Amounts Of Hafnium Research Articles

Изучение влияния содержания гафния и эрбия на формирование микроструктуры при литье алюминиевого сплава 1590 в медный кокиль

Introduction. High-magnesium aluminum alloys are widely used in the automotive, building and aerospace industries due to its low specific gravity and high strength. The characteristics of such alloys can be improved by small additions of scandium and zirconium. However, scandium is very expensive, so in new generation alloys its amount is tended to be reduced. In the recently developed 1590 aluminum alloy, this was achieved by addition of erbium and hafnium. The objective of the paper is to study the effect of erbium and hafnium concentrations on the modification of the cast structure in 1590 aluminum alloy at high solidification rates. Research Methods. The paper investigates the microstructure, chemical composition and size of intermetallic compounds in specimens from ten alloy 1590 modifications with different hafnium and erbium contents cast into a copper chill mold with a solidification rate of 10 °C/sec. The grain structure was studied using an optical microscope. The chemical composition and size of the intermetallic phases were studied using a Tescan Vega 3 scanning electron microscope. Results and discussion. It is established that as the amount of hafnium and erbium increases, the cast structure is modified. In general, grain refinement with the addition of hafnium and erbium can be explained by a higher degree of supercooling between the solid and liquid phases. At a hafnium content of 0.16 %, the dendritic structure begins to transform into an equiaxed grain structure. This transformation can be explained by the appearance of primary intermetallic compounds of the Al3Sc type in the liquid phase. Such intermetallic compounds are identified at a concentration of erbium and hafnium equal to 0.16 %. Moreover, in all alloys eutectic intermetallic compounds are identified that contained manganese and iron and had no effect on the cast structure. Comparison with previously obtained results on the grain size of specimens cast into a steel mold shows that with higher solidification rate, the structure modification in 1590 alloy is getting less efficient. This is explained by an increase in the concentration of transition elements in the solid solution, primarily scandium, necessary for the formation of primary intermetallic particles.

Mechanical and Thermal Behavior of Cu84−xAl13Ni3Hfx Shape Memory Alloys

The physical characteristics of a shape memory alloy can be controlled by different production techniques and the rate of constituents’ contribution. In this study, CuAlNiHf shape memory alloys, with three different amounts of Hf, were produced by the induction melting method. Many measurements such as differential scanning calorimetry (DSC), scanning electron microscope, energy dispersive X-ray, and the stress–strain test were carried out. The DSC measurement showed that the austenite transformation temperatures were decreased by doping more amount of hafnium into the alloy. All specimens showed a wide temperature hysteresis, which decreased by increasing Hf content. Also, the elastic modulus was raised by increasing the Hf amount. Although $${\gamma }_{1}^{{\prime}}$$ and $${\beta }_{1}^{{\prime}}$$ are the dominant phases in the CuAlNiHf with low Hf composition, substituting Cu with Hf enhanced the amount $${\beta }_{1}^{{\prime}}$$ -phase compared to $${\gamma }_{1}^{{\prime}}$$ -phase.

Establishment of Carbo-Chlorination Facility and the Preparation of High Pure Hafnium Chloride for Space Grade Applications

