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During vitrification of radioactive wastes, excessive foaming reduces processing rates within melters by hindering heat transfer from the molten glass pool to the reacting melter feed. Formulations of low‐activity waste (LAW) melter feeds, for vitrification at the Waste Treatment and Immobilization Plant at the Hanford Site, conventionally include the addition of sucrose to mitigate excessive foaming by hastening the denitration process. However, incomplete combustion of sucrose produces organics such as acetonitrile (C2H3N) that may exceed bounding limits of downstream effluent treatment facilities. Using boron nitride (BN) as an alternate reductant to sucrose, in a representative LAW melter feed reduced C2H3N production by 90% by preventing the low‐temperature sucrose–nitrate reactions. Furthermore, foaming was suppressed due to the higher decomposition temperature of BN than H3BO3 meaning a delayed reaction of a large fraction of boron with the transient glass‐forming melt until above the foam onset temperature, thus reducing the quantity and viscosity of the connected melt and trapping less gas in the foam layer. [ABSTRACT FROM AUTHOR]

There is wide industrial interest in developing robust models of long‐term (>100 years) glass durability. Archeological glass analogs, glasses of similar composition, and alteration conditions to those being tested for durability can be used to evaluate and inform such models. Two such analog glasses from a 1500‐year‐old vitrified hillfort near Uppsala, Sweden have previously been identified as potential analogs for low concentration Fe‐bearing aluminosilicate nuclear waste glasses. However, open questions remain regarding the melting environment from which these historic glasses were formed and the effect of these conditions on their chemical durability. A key factor to answering the previous melting and durability questions is the redox state of Fe in the starting and final materials. Past work has shown that the melting conditions of a glass‐forming melt may influence the redox ratio value (Fe+3/∑Fe), a measure of a glass's redox state, and both melting conditions and the redox ratio may influence the glass alteration behavior. Synthetic analogs of the hillfort glasses have been produced using either fully oxidized or reduced Fe precursors to address this question. In this study, the melting behavior, glass transition temperature, oxidation state, network structure, and chemical durability of these synthesized glass analogs is presented. Resulting data suggests that the degree of network connectivity as impacted by the oxidation state of iron impacted the behavior of the glass‐forming melt but in this case does not affect the chemical durability of the final glass. Glasses with a lower degree of melt connectivity were found to have a lower viscosity, resulting in a lower glass transition temperature and softening temperature, as well as in a lower temperature of foam onset and temperature of foam maximum. This lower degree of network connectivity most likely played a more significant role in accelerating the conversion of batch chemicals into glass than the presence of water vapor in the furnace's atmosphere. Future work will focus on using the results from this work with outcomes from other aspects of this project to evaluate long‐term glass alteration models. [ABSTRACT FROM AUTHOR]

This paper describes the development and provides comparisons of thiolated (−SH) and unthiolated Ag–Al–Si–O xerogels for iodine gas capture. These xerogels were produced from alkoxides and then heat-treated at 350 °C to provide mechanical strength for subsequent processing steps. Then, a portion of the xerogels was thiolated using (3-mercaptopropyl)-trimethoxysilane. Next, thiolated and unthiolated batches were ion-exchanged in AgNO3 solutions where Ag+ replaced Na+ in the gel network on a near 1:1 molar basis. Subsamples of the Ag-exchanged xerogels were subjected to a reduction step in H2/Ar to convert Ag+ to Ag0 where the rest of the Ag-exchanged (Ag+) were not reduced. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy revealed nanoscale Ag0 in the Ag+ samples despite no active reduction where actively reduced samples had bimodal Ag0 distribution of ∼2–3 nm hexagonal and ∼6–7 nm cubic crystallites. Synchrotron X-ray absorption spectroscopy was used to assess the oxidization states of Ag, S, and I within the different xerogel samples. The specific surface areas of the base xerogels decreased as subsequent treatments were performed on the as-made samples, albeit the decreases were smaller than aerogel equivalents of these samples from a previous study. All iodine-loaded Ag-based samples showed a mixture of β-AgI and γ-AgI. Comparisons of iodine-loading results with other Ag-based iodine sorbents show that the thiolated Ag0-xerogels in this work have one of the highest iodine-loading capacities (qe) reported to date in saturated conditions with the thiolated Ag0-xerogel showing 522 mg iodine per g of the sorbent. [ABSTRACT FROM AUTHOR]

