Ti Pd Research Articles

Surface Structures and Hydrogenation Properties of Ti–Pd Alloys Immersed in Hydrogen Peroxide

Surface Structures and Hydrogenation Properties of Ti–Pd Alloys Immersed in Hydrogen Peroxide

Regulating bimetallic active centers for exploring the structure–activity relationship toward high-performance photocatalytic nitrogen reduction

Photocatalytic ammonia (NH3) synthesis from N2 is a strategy conducive to carbon neutrality because it avoids high energy consumption and high carbon emission process in the industrial synthesis of NH3. However, the structure–activity relationship of bimetallic active centers in heterogeneous catalysts is still unclear for high-performance photocatalytic nitrogen reduction reaction (pNRR). Here, we explore in-depth the structure–activity relationship of high-performance pNRR by regulating the semi- or full-encapsulated structure model formed by the noble metal nanoparticles (Pd, Au, and Pt) and mesoporous TiO2 nanorods (NRs). Further mechanism studies revealed that the Ti–Pd bimetallic active centers at the interface of semi-encapsulated palladium-decorated mesoporous TiO2 NRs possesses ultra-high adsorption energy, which can effectively weaken the triple bond of N2 and reduce the activation energy barrier of pNRR process. Accordingly, the optimal se-Pd/m-TiO2 NRs (2.71%) photocatalyst demonstrates a NH3 production rate of up to 635.73 μg/gcat./h, reaching a high apparent quantum efficiency of 0.37% at 375 nm under mild conditions. This work not only opens an avenue to expand high-performance catalysts for N2 photofixation under mild conditions via regulating bimetallic centers but also offers atomic-level insights for understanding the internal pNRR procedure.

Effect of Hf on the microstructure and martensitic transformation behavior in Ti–Pd–Hf alloy

We investigated the microstructure and the crystallography of martensite variants in Ti–Pd–Hf alloy using electron microscopy. The martensitic transformation temperature decreased with increasing amount of Hf substituted into the Ti50−xPd50Hfx alloy. No indication of a martensitic transformation was observed in the as-quenched Ti25Pd50Hf25 and Ti10Pd50Hf40 alloys, even when the samples were cooled to 150 K. The Ti40Pd50Hf10, Ti35Pd50Hf15, and Ti30Pd50Hf20 alloys were composed of a B19 orthorhombic phase having plate-like habit-plane variants consisting of both major and minor correspondence variants several hundred nanometers in width and several tens of micrometers in length at room temperature. Lattice-invariant shear of these alloys was a {111}B19 Type I twin. A solution-treated sample of the Ti25Pd50Hf25 alloy consisted of a B2 cubic matrix with local atomic displacement and lattice distortions, and rounded H-phase particles several tens of nanometers in diameter were precipitated inside the B2 matrix upon aging of the specimen at 823 K for 10.8 ks. The as-quenched Ti10Pd50Hf40 alloy contained rounded H-phase particles several tens of nanometers in diameter embedded in a B2 matrix at room temperature. The martensitic transformation temperature in the Ti50−xPd50Hfx alloy was drastically decreased by both the fully coherent nanosized H-phase particles and the short-range order originating from clustering of solute atoms.

Effect of Hf on the Microstructure and Martensitic Transformation Behavior in Ti–Pd–Hf Alloy

Effect of Hf on the Microstructure and Martensitic Transformation Behavior in Ti–Pd–Hf Alloy

A comparison between corrosion performances of titanium grade 2 and 7 in strong reducing acids

AbstractTitanium has a good corrosion resistance, owing to a thin, compact oxide layer that is formed spontaneously when the metal is exposed to the environment. However, even titanium can be subject to corrosion, for example, when exposed to reducing strong acids. This paper aims to analyze the differences in corrosion resistance of commercially pure titanium (Ti grade 2) and the most resistant Ti–Pd alloy (Ti grade 7, ∼0.2% Pd) in a strong reducing acid environment. Immersion tests, with results collected in the form of corrosion rates, are provided in the first part of the present work. Corrosion morphology is investigated using optical microscopy and laser profilometry. Then, an electrochemical characterization of both metals has been performed by means of cathodic polarization tests, electrochemical impedance spectroscopy, and linear polarization resistance. Weight loss data, electrochemical tests, and corrosion morphology are in good agreement: H2SO4, HCl, and oxalic acid are the most aggressive chemicals for commercially pure titanium. In such conditions, the use of Ti grade 7 appears mandatory.

