Solid-Phase Transformation of Cs+- and Sr2+-Bearing Zeolite Sorbents Derived From Cenospheres to Mineral-Like Forms

2009 ◽  
Vol 1193 ◽  
Author(s):  
Sergei N. Vereshchagin ◽  
Tatiana A. Vereshchagina ◽  
Leonid A. Solovyov ◽  
Nina N. Shishkina ◽  
Nataly G. Vasilieva ◽  
...  
Keyword(s):  
Solid Phase ◽  
Xrd Analysis ◽  
Multiphase System ◽  
Crystallization Peak ◽  
Strontium Content ◽  
Temperature Range ◽  
Thermochemical Transformation ◽  
Higher Temperature ◽  
Apparent Activation Energies

AbstractThe paper describes the studies of the transformation of Cs+- and Sr2+-containing zeolite sorbents synthesized from fly ash cenospheres to crystalline mineral composition, suitable for the long-term disposal. Series of Cs+- and Sr2+-exchanged NaP1-containing sorbents were subjected to the thermochemical transformation in the temperature range 40-1100°C at atmospheric pressure in air and the progress of reaction was monitored by DSC and XRD analysis. It was shown that initial sodium zeolite undergoes two-step transformation at 736-785°C and 892-982°C forming nepheline as the principle product, with the conversion temperatures being dependant on the heating rate.The thermal treatment of Cs+-bearing zeolite sorbent led to formation of a complex multiphase system, the principal components of which were nepheline and pollucite. Increasing cesium content in the samples led to a monotonous shift of crystallization peak to the higher temperature range (1005-1006°C). A more complicated behavior was observed for Sr2+-containing samples, for which the crystallization temperature tends to increase (compared with NaP1) at lower Sr contents, but it starts decreasing parallel to the Sr2+ content at Sr2+ loadings >10 mg/g. The principal crystalline phases in Sr-NaP1 sample conversion were nepheline and Sr2+-containing feldspar, the quantity of which increased parallel to the increase of strontium content in zeolite.Apparent activation energies of thermochemical transformations were calculated and possible approaches to reduce transformation temperature are discussed and experimentally illustrated.

scholarly journals THE EFFECT OF SODIUM SILICATE AND ITS SOLUTION ON THE PROPERTIES OF REFRACTORY COMPLEX BINDER/NATRIO SILIKATO KIEKIO IR JO TIRPALO TANKIO ĮTAKA KOMPLEKSINIO KAITRAI ATSPARAUS RIŠIKLIO SAVYBĖMS

1999 ◽  
Vol 5 (3) ◽  
pp. 211-216
Author(s):  
Valentin Antonovič ◽  
Stasys Goberis ◽  
Romualdas Mačiulaitis
Keyword(s):  
Sodium Silicate ◽  
Liquid Glass ◽  
Solid Phase ◽  
Physical And Mechanical Properties ◽  
Alumina Cement ◽  
Hardening Mechanism ◽  
Temperature Range ◽  
Calcium Hydrosilicates ◽  
Higher Temperature ◽  
Complex Binder

In order to improve thermal and mechanical characteristics of a traditional binder with liquid glass a complex binder consisting of liquid glass, its hardener and alumina cement (“Gorkal 70” containing not less than 70 per cent of AI2O3) was tested. Sodium silicate and its solution effect on physical and mechanical properties of a new refractory complex binder (Table 1, Fig 2) were investigated. The results obtained show that compressive strength of binding compound with high quantity of sodium silicate (N3) is the lowest after it had been cured, dried and fired at 300–600°C (Fig 3). It was also found that the strength of a complex binder with small quantity of sodium silicate (N1) in the temperature range of 20–600°C is 2–3 times as high as that of a traditional binder with dispersed fire-clay. The study in the formation of the structure of a complex binders dilatometric tests have also been made. After initial heating at 80–500°C the compositions contracted (Fig 4) due to dehidratation. At the temperature range of 580–750°C the contraction of compositions continue due to reactions at the solid phase. The hypothesis of the hardening mechanism in the complex binder was proposed. Liquid glass tends to restrain the hydration of the alumina cement though hardeners and sodium silicate interaction result in the intense formation of sodium calcium hydrosilicates. Therefore, a complex binder contains less sodium silicate than a traditional one while being used at higher temperature.

scholarly journals High-temperature short-term and long hardness of sintered compact and porous titanium-siliceous carbide ti3sic2

