Laboratory annoyance and different traffic noise sources

The acute annoyance reaction to different noise sources (lorries, aircraft, mopeds and trains) was investigated in a laboratory experiment. Students were exposed to different noise climates at noise levels 70 and 80 dB(A) for 25 minutes, and their reactions were subsequently assessed by using a questionnaire. Their general sensitivity to noise was also evaluated. The results demonstrated that L_eq gave the best correlation with annoyance. However, lorry noise was found to be less disturbing than aircraft noise at the same L_eq value. This was more pronounced if the different noises were compared at equal peak dB(A) levels. The results suggest that other factors such as the irregularity of the noise or the individual experience of the noise are of importance for the annoyance reaction. A relationship was found between the general annoyance score and annoyance reactions in the laboratory. Questionnaires could thus be a suitable tool for identifying noise sensitive persons.     

Two-dimensional phase transition in xenon submonolayer films adsorbed on (0001) graphite

Ultra high vacuum molecular beam techniques coupled with LEED and Auger electron spectroscopy are particularly well suited to the study of surface chemical reactions because of the ability to assess the effect of the surface conditions on the reaction probability. Investigation of the hydrogen-deuterium exchange reaction on a series of low and high Miller index platinum single crystals has indicated that the steps present on the high index surfaces are necessary for the dissociation and subsequent recombination of hydrogen. We have undertaken a systematic study of a series of small molecule reactions on these stepped surfaces to determine the reaction probability on stepped platinum surfaces. Reactions involving dissociation of Ha₂, D₂, O₂, OH, NH, and CH bonds proceed on the stepped surfaces with much higher reaction probabilities than reactions requiring dissociation of N₂, or CO bonds. All of the reactions studied resulted in cosine product angular distributions except for the formation of CO₂, which exhibited a distribution more peaked at the normal to the surface.     

Dissociation reactions of CO Gas on Fe and Fe3O4 surfaces observed by Raman-ellipsometry spectroscopy

A combined system of Raman spectroscopy and ellipsometry is developed for the study of catalyst surfaces on which a chemical reaction is taking place. The dielectric function and the thickness of a surface layer or a surface compound produced in the reaction are analyzed by ellipsometry; vibrational modes of the compound and surface species are analyzed by Raman spectroscopy, and the products in the gas phase by mass spectrometry. The system is applied to the study of the Boudouard and dissociation reactions of CO molecules on Fe and Fe₃O₄ catalysts. A surface layer produced by diffused C and O atoms, a thin oxide layer produced on the Fe by the CO dissociation reaction, and graphite layers produced by the Boudouard reaction are analyzed. Raman spectra reveal the existence of several kinds of carbon species such as defective graphite and an Fe carbide formed on the Fe and Fe₃O₄ surfaces. Specific Raman bands at 1121 and 1147 cm^-1 are tentatively concluded to be produced from microscopic clusters of surface graphite. The reaction of the defective graphite with H₂ gas is found to be stepwise on a time scale of seconds.     

Temperature programmed desorption study of acetylene on a clean,H-covered,and O-covered Pt(111) surface

The reactions of acetylene on a clean, a H-covered and an O-covered Pt(111) surface were studied by temperature programmed desorption for various coverages of acetylene, and acetylene to H or O ratios. The desorption products were quantitatively determined. On a clean surface, acetylene decomposes to hydrogen and surface carbon. A small amount of self-hydrogenation to ethylene also occurs during decomposition. On a H-covered surface, hydrogenation to CH₄, C₂H₆, and ethylene, and decomposition to hydrogen and surface carbon occur simultaneously. The reactions on these two surfaces can be explained by the presence of two sites. One site is a bare surface Pt atom on which decomposition is the primary reaction pathway. The other site is a Pt atom with adsorbed H on which hydrogenation is the primary reaction pathway. On the O-covered surface, the decomposition reaction takes place together with an oxidation reaction which yields CO, CO₂, and water. The oxidation reaction probably proceeds via an intermediate that has a stoichiometry of CH. Results on the O-covered surface are consistent with the model that oxygen absorbs in islands, and the oxidation reaction takes place at the perimeter of the islands. These results are compared with those of ethylene reaction on the same Pt surfaces.     

