Kinetic parameters and thermodynamic properties of diffusion-controlled crystal growth of calcium tungstate from solutions in sodium tungstate melts by differential thermal analysis

From DTA curves, energy (E), enthalpy (H_a), entropy (S_a) and free-energy (G _a) of activation and the pre-exponential factor (k ₀) for diffusion-controlled crystal growth of calcium tungstate from solutions in sodium tungstate melts were estimated using the Arrhenius equationk _Dl=k ₀ e ^–E/RT.E increased linearly with increased cooling rate (R _T). The change ofk ₀ was parallel to that ofk _Dl and increased with increasingR _T but there was no direct correlation.H _a,S _a andG _a were unaffected by the changes of R_T and crystallization temperature (T ₀). The distance (d ₁₂), between a diffusing particle and its host crystal necessary for a successful diffusion, was estimated. Such distances increased with increasingT ₀ andR _T.

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Zusammenfassung Aus DTA-Kurven wurden Energie (E), Enthalpie (H _a), Entropie (S _a) und freie Energie (G _a) der Aktivierung, sowie der prä-exponentielle Faktor (k ₀) für das diffusionsbedingte Kristallwachstum von Calciumwolframat aus Natriumwolframatschmelzen unter Anwendung einer gewöhnlichen Arrheniusgleichungk _D=k ₀ e ^–E/RT abgeschätzt. Mit zunehmenden Abkühlgeschwindigkeiten (RT) nimmtE linear zu.k ₀ verhält sich parallel zuk _D und nimmt mit steigendemR _T zu, jedoch ohne direkte Korrelation.H _a,S _a undG _a verhielten sich unabhängig von Änderungen vonR _T und der Kristallisationstemperatur (T ₀). Die zur erfolgreichen Diffusion erforderliche Entfernung (d ₁₂) zwischen einem diffundierenden Teilchen und seinem Empfängerkristall wurde geschätzt. Diese Abstände nahmen mit steigendemT ₀ undR _T zu.

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Résumé On a estimé, à partir de courbes ATD, l'énergie (E), l'enthalpie (H _a), l'entropie (S _a) et l'enthalpie libre (G _a) de l'activation ainsi que le facteur pré-exponentiel (k ₀) de la croissance des cristaux, contrôlée par la diffusion, du tungstate de calcium, dans des solutions de tungstate de sodium fondu, à l'aide d'une équation d'Arrhenius ordinaire:k _D=k ₀ e ^–E/RT.E augmente linéairement avec les vitesses croissantes de refroidissement (R _T),k ₀ est parallèle àk _D et augmente quandR _T croît; cependant il n'y a pas de corrélation directe.H _a,S _a etH _a restent indépendants des variations d'R _T et de la température de cristallisation (T ₀). On a estimé la distance (d ₁₂) nécessaire, entre une particule en diffusion et son cristal-hôte, pour une diffusion réussie. Ces distances augmentent avec les valeurs croissantes deT ₀ etR _T.

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k _l,=k ₀ e ^–E/RT, (E), (H _a), (S _a), (G _a) (k ₀) - . (E) (R _T). (K ₀) k _l, R _T, . H _a,S _a,G _a R _T, (T ₀). (d ₁₂) «», . ₀ R _T.

     

Structure and Magnetic Properties of Solid Solutions of Molecular Magnetics Based on Ni(II) and Co(II) Complexes with Nitroxyl Radicals

Ni(II) and Co(II) complexes with deprotonated paramagnetic enaminoketones 4(3,3,3trifluorine2oxopropylidene) 2,2,5,5tetramethyl3imidazolidine1oxyl (L) and 4(3,3,3trifluorine1chlorine2oxopropylidene)2,2,5,5tetramethyl3imidazolidine1oxyl (L¹) and alcohols are shown to form continuous solid solutions Ni_xCo_1-xL₂(C₂H₅OH)₂ and Ni_xCo_1-xL₂ ¹(CH₃OH)₂. Single crystal Xray diffraction analysis showed that concentration variation practically does not affect the structural characteristics of the solid solutions. Distinguishing features if the magnetic behavior of Ni_xCo_1-xL₂ · (C₂H₅OH)₂ and Ni_xCo_1-xL₂ ¹(CH₃OH)₂ are the antiferromagnetic interaction of the moments of the nickel and cobalt sublattices inside the polymeric layers and the antiferromagnetic nature of interlayer interaction of the magnetic moments.     

