Addition Of HF Research Articles

Microstructure, mechanical properties and oxidation resistance of (Zr, Hf)Nx coatings by magnetron co-sputtering

This study investigates the influence of Hf addition to the microstructure, mechanical properties and oxidation resistance of ZrN coating. (Zr, Hf)Nx coatings with 0–4.2at.% Hf were fabricated by reactive co-sputtering in an Ar–N2 atmosphere. The solid solution-type (Zr, Hf)Nx coatings exhibit a dense and columnar structure with strong (2 0 0) preferred orientation, independent of Hf content. Abnormal grain growth was observed in the coatings with improved Hf content. The highest recorded hardness is 28.6±0.6GPa with 0.5at.% Hf addition, whereas further increasing the Hf content up to 4.2at.% decreases the hardness. The oxidation results demonstrate that the most beneficial content of Hf to improve the oxidation resistance of the ZrN coating is 1.2at.%. Reduction in inward diffusion paths for oxygen ions, the increase of stoichiometry and the high thermal stability of HfN have been identified as the primary reasons for the improvements of the oxidation resistance.

L12-Strengthened Cobalt-Base Superalloys

The discovery of the γ′-Co3(Al,W) phase with an L12 structure provided Co-base alloys with a new strengthening mechanism, enabling a new class of high-temperature material: Co-base superalloys. This review discusses the current understanding of the phase stability, deformation, and oxidation behaviors of γ′ single-phase and γ + γ′ two-phase alloys in comparison with Ni-base γ′-L12 phase and γ + γ′ superalloys. Relatively low stacking fault energies and phase stability of the γ′ phase compared with those in Ni-base alloys are responsible for the unique deformation behaviors observed in Co-base γ′ and γ + γ′ alloys. Controlling energies of planar defects, such as stacking faults and antiphase boundaries, by alloying is critical for alloy development. Experimental and density functional theory studies indicate that additions of Ta, Ti, Nb, Hf, and Ni are effective in simultaneously increasing the phase stability and stacking fault energy of γ′-Co3(Al,W), thus improving the high-temperature strength of Co-base γ′ phase and γ + γ′ two-phase superalloys.

Thermal Properties of Hf‐Doped ZrB2 Ceramics

The effect of Hf additions on the thermal properties of ZrB2 ceramics was studied. Reactive hot pressing of ZrH2, B, and HfB2 powders was used to synthesize (Zr1−x,Hfx)B2 ceramics with Hf contents ranging from x = 0.0001 (0.01 at.%) to 0.0033 (0.33 at.%). Room‐temperature heat capacity values decreased from 495 J·(kg·K)−1 for a Hf content of 0.01 at.% to 423 J·(kg·K)−1 for a Hf content of 0.28 at.%. Thermal conductivity values decreased from 141 to 100 W·(m·K)−1 as Hf content increased from 0.01 to 0.33 at.%. This study revealed, for the first time, that small Hf contents decreased the thermal conductivity of ZrB2 ceramics. Furthermore, the results indicated that reported thermal properties of ZrB2 ceramics are affected by the presence of impurities and do not represent intrinsic behavior.

Corrosion behavior of NdFeB sintered magnets in HNO3–HF acid mixture solution

Corrosion behavior of NdFeB magnet in HNO3–HF solutions was investigated using open circuit potential and polarization measurements and impedance technique. Results showed that the additions of HF increased open circuit potential, corrosion potential and film/inductive/charge transfer resistance, but decreased corrosion current density of magnet. The HF effects on the corrosion performance were closely related to the formation of NdF3 corrosion products on magnet surface, in turn which depended on its content. Also the corrosion mechanism of magnet was discussed on the basis of structural observation, composition and EIS analyses.

Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition

The low thermal stability of nanocrystalline metals severely limits their applications at high temperatures. In this study, we investigate the nanocrystalline stabilization mechanisms for Fe-14Cr alloys with 1, 2, and 4 at. pct Hf addition at 1173 K (900 °C). Microstructural characterizations using aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal high density of HfO2 nanoparticles with sizes of ~4 nm dispersed throughout the ferritic matrix. This indicates that kinetic stabilization by HfO2 nanoparticle pinning is primarily responsible for the observed high thermal stability. In addition, some Hf and Cr segregation on grain boundaries is observed in the Fe-14Cr-4Hf, suggesting the existence of thermodynamic stabilization at high Hf content. Second-phase precipitations such as hafnium carbide, M23C6, and Fe-Cr-Hf intermetallic phase are also found in the Fe-14Cr-4Hf, but their large sizes and inter-spacing suggest that their contribution to stabilization is minimal.

