Paolo Scardala

Sublimation study of the tin sulphides SnS2, Sn2S3 and SnS

Abstract The vaporization of SnS2(s) occurs following the equilibria SnS 2 ( s )→ 1 2 Sn 2 S 3 (s)+ 1 4 S 2 (g) Sn 2 S 3 ( s )→2SnS(s)+ 1 2 S 2 (g) SnS(s)→SnS(g) The vapour pressures over the condensed phases were measured by the simultaneous torsion-Knudsen effusion technique. The pressures of S2(g) over SnS2(s) and Sn2S3(s) and of SnS(g) over SnS(s) are expressed respectively by log p(kPa)=(12.41±0.40)−(11.3±0.3)× 3 T , δH 298 °=54.5±1.0 kL mol −1 log p(kPa)=(11.81±0.50)−(11.3±0.4)× 3 T , δH 298 °=112.0±2.0 kL mol −1 log p(kPa)=(9.40±0.10)−(10.7.3±0.1)× 3 T , δH 298 °=220.0±2.0 kL mol −1 where the standard enthalpies are derived by second- and third-law treatment of the results. From these data the standard heats of formation of SnS2(s) and Sn2S3(s) were calculated to be -148± 2 kJmol−1 and -253 ± 2 kJmol−1 respectively.

Some Thermodynamic Properties of C76and C84

The vapor pressures of C76 were measured over the temperature range 834−1069 K by the torsion−effusion method. The results are well represented by the following linear equation:  log(p/kPa) = (8.23...

Temperature dependence of the vaporization enthalpies of n-alkanes from vapour-pressure measurements

From vapour-pressure measurements carried out by using various techniques covering different pressure ranges, the Antoine constants of a homologous series of 10 n-alkanes (n-eicosane, n-heneicosane, n-docosane, n-tricosane, n-tetracosane, n-pentacosane, n-hexacosane, n-heptocosane, n-octacosane, and n-nonacosane) were calculated. From these constants the temperature dependence of the vaporization enthalpies and the standard sublimation enthalpies of these compounds were derived.

Study of the vaporization behaviour of Sb2S3 and Sb2Te3 from their vapour pressure measurements

Abstract New sets of total vapour pressure above solid Sb 2 S 3 and Sb 2 Te 3 were measured by the torsion method giving, for Sb 2 S 3 : lg p( Pa ) = (13.96 ± 0.20) − (10490 ± 200) T , and for Sb 2 Te 3 : lg p( Pa ) = (13.80 ± 0.30) − (10936 ± 200) T . Considerations on the vaporization behaviour of these compounds from the molecular weight of their vapour, as derived from the weight loss rate by the Knudsen method, are also reported.

Study on the thermal decomposition of Ag2S

Mesures des tensions de vapeur de soufre en fonction de la temperature au cours du processus de decomposition

Vaporization enthalpies of black and red mercury sulphides and their heat of transition from vapour pressure measurements

Abstract The total vapour pressures of red and black HgS, this latter in the metastable region, were measured by a simultaneous torsion and Knudsen apparatus and the corresponding temperature dependences are HgSred log p ( kPa ) = (8.96 ± 0.10) − (5902 ± 50) T HgSblack log p ( kPa ) = (8.50 ± 0.05) − (5582 ± 23) T The equilibrium constants of the sublimation process obtained by second-law and third-law treatment are HgS red,black → Hg(g) + 1 2 S 2 (g) the associated standard enthalpies, ΔsubH298o, for the red and black forms were calculated as 175 ± 4 kJ mol−1 and 167 ± 4 kJ mol−1 respectively. A new heat of transition from the red form to the black form, ΔtransHTo = 8 ± 2 kJ mol−1, was also derived.