Peptide-induced patterning of gold nanoparticle thin films

In this work, the use of patterned proteins and peptides for the deposition of gold nanoparticles on several substrates with different surface chemistries is presented. The patterned biomolecule on the surface acts as a catalyst to precipitate gold nanoparticles from a precursor solution of HAuCl₄ onto the substrate. The peptide patterning on the surfaces was accomplished by physical adsorption or covalent attachment. It was shown that by using covalent attachment with a linker molecule, the influence of the surface properties from the different substrates on the biomolecule adsorption and subsequent nanoparticle deposition could be avoided. By adjusting the reaction conditions such as pH or HAuCl₄ concentration, the sizes and morphologies of deposited gold nanoparticle agglomerates could be controlled. Two biomolecules were used for this experiment, 3XFLAG peptide and bovine serum albumin (BSA). A micro-transfer molding technique was used to pattern the peptides on the substrates, in which a pre-patterned poly(dimethylsiloxane) (PDMS) mold was used to deposit a lift-off pattern of polypropylmethacrylate (PPMA) on the various substrates. The proteins were either physically adsorbed or covalently attached to the substrates, and an aqueous HAuCl₄ solution was applied on the substrates with the protein micropatterns, causing the precipitation of gold nanoparticles onto the patterns. SEM, AFM, and Electron Beam Induced Current (EBIC) were used for characterization.     

Surface structure effects in the reactions of nitric oxide with hydrogen and carbon monoxide on rhodium: A comparison with the surface structure effects observed for the hydrogen-oxygen and carbon monoxide-oxygen reactions

Using field electron microscopy (FEM) and thermal desorption and reaction spectroscopy (TDS) the behaviour of various Rh single crystal surfaces towards reactions involving NO has been studied. If, after NO adsorption up to saturation at 77 K, the temperature is slowly raised the FEM results suggest that dissociation of NO starts at the (321), (331) and (533) surfaces. The reaction of NO_ads with hydrogen starts also at these surfaces (at about 360 K) suggesting that NO bond scission initiates the reaction. After initiation a surface explosion is observed. Depending on the heating rate either a clean surface or a N_ads covered surface is obtained after completion of the reaction. Apparently, the reduction of adsorbed N_ads by hydrogen can occur at a significant rate at this temperature. At a higher heating rate the formed N adatoms do not react with hydrogen and are readily desorbed as N₂ at 600 K. The reaction of NO_ads with CO starts again on the (321) and (331) surfaces. The rate of the reaction with CO is, however, much lower than that with hydrogen. For the reaction of CO_ads with NO, desorption of CO is the initiation step. The mechanisms of the reactions and the dependence of the reaction on the surface structure are discussed in relation to literature data.     

Mechanism of and method to avoid discoloration of stainless steel surfaces in laser cleaning

2 O₃. Based on Auger Electron Spectroscopy analyses and optical microscopic observations, γ-Fe₂O₃ and Fe₃O₄ are formed on the stainless steel surface in laser cleaning in the air. Since laser can induce high temperature rise in stainless steel surfaces, the above phenomenon can be explained by a thermochemical reaction between oxygen in the air and the stainless steel. With increasing laser fluences, the temperature rise in the irradiated area of stainless steel surface increases, which enhances oxygen diffusion into the surface and oxidation reaction within the irradiated area. In order to avoid discoloration of stainless steel surfaces, a vacuum system was used to reduce the oxidation reaction between oxygen and stainless steel. Received: 7 June 1996/Accepted: 30 September 1996     

Surface functionalization by nanosecond-laser texturing for controlling hydrodynamic cavitation dynamics

The interaction between liquid flow and solid boundary can result in cavitation formation when the local pressure drops below vaporization threshold. The cavitation dynamics does not depend only on basic geometry, but also on surface roughness, chemistry and wettability. From application point of view, controlling cavitation in fluid flows by surface functionalization is of great importance to avoid the unwanted effects of hydrodynamic cavitation (erosion, noise and vibrations). However, it could be also used for intensification of various physical and chemical processes. In this work, the surfaces of 10-mm stainless steel cylinders are laser textured in order to demonstrate how hydrodynamic cavitation behavior can be controlled by surface modification. The surface properties are modified by using a nanosecond (10–28 ns) fiber laser (wavelength of 1060 nm). In such a way, surfaces with different topographies and wettability were produced and tested in a cavitation tunnel at different cavitation numbers (1.0–2.6). Cavitation characteristics behind functionalized cylindrical surfaces were monitored simultaneously by high-speed visualization (20,000 fps) and high frequency pressure transducers. The results clearly show that cavitation characteristics differ significantly between different micro-structured surfaces. On some surfaces incipient cavitation is delayed and cavitation extent decreased in comparison with the reference – a highly polished cylinder. It is also shown that the increased surface wettability (i.e., hydrophilicity) delays the incipient cavitation.     

