Improvement of weld HAZ toughness at low heat input by controlling the distribution of M-A constituents

Abstract This research work focuses on how to improve the toughness of heat affected zones (HAZs) of low heat input welds in the case of high strength thermomechanically processed (TMCP) and recrystallization controlled rolled and accelerated cooled (RCR) plates with yield strengths of 355–500 MPa. Experimental work was aimed at the investigation of the intragranular nucleation of acicular ferrite or bainite in hot-rolled plates and the evaluation of the Charpy V and CTOD toughness of the most critical sub-zones of the weld HAZ using simulated specimens with a cooling time t8/5 = 5 s. The zones studied were the coarse grained HAZ (CGHAZ), the intercritically reheated coarse-grained HAZ (ICCGHAZ) and the intercritical HAZ (ICHAZ), the metallographical analyses consisted of microstructural investigations complemented with hardness measurements. Optical, scanning and transmission electron microscopy techniques were employed together with image and electron backscatter diffraction (EBSD) analysis. The test results showed that the toughness of the various sub-zones of the HAZ is improved by promoting intragranularly nucleated ferritic-bainitic (acicular) microstructure in both the CGHAZ and in the base plate. In this way, the sub-zones subjected to intercritical thermal cycles (the ICCGHAZ and the ICHAZ) develop evenly distributed M-A constituents between ferrite and bainite laths. These favourable microstructures can be achieved by using titanium killing or by avoiding niobium microalloying by using copper plus nickel alloying instead. In the laboratory experiments titanium killed steel, containing titanium-manganese oxide/manganese sulphide inclusions with a number density of 300–750 particles/mm2, develops a largely acicular ferritic microstructure in the base plate provided the austenite grain size is greater than about 120 μm and the cooling rate is in the range 6–11 °C/s down to 500 °C. Under plate mill conditions, no significant amount of acicular ferrite could be obtained, because it was not possible to achieve austenite grain sizes larger than about 70 μm after rolling. However, a significant fraction of acicular ferritic-bainitic microstructure was achieved in the CGHAZ, when the austenite grain size exceeded 90 μm. When achieved, a uniform distribution of M-A particles in an acicular ferritic-bainitic microstructure improves toughness. Cracks nucleate at numerous sites on M-A/ferrite boundaries or bainite packet interfaces, but they are initially arrested in the acicular matrix. Crack growth finally occurs by linking of the numerous arrested microcracks

Fundamental chemistry of binary S,N and ternary S,N,O anions:analogues of sulfur oxides and N,O anions

Abstract Binary S,N anions, e.g., NSN2− and SSNSS−, and related ternary S,N,O anions such as the structural isomers NSO−/SNO− and SSNO− are rarely mentioned in inorganic chemistry textbooks, despite the fact that their salts were synthesised and structurally characterised more than 30 years ago. These fundamentally important species and their conjugate acids, e.g. HNSO and HSNO, have been the focus of numerous investigations in recent years in view of their significance in disciplines as diverse as atmospheric chemistry and cell biology. This Tutorial Review provides a consolidated account of the fundamental chemistry including synthesis, spectroscopic characterisation, molecular and electronic structures, and properties of these intriguing species, and compares these aspects of their behaviour with those of isoelectronic sulfur oxides and N,O anions. A final section draws attention to the significance and applications of these simple S–N species in a broader context

Insights into the formation of inorganic heterocycles via cyclocondensation of primary amines with group 15 and 16 halides

Abstract Cyclocondensation is a major preparative route for the generation of inorganic heterocycles especially in the case of ring systems involving a Group 15 or 16 element linked to nitrogen. This Perspective will consider recent experimental and computational studies involving the reactions of primary amines (or their synthetic equivalents) with pnictogen and chalcogen halides. The major focus will be a discussion of the identity and role of acyclic intermediates in the reaction pathways to ring formation, as well as the nature of the heterocycles so formed. The similarities and differences between the chemistry of group 15 and 16 systems are emphasised with a view to providing signposts for further investigations

Neutral binary chalcogen–nitrogen and ternary S,N,P molecules:new structures, bonding insights and potential applications