In view of the increase in demand of atomic energy and also dynamic increase in the number of space flights in our country, the limitation shown by developed countries on supply of hafnium metal for strategic applications has made our country to develop indigenously for its sustainability. The technology for the setting up of the hafnium pilot plant has been initiated by C-MET Hyderabad in collaboration with VSSC (ISRO) in order to compete with rest of the world. India has a good reserve of hafnium containing zircon sand where the hafnium containing zirconium is in the range of 1:50. A good quantity of zircon sand is available in mineral rich beach sands of India. Nuclear Fuel Complex, Hyderabad has commercial plant to produce nuclear grade zirconium for producing atomic energy. Zirconium scrub raffinate solution a by-product of NFC, Hyderabad containing decent amount of hafnium and zirconium is the raw material used for developing NIOBHAT 101 alloy such as niobium and hafnium for space grade applications and nuclear reactor control rods as the hafnium is having high neutron absorbing capacity. The major steps involved are separation of zirconium and purification of hafnium by solvent extraction, preparation of hafnium oxide, feed preparation and chlorination, reduction of hafnium chloride and separation of magnesium by vacuum distillation and sponge handling. In this regard Briquetting and Carbo-Chlorination processes are very vital because the reactivity of oxides depends on the calcination and coking conditions keeping a side precipitation conditions. The phase purity and chemical purity of hafnium chloride has immense influence on the following process namely, Kroll’s Reduction. This paper enumerates the experiments conducted in obtaining phase pure hafnium chloride. The data leading to optimised process parameters for the production of phase pure material has been presented.

The Influence of Surface Preparation Method on Microstructure of HF-Modified Aluminide Coatings Deposited by CVD Method on Rene 80 and MAR M-247 Nickel Superalloys

In the article the hafnium modified aluminide coatings deposited using chemical vapour deposition (CVD) method were analyzed. The influence of surface treatment (grinding, sandblasting with different pressures) on microstructure of coatings were described. The Re 80 and M-247 nickel superalloys were used as substrate. Thickness of the obtained aluminide coating was in the range 32-45 mm on Re 80 and 40-45 mm on M-247 respectively. The average amount of Al in the additive layer was 22-24 wt% on Re 80 and about 21 wt % on M-247 base alloy. The total amount of hafnium in coatings did not exceed 2.5 wt % - usuallly below 0.5 wt %. The conducted research has shown that there is no strong influence of surface preparation methodology on microstructure of aluminide coatings obtained by CVD method.

The synthesis of hafnium nanomaterials by alkali metal reduction of hafnium tetrachloride

Hafnium tetrachloride was reduced in organic solvents with lithium powder, sodium–potassium alloy, or lithium hydride/Et3B. All reductions required sonochemical agitation to proceed at an appreciable rate, with the notable exception of the reaction of HfCl4 with Li in diethyl ether. Activation of C–H bonds occurred in all reactions, which resulted in carbon-containing products. HfCl4 was reduced on a 50-g scale with LiH/Et3B, and a 10-g scale with Li powder in pentane. All the solid products from the reductions were converted to nanomaterials by annealing under vacuum from 500 to 1,000 °C, which also resulted in the sublimation of the alkali metal salts. The nanomaterials contain a mixture of products with the α-Hf (hexagonal) structure (crystallite size 8–250 nm) and the HfC (FCC) structure (crystallite size 3–80 nm), with the amount of hafnium in the bulk annealed product varying from 88 to 99 wt%. When toluene, pentane, or triethylamine solvents were used, the presence of amorphous graphitic or carbonaceous material was also detected by solid state 13C NMR. Thermally annealed products were additionally characterized by electron microscopy and thermal analysis under Ar/O2, and have BET surface areas ranging from 2.7 to 155 m2/g.

Power Play: On the Notion of Fractional Quantum Fourier Transform

Quantum computing is a research area that has held much promise over the last decade. With the increasing min iaturization in the semiconductor industry, one of the major problems with manufac tured chips is the increased power dissi pation. Recent research from IBM and Intel has found ways of minimizing the power dissipation from the chips by replacing some part of silicon with haf nium. Though the replacing of silicon with hafnium (the first chip with even smallest amount of hafnium is still await ing production) shall be helpful, it is not the solution with the ever-increasing level of miniaturization. Ultimately, there should be some way out when the size of a transistor on a chip gets to the size of the atom, the fundamental particle of matter. With such a level of miniaturization, the quantum effects of the particles shall become prominent and, in effect, it is not able to represent data in its present form. The data at that level of miniaturization will have to be represented and structured using quantum properties of particles and the operations on data shall be performed using quantum mechanical phenomenon.

