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George W Scherer - One of the best experts on this subject based on the ideXlab platform.

  • New polymer-based treatments for the prevention of damage by salt crystallization in stone
    Materials and Structures, 2019
    Co-Authors: Serena Andreotti, Enrico Sassoni, Elisa Franzoni, George W Scherer, Encarnacion Ruiz-agudo, Paola Fabbri, Carlos Rodriguez-navarro
    Abstract:

    Salt crystallization can produce severe damage in porous stones, with a dramatic impact on cultural heritage conservation. Such damage is related to the fact that repulsive forces arise between the salt crystals and the pore wall, generating a disjoining pressure that frequently exceeds the tensile strength of stone. In this paper, new treatments are proposed, aimed at preventing salt damage by depositing a thin layer of polymeric coatings over the stone’s pore surfaces. These coating are expected to change the surface chemistry, eliminating the repulsion between the growing crystals and the pore wall and hence the development of the disjoining pressure. Several biopolymers were tested on these substrates: silica glass, calcite, and calcite subjected to a pre-treatment with Diammonium Hydrogen Phosphate (DAP), aimed at preventing calcite dissolution and acting as an anchoring substrate for the polymer coating. Selected polymer treatments were applied to porous Globigerina limestone samples, which were subjected to crystallization tests with sodium sulfate, obtaining promising results (i.e., significant reduction in stone damage), especially when the polymers were applied after the DAP treatment.

  • conversion of calcium sulfate dihydrate into calcium Phosphates as a route for conservation of gypsum stuccoes and sulfated marble
    Construction and Building Materials, 2018
    Co-Authors: Enrico Sassoni, Elisa Franzoni, Gabriela Graziani, George W Scherer
    Abstract:

    Abstract To increase the water resistance of gypsum-based stuccoes (i.e., pastes and mortars), the possible conversion of gypsum into less soluble calcium Phosphates (CaP), by reaction with an aqueous solution of Diammonium Hydrogen Phosphate (DAP), was investigated. The effect of several reaction parameters (DAP concentration, ethanol addition to the DAP solution, pH) on nature and morphology of the new CaP was explored. For the most promising formulation, the ability to improve mechanical properties and reduce solubility in water of treated stuccoes was investigated. The treatment provided better results than ammonium oxalate (an inorganic treatment frequently used for consolidation, protection and de-sulphation of carbonate stones), but the high reaction speed limited the penetration depth and the performance of the DAP-treatment.

  • Calcium Phosphate coatings for marble conservation: Influence of ethanol and isopropanol addition to the precipitation medium on the coating microstructure and performance
    Corrosion Science, 2018
    Co-Authors: Enrico Sassoni, Elisa Franzoni, Giorgio Graziani, George W Scherer
    Abstract:

    The effect of adding ethanol and isopropanol to aqueous solutions of Diammonium Hydrogen Phosphate, used to create a passivating layer of calcium Phosphates over marble, was investigated. Thanks to its weakening effect on the hydration sphere of ions in solution, ethanol allowed complete coverage of marble surface by a crack-free and pore-free layer of octacalcium Phosphate. Even better results were obtained using isopropanol, because it has lower adsorption affinity to calcite than ethanol. Treatments involving alcohols provided good acid protection and also restored cohesion among calcite grains in weathered marble.

  • Some Recent Findings On Marble Conservation By Aqueous Solutions Of Diammonium Hydrogen Phosphate
    MRS Advances, 2017
    Co-Authors: Enrico Sassoni, Elisa Franzoni, Gabriela Graziani, George W Scherer
    Abstract:

    Given the lack of satisfying treatments for consolidating marble affected by thermally induced grain detachment (the so-called "sugaring"), the use of aqueous solutions of Diammonium Hydrogen Phosphate (DAP) has recently been proposed. The idea is to form a new binding mineral (hydroxyapatite, HAP) as the reaction product between the DAP solution and the calcitic substrate. In this study, we investigated the effects of adding small quantities of ethanol (EtOH) to the DAP solution, with the aim of favoring HAP formation. The results of the study indicate that, when a 0.1 M DAP and 0.1 mM CaCl_2 solution in 10 vol% EtOH is used, complete coverage of marble surface with a crack-free coating with reduced porosity is achieved (whereas no coating is formed without EtOH addition). This is thought to be a consequence of the weakening of hydration shells of Phosphate ions in the DAP solution, thanks to the presence of ethanol molecules. When used to restore mechanical properties of weathered marble, the treatment with 10 vol% EtOH was found to significantly improve the dynamic elastic modulus after a single application and to completely restore it after a second application.