Preparation and Characterization of Activated Carbon – nFe3O4, Activated Carbon – nSiO2 and Activated Carbon – nZnO Hybrid Materials

The preparation and physicochemical characterization of activated carbon, nano metal oxides, and activated carbon – nFe₃O₄, activated carbon – nSiO₂ and activated carbon – nZnO hybrid materials has been undertaken. The materials have been characterized by scanning and transmission electron microscopy, x‐ray diffraction, CNH analysis and Fourier transform infrared spectroscopy. Surface area and porosity, ash content, pH, and point of zero charge were also measured. The results showed that the surfaces of activated carbon, nSiO₂, activated carbon – nFe₃O₄, activated carbon – nSiO₂ and activated carbon – nZnO are suitable for the sorption of cationic complexes while the surfaces of nFe₃O₄ and nZnO are favourable to the sorption of anionic complexes of heavy metals. Results also showed that the composition of the activated carbon and nano metal oxides increased the surface and micropore areas of nano metal oxides due to the large number of micropores and crevices on the surface of the hybrid materials.     

Band bending variation of the Si(111) surface during its thermal oxidation

During the thermal oxidation of Si(111) surfaces performed under ultra high vacuum conditions and investigated with various surface techniques such as Auger electron spectroscopy, low energy electron diffraction, ultra violet and X-ray induced photoemission spectroscopy, the Si 2p core level binding energy was measured and provided directly the band bending variation of the Si surface. A net interface charge then could be deduced. This is an elegant in situ method to have access to the electrical characteristics of the SiSiO₂ interface during its formation.     

The UBI-QEP method: Mechanistic and kinetic studies of heterogeneous catalytic reactions

Applications of the unity bond index-quadratic exponential potential (UBI-QEP) method in mechanistic and kinetic studies of complex heterogeneous catalytic reactions are discussed. It is shown how UBI-QEP energetics helps to answer specific questions regarding the mechanisms of various reactions on metal surfaces. Examples of the following reactions are considered: elementary reactions of hydrogen transfer (from one carbon atom connected to the metal surface to another such atom in a different surface species), H-X bond breaking with the assistance of coadsorbed oxygen, methanol synthesis, Fischer-Tropsch synthesis, ammonia synthesis and decomposition, and partial methanol oxidation to formaldehyde. Then, examples of kinetic simulations using UBI-QEP energetics are considered for the following processes: ethane hydrogenolysis, watergas shift reaction, selective hydrogenation of acetylene in ethylene-rich mixtures, oxidative conversions of hydrogen and methane on Pt and Rh surfaces, ammonia decomposition, C₁–C₂ product formation in Fischer-Tropsch synthesis over cobalt, and steam reforming of methane. It is shown how the use of UBI-QEP and Monte Carlo methods makes it possible to calculate reaction parameters that depend on temperature in the equilibrium and kinetic regimes. To increase the accuracy of simulations, we added nonenergetic parameters affecting energetics at nonzero coverages: a spatial constraint on the distance between adsorbed atoms and the distance of hot atom traveling upon oxygen dissociation on metal surfaces. The UBI-QEP/Monte Carlo simulation method is illustrated by the study of molecular oxygen adsorption on single crystalline nickel surfaces. In most UBI-QEP-based mechanistic and kinetic studies of heterogeneous catalytic reactions, good agreement is observed with experimental observations, in many cases on a quantitative level. Taking into account diversity of reactions to which the method has been applied the agreement with experiments supports the efficiency of the method in solving mechanistic and kinetic problems.     

