ESCA Techniques Research Articles

Thermal prehistory, structure and high-temperature thermodynamic properties of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions

Ceria-based solid solutions are important materials for high- and medium-temperature electrochemical applications. However, the stabilities of both binary and ternary ceria-based solid solutions are insufficient at elevated temperatures, which limits their application as solid electrolytes or SOFC cathodes. Data on the high-temperature stability of ceria-based ceramics are unavailable in the literature. In the present study, we report a thermodynamic stability investigation of Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions. The thermal prehistories of binary and ternary systems were investigated using STA, XRD, and ESCA techniques. The vaporization processes were investigated in the temperature range of 1577–2227°С via the Knudsen effusion mass spectrometry technique. Using data on the component activity in solid-phase thermodynamic properties of Y2O3-CeO2 solid solutions, which is represented as the Gibbs energy, the excess Gibbs energy was calculated as a function of the ceria mol. %. It was shown that the reduction of Ce4+ to Ce3+ in Y2O3-CeO2 and Y2O3-ZrO2-CeO2 solid solutions corresponds to less-negative Gibbs energy compared to ZrO2-CeO2 solid solutions.

Phase formation, stability and heat capacity of ternary TiO2–CeO2–ZrO2 solid solutions

Tetragonal zirconia based solid solutions are important materials for thermal barrier coatings (TBCs). The introduction of the third component to binary zirconia systems is regarded as a promising way to design novel high performance TBCs. The work reports the investigation of solid solution formation in ternary TiO2–CeO2–ZrO2 system in the range 600–1100 °C obtained by using co-precipitation from mixed aqueous solution and freeze-drying. Phase evolution and stability of solid solutions were investigated using DSC, qualitative and quantitative XRD analysis with Rietveld refinement technique. The factors affecting the kinetics of phase formation i.e. powders dispersity, agglomerate strength, crystallite size, Ce3+/Ce4+ ratio were studied using PSD, XRD and ESCA techniques. The heat capacity dependence on temperature was measured experimentally for the first time for 5TiO2–9CeO2–86ZrO2 composition via calorimetry technique using DSC. The obtained data significantly contributes to the schematic phase diagram suggested in the literature and allows to choose the optimal synthesis and processing conditions of ternary system compositions for their use for novel TBCs fabrication.

Starch-based bio-latex redistribution during paper coating consolidation

Starch-based bio-latex has been widely studied for the purpose of partially substituting petroleum-based latex as coating binder due to its environmental-friendly and sustainable natures. To engineer coating structure, it is essential to understand the bio-latex distribution during coating layer drying. In this work, bio-latex concentration at the surface and along the thickness direction of model coatings on a non-absorbent film consolidated under various conditions was detected with ATR-IR, ESCA and Cryo-SEM techniques in order to understand whether bio-latex redistribute during coating drying and how the migration occurs. The results showed that bio-latex particles moved differentially with respect to kaolin clay pigment toward the coating surface and accumulated at surface during the initial liquid drying period, however, they deprived from coating surface in the end and aggregated at the top region of coating layer. A mechanism was proposed to explain this unexpected finding, which was attributed to the sphere-like morphology with nano or submicron size and highly hydrophilic, water-swollen natures of starch-based bio-latex binder. The small-sized bio-latex particles migrated to the surface due to their higher Brownian mobility relative to pigment initially, and in the later drying stage would move back into the coating pores with water because of its water affinity as the air-water interfaces receded from the surface into the capillaries.

Dithiobiurets as Corrosion Inhibitors for Copper in 3.5% NaCl Solution

The inhibition of copper corrosion in 3.5% NaCl solution has been studied at 25 o C using three inhibitors: 1-phenyl-2,4-dithiobiuret(Inh I), 1-p-methoxyphenyl-2,4dithiobiuret(Inh II) and 1-p-chlorophenyl-2,4-dithiobiuret(Inh III). The inhibition efficiencies of these compounds have been evaluated by weight loss and electrochemical methods (impedance spectroscopy and polarisation curves). The surface study was done by using SEM and ESCA techniques. The inhibition efficiencies of the inhibitors follow the sequence Inh II > Inh I > Inh III. The inhibitors Inh I, Inh II and Inh III appear to inhibit corrosion process through the formation of a protective film which was found to consist of Cu(I)-inhibitor complex, cuprous chloride CuCl or CuCl2 complex ions or both on the surface. .

