G. Della Gatta

The chemistry of silica-supported chromium ions: Calorimetric and spectroscopic study of nitric oxide adsorption

At the surface of CO-reduced, low-loaded (0.5% by weight) chromia/silica samples, four kinds of divalent Cr ions are present. All react with NO eventually yielding linear dinitrosyl species. Differences are found as to the energetic and kinetic behaviour. The most exposed ions (A and B) readily form dinitrosyls, with NO infrared stretching vibrations at 1747–1865 and 1755–1880 cm−1, respectively. Less reactive Cr ions (designated C1 and C2) form at low coverage stable mononitrosyls (NO stretch at 1810–1815 cm−1), which change at high NO pressure into A and B dinitrosyls (C1 ions) or to new dinitrosyls (C2 ions: NO stretches at 1765–1987 cm−1). The different behaviour is explained assuming that A, B, and C ions are, before reaction, respectively 2-, 3-, and 4-coordinate to the surface.

Vapour pressures and sublimation enthalpies of urea and some of its derivatives

Abstract The sublimation enthalpy and entropy of urea and its derivatives monomethylurea ( mmu ), monoethylurea ( meu ), monopropylurea ( mpu ), dimethyl-1,1-urea (1,1- dmu ), dimethyl-1,3-urea (1,3- dmu ), and diethyl-1,3-urea (1,3- deu ) were determined from the dependence of their vapour pressures on temperature. The vapour pressures were measured by the torsion-effusion method. The corresponding pressure against temperature equations are: urea, lg ( p kPa ) = 10.30-4750( K T ) ; mmu , lg ( p kPa ) = 10.72-4562( K T ) ; meu , lg ( p kPa ) = 10.20-4496( K T ) mpu , lg ( p kPa ) = 10.83-4608( K T ) ; 1,1- dmu , lg ( p kPa ) = 11.13-4655( K T ) ; 1,3- dmu , lg ( p kPa ) = 10.78-4454( K T ) ; 1,3- deu , lg ( p kPa ) = 12.20-5047( K T ) ; where the errors associated with the slopes (±100) and intercepts (±0.18), (±0.30 for urea), were estimated.

Enthalpies of solvation in cyclohexane and in water for homologous aliphatic ketones and esters

The standard enthalpies of solution at infinite dilution were determined for homologous aliphatic ketones and esters in water and in cyclohexane, using a rotating Calvet calorimeter, and solution concentrations about 5×10−4 mole fraction. Vaporization enthalpies, obtained for each compound with an effusion calorimetric cell, were added to calculate the solvation enthalpies. Their dependence on the number of carbon atoms in the chain is discussed in terms of the Friedman and Krishnan treatment. The effect of polarization of the functional groups is evaluated, and separation from the influence of chain length and the hydrophobic interactions of the methylenes is attempted. For the aqueous solutions, the rearrangement in the structure of the solvent around solute molecules is also considered in relation to deviations from linearity. Comparisons are made with solvation enthalpies obtained for ketones and esters with branched or cyclic substitutes.

Enthalpies of solvation for N-alkylamides in water and in carbon tetrachloride at 25°C

Molar enthalpies of solution at infinite dilution have been determined at 25°C for several N-alkyl and N,N-dialkylamides in water and in carbon tetrachloride, using a Calvet-type rotating calorimeter, and solution concentrations below 5×10−2 molal. Relevant enthalpies of transfer between the two solvents also have been derived. Molar enthalpies of solvation have been obtained by adding enthalpies of vaporization to solution values. Results are compared with those of other laboratories on other substituted amides, and their dependence on the number of carbon atoms in the chain is discussed. A possible computation of solvation enthalpies of functional groups is suggested and results for hydration of peptide or similar groups present in the compounds examined are discussed in terms of current models of their hydration and hydrogen bond formation.

