Preparation,Solid‐state Characteristics,and Catalytic Properties of Promoted Vanadium Phosphate Materials

The syntheses of transition metal promoted (M = Co, Cr, Fe, Mo) supported vanadium phosphate (VPO) catalysts (TiO₂ (anatase), γ‐Al₂O₃) and their characterization by N₂‐adsorption, X‐ray diffractometry (XRD), FTIR‐spectroscopy and determination of V‐valence state is reported. The catalytic properties were checked in the heterogeneous catalytic ammoxidation of 2, 6‐dichlorotoluene to the corresponding nitrile. The catalyst samples were prepared by synthesis of the precursor compound VOHPO₄ · 0.5 H₂O, impregnation using various metal salt solutions and mixing with the support materials. The characterization revealed increased surface areas for all the promoted samples in comparison to the basic materials. XRD showed the formation of (VO)₂P₂O₇ after calcinations as well as patterns of support materials (anatase, γ‐Al₂O₃). The formation of crystalline proportions of mixed oxides were not observed. The catalytic ammoxidation runs revealed a significant effect of the promoter metals on the catalytic properties by an increase of yield by ca. 20 % compared to bulk VPO. Almost complete conversion of 2, 6‐dichlorotoluene and 81 % yield of nitrile were observed using a 25 %VPCoO/γ‐Al₂O₃ catalyst.     

Measurements on a molecular beam apparatus for mass spectrometric study of reactions in flames

Summary The formation of a molecular beam in sampling 1 torr to 1 atm. gases (Ar or H₂) is studied for three diameters of the sampling orifice. To modulate the beam, use is made of a mechanical chopper placed very near the sampling orifice. This enables us to measure the scattering of the beam by collisions between beam molecules. From our measurements it follows that these collisions are very important for >0.020 mm at an initial pressure of 1 atm. We discuss the consequences of our results for mass spectrometric studies of flames.     

Argon (10 keV) scattered from structures,induced by bombarding a Cu(100) surface; ionization and neutralization

The ion fractions, η⁺, of 10 keV argon particles, scattered from a damaged copper surface, are measured with a time of flight spectrometer. The damage was introduced by bombardment with argon ions. The scattering angle was 30°. The results for different angles of incidence, ψ, are reported. For Ψ < 10° the ion fraction is relatively high (～27% for Ψ = 4°) and decreases as Ψ increases. For Ψ = 15° the value of η⁺ is 7%, whereas for 21° < Ψ < 27° the value of η⁺ appears to be constant (～14%). An explanation is given by assuming interatomic ionization as well as neutralization processes along the trajectory of the scattered particles. The number of step-atoms, induced by ion bombardment, is estimated to be about 2 × 10¹⁴/cm².     

Quasi-triple collisions in low energy ion scattering; A possibility to determine surface debye temperatures

Calculations and measurements of energy spectra of 10 keV Kr⁺ ions, scattered from Cu(100) face at different temperatures, are reported. One of the observed phenomena is the existence of a new peak. From the temperature behaviour of this peak we obtain the surface Debye temperature.     

The structure of a stepped copper (410) surface determined by ion scattering spectroscopy

Ion Scattering Spectroscopy applied in the multiple scattering mode is used to determine the structure of a stepped Cu(410) surface. The energy of singly scattered ions is influenced by the presence of neighbour surface atoms. This effect can be used to determine interatomic distances up to about 10Å, as is shown by the results of 8 keV Ar⁺ and 11 keV Ne⁺ scattered through θ = 50°. The edge-edge distance of the stepped copper surface appears to be in accordance with the results of LEED experiments obtained by other investigators. The experiments show a good agreement with the results of the analytical 3-atom model of Poelsema. The energy of the so-called “plateau collision” appears to depend on the effective plateau length l as measured in the plane of incidence. Lengths l between 15 and 60 Å can be determined with an accuracy of 5 Å. Results are shown for 8 and 12 keV Ar⁺, θ = 40° and 60°, and 8 keV Kr⁺ θ = 40°. The experimental dependence of the energy on lis described correctly by a phenomenological model.     

Neutralization and ionization of low energy helium ions scattering from a copper surface

Ion yield measurements are presented |of 2–10 keV helium ions scattered from a copper (100) face. The scattering angle is 30°. The results are explained using a charge transfer model originally proposed by the authors. The model takes into account Auger neutralization as well as ionization and neutralization resulting from a violent collision. The present results are compared with previous] experiments in which a primary atom beam was used. Within the experimental errors the results |of both experiments can be explained using the same charge exchange parameters. A second result of the present investigation is that more convincing evidence is given for the occurrence of neutralization during the violent collision by a non-Auger process. It is probable that this process, as well as the ionization process, results from an interaction between the helium particle and the copper L shell electrons.     

Sample geometry as critical factor for stability research

Stability research on gun propellants has been widely performed by microcalorimetry since the 1980s. TNO Prins Maurits Laboratory has already a broad experience since the early 1970s. In the past many studies were performed, to investigate the influence of oxygen, humidity etc. Less attention was paid to two other important aspects, namely the sample geometry and the filling degree during the microcalorimetric test.A statement in the old Dutch military literature presents the following “It is a well-known fact that the free surface influences the decomposition rate of the gun powder, i.e. unground propellant decomposes slowly in comparison to ground propellant”. This is the same for all types of propellant (Amsterdam, February 1924), which implies research on this topic, related to the stability prediction measured by microcalorimetry is important.Since the decomposition of nitrocellulose is influenced by the amount of oxygen and the surface area, the best way to investigate the stability of gun propellants is to measure it ‘ammunition like’. This means that a combination of the propellant grain size and the filling degree of the ammunition should be used for investigation. For small caliber ammunition the filling degree is close to 95%, and for large caliber bag ammunition (e.g. 155 mm) it is around 60%. As a result on these important aspects, TNO has developed five different sizes of sample vessels, to investigate the propellant grains in the most ‘ammunition like’ condition.In this paper, an overview is given of the influences of relative humidity, different grain sizes and available oxygen. The available oxygen is adjusted by changing the oxygen content of the air or by changing the filling degree.     

Levels of coplanar PCB in flue gases of high temperature processes and their occurrence in environmental samples

Summary Coplanar PCB (IUPAC nrs. 77, 126 and 169) have been determined in samples of flue gases and solid wastes from high-temperature processes, and soils and sediment.TEQ-levels of coplanar PCB present have been compared with those of PCDD/PCDF in the samples. It is found that, while in the flue gas samples coplanar PCB contribute less than 10% to the total TEQ level, soils and sediment may contain higher levels (up to 30% of the total TEQ for the samples analyzed).Moreover the pattern of PCB in the samples from high-temperature processes apparently differs considerably from that in the soils and sediment, in which PCB 77 constitutes >70% of the coplanar PCB.     

Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations in the human brain using magnetoencephalography

We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice, and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional magnetic resonance imaging or positron emission tomography.