Addition Of HF Research Articles

Ni–(Zr/Hf)–(Nb/Ta)–Al bulk metallic glasses with high thermal stabilities

Thermal stability is a critical consideration in the application of metallic glasses as hydrogen separation material. The development of new Ni-based bulk metallic glasses (BMGs) with enhanced thermal stability is desirable. The present work investigated the alloying effects of refractory metals Hf and Ta on the Ni 60Zr 20Nb 15Al 5 bulk metallic glass. Two serial alloys, namely, Ni 60Zr 20 − x Hf x Nb 15Al 5 ( x = 0∼20 at.%) and Ni 60Zr 20Ta y Nb 15 − y Al 5 ( y = 0∼15 at.%), were investigated in the present work. The addition of Hf or Ta was revealed to be effective in improving the thermal stability of the basic alloy, while the glass-forming ability of the alloy is slightly reduced resulting from the addition of Hf or Ta. The possible mechanism of these alloying effects is discussed.

Early-Stage Oxidation Behavior of Pt-Modified γ′-Ni3Al-Based Alloys with and without Hf Addition

The early-stage oxidation behavior in air of Pt-modified γ′-Ni3Al-based alloys of composition (in at.%) Ni–22Al–30Pt with and without 0.5Hf was investigated in terms of oxidation kinetics, scale evolution and Al2O3 phase transformation. Oxidation exposures included heating to and short-term holds at 1,150 °C. Hafnium addition did not appear to affect microstructural evolution and growth rate of the oxide scales during heating to 1,150 °C; however, it was found that Hf delayed the metastable-to-α-Al2O3 phase transformation, thus allowing continued fast growth of oxide scale. After the transient oxidation stage of up to about 10 min (including heating time), Ni-rich metallic particles precipitated in the lower part of the metastable Al2O3 layer, due to a decrease in the oxygen potential resulting from scale evolution. The present results indicated that the period of oxide phase transformation was followed by the establishment of steady-state oxidation kinetics. However, the steady-state kinetics were different for the two alloy systems. Specifically, after complete phase transformation to α-Al2O3, rapid growth of oxide grains occurred on the Hf-free alloy; whereas, the oxide grain size remained small for the Hf-containing alloy. Such a difference of transformation and subsequent grain-growth behavior greatly affected oxide thickening kinetics.

Microstructure and room temperature mechanical properties of Hf and Sn-doped Nb-20Ti-5Cr-3Al-18Si alloy

Abstract In this paper, the effects of Sn and Hf additions on microstructures and room temperature mechanical properties of Nb-20Ti-5Cr-3Al-18Si alloy were investigated. The Sn addition has no significant effect on the microstructure of the alloy. Sn is preferentially partitioned in (Nb, Ti)ss rather than (Nb, Ti)5Si3. The addition of Sn decreases the solubility of Cr in (Nb, Ti)ss. The addition of Hf causes coarsening of the eutectic structure of (Nb, Ti)ss and (Nb, Ti)5Si3 and the formation of the Hf-rich γ(Nb, Ti)5Si3 along phase boundaries. With the addition of Sn the strength of the alloy decreases, while its ductility increases slightly. The Hf addition simultaneously improves strength and ductility of the alloy. The relationships between composition, microstructure and properties are discussed.

FeCrAl Alloys Produced by Roll-Bonding and Annealing of Al(RE)-Clad Stainless Steel: How Addition of Hf and Zr Affects their Oxidation Behaviour

The process involving cold rolling and annealing of Al-steel-Al sandwiches allows to produce an alloy containing more than 7 wt.% of Al. Unfortunately many α-Al2O3 scales tend to spall during thermal cycling because of thermal expansion mismatch between the alloy and the scale. Small additions to the ferritic stainless steel of oxygen reactive elements are known to improve the adhesion of α-Al2O3 scales. In this work hafnium and zirconium were added to the aluminium foil before roll bonding and their behaviour during the diffusion bonding was evaluated. This novel doping method was proven to be effective in improving scale adhesion and alloy lifetime. Moreover it allows to overcome problems related to steel alloying with reactive elements and reduces the quantity of expensive reactive elements that needs to be added to the steel foil.

