bluuebunny/crossref_metadata_2025_split huggingface dataset:
The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane, Part I
Authors: Foltz M. Frances , Coon Clifford L. , Garcia Frank , Nichols Albert L. 
Published: December 2004

AbstractPhase transitions in the α‐, β‐, γ‐, and ϵ‐polymorphs of 2,4,6,8,10,12‐hexanitrohexaazaisowurtzitane (HNIW) have been studied as a function of temperature. Described are the results of high temperature equilibrium solvation studies coupled with Fourier transform infrared spectroscopy (FTIR) for the identification of polymorphic conversion. These results are augmented by data in Part II from differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and optical hot stage microscopy(6). The thermodynamic stability order of ϵ > γ > α‐hydrate > β is shown, with the epsilon polymorph the most thermodynamically stable phase of HNTW at room temperature. The existence of multiple α‐hydrate phases is shown to complicate the determination of the equilibrium P‐T phase diagram of HNIW.
Computer‐Assisted Prediction of Novel Target High‐Energy Compounds
Authors: Pivina Tatyana S. , Shcherbukhin Vladimir V. , Molchanova Marina S. , Zefirov Nikolai S. 
Published: December 2004

AbstractA methodology of predicting novel target high‐energy compounds has been developed. A formalized approach to computer generation of structural isomers starting from previous optimized gross formula has been elaborated on the joined basis of the graph theory, molecular crystal structure modeling methods and quantum chemistry calculations. Chemical structures are generated as graphs which are subsequently converted to 3D representations. Then, some physical and chemical properties are calculated to evaluate the suitability of the generated compounds for practical purposes.Predictive capacity of this approach was demonstrated during the computer generation of new caged compounds structure with high energy content.
Increased Concentration of the Nitromethyl Aci‐Anion in nitromethane‐amine mixtures
Authors: Constantinou Constantinos P. , Pereira Carl , Chaudhri M. Munawar 
Published: December 2004

AbstractWe have investigated the concentration of the nitromethyl aci‐anion in nitromethane and nitromethane‐diethylenetriamine mixtures. Ultra‐violet absorption spectroscopy and electrical conductivity measurements have given direct experimental evidence that the aci‐anion concentration is increased as compared to that in pure nitromethane. The increase is consistent with a shift in the acid‐base equilibrium. In any one mixture that is in contact with air, we have also observed a subsequent decrease in the aci‐anion concentration as a function of time. A newly observed band in the vibrational spectrum of nitromethane has been assigned to the aci‐anion and was used to confirm the decrease in its concentration with time. We discuss the previously suggested link between the aci‐anion and the sensitivity of nitromethane and conclude that it is unlikely that there exists any correlation.
Formation of Nitroform in the Nitration of Gem‐Dinitro Compounds
Authors: Langlet Abraham , Latypov Nikolaj V. , Wellmar Ulf , Goede Patrick , Bergman Jan 
Published: December 2004

AbstractNitration of 4,6‐dihydroxypyrimidine in sulphuric acid gave nitroform as the sole product. This behaviour was tentatively explained by the formation of an intermediate, 5,5‐dinitro‐4,6‐dihydroxypyrimidine, that underwent hydrolysis in the nitrating acid to gem‐dinitroacetyl formamidine. This compound was further nitrated in the same reaction mixture to trinitroacetylformamidine which finally underwent hydrolytic cleavage to nitroform. It was also demonstrated that gem‐dinitroacetyl ureas were able to produce nitroform on nitration. The structures of the proposed trinitroacetylureas were confirmed by the isolation of one of their derivatives.
1,4‐Bis‐[1‐Methyltetrazol‐5‐yl]‐1,4‐Dimethyl‐2‐Tetrazene: A Stable, Highly Energetic Hexamer of Diazomethane (CH2N2)6
Authors: Klapötke Thomas M. , Mayer Peter , Schulz Axel , Weigand Jan J. 
Published: December 2004

