Influence Of Dew Point Research Articles

Influence of Moisture on the Electrochemical Performance of Prelithiated C/SiOx Composite Anodes for Li-Ion Batteries

Prelithiation of Si containing anodes has commonly been acknowledged as a potential solution to the challenge of the high irreversible lithium losses that still hinder the widespread adoption of this next-generation anode active material. However, upscaling and implementation in the process chain remain major hurdles for most proposed prelithiation processes. A significant part of this comes down to the high reactivity of prelithiation agents and prelithiated electrodes towards moisture. In industrial scale electrode production, dry rooms with dew point controlled atmospheres are already in use, but are a significant cost factor. Therefore, the compatibility of prelithiated electrodes with dry room conditions is a major factor for the implementation of prelithiation into existing production lines.In this work C/SiOx composite anodes are electrochemically prelithiated and subsequently subjected to industry relevant moisture levels. The influence of dew point and exposure time is examined. After exposure, the anodes are assembled into half-cells and their electrochemical performance during the first lithiation/delithiation cycle is analysed using a 3-electrode setup. The evaluation of the specific capacities and the potential curves provides information about the extent of the damage to the electrode. The results indicate a promising stability window for dew points of up to -40° C and realistic exposure times of up to one hour. Additional aging investigations in full cells against NMC622-based cathodes confirm these findings. Furthermore, electrochemical impedance spectroscopy, XPS and ToF-SIMS measurements are performed to elucidate the effect of moisture exposure on the solid electrolyte interface (SEI) composition. The results suggest the development of a double-layered SEI structure, where the first layer forms during prelithiation and is altered by moisture exposure, while the second layer forms on top of the first layer during formation. Figure 1

Influence of Dew Point on the Selective Oxidation, Microstructure and Mechanical Properties of a High-Al Low-Si Dual Phase Steel during Hot-Dip Galvanizing Process

The effect of dew point on the selective oxidation behavior, microstructure and mechanical properties of a high-Al low-Si dual phase steel is elucidated. The results showed that as dew point is increased from–30°C to +5°C, internal oxidation of alloying elements occurs, and consequently the mass of external oxides decreases, which improves the galvanisability of steel sheets. It was also observed that the dew point had an impact on the microstructure and mechanical properties of the experimental steel. With the increase of dew point, the decarburization layer on the surface was increased, leading to inferior mechanical properties. Compared with the industrial steel, the high-Al-low-Si DP steel exhibited excellent galvanisability under identical annealing conditions.

3<sup>rd</sup> Generation Hot-Dip Galvanized Steel Sheet for Automobile Manufacturing - Interface Reactions between Zinc and Metal Oxide

There is a growing demand for Advanced High Strength Steels (AHSS) in the automotive industry owing to their high specific strength and good formability. The mechanical properties satisfy the demands for improved passenger safety and decreased vehicle weight due to thinner cross sections. Hot-dip galvanizing is a common procedure to prevent corrosion of steel, galvanized steel forms the basis for further processing like organic coating. Industrially, the steel strip is annealed at 840 °C in 5 % H2 in N2 at a dew point (DP) of -30 °C. These conditions are reducing for Fe, but oxidizing for oxygen-affine alloying elements as Mn, Si and Cr. These ignoble elements form an external, covering oxide layer on the steel surface, which exhibits poor wettability for the Zn(Al, Fe)-bath. The liquid Zn(Al, Fe) has a temperature of 460 °C and contains 0,2 wt% Al to form a Fe2Al5-xZnx-layer to inhibit the growth of Fe-Zn-intermetallics. Along with the increased amount of alloying elements to improve strength and ductility of AHSS the evolving oxide layer after annealing at the steel surface deteriorates hot-dip galvanizing. The question arises what happens to the surface oxides during immersion in the Zn(Fe, Al)-bath. For this purpose annealed as well as annealed and galvanized 0.8Si-AHSS and 1.5Si-AHSS were compared by glow discharge optical emission spectroscopy (GD-OES) depth profiles. Galvanized specimens show fewer oxides at the steel-zinc-interface as annealed specimens. A possible explanation is an aluminothermic reduction of oxides by 0.2 wt% dissolved Al in the Zn(Al, Fe)-bath. Al is thermodynamically more affine to oxygen than Mn and Si and may reduce Mn- and Si-oxides. An alternative theory is the dissolution of Fe in Zn during reactive wetting, as a side effect the oxides are rinsed off too. Additionally, the influence of DP was investigated. According to Wagner’s theory of selective oxidation, a higher amount of oxygen in the annealing atmosphere leads to internal oxidation of the alloying elements. Experiments were carried out with 0.8Si-AHSS and 1.5Si-AHSS by altering the DP during annealing from -30 °C (380 ppm H2O) to 0 °C (6000 ppm H2O). Oxidation mode changed from external (DP -30 °C) to internal oxidation along grain boundaries (DP 0 °C), as predicted by Wagner. These oxide-free surface provides good reactivity to enhance reactive wetting with the Zn(Fe, Al)-bath and form a dense Fe2Al5-xZnx-layer.

