Oxygen Gettering Research Articles

Hot Uniaxial Pressing and Pressureless Sintering of AlCrCuFeMnNi Complex Concentrated Alloy—A Comparative Study

External pressure is often applied during sintering to obtain materials with improved properties. For complex concentrated alloys (CCAs), this processing step is commonly performed in vacuum. However, this can promote the evaporation of elements and increase the oxide content, thereby degrading the properties of the alloy. In this study, we compared the microstructures and properties of AlCrCuFeMnNi CCA samples obtained by hot uniaxial pressing sintering (HPS) and pressureless sintering (PLS) using a helium atmosphere purified by an oxygen getter system. The powders were prepared from mixtures of CrFeMn, AlNi and Cu and sintered by HPS at 900 °C for 1 h with an applied pressure of 30 MPa and by PLS at 1050 °C for 1 h. The samples were characterised using X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattering diffraction, density measurements and hardness tests. It was found that the oxygen getter system promoted oxygen partial pressure values at sintering temperatures similar to those of a mixture of 90% helium and 10% hydrogen. The HPS allowed us to obtain almost fully dense samples with a smaller average grain size and finer distribution of aluminium oxides than PLS. These differences increased the hardness of the samples sintered under pressure.

Properties of boron layers deposited during boronisations in W7-X

Boronisation was first used for wall conditioning in W7-X during the OP 1.2b operational period, which was characterized by the use of the fine-grain graphite Test Divertor Unit (TDU) and inertial cooling only. After this period, deposited layers were observed on all inner surfaces. Deposited layers were analyzed on 21 inner wall tiles using ion beam analysis methods, the deposited layers consisted mostly of boron with additional carbon and oxygen. During the operational period OP2.1 with an actively water cooled divertor made of carbon fiber reinforced carbon, different materials were exposed during two individual boronisations using the multi-purpose manipulator. Deposited boronisation layers on the samples were analyzed using nuclear reaction analysis. The deposited layer thicknesses showed some variation depending on substrate material and surface roughness, but a systematic dependence on material and/or roughness was not observed. Under the typical boronisation conditions at W7-X, one A × h (Ampere times hour) of boronisation results in a boronisation layer with a thickness of about 30 ± 15 × 1015B-atoms/cm2 (about 3 ± 1.5 nm) at the position of the multi-purpose manipulator. The oxygen gettering capacity of the layers is up to 0.5 – 0.9O/B.

MAX Phase Ti2AlN for HfO2 Memristors with Ultra‐Low Reset Current Density and Large On/Off Ratio

AbstractA Ti2AlN MAX phase layered thin film electrode and oxygen getter layer for HfO2‐based two‐terminal memristors is presented. The Ti2AlN/HfOx/Ti memristor devices exhibit enhanced resistive switching performance, including an ultra‐low reset current density (< 10−8 MΩ cm2), substantial on‐off ratio (≈ 6000), excellent multi‐level functionality (≈ 9 distinct states), impressive retention (up to 300 °C), and robust endurance (>200 million) as compared to conventional TiN and other alternative materials based memristors. Experimental measurements and modeling suggest that the distinctive combination of low thermal conductivity, high electrical conductivity, and unique ultra‐thin layer‐by‐layer structure of the Ti2AlN MAX phase thin film contribute to this exceptional performance with good reproducibility and stability. The results demonstrate for the first‐time the potential of this innovative sputtered MAX phase material for engineering energy‐efficient, high‐density non‐volatile digital, and analog memory devices aimed toward next‐generation sustainable artificial intelligence.

SiC as a core-edge integrated wall solution in DIII-D

Silicon carbide (SiC) is a promising material for use in a fusion reactor due to its low hydrogenic diffusivity, high temperature strength and resilience under neutron irradiation [1,2]. To assess SiC as a main wall material in DIII-D, simulations with TRIM.SP and DIVIMP are performed on a well-diagnosed L-mode discharge. The effective charge, Zeff, across the separatrix is used as a figure of merit in comparing SiC to the current graphite walls. It is found that SiC is expected to reduce Zeff, potentially by as much as ∼50 %. It is discussed how SiC may be expected to “self-condition” and create wall conditions similar to siliconization, further lowering Zeff due to efficient oxygen gettering. The potential benefits are reviewed and a path towards SiC walls in DIII-D is presented.