Tandem 1,3-azaprotiocyclotransfer–cycloaddition reactions between aldoximes and divinyl ketone. Remarkable rate enhancement and control of cycloaddition regiochemistry by hafnium(iv) chloride

The tandem 1,3-azaprotiocyclotransfer–cycloaddition reaction between aldoximes and divinyl ketone affords the exo- isomers of substituted 1-aza-8-oxabicyclo[3.2.1]octan-4-ones when a substoichiometric amount of hafnium(IV) chloride is added.

Nature of the Earth's earliest crust from hafnium isotopes in single detrital zircons

Continental crust forms from, and thus chemically depletes, the Earth's mantle. Evidence that the Earth's mantle was already chemically depleted by melting before the formation of today's oldest surviving crust has been presented in the form of Sm–Nd isotope studies of 3.8–4.0 billion years old rocks from Greenland1,2,3,4,5 and Canada5,6,7. But this interpretation has been questioned because of the possibility that subsequent perturbations may have re-equilibrated the neodymium-isotope compositions of these rocks8. Independent and more robust evidence for the origin of the earliest crust and depletion of the Archaean mantle can potentially be provided by hafnium-isotope compositions of zircon, a mineral whose age can be precisely determined by U–Pb dating, and which can survive metamorphisms4. But the amounts of hafnium in single zircon grains are too small for the isotopic composition to be precisely analysed by conventional methods. Here we report hafnium-isotope data, obtained using the new technique of multiple-collector plasma-source mass spectrometry9, for 37 individual grains of the oldest known terrestrial zircons (from the Narryer Gneiss Complex, Australia, with U–Pb ages of up to 4.14 Gyr (10–13). We find that none of the grains has a depleted mantle signature, but that many were derived from a source with a hafnium-isotope composition similar to that of chondritic meteorites. Furthermore, more than half of the analysed grains seem to have formed by remelting of significantly older crust, indicating that crustal preservation and subsequent reworking might have been important processes from earliest times.

Effect of hafnium on the structure and properties of wrought nickel-base alloys

1. In nickel-base alloys hafnium enters into the composition of nitrides of the type Ti(C, N) and Nb(C, N), partially replacing atoms of titanium, niobium, and aluminum in nitrides TiN, NbN, and AlN, and it also enters into the composition of the solid solution and strengthening γ-phase. 2. Hafnium promotes an increase in the amount of MC type carbides with a high carbon content, a reduction in M6C carbides, and removal of carbide liquation in nickel-base alloys. 3. An excess amount of hafnium in alloys leads to formation of primary phases of the type Ni, (Hf, Ti)2, and secondary phases: lamellar phase Ni3 (Ti, Hf) and Ni3 (Nb, Hf). 4. In worked alloys hafnium refines grains and it retards grain growth in the temperature range 1100–1200°C. 5. Hafnium promotes an increase in the strength properties of alloys at 20°C, and it does not alter ductility. Optimum additions of hafnium lead to a marked increase in time to failure for alloys in the temperature range 700–800°C. 6. On adding small amounts of hafnium to alloys there is an increase in the resistance of the metal to cracking near the seam during welding and during heating of welded joints.

Hot brittleness of Mo+30% W

1. The alloy of Mo+30% W is susceptible to hot brittleness at 1400–1800°C. 2. Varying the tungsten content from 28 to 35% has little effect on the susceptibility to hot brittleness. Raising the carbon content from 0.002 to 0.007% sharply reduces the reduction in section in the hot brittleness range. The addition of a small amount of hafnium (∼0.2%) to the Mo+30% W alloy reduces susceptibility to hot brittleness. 3. Increasing the strain rate within the limits of 0.5–3000 mm/min reduces susceptibility to hot brittleness. 4. The hot brittleness of the alloy is due to precipitation of phase of the Mo2C type in the grain boundaries.