Microstructural characteristics of Nb–Si based ultrahigh temperature alloys with B and Hf additions

Four Nb–Si based ultrahigh temperature alloys with compositions of Nb-22Ti-16Si-5Cr-3Al-mHf-nB ((m, n) = (0, 0), (0, 2), (4, 0) and (4, 2), respectively) (at.%) were prepared by vacuum non-consumable arc melting and then heat-treated at 1450 °C for 50 h. The effects of B and Hf additions on the phase selection, phase stability, microstructure and microhardness of these alloys under both as-cast and heat-treated conditions have been investigated. The results show that the microstructures of all the four alloys are composed of primary silicide blocks, Nbss dendrites together with one or two types of eutectic colonies around. However, the crystal structures of silicides, types of eutectic and amounts of constituent phases have obviously varied with B or Hf addition. Moreover, a low melting point three-phase eutectic is also observed in Hf-containing alloys. After 1450 °C/50 h heat-treatment, the microstructural uniformity of the alloys has been significantly ameliorated as well as their equilibrium phases have been basically obtained, and also some phase transformation reactions have occurred. The microhardness of the constituent phases present in the alloys is dependent on their types or crystal structures.

Oxidation behaviour of electron beam physical vapour deposition β-NiAlHf coatings at 1100 °C in dry and humid atmospheres

NiAl intermetallic compounds attract increasing attention for high-temperature applications due to their combination of excellent properties, especially as metallic protective coatings on superalloys or as bond coats in thermal barrier coatings (TBCs). Oxidation behaviour of the β-NiAlHf coatings prepared by electron beam physical vapour deposition (EB-PVD) was investigated at 1100 °C for short time and 100 h in 20 % O2 + Ar and 15 % H2O + Ar, respectively. The results of mass changes reveal that the addition of minor reactive element Hf significantly improves the cyclic oxidation resistance of the β-NiAl coatings in both dry and humid atmospheres. During the initial oxidation stage, water vapour retards the phase transformation from θ-Al2O3 to α-Al2O3. Moreover, compared with the case in dry atmosphere, water vapour significantly reduces the surface roughness of the oxide scales formed on EB-PVD β-NiAlHf coatings after 100 h cyclic oxidation, which corresponds with the difference of surface morphologies of the oxide scales.

Electrochemical Explorations of 9,10-Anthraquinone/Hafnium(IV) Ion Interactions in Nonaqueous Solvents

Introduction The well-defined electrochemical behavior of quinones such as 9,10-anthraquinone (AQ) in nonaqueous solvents (1,2) suggests its use as a probe for interactions of metal cations with the AQ carbonyl oxygens. In previous work from this laboratory, the interaction of AQ with added Al(III) trifluoromethanesulfonate [Al(TfO)3] in adiponitrile has been shown to produce a shift in the initial AQ reduction process to more positive potentials (3). In contrast to the behavior seen for 9-fluorenone (4), however, the second AQ reduction process disappears even at the 0.4 : 1.0 Al3+ : AQ point. This observation suggests that AQ reduction products are good ligands for the Al3+ cation, with approximately three reduced AQ ligands coordinated to one Al3+. The present work explores whether this effect extends to other metals, particularly Hf4+. The general effect of Hf4+ on the cyclic voltammetry of AQ in adiponitrile is also treated. Experimental Adiponitrile (AN) and 9,10-anthraquinone (AQ) were obtained from Aldrich Chemical Co. Hafnium trifluoromethansulfonate [hafnium triflate, Hf(TfO)4] was obtained from Alfa-Aesar. Tetraethylammonium tetrafluoroborate [TEA BF4] was purchased from Southwestern Analytical Chemicals (SACHEM). Voltammograms were acquired with a PAR283 potentiostat using PowerSuiteTM software. Potentials are reported with respect to a Ag/AgCl (0.1M EMICl in EMI BF4) reference electrode (Cypress Systems). Vitreous carbon electrodes were obtained from Cypress Systems. All experiments were carried out in a Vacuum Atmospheres drybox. Results and Discussion A cyclic voltammogram of AQ in adiponitrile without added Hf(TfO)4 is shown in Figure 1a, which shows the usual two uncomplicated successive one-electron transfers. Upon addition of Hf(TfO)4 at the 0.4 : 1.0 Hf4+ : AQ level, however, a substantial positive potential shift is observed for AQ reduction (Figure 1b). This shift is due to complexation of one of the AQ carbonyl oxygens by Hf4+. As in the case of Al3+ addition, there is none of the original second AQ redox process at this point. This observation implies that Hf4+ is complexed by multiple AQ reduction products, as was also seen for Al3+ addition. Further additions of Hf(TfO)4 give only the shifted reduction process at the 1:1 Hf4+ : AQ point, with substantially more of the small reduction peak at +0.1 V in Figure 1b. The latter observation suggests the possibility that both AQ carbonyl oxygens can undergo complexation by Hf4+ in this system. The present results indicate extensive interaction of Hf4+ with AQ, including the role of reduced AQ species as multiple ligands for Hf4+. References N. A. Macıas-Ruvalcaba and D. H. Evans, J. Phys. Chem. C, 114 , 1285 (2010).L. Jeftic and G. Manning, J. Electroanal. Interfacial Echem, 26, 195 (1970).Electrochemical Society 226th Meeting, Fall 2014, Cancum, Mexico, ECS H1-1345.D. Canby, E. Sanders,and G. T. Cheek, J. Electrochem. Soc., 160(7), G3159 (2013). Figure 1

