Retired from University of Rennes1-France. Researcher into metallurgy and chemistry. 1962-1994 in group of Pierre Vallet's coworkers, iron & manganese monoxides: wüstite & manganosite; 1988-2005, superconductors as ingredients in composites, sulfides of ThCr2Si2-type, tenorite CuO1±e, aragonite.
Abstract: A Moroccan diatomite is characterized chemically and physically. Mechanical properties of ceramics prepared by sintering at different temperatures ranging from 1050 to 1350 degrees C are studied. Compressive strength and Young modulus are determined by compression tests. Densification and evolution of the microstructure are followed by SEM and other tests.
Notes: the ratio O/Cu is lower than one â the tenorite lattice has a sub-stoichiometric oxygen or an over-stoichiometric copper content; the latter case corresponds likely to L. Ettorche's results; p. 50, missing exponent -0.504 of pO2 in formula (5) Ð=1.509 x 10-3 pO2
Abstract: A new route of solid state synthesis from hydrated salts, leading to NaCl as by product easily eliminated, is brought again into operation in the case of hydroxylapatite. An almost amorphous phase mixed with crystalline NaCl is obtained after grinding the stoichiometric mixture at room temperature during 15 mn then drying a few hours at 80 °C. After washing then heating during 15 hours at 550 °C under H2O vapor, a crystalline white substance is identified as almost ideally identical with "Calcium phosphate hydroxide, Hydroxylapatite, syn. Ca5(PO4)3(OH)" described in crystallographic powder data base JCPDS-JCDD in 1994.
Notes: polycrystalline sample, neutron diffraction, cryostatic temperature T in range [125-295K] --> a(T), b(T), c(T) at two pressures (ambient, P=4.9 kbar), mean Grüneisen coefficient 2.9 +- 0.6
Abstract: In the case of non-stoichiometric quenched wustite P' Fe(1-0.096)O, the defect structure is shown to consist most probably of clusters composed of ten vacancies and four interstitial FeIII ions. These clusters are in agreement with a lon-range ordering (2.5X, 2.5X, 5X), with some disorder in their local arrangement. The direct images of the quenched phase P", previously obtained by various authors, are reinterpreted from a (10/4) cluster model: computing simulations from this model are in good agreement with HREM from the literature.
Abstract: An updated review of the adjustment of the phase and subphases diagrams of wüstite FeyO, Fe1-zO, FeOx in the coordinates T, log(10)pO2, x. The reduction diagrams with %H2 and %CO in place of x are drawn as charts of metallurgical interest . A structural survey concerning the quenched phases P' and P" is proposed.
Notes: Omitted reference: 69Fen: B.E.F. Fender and F.D. Riley, "Thermodynamic Properties of Fe1-xO. Transitions in the Single Phase Region," J. Phys. Chem. solids, 30, 793-798 (1969)
Abstract: The long range order of defect clusters is discussed in the case of the quenched P' and P" subphases. Direct images of ordered defect cluster are interpreted in the literature in terms of clusters [6/0] or [6/2]. A cubic cluster [10/4] having the symmetry of zinc blende leads to a more convenient interpretation. The observed superstructure (5X,5X,5X) is justified at least for composition z = 0.096. The direct images are shown to be similar to the projection [001] and [101] of the lines having a maximum of vacancy density, evidenced from simple geometrical projections.
Notes: T. Ishiguro & S. Nagakura, Japan J. Appl. Phys. 24, p.L723-L726, 1985: Structure of the commensurate phase P" of wüstite Fe(0.902)O studied by HREM
Abstract: Quenched wüstite P' (ex W1) is described as a tri-incommensurate cubic structure. The space group in E6 is identified as P / F44/2,662,I4/2 [see W Plesken & W Hanrath, the lattices of six dimensional euclidean space, Math. Comput., 43, n°168, 573-587 (1984)].
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Notes: The analysis in the reciprocal space of the background in the vicinity of peaks diffracted by a single crystal under equilibrium started around 1990. From this time, information is available in the literature on the rate of free vacancies and the size of point defect clusters, even on the distribution of it.
Abstract: The stability domain of wüstite consists of 6 subdomains corresponding to 3 Wi and 3 W'i (i=1,2,3) on both sides of T=1184 K. The subdomains are separated by hyperbolic arcs. Several sets of results (log(10)pO2, T) on the boundaries with alpha- or gamma-Fe and magnetite are re-examined. The numerical assessment of integration constants ki(T,P) (k= h,s,g) depends on the adjustment of the coefficients in equations describing the oxygen potential along W'/alpha-Fe and W/gamma-Fe (external boundaries of the diagram). Proper-
ties Hio, Sio, Cpio of FeyO are tabulated as functions of T and y=1/x for W1 and W'1such as y=0.934 5 continuously between Chaudron's point at 864.7K and melting point at 1644K.