Etude cinetique de la decomposition thermique de l'anhydride chromique depose sur alumine

Résumé On présente les résultats obtenus dans l'évaluation des paramètres cinétiques de la réaction de décomposition thermique de l'anhydride chromique déposé sur de l'alumine. Grâce aux données sur l'influence de la teneur en anhydride chromique et de la vitesse de chauffage sur les paramètres cinétiques, on obtient des conclusions sur les conditions d'obtention du catalyseur Cr₂O₃/Al₂O₃.

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Results obtained in the determination of the kinetic parameters of the thermal decomposition of CrO₃ on alumina are presented. The experimental data on the effects of CrO₃ concentration and heating rate on the kinetic parameters are used to draw conclusions on the conditions of preparation of Cr₂O₃/Al₂O₃ catalysts.

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Zusammenfassung Die bei der Bestimmung der kinetischen Parameter der thermischen Zersetzungsreaktion von CrO₃ auf Aluminiumoxid-Träger erhaltenen Ergebnisse werden erörtert. Aus den Versuchsangaben über den Einfluß der Cr₂O₃-Konzentration und die Aufheizgeschwindigkeit auf die kinetischen Parameter werden Schlüsse bezüglich der Herstellungsbedingungen der Cr₂O₃/Al₂O₃-Katalysatoren gezogen.

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, Cr₃ . Cr₂O₃ , Cr₂O₃/l₂O₃.

     

A TG/DTA/MS study of the oxidation of nickel sulphide

The oxidative behaviour of synthetic millerite (Ni_0.994S) has been studied by TG and DTA in a dynamic oxygen atmosphere (0.2 l min^–1) over the temperature range 20–1000° (heating rate 10° min^–1). EGA was carried out by a coupled mass spectrometer. The reaction products at various intermediate temperatures were characterized by X-ray powder diffractometry. A reaction sequence has been deduced, in which in the temperature range 550–700° complete oxidation of Ni_0.994S had occurred with the formation of NiSO₄, Ni₃S₂, NiO and possibly-Ni₇S₆. Between 700–800°, NiSO₄ continued to be formed, whilst Ni₃S₂ and-Ni₇S₆ were oxidised. Above 800°, NiSO₄ decomposed to NiO, the latter being the only species evident above 800°.

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Zusammenfassung Das oxidative Verhalten von synthetischem Millerit (Ni_0.994S) wurde mittels TG und DTA in einer dynamischen Sauerstoffatmosphäre (0.2 l min^–1) im Temperaturbereich von 20 bis 1000° (Aufheizgeschwindigkeit 10° min^–1) untersucht. EGA wurde mit einem gekoppelten Massenspektrometer durchgeführt. Die Reaktionsprodukte bei verschiedenen Zwischentemperaturen wurden mittels Röntgen-Pulver-Diffraktometrie charakterisiert. Eine Reaktionssequenz wurde abgeleitet, nach welcher im Temperaturbereich von 550 bis 700° die vollständige Oxidierung von Ni_0.994S unter Bildung von NiSO₄, Ni₃S₂, NiO und wahrscheinlich-Ni₇S₆ vor sich geht. Zwischen 700 und 800° wird NiSO₄ auch weiterhin gebildet, während Ni₇S₂ und-Ni₇S₆ oxidiert wurden. Oberhalb von 800° wurde NiSO₄ zu NiO zersetzt, das einzig nachweisbare Produkt oberhalb von 800°.

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Résumé On a étudié l'oxydation de la millérite synthétique (Ni_0.994S) par TG et ATD en atmosphère dynamique d'oxygène (0,2 1· min^–1) et dans l'intervalle de températures allant de 20 à 1000° (vitesse de chauffage 10°· min^–1). L'analyse des gaz émis s'est effectuée avec un spectromètre de masse couplé. Les produits de réaction ont été caractérisés à diverses températures intermédiaires par diffractométrie de poudre aux rayons X. On a déduit une séquence de réactions, selon laquelle, dans l'intervalle compris entre 550 et 700°, l'oxydation complète de Ni_0.994S a lieu avec formation de NiSO₄, Ni₃S₂, NiO et probablement-Ni₇S₆. Entre 700 et 800°, la formation de NiSO₄ se poursuit tandis que Ni₃S₂ et-Ni₇S₆ sont oxydés. Au-dessus de 800°, NiSO₄ se décompose en NiO qui constitue l'unique composé qui puisse être décelé au-dessus de 800°.

