Narrow Results

Mass spectrometric studies of the composition of the gaseous phase under solid compounds of free phthalocyanine (H₂Pc) and its complexes with aluminium (AlClPc, AlFPc, (AlPc)₂O) and copper (CuPc) were performed in the temperature range up to 700 °C. It has been shown that the phthalocyanines sublime in the form of monomers, excluding one aluminium complex. All phthalocyanines under investigation sublime without thermal decomposition until 700 °C. The vapour pressure of these phthalocyanines was determined as a function of temperature by the Knudsen effusion method, in which the rate of effusion of the equilibrium vapour through a small orifice was measured. The thermodynamic parameters of the sublimation process for phthalocyanies were calculated.

The saturated vapor pressures of tetraphenylporphyrin H₂TPP, its four-coordinated metallo-complexes MTPP (M ≡ Ni, Cu, Zn, Pd, Ag, Cd) and some phenyl-substituted derivatives H₂T(R)PP (R ≡ 2-, 3-, 4-CH₃; 2-, 4-F; 2-, 3-, 4-Cl; 3-, 4-Br; 3,5-C(CH₃)₃) have been measured using the inert gas flow method. The values of sublimation enthalpy Δ_subH_m and entropy Δ_subS_m are calculated. On the basis of the kinetic vapor pressure dependence, the start temperatures of thermal destruction of the investigated porphyrins are determined. The temperatures of melting of the tetraphenylporphyrin metallo-complexes measured by the DSC method are in linear correlation with the Δ_subH_m values. The correlation between the thermodynamic functions of porphyrin sublimation (Δ_subH_m, Δ_subS_m, Δ_subG_m) and the literature data on the crystal structure of the compounds is considered. The Δ_subH_m values obtained by some authors by different methods are compared with the results of our investigations. Possible reasons for discrepancies in the results are discussed.

In this paper, we present the results of investigations of degradation processes that occur in the structure promising high-temperature anti-oxidizing of heat-resistant coating of the Si–TiSi₂–MoSi₂–B–Y system in hypersonic flows of air plasma. The coating is designed to protect a wide range of heat-resistant materials (carbon–carbon and carbon–ceramic composites, coal–graphite materials, alloys based on Nb, Mo, W, etc.). It is found that the coating operating capacity at surface temperatures $T_w\le$ 1820–1830^∘C is provided by the structural-phase state of its microcomposite main layer and formation on the coating surface of a heterogeneous passivating protective film. It is based on borosilicate glass reinforced by rutile microneedles. The mechanism of coating destruction at $T_w\ge$ 1850–1860^∘C is erosion loss of oxide film as well as generation and growth of gas-filled cavities at the “coating main layer–oxide film” interface. As the pressure of saturated vapor of gaseous oxidation products (SiO, CO, MoO₃ and B₂O₃) exceeds that of the ambient, the oxide film integrity is disrupted and oxidation process becomes active. The rates of erosion loss and sublimation grow as operating temperature increases and ambient pressure decreases.

Mass spectrometric studies of the composition of the gaseous phase for solid compounds of hexadecafluorinated phthalocyanines MPcF₁₆, M = Cu, Zn, VO and their unsubstituted MPc analogs were performed in a temperature range up to 600°C. It has been shown that phthalocyanines sublime into the form of monomers without thermal decomposition. The vapor pressure of these phthalocyanines was determined as a function of temperature by the Knudsen effusion method, in which the rate of effusion of the equilibrium vapor through a small orifice was measured. The thermodynamic parameters of the sublimation process for phthalocyanines were calculated.

Manganese porphyrins are of interest due to the optical, electronic and magnetic properties of the central metal ion, coupled to the low bandgap of the polyaromatic ring. These attractive characteristics are harnessed in solutions or in ultra-thin films, such as, for example, self-assembled monolayers. However, for devices, thicker films deposited using a controlled and reproducible method are required. Here we present the morphological, structural, chemical and optical properties of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) thin films deposited using organic molecular beam deposition, typically employed to process analogue molecules for applications such as organic photovoltaics. We find, using a combination of UV-vis and X-ray photoelectron spectroscopies, that the sublimation process leads to the scission of the Mn–Cl bond. The resultant film is a Mn(II)TPP:Mn(III)TPPCl blend where approximately half the molecules have been reduced. Following growth, exposure to air oxidizes the Mn(II)TPP molecule. Through quantitative analysis of the time-dependent optical properties, the oxygen diffusion coefficient (D) $\sim 1.9\times 10^{-17}{\mathrm{\text{cm}}}^2/\mathrm{\text{s}}$ is obtained, corresponding to a slow bulk oxidation following fast oxidation of a 8-nm-thick surface layer. The bulk diffusion D is lower than for analogous polycrystalline films, suggestion that grain boundaries, rather than molecular packing, are the rate-limiting steps in oxidation of molecular films. Our results highlight that the stability of the axial ligands should be considered when depositing metal porphyrins from the vapor phase, and offer a solvent-free route to obtain reproducible and smooth thin films of complex materials for engineering film functionalities.

Manganese porphyrins are of interest due to the optical, electronic and magnetic properties of the central metal ion, coupled to the low bandgap of the polyaromatic ring. These attractive characteristics are harnessed in solutions or in ultra-thin films, such as, for example, self-assembled monolayers. However, for devices, thicker films deposited using a controlled and reproducible method are required. Here we present the morphological, structural, chemical and optical properties of manganese(III) tetraphenylporphyrin chloride (MnTPPCl) thin films deposited using organic molecular beam deposition, typically employed to process analogue molecules for applications such as organic photovoltaics. We find, using a combination of UV-vis and X-ray photoelectron spectroscopies, that the sublimation process leads to the scission of the Mn–Cl bond. The resultant film is a Mn(II)TPP:Mn(III)TPPCl blend where approximately half the molecules have been reduced. Following growth, exposure to air oxidizes the Mn(II)TPP molecule. Through quantitative analysis of the time-dependent optical properties, the oxygen diffusion coefficient (D) ~1.9 × 10^-17 cm²/s is obtained, corresponding to a slow bulk oxidation following fast oxidation of a 8-nm-thick surface layer. The bulk diffusion D is lower than for analogous polycrystalline films, suggestion that grain boundaries, rather than molecular packing, are the rate-limiting steps in oxidation of molecular films. Our results highlight that the stability of the axial ligands should be considered when depositing metal porphyrins from the vapor phase, and offer a solvent-free route to obtain reproducible and smooth thin films of complex materials for engineering film functionalities.

Some people think that carbon and sustainable development are not compatible. This textbook shows that carbon dioxide (CO₂) from the air and bio-carbon from biomass are our best allies in the energy transition, towards greater sustainability. We pose the problem of the decarbonation (or decarbonization) of our economy by looking at ways to reduce our dependence on fossil carbon (coal, petroleum, natural gas, bitumen, carbonaceous shales, lignite, peat). The urgent goal is to curb the exponential increase in the concentration of carbon dioxide in the atmosphere and hydrosphere (Figures 1.1 and 1.2) that is directly related to our consumption of fossil carbon for our energy and materials The goal of the Paris agreement (United Nations COP 21, Dec. 12, 2015) of limiting the temperature increase to 1.5 degrees (compared to the pre-industrial era, before 1800) is becoming increasingly unattainable (Intergovermental Panel on Climate Change (IPCC), report of Aug. 6, 2021). On Aug. 9, 2021 Boris Johnson, prime minister of the United Kingdom, declared that coal needs to be consigned to history to limit global warming. CO₂ has an important social cost…