Potassium Alloy Research Articles

Size distribution of NaK droplets released during RORSAT reactor core ejection

NaK droplets consist of eutectic sodium–potassium alloy and have been released during RORSAT reactor core ejections mostly on orbits close to 950 km altitude. They contributed to the space debris environment in the centimeter and millimeter regime. NaK droplets have been modeled before in ESAs MASTER Debris and Meteoroid Environment Model. The approach is currently revised for the MASTER 2005 upgrade. The new NaK model gives estimations of the parameters of the size distribution function, which are based on physical relations only. NASA radar observations confirm this physical approach. A bimodal size distribution is derived, which is based on the Rosin–Rammler equation. The Rosin–Rammler equation is an empirical volume distribution function. The number of parameters is limited to two. It is likely that the coolant system contains two types of orifice diameters. This makes it necessary to apply the Rosin–Rammler distribution twice, resulting in a bimodal size distribution with altogether four parameters. The comparison shows that the new NaK model is in good agreement with the NASA model, which is based on radar observations. Results of orbit propagation simulation runs are presented.

Intercalation and exfoliation routes to graphite nanoplatelets

Graphite nanoplatelets with thicknesses down to 2–10 nm are synthesized by alkali metal intercalation followed by ethanol exfoliation and microwave drying. Graphite that has already been intercalated and exfoliated with an oxidizing acid is reintercalated with an alkali metal to form a first stage compound, as confirmed by powder X-ray diffraction. This can be achieved either by heating graphite and potassium or caesium at 200 °C, or at room temperature using a sodium–potassium alloy. Reaction of the intercalated graphite with ethanol causes exfoliation of the graphene layers. Microwave radiation aids in drying and results in further separation of the sheets. Thermogravimetric analysis indicates that the graphite nanoplatelets are approximately 150 °C less stable in air than pristine graphite. High aspect ratio graphite nanoplatelets offer promise as reinforcements for high strength carbon–carbon composites.

Experimental study on flow characteristics of a vertically falling film flow of liquid metal NaK in a transverse magnetic field

Experimental study was carried out on the characteristics of a vertically falling film flow of liquid metal sodium–potassium alloy (NaK-78) in a vertical square duct in the presence of a transverse magnetic field. The magnitude of the applied magnetic field was up to 0.7 T. The Reynolds number, defined by the hydraulic diameter based on the wetted perimeter length and the liquid average velocity, ranged from 8.0×10 3 to 3.0×10 4. The free surfaces of the falling film flows in both a stainless steel and an acrylic resin channels were visualized. The instantaneous film thickness of the falling film flow in the acrylic resin channel was then measured by means of the ultrasonic transmission technique. Magnetohydrodynamic (MHD) effects on the characteristics of the falling film flow were investigated by the visualization and the statistical analysis of the measured film thickness. It was found that the falling liquid NaK film was thickened and the flow was stabilized remarkably by a strong transverse magnetic field. A bifurcation of the film was recovered by the applied magnetic field. The turbulence of the flow was substantially suppressed.

High‐pressure alloying of potassium and iron: Radioactivity in the Earth's core?

High‐resolution x‐ray diffraction provides evidence that potassium (K) alloys with iron (Fe) when the two pure elements are heated together at pressures above ∼26 gigapascals (GPa). Increases of 2–3% in volume of the ε (hexagonal close packed: hcp) high‐pressure phase of Fe can be attributed to the incorporation of ∼1 atomic% (∼7000 ppm by weight) K into Fe. Our results provide experimental support for predictions, derived from quantum mechanical calculations, that pressure can induce the alloying of K with Fe due to a change in the chemical‐bonding character of K from alkaline‐ to transition‐metal. Radioactive decay through the incorporation of 40K into the core could therefore be an important source of energy deep inside the Earth, helping to power the geodynamo and mantle dynamics.

Experimental Investigation of the Activity of Sodium in a Liquid Sodium–Potassium Alloy in a Wide Temperature Range

The EMF method is applied to investigate the activity of sodium in a molten sodium–potassium alloy containing 87.2 wt. % of potassium. The measurements are performed in two different experimental setups. One of them uses glass containing sodium ions as electrolyte, and the other one uses beta-ceramics. Therefore, the limiting experimental temperature in the first case does not exceed 550 K, while in the second case, it is about 750 K. The maximal relative error of the experimental data on the activity of sodium in a liquid Na–K alloy is approximately 3%. The discrepancy between the measurement results and the experimental and theoretical data available in the literature is within this error.

