Calculation of salt activities in molten salt hydrates applying the modified BET equation,I: Binary systems

Summary On the basis of the modified BET model according to Stokes and Robinson, an equation for the calculation of salt activities in molten salt hydrates has been derived. The equation is used to describe successfully the liquidus curves of the hydrates of MgCl₂, Mg(NO₃)₂ and CaCl₂ inT-x diagrams. A promissing feature of the model is the small number of adjustable parameters and its extrapolative power.Dedicated to o. Univ._Prof. Dipl.-Ing. Dr. mont. Heinz Gamsjäger on the occasion of his 60th birthday     

Evaluation of molten inorganic salt hydrates as reaction medium for the esterification of cellulose

Molten inorganic salts and salt hydrates are highly efficient solvents for cellulose. The acetylation and deacetylation of the polymer dissolved in this group of cellulose solvents was investigated. The formation of cellulose acetates in molten salts with low water content and low acidity was confirmed by FT-IR-spectroscopy and ¹³C-CP/MAS-NMR spectroscopy. The degree of substitution was investigated by ¹H-NMR measurements after perpropionylation.     

Evaluation of molten inorganic salt hydrates as reaction medium for the derivatization of cellulose

Molten inorganic salt hydrates are highly efficient solvents forcellulose. The carboxymethylation of the polymer dissolved in this new group ofcellulose solvents was investigated. The homogeneous carboxymethylation ofcellulose in molten LiClO₄3H₂O using sodiummonochloroacetate in the presence of NaOH is possible. The formation of CMC wasconfirmed by FT- Raman spectroscopy. Structure analysis by means of HPLC afterchain degradation showed the formation of CMC with a DS of 2 after a shortreaction time of 4 h. The derivatives exhibit a statisticaldistribution of substituents along the polymer chain if prepared in moltenLiClO₄3H₂O as solvent. A substituent distributioninthe order C-6 > C-2 C-3 for anhydroglucose units (AGU) was concludedfrom ¹H-NMR measurements. The synthesis of CMC in the swellingmediumLiClxH₂O (2 x 5) yields polymers with astatistical distribution of functional groups along the chain. The watercontentof the salt melts has a dramatic influence on the DS_CMC.     

Thermodynamics of saturated lanthanide nitrate-water systems

The thermodynamic properties of saturated aqueous lanthanide nitrate solutions were determined using recently published critically evaluated solubility and activity data. The variation of the thermodynamic functions and congruent melting points as a function of atomic number are interpreted in terms of changes in inner sphere coordination number in both the solid hexahydrates and in the aquo ions, and in terms of the double-double effect.Inconsistencies in experimental solubility data are generally caused by uncertainties in solid phase composition which is shown to be due to the very small Gibbs energies accompanying transitions from stable to metastable systems differing in the number of hydrating water molecules.Presentation to First International Symposium on Solubility Phenomena, University of Western Ontario, London, Ontario, August 21–23, 1984.     

Measurement of molten salt Raman spectra by the use of fiber optics

A novel all-silica fiberoptic probe is described. Instead of cementing individual optical fibers together, the fibers are fused together within a silica tube. This all-silica probe has been used for obtaining Raman spectra of various molten salt systems at temperatures up to 720 °C. It has also been used for Raman spectral studies of samples at ambient temperatures.     

Thermal and calorimetric investigations on beryllium periodate hydrates

The thermal decompositions of two beryllium periodate hydrates, Be(IO₄)₂·8H₂O and Be(H₄IO₆)₂·2H₂O, were studied by DTA and TG in the temperature range from 298 to 1073 K, and by DSC from 298 to 723 K. The intermediates of the thermal decompositions were identified via quantitative analysis, IR spectroscopy and the TG curves. The data obtained were utilized to suggest a scheme for the thermal decompositions of the two periodates. Both compounds decompose via an anhydrous beryllium iodate, and the final residue is beryllium oxide.The enthalpies of the phase transitions were determined from the DSC curves.

