Inclusion Of Metals Research Articles

Reduction of the thermal conductivity of the thermoelectric material ScN by Nb alloying

ScN-rich (Sc,Nb)N solid solution thin films have been studied, motivated by the promising thermoelectric properties of ScN-based materials. Cubic Sc1-xNbxN films for 0 ≤ x ≤ 0.25 were epitaxially grown by DC reactive magnetron sputtering on a c-plane sapphire substrate and oriented along the (111) orientation. The crystal structure, morphology, thermal conductivity, and thermoelectric and electrical properties were investigated. The ScN reference film exhibited a Seebeck coefficient of −45 μV/K and a power factor of 6 × 10−4 W/m K2 at 750 K. Estimated from room temperature Hall measurements, all samples exhibit a high carrier density of the order of 1021 cm−3. Inclusion of heavy transition metals into ScN enables the reduction in thermal conductivity by an increase in phonon scattering. The Nb inserted ScN thin films exhibited a thermal conductivity lower than the value of the ScN reference (10.5 W m−1 K−1) down to a minimum value of 2.2 Wm−1 K−1. Insertion of Nb into ScN thus resulted in a reduction in thermal conductivity by a factor of ∼5 due to the mass contrast in ScN, which increases the phonon scattering in the material.

Determination of sediment metal background concentrations and enrichment in marine environments - A critical review.

'Background' is the concentration of metals in pristine sediment, unaltered by human activity and 'enrichment' is the extent present-day sediment metal concentrations exceed pre-anthropogenic levels (the magnitude of human-induced change). Background and enrichment are becoming more frequently used for management measures to bring sediment and the environment back to near-pristine levels. Of the six empirical methods reviewed for determining background (global values, pristine marine and fluvial sediments, catchment soils and rocks), the use of sedimentary cores has the greatest advantage. Most of the eight statistical methods reviewed are adversely affected by the polymodality and an absence of normality or log-normality, however robust regression procedures are most commonly used. Sorption hypothesis techniques require further development. Indices used to determine enrichment incorporate background levels (enrichment indices) or do not (contamination indices). Of the 20 indices reviewed, the New Nemerow Index and the Mean Enrichment Quotient rate highly in performance, based on 5 beneficial attributes assessed: use of background and normalised data, provision of thresholds, a classification scheme, and inclusion of multiple metals. Variance in background metal concentrations determined in the 43 global projects reviewed is surprisingly moderate, however regional variability may be considerable due to local catchment mineralisation. Chemical analysis of sediment should not include metals bound in the mineral matrix and weak acid extractions are advisable. The use of appropriate and effective indicators of environmental condition are critical to the protection and restoration of marine regions and ensuring that human activities are carried out in a sustainable manner to promote safe, healthy and productive ecosystems.

Imaging the Atomic Position of Light Cations in a Porous Network and the Europium(III) Ion Exchange Capability by Aberration‐Corrected Electron Microscopy

AbstractIn the present work, ETS‐10 microporous titanosilicate has been synthesized and its structure characterized by means of powder XRD and aberration corrected scanning transmission electron microscopy (Cs‐corrected STEM). For the first time, sodium ions have been imaged sitting inside the 7‐membered rings. The ion‐exchange capability has been tested by the inclusion of rare earth metals (Eu, Tb and Gd) to produce a luminescent material which has been studied by atomic‐resolution Cs‐corrected STEM. The data produced has allowed unambiguous imaging of light atoms in a microporous framework as well as determining the cationic metal positions for the first time, providing evidence of the importance of advanced electron microscopy methods for the study of the local environment of metals within zeolitic supports providing unique information of both systems (guest and support) at the same time.

Imaging the Atomic Position of Light Cations in a Porous Network and the Europium(III) Ion Exchange Capability by Aberration-Corrected Electron Microscopy.

In the present work, ETS-10 microporous titanosilicate has been synthesized and its structure characterized by means of powder XRD and aberration corrected scanning transmission electron microscopy (Cs -corrected STEM). For the first time, sodium ions have been imaged sitting inside the 7-membered rings. The ion-exchange capability has been tested by the inclusion of rare earth metals (Eu, Tb and Gd) to produce a luminescent material which has been studied by atomic-resolution Cs -corrected STEM. The data produced has allowed unambiguous imaging of light atoms in a microporous framework as well as determining the cationic metal positions for the first time, providing evidence of the importance of advanced electron microscopy methods for the study of the local environment of metals within zeolitic supports providing unique information of both systems (guest and support) at the same time.

