Study of the Adsorption of Ozone on the Surface of Ferric Oxide by Reversed-Flow Inverse Gas Chromatography

Abstract

In this work, in order to describe the impact of ozone on ferric oxide – a common constituent of building materials – in purely scientific terms, a novel methodology that of Reversed Flow–Inverse Gas Chromatography (RF–IGC or RF–GC) is proposed. Five important physicochemical quantities concerning adsorption of ozone on the solid surface of ferric oxide are determined, in five temperatures, in a time-resolved way. By means of a simple PC-program, the values of local adsorption energy, local adsorption isotherm, local monolayer capacity, probability density function for adsorption energy, and energy from lateral interactions are calculated. Thus, the role of surface heterogeneity, lateral interactions and different distributions of active sites (surface topography) on the adsorption of ozone on the surface of ferric oxide is analyzed in the way the RF–IGC method has it developed.     

Investigation of the Determination of Diffusion Coefficients of Gases into Liquids from Reversed‐Flow Gas Chromatography

Abstract

The interaction of vinyl chloride (VC) with water is used as the model system for the investigation of the determination of diffusion coefficients of gases into liquids from revered‐flow gas chromatography (RF‐GC). A thorough, full investigation of the initially suggested methodologies of RF‐GC [Anal. Chem. 1989, 61, 2231–2237 and Adv. Chromatogr. 2000, 40, 231–273] is carried out. The appropriate experimental conditions for the measurement of accurate liquid diffusivities (e.g., quiescent or stirred liquids) are investigated, and an insight into the physical meaning of the measured physicochemical parameters is attempted. In order for liquid diffusion to be the main broadening factor, it is necessary to ensure the regularity of the liquid stationary phase, which can be achieved by stirring the liquid substance under study. Furthermore, the experimentally obtained diffusion coefficients, the respective mass transfer coefficients, as well as the activation energy for the diffusion of VC in water are of the same order of magnitude and are very close to the values obtained by other techniques or calculated from empirical equations, ascertaining the potential of the presented methodology.     

Analytical Surface Roughness Parameters of a Theoretical Profile Consisting of Elliptical Arcs

The closed‐form solutions of surface roughness parameters for a theoretical profile consisting of elliptical arcs are presented. Parabolic and simplified approximation methods are commonly used to estimate the surface roughness parameters for such machined surface profiles. The closed‐form solution presented in this study reveals the range of errors of approximation methods for any elliptical arc size. Using both implicit and parametric methods, the closed‐form solutions of three surface roughness parameters, R _t , R _a , and R _q , were derived. Their dimensionless expressions were also studied and a single chart was developed to present the surface roughness parameters. This research provides a guideline on the use of approximate methods. The error is smaller than 1.6% when the ratio of the feed and major semi‐axis of the elliptical arc is smaller than 0.5. The closed‐form expressions developed in this study can be used for the surface roughness modeling in CAD/CAM simulations.     

METHODOLOGY TO COMPARE 3-D AND 2-D PARAMETERS FOR THE OPTIMIZATION OF HARD TURNED SURFACES

ABSTRACT

Hard Turning provides an alternative to grinding in some finishing applications. Average Surface Roughness R_a has been widely used in industry to establish surface texture needed for a given application. It is known that the single parameter R_a is inadequate to define the functionality of a surface texture. The quality of a surface can be determined by the nature of its interaction with another surface. Thus a surface with significant peaks will not make as good a bearing surface as a surface with deep valleys and low peaks. Two different surfaces with similar values of R_a can behave differently under fatigue loading conditions. 3-D visualization of expected surface texture will facilitate optimization of machining parameters to produce function-specific surfaces. The advantages and shortcomings of some current surface texture prediction models are discussed. A new method based on neuro-fuzzy techniques is proposed. Optimization using some 3-D surface parameters was carried out and compared with the results of those obtained using 2-D parameters.     

Investigation of the mechanism of lubrication in starch–oil composite dry film lubricants

The boundary coefficient of friction (COF) of starch–oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch‐to‐oil ratio. Based on the results, a mechanism of starch–oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (ΔG_ads) of the polar oils onto the starch surface. The analysis gave ΔG_ads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non‐polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane–starch than that for the polar oil–starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements. Published in 2006 by John Wiley & Sons, Ltd.     