Abstract1,4‐bis‐[1‐methyltetrazol‐5‐yl]‐1,4‐dimethyl‐2‐tetrazene a formal hexamer of diazomethane can be viewed as a new stable high energy density material (HEDM) with the properties necessary for a potential green chemistry gas generator. The physical properties of the new tetrazene were determined by drop hammer and combined IR and MS pyrolysis experiments. The structure and bonding are discussed on the basis of X‐ray, MO and NBO analysis.
Reproducibility across Microwave Instruments: First Example of Genuine Parallel Scale up of Compounds under Microwave Irradiation
Authors: Alcázar Jesús , Diels Gaston , Schoentjes Bruno 
Published: December 2004

AbstractOne of the major issues associated to microwave assisted organic chemistry is reproducibility. In the present article we demonstrate that reproducibility of results can be obtained from commercially available single‐mode and multimode microwave reactors. In order to make an appropriate comparison of results obtained in both systems, alkylation reactions were used as a model. Based on the reproducibility observed in these experiments, parallel scale up of compounds in one irradiation experiment is reported for the first time.
A Valuable Synthesis of Reduced Peptide Bond by Microwave Irradiation
Authors: Santagada Vincenzo , Frecentese Francesco , Fiorino Ferdinando , Cirillo Donatella , Perissutti Elisa , Severino Beatrice , Terracciano Sara , Caliendo Giuseppe 
Published: December 2004

AbstractMethyleneamine is a reduced form of the amide bond. The CH2NH group may be a useful tool for delineating important hydrogen‐bonding points and may also offer a general strategy for the production of enzyme resistance and potent competitive antagonists. This paper describes a facile synthesis of the CH2NH group by application of microwave energy. Moreover the importance of sterically hindered amino acids as well as the electronic effects of the side chain, in the synthesis of the hydroxamate and in the reductive alkylation steps, are evaluated. Room temperature, conventional heating and microwave irradiation of the reactions are compared. Synthesis by microwave irradiation gave the desired compound in higher yields and in shorter reaction times than those obtained at room temperature.
The Application of Microwaves in Combinatorial and High‐Throughput Synthesis as New Synthetic Procedure in Drug Discovery
Authors: Santagada V. , Frecentese F. , Perissutti E. , Favretto L. , Caliendo G. 
Published: December 2004

AbstractHeterocyclic compounds hold a special place among pharmaceutically important natural and synthetic materials. The remarkable ability of heterocyclic nuclei to serve both as biomimetics and reactive pharmacophores has largely contributed to their unique value as traditional key elements of numerous drugs. In both lead identification and optimization processes there is an acute need for new organic small molecules. Traditional methods of organic synthesis are orders of magnitude too slow to satisfy the demand for these compounds; so, the fields of combinatorial and automated medicinal chemistry have been developed to meet the increasing requirement of new compounds for drug discovery; within these fields, speed is of the essence. The efficiency of microwave chemistry in dramatically reducing reaction times (reduced from days and hours to minutes and seconds) has recently been proven in several different fields of organic chemistry. We believe that the time saved by using focused microwaves is potentially important in traditional organic synthesis but could be of even greater importance in high‐speed combinatorial and medicinal chemistry.
Rapid Microwave‐Promoted Cross‐Coupling Reaction of Aryl Bromides with Aryl Boronic Acids and Sodium Tetraphenylborate Catalyzed by a Reusable Polymer‐Supported Palladium Complex
Authors: Bai Lin , Zhang Yumei , Wang Jin‐Xian 
Published: December 2004

AbstractA variety of biaryls were prepared in a rapid and highly efficient manner via the cross‐coupling reaction of aryl bromides with aryl boronic acids or sodium tetraphenylborate in toluene, aqueous potassium carbonate and in the presence of a polymer‐supported palladium(II) catalyst under microwave irradiation condition. The supported catalyst was prepared directly from a commercial Merrifield resin and ultrasound dramatically accelerated the preparation of the catalyst. The polymeric catalyst can be easily separated from a reaction mixture and reused five times without decrease in activity. This suggests that a comparatively stable palladium phosphine complex is the reacting species in this special case. The reaction can be performed equally well using microwave and conventional heating, showing that microwave irradiation accelerates the reaction tremendously and in higher yields.
Microwave‐assisted Synthesis of Di‐ and trisubstituted Ureas from Thiophenoxy Carbamate Resins
Authors: Martinez‐Teipel Blanca , Green Rosalyn C. , Dolle Roland E. 
Published: December 2004