On the nanoscale oxide dispersion via in-situ atmospheric oxidation during laser powder bed fusion

In-situ oxidation during laser additive manufacturing (AM) is considered a more economical approach to producing AM oxide dispersion-strengthened (ODS) alloys. However, there is very few success in making AM ODS alloys with oxide density comparable to commercial ODS alloys made by conventional means. To explore the key mechanisms that prevent the high-density dispersion of nanoscale oxides during in-situ reactive AM, we investigated oxide dispersion by in-situ gas-phase reaction during laser powder bed fusion (LPBF) with respect to oxygen gettering elements with different oxygen affinity, getter concentration, atmospheric oxygen level, and laser parameters. Our results show that in-situ oxidation in a high-oxygen printing atmosphere during LPBF AM cannot effectively produce good-quality ODS steels, even when the amount of oxygen pick-up from the atmosphere into the melt pool is comparable to the oxygen level in commercial ODS alloys. We found that surface oxidation and oxide agglomeration in the melt pool prevent the high-density dispersion of nanoscale oxides. In addition, oxide agglomeration also contributes to a higher amount of manufacturing defects. Powder spattering plays a secondary impact on oxygen loss.

Mobility Enhancement Induced by Oxygen Gettering of TiAl for Metal Gated NMOSFETs

In this work, the influence of TiAl gate electrodes fabricated by physical vapor deposition (PVD) and atomic layer deposition (ALD) on electron mobility for metal-gated NMOSFETs is respectively investigated. Due to the specific production chemistry, the ALD TiAl film inherently contains lots of C atoms, which further suppresses its O-gettering capability. Compared to the ALD TiAl device, about 15% higher peak mobility for the PVD TiAl device is demonstrated, which is attributed to the lower bulk trap density in gate dielectric layers as revealed by the 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> noise characteristics analysis. By means of the energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis, the reduced trap density is related to the fact that PVD TiAl can extract more O atoms from gate dielectric layers than ALD TiAl, which weakens the electron trapping/de-trapping process and correspondingly enhances the mobility.

Rare-earth metals as effective getters for purification of germanium telluride glasses from oxygen impurities

The ability of rare-earth elements (REEs) to bind oxygen impurities in Ge20Te80 and Ga10Ge15Te75 telluride glasses is studied. Thermodynamic calculations and experiments show that REEs in glasses, with the exception of Eu, can significantly reduce the content of oxygen impurities chemically bound with germanium, tellurium, and gallium. The most promising oxygen getters are established to be Y, Gd, Lu, Tm, Dy, Tb, and Ho. The advantages of REEs as the getter compared to traditionally used aluminum are: more complete removal of the getter residue during the distillation of tellurium melt and chalcogenide glass; the absence of intense absorption oxide bands in the range of glass transparency; lower etching ability in relation to the silica-glass reactor.

Suppression of impurities absorption and heterophase inclusions in Ge-As-S glasses

Strong absorption from the impurities and background scattering induced by heterophase inclusions are major issue in the applications of Ge-As-S glass in mid-infrared (MIR). Here, we report that, the absorption of impurities sourced from raw materials can be removed effectively by oxygen getters and hydrogen getters under static vacuum distillation, leading to almost disappearance of the absorption at 3.11 μm due to SH, <4.08 ppm at 4.01 μm due to SH and < 11.03 ppm at 7.5 μm due to As-O, respectively, in Ge10As28S62. The impurities of H2O and CO2 can be further eliminated to near zero by dynamic distillation. On the other hand, the heterophase inclusions, originating from raw materials of sulfur, arsenic and germanium, the silica-container and deoxidizer of Mg, can be eliminated thoroughly by dynamic distillation and optimized melting temperature. We draw the fibers using unpurified and purified glasses and found that, comparing with the fiber loss of 2.87 dB/m at unpurified glass, the optical loss can be decreased to about 1.86 dB/m in purified glass without any visible particles or heterophase inclusions. All the results pave the way of developing low loss Ge-As-S glass fiber for high power laser delivery.

Compatibility of Fe-Cr-Al and Fe-Cr-Al-Mo oxide dispersion strengthened steels with static liquid sodium at 700 [formula omitted

