Scientific Papers in SCI

Abstract

The catalytic performance of a CuOx/CeO2 powder catalyst and that of a microchannel reactor or microreactor (MR) coated with the same solid was determined and compared. The catalytic activity measurements were carried out with varying O2/CO molar ratios in the feed-stream. In addition, the influence of the presence of CO2 and H2O in the reaction mixture was studied. Some discrepancies were observed between the performances of the powder catalyst and the MR depending on the O2/CO ratio. The MR presented a very good performance with a superior selectivity for CO conversion. This behaviour was due to a more efficient heat removal in the case of the MR that inhibited the H2 oxidation reaction and the r-WGS. The isothermicity of the microreactor during the process was demonstrated through the monitoring of the MR inlet and outlet temperatures.

Concerning the presence of CO2 or H2O in the feed-stream, both compounds gave rise to a decrease of the CO conversion. The negative effect on the catalytic performance was more marked when both compounds were fed together, although the principal inhibitor effect was associated to the CO2. This seems to be related with the formation of stable carbonates at the catalyst surface.

Abstract

MgB2 thin films are prepared by sequential evaporation of boron and magnesium bilayers on SiC buffered Si substrates followed by an in situ annealing. Precursor Mg–B bilayers are deposited by electron beam evaporation at room temperature. The amount of B is varied so as to result in different thickness (15 nm and 50 nm) of stoichiometric MgB2 final film after an in situ reaction with the excess Mg top layer in the vacuum. We show the distribution of the elements through the film.

X-ray photoelectron spectroscopy analyses have shown that carbon is not free in the films (except the surface of the film) and silicon is in the compound form, too. In the case of the 15 nm thick films we see a strong interdiffusion of the elements (C, B) and we observe a suppression of TC of the film to 20 K. We register different slope of the HC2(T)HC2(T) dependence – the lowest temperature value of HC2HC2 for the 15 nm thick film exceeds the one for the 50 nm thick film in spite of lower TC. We suppose that δl pinning mechanism is dominant for the 15 nm thick film.

Abstract

In the present work we have investigated the relationships existing between the optical properties and the growth mechanism, microstructure and surface roughness of SnO2 and ZnO oxide films prepared by magnetron sputtering under conditions resembling those utilized in industry. Thin films of these oxides with different thicknesses were characterized by atomic force microscopy, glancing incidence X-ray diffraction (GIXRD), X-ray reflectometry and spectroscopic ellipsometry. The roughness evolution of the film properties (density, surface roughness and refraction index) as a function of their thickness has been evaluated within the concepts of the Dynamic Scaling Theory of thin film growth. Zinc oxide films were rougher than tin oxide films of similar thickness, indicating a different growing mechanism for the two materials. Silver was evaporated onto the surface of the two oxide thin films and its earlier stages of nucleation studied by background analysis of the X-ray photoemission spectra. A different nucleation mechanism was found depending on the nature of the oxide acting as substrate. The superior performance of the zinc oxide based low emissive coatings is related with a better wetting of silver on the surface of this oxide despite the comparatively lower roughness of the tin oxide layers.

Abstract

A series of oxidised copper-cerium nanostructured catalysts prepared by impregnation of copper over ceria supports synthesized by different methods (hydrothermal with varying preparation parameters, microemulsion/precipitation), in order to achieve different specific morphologies (nanocubes, nanorods and nanospheres), have been examined with respect to their catalytic properties for preferential oxidation of CO in excess H2 (CO-PROX). The catalysts have been characterized in detail by XRD, Raman, SBET measurement, HREM, XPS, TPR and EPR, which allows establishing a model of structural characteristics of the catalysts. The characterization results have been correlated with analysis of CO-PROX catalytic properties by means of catalytic activity measurements complemented by operando-DRIFTS. Structural dependence of the CO oxidation reaction on the dispersed copper oxide entities as a function of the exposed face present at the surface of the different ceria supports is revealed. An important overall enhancement of the CO-PROX performance is detected for the sample supported on ceria nanocubes which is proposed to be a consequence of the interaction between copper oxide and (1 0 0) faces of the ceria support.