Adatom concentration distribution on an extrawide Si(111) terrace during sublimation

The formation of an adsorption layer on the Si(111) surface during sublimation at temperatures of 1000–1100 °C and subsequent quenching at T = 750 °C is studied by methods of in situ ultrahigh-vacuum reflection electron microscopy and ex situ atomic force microscopy. The adatom concentration distribution on an extrawide (~60 μm) atomically flat terrace is determined for the first time, and the diffusion length x_s = 31±2 μm at T = 1000 °C is obtained. The analysis of the temperature dependence of the equilibrium concentration of adatoms near a monatomic step allows pioneering measurements of the energy necessary for adatom detachment from the step and attachment to the terrace E _ad ≈ 0.68 eV. Based on these results, the energy parameters for some atomic processes on the Si(111) surface are estimated.     

Surface roughness and material removal rate of lapping process on ceramics

Lapping is a widely used surface finishing process for ceramics. An experimental investigation is conducted into the lapping of alumina, Ni−Zn ferrite and sodium silicate glass using SiC abrasive to study the effect of process parameters, such as abrasive particle size, lapping pressure, and abrasive concentration, on the surface roughness and material removal rate during lapping. A simple model is developed based on the indentation fracture and abrasive particle distribution in the slurry to explain various aspects of the lapping process. The model provides predictions for the surface roughness,R _a andR _t , on the machined surface and rough estimation for the material removal rate during lapping. Comparison of the predictions with the experimental measurements reveals same order of magnitude accuracy.     

Method of determination of truncation parameters from measured surface profile

The probability density function of the roughness height of a sliding surface is not always Gaussian like that of a truncated surface caused by running-in or mild wear. Therefore, it is important for obtaining contact pressure or frictional characteristics to estimate the truncation level of the non-Gaussian distribution function. This paper presents a method of determination of the two truncation parameters in the truncation model presented by King et al. [Proceedings of the 4th Leeds–Lyon Symposium on Tribology, MEP, London, 1978, p. 333]. The two truncation parameters p and β can be determined by plotting the values of skewness S_k and kurtosis K obtained from a measured profile of surface roughness on the S_k–K diagram calculated with the truncation model for various given values of parameters p and β. The height distributions reproduced by the truncation model with the truncation parameters p and β identified by the present method is in good agreement with the original ones of the measured surfaces.     

A theoretical and experimental study on transverse field radio frequency surface coils

We have analysed, theoretically and experimentally, transverse field RF surface coils comprising two parallel linear current elements (figure-of-eight, FO8). A quasi-static numerical integration of the Biot–Savart law was used to simulate the B₁ field distribution of FO8 coils comprising a range of coil diameters and linear element separations. RF coil prototypes, suitable for ¹H and ³¹P magnetic resonance imaging/spectroscopy at 1.5 T, that closely match the simulated models, were built and tested using workbench and MRI methods. A comparison with standard loop RF coils was made. Testing with phantoms showed a good agreement between the theoretical and experimental RF field distributions. Our findings should be useful to optimize the sensitivity and spatial selectivity of FO8 coils by a careful choice of the geometrical parameters. A number of applications where the use of FO8 RF coils could be of benefit are discussed, these include in vivo nuclear magnetic resonance imaging/spectroscopy.     

On the estimation variance for the specific Euler–Poincaré characteristic of random networks

The factors that determine the local magnetic properties of FeCo/SiO₂ nanocomposite powders and films have been analysed by electron energy‐loss spectroscopy (EELS) and transmission electron microscopy (TEM). Attention has been given to the chemical composition, the local electronic structure and the atomic arrangement. The results show that the nanoparticles from sol‐gel prepared powders are generally Fe‐rich, whereas they are Co‐rich in sol‐gel prepared films. In addition, a subnanometre oxide layer at the surface of the FeCo nanoparticles has been clearly observed in the powder sample. It is found that the magnetic moment should be partly governed by alloying effects. Numerical values of the near‐surface magnetic moment have been obtained using the ab‐initio layer‐KKR method. These values should be helpful in understanding the layer‐by‐layer changes of the white line ratio close to the surface of the nanoparticles.     

