Addition Of HF Research Articles

Enantioselective, Catalytic Vicinal Difluorination of Alkenes

AbstractThe enantioselective, catalytic vicinal difluorination of alkenes is reported by II/IIII catalysis using a novel, C2‐symmetric resorcinol derivative. Catalyst turnover via in situ generation of an ArIIIIF2 species is enabled by Selectfluor oxidation and addition of an inexpensive HF–amine complex. The HF:amine ratio employed in this process provides a handle for regioselective orthogonality as a function of Brønsted acidity. Selectivity reversal from the 1,1‐difluorination pathway (geminal) to the desired 1,2‐difluorination (vicinal) is disclosed (>20:1 in both directions). Validation with electron deficient styrenes facilitates generation of chiral bioisosteres of the venerable CF3 unit that is pervasive in drug discovery (20 examples, up to 94:06 e.r.). An achiral variant of the reaction is also presented using p‐TolI (up to >95 % yield).

Effects of Hf addition on the microstructure, magnetic properties and coercivity mechanism of Nd-Ce-Fe-B ribbons fabricated by melt-spinning technique

Abstract In this paper Hf doped (Nd0.8Ce0.2)13Fe82−xB5Hfx (x = 0, 0.5, 1.0, 2.0, 3.0) ribbons were fabricated by melt-spinning technique, and their microstructure, magnetic properties and coercivity mechanism have been investigated methodically. It is found that the coercivity of (Nd0.8Ce0.2)13Fe82−xB5Hfx ribbons is enhanced for 0 ≤ x ≤ 2.0 at.% while the remanence decreases slightly. The optimal comprehensive magnetic properties Jr = 7.5 kG, Hcj = 12.7 kOe, and (BH)max = 12.3 MGOe, are obtained at x = 1.0 at.%. The grain size decreased with the addition of Hf and more uniform microstructure evolved. The coercivity mechanism of the (Nd0.8Ce0.2)13Fe82−xB5Hfx (x = 0–3.0) ribbons is found to be the pinning mechanism based on the systematic investigations and analysis. The synchronization of the grain refinement and the pinning effect lead to the improvement of magnetic properties.

The effects of wide range of compositional changes on the martensitic transformation characteristics of NiTiHf shape memory alloys

The effects of composition on the martensitic transformation characteristics of NiTiHf shape memory alloys are systematically explored. Transformation temperatures (TTs) demonstrate a non-monotonic dependence on Ni and Hf concentrations. For Ni > 50 at%, TTs decrease with small Hf additions, attain a minimum or are completely suppressed, depending on Ni content, followed by a significant increase with Hf content. This initial drop in TTs becomes more pronounced with higher Ni contents and is attributed to the increase in nickel anti-site defects along with bulky substitutional Hf contributing to the increase in local lattice distortions along with the re-distribution of Ti and Hf.

Effect of Hf additions on phase stability and mechanical properties of binary W-Hf alloys: A first-principles study

In this paper, the effect of hafnium alloying element on phase stability and mechanical properties of binary tungsten-hafnium alloys was calculated using the first principles technology. Firstly, we investigated the cell volumes, lattice constants and formation energies of binary W1-xHfx (x = 0, 0.0625, 0.125, 0.1875, 0.25 and 0.5) alloys. It is shown that binary tungsten-hafnium alloys remain maintain BCC structures. When the concentration of hafnium atoms is lower than 12.5%, the structures of binary tungsten-hafnium alloys are thermodynamically stable. The elastic constants of binary tungsten-hafnium alloys were calculated based on the optimized atomic lattice. Then the elastic modulus and other mechanical parameters are deduced according to the relevant formulas. It is shown that the mechanical strength of binary tungsten-hafnium alloy decreases with increasing hafnium concentration, which is lower than the mechanical strength of pure tungsten metal. However, the mechanical strength of binary tungsten-hafnium alloys is higher than that of pure hafnium metal. In addition, it can be effective to improve the ductility of pure tungsten metal based on hafnium alloying tungsten.