Synthesis and characterization of terepthalaldehyde–thiocarbohydrazide polymer doped with Cu(II) and Zn(II) Metal ions for solar cell applications

A convenient synthesis method and the properties of a polynuclear Cu(II) and Zn(II) terapthaldehyde-thiocarbohydrazide polymeric metal complexes has been discussed in this work. A product of terepthalaldehyde–thiocarbohydrazide as condensed polymer (TThP) was synthesized by polycondensation reaction of terepthalaldehyde with thiocarbohydrazide. Two polymeric metal complexes of the condensed product [(C15H12N4S)2CuCl2]n (TThP–CuCl2) and [(C15H12N4S)2ZnCl2]n (TThP–ZnCl2) were prepared with CuCl2 and ZnCl2 metal salts separately and compared for property evaluation. Structural analysis was carried out by elemental analysis, SEM and FTIR, thermal analysis with the help of TGA and optical properties was carried with UV–visible and fluorescence techniques. TThP shows fluorescence at 424nm at an excitation wavelength of 435nm and its polymer complexes TThP–CuCl2 and TThP–ZnCl2 show fluorescence at the same wavelength with higher intensity. The band gap of the synthesized polymer metal complexes decrease from 3.3 to 2.6eV as metals varied from M=Cu(II)–Zn(II). This confirms the successful inclusion of metals in polymer back bone.

Obtaining of crystals of polyelemental solid solutions of rare earth hexaborides

Single crystals of polyelemental rare earth hexaborides with the preset formula La0.5(Ce0.1Pr0.1Nd0.1Sm0.1Eu0.1)B6 were obtained for the first time. Synthesis and crystallization were performed by the solution–melt method in an immiscible Al/Pb system. Step-by-step chemical analysis was made with the aid of a CAMEBAX microprobe. The inclusion of all rare earth metals (REMs) in the hexaboride lattice was proven, and differences in the composition of obtained crystals caused by nonstationarity of the bulk crystallization process were found. The lattice periods of the polyelemental REM hexaborides were found to be smaller than that of hexaboride of lanthanum, the main element of the metal sublattice. The measured microhardness of the new material lies within the range of the microhardness values of hexaborides of all its constituent REMs. Speculations are provided on the peculiarities of the growth mechanism, crystallization, and composition of the obtained crystals.

Combining Nitrogen Precursors in Synthesis of Non-Precious Metal ORR Catalysts with Improved Fuel Cell Performance

Platinum and platinum-alloy oxygen reduction reaction (ORR) catalysts have been implemented in the prototype, and by now also in commercial fuel cell power systems for automotive applications, successfully meeting the demanding conditions of relatively low temperature (80°C) and high acidity operating conditions of the polymer electrolyte fuel cell (PEFC). However, due to the high price of Pt, the catalyst cost is projected to account for as much as a half of the total PEFC stack cost.1 In this context, the potential replacement of Pt-based catalysts, especially in the fuel cell cathode, with non-precious metal catalysts (NPMCs) is expected to significantly reduce PEFC stack cost. Achieving such a cost benefit is, however, contingent upon reaching sufficient activity and durability with NPMC for the ORR, a requirement that the electrocatalysis research community has been striving to meet. In this presentation, we expand upon the idea of combining nitrogen precursors during NPMC synthesis to improve the performance and performance durability of non-precious metal ORR catalysts. Previously, we introduced a new non-precious metal ORR catalyst derived from two nitrogen precursors with different decomposition temperatures: easily decomposing cyanamide (CM) and more thermally stable polyaniline (PANI).2 In this approach, CM acts as an efficient pore-forming agent that allows for the formation of a highly porous structure, which in particular benefits the high-current response of the resulting electrocatalyst. Compared to the alternative approach utilizing metal-organic frameworks (MOFs),3,4 the use of cyanamide promises a very significant reduction in the NPMC cost, without sacrificing ORR activity. In an effort to further improve the PEFC performance of the two nitrogen-precursor NPMCs, we have explored approaches involving the use of ammonia treatment, the addition of various carbon supports, and inclusion of multiple transition metals. In this presentation, we will summarize the results of these studies, which have involved the extensive use of characterization techniques, such as X-ray photoelectron spectroscopy, scanning electron microscopy, scanning transmission electron microscopy, X-ray diffraction, surface area/pore distribution measurements, and nano-scale X-ray computed tomography. In the conclusion, we will also define critical factors for enhancing the performance of NPMCs in the PEFC cathode and outline directions for future research. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. Microscopy research supported through a user project at ORNL’s Center for Nanomaterials Sciences, which is an Office of Science User Facility. References Spendelow et al., DOE Fuel Cell Technologies Office, Fuel Cell System Cost-2013, (2013).Hoon T. Chung et al., “Combined nitrogen precursor approach to develop highly active non-precious metal oxygen reduction reaction catalyst.” in preparation.S. Ma et al., “Cobalt Imidazolate Framework as Precursor for Oxygen Reduction Reaction Electrocatalysts,” Chem. Eur. J. 17, 2063 (2011).Proietti et al., “Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells,” Nat. Commun. 2, 416 (2011)