Effect of Boron Addition on Oxide Scale Formation of Ni-Base Superalloys

Ni-base superalloys are commonly used as construction materials for high temperature components e.g. in the hottest sections of aero engines and industrial gas turbines due to a combination of excellent creep and high-temperature oxidation resistance at elevated temperature. Apart from major alloying elements such as Cr, Co, Al, Mo, W, Ti, modern Ni-based superalloys contain minor (between 0.01 and 1 at.%) additions of elements such as Hf, Zr or B for obtaining improved mechanical properties, in particular grain boundary strengthening. However, these minor elements also form thermodynamically very stable oxides and can therefore participate in the oxidation process. Whereas several investigations are available on the effect of Hf and Zr additions on the oxidation behaviour of high temperature alloys, hardly any publications deal with studies related to the effect of B additions on oxide formation mechanisms. In the present investigation the air oxidation behaviour of two commercially available B containing Ni base alloys (Rene80, CM247) was studied at temperatures in the range 850°C to 1050°C. After various exposure times up to 100h the oxidized samples were investigated with a number of analysis methods, including glow discharge optical emission spectroscopy (GD-OES), optical and scanning electron microscopy (SEM combined with EDX/WDX and EBSD) as well as X-Ray diffraction. B was found to become incorporated into the oxide scale whereby the participation in the oxidation process strongly depended on alloy composition. The oxidation of B resulted in its depletion from the bulk alloy and was found to be dependent on the exposure conditions, being stronger at higher exposure temperatures and longer exposure times. A modelling approach is presented to correlate B incorporation in the surface oxidation process with its depletion in the bulk alloy.

Effects of Cr and Hf additions on the microstructure and properties of Nb silicide based ultrahigh temperature alloys

Four Nb silicide based ultrahigh temperature alloys with compositions of Nb–22Ti–16Si–3Al–2B–xHf–yCr ((x, y)=(0, 0), (0, 5), (4, 0) and (4, 5)) (at%) were prepared by vacuum non-consumable arc melting. The effects of Cr and Hf additions on the phase selection, microstructure, room-temperature fracture toughness and oxidation resistance at 1250°C of the alloys have been investigated. The results show that all the four alloys are comprised of primary silicides and Nbss dendrites together with one or two types of eutectic. The Cr addition does not change the crystal structures of 5-3 silicides but imposes a significant influence on the amount, size and morphology of the constituent phases. The Hf addition suppresses the formation of α(Nb,X)5Si3 but promotes the formation of γ(Nb,X)5Si3. The combined additions of Cr and Hf also cause the formation of Cr2(Nb,X) containing three-phase eutectic. The room-temperature fracture toughness of the alloys decreases with Cr addition while increases with Hf addition. The oxidation-resistant performance of the alloys has been ameliorated by Cr addition, while it has been significantly degraded by Hf addition in the absence of Cr. Furthermore, the formation mechanism of the scale has been illustrated.

