Durabilidad del hormigón, I. Resistencia química de los cementos
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Electrical properties of polyacetylene with various cis‐trans compositions
Abstract The electrical conductivity of crystalline polyacetylene films having various cis‐trans compositions was measured. The resistivity and the energy gap of a 92,5% trans polymer were 1,01·10 4 Ω·cm and 0,56 eV, respectively, whereas the values of a 20,0% trans polymer were 2,35·10 8 Ω·cm and 0,93 eV, respectivel…
Hydrothermal chemistry of seawater from 25 degrees to 350 degrees C
Progressive heating of seawater to 350 degrees C causes it to become increasingly acid and depleted in Ca, Mg, and SO4, because anhydrite and a previously undescribed magnesium oxysulfate are precipitated. Observed composition changes and calculation of activities of dissolved species reveal a progressive increase of…
Magnetic and structural characterization of dibromo- and dichlorobis(thiazole)copper(II)
The temperature dependence of the magnetic susceptibility and the electron paramagnetic resonance spectra of the thiazole complexes dichloro- and dibromobis(thiazole)copper(II) are reported, along with a complete three-dimensional X-ray structure analysis of the dichloro complex based on counter data. The dichloro com…
Zeolites and Clay Minerals As Sorbents and Molecular Sieves
To mineralogists and earth scientists the zeolites and clay minerals have been of great interest for a very long time. Chemists and engineers became interested primarily in the years following the Second War, and their attention has for the most part been concentrated upon the zeolits. So great has been the effort exp…
Luminescence studies in poly(ethylene terephthalate) films at 77 K. Investigation of emission centres in polymers
Abstract Optical luminescence of amorphous bright poly(ethylene terephthalate) (PET) films and the changes in luminescence due to certain morphological changes have been studies at 77 K to identify the luminescent centres in this polymer. The emission spectrum consists of both fluorescence and phosphorescence with dis…
Crosslinking of polypropylene in the presence of polyfunctional monomers
Abstract The crosslinking of atactic and isotactic polypropylene initiated by organic peroxides in presence of diallyl maleate or pentaerythrityl tetramethacrylate was studied. The influence of concentration of the components of the crosslinking system as well as the effect of temperature and reaction time was followe…
Electrochemical Determination of Surface Area of Metals
The fundamental principles of the electrochemical determination of the surface area of metals are discussed. Conditions of determination and methods of calculation are analysed for smooth and powdered metals of the platinum group, nickel, the copper subgroup, and carbonaceous materials. A list of 108 references is inc…
Quadrupolar relaxation parameters for a spin7/2system
Using pulsed nuclear magnetic resonance methods the central component magnetisation recovery curves have been measured for 59 Co in a single crystal of K 3 Co(CN) 6 at 295K. By using two different sets of initial conditions it has been possible to measure the parameters W 1 and W 2 which are related to the transition…
Migration of nitrogen in electron-irradiated type Ib diamond
The 1.945 eV optical centre is produced in type Ib diamond by radiation damage and annealing at approximately 800 degrees C. The author reports that H3 (2.463 eV) centres, characteristic of irradiated and annealed type Ia diamond, have been created by heating an irradiated type Ib diamond to temperatures where nitroge…
Material dispersion in lightguide glasses
Material dispersion measurements are reported on six characteristic lightguide glass compositions. The measurements were made on bulk specimens and cover the wavelength range from 0.8 to 1.5 μm. It is observed that in these silicate glasses the wavelength at which material dispersion is zero is in all cases greater th…
Fatigue Failure in Marine Propeller Blades
Fatigue failure in marine propeller blades of Ni-Al-bronze was investigated. Calculations of alternating stress imposed on the propeller blades were carried out by unsteady lifting surface theory and the results were applied to the analysis of fatigue failure of blades. Fatigue tests in seawater were carried out by us…
Statistical bounds for the effective thermal conductivity of microsphere and fibrous insulation
The present work consists of an analytical investigation of the effective thermal conductivity of microsphere and fi- brous insulation media. Because of the statistical nature of random packing patterns of microspheres and fibers, there ex- ists a range of effective thermal conductivities for any given solid fraction…
Carbon: A New View of Its High-Temperature Behavior
An increasing body of research indicates that carbon can exist in a number of polymorphic "carbyne" forms. It is proposed that these forms occur because of a shift to triple bonding in the carbon system as temperature increases above 2600 K. It is also proposed that graphite can dissociate into triple-bonded molecules…
Structural phase transitions in the perovskite-type layer compound NH3(CH2)3NH3MnCl4
The perovskite-type layer compound NH3(CH2)3NH3MnCl4 undergoes two discontinuous structural phase transitions at 336 and 305 K, respectively. Optical, dielectric, and 35Cl NQR measurements in all three phases as well as differential thermal analysis of the phase transitions are performed. The partially deuterated comp…
The influence of kinetic processes on the electrical conductivity of donor-doped BaTiO3 ceramics
Barium titanate doped with donors is a good n-type semiconductor, the conductivity of which, however, is considerably influenced by intrinsic defects always present in these materials. Therefore not only the equilibrium behaviour of these defects but also the defect formation and the defect diffusion play an important…
Refractive index of Irtran 2 as a function of wavelength and temperature
Data are presented for the refractive index of Irtran 2, a hot-pressed microcrystalline compact of ZnS, made by the Eastman Kodak Company, from 1 microm to 15 microm and from 93 K to 283 K. The values range from 2.35 at both high temperatures and short wavelengths to 2.12 at the opposite extremes. The average value of…
Electron transport via metalloporphyrins
The controlled potential electrolysis of Ni(II) meso-tetraphenylporphyrin (Ni(II)TPP) gives at room temperature the corresponding metalloporphyrin π-cation radical [Ni(II)TPP] + • . Upon freezing a solution of the π-cation radical to 77 K an internal electron transfer occurs to give [Ni(III)TPP] + . A discussion of th…
X-ray diffuse scattering from alkali, silver, and europiumβ-alumina
Crystals of varying compensation mechanism (extra oxygen bridges or ${\mathrm{Co}}^{2+}$ substitution) and phase ($\ensuremath{\beta}$ or ${\ensuremath{\beta}}^{\ensuremath{'}\ensuremath{'}}$) have been grown by adding cobalt oxide to a melt containing NaC${\mathrm{O}}_{3}$, ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and…