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(Ni_0.994S) (0,2 . ^–1) 20–1000° 10° ^–1. - . . 550–700° Ni_0.994S NiSO₄, Ni₃S₂, NiO -Ni₇S₆. 700–800° , Ni₃S₂ -Ni₇S₆ . 800° NiO, 800°.

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We wish to thank Dr. T. Kennedy for useful discussions and Messrs. B. Sturman, I. Twaddle, K. Oliver and W. Thomas for technical assistance.     

Kinetics of carbonyl triplet reactions in water

The presence of urea during the gelling of AlPO₄–Al₂O₃ catalysts (AlPO₄/Al₂O₃ weight ratio =3) has been studied with respect to its effect on the porous texture and surface acidity of the resulting gels. An increase in pore volume and mean pore radius with no modification in surface acidity is found when the AlPO₄–Al₂O₃ catalyst is modified by the addition of 5 mol% urea in the AlPO₄ solution.

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, AlPO₄/Al₂O₃ ( AlPO₄/Al₂O₃=3) . , AlPO₄/Al₂O₃ 5 .% AlPO₄ - .

     

Microcalorimetric and FT-IR spectroscopic study of benzene adsorption on α-Fe2O3 and γ-Al2O3

The adsorption of benzene at room temperature on-Fe₂O₃ and on-Al₂O₃ powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy.On iron oxide a chemisorption-combustion step is followed by a highly exothermic adsorption step, reversible at r.t.Few combustion centres exist on alumina if reducing pretreatment is not carried out. Two reversible adsorption steps are subsequently observed and were interpreted as due to interaction with two different types of surface hydroxy groups.

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Zusammenfassung Die Adsorption von Benzol an-Fe₂O₃- und-Al₂O₃-Pulvern bei Raumtemperatur wurde mittels Wärmefluß-Kalorimetrie und FT-IR-Spektroskopie untersucht. Beim Eisenoxid folgt auf dem Chemisorptions-Verbrennungs-Schritt ein bei Raumtemperatur reversibler, stark exothermer Adsorptionsschritt. Aluminiumoxid besitzt einige Oxydationszentren, sofern keine reduzierende Vorbehandlung erfolgt. Zwei aufeinanderfolgende reversible Adsorptionsschritte treten auf und werden der Wechselwirkung mit zwei verschiedenen Typen von Oberflächenhydroxylgruppen zugeschrieben.

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-Fe₂O₃ -l₂₃. - , . , , . , .

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This work was supported by the CNR Progetto Finalizzato Chimica Fine e Secondaria. Prof. Vincenzo Lorenzelli is gratefully thanked for the kind loan of instrumental facilities and helpful discussions.     

Steroid glycosides from the starfishEchinaster sepositus

Two new steroid glycosides, which have been called echinasterosides B₁ and B₂ have been isolated from the starfishEchinaster sepositus. Using chemical transformations (methylation, hydrolysis) and also spectral methods (¹H and¹³C NMR spectroscopy and GLC-MS) the complete chemical structure of B₁ has been established as 15-acetoxy-5-cholestane-3,4,6,8,24-pentaol 24-O[O-(2)O÷ methyl--D-xylopyranosyl)-(13)--L-arabinofuranoside] (I) and that of glycoside B₂ as 5-cholestane-3,4,6,8,15,24-hexaol 24-O-[O÷(2-O-methyl--D-xylopyranosyl)-(13)--L-arabinofuranoside] (II).Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Pirodnykh Soedinenii, No. 2, pp. 246–249, March–April, 1987.     

