Formation, mechanical properties and corrosion resistance of Ti-Pd base glassy alloys

No biocompatible Ti-based glassy alloys without a harmful element have been reported. We have examined the mechanical and chemical properties of Ti-Pd-Zr-Si glassy alloy in comparison with pure Ti metal and Ti-6Al-4V alloy which have been used so far for biomaterials. The present Ti-Pd base glassy alloys do not contain Al and Ni elements which are considered to be rather toxic. Melt-spun Ti₄₅Zr_50−xPd_xSi₅ glassy alloy ribbons (x = 35, 40, 45) exhibited good bend ductility and had higher Vickers’s hardness and lower Young’s modulus as compared to pure titanium and Ti-6Al-4V alloy. In addition, the Ti₄₅Zr_50−xPd_xSi₅ glassy alloys had higher corrosion resistance and were passivated over a wide range and at the lower passive current density of approximately 10⁻² Am⁻² than at of pure titanium and Ti-6Al-4V alloy in 1 mass% lactic acid and PBS(−) solutions at 310 K.     

FT-IR,ESI and EPR studies of a Dy(III) Schiff base podand complex

IR spectroscopic, electrospray ionization mass spectrometry, structure and magnetic properties of a dysprosium(III) macroacyclic tripodal Schiff base tris((2-(5-chlorosalicylideno)amino)ethyl)amine (tren-5Clsal) complex are reported. The positions of ν(CN) stretching bonds indicate that the azomethine group nitrogen is coordinated to the rare earth ion. Two main spectral components are observed in the low magnetic field region (<300 mT) in the EPR spectra, independently of temperature. These components are attributed to the Dy³⁺ ion with an effective spin of S = 1/2. The magnetic anisotropy between 3 and 23 K is practically constant as evidenced only by a marginal change of the spread of g-factors. The g_y-factor increases strongly with an increase in temperature above 23 K, giving rise to a very high magnetic anisotropy of the complex. Such behavior of the magnetic anisotropy at a higher temperature could be an effect of the existence of an excited doublet. A very small value of the Curie–Weiss constant and the lack of any meaningful thermal changes of linewidths indicates the absence of any significant interactions between Dy(III) complexes below 20 K. The temperature dependence of the total integrated intensity above 20 K indicates the existence of an excited doublet, occurring about 33(1) K above the ground state.     

Electrophysical properties of double‐layer nickel‐base and vanadium‐base films within the intermediate temperature range

Phase composition of the double‐layer Ni‐base and V‐base films obtained and annealed in vacuum of 10^‐4–10^‐5 Pa within the temperature range of 700–900 K is studied by technique of electronography and transmission electron microscopy. Temperature dependence of resistance and temperature coefficient of resistance (TCR) was investigated. Comparison of TCR experimental data with the calculated data was made at T = 300 K on basis of semiclassical and macroscopic models and formula for TCR of alloys. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectral and magnetic properties of macroacyclic and macrobicyclic Schiff base RE complexes

IR spectroscopic, electrospray ionization mass spectrometry, TG-DTA, structure and magnetic properties of the gadolinium(III), samarium(III) and dysprosium(III) macroacyclic tripodal Schiff base, C₂₇H₂₇N₄O₃C_l3Gd(Dy, Sm) as well as gadolinium(III) and erbium(III) cryptate C₃₉H₄₇MN₉O₆ (MGd, Er) complexes are reported. The positions of ν(CN) stretching bonds indicate that the azomethine group nitrogen is coordinated to the rare earth ion. The [1:1] ligand to metal proportion in all macrocyclic and mocrobicyclic Schiff base complex samples has been confirmed by both electron ionization and electron spray molecular spectroscopy spectra. A TG-DTA analysis has indicated the presence of two water molecules in the inner-sphere of the macrobicyclic complex and confirmed that there is no water coordination of the metal ion in the macroacyclic complex. The near neighborhood of cation ions in the complexes of both types and their structure have been proposed on the basis of the above data. The temperature dependence of the EPR spectra integrated intensity has made it possible to reveal magnetic interactions in the spin system of these compounds.     

