Glow Discharge Optical Emission Spectroscopy Research Articles

Effect of Impurities on the Compatibility of Steels in Supercritical CO2 at 450°–650°C

Abstract Direct-fired supercritical CO2 (sCO2) power cycles are a pathway to low-CO2 fossil energy but contain O2 and H2O in the sCO2 from combustion. The effect of impurities on structural steels was investigated at 450°–650 °C in 30 MPa sCO2. The test matrix included 9 and 12%Cr ferritic-martensitic (FM) steels and conventional and advanced austenitic steels exposed for 1000–2000 h with and without additions of 1%O2 and 0.1%H2O to simulate the cycle after water removal. For FM steels, the mass gains and scale thicknesses were similar with and without impurities with the formation of thick, duplex Fe-rich scales in all cases including the observation that Fe2O3 only formed with 1%O2. For the austenitic steels, higher mass gains were observed at all temperatures with increased formation of Fe-rich oxides when impurities were added. Carbon ingress was assessed by bulk combustion analysis, glow discharge optical emission spectroscopy (GDOES) and measuring postexposure room temperature tensile properties. Bulk C content was strongly increased at 650 °C but not at 450° or 550 °C.

Effect of the Substrate Materials in the Fabrication of an Electrode Based on Mixed Nickel‐Iron Oxide Electrocatalyst

AbstractThe effect of different substrate materials in the fabrication of an electrode intended for use in the water oxidation reaction is investigated. The electrocatalyst is nickel‐iron oxide (NiFeOx) which is deposited by chronoamperometry on nickel, iron, titanium, and stainless steel substrates. The process of electrodeposition is optimized to achieve the lowest overpotential for the water oxidation reaction. The four electrodes are characterized by scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), and glow‐discharge optical emission spectroscopy (GDOES) to describe the effect of the substrate on the nature of the electrocatalyst layer. Electrochemical tests in 1 m NaOH are applied on the four electrodes to assess the stability and the retention of the electrocatalytic properties of the whole electrode. All electrodes show similar overpotential of ≈0.3 V at 10 mA cm−2 implying that the substrate do not affect the electrocatalytic activity of the NiFeOx. After use, the overpotential increases in a range of 30–50 mV for nickel, iron, and titanium substrates, while stainless steel retains the lowest overpotential with an increase of 10 mV. This limited variation can be the effect of smaller NiFeOx nanoparticles compared to other substrates. XPS analysis reveals that after galvanostatic electrolysis, the oxidation state of Fe shifts slightly from Fe(II) to Fe(III), likely Fe3O4 and Fe2O3, while NiO/Ni2O3 change partially to Ni(OH)2.

Corrosion of Stainless Steel in Simulated Nuclear Reactor Primary Coolant-Experiments and Modeling.

In the present paper, the effect of the evolution of primary water chemistry during power operation on the corrosion rate and conduction mechanism of oxide films on stainless steel is studied by in situ impedance spectroscopy at 300 °C/9 MPa during 1-week exposure periods in an autoclave connected to a recirculation loop. At the end of the exposure period, the samples were anodically polarized in a wide range of potentials to evaluate the stability of the passive oxide. Separate samples of the same steel were simultaneously exposed to the coolant and subsequently analyzed by glow discharge optical emission spectroscopy (GDOES) in order to estimate the thickness and the in-depth composition of the formed oxides. Impedance data were quantitatively interpreted using the mixed-conduction model for oxide films (MCM) to estimate the rates of metal oxidation at the alloy/oxide interface, oxide dissolution and restructuring at the film/coolant interface, and ion transport in the protective corrosion layer.

Electroless brassing of historical artefacts

Abstract The topic of this work was the investigation of an alternative brassing technique consisting of electroless zinc plating of a copper object in a strongly alkaline solution and subsequent annealing to achieve a characteristic brass appearance. Within the scope of the work was the determination of the mechanism of zinc deposition on the copper surface, the optimisation of the NaOH concentration (30 and 40 wt. %), time of deposition (5-120 min), as well as temperature (150 and 200 °C) and annealing time (15 – 60 min). Electrochemical methods (potentiodynamic curves and open-circuit potential), metallography, X-ray diffraction (XRD), and glow-discharge optical emission spectroscopy (GD-OES) were used to study the brassing mechanism. Electrochemical measurements have shown that zinc powder significantly decreases the surface potential of copper to the value of zinc itself and also acts as a reducing agent. The diffusion of zinc in copper was found to occur during the primary deposition of zinc with the formation of the γ phase (Cu5Zn8). The optimal NaOH concentration is 40 wt.% and the deposition time is 60 min. The optimal conditions of annealing are 200 °C and 60 min. The primary γ phase is transformed during the annealing process into β and α phases.

