Photoelectron spectroscopic and thermodynamic studies of the formation of iron boride layers on pure iron substrates in powder boriding

In-situ studies of chemical reactions and transport processes occurring in powderous rection media during the production of refractory layers on metallic substrates are impossible. However, results of the studies of the layers formed by means of suitable surface analyses, e.g. ESCA, combined with thermodynamic estimations permit these processes to be deduced. Element distribution and bonding states in the boundary region of the surface as determined from the photoelectron spectra of powder-borided high grade iron samples correlate with the occurrence of thermodynamically possible gaseous intermediate compounds which may be formed from the components of a certain boriding powder. This permits a closed model of the processes in the reaction media and at the surface of the sample during boriding to be discussed.     

Formation and oxidation of porous silicon by anodic reaction

Porous silicon film (PSF) was formed by anodic reaction in aqueous hydrofluoric acid (HF) in the range 2 ? n < 4, n being the average number of electrons flowing through the external circuit per atom of silicon dissolved. Electron diffraction pattern of as-grown PSF changes to a very broad Kikuchi pattern from a sharp Kikuchi pattern for smaller values of n. The disproportionation reactions occur at a local point of the silicon surface for n between 2 and 4. When n is nearly equal to 2, the PSF structure changes to be amorphous and the reactions occur over the entire area of the silicon surface. The oxidation of PSF proceeds with the increase of the absorption intensities of three Si-O bands at 1070, 455, and 800 cm^-1 below 600°C, and two Si-O bands which are 455 and 800 cm^-1 above 600°C. Activation energies of Si-O bands at 1070, 455, and 800 cm^-1 at oxidation below 600°C are 0.1, 0.3, and 0.6 eV respectively. The activation energy changes remarkably below and above 600°C. The oxygen distributions in oxidized porous silicon of p-type and n-type PSF are uniform and nonuniform respectively in the thickness direction.     

XPS-study of the interaction of air-oxygen with platinum surfaces

The differences in the XPS spectra of the band regions Pt4f, Ols and VB between cleaned and air exposed polycrystalline platinum samples are discussed. After defined exposure it appears PtO_ads. and a cation configuration of 5d⁸ 6s¹ for platinum. This can be shown by line shapes, especially by the double peak structure of oxygen lines and by the asymmetrical tail on the high binding energy region of Pt4f combined with valence band results.     

Raman spectroscopic studies of aluminium fluoroberyllate glasses

Aluminium fluoroberyllate glasses obtained in the vitreous domain from the quaternary system BaF₂CaF₂AlF₃BeF₂ have been studied by Raman spectroscopy. The observed bands have been assigned by comparison with those of cryolite molten aluminofluorides, and of various fluoroberyllates in the crystalline and molten state. The following species have been identified: (AlF₄)^? tetrahedral groups, (AlF₆)^?3 octahedral groups polymerized in chains, and a few polymerized species of beryllium fluoride and probably Be₂F₇^?3 dimers.     

Auger spectrometric studies on fracture surfaces of tool steel

The fracture surfaces of tool steel K-13 (Hungarian Standard) were studied by Auger electron spectroscopy. Notched specimens of 3 × 3 mm² were fractured in UHV (6 × 10⁻⁸ Pa) with a fracturer (Riber FR 100) and studied with a CMA analyser (Riber OPC 103). With our modification the fracturer was operated within the −150°C −+230°C temperature range. The fracture surfaces were tested with a scanning electron microscope (JEOL JSM 35). The evaluation of Auger spectra was based on the PHI (PALMBERG et al.). Handbook, however the backscattering correction of Jablonski was applied in some cases. The choice of adequate fracturing temperature proved to be very important. Low temperature fracture of this steel alloy is producing very rigid transgranular fracture. The effects of sample heat treatment and of fracturing temperature as well were studied in details. The Auger spectra of fracture surfaces are strongly affected by the heat treatment of the samples. The grain boundary fracture surface of a sample austenitized at 1100°C quenched and tempered at 600°C exhibited a strong enrichment of P, correlating with the enrichment of Cr, V and Mo. The transgranular fracture surface of the same sample but without tempering corresponded to the bulk composition. In some cases and spots on the fracture surfaces, giant S or P peaks were associated with secondary phases (inclusions) on the SEM pictures.     

