Roman Kozłowski

The structure and redox properties of vanadium oxide surface compounds

The redox properties of VO layers supported on TiO2, A12O3, and SiO2 have been examined and discussed in terms of structural models. On this basis monodispersed VO4 units are postulated on the (001) plane of anatase (TiO2), located at the cationic sites with two terminal and two bridging oxygens, one of the latter being removed on reduction. Dimeric, pyrovanadate-type species seem to be predominantly formed on γ-Al2O3, whereas grains of poorly crystalline V2O5 are observed on SiO2. The structure of the vanadium-oxygen species determines the number of oxygens which can be removed per V atom.

Numerical modelling of moisture movement and related stress field in lime wood subjected to changing climate conditions

Numerical modelling was used to follow the evolution of the moisture content gradient and the stress field resulting from the restrained differential dimensional response across a wooden cylinder, simulating sculptures, in response to variations in temperature (T) and relative humidity (RH). Material properties of lime wood (Tilia sp.) were used in the modelling as this wood species was historically widely used. The allowable RH variations, below which mechanical damage will not occur, were derived as functions of the amplitude, time period and starting RH level of the variation. Lime wood can endure step RH variations of up to 15% in the moderate RH region, but the allowable domain narrows when RH levels shift from the middle range. The allowable amplitude of the variations increases when time allowed for the change increases. The stress field does not vanish even for slow, quasi-static changes in RH due to structural internal restraint resulting from the anisotropy in the moisture-related dimensional change.

Structure of monolayer vanadia γ-alumina catalysts as revealed by IR spectra of probe molecules

IR spectroscopy of NH{sub 3}, CO, and CO{sub 2} as probe molecules was used to characterize surface acid and basic sites of vanadia grafted on {gamma}-alumina. NH{sub 4}{sup +} and NH{sub 3} held coordinatively at the surface sites of varying acidity were detected. Two typed of acidic alumina sites adsorbing NH{sub 3} coordinatively were postulated. They involve depleted aluminum atoms of free alumina surface and those adjacent to surface clusters of the reduced vanadium oxide. The dependence of the relative amounts of these forms on the surface coverage with vanadia and the reduction degree is described. Reduction is accompanied by coalescence of the vanadium oxide nonolayer into small clusters resulting in uncovering of free alumina surface. The adsorption of oxygen on the reduced vanadium atoms modifies the ammonia adsorption considerably.

Defect structures in the brannerite-type vanadates. I. Preparation and study of MN1−xфxV2−2xMo2xO6 (0 ≤ x ≤ 0.45)

Abstract Phases of the formula Mn1−xфxV2−2xMo2xO6 with the brannerite-type (α) structure, where ф represents a vacancy at the Mn2+ site, have been sythesized and characterized by X-ray diffraction and DTA. The X-ray data are listed for MnV2O6 and solid solution with x = 0.40. They indicate the random distribution of V and Mo over the original V sites and the random distribution of Mn and vacancies over the original Mn sites. The monoclinic cell dilates with increasing x, primarily in the direction of the b-axis. The phase diagram of the pseudobinary MnV2O6MoO3 system has been determined. The extent of the stability region for the investigated brannerite solid solution has been established (xmax = 0.45 at 583°C). Other features determined in this system were: (a) little solubility of MoO3 in the high-temperature (β) modification of MnV2O6, (b) a two-phase area of α- and β-type solid solution coexistence, (c) a eutectic point between α-type solid solution and MoO3 at 583°C and 75 mole% of MoO3 and (d) phase relationships at the liquidus.

Analysis of water adsorption by wood using the Guggenheim-Anderson-de Boer equation

The Guggenheim-Anderson-de Boer (GAB) three-parameter sorption equation has been used to interpret the adsorption and desorption isotherms of water vapour measured for 21 important cultural heritage wood species used in the past for panel paintings and woodcarving. The equation is capable of describing the full shape of the isotherms and yields meaningful physical parameters, especially the monolayer capacity from which the water accessible specific surface area can be obtained. It is demonstrated that average sorption isotherms can be derived using the GAB equation for the sorption data available for sets of specimens and that moisture properties of various wood specimens or chemically modified wood can be more easily compared.ZusammenfassungAnhand der dreiparametrigen Guggenheim-Anderson-de Boer-Sorptionsgleichung (GAB) wurden die Adsorptions- und Desorptionsisothermen von 21 kulturell wichtigen Holzarten bestimmt, die in früheren Zeiten für Tafelmalereien und Holzschnitzereien verwendet wurden. Mit dieser Gleichung kann die vollständige Form der Isothermen dargestellt werden. Sie liefert aussagekräftige physikalische Parameter, insbesondere die Monoschichtkapazität, aus der die für das Wasser zugängliche spezifische Oberfläche bestimmt werden kann. Es wird gezeigt, dass anhand der GAB-Gleichung aus den verfügbaren Sorptionsdaten für verschiedene Holzartengruppen die mittleren Sorptionsisothermen hergeleitet werden können und dass die Feuchteeigenschaften verschiedener Holzarten oder von chemisch modifiziertem Holz einfacher verglichen werden können.