AbstractThe microwave‐assisted, parallel synthesis of di‐ and trisubstituted ureas is described. Microwave irradiation provides a significant rate enhancement to the in situ thermolytic cleavage of isocyanates from polymer‐supported carbamates. The method is amenable to library production and the target ureas are generally obtained in good purities (>80%).
Secondary ion mass spectrometry at close to single‐atom concentration using DC accelerators
Authors: Purser K. H. , Litherland A. E. , Rucklidge J. C. 
Published: December 2004

AbstractExperiments have been conducted which show that secondary ion mass spectrometry (SIMS), together with the addition of a rather low voltage (2 MV) DC accelerator, can become an extremely powerful new technique in many fields of research related to the characterization of surface and bulk solids and with high spatial resolution. The technology is available today to build an instrument that would have high lateral resolution (∼ 1 μm) coupled with a secondary ion transmission coefficient from target to detector >10% with no mass interferences from molecular ions. Molecular ions can be fragmented and analyzed separately. We believe that this combination of secondary ion mass spectrometers and accelerators represents a most significant advance in analytical techniques.
XPS–ISS analysis of Al/Ni alloys
Authors: Storp S. , Berresheim K. , Wilmers M. 
Published: December 2004

AbstractThe change in the surface composition of an Al/Ni alloy (50% by weight Ni) on heating in O2 and treatment in diluted NaOH was investigated by quasi‐simultaneous XPS–ISS measurements, using a hemispherical condenser analyser both for ESCA and ISS. The oxidizing experiments were carried out in a valveless, integrated, high pressure, high temperature preparation lock.
X‐Ray photoelectron spectroscopic study of the aqueous oxidation of stellite‐6 alloy
Authors: McIntyre N. S. , Zetaruk D. , Murphy E. V. 
Published: December 2004

AbstractThe aqueous oxidation of the cobalt allow Stellite‐6 has been studied in pH 10 water 285°C, as a function of dissolved oxygen concentration and length of exposure time. The result surface films were analysed by X‐ray photoelectron spectroscopy (XPS) and other techniques. Using XPS, a quantitative measurement of the oxide and metallic surface components was obtained and depth‐concentration profiles were determined. The effect of gaseous oxidation on the surface composition was also studied, and from a comparison of the oxidation behaviour under aqueous and gas phase conditions, solid state and solution‐transport processes could be distinguished. The gas phase studies showed that cobalt ions diffuse preferentially to the outer surface. During aqueous oxidation, however, the surface composition is found to be depleted in cobalt; preferential dissolution of the cobalt component of the alloy is therefore occurring under these aqueous conditions.
A versatile time‐of‐flight atom probe for metallurgical applications
Authors: Miller M. K. , Beaven P. A. , Smith G. D. W. 
Published: December 2004

AbstractA computer‐controlled atom prove time‐of‐flight mass spectrometer system is described which permits quantitative microanalysis to be undertaken at the 1–2 nm level. Distinctive features of the system include the use of a Johnston detector, to give low noise, high gain and high detection efficiency; incorporation of a movable channel plate and screen assembly, to provide a variable aperture; and the development of a comprehensive set of computer plate and screen assembly, to provide a variable aperture; and the development of a comprehensive set of computer software, to assist in the processing of data and presentation of analytical results. The system has been used successfully in a number of metallurgical investigations. In this paper, particular attention is given to describing the operating conditions required to achieve optimum performances, and to discussing the questions of background noise reduction and the deconvolution of spectra. The quantitative analysis capability of the instrument is demonstrated by reference to the results obtained from a range of standard materials, including steels. Applications to problems of metallurgical interest are illustrated by the analysis of ultra‐fine particles in a Cu/Co alloy, and the analysis of carbides and carbide‐matrix interfaces in a 2¼Cr/1Mo steel. The spatial resolution obtainable under different operating conditions is discussed, and the particular problems involved in the study of interfaces by this technique are described in detail.
Surface and interface analysis in polymer technology: A review
Authors: Holm R. , Storp S. 
Published: December 2004