Crystallographic and spectroscopic studies on ethylenediaminetetraacetic acid (edta)

-ethylenediaminetetraacetic acid crystallizes in the monoclinic system:a = 13·273(4),b = 5·575(7),c = 16·110(6) Å, = 96·26(3),Z = 4,C2/c. The structure has been determined by direct methods with CuK diffractometer data, and refined by full-matrix least squares toR = 0·057 for 755 observed reflexions.The molecule exists in acis conformation and possesses two-fold symmetry, the diad axis passing through the central C—C bond. The nitrogen atom is protonated, and takes part in a bifurcated intramolecular hydrogen bond. A short (2·46 Å) hydrogen bond links the oxygen atoms of adjacent molecules.     

Vibrational spectroscopic studies of some lead silicate glasses

Results are presented of measurements on the infrared and laser Raman spectra of some lead silicate glasses of general formula (PbO)_x(SiO₂)_y.For the infrared spectra, the frequency dependence of the imaginary component of the complex dielectric constant was determined from a Kramers-Krönig analysis of the reflectance spectra of the glasses at normal incidence. Apparently the addition of small amounts of PbO to vitreous silica serves to modify the continuous three-dimensional silica network; whereas in those glasses with a high lead content, the influence of the cation, Pb²⁺, appears to lie between that of network former and network modifier.     

Raman spectroscopic studies of gadolinium trichloride as a function of temperature

Laser Raman spectrometry is being used in our laboratory to identify the crystal structures of lanthanide and actinide compounds. The phonon Raman spectrum of an ionic, crystalline sample is characteristic of the particular crystal structure(s) exhibited by the sample. GdCl₃ exhibits two crystal structures, UCl₃-type hexagonal and PuBr₃-type orthorhombic. In the literature it is proposed that the low-temperature form is the PuBr₃-type orthorhombic. Results of experiments in our laboratory suggest that the low-temperature form is the UCl₃-type hexagonal. Interconversion between these two forms can be accomplished with temperature. In the present work, laser Raman spectrometry was used to monitor crystal structure changes in GdCl₃ as a function of temperature and to determine the temperature at which the orthorhombic-to-hexagonal phase transformation occurs.     

Vibrational spectroscopic studies of sol-gel derived physical and chemical bonded ORMOSILs

Fourier transform infrared (FT-IR) and FT-Raman Spectroscopy have been utilized to characterize the structure of physical and chemical bonded ORMOSILs (organically modified silicates) and to compare with the physical properties, reported earlier. The classic and sono ORMOSILs were synthesized by sol-gel method via traditional- and sono-catalysis routes, respectively. The physical and chemical bonding is established by Poly(ethylene glycol) (PEG) and Poly(dimethoxysilane) (PDMS), respectively. Existence of band at ∼560 cm⁻¹ (FT-IR) and ∼490 cm⁻¹ (FT-Raman) for the sono and classic gels with 5-10 wt% of PEG indicates the presence of structural defect due to the four-membered siloxane rings. Application of long molecular PEG chain and PDMS increases this defect. Modification in the intensity and peak position of siloxane (Si-O-Si) bands is found correlative with the physical properties. The xerogels with 5-10 wt% of PEG possess a large number of residual surface silanol groups than the xerogels with long molecular PEG chains and PDMS and is found related with the ν(OH) band at ∼3470 cm⁻¹. These results are attributed to the way of hydrolysis-condensation reactions and discussed with the help of Percolation and DLVO models.     

Crystal structure and spectroscopic studies of a new organic monohydrogenmonophosphate dihydrate

The crystal synthesis and structure of a new organic monohydrogenmophosphate (3,4‐Cl₂‐CH₂C₆H₃NH₃)₂HPO₄·2H₂O are reported. This compound crystallizes in the monoclinic P2₁/n with a = 9.081(7) Å, b = 6.501(5) Å, c = 35.423(12) Å, β = 91.09(5)°, V = 2090.9(2) ų, and Z = 4. Crystal structure was solved and refined to R = 0.042, using 2543 independent reflections. It can be described by inorganic layers, including the HPO₄^‐ anions and the H₂O molecules, parallel to (a, b) planes and situated at z = 0 and z = 1/2. The interlayer spacing is occupied by the organic molecules which perform different interactions around the 3D network cohesion. A characterization of this compound by solid‐state (¹³C, ³¹P) MAS NMR and IR spectroscopies is also reported. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mass spectrometric studies of adsorption of silver on tungsten (110) surfaces