Statistical methods for linking material composition to recombination losses in optoelectronic devices.

In light of the accumulation of characterization measurement data in the industrial production of solar cell devices, the investigation of a large amount of samples by statistical means lends itself to be a useful tool to gain further insights into how the data correlate with performance parameters. However, due to the multicollinearity among high-dimensional input parameters of compositional data, revealing the underlying patterns may prove to be a difficult endeavor. In this work, we present statistics consisting of 280 thin-film solar cell samples based on Cu(In,Ga)(S, Se)2 absorber layers whose depth-resolved composition was assessed by glow-discharge optical emission spectroscopy (GDOES). After parameterization of the features of [Ga]/([Ga] + [In])and[S]/([S] + [Se]) gradings, we employ two-way clustering in order to group samples and features by their similarity. In addition, using principal component analysis, information in the dataset, which is irrelevant to the problem, is removed by dimensionality reduction. In this way, it is possible to create a map that provides an overview of the GDOES data of all samples in their entirety, including correlations among features. More importantly, it also opens up a more precise way to plan further improvements in the compositional gradings by unveiling a path along which the experimenter can read the feature changes concerned with an improvement in the open-circuit voltage deficit or any other target parameter of interest. New samples can then be assigned to existing cluster centroids to predict what target parameter value they would assume.

Influence of surfactant on conductivity, capacitance and doping of electrodeposited polyaniline films

The electrodeposition of polyaniline films is usually carried out in acid solutions such as hydrochloric acid, perchloric acid or sulfuric acid, and more rarely in organic acids such as camphorsulfonic acid (CSA). In this study, the impact of the presence of a surfactant in the electrolytic solution based on hydrochloric acid or CSA was evaluated by successively using anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB), and non-ionic (Tritonx100) surfactants. Whatever the surfactant and the acid used, the electrochemical oxidation of aniline has successfully led to the formation of a thick polyaniline (PANI) film through a quasi-reversible reaction controlled by the diffusion of aniline monomers. The nature of the surfactant was shown to affect physico-chemical properties of the film, in particular its morphological features (morphology, thickness, roughness), electrochemical activity, specific capacitance, and conductivity. For example, PANI films containing SDS had a spongy morphology when PANI films containing Tritonx100 had a more fibrous and compact structure. Glow Discharge Optical Emission Spectroscopy (GDOES) experiments also highlighted differences depending on the acid used since chloride anions, from HCl, were present only on the top surface of the PANI films when camphorsulfonate anions were present everywhere throughout the polymer film, which impacts the doping process and electrochemical activity of the films. Moreover, the specific capacitance of the PANI/CSA films is higher and more sensitive to current density variation than the one of PANI/HCl films. Finally, electrochemical impedance experiments evidenced that the conductivity of PANI films electrodeposited from CSA solutions was much higher than the one of PANI films prepared from HCl solutions, and highly dependent on the nature of the surfactant, the most conductive films being obtained in the presence of SDS and Tritonx100. Therefore, the originality of this work comes from the possibility of modulating the conductivity, capacitance and electroactivity of electrodeposited polyaniline films using surfactants of different polarity, and from the determination of the distribution of ions in the films using the GDOES technique, which is rarely used to characterise organic films.

Characterization and In Vitro Behavior of PEO Coated Mg Modified with Antibacterial Ag(I) and Cu(II) Complexes.

