XANES, EXAFS, Voltammetric, and Microhardness Studies of Manganese Dioxide-Lead-Lead Dioxide Vitroceramics

In this work we investigated the electrochemical performances and mechanical behavior of the manganese dioxide-lead dioxide-lead vitreous system. The structural and electrochemical properties of vitroceramics were investigated by the analysis of X-ray diffraction (XRD) spectra, X-ray absorption spectroscopy (XAS), and measurements of cyclic voltammetry and linear sweep voltammetry. The mechanical properties of the studied samples were determined by Vickers hardness values using the indentation method. The analysis of X-ray absorption near edge structure (XANES) data for the L3 edge of the lead and the radial distribution function data for the PbO₂ and Pb model indicate the modification of Pb-O interatomic distances by the doping process. The voltammetric study reveals the vitroceramic with x = 90 mol% Pb as the most suitable for application as a lead acid battery electrode.

Advanced zirconia ceramics stabilized with yttria and magnesia: Structure and Vickers microhardness

The samples 8YSZ containing 70, 75, 80 mol% ZrO₂ and other oxides were prepared by. a high temperature solid state reaction process. Using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and spectroscopic methods were evaluated the effect of oxide addition on the properties of yttria-doped zirconia. X-ray data shows the formation of zirconia (Y-doped), YSZ and/or tetragonal zirconia crystalline phases in all samples. IR data indicate the stretching vibrations of the Si-O bonds from tetrahedral [SiO₄] units and the stretching vibrations of the Fe-O bonds from [FeO₆] structural units, respectively. EPR results indicate the destroying of the local ordering of the Fe⁺³ ion vicinities situated in the rhombic distorted octahedral geometries by the increasing of ZrO₂ content in the host ceramic. The highest values of Vickers hardness were recorded for the ceramics containing 70 and 75 mol% ZrO₂. This superior performance can be explained considering the presence of a smaller amount of monoclinic ZrO₂ crystalline phase in the ceramic structure. The analysis of the X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) data shows the presence of Fe⁺² and Fe⁺³ ions. In the ceramics with higher ZrO₂ contents the iron atoms adopt a randomly structure due to the highly distorted [FeO₆] structural units and non-equivalent Fe-O distances in the first coordination shell.

Stabilized zirconia ceramics for dental applications

The research is aiming to obtain at room temperature a new ceramic material containing partially stabilized zirconia with different oxides after sintering used for dental and other technological purposes. Our research proposes a new method based on the use of stabilized zirconia with other oxides to obtain optimized dental material with a lower cost price and / or improved properties to allow wider use of these products to an increased number of patients in dental offices. X-ray diffraction, SEM analysis. FTIR spectroscopy, UVVis and density measurements were accomplished for the three ceramic systems. The correlation between the microstructure and the spectroscopic properties of zirconium stabilized by FTIR spectroscopy, UV-Vis helps understanding the mechanisms associated with the formation of high (tetragonal and / or cubic) temperature zirconia. Along with the simple, less costly preparation method and high purity of the ceramic products our study offers a highly desirable product for technological applications.

Characteristics and local structure of hafnia-silicate-zirconate ceramic nanomixtures

Zirconate systems having the composition 3HfO₂·15SiO₂·xY₂O₃·(82 - x)ZrO₂, where x = 2, 7 and 12 mol% Y₂O₃, were synthesized by a sol-gel method. The analysis of X-ray diffraction data showed the presence of the t-ZrO₂, m-ZrO₂, m-HfO₂, Y₂SiO₅ and Y₂Si₂O₇ crystalline phases in a ceramic nanomixture. Spectroscopic data show that the increase of the Y₂O₃ content of samples determines the increase of the t-ZrO₂, m-HfO₂ and silicate crystalline phases. Gap energy values decrease almost linearly with increasing Y₂O₃ content of samples. A detailed study of XANES data does not show a significant difference with increasing Y₂O₃ content of the samples suggesting an appreciable stability of the hafnium ions +4 oxidation state and their microvicinity. EXAFS results show that the local structure around the Hf cation is similar to that from the monoclinic crystalline HfO₂ where the Hf-O coordination number tends to 7. The bond lengths of Hf-O shells show small deviations from ∼2.12 Å and the Hf-metal paths become more structured by increasing the Y₂O₃ content of the samples.