The effect of Hf on the microstructure, transformation behaviors and the mechanical properties of Ti-Ni-Cu shape memory alloys

The effect of substitution of Hf for Ti and Cu for Ni on microstructure, martensitic transformation behavior, mechanical properties and strain recovery characteristic of quaternary Ti-Ni-Cu-Hf alloys were investigated systematically. The results reveal that the B19→B19′ martensite transformation can be controlled by tailoring the Hf contents in Ti-Ni-Cu alloys. Although the B19 and B19′ martensite coexisted in Ti-Ni-Cu alloys with the minor Hf addition, only one-stage B2→B19′ transformation was observed in heating and cooling process. The transformation temperatures and transformation hysteresis can be adjusted by optimizing the chemical composition. In addition, the superior mechanical properties and shape memory effect can be achieved by tailoring the Hf can Cu contents. The maximum shape memory effect strain of 3.06% could be obtained in Ti47Ni44Cu6Hf3 alloy. And Ti45Ni44Cu6Hf5 alloy showed the largest tensile strength of 770 MPa. The present study provided the theoretical foundation for the potential application of the Ti-Ni-Cu-Hf alloys.

Understanding the effect of Hf on thermal stability and glass forming ability of Fe57.2Co30.8Zr7-xHfxB4Cu1 (x = 3, 5, and 7) metallic glasses

Differential scanning calorimeter in non-isothermal mode has been used to study the effect of addition of Hf, in place of Zr, on the glass forming ability and thermal stability of metallic glasses of composition Fe57.2Co30.8Zr7-xHfxB4Cu1 (x = 3, 5, and 7). An increase in the content of Hf results in an increase in the primary crystallization temperature and melting temperature. The activation energy of glass transition and primary crystallization was determined using commonly used thermo-analytical models. Relatively higher activation energy was seen in sample with lowest Hf content both for the glass transition and primary crystallization processes. An increase in Hf content showed a decline in thermal stability and glass forming ability assessed through fragility index, temperature range of super cooled liquid region, and other frequently used theoretical parameters. The role of Hf in this alloy system has been rationalized on the basis of these observations.

A Study of the Effects of Al, Cr, Hf, and Ti Additions on the Microstructure and Oxidation of Nb-24Ti-18Si Silicide Based Alloys.

In Nb-silicide based alloys Al, Cr, Hf, and Ti additions are crucial for achieving balance of properties. It is not known how the simultaneous addition of Hf with Al and Ti, or Hf with Al, Cr, and Ti affects macrosegregation, and how the alloying affects hardness, Young’s modulus and bulk alloy oxidation, and contamination of the solid solution Nbss and the Nb5Si3 compound by oxygen. Two alloys with nominal compositions (at.%) Nb-24Ti-18Si-5Al-5Hf (alloy NbSiTiHf-5Al) and Nb-24Ti-18Si-5Al-5Cr-5Hf (alloy NbSiTiHf-5Al-5Cr) were studied in the as-cast and heat-treated conditions and after isothermal oxidation at 800 and 1200 °C and were compared with similar alloys without Hf. In both alloys there was macrosegregation of Si and Ti, which was more severe in NbSiTiHf-5Al. Both alloys formed Nbss+βNb5Si3 eutectic. The Nbss was stable and its Al and Cr concentrations increased with increasing Ti concentration. In both conditions the βNb5Si3 was observed in the alloys NbSiTiHf-5Al and NbSiTiHf-5Al-5Cr, and the γNb5Si3 only in the alloy NbSiTiHf-5Al. In both heat-treated alloys, separate Hf-rich Nb5Si3 grains were formed. The Si and Al concentrations in Nb5Si3 respectively decreased and increased with increasing Ti concentration. Al and Cr had a stronger hardening effect in the Nbss than Al, Cr, and Hf. Al, Cr, and Ti had a stronger negative effect on the Young’s modulus of the Nbss compared with Al, Cr, Hf, and Ti. When Nb was substituted by Ti, Cr, and Hf, and Si by Al in the βNb5Si3, the Young’s modulus was reduced compared with the unalloyed silicide. At 800 °C both alloys did not exhibit catastrophic pest-oxidation after 100 h. The Nbss and Nb5Si3 were contaminated by oxygen in both alloys, the former more severely. At 1200 °C the scales spalled-off, more severely in the alloy NbSiTiHf-5Al, where substrate that was heavily contaminated by oxygen below the scale also spalled-off. In both alloys the contamination of Nb5Si3 and Nbss by oxygen was more severe compared with 800 °C, but the silicides were not contaminated by oxygen in their bulk. The Nbss was not contaminated by oxygen only in the bulk of the alloy NbSiTiHf-5Al-5Cr.