Water affects the glass melting process by interacting with the foam layer at the glass melt surface and by influencing the batch conversion reactions. Nuclear waste aqueous slurry feed maintains a high water vapor pressure in the melter atmosphere. To investigate to what extent water vapor affects the foaming during vitrification of nuclear waste in joule‐heated cold‐top melters, a series of feed expansion experiments were performed under humid and dry atmospheres using samples of low‐activity waste (LAW) melter feed simulants. Melting of feed pellets in the presence of water vapor slightly decreased the temperature of primary foam onset for an extensively foaming feed, but did not significantly affect the feed volume expansion by foaming or the foam‐collapse temperature. Sets of feed expansion experiments and evolved gas analyses were also performed to check the effect of thermal history on conversion behavior of LAW feed samples. The thermal history was varied by testing feed samples prepared as direct slurry, loose powder, and slow‐ and fast‐dried pellets. The sample preparation methods and the sample shape were not found to influence foaming parameters, except for the direct slurry where the low‐temperature swelling prevented the foam onset and collapse temperatures to be determined. [ABSTRACT FROM AUTHOR]

Alumino‐borosilicate glass‐ceramics (GCs) containing alkali (Na), alkaline earth (Ca), rare earth (RE) (one of La ... Lu, Y), and transition metals (Zr and Mo) were formulated to test the effects of composition and RE cation size on the crystallization of simulated nuclear waste GCs. Eight‐oxide glasses were formulated in the peraluminous ([Na2Oexcess]=[Na2O]‐[Al2O3]‐[ZrO2]<0) region with 10 mol.% RE2O3 and 15 mol.% B2O3. Glasses were melted and quenched, reheated, and slow‐cooled to promote crystallization, and then characterized using quantitative X‐ray diffraction and electron probe microanalysis. Transition metal phases [powellite (Ca,Na,RE)MoO4 and zirconia (Zr,RE)O2 or zircon (Zr,RE)SiO4] always formed, while borosilicate (RE3BSi2O10) or silicate [oxyapatite (RE,Ca,Na)10Si6O26 or keiviite (RE2Si2O7)] plus borate (REBO3) phases also formed, depending on the size of the RE cation and hence its preferred coordination number. All crystalline phases were found to contain RE elements, and often phases incorporated other cations (Zr, Ca, B) which were not nominally part of their pure stoichiometry. These results suggested that the glass formulation and RE size strongly influenced the RE environment in the glass and hence the crystal phases formed. The formation of RE borosilicate, versus separate RE borate and RE silicate phases, also suggested original differences in the glass structure. [ABSTRACT FROM AUTHOR]

A glass‐ceramic waste form is being developed for immobilization of waste streams of alkali (A), alkaline‐earth (AE), rare earth (RE), and transition metals generated by transuranic extraction for reprocessing of used nuclear fuel. Benefits over an alkali borosilicate waste form are realized by the partitioning of the fission product fraction insoluble in glass into a suite of chemically durable crystalline phases through controlled cooling, including (AE,A,RE)MoO4 (powellite) and (RE,A,AE)10Si6O26 (oxyapatite). In this study, a simplified 8‐oxide system (SiO2‐Nd2O3‐CaO‐Na2O‐B2O3‐Al2O3‐MoO3‐ZrO2) was melted, then soaked at various temperatures from 1450 to 1150°C, and subsequently quenched, in order to obtain snapshots into the phase distribution at these temperatures. For these samples, small angle X‐ray and neutron scattering, quantitative X‐ray diffraction, electron microscopy, 23Na nuclear magnetic resonance, Nd3+ visible absorption, and temperature‐dependent viscosity were characterized. In this composition, soak temperatures of ≲1250°C were necessary to nucleate calcium molybdate (~10‐20 nm in diameter). Further cooling produced oxyapatite and total crystallization increased with lower soak temperatures. Both Na and Nd entered the crystalline phases with lower‐temperature soak conditions. Slow cooling or long isothermal treatments at ~975°C produced significantly higher crystal fractions. [ABSTRACT FROM AUTHOR]