Preparation of poly(ethylene glycol)-grafted silica nanoparticles using a facile esterification condensation method

Organic–inorganic hybrid nanoparticles have been prepared by the direct facile esterification condensation under extremely mild conditions as ambient temperature, moisture and atmospheric pressure, and the resulting composite particles are characterized by ESCA, FTIR, TEM, DLS, TGA, DSC, and XRD techniques. Results show that this facile graft method has high graft efficiency and the grafted poly(ethylene glycol) (PEG) accounts for about 55 wt% of the total silica composites. The resulting silica nanoparticles have core-shell structure with PEG on the outside and SiO2 in the core. As a result, the dispersion behavior of nanoparticles and the thermal stability of the grafted PEG are improved by the formation of covalent ester bonds between PEG and the reactive silica nanoparticles. The PEG phase, however, is disturbed by the proximity of the oxide phase of SiO2. Consequently, less crystal or faulty crystal of PEG is resulted when PEG is grafted onto the surfaces of silica nanoparticles.

Silicone-containing hybrid polymer dispersions designed for coating applications

The results of studies on novel aqueous silicone-containing hybrid polymer dispersions of specific architecture designed for coatings are presented. Dispersions were synthesized either via polymerization of acrylic and styrene monomers in aqueous poly(siloxaneurethaneurea) anionic dispersions prepared from the mixture of polysiloxanediol, saturated polyol and unsaturated polyol and cycloaliphatic diisocyanate or via polymerization of silicone monomers in commercially available acrylic copolymer dispersions. The effect of structural parameters of the hybrid polymers with constituted dispersion particles on the properties of dispersions, films and coatings was studied and it was found that they were significantly influenced by the share and kind of silicone component. More detailed studies of surface properties of the coatings using wettability determinations (DCA, SFE), ESCA, and AFM techniques revealed self-assembling of the surface layers depending on the chemical composition of the polymers constituting the hybrid system. The results show, that the macro-scale properties of hybrid materials (combination of organic polymers and silicones) can be tailored to the demands of particular application through designing of the specific micro- or even nano-scale architecture of the hvbrid svstem.

Plasma-Enhanced Modification of Xanthan Gum and Its Effect on Rheological Properties

The structure and rheological properties of xanthan gum (XG) modified in a cold plasma environment were investigated. XG was functionalized in a capacitively coupled 13.56-MHz radio frequency dichlorosilane (DS)-plasma conditions and, consecutively, in situ aminated by ethylenediamine. The surface structure of modified XG was evaluated on the basis of survey and high-resolution ESCA, FTIR, and fluorescence labeling techniques. The types of species generated in DS-plasma were reported using residual gas analysis (RGA). The aqueous solutions of modified XG were cross-linked and cured at room temperature to form stable gels. The dynamic rheological characteristics of virgin XG and functionalized and cross-linked XG were compared. It was found that parameters such as plasma treatment time and concentration of solutions can be optimized to form stable gels of XG. Thus, cold plasma technology is a novel, efficient, and nonenzymatic route to modify XG.

New Pathways for Modifying the Surface of High Density Polyethylene: Chemically Benign Adhesion Promotion and Subsequent Reactivity

The surface of high density polyethylene (HDPE) was modified using a two-step chemical process. HDPE panels were initially immersed in a heated, aqueous hypochlorite solution containing a carboxylic acid promoter and quenched with deionized water at room temperature following a heterogeneous chemical reaction process patented by Beholz (U.S. Patents 6,077,913 and 6,100,343). 1-5 mole percent chlorine heteroatoms were identified on the resulting HDPE surface using ESCA techniques. The surface chlorine concentration was optimized as a function of reaction time, reaction stoichiometry and number of repeated chemical treatments. The chlorinated HDPE surface was subsequently exposed to ultra-violet (UV) light and surface alkene moieties were noted using ATR FT-IR methods along with a concomitant reduction in surface chlorine from ESCA measurements. The photochemically induced free radical surface dehydrochlorination mechanism was observed to follow first-order kinetics and potentially produce a focussed pattern for information storage. Facile subsequent reactivity of the isolated surface alkene groups was demonstrated using electrophilic addition of Br2. Furthermore, poly(4-hydroxy styrene) architectures were covalently tethered to either the chlorinated or unsaturated HDPE surface in an effort to ultimately tailor surface polarity and adhesiveness as well as create laminate poly(α-olefin) containing structures. This economical and benign surface chlorination/photochemical two-step treatment process produced relatively small disposal risks as well as no apparent polymer degradation.