The use of Mg-based biomaterials with a number of their advantageous properties are overshadowed by uncontrollable metal corrosion. Moreover, the use of implants goes alongside with the threat of pathogens-associated complications. In this study, PEO coated Mg biomaterial loaded with antibacterial Ag(I) and Cu(II) complexes is produced and tested to meet both appropriate protective characteristics as well as sufficient level of antibacterial activity. To achieve a suitable level of anticorrosion protection phosphate and fluoride-phosphate electrolytes are used in the PEO process. Investigation of the surface thickness and morphology done by means of cross-section analysis and scanning electron microscopy (SEM), as well as electrochemical impedance spectroscopy (EIS) assay show precedence of the fluoride containing PEO coating and make it the material of choice for further modification with Ag(I) and Cu(II) complexes. The presence of the complexes on the PEO surface is confirmed by energy dispersive X-ray spectroscopy (EDX). X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and glow discharge optical emission spectroscopy (GDOES) are used to estimate the complexes' chemical state and depth of penetration in the coating surface. Based on the results of antibacterial assay, the modified coatings are found to be active against both Gram-positive and Gram-negative bacteria.

A new approach to three-dimensional microstructure reconstruction of a polycrystalline solar cell using high-efficiency Cu(In,Ga)Se2

A new method for efficiently converting electron backscatter diffraction data obtained using serial sectioning by focused ion beam of a polycrystalline thin film into a computational, three-dimensional (3D) structure is presented. The reported data processing method results in a more accurate representation of the grain surfaces, reduced computer memory usage, and improved processing speed compared to traditional voxel methods. The grain structure of a polycrystalline absorption layer from a high-efficiency Cu(In,Ga)Se2 solar cell (19.5%) is reconstructed in 3D and the grain size and surface distribution is investigated. The grain size distribution is found to be best fitted by a log-normal distribution. We further find that the grain size is determined by the [Ga]/([Ga] + [In]) ratio in vertical direction, which was measured by glow discharge optical emission spectroscopy. Finally, the 3D model derived from the structural information is applied in optoelectronic simulations, revealing insights into the effects of grain boundary recombination on the open-circuit voltage of the solar cell. An accurate 3D structure like the one obtained with our method is a prerequisite for a detailed understanding of mechanical properties and for advanced optical and electronic simulations of polycrystalline thin films.

Inherent Antibacterial Properties of Biodegradable FeMnC(Cu) Alloys for Implant Application.

Implant-related infections or inflammation are one of the main reasons for implant failure. Therefore, different concepts for prevention are needed, which strongly promote the development and validation of improved material designs. Besides modifying the implant surface by, for example, antibacterial coatings (also implying drugs) for deterring or eliminating harmful bacteria, it is a highly promising strategy to prevent such implant infections by antibacterial substrate materials. In this work, the inherent antibacterial behavior of the as-cast biodegradable Fe69Mn30C1 (FeMnC) alloy against Gram-negative Pseudomonas aeruginosa and Escherichia coli as well as Gram-positive Staphylococcus aureus is presented for the first time in comparison to the clinically applied, corrosion-resistant AISI 316L stainless steel. In the second step, 3.5 wt % Cu was added to the FeMnC reference alloy, and the microbial corrosion as well as the proliferation of the investigated bacterial strains is further strongly influenced. This leads for instance to enhanced antibacterial activity of the Cu-modified FeMnC-based alloy against the very aggressive, wild-type bacteria P. aeruginosa. For clarification of the bacterial test results, additional analyses were applied regarding the microstructure and elemental distribution as well as the initial corrosion behavior of the alloys. This was electrochemically investigated by a potentiodynamic polarization test. The initial degraded surface after immersion were analyzed by glow discharge optical emission spectrometry and transmission electron microscopy combined with energy-dispersive X-ray analysis, revealing an increase of degradation due to Cu alloying. Due to their antibacterial behavior, both investigated FeMnC-based alloys in this study are attractive as a temporary implant material.

Observation of preferential sputtering of Si/graphite anodes from Li-ion cells by GD-OES and its validation by neutron depth profiling

Although the loss of Li inventory (LLI) is a common aging mechanism in Li-ion batteries, there are only few methods capable of comprehensive depth profiling within the bulk of the electrode to locate the residual Li. Two post-mortem analytical methods, which can be used to obtain quantified Li depth profiles to depths greater than 10 μm from the electrode surface are neutron depth profiling (NDP) and glow discharge optical emission spectroscopy (GD-OES). In this work, the validation of GD-OES using NDP by examining the Si/graphite anodes of cylindrical 21700 cells is presented. One anode was in a pristine/fresh state, two anodes were aged to the state of health (SOH) 90% and 76% at 45 °C respectively, and suffered from heavy solid electrolyte interphase (SEI) growth, and the fourth anode was aged to SOH 60% at 0 °C and exhibited Li plating. It is demonstrated that Li plating leads to a faster sputter rate of the Li-rich anode surface. An adapted method is introduced to incorporate the changing sputter rate into the depth profile calculation. For the aged anodes, the progressive aging of the anodes leads to a higher amount of irreversibly bound Li on the anode surface.

