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Holcomb, Gordon R.

Publications and source records attributed to Holcomb, Gordon R..

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Carburization susceptibility of chromia-forming alloys in high-temperature CO 2

It is generally believed that when a chromia scale forms in high-temperature CO 2 environments, carbon uptake of alloys is nearly eliminated, thereby preventing carburization and associated degradation of properties. We quantitively assess this notion through careful examination of several chromia-forming Ni-based and Fe-based commercial alloys after long-term (10,000-h) exposures to CO 2 and air at 700°C. Here, small but measurable carbon uptake ensued independent of alloy base metal (Ni/Fe), alloy crystal structure (FCC/BCC), and chromia growth rate. The rate for Ni-based alloys was strongly dependent on Si and Mn content, highlighting the need to understand possible long-term effects on mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High-temperature oxidation of transient-liquid phase bonded Ni-based alloys in 1 bar and 250 bar carbon dioxide

Compact microchannel heat exchanger designs for supercritical CO 2 power cycles are valued for equipment size reduction and increased heat transfer. They can be fabricated via transient-liquid phase (TLP) bonding, which utilizes a lower melting point interlayer for bonding facilitation of etched thin plates. Haynes 230 and 282 TLP bonded stacks were exposed to high-purity CO 2 at 1 bar/700 °C to 4000 h and 250 bar/720 °C (supercritical) to 1500 h. All samples obeyed parabolic kinetics after an oxide buildup stage of 500-1000 h. Mass gains were similar for the base and TLP bonded alloys, and oxide thicknesses and scales did not significantly differ around the TLP bond regions. Furthermore, there were some slight oxide compositional differences for the H282 TLP samples at 250 bar. There was a slight pressure effect on mass gain, as samples exposed at the higher pressure experienced higher initial mass gains, but then slower continued oxide growth.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Volatilization Behavior of Supported Au Nanoparticle Arrays under H 2 at High Temperature

In this work, the fabrication and experimental study of model Au nanoparticle arrays (nanodots) was used to allow a direct comparison of reactive evaporation at elevated temperatures and nonambient H 2 -containing gas atmospheres with theoretical models. Strong temperature and H 2 -concentration dependencies were confirmed as expected, and the observed dependence in particle diameter with time was effectively described using a reactive evaporation and gas phase diffusion based quantitative model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Temperature-Dependence of Corrosion of Ni-Based Superalloys in Hot CO 2 -Rich Gases Containing SO 2 Impurities

Future power plants will require Ni-based superalloys resistant to high-temperature corrosion in CO 2 -rich environments containing impurities. In this work, several commercially available Ni-based alloys (617, 230, 625, 263, 740H) were exposed at 600°C, 650°C, 750°C and 1 atm to 95% CO 2 , 4% H 2 O, 1% O 2 without/with 0.1% SO 2 to simulate compositions expected in a direct-fired supercritical CO 2 power cycle. The results indicate no effect of SO 2 at 750°C, a small negative effect at 650°C, and a large negative effect at 600°C. Alloys exposed at the higher temperatures (650–750°C) formed thin Cr-rich oxide scales, whereas the lowest temperature (600°C) resulted in thicker scales consisting of non-protective oxides and sulfates. Thermodynamic analysis indicates this increased corrosion is associated with a transition in the stable compounds in contact with the gas. Understanding the factors that affect this transition will aid in the selection or design of alloys for future CO 2 -based power systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High temperature oxidation of steels in CO 2 containing impurities

Future power systems require steels that resist corrosion in high temperature CO 2 containing combustion products/impurities. Here we evaluate the corrosion behavior of several commercial steels exposed to 95% CO 2 -4 % H 2 O-1 % O 2 , with/without 0.1 % SO 2 , at 550 °C and 1 atm. High-Cr steels formed thin Cr-rich oxides and low-Cr steels thick Fe-rich oxides during SO 2 -free exposures. Additions of SO 2 had little effect on low-Cr steels but enhanced corrosion of high-Cr steels, where S within the chromia scale led to its failure and subsequent Fe-rich oxide nodule growth. Ultimately, the results are rationalized by considering the thermodynamic and kinetic factors controlling the reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Surface Finish on High-Temperature Oxidation of Steels in CO 2 , Supercritical CO 2 , and Air

Current and future power systems require steels resistant to high-temperature oxidation in CO 2 -rich environments. The introduction of structural defects by various surface treatments can profoundly affect the oxidation/corrosion behavior of steels in many environments. This effect is largely unexplored for steels exposed to high-temperature CO 2 , which is the focus of this work. We prepared Grade 22, Grade 91, 347H, and 310S steels with three different surface finishes, ranging from little to substantial surface damage, and exposed the steels to 1 bar CO 2 , 200 bar supercritical CO 2 , and laboratory air at 550 °C for up to 1500 h. Surface finish had little impact on the oxidation behavior of low-Cr (2 wt%) Grade 22 and high-Cr (25 wt%) 310S steels. In contrast, intermediate-Cr steels Grade 91 (8 wt%) and 347H (17 wt%) generally showed improved oxidation and carburization resistance with increasing extent of surface damage, which was attributed to the delay or prevention of the onset of Fe-rich oxide nodule growth. Comparison between exposure environments suggests that this effect is more complex for CO 2 compared to air and that it is additionally affected by CO 2 pressure. In conclusion, the results suggest that surface treatments should be considered as one approach to achieve improved corrosion resistance in high-temperature CO 2 , particularly for steels containing Cr levels near the transition that is required to form and maintain a protective Cr-rich oxide scale.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Simulated fireside corrosion of T91 in oxy-combustion systems with an emphasis on coal/biomass environments