Investigation of a traditional catalyst by contemporary methods: Parallel electron spectroscopic and catalytic studies on Pt black

Results of electron spectroscopy (XPS and UPS) of platinum black catalyst measured in various states of the catalyst have been summarized. XPS showed up to almost 50% carbon and up to 20% oxygen on a sample stored in air. These, however, had almost no influence on the chemical state of Pt, except for the appearance of minor surface oxide. A Pt purity of ～90% could be reached by regeneration with O₂ and H₂. The C 1s peak contained several components from individual C atoms to graphitic and polymeric hydrocarbon layers. Thus, the active catalyst was not clean Pt but metallic Pt; the impurities exerting little influence on catalytic activity. Regeneration and deactivation led also to slight structural rearrangement, as detected by XRD. Intentional deactivation with hydrocarbon–hydrogen mixtures was monitored by XPS, UPS and catalytic tests. Correlation was found between catalytic activity and selectivity in hexane reaction and the amount – and also the chemical state – of carbon accumulated during deactivating runs. A short summary of electron spectroscopy of supported Pt catalysts is also given. The main underlying idea regards solid catalyst and reactants as a dynamic system, including also solid-state changes of the former.     

Bistability and explosive transients in surface reactions: the role of fluctuations and spatial correlations

We study the dynamics of a class of catalytic surface reactions in which an adsorbed molecule undergoes dissociation giving oxygen, which then rapidly reacts with H adatoms to give water. The reaction-diffusion equations predict bistability and explosive transients similar to those observed in several low-pressure experiments. Kinetic Monte Carlo simulations reveal however that the dynamics can be strongly affected by spontaneous, inhomogeneous fluctuations of composition on the surface. In particular, bifurcation points can be displaced and the explosive character of the transients can be lost, depending on a subtle balance between the rate of reaction and the mobility of the decomposing species. These effects can be quantified on the basis of a stochastic formulation of the dynamics taking into account spatial correlations. This approach allows to better delimit the applicability of the traditional reaction-diffusion modelling in the case of reactions such as the reduction of NO _x or SO _x species on catalytic surfaces.     

Electronic excitations by chemical reactions on metal surfaces

Dissipation of chemical energy released in exothermic reactions at metal surfaces may happen adiabatically by creation of phonons or non-adiabatically by excitation of the electronic system of the metal or the reactants. In the past decades, the only direct experimental evidence for such non-adiabatic reactions has been exoelectron emission into vacuum and surface chemiluminescence which are observed in a special class of very exothermic reactions. The creation of e–h pairs in the metal has been discussed in many theoretical models but it was only recently that a novel experimental approach using Schottky diodes with ultrathin metal films makes direct measurement of reaction-induced hot electrons and holes possible. The chemical reaction creates hot charge carriers which travel ballistically from the metal film surface toward the Schottky interface and are detected as a chemicurrent in the diode. By now, such currents have been observed during adsorption of atomic hydrogen and deuterium on Ag, Cu and Fe surfaces as well as chemisorption of atomic and molecular oxygen, of NO and NO₂ molecules and of certain hydrocarbons on Ag. This paper reviews briefly exoelectron and chemiluminescence experiments and the concept of the Nørskov–Newns–Lundqvist model. The major part is devoted to the detection of chemically induced e–h pairs with thin metal film Si Schottky diodes by discussing the different influences on the chemicurrent magnitude and presenting experimental results predominantly with hydrogen and deuterium atoms. The experiments introduce a new method to investigate surface reaction kinetics and dynamics by use of an electronic device. In addition, the diodes may be used as selective reactive gas sensors.     

A DFT+U study of the catalytic activity of lanthanum nickelate

A density functional theory + Hubbard U (DFT+U) method is implemented to investigate the catalytic activity of lanthanum nickelate (LaNiO₃) for oxygen reduction reaction. Comparison of the surface energies of different LaNiO₃ surfaces shows that {001} surface has the lowest surface energy and hence maximum stability. Two possible terminations of the {001} surface namely LaO and NiO₂ are considered to carry out all our DFT calculations. Calculation of bond lengths of the atoms near the surface and adsorption energies for the reaction intermediates revealed that LaO terminated {001} surface is unstable for the process of OOH adsorption and hence not preferred for the oxygen reduction reaction. However, NiO₂ terminated {001} surface shows excellent catalytic activity for adsorption of all the reaction intermediates and hence is a favourable surface for reactions to occur. Superiority of the NiO₂ terminated {001} surface as catalyst over the LaO terminated one, is also confirmed from the total and partial density of states of the surfaces in presence of the adsorbates, which also shows that the desorption rate of the reaction intermediates is low in case of LaO terminated {001} surface compared to the NiO₂ terminated one.     

