Minoru Sakiyama

Heat Capacities and Volume Thermal Expansion of NaNO2 Crystal

Phase transitions of ferroelectric NaNo 2 crystal around 164°C were studied by calorimetric and dilatometric methods. The values of both heat capacity and molar volume show an abrupt increase at about 163°C, indicating that this transition is of the first order. In the region of 164∼165°C, a small broad peak was observed in the C p – T curve. On the other hand there appear two small anomalies in the volume expansion curve at 164.2°C and 164.7°C respectively. The total entropy of transition amounts to 1.26±0.08 e. u., which is nearly equal to R 1n2=1.377 e. u., and suggests that the orientational order of NO 2 - ions is destroyed completely in the paraelectric phase.

Construction and testing of a sublimation calorimetric system using a Calvet microcalorimeter

Abstract A sublimation calorimetric system has been constructed, in which a Calvet microcalorimeter and Knudsen-type sample containers are incorporated. Two kinds of sublimation apparatus with three kinds of sample containers have been designed. Two of the containers are furnished with a stopper, which can be placed or removed under vacuum from the outside of the apparatus. Thus, these containers are applicable to substances that are unstable in air. The latest version of the containers is applicable also to corrosive substances. The system has been tested with naphthalene and anthraquinone and found to enable us to determine sublimation enthalpies at temperatures from ambient to 450 K, for substances with saturated vapor pressures of 1 to 400 Pa, with satisfactory precision and accuracy.

Enthalpy of sublimation of benzoic acid and dimerization in the vapor phase in the temperature range from 320 to 370 K

Abstract The enthalpy of sublimation has been determined for benzoic acid as a function of temperature in the temperature range from 320 to 370 K by use of a sublimation-calorimetric system incorporating a Calvet microcalorimeter. From analysis of the effect of the (monomer + dimer) equilibria in the vapor on the observed enthalpies of sublimation, the degree of dissociation of the dimer in the saturated vapor at 298.15 K has been estimated to be higher than 0.997. The enthalpy of sublimation to give the gaseous monomer at 298.15 K is in the range from (88.9 ± 0.3) to (89.3 ± 0.3) kJ · mol −1 .

Standard enthalpies of formation of trimethyl cyanurate, malonamide, and 1,3-dimethyluracil ☆

Abstract Standard molar enthalpies of formation in the crystalline and gaseous states have been determined for trimethyl cyanurate, malonamide, and 1,3-dimethyluracil by oxygen-bomb combustion calorimetry and sublimation calorimetry. The malonamide crystal was in a metastable state. Derived values are −Δ f H m o (cr)/(kJ·mol −1 ) −Δ f H m o (g)/(kJ·mol −1 ) Trimethyl cyanurate 478.3 ± 1.2 387.9 ± 1.5 Malonamide 542.81 ± 0.53 416.4 ± 0.7 1,3-Dimethyluracil 410.51 ± 0.90 313.6 ± 1.5 The derived results are discussed in relation to molecular and crystal structures.

Sublimation calorimetric studies using a calvet microcalorimeter

Abstract Sublimation enthalpy at 298.15 K derived by linear regression analysis of sublimation calorimetric data at higher temperatures is presented for acetylurea, N,N -dimethyluracil, trimethyl isocyanurate, trimethyl cyanurate, acetylacetonates of Be(II), Cu(II), Fe(III), Cr(III), Zn(II) and Co(II), Be 4 O(O 2 CC 2 H 5 ) 6 , Be 4 O(O 2 NO) 6 and Cu(NO 3 ) 2 . Limitation of the present strategy for deriving Δ sub H o (298) and possible future improvements are discussed.

Disintegration Energy of Ferrocene Crystal in Triclinic Phase and Kinetic Study on Monotropic Transition from Monoclinic to Orthorhombic Phase

Abstract Cooling of single crystals of ferrocene below the λ-type phase transition at 163.9 K leads to crystal disintegration with explosive violence independently of the λ-type transition. The strain energy evolved at the disintegration (“the disintegration energy” for short) was determined to be (1.10 ± 0.11) kJ mol–1 by a drop calorimetry system using a low-temperature Calvet microcalorimeter. The disintegration energy was independent of the crystal size with four sieve fractions in the range 2.5–0.25 mm. The violent disintegration is interpreted here in terms of an energy transfer from the strain energy accumulated in the domain boundaries in a form of elastic energy to the kinetic energy of disintegrated crystallites. The speed of a crystallite with the grain size of 60–70 pm was estimated to be 110 m s 1. On the other hand, kinetic aspect of a monotropic transition from the undercooled monoclinic to the stable orthorhombic phase at around 190 K. has been investigated with the same drop calorimetry s...

