Third-generation advanced high-strength steels (3G AHSS) are being developed to assist in vehicle light weighting so that fuel efficiency may be improved without sacrificing passenger safety. 3G-AHSS have received significant interest from the automotive industry as a critical candidate for their unique combination of high strength and ductility. However, due to selective oxidation of the principal alloying elements such as Mn, Si, Al, and Cr at the steel surface during the annealing stage prior to immersion in the galvanizing Zn(Al, Fe) bath, the process of continuous hot-dip galvanizing of these steel is challenging. This thesis determined the influence of annealing process parameters such as oxygen partial pressure and annealing time, on the selective oxidation and reactive wetting of an Fe-0.15C-5.56Mn-1.17Si-1Al (wt%) prototype 3G AHSS during intercritical annealing as well as continuous galvanizing. Simulated annealing and galvanizing were conducted on the prototype Fe-0.15C-5.56Mn-0117Si-1Al (wt%) 3G steel; Intercritical annealing heat treatments were carried out at 690˚C in a N2-5 vol pct H2 process atmosphere under dew points of 223 K (–50 °C), 243 (–30 °C) and 268 K (–5 °C). MnO was the major oxide formed at the outmost layer of the external oxides on all annealed samples. The experimental parameters, on the other hand, had a substantial impact on the morphology, distribution, thickness, and surface oxide coverage. The greatest Mn surface concentration as well as maximum surface oxide coverage and thickness was obtained by annealing the panels under the 223 K (–50 °C) and 243 (–30 °C) dp process atmospheres. The oxides formed under these process atmospheres largely comprised coarse, compact, and continuous film nodules. In contrast, MnO nodules formed under the 268 K (–5 °C) dewpoint process, exhibited wider spacing between finer and thinner nodules, which was consistent with the internal oxidation mode, while under 223 K (–50 °C) dp process atmosphere, generally external oxidation took place. Poor reactive wetting was obtained for the panels annealed under the 223 K (–50 °C) dp process atmosphere for both the 60 s and 120 s holding times as well as the 243 K (–30 °C) dp process atmosphere for 120 s. This was attributed to the formation of a thick, compact oxide layer on the steel surface, which acted as a barrier between the substrate and Zn bath, preventing Fe dissolution from the substrate surface for the formation of the desired Fe2Al5Znx interfacial layer. However, a well-developed interfacial Fe-Al intermetallic layer was formed under the 268 K (–5 °C) and 243 (–30 °C) dp process atmospheres for intercritical annealing times of 60 s, which is indicative of a good reactive wetting since the thinner and nodule-like oxides on the steel surface after annealing encourage the reactive wetting. External oxides morphology plays a dominant role in facilitating the contact between Zn-alloy bath and the substrate via different mechanisms such as aluminothermic reduction which occurred for the sample annealed under the 268 K (–5 °C) dp process atmosphere. / Thesis / Master of Applied Science (MASc)

Third generation advanced high-strength steels (3G-AHSS) have received significant interest from leading auto steel industries and OEMs as candidate materials for reduced mass Body In White (BIW) components due to their unique combination of high specific strength and ductility. However, the continuous hot-dip galvanizing of these steels is challenging due to selective oxidation of the main alloying elements such as Mn, Si, Al and Cr at the steel surface during the annealing step prior to immersion in the galvanizing Zn(Al, Fe) bath, as extensive coverage of the substrate surface by these oxides is detrimental to reactive wetting, good coating adhesion and integrity. Simulated galvanizing treatments were conducted on two prototype Fe-0.1C-6Mn-2Si (wt pct) 3G steels; one as the reference steel and the other with 0.05 wt pct Sn added to the composition. The combined effects of annealing temperature, time, process atmosphere oxygen partial pressure and 0.05 wt pct Sn addition on the selective oxidation of the steel substrates were determined. Subsequently, the reactive wetting of the steels with respect to the pre-immersion surface structures of the samples annealed for 120 s was examined. Annealing heat treatments were carried out at 800˚C and 690˚C in