Effect Of Tantalum Research Articles

Effect of Tantalum in Sublimation Growth of Aluminum Nitride

Effect of Tantalum in Sublimation Growth of Aluminum Nitride

Effects of tantalum adhesion layer on the properties of SrBi2Ta2O9 ferroelectric thin films

The effects of tantalum (Ta) adhesion layer on the ferroelectric and microstructural properties of sol-gel-derived SrBi2Ta2O9 (SBT) films are reported in this study. Compared to the traditional titanium (Ti) adhesion layer, the Ta adhesion layer results in more favorable, highly (115) textural structure of SBT films and therefore higher polarization and dielectric constant. The remnant polarization value of the SBT films crystallized at 750 °C increases from 11.1 to 14.2 μC/cm2 at 5 V, and the dielectric constant increases from 175 to 225. The observed improvement in the electrical properties of SBT films is ascribed to the superior microstructure of Pt thin film on Ta, which has been characterized by x-ray diffraction spectrum (XRD). XRD patterns clearly indicate that the Ti adhesion layer favors c-axis crystalline structure that is undesirable for ferroelectric properties. Moreover, secondary ion mass spectrometer profiles strongly indicate that Ti atoms diffuse deeply into the bulk of SBT thin films after crystallization annealing. By using Ta as the adhesion layer material, this inhomogeneous interdiffusion phenomenon can be effectively suppressed, eliminating the formation of TiOx interfacial layer, and possibly decreasing the occurrence of undesirable second phase compound.

Effect of Tantalum in Crystal Growth of Silicon Carbide by Sublimation Close Space Technique

Investigation into the effect of tantalum on silicon carbide, grown by the sublimation close space technique, was carried out. It was established that in the presence of a small piece of tantalum in the reaction space during the crystal growth process, the surface of the epitaxial layer became extremly smooth and high-crystal-quality epitaxial layers were obtained. It was also shown that the concentrations of aluminum and titanium are different in epitaxial layers grown with and without tantalum. High-quality epitaxial layers, which were comparable to epitaxial layers grown by chemical vapor deposition, could be obtained at a high growth rate by the sublimation close space technique.

Dielectric properties of 0.65PbMg1/3(Nb(1−x)Tax)2/3-O3-.35PbTiO3

Lead magnesium niobate-lead titanate crystalline solutions 0.65PbMg1/3Nb2/3O3-0.35PbTiO3 (PMN-PT) have been investigated in this paper. The effect of tantalum partially substituting niobium (0.65PbMg1/3(Nb(1−x)Tax)2/3O3-0.35PbTiO3 (PMNTa-PT)) on dielectric properties has been studied. It was found that the transition temperature appears at 170–180°C for all the samples with and without doping. Doping 10% tantalum in 0.65PMN-0.35PT did not show the significant effect on the transition temperature. The ferroelectric characteristics were viewed from the results of dielectric measurement on samples without doping tantalum, i.e. sharp dielectric constant peak, and less frequency dispersion. The samples with 10% tantalum substitution of niobium (x=0.1) show more relaxor properties. It has broader dielectric constant peak and stronger frequency dispersion than that of the samples without doping. The samples with Ta-doping also show less frequency dependence than that of those without doping.

The effect of tantalum on the mechanical properties of a 9Cr–2W–0.25V–0.07Ta–0.1C steel

An Fe–9Cr–2W–0.25V–0.07Ta–0.1C (9Cr–2WVTa) steel has excellent strength and impact toughness before and after irradiation in the Fast Flux Test Facility (FFTF) and the High Flux Reactor (HFR). The ductile–brittle transition temperature (DBTT) increased only 32°C after 28 dpa at 365°C in FFTF, compared to a shift of ≈60°C for a 9Cr–2WV steel the same as the 9Cr–2WVTa steel but without tantalum. This difference occurred despite the two steels having similar tensile properties before and after irradiation. The 9Cr–2WVTa steel has a smaller prior-austenite grain size, but otherwise microstructures are similar before irradiation and show similar changes during irradiation. The irradiation behavior of the 9Cr–2WVTa steel differs from the 9Cr–2WV steel and other similar steels in two ways: (1) the shift in DBTT of the 9Cr–2WVTa steel irradiated in FFTF does not saturate with fluence by ≈28 dpa, whereas for the 9Cr–2WV steel and most similar steels, saturation occurs at <10 dpa, and (2) the shift in DBTT for 9Cr–2WVTa steel irradiated in FFTF and HFR increased with irradiation temperature, whereas it decreased for the 9Cr–2WV steel, as it does for most similar steels. The improved properties of the 9Cr–2WVTa steel and the differences with other steels were attributed to tantalum in solution.

