A Theoretical and Experimental Approach to E-pH Diagram for the Niobium-Water System

E-pH diagrams are usually built from thermodynamic databases available in the literature or from specific software. However, depending on the conditions and the chemical species defined for elaborating a diagram, it may present completely different immunity, passivation, and corrosion domains. In order to obtain a result closer to a real system, experimental E-pH diagrams can be built from polarization curves obtained in the evaluated conditions. This work discloses the construction of a diagram for the Nb-H<sub>2</sub>O system at 25°C from theoretical study and the specific selection of chemical species in the solutions through computer simulations. The polarization curves for the construction of the experimental diagram were gathered without the use of buffer solutions and under pH monitoring in the solution bulk throughout all assays. The methodology proposed was considered adequate since, from experimental data, a final result compatible with the classic diagram for the Nb-H<sub>2</sub>O system and the excellent corrosion resistance of niobium in aqueous media were achieved.

SUPREME THEORY OF EVERYTHING: Theoretical Formulation of The Spectral Density of Electromagnetic Radiation Emitted By A Nonblack Body

Hertzsprung-Russel Diagram (HRD) plots each star on a graph measuring the star’s brightness concerning its temperature (color) between 2000K and 50000 K. It registered about 90 percent of the stars in the universe, including the Sun, located in the main sequence branch of stars in HRD. HRD is an experimental diagram, and its theory could be supposed to be Planck's law. However, Planck's law itself is empirical and contradicts recorded astronomical experimental data. Modern astronomy can observe celestial bodies in space, with surface temperatures ranging from 0 Kelvin to millions of degrees. During this time either Planck's law or HRD didn't develop. In this paper, the spectral density of electromagnetic radiation of non-black bodies is described theoretically.

Theoretical and Experimental Researches Regarding the Performances of a New Type of Rotating Machine with Profiled Rotors

The paper establishes an original computation formula for the flow rate of the fluid transported by a new type of rotating machine with profiled rotors; the theoretical characteristic diagram of the machine - flow rate versus machine speed - is built. The scheme of the test stand used for performing measurements needed in order to build the experimental diagram is presented. The variation of the volumetric efficiency of the working machine in function of the machine speed is finally described.

Experimental and predicted crystal structures of Pigment Red 168 and other dihalogenated anthanthrones

The crystal structures of 4,10-dibromo-anthanthrone (Pigment Red 168; 4,10-dibromo-dibenzo[def,mno]chrysene-6,12-dione), 4,10-dichloro- and 4,10-diiodo-anthanthrone have been determined by single-crystal X-ray analyses. The dibromo and diiodo derivatives crystallize in P21/c, Z = 2, the dichloro derivative in P\bar 1, Z = 1. The molecular structures are almost identical and the unit-cell parameters show some similarities for all three compounds, but the crystal structures are neither isotypic to another nor to the unsubstituted anthanthrone, which crystallizes in P21/c, Z = 8. In order to explain why the four anthanthrone derivatives have four different crystal structures, lattice-energy minimizations were performed using anisotropic atom–atom model potentials as well as using the semi-classical density sums (SCDS-Pixel) approach. The calculations showed the crystal structures of the dichloro and the diiodo derivatives to be the most stable ones for the corresponding compound; whereas for dibromo-anthanthrone the calculations suggest that the dichloro and diiodo structure types should be more stable than the experimentally observed structure. An experimental search for new polymorphs of dibromo-anthanthrone was carried out, but the experiments were hampered by the remarkable insolubility of the compound. A metastable nanocrystalline second polymorph of the dibromo derivative does exist, but it is not isostructural to the dichloro or diiodo compound. In order to determine the crystal structure of this phase, crystal structure predictions were performed in various space groups, using anisotropic atom–atom potentials. For all low-energy structures, X-ray powder patterns were calculated and compared with the experimental diagram, which consisted of a few broad lines only. It turned out that the crystallinity of this phase was not sufficient to determine which of the calculated structures corresponds to the actual structure of this nanocrystalline polymorph.

Effect of Network Elasticity on Nematic Liquid Crystal/Cross-Linked Polymer Phase Diagram

ABSTRACTThe influence of elasticity on the phase behavior of a mixture of nematic liquid crystal (LC) and in-situ cross-linked polymer has been investigated. Unlike the phase diagram of the LC/pre-cured polymer, the experimental diagram of LC/cross-linked polymer phase supported by theoretical calculation showed no critical point. Instead, the binodal curve exhibits an upward asymptotic behavior as the LC volume fraction approaches unity due to domination arising from network elasticity, particularly at high LC volume fraction. An examination of the effect of cross-links segment length and network functionality on the phase diagram of LC/cross-linked polymer showed that the segment length between cross-links exerts a greater influence.

An AB Initio Calculation of the Pd-V FCC Superstructure Phase Diagram with Fourth Nearest Neighbor Cluster Interactions

ABSTRACTThe Monte Carlo technique was used to calculate the phase diagram of the fee superstructures in the Pd-V system using up to fourth nearest neighbor, concentration independent, pair and multiplet interactions. The interactions were computed by the method of Direct Configurational Averaging using a Linearized Muffin-Tin Orbital Hamiltonian cast into the tight binding form. The phase diagram was computed with a fast Monte Carlo simulation technique using environment sampling. The two fee ground states in experimental diagram are predicted to be stable. The computed transition temperatures are higher than those found experimentally.

Some aspects of the X-ray structural characterization of (Ga1−x Al x As)n1(GaAs)n2/GaAs(001) superlattices: erratum

In the paper by Kervarec, Baudet, Caulet, Auvrey, Emery & Regreny [J. Appl. Cryst. (1984). 17, 196–205], an error has been introduced. On page 202, right-hand column, the second paragraph should read: The uneven surfaces of the interfaces can be taken into account by assuming that the SL is made of a juxtaposition of perfect crystallites of the same composition x whose period varies between the extreme values of 2n 1 d 1 + 2n 2 d 2. In this hypothesis, the experimental diagram is the sum of the X-ray diagrams given by each crystallite; the value of n 1 + n 2 deduced from such a diagram is an average value in the sample zone analyzed, therefore most of the time not integer.

An interactive program for the interpretation and simulation of Laue patterns

An interactive Fortran IV program is described which allows the orientation matrix of a crystal to be determined and refined without ambiguity, from a transmission or reflection Laue photograph. The indexing method is that of Riquet & Bonnet [J. Appl. Cryst. (1979), 12, 39–41] applied to a small number of data (less than ten) and adapted for interactive use. The verification of calculated solutions or even the trial-and-error search for the right solution is made by means of the visual comparison between the experimental diagram and simulated patterns displayed on a graphic screen. In addition, the rotation angles for setting the crystal to any new orientation may be computed.