Studies of sulfonated polyethylene for biliary stent application

AbstractPalliative treatment for obstructive jaundice by endoscopic biliary stent insertion is a recent commonly used method. Unfortunately, stent reobstruction may occur within 3 to 6 months as a result of bacterial adhesion and formation of biofilm. Bacterial adhesion was postulated as the initial step of stent clogging and the bacterial enzyme activity of β‐glucuronidase led to the deposition of calcium bilirubinate. In this study, surface sulfonation of the polyethylene lumen was postulated to improve the patency of the biliary stent. Surface modification with sulfonated group formation was carried out with fuming sulfuric acid containing 20 wt % sulfuric trioxide (SO3). The reaction time varied from 1 to 3 h at room temperature. ATR‐FTIR and ESCA techniques showed that the surface amount of sulfonated functionalities increased with sulfonation time. The contact angle of the sulfonated PE, determined by the sessile drop technique, decreased compared to that of unmodified PE, but cannot be detected by the captive bubble method because of the high surface hydrophilicity. SEM micrographs indicated that the sulfonated PE inner lumen remained relatively smooth after extended sulfonation reaction. Adhesion of Escherichia coli to the sulfonated PE stents after 48‐h bile perfusion was about 10‐ to 20‐fold less than that to the unmodified PE, as observed by SEM and surface spreading method. These results indicated that the surface sulfonated groups could effectively decrease the adhesion of E. coli in human bile, probably attributable to the hydrophilic repellence between the bacterial cell membrane and sulfonated groups. This finding suggested that the sulfonated PE tubing could prolong the patency period of plastic stents and may be of great potential as a biliary stent in a real clinical setting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2450–2457, 2004

Surface Characterization of Unbleached and Oxygen Delignified Kraft Pulp Fibers

The chemical and morphological surface properties of different unbleached and oxygen delignified softwood kraft pulp fibers were evaluated by using different ESCA and SEM techniques. The results of the different techniques have revealed that the surface of unbleached and oxygen delignified kraft pulp fibers has a higher content of lignin and in some cases also extractives, in comparison with the bulk of the fibers. However, the amount of lignin obtained on the fiber surfaces differs substantially from one technique to another. The mercurization technique (mercurization followed by the determination of mercury by ESCA) gave about three to five times lower values on the surface coverage of lignin, in comparison with the normal ESCA procedure. Good correlation between the surface coverage of lignin and the total amount of lignin was obtained for all techniques, however, the best correlation was obtained for the mercurization technique. The results also show that the total and surface charges of the unbleached and oxygen delignified pulp fibers decreased with a decrease in kappa number and that the extent of fibrillation increased with a decrease in kappa number.

Application of TOF-PDMS and ESCA techniques to the characterization of phosphate layers

Application des techniques ToF-PDMS et ESCA a la caracterisation des couches de phosphates. La spectrometrie de masse par temps de vol des produits de l'emission ionique secondaire a ete effectuee avec un grand succes sur des aciers Fe-Si qui ont subi un traitement de prephosphatation. Aussi bien en emission negative que positive, nous avons pu detecter des ions caracteristiques de la couche prephosphatee : PO 2 'et PO 3 ' (pour l'emission negative), Na + et Na 2 OH + (pour l'emission positive). Ceci montre les possibilites d'analyses qualitatives de la technique PDMS pour l'etude des traitements de phosphatation des aciers. Les deux techniques utilisees au cours de cette etude (PDMS et ESCA) se sont averees tres complementaires. Elles nous ont permis de montrer que le rincage de la couche prephosphatee conduit d'une part a la conservation du phosphate de manganese a la surface et, d'autre part, a l'elimination de la couche de phosphate de sodium presque totalement.