The decrease in entropy is unexpectedly large when going from the limit-compositions yo in equilibrium with iron to y1 with magnetite. It reflects more than likely the various short and long range orderings of point defects in the aggregate; 30 equations, 3 figures, 6 tables, 120 references
Abstract: The equation log(10)PO2=(aiT-1+bi)x +ciT-1+di allows the best description of the thermogravimetric isotherms of the equilibrium between oxygen with partial pressure PO2 and solid wustite with chemical formula FeOx at temperature T >1 184 K. The coefficients ai, bi, ci and di were determined previously for the 3 wustites Wi (i=1,2,3).The analytical expression of the activities of oxygen and iron, their partial molar properties and the integral properties Ho, So and CPo is establish for the 3 Wi from this equation and the simplified relation log(10) PO2 = AoT-1 + Bo of the equilibrium of wustite with iron. A more complicate formalism following a second approximation previously developped concerning the 3 Wi' (log(10)PO2=(ai.x2+ci.x+ei)T-1 + bi.x2+di.x+fi) is chosen when numerically calculating their partial and integral properties below 1184 K. 70 equations, 4 figures
Abstract: Method of modelling of physical property f: C(luster) C(omponent) M(ethod) applied to wüstite.
The property f of a solid solution is the linear sum of the n CC properties f(i) (i=1,n), f = Σα(i).f(i). The general matrix M(z) for a wüstite Fe1-zO of any arbitrary composition z is expressed on CC(i) corresponding to the different sublattices for each set i of nonequivalent positions in the inverse spinel structure of Fe3O4. Approximations are envisaged which lead to negligible contributions and simplifications.
Notes: Fe1-zO: C11 & C12 (elastic modulus) ï¢ï¢whatever z, the elastic angular distortion is bond to constant C44; C44(Mn)/C44(Fe)=0.80/0.45; Ea(Mn)/Ea(Fe) = 262/134 ~ 2. Vibrations modes => 2 ~ C44(Mn) /C44(Fe), 2 ~ Ea(Mn)/Ea(Fe). Further application to the diffusion in magnesio- and calcio-wüstite: JR. Gavarri & C. Carel, Phase Transitions 14:103-8 (1989), the same in J. Phys. Chem. Solids 51:9. 1131-36 (1990)
Notes: The cluster components are defined making reference to Sostav-Defectnost -Svoistvo Tverdich Faz, A.N.Men, M.P.Bogdanovitch, Yu.P.Vorobiev, R.Yu.Dobrovinskii, V.M.Kamichov, V.B.Fetisov, pp.297, Ed. Nauka-Moskow (1977)
Abstract: Vallet's method of description of the wüstite subphases from the external boundaries equations of phase diagram, and the oxygen solution potential (LogpO2(RT,x)) was applied to results from the literature concerning the manganese monoxide MnOx. An equilibrium diagram between 700 and 1400°C is drawn which reveals 5 probable subphases with a main separation of the phase field at 1204°C.
Abstract: Investigation of wüstite in its homogeneity domain by means of the Cluster Component Method:
Fe1-zO, Model I (first approximation): only two structurally separate domains [zo, z2/3], [z2/3, z1]; 3 component matrixes on the boundaries Fe/W, W2/W3, W1/Fe3O4 --> analytical expression of a property f as a function of three corresponding limit components and composition parameters αi (Σαi =1, i =1,3); numerical application: the cubic lattice parameter as an example requiring 3 elemental cubic defect structures.
Abstract: Two models are elaborated of the variation of lattice parameter a as a function of composition and temperature. Factor B = BTh(Î) + BSt(z) is modeled. An empirical relation between BTh(Î) and a(Î) is discussed from the point of view of Grüneisen's law. An approximate value of the compressibility can be determined. Such correlations are interesting when studying isomorphous compounds, transition metal monoxides as examples.
Abstract: Three behaviors were previously described in equilibrium thermogravimetric studies. A primary structural model from iron to magnetite is proposed. The evolution might be different on both sides of an intermediate composition zi (Fe1-zO) such as (m-n)=4zi.k3 : the short range order of clusters (m/n) of m octahedral vacancies and n interstitials Fe3+ is bonded to the long range order; ka is the mean repeating distance, a is the cell parameter. Below zi, the clusters (m/n) surrounded by Fe3+ ions in octahedral positions might form ordered zones randomly distributed in a FeO matrix. These zones might join when z=zi. Between z0 at the limit with Fe and zi, the clusters would be partially ordered. The density of clusters might increase with decreasing k or a slight increase of their size. The inverting of wo populations of clusters (m/n)- and (m/n)+ might arise between zi and z1 at the limit with magnetite. Some microscopic observations seem to be in favor of separate behaviors (Wi).