AbstractSurface analysis methods like ESCA, AES, SIMS and ISS can provide valuable information on the structure and composition of polymer surfaces. Examples of application are the investigation of surface changes, such as the effects of weathering, etching and corona treatments, and the detection of surface deposits consisting of materials like antistatic agents, lubricants and exuded constituents. Because of their high surface sensitivity and ability to differentiate between surface and bulk phenomena, surface analysis methods are particularly suitable for the investigation of interfaces between polymers and metals, glass fibres, etc., e.g. in radial tyres, cable insulations and capacitor foils. It is pointed out that in these cases the inadequacies of the preparation methods limit the value of the analytical findings more than the inadequacies of the analysis methods.
Quantitative aspects of ion scattering spectroscopy
Authors: Haeussler E. N. 
Published: December 2004

AbstractIon scattering spectroscopy (ISS) shows up some important advantages compared to other surface analytical techniques. Because of its monolayer sensitivity and the negligible matrix effects, ISS is superior in depth profiling. Isolating materials such as glass or organic compounds can be analysed without any charging problem. Because of these advantages, interest in ISS has increased in recent years and has stimulated investigations into quantitative analysis. Although most scattering phenomena, which will be discussed, are well understood, some problems remain. To overcome these problems empirical calibration methods have been developed.
Examination of elemental nonuniformities in laser surface melted ternary copper alloys
Authors: Draper C. W. , Sharma S. P. , Yeh J. L. , Bernasek S. L. 
Published: December 2004

AbstractThe enhanced corrosion resistance of laser melted surfaces is often rationalized from the viewpoint of the homogenizing nature of the rapid quench from the liquid. We utilize Auger spectroscopy to examine elemental nonuniformities in laser surface melted ternary copper alloys (CDA‐614 and CDA‐725). In both systems we find depletion of the highest vapor pressure element from the central area of laser melt stripes, that region which reaches the highest temperature and remains molten for the greatest period of time. Although this near surface depletion is a small effect relative to the homogenization taking place over the orders of 10 and 102 µm, it may be a significant effect which should be taken into account when explaining changes in corrosion and oxidation behavior.
The reaction of NiO and α‐Al2O3 studied by Rutherford backscattering
Authors: De Roos G. , Fluit J. M. , De Wit J. H. W. , Geus J. W. 
Published: December 2004

AbstractThe interfacial reaction of NiO and α‐Al2O3 to NiAl2O4 is investigated by means of Rutherford backscattering spectrometry (RBS) using 2.95 MeV He+ ions. The NiO is obtained by oxidation at 800°C of a nickel film vapour deposited on to alumina substrates. The reaction of NiO and Al2O3 does not proceed markedly at 800°C. At ∼ 1100°C, the reaction to stoichiometric NiAl2O4 is found to be followed by a slower process leading to a spinel of the non‐stoichiometric composition NiAl2O4 · xAl2O3. At ∼ 1100°C, a marked volatilization of NiO is noted. At ∼ 1000°C the reaction also proceeds at a noticeable rate. However, at this temperature the diffusion process stops at the stoichiometric spinel composition. No volatilization of NiO is observed.
Depth resolution factor of a static gaussian ion beam
Authors: Malherbe J. B. , Sanz J. M. , Hofmann S. 
Published: December 2004

AbstractThe dependence of the depth resolution on the contribution of a Gaussian crater shape and the finite width of a Gaussian excitation beam (and/or Gaussian acceptance function) is considered. The results show that for Auger electron spectroscopy depth profiling, the contribution of the beam shapes to the depth resolution can, in most cases, be neglected. With X‐ray photoelectron spectroscopy and secondary ion mass spectroscopy depth profiling, care has to be taken to obtain a well resolved depth profile.
ESCA studies of Ni‐25 At% Fe alloy. 2—dissolution and passivation
Authors: Marcus P. , Olefjord I. 
Published: December 2004