Direct ab initio molecular dynamics study of F atom reaction with methane

The dynamics of the F + CH₄ → HF + CH₃ and F + CD₄ → DF + CD₃ reactions have been investigated using classical trajectory calculations at the MP2/cc-pvdz level of theory. The trajectories were calculated directly from electronic structure computations, and a Hessian based method with updating was used to integrate the trajectories. Using this method, product rovibrational populations and internal energy distributions were obtained for the F + CH₄ and F + CD₄ reactions. The theoretical results were compared with the available experimental data and previous calculations results. The state distributions of the reaction F + CH₄ in these calculations are in reasonable agreement with the experimental results, which indicates that the experimental behavior of the reaction could be well reproduced by the direct classical trajectory calculations at MP2/cc-pvdz level. As such, the product rovibrational populations and internal energy distributions for the reaction F + CD₄ were predicted. The same degree of agreement between theory and experiment as the F + CH₄ reaction is expected.     

Preferred listening level for speech disturbed by fluctuating noise

This paper is a sequel to an earlier one in which we investigated, among other things, the influence of stationary background noise on preferred listening level. The influence of fluctuations in noise level on preferred listening level was compared with the influence of stationary noise. It turned out that the preferred listening level for a read-aloud text, adjusted by listeners against a background of noise, is hardly influenced by fluctuations in the noise, provided the equivalent noise level (L_eq) in dB(A) remains the same. This holds both for systematically modulated noise down to 0·1 Hz and more randomly fluctuating noise such as traffic noise. Average preferred listening level proved to be an accurate measure for evaluating various conditions, such as modulation frequency and noise level, in a single experiment.     

Grafting of bifunctional phosphonic and carboxylic acids on Phynox: Impact of induction heating

Phynox, a cobalt-chromium alloy, exhibits interesting mechanical properties making it a valuable material for a number of applications. However, its applications (especially biomedical ones) often require specific surface properties that can be imparted via suitable surface functionalizations. Based on Faraday's law of induction, induction heating is a widely used method to heat metallic substrates directly and contactless. The aim of this work is to compare the influence of induction heating and a conventional heating method on the functionalization of Phynox surfaces with bifunctional (6-phosphonohexanoic and 11-phosphoundecanoic acids) monolayers in order to create a platform for a large variety of post-grafting chemical reactions, e.g. with alcohols and amines, to modify and control the surface properties. In a first part, we assess the influence of the heating method on the interaction between the two terminal moieties of the 6-phosphonohexanoic and 11-phosphoundecanoic acids and the Phynox surface by studying the grafting of n-dodecylphosphonic acid and n-dodecanoic acid separately. The suitability of such bifunctional molecules for post-grafting chemical reactions has then been assessed by studying the post-grafting of a fluorinated alcohol by the Steglich esterification reaction between the carboxylic end of the grafted bifunctional molecules and the alcohol function of the post-grafted molecule. It has been shown that induction heating can lead to a much more selective adsorption of bifunctional molecules on the surface of Phynox, leaving a higher amount of free carboxylic acid functions to react during the second modification step.     

<Emphasis Type="Italic">Ab initio</Emphasis> simulation of interface reactions as a foundation of understanding polymorphism

Chemical reactions at solid/liquid or solid/gas hybrid interfaces govern the morphogenesis of growing solid state phases. In order to understand the polymorphism of solids, the understanding of the mechanisms and kinetics of these reactions is of crucial importance, as is an insight into the morphology of said surfaces on an atomistic scale. Ab initio simulations are a valuable tool to obtain these data, especially in materials design, where many possible materials for an application may have to be examined. In such cases the fabrication of all these materials for examination and characterization can be extremely time consuming and expensive. We present methods to determine surface properties and reaction energetics from ab initio simulations and demonstrate their potential using three examples: reaction energetics for the adsorption of adhesive component molecules on alumina surfaces, the functionalization of a silica surface with a fluorocarbon layer and the investigation of the wetting behavior of the functionalized surface, and the calculation of reaction energetics for a proton transfer process in the bacterial reaction centre of photosynthesis, including quantum mechanical effects as well as solvent and continuum electrostatic influences from the surrounding medium.