The adsorption of silver on (110)tungsten was studied by a mass spectrometric molecular beam technique. The temporal behaviour of the flux of adatoms leaving the substrate was measured at fixed temperatures between 860 K and 1080 K for constant impinging rates over the range 0.2 · 10¹³ to 9.0 · 10¹³ cm⁻² s⁻¹. For moderate supersaturation the growth mode changed from the layer-by-layer growth of three monolayers to the growth of three-dimensional nuclei (Stranski-Krastanov mechanism). At equal rates of impinging and desorption flux, the equilibrium adatom concentration was determined and a set of adsorption isotherms was thus derived. The shape of the experimental isotherms was found to be broadly similar to that of the theoretical Fowler-Guggenheim isotherm for a localized adsorption model. The binding energy of an Ag atom to the substrate, the lateral binding energy of a pair of atoms, the coordination number, and the vibration frequency of the adatoms for all three monolayers were obtained by suitable fitting procedures.     

掺杂AgCl中光电子衰减特性研究

利用微波吸收介电谱检测技术,检测均匀掺杂[Fe(CN)_6]~(4-)盐的立方体AgCl微晶首次曝光后的自由和浅束缚光电子的衰减时间分辨谱.实验发现,随着掺杂浓度的增加,样品中自由光电子衰减时间逐渐从未掺杂时的116 ns延长至1133 ns.分析光电子衰减曲线还同时得到,随着掺杂浓度的增加,光电子的前期较慢衰减过程逐渐变快,后期较快衰减过程逐渐变慢,总体上衰减时间逐渐增加,且掺杂浓度变化对后期衰减影响较大.研究表明掺杂使得晶体中引入了能总体上延缓光电子衰减的浅电子陷阱,并且随掺杂浓度的增加,浅电子陷阱特征更加明显.     

Vibrational studies of metal cation reduction at oxide glass surfaces

Reduction of metal oxide metaphosphate glasses (M₂O · P₂O₅, or MO · P₂O₅, where M is a metal cation) is observed above ca. 100°C when the glass is treated with one several gaseous reducing agents such as H₂, atomic hydrogen, Hg or K. Such amorphous systems are characterized by rapid cation diffusion, with cation reduction occurring principally at the glass surface, which leads to metal cluster formation and eventual continuous metal film growth. Structural changes induced in the glass by cation migration and subsequent reduction are studied by transmission infrared spectroscopy on thin-film samples during the reaction. Scanning electron microscopy and Raman spectroscopy are also employed to study and characterize the glass surfaces. The effect of water vapor on increasing the reaction rate for the mercuric metaphosphate/hydrogen reaction is demonstrated by continuous measurements of vibrational intensity changes. Surface-adsorbed water is seen to reduce the reaction induction period with little effect on the subsequent reaction rate. These results suggest that the rate-determining step of metal ion reduction at glass surface is a diffusion-limited process.     

Molecular structure,spectroscopic, and density functional theory studies of o-Dianisidine

o-Dianisidine has been characterized by the FT-IR, UV-Vis, and X-ray single-crystal determination. The compound crystallizes in the orthorhombic space group Pbca with a = 7.2593 (4) Å, b = 21.3485 (10) Å, c = 16.5835 (11) Å and Z = 8. Density functional theory has been used in the computation of the molecular geometry and harmonic vibrational wavenumbers. The calculated molecular geometry parameters have been compared with X-ray data. UV-Vis spectra of the compound have been predicted using the time-dependent density functional theory and good agreement between the calculated and experiment is determined. Besides, molecular electrostatic potential, frontier orbital analysis, and nonlinear optical properties were performed by using density functional theory calculations.     

X-ray and infrared spectroscopic studies of potassium hydrogen bis-(2,4-dichlorophenoxyisobutyrylglycinate)

Crystals of the title compound belong to space groupP¯1, withZ=1. TheK ⁺ ions and the acidic protons occupy centers of symmetry. This and the very short OO distance of 2.430 (9) Å classify the compound as a typeA acid salt. The infrared spectrum shows the _s OHO band near 800 cm^–1 with remarkably good definition at –170°C.