Thin Film Electrodes and Electrochemical Reactions at Three-Phase Boundary in Alkaline Media: A DFT Approach

With increased energy demands, fuel cells offer a viable solution due to their efficient conversion of energy from various fuels. Switching to a basic electrolyte, many metals that would be susceptible to corrosion in an acidic environment become stable in an alkaline one. This allows for the inclusion of non-precious metals in the electrodes. However, the kinetics in an alkaline environment tend to be sluggish; this must be overcome for alkaline fuel cells to become commercially realizable. While many model electrodes have been investigated for possibility to improve the kinetics in alkaline fuel cells, this work focuses on thin film electrodes and reactions happening at the interphase between the substrate and the film. The introduction of three-phase boundaries can allow the various reaction intermediates to preferentially bind to different locations, thus possibly allowing one to break away from scaling relationships. This could ideally enable the catalyst to reach higher catalytic activity [1]. To determine the effectiveness of these electrodes, density functional theory (DFT) is employed. Before work was done to model the interphases, extensive work was done examining various moiré patterns for various oxidation states of transition metal films, with a focus on FeOxHy films. In this work, the stability of a variety of transition metal (hydr)oxide thin films on Pt and Au are first examined for stability for their future prospects of viable catalysts for fuel cell applications. In addition, phase diagrams are constructed to determine the state of the film at a given voltage, something crucial for designing optimal catalysts. A DFT + U scheme is employed to model the thin films, where U values are fitted by correcting the formation energies. While the oxidation state and strain of the film are predicted from the full film phase diagrams, the nature of the interphase needed to be determined. The focus , hydrogen evolution and CO oxidation at these interphases with each reaction occurring at a different equilibrium potentials. This knowledge necessitated the creation of phase diagrams for the interfaces, to identify the most stable oxidation state the edge may take. With these phase diagrams, the thermodynamics and kinetics for the two reactions could be calculated with DFT along with nudged elastic band (NEB) calculations to calculate the activation barriers. These results are then compared with those on a clean Pt surface. [1] R. Subbaraman, D. Tripkovic, K. Chang, D. Strmcnik, A. P. Paulikas, P. Hirunsit, M. Chan, J. Greeley, V. Stamenkovic, N. M. Markovic. Nature Materials. 11, 550 (2012)

Boosting the activity of a Au/CeO2/Al2O3 catalyst for the WGS reaction

Herein a strategy to design highly efficient Au/CeO2/Al2O3 based WGS catalysts is proposed. The inclusion of transition metals, namely Fe, Cu and Zn as CeO2 dopant is considered. All the promoters successfully increased the WGS performance of the undoped sample. The activity improvement can be correlated to structural and/or redox features induced by the dopants. The comparative characterization of the doped samples by means of XRD, Raman spectroscopy and OSC evaluation permits an accurate understanding of the boosted WGS activity arising from the Ce-promoter interaction. This study establishes distinction among both, structural and redox sources of promotion and provides a useful strategy to develop highly active Au/CeO2 based catalysts for the WGS reaction.