Study on sulfur vaporization from covellite (CuS) and anilite (Cu1.75S)

Abstract Covellite decomposes according to the reaction: 4.667CuS → 2.667Cu1.75S(S) + S2(g). The sulfur vapour pressures measured in the temperature range 551.5–627 K by the torsion-effusion method are represented by the equation: log p (kPa) = (11.30 ± 0.30) − (8290 ± 100)/T. At high temperature, the anilite vaporizes incongruently according to the equation: 16Cu1.75S(s) → 14Cu2S(s) + S2(g), and the sulfur pressures are well represented in the temperature range 770.5–877 K by the equation: log p (kPa) = (10.49 ± 0.40) − (11470 ± 300)/T. The enthalpies associated with these reactions are, ΔH°298 = 178 ± 4 kJ mol−1 and 268 ± 7 kJ mol−1 for reactions 1 and 2 respectively, obtained from second- and third-law treatment of the data. From these reactions, the heat of formation of Cu1.75S, ΔformH°298 = −74 kJ mol−1, was derived.

Vaporization enthalpies and entropies of some n-alkanes

Abstract The vapour pressure of tetracosane, pentacosane, hexacosane and octacosane were measured by the transpiration method. The values fit the following equations: Tetracosane, log p (kPa) = (8.76 ± 0.50)−(4 501 ± 250)/ T Pentacosane, log p (kPa) = (9.16 ± 0.60)−(4745 ± 300)/ T Hexacosane, log p (kPa) = (9.93 ± 0.50)−(5168 ± 200)/ T Octacosane, log p (kPa) = (10.02 ± 0.40)−(5385 ± 150)/ T From these equations the vaporization enthalpies and entropies of the n -alkanes studied were derived. Both values indicate a trend with the molecular weight.

Torsion—Knudsen effusion vapour-pressure measurement of o, m and p-chlorobiphenyls

Abstract The torsion method and a coupled torsion—Knudsen effusion apparatus were used to measure the vapour pressures of o , m and p -chlorobiphenyls. The equations selected were: o -chlorobiphenyl(l), log P (kPa) = (10.48±0.50)-(4149±230)/ T ; m -chlorobiphenyl(l), log P (kPa) = (8.68±0.47)-(3614±188)/ T ; p -chlorobiphenyl(s), log P (kPa) = (9.44±0.63)-(3849 ± 200)/ T ; and p -chlorobiphenyl(l), log P (kPa) = (8.28±0.55)-(3541±250)/ T . The free energy functions, (G o T -H o 298 )/ T , for gaseous o and p -chlorobiphenyls were also estimated.

Lead activity in liquid In-Pb alloy determined from vapour pressure measurements

Analytic pure Aldrich lead (99.9%) and indium (99.98%) were used in the alloy preparation. Stoichiometric amounts of the two components were opportunely melted under vacuum in small quartz tubes up to the temperature of about 600 K, temperature higher than the melting points of both the components and maintained at this temperature for about one day. The liquid alloys so obtained were quenched in air. The lead content of some samples of alloy was checked by chemical analysis and their homogeneity was checked by scanning electron microscopy coupled with X-ray microanalysis. This last technique was also used to check if evident surface depletion of lead surface occurred during the vaporization experiments, particularly when indium rich alloys were studied. The lead activity in seven In-Pb alloys samples was determined by a torsion method following the conventional procedure and also a procedure that permits the direct measurement of the difference between the vapour pressure of the alloy and that of pure lead. The experiments were carried out by employing a torsion graphite cell with the two effusion holes (about 1.2 mm in diameter) drilled on the same side. The torsion assembly is the same as described in a previous work [10]. By filling only one housing (b) with pure lead or indium some vaporization runs were carried out and the results obtained were plotted as shown in Fig. 1. The vapour pressure-tempera ture equations selected in literature [11] for both elements are also plotted in the same figure. The excellent agreement of the second law of vaporization enthalpy, derived from the slopes of the log c~ against 1/T equations, and from the selected logp against 1/T [11], and also the agreement (within the experimental uncertainties of the calibration constants) obtained by employing lead and indium can be taken as a check of the reliability of the used assembly. Using a same housing for vaporizing lead and its alloy, the lead activity was determined from the relation: