Spherical AlN particles synthesized by the carbothermal method: Effects of reaction parameters and growth mechanism

In this work, AlN particles with spherical morphology, smooth appearance and controllable particle size were purposely synthesized through an efficient carbothermal strategy at 1800 °C aiding with the CaF₂ additive. The influences of typical synthesis parameters, such as carbon content, CaF₂ particle size and reaction time on the formation rate, particles size and surface morphology of AlN particles were deeply and comprehensively studied. It was indicated that the intermediate Ca-aluminates was extremely essential to enhance the nitridation rate, promote the AlN growth and form the spherical morphology. More importantly, based on the systematic investigations and intensive analyses, the underlying growth mechanism of spherical AlN particles in the carbothermal process was rationally proposed and elaborated herein.     

Supercritical CO2 based processing of amorphous fluoropolymer Teflon-AF: Surfactant-free dispersions and superhydrophobic films

We report the application of a modified RESS process to create and collect in high yield nanoparticles of an amorphous fluoropolymer, Teflon-AF1600. The nanoparticles with diameters ranging from 10 to 100 nm can be synthesized from polymer solutions in supercritical CO₂ at 300 bar and 60 °C. The nanoparticles are collected by formation of dry ice in a liquid nitrogen-cooled trap. Nanoparticles embedded in dry-ice can be dispersed in organic solvents (acetone, ethanol, and n-heptane) creating surfactant-free dispersions. When dispersed in water, the nanoparticles self-assemble at the air–water interface forming a mechanically robust, superhydrophobic film. The film can support large water droplets (up to volume 250 μL) without breaking and is impermeable to water. The films cast from dispersions as well as those lifted-off water surface, are highly porous and superhydrophobic in nature (water contact angle θ_adv = 162°). This work demonstrates the utility of supercritical fluids based processing of fluoropolymers.     

化学沉淀法制备纳米二氧化硅

以水玻璃和盐酸为原料,采用化学沉淀法制备纳米SiO2。工艺条件为：温度40-50℃,pH值5—6,干燥温度110℃,焙烧温度500℃,制得的二氧化硅粒径在50-60nm,比表面积大,分散性好,达到了工业生产的标准。     

Heterogeneous photodecolorization of mixture of methylene blue and bromophenol blue using CuO-nano-clinoptilolite

CuO was incorporated into nano-particles of clinoptilolite via ion exchange and calcination processes. The obtained composite (CuO-NCP) was used for the photodeclorization process of an aqueous mixture of Methylene Blue and Bromophenol Blue. All samples were characterized by FT-IR, XRD, DRS, SEM and SEM. The optimum conditions were approximated as: 7 ppm dyes, pH 5.9, catalyst dose of 0.2 g L⁻¹ and CuO loading of 4.9%. The declorization extents of 61% and 32% were respectively obtained for MB and BPB during 180 min irradiation. The degradation extent was monitored by UV–vis spectroscopy and confirmed by chemical oxygen demand (COD).     

纳米TiO2制备的研究进展

纳米TiO2作为一种新型的无机材料正受到广泛的重视。重点介绍了国内外近年来制备TiO2的几种方法、反应原理和优缺点,并对TiO2的应用前景进行了展望。     

The sintering kinetics of ultrafine tungsten carbide powders

The sintering kinetics of nano grained tungsten carbide (n-WC) powders has been analyzed by non isothermal and isothermal sintering. Non isothermal sintering experiments reveal a multi staged sintering process in which at least three major sub-stages can be distinguished. The isothermal shrinkage strain also exhibits an asymptotic behavior with time indicating an end point density phenomenon in most of the temperature ranges. Combined microstructural and kinetic data analyses suggest that differences in the sinterability of inter and intra agglomerate pore phases introduce sub-stages in the sintering process which manifest as stagnant density regions in both the isothermal and non isothermal experiments. Kinetic analysis of the data reveals very low activation energies for sintering suggesting that particle rearrangement and agglomeration at low temperatures may be brought about by surface diffusion leading to neck growth and grain rotation. At higher temperatures rapid grain boundary diffusion by overheating along inter particle boundaries induced by sparking may be a dominant sintering mechanism. Although grain growth and densification in conventional WC powders generally obey an inverse relation to each other, in n-WC powders both can act synergistically to increase the net densification rate. In fact, complete densification cannot be achieved in n-WC powders without grain growth as one abets the other.     

