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1.
为了优化β-环糊精微球的制备工艺,采用U13*(134)均匀设计对合成工艺优化,得出最佳合成工艺为反应温度80 ℃ ,反应时间4 h,交联剂的用量8 g ,搅拌速度1000 r/min。影响微球粒径的因素:搅拌速度>反应温度。影响产量的因素:交联剂的用量>反应时间。最佳合成工艺下的微球表面圆整,具有较好的热稳定性。 相似文献
2.
β-SiAlON has been prepared by a SHS reaction performed under high nitrogen pressure on a compacted mixture of silicon and mullite. In order to optimise this reaction, the solid mixture was prepared from a liquid solution in which the mullite (2SiO2-3Al2O3) was formed by a sol–gel process. The SHS samples were characterized by using Scanning Electron Microscopy (SEM) and X-ray diffraction. A Rietveld refinement performed on the recorded diffractograms revealed a very high formation rate of β-SiAlON (more than 80 wt%) when the reaction was carried out under low nitrogen pressure. From the whole of our results, a mechanism of β-SiAlON formation has been suggested. 相似文献
3.
《应用陶瓷进展》2013,112(1):35-37
AbstractNitrogen rich multication α-SiAlON ceramics doped with Y-Ce have been densified by gas pressure sintering using α-Si3N4 or mixed β/α-Si3N4 starting powder. The effects of α-SiAlON nucleation and growth mechanisms were investigated by using di fferent sintering cycles. X-ray diffraction studies after sintering revealed that 21R polytype phase was present in addition to α -SiAlON matrix phase. Microstructural characterisation of sintered materials prepared using α-Si3N4 powder in the starting composition revealed a typical equiaxed grain morphology, as expected if the α-SiAlON nucleation step was not applied before grain growth. However, needlelike α-SiAlON grains were observed if a nucleation step was carried out before final sintering. In starting powders containing mixed β/α-Si3N4, needlelike grain morphology was also observed. The effects of different Si3N4 starting powders and sintering conditions on the grain morphology and mechanical properties are discussed. 相似文献
4.
5.
Chu Minh Ngo Hieu Duy Nguyen Nobuo Saito Thi Mai Dung Do Tadachika Nakayama Koichi Niihara Hisayuki Suematsu 《Journal of the American Ceramic Society》2022,105(3):1622-1628
β-MoO3 is a monoclinic phase of MoO3; it has been shown to be a promising material that can replace α-MoO3 in chemical, optical, electronic, and electrochromic applications. However, the difficulty in synthesizing β-MoO3 with a one-dimensional (1D) morphology has limited its use in applications requiring a large specific surface area. In the present work, β-MoO3 whiskers were prepared by thermally evaporating α-MoO3 powder in a tube furnace at temperatures (Tf) from 750 to 1000°C and under flowing O2 gas. The collected samples were identified as mainly β-MoO3 by X-ray diffraction measurements, and the highest purity β-MoO3 was obtained at Tf = 1000°C. Scanning and transmission electron microscopy observations showed that whiskers with a width of 10 nm were successfully synthesized by this method. The whiskers were confirmed to be β-MoO3 via lattice image analysis. Measurements of the temperature distribution in the tube furnace and comparisons with the Mo–O phase diagram led to the conclusion that the whiskers formed via a vapor–solid route. Prepared β-MoO3 whiskers were compared with α-MoO3 powder via the X-ray photoelectron spectroscopy characterization method. By elucidating the β-MoO3 whisker synthesis mechanism, this research provides guidance for the large-scale production of β-MoO3 whiskers. 相似文献
6.
《Ceramics International》2016,42(6):6707-6712
In this paper, the sintering behavior of β-Si6−zAlzOzN8−z (z=1) powder prepared by combustion synthesis (CS) was studied using spark plasma sintering (SPS). The CSed powder was ball milled for various durations from 0.5 to 20 h and was then sintered at different temperatures with heating rates varying from 30 °C/min to 200 °C/min. The effects of ball milling, sintering temperature, and heating rate on sinterability, final microstructure, and mechanical property were investigated. A long period of ball milling reduced the particle size and subsequently accelerated the sintering process. However, the fine powder was easily agglomerated to form secondary particles, which accordingly decreased the densification of the SPS product. The high sintering temperature accelerated the densification process, whereas the high heating rate reduced the grain growth and increased the relative density of the sintered product. 相似文献
7.