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Zusammenfassung Die thermische Zersetzung der Berylliumperiodat-hydrate Be(IO₄)₂·8H₂O und Be(H₄IO₆)·2H₂O wurde im Temperaturbereich 298–1073 K durch TG-DTA und von 298–723 K mittels DSC untersucht. Zwischenprodukte der thermischen Zersetzung wurden durch quantitative Analyse, IR-Spektroskopie und TG-Kurven identifiziert. Im Ergebnis wird ein Schema für die thermische Zersetzung der beiden Periodat-Hydrate vorgeschlagen. Beide Verbindungen zersetzen sich über wasserfreies Berylliumiodat Be(IO₃)₂ als Zwischenprodukt, das feste Endprodukt ist BeO. Die Umwandlungsenthalpien werden aus den DSC-Kurven abgeschätzt.

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— Be(IO₄)₂·8₂ Be(₄IO₆)·2₂ — 298–1073 298–723 . , . . . .

     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. III

Dehydration of double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O where M(I)Rb(I) and M(II)Mg(II), Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) has been studied by derivatograph. Thermal parameters like activation energy, order of reaction, enthalpy change etc. for each step of dehydration have been evaluated from the analyses of TG, DTA and DTG curves and these parameters are compared with corresponding salt hydrates of the NH₄ and K(I) series. These double salt hydrates are deuterated and studied similarly. Activation energies for the first step of dehydration of these salt hydrates increase with the increase of second ionisation potential of the central metal except for Mg. The nature of dehydration changes in the cases of double salt hydrates of Mg(II) and Ni(II) on deuteration. The order of reaction for each case of dehydration has been found to be unity. The enthalpy change per mole of water varies from 11.4 to 17 kcal.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. VI

Non-isothermal studies of the dehydration of double salt hydrates of the type K₂AB₄·M(II)SO₄·6H₂O where AB₄BeF^2?₄ or SeO^2?₄ and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D₂O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ～11-～19 kcal mol^?1     

Sealed tube differential thermal analysis studies of some nickel(II) salt hydrates

Sealed and open tube DTA curves are reported for nickel sulfate, nitrate, ammonium sulfate, chloride, acetate, formate and perchlorate hydrates. The endothermic peaks for the sealed tube reactions were smaller than those found for the open tubes, due to the lack of water vaporization in the former. With the exception of NiSO₄-(NH₄)₂SO₄-6H₂O, the peaks for the sealed and open tube reactions appeared at about the same initial peak temperature. The sealed tube reaction intervals (T_f-T_i) were shorter than those found for the open tube.     

Low-frequency Raman spectra of nitric acid hydrates

Raman spectra of solid nitric acid hydrates (NAM, alpha- and beta-NAD, alpha- and beta-NAT, and NAP) are obtained in the low-frequency region 20-175 cm(-1) where phonon bands show characteristic patterns. This fingerprint information, intimately related to the structure and symmetry of the unit cell, is well suited for observation of phase changes in solid nitric acid hydrates and allows the distinction of mixtures of different hydrate phases. The low-frequency spectra are correlated with the spectra of the respective symmetric NO stretching vibration (1000-1080 cm(-1)), with literature data, and with X-ray diffraction patterns.     

The structure and the Raman vibrational spectrum of the beryllium aquacation

The experimental Raman vibrational spectrum of the 5.94 m water solution of the beryllium(II) chloride has been acquired. Theoretical frequencies, infrared and Raman intensities of the vibrational spectrum of the beryllium cation tetrahydrate have been calculated by means of quantum chemical approach. The peaks of the experimental spectrum have been assigned on the basis of the results of the quantum-chemical calculations. It has been shown that the hydrating surrounding of the aquacation increases effectively the frequency of the beryllium-oxygen stretching vibration by 16% in comparison with the free complex.     