Night shift work surrounding pregnancy and offspring risk of atopic disease

BACKGROUND

Night shift work surrounding pregnancy may contribute to the risk of developing atopic diseases in offspring due to alterations in the prenatal environment, from stress.

OBJECTIVE

To examine the association of maternal night shift work surrounding pregnancy and offspring risk of developing atopic diseases from childhood to adolescence.

METHODS

We examined the association between night shift work before and during pregnancy among 4,044 mothers in the Nurses' Health Study II (NHSII) and atopic dermatitis, asthma and hay fever risk in 4,813 of their offspring enrolled in the Growing Up Today Study (GUTS). Mothers reported whether GUTS participants had ever been diagnosed with atopic dermatitis, asthma or hay fever in the GUTS Mothers' questionnaire. Generalized estimating equation regression models were used to estimate multivariable adjusted odds ratios (OR) and 95% confidence intervals (CIs).

RESULTS

There were no significant associations between pre-conception maternal night shift work and risk of atopic dermatitis, asthma or hay fever in their offspring. Among 545 mothers with information on night shift work during pregnancy, shift work also was not associated with atopic dermatitis, asthma or hay fever in the offspring. Stratified analyses by history of parental atopy and maternal chronotype showed some statistically significant findings, but they were inconsistent and no significant interaction was seen with increasing duration of night shift work.

CONCLUSION

In this study, night shift work before and during pregnancy did not increase offspring risk of developing atopic dermatitis, asthma or hay fever.

Concordance of three alternative gestational age assessments for pregnant women from four African countries: A secondary analysis of the MIPPAD trial

BACKGROUND

At times, ultrasound is not readily available in low resource countries in Africa for accurate determination of gestational age, so using alternative methods is pivotal during pregnancy. These assessments are used to aid the risk analysis for an infant and management strategies for premature delivery, if necessary. Currently, date of last menstrual period, fundal height measurements, and the New Ballard Score are commonly used in resource-limited settings. However, concordance of these measures is unknown for sub-Saharan Africa. We obtained data from an open-label randomized controlled trial, to assess the concordance of these alternative assessment methods. The purpose of our study was to determine the agreement between these alternative methods when used in sub-Saharan African populations.

METHODS

A total of 4,390 pregnant women from Benin, Gabon, Mozambique and Tanzania were included in our analysis. The assessment methods compared were: 1) reported last menstrual period, 2) symphysis-fundal height measurement, and 3) the New Ballard Score. The Bland-Altman method and intraclass correlation coefficient (ICC) were used to test the degree of agreement. Survival range gestational age, used as an inclusion criterion for further analysis, was from 22 to 44 weeks.

FINDINGS

Plots showed a lack of agreement between methods and the 95% limits of agreement too wide to be clinically useful. ICC = 0.25 indicated poor agreement. A post-hoc analysis, restricted from 32 to 42 weeks, was done to check for better agreement in this near-term population. The plots and ICC = 0.16 still confirmed poor agreement.

CONCLUSION

The alternative assessments do not result in comparable outcomes and discrepancies are far beyond the clinically acceptable range. Last menstrual period should not be used as the only estimator of gestational age. In the absence of reliable early ultrasound, symphysis-fundal height measurements may be most useful during pregnancy for fetal risk assessment and the New Ballard Score after delivery as a confirmation of these estimations and for further neonatal management. However, promotion of portable ultrasound devices is required for accurate assessment of gestational age in sub-Sahara Africa.

