Effect of Plasma Treatment on the Adhesion of Carbon Fibers to Thermoplastic Polymers

A study has been made of the effect of RF plasmas on the adhesion of carbon fibers to polycarbonate and polysulfone. Treatment in oxygen plasma significantly increased the adhesion to both polymers. The effect is lost if the treated fiber is stored in air for a week. Surface analysis using XPS indicated an increase in atom percent oxygen but the spectra were unchanged for the stored fibers even though there had been a significant loss in adhesion. It is suggested that oxygen surface functionality is responsible for the improved adhesion but that this surface activation is lost on storage. Due to a sampling depth of 5-10 nm, XPS would not be expected to detect this small change in surface functionality.     

Quantitative measurements of CO2 and CH4 using a multipass Raman capillary cell

Raman measurements of two common gases are made using a simple multipass capillary Raman cell (MCC) coupled to an unfiltered 18 around 1 fiber-optic Raman probe. The MCC, which is fabricated by chemical deposition of silver on the inner walls of a 2 mm inner diameter glass capillary tube, gives up to 20-fold signal enhancements for nonabsorbing gases. The device is relatively small and suitable for remote and in situ Raman measurements with optical fibers. The optical behavior of the MCC is similar to previously described liquid-core waveguides and hollow metal-coated waveguides used for laser transmission, but unlike the former devices, the MCC is generally applicable to a very wide range of nonabsorbing gases.     

Demonstration of a laser vorticity probe in turbulent boundary layers

A laser-based probe for the nonintrusive measurement of velocity gradient and vorticity was demonstrated in turbulent boundary layers. Unlike most other optical methods, the current technique provides an estimate of the velocity gradient, without having to first measure velocity at multiple points. The measurement principle is based on the heterodyne of coherent light scattered from two adjacent particles. The beat frequency of the heterodyne is directly proportional to the velocity gradient. The probe is assembled from commercially available, inexpensive optical components. A laser Doppler velocimeter (LDV) processor is used to analyze the heterodyne signal. A component of vorticity is obtained by using two appropriately aligned velocity gradient probes. The optical probes developed were used in turbulent boundary layers to measure local, time-frozen velocity gradients partial differential u / partial differential y, partial differential v / partial differential x, and partial differential v / partial differential y, as well as the spanwise vorticity. The measurements were compared to those inferred from LDV measurements in the same facility and to data available in the literature.     

Angular measurement of acoustic reflection coefficient for substrate materials and layered structures by V(z) technique

An experimental method to evaluate the acoustic reflection coefficient as a function of the incident angle R(θ) for substrate materials or layered structures is presented. By measuring the acoustic material signature V(z) using a highly focused acoustic lens or transducer at normal incidence, the reflection coefficient R(θ) can be reconstructed from the FFT of the complex V(z) signal (amplitude and phase of the echo). This technique has a great simplicity for the experimental procedure of R(θ) measurement. It overcomes the disadvantages of the conventional method where the finite-aperture plane beam reduces the angular precision and causes the unexpected non-specular reflection at critical incident angles. Results are given for different substrate materials, single plates and a three-layered bonded joint, and are compared to theoretical predictions.     

Effect of trisodium citrate on rheological and physical properties and microstructure of yogurt

The effect of trisodium citrate (TSC) on the rheological and physical properties and microstructure of yogurt was investigated. Reconstituted skim milk was heated at 85° C for 30 min, and various concentrations (5 to 40 mM) of TSC were added to the milk, which was then readjusted to pH 6.50. Milk was inoculated with 2% yogurt culture and incubated at 42° C until pH was 4.6. Acid-base titration was used to determine changes in the state of colloidal calcium phosphate (CCP) in milk. Total and soluble Ca contents of the milk were determined. The storage modulus (G′) and loss tangent (LT) values of yogurts were measured as a function of pH using dynamic oscillatory rheology. Large deformation rheological properties were also measured. Microstructure of yogurt was observed using confocal scanning laser microscopy, and whey separation was also determined. Addition of TSC reduced casein-bound Ca and increased the solubilization of CCP. The G′ value of gels significantly increased with addition of low levels of TSC, and highest G′ values were observed in samples with 10 to 20 mM TSC; higher ( > 20 mM) TSC concentrations resulted in a large decrease in G′ values. The LT of yogurts increased after gelation to attain a maximum at pH ∼5.1, but no maximum was observed in yogurts made with ≥ 25 mM of TSC because CCP was completely dissolved prior to gelation. Partial removal of CCP resulted in an increase in the LT value at pH 5.1. At low TSC levels, the removal of CCP crosslinks may have facilitated greater rearrangement and molecular mobility of the micelle structure, which may have helped to increase G′ and LT values of gels by increasing the formation of crosslinks between strands. At high TSC concentrations the micelles were completely disrupted and CCP crosslinks were dissolved, both of which resulted in very weak yogurt gels with large pores obvious in confocal micrographs. Gelation pH and yield stress significantly decreased with the use of high TSC levels. Lowest whey separation levels were observed in yogurt made with 20 mM TSC, and whey separation greatly increased at > 25 mM TSC. In conclusion, low concentrations of TSC improved several important yogurt characteristics, whereas the use of levels that disrupted casein micelles resulted in poor gel properties. We also conclude that the LT maximum observed in yogurts made from heated milk is due to the presence of CCP because the modification of the CCP content altered this peak and the removal of CCP eliminates this feature in the LT profiles.     

Effect of Plasma Treatment on the Adhesion of Carbon Fibers to Thermoplastic Polymers

A study has been made of the effect of RF plasmas on the adhesion of carbon fibers to polycarbonate and polysulfone. Treatment in oxygen plasma significantly increased the adhesion to both polymers. The effect is lost if the treated fiber is stored in air for a week. Surface analysis using XPS indicated an increase in atom percent oxygen but the spectra were unchanged for the stored fibers even though there had been a significant loss in adhesion. It is suggested that oxygen surface functionality is responsible for the improved adhesion but that this surface activation is lost on storage. Due to a sampling depth of 5-10 nm, XPS would not be expected to detect this small change in surface functionality.     

Studies on wears of ultrafine-grained ceramic tool and common ceramic tool during hard turning using Archard wear model

Hardened steels are difficult to be machined due to their high tensile strength and work-hardening rate, low thermal conductivity, and abrasive behavior. In this paper, finite element modeling (FEM) approaches with lagrangian increment method for 3D metal turning of hardened steel H13 by common ceramic tool and ultrafine-grained tool respectively have been investigated by simulation of DEFORM-3D software and turning test. Conditions of initial and boundary and turning process parameters have been chosen. Material properties of H13 and ceramic have been described in details. Johnson–Cook model of H13 model has been applied to the hard turning modeling. Archard wear model has been built, and the correlation coefficients were decided by reciprocating friction experiments. The simulation results showed that predicted primary turning force and maximum temperature in common ceramic are bigger than which was caused by ultrafine-grained ceramic tool for the ultrafine-grained ceramic tools have better thermal stability and bigger hardness. The wear depths of common ceramic tool are about many times than that of ultrafine-grained ceramic tool according to the simulation and experimental results. And their wear patterns are very different. The FEM simulation results have entirely explicated experimental results. The obtained results would provide the fundamental and practical guidelines of tool material choice for hard turning.     

A comparison of novel ozone-based systems and photocatalysis for the removal of water pollutants

Three ozone-based systems and a photocatalytic system have been compared for the removal of a reactive dyestuff, orange RO16, and 2-chlorophenol in relation to degradation performances and ozone and energy consumptions. These systems were (1) liquid/gas–ozone (LGO): ozone was applied as it is produced in the gas phase; (2) liquid/solid–ozone (LSO): ozone was adsorbed on particulate silica-based material and then applied to water; (3) liquid/liquid–ozone (LLO): ozone was dissolved in a water-immiscible solvent and then applied to water; and (4) photocatalytic system using titanium dioxide catalyst (PHC). All four systems were capable of degrading the pollutants but presented different characteristics. The LSO system offered the possibility of using long contact times for slow ozone reactions and the LLO system is most suitable for fast ozone reactions. Both systems offer the prospect of more efficient use of ozone by extracting specific pollutants away from the water phase to the solid or the solvent phases. The PHC system presented the lowest rates and the highest energy consumptions by a factor of up to 400 times as compared to the ozone-based systems. The four systems were classified on the basis of their energy consumption as follows: for the degradation of RO16 (LLO相似文献   

Crystallographic orientation contrast associated with Ga+ ion channelling for Fe and Cu in focused ion beam method

In this study, Cu and Fe single crystals are used to examine the change in secondary electron intensity associated with Ga(+) ion channelling in a focused ion beam (FIB) system. The single crystals having three different orientations are tilted with respect to the beam incidence and the resulting variation in the secondary electron intensity is measured through the variation in brightness of the crystals. It is shown that intensity minima appear at the beam directions normal to the lower indices of the crystal orientations. The appearance of the intensity minima including the magnitude of the minima is consistent with the prediction based on the event of ion channelling in the crystal and is affected by the crystal structure. The effect of background on the intensity minima is discussed in this study. It is suggested that the presence of the intensity minima may be used to identify a crystal orientation including a crystal structure.