Properties of molten alkali metal trifluoracetates

We have studied the thermal stabilities of the alkali metal trifluoroacetates by means of DTA and TG, and shown that they are stable in the solid form, with the exception of the lithium salt. We have determined the enthalpies of melting of these five salts. We have also studied the kinetics of decomposition of CF₃COONa, of CF₃COOK and of their mixture. This decomposition is in all cases of the first order. The mixture decomposes in two steps, the first one corresponding to the decomposition of the sodium salt.

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Zusammenfassung Die ThermostabilitÄt der Alkalitrifluoracetate wurde durch DTA und TG untersucht und festgestellt, da\ diese in der festen Form mit Ausnahme des Lithiumsalzes stabil sind. Die Schmelzenthalpie dieser fünf Salze wurde bestimmt. Die Kinetik der Zersetzung von CF₃COONa, CF₃COOK und ihrer Gemische wurde ebenfalls untersucht. Diese Zersetzung ist in allen FÄllen ein Vorgang erster Ordnung. Die Gemische werden in zwei Stufen zersetzt, wobei die erste Stufe der Thermolyse des Natriumsalzes entspricht.

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Résumé Nous avons étudié la stabilité thermique des trifluoroacétates alcalins par ATD et TG, et montré que seul le sel de lithium se décompose avant la fusion. Nous avons déterminé les enthalpies de fusion de ces cinq sels. Nous avons également étudié la cinétique de décomposition de CF₃COONa, CF₃COOK et de leurs mélanges. Cette décomposition est dans tous les cas d'ordre 1. Les mélanges se décomposent en deux étapes, la première correspondant à la thermolyse complète du sel de sodium.

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. , . , . CF₃COOK, CF₃COONa . . , .

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We are grateful to Miss H. Lartigue for technical assistance. Thanks are due to Prof. A. Buchs, Director of the Mass-spectrometry Laboratory.     

Equation of state for molten alkali metal alloys

Results on the density of binary and ternary alkali metal alloys of Cs–K, Na–K, Na–K–Cs, at temperatures from the freezing point up to several hundred degrees above the boiling point are presented. The theoretical equation of state is that of Ihm, Song, and Mason. The second virial coefficients, B(T), are calculated by using the corresponding states correlation of Boushehri and Mason. Calculation of the other two temperature-dependent parameters, α(T) and b(T), are performed by scaling rules with the latent heat of vaporization and the freezing point density as scaling constants. The results are within 5%.     

The reaction of ammonium salts in molten alkali metal nitrites

The thermal decomposition of ammonium chloride and sulphate in molten alkali metal nitrite eutectics cannot be represented by a simple stoichiometry. Nitrous oxide and nitric oxide are produced as well as nitrogen and water.Thermogravimetry is complicated by loss of solid material when the extremely rapid reaction commences at temperatures just below the melting points of the nitrite eutectics and by volatilisation of unreacted ammonium compounds, largely chloride and nitrite/nitrate from reactant solutions of ammonium chloride and ammonium sulphate, respectively.     

Electrokinetic studies of metal oxides in the presence of alkali trichloroacetates, trifluoroacetates, and trifluoromethanesulfonates

The electrokinetic potentials of anatase (titanium dioxide) and alpha-alumina were studied by means of various instruments in the presence of sodium and potassium trichloroacetates, trifluoroacetates, and trifluoromethanesulfonates at various pH, ionic strengths, and solid-to-liquid ratios. At concentrations up to 0.01 M, these salts do not induce substantial shifts in the isoelectric point of the oxides. Such behavior is typical of inert electrolytes.     

Trinuclear metal(III) trifluoroacetates

Hydrated and anhydrous trinuclear metal(III) trifluoroacetates of Cr and Fe were prepared by reaction of freshly precipitated metal oxides with trifluoroacetic acid, while manganese analogs by acid exchange. IR data show the presence of bidentate trifluoroacetate groups. The diffuse reflectance spectra suggest octahedral environment around metals.Mössbauer spectra show that iron atoms in the compounds are high spin hexacoordinated; two types of iron sites are suggested in hydrated iron compound. Low magnetic moment of chromium and iron compounds indicate antiferromagnetic coupling. Th anhydrous compounds decompose in single step with the evolution of (CF₃CO)₂O.M ₃O(O₂CCF₃)₇ form complexes [M ₃O(O₂CCF₃)₆·3Py]⁺ [O₂CCF₃]^– with pyridine.

