In-situ electrochemical synthesis of inorganic compounds for materials conservation: Assessment of their effects on the porous structure

This study refers to the application of in-situ electrochemical synthesis as an alternative method to improve the properties of porous materials against harmful external agents that deteriorate them. It is oriented to an understanding of the effects of crystallisation on the pore structure of different compounds commonly used in the restoration and conservation of porous materials (historical ceramics, building walls, sculptures, or biomedical applications). It analyses the microstructural, chemical details, and stability of the neo-formed phases that modify the pore network. The electrochemical synthesis was carried out at ambient temperature (20 °C), over high porous sandstone for crystallising Ca carbonate, Mg carbonate, Ca phosphate, and Ca oxalate compounds. Based on the neo-formed minerals, a comparison was made depending on their specific properties defining how they affected the pore structure. The characterisation included polarised light optical microscopy, environmental and field-emission scanning electron microscopy, digital image analysis, cathodoluminescence (CL-ESEM),energy-dispersive X-ray spectroscopy, and X-ray microdiffraction. Aragonite, hydromagnesite, hydroxyapatite, and whewellite were identified as the majority phases depending on the treatment. Phase transformation, dehydration, and dissolution-re-precipitation processes suggested different degrees of stability, including aragonite/calcite (CaCO3 treatment) and hydromagnesite/magnesite (MgCO3 treatment) transformations and simultaneous crystallisation of brushite/hydroxyapatite ((Ca3(PO4)2 treatment). Electrocrystallisation induced changes in inter-granular porosity, the development of secondary porosity inherent to the minerals, and differences in pore cementation depending on its mineralogy. Among the treatments, Mg carbonate reduced porosity most effectively, followed in descending order by calcium carbonate and calcium phosphate, being the calcium oxalate the less effective.This work was funded by the following projects: TOP-HERITAGE- (Technologies in Heritage Sciences (S2018/NMT_4372, Community of Madrid); MULTIMAT CHALLENGE: Multifunctional Materials for Society Challenges (S2013/MIT-2862, Community of Madrid); Additive Manufacturing: from material to application, ADITIMAT-CM (S2018/ NMT-4411, Community of Madrid); MAT2016-80875-C3-3-R, (Spanish Ministry of Science, Innovation and Universities); Author J.F.‘s participation was supported by a Spanish Ministry of Sciences, Innovation and Universities Juan de la Cierva grant

Decoupling of defect and short-range order contributions to resistivity recovery measurements in binary alloys

© 2014 American Physical Society. We report a new and improved approach that uses low-temperature resistivity recovery measurements to study the defect kinetics in metallic binary alloys. This method is able to decouple the effect related to the irradiation defect contribution to the resistivity from that of the short-range order, which is enhanced by the free migration of defects. This approach can provide reliable experimental data which are more suitable for comparisons with current computational models. Furthermore, the difference in this method with respect to the classical one is that our method gives information concerning the role of vacancies and interstitials on short-range order. The method is applied to a model alloy Fe-5%Cr, of interest for fusion applications, where short-range order effects have been previously found to play a role.Peer Reviewe

Diagnosing shock temperature with NH3_3 and H2_2O profiles

In a previous study of the L1157 B1 shocked cavity, a comparison between NH$_3$(1$_0$-$0_0$) and H$_2$O(1$_{\rm 10}$--1$_{\rm 01}$) transitions showed a striking difference in the profiles, with H$_2$O emitting at definitely higher velocities. This behaviour was explained as a result of the high-temperature gas-phase chemistry occurring in the postshock gas in the B1 cavity of this outflow. If the differences in behaviour between ammonia and water are indeed a consequence of the high gas temperatures reached during the passage of a shock, then one should find such differences to be ubiquitous among chemically rich outflows. In order to determine whether the difference in profiles observed between NH$_3$ and H$_2$O is unique to L1157 or a common characteristic of chemically rich outflows, we have performed Herschel-HIFI observations of the NH$_3$(1$_0$-0$_0$) line at 572.5 GHz in a sample of 8 bright low-mass outflow spots already observed in the H$_2$O(1$_{\rm 10}$--1$_{\rm 01}$) line within the WISH KP. We detected the ammonia emission at high-velocities at most of the outflows positions. In all cases, the water emission reaches higher velocities than NH$_3$, proving that this behaviour is not exclusive of the L1157-B1 position. Comparisons with a gas-grain chemical and shock model confirms, for this larger sample, that the behaviour of ammonia is determined principally by the temperature of the gas.Comment: Accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Gas-Phase Hydrogenation of Furfural to Furfuryl Alcohol over Cu-ZnO-Al2O3 Catalysts Prepared from Layered Double Hydroxides

Several layered double hydroxides (LDHs) with general chemical composition (Cu,Zn)1-xAlx(OH)2(CO3)x/2 .. mH2O have been synthesized by the co-precipitation method, maintaining a (M2+/M3+) molar ratio of 3, and varying the Cu2+/Zn2+ molar ratio between 0.2 and 6.0. After calcination and reduction steps, Cu/ZnO/Al2O3 catalysts were synthesized. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 thermoprogrammed reduction (H2-TPR), N2 adsorption-desorption at -196 ºC, N2O titration, X-ray photoelectron miscroscopy (XPS), NH3-thermoprogramed desorption (NH3-TPD) and CO2- thermoprogrammed desorption (CO2-TPD). The characterization data revealed that these catalysts are mainly meso-and macroporous, where Cu, ZnO and Al2O3 are well dispersed. The catalytic results show that these catalysts are active in the gas-phase hydrogenation of furfural, being highly selective to furfuryl alcohol (FOL) and reaching the highest FOL yield for the catalyst with a Cu2+/Zn2+ molar ratio of 1. In an additional study, the influence of the aging time on the synthesis of the LDHs was also evaluated. The catalytic data revealed that the use of shorter aging time in the formation of the LDH has a beneficial effect on the catalytic behavior, since more disordered structures with a higher amount of available Cu sites is obtained, leading to a higher yield towards FOL (71% after 5 h of time-on-stream at 210 ºC).The authors are grateful to financial support from the Spanish Ministry of Innovation, Science and Universities (Project RTI2018- 094918-B-C44) and FEDER (European Union) funds

