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2.
Upender Gangadharini Atiar Rahaman Molla Anal Tarafder Basudeb Karmakar 《Journal of the American Ceramic Society》2013,96(7):2155-2162
The glass–ceramics containing a rarely achievable nanocrystalline SrIINbIVO3 phase in the 53.75SiO2–18.25K2O–9Bi2O3–9SrO–9Nb2O5–0.5CeO2–0.5Eu2O3 (mol%) glass system were prepared by the melt‐quench technique followed by a two‐stage controlled heat treatment. The unusual oxidation state of Nb in SrIINbIVO3 crystal is 4+ and upon heat treatment of the samples at lower temperature of 500°C for several hours, the glass composition and chemical environment around Nb ions played a key role for the formation of SrIINbIVO3 in the glass–ceramics. The microstructure of the glass–ceramics was studied using TEM and FESEM. The TEM images advocate 10–40 nm crystallite size of SrIINbIVO3. FTIR study confirms that all the samples consist of SiO4, BiO3, BiO6, and NbO6 structural units. The refractive index at different wavelengths was found to vary in the range 1.7105–1.7905 and increase with increase in heat‐treatment time. The luminescence spectra of Eu3+‐doped glass and glass–ceramics were recorded at 465 nm excitation wavelength and the luminescence intensity is found to be increased with heat‐treatment time due to increase in crystallinity. The high intensity ratio of 5D0→7F2 to 5D0→7F1 indicates that the Eu3+‐doped nanocrystalline SrIINbIVO3 glass–ceramics are promising candidate materials as red‐light source. 相似文献
3.
Anal Tarafder Atiar Rahaman Molla Chirantan Dey Basudeb Karmakar 《Journal of the American Ceramic Society》2013,96(8):2424-2431
The precursor glass in the ZnO–Al2O3–B2O3–SiO2 (ZABS) system doped with Eu2O3 was prepared by the melt‐quench technique. The transparent willemite, Zn2SiO4 (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat‐treatment time was examined by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat‐treatment time which is caused by the partial replacement of ZnO4 units of ZS nanocrystals by AlO4 units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass‐ceramics compared with its precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7Fj (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17‐fold with the process of heat treatment. This enhancement is caused by partitioning of Eu3+ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid‐state red lasers, phosphors, and optical display systems. 相似文献
4.
Effect of wetting and drying and dilution on moisture migration through oil contaminated hydrophobic soils 总被引:3,自引:0,他引:3
Hydrophobic soils display resistance to wetting and frequently do not hold water to support good plant growth. A laboratory investigation was conducted to study moisture movement through hydrophobic soils. Test results indicated that hydrophobic soils have a critical moisture content beyond which they behave as wettable or hydrophilic soils. Soil hydrophobicity decreased and water infiltration increased when the soil was subjected to an increasing number of wetting and drying cycles. The effect of diluting hydrophobic soil with hydrophilic soil on water infiltration was also studied. The results indicated that water infiltration into soil becomes more rapid and uniform as the mass fraction of hydrophilic soil is increased in the mix. Water infiltration was observed even in hydrophobic-hydrophilic soil mixtures classified as severely water-repellent by commonly used arbitrary ordinal scales. 相似文献
5.
This paper proposes the use of a multicriteria assessment technique to evaluate the methane flow during gas extraction from a sanitary landfill. A number of parameters determine the gas generation and the feasibility for its extraction from a landfill. These parameters form a complex set of information with unknown mathematical interrelationships making potential gas flow evaluations difficult and elusive. In addition, the data available for a particular landfill are very often imprecise, uncertain, or subjective, making it even more difficult to evaluate the potential for gas extraction without conducting pilot tests. The method proposed in this paper uses fuzzy composite programming that allows for the use of imprecise information. A landfill gas potential index has been defined, which can be determined by easily obtainable climatological, geological, and landfill parameters. The landfill gas (LFG) potential index is related to the landfill gas flow using an empirical equation. The LFG potential model was calibrated and verified using data obtained from 61 landfills where gas extraction is being conducted. A sensitivity analysis was done to study the impact of variations in the input data on model output. 相似文献
6.