2004 ◽  
Vol 36 (1) ◽  
pp. 11-20 ◽  
Author(s):  
S.A. Firstov ◽  
E.P. Pechkovsky
Keyword(s):  
High Temperature ◽  
Ternary Compound ◽  
Solid Phase ◽  
Porous Titanium ◽  
Critical Values ◽  
Holding Time ◽  
Short Term ◽  
Sintered Compact ◽  
Temperature Range

The ternary compound of titanium-siliceous carbide Ti3SiC2, one of the representatives of Nan laminates, prepared by solid-phase sintering is investigated in compact and porous (q=0.03-0.41) states. Features of its short-term and long-term hardness (?=10 N) behavior in the temperature range from 20 to 1200?? at a holding time of 1-60 min were studied. It is shown that a temperature of about 700?? and holding time under load of about 10 min are critical values of the indentation procedure that correspond to an intensive decrease of hardness. The presence of porosity results in a decrease in hardness. a deformation scheme of compact and porous titanium-siliceous carbide Ti3SiC2 in the temperature range from 20 to 1200?? is proposed. .

Properties of Multilayer NTC Perovskite Thermistors Prepared by Tape Casting, Lamination and Cofiring

2014 ◽  
Vol 605 ◽  
pp. 507-510 ◽  
Author(s):  
Jan Kulawik ◽  
Dorota Szwagierczak
Keyword(s):  
Tape Casting ◽  
Negative Temperature ◽  
Solid State Reactions ◽  
Temperature Range ◽  
Fine Grained ◽  
Pt Electrodes ◽  
Endurance Tests ◽  
Small Resistance ◽  
Higher Temperature

The paper reports on processing and characterization of multilayer NTC (negative temperature coefficient) perovskite thermistors. Three materials La0.8Sr0.2Ti0.4Fe0.6O3, CaTi.0.8Co0.2O3 and CaTi0.9Y0.1O3 with the stable perovskite structure were synthesized by solid state reactions and used for preparation of slurries for tape casting. Green sheets with screen printed internal Pt electrodes were stacked, laminated isostatically and cofired at 1250-1350°C. SEM observations revealed dense, fine-grained microstructure of ceramic layers, lack of delaminations and cracks and a good cooperation between ceramic and Pt electrode layers. Resistance-temperature characteristics of the fabricated multilayer thermistors were measured in the temperature range 20-820°C. The temperature coefficients of resistance were high, ranging from-9.7 to-1%/°C. Two developed compositions CaTi.0.8Co0.2O3 and CaTi0.9Y0.1O3 were found to be suitable for use at a higher temperature range of 150-500°C. The endurance tests showed small resistance changes (below 1%) after long term ageing at 300-400°C.

scholarly journals Thermal Decomposition of HMX: Low Temperature Reaction Kinetics and their Use for Assessing Response in Abnormal Thermal Environments and Implications for Long-Term Aging

1995 ◽  
Vol 418 ◽  
Author(s):  
Richard Behrens ◽  
Suryanarayana Bulusu
Keyword(s):  
Thermal Decomposition ◽  
Solid Phase ◽  
Test Sample ◽  
Storage Conditions ◽  
Kcal Mole ◽  
Decomposition Products ◽  
Gaseous Products ◽  
Thermal Environments ◽  
Higher Temperature

AbstractThe thermal decomposition of HMX between 175°C and 200°C has been studied using the simultaneous thermogravimetric modulated beam mass spectrometer (STMBMS) apparatus with a focus on the initial stages of the decomposition. The identity of thermal decomposition products is the same as that measured in previous higher temperature experiments. The initial stages of the decomposition are characterized by an induction period followed by two acceleratory periods. The Arrhenius parameters for the induction and two acceleratory periods are (Log(A)= 18.2 ± 0.8, Ea = 48.2 ± 1.8 kcal/mole), (Log (A) = 17.15 ± 1.5 and Ea = 48.9 ± 3.2 kcal/mole), (Log (A) = 19.1 ± 3.0 and Ea = 52.1 ± 6.3 kcal/mole), respectively. The data can be used to calculate the time and temperature required to decompose a desired fraction of a test sample that is being prepared to test the effect of thermal degradation on its sensitivity or burn rates. It can also be used to estimate the extent of decomposition that may be expected under normal storage conditions for munitions containing HMX. The data, along with previous mechanistic studies conducted at higher temperatures, suggest that the process that controls the early stages of decomposition of HMX in the solid phase is scission of the N-NO2 bond, reaction of the NO2 within a “lattice cage” to form the mononitroso analogue of HMX and decomposition of the mononitroso HMX within the HMX lattice to form gaseous products that are retained in bubbles or diffuse into the surrounding lattice.