The network modifier and former role of the bismuth ions in the bismuth-lead-germanate glasses

The present work is focused on the enhancement of network former environment in lead-germanate glasses by bismuth ions doping. A series of bismuth-lead-germanate glasses with the xBi2O3·(100-x)[7GeO2·3PbO] composition glass where 0≤x≤30 mol% Bi2O3 were synthesized by melt-quenching method. The FTIR, UV-VIS spectroscopy and cyclic voltammetry were conducted on these samples to evaluate the doping effect of structure of the host matrix network. Our results indicate that direct incorporation of Bi2O3 into the lead-germanate network modifies the lead-germanate network and the internal structure of glass network is rearranged. The structural flexibility of the lead-germanate network is possible due to its incapacity to accommodate with the excess of oxygen atoms and the creation of bridging oxygen ions. Optical gap energy and refractive index were obtained as a function of Bi2O3 content. Gap energy values decrease as Bi2O3 content increased from 0 to 10 mol%. Further increase of Bi2O3 concentration beyond 10 mol% increased the gap energy values. These behaviors of the glass system can be explained by two mechanisms: (i) for x≤10 mol% Bi2O3--increase of degree of disorder of the host matrix because Bi2O3 is network modifier and (ii) for x>10 mol%--Bi2O3 acts as a network former. Cyclic voltammetry measurements using the glass system with 10Bi2O3·90[7GeO2·3PbO] composition as working electrode show the mobility of the lead ions, in agreement with UV-VIS data.

Effect of aluminum oxide codoping on copper-lead-germanate glasses

Glasses from xCuO⋅(100-x)[7GeO(2)⋅3PbO(2)⋅0.05Al(2)O(3)] system where x=0, 1, 5, 10, 20 and 30 mol% CuO were studied by FT-IR, UV-VIS and ESR spectroscopy in order to obtain information about the structural correlations and the relationship between structure and optical properties in these materials. The analyses of these IR spectra reveal that the accommodation of the network with the excess of oxygen ions is possible by the depolymerization of the germanate network in shorter chains, especially ortho- and/or pyrogermanate structural units. UV-VIS absorption spectrum of the sample with x=1% CuO begins with a rising absorption band situated at about 250 nm. This band can be assigned to the GeOGe wrong bonds such as the Ge(+2) centers. Optical study is performed to calculate the refractive index and optical band gap using UV-VIS spectra in the wavelength range 250-1,000 nm. The increase in optical band is explained on the basis of the average bond energy of the system and the number of non-bridging oxygen ions. ESR spectra of CuO substituted samples are characterized by broad peaks probably because of the formation of Cu(+2)-Ge(+2) exchange pairs which are weakly coupled though the oxygen atom.

Structural study of ternary iron-lead-germanate glass ceramics

Glass ceramics with the composition xFe(2)O(3)·(100-x)[7GeO(2)·3PbO(2)] where 0≤x≤60 mol% were obtained and studied using XRD, FTIR and UV-vis spectroscopy investigations. Heat treatment of glass samples at 400°C for 8 h led to the formation of α, γ-PbGe(4)O(9), Pb(3)Fe(2)Ge(4)O(14) and PbO(1.44) crystalline phases. The content of these crystalline phases depends of Fe(2)O(3) concentration. FTIR spectroscopy data suggest that the lead ions have a pronounced affinity towards [GeO(5)] structural units containing non-bridging oxygens and [FeO(4)] anions producing formation of the Pb(3)Fe(2)Ge(4)O(14) crystalline phase. The introduction of low concentrations of Fe(2)O(3) into the host matrix results in the formation of new absorption UV bands between 320 and 450 nm. These bands arise from to the d-d transitions of the Fe(+3) ions. The light absorption in the range from 250 to 600 nm increases with increasing iron oxide content in matrix network, accompanied with the changes on color from white to brown yellow and darker brown.

Dinuclear manganese centers in the manganese-lead-tellurate glasses

FTIR, UV-VIS and EPR spectra of manganese doped lead-tellurate glasses with composition xMnO·(100-x)[4TeO2·PbO2] where x=0, 1, 5, 10, 20, 30, 40mol% have been studied. The FTIR spectra show the formation of the Mn-O-Pb and Mn-O-Te bridging bonds by increasing of MnO concentration. The UV-VIS spectra show the Mn(+3) species exhibit pronounced absorption, which masks the Mn(+2) spin-forbidden absorption bands when Mn(+2) ions are in high concentrations in these glasses. The EPR spectra exhibit resonance signals characteristic of Mn(+2) ions. The resonance signal located at g≈2 is due to Mn(+2) ions in an environment close to octahedral symmetry, whereas the resonance at g≈4.3 and 3.3 are attributed to the rhombic surroundings of the Mn(+2) ions. The increase in the MnO content gives rise to absorption at g≈2.4 and the paramagnetic ions are involved in dinuclear manganese centers.