New inverse gas chromatographic methodology for studying mass transfer caused by the evaporation of volatile liquids

Abstract

Physico-chemical quantities related to evaporation have been simply and directly calculated by a new methodology of reversed-flow inverse gas chromatography. The only demand is a preliminary determination of quantification coefficient(s), converting the signal to solute(s) molar or volume units. Time-dependent, k_c(t) and overall mass transfer, k_c, coefficients were determined for the evaporation of methanol at temperatures from 305 to 336 K, using two diffusion column lengths (10.0 and 40.5 cm) to evaluate the effect of the mass transfer route. Mass transfer coefficients indicate the endothermic nature of evaporation, while the longer diffusion route resulted in lower k_c values. The precision in the determination of evaporation rates was high (98.3%). Time-resolved diffusion coefficients, D_g(t), were also estimated. The smaller diffusion route resulted in lower values due to the higher enrichment of the mobile phase in the solute vapors. In the case of the smaller diffusion route, the change of D_g(t) values increased from 0.1% to 0.8%, while in the longer it was less than 0.1%. The respective temperature exponent increased with the diffusion route length from 1.68 to 1.74. Removing the effect caused by the different lengths of diffusion routes, the activation energy corresponding to pure evaporation was equal to 35.2 kJ mol^?1, rather close to the literature values for methanol’s vaporization enthalpy, indicating the reliability of the new methodology. Finally, the effect of mass transfer route was estimated to be 229 MJ mol^?1 km^?1, revealing the huge amounts of heat transfer accompanying evaporation at high altitudes.     

Use of the Roughness Parameters Ssk and Sku to Control Friction—A Method for Designing Surface Texturing

The aim of this work was to show that with the use of the surface roughness parameters S_sk and S_ku we can predict tribological behavior of contact surfaces and use these parameters to plan surface texturing. This article presents a continuation of our research on virtual texturing and experimental work on surface textures in the form of channels. For this investigation, steel samples were laser surface textured in the shape of dimples with different spacings between the dimples and different dimple depths. The experimental results confirmed that the parameters S_sk and S_ku can be used to design the surface texturing, where a higher value of S_ku and more negative S_sk lead to lower friction.     

Tribological Sensitivity of PTFE/Alumina Nanocomposites to a Range of Traditional Surface Finishes

Wear tests were performed with polytetrafluoroethylene (PTFE) + Al ₂ O ₃ nanocomposites on various manufactured surfaces to determine whether or not the wear resistance of these nanocomposites is a strong function of surface preparation. Four different surface finishes of grade 304 stainless steel counterfaces were used: electropolished (R _q = 88 nm), lapped (R _q = 161 nm), wet-sanded (R _q = 390 nm), and dry-sanded (R _q = 578 nm). PTFE + Al ₂ O ₃ nanocomposites made from powders of roughly 2-20 μm PTFE (matrix) and ～44 nm Al ₂ O ₃ (filler) were prepared at filler weight percentages of 0, 1, 5, and 10% and tested on each surface finish. Additionally, 5 wt% 44-nm nanocomposites were compared to identically prepared 5 wt% 80- and 500-nm Al ₂ O ₃ filled PTFE composites on each surface. Friction coefficients were between 0.12 and 0.19 and wear rates decreased from K = 810 × 10^{? 6} mm ³ /(Nm) for the 5 wt% 500-nm alumina-filled PTFE on the dry-sanded surface to K = 0.8 × 10^{? 6} mm ³ /(Nm) for the 5 wt% 80-nm filled composite on the lapped surface. It was found that the minimum wear rate occurred on the lapped counterface for every composite, and the wear rate is a strong function of the transfer film thickness and morphology.     

Measurement of Surface Areas of Basal Plane and Polar Sites in Graphite and MoS2 Powders

Recent work on graphite and MoS₂ powders revealed that the proportion of basal plane surface in the powder is an important factor in their anti wear properties and that the proportion of the polar “edge” surface may affect the abrasive properties of these solid lubricants. A method has been developed, therefore, for the independent measurements of the total basal plane and edge surfaces in the powders. The basal plane area is determined from the amount of adsorption of n-dotriacontane from solution in n-heptane. Similarly the edge area is determined from the adsorption of n-butanol.