Synthesis and Characterization of Metal- and Non-Metal-Doped Titania Nanotubes for Solar Hydrogen Generation and Methanol Electrooxidation

Functional nanostructured TiO2 materials with unique electrical, chemical and catalytic properties are being increasingly used in many applications, including lithium-ion batteries, gas sensors, hydrogen generation, electrocatalysis and photocatalysis. A number of different pathways and processes have been developed and reported to synthesize titania nanotubes (TNTs), nanorodes, and nanospheres. The most common methods include sol-gel, hydrothermal treatment, electrophoretic deposition and electrochemical anodization. The latter technique has been utilized by many researchers to fabricate highly ordered titania nanotubes and, subsequently, doped with both metals and non-metals. The last step—inclusion of metals and non-metals into the TNT matrix—is critical for solar hydrogen generation since pure titaina is insufficient under visible light due to its wide band gap, which is around 3.2 eV. Furthermore, metal oxides such as titanium dioxide suffer from lower surface area and electrical conductivity compared with carbon-based materials for use in direct methanol fuel cells. Accordingly, they are often combined with carbon-based materials and/or transition metals to form oxide-carbon hybrid structures.Highly ordered titania nanotubes (Figure 1) were fabricated employing a simple electrochemical anodization technique in a conventional two-electrode cell with titanium foil and graphite as working and counter electrodes, respectively. Metals, including nickel and platinum, were electrodeposited on TNT or TNT-C materials using a pulsed current electrodeposition technique [1]. All samples were then characterized by scanning electron microscopy, X-ray powder diffractometry, cyclic voltammetry, and chronoamperometry. Structural examination of the samples confirmed the presence of rutile and anatase nanocrystalline TNTs after annealing at different temperatures and durations. The presence of nanoparticles, including platinum and nickel, were also confirmed.For methanol electrooxidation, the activity and durability of the hybrid catalyst layers were determined in a solution containing one molar sulfuric acid and one molar methanol. The hybrid catalyst layer showed a better performance towards methanol oxidation compared with state-of-the-art carbon-supported platinum layers. For solar hydrogen generation, the efficiency of the photoanodes was found to increase as the amount of dopant increased to 3.0%. Further increase in dopant, however, resulted in a decrease in efficiency, possibly due to a higher rate of electron-hole recombination.Reference1. S. Karimi & F.R. Foulkes, Electrochemistry Communications 19 (2012) 17-20

Computational analysis of compaction wave dissipation in porous metalized explosives

It is well established that the inclusion of reactive metals in explosive formulations can enhance post-detonation energy release but it remains unclear, even for idealized systems, how the composition and microstructure of metal containing porous solid explosives affects dissipative heating within compaction waves that is important for weak initiation of detonation. In this study, we perform inert meso-scale simulations to computationally examine how the initial porosity and metal mass fraction of aluminized HMX influences dissipation within compaction waves and we compare predictions to those given by a macro-scale compaction theory. The meso-scale model uses a hyperthermoelastic-viscoplastic and stick-slip friction theory to track the evolution of thermomechanical fields within individual particles that result from pore collapse within waves. Effective quasi-steady wave profiles are obtained by averaging meso-scale fields over space and time. The macro-scale theory predicts the variation in effective thermomechanical fields within waves due to imbalances in the phase-specific pressures and configurational stresses. Qualitative agreement exists between meso-scale and macro-scale predictions.

Human health risk from hexachlorocyclohexane and dichlorodiphenyltrichloroethane pesticides, through consumption of vegetables: estimation of daily intake and hazard quotients

People are encouraged to consume more fresh vegetables due to the high nutritional value and fibre contents in vegetables. At the same time, due to pesticidal residue in vegetables, vegetable consumption is considered as an important route of pesticides uptake by human beings. Pesticides, particularly organochlorines such as Aldrin, heptachlor and isomers of dichlorodiphe - nyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) are a major concern because of their persistence, bioaccumulation, toxicity, and long-range environmental transport ability. Hence information on such toxic contaminants in vegetables is very essential, due to human health concern. In order to assess the potential health risks associated with vegetable consumption due to pesticidal residues of DDT and HCH, sixty four samples of commonly available vegetables were collected from a local market in West Bengal, India and analysed for DDT and HCH. In this study, estimated average daily intake of HCHs and DDTs through vegetables was ranged between 5.0x10<sup>–8</sup>–9.1x10<sup>–6</sup> mg kg<sup>–1</sup> day<sup>–1</sup> with an average value of 2.0x10<sup>–6</sup> mg kg<sup>–1</sup> day<sup>–1</sup>. Human health risk was assessed in terms of incremental lifetime cancer risk and health hazard index was between 1.7x10<sup>–8</sup>–8.8x10<sup>–6</sup> and 1.5x10<sup>–7</sup>– 1.7x10<sup>–2</sup>, respectively. Generated results were compared with maximum residual levels and reference values, were within acceptable limits and suggested no health risk to the human populations. Therefore, an extensive study on vegetables with the inclusion of other persistent organic pollutants and toxic metals should be carried out to know the overall scenario of contamination of vegetables.

