Addition Of HF Research Articles

Effects of the Hf content on the microstructure and magnetic properties of Co–Hf–Ta thin films

Effects of the Hf content in Co–Hf–Ta thin films on the microstructure and magnetic properties were investigated in this study. It was found that appropriate Hf addition can effectively refine the Co grain size. Co grain sizes sharply decreased from 50 nm down to 2.3 nm with increasing the Hf content from 1.02 at.% to 2.81 at.%, leading to the reduced magneto-crystalline anisotropy. The Co–Hf–Ta thin films with small Co grains reveal low anisotropy field, low coercivity, and high resistivity. By optimizing the Hf content, the film with Hf concentration of 2.81 at.% exhibits excellent soft magnetic properties: high saturation magnetization (4 πM S ∼ 13.6 kG), and low coercivity ( H C ∼ 0.6 Oe). The effective permeability of the film reaches 800 and remains constant up to 1 GHz.

Supplementation with fiber-rich multimixtures yields a higher dietary concentration and apparent absorption of minerals in rats

Multimixtures (MMs) are dietary supplements prepared with low-cost ingredients and food by-products that are widely used in various countries to counteract malnutrition. Although MMs have a high content of minerals, they also contain high levels of dietary fiber and associated compounds, which might bind minerals and impair their absorption. In this study, we investigated the hypothesis that the increased dietary fiber content of MMs would impair gastrointestinal mineral absorption due to the metal-binding capacity of dietary fiber. Thus, the objective of the present study was to feed growing rats with a basal diet, representative of a nutritionally deficient diet, alone or supplemented with a low dietary fiber level MM, intermediate dietary fiber level MM, or high dietary fiber level MM (HF) to evaluate the apparent absorption of calcium, phosphorus, magnesium, manganese, and copper. The relative apparent calcium absorption was slightly decreased by the HF addition, with no change in the absolute apparent absorption. The absolute apparent absorption of phosphorus and magnesium was increased by the intermediate dietary fiber level MM and HF additions, whereas the manganese absorption was increased only by the HF addition. The apparent absorption of copper was not affected by the MM supplementation. The increased apparent absorption of minerals was always related to the increase in the mineral dietary concentration triggered by the MM. Thus, we concluded that the increased dietary fiber levels in the MMs increased the mineral levels, and MMs with intermediate and high fiber levels may be used to improve the mineral balance of poor diets.

Modern sampling and analytical methods for the determination of trace elements in marine particulate material using magnetic sector inductively coupled plasma–mass spectrometry

Trace elements often limit phytoplankton growth in the ocean, and the quantification of particulate forms is essential to fully understand their biogeochemical cycling. There is presently a lack of reliable measurements on the trace elemental content of marine particles, in part due to the inadequacies of the sampling and analytical methods employed. Here we report on the development of a series of state-of-the-art trace metal clean methods to collect and process oceanic particulate material in open-ocean and sea ice environments, including sampling, size-fractionated filtration, particle digestions and analysis by magnetic sector inductively coupled plasma–mass spectrometry (ICP–MS). Particular attention was paid to the analysis of certified reference materials (CRMs) and field blanks, which are typically the limiting factor for the accurate analysis of low concentrations of trace metals in marine particulate samples. Theoretical detection limits (3 s of the blank) were low for all 17 elements considered, and varied according to filter material and porosity (sub-μg L −1 for polycarbonate filters and 1–2 μg L −1 for quartz and polyester filters). Analytical accuracy was verified using fresh water CRMs, with excellent recoveries noted (93–103%). Digestion efficiencies for various acid combinations were assessed using sediment and plankton CRMs. Using nitric acid only, good recoveries (79–90%) were achieved for Mo, Cd, Ba, Pb, Mn, Fe, Co, Ni, Cu, Zn and Ga. The addition of HF was necessary for the quantitative recovery of the more refractory trace elements such as U, Al, V and Cr. Bioactive elements such as P can also be analysed and used as a biomass normaliser. Our developed sampling and analytical methods proved reliable when applied during two major field programs in both the open Southern Ocean and Antarctic sea ice environments during the International Polar Year in 2007. Trace elemental data are presented for particulate samples collected in both suspended and sinking marine material, and also within sea ice cores.