Some Pharmaceutical Properties of a New Branched Cyclodextrin, 6-O-α-(4-O- α-D-Glucuronyl)-D-glucosylβ-cyclodextrin

Some physicochemical and biological properties of a new branched cyclodextrin, 6-O--(4-O--d-glucuronyl)-d-glucosyl--cyclodextrin GUG--CyD) were investigated. Further, theinteraction of GUG--CyD with several drugs was studied by the solubility and spectroscopic methods, and compared with those of parent -CyD and 6-O--maltosyl--CyD(₂--CyD).The hemolytic activity of GUG--CyD on rabbit erythrocytes was lower than those of -CyD and ₂--CyD. GUG--CyD and ₂--CyD showed negligible cytotoxicity on Caco-2 cells up to at least 0.1 M. The inclusion ability of GUG--CyD to neutral and acidic drugs was comparable to or slightly smaller than those of -CyD and ₂--CyD, probably because of a steric hindrance of the branched sugar. On the other hand, GUG--CyD showed greater affinity for the basic drugs, compared with -CyD and ₂--CyD, owing to the electrostatic interaction of its carboxylate anion with positive charge of basic drugs. Thus GUG--CyD may be useful as a safe solubilizing agent particularly for basic drugs.     

Thermometric study of the dissociation equilibria of the maleinimidodioxime

The values of the dissociation constants of the maleinimidodioxime are potentiometrically determined at various ionic strengths, and extrapolated to zero ionic strength (pK ₁ ^T =10.41;pk ₂ ^T =11.60). From these values and from the thermometric titration curves the enthalpies of neutralization (H _N1=–21.76,H _N2=–23.77 kJ/mol) and the thermodynamic parameters of dissociation of this substance at 25.0 °C are determined ( G ₁ =59.41, G ₂ =66.23, H ₁ =34.06, H ₂ =32.05 kJ/mol; S ₁ =–85.06, S ₂ =–114.64 J/(K mol)).

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Zusammenfassung Die Werte der Dissoziationskonstanten von Maleinimidodioxim wurden potentiometrisch bei verschiedenen Ionenstärken bestimmt und auf die Ionenstärke Null extrapoliert (pK ₁ ^T =10.41;pK ₂ ^T =11.60). Aus diesen Werten und aus den thermometrischen Titrierungskurven wurden die Neutralisierungsenthalpien (H _N1=–21.76,H _N2=–23.77 kJ/mol) und die thermodynamischen Dissoziationsparameter dieser Substanz bei 25 °C bestimmt ( G ₁ =59.41, G ₂ = 66.23, H ₁ =34.06 kJ/mol, H ₂ = 32.05 kJ/mol; S ₁ =–85.06, S ₂ =–114.64 J/Kmol.

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( ₁ =10.41 ₂ =11.60) . H _N1=–21.76 H _N2=–23.77 / 25.0°:G ₁ ⁰ =59.41;G ₂ ⁰ =66.23.H ₁ ⁰ =34.06₂ H ₂ ⁰ = 32.05 /,S ₁ ⁰ =–85.06;S ₂ ⁰ =–114.64 /.

     

Fast non-destructive determination of silicon in coal by means of /n,n′ γ/ and /n, γ/ processes

The possibilities were evaluated of nondestructive determination of silicon content in large-scale samples of coal /about 20–50 kg/, based on the spectrometry of prompt -radiation from processes /n, n /, E=1779 keV and /n, /, E=3539 keV and 4935 keV. The neutron sources were either²⁴¹Am–Be or²⁵²Cf located additionally in D₂O moderator. A Ge/Li/ detector was used for -radiation detection. In exposure times of up to 2 h, the detection limits of 1.3% and 0.9% and accuracies of silicon determination of 0.66% and 0.40% have been achieved in case of /n, / and /n, n / processes, respectively.     

Order and disorder in mixed metal linear chains: The homo and heterobimetallic EDTA (M(H2O)4OIOII)[M′(EDTA)] · 6H2O complexes (M = Mg,Mn, Co,Zn and Ni; M′ = Co,Ni, Cu and Zn)

Summary Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6H₂O where + + + + + =2, 01, 0,,2, 0, 1.This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure.Due to this preference, and also to the structural features, the heterobimetallic MM(EDTA) · 6H₂O compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes.     

Entropy in dissimilarity and chirality measures

Within the prospect of quantifying the geometrical dissimilarity of molecular models on the basis of a thermodynamical formalism, the algebra of stereogenic pairing equilibria is reviewed and applied to molecular geometry: developing Rassat's proposition, an interaction energy of two figures F and F is taken as proportional tod _H ^Emphasis>/2 (F, F), whered _H denotes the Hausdorff distance. IfG is a group of rotations in E _n the geometrical version of the general equation (E) of the chemical algebra defines a distance extensionD _p(F,F) ofd _H(F,F), which is independent of the orientations of F and F, and where the coefficientp is interpreted as the reciprocal of a temperature-like parameter:p 1/T. At K (p = ), no formal entropy contributes to the definition of the uniform distanceD . At K (p = 0), the discrimination between homo- and hetero-pairing of figures by the harmonic distance Do is averaged over orientation states. Temperature-dependent chirality measuresc _p are derived fromD _p, andc is analogous to Mislow's chirality measure. If T and oT are normalized enantiomorphic triangles with coincident centroids inE ₂,c _p(T) =D _p (T, T) is calculated forp = 0 andp = , and discussed for 0 <p < . Finally, the Hausdorff interaction model is putatively related to energy profiles versus dihedral angle inmeso- anddl-molecules.     

Thermal Behaviour of some dioxane adducts ofM(C6F5)2 (M=Pd,Pt)

The thermal treatment of the pentafluorophenyl derivativesM(C₆F₅)₂Dx_n [M=Pd (n=2, 3) or Pt (n=2); Dx=dioxane] leads to the formation of the new dioxane adducts M(C₆F₅)₂Dx (M=Pd, Pt) and Pt(C₆F₅)₂Dx_1.5. Calculations of the order of reaction and the activation energy of some of the decomposition reactions are described. The values were determined by the Coats-Redfern and Freeman-Carroll methods. Structural data on the isolated intermediates were obtained by infrared spectroscopy and magnetic susceptibility measurements.

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Zusammenfassung Die thermische Behandlung der PentafluorphenylderivateM(C₆F₅)₂Dx_n [M=Pd (n=2, 3) oder Pt (n=2); Dx=Dioxan] führt zu der Bildung der neuen DioxanaddukteM(C₆F₅)₂Dx (M=Pd, Pt) und Pt(C₆F₅)₂Dx_1.5. Die Berechnungen der Reaktionsordnung und der Aktivierungsenergie einiger Zersetzungsreaktionen werden beschrieben. Die Werte wurden durch die Methoden von Coats-Redfern und Freeman-Carroll bestimmt. Die Strukturangaben der isolierten Zwischenprodukte wurden durch Infrarotspektroskopie und Messung der magnetischen Suszeptibilität erhalten.

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(₆F₅)₂, M=Pd n=2, 3 Pt _n=2, - , -M(C₆F₅)₂ (=Pd, Pt) (₆F₅)_21,5. , — —. .

     

Ferric chloride catalyzed photooxidation of alkanes by air in organic solvents

In the presence of catalytic amounts of FeCl₃, alkanes (cyclohexane, n-hexane), toluene and ethylbenzene are oxidized by air oxygen to CH₃CN, (CH₃)₂CO or CH₂Cl₂ under visible light irradiation to yield ketones and alcohols.

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FeCl₃ (, -), CH₃CN, (CH₃)₂CO CH₂Cl₂ .

     

First and second thermodynamic mixing properties of ethylbenzene +n-alkanes: Experimental and theory

Isobaric expansibilities _P and isothermal compressibilities _T have been determined at 25 and 45°C for binary mixtures of ethylbenzene + n-tetradecane and + n-hexadecane and the corresponding excess functions (V ^E /T)_P and (V ^E /P)_T have also been obtained. With these data and supplementary literature values, the following second order mixing properties are also reported at 25°C: _S ^E , (V ^E /P)_T, C_V and (VT). All mixing quantities have been compared with the results obtained at 25°C by using the Prigogine-Flory-Patterson theory of liquid mixtures. The predicted values suggest that the ability of ethylbenzene as a breaker of the pure n-C_n orientations is similar to what we found for toluene and higher than for p-xylene.     

