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1.
On the modelling of solid state reactions.Synthesis of YAG 总被引:2,自引:0,他引:2
Feliksas?Ivanauskas Aivaras?Kareiva Bogdanas?LapcunEmail author 《Journal of mathematical chemistry》2005,37(4):365-376
There is a model of yttrium aluminium garnet (YAG) synthesis presented in this article. The developed model is based on nonlinear reaction–diffusion partial differential equations. The solution was carried out numerically using finite difference techniques. We got dependability curves for diffusion and reaction rates and offered possible method to localize values of diffusion and reaction rate constants precisely enough.AMS subject classification: 35K57, 65M06 相似文献
2.
Ma?vydas Mackevi?ius Feliksas Ivanauskas Aivaras Kareiva Darius Jasaitis 《Journal of mathematical chemistry》2012,50(8):2291-2302
Recently, we presented a method for estimation of the diffusion and reaction rates of synthesis at high temperatures using limited information, such as synthesis time and dimensions of reactants, from real laboratory experiments (Mackevi?ius et?al. in Central Eur J Chem 10(2):380–385, 2012). There, we restricted ourselves to the one- and two-dimensional models. Having both adapted our computing program to the three-dimensional case and significantly speeded it up, now we are able present the results in the three-dimensional model. Solving an inverse modeling problem, we obtain explicit formulas for the diffusion coefficient and reaction rate as functions of temperature. We calculate the activation energies and other parameters, thus obtaining conditions for occurrence of synthesis. In addition, using the results of the three-dimensional model, we find the optimal temperature for energy consumption in the YAG synthesis. 相似文献
3.
Yu. S. Škadauskas O. P. Škadauskene A. A. Kareiva 《Journal of Analytical Chemistry》2001,56(6):530-533
A procedure has been developed for the extraction–photometric determination of thallium as an ion-pair complex with bromide ions and toluylene blue. The procedure allows thallium to be determined in Tl–Cu-containing high-T
csuperconducting materials based on Cu, Ca, Ba, Sr, La, Pb, In, and Hg immediately after sample dissolution without separating Tl from its concomitants. 相似文献
4.
Ligita Valeikiene Inga Grigoraviciute-Puroniene Arturas Katelnikovas Aleksej Zarkov Aivaras Kareiva 《Molecules (Basel, Switzerland)》2021,26(7)
In the present work, Cr-substituted Mg3Al1−xCrx layered double hydroxides (LDHs) were synthesised through the phase conversion of sol-gel-derived mixed-metal oxides in an aqueous medium. The chromium substitution level in the range of 1 to 25 mol% was investigated. It was demonstrated that all synthesised specimens were single-phase LDHs. The results of elemental analysis confirmed that the suggested synthetic sol-gel chemistry approach is suitable for the preparation of LDHs with a highly controllable chemical composition. The surface microstructure of sol-gel-derived Mg3Al1−xCrx LDHs does not depend on the chromium substitution level. The formation of plate-like agglomerated particles, which consist of hexagonally shaped nanocrystallites varying in size from approximately 200 to 300 nm, was observed. Optical properties of the synthesised Mg3Al1−xCrx LDHs were investigated by means of photoluminescence. All Cr-containing powders exhibited characteristic emission in the red region of the visible spectrum. The strongest emission was observed for the sample doped with 5 mol% Cr3+ ions. However, the emission intensity of samples doped with 1–10 mol% Cr3+ ions was relatively similar. A further increase in the Cr3+ ion concentration to 25 mol% resulted in severe concentration quenching. 相似文献
5.
Mathur S. Shen H. Lecerf N. Jilavi M.H. Cauniene V. Jørgensen J-E. Kareiva A. 《Journal of Sol-Gel Science and Technology》2002,24(1):57-68
Superconducting oxide ceramics of composition Y(Ba1–x
Sr
x
)2Cu4O8 (x = 0.00, 0.10, and 0.20) have been prepared by a simple sol-gel method based on the complexation of metal ions in aqueous medium, by chelating acetate and tartarate ligands. Homogeneous sols were obtained by complexing copper ions with tartaric acid, which prevented the flocculation of copper acetate during the gelation process. Single-phase bulk samples were obtained after firing the mixed-metal polymeric acetate-tartarate precursor to 835°C for 70 h in flowing oxygen atmosphere. Thermal decomposition of the gels was studied by thermogravimetry. Effect of strontium substitution on the properties of the compounds was studied by X-ray powder diffraction, electron microscopy, X-ray photoemission spectroscopy and resistivity measurements. These data indicate that nearly monophasic Y(Ba1–x
Sr
x
)2Cu4O8 superconducting samples were obtained for x < 0.30. The Sr-doping in the YBa2Cu4O8 (Y-124) phase shows a pronounced effect on the superconducting properties enhancing the critical temperature from 78 K (for the non-substituted sample) to 88 K (for Y(Ba1–x
Sr
x
)2Cu4O8). 相似文献
6.
7.
G. Nenartaviciene K. Tõnsuaadu D. Jasaitis A. Beganskiene A. Kareiva 《Journal of Thermal Analysis and Calorimetry》2007,90(1):173-178
In this study the formation of chromium substituted YBa2Cu4O8 (Y-124) superconductors has been investigated by TG/DTA measurements. The YBa2(Cu1−xCrx)4O8 ceramics with nominal compositions of x=0.01, 0.03, 0.05, 0.10 and 0.20 have been prepared by an aqueous sol-gel method using aqueous mixtures of the corresponding
metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. To assist
the interpretation of the results obtained the synthesis products were additionally characterized by X-ray powder diffraction
(XRD) and resistivity measurements. It was determined that doping the YBa2Cu4O8 phase with chromium has a strong effect on the phase purity and superconducting properties of the synthesis products. 相似文献
8.
9.
Let (a,b)∈Z2, where b≠0 and (a,b)≠(±2,−1). We prove that then there exist two positive relatively prime composite integers x1, x2 such that the sequence given by xn+1=axn+bxn−1, n=2,3,… , consists of composite terms only, i.e., |xn| is a composite integer for each n∈N. In the proof of this result we use certain covering systems, divisibility sequences and, for some special pairs (a,±1), computer calculations. The paper is motivated by a result of Graham who proved this theorem in the special case of the Fibonacci-like sequence, where (a,b)=(1,1). 相似文献
10.
The paper presents the results of studies on thermogravimetric (TG) characterization of precursors and Hg-based superconductors synthesized by the sol-gel method. TG experiments were performed in an oxygen flow in order to understand the decomposition mechanisms of the fabricated gels and to determine the synthesis temperature of the intermediate precursors for the HgBa(2)CaCu(2)O(6+delta), HgBa(2)Ca(2)Cu(3)O(8+delta), and Hg(1-x)Tl(x)Ba(2)Ca(2)Cu(3)O(8+delta) superconductors. The optimum annealing temperature for a desired oxygen content in the superconducting compounds has been established by thermogravimetric measurements. To assist the interpretation of the obtained results the elemental analyses of the synthesized products were performed by AAS and EDS (SEM) methods. 相似文献