scholarly journals Using Fission-Track Radiography Coupled with Scanning Electron Microscopy for Efficient Identification of Solid-Phase Uranium Mineralogy at a Former Uranium Pilot Mill (Grand Junction, Colorado)

Geosciences ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 294
Author(s):  
Raymond H. Johnson ◽  
Susan M. Hall ◽  
Aaron D. Tigar
Keyword(s):  
Fission Track ◽  
Solid Phase ◽  
Nuclear Research ◽  
Thin Sections ◽  
Nuclear Research Reactor ◽  
Elemental Data ◽  
Individual Grains ◽  
Scanning Electron ◽  
Section Sample

At a former uranium pilot mill in Grand Junction, Colorado, mine tailings and some subpile sediments were excavated to various depths to meet surface radiological standards, but residual solid-phase uranium below these excavation depths still occurs at concentrations above background. The combination of fission-track radiography and scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS) provides a uniquely efficient and quantitative way of determining mineralogic associations of uranium that can influence uranium mobility. After the creation of sample thin sections, a mica sheet is placed on those thin sections and irradiated in a nuclear research reactor. Decay of the irradiated uranium creates fission tracks that can be viewed with a microscope. The fission-track radiography images indicate thin section sample areas with elevated uranium that are focus areas for SEM-EDS work. EDS spectra provide quantitative elemental data that indicate the mineralogy of individual grains or grain coatings associated with the fission-track identification of elevated uranium. For the site in this study, the results indicated that uranium occurred (1) with coatings of aluminum–silicon (Al/Si) gel and gypsum, (2) dispersed in the unsaturated zone associated with evaporite-type salts, and (3) sorbed onto organic carbon. The Al/Si gel likely formed when low-pH waters were precipitated during calcite buffering, which in turn retained or precipitated trace amounts of Fe, As, U, V, Ca, and S. Understanding these mechanisms can help guide future laboratory and field-scale efforts in determining long-term uranium release rates to groundwater.

scholarly journals Biogeochemical Controls on the Potential for Long-Term Contaminant Leaching from Soils Developing on Historic Coal Mine Spoil

Soil Systems ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 3
Author(s):  
David Singer ◽  
Elizabeth Herndon ◽  
Laura Zemanek ◽  
Kortney Cole ◽  
Tyler Sanda ◽  
...  
Keyword(s):  
Coal Mine ◽  
Solid Phase ◽  
Microbial Community Composition ◽  
Toxic Metal ◽  
Soil Formation ◽  
Mineral Weathering ◽  
Mine Spoil ◽  
Secondary Phases ◽  
Undisturbed Soil

Coal mine spoil is widespread in US coal mining regions, and the potential long-term leaching of toxic metal(loid)s is a significant and underappreciated issue. This study aimed to determine the flux of contaminants from historic mine coal spoil at a field site located in Appalachian Ohio (USA) and link pore water composition and solid-phase composition to the weathering reaction stages within the soils. The overall mineralogical and microbial community composition indicates that despite very different soil formation pathways, soils developing on historic coal mine spoil and an undisturbed soil are currently dominated by similar mineral weathering reactions. Both soils contained pyrite coated with clays and secondary oxide minerals. However, mine spoil soil contained abundant residual coal, with abundant Fe- and Mn- (oxy)hydroxides. These secondary phases likely control and mitigate trace metal (Cu, Ni, and Zn) transport from the soils. While Mn was highly mobile in Mn-enriched soils, Fe and Al mobility may be more controlled by dissolved organic carbon dynamics than mineral abundance. There is also likely an underappreciated risk of Mn transport from coal mine spoil, and that mine spoil soils could become a major source of metals if local biogeochemical conditions change.

Effect on Cs removal of solid-phase metal oxidation in metal ferrocyanides

2017 ◽  
Vol 105 (12) ◽  
Author(s):  
Keun-Young Lee ◽  
Jimin Kim ◽  
Maengkyo Oh ◽  
Eil-Hee Lee ◽  
Kwang-Wook Kim ◽  
...  
Keyword(s):  
Treatment Process ◽  
Solid Phase ◽  
Storage Conditions ◽  
Radioactive Cesium ◽  
Metal Oxidation ◽  
Aging Period ◽  
Higher Temperature ◽  
Increasing Temperature ◽  
And Storage ◽  
Cobalt And Nickel

AbstractMetal ferrocyanides (MFCs) have been studied for many years and are regarded as efficient adsorbents for the selective removal of radioactive cesium (Cs) from contaminated aqueous solutions. Although their efficiency has been demonstrated, various investigations on the physicochemical, thermal, and radiological stability of the solids of MFCs are required to enhance the applicability of MFCs in the treatment process. We observed that the Cs adsorption efficiencies of cobalt and nickel ferrocyanides decreased as their aging period increased, while the Cs adsorption efficiencies of copper and zinc ferrocyanides did not decrease. The tendencies of these ferrocyanides were accelerated by exposure of the solids at a higher temperature for a longer time. Our comprehensive analyses demonstrated that only the oxidizable metals in the MFCs can be oxidized by aging time and increasing temperature; also, this affects the Cs removal efficiency by decreasing the exchangeable sites in the solids. The chemical stability of MFCs is very important for the optimization of the synthesis and storage conditions.