Influence of Hf solute additions on the precipitation and hardenability in Ni-rich NiTi alloys

Very Ni-rich NiTi alloys have recently been shown to have an unusually high hardness, comparable to tool steels, and other attributes that make them promising candidates for bearing and related applications. This high hardness has been associated with the precipitation of a large volume fraction of Ni4Ti3 platelets, resulting in a matrix that consists of narrow B2 matrix channels. In this work, a series of Ni-rich ternary alloys with dilute solute additions of Hf (54Ni–45Ti–1Hf, 55Ni–44Ti–1Hf, 54Ni–44Ti–2Hf, and 56Ni–40Ti–4Hf (at.%)) have been investigated. Transmission electron microscopy confirmed a B2 NiTi matrix phase containing nanoscale Ni4Ti3 platelets, H-phase precipitates, and R-phase; however, the H-phase and R-phase were not present initially but only after aging for a period of time. At aging times greater than ∼100h at 400°C, all ternary alloys showed a slight secondary increase in hardness, which was attributed to H-phase precipitation and growth within the B2 channels. In the particular case of the 56Ni–40Ti–4Hf alloy, hardness increased with aging to a maximum value of 679VHN, which was greater than all other binary or ternary alloys examined. Additionally the H-phase appeared to alter or delay the typical breakdown sequence of the metastable Ni4Ti3 strengthening phase by removing the excess Ni needed for its decomposition. The collective results provide new material insights for creating a next-generation NiTi based bearing alloy.

Interaction between Nb-Silicide Based Alloys and Y<sub>2</sub>O<sub>3</sub> Crucible

Y2O3 crucibles have been prepared for as-cast Nb-22Ti-16Si-2Al-2Cr-2Hf and Nb-22Ti-16Si-2Al-2Cr alloys at 1950 °C. The microstructures, metal-crucible interfaces and contaminations were evaluated. Experimental results demonstrated that a mild interface reaction occurred between the Y2O3 crucibles and Hf, resulting in some inclusions dispersed in the metallic matrix. However, without Hf addition, no apparent reaction layers or inclusions were found. Both alloys were slightly contaminated with oxygen as the result of slow thermal dissociation of Y2O3, and its extent depended on Hf contents and holding times.

Key Steps Influencing the Formation of Aluminosilicate Nanotubes by the Fluoride Route

AbstractImogolite is usually formed by means of a three-step process involving the use of large amounts of water with long crystallization times and low yields, preventing large-scale synthesis. These drawbacks can be overcome by synthesis in the presence of fluoride, an approach which has been demonstrated to be suitable for the synthesis of other phyllosilicates. In the present study, the nature of the Al and Si sources, the Al/Si molar ratio, the volume of H2O for the redispersion of the gel after desalination, the F/Si molar ratio, as well as the crystallization temperature and time have been varied to investigate their role in the crystallization of imogolite. The structural properties of the as-synthesized samples were characterized by X-ray diffraction, infrared spectroscopy, and 29Si, 27Al, and 19F magic angle spinning nuclear magnetic resonance spectroscopy. The results show that the imogolite nanotubes can be prepared with high yields (>55%) from AlCl3·6H2O and Na4SiO4 aqueous solutions with an Al/Si molar ratio of 2.5, addition of HF for a F/Si molar ratio of 0.1–0.2, and 4 days of crystallization at 98°C.

Optimized extraction of a single-chain variable fragment of antibody by using aqueous micellar two-phase systems

In this work, the purification of a single-chain variable fragment (scFv) of an antibody by using liquid–liquid extraction in aqueous micellar two-phase systems was optimized by means of central composite design. Protein partitioning assays were performed by using the selected system composition in previous works: Triton X-114 at 4% wt/wt, yeast fermentation supernatant at 60% wt/wt, McIlvaine buffer pH 7.00. The other system component concentrations, Cibacron Blue F3GA (CB), Fabsorbent™ F1P HF (HF) and NaCl, were selected as independent variables. ScFv recovery percentage (%R) and purification factor (PF) were selected as the responses. According to the optimization process both, scFv recovery percentage and purification factor were favored with the addition of HF and NaCl in a range of concentrations around the central point of the second central composite design (HF 0.0120% w/w, CB 0.0200% w/w, NaCl 0.200% w/w). These experimental conditions allowed the concentration and pre-purification of scFv in the micelle-rich bottom phase of the systems with a recovery percentage superior to 88% and a purification factor of approximately 3.5. These results improved the previously presented works and demonstrated the convenience of using aqueous micellar two-phase systems as a first step in the purification of scFv molecules.

