Addition Of HF Research Articles

Perfluoroalcohols: The Preparation and Crystal Structures of Heptafluorocyclobutanol and Hexafluorocyclobutane‐1,1‐diol

AbstractThe first X‐ray crystal structure of an α‐fluoroalcohol is reported. Heptafluorocyclobutanol was obtained in quantitative yield from hexafluorocyclobutanone by HF addition in anhydrous hydrogen fluoride. The compound was characterized by its X‐ray single crystal structure. Heptafluorocyclobutanol readily undergoes hydrolysis to hexafluorocyclobutane‐1,1‐diol, which was also structurally characterized by X‐ray diffraction.

Perfluoroalcohols: The Preparation and Crystal Structures of Heptafluorocyclobutanol and Hexafluorocyclobutane-1,1-diol.

The first X-ray crystal structure of an α-fluoroalcohol is reported. Heptafluorocyclobutanol was obtained in quantitative yield from hexafluorocyclobutanone by HF addition in anhydrous hydrogen fluoride. The compound was characterized by its X-ray single crystal structure. Heptafluorocyclobutanol readily undergoes hydrolysis to hexafluorocyclobutane-1,1-diol, which was also structurally characterized by X-ray diffraction.

Molten-salt fabrication of (N,F)-codoped single-crystal-like titania with high exposure of (001) crystal facet for highly efficient degradation of methylene blue under visible light irradiation

Abstract

Microstructural and mechanical characterisation of Fe-14Cr-0.22Hf alloy fabricated by spark plasma sintering

Fe-14Cr pre-alloyed powder and pure Hf powder were mechanically alloyed to produce powder with nominal composition Fe-14Cr-0.22Hf (wt. %) that was consolidated by the spark plasma sintering (SPS) technique in order to investigate the ability of Hf to produce a nanometric dispersion of oxide particles in a ferritic matrix. Comprehensive microstructural and mechanical characterisation of the as-milled powder and the consolidated material was performed using electron microscopy, X-ray diffraction, atom probe tomography and indentation techniques. It was shown that Hf additions can effectively produce, by internal oxidation, a fine scale dispersion of Hf-O nanoparticles in the consolidated material. A uniform grain structure was produced in the alloy. Although the nanoparticle dispersion was not homogeneous at the finest scale, the resulting dispersion strengthening contributed significantly to the hardness. According to these results, internal oxidation of reactive elements rather than direct addition of oxides may offer additional opportunities in the design and development of oxide dispersion strengthened steels.

Speciation analysis of thallium in tobaccos using liquid chromatography inductively coupled plasma mass spectrometry

An inductively coupled plasma mass spectrometer (ICP-MS) was used as a liquid chromatographic detector for the speciation analysis of thallium in tobacco and cigarette ash samples. In this study, ionic Tl species, namely Tl(I) and Tl(III) were well separated in less than 2 min by reversed-phase high performance liquid chromatography (RP-HPLC). The stationary and mobile phases were C8 column and 7 mmol L−1 tetrabutylammonium phosphate (TBAP), 6 mmol L−1 diethylenetriamine pentaacetic acid (DTPA) in 2% (v/v) methanol solution (pH 5) respectively. Effluent from the HPLC column was delivered to the nebulizer of the ICP-MS for the determination of Tl. Detection limit was 0.003 ng mL−1 for both Tl(I) and Tl(III) compounds based on peak height. The relative standard deviation of peak areas for five injections of a mixture containing 1 ng Tl mL−1 each species was better than 1%. The Tl species were quantitatively leached from the tobacco and the ash into a solution of 5 mmol L−1 DTPA in 100 mmol L−1 ammonium acetate with/or without HF in an ultrasonic bath during a period of 20 min. The addition of HF improved the extraction of Tl from the ash sample. The extraction efficiency of Tl from tobacco was in the range 98–110%. Speciation analysis by HPLC-ICP-MS on tobacco samples showed a satisfactory agreement with the total Tl concentration obtained by ICP-MS analysis of completely dissolved samples. Tl(I) was the only detectable Tl species in tobacco samples analyzed, however both Tl(I) and Tl(III) were present in the cigarette ash.

