bluuebunny/crossref_metadata_2025 huggingface dataset:
Consistency of the strontium transport parameters in Boom Clay obtained from different types of migration experiments
Authors: Aertsens Marc , Maesa Norbert , Gompel Marc Van
Published: April 2011

The consistency of migration parameters obtained by different methods is examined for strontium in Boom Clay. In addition to a previous in-situ percolation experiment and electromigration experiments (using an electrical field as driving force), a lab percolation test and two through-diffusion tests (on clay cores of different lengths) have been performed.

All experiments lead to a robust value for the apparent diffusion coefficient of strontium between 5 ? 10−12m2/s and 1 ? 10−11m2/s.

No reliable value is obtained for the product ηR of the diffusion accessible porosity and theretardation factor R. For one of the through-diffusion experiments, the concentration decrease inthe inlet as a function of time was fitted simultaneously with the strontium profile in the clay,leading to a ηR value around 400. Estimating ηR at the inlet/clay interface as the ratio of thebulk concentration and the pore water concentration leads to a similar value. The valuesobtained from the strontium profiles in the percolation and electromigration experiments are inline as well. However, fitting for both through-diffusion tests the outlet concentrations versustime leads to very low and unrealistic values of ηR (0.15 and 0.5).

Modeling shows that the transport of strontium in Boom Clay cannot be satisfactorilydescribed with the current assumptions (like e.g. instantaneous linear sorption equilibrium andboundary conditions), meaning that there is a problem to obtain a reliable value for the product ηR for strontium in Boom Clay.
The Influence of Groundwater on the Stability of Silica Colloids
Authors: Holtta Pirkko , Lahtinen Mari , Hakanen Martti , Lehto Jukka , Juhola Piia
Published: April 2011

Non-cementitious grouts have been tested in Olkiluoto for the sealing of fractures with the small hydraulic apertures. A promising non-cementitious inorganic grout material for sealing the fractures with the apertures less than 0.05 mm is commercial colloidal silica called silica sol. The potential relevance of colloid-mediated radionuclide transport is highly dependent on their stability in different geochemical environments. The objective of this work was to follow stability of silica sol colloids in low salinity Allard and saline OLSO reference groundwater (pH 7–11) and in deionized milliQ water. Stability of silica sol colloids was followed by measuring particle size distribution, zeta potential, colloidal and reactive silica concentrations. The particle size distributions were determined applying the dynamic light scattering (DLS) method and zeta potential based on dynamic electrophoretic mobility. The colloidal silica concentration was calculated from DLS measurements applying a calibration using a standard series of silica sol. Dissolved reactive silica concentration was determined using the molybdate blue (MoO4) method.

These results confirmed that the stability of silica colloids dependent significantly on groundwater salinity. In deionized water, particle size distribution and zeta potential was rather stable except the most diluted solution. In low salinity Allard, particle size distribution was rather constant and the mean particle diameter remained less than 100 nm. High negative zeta potential values indicated the existence of stable silica colloids. In saline OLSO, particle size distribution was wide from a nanometer scale to thousands of nanometers. The disappearance of large particles, decrease in colloidal particle concentration and zeta potential near zero suggest flocculation or coagulation. Under prevailing saline groundwater conditions in Olkiluoto silica colloids released from silica sol are expected to be instable but the possible influence of low salinity glacial melt water has to be considered.
Migration Behavior of Potassium and Rubidium in Compacted Bentonite Under Reducing Condition With Iron Corrosion Product
Authors: Idemitsu Kazuya , Ikeuchi Hirotomo , Akiyama Daisuke , Inagaki Yaohiro , Arima Tatsumi
Published: April 2011

Carbon steel overpack will corrode by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The iron corrosion products can migrate in bentonite as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. This replacement of sodium with ferrous ion may affect the migration behavior in the altered bentonite not only for redox-sensitive elements but also the other ions. Therefore the authors have carried out electromigration experiments of potassium or rubidium with source of iron ions supplied by anode corrosion of iron coupon in compacted bentonite. Five to fifteen micro liter of tracer solution containing 3.3 M of KCl or 2.2 M of RbCl was spiked on the interface between an iron coupon and bentonite, which dry density was around 1.4 Mg/m3, before assembling. The iron coupon was connected as the working electrode to the potentiostat and was held at a constant supplied potential between - 600 and 300 mV vs. Ag/AgCl reference electrode for up to 8 days. Potassium could migrate faster and deeper in bentonite specimen than iron in each condition. On the other hand rubidium could migrate slower than iron. Migration velocity was a function of applied electrical potential and 8 to 14 nm/s for potassium, 5 to 10 nm/s for iron and 3 to 5 for rubidium, respectively. Dispersion coefficient was also a function of applied potential and 10 to 14 × 10−12 m2/s for potassium, 4 to 8 overv 10−12 m2/s for rubidium and 2 to 4 overv 10−12 m2/s for iron, respectively. Diffusion experiments were also carried out for comparison. Potassium and rubidium might migrate slightly slower in the altered bentonite by iron corrosion than in ordinary compacted bentonite.
Corrosion Behavior of High Burnup Spent Fuel in Highly Alkaline Solutions
Authors: Loida A. , Gens R. , Metz V. , Lemmens K. , Cachoir C. , Mennecart T. , Kienzler B.
Published: April 2011