Abstract: Lithium and sodium aluminosilicates are important glass‐forming systems for commercial glass‐ceramics, as well as being important model systems for ion transport in battery studies. In addition, uncontrolled crystallization of LiAlSiO4 (eucryptite) in high‐Li2O compositions, analogous to the more well‐known problem of NaAlSiO4 (nepheline) crystallization, can cause concerns for long‐term chemical durability in nuclear waste glasses. To study the relationships between glass structure and crystallization, nine glasses were synthesized in the LixNa1‐xAlSiO4 series, from x = 0 to x = 1. Raman spectra, nuclear magnetic resonance (NMR) spectroscopy (Li‐7, Na‐23, Al‐27, Si‐29), and X‐ray diffraction were used to study the quenched and heat‐treated glasses. It was found that different LiAlSiO4 and NaAlSiO4 crystal phases crystallize from the glass depending on the Li/Na ratio. Raman and NMR spectra of quenched glasses suggest similar structures regardless of alkali substitution. Li‐7 and Na‐23 NMR spectra of the glass‐ceramics near the endmember compositions show evidence of several differentiable sites distinct from known LixNa1‐xAlSiO4 crystalline phases, suggesting that these measurements can reveal subtle chemical environment differences in mixed‐alkali systems, similar to what has been observed for zeolites. [ABSTRACT FROM AUTHOR]

Nepheline (Na6K2Al8Si8O32) is a rock-forming tectosilicate mineral which is by far the most abundant of the feldspathoids. The crystallization in nepheline-based glass-ceramics proceeds through several polymorphic transformations - mainly orthorhombic, hexagonal, cubic - depending on their thermochemistry. However, the fundamental science governing these transformations is poorly understood. In this article, an attempt has been made to elucidate the structural drivers controlling these polymorphic transformations in nepheline-based glass-ceramics. Accordingly, two different sets of glasses (meta-aluminous and per-alkaline) have been designed in the system Na2O-CaO-Al2O3-SiO2 in the crystallization field of nepheline and synthesized by the melt-quench technique. The detailed structural analysis of glasses has been performed by 29Si, 27Al, and 23Na magic-angle spinning - nuclear magnetic resonance ( MAS NMR), and multiple-quantum MAS NMR spectroscopy, while the crystalline phase transformations in these glasses have been studied under isothermal and non-isothermal conditions using differential scanning calorimetry ( DSC), X-ray diffraction ( XRD), and MQMAS NMR. Results indicate that the sequence of polymorphic phase transformations in these glass-ceramics is dictated by the compositional chemistry of the parent glasses and the local environments of different species in the glass structure; for example, the sodium environment in glasses became highly ordered with decreasing Na2O/CaO ratio, thus favoring the formation of hexagonal nepheline, while the cubic polymorph was the stable phase in SiO2-poor glass-ceramics with (Na2O+CaO)/Al2O3 > 1. The structural origins of these crystalline phase transformations have been discussed in the paper. [ABSTRACT FROM AUTHOR]

