Hydration and hardening processes of Portland cements obtained from clinkers mineralized with fluoride and oxides

The hydration and hardening processes of Portland cements prepared from clinkers mineralized with sodium fluoride and/or oxides (SnO₂ or CuO) was studied. Type I cements (CEM I) were prepared by grinding with gypsum (5%) of clinkers obtained by the burning of an industrial raw mix with different mineralizers: sodium fluoride, oxides (CuO and SnO₂) or mixtures of sodium fluoride and oxide (NaF + CuO or NaF + SnO₂). The influence of foreign ions on the clinker morphology was assessed by scanning electronic microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The hydration processes of modified cements were examined by X-ray diffraction analysis (XRD) and thermal analysis techniques (TG and DTA). The main properties of the cements, i.e., flexural and compressive strengths, setting time, and soundness were also determined. A good correlation between the chemically bound water or portlandite content in pastes hydrated 2–28 days and compressive strength developed by mortars was observed. The influence of mineralizers on the kinetic of hydration processes and main properties of cements is different—0.5% NaF and 0.5% SnO₂ and their mixture increase the rate of cement hydration and hardening processes, opposite to 0.5% CuO that reduce the rate.     

Interactions between Keggin-Type Lacunary Polyoxometalates and Ag Nanoparticles: A Surface-Enhanced Raman Scattering Spectroscopic Investigation

Interactions between two Keggin-type lacunary polyoxometalates (POMs), PW₁₁O and SiW₁₁O, and pre-formed citrate-protected colloidal Ag nanoparticles (NPs) were studied by surface-enhanced Raman scattering (SERS) and UV-Vis spectroscopies. Clear SERS evidence of displacing the originally surface-bound citrate ions by the subsequently added POMs indicates a stronger metal–ligand interaction between the POMs and the Ag NPs. Accompanied red-shifts in the surface plasma peak position of the Ag NPs were also observed for both POMs. The simultaneous presence of a number of SERS vibrational bands which can be assigned to vibrational modes of the POM molecule suggests that its overall structure is intact upon adsorption. Based on the SERS observations, a bonding between the penta-dentate aperture of the POMs and the Ag NP surface was proposed.Dedicated to the retirement of Michael Pope.     

Characterization of Al/Al2O3/NiOx solar absorber obtained by spray pyrolysis

The aim of this paper is to obtain high efficient and inexpensive spectral selective solar absorbers, for solar thermal flat plat collectors using a simple technique – spray pyrolysis deposition (SPD). To achieve maximum solar absorptance and minimum thermal emittance, the following parameters are optimized: the precursor solution concentration and composition, substrate temperature and annealing treatment. The structural and morphological properties of the films were investigated by X-ray diffraction, atomic force microscopy and contact angle measurements. The thermal emittance and solar absorptance of as-deposited films were correlated with the chemical composition, crystalline structure and morphology. The results prove that coatings with excellent spectral selective properties (normal solar absorptance of 0.92 and a normal thermal emittance of 0.03) can be obtained by SPD.     

mer-[Fe III(bpca)(CN)3]-: a new low-spin iron(III) complex to build heterometallic ladder-like chains

The novel mononuclear complex PPh(4)-mer-[Fe(III)(bpca)(3)(CN)(3)].H(2)O (1) [PPh(4)(+) = tetraphenylphosphonium cation and bpca = bis(2-pyridylcarbonyl)amidate anion] and ladder-like chain compound [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)] [Fe(III)(bpca)(CN)(3)]].3H(2)O (2) have been prepared and characterized by X-ray diffraction analysis. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in mer arrangement and a tridentate N-donor ligand building a distorted octahedral environment around the iron atom. Compound 2 is an ionic salt made up of cationic ladder-like chains [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)]](+) and uncoordinated anions [Fe(III)(bpca)(3)(CN)(3)](-). The magnetic properties of 2 correspond to those of a ferrimagnetic chain with significant intrachain antiferromagnetic coupling between the low-spin iron(III) centers and the high-spin manganese(II) cations. This compound exhibits ferrimagnetic ordering below 2.0 K.     