Soft magnetic properties and glass formability of Y–Fe–B–M bulk metals (M = Al, Hf, Nb, Ta, and Ti)

The glass formability, magnetic properties and thermal stability of the Y–Fe–B–M bulk metals (M = Al, Hf, Nb, Ta, and Ti) alloys have been investigated. For (Y 0.06Fe 0.72B 0.22) 98M 2 series alloys, Al or Hf addition deteriorates the glass forming ability (GFA), but Nb or Ta addition broadens supercooled region from 50.2 °C for ternary rod to 61.5 °C for M = Ta and 62 °C for M = Nb, respectively. The bulk glassy rod as large as 3 mm in diameter can be obtained. However, their magnetization and Curie temperature are reduced due to the magnetic dilution by the addition of these nonmagnetic elements. On the other hand, for Y 4Fe 72B 22M 2 series alloys, almost all the substitution elements, except Al, can improve GFA of alloy rod, making the diameter of bulk glassy rod as large as 3 mm for Ti or Hf substitution and 4 mm for Ta or Nb substitution, respectively. It is arisen from the further expansion of the supercooled region to 70.4–84.2 °C. In this study, Y 4Fe 72B 22Ta 2 amorphous rod displays the optimal glass forming ability and also good soft magnetic properties of σ s = 123 emu/g, H c = 0.2 Oe, and T C = 276 °C.

A new and highly efficient formaldehyde absorbent of polyoxymethylene

AbstractA new type of highly efficient formaldehyde (FA) absorbent of polyoxymethylene (POM), hexamethylenediamine–formaldehyde polycondensates (HF) was prepared by the condensation reaction of hexamethylenediamine (HA) and FA. The effects of the synthetic technique including FA/HA molar ratio, reaction temperature and dispersant dosage on the thermal stability of POM/HF were studied, and finely divided, slightly branched HF polycondensates with high molecular weight and relatively high processing thermal stability were obtained. The thermal stabilization effect of HF on POM was studied through the isothermal weight loss analysis, FA emission amount (FEA) measurement, and balance torque analysis, which showed that HF had better thermal stabilization effect on POM than the commonly used FA‐absorbent melamine (MA). In order to improve the crystallization performance and mechanical properties of POM, the nucleation effect of HF on POM was studied by means of polarized light microscopy (PLM), isothermal and nonisothermal differential scanning calorimetry (DSC), indicating that HF had remarkable nucleation effect on POM. The investigation of mechanical properties showed that the addition of HF could improve the impact toughness of POM to a certain degree. Copyright © 2008 John Wiley & Sons, Ltd.

Subcontinental lithospheric mantle origin of high niobium/tantalum ratios in eclogites

Eclogites have been suggested as high niobium/tantalum reservoirs that complement the low niobium/tantalum ratios of the silicate Earth. However, the hafnium isotopic composition of eclogite fragments suggest that the high niobium/tantalum signature of eclogites is unlikely to be primary. Instead, it probably reflects chemical modification during residence in the subcontinental lithospheric mantle. Ratios of non-volatile elements such as zirconium, niobium (Nb) and tantalum (Ta) in the unfractionated Earth are commonly assumed to be similar to those in the class of meteorites known as chondrites1. However, the Nb/Ta ratio of the Earth’s major silicate reservoirs—the crust and mantle—is subchondritic, hinting at the existence of a complementary reservoir with high Nb/Ta (refs 2, 3). Eclogites, which are high-pressure metamorphic rocks that often form in subduction zones, can contain the mineral rutile (titanium dioxide) with high Nb/Ta. They have therefore been inferred to constitute this complementary reservoir2. More recent evidence from natural samples, however, suggests that residual eclogites have low Nb/Ta, which is confirmed by experiments3,4,5,6. Here, we present the Nb and Ta concentrations and hafnium (Hf) isotope compositions of rutiles from eclogite fragments that were entrained from the subcontinental lithospheric mantle in kimberlite melts. Rutiles with high 176Hf/177Hf ratios generally have subchondritic Nb/Ta (<19.9 (refs 3, 7)), similar to undisturbed melt residues of broadly basaltic precursors. On the other hand, rutiles with suprachondritic Nb/Ta ratios have low 176Hf/177Hf, suggesting Hf addition from a fluid or melt ultimately derived from ancient (≥2.9 Gyr), chemically modified (metasomatized) subcontinental lithospheric mantle, which has similarly low 176Hf/177Hf (ref. 8). Our results suggest that eclogites are unlikely to represent the high Nb/Ta reservoir; instead, the high Nb/Ta signatures of some eclogites are probably generated by metasomatism during long-term residence in the subcontinental lithospheric mantle.