We report on the influence of Fe2O3 on the crystallization kinetics of nepheline (Na2O·Al2O3·2SiO2)-based sodium aluminosilicate glasses. A series of glasses with varying Al2O3/ Fe2O3 content were synthesized in the system 25Na2O-(25-x) Al2O3-xFe2O3-50SiO2 (x varies between 0 and 5 mol%) through melt-quench technique. A systematic set of experiments were performed to elucidate the influence of iron speciation (Fe2+/Fe3+) on the crystallization kinetics of these glasses including: (1) obtaining the details of nonisothermal crystallization kinetics by differential scanning calorimetry, (2) determining the influence of heat treatment on the structure and iron coordination in glasses by X-ray photoelectron spectroscopy and wet chemistry, and (3) following the crystalline phase evolution in glasses in air and inert environments by Xray diffraction and scanning electron microscopy. The crystallization of two polymorphs of NaAlSiO4--carnegieite (orthorhombic) and nepheline (hexagonal)--was observed in all the glasses, wherein the incorporation of iron promotes the formation of nepheline over carnegieite while shifting the crystallization mechanism from surface to volume. The influence of environment (air versus inert) and iron content on the crystallization kinetics of these glasses is contextualized from the perspective of the devitrification problem usually observed in sodium- and alumina-rich high level nuclear waste glasses. [ABSTRACT FROM AUTHOR]

Nepheline crystallizes upon slow-cooling in some melts concentrated in Na2O and Al2O3, which can result in a residual glass phase of low chemical durability. Nepheline can incorporate many components often found in high-level waste radioactive borosilicate glass, including glass network ions (e.g., Si, Al, Fe), alkali metals (e.g., Cs, K, Na, and possibly Li), alkaline-earth metals (e.g., Ba, Sr, Ca, Mg), and transition metals (e.g., Mn, and possibly Cr, Zn, Ni). When crystallized from melts of different compositions, nepheline composition varies as a function of starting melt composition. Five simulated high-level nuclear waste borosilicate glasses shown to crystallize large fractions of nepheline on slow-cooling were selected for study. These starting melt compositions contained a range of Al2O3, B2O3, CaO, Na2O, K2O, Fe2O3, and SiO2 concentrations. Compositional analyses of nepheline crystals in glass by electron probe micro-analysis (EPMA) indicate that nepheline is generally rich in silica, whereas boron is unlikely to be present in any significant concentration, if at all, in nepheline. Also, several models are presented for calculating the fraction of vacancies in the nepheline structure. [ABSTRACT FROM AUTHOR]

The selection of raw materials affects the rate of batch-to-glass conversion. In all-electric melters, foam under the batch blanket limits the heat flux from the molten glass, thus slowing the rate of melting. Our study, in which we compare the melting behaviors of three batches formulated to vitrify high-alumina high-level waste, shows that a slowly dissolving refractory component can cause excessive foaming. Faster melting batches with gibbsite [ Al(OH)3] or boehmite [ AlO(OH)] as an alumina source produced substantially less foaming than a batch with corundum ( Al2O3). Although gibbsite and boehmite dissolved below 500°C, corundum was still present in the batch up to 900°C; hence, the glass-forming melt lacked alumina in the batch with corundum. The low viscosity of that batch caused the open pores to close prematurely at 660°C, trapping gases and expanding to foam. This would explain the literature-reported slow melting rate of a batch with corundum, as compared to batches with gibbsite and boehmite. [ABSTRACT FROM AUTHOR]

We report clinical and molecular mechanisms relating the process of inflammation involved in the progression of obesity and the metabolic syndrome, emphasizing the cardiovascular problems developed in Hispanic populations. Namely, the incidence, component characteristics and complications of obesity and metabolic syndrome in island Puerto Ricans are described and evidence is presented supporting the fact that the metabolic syndrome may be milder in Puerto Rico than in the mainland United States because it is characterized by less aggressive coronary artery disease and a relatively normal lipid profile. Moreover, data supports the fact that increased serum cholesterol levels produce less myocardial infarctions in Puerto Rico than in mainland Hispanics and Caucasians. In addition, the incidence of ventricular tachycardia, a complication caused by remodeling and ischemia of the heart, may be lower in Puerto Rico than in the United States, although the prevalence of the metabolic syndrome is higher in the island. On the other hand, there is evidence of a rising epidemic of obesity and vascular inflammation in Puerto Rico that suggests that cardiovascular morbidity and mortality in the island will continue to increase in the future decades.

