Phase transitions in potassium nitrate

It is shown that the heat of transition of the phase change II → I at 129° on heating KNO₃ is dependent on the thermal history of the sample, since it involves two steps, viz., II→ III and III→ I at 2° interval. During cooling, the latter step is fast and truly reversible, though with a temperature hysteresis. The former step is sluggish and is dependent both on temperature and time. Our results indicate that KNO₃ can be used for calibration purpose only if the material has not been heated beyond 128° in the immediately preceding three hours.     

Phase transitions in calcium nitrate thin films

Calcium carbonate is a ubiquitous mineral and its reactivity with indoor and outdoor air pollutants will contribute to the deterioration of these materials through the formation of salts that deliquesce at low relative humidity (RH). As shown here for calcium nitrate thin films, deliquescence occurs at even lower relative humidity than expected from bulk thermodynamics and lower than the recommended humidity for the preservation of artifacts and antiques.     

Thermoanalytical investigations of thallous nitrate

Thallous nitrate was investigated using TG, DTA, and DSC in conjunction with gas chromatography and X-ray diffraction analysis. TG showed a weight loss beginning at 380° with a 50 percent loss by 520°. This weight loss was demonstrated to be caused by boiling rather than thermal decomposition. The DTA extrapolated onset temperature for the boiling was 467°. Two solid-solid transition points and the melting point were determined by DTA to be 77, 145, and 207°, respectively. Heat of transition values determined by DSC were 0.15 kcal/mole at 77°, 0.87 kcal/ mole at 145°, and 2.18 kcal/mole for the melting at 207°.

---

Zusammenfassung Thallium(I)nitrat wurde mittels TG, DTA und DSC, mit Gaschromatographie und Röntgendiffraktionsanalyse gekoppelt, untersucht. TG zeigte einen beginnenden Gewichtsverlust ab etwa 380° und einen Verlust von 50% bis 520°. Es wurde gezeigt, daß dieser Gewichtsverlust eher vom Sieden als von der thermischen Zersetzung verursacht wird. Die aus DTA-Daten extrapolierte Anfangs-Siedetemperatur war 467°. Die Fest-festphasen Übergangspunkte und der Schmelzpunkt lagen, wie durch DTA ermittelt, bei 77, 145, bzw. 207°. Die mittels DSC bestimmten Wärmen der Übergangswerte betrugen 0.15 kcal/Mol bei 77°, 0.87 kcal/Mol bei 145° und 2.18 kcal/Mol für das Schmelzen bei 207°.

---

Résumé On a étudié le nitrate de thallium(I) par TG, ATD et DSC conjointement à la Chromatographie en phase gazeuse et à l'analyse par diffraction des rayons X. La TG révèle une perte de masse à partir d'environ 380°, avec une perte de 50 p. c. à 520°. On montre que cette perte de masse est provoquée par l'ébullition plutôt que par la décomposition thermique. La température initiale de l'ébullition, extrapolée à partir des données ATD, est de 467°. Deux points de transition solide-solide ainsi que le point de fusion ont été déterminés par ATD et correspondent aux températures respectives de 77, 145 et 207°. Les valeurs des chaleurs de transition ont été déterminées par DSC: 0.15 kcal, mol^–1 à 77°, 0.87 kcal. mol^–1 à 145 et 2.18 kcal. mol^–1 pour la fusion à 207°.

---

, , - . , 380° 50% 520°. , , . 467°. - , , 77, 145 207°. , , 0.15 / 77°, 0,87 / 145° 2.18 / 207°.

---

---

The authors thank F. J. Conrad and W. J. Andrzejewski for gas analysis results and G. T. Gay for X-ray diffraction analyses.This work was supported by the United States Department of Energy.     

Polychlorination of thiophene. A reinvestigation

Some old controversies in the literature with regard to the structures of trichlorothiophenes have been elucidated. In the course of these studies, we found that the best method for the preparation of 2,3,5-trichlorothiophene is the direct chlorination of thiophene in the presence of catalytic amounts of ferric chloride. If 2,5-dichlorothiophene is available 2,3,5-trichlorothiophene can also be obtained in good yields through chlorination with thionyl chloride and sulfuryl chloride, using aluminum trichloride as catalyst.     

Phase transitions in the product of spontaneous polymerization of the acrylamide complex of calcium nitrate

Phase transitions in the spontaneously polymerized acrylamide-calcium nitrate system have been studied by X-ray diffraction analysis. The polymerization occursvia the stage of formation of crystalline particles, which exist in a homogeneous solution and are identical to crystallites in chemical composition. At the stage of particle formation, the degree of crystallinity is 60 %, the particle size is 65 nm, and paracrystallinity is 0.0208. An amorphous metal-containing polymer is the final structural state of the system.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1764–1766, September, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4162).     