Effectiveness of platinum and iridium in improving the resistance of Ni‐Al to thermal cycling in air–steam mixtures

AbstractThe aim of this work was to assess the value of platinum and iridium additions, with and without hafnium, to binary Ni‐Al alloys, intended to act as models for aluminide coatings. Attention was focused on a (γ + γ′) Ni‐22Al alloy, but comparisons were made withβ‐Ni‐50Al. All compositions are given in at%. Alloys were exposed to flowing gases at a total pressure of 1 bar for one thousand 1 h cycles at 1200 °C. Compared to binary Ni‐Al alloys, the Pt‐modified alloys performed much better (with or without Hf) in dry air. Thermal cycling in air + 12% H2O led to more rapid weight losses, due to enhanced spalling. Again, the addition of Pt was beneficial, but weight losses were still significant in the absence of Hf additions. A Ni‐22Al‐15Pt + Hf alloy slowly lost weight by scale spallation over 1000 cycles, but a Ni‐22Al‐30Pt + Hf alloy resisted weight loss. Partial substitution of Ir for Pt was beneficial in both wet and dry air. However, in the case of wet air, Hf additions were necessary to prevent slow spallation losses.

Biocompatibility of uncoated and diamond-like carbon coated Ti–20%Hf alloy

Biocompatibilities of uncoated and diamond like carbon (DLC) coated Ti–20%Hf alloy have been investigated by means of 3T3 mouse fibroblast cell viability quantification using flow cytometry. For comparison, similar tests were performed for pure Ti, Hf, and V as well as a commercial orthopaedic alloy, Ti–6Al–4V. Under the test conditions used, the biocompatibilities of uncoated and DLC coated Ti–20%Hf alloy, pure Hf, and Ti–6Al–4V alloy were comparable to that of pure Ti, a metal known for its superior biocompatibility, while pure V clearly exhibited the lowest biocompatibility of all the materials that were evaluated. The addition of Hf to Ti resulted in significant solid solution strengthening and at 20%Hf concentration the hardness of this alloy was comparable to that of the Ti–6Al–4V alloy. Ti–Hf alloys and wear resistant, low friction DLC coatings may either be used in conjunction with or may independently hold promise for orthopaedic implants and possibly other biomedical applications.

Mechanical properties of ternary molybdenum–rhenium alloys at room temperature and 1700 K

Molybdenum–rhenium alloys have a lower ductile-to-brittle transition temperature than molybdenum, which is advantageous in applications requiring improved room temperature ductility or impact toughness. However, at high temperatures rhenium strengthens molybdenum only slightly. This work screens the effect of alloying additions of Ti, Nb, Ta, and Hf on the room temperature ductility and high temperature strength of Mo–26 at.% Re (Mo–40.5 wt.% Re). Hafnium is found to be a particularly effective high temperature strengthener.

Microstructure and room temperature fracture toughness of cast Nbss/silicides composites alloyed with Hf

The effect of Hf addition on microstructure and room temperature fracture toughness of cast Nb-16Si alloy was investigated. The Hf addition changes significantly the microstructural morphology of Nb-16Si alloys, which includes microstructure refinement and disappearance of eutectic colonies. Fracture toughness of the alloys improves with increasing Hf content. The improvement in fracture toughness is mainly attributed to the microstructural change by Hf addition. The Hf addition leads to a transition of Nb solid solution fracture manner from brittle cleavage to plastic stretching.

β-Ti( M) solid solution formation and its thermal stability in a NiAl–Cr(Mo)–(Hf,Ti) near eutectic alloy

The effects of combined additions of Ti and Hf to NiAl–Cr(Mo) eutectics on the as-cast microstructure and its thermal stability are investigated through SEM, EDS and TEM, with focus on the formation mechanism of β-Ti( M, M = Hf,Cr,Ni) solid solution phase and its thermal stability after short-term heat treatment. The results show that, due to the presence of large concentrations of β-phase forming and stabilizing elements dissolved into the Ti solid solution phase during solidification, the thermodynamically metastable β-phase was preserved at room temperature. With respect to its thermal stability, within the experimental range examined, the β-Ti( M) solid solution phase, is not influenced. From the practical application point of view, this β-Ti( M) solid solution phase may offer application as a strengthening phase for the design of NiAl–Cr(Mo)–Hf based alloys.