The Density of Liquid Sodium–Potassium Eutectic

The experimental investigations of the density of molten sodium–potassium alloys of eutectic composition, described in the literature, are briefly reviewed. This review is used to estimate the confidence error of the measurement results. The least squares method is used to simultaneously process the entire body of the experimental data on the density of the liquid Na–K eutectic. An approximating equation is derived for the temperature range from the melting point of the sodium–potassium eutectic to 1300 K. The mean-square error of the calculated values of the density of Na–K eutectic melt in the given temperature range is determined.

Thermal Experiments on a Model of a Target for an Accelerator-Driven System

The results of experiments performed on a model of a window target of an accelerator-driven system are presented. The model, the special features of the structure, and the measurement systems and methodological approaches are briefly described. A eutectic sodium–potassium alloy is used to simulate the lead–bismuth eutectic alloy. The following characteristics were measured directly in the experiments or obtained by analyzing the experimental data: coolant flow rate, power, absolute coolant temperature as a function of distance from the target membrane, the absolute temperature of the membrane surface as a function of the distance from the membrane center, the standard deviations of the indicated quantities and the pulsations of the coolant and membrane temperatures. The measurements showed that large temperature pulsations are observed on the membrane surface; these must be taken into account when analyzing the strength characteristics of a real target setup.

Activity of the Components of Binary Alloys of Alkali Metals: Na–K System

The activity coefficients of the components of the Na–K binary system are determined proceeding from the thermodynamic conditions of liquid–vapor equilibrium. The obtained data are in satisfactory agreement with the results of calculation of these activity coefficients by the pattern of the liquidus curve and using integral heats of mixtures of sodium–potassium alloys, as well as with the experimental data obtained by the emf method and by the effusion method.

Sodium–Potassium Alloy for the Reduction of Monoalkyl Aluminum(III) Compounds

Monoalkylaluminum(III) compounds of the type RAlX2 {R=Cp* (C5Me5), X=Cl, Br, I (1–3); (BisAlCl2)2 (Bis=(Me3Si)2CH) (5); TrisSi [(Me3Si)3Si], X=Cl, Br, I (6–8); CycTris [(CycMe2Si)(Me3Si)2C], X=Me, F, Cl, Br, I (11–15)} were prepared and characterized by NMR-, IR-, and mass spectroscopy as well as elemental analysis. The single-crystal X-ray structures of Cp*AlBr2, TrisSiAlX2·THF (X=Cl, Br, I), CycTrisAlX2·THF (X=Me, Cl, Br, I), and [CycTrisAl(μ-O(CH2)3CH2)]2 are reported. The monoalkylaluminum(I) compound (Cp*Al)4 (4) was isolated after the reduction of Cp*AlX2 (X=Cl, Br, I) using a Na/K alloy. The yield of (Cp*Al)4 has been improved compared to the previously reported method. However, completely different products were obtained when the THF adducts of TrisSiAlI2·THF and CycTrisAlI2·THF were used for the reduction with Na/K alloy. In the former case, the cleavage of the Si–Al bond was observed with the formation of elemental aluminum and (TrisSi)2, while in the latter the THF ring opening reaction occurred. CycTrisAlF2·THF was prepared by reacting CycTrisAlMe2·THF with Me3SnF.

Rayleigh–Bénard convection in liquid metal layers under the influence of a vertical magnetic field

The influence of a vertical magnetic field on the integral heat transfer and the temporal dynamics of liquid metal Rayleigh–Bénard convection is studied in an experiment using a small Prandtl number (Pr≈0.02) sodium potassium alloy Na22Kr78 as a test fluid. The test section is a rectangular box of large aspect ratio 20 : 10 : 1 that covers a parameter range of Rayleigh numbers, 103<Ra<105, and Chandrasekhar numbers, 0<Q<1.44×104. The integral heat transfer across the layer is evaluated from the measured temperatures at the upper and the lower boundary and the applied heat flux. Local, time-dependent temperatures are obtained from a four-element temperature probe placed in the middle of the liquid metal layer. The noncoplanar arrangement of the thermocouples enables the evaluation of the time-dependent temperature gradient vector that allows us to estimate the local isotropy properties of the time-dependent flow. From the damping effect of Joule dissipation, the convective heat transport decreases monotonically with increasing Chandrasekhar numbers. Fluctuations of the temperature field are damped significantly by the magnetic field. However, this effect is selective with respect to frequency. Long period fluctuations are strongly damped whereas short period fluctuations are less damped or may even be amplified. The observations show that significant convective heat transport is practically always associated with time-dependent flow. The fluctuating part of the local temperature gradient confirms the horizontal isotropy of the velocity field; no predominant orientation of time-dependent flow structures is established either with or without a magnetic field.