Corrosion behavior of high-level waste container materials Ti and Ti–Pd alloy under long-term gamma irradiation in Beishan groundwater* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51471160, 11775102, and 11965001) and the Fundamental Research Funds for the Central Universities, China (Lanzhou University, Grant No. lzujbky-2018-19).

Titanium and titanium–palladium alloys are important potential materials for nuclear waste container, which will endure both intense γ-irradiation and groundwater erosion. Therefore, it is very important to investigate the corrosion behavior of the container materials. In this research, the cumulative dose effect of TA8-1 type titanium–palladium alloy (TA8-1) and TA2-type pure titanium (TA2) under γ-irradiation was studied based on the geological disposal of nuclear wastes. The irradiation experiments were performed at room temperature using 60Co gamma sources with a 5.0-kGy⋅h−1 intensity for 40, 80 or 160 days, respectively. The pH value and conductivity of Beishan groundwater were investigated. The results showed that the pH value changed from alkaline (8.22) to acidic (2.46 for TA8-1 and 2.44 for TA2), while the un-irradiated solution remained alkaline (8.17 for TA8-1 and 8.20 for TA2) after 160 days. With the increase of irradiation dose, the conductivity increases rapidly and then tends to become stable, which indicates that the titanium dioxide corrosion layer formed on the surface of the sample surface effectively prevents further corrosion. Meanwhile, XRD and SEM–EDS analysis results show that the main components of corrosion products are TiO2 and TiO. The titanium on the surface of the sample is oxidized, resulting in slight uneven local corrosion. The results show that TA8-1 and TA2 are suitable to be used as candidate materials for high-level waste (HLW) disposal containers due to their excellent performance under long-term and high-dose irradiation corrosion.

Structural and Secondary Electron Yield Properties of Titanium-Palladium Films with Laser-Treated Copper Substrate for Application in Neutron Generators.

Secondary electron emission (SEE) of the oxygen-free high-conductivity copper (OFHC) target surface in neutron generators limits the stability and improvement of the neutron yield. A novel-type target of titanium–palladium films coated on laser-treated OFHC target substrate was proposed and explored in this work to obtain low secondary electron yield (SEY) without introducing any components. The combination of Ti–Pd films and laser-treated OFHC substrate can effectively suppress secondary electron emission and enhance the adsorption ability to hydrogen isotopes with the existence of Pd film. The surface morphologies, surface chemical states, and SEYs of Ti–Pd films with laser-treated OFHC substrate were studied systematically for the first time. The XPS results showed that the laser-treated OFHC substrate surface was basically covered by Pd film. However, the Pd film surface was partially oxidized, with percentages of 21.31 and 10.02% for PdO and PdO2, respectively. The SEYs of Ti–Pd films with laser-treated OFHC substrate were all below 1 within the investigated primary energy range of 100–3000 eV, which would be sufficient for application in neutron generators. Specifically, the maximum SEY (δmax) of laser-treated OFHC substrate coated by Ti–Pd films was 0.87 with corresponding incident electron energy of 400 eV.

Cross β-arylmethylation of alcohols catalysed by recyclable Ti-Pd alloys not requiring pre-activation.

Ti-Pd alloy catalysts were developed for the cross β-arylmethylation between arylmethylalcohols and different primary alcohols via a hydrogen autotransfer mechanism. The alloy catalysts could be reused multiple times without the need for pre-activation. Analysis of the reaction solution by inductively coupled plasma atomic absorption spectroscopy indicated that only a minimal amount of Ti and no Pd was leached from the catalyst.

Strain glass by aging in Ti–Pd–Fe shape memory alloys

Up to now, most of strain glasses are achieved by doping point defects into martensitic alloys. Here we report a strain glass in a Ti54Pd36Fe10 shape memory alloy achieved by low-temperature aging. Aging at 523 K generates Ti2Pd-like nanoprecipitates, which are responsible for the formation of strain glass. By continuously increasing the aging time, we studied how the strain glass transition gradually evolves from a martensitic transformation. A short aging time (12 min) is enough to generate strain glass, while the martensite still persists as the aging time increases to 300 min. A temperature–aging time phase diagram is established accordingly.

