Search

We acknowledge the support of Research Fund for Coal and Steel under grant agreement No. 709923, Academy of Finland for Genome of Steel grant No. 311934, Business Finland for Grant No. 4478/31/2019, Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2., Electric arc furnaces and ladle furnaces have an important role in the future of steelmaking where CO 2 emissions have to be mitigated to an acceptable level. One way to address this goal is to optimize and improve the current practices by adjusting the chemistry and reactions with material additions or gas injections. These procedures would greatly benefit from on-line slag composition analysis. Since the electric arcs radiate throughout the melting, optical emission spectroscopy is a potential method for such analysis. In this study, optical emissions from the electric arc are measured in a laboratory environment. Dozens of atomic emission lines were correlated with Cr 2O 3, Fe 2O 3, Al 2O 3, SiO 2, MnO, MgO, CaO, CaF 2, V 2O 5, and Ni content of the slag together with correlation between CaF 2 and molecular optical emission bands of CaF. Optimal spectral resolution for industrial applications was deducted to be between 0.022 and 0.179 nm. © 2021, The Author(s). --//-- Published under the CC BY license., Academy of Finland for Genome of Steel 311934, 4478/31/2019; Research Fund for Coal and Steel 709923; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.

International audience

We report on vacuum ultraviolet (VUV) excited photoluminescence (PL) spectra emitted from a chemical vapor deposited MoS2 few-layered film. The excitation spectrum was recorded by monitoring intensities of PL spectra at similar to 1.9 eV. A strong wide excitation band peaking at 7 eV was found in the excitation. The PL excitation band is most intensive at liquid helium temperature and completely quenched at 100 K. Through first-principles calculations of photoabsorption in MoS2, the excitation was explicated and attributed to transitions of electrons from p- and d- type states in the valence band to the d- and p-type states in the conduction band. The obtained photon-in/photon-out results clarify the excitation and emission behavior of the low dimensional MoS2 when interacting with the VUV light sources.

A high titania slag that is used as a feedstock for TiO2 manufacturing is obtained by ilmenite smelting (FeO.TiO2). The composition of the slag obtained by smelting is dependent on the composition of the mineral used for slag preparation, i.e., ilmenite in our study. At the laboratory scale, ilmenite slags are mostly obtained by using ilmenite as the raw material. An easy and simple way would be to prepare the synthetic slag using the individual components and heating them to high temperature in a furnace. The titania slag has a high oxidizing nature and requires an inert atmosphere to prevent oxidation of the slag as well as the molybdenum crucible. This paper describes the preparation of synthetic ilmenite slag using an induction furnace and the study of the composition and the phases formed in the slag. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma-optical emission spectroscopy (ICP-OES) were used as analytical techniques for studying the slag. A comparison between obtained synthetic slag and industrial ilmenite slag was performed to test the possibility of preparing slags in the laboratory as per the required composition. The slags show similar phase formation as obtained in industrial ilmenite slags, which means that the synthetic slags are identical to the industrial slags.

In this thesis, the electronic structure and electrodynamical processes of atomic mercury and potassium are studied experimentally and theoretically. Experimental measurements were carried out by means of both conventional photoelectron spectroscopy and multielectron coincidence technique utilizing magnetic bottle time-of-flight electron spectrometer together with pulsed synchrotron radiation. The thesis focuses on the theoretical modelling and interpretation of the experimentally observed transitions and binding energies. The calculations were carried out with relativistic multiconfiguration Dirac-Fock (MCDF) and non-relativistic Hartree-Fock (MCHF) methods. Theoretical results were used to interpret the experimental data in order to study the electron binding energy level structure and electron transition dynamics of these atoms.

Aerosol particles play significant roles in atmospheric processes but their effects pose large uncertainties in climate predictions. This thesis presents computational and experimental studies of aqueous organic and organic-inorganic solutions that serve as model systems of cloud droplets for better understanding of aerosols and their impact on climate. Carbon and oxygen K-edge X-ray Absorption Spectroscopy (XAS) has been applied in order to study molecular level interactions in aqueous solutions of glyoxal and methylglyoxal and to investigate potential salting effects with addition of inorganic salts to the solutions. The spectra were used for identification of chemical bonds and hydrated forms in the solutions. Carbon K-edge XAS was applied also for the study of binary aqueous solutions comprising surfactantssodium hexanoate and sodium octanoate. The solutions were measured for concentrations of solutes above and below the critical micelle concentration in order to observe the formation of micelles in the solution. In the case of aqueous sodium octanoate changes in the shapes of the spectra with increasing concentrations suggest changes in the chemical environment of the carbon atoms that could possibly be related to micelle formation. COSMOtherm, a software based on COSMO-RS (COnductor like Screening MOdel for Real Solvents), was used to predict solubilities and activity coefficients for C₂–C₁₂ fatty acids with even number of carbon atoms and their sodium salts in binary aqueous solutions and also in ternary solutions, comprising inorganic salts. The computed values indicate that COSMOtherm can be used to provide information about atmospheric organic components of aqueous solutions where experimental data are currently inaccessible. The results of these studies contribute to understanding of cloud microphysics and may be used to improve accuracy of atmospheric model predictions. Abstrakti Aerosolihiukkasilla on merkittävä rooli ilmakehän prosesseissa, mutta niiden vaikutuksiin liittyy suuria epävarmuuksia ilmastoennusteissa. Tässä tutkielmassa on tehty laskennallisia ja kokeellisia tutkimuksia orgaanisten aineiden vesiliuoksista sekä epäorgaanisten suolojen kanssa että ilman niitä. Nämä vesiliuokset ovat mallisysteemejä pilvipisaroille, ja niiden tutkimus auttaa ymmärtämään paremmin aerosoleja ja niiden ilmastovaikutuksista. Hiilen ja hapen K-kuoren röntgenabsorptiospektroskopialla tutkittiin molekyylitason vuorovaikutuksia glyoksaalin ja metyyliglyoksaalin vesiliuoksissa ja näiden orgaanisten aineiden aiheuttamia mahdollisia muutoksia epäorgaanisten suolojen liukoisuuteen. Röntgenabsorptiospektrejä käytettiin kemiallisten sidosten ja hydratoituneiden muotojen tunnistamiseen. Hiilen K-kuoren röntgenabsorptiospektroskopiaa sovellettiin myös pinta-aktiivisia aineita (natriumheksanoaattia ja -oktanoaattia) sisältävien vesiliuosten tutkimiseen. Mittauksia tehtiin pinta-aktiivisten aineiden pitoisuuksille molemmin puolin ns. kriittistä misellikonsentraatiota, jossa misellien muodostumisen tulisi alkaa; natriumoktanoaatin vesiliuoksen tapauksessa spektrien muoto muuttui pitoisuuden kasvaessa, mikä kertoo hiiliatomien kemiallisen ympäristön muutoksesta mahdolliseen misellien muodostumiseen liittyen. COSMOtherm on COSMO-RS-menetelmään (COnductor like Screening MOdel for Real Solvents) perustuva mallinnusohjelma, jota käytettiin ennustamaan parillisen määrän hiiliatomeja sisältävien C₂–C₁₂ rasvahappojen ja niiden natriumsuolojen liukoisuuksia ja aktiivisuusvakioita vesiliuoksissa ja epäorgaanisia suoloja sisältävissä vesiliuoksissa. Laskennalliset tulokset osoittivat, että COSMOtherm voi antaa arvokasta tietoa ilmakehässä esiintyvien orgaanisten aineiden vesiliuoksista, erityisesti tapauksissa, joissa kokeellisia arvoja ei ole vielä saatavilla. Tutkimusten tulokset auttavat ymmärtämään pilvien mikrofysiikkaa ja niitä voidaan käyttää ilmakehämallien ennusteiden tarkentamisessa.