  • Preliminary study on the use of ammonium Phosphate for the conservation of marble-imitating gypsum-stuccoes
    2016
    Co-Authors: Enrico Sassoni, George W Scherer, Gabriela Graziani, Elisa Franzoni
    Abstract:

    In this study, a novel method for consolidation and improvement of resistance to water of gypsum-stuccoes was preliminarily investigated. The idea is treating gypsum with an aqueous solution of Diammonium Hydrogen Phosphate (DAP, (NH4)2HPO4) to form hydroxyapatite (HAP, Ca10(PO4)6(OH)2), which has much lower solubility than gypsum. Tests carried out on gypsum paste samples, manufactured to resemble historic stuccoes, showed that, after treatment with the DAP solution, a significant improvement in mechanical properties was achieved and brushite (CaHPO4∙2H2O) was formed (alongside some other by-products, that can be removed by an additional poultice treatment). Even if brushite is more soluble than HAP, still its formation is expected to be beneficial for stuccoes conservation, as brushite is significantly less soluble than gypsum.

A Shimada - One of the best experts on this subject based on the ideXlab platform.

V. Venugopal - One of the best experts on this subject based on the ideXlab platform.

  • Microwave assisted low temperature synthesis of sodium zirconium Phosphate (NaZr_2P_3O12)
    Journal of Thermal Analysis and Calorimetry, 2004
    Co-Authors: A. H. Naik, N. V. Thakkar, S. R. Dharwadkar, K. D. Singh Mudher, V. Venugopal
    Abstract:

    Sodium zirconium Phosphate [NaZr_2P_3O_12], a potential ceramic matrix for fixation of high level nuclear waste, was synthesized by heating the mixture of sodium carbonate [Na_2CO_3], zirconyl nitrate hydrate [ZrO(NO_3)_2·5H_2O] and ammonium diHydrogen Phosphate [NH_4H_2PO_4] in air, in a resistance heated furnace and a microwave heating system respectively in the temperature range 450 to 650°C. The mixture heated for 1 h in a resistance furnace at 450°C yielded a poorly crystalline NaZr_2P_3O_12 [NZP]. Increasing the temperature to 650°C produced a highly crystalline product. The same mixture heated in a microwave oven at 450°C for 1 h however, yielded the most crystalline NZP. In an alternate method, the mixture of sodium diHydrogen Phosphate (NaH_2PO_4), zirconium dioxide (ZrO_2) and Diammonium Hydrogen Phosphate [(NH_4)_2HPO_4] heated in resistance furnace at 650°C for the same period did not react in air. It also did not yield the pure product at 450°C when heated in microwave assembly for 1 h.

  • Microwave assisted low temperature synthesis of sodium zirconium Phosphate (NaZr_2P_3O_12)
    Journal of Thermal Analysis and Calorimetry, 2004
    Co-Authors: A. H. Naik, N. V. Thakkar, S. R. Dharwadkar, K. D. Singh Mudher, V. Venugopal
    Abstract:

    Sodium zirconium Phosphate [NaZr_2P_3O_12], a potential ceramic matrix for fixation of high level nuclear waste, was synthesized by heating the mixture of sodium carbonate [Na_2CO_3], zirconyl nitrate hydrate [ZrO(NO_3)_2·5H_2O] and ammonium diHydrogen Phosphate [NH_4H_2PO_4] in air, in a resistance heated furnace and a microwave heating system respectively in the temperature range 450 to 650°C. The mixture heated for 1 h in a resistance furnace at 450°C yielded a poorly crystalline NaZr_2P_3O_12 [NZP]. Increasing the temperature to 650°C produced a highly crystalline product. The same mixture heated in a microwave oven at 450°C for 1 h however, yielded the most crystalline NZP. In an alternate method, the mixture of sodium diHydrogen Phosphate (NaH_2PO_4), zirconium dioxide (ZrO_2) and Diammonium Hydrogen Phosphate [(NH_4)_2HPO_4] heated in resistance furnace at 650°C for the same period did not react in air. It also did not yield the pure product at 450°C when heated in microwave assembly for 1 h.