Study of the Structure and Properties of High-Temperature Shape-Memory Alloys of the Ti–Pd–Ni and Ni–Ti–Hf Systems

Abstract—Comprehensive studies on retrieving information about the elemental and local phase composition, phase transition temperatures, and mechanical and thermomechanical characteristics of high-temperature shape-memory alloys of the Ti–Pd–Ni and Ni–Ti–Hf systems in the as-received condition and after thermal treatment have been carried out. The results of this study are necessary for the development of various safety devices used in nuclear power facilities.

Features of the Temperature Dependence of the Specific Contact Resistance of Au–Ti–Pd–n+–n-Si Diffusion Silicon Structures

The temperature dependences of the specific contact resistance of silicon ρc with a doping step are measured experimentally and described theoretically. The measurements are performed in the temperature range from 4.2 to 380 K. It is established that the contacts of the studied Au–Ti–Pd–n+–n-Si structures are ohmic. It is shown that minimal ρc is implemented at T = 75 K. Its value rises both with a decrease in temperature (due to the freezing effect) and with an increase in temperature (due to the electron-enriched layer at the boundary with the bulk material). It is established that the bulk electron concentration strongly decreases in the near-contact region in a layer with a thickness on the order of one micron due to the compensation of silicon by deep acceptors appearing because of the formation of a rather high vacancy concentration during stress relaxation and the appearance of a high dislocation density, as well as due to their diffusion from the contact after heating to 450°C. The data on the occurrence of vacancy-type defects are confirmed by X-ray measurements. The dislocation density in the studied structures is also estimated from X-ray measurements.

Bulk Ti–Pd Alloys as Easily Recyclable and Preactivation-Free Heterogeneous Catalysts for Cross-Coupling Reactions

Abstract Ti–Pd alloys have been found to be novel heterogeneous palladium catalysts for organic cross-coupling reactions. Catalyst preactivation is not necessary, resulting in facile recovery and reuse of the catalysts. Palladium is not leached into the reaction solution and the catalysts can be recycled several times without losing their catalytic activity.

Особенности температурной зависимости удельного контактного сопротивления диффузионных кремниевых структур Au-Ti-Pd-n-=SUP=-+-=/SUP=--n-Si

AbstractThe temperature dependences of the specific contact resistance of silicon ρ_ c with a doping step are measured experimentally and described theoretically. The measurements are performed in the temperature range from 4.2 to 380 K. It is established that the contacts of the studied Au–Ti–Pd– n ^+– n -Si structures are ohmic. It is shown that minimal ρ_ c is implemented at T = 75 K. Its value rises both with a decrease in temperature (due to the freezing effect) and with an increase in temperature (due to the electron-enriched layer at the boundary with the bulk material). It is established that the bulk electron concentration strongly decreases in the near-contact region in a layer with a thickness on the order of one micron due to the compensation of silicon by deep acceptors appearing because of the formation of a rather high vacancy concentration during stress relaxation and the appearance of a high dislocation density, as well as due to their diffusion from the contact after heating to 450°C. The data on the occurrence of vacancy-type defects are confirmed by X-ray measurements. The dislocation density in the studied structures is also estimated from X-ray measurements.

Theoretical and experimental modelling the specific resistance of vertical ohmic contacts Au–Ti–Pd–n+-n-n+-Si in IMPATT diodes

Theoretical and experimental modelling the specific resistance of vertical ohmic contacts Au–Ti–Pd–n+-n-n+-Si in IMPATT diodes

Structure of quenched alloys of the Ti–Pd system

The quenched alloys of the Ti–Pd system containing 2–15 at % Pd have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and measurements of the microhardness. It has been found that, in the course of quenching, epy alloys containing 2, 3, and 5 at % Pd undergo a eutectoid decomposition into the α phase and Ti2Pd intermetallic compound, and the Ti–7 at % Pd and Ti–9 at % Pd alloys undergo a β → α' martensitic transformation. In the alloys with Pd contents of more than 9 at %, the β phase is fixed in the metastable state. The complete stabilization of the β phase takes place in the alloys containing 11 at % Pd and more. It has been found that the formation of the orthorhombic α" phase and metastable ω phase in the quenched alloys of this system does not occur.