Development and tests of B 4C-covered heat shields for TJ-II

The Neutral Beam Injection System for the Spanish Stellarator will start in 2001. This heating system consists of two beam lines and will inject about 2 MW into the plasma. The ‘groove region’ of the vacuum vessel (Proc. 18th Symp. On Fusion Technol. (1994) 771) will be exposed to thermal loads as high as 5 MW/m 2 (Fus. Technol. Vol. 35, (1999)). A heat resistant material must cover the present stainless steel groove protection plates. Plasma-sprayed boron carbide (B 4C) seems to fulfil all the requirements, in addition needs little room and therefore does not reduce the size of the plasma. The development of the B 4C-covered plates was done in two steps. In the first one, stainless steel plates with simplified geometry were covered with B 4C and tested at the JET Neutral Beam Test Bed. To analyse damages after the tests, surface analysis by means of SEM, ESCA and Auger techniques have been done at Ciemat. The second step comprises the plasma spraying of stainless steel plates with the real geometry. In order to achieve a sufficiently good adhesion of the B 4C-layer an intermediate layer of NiCr was sprayed. Standard tests of these plates at the manufacturer have successfully been terminated. The heat load cycling remains to be done in the near future.

The role of tartrate ions in the phosphonate based inhibitor system

Corrosion of steel in oxygen saturated environment is inhibited by insoluble products, with the metals ions existing in the solution, which precipitate on the surface to form a three-dimensional protective layer. Addition of tartrate with organophosphonic acid (2-carboxyethylphosphonic acid) and zinc metal cation enhances the inhibition efficiency of steel in neutral environment. Using weight change method, polarization and AC impedance techniques determined the inhibition efficiencies. The composition of the protective layer was determined by using UV–VIS reflectance, UV–VIS luminescence and ESCA techniques.

Surface modification of polyethylene membranes using phosphorylcholine derivatives and their platelet compatibility

To fabricate a platelet-compatible polymer, phosphorylcholine (PCe) was introduced onto the surface of polyethylene (PE) using a novel synthetic process. Acrylic acid was graft-copolymerized on the surface of PE by UV irradiation, using both the peroxide preirradiation and the simultaneous methods. Benzophenone and Michler's ketone were used as an initiator and sensitizer in this investigation, respectively. To investigate the spacer effect on the platelet compatibility of the PE membrane surface, PCe with various spacer lengths was introduced onto the surface of PE by a series of chemical reactions. Ethylene glycol, butanediol, poly(propylene glycol), and poly(tetramethyl glycol) were used as spacers. The modifications of the PE membrane surface were analyzed by contact-angle, ATR-FTIR, and ESCA techniques. The platelet compatibility of the PCe-modified polymer was evaluated by the in vitro platelet adherent test. It was found that the platelet compatibility of the PE film surface was affected by the existence of various functional groups on the film surface. The length of the lipophilic spacer between PCe groups and the PE surface will affect the biomimetic properties of the membrane surface.

Methane conversion to syngas over Pt-based electrode in a solid oxide fuel cell reactor

Electrocatalytic oxidation of methane over Pt-based electrode-catalyst in a solid oxide fuel cell reactor CH 4 Pt0.9ZrO 2+0.1Y 2O 3|Pt, air was studied at 800°C and atmospheric pressure. SEM and ESCA techniques were used to characterize the electrode-catalyst. It is found that the Pt-based electrode is an active electrode-catalyst for partial oxidation of methane (in a diluent absence) to syngas, concentration ratio being [H 2]/[CO]≈2. Methane conversion and carbon monoxide selectivity attained 97% and 95%, respectively. Under these conditions, reactor is operated in a fuel cell mode and the electrode-catalyst is stable (to coking, too).

Structure of Molybdenum Supported on α-, γ-, and χ-Aluminas in Relation to Its Epoxidation Activity

The structures of Mo supported on α-, γ-, and χ-aluminas were analyzed by ESCA, XRD, IR, and XAFS techniques, and the relationship between the structure of Mo and its catalytic activity for the epoxidation of allyl alcohol was discussed. The ranges of the Mo-monolayer formation as estimated by the ESCA technique were less than 18, 15, and 1 wt% of Mo-loading for γ-, χ-, and α-aluminas, respectively. However, MoO3was detected by an XRD analysis at 10 wt% of Mo-loading for γ- and χ-aluminas; the ESCA technique overestimated the range of the monolayer. The monolayer on γ- and χ-aluminas as apparently determined by the ESCA analysis consisted of isolated tetrahedral Mo, octahedral polymolybdate, and a small amount of MoO3. The monolayer on α-alumina contained only tetrahedral Mo-species. MoO3was predominantly formed after the completion of the monolayer on all aluminas. The epoxidation activity of Mo was low in the monolayer region; especially, isolated tetrahedral Mo was completely inactive. MoO3was the most active species for the epoxidation, and peroxo-type oxygen bound to Mo was deduced to be the active species.