Effect of tantalum on the properties and structure of hard alloys based on titanium carbonitride

It is determined that the introduction of tantalum (as a carbide) into TiCN−Ni−Mo and TiCN−Ni−Mo—WC hard alloys increases their bending strength, which was evaluated in the milling of steel. It is shown that sintering of the initial mixtures of titanium carbonitride with nickel and molybdenum is followed by the formation of the so-called “K-phase,” which exists mainly in the form of a coating on the TiCN grains. This phase is a complex carbonitride, according to the results of X-ray probe microanalysis (the given structure is referred to as “coaxial” in the literature). It is proposed that the K-phase alone is responsible for the increased strength of titanium-carbonitride-based hard alloys which contain tantalum and have a nickel-molybdenum binder. From this standpoint, it is suggested that pre-made complex tantalum-bearing titanium carbonitride (instead of TiCN) be used as the raw material in hard-alloys production.

Effect of alloying of metal matrix on recrystallization of tungsten fiber

Effect of tantalum, as alloying element, on the kinetics and mechanism of interactions of W-fiber in Ni-W, Co-W and Fe-W composites, fabricated by P/M processing, have been studied at 1100-1300° C for 1-50 h. It has been found that by alloying the Fe, Co and Ni-matrices with 2 at.% Ta, diffusion of the matrix-atoms into the fiber can be controlled which results in remarkable suppression of the W-fiber recrystallization. Formation of NiW, Fe2W and CO3W intermetallic compounds at the fiber/matrix interface has been avoided by raising the temperature of the specimen at a rate of 60° Cjmin -1 up to 1100° C. The effectiveness of tantalum has been confirmed by the EPMA results and activation energy data.

Effect of tantalum or Stellite ion beam mixing surface treatment on passivity and pitting of corrosion-resistant steel in NaCl solution

Tantalum or Stellite alloy was deposited on steels by d.c. magnetron sputtering and then was bombarded by 200 keV Xe + or N +. Passivity and pitting corrosion behaviour in NaCl solution were studied using the potentiodynamic anodic polarization technique. It was found that corrosion resistances were greatly improved by this treatment. The anodic polarization current densities for all tantalum or Stellite ion-beam-mixed specimens have been decreased by one order of magnitude or more and the corrosion potential E corr and pitting breakdown potential E br were all increased with respect to the values for their corresponding substrate materials. Anodic polarization curves and details of the morphology of the corroded samples are presented. The chemical composition of surfaces before and after corrosion was obtained using scanning electron microscopy-energy-dispersive X-ray analysis; Rutherford backscattering X-ray photoelectron spectroscopy were also used for these samples.

Effects of Ta addition in CoNi/Cr double layer film sputtered in low Ar gas pressure

The effects of tantalum and chromium up to 5 at.%, added to the CoNi magnetic layer, on the magnetic properties and media noise of a CoNi/Cr double-layer magnetic recording medium, have been investigated. The CoNi magnetic layer and Cr underlayer were deposited at argon gas pressures as low as 2 and 0.2 mTorr, respectively, using a facing-targets sputtering apparatus. Addition of Cr to CoNi layers with high remanence squareness shows slight improvement of medium noise. The addition of Ts shows significant noise reduction, to the extent of about 3 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effects of tantalum on the microstructure of two polycrystalline nickel-base superalloys: B-1900 + Hf and MAR-M247

Changes in the γ/γ'/carbide microstructure as a function of Ta content were studied in conventionally cast B-1900 + Hf and both conventionally cast and directionally solidified MAR-M247.* The effects of tantalum on the microstructure were found to be similar in both nickel-base superalloys. In particular, the γ' and carbide volume fractions increased approximately linearly with tantalum additions in both alloys. The γ' phase compositions did not change as tantalum additions were made with the exception of an increase in the tantalum level. Bulk tantalum additions increased the tantalum, chromium, and cobalt levels of the γ phase in both alloy series. The increase in the concentrations of the latter two elements was attributed to a decrease in the γ phase fraction with increasing bulk tantalum level and nearly constant γ' /γ partitioning ratios. It was demonstrated that the large increase in the γ ' volume fraction was a result of tantalum not affecting the partitioning ratios of the other alloying elements. The addition of tantalum led to a partial replacement of the hafnium in the MC carbides, although the degree of replacement was reduced by the solutionizing and aging heat treat-ment. In addition, chromium-rich M23C6 carbides formed as a result of MC carbide decomposition during heat treatment.