Notes: Addendum -Two invariant points are missing in the present Wi' subphases diagram. Point X: x=1.0857, T=1086.1K, log(10)pO2=-17.984, point Y: x=1.0857, T=1068.4, log(10)pO2=-18.424. They are the tips of a short segment of the boundary W1'/W3', which is vertical (whatever T for x=1.0857) in phase diagram T(x). They are present in paper "The Fe-O (iron-oxygen) phase diagram in the range of the nonstoichiometric monoxide and magnetite at the Fe-rich limit. Reduction Diagrams, Bulletin of Alloys Phase Diagrams (J. of Phase Equilibria), Pierre Vallet, Claude Carel, 10: 3. 209-218 (1989)"
Notes: A step in the course of improving our knowledge of the defect structure of wüstite(s). Most of the conclusions in this paper will be debated, confirmed or contradicted.
Notes: Something like an updated review about wüstite(s) crystal structure, a component of the stormy competition icluding past studies on the description of departures from NaCl packing (superstructures, isolated vacancies and Fe3+, defect clusters, long range orderings) in quenched wüstites and the first attempts to approach them in wüstites under equilibrium.
Abstract: Something like an updated review of results from Vallet's group experimental studies and several sets of experiments from the literature, which seem to demonstrate the validity of wüstite subphases and the corresponding equilibrium diagram.
Notes: In the point of view of the cubic cell parameter, there is a rather strong analogy between the information from quenched polycrystalline wüstite and single crystals under equilibrium.
(see fig. 8 as a summary)
Abstract: Accurate measurements under equilibrium (CO/CO2) of the cell parameter a of a single crystal of wüstite were available in the literature. The authors conclude to a monotonous ascending variation of a(T) at constant composition x=1.109, between 919 and 1177°C. It is shown how this behavior can be separated statistically into 2 curved segments corresponding likely to W3 and W2 in the phase diagram of wüstite following Vallet-Raccah.
At the same time, the whole set of breadth measurements of peak (420) at 1050°C seems to be likely distributed following two sets on both sides of the value x =1.0805, corresponding to the subphases W1and W2.
Abstract: The molar paramagnetic susceptibilty is measured, by the Faraday method, along 8 isotherms (920-1060°C) as function of the non-stoichiometry (equilibrium CO/CO2):. Molar susceptibility ΧM = (-4.478 x + 8.633)/(T - 687.1 x + 840.4)
Interpretation following Anderson-Van Vleck theory: ferromagnetic interactions in alternate planes (100) lead to an antiferromagnetic superstructure of Q-type, in alternate planes (111) of R-type. In both cases, mean interaction coefficients are determined as function of composition.
Abstract: Accurate measurements under equilibrium (CO/CO2) of the cell parameter of a single crystal were published. A monotonous behavior at 950 and 1050°C was concluded by the authors. A new interpretation is given by separating the sets at both temperatures into subsets for which parabolic variations are determined by least squares. The intersections correspond rather well with the internal boundaries W1/W2 and W2/W3 in the phase diagram previously given by Vallet and Raccah.
Abstract: Notes: The weight decrease ÎM/ÎMo in isothermal reduction runs (from the literature, PFJ Landler & KL Komarek) carried out above 911°C under fixed H2/H2O inside the limits of the stability field: an analysis by means of empirical formula log(ÎM/ÎMo) = nlogt + K à three successive linear segments joined by a brief anharmonic transition curve can be adjusted. Three rates (n~0.75, 0.45, 0.25) likely corresponding to changes in diffusion process (why not to three defects or associations of them?) are observed. A reduction rate (n~1.0) with a discontinuity as transitional effect is observed for some runs. It could correspond to the reduction of Fe3O4 present in the sample (after a stage under static atmosphere?). A mean diffusion coefficient can be calculated from [log(1- ÎM/ÎMo) = log 8/pi2- log(pi2Dloge:L2).t].)
Abstract: Samples FeOx quenched from temperature θ between 890 and 1340°C at mean composition x=1.1025: the plot of cubic parameter "a" as a function of θ can be separated into 3 parabolic segments ai(θ) whose intersections are close to those on W1/W2 and W2/W3 boundaries in the wüstite phase diagram.