DSC study of melting and solidification of salt hydrates

Most salt hydrates, especially those proposed for thermal-energy-storage applications, melt incongruently. In static systems, this property often leads to differences between the enthalpy of fusion and enthalpy of solidification. By means of differential scanning calorimetry (DSC), these differences have been determined for several salt hydrates. For Na₂SO₄ · 10 H₂O, the enthalpy of solidification at or near the peritectic temperature is never more than 60% of the enthalpy of fusion; further cooling leads to a second phase transition at a temperature corresponding to eutectic melting of mixtures of ice and this hydrate. This asymmetrical melting and freezing behavior of Na₂SO₄ · 10 H₂O decreases its potential as an energy-storing medium and also limits its usefulness for temperature calibration of DSC instruments. Sodium pyrophosphate decahydrate, Na₄P₂O₇ · 10 H₂O, although in some ways a higher temperature analog of Na₂SO₄ · 10 H₂O, exhibited a smaller discrepancy between the enthalpies of fusion and of solidification; its relatively high transition temperature permits a more rapid solidification reaction than is the case for Na₂SO₄ · 10 H₂O. For Mg(NO₃)₂ · 6 H₂O, a congruently melting compound, the magnitude of ΔH of crystallization equalled ΔH of fusion, even when supercooling occurred; a solid-state transition at 73°C, with ΔH = 2.9 cal g^?1, was detected for this hydrate. MgCl₂ · 6 H₂O, which melts almost congruently, exhibited no disparity between ΔH of crystallization and ΔH of fusion. CuSO₄ · 5 H₂O and Na₂B₄O₇ · 10 H₂O exhibited marked disparities. Na₂B₄O₇ · 10 H₂O formed metastable Na₂B₄O₇sd 5 H₂O at the phase transition; this was derived from the transition temperature and verified by relating the observed ΔH of transition to heats of hydration. Peritectic solidification of hydrates can be viewed as a dual process: crystallization from the liquid solution and reaction of the lower hydrate (or anhydrate) with the solution; where ΔH of solidification appears to be less in magnitude than the ΔH of fusion, the difference can be attributed to slower reaction rate between solution and the lower hydrate. New or previously unreported values for ΔH of fusion obtained in this study were, in cal g^?1: Mg(NO₃)₂ · 6 H₂O, 36; Na₄P₂O₇ · 10 H₂O, 59; CuSO₄ · 5 H₂O, 32; Na₂B₄O₇ · 10 H₂O, 33.     

The determination of aluminium by the ammonium benzoate method : An investigation into factors affecting the separation and estimation of aluminium and beryllium

An investigation has been made into the separation of aluminium from beryllium by the ammonium benzoate method. It has been shown (a) that over a wide range of concentrations aluminium can be determined with a maximum error of 2 %, (b) that the beryllium can be estimated after the removal of the aluminium with an error of not more than 2 % if the proportion of alumina, to beryllia is not more than 1 : 1. If the proportion of alumina to beryllia is greater than 1 : 1 considerable inaccuracy in the beryllium determination will result due to the co-precipitation of the beryllium with the aluminium benzoate; (c) that a double precipitation is required to obtain a satisfactory separation of aluminium and beryllium, (d) that although KoLTOFF el al. reported partial precipitation of beryllium with ammonium benzoate, this does not occur if tlie PH is carefully controlled between 3.5–4.0, and (e) it has been confirmed that ammonium benzoate precipitates aluminium quantitatively at PH 3.5ú4.0 wlilst beryllium does not commence to precipitate until about PH 6.5.     

Thermodynamic studies of clathrate hydrates

Thermodynamic studies of clathrate hydrates, mainly of structures I and II, are considered in this review which is based on 147 references. There are two main subjects. The first is the host lattice energy and the guest-host interaction energy, both of these quantities being related to the enthalpy of dissociation and composition of the hydrates. The second subject concerns orientational ordering phenomena occurring in both host and guest, as reflected in the low temperature heat capacity. The classical theoretical treatment of clathrate formation has been reconsidered on the basis of recent experimental results. Particular emphasis has been given to orientational ordering since this topic is undoubtedly central to clarifying the nature of clathrate hydrates.Ausgehend von 147 Literaturangaben wurden in diesem Review thermodynamische Untersuchungen von Klathrathydraten hauptsächlich der Struktur I und II betrachtet. Es gibt zwei Hauptaugenmerke. Als erstes die Wirtsgitterenergie und die Gast-Wirt-Wechselwirkungsenergie, beide bezogen auf die Dissoziationsenthalpie und die Bildungsenthalpie der Hydrate. Das zweite Hauptaugenmerk betrifft Orientierungs-Konditionierungserscheinungen sowohl in Wirt als auch Gast, wie in den Wärmekapazitäten bei niedrigen Temperaturen widergespiegelt wird. Auf der Basis jüngster experimenteller Ergebnisse wurde die klassische theoretische Betrachtung über die Bildung von Klathraten überprüft. Der Orientierung-Konditionierung wurde besonderer Nachdruck verliehen, da dies zweifellos eine entscheidende Rolle bei der Klärung der Natur der Klathrathydrate spielt. 147 I II. . «» « — », . «» « », . . , .