Synthesis, properties and structures of the tris(cyclopentadienyl)thorium(III) complexes [Th{η 5-C 5H 3(SiMe 2R) 2-1,3} 3] (R=Me or tBu)

The homoleptic, dark-blue, crystalline (disubstituted-cyclopentadienyl)thorium(III) complexes [Th{η 5-C 5H 3(SiMe 2R) 2-1,3} 3] (R=Me 1 or t Bu 3) were obtained in good yield from the appropriate tris(cyclopentadienyl)thorium(IV) chloride by treatment with an excess of sodium–potassium alloy in toluene at 20–35 °C with sonication. Complex 1 was also accessible by a similar reduction of [ThCp″ 2Cl 2] [Cp″=η 5-C 5H 3(SiMe 3) 2-1,3]; with possibly a transient Th(II) cyclopentadienyl as intermediate. Complex 1 with wet toluene afforded [(ThCp″ 3) 2(μ-O)] ( 2); it was unreactive with THF, DME, CO or H 2, but with Na–K alloy in THF it afforded a green, diamagnetic, readily oxidisable cyclopentadienylthorium complex. Complexes 1 and 3 showed singlet EPR spectra in methylcyclohexane at 298 K, whence it is concluded that they have a 6d 1 rather than a 5f 1 electronic ground state. Variable temperature EPR spectra, magnetic measurements and optical spectra of 1 are described and discussed. The X-ray structures of crystalline 1 and 3 show that each has approximate D 3 h symmetry about the Th atom, which can be regarded as bound to the centroid of each of the three cyclopentadienyl rings.

Characterization of potassium and sodium–potassium alloy solutions containing metal anions and complexed cations by means of NMR and ESR techniques

The influence of a complexing agent, kind of solvent and temperature on the stability and ionic composition of potassium and sodium–potassium alloy solutions containing metal anions and complexed cations as well as solvated electrons are discussed basing on the analysis of alkali metal NMR and ESR spectra. Surprisingly it seems that the stability of metal solutions in tetrahydrofuran at ambient temperature is inversely proportional to the durability of K + complex in the case of five studied ligands. The most stable metal solutions were obtained using 15-crown-5. It was shown that the characteristic blue colour of metal solutions is not connected with the presence of solvated electrons but with metal anions.

Extinction coefficient and skin depth of alkali metals from 10 to 1000 nm

The alkali metals have often been characterized as being transparent to optical radiation in the ultraviolet. An investigation was performed to evaluate the feasibility of exploiting this so-called transparency phenomenon for laser doppler velocimetry in these metals. The extinction coefficient, skin depth and skin depth divided by wavelength were determined from the literature for wavelengths between 10 and 1000 nm. Data is included for lithium, sodium, potassium, rubidium, cesium, and a sodium- 75% potassium alloy. The results show that the skin depths are less than 3 μm, and the prospects for perfoming liquid metal laser doppler velocimetry are poor. The compilation of the data in one document and in a common format may be useful to other researchers.

Preparation of polycarbosilanes and polysilanes from (trimethylsilylmethyl)chlorosilanes

The one-step conversion of (Me3SiCH2)SiCl3 to polycarbosilanes by reaction with three molar equivalents of the alkali metals lithium, sodium, or sodium potassium alloy is reported. The expected network polysilanes were not isolated. Under similar conditions (Me3SiCH2)SiHCl2 gives polysilanes. The low molecular weight polymers have been characterized by elemental analyses, gpc, and FT-IR, NMR, UV-vis, and mass spectroscopies.

Zur Chemie des Galliums, III [1] Darstellung und Struktur eines tetra(amino)substituierten Digallans Chemistry of Gallium, III Synthesis and Structure of a Tetraamino-Substituted Digallane

Abstract Dehalogenation of tmp2GaCl (tmp = 2,2,6,6-tetramethyl piperidino group) with sodium/ potassium alloy leads to the digallane (tmp)2Ga-Ga (tmp)2 as a pale yellow solid. Alterna­tively this digallane is prepared in good yields by reaction of four equivalents of tmpLi with Ga2Cl4·2 dioxane. Ga2(tmp)4 is characterized by MS. NMR (1H and 13C) and X ray structure determination. The gallium-gallium bond length is 252.5(1) pm and its two GaN2 units are twisted by 31° against each other.