Synthesis, structural characterisation and antibacterial activity of Ag+-doped fluorapatite nanomaterials prepared by neutralization method

Silver doped fluorapatite nanopowders were synthesised by neutralization method, which consists of dissolving Ag2O in solution of HF and H3PO4 and addition to suspension of Ca(OH)2. The powder XRD, SEM and FTIR studies indicated the formation of a fluorapatite nanomaterials with average length of the particles is about 80nm and a width of about 15nm. The FTIR studies show that carbonate content in samples is very small and carbonte ions substitute both phosphate and hydroxyl groups in the crystal structure of samples, forming AB-type fluorapatite. Antibacterial studies have demonstrated that all Ag+-doped fluorapatite samples exhibit bactericidal effect against pathogens: Staphylococcus aureus, Micrococcus luteus and Kllebsiela pneumoniae. Antibacterial activity increased with the increase of Ag+ in the samples. The atomic force microscopy studies revealed extensive damage to the bacterial cell envelops in the presence of Ag+-doped fluorapatite particles which may lead to their death. The synthesized Ag+-doped fluorapatite nanomaterials are promising as antibacterial biomaterials in orthopedics and dentistry.

ChemInform Abstract: The Direct anti‐Markovnikov Addition of Mineral Acids to Styrenes.

AbstractEfficient procedures are elaborated for the anti‐Markovnikov addition of HCl, HF, phosphoric acids, and sulfonic acids, to alkenes in the presence of a photoredox catalytic system containing an acridinium sensitizer.

Synthesis and characterization of pure STW-zeotype germanosilicate, Cu- and Co-substituted STW-zeotype materials

Pure STW-type germanosilicate (denoted as GeSi-STW), Cu- and Co-containing STW-zeotype (denoted as Cu-STW and Co-STW) materials were synthesized by the hydrothermal method in the presence of an organic structure-directing agent (OSDA), N,N-diethylethylenediamine (DEEDA). The effects of the reaction mixture ratio and the incorporation of transition metals M (M=Cu and Co) on the synthesis of the pure product was investigated. The synthesized samples were characterized by powder and single-crystal X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma analysis (ICP), thermogravimetric and differential scanning calorimetry (TG–DSC) analysis and UV–vis diffuse reflectance spectra (DRS). The results reveal that the crystallization time, the concentration of H2O in the reaction mixture and the addition of HF all have an important impact on the synthesis of pure STW-type zeolite. GeSi-STW is stable up to 800°C, and has much higher thermal stability than SU-32 (stable to 400°C). Co and Cu have been introduced for the first time into STW-zeotype materials.

Structural phase transformations and shape memory effect in ZrCu along with Ni and Hf additions

Ni replacement of Cu in ZrCu high temperature shape memory alloy results in the increase of the temperatures of the martensitic transformation (MT) [1]. Once the Ni content reaches 20 at.%, the temperatures of MT are becoming higher than the temperature of crystallization of the amorphous alloy with the same composition [2] and crystallization from the amorphous state in this case takes place through formation of B19` phase without any visible signs of the nanoscale phase separation. In this regard, little is known about the influence of Hf additions onto phase transformations in ZrCu. The present work is dedicated to the study of structure and phase formation upon alloying of ZrCu by Ni and Hf by means of structural and thermal analysis. Their influence onto shape memory behavior will be discussed.

Control synthesis and formation mechanism of sphere‐like titanium dioxide

Using a simple hydrothermal method without surfactants and templates, different morphologies of titanium dioxide (TiO2) have been synthesised such as nanocubes, nanosheets and microspheres. The effects of the addition of hydrofluoric acid (HF) and hydrogen peroxide (H2O2) in the preparation of TiO2 were studied. It was found that more H2O2 may accelerate the formation of a spherical morphology and that HF has three roles: dissolving Ti powder, retarding the hydrolysis of titanium precursor and reducing surface energy. Reaction time has a significant effect on morphological transformation. The aggregation of microstructures is described, the effects of the addition of HF and H2O2 on the condition of aggregation have been studied. Photocatalysis measurements showed that sphere-like TiO2 consisting of nanocubes exhibited the highest activity for degrading rhodamine B under UV light.

Effects of Hf incorporation on indium zinc oxide thin-film transistors using solution process

Thin-film transistors (TFTs) were fabricated by employing amorphous hafnium indium zinc oxide (HIZO) thin films as the active channel layer by the solution process. Thermogravimetry-differential thermal analysis, transmittance measurements, atomic force microscopy, scanning electron microscopy, x-ray diffraction, and Fourier transform infrared analysis were used to study the formation, structure, and optical properties of the HIZO films. The results showed that the addition of Hf to the IZO system resulted in suppression of carrier generation. The HIZO TFTs exhibited lower off-currents and higher onoff current ratios than IZO TFTs without Hf doping. HIZO TFTs with a Hf doping content of 5 at. % obtained a threshold voltage of 3.7 V, a mobility of 0.27 cm2 V-1 s-1, a subthreshold swing of 1.2 V/dec, and an on-off current ratio of 106.