Non-metallic inclusions form an essential parameter for assessing steel cleanliness. The chemical composition of the inclusions and content found in the steel matrix can be detrimental to both the steelmaking process and steel properties. Therefore, a characterisation technique that has features such as an improved duration for sample preparation, a non-destructive and relatively fast result analysis is of high interest to both researchers and steelmakers. The main objective of this study is to use Raman spectroscopy as an analytical technique to characterise synthetic non-metallic inclusions mostly associated with aluminium-killed calcium treated steels. The work first examines the possibility of estimating individual phase content for synthetic inclusion mixtures consisting of CA, C12A7, C3A, MgO.Al2O3 and CaS phases by using Raman spectroscopy. Observations made from the Raman spectra measured provide qualitative information for the specific phases present in the samples. The results from the study using calibration models are satisfactory in quantifying the specific phase content present in the sample mixtures based on the Raman spectral data. Additionally, this study investigates the potential use of Raman spectroscopy as a characterisation technique for inclusion evolution studies and to predict the liquidus region within a CaO–Al2O3 binary system under steelmaking temperatures. This is done by using different synthetic inclusion phases to generate the sample matrix that has varying phase content for possible inclusion evolution routes. The experimental measurements performed with Raman spectroscopy prove to have a relatively short duration for sample preparation, fast results, and the synthetic inclusion phases can be distinguished based on their characteristic Raman bands features. Consequently, this study shows that Raman spectroscopy can potentially be used as an analytical technique for inclusion studies in steel samples since the steel matrix is Raman inactive. Tiivistelmä Ei-metalliset sulkeumat ovat tärkeä teräksen puhtauden arviointikriteeri. Sulkeumien kemiallinen koostumus, koko ja muoto teräsmatriisissa voivat vaikuttaa haitallisesti teräksen valmistusprosessiin ja teräksen ominaisuuksiin. Karakterisointitekniikka, joka lyhentää näytteiden käsittelyaikaa ja mahdollistaa ainetta rikkomattoman testauksen ja tulosten suhteellisen nopean analysoinnin, on erittäin kiinnostava sekä tutkijoille että teräsvalmistajille. Tämän tutkimuksen päätavoitteena on käyttää Raman-spektroskopiaa analyysitekniikkana synteettisten ei-metallisten sulkeumien karakterisoimiseksi alumiinitiivistetyissä ja kalsiumkäsitellyissä teräksissä. Tutkimuksessa tutkitaan ensin mahdollisuutta määrittää yksittäisen faasin kemiallinen koostumus synteettisissä inkluusioseoksissa, joissa on CA, C12A7, C3A ja MgO-Al2O3, sekä CaS-faaseja käyttämällä Raman-spektroskopiaa. Mitatusta Raman-spektristä tehdyt havainnot osoittavat, että näyteseosten koostumus on määritettävissä tutkituille näytteille. Kalibrointimalleja käyttämällä saadut tulokset osoittavat, että faasiosuuksien määrittäminen onnistuu riittävällä tarkkuudella Raman-spektridatan avulla. Lisäksi tutkimuksessa tutkitaan Raman-spektroskopian käyttöpotentiaalia karakterisointitekniikkana sulkeumien analysoinnissa ja likvidusalueen laajuuden ennakoinnissa binäärissä CaO–Al2O3 systeemissä teräksenvalmistuslämpötiloissa. Tutkimuksessa on luotu erilaisia synteettisiä monikomponenttisulkeumia käyttämällä näytematriisi, joka sisältää laajasti eri faasikoostumuksia, sulkeumien mahdollisten kehitysreittien tutkimiseksi. Raman-spektroskopiaa hyödyntämällä tehdyissä testeissä on osoittautunut, että näytteiden valmistelu vaatii aiempaa vähemmän aikaa, tulokset saadaan aiempaa nopeammin ja synteettisten sulkeumien koostumus voidaan identifioida faaseille ominaisten Raman-sidosten perusteella. Tutkimus osoittaa siten, että Raman-spektroskopiaa voidaan hyödyntää analyysitekniikkana teräsnäytteiden sulkeumatutkimuksissa, koska teräsmatriisi on passiivinen Raman-säteilylle.

Electric arc furnaces (EAFs) and ladle furnaces (LFs) are the main recycling units for scrap metal. With lower CO₂ emissions than traditional ore-based steelmaking, the importance of EAFs can be expected to increase in the future. Increasing steel production rates and demand for high-quality and special steels require innovative process control systems to be developed for the steel industry. However, the harsh conditions inside the furnaces set strict requirements for durability and viable data acquisition methods for online measurement systems. In this thesis, the applicability of optical emission spectroscopy (OES) as an online measurement system for industrial EAFs and LFs is discussed, based on the results from pilot-scale and industrial EAFs, and an industrial LF. The electric arc has been characterised with OES, plasma diagnostics, and image analysis in the pilot-scale EAF measurements. These studies highlighted the influence of slag composition on the overall properties of the electric arc, the electrical parameters of the furnace, and the arc length{voltage relation. The majority of the atomic emission lines in the electric arc OES spectra were observed to originate from the slag components.> In the industrial EAF campaign, high alloyed steel grade was observed to have high-quality arc spectra within 30 mins before tapping and higher radiative heat transfer compared with the carbon steel grade. The spectra from the carbon steel grade, on the other hand, were used to observe how spectra evolve during slag foaming. Additionally, the molten bath surface temperature was estimated from the OES spectra. The slag composition was evaluated with OES in the industrial LF campaign, indicating that the CaF₂, MgO, and MnO content of the slag could be evaluated from the spectra.

When one asks about the properties of visual signals stimulating nervous systems, the ultimate interest lies in determining how the signal is encoded and transferred across the receptor barrier, how much and what kind of information is passed further to the higher visual centers and what is lost. The research presented in this dissertation attempts to explore quantitatively some detailed aspects of information processing by microvillar photoreceptors. Until recently, three methods were used to measure or estimate information transfer from the visual scene to the photoreceptor: Shannon’s information capacity, the closely related linear coherence rate and the compression entropy rate. In the first research article of this dissertation, a novel information calculation method based on principal component analysis, the mutual information rate, was developed. In the second publication, the influence of a physiological delay in the photoreceptor response on the information rate estimates by the Shannon method-related coherence rate algorithm was explored and a technique to compensate the associated error was proposed. The third study addresses the question of whether photoreceptors can more efficiently transfer information arriving from natural sources than from common artificial visual stimuli. Natural stimuli have interesting statistical properties in the form of higher order correlations (HOC), arising from the presence of features representing surfaces, textures, and object boundaries. This problem was investigated in the most extensive study to date, using blowfly Calliphora vicina photoreceptors as a model. The individual photoreceptors encode input information by a form of Weber’s law, with the HOC in natural sequences reducing information transfer by decreasing the number of local contrast events that exceed the noise-imposed threshold.