a N2-5 vol pct H2 process atmosphere under three dew points of –50˚C, –30˚C and +5˚C, covering process atmosphere oxygen partial pressures within the range of 1.20  10-27 atm to 1.29  10-20 atm. MnO was present at the outmost layer of the external oxides on all samples after annealing. However, the morphology, distribution, thickness and surface coverage were significantly affected by the experimental variables. Annealing the reference steel under the low dew point process atmospheres, i.e. –50˚C and –30˚C, resulted in the highest Mn surface concentration as well as maximum surface oxide coverage and thickness. The oxides formed under these process atmospheres generally comprised coarse, compact and continuous film forming nodules, whereas the surface morphologies and distributions obtained under the +5˚C dew point process atmosphere, which was consistent with the internal oxidation mode, exhibited wider spacing between finer and thinner MnO nodules. The grain boundary internal oxide networks had a multi layer structure with SiO2 and MnSiO3 at the oxide cores and shells, respectively. Significant morphological changes were obtained as a result of Sn addition. The continuous film-like external MnO nodules were modified to a fine and discrete globular morphology, with less surface coverage by the oxides and reduced external oxide thickness. Both the external and internal oxidations followed parabolic growth kinetics, where the depth of the internal oxidation zone decreased with Sn addition and decreasing oxygen partial pressure. Poor reactive wetting was observed for the reference steel substrates that were annealed for 120 s under the –50˚C and –30˚C dew point process atmospheres at 800˚C and under the –50˚C dew point atmosphere at 690˚C, such that no integral metallic coating was formed after the 4 s immersion in the Zn(Al, Fe) bath. By contrast, excellent coating quality was obtained for the Sn-added steels when the –30˚C and +5˚C dew point process atmospheres were employed when annealing at 690˚C. The remainder of the experimental conditions demonstrated good reactive wetting with intermediate coating quality. For the two reference steels annealed at 800˚C under the –50˚C and –30˚C dew point process atmospheres, poor reactive wetting was due to full coverage of the surface by 116 nm and 121 nm thick and continuous MnO films. In the case of the 690˚C  –50˚C reference steel with the external layer thickness of only 35 nm, however, poor wetting was attributed to substantial coverage of the surface by continuous, film-like oxides. In both cases, exposure of the underlying substrate to the bath alloy and an intimate contact between the substrate Fe and the bath dissolved Al could not take place and the formation of the Fe2Al5Znx interfacial layer was hidered. For the processing conditions that satisfactory reactive wetting was obtained despite the pre-immersion selective oxidation of the surfaces, several reactive wetting mechanisms were determined. For the samples with a sufficiently thin external MnO layer, good reactive wetting was attributed to partial reduction of MnO by the bath dissolved Al, as well as bridging of the Mn sub-oxides by the Zn coating or Fe2Al5Znx interfacial intermetallics. Partial or full formation of the Fe2Al5Znx interfacial layer was observed in the successfully galvanized substrates with Fe-Al crystals formed between, underneath and also on top of the reduced oxides. Furthermore, for cases with widely-spaced, fine oxide nodules, it was found that the liquid bath alloy was able to infiltrate the external oxide/substrate interface, resulting in surface oxide lift-off and enhanced coating adhesion. It was globally concluded that the thin, discrete and fine globular morphology of external MnO, resultant of annealing the steel substrates with 0.05 wt pct Sn addition under the process atmosphere oxygen partial pressures consistent with internal oxidation, allowed for an enhanced reactive wetting by the Zn(Al, Fe) galvanizing bath which was manifested by increased amount of Al uptake and population of the Fe2Al5Znx intermetallics at the coating/steel interface. / Thesis / Doctor of Science (PhD)