Effect of hafnium micro-addition on precipitate microstructure and creep properties of a Fe-Ni-Al-Cr-Ti ferritic superalloy

The Fe-Ni-Al-Cr (FBB8) ferritic alloy contains B2-ordered NiAl precipitates which, upon minor addition of Ti to the alloy, display L21-ordered Ni2TiAl sub-precipitates; this improves creep resistance, consistent with an increase in coherency strains from the hierarchical NiAl/Ni2TiAl precipitates. Here, we study the effect of a small addition of Hf (0.5 wt%) to FBB8-1.5wt.%Ti alloy on precipitate structure and creep properties. The main microstructural changes with Hf addition are relatively minor: (i) decrease of mean radius of Ni2TiAl/NiAl hierarchical precipitates from 84 ± 14 to 78 ± 13 nm, (ii) increase of volume fraction of these precipitates from 18 ± 2 to 19 ± 2%, (iii) increase of their number density from 9 ± 0.3 × 10−19 to 11 ± 0.3 × 10−19 m−3, and (iv) decrease of precipitate edge-to-edge distance from 187 ± 57 to 160 ± 48 nm. The larger volume fraction, higher number density and smaller edge-to-edge distance of B2/L21 precipitates in the FBB8-1.5Ti-0.5Hf alloys, are all favorable to higher creep resistance for a strengthening mechanism based on precipitate climb bypass. However, the threshold stress for creep at 700 °C decreases upon Hf addition to FBB8-1.5Ti, from 156 to 122 MPa. The lower creep resistance is explained by a decrease of the lattice misfit between the Hf-enriched B2-precipitates and the bcc-matrix, and by a decrease of the volume fraction of L21-Ni2TiAl sub-precipitates within B2-NiAl precipitates from 16 ± 4% to 10 ± 3% without and with Hf, respectively.

MC Carbide Characterization in High Refractory Content Powder-Processed Ni-Based Superalloys

Carbide precipitates in Ni-based superalloys are considered to be desirable phases that can contribute to improving high-temperature properties as well as aid in microstructural refinement of the material; however, they can also serve as crack initiation sites during fatigue. To date, most of the knowledge pertaining to carbide formation has originated from assessments of cast and wrought Ni-based superalloys. As powder-processed Ni-based superalloys are becoming increasingly widespread, understanding the different mechanisms by which they form becomes increasingly important. Detailed characterization of MC carbides present in two experimental high Nb-content powder-processed Ni-based superalloys revealed that Hf additions affect the resultant carbide morphologies. This morphology difference was attributed to a higher magnitude of elastic strain energy along the interface associated with Hf being soluble in the MC carbide lattice. The composition of the MC carbides was studied through atom probe tomography and consisted of a complex carbonitride core, which was rich in Nb and with slight Hf segregation, surrounded by an Nb carbide shell. The characterization results of the segregation behavior of Hf in the MC carbides and the subsequent influence on their morphology were compared to density functional theory calculations and found to be in good agreement, suggesting that computational modeling can successfully be used to tailor carbide features.

The Effect of Hf Substituting for Cu on the Glass-Forming Ability, Crystallization Behavior, and Saturation Magnetization in Fe85Si2B8P4Cu1−xHfx Alloys

The effect of Hf substituting for Cu on the glass-forming ability (GFA), crystallization behavior, and saturation magnetization (Ms) in Fe-rich Fe85Si2B8P4Cu1−xHfx alloys has been investigated. The result shows that the addition of Hf plays a positive role in improving GFA, and the Fe85Si2B8P4Cu0.5Hf0.5 alloy ribbon shows an entirely amorphous structure. Both the ribbons of Fe85Si2B8P4Cu1 and Fe85Si2B8P4Cu0.5Hf0.5 have two obviously exothermic crystallization peaks, and the addition of Hf improves the onset temperatures of both first and second crystallization peaks, and leads to the improvement of the thermal stability of the amorphous alloys. For the Fe85Si2B8P4Cu0.5Hf0.5 ribbon, after annealing at 623 K, crystallization seeds with sizes of 2–4 nm are found and the initial crystallization has occurred; as the annealing temperature is increased to 723 and 823 K, the size distribution of most of the grains is about 20 nm and bigger than 20 nm, respectively. The Ms of the Fe85Si2B8P4Cu0.5Hf0.5 ribbon is about 154 emu/g, which is obviously lower than 205 emu/g of the Fe85Si2B8P4Cu1 ribbon. However, after annealing at 723 K, the Ms increases to 212 emu/g for the former alloy. The newly developed amorphous/nanocrystalline Fe-Si-B-P-Cu-Hf alloy with excellent soft magnetic properties shows a potential application for substituting partial Si steels.