Mechanical properties and stability of TiPt-M (M = Ru, Co, Cu, Zr and Hf) for high temperature applications

Shape memory alloys are smart materials that can remember their shape after being deformed. This is due to their unique properties, shape memory effect and super-elasticity, which occurs because of phase transformation. High temperature shape memory alloys are being developed in order to increase the application area of shape memory alloys. There is an increasing demand of shape memory alloys, which can be used in high temperatures environments such as in aerospace, actuators, sensors in the automotive industry. The first-principle approach was employed to investigate the effect of ternary alloying with Ru, Co, Cu, Zr and Hf on the equi-atomic B19 TiPt alloy. The supercell approach based on the B19 TiPt structure was used to construct various compositions containing a third element with reduced Pt content, and evaluate their thermodynamic and mechanical stability. The Ru, Co and Cu calculations were performed to compare their effects on the TiPt relative to Zr and Hf addition. It was found that partial substitution with Ru was the most stable structure as compared to the Hf, since it displayed the lowest heats of formation. Their martensitic transformation temperature increased due to their lowest C′ shear modulus. However, the addition of Cu reduced the transformation temperature of the TiPt. All structures were found to be completely anisotropic.

Leaching of gallium from corundum flue dust using mixed acid solution

Abstract In order to extract gallium from a high-silica-content flue dust generated in corundum production, a mixed acid solution of H2SO4 and HF was used for leaching, and test parameters of the leaching process were optimized. Experimental results show that the leaching rate of gallium was only 38% when H2SO4 was used as leaching agent. Composition analysis results of micro areas in this corundum flue dust indicate that the content of gallium in silica-enriched phases was high; this portion of gallium was insoluble in H2SO4 solution. The leaching rate of gallium increased significantly with addition of HF due to corrosion of silica. Effects of reaction time, temperature, and concentrations of HF and H2SO4 on leaching rates of gallium were investigated. The leaching rate of gallium reached 91% when this corundum flue dust was leached in a mixed acid solution of H2SO4 and HF for 4 h, at a temperature of 80 °C, with a liquid-to-solid ratio of 5:1 (mL/g). The optimal concentrations of H2SO4 and HF in the mixed acid solution were 1.5 and 6.4 mol/L, respectively.

Novel room-temperature synthesis of MIL-100(Fe) and its excellent adsorption performances for separation of light hydrocarbons

