Efficient solid-state microwave-promoted complexation of a mixed dioxa-diaza macrocycle with an alkali salt. Synthesis of a sodium ethyl 4-benzeneazophosphonate complex

The first example of microwave-promoted solid-state synthesis of an alkali complex derived from a heteromacrocyclic compound has been described. The 15-membered mixed dioxa-diaza macrocycle 5,6,14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene (L) by reaction with sodium ethyl [4-α-(benzeneazoanilino)-N-benzyl]phosphonate (NaEP · 1.5H₂O) yielded the sodium complex [Na(L)(μ-EP) · H₂O]₂, as a diphosphonate-bridged dinuclear species. The new complex was identified and characterized on the basis of elemental and thermal (TG and DTA) analyses as well as by IR, ¹H and ¹³C nuclear magnetic resonance, and ESI and LDI mass spectroscopic studies. The results obtained by the reaction carried out under focused microwave conditions are compared with those obtained by conventional thermal reactions, both in the solid-state and in solution.     

Retention of differential and integral calculus: a case study of a university student in physical chemistry

This paper reports a study on retention of differential and integral calculus concepts of a second-year student of physical chemistry at a Danish university. The focus was on what knowledge the student retained 14 months after the course and on what effect beliefs about mathematics had on the retention. We argue that if a student can quickly reconstruct the knowledge, given a few hints, this is just as good as retention. The study was conducted using a mixed method approach investigating students’ knowledge in three worlds of mathematics. The results showed that the student had a very low retention of concepts, even after hints. However, after completing the calculus course, the student had successfully used calculus in a physical chemistry study programme. Hence, using calculus in new contexts does not in itself strengthen the original calculus learnt; they appeared as disjoint bodies of knowledge.     

Phase relations of hexagonal ferrimagnetic oxides I. The material subsystem BaFe2O4-Fe2O3-ZnFe2O4 at 1200°C

Reaction products of BaO, Fe₂O₃ and ZnO were obtained after prolonged firings at 1200°C, by the air quenching technique. The region of Fe₂O₃ solid solution in zinc spinel and the U phase solubility in the Z phase determine three pseudoternary regions of phase equilibria. The occurence of the M, X, W and Y phases delimitates nine additional three-phase regions. On the basis of the results obtained by X-ray diffractometry and optical microscopy, the 1200°C isothermal section for the subsystem BaO · Fe₂O₃-Fe₂O₃-ZnO · Fe₂O₃ was constructed.     

N–H···O=P hydrogen-bonded dimers as the main structural motif of aminophosphonate diesters

Abstract  

Crystal and molecular structures of three aminophosphonate diesters, diethyl and dibutyl [α-(quinolin-3-ylamino)-N-benzyl]phosphonates (1 and 2) and dibutyl [α-anilino-(quinolin-3-yl)methyl]phosphonate (3) were reported and comparatively discussed. Characteristic structural features for these compounds are strong N–H···O=P hydrogen bonds that connect two organophosphorus molecules in cyclic centrosymmetric dimer. Phosphoryl oxygen forms additional interaction with a C–H donor from the nearby aromatic group. Dimer formation in solution was also confirmed using electrospray ionization mass spectrometry. Mass spectra of six structurally similar aminophosphonate derivatives, 1–3 along with diethyl [α-anilino-(quinolin-3-yl)methyl]phosphonate (4), diethyl and dibutyl [α-anilino-(quinolin-2-yl)methyl]phosphonates (5 and 6) were studied and dimolecular ions [2M + Na]⁺ and [2M + H]⁺ were observed.     

Phase relations of hexagonal ferrimagnetic oxides II. The material subsystem Sr7Fe10O22-Fe2O3-ZnFe2O4 at 1100°C

Phase relations at 1100°C of reaction products of SrO, Fe₂O₃ and ZnO were determined by the air-quenching technique. Five ternary fields of phase equilibrium are delimited by the occurrence of M, X, W phases and a pseudobinary one by the low solubility of Fe₂O₃ in zinc spinel. The U, Z and Y compounds, which were present in the BaO-Fe₂O₃-ZnO system, were not obtained. On the basis of the results obtained by X-ray diffractometry and optical microscopy, the 1100°C isotherm of the subsystem 7 SrO · 5 Fe₂O₃-Fe₂O₃-ZnO · Fe₂O₃ was constructed.     

SEM/EDS investigation of one-step flame sprayed and fused Ni-based self-fluxing alloy coatings on steel substrates

Abstract

This study presents the results of light optical and scanning electron microscopy as well as energy dispersive spectroscopy investigation of the Ni-based self-fluxing alloys (NiCrBSi, NiCrWBSi and NiCrBSi + WC) deposited on steel substrates (heat treated carbon steel C45, heat treated low-alloyed steel 42CrMo4 and austenitic stainless steel X6CrNiMo18-10-2) by one-step flame spraying and fusing process. The microstructure of coatings and coating/substrate interface but also the effects of deposition technology on the heat-treated steel substrates which have frequently been used in practice were investigated. The influence of the sample size on the microstructure was also discussed. A proof is given of the change in the structure of coating, coating/substrate interface and substrate due to high fusing temperature, depending on type of steel substrate (and relating thermal properties), coating thickness but also on dimensions of the sample.     

Analysis of Waxes on Historical Samples by Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Analysis of the composition of binders applied to different historical objects is an important analytical task. On the basis of the...     

Magnetic characterization of Ca substituted Ba and Sr hexaferrites

A magnetic characterization has been worked out for the solid solution from Ba and Sr hexaferrites (BaFe_{1 2}O_{1 9}, SrFe_{1 2}O_{1 9}) towards CaO-xFe₂O₃ (2 ? x ?5.5). Measurements of Curie temperature, saturation magnetization, magnetic anisotropy, together with Mössbauer characterization indicate that the intrinsic properties of the studied compounds do not change appreciably with increasing Ca content. These results, together with the X-ray data, are consistent with the formation of an undistorted M-type cell with a low content of iron and oxygen vacancies.     

Electrochemical reduction of p-nitrosodiphenylamine in, a cationic micellar system

The electroreduction of p-nitrosodiphenylamine (p-NDPA) in an alkaline aqueous solution containing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was investigated by polarography, cyclic and rotating disc voltammetry. It was found that the reduction of p-NDPA in cationic micellar systems takes place by the ECE mechanism, and, compared to the reduction of the same compound in a homogeneous water solution, has a somewhat lower rate of the overall electrode reaction. The lower reaction rate of p-NDPA reduction in micellar medium is probably due to three main factors: solubilization of p-NDPA in CTAB micelles, adsorption of monomeric surfactant species at the electrode surface and a lower rate of the base catalyzed dehydration reaction (C-step) in the micellar system.