Structure and Inter-Diffusion Coefficients of Liquid Na<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys

Structure and atomic transport properties of liquid Na-K alloys are reported. Inter-diffusion coefficients of liquid Na _x K_1−x , alloys are calculated using scaling law proposed by Samanta et al. following Dzugutov which express the possible relationship between the excess entropy and diffusion coefficient. The interatomic interactions are described from the individual version of the electron-ion potential proposed by Fiolhais et al. The partial pair distribution functions and structure factors are calculated from the solution of Ornstein-Zernike integral equation with Rogers-Young closure. The evaluation with the composition of static structure and inter-diffusion properties are discussed.     

Magnetic properties of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles in carbon nanotubes

The interlayer coupling in an Fe/Cr/Fe layer system with wedge-type chromium spacers was investigated as a function of the chromium-layer thickness and temperature using Kerr magnetometry. The system with a moderate roughness demonstrates an interlayer coupling that can be well described in the framework of the biquadratic coupling model. The smoother sample shows interlayer coupling that can be described using both the biquadratic coupling and the proximity magnetism model proposed by Slonczewski.     

Electronic structures of Heusler alloy Co2FeAl1-xSix surface

We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) be-come close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.     

Structure and principal electrophysical properties of Ge<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>-Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

In the process of thermal treatment of deposited Ge_0.85Si_0.15 films, a number of peculiarities were found related to the character of their conductivity. The films of Ge_0.85Si_0.15 solid solutions are rather resistant to thermal quenching. It was shown experimentally that irradiation with electrons under an accelerating voltage enhances the crystallization in the films and lowers their electric conductivity.     

Formation of ferromagnetism in pseudobinary PrNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (2.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 5) solid solutions

The structure and magnetic properties of the PrNi_{5 − x} Cu _x alloys have been studied in a composition range of 2.5 ≤ x ≤ 5. Single-phase solid solutions with a hexagonal structure of the CaCu₅ type have been shown to be realized within this composition range. It has been found that upon the introduction of nickel into the Van Vleck paramagnet PrCu₅ the ground state of the alloys with x ≤ 4.3 becomes ferromagnetic. All the compositions under study exhibit high magnetocrystalline anisotropy of the “easy-basal-plane” type. With allowance for the literature data available, a complete magnetic phase diagram of the PrNi_{5 − x} Cu _x system was constructed; it is characterized by two maxima in the compositional dependence of the Curie temperature. The earlier suggested model of the effect of local random crystal fields on the magnetic state of Pr³⁺ ions in alloys with low copper contents was shown to be applicable also for the explanation of magnetic properties of alloys with low nickel contents. The results of this study confirm the hypothesis about the determining role of local irregular crystal fields in the formation of the magnetic properties of the pseudobinary PrNi_{5 − x} Cu _x intermetallic compounds.     

Experimental evaluation of quinolinium and isoquinolinium derivatives as corrosion inhibitors of mild steel in 0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution

The 1-methylquinolinium iodide (I) Qui⁺, I^– and 2-methylisoquinolinium iodide isoQui⁺, I^– were investigated as a corrosion inhibitors for mild steel in sulfuric acid using electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The results indicated that the corrosion inhibition efficiency and extent of surface coverage were increased with increase in inhibitors concentrations. Polarization curves revealed that both inhibitors acted as a mixed-type inhibitor. The thermodynamic parameters were evaluated for corrosion inhibition process. The adsorption of both inhibitors on mild steel surface obeyed Langmuir adsorption isotherm.     

Magnetic properties and structure of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi<Subscript>2</Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1.5)

Crystal structure, magnetization, coercive force, magnetic susceptibility, and anisotropic magnetostriction of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi₂Mn _x (0 ≤ x ≤ 1.5) have been studied. The samples with x ≤ 1 have an fcc structure, whereas TbNi₂Mn_1.25 has a rhombohedral structure of the PuNi₃ type. It has been found that the magnetic ordering temperature increases sharply when manganese is added. As the Mn concentration grows, the magnetization and the magnetostriction decrease monotonically, while the coercive force increases. The experimental data obtained have been interpreted on the assumption that a partial substitution of manganese for terbium in TbNi₂Mn _x leads to local distortions of the crystal field acting on Tb ions, to the appearance of a local uniaxial random anisotropy, and to the formation of a noncollinear magnetic structure in the terbium sublattice.     

