Contribution to the Ti‐Bi phase diagram

The system Ti‐Bi has been investigated by solid/liquid diffusion couples at 400, 500, 600 and 700 °C. Indication that the growth rate of the diffusion layers at 500 °C is linear has been found, with a growth constant of around 5 × 10^–11 m.s^–1. The existence of the Ti₂Bi phase has been confirmed. Some formerly unknown binary phases (TiBi, Ti₂Bi₃, TiBi₂) have been observed. The phase TiBi is, probably, identical with Ti₈Bi₉ reported previously. All intermediate phases suffer air corrosion, but in various degrees. A tentative variant of the Ti‐Bi phase diagram, including the newly found compounds, has been constructed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of manganese additions on the structure changes proceeding in rapidly solidified Al-Cu alloys

The effect of Mn additions (0… 2 wt%) on the decomposition of rapidly solidified Al-4.0 wt% Cu alloys (cooling rate 10³ to 10⁴ K/s; LQ treatment) were studied during ageing between RT and 450 °C by hardness, X-ray methods and electron microscopy. The results were compared with alloys homogenized in the region of the solid solution (SQ treatment). (i) The LQ treatment results in a quite better homogeneous distribution of the alloyed elements than the SQ one, that is less particles of intermetallic phases are present in the ascast state. (ii) At T < 250 °C Mn additions affect the decomposition kinetics by trapping of vacancies (retardation) and the diminution of the solubility of Cu atoms (acceleration). The first effect dominates in the stage of G.P. zone formation, the second one during precipitation of intermediate phases. (iii) At T ≧ 300 °C the intermetallic compound Cu₂Mn₃Al₂₀ forms associated with a significant increase of the hardness.     

Structure,Crystallization and Electrochemical Corrosion Behaviour of Amorphous Cu66Ti34 Alloy

The effect of thermally induced structural changes on electrochemical corrosion behaviour of amorphous Cu₆₆Ti₃₄ alloy is studied using electrochemical potentiodynamic polarization technique in conjunction with XRD, TEM and DTA. The heat treatment has been carried out at two temperatures: 300 °C — where the process of structural relaxation is only possible and 500 °C — where crystallization of the alloy occurs. As model corrosive media 1N H₂SO₄ and 1N HNO₃ solutions are used. The short range order of the amorphous samples is studied with the total pair correlation function. Some changes of the interatomic distances and a tendency to increasing of the density of the amorphous structure after low temperature heating are established. The crystallization leads to formation of Cu₃Ti₂, β-Cu₃Ti and Cu₂Ti crystalline phases. It has been found that structural relaxation may have a beneficial effect on the susceptibility of the amorphous alloy to passivation, while crystallization lowers considerably its corrosion resistance.     

Application of diffusion couple technique for the determination of the Ti‐Bi‐Sn phase diagram

The system Ti‐Bi‐Sn has been investigated by solid/liquid diffusion couples at 500, 600, 700 and 800°C. A non‐negligible solubility of Sn into solid Bi is found. Diffusion layers of the recently revealed ternary compound Ti₃BiSn have been observed, thus its existence has been confirmed. Data about the homogeneity ranges of the binary end‐system compounds have been obtained. The assessed growth constants of the diffusion layers are comprised in the interval 10^‐12 –10^‐14 m².s^‐1. The phases participating in the hypothetical ternary eutectic reaction, probably are: (Bi), (Sn), Liquid and Ti₂Sn₃. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the tin‐rich region of the Sn‐Zn‐Ti system

The tin‐rich region of the system Sn‐Zn‐Ti system has been studied by diffusion couples, differential scanning calorimetry and electron microprobe analyses. Ternary eutectic reaction occurs at 193.7°C near to the binary tin‐zinc eutectic point and titanium content less than 0.9 at.% Ti. Three ternary compounds with approximate formulae: Ti₈Sn₅Zn₂ to Ti₅Sn₃Zn, TiSn₄Zn₅ and Ti₂Sn₄Zn₃ have been observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diffusion couple studies of the Ti‐Bi‐Zn system

