Bruno Brunetti

On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide Perovskites

The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid organic-inorganic solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodynamic stability of the materials towards decomposition, which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that all the materials decompose to the corresponding solid lead (II) halide and gaseous methylamine and hydrogen halide, and the decomposition is well detectable even at moderate temperatures (~60 °C). Our results suggest that these materials may be problematic for long term operation of solar devices.

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...

Silicon supported TiC films produced by pulsed laser ablation

The selection of optimal conditions for preparing TiC coatings on oriented silicon, based on PLAD technique, was carried out by applying surface analysis (SEM, EDS, XPS, image analysis) on a series of films realised under different processing conditions. Consideration were made on the film characteristics as a function of laser fluence and informations, about the physico-chemical aspects of the ablation phenomena, were obtained.

Vaporization of the prototypical ionic liquid BMImNTf2 under equilibrium conditions: a multitechnique study

The vaporization behaviour and thermodynamics of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide (BMImNTf2) were studied by combining the Knudsen Effusion Mass Loss (KEML) and Knudsen Effusion Mass Spectrometry (KEMS) techniques. KEML studies were carried out in a large temperature range (398-567) K by using effusion orifices with 0.3, 1, and 3 mm diameters. The vapor pressures so measured revealed no kinetically hindered vaporization effects and provided second-law vaporization enthalpies at the mean experimental temperatures in close agreement with literature. By exploiting the large temperature range covered, the heat capacity change associated with vaporization was estimated, resulting in a value of -66.8 J K(-1) mol(-1), much lower than that predicted from calorimetric measurements on the liquid phase and theoretical calculations on the gas phase. The conversion of the high temperature vaporization enthalpy to 298 K was discussed and the value Δ(l)(g)H(m)(298 K) = (128.6 ± 1.3) kJ mol(-1) assessed on the basis of data from literature and present work. Vapor pressure data were also processed by the third-law procedure using different estimations for the auxiliary thermal functions, and a Δ(l)(g)H(m)(298 K) consistent with the assessed value was obtained, although the overall agreement is sensitive to the accuracy of heat capacity data. KEMS measurements were carried out in the lower temperature range (393-467) K and showed that the largely prevailing ion species is BMIm(+), supporting the common view of BMImNTf2 vaporizing as individual, neutral ion pairs also under equilibrium conditions. By monitoring the mass spectrometric signal of this ion as a function of temperature, a second-law Δ(l)(g)H(m)(298 K) of 129.4 ± 7.3 kJ mol(-1) was obtained, well consistent with KEML and literature results. Finally, by combining KEML and KEMS measurements, the electron impact ionization cross section of BMIm(+) was estimated.

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.

Torsion and Knudsen measurements of cobalt and nickel difluorides and their standard sublimation enthalpies

Abstract The vapour pressure of CoF 2 and NiF 2 were measured by the torsion-effusion and Knudsen-effusion methods. From second- and third-law treatment of the results standard sublimation enthalpies of both difluorides were derived. Some considerations on the Gibbs energy function of solid NiF 2 are reported.

On the vapourization thermodynamics of cobalt trifluoride

Abstract The sublimation of CoF 3 (s) was studied. The temperature dependence of the total vapour pressures as measured by the torsion method in the temperature range 700–830 K fit on the equation: log( p kPa )=(11.60±0.20)− 10630±400) ( T K ) Both the sublimation reactions: Cof 3 (s)= Cof 3 (g) (1) 2Cof 3 (s)=2Cof 2 (s)+F 2 (g) (2) occur during the vapourization of CoF 3 (s) where the molar fraction of the reaction (1) was found equal to 0.60±0.05, practically constant in the covered experimental temperature range. The standard enthalpies Δ sub H°(298)=216±4 and 204±3 kJ mol −1 for reactions (1) and (2) respectively were derived from second- and third-law treatment of the data. New values for the enthalpy of formation of CoF 3 (s) and CoF 3 (g) equal to −773±5 and −557±10 kJ mol −1 , respectively, were derived.

High Temperature Interaction Between H2, CH4, NH3 and Ilmenite

Three different reductive gaseous agents H2, CH4 and NH3 have been employed to investigate the high temperature reduction of ilmenite (FeTiO3). Thermogravimetry and mass spectrometry techniques have been utilized in the investigation of the reactions behavior. Considerations have been made on the parallel reactions due to the change of the components ratio ongoing the reduction process. In particular the catalytic effect of the metallic iron on the decomposition of methane in the second reaction and of ammonia in the last one is being discussed as well as the formation of important by‐products.

Vapour pressures and sublimation enthalpies of cobalt and nickel dibromides

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. The vapour pressure of CoBr 2 and NiBr 2 were measured by the torsion effusion and Knudsen effusion methods. From second- and third-law treatment of the results the standard sublimation enthalpies of both dibromides, D sub H°(298r=216p1 and 226p1kJmol −1 for CoBr 2 and NiBr 2 , were derived.

Toward the Elucidation of the Competing Role of Evaporation and Thermal Decomposition in Ionic Liquids: A Multitechnique Study of the Vaporization Behavior of 1-Butyl-3-methylimidazolium Hexafluorophosphate under Effusion Conditions

The evaporation/decomposition behavior of the imidazolium ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6) was investigated in the overall temperature range 425-551 K by means of the molecular-effusion-based techniques Knudsen effusion mass loss (KEML) and Knudsen effusion mass spectrometry (KEMS), using effusion orifices of different size (from 0.2 to 3 mm in diameter). Specific effusion fluxes measured by KEML were found to depend markedly on the orifice size, suggesting the occurrence of a kinetically delayed evaporation/decomposition process. KEMS experiments revealed that other species are present in the vapor phase besides the intact ion pair BMImPF6(g) produced by the simple evaporation BMImPF6(l) = BMImPF6(g), with relative abundances depending on the orifice size-the larger the orifice, the larger the contribution of the BMImPF6(g) species. By combining KEML and KEMS results, the conclusion is drawn that in the investigated temperature range, when small effusion orifices are used, a significant part of the mass loss/volatility of BMImPF6 is due to molecular products formed by decomposition/dissociation processes rather than to evaporated intact ion pairs. Additional experiments performed by nonisothermal thermogravimetry-differential thermal analysis (TG-DTA) further support the evidence of simultaneous evaporation/decomposition, although the conventional decomposition temperature derived from TG curves is much higher than the temperatures covered in effusion experiments. Partial pressures of the BMImPF6(g) species were derived from KEMS spectra and analyzed by second- and third-law methods giving a value of ΔevapH298K° = 145.3 ± 2.9 kJ·mol-1 for the standard evaporation enthalpy of BMImPF6. A comparison is done with the behavior of the 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide (BMImNTf2) ionic liquid.