Acidity and basicity of hydrotalcite derived mixed Mg-Al oxides studied by test reaction of MBOH conversion and temperature programmed desorption of NH3 and CO2

Mg-Al hydrotalcites intercalated with five different interlayer anions—CO₃²⁻, SO₄²⁻, Cl⁻, HPO₄²⁻ or terephthalate—were synthesized by either the coprecipitation or ion-exchange method. The structure of the as-synthesized samples and the presence of intended anions in the interlayer gallery of hydrotalcites were determined by X-ray diffraction and FTIR spectroscopy. On calcination at 600 °C the materials were transformed into mixed metal oxides. The kind of the counterbalancing anions present in the parent hydrotalcite influences strongly textural parameters of the obtained Mg-Al oxides. Both temperature-programmed desorption of NH₃ and CO₂, and test reaction of 2-methyl-3-butyn-2-ol (MBOH) conversion were used to determine the acidity and basicity of the samples. The hydrotalcite derived mixed Mg-Al oxides showed the presence of Brønsted and Lewis acid and base sites. However, the strong basic character of the solids caused that acetone and acetylene were observed as the major products of MBOH conversion.     

Effect of surface treatment on segregation of impurities in haematite

Surface segregation of various impurities such as Mg, Si, Ca, Al and Cr were determined for the haematite phase (Fe₂O₃) annealed in two different gas compositions involving (1) air at 1173 K, and (2) a gas mixture containing sulphur at 773 K. The objective of work was to establish the effect of the gas-phase composition on segregation of lattice defects. The near-surface segregation profiles of the impurities were determined by secondary ion mass spectrometry. The depth profile analysis was made by sputtering using an Ar⁺ primary beam of energy 30 keV. The surface charge was neutralized by an electron gun. It was found that annealing Fe₂O₃ under a gas phase containing sulphur resulted in the formation of an Fe(SO₄)₃ surface layer. It was observed that the two surface treatment procedures applied (both with and without sulphur) result in Mg enrichment in the near-surface region of Fe₂O₃. Si and Ca exhibit an enrichment and impoverishment after the surface treatments 1 and 2, respectively. Finally, the near-surface layer is impoverished in Cr and Al after both types of surface treatment. Experimental results are discussed in terms of segregation driving forces of the respective elements and the possible effect of sulphur on the gas-solid heterogeneous kinetics.     

Order Distance Estimation in Porous Glasses via Transformed Correlation Function of Small-Angle Scattering

A mesoporous two-phase system, consisting of colloidal silica in the cavities of the main silica frame work of a macroporous glass, was investigated by use of Small-Angle X-ray scattering. The transformed correlation function _T(r) was determined for this material for distances r<40 nm. The application of the intrinsic properties of _T(r) yields estimations for two fundamental order distances L ₁=11 nm and L ₂=120 nm of the~porous glass possessing a clear geometric interpretation: L ₁, a short-order-range, is the mean chord length of the mesopores plus the mean chord length in the secondary particles. L ₂, a long-order-range, is an estimation of the mean diameter of a macropore plus the mean free distance in the silica framework which separates two nearly parallel segments of two adjacent macropores.     

Selective oxidation of ammonia to nitrogen on transition metal containing mixed metal oxides

The selective catalytic oxidation of ammonia to nitrogen (NH₃-SCO) has been studied over hydrotalcite derived mixed metal oxides containing Cu, Co, Fe or Ni. XRD, BET, NH₃-TPD and TPR techniques were used for catalysts characterization. Results of NH₃-SCO were compared with those of selective catalytic reduction of NO with NH₃ (NO-SCR). Reaction mechanism was studied by temperature-programmed surface reaction (TPSR) and activity tests with a various contact time. Catalytic performance of the studied samples depends on both kind and loading of transition metals in the mixed metal oxide system. The Cu-containing samples have been found to be the most active catalysts of the NH₃-SCO process. Transition metal loading strongly influences distribution of ammonia oxidation products. The highest selectivity to N₂ was measured for the catalysts with the lowest transition metal content.     

Quality assessment for a visual and automatic license plate recognition

Video transmission and analysis is often utilized in applications outside of the entertainment sector, and generally speaking this class of video is used to perform specific tasks. Examples of these applications include security and public safety. The Quality of Experience (QoE) concept for video content used for entertainment differs significantly from the QoE of surveillance video used for recognition tasks. This is because, in the latter case, the subjective satisfaction of the user depends on achieving a given functionality. Recognizing the growing importance of video in delivering a range of public safety services, we focused on developing critical quality thresholds in license plate recognition tasks based on videos streamed in constrained networking conditions. Since the number of surveillance cameras is still growing it is obvious that automatic systems will be used to do the tasks. Therefore, the presented research includes also analysis of automatic recognition algorithms.     