Grain growth and secondary recrystallization in iron

The effect of impurities and of slight deformations as factors modifying the kinetics of normal grain growth after primary recrystallization in pure iron is investigated. Samples of pure iron and Armco iron, each with or without a content of precipitated oxides, were examined.Inclusions inhibit grain growth up to high temperatures, whilst the influence of strain depends on its amount: very low deformations (∼2%) generally block grain growth; for deformations around 5%, secondary recrystallization takes place; higher deformations (∼10%) accelerate the early stages of growth, leading to not very large final grain dimensions. 2.0% elongation has been found to be, in our conditions, the critical strain limit for secondary recrystallization.

Enthalpies of fusion and solid-to-solid transition, entropies of fusion for urea and twelve alkylureas

Abstract Enthalpies and temperatures of fusion have been measured by differential scanning calorimetry for urea and a number of its mono- and di-alkyl derivatives. Enthalpies obtained are: urea, 14.79 kj mol−1; monomethylurea, 15.75 kJ mol−1 ; monoethylurea, 13.94 kJ mol−1 ; monopropylurea, 14.63 kJ mol−1 ; monoisopropylurea, 17.40 kJ mol−1 ; monobutylurea, 14.55 kJ mol−1 ; monotertbutylurea, 33.13 kJ mol−1 ; dimethyl-1,1 urea, 29.61 kJ mol−1 ; dimethyl-1,3 urea, 13.62 kJ mol−1; diethyl-1,1 urea, 16/78 kJ mol−1 ; diethyl-1,3 urea, 12.46 kJ mol−1 ; dibutyl-1,3 urea, 14.87 kJ mol−1; trimethyl-1,1,3 urea, 14.30 kJ mol−1. Entropies of fusion have been derived from the experimental results. By temperature scanning starting from r.t. some solid-to-solid transitions for four alkylureas have also been detected, all hitherto unreported. Temperatures and enthalpies of transition are: for monoisopropylurea, 375.5 K and 2.31 kJ mol −1 ; for monobutylurea (two transitions), 313.1 K and 7.02 kJ mol−1 , 344.9 K and 0.88 kJ mol−1 ; for diethyl-1,3 urea, 339.4 K and 1.87 kJ mol−1 ; for dibutyl-1,3 urea, 311.5 K and 11.10 kJ mol−1.

Sublimation enthalpy of eleven alkyl derivatives of urea

Abstract Sublimation enthalpies of eleven alkyl dervatives of urea (monomethylurea, monoethyl-urea, monopropylurea, monoisopropylurea, monoisobutylurea, mono- t -butylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,3-diethylurea, 1,3-dibutylurea and 1,1,3-trimethylurea) were determined from second-law treatment of vapour pressures measured by the torsion-effusion method and compared with earlier results.

Enthalpies of sublimation and fusion of monophenylurea and diphenyl-1,3 urea

Abstract The sublimation enthalpies of monophenylurea (MPhU) and diphenyl-1,3 urea (1,3-DPhU) have been derived from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method. Values obtained are: 136 kj mol −1 for MPhU and 152 kJ mol −1 for 1,3-DPhU, where the estimated errors are comprised within 6 kJ mol −1 Enthalpies and temperatures of fusion have been measured by differential scanning calorimetry, leading to 23.7 kJ mol −1 and 420.6 K for MPhU, and 34.6 kJ mol −1 and 512 K for 1,3-DPhU. Poor reproducibility of results for 1,3-DPhU seems be due to the beginning of decomposition. No solid-to-solid transitions have been revealed from r.t. to fusion for both compounds.

Vaporization enthalpies of a series of α, ω-alkanediols from vapour pressure measurements

Abstract The standard molar vaporization enthalpies of a homologous series of six α,ω-allkanediols (n = 6, 8, 10, 12, 14, 16) were determined from the temperature dependence of their vapour pressure measured by the torsion-effusion and Knudsen-effusion methods.

Interactions in aqueous solutions of alkylthioureas. Excess enthalpies at 298.15 K

Abstract The enthalpies of dilution in water of five alkylthioureas were determined at 298.15 K. Comparison of the concentration coefficients of the excess enthalpies with those of alkylureas in water makes possible an identification of similar behaviours, determined by weak and comparable interactions, mediated or assisted by the solvent. A preliminary application of the Savage-Wood additivity of group method gave results supporting the validity of the model assumed for these interactions in preceding papers.