Abstract

TiO2-based photocatalyst materials were synthesized through a sol–gel method, followed either by: (1) hydrothermal treatment (150 °C/24 h), or (2) heat treatment (calcination) in a temperature range between 400 and 900 °C. The resulting materials were characterized through BET, XRD, TEM, FTIR, RAMAN, laser diffraction and UV–Vis Diffuse Reflectance Spectroscopy. Photoactivity of the various materials was checked against photocatalytic water-splitting for hydrogen production and a relationship between TiO2 structure and hydrogen production capacity was identified. Optimum results were obtained for anatase-rutile mixtures in a ratio of 87:13. The activity of the home-made photocatalysts was also compared (under the same conditions) with the best commercially available materials which have been widely described in the literature: Hombikat UV100, Millenium PC100, Kronos vlp7000,Degussa P25and Kemira 625.

Abstract

g-C3N4 and TiO2 hybrid structures are synthesized by means of a simple impregnation method having good photoactivities for the degradation of phenol under UV irradiation. From the wide structural and surface characterization we have stated that the presence of g-C3N4 notably affect the surface feature of TiO2 (surface area and pore size distribution). Enhanced photoactivities have been obtained for composites systems. The best result was obtained for 2 wt% loading of g-C3N4 leading to a 70% of improvement with respect to bare TiO2 in the reaction rate. The effective charge carrier separation was proposed as the responsible of such improved photoactivity.

Abstract

Silver nanoparticles (NPs) depicting well defined surface plasmon resonance (SPR) absorption were deposited on flat substrates by physical vapor deposition in a glancing angle configuration. The particles were characterized by scanning electron microscopy and atomic force microscopy and their optical properties examined by UV–vis absorption spectroscopy using linearly polarized light. It was found that, depending on the amount of deposited silver and the evaporation angle, part of the 'as-prepared' samples present NPs characterized by an anisotropic shape and a polarization dependent SPR absorption and different colors when using polarized white light at 0° and 90°. Low-power irradiation of these materials with an infrared Nd-YAG nanosecond laser in ambient conditions produced an enhancement in such dichroism. At higher powers, the dichroism was lost and the SPR bands shifted to lower wavelengths as a result of the reshaping of the silver NPs in the form of spheres. The possible factors contributing to the observed changes in dichroism are discussed.

Abstract

Europium-doped calcium hydroxyapatite and fluoroapatite nanophosphors functionalized with poly(acrylic acid) (PAA) have been synthesized through a one-pot microwave-assisted hydrothermal method from aqueous basic solutions containing calcium nitrate, sodium phosphate monobasic, and PAA, as well as sodium fluoride in the case of the fluoroapatite particles. In both cases a spindlelike morphology was obtained, resulting from an aggregation process of smaller subunits which also gave rise to high specific surface area. The size of the nanospindles was 191 (32) × 40 (5) nm for calcium hydroxyapatite and 152 (24) × 38 (6) nm for calcium fluoroapatite. The luminescent nanoparticles showed the typical red luminescence of Eu3+, which was more efficient for the fluoroapatite particles than for the hydroxyapatite. This is attributed to the presence of OH– quenchers in the latter. The nanophosphors showed negligible toxicity for Vero cells. Both PAA-functionalized nanophosphors showed a very high (up to at least 1 week) colloidal stability in 2-(N-morpholino)ethanesulfonic acid (MES) at pH 6.5, which is a commonly used buffer for physiological pH. All these features make both kinds of apatite-based nanoparticles promising tools for biomedical applications, such as luminescent biolabels and tracking devices in drug delivery systems.

Abstract

Background

This paper provides some clarifications regarding the use of model-fitting methods of kinetic analysis for estimating the activation energy of a process, in response to some results recently published in Chemistry Central journal.
Findings

The model fitting methods of Arrhenius and Savata are used to determine the activation energy of a single simulated curve. It is shown that most kinetic models correctly fit the data, each providing a different value for the activation energy. Therefore it is not really possible to determine the correct activation energy from a single non-isothermal curve. On the other hand, when a set of curves are recorded under different heating schedules are used, the correct kinetic parameters can be clearly discerned.
Conclusions

Here, it is shown that the activation energy and the kinetic model cannot be unambiguously determined from a single experimental curve recorded under non isothermal conditions. Thus, the use of a set of curves recorded under different heating schedules is mandatory if model-fitting methods are employed.
 

Abstract

This study reports the use of 1-butyl-3-methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template-framework system and location of the template provides further insight into the mechanism of synthesis.