《Ceramics International》2015,41(4):5348-5354
β-Si3N4 seed crystals were synthesized by sintering (α+β)-Si3N4 powders with Y2O3+MgO additives at 1800 °C. Full α- to β-phase transformation was achievable at 1800 °C for 1 h. The pre-existing β-Si3N4 particles acted as nuclei during a sintering process. The length and mean aspect ratio of β-Si3N4 seed grains could be tailored by careful control of α/β-Si3N4 ratio, which resulted in various nuclei and driving force. The sample A95B5 with 5% β-nuclei shows a bimodal size distribution containing large amount of abnormal elongated β-Si3N4 grains with remarkable large diameter. With increasing the β-phase content from 5 wt% to 100 wt%, the average diameter and aspect ratio of the β-Si3N4 single crystals decreased from 1.43 µm to 0.92 µm and from 4.36 to 2.79, respectively. 相似文献
8.
《Journal of the European Ceramic Society》1999,19(16):2711-2721
Properties of carbothermally prepared Ca-α-SiAlON and β-SiAlON powders and aqueous suspensions thereof were determined. The isoelectric points of Ca-α-SiAlON and β-SiAlON were 3·4 and 4·6. After addition of deflocculant, Dolapix CE64, the behaviour of both suspensions is nearly identical. The isoelectric points become 5·5 and 5·3, respectively. Despite differences in bulk composition, grain size distribution, grain size and shape, both SiAlON suspensions show a similar dependence of a zeta potential on pH. Optimum slip casting properties, i.e. lowest viscosity values (below 10 mPa s), the highest absolute zeta potential values, the smallest floc size and sediment volume were found between pH 10–11 for both powders. The potentials of the different suspension characterisation techniques were compared and zeta potential and viscosity measurements were found the most convenient. 相似文献
9.
Yang Gao Junya Iihama Daiki Hamana Ryo Iwasaki Sawao Honda Toru Asaka Munni Kumari Tomokatsu Hayakawa Samuel Bernard Philippe Thomas Yuji Iwamoto 《International Journal of Applied Ceramic Technology》2023,20(2):768-779
A series of β-SiAlON:Eu2+ phosphors were synthesized from single-source precursors, perhydropolysilazane chemically modified with Al(OCH(CH3)2)3, AlCl3, and EuCl2. The single-source precursors were converted to β-SiAlON:Eu2+ phosphors by pyrolysis under flowing N2 or NH3 at 1000°C, followed by heat treatment at 1800°C under an N2 gas pressure at 980 kPa. By varying the molar ratio of the chemical modifiers, β-SiAlON:Eu2+ with the compositions close to the theoretical ones expressed as Si6−zAlzOz−2yN8−z+2y:yEu2+ were synthesized, where the z values and Eu2+ contents were controlled in the ranges of .44–.78 and .35–1.48 mol%, respectively. The polymer-derived β-SiAlON:Eu2+ phosphors exhibited green emission under excitation at 460 nm attributed to the 4f7–4f6(7f3)5d1 transition of dopant Eu2+. High-angle annular dark-field-scanning transmission microscopy analysis confirmed that the doped-Eu2+ existed interstitially within the channels along the c axis of host β-SiAlON. Compared with the conventional powder metallurgy route, the polymer-derived ceramic route in this study offers some advantages in the grain growth of host β-SiAlON and photoluminescence properties in terms of green emission intensity under excitation at 460 nm, and the highest intensity was achieved for the polymer-derived β-SiAlON:Eu2+ with z = .64 and .37 mol% Eu2+. 相似文献
10.