Effect of Cu2+ on deposition mechanism and structure of ZrO2-based conversion coatings on AA6060 aluminium alloys and their susceptibility to filiform corrosion

Zirconium oxide-based conversion coatings (CCs) were prepared from hexafluorozirconic acid, H2ZrF6, with and without CuII as an additive. The CCs were prepared on primary and recycled AA6060. The deposition mechanism, structure, electrochemical properties and effectiveness in protection against filiform corrosion (FFC) have been explored. In presence of CuII additives, a two step deposition mechanism is observed, evidenced by open circuit potential measurements and in situ dynamic electrochemical impedance spectroscopy. Copper deposits predominantly as copper(II) hydroxyfluoride on the top surface, and metallic Cu0 at the metal/CC interface, as evidenced by x-ray photoelectron spectroscopy and glow-discharge optical emission spectroscopy. The presence of a CuII additive induces a different distribution of the ZrO2-based products. After deposition of a weak organic model coating, aluminium pretreated with the CuII-containing system shows a 10%–30% lower maximum filament length compared to the CuII-free system in FFC tests, despite a ca. one order of magnitude higher cathodic activity of the former.

Analysis of hydrogen in a hydrogenated, 3D-printed Ti–6Al–4V alloy by glow discharge optical emission spectroscopy: sample heating effects

In the analysis of hydrogen in a hydrogenated, 3D-printed Ti–6Al–4V alloy by GDOES, hydrogen diffuses from the depth due to sample heating, enters the plasma and affects the signal response. A model of heat conduction within the sample is presented.

Concomitant ion matrix effects in SCGD-OES enhanced with formic acid

SCGD-OES is an attractive approach for on-line and in situ elemental analysis. This communication deals with concomitant ion matrix effects, especially if formic acid is added to improve sensitivity, and including a brief mechanistic discussion.

Deposition Mechanism, Structure and Corrosion Protection of ZrO2-Based Conversion Coatings on AA6060 Primary and Recycled Aluminum Alloys

Chemical conversion coatings (CC) are amongst the most common surface pretreatments for aluminium alloys before further organic coating steps. The presence of a conversion layer can increase the resistance towards underpaint corrosion such as filiform corrosion (FFC). Here we explore the deposition mechanism, structure and protective properties against FFC of a ZrO2-based CC on AA6060 aluminium alloy by means of electrochemical techniques as open circuit potential measurements, potentiodynamic polarization and dynamic electrochemical impedance spectroscopy (dEIS). Surface composition and elemental distribution are characterized by X-ray photoelectron spectroscopy (XPS), Glow Discharge Optical Emission Spectroscopy (GD-OES) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The variation of important parameters such as charge transfer resistance and capacitance during the conversion layer deposition gives insight into the deposition mechanism. GD-OES and XPS shed light into the structure and composition of the formed CC layer constituted of a mixture of Zr (hydr)oxides based products, redistribution of alloy elements and the nature of deposited additives. Finally, FFC tests reveal a comparable performance between primary and recycled alloys.