Propylene is the second most important starting chemical in the petrochemical industry after ethylene. Unlike ethylene, propylene readily undergoes substitution reactions including polymerisation, oxidation, halogenation, hydrohalogenation, alkylation, hydration, oligomerization and hydroformylation, which lead to a wide variety of important downstream products. One of the principal uses of propylene is to produce key chemicals from selective oxidation. In 2016, the world annual production of propylene is about 94 million tonnes, and the global proportion used to produce selective oxidation product is over 18%. They constitute a key part of the chemical industry and contribute towards substantial economic benefits. The application of Ag based heterogeneous catalysts to selective propylene oxidation is a key factor in the synthesis of nearly all downstream chemicals, however billions of pounds are lost every year due to unplanned reactor shutdown, safety control and environment unfriendly emission control as a results of inefficiency catalytic selectivity and activity. Despite, both theoretical and experimental research works have been intensively involved, the fundamental reason leading to these effects are not yet well understood. The work presented in this thesis explores a range of novel modification techniques that alter the activity of Ag nanocatalysts for selective propylene oxidation, especially in propylene epoxidation. Particular focus is placed on developing surface modified Ag catalysts through morphology control, surface architecture engineering with another sublayer metal. Using a combination of modelling, novel and traditional materials characterisation methods, it is found that these modification result in some significant electronic and/or geometric alterations to the Ag nanoparticles surface. The Ag-Ag bond distance can be dramatically enlarged by exposing a high-index Ag surface or a core-shell structure with monolayer Ag shell. When interacting with molecular oxygen, the molecular oxygen adsorption and dissociation behaviour is sensitive to the geometric changes in Ag surface. This leads to an enhanced selectivity toward propylene epoxidation than combustion resulting from preventing a C-H bond cleavage. Finally, be creating atomically dispersed Ag on zeolite, a completely different interaction between molecular oxygen and single atom Ag were discovered comparing to on a extensive silver surface. This leads to the observation of an excitingly new propylene oxidation reaction producing ethanol and CO₂ resulting from C=C bond cleavage. Overall, the research presented within this thesis demonstrated a number of methods for the intelligent design of novel heterogeneous Ag catalysts with remarkable activity and selectivity toward specific selective propylene oxidation. These modification methods are believed to be potentially applicable to a wide range of other catalytic reactions.

No description available.

L'activation de la liaison Csp3-H peu réactive et sa fonctionnalisation en liaison carbone-hétéroatome constituent un défi pour les chimistes de synthèse. Un exemple d'intérêt industriel est la réaction d'oxydation du cyclohexane, dont les produits finaux (cétone et alcool) sont des intermédiaire clés pour la production de polyamides tels que les Nylon-6 et 6,6. Parmi les possibilités d'activation, la catalyse représente une méthode de choix. Dans le cadre de cette thèse des suspensions aqueuses à base de nanoparticules ont été évaluées en termes de stabilité et de performances catalytiques. Dans un premier temps, des colloïdes de ruthénium ont été synthétisés à partir de RuCl3,3H2O et caractérisés par des analyses physico-chimiques (MET, SPX, SAXS, UV-visible, etc.). Des espèces actives de Ru+3 dont la structure est de type Ru(OH)3-xClx ont été obtenues. Après optimisation des conditions de réaction, des conversions élevées, associées à des sélectivités pertinentes vis-à-vis de la cétone (jusqu'à 98%), ont été obtenues. Des études cinétiques et mécanistiques ont montré que la voie radicalaire est prépondérante. De plus, ces colloïdes de Ru aisément recyclables ont également été testés avec succès en oxydation d'autres hydrocarbures saturés et insaturés. Dans un second temps, un catalyseur à base de dioxyde de manganèse, métal moins coûteux et abondant, a été synthétisé par un procédé redox original, à partir de KMnO4 et en présence d'un ammonium quaternaire à tête polaire hydroxylée (HEA16Cl), qui joue simultanément le rôle de réducteur et d'agent stabilisant. Ce système s'est révélé être une alternative pertinente aux procédés à base de métaux nobles. Les nanobâtonnets