Thermal behavior, structural relaxation and magnetic study of a new Hf-microalloyed Co-based glassy alloy with high thermal stability

In the present work, the influence of a minor Hf addition on the atomic structure, crystallization behavior, thermal stability and magnetic properties of a Co-based metallic glass was studied. Thermal analysis indicates that the thermal stability of new glassy ribbons microalloyed with 2.5 at.% Hf is notably enhanced through increasing the incubation time prior to devitrification and enlarging the width of the supercooled liquid region from 72 K to 96 K. Magnetic studies reveal that the new glass exhibits an excellent soft magnetic behavior, i.e., a very low coercivity of 0.26 A/m in the relaxed state, and a comparable saturation magnetization as the Hf-free ribbon. Structural relaxation of the Hf-containing alloy upon isothermal annealing below the glass transition temperature, Tg, was investigated by differential scanning calorimetry (DSC) and high-energy synchrotron X-ray diffraction (XRD). The evolution of the recovered enthalpy with annealing time can be expressed by the Kohlrausch-Williams-Watts (KWW) exponential function with a Kohlrausch exponent of 0.88, indicating a broad spectrum of relaxation times. Analysis of the reduced pair correlation functions, G(r), reveals volume shrinkage upon annealing caused by elimination of liquid-like sites including free-volume and anti-free-volume according to the shift in the positions of the G(r) maxima in the medium-range scale. The influence of structural relaxation on the variation of the Curie temperature and the coercivity of the new Hf-microalloyed glassy ribbon is discussed. A faster evolution of the Curie temperature with annealing time compared to the coercivity indicates a preferential dependence of the former on the chemical short-range order (SRO).

Microstructure and mechanical properties of foundry Al-Si-Cu-Hf alloy

Solidification microstructure, precipitation microstructure, and mechanical properties of foundry Al-Si-Cu-Hf alloy were investigated to elucidate the role of Hf during the solidification and precipitation processes. In the as-casting condition, α-Al dendrites, eutectic Si phases, and intermetallic compounds (Al2Cu, the needle-like β-Fe and Chinese-script α-Fe) were observed in the base alloy. However, no β-Fe was detected in the modified alloy, strongly indicating that Hf addition promotes the formation of the α-Fe phase but suppress the formation of the β-Fe phase. Furthermore, Hf addition can result not only in the formation of Hf-containing intermetallic compounds with different morphologies, which were identified as Si2Hf, but also, more importantly, in a significant decrease in the size, number, density, and volume fraction of porosity. After treatment with solution at 520 °C for 20 h, the formation of thermally stable Si2Hf precipitate was observed. After aging treatment at 180 °C up to 72 h, a delayed aging hardening was observed, which may be because Hf addition suppressed the formation of θ’ precipitate. Clearly, Hf addition in Al-Si-Cu alloy can modify the solidification microstructure and the precipitation microstructure, which is believed to be beneficial for mechanical properties. Indeed, a significant increase in elongation by 51.4% without a sacrifice of strength was obtained, compared with the unmodified Al-Si-Cu alloy. This investigation highlights the importance of a well-controlled solidification microstructure and precipitation microstructure for the improvement of mechanical properties, in particular to elongation.

How grain boundary chemistry controls the fracture mode of molybdenum

The design of metallic alloys with superior properties requires a deep understanding of the atomistic processes governing the materials behavior. In this paper, we present results providing a close link between grain boundary (GB) chemistry and fracture behavior in a Mo-Hf alloy. By combining atom probe tomography and ab-initio simulations of GBs, we unravel the origin for the transition between intergranular and transgranular fracture in technological Mo-Hf alloys. The main agent affecting GB strength is not the primary alloying element Hf, but rather the impurities O, C and B. With larger Hf additions, an intricate interplay between segregation and precipitation leads to a strong GB enrichment of C and B and to a depletion of O and Hf resulting in a higher cohesion of the GBs and thus, leading to a change in fracture mode. Our investigation exemplarily demonstrates that smallest additions of solutes can be decisive for understanding fracture behavior on the macroscale.

High {0 0 1} faceted TiO2 nanoparticles for the valorization of oxygenated compounds present in aqueous biomass-derived feedstocks

{0 0 1} faceted TiO2 catalysts are hydrothermally synthesized by using titanium(IV) isopropoxide and butoxide precursors (ISO and BUT TiO2 samples) together with HF addition. Their activity and stability are evaluated in the catalytic condensation of light oxygenated organic compounds present in an aqueous model mixture simulating a real bio-refinery effluent, under moderate operation conditions. High {0 0 1} faceted TiO2 catalysts show organic products yields superior to those attained with other TiO2 samples (anatase, rutile, and P25). This enhanced catalytic activity relates to their physico-chemical and textural properties, such as high surface area (≈100 m2/g), regular morphology (platelets conformed by partially agglomerated TiO2 nanoparticles), and adequate Lewis acidity. XRD and Raman measurements evidence the unique presence of anatase crystalline phase in both ISO and BUT materials, in which the use of HF during synthesis produces the preferential growth of TiO2 crystals mainly exposing the {0 0 1} plane. This effective {0 0 1} facet exposition directly determines catalytic results. Moreover, TiO2 ISO catalyst shows outstanding stability under reaction conditions, maintaining practically unaltered their activity after several re-uses. In particular, Lewis acid sites present in TiO2 faceted materials are more stable in the presence of organic acids under aqueous environments. This opens new possibilities for the application of these materials in the valorization of light oxygenated compounds present in biomass-derived aqueous effluents.