Photo-induced properties of anodic oxide on Ti–Pd alloy prepared in acetic acid electrolyte

Photo-induced properties of titanium dioxide on Ti–Pd alloy, prepared by anodic oxidation in acetic acid electrolytes have been studied and compared with those of the oxide on pure Ti. The photocatalytic activity of the anodic oxide on Ti–Pd was superior to that of the anodic oxide on Ti, and the highest photocatalytic activities were found for the anodic oxide prepared in electrolytes with 1 M or 2 M acetic acid. This superiority was attributed to PdO incorporation into the anodic oxide, which facilitates charge separation. Both photocatalytic activity and hydrophilicity of the anodic oxide varied with the acetic acid concentration in the electrolyte, and were related to the surface morphology of the anodic oxides, which is controlled by the electrochemical reaction. It is concluded that photo-induced properties are imparted to the corrosion-resistant Ti–Pd alloy by anodic oxidation in acetic acid aqueous solutions.

The compositional stability of the P-phase in Ni–Ti–Pd shape memory alloys

The precipitation of the P-phase in Ni–Ti–Pd and Ni–Ti–Pt shape memory alloys has been shown to dramatically increase the martensitic transformation temperature and strength in Ni-rich ternary alloys, yet little is known about the phase's compositional stability. Therefore, the compositional limits of the P-phase have been systematically studied by varying the Pd and Ni content while maintaining the general P-phase Ti11(Ni + Pd)13 stoichiometry. Each alloy was solutionized at 1050 °C followed by water quenching, and aging at 400 °C for 100 h. Four distinct phases were identified by electron and x-ray diffraction: Ti2Pd3, B2 NiTi, P- and P1-phases. The latter precipitate phases became more stable with increasing Ni at the expense of the Pd content. Atom probe tomography revealed the P-phase composition to be 45.8Ti–29.2Ni–25Pd (at.%) or Ti11(Ni7Pd6) as compared to the P1-phase 44.7Ti– 45.8Ni–9.4Pd (at.%) or Ti5Ni5Pd.

Advanced Electron Microscopy Characterisation of Important Precipitation and Ordering Phenomena in Shape Memory Systems

The present paper discusses some important aspects of precipitation and ordering in alloy systems that show a martensitic transformation and can or are used as shape memory or superelastic metallic systems. The precipitates are investigated by a variety of conventional and advanced electron microscopy techniques, including atomic resolution, 3D slice-and-view, energy loss spectroscopy etc. Depending on the system, such secondary phases can decrease the probability of a displacive transformation by changing the phase stability in the system, such as in the case of Ni–Al or Ni–Ti–Pd, or can mechanically hinder the passage of the transformation interface, as in Ni–Ti–Nb. On the other hand, properly controlling the nucleation and growth of some precipitates can strongly improve the properties of some types of materials, as is the case for the well-known Ni4Ti3 precipitates.

Исследование удельного сопротивления омических кон­так­тов Au—Ti—Pd—n-Si для лавинно-пролетных диодов

Both contact resistivity of Au—Ti—Pd—n-Si ohmic contact and mechanism of current flow are studied in the 100—360 K temperature range. A method is proposed for reduction of error in determination of contact resistivity based on analysis of statistical dependences of the measured contact resistivity values (which are in the range of (0.9—2)•10–5 Ω•cm2). On the basis of the contact resistivity temperature dependence, it is found for an ohmic contact with barrier height of 0.22 eV that the field mechanism of current flow is predominant in the 100—200 K temperature range, while thermal-field emission with activation energy of 0.08 eV is predominant in the 200—360 K temperature range.

Ti modified Pd–Ag membranes for hydrogen separation

An investigation was carried out into Pd–Ag separation membranes to check whether a reduction in their Pd content was possible through the incorporation of a third element, namely Ti. For this purpose a combinatorial thin film deposition system was developed incorporating three sputter targets arranged in triangular form. The system had a substrate in the form of a magazine, 6 inch in diameter, accommodating 21 discs arranged again in triangular form aligned with the targets underneath. With this geometry, a library of thin film membranes was obtained in a single experiment covering a wide compositional field, Pd content up to of approx. 75%. The thin film library was then screened with respect their tendency to react with hydrogen. This was accomplished by the resistivity measurements carried out on the membranes, while they are subjected to heating–cooling cycle under hydrogen, the values being compared with identical cycle carried out under argon. Since permeability is a product of hydrogen solubility and diffusivity, membranes that react with hydrogen, i.e. either forming a solid solution or a hydride, delineate compositions which are candidates for separation membranes. In the present work, this procedure was applied to a portion of Ag–Ti–Pd ternary system aiming for separation membranes with f.c.c. crystal structure. Mapping based on the resistivity measurement indicated, Ag35Ti22Pd43, Ag13Ti25Pd62 and their near compositions as possible candidates for separation membranes.