This study is focused on the alteration behavior of spent nuclear fuel when exposed to highly alkaline groundwater. Contact of highly alkaline solution with the waste product is considered in the Belgian concept for disposal in the Boom Clay formation. According to the “supercontainer design” the fuel will be encapsulated in carbon steel canisters, surrounded by a concrete over-pack. After saturation of the engineered barriers by porewater, interactions with the concrete will result in solutions rich in NaOH, KOH and Ca(OH)2. Using this type of solution at pH 12.5, spent nuclear fuel corrosion experiments were conducted over 378 days. Under anoxic conditions, parallel experiments were performed (a) in the absence of Fe phases and (b) in the presence of solid Fe phases representing container (corrosion) products. Both types of experiments resulted in relatively low matrix dissolution rates, around 10-7 per day, according to the fractional release of Sr. Solution concentrations of actinides are close to or below the detection limit, indicating an effective retention of these radioelements in the system. The observed precipitation of a Ca rich phase onto the surfaces of the corroded fuel samples may be related to the inhibited re-lease of actinides, Sr and other matrix bound radioelements.
Synthesis and characterization of sodalite as matrix for conditioning chloride spent salts from pyroprocesses
Authors: Angelis G. De , Bardez-Giboire I. , Mariani M. , Capone M. , Chartier M. , Macerata E.
Published: April 2011

Two different methods have been used to synthesize sodalite for conditioning of chloride salt wastes coming from pyroprocesses: the first one, starting from kaolinite through the intermediate nepheline phase; the second one, starting from silica and sodium aluminate reagents, directly. The obtained products have been characterized by means of several analyses. In particular, different instrumental techniques – stereomicroscopy, scanning electron microscopy (SEMEDS), density measurements, thermogravimetric analysis, X-rays diffraction, FTIR spectroscopy – were performed revealing that the synthesis from kaolinite is the best method, provided that rigorous conditions are followed. The use of an argon atmosphere for the preparation of pellets of reagents is strictly necessary for the obtainment of a good quality product.
Complete Thermoelectric Generator Performance Measurement
Authors: Koenig Jan D. , Nussel Ulrike , Bartel Markus , Vetter Uwe
Published: April 2011

The standardization of thermoelectric generator (TEG) performance measurement is of a major interest for a usage of them in industrial energy harvesting application. The effects influencing the TEG measurement are regarded and are addressed in this article. The dramatic influences of different measurement parameters are pointed out. The output power dependence on the contact pressure is investigated as a major attempt. The influence of contact pressure on the temperature of the TEG-substrate at the hot side is observed with a high resolution IR camera.

Different approaches are discussed in order to obtain the accurate efficiency of a TEG. The heat flux method is influenced by many effects that can falsify the results. The Harman method is used as another approach to determine the figure of merit to calculate the efficiency.
Atomic Level Analysis of Amino Acids by the Scanning Atom Probe
Authors: Nishikawa Osamu , Taniguchi Masahiro , Ikai Atsushi
Published: April 2011

Atom probe (AP) is known to be a unique instrument that makes possible to mass analyze a specimen at atomic level. However, its application is mostly limited to metals and semiconductors because the AP analysis proceeds by field evaporating surface atoms applying the high field, 20-40 V/nm, on the specimen surface. In order to generate such a high field the analyzed area is an apex of a sharp tip. Metals and semiconductors can be formed in such a sharp tip easily. However, the formation of a sharp organic and bio molecule tip is not easy. Thus, we introduced a funnel shaped micro extraction electrode that scans over a specimen surface and confines the high field in a narrow space between the micro open hole at the apex of the electrode and a micro protrusion on a specimen surface. Thus, this type of the AP is named as scanning atom probe (SAP). Then, organic and bio molecules can be deposited on the micro protrusion on the specimen surface. The AP analysis of metals indicates that the field evaporation of metal atoms proceeds one atom by one atom implying that the binding between metal atoms are uniform and non-directional. On the other hand most atoms of non-metallic specimens are field evaporated as clustering atoms. For example, doubly charged thiophene monomers are detected when polythiophene is analyzed. This indicates that one sulfur and four carbon atoms are strongly bound. Similarly, the mass spectra of highly pure single walled carbon nano tubes (SWCNT) exhibit sharp mass peaks of C2+ and C+ indicating that carbon atoms are bound by non-directional strong bonds. This implies that the unique feature of the AP is not only in the identification of individual ion but also in the investigation of binding states of the atoms forming the materials. For the present analysis amino acids are deposited on a small ball of the SWCNT fibers in order to avoid the catalytic reaction of metals. The SWCNT ball is dipped in a solution of sample molecules. The glycine solution is made by dissolving 1 gram of glycine in 15 ml pure water. Cystine, leucine and methionine solutions are made by dissolving 50 mg of the molecules in 1 ml of 0.1 N HCl. Discrimination of the carbon ions of the SWCNT from the fragment ions of the molecules is relatively easy because nearly all of the SWCNT carbon ions are detected as C2+ and C+. Glycine is the smallest amino acid formed by a carboxy group, an amino group and a CH2 group. Thus, it is assumed that the analysis will provide a guideline for the analysis of larger molecule. However, the identification of fragments ions is not easy because many different fragments have the same mass such as CH3 and NH. This indicates that mass analyzer for the bio-molecules requires a mass spectrometer with the mass resolution m/Δm higher than 10,000. The characteristic mass spectra of the amino acids and the structure of a new SAP with a position sensitive ion detector with a spiral delay line will be presented.
Electron Microscopy Characterization of Humidity Ball-Milling AlCuFe Intermetallic Powders
Authors: Patiño-Carachure C. , Téllez-Vazquez O. , Bedolla-Jacuinde A. , Esparza R. , Ángeles-Chávez C. , Perez R. , Rosas G.
Published: April 2011