Effects of Hf addition on the thermal stability of 16Cr-ODS steels at elevated aging temperatures

In this paper, the effects of hafnium (Hf) addition on the thermal stability of the microstructure and tensile properties of Al-containing 16Cr-ODS steels were investigated. High temperature aging tests of the ODS steels with and without Hf were conducted at 750 °C, 950 °C and 1150 °C for 100 h respectively. And the microstructure evolution after thermal aging was investigated using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicated that Hf addition could improve the coarsening resistance of the oxide particles and the grains during aging treatment due to the formation of stable Y2Hf2O7 particles. Tensile tests on the aged-steels showed that the ultimate tensile strength and yield strength of 16Cr-Hf-ODS steel were higher than those of 16Cr-ODS steel. It was considered that the excellent thermal stability and tensile properties of 16Cr-Hf-ODS steel were related with the refined microstructure.

Up-grading of locally produced metallurgical grade silicon (MG-Si)

Locally produced metallurgical grade silicon (MG-Si ~ 97%) was upgraded by using wet-milling process. This is including milling of MG-Si in presence of 2M HCl solution for different time periods up to 60 min. The effect of milling time in HCl solution was studied. Soaking of the milled products (at optimum milling time 15 min) with continuous stirring in the same solution of 2M HCl for interval time up to 240 min also were investigated. Finally, the effect of addition of 2M HF to the milled product was discussed. The leached samples were investigated by X-ray fluorescence (XRF), and scanning electron microscope (SEM). It was found that, 99.92% purity of MG-Si was achieved after 15 min milling time with 2M HCl followed by addition 2M HF for 240 min with continuous stirring. About 97 % removal efficiency of the impurities was obtained.

Improved magnetic properties and thermal stabilities of Pr-Nd-Fe-B sintered magnets by Hf addition

Nd2Fe14B-type permanent magnets have been widely applied in various fields such as wind power, voice coil motors, and medical instruments. The large temperature dependence of coercivity, however, limits their further applications. We have systematically investigated the magnetic properties, thermal stabilities and coercivity mechanisms of the (Pr0.2Nd0.8)13Fe81-xB6Hfx (x=0, 0.5) nanocrystalline magnets fabricated by a spark plasma sintering (SPS) technique. The results indicate that the influence of Hf addition is significant on magnetic properties and thermal stabilities of the (PrNd)2Fe14B-type sintered magnets. It is shown that the sample with x = 0.5 at 300 K has much higher coercivity and remanent magnetization than those counterparts without Hf. The temperature coefficients of remanence (α) and coercivity (β) of the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets are improved significantly from -0.23 %/K, -0.57 %/K for the sample at x = 0 to -0.17 %/K, -0.49 %/K for the sample at x = 0.5 in the temperature range of 300-400 K. Furthermore, it is found out that the domain wall pinning mechanism is more likely responsible for enhancing the coercivity of the (Pr0.2Nd0.8)13Fe81-xB6Hfx magnets.

Effect of Hf addition on the glass forming ability, thermal and magnetic properties in the (Fe86B13Cu1)100 − xHfx alloys

In this study, the effect of Hf addition on the glass formation ability (GFA), micro structural, thermal and magnetic properties were investigated in the Fe-B-Cu alloy with high saturation magnetization (Ms). It is found that the addition of Hf is beneficial for improving GFA of (Fe86B13Cu1)100−xHfx Alloys. The melt-spun ribbons at x=0.75 and x=1.0 show an entirely amorphous structure by x-ray diffraction and have two obvious separated exothermic peaks on DSC curves, Hf element plays a positive role on postponing the first crystallization and improved the thermal stability of the amorphous Fe-B-Cu-Hf alloys. As x=0.75, the melt-spun ribbon has a higher apparent activation energy of Fe3B phase than of the ribbon at x=1.0, and the first crystallization is easier than the second crystallization. Therefore it was easy to obtain an α-Fe/amorphous dual phases structure alloy ribbons with few or without Fe3B phase by a suitable annealing process near peak temperature of the first crystallization. After annealing, the saturation magnetization (Ms) was tested by vibrating sample magnetometer, and the value of x=0.75 changes slightly first, then increase obviously and reach the maximum 220emu/g at 750K higher Tp2. This alloy shows a good glass forming ability and a high saturation magnetization.