Structural properties of molybdenum-lead-borate glasses

Glasses and glass ceramics in the system xMoO₃·(100 - x)[3B₂O₃·PbO] with 0 ≤ x ≤ 30 mol% have been prepared from melt quenching method and characterized by means of X-ray diffraction, FTIR, UV-VIS and EPR spectroscopy. We have examined and analyzed the effects of systematic molybdenum ions intercalation on lead-borate glasses and glass ceramics with interesting results. The observations present in these mechanisms show the lead ions bonded ionic have a strong affinity towards [BO₃] units containing non-bridging oxygens and [MoO₄]²⁻ molybdate units. The pronounced affinity towards molybdate anions yields the formation of the PbMoO₄ crystalline phase. Then, the excess of oxygen can be supported into the glass network by the formation of [MoO₆] and [Mo₂O₇] structural units. Pb²(+) ions with 6s² configuration show strong absorption in the ultraviolet due to parity allowed s²-sp transition and yield an absorption band centered at about 310 nm. The changes in the features of the absorption bands centered at about 310 nm can be explained as a consequence of the appearance of additional absorption shoulder due to photoinduced color centers in the glass such as the formation of borate-molybdate and lead-molybdate paramagnetic defect centers in the glasses. The concentration of molybdenum ions influences the shape and width of the EPR signals located at g ∼ 1.86, 1.91 and 5.19. The microenvironment of molybdenum ions in glasses is expected to have mainly sixfold coordination. However, there is a possibility of reduction of a part of molybdenum ions from the Mo⁶(+) to the Mo⁵(+) and Mo⁴(+) to the Mo³(+) states.

Dual role of the six-coordinated molybdenum and lead ions in novel of photochromic properties of the molybdenum-lead-borate glasses

Transparent glasses were prepared by conventional melting-quenching method in the xMoO(3).(100-x)[3B(2)O(3).PbO] system where 0<or=x<or=15 mol%. By increasing the MoO(3) content up to 20 mol% the PbMoO(4) crystalline phase appears. These systems exhibit a photochromic effect which can be induced through laser exposures (lambda=633 nm) directly on the bulk sample. Structural investigations by FTIR spectroscopy show that the photosensitive effect is due to a reduction of Mo(6+) to Mo(4+) and/or Mo(5+) promoted by the oxidation of Pb(2+) and some structural changes of the borate network.

Infrared spectroscopic and DFT investigations of the vanadate-tellurate glasses structures

Vanadate-tellurate vitreous systems with composition (1-x)TeO(2).xV(2)O(5) where x=0.3 and 0.4 have been prepared by the conventional melt-quench method. The structural aspects have been investigated using FTIR spectroscopy and the density functional theory (DFT) calculations. The present study provides the interesting information concerning devitrification behavior of the vanadate-tellurate vitreous system which occur Te(2)V(2)O(9) crystalline phase. The structure of the heat-treated glasses was found to consist mainly of rings containing [TeO(3)], [TeO(4)], [VO(4)] and some [VO(5)] structural units.

Unusual duodenal presentation of leishmaniasis

This case report describes an atypical case of duodenal leishmaniasis in an elderly patient not infected with human immunodeficiency virus. Investigation of this 84 year old woman with a constitutional syndrome and dysphagia revealed anaemia of chronic disorder, a high erythrocyte sedimentation rate, and polyclonal hypergammaglobulinaemia. Abdominal ultrasonography revealed thickening of the stomach wall, which was seen to be inflamed during gastroscopy. Duodenal histology revealed numerous leishmania amastigotes within macrophages. This was confirmed by bone marrow biopsy and leishmania serology. This case report stresses the importance of atypical symptoms and the unusual location of visceral leishmaniasis, not only in immunodepressed patients, but also in elderly immunocompetent patients.