The corrosion behavior and tensile properties of oxide dispersion strengthened (ODS) FeCr, FeCrAl, FeCrAlMo steels and 316H stainless steel were evaluated after 1000 h at 700 ∘C in static sodium with and without an oxygen getter (Zr foil). Without Zr foil to getter the dissolved oxygen in the liquid sodium, combined oxidation (formation of Cr, Fe-rich or Al-rich oxides) and dissolution of the studied materials was observed. For the ODS FeCr, Cr- and Fe-rich oxide formation and dissolution induced Cr depletion in the underlying alloy and led to the formation of laves phases that were observed to be detrimental to the room temperature tensile properties. For ODS FeCrAlMo and FeCrAl Al-rich oxide formation and dissolution resulted in Al depletion in the underlying alloys but did not impact tensile properties at room temperature. For 316H temperature induced sensitization combined with oxidation decreased room temperature tensile properties. With Zr foil added as oxygen getter, roughened surfaces and Al depletion profiles suggested the dissolution of ODS FeCr and FeCrAl into the liquid sodium while limited dissolution was observed for ODS FeCrAlMo and 316H. For the 316H and ODS FeCrAlMo steels, precipitates were formed at the grain boundaries after exposure. Tensile properties of ODS FeCr, FeCrAl and FeCrAlMo were not affected by the 1000 h corrosion exposure with Zr foil added to the sodium but for 316H temperature-induced grain boundary sensitization negatively affected the tensile properties.

Comparison of topotactic and magnetic structures for manganite oxide films

Deliberate manipulation of topotactic transformation via oxygen insertion/extraction offers a feasible way to precisely tune oxygen concentration, B–O coordination occupation and resultant electronic functionalities of perovskite (ABO3)-based oxides. Herein, two methods, a post-annealing CaH2 treatment and an in-situ oxygen-vacancy diffusion using oxygen getter layer, were conducted to achieve topotactic transitions from perovskite to brownmillerite of La0·7Sr0·3MnO3-δ (LSMO, 0 ≤ δ ≤ 0.5) films. The results revealed that delicate control of oxygen composition is the crucial factor for evolutions of crystalline structure and subsequent magnetic properties of LSMO films. In particular, the brownmillerite LSMO film treated by the in-situ oxygen getter layer possesses desirable structural stability over time. In contrast, the topotactic LSMO films using reduction agents CaH2 exhibit compositional and structural inhomogeneities. These findings suggest that adjustable topotactic transformation through anionic oxygen provides a facile strategy for designing multifunctional perovskite-derivative oxide materials.

Effect of Oxygen Impurity on Thermal Conduction Rate of Polycrystalline Si3N4

Heat transfer with homogeneous structures of Si3N4 system and the effects of oxygen defects in the Si3N4 grains are reported by Jung Woo Lee and co-workers in article number 2100566. The oxygen defects in the grains are moving to the surface of the grains and effectively captured by oxygen getter. The inhibition of the Si3N4 grain oxidization improves a spontaneous dissipation of thermal energy.

Hole and Electron Doping of Topochemically Reduced Ni(I)/Ru(II) Insulating Ferromagnetic Oxides

LaxSr2-xNiRuO6, LaxSr4-xNiRuO8, and LaxSr3-xNiRuO7 are, respectively, the n = ∞, 1, and 2 members of the (Lax/2Sr1-(x/2))nSr(Ni0.5Ru0.5)nO3n+1 compositional series. Reaction with CaH2, in the case of the LaxSr2-xNiRuO6 perovskite phases, or Zr oxygen getters in the case of the LaxSr4-xNiRuO8 and LaxSr3-xNiRuO7 Ruddlesden-Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1-(x/2))nSr(Ni0.5Ru0.5)nO3n-1 compounds (LaxSr2-xNiRuO4, LaxSr4-xNiRuO6, and LaxSr3-xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. The x = 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+ and Ru2+ centers they contain. Increasing the La3+ concentration (x > 1) leads to a reduction of some of the Ru2+ centers to Ru1+ centers and a suppression of the ferromagnetic state (lower Tc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+ concentration (x < 1) oxidizes some of the Ru2+ centers to Ru3+ centers and enhances the ferromagnetic coupling (increased Tc, increased saturated ferromagnet moment) for the n = ∞ and n = 2 samples but appears to have no influence on the magnetic ordering temperature of the n = 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.

Magnetoelectric Behavior of 0-3 Co/BaTiO &lt;sub&gt;3&lt;/sub&gt;-Composites

Reduction of Co3O4/BaTiO3 in forming gas followed by sintering in flowing nitrogen with carbon as oxygen getter was applied for the syntheses of magnetoelectric 0-3 Cox/(BaTiO3)1-x composites (x = 0.1 ­­– 0.8). Phase pure BaTiO3 and a mixture of hexagonal and cubic Co were obtained with void-free embedding of micrometer-sized ferromagnetic Co particles in the ferroelectric BaTiO3 matrix. No incorporation of Co in the BaTiO3 matrix occurred and the nominal Co contents agree well with the experimental ones derived from Rietveld refinements and magnetic measurements. A complex field dependence of the magnetoelectric coefficient (αME) was found with at least two local maxima/minima and a pronounced hysteresis when the magnetic field and the polarization are oriented perpendicular to each other. The sample Co0.5/(BaTiO3)0.5 exhibits the largest αME values. The low-temperature phase transitions of BaTiO3 (tetragonal → orthorhombic → rhombohedral) can be observed in the temperature dependence of αME. In contrast to other composites the integral of αME and the magnetostriction of (hexagonal) cobalt show a distinctively different magnetic field behavior, which might be due to the additional presence of the cubic Co modification.