Impurity phases and their removal in Si purification with Al–Si alloy using transition metals as additives

In order to discuss the effects of transition metals such as Zr, Hf, and Ti on the removal of impurities (B, P, Fe, Al, Ca, Ti, V, Cu, Ni, Mn, Zr, and Hf) in the purification of metallurgical-grade Si (MG-Si) with Al–Si alloy, the impurity phases formed after solidification were investigated by electron probe microanalysis (EPMA) and their removal by acid leaching was performed. EPMA investigation showed that β-Al5FeSi was the main impurity phase aside from Al in the sample without additives. However, after adding Zr, Hf, or Ti, the ZrSi2, HfSi2, or TiSi2compound dissolved in small amounts of Al was the most observed phase besides β-Al5FeSi and Al. Impurities such as V, Ni, and Mn were more likely to coexist with β-Al5FeSi when Hf or Zr was employed as the impurity getter. However, V preferentially coexisted with TiSi2 when Ti was added. The leaching results showed that the addition of Zr, Hf, or Ti significantly enhanced the extraction of B and slightly enhanced that of other impurities. The added Zr, Hf, and Ti were eliminated efficiently with the other impurities, reaching extraction ratios of 99.998%, 99.9994%, and 99.997%, respectively.

Microstructural and oxidation behavior of Ni[sbnd]Cr[sbnd]Al super alloy containing hafnium at high temperature

In this research, Ni12Cr4.5AlxHf alloys containing 0.1, 0.2 and 0.4 wt% Hf were produced and their isothermal oxidation behavior has been studied in air for 100 h at the temperature of 1000 °C. Microstructures of the oxidized samples were examined using scanning electron microscopy (SEM). The samples were observed to exhibit different microstructures, and oxidation behavior depending on their chemical composition. The results indicated that the sample containing 0.4 wt% Hf had the lowest weight gain, while the weight gain of the sample without Hf was the highest. Layer investigations show that an external scale of spinel overlying a region of internal oxides precipitates was formed on Ni12Cr4.5Al. On the other hand, an external Al2O3 formed on the samples containing Hf additions. The improvement in the oxidation resistance is believed to be due to the transition between the internal and external oxidation of aluminum and also due to the formation of the relatively continuous, adherent and protective Al2O3 oxide layer on the surface of the Ni12Cr4.5Al0.4Hf alloy. Microstructural investigations using SEM show that the layer adhesion can be affected by mechanical keying at the alloy/scale interface resulting from the pegs' formation during oxidation.

Erratum to: Effect of Hf and Li on the structure and electrical properties of Bi0.5Na0.5TiO3 lead-free ceramics

Lead-free (Bi0.5Na0.5−y Li y )(Ti1−x Hf x )O3 piezoelectric ceramics were prepared using a conventional solid-state method, and the effects of Li and Hf on phase structure and electrical properties were systematically investigated. All the ceramics exhibited a rhombohedral phase, which is independent on the doped Li and Hf elements and contents. With the increase of Hf4+ or Li+, their T d values gradually decreased. Their piezoelectric and dielectric properties can be effectively enhanced by optimizing the amount of Hf4+ and Li+, and maximum d 33 value of ~100 pC/N and e r value of ~850 were achieved for x = 0.03, y = 0.1 and x = 0.12, y = 0, respectively. In addition, it was found that the ferroelectric and strain behavior was gradually weakened with the addition of Li and Hf. This research helps understand the influence of Li and Hf on the structure and properties of bismuth sodium titanate materials.

Magnetic properties and microstructure of melt-spun Ce17Fe78−xB6Hfx (x = 0–1.0) alloys

Ce17Fe78−xB6Hfx (x=0–1.0) alloys were fabricated by a melt-spinning technique in order to study their magnetic properties and microstructure. Magnetic investigations of Ce17Fe78−xB6Hfx (x=0–1.0) alloys show that the room-temperature coercivity increases linearly from 352kA/m at x=0 to 420kA/m at x=1.0. The Curie temperature (Tc) decreases monotonically from 424.5K to 409.1K. The Ce L3-edge X-ray absorption near edge structure (XANES) spectrums reveal that there is more Ce4+ in ribbons under total electron yield (TEY) than fluorescence yield (FY). Hf addition has no effect on the weight of Ce3+ and Ce4+ in CeFeB-based alloys. The grain refinement and microstructure uniformity are essential for improving the magnetic properties of Hf-doped alloys. This paper may shed light on the further development of the Ce-based magnets and offer a feasible way for using the rare earth resources effectively.