Study of polymerization processes in acid and base catalyzed silica sol-gels

Raman spectroscopy has been employed in conjunction with ²⁹Si NMR and the molybdenum chemical technique to study the polymerization process of silica sol-gels under pH conditions ranging from 1 to 9. A qualitative correlation between the rate of hydrolysis and the size of the resulting polymeric particles has been tentatively proposed. The extent to which the relative Raman intensity simultaneously proves information regarding particle dimensions, shape and degree of condensation has been discussed. A quantitative comparison between the monomer concentration as determined by the molybdenum chemical technique and by ²⁹Si NMR has been provided.     

Crystal structures and mesomorphic properties of Schiff base homologs and derivatives,and magnetic properties of their dimeric and dinuclear copper(II) complexes

Three N₂O₄ Schiff. base homologs, H₂L1 (n = 8), H₂L3 ((n = 9), and H₂L4 (n = 10) were obtained from the reactions of 2-HOC₆H₄CHO with H₂N(CH₂)_8-10NH₂, while a derivative of H₂L1, namely, H₂L2, was obtained from the reaction of 3,5-X₂-2-HOC₆H₂CHO (X = tert-butyl) with H₂N(CH₂)₈NH₂. The Schiff bases H₂L2 (triclinic; P-1), H₂L3 (monoclinic; C2/c), and H₂L4 (monoclinic; P21/c) were single crystals with low melting temperatures (less than 100°C). The homologs exhibited mesomorphisms, while the derivative was not mesomorphic and did not reform crystals from its melt. Copper(II) complexes of H₂L1, H₂L2 and H₂L4 were dimeric, while that of H₂L3 was dinuclear with chelating CH₃COO ligand. These complexes were paramagnetic with insignificant interactions between the copper(II) atoms and have high decomposition temperatures (T_dec = 268–304°C). Their melting temperatures (T_melt = 138.9–190.2°C) were higher than the corresponding Schiff bases, but they were not mesomorphic.     

Growth of carbon-doped base GaAs/AlGaAs HBT by gas-source MBE using TEG, TEA, TMG, AsH3, and Si2H6

High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI₂H₆ (n = 9 × 10¹⁷ cm^-3), and the base layer (92.5 nm) was doped with carbon from TMG (p = 4 × 10¹⁹ cm^-3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 10⁴ A/cm². The device characteristics of our carbon-doped HBTs were found to be stable under current stress.     

Two routes of forming nanorods on the base of nanoparticles

With ZnS nanoparticles as raw materials, two kinds of nanorods were fabricated. When ZnS nanoparticles were dispersed in Zn(NO₃)₂ solution and were treated in a sealed autoclave at 150 °C for 24 h, ZnO nanorods formed. ZnS nanoparticles work as a source of monomers for the growth of ZnO nanorods. With increase of concentration of Zn(NO₃)₂ solution, the products present long nanorods, short nanorods, star structure and bulk particle sequentially. When ZnS nanoparticles were kept in a solution at room temperature, ZnS nanorods formed after 21 days. ZnS nanoparticles work as assembly parts. They fit together spontaneously and present ZnS nanorods with many parallel stripes along the lengthways surface. To check the generality of self-assembling, PdS and Y₂S₃ nanorods were also fabricated.     