Abstract

The thermopower coefficients of bio-SiC and SiC/Si ecoceramics prepared from sapele tree wood have been measured in the temperature interval 5–300 K. The measurements have been performed both along and perpendicular to empty (bio-SiC), as well as empty and partially silicon-filled (SiC/Si) channels in the samples. In bio-SiC, a contribution to thermopower associated with electron drag by phonons has been shown to exist within the temperature interval 5–200 (250) K. No such effect is realized in SiC/Si. This is assumed to derive from the presence in this material of heavily doped silicon embedded in SiC channels and the dominant part it plays in the behavior of the thermopower of this ceramics. The results obtained for the thermopower are compared with the available data for bio-SiC prepared from white eucalyptus tree wood and heavily doped bismuth.

Abstract

A simple and fast (7 min) procedure for synthesis of gadolinium phosphate nanocubes (edge = 75 nm) based on the microwave-assisted heating at 120 °C of gadolinium acetylacetonate and phosphoric acid solutions in buthylene glycol is reported. These nanocubes were highly crystalline and crystallized into a tetragonal structure, which has not been ever reported for pure gadolinium phosphate. Determination of such crystal structure has been carried out here for the first time in the literature by means of powder X-ray diffraction. The developed synthesis procedure was also successful for preparation of multifunctional europium(III)-doped the gadolinium phosphate nanocubes, which were nontoxic for cells and exhibited strong red luminescence under UV illumination and high transverse relaxivity (r2) values. These properties confer them potential applications as biolabels for in vitro optical imaging and as negative contrast agent for magnetic resonance imaging.

Abstract

Nanocrystalline SnS powder has been prepared using tin chloride (SnCl₂) as a tin ion source and sodium sulfide (Na₂S) as a sulfur ion source with the help of ultrasound irradiation at room temperature. The as-synthesized SnS nanoparticles were quantitatively analyzed and characterized in terms of their morphological, structural, and optical properties. The detailed structural and optical properties confirmed the orthorhombic SnS structure and a strongly blue shifted direct band gap (1.74 eV), for synthesized nanoparticles. The measured band gap energy of SnS nanoparticles is in a fairly good agreement with the results of theoretical calculations of exciton energy based on the potential morphing method in the Hartree–Fock approximation.

Abstract

This work reports the electrochromic evaluation of WxSiyOz and WOx glad thin films deposited by reactive magnetron sputtering at glancing angle. Their electrochemical properties were assessed by the analysis of cyclic voltammetry and chronoamperometry measurements in 0.1 M HClO4, whereas their optical properties were determined by studying their transmission and absorption spectra under operation conditions. Both types of thin films presented outstanding electrochromic properties characterized by a fast response, a high coloration and a complete reversibility after more than one thousand cycles.

Abstract

A fully comprehensive study of the tribological behavior of palladium nanoparticles (Pd NPs) capped by tetrabutylammonium chains using a ball-on-disk tribometer under different conditions of applied load, concentration, tribometer motion, linear speed and nature of the counterface is revised. A low concentration of NPs (2 wt%) in tetrabutylammonium acetate was found sufficient to improve the tribological properties due to the formation of a protective transfer film (TF) comprised of metallic Pd. The increase of the applied load (up to 20 N, 1.82 GPa of contact pressure) confirmed the excellent extreme-pressure behavior avoiding the counterfaces from severe wear. After a running-in period whose duration depends on the operating conditions, the TF build-up allows to maintain a low contact electrical resistance through the contact (<0.1 kΩ) during the entire test. When the Pd NPs are used with ceramic counterfaces, the nanoparticles increase the load-bearing capabilities and performance of the base without forming TF, likely by mixed or boundary lubrication and healing effects. Finally, the Pd NPs are demonstrated to be useful as a thin solid lubricant film in reciprocating motion yielding a comparable tribological behavior. Hence, the presented surface Pd NPs can be very helpful to extend life of sliding components due to their high strength resistance providing a gateway to electrical conduction as well.

Abstract

In the present work we determined the chromatic coordinates (L*, a*, b*) and ultrasound propagation speeds on the three spatial planes (Vx, Vy, Vz) of three ornamental granites (Aqueduct of Segovia, Spain) before, during, and after being subjected to 70 cycles of two types of accelerated ageing (typical of cold regions): a) freezing/thawing and cooling/heating (T1), and b) freezing/thawing and cooling/heating + salt crystallization (T2). A multivariate technique (Canonical Biplot) was applied to the data obtained, with the observation of significant variations between the two types of accelerated artificial ageing as compared with those obtained in quarry rock in the three chromatic coordinates (L*, a*, b*). With regard to the ultrasound propagation speed, we only detected differences in the results of the T2 artificial ageing treatment with respect to those of quarry rock. This fact is confirmed by the estimated data of resistance to compression.

Abstract

Monoclinic Tb:CePO4 nanophosphors with a spindle-like morphology and tailored size (in the nanometer and micrometer range) have been prepared through a very simple procedure, which consists of aging, at low temperature (120 °C), ethylene glycol solutions containing only cerium and terbium acetylacetonates and phosphoric acid, not requiring the addition of surfactants or capping agents. The influence of the heating mode (conventional convection oven or microwave oven) and the Tb doping level on the luminescent, structural and morphological features of the precipitated nanoparticles have also been analyzed. This study showed that microwave-assisted heating resulted in an important beneficial effect on the luminescent properties of these nanophosphors. Finally, a procedure for the functionalization of the Tb:CePO4 nanoparticles with aspartic-dextran is also reported. The functionalized nanospindles presented negligible toxicity for Verocells, which along with theirs excellent luminescent properties, make them suitable for biomedical applications.

Abstract

This paper describes the deep analysis of cerium conversion coatings developed with thermal activation on AA5083 under optimum processing conditions. Scanning electron microscopy (SEM), electron dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were employed to study these layers. Ar+ sputtering was also employed to analyse the coatings' core. Although conversion coatings based on Ce salts have been widely characterised in the literature for different aluminium alloys, the coatings developed with thermal activation on Al–Mg alloys have not been previously investigated with these techniques. SEM/EDX studies have demonstrated the existence of a heterogeneous layer formed by a film of aluminium oxide/hydroxide on the matrix as well as a series of dispersed islands of cerium deposited on the cathodic intermetallics. These results have been further confirmed by means of XPS. The XPS and AES results revealed that the outer layer comprises a mixture coating of Ce3 + (70%) and Ce4 + (30%) compounds. Although only Ce3 + compounds were detected at the inner part of the coating, possible reduction of Ce(IV) to Ce(III) due to the Ar+ beam could not be discarded. Obtained results allowed authors to confirm that the cerium conversion coatings developed have a similar structure to those previously reported for other aluminium alloys.

Abstract

Nanoporous silica microparticles (NSiO2-MP) are considered to be potential drug delivery systems and scaffolding platforms in tissue engineering. However, few biocompatibility studies regarding NSiO2-MP interaction with the immune system have been reported. Toll-like receptors (TLR) are involved in host defence as well as autoimmune and inflammatory diseases. The results show that NSiO2-MP up to 100 μg ml−1 do not affect macrophage cell viability after 24 h cell culture. Moreover, NSiO2-MP do not compromise the cell viability of TLR-activated Raw 264.7 cells, for either cell surface TLR (TLR1/TLR2/TLR4/TLR6) or endocytic compartment TLR (TLR3/TLR7/TLR9). Furthermore, Raw 264.7 cells do not respond to NSiO2-MP exposure in terms of IL-6 or IL-10 secretion. NSiO2-MP co-treatment in the presence of TLR ligands does not impair or enhance the secretion of the pro-inflammatory cytokine IL-6 or the regulatory cytokine IL-10. Thus, NSiO2-MP do not affect macrophage polarization towards a pro-inflammatory or immunosuppressive status, representing added value in terms of biocompatibility compared with other SiO2-based micro- and nanoparticles.

Abstract

A systematic study of [M(H2O)n(OH)m]q+ complexes of Te(IV) and Bi(III) in solution has been undertaken by means of quantum mechanical calculations. The results have been compared with previous information obtained for the same type of Po(IV) complexes ( J. Phys. Chem. B 2009, 113, 487) to get insight into the similarities and differences among them from a theoretical view. The evolution of the coordination number (n + m) with the degree of hydrolysis (m) for the stable species shows a systematic decrease regardless the ion. A general behavior on the M–O distances when passing from the gas phase to solution, represented by the polarizable continuum model (PCM), is also observed: RM–O values corresponding to water molecules decrease, while those of the hydroxyl groups slightly increase. The hydration numbers of aquaions are between 8 and 9 for the three cations, whereas hydrolyzed species behave differently for Te(IV) and Po(IV) than for Bi(III), which shows a stronger trend to dehydrate with the hydrolysis. On the basis of the semicontinuum solvation model, the hydration Gibbs energies are −800 (exptl −834 kcal/mol), −1580 and −1490 kcal/mol for Bi(III), Te(IV), and Po(IV), respectively. Wave function analysis of M–O and O–H bonds along the complexes has been carried out by means of quantum theory of atoms in molecule (QTAIM). Values of electron density and its Laplacian at bond critical points show different behaviors among the cations in aquaions. An interesting conclusion of the QTAIM analysis is that the prospection of the water O–H bond is more sensitive than the M–O bond to the ion interaction. A global comparison of cation properties in solution supplies a picture where the Po(IV) behavior is between those of Te(IV) and Bi(III), but closer to the first one.