Phase transitions of ammonium nitrate doped with alkali nitrates studied with fast X-ray diffraction

Dried samples of ammonium nitrate (AN) containing 1, 3, 5 mol% KNO₃, RbNO₃ and CsNO₃ were investigated with temperature resolved X-ray diffraction. The samples were cycled with 2 temperature programs from –70° to 100° and –70° to 150°C, resp. DSC measurements were made for comparison.KNO₃ extends the stability range of phase III. The supercooling observed with the transitions II/III and III/IV was so severe that the phases III and IV could be skipped leading to the transitions II/IV and III/V. No hindered nucleation was observed on heating.RbNO₃ gives dried AN the properties of the humid nitrate. Phase III appeared on heating but was skipped on cooling, when the sample had been heated to 150°C. Hindered nucleation was observed.CsNO₃ stabilizes the phases II and V. No strong hysteresis or supercooling was observed.

---

Zusammenfassung Trockene Ammoniumnitratproben (AN) mit einem Gehalt von 1, 3 bzw. 5 mol% KNO₃, RbNO₃ und CsNO₃ wurden mittels Röntgendiffraktion in Abhängigkeit von der Temperatur untersucht. Die Proben durchliefen 2 Temperaturprogramme (von 70° auf 100° und von –70° auf 150°C). Zum Vergleich wurden DSC-Messungen durchgeführt.KNO₃ erweitert den Stabilitätsbereich der Phase III. Die Unterkühlung bei den Übergängen II/III und III/IV war so ausgeprägt, daß man die Phasen III und IV überspringen konnte, um die direkten Phasenübergänge II/IV und III/V zu erhalten. Beim Erhitzen wurde keine behinderte Keimbildung beobachtet.RbNO₃ verleiht trockenem AN die Eigenschaften von feuchtem Nitrat. Phase III tritt zwar beim Erhitzen auf, wird aber beim Abkühlen ausgelassen, wenn die Probe zuvor auf 150°C erhitzt wurde. Es wurde eine behinderte Keimbildung beobachtet.CsNO₃ stabilisiert die Phasen II und V. Es wurde keine ausgeprägte Hysterese oder Unterkühlung beobachtet.

     

Phase transitions in mesophase macromolecules. III. The transitions in poly(ethylene terephthalate-co-p-oxybenzoate)

The glass and melting transitions of poly(ethylene terephthalate-co-p-oxybenzoate)s have been studied by differential scanning calorimetry. Despite the higher glass transition expected for polyoxybenzoate, there is almost no change in the glass transition temperature up to 63 mol % oxybenzoate (353 ± 4 K). At high oxybenzoate concentration there seems to be a discontinuous jump to a glass transition of 450 K. This high glass transition has been observed in two-phase materials down to 30 mol % oxybenzoate. The melting transition shows signs of isodimorphism with a minimum in melting temperature at about 60–70 mol % oxybenzoate, 60 K below the melting temperature of poly(ethylene terephthalate). The thermal properties are little affected by the change of the noncrystalline parts of the molecules to a mesophase structure. The transition to the isotropic phase could not be analyzed because of prior decomposition.     

Reduction with N-benzyl-1,4 dihydronicotinamide. A reinvestigation.

3- or 4-Formylpyridines, cyclohexen -2 one andg-nitrostyrene can be reduced with BNAH: these substrates were previously reported to be inert or very unreactive toward this reagent.     

Nitrosonium nitrate: A simple cryogenic preparation and phase transitions

A simple method is suggested for the preparation of pure nitrosonium nitrate (NO⁺ NO ₃ ^– ) thin films, by deposition of nitrogen dioxide from the gas phase onto a cold tip under specified conditions and subsequent warming up of the layer. Fourier-transform infrared spectra were used for its characterization and to determine its purity. The NO⁺ NO ₃ ^– solid thus formed was found to be stable up to 230 K. Raman examination of temperature cycling effects on thev(NO⁺) band and on the phonon region of the thin films indicates one amorphous and two crystalline phases. Amorphous-crystalline and crystalline-crystalline transition temperatures are reported.     

Phase transitions in polymer brushes

Liquid crystalline ordering in planar polymer brushes is investigated theoretically by numerical calculations within a self-consistent field approximation. The brushes are formed by macromolecules with mesogenic groups in main chain and immersed in a solvent. Existence of a microphase segregated brush (MSB) regime with a collapsed orientationally ordered intrinsic sublayer and a swollen external sublayer is shown. At small grafting density, the transition from a conventional brush state to the microphase segregated state is a jump-wise first order phase transition for a finite chain length (N). The magnitudes of the jumps in the average characteristics of the brush tend to zero in the limit N → ∞ since this transition occurs only in a vanishingly small part (∝ N^−1/2) of the brush. High compressibility of MSB brush is demonstrated. The origin of phase transition in planar brushes is discussed.     