An Al58Cu25Fe17 alloy composition was produced by conventional casting technique. In order to take advantage from the hydrogen-environmental embrittlement reaction, which affects these alloys, this research was carried out subjecting prealloyed powders to wet-ball milling. Through these experiments it has been possible to evaluate the particle size reduction as consequence of hydrogen fracture and milling energy. The morphological and structural characteristics of the samples were performed using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The experimental results indicate that the samples with higher contents of humidity have a good particle size reduction. With the increment of milling time, the particle size was diminished even more reaching nanometer size scale.
The Effect of Temperature and Time on the Formation of a Reaction Interlayer During Aluminizing of a Carbon Steel
Authors: Torres R. , López V.H. , Arredondo J.P. , García R. , Verduzco J.A. , Mondragón M.L.
Published: April 2011

A kinetic study was performed on the growth of a reaction interlayer between molten Al and carbon steel substrates at temperatures between 665 to 820°C by holding Al/flux/steel assemblies, in a tube furnace, at temperature for times up to 120 min. An Ar atmosphere and a K-Al-F based flux were used to enable spreading of molten Al on the steel substrates. Chemical and microstructural characterization of the samples revealed that the interlayer is composed of FeAl3 and Fe2Al5, being the second phase significantly thicker. The Fe2Al5 phase grows toward the steel with a tongue like morphology. Isothermal growth profiles of the reaction interlayer followed a parabolic behavior, meaning that at the beginning the reaction is very rapid and once that a continuous interlayer is formed the growth of the interlayer is controlled by interdifussion of species across the interlayer.
Microstructural Characterization of 316L-Type Stainless Steel Exposed to SiFX Species in Argon Atmosphere
Authors: Gamón E. , Pech-Canul M. I. , López-Cuevas J. , Leal-Cruz A. L. , Pech-Canul M. A.
Published: April 2011

Nowadays, Si3N4 coatings are used to increase the hardness of 316L-type stainless steel for a wide variety of applications. These coatings are normally prepared by chemical vapor deposition (CVD) or variant techniques such as the hybrid solid-gas precursor system chemical vapor deposition (HYSYCVD), where Na2SiF6 is used as a solid precursor. Within the reaction chamber the Si-F gas species interact with nitrogen precursors to form Si3N4; however, during silicon nitride formation there is always certain amount of residual Si-F gas species which may affect the integrity of the steel surface. Therefore, in this work the effect of the Si-F species on the surface of 316L type stainless steel under argon atmosphere has been investigated. Stainless steel samples were prepared under two surface conditions (abraded and mirror polished), and were exposed to Si-F species considering various parameters such as: argon gas flow rate equal to 10 cm3/min, different temperatures (300, 500, 700, 900°C), and three exposure times (30, 60, 90 minutes). After exposure, the substrates were characterized by X-ray diffraction (XRD) and by scanning electron microscopy (SEM). The results show that the FeF2 phase is formed at low temperatures while the formation of different oxides is directly related to the processing temperature. What is more, these oxides are also strongly influenced by processing time; however temperature is the parameter that most significantly influences the oxides formation.
Flame Retardant Protective Coating Applied in Textile 100% Acrylic Fabrics
Authors: Olvera-Gracia M. , Kryshtab T. , Paniagua-Mercado A.M. , Aguilar-Hernández J.
Published: April 2011

Textile 100 % acrylic fabrics have been used in tapestry for a long time. One of the drawbacks of this type of fabrics is its great flammability. Textile fabrics are coated with flame retardant in order to reduce the flammability. We present some results concerning the use of commercial products (Flame-Out, Borax (Na2B4O5(OH)4•8H2O), and Hexametaphosphate of Sodium (Na16P14O43) as flame retardants for textile 100 % acrylic fabrics. The flame retardant capabilities, mechanical properties and structural characteristics of the textile fabrics before and after the use of these products were investigated throughout the special textile methods for inflammability and mechanical resistibility as well as infra-red spectroscopy, X-ray diffraction and scanning electronic microscopy. After the use of the flame retardants the mechanical properties of the fabrics were improved or at least remained the same as compared to fabrics without any treatment. The use of Borax / Hexametaphosphate from Sodium /Water results in the essential increase of combustion retardation time about 2 minutes as compared with 8 seconds for untreated fabrics.
Photopyroelectric Calorimeter for Phase Transitions Monitoring: Application to Chocolate
Authors: Martínez-Ordoñez E. I. , Marín E. , Díaz-Góngora J. A. I. , Calderón A.
Published: April 2011

In this work we report about the design and construction of a simple and cheap calorimeter for phase transitions monitoring using Peltier elements and based in the well known inverse (front) photopyroelectric method for thermophysical characterization of materials. We describe its application for the detection of phase transitions in chocolate samples, as an alternative, for example, to the most widely used and more expensive Differential Scanning Calorimetry technique. The manufacture of chocolate requires an understanding of the chemistry and the physical properties of the product. Thus the involved problems during the confection process are those of the so-called materials science. Among them, those related with tempering are of particular importance. Because the fats in cocoa butter experience the so-called polymorphous crystallization, the primary purpose of tempering is to assure that only the best form is present in the final product. One way to characterize this is by measurement of the temperature dependence of the thermal properties of the chocolate and the monitoring of the temperature at which phase transitions take place. We show that the photopyroelectric method, aided with Peltier cells temperature control, can be a useful choice for this purpose.
Surface investigation of NiTi rotary endodontic instruments after magnetoelectropolishing
Authors: Hryniewicz Tadeusz , Rokosz Krzysztof , Rokicki Ryszard
Published: April 2011

