Propriedades funcionais e comportamento eletroquímico em células com eletrólitos sólidos à base de galatos e silicatos

Doutoramento em Ciência e Engenharia de MateriaisThis work was focused on the analysis of transport, thermomechanical and electrochemical properties of a series of perovskite-like oxide materials and composites for potential applications as anodes of intermediate-temperature solid oxide fuel cells (SOFCs) with lanthanum gallate and silicate solid electrolytes. The primary attention was centered on A(Mn,Nb)O3-δ (A = Sr, Ca) and (La,Sr)(Mn,Ti)O3-based systems, lanthanum chromite substituted with acceptor-type and variable-valence cations, and various Ni-containing cermets. Emphasis was given to phase stability of the materials, their crystal structure, microstructure of porous electrode layers and dense ceramics, electronic conductivity, Seebeck coefficient, oxygen permeability, thermal and chemical induced expansion, and anodic overpotentials of the electrodes deposited onto (La,Sr)(Ga,Mg)O3- and La10(Si,Al)6O27- based electrolyte membranes. In selected cases, roles of oxygen diffusivity, states of the transition metal cations relevant for the electronic transport, catalytically active additives and doped ceria protective interlayers introduced in the model electrochemical cells were assessed. The correlations between transport properties of the electrode materials and electrochemical behavior of porous electrodes showed that the principal factors governing anode performance include, in particular, electronic conduction of the anode compositions and cation interdiffusion between the electrodes and solid electrolytes. The latter is critically important for the silicatebased electrolyte membranes, leading to substantially worse anode properties compared to the electrochemical cells with lanthanum gallate solid electrolyte. The results made it possible to select several anode compositions exhibiting lower area-specific electrode resistivity compared to known analogues, such as (La,Sr)(Cr,Mn)O3-δ.Este trabalho é dedicado à análise das propriedades de transporte, termomecânicas e eletroquímicas de materiais óxidos com estrutura do tipo perovskite e de compósitos para utilização como ânodo em pilhas de combustível de eletrólito sólido (PCES), com funcionamento a temperaturas intermédias, utilizando eletrólitos de galato e de silicato de lantânio. De entre os materiais estudados, destacam-se os sistemas à base das perovskites A(Mn,Nb)O3-δ (A = Sr, Ca) e (La,Sr)(Mn,Ti)O3, os cromitos de lantânio substituidos por catiões aceitadores de electrões e com valência mista e os compósitos do tipo “cermet” contendo Ni. É dada ênfase à estabilidade e estutura destes materiais, bem como à microestrutura das camadas porosas dos elétrodos e de cerâmicos densos, à condutividade eletrónica, ao coeficiente do Seebeck, à permeabilidade de oxigénio, à expansão térmica e química e à sobretensão anódica dos elétrodos depositados nas membranas de eletrólitos à base de (La,Sr)(Ga,Mg)O3 e La10(Si,Al)6O27. Numa seleção dos estudos efetuados incluiu-se a avaliaҫão da difusão de oxigénio, do estado de oxidação dos catiões dos metais de transiҫão relevantes para o transporte deeletrões, da atividade catalítica dos aditivos e das camadas protetorasde céria introduzidas no modelo das celulas eletroquímicas. A correlaҫão entre as propriedades de transporte dos materiais de ânodo e o comportamento eletroquímico dos elétrodos porosos indica que os fatores principais, responsáveis pelo desempenho dos ânodos, incluem, em particular, a condutividade eletrónica das composiҫões dos ânodos e a difusão de catiões entre as fases do eletrólito sólido e do elétrodo. Este último fator é especialmente crítico no caso das membranas à base de silicato de lantânio, prejudicando significativamente as propriedades dos ânodos, quando comparadas com as das células eletroquímicas fabricadas com galato de lantânio como o electrólito sólido. Os resultados obtidos neste trabalho permitem escolher as composições dos ânodos que possuem os valores da resistividade por área do eléctrodo mais baixos, comparativamente a alguns materiais análogos já estudados, tal como (La,Sr)(Cr,Mn)O3-δ