Determination of porosity of reduced hematite by stereologic methods

The stereologic analysis of a solid grain has been applied for determination of its porosity. The investigations were carried out on a natural hematite grain reduced to magnetite at 723 K. Stereologic analysis enabled the porosity of this material to be determined on the basis of independently measured grain contours and volume fractions of grain components: hematite, magnetite and pores. A conformity criterion has been formulated, regarding determination of grain volume on the basis of known densities of components and their measured volume fractions in the grain, and on the basis of weight and apparent grain density measurements. The volume increase accompanying reduction of hematite to magnetite, determined from these independent measurements, was in the range 7–19%. By measuring Ferets diameter, the volume of the convex envelope of the grain increased as a result of phase transformation by about 11%. Simultaneously, the volume of the solid phase was found to decrease by 1.5%. The total porosity of the reduced grain, determined by stereologic analysis amounted to 17.5%; 7.7% of which was related to cracks and large pores, and 9.8% to small pores in the magnetite phase. The porosity value determined by the classical mercury method was approximately the same.     

Verification of schedulability for real-time programs

Assume that a real-time programP ^T consisting of a number of parallel processes is executed on a system having a setPr of processors which are shared between the processes by a real-time schedulerS ^T. Assume that P^T must meet some timing deadlines. We show that such an implementation ofP ^T can be represented as a transformationL(P ^T) and that the deadlines ofP ^T will be met if they are satisfied by the timing properties of the transformed program. The condition for feasibility of a real-time program executed under a scheduler is formalized and rules are provided for verification. The schedulerS ^T can be specifiedgenerically and applied to different programs, making it unnecessary to introduce low-level operations such as scheduling primitives into the programming language. Thus real-time program specification and Schedulability can be considered in the same framework and the timing properties of a program can be determined at the specification level. By separating the specification of the scheduler from that of the program, the feasibility of an implementation can be proved by considering a scheduling policy rather than its implementation details.     

Unconventional fractional quantum Hall effect in monolayer and bilayer graphene

The commensurability condition is applied to determine the hierarchy of fractional fillings of Landau levels in monolayer and in bilayer graphene. The filling rates for fractional quantum Hall effect (FQHE) in graphene are found in the first three Landau levels in one-to-one agreement with the experimental data. The presence of even denominator filling fractions in the hierarchy for FQHE in bilayer graphene is explained. Experimentally observed hierarchy of FQHE in the first and second Landau levels in monolayer graphene and in the zeroth Landau level in bilayer graphene is beyond the conventional composite fermion interpretation but fits to the presented nonlocal topology commensurability condition.     

Polyurethane-POSS hybrids: Molecular dynamics studies

A series of hybrid polyurethane-POSS materials have been synthesized on the basis of poly(tetramethylene glycol) (Terathane 1400^®) as soft component, 4,4′-methylenebis(phenylisocyanate) (MDI) as hard component, and 1,4-butanediol as chain extender. POSS particles properly modified have been tethered on the main chain by substitution of the chain extender to weight fractions up to 10%. AFM measurements indicate the formation of POSS crystallites in the PU matrix, extended structures at low POSS content and more regular, smaller structures at higher POSS content. A detailed investigation of molecular mobility by means of Differential Scanning Calorimetry (DSC), Thermally Stimulated Depolarization Currents (TSDC) and, mainly, Broadband Dielectric Relaxation Spectroscopy (DRS) has been conducted in all samples of the series and in addition in neat Terathane, as reference. Four relaxations have been studied in detail: two secondary relaxations γ and β, the segmental α relaxation (dynamic glass transition) and an α′ relaxation slower than α associated with crystallinity in neat Terathane and with the presence of hard microdomains in the polyurethane and the hybrids. Secondary relaxations remain unaffected by POSS. The glass transition temperature rises by a few degrees and, in consistency with that, segmental dynamics slightly slows down with increasing POSS content. In addition, the dielectric strength of the segmental relaxation decreases with increasing POSS content, suggesting that a fraction of polymer is immobilized, making no contribution to the relaxation. These results are discussed in relation to morphology.     

The effect of particle size and volume fraction on the aging behavior of a liquid-phase sintered SiC/aluminum composite

The aging response of a SiC particulate reinforced powder metallurgy aluminum composite was examined as a function of particle size and volume fraction. The addition of SiC particles ranging in size from 24 to 142μm at 9 vol pct had no effect on the aging kinetics of the composites. Acceleration of the aging behavior or inhibition of the initial stage of the age-hardening process was observed at 18 and 27 vol pct. The accelerated aging kinetics were consistent with smaller particles creating larger thermal misfit dislocation densities. In addition, it was shown that different combinations of ceramic particle size and volume fraction lead to similar effects on the aging behavior. Loss of the initial hardening response was attributed to the suppression of Guinier-Preston (GP) zone formation due to the annihilation of excess vacancies at the thermal misfit dislocations. Formerly Graduate Student, Department of Metallurgical and Materials Engineering, Michigan Technological University