Peripheral arterial disease (PAD) is a significant cause of morbidity and mortality worldwide. Lifestyle changes, like the cessation of the use of tobacco as well as a modification of dietary and exercise habits, can be the most cost-effective interventions in patients with PAD. Smocking cessation is the most important intervention, since it increases survival in these patients. Antiplatelet therapy is an essential component in the treatment of peripheral arterial disease (PAD) of the lower extremities. In addition to delaying arterial obstructive progression, these agents are most usefull in reducing adverse cardiovascular events such as non-fatal myocardial infarction (MI), stroke and vascular death. Mainstay of treatment continues to be aspirin monotherapy (75-325mg daily). Current treatment for lower extremity PAD is directed towards the relief of symptoms and improvement in QoL. The two agents which have consistently been found to be most efficient in achieving these goals are cilostazol and naftidrofuryl oxalate. Naftidrofuryl oxalate may emerge as the most efficient and cost-effective treatment for symptom relief.

A cross-sectional study examined adults aged 21 to 35 years who underwent left cardiac catheterization in the Cardiovascular Center for Puerto Rico and the Caribbean during 2008-2012 due to myocardial infarction. Demographic characteristics, clinical risk factors, and the extent of CAD were documented. Chi-square statistic or Fisher's exact test was used to compare the distribution of demographic, clinical, and lifestyle characteristics across CAD extent. Polytomous logistic regression models were fitted to estimate the prevalence odds ratios (POR) with 95% confidence intervals (Cl) for non-obstructive and obstructive coronary disease (OCD) compared with normal coronary anatomy. Statistical analyses were performed using Stata 11.0. Sixty-three (n = 63) adults were evaluated (81% were men). The mean age was 31 ± 4 years. The most frequent clinical risk factors were history of tobacco use, hyper tension, and dyslipidemia. Obesity was present in 45.9% of subjects and OCD was present in 52.38% of subjects. Obesity and family history of CAD were significantly associated with OCD when adjusted by age. Obese patients had 5.94 times the possibility of having OCD than normal weight patients. Obesity was the most important treatable predictor of premature obstructive CAD in our young adult population.

Two groups of patients were studied to find out the levels of angiotensin-II and endothelin-I in the coronary and peripheral circulation. Group A consisted of eight patients with diabetes mellitus type 2 and coronary artery disease; and Group B with diabetes mellitus without coronary artery disease. Significant differences were found between Group A and B in the levels of both peptides peripherally and intracoronary. This shows the importance of these peptides in the origin of coronary artery disease and progression of the disease in diabetics with coronary artery disease.

Nuclear-waste melter feeds are slurry mixtures of wastes with glass-forming and glass-modifying additives (unless prefabricated frits are used), which are converted to molten glass in a continuous electrical glass-melting furnace. The feeds gradually become continuous glass-forming melts. Initially, the melts contain dissolving refractory feed constituents that are suspended together with numerous gas bubbles. Eventually, the bubbles escape, and the melts homogenize and equilibrate. Knowledge of various physicochemical properties of the reacting melter feed is crucial for understanding the feed-to-glass conversion that occurs during melting. We studied the melter feed viscosity during heating and correlated it with the volume fractions of dissolving quartz (SiO2) particles and the gas phase. The measurements were performed with a rotating spindle rheometer on the melter feed heated at 5 K/min, starting at several different temperatures. The effects of undissolved quartz particles, gas bubbles, and compositional inhomogeneity on the melter feed viscosity were determined by fitting a linear relationship between the logarithm of viscosity and the volume fractions of suspended phases.