The purpose of the study was to reveal the effects of a new electropolishing process carried out under a constant magnetic field, termed as magnetoelectropolishing (MEP). In this work we investigated Nitinol rotary endodontic instruments by surface and morphology change after MEP. The MEP process greatly affects both surface also mechanical properties like the bending and fatigue resistance.

The investigation covered surface interferometry measurements, X-ray Photoelectron Spectroscopy (XPS) studies, and Scanning Electron Microscopy (SEM) with EDAX studies referred to two groups of endodontic instruments: ready-to-use or as-received (AR) files, and magnetoelectropolished (MEP) instruments, in comparison with the instruments surface after a conventional electropolishing (EP). The treated surfaces of NiTi endodontic files were studied by interferometric method in view of getting multiple surface characteristics, together with digital data concerning the arithmetic mean height Sa and the maximum height of scale limited surface Sz.

The investigation results obtained have indicated a considerable improvement of MEP surface in comparison with both AR and EP surfaces. Such a surface after MEP reveals several positive features, decreased roughness, elimination of metallic state (here Ni and Ti elements) in the surface film, much enriched with titanium oxides and diminished nickel oxides. The study results show that the contents of Ni compounds is higher after EP (18.3%) than after MEP (10.2%), whereas the contents of Ti compounds is higher after MEP (83.4%) than after EP (76.6%). The total Ti/Ni ratio indicates almost double surpass of titanium over nickel in the surface film after MEP in comparison with the total amount of that ratio after EP.

The qualitative investigation of fatigue tests have indicated much better performance of NiTi endodontic file samples after MEP than those related to AR and/or after EP. We have proved that the magnetoelectropolishing process may further modify surface. The following studies are to be directed onto performance and specific mechanical properties of the endodontic files at work.
SiGe Nanowires Grown by LPCVD: Morphological and Structural Analysis
Authors: Rodríguez Andrés , Sangrador Jesús , Rodríguez Tomás , Ballesteros Carmen , Prieto Carmelo , Jimenez Juan
Published: April 2011

SiGe nanowires were grown by the vapor-liquid-solid method using a low pressure chemical vapor deposition reactor and different flows of the GeH4 and Si2H6 gas precursors. The morphology of the nanowires was studied by field emission scanning electron microscopy, and the length, diameter and density of nanowires were determined. Their structure and crystallinity were analyzed by transmission electron microscopy and its related techniques. Energy dispersive X-ray emission of individual nanowires as well a Raman spectroscopy were used to determine their composition and to analyze its homogeneity.
Surface Molecular Vibrations as a Tool for Analyzing Surface Impurities in Copper Phthalocyanine Organic Nanocrystals
Authors: Nauka K. , Zhao Yan , Ng Hou-T , Hanson Eric G.
Published: April 2011

Comparison of the IR spectra of the Cu-phthalocyanine (CuPc) nanocrystals obtained using surface sensitive attenuated total reflectance (ATR) and bulk sensitive transmittance sample configurations revealed small but measurable changes of some vibrational frequencies of the molecules at the surface of nanocrystals with the outermost part of the surface CuPc molecules being the most affected. These changes are caused by electrostatic interactions between the polar components of the molecules on the surface of nanocrystals and external polar molecular species vicinal to the nanocrystals. The external polar species can be either chemically bonded to the CuPc nanocrystal's surface or they can reside in its vicinity without forming a chemical bond with the nanocrystal. Molecular modeling (DMOL3 - Materials Studio and Gaussian calculations) of the impact of selected external polar species vicinal to a CuPc molecule on the CuPc molecular vibrations confirmed experimentally observed changes in the vibrational frequencies of the selected CuPc molecular bonding configurations and provided detailed information on the forces involved in these interactions. The population of external polar species vicinal to the CuPc surface can be modified by washing the nanocrystals or by introducing polar molecular additives miscible with the CuPc nanocrystals. Reduction in the number of external polar additives was accomplished by either centrifuging the aqueous dispersion of the nanocrystals or by organic solvent-based Soxhlet extraction, while their number was increased by soaking (followed by drying) the nanocrystals in high and low pH aqueous solutions containing SO3- and OH- ions. These quantitative and qualitative modifications of the population of external polar species surrounding CuPc nanocrystals were reflected in the corresponding changes of the selected vibrational frequencies of the CuPc surface molecules providing an effective tool for not only recognizing the molecular species vicinal to a nanocrystal but also quantifying their concentration. Some of these modifications can also be observed with a naked eye in the form of noticeable color changes of the CuPc nancrystalline powder. This is due to the extremely high visible extinction coefficient of the CuPc nanocrystals causing that the impinging light is mostly absorbed/reflected within the surface region of the nanocrystals. Changes of the electronic structure within this region, caused by the interactions with the vicinal polar species, shift the vis absorption/reflection spectra changing the observed color of the nanocrystalline powder. Similar results were obtained for other molecular nanocrystals, including yellow chromophore molecules. Preliminary data indicate that the described analytical method of analyzing the molecular polar species vicinal to a molecular nanocrystal could find variety of applications ranging from molecular device fabrication to pharmaceutical materials.
Effect of Film Morphology on Charge Transport in C60-based Organic Field Effect Transistors
Authors: Ullah Mujeeb , Kadashchuk Andrey K. , Stadler Philipp , Kharchenko Alexander , Pivrikas Almantas , Simbrunner Clemens , Sariciftci Niyazi Serdar , Sitter Helmut
Published: April 2011