Effect of dew point during heating on selective oxidation of TRIP steels

The influence of dew point during heating on the selective oxidation behavior of two kinds of transformation-induced plasticity (TRIP) steel was studied by means of a hot dip process simulator. The selective oxidation behavior of alloying elements on the surface was studied by glow discharge optical emission spectroscopy (GDOES) and scanning electron microscopy (SEM). For the Al-bearing TRIP steel, less Al-rich oxides were found on the steel surface and there was less Mn on the surface when the dew point during heating was much low. On the contrary, for the Si-bearing TRIP steel, more film-like Si-rich oxides were found on the steel surface and there was more Mn on the surface when the dew point during heating was low.

The influence of dew point during annealing on the power loss of electrical steel sheets

Decarburization is a necessary part of the processing of electrical steels if their carbon content is above a certain level. The process is usually carried out in a wet hydrogen–nitrogen atmosphere. Having a high dew point has a negative influence on the power loss, though. This is due to oxidation of the steel, which hinders domain wall motion near the surface. In this study, an increase of the power loss was only observed at a fairly high dew point (>20 °C). It was also only at these high dew points where a subsurface oxide layer was observed. The surfaces of samples with and without this layer were etched in steps. The magnetic properties of the etched samples corresponded well with the expected behavior based on GDOES profiles of the samples.

Hot Dip Galvanizing Simulation of Interstitial Free Steel by Liquid Zinc Spin Coater: Influence of Dew Point on Surface Chemistry and Wettability

In order to establish the relationship between surface chemistry and wettability as a function of dew point, an attempt has been made to simulate the hot-dip galvanizing process with an ‘in-house’ built Liquid Zinc Spin Coater. Interstitial free (IF) steel was annealed at 820°C in N2-5%H2 gas atmospheres with dew points of -79°C, -29°C and 0°C, respectively. The wettability tests were conducted at 470°C at low dew point of -79°C. Surface analyses prior to wetting were carried out by using X-ray photoelectron spectroscopy (XPS) and Field Emission Scanning Electron Microscopy (FE-SEM). As expected, external oxidation of Al was observed only at the low dew point. With increasing dew point the oxidation of Cr and Si becomes internal. The formation of manganese silicates was observed at all dew points. While sulphur was detected on the specimen surface after all annealing conditions, the segregation of P starts to be significant at dew point 0°C by forming Mn-phosphates. Despite the surface oxides, specimens annealed at all dew points are in the wetting regime by liquid zinc. Investigations on the steel/zinc interface of IF steel by using the liquid zinc spin coater were successful.

Influence of dew point on surface reactions during sintering of austenitic stainless steel

Influence of dew point on surface reactions during sintering of austenitic stainless steel