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Dreikernige Metall(III)-Trifluoracetate

Zusammenfassung Es wurden hydratisierte und wasserfreie dreikernige Metall(III)-Trifluoracetate von Cr und Fe mittels der Reaktion von frisch gefälltem Metalloxid und Trifluoressigsäure dargestellt; die Mangan-Analogen wurden über Säure-Austausch gewonnen. Die IR-Daten zeigen die Präsenz von zweizähnigen Trifluoracetat-Gruppen an. Die diffuse-reflectance-Spektren sprechen für eine octahedrale Umgebung rund um das Metall. DieMössbauer-Spektren zeigen, daß die Eisenatome in den entsprechenden Verbindungen high-spin hexakoordiniert sind; dabei werden in den hydratisierten Eisenverbindungen zwei Typen von Eisenatomen gezeigt. Ein niederes magnetisches Moment der Chrom- und Eisen-Verbindungen zeigen eine antiferromagnetische Kopplung an. Die wasserfreien Verbindungen zersetzen sich in einem einzigen Schritt unter Entwicklung von (CF₃CO)₂O. Mit Pyridin bilden die VerbindungenM ₃O(O₂CCF₃)₇ die Komplexe [M ₃O(O₂CCF₃)₆·3Py]⁺ [O₂CCF₃]^–.

     

Consecutive recovery of uranium oxides from uranyl-containing molten alkali metal sulfate electrolytes

The oxygen coefficient (atomic ratio O/U) of a cathode product and the cathode current yield in consecutive recovery of uranium oxides from molten salt mixtures (nLi₂SO₄ + (1 ? n)Cs₂SO₄) + UO₂SO₄ and (Li,Na,K)₂SO₄ + UO₂SO₄ in air were analyzed as dependent on the electrolyte and the mean solvent-salt cation radius. The increasing mean solvent-salt cation radius and decreasing UO₂SO₄ concentration in the electrolyte during long-term electrolysis suppress the solvolysis of uranyl ions and decrease the oxygen coefficient in the cathode product. The cathode current yield decreases systematically during electrolysis and drops to zero long before the uranium is completely recovered from the melt. The ultimate uranium recovery increases as the mean solvent-salt cation radius increases.     

Electronic absorption spectra of solutions of molecular chlorine in molten alkali metal chlorides

Electronic reflection absorption spectroscopy has been used for measuring the electronic spectra of chlorine solutions in molten alkali metal chlorides 2CsCl-NaCl, KCl-NaCl, and CsCl in the range 240–400 nm. Absorption bands of chloride melts are interpreted as electronic transitions in the molecular group Cl₂ and in the triatomic linear group Cl ₃ ^? of symmetry D _∞h and C _∞V .     

Mixed-ligand complexes of alkaline-earth metal trifluoroacetates with monoethanolamine

The mixed-ligand complexes of the formula [M(CF₃COO)₂(MEA) _n ] (MEA is monoethanolamine; M = Ca (I) and Sr (II), n = 1.5; M = Ba (III), (n = 1) were obtained from appropriate salts M(CF₃COO)₂ · nH₂O and MEA in ethanol. Complexes I–III were characterized by elemental analysis data and IR spectra. Slow crystallization of a solution of complex III in air gave a single crystal of the formula [Ba(CF₃COO)₂(MEA)(H₂O)], which is a coordination polymer with C.N.(Ba) 9 (X-ray diffraction data). Thermal analysis showed that complexes I–III decompose under argon and in air to the corresponding fluorides at T < 400°C.     

Interaction of rare-earth oxides with binary molten mixtures of zirconium and alkali metal fluorides

Isothermal saturation, inductively coupled plasma mass spectrometry (ICP-MS), and X-ray powder diffraction were used to study solubilities of La₂O₃, Sm₂O₃, and Ho₂O₃ in the eutectic mixtures of LiF-ZrF₄, NaF-ZrF₄, and KF-ZrF₄ systems at temperatures from 873 to 1073 K. The solubilities of rare earth oxides in the molten fluorozirconate systems studied decrease in the increasing order of Ln³⁺ ion radii and in the increasing order of alkali metal cation radii in the binary mixture. The thermodynamic parameters of dissolution calculated for the oxides imply the dominance of a chemical dissolution mechanism, and this implication was supported by X-ray powder diffraction data.     

A thermogravimetric study of acidic and basic solutes in two molten alkali metal nitrate eutectics

The reaction of ten oxyanions and oxides, acting as Lux—Flood acids have been studied in both lithium nitrate—potassium nitrate and sodium nitrate—potassium nitrate eutectics and the stoichiometries of the reactions established. A series of acids arranged in order of decreasing strength has been drawn up, which is very similar for both eutetic solvents.Five Lux—Flood bases have also been studied in these two solvents. Sodium carbonate proved to be very stable to 500°C. Sodium peroxide revealed significant differences in stability and solubility in the two solvents, while lithium, sodium and potassium hydroxides showed differences in the two melts and also considerable differences between each other, suggesting that little cation exchange takes place in these solutions.     