Impact of Indoor Heating on Painted Wood - Monitoring the Altarpiece in the Church of Santa Maria Maddalena in Rocca Pietore, Italy

Abstract Triangulation laser displacement sensors were applied to the continuous in-situ monitoring of the dimensional response of the wooden altarpiece in the Church of Santa Maria Maddalena in Rocca Pietore, Italy, to variations in indoor temperature and relative humidity (RH) between December 2002 and March 2005. Further, a small inductive sensor was used to monitor the width of a crack in one of the elements. The measurements demonstrated that only the external layer of wood, several millimetres thick, continually absorbs and releases water vapour following external variations in RH. For massive elements, this leads to gradients in the moisture content through the wood, a restraint of the dimensional change and a development of stress, which is the main threat to the integrity of the wood and the decorative layer. Particularly strong RH variations and related high stress levels were produced by the intermittent heating system based on the inflow of warm air. To incorporate requirements for preservation, heating systems must provide a localized comfortable temperature in the area occupied by people without changing the natural climate of the church as a whole.

Laser Sensors for Continuous In-Situ Monitoring of the Dimensional Response of Wooden Objects

Abstract The application of triangulation laser displacement sensors to the continuous in-situ monitoring of the response of wooden cultural objects to variations in temperature and relative humidity in their environment is reported. The sensors are robust, fast and precise, provide non-contact measurements, and are capable of operating in the field. They have been applied to monitor the response of the altarpiece in the church of Santa Maria Maddalena in Rocca Pietore, Italy, to fluctuations in temperature and relative humidity caused by the use of the heating system. Complex short-, medium- and long-term responses of a variety of carved wooden elements have been recorded.

Defect structures in the brannerite-type vanadates. IV. The crystal structure of Mn1−x⊘xV2−2xMo2xO6; x = 0.53

Abstract The crystal structure of Mn 1−x ⊘ x V 2−2x Mo 2x O 6 ; x = 0.53 of the brannerite type has been refined to R = 0.029. The space group is C2. The bond length-bond strength calculations indicate a short-range ordering of Mo6+ and vacancies, resulting in the formation of MoO⊘OMo clusters which are distributed at random in the host vanadate structure.

CoTeMoO6, Co4TeMo3O16: Two new cobalt molybdotellurates

Abstract It has been found that a solid-state reaction of CoMoO 4 with TeO 2 at 500°C yields a new compound of the formula CoTeMoO 6 . This compound is also formed in the course of annealing of CoMoO 4 H 6 TeO 6 mixtures. Another new compound, the cobalt molybdotellurate containing Te 6+ , was prepared by a solid-state reaction of Co 5 TeO 8 with MoO 3 . It has the formula Co 4 TeMo 3 O 16 . Both CoTeMoO 6 and Co 4 TeMo 3 O 16 have been characterized by X-ray method. The latter has the structure of a wolframite type with the unit cell dimensions a = 4.66, b = 5.67, c = 4.96 A, β ⋍ 90°.

Defect structures in the brannerite-type vanadates. II. Mechanism of the solid-state synthesis of Mn1−xфxV2−2xMo2xO6 (0 ≤ x ≤ 0.33)

The mechanism of solid-solid reactions in mixtures of the three components Mn2O3, V2O5, MoO3 has been studied by X-ray and thermogravimetric methods. The synthesis of Mn1−xфxV2−2xMo2xO6 (MV-100x) solid solutions proceeds along three main reaction paths: (a) direct formation from oxides due to efficient surface diffusion of MoO3 and V2O5 over Mn2O3 grains, (b) formation of MnMoO4 followed by its reaction with V2O5 to MV-33 and dilution of the obtained phase with V2O5 and Mn2O3, and (c) reaction of preformed MnV2O6 and MnMoO4 with V2O5 in which MV-20 appears as an intermediate (valid for x > 0.20). The contribution of these paths to the overall reaction depends on the composition of the initial mixture (x), temperature, and surface area of Mn2O3. If the synthesis of a single-phase solid solution in a MoO3-poor region (x < 0.20) is aimed at, thermal treatment parameters should be selected in such a way as to prevent the preformation of MnV2O6, which, once formed, is not subsequently converted to the equilibrium phase.