Study of the effect of the base,the silica and the niobium sources on the [Nb]-MCM-41 synthesized at room temperature

[Nb]-MCM-41 was synthesized at room temperature by varying the base (tetramethylammonium hydroxide or ammonium hydroxide), the silica source (tetraethyl orthosilicate or tetramethyl orthosilicate), the niobium source (ammonium niobium oxalate, NH₄[NbO(C₂O₄)₂(H₂O)₂] · 3H₂O, or potassium niobate, K₈Nb₆O₁₉) and the order of addition of the niobium source (before or after the silica source). These variations were determinant in the amount of niobium incorporated into the framework and in the structural order of the [Nb]-MCM-41 obtained. Only one method led to the formation of [Nb]-MCM-41 with the desired characteristics and active in the epoxidation of cis-cyclooctene with tert-butyl hydroperoxide leading to 19% conversion and 95% selectivity for cyclooctene oxide after 10 h.     

Synthesis and crystal structure of cobalt(III) complex with a Schiff base and azide

The cobalt(III) complex, [Co(L)₂(N₃)₂]₂(ClO₄)₂, L being a Schiff base N-[phenyl(pyridin-2-yl)methylene]aniline has been synthesized and the crystal structure determined using X-ray crystallography. The complex crystallizes in triclinic system, space group P-1 with unit cell parameters a=10.9367(9) ?, b=18.0817(17) ?, c=20.1629(16) ?, α=111.341(2)°, β=91.622(2)°, γ=107.5030(10)°, V=3499.1(5) ?³ and Z=2. It crystallizes with two independent molecules in the asymmetric unit. The two cobalt atoms are hexa-coordinate and have a distorted octahedral geometry, satisfied by four nitrogen atoms from two molecules of the Schiff base and two nitrogen atoms from the monodentate azide group. The perchlorate ions are non-coordinating.     

Understanding the mechanisms of reaction and release of acid–base indicators entrapped in hybrid gels

The reactivity and release of acid–base indicators entrapped in silica and hybrid silica gels were studied. Methyl orange (MO), methyl red (MR), and phenyl red (PR) were used as the indicators. Tetraethoxysilane (TEOS), n-propyltriethoxysilane (PTES), and bis(trimethoxysilyl)hexane (TSH) were used as gel precursors. HCl (0.01 M) and NaOH (0.01 M) solutions were used as the media for acid–base reaction and release in the experiments. The effects of organosilane addition were examined to understand the processes and mechanisms of reaction and release of the indicators entrapped in the gels. The experimental results suggest that adding the organosilanes lowers the pore size and pore volume of the gels, and therefore suppresses the indicator release, but does not present any obvious effects on the acid–base reactivity of the entrapped indicators. MR entrapped in the gels has no acid–base response, while MO and PR entrapped in the gels can present acid–base response without definite acid–base indicating pH ranges. Only the color change pH values can be determined, which present a ‘lag effect’ or ‘hysteresis’ compared with the cases of the free indicators in solutions. The reactivity of the entrapped indicators is suggested to be mainly determined by their chemical nature, the interactions between the indicators and the gel matrices, and the possible involvement of the indicators in the sol–gel process. In general more indicators were found to release in basic solutions than in acidic solutions. For all the entrapped indicators, in acidic solutions through the whole release process, and in basic solutions at the beginning of the release, the indicator release was found to follow the sequence of TEOS Gel > TEOS/PTES Gel > TEOS/TSH Gel. The overall release process is diffusion-controlled, and the release is mainly affected by the textural properties of the gels, the interactions between the gel matrices and the indicators, and the indicator solubility.     

Synthesis and base promoted intramolecular nucleophilic reaction of 8-hydroxy-1,2,3,4-tetrachloro-9,9-dimethoxy-1α,4α,4aα,6,7,8β,8aα-hexahydro-1,4-methanonaphthalene-5(1H)-one

Catalytic hydrogenation of two substituted hexahydro-1,4-dimethanonaphthalene-5,8-diones results in reduction of the enedione carbon-carbon double bond with concomitant reduction of only one of the two chemically equivalent C=O groups. Reaction of one partially reduced product with base results in intramolecular addition to the carbon-carbon double bond.     