Влияние цементного и бесцементногоэндопротезирования крупных суставов на системныйиммунный ответ

With the purpose of the study of organism systemic immune response to the use of the cement and cementless fixation of endoprostheses in the nearest and remote terms after implantation the analysis of the indices of the immune state of 109 patients with gonarthrosis and coxarthrosis of III stage aged from 40 to 73 was carried out. The authors draw a conclusion that the reaction of immune system to actively functioning implant makes itself by the moderate activation of humoral immunity and the hyperproduction of TNFa against the background of the moderate depression of a cellular component of immune system. The dynamics of the indices of systemic immune response to large joints replacement are conditioned by surgical intervention directly and don't depend on the type of the fixation of implant.С целью изучения системного иммунного ответа организма на использование цементной и бесцементной фиксации эндопротезов в ближайшие и отдаленные сроки после имплантации выполнен анализ показателей иммунного статуса 109 больных остеоартрозом (ОА) коленного и тазобедренного суставов III стадии в возрасте от 40 до 73 лет. Авторы делают вывод о том, что реакция иммунной системы на активно функционирующий имплантат проявляется умеренной активацией гуморального иммунитета и гиперпродукцией TNFa на фоне умеренной депрессии клеточного звена иммунной системы. Динамика показателей системного иммунного ответа на эндопротезирование крупных суставов обусловлена непосредственно хирургическим вмешательством и не зависит от вида фиксации имплантата

Mixed conductivity and stability of CaFe2O4−δ.

The total conductivity of CaFe2O4-delta, studied in the oxygen partial pressure range from 10(-17) to 0.5 atm at 1023-1223 K, is predominantly p-type electronic under oxidizing conditions. The oxygen ion transference numbers determined by the steady-state oxygen permeation and faradaic efficiency measurements vary in the range of 0.2 to 7.2 x 10(-4) at 1123-1273 K, increasing with temperature. No evidence of any significant cationic contribution to the conductivity was found. The Mossbauer spectroscopy, thermogravimetry, and X-ray diffraction (XRD) showed that the orthorhombic lattice of calcium ferrite is essentially intolerant to the oxygen vacancy formation and to doping with lower-valence cations, such as Co and Ni. The oxygen nonstoichiometry (delta) is almost negligible, 0.0046-0.0059 at 973-1223 K and p(O-2) = 10(-5)-0.21 atm, providing a substantial dimensional stability of CaFe2O4-delta ceramics. The average linear thermal expansion coefficients, calculated from the controlled-atmosphere dilatometry and high-temperature XRD data, are (9.6-13.9) x 10(-6) K-1 in the oxygen pressure range from 10(-8) to 0.21 atm at 873-1373 K. Decreasing P(02) results in a modest lattice contraction and in the p-n transition indicated by the conductivity and Seebeck coefficient variations. The phase decomposition of CaFe2O4-delta occurs at oxygen chemical potentials between the low-p(O-2) stability limit of Ca2Fe2O5-delta brownmillerite and the hematite/magnetite boundary in binary Fe-O system. © 2008, Electrochemical Society Inc

Electrophysical and thermomechanical properties of perovskites La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta) (A = Ca, Sr, Ba) used as fuel cell anodes: the effect of radius of alkali-earth cation

The effect of the radius of the alkali-earth cation substituted into the A sublattice of La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta) (D = DD degrees, Sr, Ba) perovskites on their stability and transport and thermomechanical properties is considered. The increase in the cation radius is shown to improve the phase stability and decrease the conductivity under both oxidative and reductive conditions. The thermal and chemical expansion of La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta) ceramics is studied by dilatometry in controlled atmospheres and a wide temperature range at p(O-2)=10(-21)-0.21 atm. The coefficients of thermal expansion of La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta) are in the interval of (10.7-14.3)x 10(-6) K-1, i.e., compatible with those of standard solid electrolytes of solid-oxide fuel cells. The maximum chemical expansion does not exceed 0.2% at isothermal reduction in the COaEuro'CO2 mixture

Oxygen Nonstoichiometry, Mixed Conductivity, and Mössbauer Spectra of Ln0.5A0.5FeO3−δ (Ln = La−Sm, A = Sr, Ba): Effects of Cation Size

Increasing the difference of the Ln3+ and A2+ cation radii in perovskite-type Ln0.5A0.5FeO3−δ (Ln = La, Pr, Nd, Sm; A = Sr, Ba) results in higher oxygen deficiency and lower oxygen-ionic and p-type electronic conductivities, determined using the oxygen permeation and total conductivity measurements at 973−1223 K. The relationships between the anion transport and A-site cation size mismatch remain essentially similar in air and under reducing conditions when most iron cations become trivalent, thus confirming critical influence of oxygen-vacancy trapping processes induced by the lattice strain. At low temperatures, analogous correlation is also observed for quadrupole splittings derived from the Mssbauer spectra of oxygen-stoichiometric Ln0.5A0.5FeO3. Contrary to the ionic conductivity variations, the role of surface exchange kinetics as a permeation-limiting factor, evaluated from the membrane thickness dependence of oxygen fluxes, tends to decrease on Ba2+ doping and on decreasing Ln3+ size in Ln0.5Sr0.5FeO3−δ series. The n-type electronic conduction and low-p(O2) stability at 1223 K are substantially unaffected by the cation radius mismatch

Nonstoichiometry, thermal expansion and oxygen permeability of SmBaCo2-xCuxO6-delta

Phase relationship analysis in the pseudobinary SmBaCo2 - xCuxO6 - delta system at 1000-1100 degrees C in air revealed the existence of solid solutions with the layered perovskite and 123-type structures, formed within the ranges of 0 0.1, and to increase oxygen deficiency studied by thermogravimetry and iodometric titration. The electrical conductivity and thermal expansion of Cu-substituted cobaltites decrease on doping, while the steady-state Oxygen permeability exhibits an opposite trend, in correlation with the oxygen content variations. The average thermal expansion coefficient of SmBaCo1.4Cu0.6O6 - delta ceramics, where the level of ionic transport is comparable to that in most permeable cobaltite-based mixed conductors, is 16.9 x 10(-6) K-1 at 25-1000 degrees C in air. At the same time, copper additions increase chemical reactivity of the materials with doped ceria electrolytes. (C) 2014 Elsevier B.V. All rights reserved

Stability, mixed conductivity, and thermomechanical properties of perovskite materials for fuel cell electrodes based on La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta), La0.5Ba0.5Ti0.5Fe0.5O3-delta, and (La0.5D0.5)(0.95)Cr0.5Fe0.5O3-delta (A = Ca, Ba)

For materials based on ferrites and manganites with DD degrees(2+) and D'D degrees(2+) cations substituted into D sublattice, the functional properties are studied and the prospects as electrode materials for solid-oxide fuel cells are assessed. The electronic conductivity of materials based on La(0.5)A(0.5)Mn(0.5)Ti(0.5)O(3-delta) is shown to decrease with the increase in the ionic radius of alkali-earth substituent; however, for La0.5D'D degrees 0.5Mn0.5Ti0.5O3-delta and La0.5D'D degrees 0.5Fe0.5Ti0.5O3-delta, the appearance of n-conduction is observed during reduction, which may provide adequate conductivity under anodic conditions. Under the conditions of fuel cell operation, the thermal expansion coefficients of these materials are (13.0-13.5) x 10(-6) K-1. The thermal and chemical expansion increases with the increase in the radius of alkali-earth cation; the latter value does not exceed 0.2%, which is acceptable for preparation of electronic layers. The transition of oxygen through membranes based on materials studied is determined to the large extent by the kinetics of surface exchange which depends on the rate of delivery of oxygen vacancies to the surface. Doping of ferrites with chromium or titanium decreases the electronic and ionic conductivity; however, the presence of substituents in D' sublattice makes it possible to stabilize the perovskite phase in a wide range of NEuro(D-2), decrease the thermal and chemical expansion, and prevent to the large extent the ordering of oxygen vacancies, which allows one to consider these materials as the candidates for electrodes in symmetrical solid-oxide fuel cells