Analysis of Pre-Treatment Processes to Enable Electroplating on Nitrided Steel

Nitrided steel is being used to increase the lifetime and wettability of selective soldering nozzles. In this environment, the liquid solder wets to the surface of the nozzle to enable control of the solder flow during the soldering process. Pre-treatment is a key step in the processing of parts for electroplating. Pre-treatment usually involves degreasing and acidic pickling steps in order to remove adsorbed oil-based compounds and oxides respectively. These steps ensure a well-structured and adherent electroplated coating to the part.Surface treatments such as nitriding alter the surface composition of steels and thereby change the conductivity/surface activity. Typically, a nitrided surface contains a dual-phase surface layer followed by a diffusion zone consisting of the formed nitrides and finally a transition zone to the bulk material. Generally, this surface treatment is performed to harden materials without the risk of dimensional changes. For a selective soldering application, it reduces the dissolution of material into the solder during operation while also improving the wetting of the nozzle.The electroplated coatings for the selective soldering nozzles consist of 10 microns of nickel and 10 microns of tin. This structure allows for near-instant wetting and use of the nozzle. Furthermore, the electroplated layers provide corrosion protection for the nozzle ensuring no oxide or scale layers will form that may require flux for cleaning.A range of chemical and electrochemical pre-treatment steps were explored to prepare and optimally activate the nitride-hardened steel surfaces for electroplating. The processes included: hot degreasing and electrolytic degreasing with alkaline detergents; electrolytic descaling in a solution containing sodium hydroxide; chemical pre-descaling process with potassium permanganate; varying the compositions of pickling in inorganic acids; different formulations for nickel strike electrolytes for plating onto ferrous alloys.Mass loss measurements provided an estimation of the thickness of the material removed due to acid pickling. Scanning electron microscopy was employed to assess changes in the surface due to the pre-treatment. Open circuit potential measurements were applied to measure the surface activity before any pre-treatment and also the change in surface conductivity/activity post-treatment. Nanoindentation measurements were used to assess the change in surface hardness as a result of the nitriding treatment and also to check for the presence of the remaining hardened nitrided layer after pre-treatment. Glow discharge optical emission spectroscopy was utilised to study the elemental depth profile of the nitrided parts. Crystalline structure was studied through x-ray diffraction. After pre-treatment, a Woods nickel strike was applied to prepare the surface for further electroplating with bright tin. SEM analysis of the cross-sections of the coated specimens was used to analyse the coating microstructure. Thickness of the electrodeposited coatings were confirmed with x-ray fluorescence. Thermal shock tests were performed to confirm that the adhesion of the coating was sufficient.Approximately half of the nitrided layer was removed by pre-treatment in order to activate the surface for electroplating. More severe pre-treatment was required compared to electroplating non-hardened parts to activate the surface. Surface conductivity/surface activity was altered as measured by OCP resulting from the pre-treatment.This work has analysed the surface modification of nitride-hardened steels during the pre-treatment steps required to initiate electroplating and has shown that it is possible to prepare nitride-treated steels for electroplating. The results can be used to develop more optimal pre-treatment processes for electroplating nitrided steels.

(Invited) Lithium Plating as a Critical Ageing Mechanism in Lithium-Ion Batteries – Detection by Advanced Methods and Mitigation

The cycle life of Li-ion batteries is limited by aging on the material and electrode level. Prolonging the battery life helps increasing sustainability, reducing the dependency from critical raw materials, and safes costs. The first step in extending battery life is to understand the underlying degradation mechanisms. Post-Mortem analysis of commercial and pilot-line made cells showed that Lithium plating is a very relevant and severe aging mechanism which can lead to high aging rates and decrease safety properties.1 In this talk, we analyse the aging mechanism of Lithium plating on cell and electrode level.On cell level, capacity fade per time yields aging rates, which are temperature dependent. This temperature dependency is analyzed via Arrhenius plots. The Arrhenius plots for cycling aging show a typical V-shape with a low and a high temperature branch.2–4 A minimum in the Arrhenius plot corresponds to the maximum cycle life of the battery, while the low temperature branch indicates Lithium plating. Interestingly, the minimum in the Arrhenius plot shifts with the charging C-rate, the battery type,3,4 and – in case of non-linear capacity fade curves – with aging.4 In the last years, our group developed new semi-quantitative methods based on glow discharge optical emission spectroscopy (GD-OES) depth profiling for detection of Lithium plating on graphite5 and on Si/graphite composite anodes.6 Furthermore, a new in situ optical microscopy method with cross-sectioned full cells allows direct observations of the electrodes during charging and discharging.7,8 The color change of lithiated graphite in combination with simultaneous electrochemical data gives insight into the charging behavior of anodes. Under slow charging conditions (0.1C), the lithiation of the anode is observed to be homogeneously. Most interestingly, at 1C transport limitations come into play and lithiation fronts moving from the anode surface to the current collector can be directly observed and quantified by image analysis. Our results of both methods5,6,8 and in full consistence with simulations by others9 show that Lithium is mainly deposited on the anode surface, i.e. near the separator (see Figure).Finally, we show that Lithium deposition can be prevented by avoiding anode potentials < 0 V vs. Li/Li+ in commercial cells and cells from our pilot-line. Interestingly, Si/graphite anodes in pouch full cells show a lower susceptibility to Lithium plating at low temperatures with increasing Si content and the same anode areal capacity and N/P ratio. This suggests that the transport limitations in the pores of these Si/graphite anodes are reduced due to lower anode coating thickness. References T. Waldmann, B.-I. Hogg, and M. Wohlfahrt-Mehrens, J. Power Sources, 384, 107–124 (2018).T. Waldmann, M. Wilka, M. Kasper, M. Fleischhammer, and M. Wohlfahrt-Mehrens, J. Power Sources, 262, 129–135 (2014).X.-G. Yang and C.-Y. Wang, J. Power Sources, 402, 489–498 (2018).G. Kucinskis et al., J. Power Sources, 549, 232129 (2022).N. Ghanbari, T. Waldmann, M. Kasper, P. Axmann, and M. Wohlfahrt-Mehrens, J. Phys. Chem. C, 120, 22225–22234 (2016).M. Flügel, K. Richter, M. Wohlfahrt-Mehrens, and T. Waldmann, J. Electrochem. Soc., 169, 050533 (2022).C. Hogrefe et al., J. Electrochem. Soc., 169, 050519 (2022).C. Hogrefe, T. Waldmann, M. Hölzle, and M. Wohlfahrt-Mehrens, J. Power Sources, 556, 232391 (2023).S. Hein and A. Latz, Electrochimica Acta, 201, 354–365 (2016). Acknowledgement The authors would like to acknowledge the Federal Ministry for Economic Affairs and Climate Action (BMWK) for financial support of the Structur.e project (03ETE018E), the German Federal Ministry of Education and Research (BMBF) for funding of the project CharLiSiKo (03XP0333A) and the TEESMAT project (Horizon 2020 E.U. Framework Program, Grant Agreement N° 814106, http://www.teesmat.eu). Figure 1

