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31.
Growing whiskers on the inner wall of glass capillary columns is an easy roughening technique which allows efficient coating of the columns with any stationary phase. The advantages and disadvantages of whisker surfaces are discussed. Several examples are presented to illustrate the possibilities of whisker-wall coated open tubular (WWCOT) columns. 相似文献
32.
R. G. Zoeller N. G. Ugras K. D. Möller 《International Journal of Infrared and Millimeter Waves》1988,9(5):497-504
A Fourier Transform Spectrometer using a 250 Watt Mercury lamp, a lamellar grating and a pumped He-cooled detector is applied to the millimeter wave spectral region. The pure rotation spectrum of CH2F, the transmission of graphite particles in a cloud chamber, the interference on round copper dots and the absorption of iron whiskers have been observed. 相似文献
33.
TEMPO-mediated surface oxidation of cellulose whiskers 总被引:3,自引:0,他引:3
Cellulose whiskers resulting from HCl acid hydrolysis of tunicin were subjected to TEMPO-mediated oxidation under various conditions and the extent of the resulting oxidation was characterized by Fourier-transform infrared spectroscopy (FT-IR), conductimetry, X-Ray diffraction analysis and transmission electron microscopy (TEM). With degree of oxidation of up to 0.1 the samples kept their initial morphological integrity and native crystallinity, but at their surface the hydroxymethyl groups were selectively converted to carboxylic groups, thus imparting a negative surface charge to the whiskers. When dispersed in water these oxidized whiskers did not flocculate and their suspensions appeared birefringent when viewed between cross polarizers, thus indicating a liquid crystalline behavior. 相似文献
34.
Optimization of the isolation of nanocrystals from microcrystalline cellulose
by acid hydrolysis 总被引:16,自引:0,他引:16
The objective of this work was to find a rapid, high-yield process to obtain an aqueous stable colloid suspension of cellulose
nanocrystals/whiskers. Large quantities are required since these whiskers are designed to be extruded into polymers in the
production of nano-biocomposites. Microcrystalline cellulose (MCC), derived from Norway spruce (Picea abies), was used as
the starting material. The processing parameters have been optimized by using response surface methodology. The factors that
varied during the process were the concentration of MCC and sulfuric acid, the hydrolysis time and temperature, and the ultrasonic
treatment time. Responses measured were the median size of the cellulose particles/whiskers and yield. The surface charge
as calculated from conductometric titration, microscopic examinations (optical and transmission electron microscopy), and
observation of birefringence were also investigated in order to determine the outcome (efficiency) of the process. With a
sulfuric acid concentration of 63.5% (w/w), it was possible to obtain cellulose nanocrystals/whiskers with a length between
200 and 400 nm and a width less than 10 nm in approximately 2 h with a yield of 30% (of initial weight). 相似文献
35.
J. F. Gates Clarke 《Journal of separation science》1979,2(6):357-360
Recent attempts to reproduce a literature method for etching of Pyrex glass capillary columns with ?etching ether”? resulted in reduction of the columns to dust through a violent explosion. Although modifications of the method produced etched columns, we found that less than satisfactory results were achieved. Introduction of etching ether by simply coating the column with a thin film of the ether produced an evenly etched column with well defined whiskers. Several observations made during the etching process will also be discussed. 相似文献
36.
Silicon carbide whiskers (SiCW) were synthesized through sol-gel process by impregnating the rayon fibres with sols of methyltriethoxysilane (MTEOS), phenyltriethoxysilane (PTEOS) and dimethyldiethoxysilane (DMDEOS) and pyrolyzing the impregnated rayon fibres at 1400°C in argon atmosphere. The SiCW synthesized through this method were needle like, straight and their aspect ratio was found to be greater than 100 except in the case where DMDEOS was used as silica source. 相似文献
37.
《中国化学会会志》2018,65(2):289-292
Boric acid/Mg (magnesiothermic or metal sintering aid)/C (activated carbon)/N2 or Ar (atmosphere)/additives (mesoporous SiO2 or mesoporous SiC or SiC/Si3N4 whiskers) systems were used in the one‐step synthesis of mesostructured B4C (221.04 m2/g). In this study, a mixture of the active precursors was allowed to react via a self‐sustaining reaction (high‐energy ball milling process). Also, the properties of the samples prepared using powdered activated carbon (PAC) and SiC/Si3N4 whiskers (concentration in the range 5–10 wt%) as sources of carbon were investigated. X‐ray diffraction results proved the presence of crystalline boron carbide in the peak positions of B4C (B12C3). The advantage of the present route for yielding mesostructured B4C powder seems to be limited by the growth of carbide crystals. This restriction is believed to be imposed by a lack of whisker additives around the pores where B4C crystals grow. The results also show that the best mesoporous additive for the synthesis of nanoscale boron carbide is mesoporous SiC. The effect of the concentration of CO (reduction of α‐Fe2O3 to Fe by CO) on the B4C synthesis suggests that, in addition to the concentration of CO, the pressure of the N2 atmosphere is an important factor in the synthesis of mesostructured B4C. 相似文献
38.
39.
Hexagonal aluminum nitride (AlN) whiskers have been synthesized at 1873 K under a flowing nitrogen atmosphere. The synthesized whiskers are long straight filaments with diameters between 1 and 5 μm and length in the cm range. In order to investigate its “oxidation resistance”, a series of experiments have been performed. The oxidation behavior was quite different in the experimental temperature range assigned, which can be attributed to the kinetic factor and the morphological development during oxidation process. It was chemical controlled at lower temperature while both chemical reaction and diffusion controlled at medium temperature. Further accelerating of temperature to 1473 K, AlN whiskers was peeled into smaller parts, which increased the oxidation rate and hence showed powder-like oxidation behavior. Our new kinetic theory has been applied to study the oxidation behavior of AlN whiskers. The comparison of the experimental data with the theoretical ones validates the applicability of the new model. 相似文献
40.
Environmentally-friendly SPI/cellulose whisker composites were successfully prepared using a colloidal suspension of cellulose whiskers, to reinforce soy protein isolate (SPI) plastics. The cellulose whiskers, having an average length of 1.2 microm and diameter of 90 nm, respectively, were prepared from cotton linter pulp by hydrolyzing with sulfuric acid aqueous solution. The effects of the whisker content on the morphology and properties of the glycerol-plasticized SPI composites were investigated by scanning electron microscopy, dynamic mechanical thermal analysis, differential scanning calorimetry, ultraviolet-visible spectroscopy, water-resistivity testing and tensile testing. The results indicated that, with the addition of 0 to 30 wt.-% of cellulose whiskers, strong interactions occurred both between the whiskers and between the filler and the SPI matrix, reinforcing the composites and preserving their biodegradability. Both the tensile strength and Young's modulus of the SPI/cellulose whisker composites increased from 5.8 to 8.1 MPa and from 44.7 to 133.2 MPa, respectively, at a relative humidity of 43%, following an increase of the whisker content from 0 to 30 wt.-%. Furthermore, the incorporation of the cellulose whiskers into the SPI matrix led to an improvement in the water resistance for the SPI-based composites. 相似文献