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Comparison of the Combined Oxidation and Sulphidation Behavior of Nickel- and Cobalt-Based Alloys at High Temperature

Publication date: Available online 20 November 2020

Source: Journal of Materials Research and Technology

Author(s): Carlo Mapelli, Chiara Casalino, Andrea Strada, Andrea Gruttadauria, Silvia Barella, Davide Mombelli, Eugenio Longaretti, Francesco Perego

Republished by Plato

Published

on


Elsevier

Available online 20 November 2020

Journal of Materials Research and Technology

open access

Summary

The combined oxidation-sulphidation behaviour at high temperature of two nickel-based and two cobalt-based cast alloys is analysed and discussed. These materials are evaluated in view of their possible application for building the components of the high temperature heating furnace up to 1380°C. Typical service conditions combine extremely high temperatures with the simultaneous presence of sulphur-bearing impurities, due to the combustion of fuels derived from the coke production. The main requirements for this demanding application are simultaneous resistance to high thermal levels and to degradation caused by oxidation and sulphurization. The atmosphere chosen to simulate this harsh environment consists of atmospheric air enriched by 12% of sulphur. The testing procedure has been performed at three temperatures (1080 °C, 1180 °C and 1280 °C) and three times of exposure (24 h, 48 h and 96 h). Macroscopic observations have been coupled to microstructural investigations, performed by SEM-EDS. The analysis is mainly focused on the identification of the microstructural alterations experienced by each alloy and on the extent of internal attack caused by oxygen and sulphur. The combination of the macroscopic experimental data and the information from the microstructural observations alloys have been shown to point out the performances of alloy grade throughout the testing trials in order to define the chemical compositions associated to the moderate weight loss and limited depth of surface attack. The new chemical composition of a Ni-superalloy points out performance of corrosion resistance that are even better than the cobalt based alloys usually selected for such working conditions.

Keywords

Nickel-based superalloy

Cobalt-based superalloy

Oxidation behavior

sulphidation behavior

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S223878542031975X?dgcid=rss_sd_all

Material

Improving the mechanical strength of carbon-carbon composites by oxidative stabilization

Publication date: Available online 28 November 2020

Source: Journal of Materials Research and Technology

Author(s): Ji Hong Kim, Ayoung Jo, Yun Jeong Choi, Ki Bong Lee, Ji Sun Im, Byong chol Bai

Republished by Plato

Published

on

Elsevier

Available online 28 November 2020

Journal of Materials Research and Technology

open access

Abstract

Carbon/carbon composite has superior properties, so it has been expected to use various industrial fields. However, low mechanical strength (than conventional structural materials) works as a hurdle, so the use of oxidative stabilization to improve the mechanical strength of carbon/carbon composites was studied. The oxidation process was performed at 220∼350 °C based on thermogravimetric analysis (TGA). The compressive strength of the oxidized sample at 290 °C was 212 MPa, which is 2.5 times greater than that of the non-oxidized sample (84 MPa). However, the oxidation temperature of more than 290 °C decreased the compressive strength (199 MPa at 350 °C). This tendency was in accordance with the TGA and X-ray photoelectron spectroscopy (XPS) results. The effect of oxidative stabilization can be explained by two factors: the polymerization of the used binder pitch by the crosslinking effect by induced oxygen and improvement of the affinity between the coke and binder pitch.

Keywords

Carbon-carbon composite

Oxidative stabilization

Mechanical strength

Oxygen crosslinking

Coke/Pitch affinity

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320317?dgcid=rss_sd_all

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Material

Impact of alkaline and acid treatment on the surface chemistry of a hot-dip galvanized Zn-Al-Mg coating

Publication date: Available online 28 November 2020

Source: Journal of Materials Research and Technology

Author(s): Burak William Çetinkaya, Fabian Junge, Gregor Müller, Florian Haakmann, Klaus Schierbaum, Miroslaw Giza

Republished by Plato

Published

on

Elsevier

Available online 28 November 2020

Journal of Materials Research and Technology

open access

Abstract

The surface chemistry of an exemplary hot-dip galvanized Zn-Al-Mg coating comprising 1.6 wt.% aluminum and 1.1 wt.% magnesium was characterized by means of secondary and transmission electron microscopy as well as synchrotron radiation X-ray photoelectron spectroscopy. Lamellae of the coating prepared via focused ion beam technique were examined through energy dispersive X-ray analysis. Further the effect of alkaline and acid treatment respectively was investigated by employing time of flight secondary ion mass spectroscopy, energy dispersive X-ray analysis and glow discharge optical emission spectroscopy. Throughout this work it is shown that both alkaline (NaOH) and acid (H2SO4) solutions alter the chemical composition when applied to the coating surface. With the native Zn-Al-Mg system yielding a complex microstructure covered by a magnesium and aluminum rich oxide film, highly alkaline surroundings (pH > 13) caused a decrease of aluminum at the uppermost surface. Every deployed acid solution (pH < 2.4) lead to a preferred pickling of the magnesium compounds including the oxide layer plus the intermetallic MgZn2 phases of the coating. Exposure to both highly alkaline and acid environments corresponded to a higher proportion of zinc at the coating surface measured by all applied surface analytical tools indicating that the modification of the chemical composition took place on both nanoscopic and microscopic scale.

Keywords

hot-dip galvanizing

Zn-Al-Mg coating

surface characterization

alkaline cleaning

acid treatment

© 2020 Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320366?dgcid=rss_sd_all

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Material

High-temperature thermodynamics of ZnO–NH4Cl–H2O system

Publication date: Available online 28 November 2020

Source: Journal of Materials Research and Technology

Author(s): Duoqiang Zhao, Shenghai Yang, Yongming Chen, Yafei Jie, Jing He, Chaobo Tang

Republished by Plato

Published

on

Elsevier

Available online 28 November 2020

Journal of Materials Research and Technology

open access

Abstract

On the basis of the principles of simultaneous equilibrium, conservation of mass, and aqueous electronic charge neutrality and the correspondence principle of ion entropy, the high-temperature thermodynamics of the ZnO–NH4Cl–H2O system was studied to predict solubility and construct Zn species distribution. The model was constructed precisely by using the MATLAB program. The total Zn2+ concentration in the solution was affected significantly by temperature and total ammonium concentration. ZnNH3Cl3 was the predominant species in the ZnO–NH4Cl–H2O system. The solubility of zinc diammine chloride in NH4Cl solution (>2 mol·L-1) in the temperature range of 303–353 K was determined using equilibrium experiments, which had results that agreed well with the theoretical value. The data and high-temperature thermodynamic model used in this paper are reliable.

Keywords

Zinc hydrometallurgy

Ammonium chloride

High-temperature thermodynamics

Ion entropy

© 2020 The Author(s). Published by Elsevier B.V.

Source: https://www.sciencedirect.com/science/article/pii/S2238785420320329?dgcid=rss_sd_all

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