Auswahl der wissenschaftlichen Literatur zum Thema „Oxysulphides“

Abstract The work concerns the studies on non-metallic inclusions occuring in laser-welded Si-Al TRIP steel containing Nb and Ti microadditions. Laser welding tests of 2 mm thick thermomechanically rolled sheets were carried out using keyhole welding and a solid-state laser. The results of laser welding in the air atmosphere for the heat input value of 0.048 kJ/mm are included. The distribution, type and chemical composition of non-metallic inclusions formed in the base metal, heat-affected zone, and fusion zone are analysed in detail. It was found that the base metal contains rare, fine oxysulphides. Their chemical composition was modified by rare earth elements. Numerous oxide inclusions of a various size and a chemical composition occur in the fusion zone. The dependence between a size of particles and their chemical composition was observed. A microstructure of steel was assessed using light microscopy and scanning electron microscopy techniques.

Abstract Corrosion resistance of the X4MnSiAlNbTi27-4-2 and X6MnSiAlNbTi26-3-3 type austenitic steels, after hot deformation as well as after cold rolling, were evaluated in 3.5% NaCl solution using potentiodynamic polarization tests. A type of nonmetallic inclusions and their pitting corrosion behaviour were investigated. Additionally, the effect of cold deformation on the corrosion resistance of high-Mn steels was studied. The SEM micrographs revealed that corrosion damage formed in both investigated steels is characterized by various shapes and an irregular distribution at the metallic matrix, independently on the steel state (thermomechanically treated or cold worked). Corrosion pits are generated both in grain interiors, grain boundaries and along the deformation bands. Moreover, corrosion damage is stronger in cold deformed steels in comparison to the thermomechanically treated specimens. EDS analysis revealed that corrosion pits preferentially nucleated on MnS and AlN inclusions or complex oxysulphides. The morphology of corrosion damage in 3.5% NaCl supports the data registered in potentiodynamic tests.

AbstractThe work addresses the production of medium-Mn steels with an increased Al content. The special attention is focused on the identification of non-metallic inclusions and their modification using rare earth elements. The conditions of the thermomechanical treatment using the metallurgical Gleeble simulator and the semi-industrial hot rolling line were designed for steels containing 3 and 5% Mn. Hot-working conditions and controlled cooling strategies with the isothermal holding of steel at 400°C were selected. The effect of Mn content on the hot-working behaviour and microstructure of steel was addressed. The force-energetic parameters of hot rolling were determined. The identification of structural constituents was performed using light microscopy and scanning electron microscopy methods. The addition of rare earth elements led to the total modification of non-metallic inclusions, i.e., they replaced Mn and Al forming complex oxysulphides. The Mn content in a range between 3 and 5% does not affect the inclusion type and the hot-working behaviour. In contrast, it was found that Mn has a significant effect on a microstructure.

The paper reports laboratory test findings on the impact of steel oxidation level on distribution features of non-metallic inclusions in low-alloyed structural steels. An analysis of the effect of various oxidation methods of steel on the distribution and formation of non-metallic inclusions is made. The results reveal a relation between the amount of sulphide and oxisulphide inclusions formed and steel oxidation level. The release of oxisulphide from the melt is accompanied with a decrease in the amount of both oxygen and sulphur. After oxygen content has achieved an equilibrium value, only “pure” sulphides are formed, which may deteriorate steel plastic properties. Thus, sulphides start precipitating only when oxygen content in the melt falls to a very low value. An increase in the amount of oxysulphides is accompanied with a decrease in sulphur concentration in the melt which reduces sulphide phase concentration at grain boundaries and stabilizes plastic properties. Thus the negative effect of sulphur can be reduced not only by decreasing its content in steel through expensive secondary steelmaking methods but also by controling the amount, shape and types of oxide, sulphide and oxisulphide inclusions in steel.