Influences of annealing and hafnium concentration on the microstructures of sputter deposited β-NiAl coatings on superalloy substrates

This study was conducted to establish the influences of high hafnium concentrations and high temperature annealing on the microstructures of β–NiAl coatings. Binary NiAl and ternary NiAl-1.0at.% Hf coatings were deposited onto CMSX-4® superalloy substrates via unbalanced DC magnetron sputtering. Investigations were conducted using scanning electron microscopy, electron probe microanalysis, transmission electron microscopy, X-ray diffraction, and three-dimensional atom probe tomography in an effort to determine the influences of annealing on the coating microstructures and coating/substrate interdiffusion. All as-deposited coatings were found to consist of a B2 structured solid solution consistent with the Ni-rich β–NiAl. Post-deposition annealing at 1000°C resulted in significant coating-substrate interdiffusion and in the formation of an interdiffusion zone, the extent/thickness of which decreased with the addition of Hf. Annealing additionally produced γ′–Ni3Al precipitates in the binary coatings and nanometer-sized Hf-rich precipitates in Hf-containing coatings. The majority of these precipitates were identified as the equilibrium Heusler (i.e., Ni2AlHf) phase; however, when Hf-containing specimens were annealed in a high carbon environment, significant concentrations of carbon were incorporated into the coatings. This sometimes resulted in the formation of HfC precipitates. The results have been analyzed and discussed relative to previous research on sputter deposited NiAl–Hf coatings.

High Temperature Alloys from Nb-Cr-Si System with Minor Additions

Several Nb based alloys (Nb-20Mo-15Si-25Cr, Nb-20Mo-15Si-25Cr-5B, Nb-20Si-20Cr-5Al, and Nb-20Cr-20Si-5Hf) have been prepared to evaluate the oxidation resistance from 700 to 1400°C in air. The phase identification was determined by calculating the isothermal sections in this temperature range using PANDATTM software. The experiments involve static heating for 24 hours (short term oxidation, STO) or 7 cycles of 24 hour heating (long term oxidation, LTO). Weight gain per unit area as a function of either temperature (STO) or time (LTO) has been used to determine their oxidation resistance. However, SEM, EDS on SEM, x-ray mapping, and XRD have been used to evaluate the oxide scale characterization and the influence of various microconstituent effects have been determined. It appears that B addition may be beneficial while Al is advantageous in comparison to Hf addition. The problem of pesting, typically, in a range of temperature from 900 to 1100°C needs to be controlled through minor additions since the alloys exhibit fairly good resistance at lower and higher temperatures up to 1400°C.

Oxidation behaviour of TiAl-based intermetallic coatings on γ-TiAl alloys

Abstract TiAl-based intermetallic layers with additions of Ag, Cr, Y and Hf were deposited on γ-TiAl specimens using magnetron sputtering. The oxidation behaviour of the coated Ti-45Al-8Nb (at.%) alloy was investigated at 850 °C and 900 °C under cyclic oxidation conditions in air. The ternary Ti-50Al-2Ag (at.%) coating did not provide oxidation protection to the substrate material at 850 °C. Two-phase γ-TiAl + Ti(Cr, Al)2 Laves coatings exhibited high oxidation resistance at 900 °C for up to 1000 cycles of 1 h dwell time at high temperature. During thermal exposure phase dissolution and transformation occurred. The slow oxide growth rates observed for the Ti – Al – Cr intermetallic layers were associated with the formation of a thin continuous alumina top scale established by the Laves, B2 and Z-phases. Small additions of hafnium and yttrium improved the oxidation resistance. In contrast, Ti – Al – Cr – Ag coatings exhibited poor oxidation behaviour at 900 °C.

Influence of Al and Hf Addition on the Oxidation Resistance of Nb-20Si-20Cr-5(Al, Hf) Alloys

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Effect of Hf on the growth of Al coatings on-martensite ferritic by means of CVD-FBR steels

In recent decades, there has been a marked interest for increasing the temperature and vapor pressure in the power generation plants with the aim of reducing fuel consumption. So, there would be a reduction in the emissions of pollutants such as CO2, SO2 and NOx. To achieve these improvements, it is required on one hand, to develop new ferritic-martensitic steels with Cr contents between 9-12% and on the other hand, to improve resistance against oxidation of the existing ones by using surface engineering. For this reason, the following work is intended to obtain Al and Al-Hf coatings and evaluate the effect of the addition of Hf to the bed on the growth of the coating of Al. In order to optimize the deposition process, a thermodynamic study was conducted using Themocalc program. Al and Al-Hf layers were deposited at three different temperatures in the range of 500 to 600 º C. The coatings were subsequently characterized by DRX and SEM / EDS. According to the results, it was found that for both cases, the layers were mainly formed by intermetallic compounds Fe2Al5 and FeAl3.