A convenient and rapid method of estimating the proportions of basal plane and edge areas in the solid lubricants is to determine the integral heat of preferential adsorption of n-dotriacontane and n-butanol using the flow calorimeter.

The saturation of a sample of graphite or MoS₂ powder can be carried out by percolation with a succession of dilute solutions in n-heptane, and the total heats evolved are obtained in the form of peaks on the chart of a potentiometric recorder. The method can measure easily basal plane and edge surface areas down to 0.1 m²/g for graphites and can be used tentatively for MoS₂.     

Measurement of surface roughness of metals using binary speckle image analysis

In this paper, results from an optical technique for measuring surface roughness using image analysis of speckle pattern images are presented. The technique coined as statistical properties of binary images (SPBI) utilizes the combined effects of speckle and scattering phenomena. The speckle patterns obtained with a He–Ne laser were binarized and examined. The parameters such as bright and dark regions and their ratios obtained from this model to evaluate the surface roughness were compared with the surface roughness parameter R_a obtained from a profilometer. It was found that there is a strong relationship between these parameters and R_a, especially in the range of λ<R_a<2λ where λ is He–Ne laser wavelength. Although, it is a relative method, it has great potential to be used for in-process measurement and automation due to the simplicity of optical system used. The proposed method for the surface roughness combined with a non-contact optical measuring system is applied to samples from 0.5825 to 1.9 μm of steel (CK 45) through CNC face-milling process.     

Electron energy-loss spectroscopy study of thin film hafnium aluminates for novel gate dielectrics

We have used conventional high‐resolution transmission electron microscopy and electron energy‐loss spectroscopy (EELS) in scanning transmission electron microscopy to investigate the microstructure and electronic structure of hafnia‐based thin films doped with small amounts (6.8 at.%) of Al grown on (001) Si. The as‐deposited film is amorphous with a very thin (～0.5 nm) interfacial SiO_x layer. The film partially crystallizes after annealing at 700 °C and the interfacial SiO₂‐like layer increases in thickness by oxygen diffusion through the Hf‐aluminate layer and oxidation of the silicon substrate. Oxygen K‐edge EELS fine‐structures are analysed for both films and interpreted in the context of the films’ microstructure. We also discuss valence electron energy‐loss spectra of these ultrathin films.     

What environmental transmission electron microscopy measures and how this links to diffusivity: thermodynamics versus kinetics

Environmental or in situ electron microscopy means the observation of material in its native environment, which can be gaseous or liquid, as compared to more traditional post‐mortem electron microscopy carried out under (ultra) high vacuum conditions. Experiments can be performed on bulk samples in scanning electron microscopes or on thinned samples in transmission (scanning) electron microscopes. In the latter, the movement, in real time and in situ, of nanoparticles, clusters or even single atoms on the surfaces of thinned material or within a liquid can be observed. It is argued here that due to the changes that a specimen typically undergoes during in situ observation, electron irradiation effects are difficult to evaluate and so thermodynamic parameters, such as activation energies for diffusion and segregation, which are governed by movements of only a minority of atoms in the specimen, cannot be reliably determined because of the potentially high energy transfer by the irradiating electron beam to some atoms in the sample. In order to measure diffusivities reliably, radiation effects and surface diffusion need to be excluded or kept minimal so as not to disturb the measurements, which can be checked by repeating experiments and comparing results as function of time and dose for the same position, at different positions or for different specimen thicknesses. Kinetic measurements of nucleation and growth phenomena, such as Ostwald ripening, are possibly influenced to a far lesser degree by irradiation effects, as a majority of atoms actively participate in these processes and if a small fraction of them will get extra energy from the irradiation process then their influence on the overall kinetics may be rather minor.     