The critical factor that limits the efficiencies of organic electronic devices is the low charge carrier mobility which is attributed to disorder in organic films. In this work we study the effects of active film morphology on the charge transport in Organic Field Effect Transistors (OFETs). We fabricated the OFETs using different substrate temperature to grow different morphologies of C60 films by Hot Wall Epitaxy. Atomic Force Microscopy images and XRD results showed increasing grain size with increasing substrate temperature. An increase in field effect mobility was observed for different OFETs with increasing grain size in C60 films. The temperature dependence of charge carrier mobility in these devices followed the empirical relation named as Meyer-Neldel Rule and showed different activation energies for films with different degree of disorder. A shift in characteristic Meyer-Neldel energy was observed with changing C60 morphology which can be considered as an energetic disorder parameter.
Controlling the Physical Properties of Random Network Based Shape Memory Polymer Foams
Authors: Singhal Pooja , Wilson Thomas S , Maitland Duncan J
Published: April 2011

Shape memory polymers (SMPs) are increasingly being considered for use in minimally invasive medical devices. For safe deployment of implanted devices it is important to be able to precisely control the actuation temperature of the device. In this study we report the effect of varying monomer composition on the glass transitions/actuation temperatures (Tg) of novel low density shape memory foams. The foams were based on hexamethylenediisocyanate (HDI), triethanolamine (TEA) and tetrakis (2-hydroxyl propyl) ethylenediamine (HPED), and were produced via a combination of chemical and physical blowing process. The process for post-foaming cleaning was also varied. Foams were characterized by DSC, DMA, and for shape memory. No clear trends were observed for foam samples without cleaning, and this was attributed to process chemicals acting as plasticizers. In foams cleaned via washing and/or sonication, the Tg was observed to decrease for compositions that were higher in the TEA content. Also, no change in shape memory behavior was observed for varying compositions. This work demonstrates the ability to tailor actuation transition temperature while maintaining shape memory behavior for low density foams suitable for aneurysm treatment.
Synthesis of nanostructured metal (Fe, Al)-C60 composites
Authors: García I. I. Santana , Febles V. Garibay , Calderon H. A.
Published: April 2011

Composites of M-2.5 mol. % Fullerene C60 composites (where M= Fe or Al) are prepared by mechanical milling and Spark Plasma Sintering (SPS). The SPS technique has been used to consolidate the resulting powders and preserve the massive nanostructure. Results of X-Ray Diffraction and Raman Spectroscopy show that larger milling balls (9.6 mm in diameter) produce transformation of the fullerene phase during mechanical milling. Alternatively smaller milling balls (4.9 mm in diameter) allow retention of the fullerene phase. SEM shows homogeneous powders with different particle sizes depending on milling times. Sintering produces nanostructured composite materials with different reinforcing phases including C60 fullerenes, diamonds and metal carbides. The presence of each phase depends characteristically on the energy input during milling. Transmission Electron Microscopy (TEM) and Raman Spectroscopy show evidence of the spatial distribution and nature of phases. Diamonds and carbides can be identified for the sintered Fe containing composites with a relatively high volume fraction.
Preparation and Mechanical Characterization of a Polymer-Matrix Composite Reinforced with PET
Authors: Elena Salazar–Nieto J. , Altamirano–Torres Alejandro , Sandoval–Pérez Francisco , Rocha–Rangel Enrique
Published: April 2011

In this study, polymer-matrix composites are fabricated by mixing liquid epoxy resin with 0, 15, 20 and 25 wt % of PET. PET is used as a reinforcement material since it can be recycled and this implies a beneficial environmental impact. After mixing, specimens are dried at room temperature during 24 h and then cured at 150°C during 0.5, 0.75 and 1 h. Then mechanical tests are performed. Experimental results obtained from the flexion test for 100 % epoxy resin and 15 % PET samples, without curing treatment show values of 30 and 21 MPa, respectively. Flexure strength values for the same samples but after curing treatment are: 56, 90, 32 MPa and 69, 64, 70 MPa, for 0.5, 0.75 and 1 h of treatment, respectively. These data show an important increase in the flexure strength for the sample reinforced with 15 % PET and curing time of 1h. This is most likely due to the behavior of PET's powders at this temperature and time. They can partially melt improving the adhesion to the polymeric matrix. For a curing time of 0.75h, this property decreases, due to the high porosity developed in the composite and the poor adhesion between polymeric matrix and reinforced material.
Microstructure Characterization of Textured Nickel Using Parameters of Extinction
Authors: Cadena Arenas A. , Kryshtab T. , Palacios Gómez J. , Gómez Gasga G. , de la Torre A. De Ita , Kryvko A.
Published: April 2011