Samples quenched from 1340°C (composition x in range1.046 - 1.1025): from x=1.063 appears an anomalous dispersion which can be explain by forecasted hyperbolic W1/W2 and W2/W3 boundaries in the upper left corner of phase diagram θ(x).
Notes: Related paper: On the boundaries of the domain of solid wustite. General diagram (in French). Pierre Vallet et Paul Raccah, Compt. Rend. Acad. des Sc. Paris 258, 3679-82 (1964): first approximation of the equilibrium diagram with 3 subdomains (See 2011 INDEX: P. Vallet & Associates, Iron & manganese monoxides - wüstite & Manganosite - various transformations)
Abstract: A systematic dilatometric study concerns the boundary between the subdomains of W3 and W2 in range 900-1050 °C. The thermodynamically predicted boundary is confirmed. A "catastrophic" precipitation of magnetite Fe3O4 has been observed at 930 °C for Fe(1-0.11)O. This phenomenon likely corresponds to a metastable boundary between W3 and Fe3O4.
Abstract: A Morocco diatomite is characterized chemically and physically. Mechanical properties of ceramics prepared by sintering at different temperatures ranging from 1050 to 1350°C are studied. Compressive strength and Young modulus are determined by compression tests. Densification and evolution of the microstructure are followed by SEM and other tests.
Abstract: Model II: application of C.C.M. to Wi, i) choice of 4 C(luster) C(omponents) -->4 component associate matrixes M(i) and properties f(i), ii) equation system related to CC concentration α(i) (i=1,4), iii) development of property f on the α(i) and f(i). In the case of f describes the short range order, the three stages envisaged here might correspond to the 3 Wi.
Abstract: Speculative remarks on the departures from stoichiometric rocksalt structure; comments on the relation between short and long range orders m-n=4zk3 as initiated in related paper 2) below;
Abstract: Vallet's method of description of the wüstite subphases from the external boundaries equations of phase diagram, and the oxygen chemical potential (LogpO2(T,x)) was applied to results from the literature concerning the manganese monoxide MnOx. An equilibrium diagram between 700 and 1400°C is drawn which reveals 5 probable subphases with a main separation of the phase field at 1204°C.
Abstract: The equilibrium phase field is proposed for the first time to be separated into 2 main subdomains by the isothermal surface at 911°C. Above this temperature would exist three subphases Wi (i=1,2,3). Because of a more complex thermodynamic behavior below this temperature, the half empirical relation [logpO2 = (ai.T-1+ bi) x + ci.T-1 + di] is not sufficient. Some experimental evidences of existence of the Wi are presented.
Abstract: The nonstoichiometric iron monoxide or wüstite FeOx (Fe1-zO) is described with a new approach by Pierre Vallet and coworkers, 54 references from 1961 (P Raccahâs thesis, thermogravimetry under equilibrium) to 1998 (C Carel, JR Gavarri). The stability domain (LogpO2,T,x) is separated into 2 subdomains by the isothermal line at 911 °C. Each of them contains 3 subdomains which define varieties or subphases or pseudophases Wi and Wâi (i = 1,2,3). Their molar thermodynamic properties are numerically assessed. An analysis (C Carel, 1967) of a reduction kinetics study evidences 3 separate diffusion processes. Following Valletâs approach, an analysis of emf measurements suggests a likely stability domain of the manganese monoxide or manganosite (Mn1-zO) with the existence of 5 subphases with an isothermal separation at 1202°C. Sets of measurements as functions of x and T of the cell parameter for both polycrystalline quenched samples and single crystals under equilibrium show intersections at thermodynamically forecast values. The point defect cluster [10 octahedral vacancies / 4 tetrahedral Fe3+] with blende ZnS structure is the most likely (JR Gavarri, D Weigel) in quenched w. An energetic stability model is proposed taking into account Ca++ or Mg++. Quenched phase Pâ (ex W1) is described as a modulated cubic tri-incommensurate lattice (pX)3 where p<2.7 and >2.5 is irrational. Quenched phase Pâ (ex W2-W3) is described as a commensurate superstructure (5X, 5X, 2.5X) of cubes (2X)3 formed of a [10/4] cluster with a distorted FeO envelope. The Cluster Component Method (AN Men) allows a tensor modeling of physical properties of the Wi. Elemental components of the most general spinel structure are required in the case of modeling the defect structure with more numerous defects near the Fe-rich limit.
Notes: 30 of the 54 papers in INDEX Vallet & Associates are embedded in C Carel publicationslist