Phase transitions in chlorobenzene-cis-decalin mixtures

The dielectric constant ?' and loss tangent tan δ of chlorobenzene-cis-decalin mixtures have been measured in the temperature range 77 K to 330 K and frequency range 0.1 to 100 kHz. On cooling, ?' increases with decreasing temperature upto about 135 K, after which it drops rapidly with decreasing T followed by a slow decrease. This indicates that the liquid mixture goes to an amorphous phase which transforms to a glass phase of restricted dipole rotation below T_g; however, the peak in ?' is due to relaxation in the amorphous phase (α relaxation) and does not give an exact T_g. On heating, the behaviour of the cooling curve is retraced upto 160 K, after which ?' drops suddenly to a value lower than that at 77 K in the glass phase. This indicates the transition to a crystalline phase in which dipole rotational freedom is completely lost. The crystalline phase changes to a eutectic liquid phase of high ?' at a temperature (200 K) lower than the melting point of chlorobenzene and cis-decalin. Dielectric dispersion is observed only in the glass and amorphous phases. The dielectric relaxation time is independent of the concentration of chlorobenzene.     

The clemmensen reaction of tigogenin. A reinvestigation

The reaction of tigogenin ($\text{1b}$) with amalgamated zinc yields tetrahydrotigogenin ($\text{2b}$) and the furostan $\text{3}$. While $\text{2b}$ undergoes acid catalyzed elimination to give the rearranged product $\text{7}$, $\text{3}$ spontaneously decomposes to a mixture of $\text{4}$ and $\text{5}$.     

Variations in the cooling transitions of potassium nitrate

Because of questions concerning the suitability of potassium nitrate as a dynamic temperature standard for DTA, the relation between the experimental procedure and the resulting curves was ascertained for the Standard Reference Material KNO₃. The material behaves differentlyon cooling in open pans than in cylindrical holders because confinement in the latter case initiates reversion to the room temperature form. Under the conditions of use as a dynamic temperature reference material, the curves are accurately reproducible.

---

Zusammenfassung Zur Überprüfung der Eignung von Kaliumnitrat als dynamische Temperatur-Eichsubstanz für die DTA, wurde der Zusammenhang des Versuchsvorganges und der erhaltenen Kurven für das Standard-Referenz-Material KNO₃ untersucht. Die Substanz verhält sich bei der Kühlung in offenen Tiegeln und in zylindrischen Behältern unterschiedlich, da in letzteren die Begrenztheit die Reversion zur Zimmertemperatur-Form in Gang setzt. Unter den für das dynamische Temperatur-Referenz-Material gegebenen Bedingungen sind die Kurven gut reproduzierbar.

---

Résumé En raison de l'emploi du nitrate de potassium comme étalon de température en ATD, on a étudié l'influence des conditions d'expérience sur les courbes obtenues. Le comportement de ce corps est différent si on effectue le refroidissement dans des capsules ouvertes ou dans des creusets cylindriques. Dans ce dernier cas, le manque d'espace initie le retour à la forme stable delà température ambiante. Dans les conditions d'emploi comme matériau de température étalon, les courbes sont exactement reproductibles.

---

. - , , .

---

---

One of us is indebted to the U. S. National Science Foundation for support of part of this study.     

Plenary Lecture. Phase transitions and critical phenomena in polar smectic A liquid crystals

Since the discovery of a phase transition between two polymorphic forms of the smectic A phase, there has been a considerable amount of experimental as well as theoretical work on strongly polar materials exhibiting different smectic A phases. These studies have led to the observation of a variety of new phase transitions and critical phenomena which are rarely encountered in any other area of condensed matter physics. We review briefly some of these important results.     

Plenary Lecture. Phase transitions and critical phenomena in polar smectic A liquid crystals

Since the discovery of a phase transition between two polymorphic forms of the smectic A phase, there has been a considerable amount of experimental as well as theoretical work on strongly polar materials exhibiting different smectic A phases. These studies have led to the observation of a variety of new phase transitions and critical phenomena which are rarely encountered in any other area of condensed matter physics. We review briefly some of these important results.     

Raman and i.r. spectra of zinc,cadmium and calcium nitrate: A study of the low temperature phase transitions in calcium nitrate

Raman and i.r. spectra have been obtained for anhydrous Ca(NO₃)₂ at 298, 273, 195 and 77 K and for Cd(NO₃)₂ and Zn(NO₃)₂ at 298 and 77 K. The vibrational spectrum of Ca(NO₃)₂ at room temperature is in excellent agreement with a factor group analysis based on the T_h⁶ space group. Below room temperature, new bands appear which indicate that Ca(NO₃)₂ undergoes two phase changes between 77 and 298 K (Phase III

Phase II

Phase I). Anhydrous Cd(NO₃)₂ and Zn(NO₃)₂ do not appear to undergo phase changes between 77 and 298 K. The Raman spectra of Ca(NO₃)₂ (III), Ca(NO₃)₂ (II), Cd(NO₃)₂ (II) and Zn(NO₃)₂ suggest the presence of crystallographically non-equivalent sets of nitrate groups. Assignments have been aided by the use of ¹⁸O enriched nitrates.