排序方式: 共有14条查询结果,搜索用时 15 毫秒
1.
Irina Klimova Tiit Kaljuvee Valdek Mikli Andres Trikkel 《Journal of Thermal Analysis and Calorimetry》2013,111(1):253-258
Urea is one of the main nitrogen fertilizers used in agriculture. But being well soluble in water, hardly 50% of its nitrogen is assimilated by plants. One possibility to eliminate this disadvantage is to use coating agents for modification of urea to obtain a controlled-realized fertilizer. The aim of this research was to study the influence of different lime-containing additives on the thermal behavior and decomposition kinetics of urea in oxidizing atmosphere. Commercial fertilizer-grade urea (46.4% N) and analytical-grade CaO, MgO, CaCO3, MgCO3 were used in the experiments. In addition, one Estonian limestone and one dolomite sample were used as additive or coating material. The experiments with a Setaram Setsys 1750 thermoanalyzer coupled to a Nicolet 380 FTIR Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 900 °C at the heating rate of 5 °C min?1 and to calculate kinetic parameters, additionally, at 1, 2, and 10 °C min?1 in the atmosphere containing 80% of Ar and 20% of O2. The differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results obtained indicate that thermooxidative decomposition of urea as well as the blends of urea with lime-containing materials and urea prills coated with limestone or dolomite powder follows a complex reaction mechanism. 相似文献
2.
Tõnsuaadu K Gruselle M Villain F Thouvenot R Peld M Mikli V Traksmaa R Gredin P Carrier X Salles L 《Journal of colloid and interface science》2006,304(2):283-291
The sorption mechanism of Ru3+ ions on hydroxy (HAp), carbonate (CO3HAp), and fluor apatites (FAp) has been studied in detail. Ru apatites were obtained by reaction of the apatites with RuCl3 in aqueous solution. The structure and composition of the ruthenium-modified apatites were studied by several techniques: elemental analysis, XRD, EXAFS, IR, NMR, SEM-EDS, TEM, and thermal analysis. The amount of Ru in the modified apatite varies from 7.8 to 10.5 wt% and is not related to the initial composition or the specific surface area of the apatite. The different characterization techniques show that in the Ru-modified apatites Ru is surrounded by six oxygen atoms and do not contain any chlorine. For Ru-HAp and Ru-CO3HAp the new phase is amorphous whereas it is crystalline for FAp. The catalytic oxidation ability is higher for Ru-HAp and Ru-CO3HAp compared to Ru-FAp apatite in the oxidation of benzylic alcohol. 相似文献
3.
Ella Duvanova Illia Krasnou Andres Krumme Valdek Mikli Serhii Radio Georgiy M. Rozantsev Yevgen Karpichev 《Molecules (Basel, Switzerland)》2022,27(8)
Novel composite self-disinfecting films of polylactic acid (PLA) filled with nanosized particles of double sodium–copper(II) paratungstate B Na2Cu3(CuOH)2[W12O40(OH)2]·32H2O (POM) were developed. The solvent casting (POM/PLA film) and solvent-free melt extrusion methods (Extr. POM/PLA film) were applied for film preparation. The copper (II) ion release to water from both types of the films after 10 days at different temperatures demonstrated that the PLA matrix acts as a diffusion barrier, and the resulting concentration of released copper in water at room temperature remained low, at 0.79% for POM/PLA film and 0.51% for Extr. POM/PLA film. The POM-containing films reveals a significant inhibitory effect against E. coli ATCC 25922 in the agar diffusion test. The numbers of CFUs in washes of the films after incubation for 24 h were found to be 3.6 log CFU mL–1 (POM/PLA film) and 4.1 log CFU mL–1 (Extr. POM/PLA film). The films combine the antibacterial properties of POM and a bio-based polymer matrix, which makes them a prospective coating material for applications in hospital indoor environments. Excellent thermal stability of POM gives a technological advantage for industrial manufacturing to allow the processing of novel composite material in the solvent free (molten) state. 相似文献
4.
Angelina K. Stoyanova-Ivanova Stanimira D. Terzieva Boris L. Shivachev Valdek Mikli Latinaka K. Vladimirova 《Central European Journal of Physics》2008,6(1):76-79
We have studied the effect of the ratio of different rare-earth element on the superconducting properties and phase formation
of (Nd0.33Eu0.08Gd0.58)Ba2Cu3O
z
ceramic. Bulk NEG samples were prepared using the solid-state reaction process. The superconducting transition for Nd0.33Eu0.08Gd0.58Ba2Cu3O
z
is T
c
≈90 K and the value of the critical current density (J
c
) is 13.9 A/cm2 at 77 K under zero magnetic fields. This value is twice as high when compared with the (J
c
) value of YBCO systems (J
c
= 7.31 A/cm2). The obtained bulk sample was used for the production of superconducting Ag-sheathed tapes by OPIT method including hot
rolling. The critical current density of the obtained tape (337 A/cm2) is one order higher than the one of the bulk sample.
相似文献
5.