In this work, evolution of structural properties of anhydrous and hydrated alkali halide clusters are studied using synchrotron radiation based photoelectron spectroscopy. Alkali metal core level spectra of small anhydrous RbCl, RbBr, CsCl and CsBr clusters indicate a NaCl structure. For larger CsBr clusters a structural phase transition to CsCl structure is likely the case. Alkali halide core level spectra of mixed RbBr-water clusters indicate that at dilute concentration the salt is dissolved by the water cluster but ion pairing increases with concentration. Modeling of gas phase cluster formation and electronic structure calculations of core level chemical shifts are used to interpret the experimental spectra.

The main cause of temperature and composition fluctuations in the electric arc furnace (EAF) process is the scrap used as a raw material. Process conditions in EAF can vary significantly from heat to heat because there is no accurate information of scrap composition. Due to harsh process conditions, there are currently few sensors available for direct on-line measurement of the EAF process. In this work new information about stainless steelmaking EAF process conditions is sought with optical emission spectrum measurement. The measurement system relies on transportation of the light emitted from the measured furnace to a remotely situated spectrometer. Analysing the slag composition from the arc emission spectrum was tested in the laboratory and on a pilot scale. The laboratory measurements indicate that changes in the amount of CrOx and MnO in the slag have the highest impact on optical emission spectra. The pilot scale measurements show that the Cr2O3 content of the slag can be measured from the arc emission spectrum using suitable reference lines with an average absolute error of 0.62 %-points and a standard deviation of 0.49 %-points. The results from measurements at Outokumpu Stainless Oy, Tornio Works, indicate that measurement of the optical emission spectrum from industrial EAF is feasible in a practical sense, and can be used in analysing of EAF atmosphere, scrap melting and slag surface. Furthermore, the results of industrial measurements indicate that the atoms in the arc plasma mainly originate from the slag. The measurement of scrap melting could be potentially used in EAF control in optimization of arc voltages and second scrap bucket charging. The potential use of slag CrOx measurements is in optimization of reductant additions as well as defining the further processing of EAF slag. Tiivistelmä Valokaariuunien ohjaus on perinteisesti ollut uunioperaattorin käsissä. Valokaaariuuniprosessin on-line mittaukseen on olevassa vähän menetelmiä johtuen uunin hyvin haastavaista olosuhteista. Tässä työssä on tutkittu optiseen emissiospektroskopiaan perustuvaa menetelmää uuden jatkuva-aikaisen tiedon tuottamisessa valokaariuuniprosessista. Mittausjärjestelmä perustuu valon keräämiseen mitattavasta uunista valokuidun avulla, joka johtaa valon analysoitavaksi etäälle prosessista sijoitettuun spektrometriin. Mittauksia suoritettiin laboratorio-, pilot- ja tehdas-mittakaavassa. Valokaariuunin kuonan koostumuksen analysointia testattiin laboratorio- ja pilot-mittakaavan uuneilla. Laboratoriomittaukset osoittivat että kuonan komponenteista CrOx ja MnO ja vaikuttavat eniten mitattuun emissiospektriin. Pilot-mittakaavan kokeissa havaittiin, että kuonan Cr2O3-pitoisuutta voidaan mitata valokaaren emissiospektristä 0,62 %-yksikön keskimääräisellä absoluuttisella virheellä ja 0,49 %-yksikkön hajonnalla. Teollisella valokaariuunilla suoritetuista mittauksista havaittiin että optisen emissiospektrin mittaus voidaan suorittaa ilman ylitsepääsemättömiä teknisiä esteitä. Mittauksen tuloksia voidaan puolestaan käyttää kaasufaasin reaktioiden, romun sulamisen ja kuonapinnan ominaisuuksien arvioinnissa. Valokaaren emissiospektrin analyysi osoitti, että valokaaren plasman komponentit ovat pääosin peräisin kuonasta, joka mahdollistaa kuonan koostumuksen arvioinnin valokaaren emissiospektrin perusteella. Romun sulamisen mittausta voidaan prosessinohjauksessa käyttää jänniteportaiden ja toisen korin panostuksen optimointiin. Kuonan kromipitoisuuden mittaamista voidaan puolestaan käyttää pelkistinaineiden lisäyksen optimointiin ja kuonan jatkokäsittelyn valintaan.