X ray diffraction (XRD) is the common technique for texture analysis by means of pole figure (PF) measurement. PF reflects the grains orientation distribution but contains no information about grain microstructure. The reflected intensity can be affected by the extinction phenomenon that reduces the pole density (PD). The parameters of extinction are related to the crystal microstructure. The parameter of the primary extinction is connected with domain size and parameter of the secondary extinction is related to the angle of domains disorientation that depends on dislocation density in domain boundary. An original XRD method is proposed for correction of PD, considering extinction phenomenon, and separation of the extinction parameters in the case of textured aluminum. The problem is solved under some assumptions. In the present work cold rolled nickel with and without annealing at 600 °C is investigated. The validity of the proposed assumptions for Ni is evaluated in terms of the extinction length. The corrected PD in the maximum of PF and the parameters of the primary and secondary extinction are calculated using the first order reflection for CuKα- and CoKα- radiations and the second order reflection for one of the used wavelengths. Both in cold rolled sample without annealing and in the annealed sample the primary and secondary extinctions are present simultaneously. According to the obtained parameters of extinction the microstructure of textured nickel is evaluated and their modification at the annealing process is demonstrated.
Alumina-Based Functional Materials Hardened with Al or Ti and Al-nitride or Ti-nitride Dispersions
Authors: Miranda-Hernández José G. , Refugio-Garcia Elizabeth , Garfias-García Elizabeth , Rocha-Rangel Enrique
Published: April 2011

The synthesis of Al2O3-based functional materials having 10 vol. % of fine aluminum or titanium and aluminum-disperse or titanium-dispersed nitride hardened-particles has been explored. Two experimental steps have been set for the synthesis; specifically, sintering of Al2O3-aluminum or Al2O3-titanium powders which were thoroughly mixed under high energy ball-milling, pressureless-sintered at 1400°C during 1 h in argon atmosphere and then for the second step it was induced formation of aluminum nitride or titanium nitride at 500°C during different times (24, 72 and 120 h) by a nitriding process via immersion in ammoniac salts. SEM analyses of the microstructures obtained in nitride bodies were performed in order to know the effect of the ammoniac salts used as nitrating on the microstructure of aluminum or titanium for each studied functional material. It was observed that an aluminum nitride or titanium nitride layer growth from the surface into the bulk and reaches different depth as the nitriding time of the functional material was increased. The use of aluminum or titanium significantly enhanced density level and hardness of the functional materials.
Synthesis of a novel biopolymer by means of Thiol-Ene Photopolymerization using diallyl sucrose and dithiotreitol as comonomers
Authors: Ortiz Ricardo Acosta , Martinez Antelmo Yasser Ruiz , Valdez Aida E García , Duarte María Lydia Berlanga
Published: April 2011

A novel biopolymer derived from diallyl sucrose (A2S) and dithiotreitol (DTT) was prepared by means of Thiol-Ene Photopolymerization. A2S was prepared by alkylating the sucrose with allyl bromide, using water as solvent. After purification by column chromatography, a fraction (F2A2S) with 94% diallyl sucrose (A2S), 4 % of triallyl sucrose (A3S) and 2 % of monoallyl sucrose (A1S) was obtained. This fraction was subsequently photopolymerized with Dithiothreitol (DTT) which is a difunctional thiol. Kinetics of photopolymerization were determined by means of Real-Time Infrared spectroscopy. It was found that the photocurable formulation with DTT and F2A2S, polymerized rapidly in the presence and absence of a photoinitiator, at low intensities of UV light. After bulk polymerization, a flexible material with high elastic modulus and a Tg of 30 °C was obtained. Besides, the polymer displayed moderate water absorbance properties as a result of the presence of multiple hydroxyl groups. This property was pH dependent with maximum absorbance at pH=14. The polymer degraded rapidly under acidic conditions
Elaboration and Evaluation of Membranes from Biopolymers as Delivery System of Plant Extracts
Authors: A Rodríguez-García , Galán-Wong L.J. Luis J. , K. Arévalo-Niño
Published: April 2011

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are considered key pathogens in periodontitis that is the principal cause of tooth loss in adults. The treatment of periodontal disease consists on the use of chemicals which can alter oral microbiota and have undesirable side-effects such as vomiting, diarrhea and tooth staining

At recent years, the use of natural sources like biomaterials such as biopolymers and plant extracts are enjoying great popularity. Chitosan and pullulan are polymers that have been proposed due to their favorable properties such as biocompatibility, biodegradability, adhesion ability and nontoxicity

The aim of this study was to develop films from chitosan and pullulan containing plant extracts as delivery system and determine the in vitro antibacterial activity against periodontopathogen microorganisms and their stability under different conditions of storage
Concrete Biodeterioration in the U.S.-Mexico Border Region
Authors: Rendon L. E. , Lara M. E. , Rendon S. K. , Rendon M. , Li X.
Published: April 2011

Concrete biodeterioration is defined as the damage that the products of microorganism metabolism, in particular sulfuric acid, do to hardened concrete. In Canada and in the northern part of the United States, sewer failures from concrete biodeterioration are almost unknown. In the southern part of the United States and in Mexico, however, it is a serious and expensive problem in sewage collection systems, which rapidly deteriorate. Also, leaking sewage systems result in the loss of groundwater resources particularly important in this arid region. Almost every city in the Mexican-American border region, who's combined population is more than 15 million people, faces this problem. The U.S. cities have made some provision to face these infrastructure problems, but the Mexican cities have made less effort. We recommend here the Mexican norm (NMX-C-414-ONNCCE-2004) [1] to be reviewed, or at least that a warning be issued as a key measure to avoid concrete biodeterioration.
Cadmium(II) and Lead(II) removal by Chlorella sp. Immobilized and E. coli genetically engineered with mice Metallothionein I
Authors: Almaguer-Cantú V. , Morales-Ramos L. , Arevalo-Niño K. , Garza-González M.T. , Balderas-Rentería I.
Published: April 2011