Coarsening kinetics during solidification of Ni-Al-Ta dendritic monocrystals

Several dendritic monocrystals of nickel-rich Ni-Al-Ta alloys were directionally solidified at about 0.25 m/h−1 under a gradient of 8 × 10−3 K/m−1. The solid-liquid interface was fossilized at a given moment by rapidly quenching the remaining liquid. In some specimens crystal pulling was interrupted for various lengths of time prior to quenching. The quenched solid-liquid interfaces were used for a convenient and rapid evaluation of: 1) isothermal coarsening kinetics of the dendritic solid at a temperature between the liquidus and the eutectic temperatures and; 2) dendrite coarsening kinetics during solidification. It was found that extension to the ternary Ni-Al-Ta system of a model previously developed for binary systems predicted isothermal dendrite coarsening kinetics in close agreement with experimental results. Agreement for coarsening kinetics during solidification was less good. An increase in tantalum or aluminum contents slowed down coarsening, yielding finer microstructures. At equal atomic percental increase in concentration, the effect of tantalum was more significant than that of aluminum.

12Cr-l Mo-0.2V鋼のクリープ破断強さにおよぼすTaおよびNの影響

12Cr-l Mo-0.2V鋼のクリープ破断強さにおよぼすTaおよびNの影響

The melting temperature of uranium at high pressures

An investigation is reported into the effect of pressure on the melting temperature of uranium. The uranium was encapsulated in tantalum and nllowance was made for the slight alloying effects of tantalum and uranium oxide. The experiments were carried out in a piston-cylinder apparatus essentially similar to that described by Cohen et al., (J. Phys. Chem. Solids; 27: 179(1966)). The estimated, corrected melting curve for pure uranium is presented for pressures from 9 to 41.4 kbar. (UK)

Solid solution strengthening in Nb-Ta and Nb-Mo alloy single crystals

The strength of Nb, Nb-Ta, and Nb-Mo alloys was investigated in tension and compression as a function of composition, temperature, and strain rate. The room-temperature properties show molybdenum to have a significant effect on the strength of niobium while the effects of tantalum are nearly zero. The room-temperature strength is shown to be well correlated with the atomic misfit parameter. Analysis of the low-temperature behavior of Nb-Ta alloys indicates that they behave similarly to the pure metal while Nb-Mo alloys show a marked deviation from this behavior. The strengthening phenomena occurring in the Nb-Mo alloys at low temperature is interpreted as being an impurity interaction. A transition between the mechanism operating in the pure metal and the impurity interaction occurs at low solute contents.

Tantalum doping and high resistivity in aluminium antimonide

Aluminium antimonide crystals grown by the Czochralski method from melts doped with tantalum are found to have a lower residual acceptor concentration and increased free hole mobility than crystals from undoped melts. An investigation of the effect of tantalum on the segregation of particular impurities shows that tantalum will `getter' certain impurities, for example carbon and copper. The mechanism is obscure. The segregation of tantalum is found to be abnormal. A value of 0.80 has been obtained for the effective segregation coefficient of tellurium. Doping the melt with tantalum and tellurium has given n- and p-type crystals with resistivities from 104 to 1010 Ω cm at room temperature. The variation of resistivity with temperature reveals the presence of levels with activation energies from 0.40 to 0.80 ev. A value of 14.4 ± 1 has been obtained for the static dielectric constant of aluminium antimonide from capacity measurements on the high resistivity crystals. Photoconductive decay times of 0.5 to 1 msec have been observed in these high resistivity crystals.

The late effects of tantalum 182 radiation on the cerebral cortex of monkeys.

The late effects of tantalum 182 radiation on the cerebral cortex of monkeys.