Structural and energetic properties of carbosils hydrothermally treated in the classical autoclave or the microwave reactor

2017

J Therm Anal Calorim

Self Cite

The paper presents the studies on determination of physicochemical and structural properties of hydrothermally treated (HTT) silica gel Si-60, using the differential scanning calorimetry (DSC) and N 2 adsorption methods. Modification was performed in overheated water vapours or under the liquid water layer using various sources of thermal energy (in the classical autoclave or in the high-pressure microwave reactor). The characteristics of porous structure were determined on the basis of low-temperature nitrogen adsorption/desorption isotherms and using the calorimetric data (DSC) of thermal effects of phase transition of water introduced inside pores of the studied materials. Great compatibility of the characteristics obtained by means of the above-mentioned methods was proved. As follows from the SEM analysis, during HTT silica is rebuilt resulting in great changes of surface morphology and porous structure of the materials. The range of these changes depends on both the applied system (water vapour/liquid water) and the kind of used energy (classical/microwave).

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Application of differential scanning calorimetry to study porous structure of hydrothermally modified silicas

Charmas

2017

J Therm Anal Calorim

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“…These data were used as initial ones for calculation of energetic characteristics of the tested samples. This method was described precisely in [30, 31]. On the basis of the obtained data, total concentrations of water adsorbed on the surface of studied adsorbents (mg/g) were calculated.…”

Section: Methodsmentioning

confidence: 99%

Complex investigations of structural and thermal properties of silica-titania adsorbents

Charmas

Лебода

et al. 2011

J Therm Anal Calorim

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Mesoporous titanium-containing silicas with different Titania contents were investigated. The structural parameters of the materials were characterized by low-temperature adsorption/desorption of nitrogen and X-ray diffraction analysis. The thermodesorption of water using the quasi-isothermal thermogravimetry as well as the differential scanning calorimetry were used to characterize thermal and surface properties of these materials. 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 formation of biporous structure inside the tested materials. The water thermodesorption from the surface proceeds in two or three stages, which is connected mainly with pore distribution and TiO2 content. One can observe the increase of the total surface free energy (ΔGΣ) with the increasing TiO2 content, but the largest ΔGΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbent of intermediate content (30%) of TiO2. Freezing temperature of water contained in the pores of the studied materials is connected largely with their porous structure. Due to the well developed porous structure, the water freezing process is a multi-stage one.

“…This technology makes it possible to carry out chemical reactions which could not be performed under traditional conditions in such a short time or with such a high yield (Vanetsev et al 2002;Khollam et al 2001). The results of large investigations over the application of microwaves in hydrothermal modification of carbon-silica adsorbents are presented in paper (Skubiszewska-Zięba 2008). There are a few requirements which have to be fulfilled to use the microwaves as a source of thermal energy.…”

Section: Introductionmentioning

confidence: 97%

The impact of microwave energy on the results of silica gel hydrothermal modification

2010

Adsorption

Self Cite

Two series of the hydrothermally treated (HTT) silica gel samples using the microwave reactor or the classical autoclave have been prepared. The HTT modification processes have been performed under the liquid water layer or in the water vapour. The initial and HTT silica samples were examined by means of adsorption (N 2 ), thermogravimetric (TG) and infra red (FTIR-ATR) methods. On the basis of the obtained results it was stated that even a short time of HTT modification using microwaves is enough to make distinct changes in the porous structure of silica. The time and pressure are the most influential parameters during HTT using microwaves. However, in the case of the samples modified in the classical autoclave the most important factors are temperature and time. The hydrothermally modified silica samples possess different concentration of intraglobular water dependently on applied treatment conditions and water state.