Common Perceptions about the Use of Fillers in Silicone Rubber Insulation Housing Composites

This paper discusses the lessons learned about fillers that are added to silicone rubber insulation housing composites, in order to improve the erosion resistance against the dry-band arcing are presented and common perceptions. Common practices that employ alumina tri-hydrate are reviewed, including the additional influential effect of the water of hydration in the suppression of the dry-band arcing. The effect of the water of hydration is shown to be dependent on various factors, such as the hydrated filler level and the type of the hydrated filler. More recent paradigms in which hydrated fillers have not been employed are also reviewed. Volume and shield actions of fillers are essential aspects that need to be understood in the design of silicone rubber insulation housing composites for new applications such as HVDC. In addition, the thermal degradation mechanisms of silicone rubber and the corresponding suppression effects of the added fillers are summarized.

Orthovanadate wakefieldite-(Ce) in symplectites replacing vanadium-bearing omphacite in the ultra-oxidized manganese deposit of Praborna (Aosta Valley, Western Italian Alps)

Because of their unique structure and properties, rare-earth (REE) orthovanadates have been extensively employed for decades in advanced ceramics, in particular in the laser industry in replacement of Nd:YAG. A Ca-bearing REE orthovanadate with the empirical formula (Ce0.279Ca0.271Y0.267Gd0.057Nd0.055Dy0.032Sm0.027La0.020Th0.027Sr0.002)(V0.9085+Cr0.0673+Fe0.0173+As0.0055+)O4⋅nH2O has been found in metacherts from Praborna (Italian Alps) as micrometer-sized euhedral crystals in clinopyroxene + plagioclase symplectites replacing eclogite-facies vanadium-bearing omphacite (Aegirine55–48Jadeite42–33Diopside10–8 with V2O3 ≤ 1.39 wt%). We applied the synchrotron radiation, single crystal, micro-diffraction technique, recently optimized at ID09A beamline (ESRF, France), to determine the crystal structure of this mineral. It is tetragonal and isostructural with zircon, with a = 7.2233(12) Å, c = 6.3949(18) Å, V = 333.66(13) Å3, Z = 4, space group I41/amd, and it has been therefore identified as Ca- and Y-bearing wakefieldite-(Ce) (ideally CeV5+O4). Cell parameters are in agreement with those of synthetic Ce0.7Ca0.3VO4. Raman spectra of the studied wakefieldite-(Ce) are comparable with natural and synthetic wakefieldite-(Ce) spectra and revealed the presence of OH groups and/or water of hydration, which is also suggested by the low totals in microprobe analyses. Mass balance indicates that wakefieldite-(Ce) is a by-product of the omphacite breakdown; omphacite and Mn-rich epidote, a minor reactant, provided vanadium and REE, respectively. Petrological observations and thermodynamic modeling suggest that the mineral, coexisting with hematite, Mn-rich epidote, and braunite, formed during retrogression to greenschistfacies conditions at ultra-oxidized conditions (DFMQ ≥ +16 log units), which are often observed in Mn-oxide ores. Wakefieldite is an effective scavenger of REE in oxidized geological environments at P-T conditions that range from sedimentary to medium-grade metamorphic settings, even where the REE bulk concentration is negligible. Its rarity reflects both the overall low abundance of vanadium and the need for ultra-oxidized conditions that are rarely achieved in metamorphic rocks, where REE phosphates (i.e., monazite, xenotime) are commonly found instead.

H-bonds and DNA

Hydrogen bonds or ‘H-bonds’ are polar, non-covalent bonds or interactions between a hydrogen atom (H) attached to a more electronegative atom, such as oxygen (O) or nitrogen (N), which partially pulls the electron cloud away from the H, leaving it electropositive—with another electronegative atom, such as O or N from a different molecule or from a different part of the same molecule. H-bond interactions play a huge role in the biochemistry of living processes, and in the structures and interactions of biological molecules, with each other and with different molecules including water. Nature's natural solvent, water, is itself a dynamic H-bonded polar structure, which strongly affects solubility and, as (dynamic) water of hydration, interactions between molecules. Compared with covalent and ionic bonds, H-bonds are individually much weaker (<20 kJ/mol), which make them ideal for molecular recognition phenomena. When many H-bonds come together they can form strong insoluble structures such as cellulose and the impermeable derivative of cellulose known as chitin, or helical structures with intra-chain stabilizing H-bonds such as the α-helix. Perhaps the most important H-bonded structure of them all is DNA.