Effects of incorporation of Si or Hf on the microstructure and mechanical properties of Ti–Al–N films prepared by arc ion plating (AIP)

Ti–Al–N, Ti–Al–Si–N and Ti–Al–Hf–N films were deposited on 1Cr11Ni2W2MoV stainless steel by arc ion plating (AIP) with a Ti 70Al 30, a Ti 60Al 30Si 10 and a Ti 68Al 30Hf 2 cathode, respectively. The effects of Si or Hf addition on the composition, microstructure and mechanical properties of the Ti–Al–N films were investigated by EPMA, TEM, SEM, XRD, micro-hardness and wear tests. The results show that all the deposited films possessed B1 structure. With the incorporation of Si or Hf, the texture of Ti–Al–N films remarkably changed from preferred orientation of (220) to mixture broadened orientations of (111), (200) and (220), the mean crystallite size of Ti–Al–N decreased from ~ 90 nm to ~ 30 and ~ 15 nm and no peaks of crystalline Si 3N 4 were detected from XRD analyses. Due to the addition of Si or Hf, the micro-hardness of Ti–Al–N films increased remarkably from 23.5 Gpa to 33.6 or 29.5 GPa, and the wear resistance was also enhanced. The effects of incorporation of Si or Hf on the microstructure and mechanical properties of Ti–Al–N films are discussed.

Thermodynamic modeling and experimental investigation of the Ni-rich corner of the Ni–Al–Hf system

Ni-based superalloys with the addition of Hf show promising oxidation resistance and exhibit further improvements in thermal barrier coating (TBC) lifetime. To understand the beneficial effects of Hf on oxidation resistance, it is essential to have phase equilibrium information for some key ternaries, such as Ni–Al–Hf. The phase relationships in the ternaries and multi-component systems serve as a roadmap for alloy design and processing control. In this study, the phase constituents of selected Ni-rich Ni–Al–Hf ternary alloys and their microstructures were investigated in both as-cast and long-term annealed states using SEM, XRD and EPMA. A thermodynamic description of the Ni–Al–Hf system was developed based on those of the constituent binaries and ternary experimental data obtained in the present study as well as those reported in literature. The calculated liquidus projection and isothermal sections at 1273, 1403 and 1433 K are in accord with the experimental results.

A New Synthesis of Trifluorinated Compounds via 1,1‐Dichloro‐1‐alkenes in Superacid.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Corrosion Behavior of Zirconium Based Alloys in Simulated Body Fluids

The corrosion behavior of Zr-Ti and Zr-Hf alloys with various concentrations in properly deaerated Hanks’ solution were investigated by electrochemical techniques. The effects of the thermal treatment with the purpose of homogenization of chemical composition on the pitting potentials of the Zr-Ti alloys were also examined. The results indicated that sufficient addition of Ti to Zr improved its corrosion resistance, especially in terms of the pitting potential and the passive current density. On the other hand, addition of Hf totally lowered the corrosion resistance of the alloy. The thermal treatment improved the pitting corrosion property of Zr-Ti alloys, and Zr alloys with over 5mol% Ti showed much higher pitting potentials than that of pure Zr. The treatment also improved the reproducibility of the measurement and narrowed the data scattering. This phenomenon was discussed with the model of rapidly-cooled metallographic structure.

Electrochemical deposition of Te and electroless deposition of Se nanoparticles in etched tracks of Au + ions in SiO 2 layer on n-Si(1 0 0) wafers

The techniques for Te electrodeposition and Se electroless deposition into nanoporous SiO 2 layer on n-Si(1 0 0) substrate are developed. To produce a porous SiO 2 layer, scanned beams of 400 MeV Au + ions are employed for the bombardment of silicon oxide thermally grown on Si(1 0 0) substrate. Pores are formed by chemical etching of the irradiated SiO 2 layer in dilute HF. Etching results in the formation of the uniform pores randomly distributed over the surface and shaped like truncated cones with base diameters of 100 and 250 nm. Electrodeposition of Te into nanopores of SiO 2 layer takes place at potentials below the silicon flat band potential. Te electrodeposited selectively into the nanopores – deposition on insulating SiO 2 layer – is excluded. Electrodeposition of Se into nanopores takes no place due to Se reduction to H 2Se. Chemical interaction of H 2Se and H 2SeO 3 in the solution leads to the formation of roundish Se particles on SiO 2 surface near the pores. Precipitation of Se into nanopores is realized by electroless deposition from SeO 2 solution with addition of HF.