Niels J. Sijbrandi Ad J. Kimenai Edwin P.C. Mes René Broos Georg Bar Martin Rosenthal Yaroslav I. Odarchenko Dimitri A. Ivanov Jan Feijen Pieter J. Dijkstra 《Polymer》2012,53(19):4033-4044
Segmented poly(ether ester amide)s comprising glycine or β-alanine extended bisoxalamide hard segments are highly phase separated thermoplastic elastomers with a broad temperature independent rubber plateau. These materials with molecular weights, Mn, exceeding 30 × 103 g mol?1 are conveniently prepared by polycondensation of preformed bisester–bisoxalamides and commercially available PTHF diols. FT-IR revealed strongly hydrogen bonded and highly ordered bisoxalamide hard segments with degrees of ordering between 73 and 99%. The morphology consists of fiber-like nano-crystals randomly dispersed in the soft polymer matrix. The micro-structural parameters of the copolymers were addressed by simultaneous small- and wide-angle X-ray scattering. It is shown that the crystals have strictly identical thickness, which is close to the contour length of the hard segment. The long dimension of the crystals is identified with the direction of the hydrogen bonds. The melting transitions of the hard segments are sharp, with temperatures up to 170 °C. The studied polymers have an elastic modulus in the range of 139–170 MPa, a stress at break in the range of 19–31 MPa combined with strains at break of higher than 800%. The segmented copolymer comprising the β-alanine based bisoxalamide hard segment with a spacer of 6 methylene groups has a melting transition of 141 °C which is higher than the melting transition of its glycine analogue of 119 °C. Likewise, the fracture stress increased from 22 to 31 MPa when the glycine ester group in the hard segment was replaced with β-alanine. The improved thermal and mechanical properties of the latter polymers is related to the crystal packing of the β-alanine based hard segments in the copolymer compared to the packing of the hard segments comprising glycine ester groups. 相似文献
11.
《Inorganic chemistry communications》2002,5(10):747-750
MnOOH and β-MnO2 whiskers are obtained for the first time in our work. MnOOH whiskers are chemically synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The product is obtained under extremely low surfactant concentrations under basic conditions, using MnSO4·H2O as the manganese source and ethylamine as the alkali source. After the subsequent heat treatment of MnOOH at 300 °C for 1 h, β-MnO2 whiskers retaining the similar morphologies are obtained. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) are used to characterize the products. 相似文献
13.
We successfully prepared β-SiAlON:Eu2+ phosphors with composition of EuxSi6?zAlzOyN8?y (y = z ? 2x, x = 0.018, z = 0.23) by gas-pressured synthesis for application to LED. The crystal phase, microstructure, PL emission and thermal quenching properties were investigated in detail. The β-SiAlON:Eu2+ phosphors absorbed broad UV–vis spectral region, and showed a single intense broadband emission near 538 nm. The Stokes shift and zero-phonon line were calculated mathematically, and also estimated from the spectral data. The β-SiAlON:Eu2+ green phosphor showed superior thermal quenching properties compared to commercial silicate (SrBaSiO4:Eu2+) green phosphor. The white light-emitting diode (LED) using the prepared β-SiAlON:Eu2+ green phosphor exhibited high color gamut, and good optical stability in high working temperature. 相似文献
14.
《Ceramics International》2016,42(6):7290-7299
The present study presents the effect of addition of diluents on the crystal morphologies and the impact on the oxidation resistance of β-SiAlON powders obtained from combustion synthesis method. Pure β-SiAlON were synthesized with diluents. It was observed by SEM that the diluents resulted in the transformation from large hexagonal column-shaped crystals to fine isotropic grains. Oxidation experiments were conducted by thermogravimetric analysis (TGA) in the temperature range from 1200 °C to 1400 °C. The TGA results indicated that oxidation was controlled by mixed chemical reaction and diffusion process. The chemical reaction step was found to be rate-controlling at low oxidation temperatures (1200 °C and 1300 °C), while at high temperature (1400 °C), diffusion was found to control the reaction rate. Oxidation products were investigated by X-ray Diffraction (XRD) analysis and found to be made up of SiO2, Al2O3. This research aims to provide guidance for the fabrication of β-SiAlON by combustion synthesis, thus facilitating its further application in high temperature industry. 相似文献
15.
Hitoshi Sasaki Yasunori Oumi Masahiro Sadakane Tsuneji Sano 《Journal of the European Ceramic Society》2010,30(6):1537-1541
Single phase Ca-α-SiAlON was synthesized for the first time by the carbothermal reduction-nitridation of a physical mixture of Y-type zeolite and CaO. Under well-optimized conditions, which included both a Si/Al ratio of 2.8 for the starting Y-type zeolite and a Ca/Al ratio of 0.63–0.75, highly crystalline, pure Ca-α-SiAlON was obtained. The formation of pure Ca-α-SiAlON was also confirmed by 27Al and 29Si MAS NMR measurements. 相似文献
16.