Surface micromorphology of dental composites [CE‐TZP]‐[Al2O3] with Ca+2 modifier

The objective of this study was to characterize the three‐dimensional (3D) surface micromorphology of the ceramics produced from nanoparticles of alumina and tetragonal zirconia (t‐ZrO₂) with addition of Ca⁺² for sintering improvement. The 3D surface roughness of samples was studied by atomic force microscopy (AFM), fractal analysis of the 3D AFM‐images, and statistical analysis of surface roughness parameters. Cube counting method, based on the linear interpolation type, applied for AFM data was used for fractal analysis. The morphology of non‐modified ceramic sample was characterized by the rather big (1–2 μm) grains of α‐Al₂O₃ phase with a habit close to hexagonal drowned in solid solution of t‐ZrO₂ with smooth surface. The pattern surfaces of modified composite content a little amount of elongated prismatic grains with composition close to the phase of СаСеAl₃О₇ as well as hexahedral α‐Al₂O₃‐grains. Fractal dimension, D, as well as height values distribution have been determined for the surfaces of the samples with and without modifying. It can be concluded that the smoothest surface is of the modified samples with Ca⁺² modifier but the most regular one is of the non‐modified samples. A connection was observed between the surface morphology and the physical properties as assessed in previous works. Microsc. Res. Tech. 78:840–846, 2015. © 2015 Wiley Periodicals, Inc.     

Fluorescence relaxation in 3D from diffraction-limited sources of PAGFP or sinks of EGFP created by multiphoton photoconversion

The relaxation of fluorescence from diffraction‐limited sources of photoactivatable green fluorescent protein (PAGFP) or sinks of photobleached enhanced GFP (EGFP) created by multiphoton photo‐conversion was measured in solutions of varied viscosity (η), and in live, spherical Chinese hamster ovary (CHO) cells. Fluorescence relaxation was monitored with the probing laser fixed, or rapidly scanning along a line bisected by the photoconversion site. Novel solutions to several problems that hamper the study of PAGFP diffusion after multiphoton photoconversion are presented. A theoretical model of 3D diffusion in a sphere from a source in the shape of the measured multiphoton point‐spread function was applied to the fluorescence data to estimate the apparent diffusion coefficient, D_ap. The model incorporates two novel features that make it of broad utility. First, the model includes the no‐flux boundary condition imposed by cell plasma membranes, allowing assessment of potential impact of this boundary on estimates of D_ap. Second, the model uses an inhomogeneous source term that, for the first time, allows analysis of diffusion from sources produced by multiphoton photoconversion pulses of varying duration. For diffusion in aqueous solution, indistinguishable linear relationships between D_ap and η⁻¹ were obtained for the two proteins: for PAGFP, D_aq= 89 ± 2.4 μm² s⁻¹ (mean ± 95% confidence interval), and for EGFP D_aq= 91 ± 1.8 μm² s⁻¹. In CHO cells, the application of the model yielded D_ap= 20 ± 3 μm² s⁻¹ (PAGFP) and 19 ± 2 μm² s⁻¹ (EGFP). Furthermore, the model quantitatively predicted the decline in baseline fluorescence that accompanied repeated photobleaching cycles in CHO cells expressing EGFP, supporting the hypothesis of fluorophore depletion as an alternative to the oft invoked ‘bound fraction’ explanation of the deviation of the terminal fluorescence recovery from its pre‐bleach baseline level. Nonetheless for their identical diffusive properties, advantages of PAGFP over EGFP were found, including an intrinsically higher signal/noise ratio with 488‐nm excitation, and the requirement for ∼1/200th the cumulative light energy to produce data of comparable signal/noise.     

Measurement of geometrical parameters in cocontinuous polymer blends: 3D versus 2D image analysis

Formulae of stereology are used to estimate 3D geometrical parameters of cocontinuous structures measured from 2D micrographs of polymer blends. 3D images of symmetric and nonsymmetric polymer blends made of fluorescently labelled polystyrene and styrene‐ran‐acrylonitrile copolymer were obtained with laser scanning confocal microscopy. Geometrical parameters of the blend interface, specifically volume fraction, surface area per unit volume (S _V ) and average of local mean curvature were measured directly from the 3D images and compared to the values estimated from analysis of a number of 2D slices combined with stereological relations. When the total length of phase boundary considered in the analysis of the 2D slices (L_Tot ) was at least 6000 times bigger than the characteristic length of the microstructure (S^?1_V ), the standard deviation for all the parameters measured became negligible. However, considerable discrepancies between the average values computed from 3D and 2D images were observed for any value of L_Tot . The mean curvature distribution was also measured from both the 3D images and the 2D slices. The distribution was estimated from the 2D slices but with a width about 2.4 times that of the true value obtained from the 3D images.