The system Ti‐Bi‐Zn has been investigated using diffusion couples consisting of solid Ti and liquid (Bi+Zn) phase. The diffusion paths at 400, 500, 700 and 800 °C have been traced by means of electron microprobe analyses. The growth constants of the diffusion layers are roughly assessed. The phase diagram data obtained in this investigation are compared with previous studies of equilibrated alloys. The existence of the ternary compound TiBiZn has been confirmed. The formation of another phase with approximate formulae Ti₄Bi₃Zn to Ti₉Bi₇Zn₄ has been observed at high temperatures. The latter compound as well as the ternary extension of the Ti_XBi_Y (X ≈ 5, Y ≈ 6) phase react easily with air. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interactions between YBa2Cu3O7-x and K2Co3

The interactions between YBa₂Cu₃O_7-x and K₂CO₃ have been studied using thermochemical methods, isothermal annealing of diffusion pairs, optical microscopy, X-ray diffraction, and microprobe analyses. The experiments have shown existence of solubility of YBa₂Cu₃O_7-x or its constituents in both solid and liquid K₂CO₃. The barium ions are preferably dissolved in K₂CO₃, whereas potassium cations do not enter massively into the bulk of the YBa₂Cu₃O_7-x-phase. A eutectic-type phase diagram is supposed for the system K₂CO₃–YBa₂Cu₃O_7-x. The so called “green phase” Y₂BaCuO₅ and a K–Cu–O compound have been found in the contact zone at 813 °C while a “black phase” layer with nominal composition Y_1.6Cu_2.8O_5.4 has grown at 707 °C.     

Effect of Boron Doping in Bi-based 2223 Superconductors

Samples with the stoichiometric composition Bi_2−xPb_xSr₂Ca₂Cu_3−yB_yO_z (x = 0.3, y = 0.2, 0.25, 0.3, 0.4) ceramics were prepared by a solid state reaction method. The samples were annealed at 850 °C for 100 hours (treatment A), and the other at 850 °C for 200 hours (treatment B). From the X-ray diffraction data of a ceramic sample it is revealed that all the samples were mixed phases of 2212 and 2223. The variation of the lattice parameters with the dopant level are represented. From the D.C. four-probe electrical resistivity data it was found that for the samples subjected to treatment B the T_c(0) values were higher than those with treatment A. The A.C. susceptibility data were collected by change in the inductance method. The effect of boron doping on the phase formation and T_c(0) is presented and the volume fraction of the phases estimated from the X-ray data. The presence of boron in the samples was confirmed by the inductive coupled plasma method. The microstructure of the samples was studied by scanning electron microscopy.     

Synthesis of single-phase Al–Cu–Fe quasicrystals using high-energy ball-milling

Due to their unique combination of physical, thermal and mechanical properties, aluminium-based quasicrystals are of great interest for many applications such as low friction hard coatings. Nevertheless, as quasicrystalline phases are usually stable only within narrow composition domains, their production on an industrial scale meets some difficulties.Alloys with nominal composition Al₆₇Cu₂₃Fe₁₀ were prepared by high-energy ball-milling of elemental powders. The as-milled powder specimens consist of a nanocrystalline Al(Cu,Fe) solid solution. The structural phase transitions of the ball-milled Al–Cu–Fe nanopowders during constant rate heating were investigated by in situ X-ray diffraction at the B2 beamline at desy-hasylab (Hamburg, Germany). High-quality single-phase quasicrystalline (QC) powders were obtained from nanocrystalline precursors by slow heating to temperatures above 750 °C. The QC phase is preserved upon quenching and is stable during subsequent heating runs up to 800 °C.     

Nucleation of an MTG YBa2Cu3Oy

The kinetics of the appearance of the superconducting 123 phase in partially melted at 1200 °C YBCO samples has been studied in the temperature range of low undercoolings from 1040 °C to 920 °C. An EDS analysis of the phases formed at different stages of the cooling of the melt has been performed and the experimental conditions for crystallization of 123 phase with finely dispersed 211 phase in it have been established. The results have been interpreted in terms of the classical theory of nucleation and they have been applied to the MTG process for formation of highly textured YBa₂Cu₃O_y materials.     