Study of EETMOS hydrolysis and polycondensation by 29Si NMR spectroscopy. Application to optical 3D waveguides fabrication

In the last few years, ORganically MOdified SIlicates R x Si(OR) 4− x (ORMOSIL) prepared by the sol–gel process were particularly attractive for the making of integrated optics. A composition based on 3-(trimethoxysilyl)propylmethacrylate (MAPTMS) has already allowed the industrial manufacturing of optical integrated devices. For this kind of material, the polymerization of the organic network is based on free radical curing under UV laser exposure. This type of polymerization has some disadvantages, in particular, it is inhibited by oxygen. To optimize the final properties, we tried to obtain waveguides with another hybrid precursor [2-(3,4 epoxycyclohexylethyltrimethoxysilane)] (EETMOS) using cationic polymerization. The main advantage of cationic polymerization is its ability to allow cure reaction in the presence of oxygen, unlike radical polymerization. We have chosen cycloaliphatic compounds because of their well known high polymerization rates. The polymerization of the organic network of this hybrid material requires a cationic photoinitiator corresponding to our LASER writing wavelength ( λ = 262 nm). In this work, hydrolysis and polycondensation of EETMOS-based solution are followed by 29Si NMR. The main objective is to obtain the highest reactive multifunctional oligomer with the lowest OH groups content. The effects of pH, hydrolysis rate, HF and photoinitiator additions are studied in order to obtain the most optimized solution. Based on our results, we obtained 3D waveguides with a cross section of 5 × 5 μm 2.

Isothermal Oxidation Behavior of a Cast Ni3Al-Base Superalloy MX 246A

Abstract The oxidation behavior of a cast Ni 3 Al-base superalloy MX246A in air over the temperature range of 1000°C to 1200°C for period up to 100h has been studied. The results indicate that the average oxidation rate of MX246A containing 0.5Hf and 0.01 Y additions is as low as 0.0639g/m 2 ·h under the condition of 1100°C./100h, while the undoped alloy MX246 is 0.2683 g/m 2 ·h. An analysis of structure of the surface oxidation scales through X-ray, and a research into the microstructure and composition of the oxide by means of a scanning electronic microscope with an EDAX unit. The results show that oxidation scale are composed of besides NiO NiAl 2 O 4 and NiCr 2 O 4 . as well as a considerable quantity of α-Al 2 O 3 . The results also show that the addition of Hf and Y into MX246A significantly improves the oxidation resistance property of the alloy. Hf is effective mainly in the formation of HfO 2 which is more stable in the strengthening of adhesion between the oxidation layer and the substrate, while Y restrains the segregation of Sulfur on the oxidation scale/substrate interface, as well as changing the morphology and composition of the oxidation scale, the degree of inner oxidation and the diffusion layer.

Effection of Alloying Elements on Microstructures of MX 246 and MX 246A Ni3Al-Based Alloys

The effects of alloying elements on microstructure of two compositions of Ni3Al-based alloys, MX 246 and MX 246A have been studied in this article. The results show that “starburst” γ - eutectic phases are large and their amount is about 18% in MX246. Majority NiZr and a little of ZrC are formed in the boundaries of γ - eutectic phases. Microstructure at 1200°C shows that NiZr phases have been melted completely, which cause the decrease of melting point of phases to about 1125°C. With increasing alloying additions such as Mo and Hf. γ - eutectic phases are dispersive, uniform, small, and their amount is decreased to about 4%. Carbides and borides are formed in MX246A. The volume fractions of the phases in MX246A and the chemical compositions of the phases have been quantitatively analyzed. The results show that carbides and borides are about 1.12% in MX246A and the main carbides are TiC. HfC and the borides are (Ni0.086Cr0.08/Wa0.094Mo0.376Ti0.334 Hf0.024) 3B2. TEM observation results show that with increasing alloying element additions such as Mo and Hf, a lot of γ - interface misfit dislocations are produced in the interface of γ and phase and they are interacted with the nanometer particles. phases are all stable in MX246A at 1200°C. The stability of phase is increased with the addition of Mo and Hf. In addition, there are many white spot phases which are mainly NiMo phases, and a little (NiMo)6C and (MoTi)6C gathering in some interdendrite areas.