反应结合氧化铝陶瓷制备新工艺

本文评述了反应结合氧化铝陶瓷的制备工艺原理,配料组成,研磨与原料细度,成形压力和升温速率等对陶瓷性能的影响。介绍了几种反应结合氧化铝陶瓷制造实例。     

反应注射成型充模过程驻留时间分析

在反应注射成型实际生产过程中，如何选择工艺参数是一个一直使操作者为难的问题。本文利用反应注射成型过程中驻留时间的概念，通过对喷泉流模型进行适当的简化分析，得出在ＲＩＭ充模过程中驻留时间与模腔无量纲纵向ｘ坐标和模腔厚度ｚ坐标之间的关系，并得出最大驻留时间线１＝２ｘ３（１－ｚ２），作出充模过程驻留时间分布曲线。忽略ＲＩＭ充模过程的热传导项，无量纲温度Ｔ与反应进度Φ相同，是流体在模腔内驻留时间线的等值线。将数值计算的反应进度值、温度值与模型计算作比较，基本符合，偏差的出现是由于模型中对前流区的简化处理，恒定粘度假设以及忽略热传导作用。为避免在充模过程中出现过早凝胶现象，在反应进度达到凝胶点时驻留时间不应大于１，这一结论有助于ＲＩＭ加工过程工艺参数的选择     

羟基乙腈合成工艺研究与设计要点

介绍羟基乙腈性质、制备方法和主要应用情况。叙述了间歇式羟基乙腈工艺的主要影响因素,并且从工艺设计原理的角度上讨论了生产中要注意事项和解决措施。     

Investigation of nano particle additives on lithium doped KNN lead free piezoelectric ceramics

Lead free potassium sodium niobate modified piezoelectric ceramics were synthesized through conventional mixed oxide method. Crystal structure and microstructure were analyzed by X-ray diffraction and scanning electron microscopy (SEM). The effects of nano ZnO, CuO and SnO₂ additives as the nano scale sintering aids, on microstructure and electrical properties of (K₀₅₀Na_0.50)_0.94Li_0.06NbO₃ (KNNL-6) ceramics were investigated. The optimum dielectric and piezoelectric properties of ?_r = 560, d₃₃ = 215 pC/N and tan δ = 0.008 were obtained for pure KNNL-6 that sintered at 1000 °C for 2 h. The results show that with addition of nano particle sintering aids, the piezoelectric coefficient d₃₃ of (K₀₅₀Na_0.50)_0.94Li_0.06NbO₃ ceramics was decreased. The decrease in piezoelectric charge coefficient could be due to the hardening effect, which lowers the piezoelectric charge.     

制药工艺学中培养基于反应机理和动力学的学习思维方式

课程教学的意义本质上是该学科思维方式的培养,制药工艺学教学的主线应该是培养建立在药物合成反应机理与动力学基础之上的专业思维方式.我们通过一些过程化学研究的实例,科学地讲授以反应机理与动力学决定制药工艺配置的思维模式与研究方法学,从而合理地服务于教学、科学研究和药物制造.     

MEASURED ATMOSPHERIC NEW PARTICLE FORMATION RATES: IMPLICATIONS FOR NUCLEATION MECHANISMS

Measured production rates of tropospheric ultrafine particles (~3nm diameter) are reported for the first time and are shown to be orders of magnitude greater than nucleation rates predicted by the binary theory of homogeneous nucleation for sulfuric acid and water. Furthermore, the functional dependence of observed particle formation rates on sulfuric acid vapor concentrations is much weaker than predicted by binary theory. We present arguments to show that these discrepancies might be due to the participation of a species such as ammonia which could stabilize subcritical clusters, thereby enhancing nucleation rates. The data suggest that atmospheric nucleation may occur by a collision-limited process, rather than by a condensation/evaporation controlled process as is assumed in the classical theory.     

A comparative study of the composition of anthracene oil polymerized by different treatments

An industrial anthracene oil (AO) was polymerized by thermal treatment with the aid of AlCl₃, sulphur and air. The composition of the reaction products was investigated by size exclusion chromatography (SEC) and synchronous UV-fluorescence spectroscopy. The SEC profiles show significant differences in the composition of the polymerized products. This suggests that the reactivity of the AO components and the mechanisms of polymerization are different. With sulphur and air, the polymerization involves a low number of AO components, which selectively react to form intermediate and large polymers. AlCl₃ causes a more extensive polymerization, giving rise to a product in which the fraction of oligomers of intermediate size (500–700 u) is predominant. Synchronous UV-fluorescence spectroscopy corroborates and supports the SEC results.