Solvothermal synthesis of micron-sized spherical particles in TiO2–ZrO2 binary system

We prepared TiO₂–ZrO₂ binary oxide particles with various Ti/(Zr+Ti) mole ratios (x) from the solutions containing Ti(OC₃H₇ⁱ)₄, Zr(OC₃H₇ⁿ)₄ and acetylacetone (acac). The spherical particles of 1–5 μm in diameter were obtained via solvothermal treatment at 150 °C. The spheres were anatase at x=1 and amorphous at x=0–0.8. The spheres were thought to be formed through the moderate hydrolysis and nucleation provided by the chelation of the alkoxides by acac. Crystalline TiO₂–ZrO₂ particles were obtained by the heat treatment of the as-precipitated spheres, and the crystalline phase changed with the Ti/(Zr+Ti) mole ratios. Pure ZrO₂ and TiO₂, ZrO₂ doped with Ti⁴⁺, TiO₂ doped with Zr⁴⁺ and ZrTiO₄ phases were produced, and the spherical shape remained after the heat treatment at 500–750 °C.     

Amorphous and quasicrystalline Ti–Ni–Zr powders synthesized by mechanical alloying

The formation of amorphous and quasicrystalline phases in the Ti₄₅Zr₃₈Ni₁₇ system both directly by mechanical alloying and after subsequent annealing was studied. The presence of amorphous, icosahedral quasicrystalline and the Ti₂Ni-type with a fcc structure phases together with the initial metallic components was found in as-milled samples by X-ray diffraction. An increase of the milling time results in an increase of the amorphous phase content. Icosahedral quasicrystalline phases of Ti–Ni–Zr system were produced by mechanical alloying and subsequent annealing. Differential scanning calorimetry studies up to 520 °C showed an extended exothermal effect starting from 300 °C, which corresponds to the crystallization of the as-milled samples. The shape and size of the particles of the alloys were investigated by scanning electron microscopy and argon adsorption. The Specific area surface of the as-milled sample was rather small, in agreement with scanning electron microscopy data. The kinetics of the hydrogenation of the amorphous alloy Ti₄₅Zr₃₈Ni₁₇ at different temperatures was studied.     

Photoemission studies of Titanium Oxides

Titanium exposed to dry air at varying temperatures are studied by X-ray photoelectron spectroscopy (XPS) in combination with low energy Ar ion sputtering. The 2 nm deposit formed at room temperature in 30^d is an oxide mixture with chiefly Ti₂O₃. This result is indicated by the Ti(2p) level binding energy, FWHM and asymmetry. The dry air exposures at high temperatures resulted in oxide species of nonstoichiometric TiO_2–x. As proposed from sputtering effects to XP-spectra the oxygen deficient TiO_2–x surface region includes Ti³⁺-interstitials. These interstitials act as donors (emission to (3d)-states) and hinder the oxygen diffusion via interstitials (temperature: ≦ 550 °C). It is to be noted that electron emission from donor states is favoured in deeper lying (2p)-states by decreasing concentration of oxygen vacancies.     

AES study of the low temperature growth of Cu2−xS on CdS

The growth mechnism of Cu_2?xS on CdS substrates was studied by Auger electron spectroscopy, when a CuCl(film)-CdS- (substrate) specimen was heat treated at ∽200°C. It was found that the reaction to form Cu_2?xS would occur before heat treatment (at ∽50°C). Depth-profile measurement of a Cu_2?xS-CdS specimen heat treated for ∽40 min at ∽200°C showed that the junction had a diffuse interface composed of Cu, Cd, and S with a thickness of ∽500 Å, and also that Cu and Cd atoms diffused into CdS substrate and Cu_2?xS layer, respectively, to a depth of 300–600 Å.     

Hydrogen in Cu?Ti and Ni?Ti Metallic Glasses

The hydrogen solubility and its effect on the crystallization of Cu Ti and Ni Ti glasses were studied by differential scanning calorimetry, thermogravimetry, and X-ray diffraction. Dependence of the crystallization products of the hydrogenated Ti-based alloys on the hydrogen content was found. Whereas in Cu-Ti alloys hydrogenation leads to drastic decreasing in the thermal stability due to phase separation in the amorphous state and to formation of microcrystalline structure during crystallization, in Ni Ti system hydrogen produces hydrides with Ni as well with Ti, which after heat treatment decompose, and finally the same crystalline phases as in unhydrogenated alloy are formed. The isothermal crystallization kinetics of the maximum hydrogenated Cu₅₀Ti₅₀ amorphous alloy was also investigated to obtain additional information about this transformation leading to nano-crystalline material.     