Laser Damage Studies of Silver Gallium Sulfide Single Crystals

AbstractAlthough AgGaS2 single crystals have desirable optical and nonlinear properties, the low laser damage threshold has limited their application for tunable infrared laser sources. Crystals have been studied by ESCA and Auger techniques and the surface of polished crystals has been found to be silver deficient, while the bulk composition is closer to stoichiometry.

Emission from Zeolite‐Occluded Manganese–Diimine Complexes

Manganese complexes of 2,2'-bipyridine (bpy) and 1,10-phenantroline (phen) have been synthesised in the supercages of cubic NaX and NaY and in the hypercages of the hexagonal NaEMT faujasites. The coordination and redox chemistry were studied with ESCA, CA, FT-IR, FT-Raman, diffuse reflectance and emission techniques. FT-IR/FT-Raman shows cis coordination for all complexes and a high Mn-N stretching frequency in the phen complexes as a result of steric constraints imposed by the ligand. [Mn(bpy)2 ]2+ in the different zeolites shows metal-to-ligand charge transfer (MLCT; at 495 nm); for [Mn(phen)2 ]2+ -NaY the MLCt is broadened owing to complex distortion. On MLCT excitation [Mn(bpy)2 ]2+ complexes show an ipsochromic shift in the emission and an increase in quantum yield with increasing steric restrictions imposed by the zeolite. The ipsochromic shift of the emission band of [Mn(phen)2 ]2+ in NaY results from the combined effect of the ligand field (this suggests emission from a CT state) and of coordinative distortion. The key factor influencing the emission properties is found to be the overall matrix-induced complex distortion. Cation stabilisation of the ligand anion affects emission indirectly. The decay times for [Mn-(bpy)2 ]2+ -NaY are in the millisecond range (7.5-11.5 ms). A proposed model for excitation and emission properties of zeolite-occluded MnII complexes involves excitation of a quartet CT state, intersystem crossing and subsequent emission. The enhanced stability of the coordination sphere in the zeolite allows complexes to luminesce from a CT state, which is not detected in solution. The zeolite behaves as a supramolecular cryptating agent, protecting complexes from photodissociation.

Comparison of the Reactivity of Different Sodium Compounds and Ca(OH)2 Towards SO2 and Mixtures of SO2 and NOx

The reactivity of solid substances towards acid gases (SO2, NOx) was studied with a view to finding the best conditions for an efficient removal of the gases. The solids included various sodium compounds (sodium bicarbonate, active soda, sodium carbonate monohydrate, dense soda ash) and Ca(OH)2, and the reaction with sulfur dioxide was examined over a broad range of experimental variables (temperature, gas composition). The reactivity of selected samples was also investigated in reactions with gaseous mixtures containing SO2 and NOx in the dependence on temperature, the SO2/NOx and NO/NO2 ratios and the hydrodynamic conditions of the fixed bed flow reactor. The ESCA and SEM techniques were employed to identify the solid reaction products and to study their evolution as a function of reaction parameters. It was found that with the NaHCO3 precursor, a simultaneous removal of 90% SO2 and nearly 50% NOx is feasible. The results indicate that NaHCO3 shows promise particularly for the purification of waste gases from incinerators and power plants.

ESCA studies on copper-cobalt based catalysts

The copper-cobalt catalysts for alcohol synthesis were prepared and studied by ESCA techniques (XPS and XAES) and TPR. The valence states of the surface elements were investigated for Co−Cu−Y based catalysts, and it was found that there were some reoxidation during the reaction. From the XPS and XAES results, strong interactions between copper and cobalt in the samples were presented, in agreement with the TPR experiments. The interacted copper-cobalt units could be the active sites for higher alcohol synthesis.