de MnO2 se sont ainsi montrés actifs en oxydation du cyclooctane avec une sélectivité totale en cétone. / The activation of the Csp3-H bond and its transformation into a carbon-heteroatom bond remains a great challenge for the organic chemistry. An example of industrial application is the oxidation reaction of cyclohexane, leading to the production of the corresponding ketone and alcohol, key intermediates of Nylon-6 and Nylon-6,6 polyamides. Among the strategies to activate this unreactive bond, catalysis affords a relevant and sustainable tool. In this work, aqueous suspensions of metal nanoparticles were evaluated in terms of their stability and catalytic performances. Firstly, ruthenium colloids were synthesized from RuCl3.3H2O and fully characterized by various physico-chemical analyses (TEM, XPS, SAXS, UV-visible, etc.). Ru+3 active species were obtained, with a Ru(OH)3-xClx structure. After optimization of the reaction conditions, high conversions, combined with pertinent selectivities towards the ketone (up to 98%), were achieved. The presence of radical species was proved through kinetic and mechanistic studies. Furthermore, these easily recyclable Ru colloids were also evaluated in the oxidation of several saturated and unsaturated hydrocarbons. Secondly, a catalyst based on manganese dioxide, a cheap and abundant metal, was synthesized by an original redox process, starting from KMnO4 and in the presence of a hydroxylated quaternary ammonium (HEA16Cl), which plays the role of a reducing and stabilizing agent. This system proved to be a relevant alternative to methodologies based on noble metals. The MnO2 nanorods showed a good activity in the cyclooctane oxidation with a 100% selectivity towards the ketone.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18808号 / 理博第4066号 / 新制||理||1585(附属図書館) / 31759 / 京都大学大学院理学研究科化学専攻 / (主査)教授 丸岡 啓二, 教授 時任 宣博, 教授 大須賀 篤弘 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Medium Mn (med-Mn) third generation advanced high strength steels (3G AHSSs) are promising candidates for meeting automotive weight reduction requirements without compromising passenger safety. However, the thermal processing of these steels should be compatible with continuous galvanizing line (CGL) processing capabilities as it provides cost-effective, robust corrosion protection for autobody parts. Hence, the main objective of this Ph.D. research is to develop a CGL-compatible thermal processing route for a prototype 0.2C-6Mn-1.5Si-0.5Al-0.5Cr-xSn (wt%) (x = 0 and 0.05 wt%) med-Mn steel that will result in the 3G AHSS target mechanical properties (24,000 MPa%  UTS × TE  40,000 MPa%) and high-quality galvanized coatings via enhanced reactive wetting. It was found that the starting microstructure, intercritical annealing (IA) time/temperature, and Sn micro-alloying had a significant effect on the retained austenite volume fraction and stability and, thereby, the mechanical properties of the prototype med-Mn steel. For the as-received cold-rolled (CR) starting microstructure, the intercritical austenite nucleated and grew on dissolving carbide particles and resulted in blocky retained austenite. However, Sn micro-alloying significantly effected the intercritical austenite chemical stability by segregating to the carbide/matrix interface and retarding C partitioning to the intercritical austenite. This resulted in lower volume fractions of low stability retained austenite which transformed to martensite (via the TRIP effect) at low strains, thereby quickly exhausting the TRIP effect and resulting in a failure to sustain high work hardening rates and delay the onset of necking. Consequently, the Sn micro-alloyed CR starting microstructure was unsuccessful in achieving 3G AHSS target mechanical properties regardless of the IA parameters employed. Contrastingly, the CR starting microstructure without Sn micro-alloying was able to meet target 3G mechanical properties via intercritical annealing at 675 °C × 60 s and 120 s, and at 690 °C × 60 s owing to sufficiently rapid carbide dissolution and C/Mn partitioning into the intercritical austenite such that it had sufficient mechanical and chemical stability to sustain a gradual deformation-induced transformation to martensite and maintain high work hardening rates. On the other hand, the martensitic (M) starting microstructure produced higher volume fractions of chemically and mechanically