Refinement of Oxide Particles by Addition of Hf in Ni-0.5 mass%Al-1 mass%Y<SUB>2</SUB>O<SUB>3</SUB> Alloys

The effect of adding minor elements, such as Ti, Mg, Zr, Ca or Hf, on the size of oxide particles was investigated in Ni-based ODS alloy, Ni-0.5 mass%Al- 1 mass% Y 2 O 3 . Among these elements, Hf is the most effective at refining the oxide particles, particularly at a concentration of 0.8 mass% Hf, as verified by TEM observation and hardness measurement. X-ray diffraction measurements indicate that the formation of Y 2 Hf 2 O 7 is responsible for the refinement of oxide particles. The Hf is also effective for a commercial superalloy of PM 1000.

Effects of Hf and CNTs on structure and magnetic properties of TbCu 7-type Sm–Co magnets

SmCo 7, SmCo 6.9Hf 0.1, SmCo 6.9Hf 0.1(CNTs) 0.05 and SmCo 6.9Hf 0.1(CNTs) 0.1 as-cast alloys and ribbons melt-spun at the speed of 40 m/s are prepared. The X-ray diffractometer, electron microscope and magnetometer are employed to investigate the effects of Hf and CNTs on structure and magnetic properties of the as-cast alloys and ribbons. The results show that Hf and CNTs additions in SmCo 7 alloys can stabilize TbCu 7 structure. Hf addition can form HfCo 2 grain boundary phase. Fine dispersed Hf(CNTs) grain boundary phase can be derived from simultaneous addition of Hf and CNTs. The four types of ribbons all consist of TbCu 7-type Sm(Co,Hf) 7 main phase. Cooling rate is the key factor of forming TbCu 7-type phase. It is attempted that the grain boundaries with CNTs addition mainly consist of Sm(Co,Hf) 7(CNTs) x . The coercivity, remanence and remanence ratio of the ribbons all increase with Hf and CNTs additions. The comprehensive magnetic properties of SmCo 6.9Hf 0.1(CNTs) 0.05 ribbons are H ci = 13.95 kOe, M r = 48.85 emu/g, M 2T = 61.09 emu/g and M r/M 2T = 0.80. Excessive CNT addition may worsen the magnetic properties.

Microstructural selection in conventionally and rapidly solidified Sm–Co–T alloys

Abstract Microstructural selection maps under conventional solidification conditions have been determined in the vicinity of the binary eutectic point for Sm–Co–T alloys, with T = Nb, Mo, Ag, Zr, Ti, Hf and V up to 3 at.%. All additions except V were observed to disrupt the eutectic solidification front and lead to primary Co or Sm 2 Co 17 formation from the melt. An alloy with a composition of (Sm 0.09 Co 0.91 ) 97 V 3 was observed to have a eutectic structure. The alloying additions of Nb, Mo, Ag and Zr resulted in an expansion of primary Co formation, ultimately leading to deleterious effects on the magnetic properties. The addition of Ti and Hf extended the region over which primary Sm 2 Co 17 formed, potentially allowing the production of permanent magnet materials with higher Co content. Subsequent analysis of rapidly solidified Sm–Co–V alloys resulted in composition-magnetic property maps. Excellent magnetic properties were observed in the as-solidified state for (Sm 0.09 Co 0.91 ) 97 V 3 . The coercivity was determined to be 5 kOe and the energy product was 4.3 MGOe, which decreased as both the Sm/Co ratio and V content were changed. The melt-spun microstructure consisted of primary Sm 2 Co 17 and interdendritic Co more indicative of peritectic solidification, and the morphology of the phases changed as the Sm/Co ratio changed. The different conventionally and rapidly solidified microstructures suggest alteration of the equilibrium phase relationships due to high undercoolings.

Determination of metals in coal fly ashes using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry

A method for determination of Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn in coal fly ash samples using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) is proposed. The digestion procedure consisted in the sonication of the previously dried sample with hydrofluoric acid and aqua regia at 80 °C for 30 min, elimination of fluorides by heating until dryness for about 1 h and dissolution of the residue with nitric acid solution. A classical digestion method, used as comparative method, consisted in the addition of HCl, HNO 3 and HF to 1 g of sample, and heating on a hot plate until dryness for about 6 h. The proposed method presents several advantages: it requires lower amounts of sample and reagents, and it is faster. It is also advantageous when compared to the published methods, which also use ultrasound-assisted digestion procedure: lower detection limits for Co, Cu, Ni, V and Zn, and it does not require shaking during the digestion. The detection limits (μg g −1) for Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn were 0.06, 0.37, 1.0, 25, 0.93, 0.45, 4.0, 1.7 and 4.3, respectively. The results were in good agreement with those obtained by the classical method and reference values. The exception was Cr, which presented low recoveries in classical and proposed methods (83 and 87%, respectively). Also, the concentration for Cu obtained by the proposed method was significantly different from the reference value, in spite of the good recovery (91 ± 1%).