Abstract

Catalysed sodium borohydride hydrolysis is a high-potential method to produce hydrogen for portable applications. Co–B catalysts are the most chosen because they are easily prepared, cheap and efficient. The addition of small amounts of Ru produces a significant enhancement in catalytic activity.

In the present work a series of Co–Ru–B catalysts with variable Ru content was prepared, isolated and characterized. The comprehension of the synergistic effect was achieved trough the incorporation of the nanostructural dimension to the study of surface and bulk chemical states of the involved atoms along the series. It was found that up to 70% (of total metal) atomic content of Ru the catalysts can be considered isostructural to the single Co–B catalyst in the nanoscale. A structural transition occurs in the case of the pure Ru–B material to produce a boron deficient material with higher nanoparticle size. This structural transition together with Co segregation and Ru dispersion play a key role when explaining a [OH−] dependent effect.

The inexistence of borate layers in Ru rich catalysts is suggestive in the research for non deactivating catalysts.

Abstract

In this paper, the possibility of mechano-chemical synthesis, as a single step process for preparation of nanostructured nickel aluminate spinel powder from NiO/Al2O3 spent catalyst was investigated. Powder samples were characterized in terms of composition, morphology, structure, particle size and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and volumetric adsorption of nitrogen. It was found that formation of spinel was possible after 60 h of milling with no heat treatment. Additionally, influence of mechanical activation on the heat treatment temperature was discussed. It was observed that heat treatment of 15 h milled sample at 1100 °C is enough to produce nickel aluminate spinel. A product of direct mechanical milling showed higher value of surface area (42.3 m2/g) and smaller crystallite size (12 nm) as compared to the heat treated product.

Abstract

NiO/8YSZ (8 mol% Y ₂O ₃-stabilized ZrO ₂) composites with different NiO contents (10, 20 and 40 mol%) have been fabricated by a conventional route of mechanical mixing of NiO and 8YSZ powders and sintering at 1500 °C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. In 10 and 20 mol% NiO/8YSZ, the composite is formed by isolated NiO particles surrounded by zirconia matrix grains; this phase is interconnected in the 40 mol% NiO/8YSZ composite. Mechanical tests at constant strain rate and at constant load were conducted on these materials at temperatures of up to 1350 °C. Different behaviors were found depending on the percolation of the NiO phase. Microstructural observations after deformation are essential to understand the overall mechanical behavior of the composites.

Abstract

The influence of PVP on the magnetic properties of NiSn nanoparticles prepared by polyol method has been studied. NiSn nanoparticles exhibit superparamagnetic behavior although there is a ferromagnetic contribution due to particles agglomerated below the blocking temperature. The particle size is controlled by the addiction of PVP in varying amounts. The addition of PVP also favours the particles isolation, narrow the particle size distribution and decrease the interparticle interaction strength increasing the superparamagnetic contribution.

Abstract

In this work, the carboxylic acid derivatives of a free-base porphyrin, 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin, and 10 of its metal derivatives (TCPPs) have been used for optical gas sensing. For this purpose, microstructured columnar TiO2 thin films prepared by GAPVD (glancing angle physical vapor deposition) have been used as host materials for the porphyrins as they are non–dispersive and porous, allowing their use for UV–visible spectroscopy and gas sensing. The chemical binding between the dye molecules and the TiO2 has been studied through infrared spectroscopy, and the obtained spectral changes have been found to be compatible with chelating and/or bidentate binding modes of the carboxylate groups on the TiO2 surface. When hosted in the film, the UV–visible spectra of the porphyrins featured a blue shift and broadening of the Soret band with respect to the solution, which has been attributed to the formation of π–π aggregates between porphyrin molecules. The composite porphyrin/TiO2 films obtained from each of the 11 porphyrins have been exposed to 12 different volatile organic compounds (VOCs), and their respective gas–sensitive properties have been analyzed as a function of the spectral changes in their Soret band region in the presence of the analytes. The set of composite films has shown high selectivity to the analyzed volatile compounds. For each analyte, an innovative way of showing the different responses has been developed. By means of this procedure, an imagelike recognition pattern has been obtained, which allows an easy identification of every compound. The kinetics of the exposure to several analytes showed a fast, reversible and reproducible response, with response times of a few seconds, which has been attributed to both the sensitivity of the porphyrins and the high porosity of the TiO2 films. Also, increasing concentrations of the analytes resulted in an increase in the magnitude of the response, indicating that the sensor behavior is also concentration-dependent.