《应用陶瓷进展》2013,112(3):174-177
AbstractKinetic equation of oxidation process with diffusion controlled step in solid product layer is deduced, in which the influence of particle size distribution of β-SiAlON on the reaction rate has been taken into account. This equation was applied to the oxidation of β-SiAlON powder, and fitted well with the experimental data. Comparisons with the results offered by the model using one and two effective radiuses are also included, from which it can be seen that the model considering particle size distribution is the best for describing the kinetics of powder system. The activation energy ΔE of oxidation of β-SiAlON powder is also obtained, which is 258 kJ mol?1. 相似文献
17.
《Journal of the European Ceramic Society》1999,19(2):175-185
β-SiAlON powders have been prepared by carbothermal nitridation of kaolin or SiO2 plus Al2O3 mixtures at 1450-1800°C and elevated nitrogen pressures (1-50 bar). Powders with widely variable particle size and morphology were obtained depending on temperature, pressure, gas-flow rate, and raw-material type. An elevated nitrogen pressure effectively reduced SiO loss and suppressed SiC formation. Pure β-SiAlON powder of composition Si2·8Al3·2O3·2N4·8 and with a fine particle size (∼1 μm) was produced at 1650°C, 50 bar N2 and a high gas-flow rate for 2 h. The nitridation rate was hampered by an increase of the CO concentration in the system. 相似文献
18.
《Catalysis communications》2003,4(8):353-359
As part of a larger program on the combinatorial design of metal carbides for catalytic reaction studies, we have investigated the role of H2:C3H8 ratio (1–5), carburization temperature (773–973 K) and reaction time (1–4 h) on the conversion of silica-supported Mo–W sulphide to the carbide product. While all three factors are important determinants of the physiochemical properties, namely; BET surface area, pore volume, acid site concentration and strength of the acid site, statistical analysis revealed that two-factor interactions were also significant and hence offer promising directions for further inquiry that may lead to synergistic effects in new catalyst formulations. 相似文献
19.
通过化学-酶相耦合的方法,成功制备出e.e.值>99%的S-β-萘乙醇,使其光学纯度达到了制备R-2-萘乙胺的要求。研究中以β-萘乙酮为原料,经硼氢化钠还原得到外消旋的β-萘乙醇。经过酶催化动力学拆分,β-萘乙醇中R型底物100%全转化为酯,S构型底物型被保留,这样体系中S构型底物的e.e.值达到近100%。本文还考察了若干因素对酶催化动力学拆分过程的影响,并最终确定了酶催化动力学拆分β-萘乙醇制备S-β-萘乙醇的最适条件:反应温度45 ℃ ,溶液为甲苯,底物浓度为100 mmol/L。 相似文献
20.
《Ceramics International》2022,48(12):16861-16867
The different content of wollastonite was added to raw materials to prepare β-SiAlON ceramics; furthermore, in this study, the effect of wollastonite on the physical, chemical, and biological properties of β-SiAlON was explored. X-ray diffraction and scanning electron microscopy (SEM) demonstrated that Ca in β-SiAlON was uniformly distributed; however, the addition of wollastonite did not lead to the formation of the Ca-α-SiAlON phase. Wollastonite addition improved the sintering performance and increased the compressive strength of β-SiAlON ceramics. Moreover, SEM demonstrated that by adding wollastonite, the bonding of the sample became tighter. Ion release results demonstrated that the material had low ion release and stable chemical properties. Moreover, in cellular experiments, when the content of wollastonite is <12 wt% in β-SiAlON ceramics, β-SiAlON ceramics with or without Ca demonstrated satisfactory biocompatibility. The presence of some amount of Ca did not affect the adhesion, spreading, and proliferation of the MC3T3-E1 cells. Moreover, when wollastonite is <12 wt%, culturing MC3T3-E1 cells in the leaching solution of β-SiAlON ceramics confirmed that bone formation is unaffected. Thus, β-SiAlON ceramics containing Ca (wollastonite <12 wt%) demonstrated good physical and chemical properties; however, the biological properties remain unaffected. Therefore, the ceramics that were prepared are bioactive materials having excellent properties. 相似文献