Microstructures and corrosion properties of casting <Emphasis Type="Italic">in situ</Emphasis> Al<Subscript>3</Subscript>Ti-Al composites

The effects of Ti content and the alloying elements of Si and Cu on the microstructures of casting in situ Al_3Ti-Al composites were investigated. Simultaneously, their corrosion properties were also discussed. The results indicate that the aspect ratios of Al_3Ti platelets in different Al based composites are different although all of them are in flaky shape. The morphologies of Al_3Ti phase are not only determined by Ti content, but are also related to the alloying elements. The grain refining role of Al_3Ti phase in the pure Al and Al-Cu based composites is more effective than that in the Al-Si based composite. The addition of Ti decreases the corrosion resistance of pure Al and Al alloys. The corrosion resistances of the composites are dependent on both the corrosion characteristics of the corresponding matrixes and the distribution of Al_3Ti platelets.     

Magnetocaloric effect in Ni-Mn-<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = Ga,In, Sn,Sb) Heusler alloys

A review is given of experimental and theoretical works concerning the investigation of magnetic and structural phase transitions and of the magnetocaloric effect in Ni-Mn-X (X = Ga, In, Sn, Sb) Heusler alloys possessing unique properties, such as the existence of coupled magnetostructural and metamagneto-structural phase transitions, giant magnetocaloric effect, shape-memory effect in the ferromagnetic state, giant magnetodeformation and magnetoresistance, exchange anisotropy. A conclusion is made that the Heusler alloys, because of their unique properties, are promising for the application in various engineering devices, including technology of magnetic refrigeration.     

<Emphasis Type="Italic">J</Emphasis>-<Emphasis Type="Italic">Q</Emphasis> Characterization of Constraint Effects of a Three-Dimensional Cracked Specimen

Failure assessment of the integrity of a ductile flawed structural component is done currently by a one-parameter fracture mechanics approach. The J-integral is the one-parameter used; it has proven to be useful in order to predict ductile crack initiation. However, when tension loading dominates and/or a fully plastic condition develops around the crack, the J-integral alone does not describe completely the crack-tip stress field and a second parameter is needed. In this work, an accurate modeling of the elastic-plastic stress field around a deep crack in a three-dimensional three-point bend specimen is carried out. Numerical results for the crack-tip stress field are used to evaluate a crack-tip constraint parameter Q, in terms of applied loading, from contained plasticity to large-scale yielding. The parameter Q, measures the degree of stress triaxiality and constraint around the crack-tip. In order to obtain the stresses in the near-crack-tip field with high accuracy, a detailed mesh with higher order three-dimensional finite elements is located around the crack front. The modeling of crack-tip blunting deformation is performed by using a small notch radius in the crack-tip. Large-strain and finite-rotation nonlinear behavior effects around the crack-tip are included. The material, an ASTM A 516 steel, is modeled with incremental theory of plasticity. Numerical results of the Q triaxiality parameter are presented for increasing level loads to obtain an extended yield condition. Additional results of J-integral parameter and crack-tip opening displacement, for different load ratios and for different position across the specimen thickness are shown.     

Optical and magnetooptical properties of Heusler alloys <Emphasis Type="Italic">X</Emphasis>MnSb (<Emphasis Type="Italic">X</Emphasis> = Co,Pt)

The ellipsometry method (with photon energies ħω= 0.1–5.0 eV) has been used to study the optical properties of the CoMnSb phase with a structure of the L2₁ type. Infrared-absorption features indicating the existence of a pseudogap in the density of states at the Fermi level N(E _F) have been revealed. The transverse Kerr effect in CoMnSb and PtMnSb has been measured at photon energies ħω = 0.4–4.5 eV. It has been shown that the observed peaks of magnetooptical activity in CoMnSb are due to the off-diagonal component ɛ _ij of the tensor of the complex dielectric constant [^(e)]\hat \varepsilon. Spectral dependences of the magnetooptical effect δ _q quadratic in magnetization M have been studied for the first time for PtMnSb for the s and p polarizations of the light wave. In the region where a giant Kerr effect (ħω ∼ 1.7 eV) is observed in PtMnSb, a sharp increase in the δ _q effect has been revealed caused by the change in the diagonal component ɛ _ii of the tensor] of the dielectric constant in an external magnetic field. Based on the δ _q spectra for the p polarization of the light wave, additions have been calculated to the real and imaginary parts of the diagonal component of the [^(e)]\hat \varepsilon tensor in the magnetic field (Re(Δɛ _ij ) ^p and (Δɛ) _ij ) ^p , respectively). The spectrum of Im(Δε _ij ) ^p has been analyzed in terms of the existing concepts on the electron structure of PtMnSb.     