Enhanced thermal conductivity in Si3N4 ceramics prepared by using ZrH2 as an oxygen getter

This work reports the two-step sintering method and thermal conductivity of Si3N4 doped with 1.5 wt% MgO and varied contents of ZrH2 in the range of 0-5 wt%. The metal hydride reduction reaction in the first step sintering allows the in situ generations of ZrO2 and the elimination of native SiO2. A smaller amount of liquid phase with reduced oxygen content was produced during the second step sintering as a result of the replacement of ZrO2 by ZrH2. With the aid of ZrH2 as an oxygen getter, the native oxygen in those ZrH2-doped samples was removed via a route of SiO2 →ZrO2 →SiO(g). Consequently, the densified Si3N4 ceramics with larger volume percent of elongated purified β-Si3N4 grains and less glassy phase were obtained. Ultimately, the optimal thermal conductivity of 116.4 W m−1 K−1 was achieved after sintered at 1900 °C for 12 h by using 3 wt% ZrH2 and 1.5 wt% MgO as additives.

The effect of Si content on the structure and tribological performance of MoS2/Si coatings

In the present work, the synthesis of MoS2/Si coatings was conducted to study the effect of Si on the microstructure of the MoS2/Si coatings and their tribological behavior. With the adoption of advanced characterization methods, the results reveal that the introduction of Si plays significant roles in determining the morphologies and structures of the MoS2/Si coatings. The results demonstrate that the increase of Si content can cause the changes of the coatings from a typical porous with columnar morphology to a non-porous with featureless morphology, while as the Si content continues to increase up to a much higher content (i.e., 17.3 at.%) the coatings with composite structure change to the a multilayer nanostructure. The tribological tests results point out that the MoS2/Si coatings with a composite structure perform better tribological properties as the content of Si rises from 0 to 14.7 at.%, owing to the combination of the increase in hardness and the oxygen gettering effect of Si. However, the MoS2/Si coatings with a multilayer nanostructure formed under a much high Si content (17.3 at.% Si) display poor tribological properties as the excessive Si inhibits the formation of the transfer film upon severe three-body abrasive wear.

Influences of the ZrC coating process and heat treatment on ZrC-coated kernels used as fuel in Pu-burner high temperature gas-cooled reactor in Japan

ABSTRACT The concept of Pu-burner high temperature gas-cooled reactor (HTGR) has been proposed to more safely reduce the amount of recovered Pu. In the Pu-burner HTGR concept, coated fuel particles with ZrC-coated yttria-stabilized zirconia containing PuO2 (PuO2-YSZ) kernels are employed for very high burn-up and high nuclear proliferation resistance. The role of ZrC layer is that of oxygen getter. CeO2-YSZ kernels were fabricated to simulate the PuO2-YSZ kernel and coated with a ZrC layer. In this study, we clarified that both Ce-rich grains and Zr-rich grains were densely distributed in surface regions of the as-fabricated CeO2-YSZ kernel. However, we have already clarified that the surface region of the CeO2-YSZ kernel coated with a ZrC layer was porous and mainly consisted of Zr-rich grains. These experimental results confirmed that Ce-rich grains were selectively corroded during the ZrC coating process. Then, the chemical stability of Zr-rich grains would be higher than that of Pu-rich grains. Thus, it would be more difficult to extract Pu from PuO2-YSZ kernels (in which almost all grains are Zr-rich) than from PuO2-YSZ kernels (in which many Pu-rich grains are included). Influences of the sintering of fuel compact on the microstructure of the ZrC-coated CeO2-YSZ kernel is also reported.