Study of the combustion of a fire retardant coating by thermal analysis and different complementary techniques

An intumescent fire retardant coating can effectively control fire spread and damage. Its dual purpose is to confine the surface spread of flame to the boundaries of an already established fire, and to retard the penetration of heat and flame to and through the coated surface. Our composition expanded and provided an insulation layer between the flame source and the combustion substrate, and liberated a quantity of primarily non-flammable decomposition products which tended to extinguish the flame. The main ingredients of the coating were cellulose acetate butyrate and HMDI (Desmodur N) for Polyurethane, and Chlorowax-70 (chlorinated paraffins) as fire retardant component. This fire retardant coating was applied to wood panels, and tested in a 2-foot tunnel, its flame spread rating being measured. The effects of three parameters of interest were investigated: the type of wood used, the percentage of Chlorowax, and the coating thickness. It was found of interest to study the oxidation of the coating using different techniques, e.g. flash pyrolysis under oxygen and GC/MS for analysis of the decomposed products. Combustion studies of the coating were also conducted using DSC and thermogravimetry, either with the scanning mode or under isothermal conditions. Comparisons were made between the results obtained from pyrolysis and combustion.

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Zusammenfassung Ein schwellender feuerhemmender Überzug kann Ausbreitung und Schäden von Feuer wirksam einschränken und wird zwei Zwecken gerecht: Verhinderung der Ausbreitung von ausgebrochenem Feuer und Schutz der überzogenen Oberfläche vor Hitze- und direkter Flammeneinwirkung. Die beschriebene Komposition quillt und bildet eine Isolationsschicht zwischen der Flammenquelle und dem brennbaren Material, liefert zugleich aber auch eine gewisse Menge von nichtbrennbaren, die Flamme erstickenden primären Zersetzungsprodukten. Die Hauptbestandteile des Überzugs sind Celluloseacetat und -butyrat und HMDI (Desmodur N) für Polyurethan sowie Chlorowax-70 (chlorierte Paraffine) als feuerhemmende Komponente. Dieser feuerhemmende Überzug wurde auf Holzplatten aufgebracht und in einem 2ft-Tunnel getestet, wobei die Flammenausbreitungsgeschwindigkeit gemessen wurde. Der Einfluß von drei interessierenden Parametern wurde untersucht: Typ des benutzten Holzes, Anteil von Chlorowax und Überzugsschichtdicke. Es erwies sich als interessant, die Oxydation des Überzugmaterials mit verschiedenen Techniken zu untersuchen, z.B. durch Schnellpyrolyse und Analyse der Zersetzungsprodukte mittels GC/MS. Verbrennungsuntersuchungen des Überzugmaterials wurden auch mittels DSC und Thermogravimetrie entweder nach der scanning-Arbeitsweise oder unter isothermen Bedingungen ausgeführt. Die bei Pyrolyse und Verbrennung erhaltenen Ergebnisse werden miteinander verglichen.

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. -, , — . , . - ( ) ( ) . , . : , . , , , - . . , .

     

Kinetic data on the interaction between triplet anthraquinone and 2-naphthol in oxygen

During the photooxidation of ethylbenzene in the presence of 2-naphthol a new interaction has been found between the sensitizer anthraquinone and the inhibitor. The quantum yield and the kinetics of this interaction have been investigated in the temperature interval of 28–98°C.

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-, , 28–98°C , .

     

Complexes of O2? radical ions with palladium and platinum compounds in solutions

Coordination of O ₂ ^– radical ions with palladium and platinum compounds in solutions has been detected by the ESR technique.

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- O ₂ ^– .

     

Studies on the catalytic decomposition of nitrous oxide on lanthanum cobaltate

The catalyst LaCo₂O₄ crystallizing in CaFe₂O₄ type structure has been synthesized and its physicochemical characteristics evaluated. The kinetics of decomposition of nitrous oxide, studied in the temperature range 400–460°C at 50 and 200 Torr of the reactant gas, was found to obey an expression corresponding to strong inhibition by product oxygen. A reaction mechanism has been proposed based on the existence of Co²⁺–O^2––Co³⁺ clusters on the surface.

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LaCo₂O₄, CaFe₂O₄, - -. , - 400–460°C 50 200 Qu , -, . Co²⁺–O^2––Co³⁺ .