AbstractThe surface compositions of a Ni‐25 at% Fe single crystal (100) and (110) were analysed by ESCA with respect to the electrochemical behaviour in 0.05 M H2SO4 (anodic dissolution and passivation). When the alloy surface is exposed to the electrolyte solution, or anodically polarized in the active region (anodic dissolution), iron is selectively dissolved and the surface is enriched with nickel. A stationary surface composition is attained which does not depend on the polarization potential or dissolution current. Once the stable surface composition is attained, the anodic dissolution of nickel and iron takes place with the same ratio as in the alloy. The extent of the surface enrichment with nickel, calculated from a layer by layer model for XPS signal intensities is found to be almost one monolayer of nickel at the alloy surface, each following plane in depth having the same composition as the bulk (Ni3Fe). The passive film is enriched with nickel. It consists or an inner layer of nickel oxide (NiO) and an outer layer of nickel and iron hydroxides. The thickness of the passive film is 8–10 Å. The alloy/oxide interface is also enriched with Ni in its metallic state.
Basic assumptions and recent developments in quantitative XPS
Authors: Carlson T. A. 
Published: December 2004

AbstractA review is made of the basic assumptions used in quantitative XPS. Particular attention is paid to problems of electron shake up and shake off, and to the angular distribution of ejected photoelectrons. Following this review, the interaction of XPS with other surface analyses is discussed and illustrated for UPS, ISS, and photon‐induced AES. The paper is concluded with a discussion of the future possible uses and advantages of synchrotron radiation for XPS including the development of XPS for microprobe analysis.
Proposition of an algorithm for calculating the surface composition from auger electron intensities
Authors: Jabłolński Aleksander 
Published: December 2004

AbstractFollowing the practice of electron probe microanalysis, a universal computer program is proposed which calculates the surface composition of binary alloys from the measured Auger electron intensities. The program can be applied for the usual experimental procedures, i.e. the relative sensitivity factor approach, and the direct comparison with a standard. The calculations are made for two models of the surface region; firstly, a uniform composition within the sampling depth of Auger electrons, and secondly, surface enrichment limited to the first monolayer. The relation of the Auger electron intensity to the surface concentration is expressed in terms of three matrix dependent correcting factors; the backscattering factor, the inelastic mean free path and the total number of atoms in a unit volume. The backscattering factor is assumed to vary linearly with the mass fraction of a given element in the bulk. The corrections for inelastic mean free path and number of atoms per unit volume are calculated for the bulk composition or the surface composition depending on the model of the surface region. The EXTENDED FORTRAN program, in addition to calculating the surface composition, has other auxiliary facilities such as plotting the calculated results, and calculating the extent of surface segregation when the model of monolayer enrichment is not valid.
Quantitative comparison of direct and derivative AES with XPS of metal sulfides
Authors: Griffis Dieter P. , Linton Richard W. 
Published: December 2004

AbstractIntegral area measurements of Auger intensities for various metal sulfides give comparable quantitative results to those obtained from derivative peak‐to‐peak heights. Highest precisions for sulfur sensitivity factors were obtained by: (a) intensity measurements involving integration of background‐subtracted N(E) lineshapes, (b) matrix corrections for electron mean free path and backscattering factor, (c) the use of XPS‐derived surface stoichiometries rather than assumed bulk stoichiometries for the metal sulfide standards. Despite the inherent inaccuracies of XPS quantitation, the XPS results help to correct for surface deviations from bulk stoichiometry owing to surface contamination, facile S surface oxidation, and preferential S loss usually observed during Ar+ sputter cleaning. The integral area Auger measurement techniques are particularly promising for electron‐beam sensitive materials which often cannot be characterized using high primary electron doses and conventional energy‐analyzer potential modulation differentiation.
An experimental and theoretical study of the transmission function of a commercial hemispherical electron energy analyser
Authors: Hughes A. E. , Phillips C. C. 
Published: December 2004

AbstractThe electron energy analyser transmission (peak area/incident current) of a VG Scientific ESCALAB has been measured as a function of kinetic energy, analyser energy and source position for a point source of electrons in the sample plane (produced using a specially designed mini electron gun). Results have been obtained in both CAE (constant analyser energy) and CRR (constant retard ratio) modes. The results are extrapolated to give the energy dependence of the analyser transmission for an extended current source, such as encountered in routine XPS analysis applications. A detailed theoretical study explains the rationale behind this data extrapolation and predicts an analyser transmission in fair agreement with experimental results, possible causes for the discrepancies between theory and experiment are discussed.