Realization of room-temperature synthesis of MOFs with trivalent metal ions as coordination centres is a significant challenge for lowering the production cost of MOFs. Herein, a novel strategy of oxidizing radical-promoted facile synthesis of MIL-100(Fe) at room temperature was firstly proposed. The use of benzoquinone as oxidizing radicals successfully promoted room-temperature synthesis of MIL-100(Fe) without HF addition. The resulting RT-MIL-100(Fe) was characterized and its separation performance for recovery of C2H6 and C3H8 from natural gas was examined. RT-MIL-100(Fe) exhibited high BET surface area of 2482 m2·g−1, and its adsorption capacities of RT-MIL-100(Fe) for CH4, C2H6 and C3H8 were 0.36, 2.22 and 6.78 mmol·g−1 at 100 kPa and 298 K, respectively, exhibiting preferable adsorption of C2H6 and C3H8 over CH4. Its IAST-predicted selectivities reached as high as 33.3 and 6.0 for C3H8/CH4 and C2H6/CH4 binary mixtures at 298 K, respectively. The distribution of interaction energy for methane, ethane and propane were simulated using Metropolis method, which is corresponding to the experiment results. Breakthrough experiments confirmed that C1–C3 ternary gas mixtures can be well separated using the fixed bed of RT- MIL-100(Fe) under ambient conditions. RT-MIL-100(Fe) as an iron-based MOFs is very promising for the recovery C2 and C3 from natural gas. More importantly, this novel synthesis technology proposed in this work for room-temperature preparation of MIL-100(Fe) is an energy-saving and environmental friendly methodology.

Microstructure of Al–Si–Mg alloy with Zr/Hf additions during solidification and solution treatment

In this study, the morphology, composition and evolution of intermetallics in Al–7Si–0.3Mg, Al–7Si–0.3Mg–0.47Hf, Al–7Si–0.3Mg–0.16Zr and Al–7Si–0.3Mg–0.14Zr–0.44Hf alloys were characterized by optical microscope (OM), scanning electron microscope (SEM) with energy-dispersive spectrometer (EDS) and transmission electron microscope (TEM). The AlSiZr, AlSiHf and AlSiZrHf phases are formed with additions of Zr and/or Hf in base alloy during solidification, especially the AlZrHf primary particles. The three-dimensional morphology of the AlZrHf particle evolves from 10-polyhedron-like to compressed cube-like during solidification. The new AlZrHf phase experiences partial dissolution after solution treatment, while the others remain in the initial morphology. High Si contents lead to form thermally stable Zr/Hf-rich precipitates in Zr/Hf-containing alloys during solution treatment, especially the nanobelt-like Si2Zr, Si2Hf and Si2(Zr,Hf) precipitates. Particular orientation relationships and the growth mechanism are identified. The finding of the work broadens the elevated temperature application of Al–Si–Mg in modern automotive aluminum engine.

High-temperature oxidation behaviour of minor Hf-doped β-NiAl single crystals in dry and humid atmospheres

Oxidation behaviour of undoped β-NiAl and β-NiAl-0.05Hf single crystals were investigated at 1100 °C in 20 vol% O2 + Ar and 15 vol% H2O + Ar, respectively. On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystalline β-NiAl, severe-scale spallation is observed for β-NiAl-0.05Hf single-crystal alloy, especially in dry atmosphere. It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale–substrate interface, which promotes the conditions required for reactive element effect. Once the reactive element effect of Hf does not work, its strong affinity with oxygen will accelerate the process of high-temperature oxidation. However, the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance of β-NiAl single crystal, resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere. In addition, interfacial cavities are observed in dry and humid atmospheres, which may eventually result in the spallation of the oxide scale.

Purification of metallurgical-grade silicon using Si–Sn alloy in presence of Hf, Zr, or Ti

Hf, Zr, or Ti was employed as additive to enhance removal of the main impurities from metallurgical-grade Si (MG–Si) during the Si–Sn alloy refining process. The microstructure of Si-Sn alloy without/with Zr, Hf, or Ti was observed and analyzed by electron probe microanalysis (EPMA) to investigate the distribution of impurities. Compositions of intermetallic phases precipitated in Sn or among the grain boundaries of Si were quantitatively analyzed using EPMA. The mechanisms of their formation and the removal of impurities are discussed. The results of Si refining showed that the addition of Hf or Zr slightly enhanced the removal of Al. The high refining temperature in the Si-Sn alloy refining process was responsible for the low extraction of B. Most of Zr, Hf, or Ti was removed simultaneously with other impurities during the Si–Sn alloy refining process.