Breaking up the wall: metal-enrichment in Ovipositors, but not in mandibles, co-varies with substrate hardness in gall-wasps and their associates.

The cuticle of certain insect body parts can be hardened by the addition of metals, and because niche separation may require morphological adaptations, inclusion of such metals may be linked to life history traits. Here, we analysed the distribution and enrichment of metals in the mandibles and ovipositors of a large family of gall-inducing wasps (Cynipidae, or Gall-Wasps) (plus one gall-inducing Chalcidoidea), and their associated wasps (gall-parasitoids and gall-inquilines) (Cynipidae, Chalcidoidea and Ichneumonoidea). Both plant types/organs where galls are induced, as well as galls themselves, vary considerably in hardness, thus making this group of wasps an ideal model to test if substrate hardness can predict metal enrichment. Non-galler, parasitic Cynipoidea attacking unconcealed hosts were used as ecological “outgroup”. With varying occurrence and concentration, Zn, Mn and Cu were detected in mandibles and ovipositors of the studied species. Zn tends be exclusively concentrated at the distal parts of the organs, while Mn and Cu showed a linear increase from the proximal to the distal parts of the organs. In general, we found that most of species having metal-enriched ovipositors (independently of metal type and concentration) were gall-invaders. Among gall-inducers, metals in the ovipositors were more likely to be found in species inducing galls in woody plants. Overall, a clear positive effect of substrate hardness on metal concentration was detected for all the three metals. Phylogenetic relationships among species, as suggested by the most recent estimates, seemed to have a weak role in explaining metal variation. On the other hand, no relationships were found between substrate hardness or gall-association type and concentration of metals in mandibles. We suggest that ecological pressures related to oviposition were sufficiently strong to drive changes in ovipositor elemental structure in these gall-associated Hymenoptera.

Ionization within the Local Cavity by Hot White Dwarfs

ABSTRACTWe present estimates of the contribution from 33 nearby (d < 100 pc) hot DA white dwarfs to the total ionization of the Local Cavity. The EUV spectra of these white dwarfs have been derived using non-LTE stellar atmosphere models (with the inclusion of metals where necessary) to calculate the incident flux at the Earth using up-to-date distances and interstellar column densities. Our model spectra give a very good approximation to the spectra obtained with observations from the NASA Extreme Ultraviolet Explorer satellite. The number of Lyman continuum photons per second emitted by each of the white dwarfs for wavelengths over the 30–912 Å range was then derived. Using these numbers, the respective sizes of the ionized Strömgren spheres of HII were then calculated for each star under the assumption of ambient interstellar electron density values of ne = 0.04 cm-3 and 0.10 cm-3. The location and sizes of these ionized regions have been plotted on a 3D map of the neutral absorption contours of the local ISM, as derived for both in-plane and out of plane directions. A similar procedure was also carried out for the determination of the sizes of the ionized HeII regions surrounding the same 33 white dwarfs. We conclude that only a few of the very hottest DA white dwarfs located within the Local Cavity can possess appreciably sized ionized Strömgren spheres of HII and HeII. The size of these ionized regions can potentially range between 20 pc and 40 pc in diameter, dependent on the ambient value of the electron density of the interstellar medium. However, the volumetric filling factor of these ionized spheres within the Local Cavity is small (∼6%), even at the lowest value of electron density considered in this study (i.e., ne = 0.04 cm-3). Thus, the contribution from DA white dwarfs to the ionization of both the local interstellar cloud complex and other clouds located within the Local Cavity is of secondary importance compared to the ionization contribution provided by the two early B-type stars of ϵ and β CMa.

