The Synthesis of Boron Carbide Ceramic via Electrospinning Technique

In this study, polyvinyl alcohol (PVA) and boric acid (BA) were mixed in an aqueous medium by heating in order to prepare a PVA/BA hybrid material. The viscosity and pH values of the PVA/BA hybrid material mixed in various proportions were determined. Then the hybrid polymer was electrospun to give dimensions to fibers. The FT-IR spectra of these fibers revealed that BA chemically reacted with PVA and formed B–O–C bonds. The fibers were first calcified at 500 °C and then the calcified products were pelleted and exposed to the sintering process at 1300 °C. The XRD peaks of the sintered product were seen at 2θ = 34.7 and 37.7° verified the formation of boron carbide. The study proved that it was possible to use sub-micron fibers for the production of sub-micron boron carbide material.     

Sintering of Zinc Oxide Doped with Antimony Oxide and Bismuth Oxide

The phase change, densification, and microstructure development of ZnO doped with both Bi₂O₃ and Sb₂O₃ are studied to better understand the sintering behavior of ZnO varistors. The densification behavior is related to the formation of pyrochlore and liquid phases; the densification is retarded by the former and promoted by the latter. The pyrochlore phase, whose composition is Bi_3/2ZnSb_3/2O₇, appears below 700°C. The formation temperature of the liquid phase depends on the Sb/Bi ratio: about 750°C for Sb/Bi < 1 by the eutectic melting in the system ZnO—Bi₂O₃, and about 1000°C for Sb/Bi > 1 by the reaction of the pyrochlore phase with ZnO. Hence, the densification rate is determined virtually by the Sb/Bi ratio and not by the total amount of additives. The microstructure depends on the sintering temperature. Sintering at 1000°C forms intragrain pyrochlore particles in ZnO grains as well as intergranular layers, but the intragrain particles disappear at 1200°C by the increased amount of liquid phase, which enhances the mobility of the solid second phase.     

Preparation of Porous Tin Oxide Nanobelts Using the Electrospinning Technique

The electrospinning method is adopted to prepare utralong PEO/stannic hydroxide composite nanofibers. Tin-oxide nanobelts can be obtained by calcination of the composite nanofibers in an open atmosphere. The nanobelts were characterized by a field emission scanning electron microscope, X-ray diffraction, a transmission electron microscope, a Raman spectromicroscope, and Fourier transform infrared spectroscopy. Microstructural analysis has shown that the nanobelts prepared consist of a continuous network of interconnected SnO₂ grains. As a result, the SnO₂ nanobelts possess a high surface area and continuous porosity, which may be applied for the fabrication of sensitive gas sensors.     

Preparation of Synthetic Cordierite by Solid-State Reaction via Bismuth Oxide Flux

A comparative study of the solid-state reaction synthesis of cordierite with and without the use of a flux was performed, varying the sintering temperatures between 900° and 1400°C. Bi₂O₃ proved to be a useful additive for lowering the temperature needed for the reaction to take place. The deviation from the ordered β-cordierite phase was analyzed using the distortion index Δ as a factor of merit. The values obtained for Δ in all compositions showed that cordierite tended to a much-ordered structure with increased sintering temperatures.     

Preparation of Cordierite below 1000°C via Bismuth Oxide Flux

Bismuth oxide has been found to be a useful flux for the preparation of dense body cordierite (Mg₂Al₄Si₅O₁₈). The addition of as little as 2 at.% of bismuth ion to the appropriate stoichiometric mix of commercially available oxide starting materials gives fully dense cordierite after firing for 12 h at 1000°C. The lower-temperature limit for this reaction is 960°C, with essentially no reaction occurring below this temperature. There is also a temperature-dependent induction period prior to cordierite formation. The microstructure of the sintered body has the residual bismuth oxide flux distributed in discontinuous domains at the grain boundaries and at the triple points. The cordierite body has a dielectric constant of 5.0, unperturbed by the presence of the bismuth oxide.     

Preparation of Zinc Oxide Nanofibers by Electrospinning

Ultra-thin fibers of zinc oxide (ZnO) were prepared by sol–gel processing and the electrospinning technique using poly(vinyl acetate) and zinc acetate as precursors. The fibers were characterized by thermogravimetric analysis, scanning electron microscopy, Fourier-transfer infrared, and X-ray diffraction, respectively. The results showed that the diameter of the precursor fibers increased with increasing zinc acetate content, and the size of the inorganic ZnO nanofibers decreased obviously as the calcining time increased.     