Abstract

The pore size distribution of mesoporous thin films is herein investigated through a reliable and versatile technique coined specular reflectance porosimetry. This method is based on the analysis of the gradual shift of the optical response of a porous slab measured in quasi-normal reflection mode that occurs as the vapor pressure of a volatile liquid varies in a closed chamber. The fitting of the spectra collected at each vapor pressure is employed to calculate the volume of solvent contained in the interstitial sites and thus to obtain adsorption–desorption isotherms from which the pore size distribution and internal and external specific surface areas are extracted. This technique requires only a microscope operating in the visible range attached to a spectrophotometre. Its suitability to analyze films deposited onto arbitrary substrates, one of the main limitations of currently employed ellipsometric porosimetry and quartz balance techniques, is demonstrated. Two standard mesoporous materials, supramolecularly templated mesostructured films and packed nanoparticle layers, are employed to prove the concept proposed herein.

Abstract

NiO/8YSZ (8 mol% Y2O3-stabilized cubic ZrO2) and NiO/3YTZP (3 mol% Y2O3-stabilized tetragonal ZrO2) composites with different NiO contents have been fabricated by a conventional route of mechanical mixing of NiO and zirconia powders and sintering at 1500 °C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. The composites show a duplex microstructure formed by equiaxed grains of NiO and ZrO2, without any intermediate phase. Compressive mechanical tests at constant strain rate were carried out at temperatures between 1150 and 1350 °C under different environments: air, inert (Ar) and reducing (5% H2/95% Ar) atmospheres. The overall creep behavior of the composites is essentially controlled by the zirconia matrix, due to the softness of the NiO phase in the experimental conditions used in this study. The creep strength is not affected by oxygen partial pressure. However, a large decrease in creep resistance under reducing conditions was observed in samples submitted to in situ redox cycling.

Abstract

A system with a continuous reactor to produce hydrogen by sodium borohydride hydrolysis was designed and built. The purpose was to test a supported Co–B catalyst durability upon cycling and long life experiments in high conversion conditions. A Stainless Steel monolith was built and calcined to improve adherence. For comparison a Ru–B catalyst was tested upon cycling. Both Co–B and Ru–B catalysts are durable during 6 cycles and then deactivate. A known reactivation procedure has proven to be more effective for the Co–B than for the Ru–B catalyst. This is related to stronger adsorption of B–O based compounds on the Co–B catalyst which is reversible upon acid washing. For the Ru–B catalyst deactivation may be more related to particle agglomeration than to the adsorption of B–O based species. The continuous system enlarges the catalysts durability because of the continuous borate elimination at elevated temperatures.

Abstract

Magnetron sputtered chromium aluminium nitride films are excellent candidates for advanced machining and protection for high temperature applications. In this work CrAlN-based coatings including Y or Zr as dopants (≈ 2 at.%) are deposited by d.c. reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N2 mixtures. The hardness properties are found in the range of 22–33 GPa with H/E ratios close to 0.1. The influence of the dopant element in terms of oxidation resistance after heating in air at 1000 °C is studied by means of X-ray diffraction (XRD), cross-sectional scanning electron microscopy (X-SEM) and energy dispersive X-ray analysis (EDX). The microstructure and chemical bonding are investigated using a transmission electron microscope (TEM) and electron energy-loss spectroscopy (EELS) respectively. The improvement in oxidation resistance as compared to pure CrN coating is manifested in the formation of a Al-rich outer layer that protects the underneath coating from oxygen diffusion. The best performance obtained with the CrAlYN film is investigated by in situ annealing of this sample inside the TEM in order to gain knowledge about the structural and chemical transformations induced during heating.