Abstract Early theoretical and experimental investigations of inorganic sulfur–nitrogen compounds were dominated by (a) assessments of the purported aromatic character of cyclic, binary S,N molecules and ions, (b) the unpredictable reactions of the fascinating cage compound S₄N₄, and (c) the unique structure and properties of the conducting polymer (SN)ₓ. In the last few years, in addition to unexpected developments in the chemistry of well-known sulfur nitrides, the emphasis of these studies has changed to include nitrogen-rich species formed under high pressures, as well as the selenium analogues of well-known S,N compounds. Novel applications have been established or predicted for many binary S/Se,N molecules, including their use for fingerprint detection, in optoelectronic devices, as high energy-density compounds or as hydrogen-storage materials. The purpose of this perspective is to evaluate critically these new aspects of the chemistry of neutral, binary chalcogen–nitrogen molecules and to suggest experimental approaches to the synthesis of target compounds. Recently identified ternary S,N,P compounds will also be considered in light of their isoelectronic relationship with binary S,N cations

Selenium– and tellurium–nitrogen reagents

Abstract The reactivity of the chalcogen-nitrogen bond toward main-group element or transition-metal halides, as well as electrophilic and nucleophilic reagents, is the source of a variety of applications of Se–N and Te–N compounds in both inorganic or organic chemistry. The thermal lability of Se–N compounds also engenders useful transformations including the formation of radicals via homolytic Se-Nbondcleavage. These aspects of Se-N and Te-N chemistry will be illustrated with examples from the reactions of the binary selenium nitride Se₄N₄, selenium-nitrogen halides [N(SeCln)2]+ (n = 1, 2), the synthons E(NSO)2 (E = Se, Te), chalcogen-nitrogen-silicon reagents, chalcogen(IV) diimides RN=E=NR, the triimidotellurite dianion [Te(NtBu)₃]2−, chalcogen( II) amides and diamides E(NR₂)₂ (E = Se, Te; R = alkyl, SiMe₃), and heterocyclic systems.This article has previously been published in the journal Physical Sciences Reviews, Volume 4, Issue 5, 20170125, ISSN (Online) 2365-659X, DOI: https://doi.org/10.1515/psr-2017‐0125

Selenium– and tellurium–halogen reagents

Abstract Selenium and tellurium form binary halides in which the chalcogen can be in formal oxidation states (IV), (II) or (I). They are versatile reagents for the preparation of a wide range of inorganic and organic selenium and tellurium compounds taking advantage of the reactivity of the chalcogen-halogen bond. With the exception of the tetrafluorides, the tetrahalides are either commercially available or readily prepared. On the other hand, the low-valent species, EX₂ (E = Se, Te; X = Cl, Br) and E₂X₂ (E = Se, Te; X = Cl, Br) are unstable with respect to disproportionation and must be used as in situ reagents. Organoselenium and tellurium halides are well-known in oxidation states (IV) and (II), as exemplified by REX₃, R₂EX₂ and REX (R = alkyl, aryl; E = Se, Te; X = F, Cl, Br, I); mixed-valent (IV/II) compounds of the type RTeX2TeR are also known. This chapter surveys the availability and/or preparative methods for these widely used reagents followed by examples of their applications in synthetic inorganic and organic selenium and tellurium chemistry. For both the binary halides and their organic derivatives, the discussion is subdivided according to the formal oxidation state of the chalcogen.This article has previously been published in the journal Physical Sciences Reviews, Volume 3, Issue 12, 20180060, ISSN (Online) 2365‐659X, DOI: https://doi.org/10.1515/psr-2018‐0060