Oxidation of Alloy 690 in Simulated Pressurized Water Reactor Primary Coolant – Experiments and Modeling

During normal operation of the primary loop of a water cooled-water moderated energy reactor (WWER), the associated water chemistry evolves from an initially high-boron high-potassium (beginning-of-cycle, 1200 ppm B and 8 ppm K) to significantly lower concentrations (ca. 400 ppm B and 3.5 ppm K) at the end of the respective campaign. In addition to that, the concentration of Li produced by transmutation of B reaches ca. 0.7 – 0.9 ppm. To the best of our knowledge, the effect of such water chemistry changes on pressurized water reactor (PWR) internals such as Alloy 690 have not been studied yet. Such a study appears relevant also within the frames of a discussion for a possible transition from B-Li to B-K water chemistry in PWRs.In the present paper, the effect of evolution of primary water chemistry during operation on the corrosion rate and conduction mechanism of oxide films on Alloy 690 is studied by in-situ impedance spectroscopy at 280 °C / 8 MPa during 1-week exposures in an autoclave connected to a re-circulation loop. Impedance measurements were performed in three-electrode mode featuring a Pt sheet counter electrode and a Pd electrode negatively polarized with a current of -10 µA vs. another Pt to approximate the reversible hydrogen electrode (RHE). Spectra were recorded at the corrosion potential in a frequency range 10 kHz – 0.1 mHz using an ac amplitude of 50 mV (rms). At the end of exposure, the samples were polarized in the range of potentials -0.1 to 0.5 V vs. RHE to evaluate the stability of the passive oxide. Separate samples of Alloy 690 were simultaneously exposed in the autoclave and subsequently analyzed by Glow-Discharge Optical Emission Spectroscopy (GDOES) in order to estimate the thickness and the in-depth composition of the formed oxides.Impedance data were quantitatively interpreted using the Mixed-Conduction Model for Oxide Films (MCM) to estimate the rates of metal oxidation at the alloy/oxide interface, oxide dissolution and restructuring at the film/coolant interface and ion transport in the protective layer. The effect of water chemistry evolution on corrosion rate and conduction mechanism in the oxide on Alloy 690 in primary coolant is discussed on the basis of the obtained parameters.Acknowledgments: This study is funded by the European Union-NextGenerationEU, through the National Recovery and Resilience Plan of the Republic of Bulgaria, project № BG-RRP-2.004-0002 (BiOrgaMCT).