The oxidation performance of plasma-sprayed NiAl bond coat: Effect of Hf addition in bond coat and substrate

NiAl bond coats with and without Hf addition (0.1 at.%) were deposited on two types of superalloy substrates (i.e., DZ125L, no Hf, and DZ125, 0.51 at.% Hf) using plasma spraying technique, and isothermally oxidized at 1150 °C. It demonstrates that Hf addition in the bond coat is more effective than in the superalloy substrate for improving the bond coat oxidation resistance. In addition, though the substrate chemistry could affect the bond coat oxidation performance, this effect was very sensitive to the chemistry of the bond coat - obvious for the RE (reactive element)-free NiAl bond coat, but less obvious for the RE-containing bond coats (NiAlHf and NiCoCrAlY). Moreover, compared with the NiCoCrAlY bond coat, the NiAlHf bond coat showed significantly improved oxidation resistance, regardless of the substrate chemistry, suggesting that NiAlHf bond coat prepared by plasma spraying is a promising candidate for the thermal barrier coating application.

Green and time-saving synthesis of MIL-100(Cr) and its catalytic performance

Abstract MIL-100(Cr) is an important member of metal-organic frameworks due to its large surface area, unique pore structure, good stability and unsaturated metal sites. Generally, this material was synthesized with the addition of HF and solvent for a long crystallization time (96 h). In this work, we report that MIL-100(Cr) can be synthesized under HF- and solvent-free conditions in a short crystallization time (15 h). The obtained MIL-100(Cr) possessed high surface area and rich porosity. Additionally, such material exhibited enhanced catalytic performance in the oxidation reaction of benzyl alcohol, demonstrating that it has potential applications in catalysis.

Physical Properties of Candelilla Wax, Monoacylglycerols, and Fully Hydrogenated Oil Oleogels

AbstractOleogels have been studied in the past decade due to their potential to replace saturated fat in foods. Oleogelators have been mostly studied alone or in binary systems. Sometimes a single oleogelator cannot achieve all the technological properties necessary for a specific food application. Thus, the aim of this work was to investigate the interaction between candelilla wax (CLX), monoacylglycerols (MAG), and a fully hydrogenated oil (hardfat [HF]) in soybean and high‐oleic sunflower oils and to evaluate their physical properties. The concentration of the total oleogelator was between 5% and 10%, from pure CLX (5%), sample OP, up to many combinations of MAG, HF, and CLX samples O1, O2, O3, O4, O5, and O6. Samples were evaluated according to their microstructure, melting properties, rheological behavior, hardness, oil‐binding capacity (OBC), and thermal stability. Results showed that the addition of MAG and HF to CLX created a softer gel but improved its rheological properties. Changes in the physical properties were related to the various proportions of CLX, MAG, and HF rather than the overall concentration of structuring agents. For example, for a total concentration of 5% of the structuring agent, a decrease in the CLX concentration from 5% to 3% and the addition of HF and MAG resulted in a softer crystalline network. Increasing the overall concentration of oleogelators by increasing the amount of HF and/or MAG and maintaining the concentration of the CLX constant did not improve the hardness of the gel. This study showed that at least 3% of CLX must be added to the system to obtain a semisolid material independently of the amount of MAG and/or HF added.

Ordering suppression and excellent ductility in soft-magnetic Fe-6.5 wt%Si sheet by Hf addition

