Calorimetric Investigation of the Relaxation Phenomena in Amorphous Lyophilized Solids

Studying the thermal history and relaxation of solid amorphous drug product matrices by calorimetry is a well-known approach, particularly in the context of correlating the matrix parameters with the long-term stability of freeze-dried protein drug products. Such calorimetric investigations are even more relevant today, as the application of new process techniques in freeze-drying (which strongly influence the thermal history of the products) has recently gained more interest. To revive the application of calorimetric methods, the widely scattered knowledge on this matter is condensed into a review and completed with new experimental data. The calorimetric methods are applied to recent techniques in lyophilization, such as controlled nucleation and aggressive/collapse drying. Phenomena such as pre-Tg events in differential scanning calorimetry and aging shoulders in isothermal microcalorimetry are critically reviewed and supplemented with data of freeze-dried products that have not been characterized with these methods before.

Exploratory investigations on metal-based fuels for air-breathing propulsion

Air-breathing solid fueled propulsion devices represent rugged, cheap, and rather simple options, out of the ramjet (RJ) category, which can contribute to volume containment and structural weight reduction. In the case of a ducted rocket, a fuel-rich propellant is burned in a primary combustion chamber and part of the oxidizer is taken from the atmosphere to complete the combustion inside a ram burner before exhaust. The use of metal additives contributes to the development of high-energy density materials, featuring better volumetric specific impulse. Metal powders are characterized by high energetic content per unit volume but can feature issues of difficult ignition, generation of condensed combustion products (CCPs), and incomplete combustion. The present work discusses a series of exploratory investigations on aluminum-based pyrolants. Thermochemical analyses, calorimetric investigations, and combustion tests will be considered, looking at improvements introduced by metal addition.

A Calorimetric and Thermodynamic Investigation of the Synthetic Analogue of Mandarinoite, Fe2(SeO3)3∙5H2O

Thermophysical and thermochemical calorimetric investigations were carried out on the synthetic analogue of mandarinoite. The low-temperature heat capacity of Fe2(SeO3)3∙5H2O(cr) was measured using adiabatic calorimetry between 5.3 and 324.8 K, and the third-law entropy was determined. Using these Cp,mo(T) data, the third law entropy at T = 298.15 K, Smo, is calculated as 520.1 ± 1.1 J∙K–1∙mol–1. Smoothed Cp,moT values between T → 0 K and 320 K are presented, along with values for Smo and the functions [HmoT-Hmo0] and [ΦmoT-Φmo0]. The enthalpy of formation of Fe2(SeO3)3∙5H2O(cr) was determined by solution calorimetry with HF solution as the solvent, giving ΔfHmo(298 К, Fe2(SeO3)3∙5H2O, cr) = –3124.6 ± 5.3 kJ/mol. The standard Gibbs energy of formation for Fe2(SeO3)3∙5H2O(cr) at T = 298 K can be calculated on the basis on ΔfHmo(298 К) and ΔfSmo(298 К): ΔfGmo(298 К, Fe2(SeO3)3∙5H2O, cr) = ‒2600.8 ± 5.4 kJ/mol. The value of ΔfGm for Fe2(SeO3)3·5H2O(cr) was used to calculate the Eh–pH diagram of the Fe–Se–H2O system. This diagram has been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behaviors of selenium and iron in the surface environment have been quantitatively explained by variations of the redox potential and the acidity-basicity of the mineral-forming medium. These parameters precisely determine the migration ability of selenium compounds and its precipitation in the form of solid phases.

Thermal and calorimetric investigations of titania–silica composites

The paper presents the studies of effects of TiO2 amount differentiation on the structural and thermal properties of titania–silica complex oxides prepared by chemical vapor deposition of TiCL4 onto the Si-40, Si-60, and Si-100 silica gels. The mesoporous materials, characterized by a varied pore structure with highly developed surface and large pore volume, were obtained. The porous structure of materials under investigations was characterized by the low-temperature nitrogen adsorption–desorption method as well as by power spectral density calculated from the calorimetric investigations of water confined in the pores. Moreover, the thermodesorption of water using the quasi-isothermal thermogravimetry was used to characterize their thermal and surface properties. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent–water interfaces were calculated. It was stated that the increase of titania content causes a gradual decrease of specific surface area and has a significant effect on the porous structure formation. The water thermodesorption from the surface proceeds in few stages because of the porosity created by TiO2. The decrease in the total surface free energy (Δ GΣ) can be observed with the increasing TiO2 content. The largest Δ GΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbents of Si-100 series. The lowering of the freezing/melting points of water contained in the pores of the studied materials is strongly connected with their porous structure.