Fujii Noriko - One of the best experts on this subject based on the ideXlab platform.

  • Article Tryptophanase-Catalyzed L-Tryptophan Synthesis from D-Serine in the Presence of Diammonium Hydrogen Phosphate
    2016
    Co-Authors: A Shimada, Haruka Ozaki, Takeshi Saito, Fujii Noriko
    Abstract:

    Abstract: Tryptophanase, an enzyme with extreme absolute stereospecificity for optically active stereoisomers, catalyzes the synthesis of L-tryptophan from L-serine and indole through a β-substitution mechanism of the ping-pong type, and has no activity on D-serine. We previously reported that tryptophanase changed its stereospecificity to degrade D-tryptophan in highly concentrated Diammonium Hydrogen Phosphate, (NH4)2HPO4 solution. The present study provided the same stereospecific change seen in the D-tryptophan degradation reaction also occurs in tryptophan synthesis from D-serine. Tryptophanase became active to D-serine to synthesize L-tryptophan in the presence of Diammonium Hydrogen Phosphate. This reaction has never been reported before. D-serine seems to undergo β-replacement via an enzyme-bonded α-aminoacylate intermediate to yield L-tryptophan

  • tryptophanase catalyzed l tryptophan synthesis from d serine in the presence of Diammonium Hydrogen Phosphate
    International Journal of Molecular Sciences, 2009
    Co-Authors: A Shimada, Haruka Ozaki, Takeshi Saito, Fujii Noriko
    Abstract:

    Tryptophanase, an enzyme with extreme absolute stereospecificity for optically active stereoisomers, catalyzes the synthesis of L-tryptophan from L-serine and indole through a β-substitution mechanism of the ping-pong type, and has no activity on D-serine. We previously reported that tryptophanase changed its stereospecificity to degrade D- tryptophan in highly concentrated Diammonium Hydrogen Phosphate, (NH4)2HPO4 solution. The present study provided the same stereospecific change seen in the D- tryptophan degradation reaction also occurs in tryptophan synthesis from D-serine. Tryptophanase became active to D-serine to synthesize L-tryptophan in the presence of Diammonium Hydrogen Phosphate. This reaction has never been reported before. D-serine seems to undergo β-replacement via an enzyme-bonded α-aminoacylate intermediate to yield L-tryptophan.

A C. Tas - One of the best experts on this subject based on the ideXlab platform.

  • Chemical preparation of carbonated calcium hydroxyapatite powders at 37°C in urea-containing synthetic body fluids
    Journal of The European Ceramic Society, 1999
    Co-Authors: D Bayraktar, A C. Tas
    Abstract:

    An important inorganic phase of synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a single-phase ceramic powder. Carbonated HA powders were formed from calcium nitrate tetrahydrate and Diammonium Hydrogen Phosphate salts dissolved in aqueous ‘synthetic body fluid’ (SBF) solutions, containing urea (H2NCONH2), at 37C and pH of 7.4, by using a novel chemical precipitation technique. These powders were also found to contain trace amounts of Na and Mg impurities in them, originated from the use of SBF solutions, instead of pure water, during their synthesis. The characterization and chemical analysis of the synthesized powders were performed by powder X-ray diAraction (XRD), Fourier-transformed infra-red spectroscopy (FT‐IR), and inductively-coupled plasma atomic emission spectroscopy (ICP‐AES). # 1999 Elsevier Science Ltd. All rights reserved.

  • Biomimetic Preparation of ha Precursors at 37°C in Urea- and Enzyme Urease-Containing Synthetic Body Fluids
    MRS Proceedings, 1999
    Co-Authors: D Bayraktar, A C. Tas
    Abstract:

    AbstractAn important inorganic phase of synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a single-phase and sub-micron bioceramic powder. Carbonated HA precursors were synthesized from calcium nitrate tetrahydrate and Diammonium Hydrogen Phosphate salts dissolved in “synthetic body fluid” (SBF) solutions, containing urea (H2NCONH2) and enzyme urease, under the biomimetic conditions of 37°C and pH 7.4, by using a novel chemical precipitation technique.