stable lamellar retained austenite regardless of Sn micro-alloying. Intercritical annealing at 650 °C × 60 s and 675 °C × 60 s and 120 s produced 3G AHSS target mechanical properties. It was shown that the stable lamellar retained austenite transformed gradually during deformation. Furthermore, deformation-induced nano-twin formation in the retained austenite was observed, suggesting the TWIP effect being operational alongside the TRIP effect. As a result, a continuous supply of obstacles to dislocation motion was maintained during deformation, which aided in sustaining a high work hardening rate and resulted in a high strength/ductility balance, meeting 3G AHSS target properties. Based on these results, the martensitic starting microstructure without Sn micro-alloying and the M-675 °C × 120 s IA condition were chosen for the selective oxidation and reactive wetting studies. The selective oxidation study determined the effect of a N2-5H2-xH2O (vol%) process atmosphere pO2 (–30, –10, and +5 °C dew point (Tdp)) on the composition, morphology, and spatial distribution of the external and internal oxides formed during the austenitizing and subsequent intercritical annealing cycles. The objective of this study was to identify the process atmosphere for the promising M-675 °C × 120 s heat treatment that would result in a pre-immersion surface that could be successfully galvanized in a conventional galvanizing (GI) bath. The austenitizing heat treatment (775 °C × 600 s) used to produce the martensitic starting microstructure resulted in thick (~ 200 nm) external oxides comprising MnO, MnAl2O4, MnSiO3/Mn2SiO4, and MnCr2O4, regardless of the process atmosphere pO2. However, intermediate flash pickling was successful in dissolving the external oxides to a thickness of approximately 30 nm along with exposing metallic Fe in areas which contained relatively thin external oxides. Furthermore, extruded Fe nodules that were trapped under the external oxides were revealed during the flash pickling process. Overall, flash pickling resulted in a surface consisting of dispersed external oxide particles with exposed metallic substrate and extruded Fe nodules. This external surface remained unchanged during IA owing to the multi-micron (~ 2–8 µm) solute-depleted layer that formed during the austenitizing heat treatment. Subsequent galvanizing in a 0.2 wt% (dissolved) Al GI bath with an immersion time of 4 s at 460 °C was successful in achieving high-quality, adherent galvanized coatings through multiple reactive wetting mechanisms. The dispersed nodule-type external oxides along with exposed substrate and extruded Fe nodules on the pre-immersion surface facilitated direct wetting of the steel substrate and promoted the formation of a robust and continuous Fe2Al5Znx interfacial layer at the steel/coating interface. Additionally, oxide lift-off, oxide wetting, bath metal ingress, and aluminothermic reduction were operational during galvanizing. The galvanized med-Mn steels met 3G AHSS target mechanical properties. Overall, this Ph.D. research showed that it is possible to employ a CGL-compatible thermal processing route for med-Mn steels to successfully produce 3G AHSS target mechanical properties as well as robust galvanized coatings. / Thesis / Doctor of Philosophy (PhD) / One of the largest challenges associated with incorporating the next generation of advanced high strength steels into the automotive industry lies in processing these steels in existing industrial production lines. In that regard, a two-stage heat treatment with an intermediate flash pickling stage and process atmosphere compatible with existing industrial continuous galvanizing line technology was developed for a prototype medium-Mn steel. The heat-treated prototype steel met the target mechanical properties outlined for the next generation of advanced high strength steels. Furthermore, the heat treatment and process atmosphere utilised in this research produced a surface that facilitated the successful galvanizing of the prototype medium-Mn steel. This adherent and high-quality galvanized coating will provide robust corrosion protection if the candidate medium-Mn steel is used in future automotive structural applications.

No description available.

QC 20100927