A Survey of Mathematical Correction Procedures in X-Ray Spectrometry

X-ray spectrometry is an old technique dating back some sixty-odd years and although most of the early interest revolved around the qualitative aspects of the method it wasn't long before attempts were made to obtain quantitative data. One of the first recorded attempts was that by Coster and von Hevesey who in 1923 accurately determined the amount of hafnium in zirconium using tantalum as an internal standard. Glocker and Schreiber were the first to attempt calculation of X-ray characteristic line intensity from first principles although no attempt was made at that time to correct for secondary fluorescence. In von Hevesey's book, “Chemical Analysis by X-Rays,” published in 1932 , a whole chapter is devoted to what is called “Disturbing effects and their avoidance.” Among the effects discussed were primary and secondary absorbtion and third element effects. Matrix correction equations were developed although most of the quantitative work at that time was done using internal standards.

Hafnium tantalum nitride resistive sea for the silicon diode-array camera tube target

A new material has been developed as a resistive sea for the silicon diode-array camera tube target. The material is prepared by reactive sputtering of a hafnium tantalum cathode in a nitrogen atmosphere. By adjusting the relative amounts of hafnium and tantalum in the cathode or by changing the sputtering parameters, the resistivity of the hafnium tantalum nitride sea may be optimized. The nitride may be heated to 350°C during camera tube bakeout with no degradation in performance. By controlling the film deposition conditions, electrostatic focus camera tubes have been made with excellent aging, dark current, lag, and resolution characteristics.

Interactions of silver halide sols with hydrolyzed hafnium species

Coagulation and reversal of charge effects of freshly prepared and heated solutions of hafnium tetrachloride have been studied as a function of the pH using aged silver halide sols and solsin statu nascendi. It was shown that the critical coagulation concentration and the critical stabilization concentration (due to charge reversal) increased with increasing pH. These observations have been related to the hydrolysis of the hafnium ion. At pH values above ∼4 essentially the entire amount of hafnium is present in the form of the neutral soluble, species Hf(OH)4. This accounts for the inability of the hafnium solutions to reverse the charge of the sols at higher pH values. The adsorption measurements carried out with the aid of the radioactive isotope181Hf showed that the neutral hydrolyzed species are strongly adsorbed on negatively charged silver iodide particles. The adsorbed amounts of hafnium on a AgI sol are considerably larger than in the case of charged hydrolyzed ions (such as hydrolyzed thorium ions) on a similar sol. This is explained by the ability of the neutral hafnium species, Hf(OH)4. to form a close-packed adsorbed layer. The results confirm previous findings that the enhanced adsorption of hydrolyzed ions is caused by the presence of the hydroxyl group, whereas the ionic charge plays a negligible role in this case.

Cation-exchange separation of hafnium and zirconium from accompanying ions

Hafnium and zirconium are not retained on the strongly acidic cation-exchange resin Dowex 50 from a mixture consisting of methanol and 12 M nitric acid (19:1) which is 0·1 Min trioctylphosphine oxide. On the other hand most other elements investigated are strongly adsorbed on the resin from this medium so that they are readily separated from hafnium and zirconium. These elements include titanium, rare earths, alkali metals, alkaline earth metals, iron, cobalt, manganese and zinc. This separation technique has been found to be suitable for the separation of tracer and milligram amounts of hafnium and zirconium from accompanying metal ions. If in place of methanol other organic solvents such as acetone, tetrahydrofuran and methyl glycol are used the selectivity of the separation of zirconium and hafnium from the other elements is decreased. The same effect is observed when hydrochloric acid is used in the mixtures instead of nitric acid.

Fluorescence Analysis of Trace Amounts of Hafnium in Zirconium Using a Silicon Crystal

AbstractThe proper choice of an analyzing crystal sometimes makes It possible to suppress second-order reflections which interfere with X-ray fluorescence analysis. Some of the problems associated with the analysis of small amounts of hafnium in zirconium, using a silicon crystal and a pulse-height analyzer, are discussed.