Preparation of Hydroxyapatite Fibers by Electrospinning Technique

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA) fibers were prepared by electrospinning a precursor mixture of Ca(NO₃)₂·4H₂O and (C₂H₅O)₃PO with a polymer additive, followed by a thermal treatment. The X-ray diffraction (XRD) analysis of the annealed composite fibers revealed that pure HA phase could be obtained by annealing at 600°C for 1 h. The scanning electron microscopy (SEM) analysis showed the surface of as-electrospun composite fibers with an average diameter of 50 μm was smooth due to the amorphous nature of the polymer. However, the surface of the calcined HA fibers was rough because of the complete removal of the polymer. The pure HA fibers obtained by electrospinning in this work were up to 10 mm in length and 10–30 μm in diameter and the hydroxyapatite grain size was ∼1 μm in the HA fibers.     

氧化铋薄膜的制备及其性能表征

利用化学水浴沉积法在室温下制备了多晶氧化铋薄膜,并在350℃的空气气氛条件下进行退火处理,得到纯的α-Bi2O3,薄膜.对它们的晶相结构、光电性能进行测试.从X衍射分析结果来看,在退火过程中,薄膜结构由四方相和非化学计量相向单斜相转变.光学性质显示退火处理的薄膜吸收边缘明显的向长波的方向移动,发生红移现象,而且禁带宽度减少了0.4eV.退火后的薄膜在室温下暗电导率下降2个数量级.电导率的变化显示具有半导体行为的性质.     

熔融静电纺丝技术制备聚甲醛纤维

通过DSC测试得出聚甲醛的熔融温度为170℃,并通过试验确定最佳的纺丝温度为190℃。研究了聚甲醛质量分数和纺丝电压对静电纺聚甲醛纤维直径的影响,确定最佳的纺丝条件为:聚甲醛质量分数90%,电压14 k V。对聚甲醛纤维的表面形态及热性能进行了测试,结果显示:聚甲醛纤维表面光滑且粗细均匀;结晶度较高,为68.84%;熔点比纯聚甲醛熔点低,为160.25℃。     

铋离子掺杂固体氧化物燃料电池阴极材料的研究进展

固体氧化物燃料电池(SOFC)是一种可以将燃料中的化学能直接转化为电能的发电装置,具有燃料选择灵活、效率高、环境友好等优点。基于SOFC运行成本和长期稳定性的要求,降低工作温度已成为当前研究的热点。传统阴极较低的催化活性制约了SOFC的技术发展,因此开发具有良好催化性能的阴极材料至关重要。大量的研究表明,铋离子的掺杂能够有效提高材料的电导率和氧催化活性。从铋离子掺杂的角度出发,综述了铋离子掺杂对阴极材料的制备、结构、电导率和电化学性能的影响,并对掺铋SOFC阴极材料未来的发展趋势进行了展望。     

采用高速剪切反应器生产超细氧化铋工艺探讨

利用硝酸铋溶液和碳酸铵溶液为原料，采用高速剪切反应器，500℃煅烧后可以生产出高纯、超细的氧化铋粉末。该方法制备出的氧化铋平均粒度0．71μm且粒度范围分布窄，颗粒形貌为类球形，晶相为纯α相，指标达到电子压敏陶瓷要求。由于粒度细小，可以在电子压敏陶瓷球磨工艺减少球磨工艺，并具有更好的分散效果。本文对超细的氧化铋粉末形成机理也进行了探讨。     

静电纺丝技术制备LaAlO3 纳米纤维与表征

采用静电纺丝技术制备了PVP/[La(NO3)3+Al(NO3)3]复合纳米纤维,经过800 ℃焙烧8 h热处理后成功制备出大量的LaAlO3 纳米纤维.采用XRD、SEM、EDS、TEM、SAED、FTIR等测试技术对样品进行了系统地表征.结果表明,PVP/[La(NO3)3+Al(NO3)3]复合纳米纤维为非晶态,所制备的LaAlO3 纳米纤维为菱形晶系,空间群为R3m.PVP/[La(NO3)3+Al(NO3)3]复合纳米纤维表面光滑,平均直径约为180 nm;LaAlO3 纳米纤维的平均直径为80 nm,长度大于300 μm.LaAlO3 纳米纤维由纳米粒子构成,纳米粒子平均直径为15 nm,为多晶结构.对LaAlO3 纳米纤维的形成机理进行了讨论.     