2D Halide Perovskite Phase Formation Dynamics and Their Regulation by Co‐Additives for Efficient Solar Cells

AbstractThe incorporation of large organic ammonium ions renders the crystallization dynamics and layer formation process of halide perovskites complex, difficult to control, and leads to problems of suppressed charge transport with the formation of tiny‐sized grains. In this paper, the use of methylammonium chloride (MACl) and an excess of PbI2 is introduced as a co‐additives in the precursor solution for the control of phenylmethylammonium or benzylammonium (PMA+ spacer) and formamidinium (FA+)‐based quasi‐2D PMA2FAn−1PbnI3n+1 (n = 5) perovskite layers formation. By this method, the morphology of the layer, the inner phase distribution, and the charge transport properties are improved. By employing glow discharge‐optical emission spectroscopy (GD‐OES) and other techniques, it is revealed that the quasi‐2D perovskites prepared in the presence of co‐additives exhibit uniform removal dynamics of the solvent across the film. Furthermore, the grain growth mode, upon thermal annealing, is lateral. It results in large, monolithic grains with low‐trap state density and excellent substrate coverage. Particularly, co‐additives improve the cations dispersion upon the crystallization process, thus suppressing the low‐n phase formed through the aggregation of spacer cations and accelerating the formation of the high‐n phase.

Surface characteristics and tribological behavior of 3D-printed 316 L steel after plasma assisted low temperature carburizing

Conventional carburizing treatments of steels are usually carried out above 550 °C thus they are not suitable for austenitic stainless steels because surface hardening is achieved to detriment of corrosion resistance. To overcome this drawback different carburizing treatments at lower temperature have been developed and among them one of the most efficient is a plasma assisted process at 475 °C. With respect to austenitic stainless steels produced through traditional processes additive manufacturing allows to obtain mechanical parts of complex shape with enhanced strength and without loss of ductility. However, for certain applications the components still suffer of limited hardness and wear resistance. In this work the plasma assisted process at 475 °C has been employed to treat the 316 L steel manufactured by Laser Powder Bed Fusion (L-PBF) with the aim of improving its tribological behavior. The treatment time was 7 h and gas mixtures (CH4 + H2) with different amounts of CH4 have been used. The samples were then submitted to wear tests in pin-on-flat (POF) mode at room temperature with applied loads of 10 N and 20 N. The surface characteristics were examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy (RS), glow discharge optical emission spectroscopy (Rf-GDOES), and X-ray photoelectron spectroscopy (XPS). The results show that plasma treatments induce the formation of a ~ 25 μm thick layer of expanded austenite (S-phase) that is covered by a diamond like carbon (DLC) over-layer of ~2 μm. Such over-layer exhibits a complex sub-structure: the inner part consists of amorphous C (sp2 bonds) with a degree of topological disorder depending on the gas mixture whereas in the external part both sp2 (graphite-like) and sp3 (diamond-like) bonds are present with relative amounts changing with the distance from the surface. Independently on the gas mixture used in plasma treatment, all the samples exhibit a wear resistance much better than that of the untreated material. Moreover, wear resistance also depends on plasma treatment conditions: the greater the CH4 content, the lower the wear resistance. The results have been discussed by considering the intrinsic DLC brittleness that fractures and detaches from the metal surface during the tests thus hard debris take part to the wear process acting as abrasive particles.

Metallurgical interactions in solid/liquid diffusion couples of AA4343/AA3xxx/AA4343 layered aluminum sheet

The effect of pre-stretching on solid-liquid interaction, microstructure and brazing performance of AA4343/AA3xxx/AA4343 layered aluminum sheet during brazing at the atomic level (solid solution), nanoscale (dislocation) and micron level (grain boundary) are studied by glow discharge optical emission spectrometry (GDOES), scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The microstructure after brazing largely depends on the forming condition. The driving force of liquid film migration (LFM) is the reduction of stored deformation energy. The interaction between the liquid clad and solid core layers changes the elemental distribution and microstructure, which in turn affects the brazing performance of the sheet. The results reveal the mechanism of solid-liquid interaction of layered aluminum sheet during brazing and clarify the driving force of LFM of layered aluminum sheet during brazing. Consequently, these results provide important insights for the design and theoretical research of functional layered aluminum sheet.