ABSTRACT VANADIUM AND MOLYBDENUM INCORPORATED MCM-41 CATALYSTS FOR SELECTIVE OXIDATION OF ETHANOL G&uuml / &ccedil / bilmez, YeSim Ph.D., Department of Chemical Engineering Supervisor : Prof. Dr. Timur Dogu Co-Supervisor: Prof. Dr. Suna Balci June 2005, 144 pages In this study, V-MCM-41, MCM-41 and Mo-MCM-41 catalysts were synthesized by the one-pot alkaline and acidic synthesis methods. The as-synthesized catalysts were found to have high BET surface areas (430-1450 m2/g), homogeneous pore size distributions (2-4 nm), good crystalline patterns and high metal loading levels (Metal/Si atomic ratio in the solid = 0.01-0.16) as determined by the characterization studies. MCM-41 and Mo-MCM-41 catalysts were highly active in the selective oxidation of ethanol with conversion levels of 56% and 71%, respectively, at 400oC for an O2/EtOH feed ratio of 0.5. Both catalysts had very high selectivities to acetaldehyde at temperatures below 300oC. Conversions exceeded 95% with the V-MCM-41 catalyst having a V/Si molar ratio (in the solid) of 0.04 in the temperature range of 300oC-375oC for the O2/EtOH feed ratios of 0.5-2.0. Acetaldehyde selectivities changed between 0.82-1.00 at the temperature range of 150oC-250oC. Ethylene, which is listed as a minor side product of the selective oxidation of ethanol in literature, was produced with a maximum yield of 0.66 at 400oC at the O2/EtOH feed ratio of 0.5. This yield is higher than the yields obtained in the industrial ethylene production methods such as thermal cracking and oxidative dehydrogenation of ethane. Besides, the feedstock used in this work is a non-petroleum chemical, namely ethanol, which can be produced from sugar and crop wastes by fermentation. Thus, the findings of this study are also proposed as an alternative ethylene production method from a non-petroleum reactant at lower temperatures with higher yields. &Ouml / Z ETANOL&Uuml / N SE&Ccedil / iCi OKSiDASYONUNDA KULLANILMAK &Uuml / ZERE VANADYUM VE MOLiBDEN i&Ccedil / EREN MCM-41 KATALiZ&Ouml / RLERiNiN &Uuml / RETiMi G&uuml / &ccedil / bilmez, YeSim Doktora, Kimya M&uuml / hendisligi B&ouml / l&uuml / m&uuml / Tez Y&ouml / neticisi : Prof. Dr. Timur Dogu Ortak Tez Y&ouml / neticisi: Prof. Dr. Suna Balci Haziran 2005, 144 sayfa Bu &ccedil / aliSma kapsaminda, dogrudan sentez metoduyla, alkali ve asit ortamlarinda, V-MCM-41, MCM-41 ve Mo-MCM-41 kataliz&ouml / rleri sentezlenmiStir. Bu Sekilde sentezlenen kataliz&ouml / rlerin y&uuml / ksek BET y&uuml / zey alanlarina (430-1450 m2/g), homojen g&ouml / zenek boyutu dagilimlarina (2-4 nm), iyi kristal yapilarina ve y&uuml / ksek metal y&uuml / kleme oranlarina (Metal/Si katidaki molar orani =0.01-0.16) sahip olduklari karakterizasyon &ccedil / aliSmalari sonucunda g&ouml / r&uuml / lm&uuml / St&uuml / r. MCM-41 ve Mo-MCM-41 kataliz&ouml / rleri etanol&uuml / n se&ccedil / ici oksidasyonunda, 400oC&amp / #8217 / de ve reakt&ouml / r giriSinde 0.5&amp / #8217 / lik O2/EtOH oraninda, sirasiyla, 56% ve 71% d&ouml / n&uuml / S&uuml / m seviyeleriyle, y&uuml / ksek aktivite g&ouml / stermiSlerdir. Her iki kataliz&ouml / r de 300oC&amp / #8217 / nin altinda &ccedil / ok y&uuml / ksek asetaldehit se&ccedil / iciligi g&ouml / stermiStir. D&ouml / n&uuml / S&uuml / m degerleri, V/Si katidaki molar orani 0.04 olan V-MCM-41 kataliz&ouml / r&uuml / i&ccedil / in / 300oC-375oC araliginda ve 0.5-0.2 O2/EtOH reakt&ouml / r giriSi oranlarinda, 95%&amp / #8217 / i ge&ccedil / miStir. Asetaldehit se&ccedil / icilikleri, 150oC-250oC araliginda, 0.82-1.00 arasinda degiSmiStir. Literat&uuml / rde, etil alkol&uuml / n se&ccedil / ici oksidasyonunda &ouml / nemsiz bir yan &uuml / r&uuml / n olarak s&ouml / z&uuml / ge&ccedil / en etilen, 400oC&amp / #8217 / de ve 0.5&amp / #8217 / lik O2/EtOH reakt&ouml / r giriS oraninda 0.66 maksimum verimle &uuml / retilmiStir. Bu verim degeri isil par&ccedil / alanma ve etanin kismi oksidasyonu gibi end&uuml / striyel etilen &uuml / retim yollariyla elde edilen verimlerden daha y&uuml / ksektir. Ayrica, bu &ccedil / aliSmada kullanilan etanol petrol-bazli olmayan bir hammaddedir ve Seker pancari atiklarindan fermentasyonla &uuml / retilebilmektedir. Bu sebeple, bu &ccedil / aliSmadaki bulgular, petrol-bazli olmayan bir hammaddeden, daha d&uuml / S&uuml / k sicaklikta, daha y&uuml / ksek verimle etilen elde etmek i&ccedil / in alternatif bir &uuml / retim metodu olarak da &ouml / nerilmiStir. Anahtar Kelimeler: Etilen, Etil alkol, Se&ccedil / ici Oksidasyon, MCM-41, V-MCM-41, Mo-MCM-41, Oksidatif Dihidrojenasyon, Kismi Oksidasyon