静电纺丝制备聚醚酮酮超细纤维

用溶液静电纺丝方法制备了聚醚酮酮超细纤维,用扫描电子显微镜研究了实验过程中纺丝电压、纺丝距离、流量、纺丝液浓度对于聚醚酮酮纤维直径和形貌的影响,并对多个纺丝参数的影响规律进行了分析。实验结果表明,在一定条件下纺丝电压和纺丝距离对纤维直径影响较小,而流量和纺丝液浓度能显著影响纤维直径,在小流量、低浓度容易得到较细的纤维,并且纤维直径分布集中。     

Phototrogy of Alkaline Earth Tungstates Doped with Bismuth

Calcium, strontium, and barium tungstates and their solid solutions, doped with a small amount of bismuth, color remarkably on exposure to ultraviolet light and return to the original white by thermal fading or optical bleaching. The factors affecting the darkening and fading processes were studied experimentally. Under the same irradiation conditions the intensity of uv-induced coloration depended on the Bi content and preparation temperature of the tungstates. Bi contents higher than 0.1 molyo and preparation temperatures higher than 1250°C gave strong coloration. The rate of fading of uv-induced color increased with increasing Bi content. The fading was accelerated by heating; almost all the uv-induced color disappeared at 230°C in 30 min. The fading rate was also increased by visible light exposure. The uv-induced absorption spectra varied systematically with the composition of the tungstates.     

掺铝氧化锌薄膜的制备及应用研究进展

综述了掺铝氧化锌薄膜的各种制备方法,包括磁控溅射法、脉冲激光法和溶胶凝胶法等;重点分析了掺铝氧化锌(ZAO)薄膜的结构、导电机理及光电性能;最后对薄膜的存在问题和应用情况进行了分析。     

纳米WO3掺杂CNTs材料的制备及其气敏性能测试

通过水热法合成纯WO3,并采用原位水热合成的方法制备不同碳纳米管掺杂量(0.2%,0.4%,0.6%,0.8%,1.0%)WO3/CNTS复合材料。复合之前,从四种纯WO3(K2SO4为添加的矿化剂且含量依次为15 g、30 g、40 g、0 g)中选取一种气敏性能最好的合成工艺。结果表明无K2SO4的合成工艺较好,同时对四种纯WO3进行了XRD表征,结果显示无K2SO4的氧化钨为两相晶体,且粒径较小。纯WO3与S-WCNTS掺杂制备复合材料,然后由复合材料制备气敏元件,对H2S进行气敏测试,结果表明S-WCNTS含量为0.6%的复合材料效果最佳,恢复性好且工作电压较低,可达2.68 V,且检出限可达到3 mg/kg,连续曲线的测定也较好。     

Preparation of Stabilized Nanosized Tin Oxide Particles by Hydrothermal Treatment

Stable colloidal suspensions of tin oxide (content 0.9–6.1 wt%) were synthesized by subjecting conventionally prepared tin oxide gels to hydrothermal treatment with an ammonia solution (pH 10.5) at 200°C for 3 h in an autoclave. Based on X-ray diffractometry analyses, the tin oxide crystallites after hydrothermal treatment were resistant to thermal growth at elevated temperatures, and this feature became more conspicuous as the tin oxide content of the colloidal suspension decreased. For the powder derived from a 1.8 wt% colloidal suspension, for example, the mean sizes of the tin oxide crystallites were 7.5 and 13 nm after calcination at 600° and 900°C, respectively, in comparison with corresponding values of 13.5 and 29 nm for the untreated gel-derived powder. Thin film spin-coated from the same suspension had good uniformity, packed with tin oxide grains (crystallites) of a mean size of 6 nm after calcination at 600°C. Optical determination of the tin oxide sol particle size, as well as gravimetric analysis of the dehydration from the powder samples, were conducted to determine effects of hydrothermal treatment.     

氧化铋超细粉体制备过程热分析研究

以硝酸铋为反应原料,利用尿素为沉淀剂,采用均匀沉淀法制备了Bi2O3超细粉体。利用TG-DSC及XRD 对所制备的Bi2O3超细粉体进行了表征。研究结果表明,尿素均匀沉淀法合成的前驱体成分主要为(BiO)2(CO3)3、Bi(OH)3 和BiOOH的混合物,确定最佳煅烧温度范围为560℃-620℃。XRD分析结果表明:均匀沉淀法制备得到单斜晶型α- Bi2O3,且纯度高。     

铌酸钙锶铋的制备及其发光性能的研究

采用高温固相法制备荧光材料CaSrNb2O6：Bi3＋,其中Bi3＋的最佳掺杂浓度是0.2%,Sr2＋的最佳掺杂浓度为0.8%,样品的最宜煅烧温度为1300℃,最佳保温时间为1.5 h,用XRD,SEM以及荧光光谱等手段对所合成的荧光粉进行了表征。结果表明,样品在近紫外光315 nm激发下,产生位于350～600 nm的宽带发射峰。