Structure of a ring enlarged product from the base induced rearrangement of dibromomethylenebenzonorbornene

The base-catalyzed rearrangement reactions of 2-bromomethylenebenzonorbornene8 and 2,2-dibromomethylenebenzonorbornene9 were studied. Reaction of8 with potassiumtert-butoxide in THF gave only the enol ether11 whose formation is rationalized via a carbene-cycloalkyne mechanism. However, treatment of9 with phenyllithium in THF at –40°C gave the ringenlarged dibromide13 whose structure is reported herein. The ring-enlarged product13 is rationalized in terms of carbanionic rearrangement. Quantum mechanical calculations are consistent with these observations.     

Structure and characterization of O,O-diethylthiophosphorylhydrazine o-vanillin Schiff base nickel(II) complex: NiC24H36N4O8P2S2

The crystal and molecular structure of the complex of Ni[(C₂H₅O)₂PSNHNCPh(o-O)OMe]₂ has been determined by X-ray crystallography. The compound crystallizes in the monoclinic system, space group P2₁/n, with lattice parameters a = 14.805(3), b = 7.9550(16), c = 15.176(3) Å, = 117.94(3), and Z = 2. The unit cell contains two centrosymmetric molecules of O,O-diethylthiophosphorylhydrazine o-vanillin Schiff base nickel(II). The nickel(II) ion is coordinated in a slightly distorted trans square-planar configuration, the distortion consisting of a reduction of the N—Ni—O angle with the chelate rings from the ideal value of 90° to 87.69°. The coordination geometry of nickel(II) is square planar with two equivalent Ni—N and Ni—O bonds. The two phenyl rings and the phosphorylhydrazine moieties are in one plane forming an extensive delocalized system. Within each molecule, the two ligands are linked by a pair of N—H···O hydrogen bonding interactions. In the solid state, the title compound form a hydrogen bonding network through C—H···O intermolecular hydrogen bonding.     

Three-dimensional visualization and characterization of morphology and internal microstructural features of primary silicon crystals in a cast Al–Si base alloy

Primary Si crystals are usually present in the cast microstructures of near-eutectic, eutectic, and hyper-eutectic Al–Si base alloys. Three-dimensional digital images of individual primary Si crystals present in a permanent mold cast unmodified Al-12 wt% Si-1 wt% Ni base alloy are reconstructed using a combination of montage serial sectioning and three-dimensional digital image processing techniques. Octahedral, prismatic, and plate-like three-dimensional morphologies of the primary Si crystals are present in the microstructure. Some of the primary Si crystals contain interior regions/islands of Al-alloy that are completely enclosed in the corresponding Si crystals indicating certain variations in the crystal growth velocities during the evolution of these crystals. The boundaries of these interior regions/islands are non-faceted smooth and curved indicating re-melting of the Al-rich islands and re-dissolution of some Si near these internal boundaries in the Al-alloy as a result of the heat generated by liquid-to-solid transformation of Si away from the islands.     

Asymmetric base pairing in the complex 5-fluorocytosinium chloride/5-fluorocytosine monohydrate

The structure of the complex 5-Fluorocytosinium chloride/5-Fluorocytosine monohydrate has been studied by X-ray diffraction methods. It crystallizes in the monoclinic system, space group P 2₁ /n, a = 7.1257 (15), b = 8.351 (3), c = 21.520 (4) ?, β = 92.89 (8)°, V = 1279.0 (6) ?³, Z = 4. The structure consists of triple hydrogen-bonded 5-Fluorocytosine pairs, water molecules and chloride anions. Asymmetric reversed Watson-Crick base pairing occurs between one protonated (5FcytH⁺) and one neutral 5-Fluorocytosine (5Fcyt) molecule.     

