Performance of chromia- and alumina-forming Fe- and Ni-base alloys exposed to metal dusting environments: The effect of water vapor and temperature

Fe- and Ni-base alloys including an alumina-forming austenitic alloy were exposed for 500h under metal dusting environments with varying temperature, gas composition and total pressure. For one H2–CO–CO2–H2O environment, the increase in temperature from 550 to 750°C generally decreased metal dusting. When H2O was added to a H2–CO–CO2 environment at 650°C, the metal dusting attack was reduced. Even after 5000h at a total pressure of 9.1atm with 20%H2O, the higher alloyed specimens retained a thin protective oxide. For gas mixtures containing little or no H2O, the Fe-base alloys were less resistant to metal dusting than Ni-base alloys

Experimental and computational studies of the production of 1,3-butadiene from 2,3-butanediol using SiO2-supported H3PO4 derivatives

Silica-supported phosphoric acid and metal phosphate catalyzed 1,3-butadiene (BDE) production from 2,3-butanediol (2,3-BDO) was studied using experimental and computational techniques. The catalyst was initially tested in a continuous flow reactor using commercially available 2,3-BDO, leading to maximum BDE yields of 63C%. Quantum chemical mechanistic studies revealed 1,2-epoxybutane is a kinetically viable and thermodynamically stable intermediate, supported by experimental demonstration that this epoxide can be converted to BDE under standard reaction conditions. Newly proposed E2 and SN2′ elementary steps were studied to rationalize the formation of BDE and all detected side-products. Additionally, using quantum mechanics/molecular mechanics (QM/MM) calculations, we modeled silica-supported phosphate catalysts to study the effect of the alkali metal center. Natural population analysis showed that phosphate oxygen atoms are more negatively charged in CsH2PO4/SiO2 than in H3PO4/SiO2. In combination with temperature-programmed desorption experiments using CO2, the results of this study suggest that the improved selectivity achieved when adding the metal center is related to an increase in the basicity of the catalyst.R.S.P. and J.V.A.-R. acknowledge the RMACC Summit supercomputer, supported by the NSF (ACI-1532235 and ACI1532236), and the Extreme Science and Engineering Discovery Environment (XSEDE) allocations TG-CHE180056 and TG-CHE200033. J.V.A.-R. acknowledges financial support through the Gobierno de Aragón-Fondo Social Europeo (Research Group E07_23R) and a Juan de la Cierva Incorporación contract from the Ministry of Science and Innovation (MCIN) and the State Research Agency (AEI) of Spain, and the European Union (NextGenerationEU/PRTR) under grant reference IJC2020-044217-I. S.K. acknowledges XSEDE allocation TG-CHE210034 and the National Renewable Energy Laboratory Computational Science Center. This work was authored in part by the National Renewable Energy Laboratory, managed and operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office and in collaboration with the Consortium for Computational Physics and Chemistry (CCPC) and the Chemical Catalysis for Bioenergy Consortium (ChemCatBio). G.R.H., X.H., F.G.B, K.A.U., B.C.K., R.E.D., and D.R.V. acknowledge funding from the Chemical Catalysis for Bioenergy consortium by the Bioenergy Technologies Office in the DOE Office of Energy Efficiency and Renewable Energy. Microscopy was performed in collaboration with the Chemical Catalysis for Bioenergy Consortium under contract no. DE-AC05-00OR22725 with Oak Ridge National Laboratory (ORNL) and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Part of the microscopy research was also supported by the Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. The results and analysis presented in this paper were partially possible thanks to the access granted to computing resources at the Galicia Supercomputing Center, CESGA, including access to the FinisTerrae supercomputer, the Red Española de Supercomputación (grant number QH-2023-1-0003) and the Drago cluster facility of SGAI-CSIC.Peer reviewe

Fabrication of Oxide Dispersion Strengthened Bond Coats with Low Al2_{2}O3_{3} Content

Nanoscale oxide dispersions have long been used to increase the oxidation and wear resistance of alloys used as bond coatings in thermal barrier coatings. Their manufacturing via mechanical alloying is often accompanied by difficulties regarding their particle size, homogeneous distribution of the oxide dispersions inside the powder, involving considerable costs, due to cold welding of the powder during milling. A significant improvement in this process can be achieved by the use of process control agent (PCA) to achieve the critical balance between cold welding and fracturing, thereby enhancing the process efficiency. In this investigation, the influence of the organic additive stearic acid on the manufacturing process of Al2O3-doped CoNiCrAlY powder was investigated. Powders were fabricated via mechanical alloying at different milling times and PCA concentrations. The results showed a decrease in particle size, without hindering the homogeneous incorporation of the oxide dispersions. Two powders manufactured with 0.5 and 1.0 wt.% PCA were deposited by high velocity oxygen fuel (HVOF) spraying. Results showed that a higher content of elongated particles in the powder with the higher PCA content led to increased surface roughness, porosity and decreased coating thickness, with areas without embedded oxide particles