Bulk metallic glass formation in Cu–Zr–Ti ternary system

The formation of bulk metallic glasses (BMG) in the Cu-rich Cu–Zr–Ti ternary system is studied by using the ‘e/a-variant line criterion’. Three such lines, (Cu₉Zr₄)_1−xTi_x, (Cu_61.8Zr_38.2)_1−xTi_x and (Cu₅₆Zr₄₄)_1−xTi_x, are defined in the Cu–Zr–Ti system by linking three binary compositions Cu₉Zr₄, Cu_61.8Zr_38.2 and Cu₅₆Zr₄₄ to the third element Ti. The binary compositions Cu₉Zr₄, Cu_61.8Zr_38.2 and Cu₅₆Zr₄₄ correspond to specific Cu–Zr binary clusters. BMGs are obtained by copper mould suction casting method with Ti contents of 7.5–15 at.%, 7.5–12.5 at.% and 5–12 at.%, respectively along the (Cu₉Zr₄)_1−x Ti_x, (Cu_61.8Zr_38.2)_1−xTi_x and (Cu₅₆Zr₄₄)_1−xTi_x lines. The BMGs on each composition line manifest decreased thermal stabilities and glass forming abilities (GFAs) with increasing Ti contents. The maximum GFA appears at Cu₆₄Zr_28.5Ti_7.5, with characteristic thermal parameters of T_g = 736 K, T_x = 769 K, T_g/T_l = 0.627 and γ = 0.403, which are all superior to those reported for the known Cu₆₀Zr₃₀Ti₁₀ BMG.     

A comparison of the crystallization behavior of liquid-quenched and vapor-quenched amorphous Cu60Ti40

The crystallization behavior of two Cu₆₀Ti₄₀ amorphous alloys, one prepared by a vapor-quench (VQ) process and one by a liquid-quench (LQ) process, has been studied using differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. Microstructural studies show that the two alloys have the same transformation sequence under similar annealing conditions. However DSC measurements of the crystallization temperature during isochronal annealing and of the incubation time for crystallization during isothermal annealing show that the LQ alloy is more thermally stable and therefore more structurally relaxed. TEM analysis of the partially annealed microstructures gives some insight into the mode of crystal nucleation and growth as a function of temperature. During isothermal annealing significant differences are observed for the two alloys in the shape and orientation of the crystals and in the crystal structure formed. Whereas the VQ alloy transforms polymorphicaly into the intermetallic Cu₃Ti₂, the LQ alloy forms the Ti-rich phase, Cu₄Ti₃. The two phases are closely related in structure and composition. The differences observed for the two alloys are discussed in terms of greater structural relaxation and short range order in the LQ alloy resulting from the mode of synthesis.     

Die Berechnung von Kriterien für die Abscheidung reiner Phasen binärer Systeme beim chemischen Transport und der Transport im System Cu-O

A thermodynamical analysing method is described of the deposition of binary solids AB_x, which specially takes into account the influence of the coexistence equilibria in the A—B-system. This analysis is applicated to the Cu—O system. It permits to calculate the conditions, under which Cu₂O is deposited without deposition of any other phases. The deposition of cuprous oxide by CTR-techniques is investigated using hydrogen halides as transport media. The experiments result in the growth of Cu₂O-monocrystals (2 × 2 × 2 mm) only if HCl is used as transport medium. Using HI the simultaneous deposition of Cu₂O and Cu is observed.     

Flux growth and characterization of Ti‐ and Ni‐doped forsterite single crystals

Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h^‐1. These synthetic, well‐characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of nanocrystalline and amorphous phases in Cu80P20, Ni82P18 and Cu87Ni13 mechanically alloyed systems

Variations in the crystallite size and stored strain caused by mechanical milling of binary alloy systems of copper, nickel and phosphor were compared. During mechanical alloying process, an amorphous phase is partially produced in CuP and NiP alloy systems and only a nanoscale crystalline phase in CuNi alloy system. The CuP alloy system first forms a Cu₃P intermetallic compound and then the partial amorphous phase by the reaction of primary copper phase and Cu₃P intermetallic compound, while the NiP alloy system directly forms a partial amorphous phase by the reaction of primary nickel and phosphor phases. When the crystallite sizes of primary copper and nickel phases become of the order of a few nanometers in the CuP and NiP alloy systems, they are in an almost strain-free state.