Synthesis, crystal structures and magnetic properties of cyanide- and phenolate-bridged [M(III)NiII]2 tetranuclear complexes (M=Fe and Cr)

The binuclear complex NiII2L(H2O)2(ClO4)2(1) and the neutral tetranuclear bimetallic compounds [{M(III)(phen)(CN)4}2{NiII2L(H2O)2}].2CH3CN with M=Fe (2) and Cr (3)[H2L=11,23-dimethyl-3,7,15,19-tetraazatricyclo[19.3.1.1(9,13)]hexacosa-2,7,9,11,13(26),14,19,21(25),22,24-decaene-25,26-diol] have been synthesized and the structures of and determined by single crystal X-ray diffraction. and are isostructural compounds whose structure is made up of centrosymmetric binuclear cations [Ni2(L)(H2O)2]2+ and two peripheral [M(phen)(CN)4]- anions [M=Fe (2) and Cr (3)] acting as monodentate ligands towards the nickel atoms through one of their four cyanide nitrogen atoms. The environment of the metal atoms in 2 and 3 is six-coordinated: two phen-nitrogen and four cyanide-carbon atoms at the iron and chromium atoms and a water molecule, one cyanide-nitrogen and two phenolate-oxygens and two imine-nitrogens from the binucleating ligand L2- at the nickel atom build distorted octahedral surroundings. The values of the FeNi and CrNi separations through the single cyanide bridge are 5.058(1) and 5.174(2)A respectively, whereas the Ni-Ni distances across the double phenolate bridge are 3.098(2)(2) and 3.101(1) A (3). The magnetic properties of have been investigated in the temperature range 1.9-290 K. The magnetic behaviour of corresponds to that of an antiferromagnetically coupled nickel(II) dimer with J=-61.0(1) cm-1, the Hamiltonian being defined as H=-J S(A).S(B). An overall antiferromagnetic behaviour is observed for and with a low-lying singlet spin state. The values of the intramolecular magnetic couplings are J(Fe-Ni)=+17.4(1) cm-1 and J(Ni-Ni(a))=-44.4(1) cm-1 for and J(Cr-Ni)=+11.8(1) cm-1 and J(Ni-Ni(a))=-44.6(1) cm-1 for [H=-J(M-Ni)(S(M).S(Ni)+S(Ma).S(Nia))-J(Ni-Nia)S(Ni)S(Nia)]. Theoretical calculations using methods based on density functional theory (DFT) have been employed on in order to analyze the efficiency of the exchange pathways involved and also to substantiate the exchange coupling parameters.     

The first evidence for a transient stibaallene ArSbCCR2

Dechlorofluorination of ArSb(F)-C(Cl)CR₂ (CR₂ = fluorenylidene, Ar = 2,4,6-tri-tert-butylphenyl) by tert-butyllithium afforded a 3,4-bis(fluorenylidene)-1,2-distibacyclobutane. The formation of the latter probably involves the transient stibaallene ArSbCCR₂ followed by a head-to-head dimerization via two SbC double bonds. Molecular orbital calculations at the ab initio and DFT levels support the head-to-head dimerization of ArSbCCR₂ with the formation of a 1,2-distibacyclobutane.     

SERS assessment of the cancer-specific methylation pattern of genomic DNA: towards the detection of acute myeloid leukemia in patients undergoing hematopoietic stem cell transplantation

In this label-free surface-enhanced Raman scattering (SERS) study of genomic DNA, we demonstrate that the cancer-specific DNA methylation pattern translates into specific spectral differences. Thus, DNA extracted from an acute myeloid leukemia (AML) cell line presented a decreased intensity of the 1005 cm⁻¹ band of 5-methylcytosine compared to normal DNA, in line with the well-described hypomethylation of cancer DNA. The unique methylation pattern of cancer DNA also influences the DNA adsorption geometry, resulting in higher adenine SERS intensities for cancer DNA. The possibility of detecting cancer DNA based on its SERS spectrum was validated on peripheral blood genomic DNA samples from n = 17 AML patients and n = 17 control samples, yielding an overall classification of 82% based on the 1005 cm⁻¹ band of 5-methylcytosine. By demonstrating the potential of SERS in assessing the methylation status in the case of real-life DNA samples, the study paves the way for novel methods of diagnosing cancer.

Graphical abstract

     

A lower bound for the stability radius of time-varying systems

We introduce and characterize the stability radius of systems whose state evolution is described by linear skew-product semiflows. We obtain a lower bound for the stability radius in terms of the Perron operators associated to the linear skew-product semiflow. We generalize a result due to Hinrichsen and Pritchard.

     

LaCoO3 formation from precursors obtained by water-based sol–gel method with citric acid

In the present work the LaCoO₃ formation from gel precursors obtained by water-based sol–gel method with citric acid was studied. As precursors La and Co nitrates were used. The obtained gels were analyzed by TG/DTA and TG/AGE. The decomposition of the gels takes place in two main steps with the evolution of the same volatile compounds (H₂O, CO₂ si NO₂) leading to the conclusion that two types of bonding of the components in the gels occurred. The decomposition of the gels takes place up to 400 °C. The gels thermally treated at 600 °C lead to single pure perovskite rhombohedral phase of lanthanum cobalt oxide (LaCoO₃).