Assessment of Heavy Metals Pollution in Sediments of the Korbevačka River in Southeastern Serbia

The Korbevačka River is located in the southeastern part of Serbia. This river is a main recipient of all kinds of pollutants from the Pb−Zn mine “Grot.” Sediments from the Korbevačka River were studied to determine the distribution of the metals along the river, assess the quality of sediment, and find the degree of contamination. The concentration of iron, manganese, nickel, copper, zinc, cadmium, lead, mercury, arsenic, chromium, and barium were determined. River sediments were collected and analyzed for heavy metal concentration using atomic absorption spectrophotometer. The degree of pollution in the sediments of the Korbevačka River has been evaluated based on Canadian sediment quality guidelines, enrichment factor (EF), geo-accumulation index (Igeo) and pollution load index (PLI). Inter-metal associations have been evaluated by Pearson correlation coefficients (r). The results indicated that: (1) sediments have been polluted with Pb, Cd, Zn, and Cu and have high anthropogenic influences; (2) the calculation of geo-accumulation index suggests that the Korbevačka River sediments have background concentrations of Fe, Cr, and Ni (Igeo < 1); (3) the co-precipitation (inclusion, occlusion, and adsorption) of heavy metals (except As and Ba) with Mn and Fe geochemical phases.

Heavy Metal Analysis of Ortho MTA and ProRoot MTA

Introduction Recently, several kinds of mineral trioxide aggregate (MTA)-based products have been introduced in endodontics. Ortho MTA (BioMTA, Seoul, Republic of Korea) is one of those products, which was developed for retrograde filling, perforation repair, orthograde root canal obturation, and direct pulp capping. The inclusion of heavy metals in MTA-based materials is of concern because they come into direct contact with hard and soft tissues. The aim of this study was to investigate and compare the levels of arsenic (As), chromium (Cr), hexavalent chromium (Cr 6+), and lead (Pb) in Ortho MTA and ProRoot MTA. Methods One gram of each MTA was digested using a mixture of hydrochloric and nitric acids and filtered. The As, Cr, and Pb in the resulting filtrates were analyzed by inductively coupled plasma–optical emission spectrometry. The level of Cr 6+ was measured by the methods suggested in the Korean Standard L 5221. The results were statistically analyzed using the Mann-Whitney U test. Results The concentration of As in ProRoot MTA was 1.16 ppm, but As was not detected in Ortho MTA. Cr 6+ and Pb were not detected in either MTA. Ortho MTA contained significantly less Cr than ProRoot MTA ( P < .05). Conclusions Ortho MTA and ProRoot MTA meet the ISO specification 9917-1 regarding the safety limits of As and Pb and are safe biomaterials when the purity of As, Cr 6+, and Pb is considered.

Structure of vacancy-ordered single-crystalline superconducting potassium iron selenide

With single crystal X-ray diffraction studies, we compare the structures of three sample showing optimal superconductivity, K0.774(4)Fe1.613(2)Se2, K0.738(6)Fe1.631(3)Se2 and Cs0.748(2)Fe1.626(1)Se2. All have an almost identical ordered vacancy structure with a ({\sqrt}5 x {\sqrt}5 x 1) super cell. The tetragonal unit cell, space group I4/m, possesses lattice parameters at 250K of a = b = 8.729(2) {\AA} and c = 14.120(3) {\AA}, a = b = 8.7186(12) {\AA} and c = 14.0853(19) {\AA} and at 295 K, a = b = 8.8617(16) {\AA} and c = 15.304(3) {\AA} for the three crystals, respectively. The structure contains two iron sites; one is almost completely empty, whilst the other is fully occupied. There are similarly two alkali metal sites that are occupied in the range of 72.2(2) % to 85.3(3) %. The inclusion of alkali metals and the presence of vacancies within the structure allows for considerable relaxation of the FeSe4 tetrahedron, compared with members of the Fe(Te, Se, S) series, and the resulting shift of the Se - F - Se bond angles to less distorted geometry could be important in understanding the associated increase in the superconducting transition temperature. The structure of these superconductors distinguishes themselves from the structure of the non-superconducting phases by an almost complete absence of Fe on the (0 0.5 0.25) site as well as lower alkali metal occupancy that ensures an exact Fe2+ oxidation state, which are clearly critical parameters in the promotion of superconductivity.

