Silicon oxycarbide ceramics with reduced carbon by pyrolysis of polysiloxanes in water vapor

SiOC ceramics pyrolyzed from polysiloxanes are usually black because of the formation of excess carbon in the ceramic network. Here we show that the pyrolysis of polysiloxanes in water vapor significantly reduces carbon from SiOC and yields a white SiOC ceramic. Chemical analysis shows the amount of carbon in the white ceramic is only half of that in the black one pyrolyzed in argon. ²⁹Si nuclear magnetic resonance spectral (NMR) analysis indicates the reduction of the carbon-rich [SiC₄] and [SiC₂O₂] units with the enhanced formation of the oxygen-rich [SiO₄] and [SiCO₃] units by the water pyrolysis. Importantly, this water pyrolysis resultant carbon reduction is realized in a bulk polysiloxane, and the white SiOC ceramic is obtained in a bulk body with the retained shape of the precursor body. The water pyrolysis can be adopted as an effective mean to tailor the structure of PDCs via the simple introduction of water vapor in pyrolysis.     

煤的各向电异性与其大分子结构间的关系

从理论和实验两个方面研究了煤的各向电异性与煤大分子结构间的关系。在垂直于煤层面方向上的势垒比平行于煤层面方向的高，这就是煤具有各向电异性的根本原因。煤化程度越高，煤的各向电异性越明显。     

复合电沉积机理研究进展

随着复合电镀的发展，一些新型复合镀层应运而生，但对复合电沉积机理的研究仍远非充分。本文对截至目前国内外对这一过程所做的研究工作做一综合的评述，旨在承前启后，更好地完善和丰富这一理论。     

甲壳质及其衍生物的制备与应用

甲壳质是一种丰富的天然资源。近年来，甲壳质及其衍生物的开发应用受到国内外的重视，越来越多的产品将从实验室走向市场，本文介绍了甲壳质及其衍生物的制备方法及其在工业、农业、医药、环保、生物学等领域的应用。     

一次低烧SrTiO3基晶界层电容器的研究

研究了以Ｌｉ２ＣＯ３为助烧结剂、Ｓｒ（Ｌｉ１／４Ｎｂ３／４）Ｏ３为施主掺杂剂、Ｂｉ２Ｏ３和ＳｉＯ２为晶界绝缘剂的ＳｒＴｉＯ３基晶界层电容器的一次低温烧成技术。初步探索了Ｔｉ／Ｓｒ比值、施主掺杂剂、绝缘剂对显微结构及介电性能的影响。在１１５０℃烧成温度下，获得了εａｐｐ〉３．５×１０＾４；ｐ〉１．０×１０＾１１Ω·ｃｍ；ｔｇδ〈１．０％；ΔＣ／Ｃ〈±５．０％（－２５￣＋８５℃）的ＳｒＴｉＯ３基晶界层     

Low-fired fluoride microwave dielectric ceramics with low dielectric loss

Low-fired fluoride microwave dielectric ceramics (LiF, CaF₂, SrF₂ and BaF₂) were prepared through a simple one-step sintering process. Fluoride ceramics, especially LiF, which had the lowest sintering temperature of 800?°C, could be well sintered below 1050?°C. Rietveld refinement results showed that LiF, CaF₂, SrF₂ and BaF₂ ceramics crystallized into a cubic structure with space group Fm-3m. The relative permittivity (ε_r), quality factor (Q?×?f) and temperature coefficient of the resonant frequency (τ_f) of the fluoride ceramics were closely related to relative density, the ionic polarizability of the primitive unit cell, the packing fraction and the bond valence. In this series of low-permittivity fluoride ceramics, LiF, CaF₂ and BaF₂ could be co-fired with Ag powders, and LiF ceramic exhibited the highest Q×f value of 73880?GHz, which is comparable to those of traditional oxide microwave dielectric ceramics.     

Grain growth kinetics and growth mechanism of columnar Al2O3 crystals in xNb2O5–7.5La2O3-Al2O3 ceramic composites

xNb₂O₅–7.5La₂O₃-Al₂O₃ ceramic composites with in-situ-grown columnar Al₂O₃ crystals were successfully prepared by microwave sintering at 1450–1525?°C using α-Al₂O₃, Nb₂O₅, and La₂O₃ powders as raw materials. X-ray diffraction results indicated that the main phases were Al₂O₃, LaNbO₄, and Nb₂O₅ in the prepared samples. A field emission scanning electron microscope (FESEM) showed that the Al₂O₃ crystals appeared as columnar in the structure. Moreover, the grain size of the columnar Al₂O₃ crystals increased with the Nb₂O₅ content. The ratio of the major axis to the minor axis of the crystals was largest when the Nb₂O₅ content was 15?vol%. Furthermore, the grain-growth kinetics index (n), growth activation energy (Q), and growth mechanism of the columnar Al₂O₃ crystals were studied. The results indicated that the Nb₂O₅ addition could promote formation and growth of columnar Al₂O₃ crystals, and the grain-growth activation energy indicated that the dissolution process controls the crystal growth. The growth mechanism of the columnar Al₂O₃ crystals was also studied. The present work demonstrated that Nb₂O₅ is a good additive for the preparation of Nb₂O₅–7.5La₂O₃-Al₂O₃ composite ceramics with columnar Al₂O₃ crystals.     

Preparation and photocatalytic activity of BiOI/MnxZn1-xFe2O4 magnetic photocatalyst

BiOI/Mn_xZn_1-xFe₂O₄ magnetic photocatalysts were successfully prepared for the first time. With the degradation of simulated RhB wastewater as a pointer to the photocatalytic reaction and combined with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and vibrating sample magnetometer (VSM), the reasons influencing the photocatalytic performance of the magnetic photocatalysts were further explored. The excessive or insufficient Mn-Zn ferrite both leads to a relatively low photocatalytic activity. When the calcination temperature reaches to 200 and 400?°C, the photocatalytic activity is enhanced significantly, but the main active component in the photocatalysts has changed from BiOI to Bi₅O₇I at 400?°C. The nanocomposites prepared under alcohol water environment with hollow microspheres morphology possess a highly photocatalytic efficiency, and the RhB degradation rate within 4?h in the ethanol water environment is significantly higher than that in pure water (98% vs. 59%).