Boron synergies in lithium film performance

Fusion experiments use lithium and boron getters to capture impurities and control the density of fuel species in the plasma. In the TJ-II Stellarator, the addition of a boron-carbon substrate was found to extend the lifetime of the very reactive lithium wall conditioning. However, the synergies between the lithium layer and the underlying boron-carbon, or the effect of a glow discharge cleaning, on oxygen and deuterium gettering are not fully understood. Laboratory experiments were therefore initiated to gain deeper insight on the getter properties of B(C)/Li walls. The coatings were exposed to oxygen gas and plasmas while the capture and release of O was followed by mass spectrometry. Without the boron substrate, the maximum oxygen uptake is half the number of lithium atoms in the film for both oxygen gas and oxygen plasma. Conversely, the behaviour of B(C)/Li walls depends on the nature of the oxidation process: molecular oxygen (O:Li ≈ 0.15) or plasma (O:Li ≈ 0.50). The oxygen plasma gettering is thus preserved against molecular oxidation, e.g. an overnight exposure to the residual gas. While oxygen is known to promote hydrogen retention in lithium, the oxygen content of a B(C)/Li coating shows little effect on deuterium retention. Unlike simple lithium, the oxygen and deuterium gettering of B(C)/Li recovers after a helium glow discharge treatment. These advantageous features clearly point to a change in chemistry, with complex interactions between film constituents and the oxygen-rich environment of magnetic fusion devices.

Suboxide interface induced digital-to-analog switching transformation in all Ti-based memristor devices

Oxidation of TiN is a diffusion-limited process due to the high stability of the TiN metallic state at the TiN/TiO2 junction. Hence, the TiN/TiO2/TiN device being the inability to form a suitable interfacial layer results in the exhibition of abrupt current (conductance) rise and fall during the set (potentiation) and reset (depression) processes, respectively. Interfacial engineering by depositing Ti film served as the oxygen gettering material on top of the TiO2 layer induces a spontaneous reaction to form a TiOx interfacial layer (due to the low Gibbs free energy of suboxide formation). Such an interface layer acts as an oxygen reservoir that promotes gradual oxidation and reduction during the set and reset processes. Consequently, an excellent analog behavior having a 2-bit per cell and robust epoch training can be achieved. However, a thick interfacial layer may degrade the switching behavior of the device due to the high internal resistance. This work suggests that interfacial engineering could be considered in designing high-performance analog memristor devices.

Influence of oxygen on copper gettering in hydrocarbon molecular ion implanted region using atom probe tomography

The gettering behavior in a hydrocarbon molecular (C3H5) ion implanted region was investigated using atom probe tomography (APT) with the aim of improving electrical properties of CMOS image sensors (CISs) and stacked CISs. APT clarified the formation of carbon atom agglomerates with copper and oxygen gettering capability in the C3H5 ion implanted region. However, there were no oxygen atoms near the copper atoms in the C3H5 ion implanted region. In addition, the copper gettering capability of each carbon atom agglomerates decreased with increasing ratio of the number of oxygen atoms to that of carbon atoms in the carbon atom agglomerates. The copper and oxygen gettering mechanism was considered to involve the formation of a complex with carbon-containing gettering sites. Oxygen degrades the copper gettering capability of carbon atom agglomerates by the formation of stable complexes with carbon-containing gettering sites, which can also act as copper gettering sites. Consequently, the oxygen concentration in the C3H5 ion implanted regions is an important factor in improving the electrical properties of CISs and stacked CISs.

The origin and formation of oxygen inclusions in austenitic stainless steels manufactured by laser powder bed fusion

The origins of nano-scale oxide inclusions in 316L austenitic stainless steel (SS) manufactured by laser powder bed fusion (L-PBF) was investigated by quantifying the possible intrusion pathways of oxygen contained in the precursor powder, extraneous oxygen from the process environment during laser processing, and moisture contamination during powder handling and storage. When processing the fresh, as-received powder in a well-controlled environment, the oxide inclusions contained in the precursor powder were the primary contributors to the formation of nano-scale oxides in the final additive manufactured (AM) product. These oxide inclusions were found to be enriched with oxygen getter elements like Si and Mn. By controlling the extraneous oxygen level in the process environment, the oxygen level in AM produced parts was found to increase with the extraneous oxygen level. The intrusion pathway of this extra oxygen was found to be dominated by the incorporation of spatter particles into the build during processing. Moisture induced oxidation during powder storage was also found to result in a higher oxide density in the AM produced parts. SS 316L powder free of Si and Mn oxygen getters was processed in a well-controlled environment and resulted in a similar level of oxygen intrusion. Microhardness testing indicated that the oxide volume fraction increase from extraneous oxygen did not influence hardness values. However, a marked decrease in hardness was found for the humidified and Si-Mn free AM processed parts.