Introduction of selenium and tellurium into reaction systems

Abstract There are several commercial selenium and tellurium compounds that are useful in synthetic chemistry. The introduction of selenium and tellurium into both organic and inorganic compounds frequently begins with the elements. This chapter provides an overview of the main reactivity of the hexagonal allotropes of selenium and tellurium, which are the most stable form of the elements under ambient conditions. While the two elements have very similar chemical properties, there are also notable differences. Upon reduction, both elements form mono- and poly-chalcogenides, which are useful nucleophilic reagents in several reactions. The elements also react with many main group compounds as well as with transition metal complexes. They also form homopolyatomic cations upon oxidation. Both selenium and tellurium react with Grignard reagents and organyllithium compounds affording organylchalcogenolates, which upon oxidation form dichalcogenides that are themselves useful reagents in organic synthetic chemistry as well as in materials applications. This chapter provides a short introduction to the various topics that will be developed further in the subsequent chapters of this book.This article has previously been published in the journal Physical Sciences Reviews, Volume 4, Issue 4, 20180059, ISSN (Online) 2365-659X, DOI: https://doi.org/10.1515/psr-2018-0059

Experimental and Computational Investigations of Platinum Complexes of Selenium Diimide and Some Novel Selenium-Nitrogen Ligands

The reaction of selenium diimide Se[N(t-Bu)]2 and PtCl2 afforded an N,N’-chelated complex [PtCl2{N,N’-Se[N(t-Bu)]2}] (1) in good yield and [PtCl2{N,N’-SeO[NH(t-Bu)]2}] (2) as a minor product. Attempts to prepare 2 by direct reaction of SeOCl2 with Li[NH(t-Bu)] in toluene followed by addition of PtCl2 produced cyclic Se4[N(t-Bu)]4 in solution (77Se NMR spectrum) and a small amount of the complex [PtCl3{Se,Se’,Se”-Se4[N(t-Bu)]4}][Pt2Cl5{Se,Se’,Se”-Se3[N(t-Bu)]2}]∙3MeCN (3∙3MeCN), which contains tridentate Se4[N(t-Bu)]4 in the cation and the novel, acyclic bridging ligand [SeN(t-Bu)SeN(t-Bu)Se]2- in the anion. The reaction of Se[N(t-Bu)]2 with [PtCl2(NCPh)2] in THF produced the dinuclear complex [Pt2Cl6{SeN(t-Bu)C(Ph)NH}2]∙2C4H8O (4∙2THF) as the major product and only a few crystals of 1. The possible formation of SeO[NH(t-Bu)]2 or 2 by the reaction of Se[N(t-Bu)]2 or 1, respectively, with adventitious water and the pathway for the production of 4 were investigated through revPBE GGA/def2-TZVP calculations. The X-ray structures of 1, 2, 3∙3MeCN, and 4∙2THF have been determined.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Computational investigations of 18-electron triatomic sulfur–nitrogen anions

Abstract MRCI-SD/def2-QZVP and PBE0/def2-QZVP calculations have been employed for the analysis of geometries, stabilities, and bonding of isomers of the 18-electron anions N₂S²⁻, NS₂⁻, and NSO⁻. Isomers of the isoelectronic neutral molecules SO₂, S₂O, S₃, and O₃ are included for comparison. The sulfur-centered acyclic NSN2⁻, NSS⁻, and NSO⁻ anions are the most stable isomers of their respective molecular compositions. However, the nitrogen-centered isomers SNS⁻ and SNO⁻ lie close enough in energy to their more stable counterparts to allow their occurrence. The experimental structural information, where available, is in good agreement with the optimized bond parameters. The bonding in all investigated species is qualitatively similar, though electron density analyses reveal important quantitative differences that arise from bond polarization. Most of the investigated systems can be described with a single configuration wave function, the two notable exceptions being isomers SSS and OOO that show some diradical character. The computed MRCI-SD/def2-QZVP absorption maxima for SNS⁻ and NSS⁻ are 342 and 327 nm, respectively. The corresponding PBE0/def2-QZVP values in acetonitrile are 353 and 333 nm. These data support the proposed initial formation of SNS⁻ from electrochemical or chemical reduction of SSNS⁻ based on experimental UV–vis spectra. The interconversion of SNS⁻ and NSS⁻ is calculated to be facile and reversible, leading to an equilibrium mixture that also includes the remarkably stable dianion SNSNSS²⁻. Thus, salts of either SNS⁻ or NSS⁻ with bulky organic cations represent feasible synthetic targets