Atiar Rahaman Molla Anal Tarafder Basudeb Karmakar 《Journal of Materials Science》2011,46(9):2967-2976
Glasses were prepared by the melt-quench technique in the K2O–SiO2–Bi2O3–TiO2 (KSBT) system and crystallized bismuth titanate, BiT (Bi4Ti3O12) phase in it by controlled heat-treatment at various temperature and duration. Different physical, thermal, optical, and
third-order susceptibility (χ3) of the glasses were evaluated and correlated with their composition. Systematic increase in refractive index (n) and χ3 with increase in BiT content is attributed to the combined effects of high polarization and ionic refraction of bismuth and
titanium ions. Microstructural evaluation by FESEM shows the formation of polycrystalline spherical particles of 70–90 nm
along with nano-rods of average diameter of 85–90 nm after prolonged heat treatment. A minor increase in dielectric constants
(εr) has been observed with increase in polarizable components of BiT in the glasses, whereas a sharp increase in εr in glass–ceramics is found to be caused by the formation of non-centrosymmetric and ferroelectric BiT nanocrystals in the
glass matrix. 相似文献
7.
The neck curvature obtained in sintering two spherical particles is related to the neck radius of the contact area and the radius of the particles. The radius of the neck curvature, when expressed in terms of the fractional shrinkage, leads to an elegant method of evaluating the activation energy corresponding to the operating mechanism at different stages of sintering. The calculated values of activation energy confirm the diffusion mechanisms operative at different temperatures and different sintering durations. 相似文献
8.
Jyoti P. Ghosh Ruohong Sui Cooper H. Langford Gopal Achari Curtis P. Berlinguette 《Water research》2009,43(18):4499-4506
A comparative study on the photocatalytic activities of four different catalysts, P-25 TiO2, TiO2 nanofibers, tin-doped TiO2 nanofibers under UV light irradiation at 350 nm, and coumarin (C-343) coated TiO2 nanofibers at 436 nm light emitting diodes (LED) is reported. Catalysts performance has been compared based on their reflectance spectrum and activity. A common water contaminant 4-chlorophenol was used as a substrate to compare the activity of the different catalysts under both direct and dye sensitized conditions. Results indicated that amongst the four different catalysts the activity of P-25 was the highest. However the activity of C-343 coated TiO2 nanofibers in the LED (436 nm) based reactor was competitive. Identification of reaction intermediates implied that the reaction pathways under UV (band gap) and visible (dye sensitized) irradiation were different. Nonetheless, ring opening took place in all reactions with both maleic and dihydroxymaleic have been identified as intermediates. The study indicates that ordered arrays of TiO2 irradiated by panels of arrays of low cost high intensity LEDs might be used for the design of reactors. The near monochromaticity, long life, and operation under direct currents are advantages of using LEDs. 相似文献
9.
Self-aldol condensation of cyclohexanone yields a mixture of 2-(1-cyclohexenyl)cyclohexanone (I), 2-cyclohexylidenecyclohexanone
(II) and subsequent condensation products. An acid-treated clay catalyst was employed to selectively obtain the β γ-unsaturated
ketone (I). (I) was separated from the reaction mixture by fractional vacuum distillation and subsequently esterified with
acetic acid to synthesise the corresponding ester, 2-(2-cyclohexyl acetate)cyclohexanone, a precursor of [1,1-biphenyl]-2,2'-diol,
which has applications in plasticizers, pesticides, as a diluent in epoxy resins, etc. The applicability of cation exchange
resins and an acid-treated clay for the esterification of 2-(1-cyclohexenyl)cyclohexanone with acetic acid was explored.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
A quasi-state stress-field generated in an orthotropic elastic circular disk by a heat source rotating on a concentric circular path is investigated. An exact solution is developed in terms of doubly infinite series, using a stress-function approach. Numerical results are given for a boron-epoxy fiber-reinforced composite material and the effect of orthotropy on the distribution of thermal stresses is studied by comparing the orthotropic results with those for an isotropic material. 相似文献