resulted in severe warpage, and uneven morphology. This problem should be overcome by using fast cooling on both the inside and outside surfaces of the plastic.     

Whisker reinforcement of glass-ceramics

Silicon carbide whisker reinforcement of anorthite and cordierite glass ceramics has been studied. At 25 vol% whisker loading the flexural strengths increased from 65–103 MPa to 380–410 MPa, the fracture toughnesses increased from 1.0–1.5 MPa m^1/2 to 5.2–5.5 MPa m^1/2. The strengths decline to 240–276 MPa at 1200 °C. The reasons for the decrease in strength with temperature are discussed. Whiskers from two different sources with differences in diameters and aspect ratios were evaluated and the effect of the whisker morphology on the composite properties was studied. It was found that larger diameter, higher aspect ratio whiskers result in improved composite performance. The composites were also characterized in terms of their thermal properties, i.e. thermal expansions and thermal conductivities. The thermal expansion coefficient from 25–1000 °C for anorthite-based composite was 4.6×10^–6 °C^–1 and that for the cordierite-based composite was 3.62×10^–6 °C^–1. The thermal conductivities at 1000 °C were 3.75 and 4.1 Wm^–1 K^–1 for cordierite and anorthite composites, respectively.