Thermoanalytical characterization of 1,3-dimethyluracil and malonamide crystals

Abstract DSC measurements showed that 1,3-dimethyluracil crystals prepared by vacuum sublimation or recrystallization from various solutions were in most cases in a stable phase (cr2) at 300 K. When heated, the stable crystals did not transform to the high temperature stable phase (cr1). The superheated crystals melted at 394 K; this liquid then underwent a monotropic transformation to phase cri, which finally melted at 398 K. A melt-crystallized sample (phase cr1) did not readily transform into phase cr2 on cooling, whereas crystals in phase cr1 formed by the above-mentioned monotropic transformation from the liquid state transformed readily into phase cr2 at 380 K on cooling. DSC measurements on malonamide crystals indicated the occurrence of a high and a low temperature stable phase (cr1 and cr2, respectively) and a metastable phase (cr3) formed by melt-crystallization. Phase cri supercooled on cooling. Schematical Gibbs energy and enthalpy diagrams are given for both compounds.

Combustion and sublimation calorimetric studies on acetylurea and trimethyl isocyanurate

Abstract Standard enthalpies of formation in the crystalline and gaseous states have been determined for acetylurea and trimethyl isocyanurate by oxygen bomb-combustion calorimetry and sublimation calorimetry. Derived values are as follows: −Δ f H m o (c) −Δ f H m o (g) (kJ·mol −1 ) (kJ·mol −1 ) CH 3 CONHCONH 2 544.21 ± 0.54 441.16 ± 0.86 CON(CH 3 )CON(CH 3 )CON(CH 3 ) 677.92 ± 0.97 589.7 ± 1.5 Stabilization energies related to intramolecular interaction between π-electrons of carbonyl groups and lone-pair electrons of adjacent nitrogen atoms have been evaluated for acetamide and urea as well as for these compounds as enthalpy changes of “isodesmic” reactions using ethane as a reagent for the cleavage of CON bonds and are discussed.

Reactions of methylhydropolysiloxanes with active clay and cupric oxide: synthesis of lower members of hydrogen end-blocked dimethylpolysiloxanes

Abstract It was found that active clay is applicable to the rearrangement at room temperature between 1,1,3,3-tetramethyldisiloxane, H(CH3)2SiOSi(Ch3)2H, and octamethylcyclotetrasiloxane, [(CH3)2SiO]4, without appreciable fission of the SiH bonds. Properties of the rearranged products: hydrogen end-blocked dimethylpolysiloxanes, H(CH3)2SiO[(CH3)2SiO]nSi(CH3)2H (n = 1–4), are reported. Cupric oxide reacts with above mentioned disiloxane to give 1,1,3,3,5,5-hexamethyltrisiloxane. In this case, the cleavage of SiOSi linkage as well as the expected oxidation of the SiH bonds took place. The effective chemical species for the rearrangement is not clear; however, it is presumably a kind of hydride of copper. On the other hand, cupric oxide does not oxidize the SiH bonds in 1,3,5,7-tetramethylcyclotetrasiloxane, [H(CH3)SiO]4, but the oxidative cleavage of the methyl groups attached to silicon presumably proceeds in the presence of oxygen at higher temperatures. The cupric oxide reagent does not activate the rearrangement of hexamethyldisoloxane and octamethylcyclotetrasiloxane.

Standard enthalpies of formation of beryllium acetylacetonate(cr) in its stable and metastable states, beryllium oxypropionate(cr), and beryllium oxynitrate(cr)

Abstract Standard molar enthalpy changes were determined by solution-reaction calorimetry for the reactions: Be(C 5 H 7 O 2 ) 2 (cr) + H 2 SO 4 (l) + 4H 2 O(l) = BeSO 4 ·4H 2 O(cr) + 2C 5 H 8 O 2 (l) Be 4 O(C 2 H 5 CO 2 ) 6 (cr) + 4H 2 SO 4 (l) + 15H 2 O(l) = 4BeSO 4 ·4H 2 O(cr) + 6C 2 H 5 CO 2 H(l) and Be 4 O(NO 3 ) 6 (cr) + 4H 2 SO 4 (l) + 15H 2 O(l) = 4BeSO 4 ·4H 2 O(cr) + 6HNO 3 (l) The standard molar enthalpies of formation at 298.15 K were derived for the title compounds from the enthalpy changes: Compound −Δ f H m o /(kJ·mol −1 ) Be(C5H7O2)2(cr, α) 1233.2 ± 2.2 Be(C5H7O2)2(cr, γ) 1233.1 ± 2.2 Be4O(C2H5CO2)6(cr) 4738.2 ± 2.4 Be4O(NO3)6(cr) 2641.9 ± 7.7 No significant difference was found in ΔfHmo between the stable (α) and metastable (γ) phases at 298.15 K of beryllium acetylacetonate.