Liquid Metal Flow Through a Right Angle Bend in a Strong Magnetic Field

AbstractIn designing a self-cooled liquid metal blanket based on the poloidaltoroidal flow concept, the magnitude of the MHD pressure drop and the character of the velocity distribution in the first wall coolant channels, that result from 3-dimensional MHD effects associated with the required right angle bends in the coolant flow, represent important design issues. To address these issues and to verify the relevant models used in the design, a joint MHD-experiment was conducted by Argonne National Laboratory (AND and Kernforschungszen-trum Karlsruhe (KfK). The test article was designed and built at ANL, and the experiments were performed at KfK’s MEKKA facility using a 3.6 Tesla superconducting solenoid magnet and a eutectic sodium potassium alloy working fluid. In the experiments, detailed voltage and pressure distributions on the duct walls and voltage distributions within the liquid metal were measured under a variety of Hartmann numbers and interaction parameters. Representative results from these mea...

An EPR study of 1-adamantylmethyl radicals

The 1-adamantylmethyl, di(1-adamantyl)methyl, and tri(1-adamantyl)methyl radicals have been prepared by photolysis of hexabutylditin in presence of the corresponding bromide, the 1-adamantylhydroxymethyl radical by photolysis of di-tert-bulyl peroxide in presence of 1-adamantylmethanol, and the di-1-adamantylketyl radical anion by photolysis of di-1-adamantyl ketone in presence of sodium–potassium alloy. The EPR 1H and 13C hyperfine coupling constants which are observed in these radicals and in the tetra-1-adamantylcyclobutadiene radical cation are discussed in terms of the structures of the radicals.The di-1-adamantylmethyl radical decays in cyclopentane at 310 K and in toluene at 180–240 K by clean pseudo first-order kinetics. The reaction is much faster in the latter solvent, implying that it involves abstraction of benzylic hydrogen. At 190 K in pentane, the decay shows second-order kinetics. The decay of the tri-1 -adamantylmethyl radical shows more complicated behaviour.

Effect of randomization on oxidative stability of vegetable oils at two different temperatures

Five vegetable oils were each randomized by chemical means (with the use of a sodium potassium alloy) and by enzymatic means (using a nonspecific lipase). The success of the randomization procedure was confirmed via positional analysis. The oxidative stabilities of the native and chemically randomized oils were determined at storage temperatures of 28°C and 55°C using absorbance at 234 nm as indicative of conjugated diene content. No difference between curves occurred in oils stored at 55°C, however, at the lower temperature all chemically randomized oils had significantly steeper slopes (P<0.05), suggesting a lower stability. When both enzymatically and chemically randomized oils were compared to native oils at 28°C, no significant difference occurred between slopes of native and enzymatically randomized oils, however, the end content of conjugated dienes was significantly higher for chemically randomized canola, corn and soybean oils (P<0.05). No difference was seen between the slopes of the three different oils from either linseed or sunflower. Since both of these oils exhibited higher oxidation rates, it is possible that observation of differences between the stability of native and chemically randomized oild is dependent upon the rate of the reaction.

Adhesive Energies at Potassium Alloys Interfaces

The density functional formalism is used to study the adhesive energies at interfaces of disordered alkali-metal alloys: K-Cs, K-Rb, K-Na. Similarly like for pure metals the range of strong bonding is about 4-5 a.u. The possibility of metal transfers is discussed. The calculated adhesion binding energy curves can be scaled into a universal curve as a function of separation.

De Haas-van Alphen measurements of the volume dependence of the electron scattering time in dilute potassium alloys

The volume dependence of tau k*, the electron scattering lifetime, has been obtained in KNa, KRb and KCs from de Haas-van Alphen measurements. The volume dependence of tau k* has also been deduced from the volume dependence of the electrical resistivity rho , and from the diffusion thermopower, S, using pseudopotential relations between these properties and between tau k* and tau rho *, the electron relaxation time occurring in rho and S. The values of d ln tau k*/d ln V obtained in these ways have been compared. In KRb good agreement can be obtained between the DHVA, resistivity and thermopower measurements, provided that in the analysis of the DHVA data the value for d in X/d ln V is taken to be approximately that for free electrons, where X is the Pauli spin susceptibility. On the same basis the agreement in KCs is rather poor mainly because of the difficulty in estimating the volume dependence of ( tau rho *- tau k*). In KNa the values of d ln tau k*/d ln V obtained from the DHVA and resistivity measurements are in agreement but that deduced from the thermopower is not; it has a value which is almost a factor of two different. The measured values of d ln tau k*/d ln V are compared with values calculated within the Ziman pseudoatom model.