The pollution caused by heavy metals is one of the major environmental problems that is imperative to be solved. New technologies, easy to implement and to adapt to any system, deserve special attention and are a focus of this work the ability of Chlorella sp. and E. coli genetically engineered with mice metallothionein I, both immobilized in alginate of calcium to remove Cd(II) and Pb(II) from aqueous solutions was investigated in batch assays for the treatment of diluted aqueous solutions. The kinetics, sorption capacities and sorption percentage were determined. The influence of metal concentration in solution is discussed in the terms of Langmuir isotherm and constants. Sorption capacities increased with increasing metal concentration in solution. For solution containing 300 mg/L of metal, the observed uptake capacities were 94.941±1.094 mgCd/gChlorella., 24.076±2.292 mgCd/gE.coli and 239.17±2.478 mgPb/gChlorella, 37.952±4.245 mgPb/gE.coli. The Langmuir constants to Chlorella sp. were qmax=285.72(mgPb/g), b=0.0276(l/mgPb), qmax=103.65(mgCd/g) and b=0.0005(l/mgCd) while to E. coli were qmax=28.141(mgPb/g), b=0.113(l/mgPb), qmax=24.272(mgCd/g) and b =0.019(1/mgCd). The biomass of the algae showed to have better capacity of metallic sorption that the biomass of the bacteria genetically engineering. The study proved that microorganisms biomass is a suitable material for the removal of the studied heavy metals ions from aqueous solutions, achieving removal efficiencies higher than 90%, and could be considered as a potential material for treating effluent polluted with Cd(II) and Pb(II) ions.
Synthesis and Thermoluminescence of New ZnO Phosphors
Authors: Cruz-Vázquez C. , Borbón-Nuñez H. A. , Orante-Barrón V. R. , Burruel-Ibarra S. E. , Castaño V. M. , Bernal R.
Published: April 2011

In this work, the synthesis and thermoluminescence properties of new ZnO phosphors obtained by a chemical method are reported. Some samples were exposed to beta particle irradiation for doses ranging from 10.0 up to 6,400 Gy, and it was found that the thermoluminescence response as a function of dose is linear for doses below 200 Gy, and sublinear with no saturation clouds for greater doses. A broad shape glow curve with maximum located above 230 °C, that shifts to lower temperatures as dose increases, indicating that second order kinetics thermoluminescence processes are involved. The lower detection limit was estimated to be 13 Gy. We conclude that the phosphors under study are promising to develop dosimeters for high dose radiation dosimetry.
Transformations of Supported Heteropoly Compounds in Oxidative Conversion of Alkanes
Authors: Tungatarova Svetlana A.
Published: April 2011

Dynamics of structural transformation of supported heteropoly compound was investigated by IR-spectroscopy, XRD, TPR, and TPO methods. The 15-30 wt.% H3PMo12O40and H3PV2Mo10O40, supported on SiO2catalysts were investigated in process under various conditions by interaction with O2(air) in the presence of water vapor, H2, alkane in TPR regime, O2in TPO regime (298-1273K) and H2O (298, 923K). The rank of reversible structural conversion of supported heteropoly compounds was established under influence of temperatureand medium. These new findings of reversible structural cycle explains the stability of the 12th series Mo heteropoly compounds supported on Si-containing carrier at high temperatures (873-1073K) which is close to the actual operation temperatures of the partial oxidation reactions and oxidative dehydrogenation of alkanes.
Study of the Formation of WOx Nanostructures Supported on Zirconia Prepared by Different Synthesis Routes
Authors: Hernández Martha L. , Montoya Ascención , angel Paz Del , Paredes Silvia P. , Flores Sergio O.
Published: April 2011

Different synthesis procedures of Pt supported on tungstated zirconia catalysts (Pt/WOx-ZrO2) were investigated with the aim to elucidate the different WOx nanostructures developed on the zirconia surface depending on the preparation route. Pt/WOx-ZrO2 catalysts were synthesized by the coprecipitation and impregnation methods and pretreated by various procedures such as different calcinations temperatures or the use of reflux. The catalysts characterization was carried out by X-ray diffraction (XRD), Raman spectroscopy, transmission and scanning electron microscopy (TEM, SEM) and nitrogen physisorption, and the catalytic activity was evaluated in the n-hexane isomerization reaction. The results indicate that the development of active sites for isomerization of n-hexane is enhanced by the stabilization of the WOx nanostructures on the surface of zirconia, before the formation of the WO3 crystallites, and it largely depends on the synthesis method.
Thermal Diffusivity Measurement of Pure Te, (Hg1−x Cdx)1−yTey and (Hg1−xZnx)1−yTey
Authors: Maleki Hossein , Holland Lawrence R.
Published: April 2011