Synthesis of the first representative of dicarbothiacyanine dyes with completely fluorinated polymethine chain

2-Iodobenzothiazole was reacted with tributyl(pentafluorobutadienyl)tin in the Stille reaction conditions to give 2-pentafluorobutadienylbenzothiazole 1. The quaternary salt of 1 via interaction with 2-fluoromethylbenzothiazole methylene base, obtained in situ, forms two cyanine dyes 8 and 9 as a result of nucleophilic attack of two different positions of perfluorobutadiene chain. The pure 2-fluoromethylbenzothiazole methylene base (in a dimer form) was obtained by deprotonation of the corresponding salt by NaH and on reacting with 1 forms the dye base 11 that underwent electrocyclization and subsequent HF addition to form the cyclohexadiene 12 identified by X-ray analysis data. Upon quaternization and HF abstraction by toluidine the recyclization occurred and dye 8 – the first representative of dicarbothiacyanine dyes with perfluorinated polymethine chain – was obtained. It has λ max = 691 nm, that is 41 nm more than in non fluorinated dye, vinylene shift is equal to 111 nm.

Effect of hafnium on creep behavior of a corrosion resistant nickel base superalloy

The effect of the selective additions of hafnium (Hf) on the variation of creep life and microstructure of an experimental nickel base superalloy has been investigated. Artificial neural networks (ANNs) were utilized to predict the effect of Hf content on the creep rupture life at temperatures of 850–950 °C and showed that, with the addition of Hf, the creep life was prolonged. This effect was more pronounced at low stress than at high stress and was most noticeable with the first 0–0.6 wt% of Hf addition. Analysis of the correlation between microstructure and creep life of 0.4 wt% Hf doped alloy revealed that at low stresses the initiation and propagation of microcracks from MC carbides was retarded, and the beneficial effect of grain boundary strengthening on creep life was significant, although the tendency of appearance of γ′ rafting in 0.4 wt% Hf doped alloy is very close to that in Hf-free alloy. This was in agreement with above ANNs prediction. In addition, the relationship between the appearance of γ′ rafting and lattice misfit with regards to Hf content was discussed.

Microstructure and mechanical properties of NiAl–Cr(Mo)–Hf/Ho near-eutectic alloy prepared by suction casting

Abstract The microstructure and mechanical properties of 0.15 at.% Hf and 0.2 at.% Ho doped Ni-33Al-28Cr-6Mo near-eutectic alloys prepared by conventional casting and suction casting were investigated. The results reveal that the addition of Hf and Ho results in the formation of Ni2AlHf and Ni2Al3Ho phases, respectively, along the NiAl and Cr(Mo) phase interface in intercellular regions. Compared with the conventional-cast alloy, the microstructure of suction-cast alloy is well optimized, characterized by the thin interlamellar spacing, high proportion of eutectic cell area and fine homogeneously distributed Ni2AlHf and Ni2Al3Ho phases. Furthermore, the room temperature mechanical properties of the suction-cast alloy improve significantly, which can be attributed to fine microstructure, uniform distribution of the Ni2AlHf and Ni2Al3Ho phases and solid solubility extension.

Effects of Hf and CNTs on magnetic transformation and thermal stabilities of TbCu 7-type Sm–Co matrix ribbon magnets

SmCo 7, SmCo 6.9Hf 0.1, SmCo 6.9Hf 0.1(CNTs) 0.05 and SmCo 6.9Hf 0.1(CNTs) 0.1 melt-spun ribbons are prepared at a speed of 40 m/s. The phase structure, magnetic transformation and thermal stability of the ribbons are studied using thermal analysis, high temperature in-situ XRD and thermomagnetic analysis. The results show the Hf and CNTs (carbon nanotubes) additions have no influence on the formation of TbCu 7-type structure. Nevertheless, Hf addition may cause large heat storage; CNTs addition can lead to crystal-boundary blocking effect. The M– T curves of SmCo 7 matrix ribbons can all be divided into seven stages. The 1:7H decomposition, CoC x precipitation and 1:5 phase decrease successively emerge when the temperature increases from room temperature to 1100 °C.