Application of magnesium hydroxide nanocoatings on cellulose fibers with different refining degrees

Paper aging and protection are of crucial interest for improving the preservations of library collections and archives. Highly aging-resistant cellulose fiber sheets were obtained by treatment with magnesium hydroxide nanoparticles (Mg(OH)(2)). The procedure was tested on the sheets made of bleached (B) and refined unbleached (UB) pine cellulose fibers as well as their 50%/50% mixture (M). The mor and structural properties of the obtained sheets were studied by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) methods. Stress-strain, smoothness and pH measurements were employed to determine the changes in physical-chemical characteristics of the sheets after mixing two types of the fibers and subsequent treatment with Mg(OH)(2). It has been shown that the sheets made of the fiber mixture show a higher tensile index and smoothness. The modification with Mg(OH)(2) nanoparticles induces an increase in the pH of the sheets to slightly basic values (around pH 8), facilitates the inter-fiber bonding and additionally enhances the smoothness of the sheets. Finally, by exposing the sheets to thermo-hygrometric accelerated artificial ageing, it was found that the physical properties of the treated sheets were not significantly dependent on the environmental factors.This study was supported by the Geomaterials 2 Programme (S2013/MIT_2914),the Innovation and Education Ministry (ref. MAT2013-47460-C5-5-P) and the Autonomous Region Program of Madrid, MULTIMAT CHALLENGE (ref.S2013/MIT-2862

Synthesis and morpho-structural characterization of nanostructured magnesium hydroxide obtained by a hydrothermal method

Controlled magnesium hydroxide particles were successfully synthesized via a simple hydrothermal method. The influence of temperature and reaction time on the hydrothermal synthesis of Mg(OH)(2) was studied. The results provide new parameters to control the morphologies, particle sizes, agglomeration level and crystallographic structures of the brucite nanosized. The physic chemical properties of synthesized Mg(OH)(2) nanoparticles have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED), high resolution transmission electron microscopy (HR-TEM) and thermogravimetry/differential scanning calorimetry (TG/DSC). It has been shown that the prolongation of reaction time improves the crystalline degree of magnesium hydroxide particles. It was also possible to detect a relevant increase in the degree of crystallinity and a faster crystal growth with defined hexagonal morphologies in the samples obtained at higher temperature. Our results show that this simple hydrothermal route is highly interesting for the large scale production of these nanomaterials. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.This study has been supported by the Geomaterials Programme (S2009/MAT-1629) and the ESTRUMAT Programme (S2009/MAT-1585) and it has been carried out in the Department of Materials Science and Engineering and Chemical Engineering of the University Carlos III of Madrid, Spain. The authors are grateful to the National Center for Electron Microscopy (CNME) for its support with TEM

Atomic scale study of the dehydration/structural transformation in micro and nanostructured brucite (Mg(OH)(2)) particles: Influence of the hydrothermal synthesis conditions

Micro and nanostructured brucite (Mg(OH2)) particles synthesized by hydrothermal method from solutions with high content of hydrazine (0.14 M) and nitrate (0.24 g) were compared with samples obtained from low hydrazine content (0.0002 M) and nitrate (0.12 g). The samples were heated at 180 degrees C for 4 h, 6 h and 12 h. XRD, TEM-HRTEM, SAED and image analysis techniques were used for the morphological and structural characterization. The effect of electron beam irradiation on the brucite dehydration was observed in atomic resolution images at 300 kV. Hexagonal crystals show differences in crystallinity, strains and kinetic of reaction. High hydrazine/nitrate samples have slightly larger crystals with better crystallinity, showing a strong preferential orientation. Rietveld refinements show how unit cell parameters are bigger in samples obtained with higher hydrazine/nitrate content, confirming also the preferential orientation along the 0001 plane. Differences in the dehydration process show the rapid formation of a porous surface, the amorphised cortex or the presence of highly oriented strains in samples prepared from higher hydrazine/nitrate content. Conversely, crystals slightly smaller with randomly scattered defect surfaces showing the Mg(OH)(2)/MgO interphase in samples prepared with low hydrazine/nitrate content. Significant differences in the kinetic of reaction indicate how the dehydration process is faster in samples prepared with high hydrazine/nitrate content. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.This present research was funded by the Community of Madrid under the GEOMATERIALES II project (S2013/MIT-2914), by the Complutense University of Madrid’s Research Group: “The alteration and conservation of stone heritage” (921349), the Autonomous Region Program of Madrid, MULTIMAT-CHALLENGE (ref. S2013/MIT‐2862), the Innovation and Education Ministry ref. (MAT2013-47460-C5-5-P), the Mat201019837/C06-05 and the Ministry of Education, Science and Technological Development of Serbia (OI 1612046) projects. The authors are indebted to the Petrophysical Laboratory IGEO, affiliated with the Moncloa Campus of International Excellence CEI-09-009(UCM-UPM), the Heritage Laboratory Network in Science and Technology for Heritage Conservation (RedLabPat,) and the Materials Science Department (Carlos III University of Madrid)