The thermal diffusivities of (Hg1−xCdx)1−yTey and (Hg1−xZnx)1−yTeywith 0.55 ≤ y ≤ 1.0 and 0.0125 ≤ x ≤ 0.05465 and of pure Te are measured over a wide temperature range by the laser flash technique. The diffusivity of near pseudobinary Hg1−xCdxTe solids decrease more rapidly with temperature approaching the melting point than pseudobinary solids previously reported. The solid diffusivity for x=0.02817 is 0.83 mm2/s at 371°C, decreasing to 0.22 mm2/s at 614°C. The diffusivity of Te rich (Hg1−xCdx)1−yTey melt increases with x and with temperature. The melt diffusivity for x=0.03934 is 0.91 mm2/s at 485°C, increasing to 4.93 mm2/s at 851°C. For Te rich (Hg1−xZnx)1−yTey melt with x=0.0125 and y=0.7944 there appears to be a minimum diffusivity of about 2.6 mm2/s near 700°C. The thermal diffusivity of pure Te solid is 0.97 mm2/s at 300°C and decreases to 0.64 mm2/s at 439°C. The melt diffusivity is 1.52 mm2/s at 486°C, increasing to 3.48 mm2/s at 584°C.
Mapping of Defects in Metal-Semiconductor-Metal (MSM) Detectors in Hg1−xCdxTe by Nuclear Microprobe
Authors: Leech Patrick W. , Dooley Sean P. , Jamieson David N.
Published: April 2011

The incidence of compositional and structural inhomogenieties in MSM detectors based on Hg1−xCdxTe/GaAs and Hg1−xCdxTe/GaAs/Si has been examined by nuclear microprobe. With a 2 MeV He+ beam focussed to ≤5 μm, the microprobe has demonstrated the capability for RBS channelling in the active region of a Hg1−xCdxTe device and the imaging of defects by Channelling Contrast Microscopy (CCM). A series of linear growth defects in some Hg1−xCdxTe devices were identified using CCM. The channelling RBS spectra from these regions have shown an increase in χmin compared with the surrounding high quality crystal. The occurence of these defects was associated with a degradation in the performance of affected devices in an array. RBS spectra have also revealed the presence of an anomalous CdTe layer, correlating with a significant reduction in dark current and increase in breakdown voltage of these devices. RBS channelling of individual devices has identified differences in χmin between arrays which were prepared under equivalent conditions of growth and processing.
HgCdTe MBE Technology: A Focus on Chemical Doping
Authors: Wu Owen K.
Published: April 2011

HgCdTe MBE technology is becoming a mature growth technology for infrared focal plane array applications. The ability to dope HgCdTe with In(n-type) and As(p-type) dopants in-situ provides greater flexibilities for fabricating heterojunction devices. In this paper, we will first discuss the current status of HgCdTe MBE growth and then focus on the key results in the control of In(n-type) doping, various approaches and breakthroughs in the growth of As(p-type) doped HgCdTe and issues related to doping such as memory effects and dopants activation. In addition, device results from double layer heterojunction structure(DLHJ) will be briefly discussed.
IV-VI on Fluoride/Si Structures for IR-Sensor Array Applications
Authors: Fach A. , Maissen C. , Masek J. , Teodoropol S. , Zogg H.
Published: April 2011

Epitaxial narrow gap IV-VI layers on Si-substrates offer an alternate to Hg1−xCdxTe for IR-focal plane arrays with similar ultimate sensitivities. We report on the following improvements in reaching the goal of an easily producible fully monolithic IV-VI-on-active-Si IRFPA: (1) Up to now, compatibility with the Si-substrate was reached through use of a stacked CaF2/BaF2 buffer layer. This layer is replaced by a very thin CaF2 buffer only, which is more suitable for photolithographic processing. (2) Fine resolution wet etching of the IV-VI layers is much easier and reproducible with this new type of buffer. (3) Good homogeneity of cut-off wavelengths is obtained: For a 12 mm long linear Pb1−xSnxSe array with 10.2 μm cut-off wavelength at 95K, the variation in cut-off is smaller than 0.1 μm. (4) The thermal mismatch strain relaxes by dislocation glide even at cryogenic temperatures and after many thermal cycles.
High-Performance Lead Telluride-Based Photodetectors
Authors: Akimov Boris A. , Khokhlov Dmitriy R.
Published: April 2011

We present the new class of the far infrared photodetectors based on the lead-tin tellurides doped with the group III impurities. The persistent photoconductivity effect appearing in these materials provides an internal signal integration resulting in a considerable increase in the signal-to-noise ratio. The techniques of the photomemory quenching are discussed. In some regime of quenching the effect of giant quantum efficiency stimulation has been observed. The possibility of generation of the photoinduced spatially nonequilibrium states provides the physical evidence for the construction of an integrating “continuous” focal-plane array based on Pb1−xSnxTe(In).
Effect of Solutal Convection During the Growth of Silicon in a Sandwich System
Authors: Dost Sadik , Djilali Ned , Erbay Saadet , Erbay Husnu A.
Published: April 2011

This paper considers the modelling of Liquid Phase Epitaxial (LPE) growth of silicon in a substrate-solution-substrate “sandwich” system. Unsteady two-dimensional numerical simulations which take into account fluid flow and mass transfer are presented for a growth experiment. Except in the initial stages, solutal convection is found to be dominant throughout the process. Convection is, however, mostly confined to the upper half of the growth cell, resulting in growth of a layer on the upper substrate, which is about twice as thick as that on the lower substrate. This result is in good agreement with available experiment data. Another interesting consequence of the convection patterns is the formation of a smooth flat surface on the lower substrate and a wavy irregular one on the upper substrate.