Oxy-combustion is the burning of a fuel in oxygen rather than air for the ease of capture of CO2 for reuse or sequestration. Corrosion issues associated with the change in heat exchanger tube operating environment (replacement of most of the N 2 with CO 2 and potentially higher SO x levels) from air- to oxy-combustion were examined. The ferritic-martensitic alloy T91 was used in accelerated fireside corrosion tests using several different gas compositions and ash deposit overcoats to simulate air-fired, oxy-fired coal, and oxy-fired co-fired coal/biomass conditions. Initial corrosion was observed after 240 h of exposure by examining cross-sections with retained ash. Metal section losses were determined after exposures of up to 1440 h at 600-700 °C. Severe corrosion was observed, and a corrosion response with respect to ash deposit chemistry was observed. Corrosion response differences with respect to gas phase chemistry were minimal. Alloy-oxide scale-ash morphologies were consistent with oxide fluxing mechanisms.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2019

High temperature oxidation of Ni alloys in CO 2 containing impurities

Next-generation power systems need structural alloys resistant to high-temperature oxidation in CO 2 containing combustion impurities. In this report we evaluate the oxidation performance of several commercial Ni alloys exposed to 95%CO 2 -4%H 2 O-1%O 2 , with/without 0.1% SO 2 , at 750°C and 1 atm. All alloys formed protective chromia layers and showed no signs of carburization or sulfidation, and minimal chromia volatilization. The microstructural evolution of the alloy surface, secondary oxidants, and minor alloy additions all played a part in promoting protective chromia formation/growth. The results show that Ni alloys are promising candidates for high-temperature portions of next-generation CO 2 -based power systems.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A review of the thermal expansion of magnetite

Thermal expansion data from various sources were placed on an equivalent basis and fitted true (α T ) and mean (α M ) coefficients of thermal expansion were generated. Recent models of oxide spallation in boiler tubes cite and use Central Electricity Generating Board (CEGB) data for αM, but details of how the CEGB data was generated were not known. Here, the CEGB data were found to be derived from an earlier source but given (unconventionally) in terms of small temperature step α M increments.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The role of metal vacancies during high-temperature oxidation of alloys

An improved understanding of high-temperature alloy oxidation is key to the design of structural materials for next-generation energy conversion technologies. An often overlooked, yet fundamental aspect of this oxidation process concerns the fate of the metal vacancies created when metal atoms are ionized and enter the growing oxide layer. In this work, we provide direct experimental evidence showing that these metal vacancies can be inseparably linked to the oxidation process beginning at the very early stages. The coalescence of metal vacancies at the oxide/alloy interface results initially in the formation of low-density metal and eventually in nm-sized voids. The simultaneous and subsequent oxidation of these regions fills the vacated space and promotes adhesion between the growing oxide and the alloy substrate. These structural transformations represent an important deviation from conventional metal oxidation theory, and this improved understanding will aid in the development of new structural alloys with enhanced oxidation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Structural Evolution of a Ni Alloy Surface During High-Temperature Oxidation

We show that considerable structural transformations occur at a Ni alloy surface during the transient stages of high-temperature oxidation. This was demonstrated by exposing the alloy to high-temperature CO 2 for short times at both atmospheric and supercritical pressures. A protective Cr-rich oxide layer formed after only 5 min at 700 °C and persisted for longer exposures up to 500 h. Voids formed and grew over time by the condensation of metal vacancies generated during oxidation, while the alloy surface recrystallized after sufficient oxidation had occurred. The oxygen potential established at the oxide/alloy interface led to oxidation along the newly formed grain boundaries as well as adjacent to and inside of the voids. Al, the most stable oxide-former and present at low concentration in the alloy, was preferentially oxidized in these regions. Furthermore, the results provide an improved understanding of the internal oxidation of Al and its role in enhancing scale adhesion for this class of Ni alloys.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2017

Mechanistic insights into the oxidation behavior of Ni alloys in high-temperature CO 2

We present results of a Ni superalloy oxidized for short times in high purity CO 2 and similarly in Ar containing ≤ 1 ppb O 2 . A detailed analysis of the oxidized surfaces reveals striking similarities for the two exposure environments, suggesting O 2 impurities control the oxidation process in high-temperature CO 2 . Selective oxidation results in Cr-rich oxide layers grown by 2 outward diffusion, while Cr vacancies left in the metal contribute to significant void formation at the oxide/metal interface. Unlike for most of the alloy surface, the oxidation behavior of secondary phase metal carbides is considerably different in the two environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