Molybdenum disulfide (MoS2) is an actively pursuing material of the 2D family due to its semiconducting characteristics, making it a potential candidate for nano and optoelectronics application. MoS2 growth from molybdenum and sulphur precursors by chemical vapor depositions (CVD) is used widely, but molybdates’ conversion into MoS2 via CVD is overlooked previously. Direct growth of MoS2 on the desired pattern not only reduces the interfacial defects but also reduces the complexities in device fabrication. In this work, we combine the wet synthesis and chemical vapor deposition method where sodium molybdate and L-cysteine are used to make a solution. With the dip coating, the mixture is coated on the substrates, and then, chemical vapor deposition is used to convert the chemicals into MoS2. Raman spectroscopy revealed the presence of oxysulphides (peaks number value) other than A 1 g and E 2 g 1 , where heat treatment was performed in the presence of Ar gas flow only. On the other hand, the films reducing in the presence of sulphur and argon gas promote only A 1 g and E 2 g 1 peaks of MoS2, which confirms complete transformation. XRD diffraction showed a very small change in the diffraction peaks and value of strain, whereas SEM imaging showed the flakes formation for MoS2 samples which were heated in the presence of sulphur. X-ray photoelectron spectroscopy is also performed for the chemical composition and to understand the valence state of Mo, S, and O and other species.

Aujourd'hui, dans les véhicules individuels, les piles à combustible concurrencent les batteries Li-ion par de nombreux avantages. Donc, remplacer les métaux nobles par des métaux plus abondants dans des catalyseurs est essentiel pour les rendre abordables. Le molybdène peut être un bon candidat puisque certains composés (ex. MoS2, MoO2) ont une activité pour la réduction de l’oxygène (ORR). Les oxysulfures de molybdène, relativement méconnus, pourraient être utilisés comme électrodes pour les batteries Li-ion ou les catalyseurs grâce à leur structure poreuse sous formes amorphes (couches minces et poudres massives). Leur synthèse colloïdale à basse température, favorisant les matériaux nanométriques et évitant des synthèses énergivores, est très peu étudiée. Il en va de même pour leur réactivité catalytique en ORR. Ici, la synthèse colloïdale bien connue d'oxysulfures de lanthanides à basse température (environ 300 °C), produisant par exemple Gd2O2S, est étendue à l’usage de précurseurs de molybdène. Nous avons étudié deux voies de synthèse basées sur celle des nanoplaquettes de Gd2O2S : par un protocole en deux étapes (ajout d'un précurseur de Mo à des nanoplaquettes de Gd2O2S fraîchement formées et non lavées) ou un autre en une étape (ajout simultané des deux précurseurs métalliques). L'analyse structurale a montré que la première méthode conduit possiblement à un dépôt de tétraèdres isolés de molybdate sur des nanoplaquettes de Gd2O2S sans changer leur forme et leur taille, tandis que la deuxième conduit plutôt à un environnement local de Mo plus sulfuré. En ORR, seuls les échantillons dopés au molybdate (à faible dose) ont montré des résultats positifs, qui sont directement liés à la présence de Mo. D'autres travaux exploratoires sur les synthèses sans Gd sont en cours pour compléter l'étude sur la structure et le mécanisme de formation des matériaux concernés. Dans l'ensemble, il s'agit de la première tentative d’application de la synthèse de l'oxysulfure de lanthanide pour synthétiser des oxysulfures de molybdène
Today, in personal vehicles, fuel cells are competing with the Li-ion batteries to provide the next technological leap. Hence, replacing noble metal by non-noble metal catalysts is essential to make them affordable. Molybdenum can be a good candidate as some compounds (e.g. MoS2, MoO2) are showing activity for the Oxygen Reduction Reaction (ORR). Uncommon molybdenum oxysulfides could be used as electrodes for Li-ion batteries or catalysts thanks to their porous structure in amorphous forms (thin films and bulk powders). Their colloidal synthesis at low temperature, favoring the nanoscaled materials and bypassing the simple energy-consuming synthesis, is barely reported. The same goes for their ORR catalytic reactivity, which was almost never studied. Here, the well-known colloidal synthesis of lanthanide oxysulfides at low temperature (around 300 °C), producing nanoparticles such as Gd2O2S, is extended to the use of Mo molecular precursors. We studied two pathways: by a two-step protocol (adding the Mo precursor to freshly formed, unwashed Gd2O2S nanoplates) or a one-step protocol (adding simultaneously both metallic precursors). The structural analysis showed that the first method possibly leads to a deposition of isolated molybdate tetrahedrons on Gd2O2S nanoplates without changing their shape and size, while the latter one leads to a more sulfide-like environment of Mo. As observed, only molybdate-doped samples (at low dose) showed positive results in terms of electrochemical activity, which is found related directly to the Mo’s presence. Other explorative work on the syntheses without Gd is being pursued to complement the study on the structure and the formation mechanism of the interested materials. Overall, this is the first attempt to synthesize molybdenum oxysulfide by applying the synthesis method of lanthanide oxysulfide