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Contribution No. 155 from the Chemical Thermodynamics Laboratory.     

The low-frequency Raman and IR spectra of nitric acid hydrates

The low-frequency region of the infrared and Raman spectra of nitric acid hydrates is analyzed. Theoretical calculations of the vibrational normal modes of the crystals of nitric acid monohydrate and the β-phases of the dihydrate and trihydrate are carried out, focusing the results in the regions below 175 cm⁻¹ and near the symmetric stretch of the nitrate ion NO₃⁻, around 1000–1100 cm⁻¹. A prediction of the corresponding infrared spectra is presented. A joint study is performed of the calculated normal modes, the predicted IR spectra, and the recently published Raman spectra of these compounds, based on symmetry considerations and using the atomic displacements associated to each normal mode as a further source of information. Although most of the modes present a strong mixture of atomic motions, assignments can be proposed for some of the vibrations.     

Preparation and characterization of salt hydrates encapsulated in polyamide membranes

Thermodynamic water activity control is a common technique in organic-phase biocatalysis. This can be accomplished by using the transitions of salt hydrates between their various hydrated forms as a water buffer. While this technique is well established, the use of free salt crystals in the reaction mixture poses numerous problems such as difficult recovery and poisoning of the biocatalyst. This article outlines a novel technique for the encapsulation of such materials which avoids these difficulties. The characterization of the capsules and their use as water activity buffers has also been described. Hydrates of Na₂HPO₄ were encapsulated in a polyamide membrane by interfacial polycondensation (IPC) of sebacoyl dichloride and diethylene triamine soaked onto the surface of the salt crystals. This technique, non-aqueous interfacial polycondensation (NAIPC) circumvents the need for the use of an aqueous phase to supply the polar reactant, the amine, thereby facilitating the encapsulation of water soluble materials. The coatings thus produced have an asymmetric membrane-like structure. A thin, non-porous, layer around the salt crystal supports a superstructure of porous polymer. This composite structure facilitates diffusion of material through the capsule wall and the use of hydrophilic polyamides for encapsulation promotes the transport of water. The capsules produced were between 0.5 and 2.5 mm in size and were of adequate mechanical strength to withstand osmotic pressure differences upto 26 bar and resist attritive forces experienced during their use.     

Simultaneous determination of beryllium and aluminium in mixtures using derivative spectrophotometry

The spectrophotometric determination of beryllium and aluminium with 5,8-dihydroxy-1,4-naphthoquinone in the presence of a non-ionic surfactant is reported. Absorption maxima, molar absorptivity and Sandell's Sensitivity of 1:2 (M:L) beryllium and aluminium complexes are, 585 nm and 598 nm, 1.63 x 10(4) l.mole(-1).cm(-1) and 2.04 x 10(4) l.mole(-1).cm(-1), and 0.55 ng/cm(2) and 1.32 ng/cm(2) respectively. Beer's law is obeyed between 7.20-3.96 x 10(2) ng/ml beryllium and 1.08 x 10(1)-1.08 x 10(3) ng/ml aluminium. A method for simultaneous determination of beryllium and aluminium in their mixture using derivative spectra is described. The range 3.6 x 10(1)-3.6 x 10(2) ng/ml beryllium could be determined in the presence of 1.08 x 10(2)-1.08 x 10(3) ng/ml aluminium, and vice versa.