Composition, Microstructure, and Water Vapor Effects on Internal/External Oxidation of Alumina-Forming Austenitic Stainless Steels

A family of creep-resistant austenitic stainless steels based on alumina (Al2O3) scale formation (AFA alloys) for superior high-temperature oxidation resistance was recently identified. Excellent oxidation behavior was observed at 650 and 700 °C in air with 10% water vapor. However, particularly at 800 °C, the presence of water vapor greatly increased the tendency for internal oxidation of Al. Water vapor also enhanced subscale Al depletion in some AFA alloys relative to dry air exposure. Increased levels of Nb additions were found to significantly improve oxidation resistance, as were reactive element additions of Hf and Y. Computational thermodynamic calculations of the austenitic matrix phase composition and the volume fraction of MC, B2-NiAl, and Fe2Nb base Laves phase precipitates were used to interpret oxidation behavior in terms of two-phase oxidation theory, reservoir effect, and the third-element effect of Cr. Of particular interest was the enrichment of Cr in the austenitic matrix phase by additions of Nb, which aided the establishment and maintenance of alumina. Higher levels of Nb additions also increased the volume fraction of B2-NiAl precipitates, which served as an Al reservoir during long-term oxidation. Implications of these findings for the design of AFA alloys with increased upper use temperature limits are discussed.

Microstructure and mechanical properties of Hf and Ho doped NiAl–Cr(Mo) near eutectic alloy prepared by suction casting

The microstructure and mechanical properties of 0.15 at.% Hf and 0.2 at.% Ho doped Ni–33Al–28Cr–6Mo near eutectic alloys prepared by conventionally casting and suction casting were investigated. The results reveal that the addition of Hf and Ho results in the formation of HfAlNi 2 and HoNi 2Al 3 phases respectively along the NiAl and Cr(Mo) phase interface in intercellular regions. Compared with the conventional-cast alloy, the suction casting optimizes the microstructure of the alloy further, which can be characterized by the refined NiAl/Cr(Mo) eutectic lamellar, high proportion of eutectic cell, and fine and homogeneously distributed HfAlNi 2 and HoNi 2Al 3 phases. In addition, the compression tests show that the suction-cast alloy has better mechanical properties, which can be attributed to the fine microstructure and uniform distribution of the HfAlNi 2 and HoNi 2Al 3 phases.

Formation of Silicon Nanoporous Structures Induced by Colloidal Gold Nanoparticles in HF/H2O2 Solutions

We developed an efficient method for the production of unique porous silicon structures, capable of achieving very small (less than 20 nm diameter) and uniform pore sizes, without the need for an external electrochemical cell or precoating of a discontinuous metal film. The method consists of the immersion of Si into a colloidal suspension of Au nanoparticles (NPs) containing a HF/H2O2 mixture. Gold colloids are known to be stable in neutral aqueous solutions, mainly because of the electrostatic repulsion between nanoparticles that carry the same negative surface charge. In acidic solutions obtained, for example, by addition of HF, however, conventional Au NPs colloids tend to lose their negative charge and to precipitate. A novel colloidal solution avoids NP precipitation upon acidification and thus enables Au NPs adsorption onto the Si surface, which triggers Si etching along definite crystallographic directions. The etching process occurs independently of the Si doping type or doping level. Because of ...

Sulfur Segregation at Al2O3/γ-Νi + γ′-Ni3Al Interfaces: Effects of Pt, Cr and Hf Additions

The interfacial chemistry that developed as a result Al2O3-scale growth on γ-Νi + γ′-Ni3Al alloys at 1150 °C was studied using scanning Auger microscopy after the oxide layer was scratched to spall under ultra-high vacuum. The extent of scale spallation was used to evaluate semi-quantitatively the interfacial strength. The alloys investigated were primarily γ′ in structure, containing 22 at.% Al plus further additions of Pt, Cr and/or Hf. In the case of the binary γ + γ′ alloy, it was found that a sub-monolayer of sulfur segregated at the alloy/scale interface. Platinum reduced and hafnium eliminated sulfur segregation, but chromium enhanced it through Cr–S co-segregation, even on Pt- and Hf-containing alloys. Platinum also segregated slightly at the alloy/scale interface. The interface strength was a strong function of the sulfur content. Beyond the effect of eliminating S segregation, Pt and Hf both showed additional beneficial effects on alumina scale adhesion.