Neste trabalho foram estudados os fenômenos fotoinduzidos apresentados pelos filmes oxisulfetos de composição: 90% GeS2 + 10% Ga2 O3. Os filmes foram depositados em substrato de borosilicato pela técnica de evaporação por feixe de elétrons. A partir dos espectros de transmissão, a energia do bandgap, o índice de refração e a espessura foram determinados por diferentes métodos de análise. Para determinar as condições que otimizamos o efeito da fotoexpansão, as amostras foram expostas à radiação UV com energia acima do bandgap (3,5 eV), variando a densidade de potência (7,1 - 47,2 mW/mm2), tempo de exposição (30 180 min) e a espessura do filme (0,37 4,80 m). As áreas expostas foram analisadas usando um perfilômetro e valores de fotoexpansões variando de 0,03 a 0,16 m foram obtidos, cujo valor máximo foi encontrado para um filme com 1,80 m de espessura após iluminação com 24,3 mW/mm2 durante duas horas. Medidas da borda de absorção óptica revelaram um deslocamento para menores comprimentos de onda após a iluminação. O efeito de fotoclareamento foi acompanhado por uma diminuição do índice de refração, medido pela técnica de acoplamento de prisma. Os resultados revelaram a influência do oxigênio incorporado na matriz vítrea quando comparado ao Ga10Ge25S65. Consideramos que as mudanças fotoinduzidas são causadas por mudanças estruturais, como pôde ser verificado por medidas de espalhamento Raman nas configurações HH e HV. A dependência dos espectros Raman com a polarização da luz, observada em filmes iluminados e não-iluminados, é uma evidência direta para a ocorrência de importantes mudanças estruturais causadas por irradiação óptica, principalmente nas ligações Ge-S. As composições químicas foram determinadas por EDX e indicaram um aumento de oxigênio na superfície iluminada que pode estar associado ao aumento das ligações Ga-O-Ga. Como aplicação destes fenômenos fotoinduzidos, a fotoexpansão foi usada para a produção de redes de difração. As medidas de eficiência de difração e as imagens de microscopia de força atômica demonstraram que a fotoexpansão cria uma rede de relevo na superfície do vidro.
Photoexpansion and photobleaching effects were observed in 90% GeS2 + 10% Ga2O3 films. The films were deposited onto borosilicate substrates by electron beam evaporation technique. From transmission spectra, their bandgap energy, refractive index and thickness were determined by different analysis methods. To evaluate the photoinduced effects and find the optimal conditions to get the largest photoexpansion, the samples were exposed above bandgap light (~ 351 nm), varying power density (7.1- 47.2 mW/mm2), exposure time (30 120 min) and film thickness (0.37 4.80 m). The exposed areas were analyzed using profilemeter and photoexpansions from 0.03 to 0.16 m were obtained, whose maximum value was found for a 1.80 m thick film after 24.3 mW/mm2 illumination during 120 min. Fractional expansion (_V/V) from 8% to 30% was obtained and optical absorption edge measurements revealed a blue shift after illumination. This photobleaching was accompanied by a decrease in refractive index, as measured with the prism-coupling technique. The results reveal the influence of incorporated oxygen in the glass matrix when compared with Ga10Ge25S65 [1]. The chemical compositions were measured using an energy dispersive analyzer (EDX) and no significant difference could be observed between the compositions of illuminated and nonilluminated samples. So, we supposed that the photoinduced changes are caused by photostructural changes as well observed with Raman-scattering measurements in HH and HV configurations. The dependence of Raman spectra with the polarization of the light, observed in illuminated and non-illuminated films, is a direct evidence for the occurrence of important structural changes in local bonding configuration caused by optical irradiation. As application of the induced phenomenon, photoexpansion effect has been used to produce diffraction gratings. Atomic microscopy images and diffraction efficiency data indicate that photoexpansion leads to relief gating on the glass surface.