Contrasting effects of fire on populations of two small rodent species in fragments of Atlantic Forest in Brazil

2004 ◽  
Vol 20 (2) ◽  
pp. 225-228 ◽  
Author(s):  
Marcos de Souza Lima Figueiredo ◽  
Fernando Antonio dos Santos Fernandez
Keyword(s):  
Atlantic Forest ◽  
Feedback System ◽  
Rodent Species ◽  
Primary Forest ◽  
Small Rodent ◽  
Forest Species ◽  
The Core ◽  
Higher Temperature ◽  
Disturbed Habitats

Habitat fragmentation causes a sharp increase in the forested area affected by edge effects (Murcia 1995). Compared with the core of the forest, edges present higher litterfall rates, air and soil humidity reduction, higher temperature and increased wind incidence (Bierregaard et al. 1992, Didham & Lawton 1999, Laurance et al. 1998, Matlack 1993). These features of edges may increase the probability of fire occurrence, especially if the surrounding vegetation is composed of grasses (D'Antonio & Vitousek 1992, Freifelder et al. 1998). After a fire, the damaged edge will grow substantial amounts of herbaceous vegetation, extending the inflammable area into the forest, and thereby creating a positive feedback system of fire susceptibility and intensity (Cochrane & Schulze 1999, Cochrane et al. 1999). Fires may affect the structure and composition of the vegetation (Cochrane & Schulze 1999, Didham & Lawton 1999, Sanaiotti & Magnusson 1995), favouring, in the long-term, the dominance of the community by species characteristic of disturbed habitats and making the habitat unsuitable to primary forest species (Malcolm 1994, Possingham et al. 1994). Unfortunately, there are few studies on the effects of fires on neotropical small-mammal populations (Borchert & Hansen 1983, Ojeda 1989, Vieira & Marinho-Filho 1998). The objective of this study was to analyse the influence of a fire on populations of two rodent species, Akodon cursor (Winge) and Oecomys concolor (Wagner) in two fragments of Atlantic Forest in Brazil.

scholarly journals Synthesis and characterization of PIL/pNIPAAm hybrid hydrogels

2016 ◽  
Vol 2 (1) ◽  
pp. 1-4
Author(s):  
Sylvia Pfensig ◽  
Daniela Arbeiter ◽  
Klaus-Peter Schmitz ◽  
Niels Grabow ◽  
Thomas Eickner ◽  
...  
Keyword(s):  
Mechanical Characterization ◽  
Heating Temperature ◽  
Controlled Drug Release ◽  
Solution Temperature ◽  
Scanning Calorimetry ◽  
Critical Solution Temperature ◽  
Temperature Range ◽  
Hybrid Hydrogels ◽  
Higher Temperature

AbstractIn this study, varying amounts of NIPAAm and an ionic liquid (IL), namely 1-vinyl-3-isopropylimidazolium bromide ([ViPrIm]+[Br]−), have been used to synthesize hybrid hydrogels by radical emulsion polymerization. Amounts of 70/30%, 50/50%, 30/70%, 15/85% and 5/95% (wt/wt) of PIL/pNIPAAm were used to produce hybrid hydrogels as well as the parental hydrogels. The adhesive strength was investigated and evaluated for mechanical characterization. Thermal properties of resulting hydrogels have been investigated using differential scanning calorimetry (DSC) in a default heating temperature range (heating rate 10 K min−1). The presence of poly ionic liquids (PIL) in the polymer matrix leads to a moved LCST (lower critical solution temperature) to a higher temperature range for certain hybrid hydrogels PIL/pNIPAAm. While pNIPAAm exhibits an LCST at 33.9 ± 0.3°C, PIL/pNIPAAm 5/95% and PIL/pNIPAAm 15/85% were found to have LCSTs at 37.6 ± 0.9°C and 52 ± 2°C, respectively. This could be used for controlled drug release that goes along with increasing body temperature in response to an implantation caused infection.

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