Formation of crystalline phases by means of solid state reactions at the base of vitreous industrial slags

In comparison with the solid state synthesis from the oxide components melilites are formed from vitreous materials with added oxides at lower temperatures and with higher velocity of reaction resulting in larger and more idiomorphic crystals. The crystallization mechanism of the applied vitreous materials is important for the course of the formation of the texture during sintering depending on their chemical composition. In copper slag with polyphase composition the melilite forming reaction starts during the crystallization of pyroxene using the newly relased relictic glass phase in statu nascendi. Lateron, at higher temperatures the pyroxene also reacts with other components to form melilite. In phosphor furnace slag with stoichiometric composition the polymorphic transformation of calcium silicate (CS) is important for the formation of melilite. The change of the glass structure during the nucleation of wollastonite is the process initiating the reaction. Later at higher temperatures the polymorphic transformation of metastable pseudowollastonite accelerates the formation of melilite. It could be proved that the excess of free energy in glasses speeds up crystal forming reactions with admixture components in sintering processes. The mechanism of structural and phase change processes is reflected in the temperature dependence of reaction velocity.     

The role of a dielectric medium in a smectogenic Schiff base compound: A computational analysis

A computational analysis of ordering in a smectogenic Schiff base compound, N-(4-n-heptyloxybenzylidine)-4-hexylaniline, has been carried out with the help of quantum mechanics and computer simulation. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic-charge and atomic dipole moment at each atomic center. The modified Rayleigh-Schrödinger perturbation theory with the multicentered-multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a “6-exp” potential function has been assumed for short-range interactions. The interaction-energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium at the phase-transition temperature (353 K). An attempt has been made to develop a new model of a smectogen in a dielectric medium. The present investigation provides theoretical support to the experimental observations.     

A dimeric pervanadyl (VO2+) complex with a tridentate Schiff base ligand

A di(-oxo)-bridged dinuclear complex, [VO₂(pamh)]₂ was isolated by reacting bis(acetylacetonato)vanadium(IV) and the Schiff base, N-(anisoyl)-N-(picolinylidene)-hydrazine (Hpamh) in acetonitrile. The complex crystallizes in the space group ;1; (#2) on crystallographic inversion center. Crystal data: a = 8.2202(12) Å, b = 9.8389(19) Å, c = 10.1907(17) Å, = 68.245(15)°, = 74.47(2)°, = 66.710(19)°, V = 696.0(2) ų, and Z = 1. The physical properties of the complex and the structural parameters are consistent with the +5 oxidation state of the metal ions. The monomeric VO₂(pamh) unit is square-pyramidal. The planar mononegative ligand (pamh^–) coordinates the metal ion via the pyridine-N, the imine-N, and the amide-O atoms. One of the oxo groups completes the NNOO basal plane and also participates in the Vndash;Ondash ;V bridge formation. The other oxo group satisfies the fifth apical coordination site. The molecular structure of the dimeric complex, [VO₂(pamh)]₂ can be described as two edge-shared distorted VO₄N₂ octahedra.     

The preparation of carbon aerogels based upon the gelation of resorcinol-furfural in isopropanol with organic base catalyst

Carbon aerogels with high BET surface area were developed by sol-gel polycondensation of resorcinol and furfural in isopropanol using hexamethylenetetramine (HMTA) as a catalyst, and then directly drying the organic gels under isopropanol supercritical conditions, followed by carbonization under a nitrogen atmosphere. The preparation conditions of carbon aerogels were explored by changing the mole ratio of resorcinol to basic catalyst HMTA (R/C), the ratio of resorcinol to isopropanol (R/I), and the mole ratio of resorcinol to furfural (R/F). The effect of these preparation conditions on the porous structure of the carbon aerogels obtained was studied by nitrogen adsorption isotherms. According to the characterizations of TEM, SEM and nitrogen adsorption, the carbon aerogels obtained have a three-dimensional network that consists of carbon nano-particles with size from 20 to 30 nm, which define numerous micropores, mesopores and macropores. HMTA reacts not only as a catalyst but also as a reagent in the gelation polymerization. XRD characterization indicates that carbon aerogels have disordered nanocrystalline structures similar to activated carbon.