Effect of alcohol on the corrosion of al alloys in 1 N H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution Part I

The aim of this paper is to examine the effects of alcohol (1-buten-3-ol-l, 2-methyl-3-butyn-2-ol, 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 3-methyl-1-pentyn-3-ol, 5-hexen-1-ol) on the corrosion of Al alloys. The inhibiting effect of alcohol was investigated by electrochemical current-potential curves, atomic absorption spectrometry (AAS), metal microscopy,SEM and EDS. The results showed that alcohol (1-buten-3-ol, 2-methyl-3-butyn-2-ol, 3-methyl-2-buten-1-ol, 3-methyl-3-buten-1-ol, 3-methyl-1-pentyn-3-ol, 5-hexen-1-ol) had an inhibiting effect on the corrosion of aluminium alloys. Experimental results show that corrosion of alloys in H₂SO₄ solution have been effected by elements in alloys such as Cu, Zn, Mg and adsorption of alcohol on the surface of alloys in H₂SO₄ solution obeys Temkin adsorption isotherm. The use of alcohol in H₂SO₄ solution were shifted corrosion potentials (E_cor) to more negative values and acted as cathodic inhibitors on the aluminum alloys. EDS analysis of alloys displayed different intermetallic compounds on the surface of alloys, which might have changed the activity of alcohols depending on the surface morphology of alloys. This paper has showed that these alcohol inhibited corrosion of aluminium alloys in H₂SO₄ solution. The concentration of 20 mM alcohol was shown that above 90% inhibition was achieved, which is a rather high value.     

Effect of millimeter-range electromagnetic radiation on the biosynthesis of extracellular hydrolytic enzymes in <Emphasis Type="Italic">Aspergillus</Emphasis> and <Emphasis Type="Italic">Penicillium</Emphasis> micromycetes

The influence of the following parameters of millimeter-range electromagnetic radiation on the biosynthesis of extracellular hydrolases and the life cycle of Aspergillus niger 33 and Aspergillus niger 33–19 CNMN FD 02A fungi (producers of amylases) and Penicillium viride CNMN FD 04P fungus (a producer of pectinases) is studied: the wavelength (λ = 4.9, 5.6, and 7.1 mm), the irradiation mode (periodic and continuous), and the duration of exposure (10–60 min). It is established that the efficiency of the irradiation exposure depends on the physical parameters of the radiation and the properties and functional state of the strains. The optimal irradiation conditions allowing the biosynthesis and secretion of extracellular hydrolases to be enhanced by up to 44.4–49.4% as compared with the control groups are established for each particular strain. Moreover, in the case of Aspergillus niger 33–19 CNMN FD 02A micromycetes, the acceleration of the growth cycle by 48 h is observed.     

Calculating phase diagrams using <Emphasis Type="Italic">PANDAT</Emphasis> and panengine

Knowledge of phase equilibria or phase diagrams and thermodynamic properties is important in alloy design and materials-processing simulation. In principle, stable phase equilibrium is uniquely determined by the thermodynamic properties of the system, such as the Gibbs energy functions of the phases. PANDAT, a new computer software package for multicomponent phase-diagram calculation, was developed under the guidance of this principle. Author’s Note: Trial versions of PANDAT and PanEngine may be downloaded at www.computherm.com. Editor’s Note: A related article, “Our Experience in Teaching Thermodynamics at the University of Wisconsin, Madison,” by Y. Austin Chang and W.A. Oates, is available on-line only at www.tms.org/pubs/journals/JOM/0312/Chang/Chang-0312.html. For more information, contact S.-L. Chen, Compu-Therm LLC, 437 South Yellowstone Drive, Madison, Wisconsin 53719, USA; chen@chorus.net.     

MO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>–ZrO<Subscript>2</Subscript> coatings with M=Al,Mg, Zr,Ti, and Nb on valve metals

Coatings formed on aluminum, titanium, magnesium, zirconium, and niobium by means of plasma-electrolytic oxidation in an aqueous electrolyte containing MgZrF are studied. All elements involved in the composition of the complex compound are present in the coatings. Contents of the elements involved in the inner sphere are the largest. Phase and elementary compositions of the coatings depend on the nature of the valve metal. All coatings contain ZrO₂ in either cubic or monoclinic modifications. The main phase of the coatings formed on magnesium is MgF₂. According to the surface structure, the coatings can be divided into three groups: large-pore (on Mg, Al, and Ti), small-pore (on Nb), and compact with a wavy surface (on Zr).