Stanimira D. Terzieva Angelina K. Stoyanova-Ivanova Boris L. Shivachev Bonka M. Terzijska Andrzej J. Zaleski Halina Misiorek Valdek Mikli 《Central European Journal of Physics》2009,7(1):84-88
Sintering effects in YBa2Cu3Oz samples with quasi-equal rare earth substitution have been investigated. It has been shown that the Y-123 type compound can
be formed when gadolinium is partially substituted (in this case 50% atomic substitution) for yttrium. The superconducting
compound was obtained by the optimized ceramic method, including solid-state reaction, melting and sintering, controlled by
X-ray diffraction. The microstructure was investigated by SEM and energy dispersive X-ray analyses. An AC susceptibility measurement
has shown that T
c
=93 K. Temperature-dependece of the thermal conductivity (4.5–300 K) of the polycrystalline Y0.5Gd0.5Ba2Cu3O6.94 sample was also measured.
相似文献
6.
Chemical spray pyrolysis was applied to grow ZnO nanorod arrays from zinc chloride solutions with pH=2 and 5 on glass/ITO substrate at 480 and 550 °C. The obtained structures were characterized by their morphological, electrical and PL properties. According to SEM, deposition of acidic solutions retards coalescence of the growing crystals. The charge carrier density in ZnO nanorods was determined from the C-V characteristics of ZnO/Hg Schottky barrier. Carrier densities ∼1015 cm−3 and slightly above 1016 cm−3 were recorded for ZnO deposited at 550 and 480 °C, respectively. According to PL studies, intense UV-emission is characteristic of ZnO independent of growth temperature, the concentration of oxygen vacancy related defects is lower in ZnO nanorods deposited at 550 °C. Solution pH has no influence on carrier density and PL properties. 相似文献
7.
Tiit Kaljuvee Igor Štubňa Peeter Somelar Valdek Mikli Rein Kuusik 《Journal of Thermal Analysis and Calorimetry》2014,118(2):891-899
Thermal behavior of green clay samples from Kunda and Arumetsa deposits (Estonia) as potential raw materials for production of ceramics and the influence of previously fired clay and hydrated oil shale ash additives on it were the objectives of this research. Two different ashes were used as additives: the electrostatic precipitator ash from the first field and the cyclone ash formed, respectively, at circulating fluidized bed combustion (temperatures 750–830 °C) and pulverized firing (temperatures 1,200–1,400 °C) of Estonian oil shale at Estonian Power Plant. The experiments on a Setaram Labsys Evo 1600 thermoanalyzer coupled with Pfeiffer OmniStar Mass Spectrometer by a heated transfer line were carried out under non-isothermal conditions up to 1,050 °C at the heating rate of 5 °C min?1 in an oxidizing atmosphere containing 79 % of Ar and 21 % of O2. Standard 100 µL Pt crucibles were used, the mass of samples was 50 ± 0.5 mg, and the gas flow 60 mL min?1. The results obtained indicate the complex character of transformations and show certain differences in the thermal behavior of Arumetsa and Kunda clays and their mixtures with oil shale ashes depending on the chemical and mineralogical composition of the clays as well as of the oil shale ashes studied. 相似文献
8.
Valdek Mikli 《Mikrochimica acta》2006,155(1-2):205-208
The study covers a problem frequently encountered in the quantification of the results of wavelength-dispersive spectrometry
(WDS) for the composition analysis of thin films. The characteristics of a Parallel Beam Spectrometer and traditional WDS
systems were examined and olivine mineral – (Mg, Fe)2SiO4 (O – 44.03 wt%, Mg – 31.1 wt%, Si – 19.56 wt%, Fe – 5.06 wt%, Ni – 0.16 wt%, Mn – 0.09 wt%) was used as a reference material.
Low accelerating voltage at 7 kV and beam current 400 nA were applied. Both methods yielded 30–35% of Mn. This is attributed
to the overlapping of the MnLα first-order and the MgKα second-order lines. Studies of the influences of the second- and the
third-order lines show that the second-order lines from Kα and Lα X-ray counts affected significantly the obtained WDS spectra
when the influence of Mα counts was insignificant. Furthermore, the third-order lines did not have a marked effect on the
analysis results. 相似文献
9.
A.K. Stoyanova-Ivanova S.D. Terzieva A.D. Staneva V. Mikli R. Traksmaa Y.B. Dimitriev V.T. Kovachev 《Central European Journal of Chemistry》2006,4(1):166-173
We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-x
CaxBa2Cu3O7-δ
(RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive
spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established
between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium
is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. 相似文献
10.
I. Rudjak T. Kaljuvee A. Trikkel V. Mikli 《Journal of Thermal Analysis and Calorimetry》2010,99(3):749-754
The thermal behaviour of ammonium nitrate (AN) and its prills coated with limestone and dolomite powder was studied on the
basis of commercial fertilizer-grade AN and six Estonian limestone and dolomite samples. Coating of AN prills was carried
out on a plate granulator and a saturated solution of AN was used as a binding agent. The mass of AN prills and coating material
was calculated based on the mole ratio of AN/(CaO + MgO) = 2:1. Thermal behaviour of AN and its coated prills was studied
using combined TG-DTA-FTIR equipment. The experiments were carried out under dynamic heating conditions up to 900 °C at the
heating rate of 10 °C min−1 and for calculation of kinetic parameters, additionally, at 2, 5 and 20 °C min−1 in a stream of dry air. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman
was used to calculate the kinetic parameters. The results of TG-DTA-FTIR analyses and the variation of the value of activation
energy E along the reaction progress α indicate the complex character of the decomposition of neat AN as well as of the interactions
occurring at thermal treatment of AN prills coated with limestone and dolomite powder. 相似文献