Development of High-Compressive Heavyweight Concrete Based on Portland Cement and Supplementary Cementitious Materials

The manufacture of optimized heavyweight concrete takes into consideration the type of aggregates, composition of blended cement, water-to-cement ratio, additives etc. The density of concrete depends mainly on the specific gravity of the used aggregates. Generally, concretes with specific gravities higher that 2600 kg m-3 are called heavyweight concretes and aggregates with specific gravity higher than 3000 kg m-3 are considered as heavyweight aggregates according to EN [1,2]. Concrete is a low cost material and easy to produce in varied compositions when compared to other shielding materials based on ceramics [3]. It is composed of a well-proportioned mixture of light and heavy nuclei. It is therefore efficient both in absorbing gamma rays and in slowing down fast neutrons by elastic and inelastic scattering [2]. Light materials, especially hydrogenous materials which contained in the water of hydration of the set cement (concrete) attenuate fast neutrons as a consequence of the high cross-section of hydrogen [4].

Synthesis, Structural Chemistry, and Biological Studies on Various Divalent Copper Chelates of Novel Ligands Derived from Food Preservative, Dehydroacetic Acid, with Anilines

Various six coordinated copper(II) complexes of novel (E)-4-hydroxy-6-methyl-3-(1-(p-tolylimino) ethyl-2H-pyran-2-one (HL1) and (E)-3-(1-(4-chlorophenylimino) ethyl-4-hydroxy-6-methyl-2H-pyran-2-one (HL2) derived from 3-Acetyl-2-hydroxy-6-methyl-4H-pyran-4-one (dehydroacetic acid, DHA) and aniline derivatives (p-chloroaniline and p-toluidine) were fabricated. The coordination mode of Schiff base donor atoms with copper ions was well investigated by thermal and elemental analyses, FTIR, UV-vis, 1H, 13C-NMR spectral tools and measurements of magnetic susceptibility as well as molar conductance at ambient temperature. The novel neutral bidentate Schiff base ligands (HL1 and HL2) linked to Cu(II) cation via the azomethine-N and hydroxyl-O atoms and to acetate and nitrate anions in bidentate bridging mode to form polymeric octahedral complexes. The thermal study showed the stepwise removal of water of hydration and anions and decomposition of these chelates. The decomposition products were examined and the relative thermal stabilities of these chelates were evaluated. Different parameters of activation were derived from the thermal curves by Coats–Redfern methodology. The degradation steps of the metal complexes had positive free energy values indicating their non-spontaneous nature. The antifungal and antibacterial activities of all investigated compounds were also studied. The magnetic susceptibility measurements and conductance data were investigated and provided evidence for the non-electrolytic character of the complexes.

Preparation and characterization of iron(III) 99Mo-molybdate(VI) gels for the assessment of 99mTc elution performance

New iron(III)99Mo-molybdate(VI) gels (Fe99Mo) of high Mo content were prepared by the precipitation/filtration method.99Mo–MoO3dissolved in NaOH was added to aqueous solutions of Fe(NO3)3at Mo/Fe mole fractions ~2.21 and 1.99 with continuous stirring at ambient room temperature. Two different Fe99Mo were precipitated from the mixed solutions adjusted at pH 2 and 4.7. The amount of water of hydration increased with the increasing the gel settling time and pH of the mixed solution. The matrices were characterized by radiometric, XRD, SEM, XRF, FT-IR, TGA, and DTA measurements. Small chromatographic columns of 2.0 g Fe99Mo containing ≥800 mg Mo tagged with 740 MBq99Mo were eluted with 5 mL saline solution. Highly reproducible99mTc elution indices suitable for preparation of99Mo/99mTc generators were achieved from generator supported with 0.5 g Al2O3filter. Elution performance of99mTc radionuclide was highly dependent on the gel structural properties.

Two cadmium coordination polymers with bridging acetate and phenylenediamine ligands that exhibit two-dimensional layered structures

Poly[tetra-μ2-acetato-κ8O:O′-bis(μ2-benzene-1,2-diamine-κ2N:N′)dicadmium], [Cd2(CH3COO)4(C6H8N2)2]n, (I), and poly[[(μ2-acetato-κ2O:O′)(acetato-κ2O,O′)(μ2-benzene-1,3-diamine-κ2N:N′)cadmium] hemihydrate], {[Cd(CH3COO)2(C6H8N2)]·0.5H2O}n, (II), have two-dimensional polymeric structures in which monomeric units are joined by bridging acetate and benzenediamine ligands. Each of the CdIIions has an O4N2coordination environment. The coordination geometries of the symmetry-independent CdIIions are distorted octahedral and distorted trigonal antiprismatic in (I) and distorted antiprismatic in (II). Both compounds exhibit an intralayer hydrogen-bonding network. In addition, the water of hydration in (II) is involved in interlayer hydrogen bonding.