Fe-6.5 wt%Si alloy is superior to other materials in terms of its soft magnetic performance but its lack of ductility leads to poor workability and large restriction on shaping. It is quite challenging to improve ductile performance without sacrificing soft magnetic properties. In this work, an excellent ductile behavior is observed in the Fe-6.5 wt%Si alloy with a slight addition of Hf, together with low coercivity of 0.73 ± 0.005 Oe and low core loss P1/10k of 13.4 ± 0.41 W/kg. The Hf-added Fe-6.5 wt%Si alloy exhibits an elongation to fracture of 18.4 ± 2.5% and an ultimate tensile strength of 906 ± 30 MPa, which are much higher than the corresponding values (5.2 ± 1.8% and 755 ± 63 MPa) of the Hf-free Fe-6.5 wt%Si alloy. X-ray diffraction analysis and high-resolution transmission electron microscopy observations reveal that Hf addition brings about formation of Hf-enriched Hf-Fe-Si precipitates with face-centered-cubic structure, which is found to play a significant role in effectively suppressing formation of Fe-Si ordered phase, and thus greatly improving ductility of the alloy. A mechanism based on precipitation-dependent atomic rearrangements is proposed to explain the desirable suppression of Fe-Si ordered phase.

Low cycle fatigue behaviour at 300 °C and microstructure of Al-Si-Mg casting alloys with Zr and Hf additions

The strain-controlled low cycle fatigue (LCF) behaviour at 300 °C and the microstructure of Al-7Si-0.3Mg casting alloys with additions of Zr and/or Hf are studied. Microstructural characteristics are investigated in detail by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the Zr- and/or Hf-rich primary particles and precipitates form in the alloys and have a significant effect on the fatigue properties. The cyclic softening characteristics are mainly attributed to the combination of the effects of the interaction of dislocations with nanobelt-like precipitates and an over-ageing phenomenon in the Mg2Si phase during the LCF test at 300 °C. The dislocations climbed over the nanobelt-like precipitates and tangled around the rectangle-like precipitates. Fatigue cracks initiated from the specimen surface, and crack propagation was characterized by dimple-like features coupled with fatigue striations. The best fatigue resistance of Al-7Si-0.3Mg-0.14Zr-0.44Hf casting alloy is related to the combination of morphological changes of the primary phase, the pinning effect of the Zr + Hf-rich precipitates and the different fracture characteristics.

Preface

A highly faceted {001} TiO2 catalyst was hydrothermally synthesized by using Ti(IV)-isopropoxide precursor with aqueous HF addition. WO3 was synthesized by following a reported method. Coupled TiO2-WO3 samples were synthesized by adding the corresponding amount of WO3 to fluorinated TiO2 gel followed by a hydrothermal treatment. Additionally the synthesized systems were characterized by using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS) and N2-adsorption (BET) for specific surface area determination. The photocatalytic activity of the single and coupled oxides was measured by means of three model reactions: the photo-oxidation of phenol (as a colourless substrate) and methyl orange (as a dye) and the photoreduction of Cr(VI) as K2Cr2O7. The coupling of WO3 with a highly faceted {001} TiO2 makes it possible to optimize the photocatalytic properties of the faceted material. In fact, {001} faceted TiO2 by itself presents a substantial improvement with respect to commercial TiO2(P25), as it can implement its photoactivity after the incorporation of WO3 with promising results, which can reduce the limitations of TiO2 in terms of its photoactivity, taking advantage of a higher percentage of solar radiation.

Effect of Hafnium Addition in 60NiTi Alloy Hardened Under Open Atmosphere Conditions

Vacuum furnaces or furnaces backfilled with inert argon gas are commonly employed to conduct hardening treatment on 60NiTi alloy. However, vacuum furnaces with the possibility of drop-quenching the solutionized parts are not easily available, and backfilling the furnaces with inert argon gas is costly. In this research, the hardening treatments were carried out in an air-exposed environment. As expected, reaction of Ti with oxygen gas existing in air during heat treatment resulted in formation of an oxide layer on the surface. This led to the depletion of Ti from the NiTi matrix and consequent formation of Ni-rich zones causing precipitation of soft Ni-rich phases. It was found that the addition of 1 at.% hafnium (Hf) prevented the soft Ni-rich phases formation in the matrix of the outer surface regions. This result suggests that Hf addition can be considered as a solution to harden a 60NiTi alloy under cost-effective open atmosphere heat treatment conditions.