Hydrogen storage over alkali metal hydride and alkali metal hydroxide composites

Alkali metal hydroxide and hydride composite systems contain both protic(H bonded with O) and hydridic hydrogen. The interaction of these two types of hydrides produces hydrogen. The enthalpy of dehydrogenation increased with the increase of atomic number of alkali metals,i.e.,-23 kJ/molH2 for LiOH-LiH, 55.34 kJ/molH2 for NaOH-NaH and 222 kJ/molH2 for KOH-KH. These thermodynamic calculation results were consistent with our experimental results. H2 was released from LiOH-LiH system during ball milling. The dehydrogenation temperature of NaOH-NaH system was about 150℃; whereas KOH and KH did not interact with each other during the heating process. Instead, KH decomposed by itself. In these three systems, NaOH-NaH was the only reversible hydrogen storage system, the enthalpy of dehydrogenation was about 55.65 kJ/molH2, and the corresponding entropy was ca. 101.23 J/(molH2 K), so the temperature for releasing 1.0 bar H2 was as high as 518℃, showing unfavorable thermodynamic properties. The activation energy for hydrogen desorption of NaOH-NaH was found to be57.87 kJ/mol, showing good kinetic properties.     

Hydrogen storage over alkali metal hydride and alkali metal hydroxide composites

Alkali metal hydroxide and hydride composite systems contain both protic(H bonded with O) and hydridic hydrogen. The interaction of these two types of hydrides produces hydrogen. The enthalpy of dehydrogenation increased with the increase of atomic number of alkali metals,i.e.,-23 kJ/molH2 for LiOH-LiH, 55.34 kJ/molH2 for NaOH-NaH and 222 kJ/molH2 for KOH-KH. These thermodynamic calculation results were consistent with our experimental results. H2 was released from LiOH-LiH system during ball milling. The dehydrogenation temperature of NaOH-NaH system was about 150℃; whereas KOH and KH did not interact with each other during the heating process. Instead, KH decomposed by itself. In these three systems, NaOH-NaH was the only reversible hydrogen storage system, the enthalpy of dehydrogenation was about 55.65 kJ/molH2, and the corresponding entropy was ca. 101.23 J/(molH2 K), so the temperature for releasing 1.0 bar H2 was as high as 518℃, showing unfavorable thermodynamic properties. The activation energy for hydrogen desorption of NaOH-NaH was found to be57.87 kJ/mol, showing good kinetic properties.     

甲烷在熔融碱金属碳酸盐中的还原行为研究

针对CH4在熔融碳酸盐中转化的新体系,研究了CH4在熔融碳酸盐介质中的还原行为.对CH4与熔融碳酸盐(Li2CO3、Na2CO,、K2CO3)的反应产物组分作了热力学分析,进行了实验研究,并对反应机制进行民探讨,研究结果表明,气体产物中CO、CO2的含量随反应温度的升高而增加;随反应时间的增加而降低;反应活性大小变化规律为:Li2CO3>Na2CO3>K2CO3,实验结果与理论分析相符.混合熔融盐具有更高的CO选择性,并且气体产物中CO、CO2浓度及CH4转化率随反应时间增加降低较快,较纯组分更适合作CH4转化反应介质.反应机制的推测表明H2、CO、CO2的产生分别来自于CH4裂解及裂解C与熔融碱金属碳酸盐的反应.     

Entropy predictions in molten binary alkali halide mixtures

Excess entropies for all the common anion molten binary alkali halide mixtures have been predicted, for the first time, using an extension of the conformal solution theory. The calculated entropies are in good agreement with available experimental results.     

Properties of molten carboxylates

Data are presented for the heats of phase changes and specific heats for the even chain length lead(II) carboxylates from hexanoate to octadecanoate. Structures are proposed by analogy to the properties of “fused” aqueous ampiphilic mesophases. Optical examination under a polarising microscope suggests the phase sequence

for the dodecanoate and lower chain length soaps. For tetradecanoate, and above, the V₂ phase is absent and the G phase melts directly to the liquid. The chain length dependence of the entropies of the crystal→G and G→V₂ or G→liquid transitions demonstrates that disordering of the hydrocarbon chain is a stepwise process. The entropy of the V₂→liquid transition is consistent with the melting of a globular solid and may indicate an average micelle size of 4 carboxylate molecules. This leads to a model of the isotropic liquid consistent with the viscosity data previously presented².     

A voltammetric and chronopotentiometric study of molten alkali acetates

The electrochemical behaviour of water, hydrogen ion, and molecular hydrogen has been investigated in (Na,K) acetate melt at 250 degrees with bright platinum electrodes by means of chronopotentiometry and voltammetry.