Analyses of Heavy Metals in Mineral Trioxide Aggregate and Portland Cement

Introduction Portland cement is used in the construction industry as a binder in concrete. It is manufactured from chalk, limestone, and clay, which are clinkered at very high temperatures and ground with gypsum to form Portland cement. The raw materials and the manufacturing process can result in the inclusion of heavy metals in Portland cement. Portland cement with a four to one addition of bismuth oxide is marketed as mineral trioxide aggregate (MTA), which is used mainly as a dental material. Heavy metal inclusion can be of concern because MTA is in contact with hard and soft tissues. Methods Measurements of arsenic, lead, and chromium in hydrated gray and white Portland cement, ProRoot MTA, and MTA Angelus were conducted with graphite furnace atomic absorption spectrophotometry after acid digestion on the hydrated material. The leaching of the metal ions from the solid material in water and simulated body fluid (SBF) was also determined. Results All cement types showed high relative values of leached chromium compared with arsenic and lead in both the total metal content and leached species. The gray Portland cement showed the highest total amount of metal. The white Portland and both MTAs had lower values for all the leached metal ions. Conclusions Both MTAs released more arsenic than the amount specified in ISO 9917-1 (2007). Portland cements and MTAs showed evidence of heavy metals in the acid-soluble form as well as leaching in deionized water and SBF. MTA contained levels of arsenic higher than the safe limit specified by the ISO 9917-1 (2007).

Hydration Characteristics of Calcium Silicate Cements with Alternative Radiopacifiers Used as Root-end Filling Materials

Introduction Mineral trioxide aggregate (MTA) is composed of calcium silicate cement and bismuth oxide added for radiopacity. The bismuth oxide in MTA has been reported to have a deleterious effect on the physical and chemical properties of the hydrated material. This study aimed to investigate the hydration mechanism of calcium silicate cement loaded with different radiopacifiers for use as a root-end filling material. Methods Calcium silicate cement loaded with barium sulfate, gold, or silver/tin alloy was hydrated, and paste microstructure was assessed after 30 days. In addition, atomic ratio plots of Al/Ca versus Si/Ca and S/Ca and Al/Ca were drawn, and X-ray energy dispersive analysis of the hydration products was performed to assess for inclusion of heavy metals. The leachate produced from the cements after storage of the cements in water for 28 days and the leaching of the radiopacifiers in an alkaline solution was assessed by using inductively coupled plasma. Results The hydrated calcium silicate cement was composed of calcium silicate hydrate, calcium hydroxide, ettringite, and monosulfate. Unhydrated cement particles were few. No heavy metals were detected in the calcium silicate hydrate except for the bismuth in MTA. Calcium was leached out early in large quantities that reduced with time. The barium and bismuth were leached in increasing amounts. Copper was the most soluble in alkaline solution followed by bismuth and barium in smaller amounts. Conclusions The bismuth oxide can be replaced by other radiopacifiers that do not affect the hydration mechanism of the resultant material.

Expression of Ni-Fe hydrogenase structural genes derived from Thiocapsa roseopersicina in Escherichia coli

Obtaining high amounts of pure hydrogenase is a key objective, because this enzyme may be used in fuel cells and H 2 sensors. In this aspect, the HydSL Ni‐Fe hydrogenase from the purple sulfur bacterium Thiocapsa roseopersicina , which exhibits a high activity and is resistant to elevated temperatures and oxygen, is of special interest. Unfortunately, since T. roseopersicina is difficult to culture and synthesizes the HydSL Ni‐Fe hydrogenase at a very low level, the production of this enzyme in Escherichia coli would be invaluable. To study this possibility, we investigated the products of expression of structural genes encoding two subunits of the HydSL Ni‐Fe hydrogenase in this heterologous system. The major part of the protein was present in inclusion bodies, and a smaller part was in solution. Electron micrographs revealed different structure and electron density of inclusion bodies corresponding to the products of two different structural genes. We assumed that the difference in the electron density may be due to inclusion of metals in one of the subunits. Hydrogenase (EC 1.12.xx) is an enzyme catalyzing the reaction of molecular oxygen activation. Depending on the metal contained in the active site of the enzyme, all enzymes of this class are divided into Fe-containing hydrogenases, Ni‐Fe-containing hydrogenases, and hydrogenases whose reaction site contains an iron ion that is not incorporated into the protein globule but is present as a cofactor [1]. The interest to hydrogenases is determined by both active studies of the formation of the structure and the mechanism of action of complex metalloenzymes and the possibility of their use in practice in fuel cells and H 2 sensors.