Papers by Keyword: Water Adsorption

Abstract: Titanium(IV) oxide was embedded into carbon nanotubes through sonication. The water adsorption properties of the carbon nanotubes, titanium(IV) oxide and the titanium(IV) oxide embedded carbon nanotubes have been studied using near infrared spectroscopy and second derivative techniques. Each sample was evacuated, then exposed to 40% and 60% relative humidity to adsorb water molecules and the evolving adsorption near infrared spectra were studied. Adsorption properties were further studied by gravimetric analysis. Near infrared spectroscopic and Scanning Electron Microscopic studies confirm that the titanium(IV) oxide has been embedded into the carbon nanotube samples. The water adsorption profiles show that the TiO₂ adsorbs more water at a relative humidity of 60% than at relative humidity of 40%. However, the titanium(IV) oxide embedded in CNTs loses its ability to adsorb water. Embedding of titanium(IV) oxide in CNT has altered the adsorption properties of pure TiO₂.

Abstract: The adsorption of water on aluminium (III) oxide nanoparticle surface was studied by near infrared (NIR) spectroscopy. The comparison of NIR spectra at 40% and 60% humidity were reported in this work and were analyzed using second derivative techniques. The second derivative spectra were used to understand the chemistry of adsorption of water molecules. Small amounts of samples were dried under vacuum at 230 °C before the analysis. The analysis of the spectra confirms the presence of three different hydroxyl groups on aluminium (III) oxide surface. The spectra acquired during the adsorption of water molecules show the characteristic peaks in the range of 5400-5100 cm^-1 corresponding to the combination band of water molecules hydrogen bonded with hydroxyl groups. There is also evidence for the presence of free water in the bulk of aluminium oxide. Furthermore, the mass of water adsorption on Al₂O₃ nanoparticle surface have been determined by gravimetric analysis. The gravimetric analysis confirms the adsorption of water molecules by aluminium (III) oxide surface.

Abstract: Water adsorption in proteins is the crucial process of protein folding and structure stabilizing. Adsorption of water on proteins can be evaluated by near-infrared spectroscopy, a useful technique for observing combination frequency of a water molecule. In this work, albumin, lysozyme, and silk, were used as models for α-helix and β-pleated sheet proteins. Their NIR spectra during water adsorption process were measured by using an NIR spectrometer equipped with a transflectance accessory. Moreover, the quantitative adsorption of water was determined by gravimetric technique. The results indicate that, there are five different NIR absorptions arise from the OH combination frequencies of water adsorbed by albumin in the 5300-5100 cm^-1 region. But there are only four absorptions for lysozyme and silk. The OH combination frequencies arising from water molecules in albumin indicate that it acquires free water molecules (5280 cm^-1) and adsorbed water molecules through carbonyl-water interactions (5248 and 5160 cm^-1) and amino-water interactions (5200 and 5120 cm^-1). Interestingly, there is no indication for the presence of free water molecules in lysozyme and silk. Furthermore, the gravimetric results indicate that the rate of water adsorbed follows the order R_W.Alb<R_W.Lys<R_W.Sil and total mass of water adsorbed per gram solid follows the order W_Alb<W_Lys=W_Sil.

Abstract: The principal directions in the development of construction material industry include expansion of raw material sources, quality improvement of raw materials subjected to preliminary treatment, application of modifying components, constructive and technological modernization of manufacturing process. Manufacturing of ceramic bricks is one that dominates this industry. We know that there isn’t enough conditional clay suitable for ceramics production in most East regions of Russia and West Siberia. However, in many regions there are powerful heat power plants and highly-developed metallurgical enterprises, which produce sideline products alongside with basic output. The issue of complex utilization of wastes produced by power engineering and metallurgy has not been successfully resolved yet. Slag and other silica-containing sideline products of main production have not practically been used to the full. Nevertheless, it’s necessary to note, that disperse condition of silica-containing wastes as well as their physical and chemical characteristics predetermine prospective application of silica-containing materials in ceramics.

Abstract: The effects on the waterproofness, the flexural and compression strength of cement mortar were investigated under single mixing and complexes mixing conditions of 4 kinds of modifiers, Polycarboxylic water-reducing agent, composite waterproofing agent, Sulphoaluminate expansion agent and fly ash. The results show that it is better in improving the water-resisting property and impermeability of mortar when complexes mixing any two of the 4 kinds of modifiers than single mixing. The mortar has the best water-resisting property and impermeability with the contents of 0.75% Polycarboxylic water-reducing agent and 6% composite waterproofing agent.

Abstract: Industrial transition to a totally new level of resources and energy saving necessitates improving the technical level of building materials manufacturing, growing their raw materials base, the assortment, enhancing the quality of manufactured products, cutting their cost price. It requires, first of all, carrying out more detailed research in properties of clay and clay loams, and selecting optimal additives for pottery works. Such disadvantages of clays as burning sensitivity, low compression resistance and flexural strength in a burnt state, low frost resistance cause the impossibility of their application without corrective additives. It is quite difficult to find an additive which can solve all the technological problems mentioned above. This paper provides the development of mixture "clay – electro-melting slag" for ceramic brick, moreover, addition of a steel-smelting slag in the fusion mixture results in the change in mixing water content of ceramic masses, strength and coloration of ceramic samples.

Abstract: This work aimed to examine the influence of carbonation on the water sorption isotherms of cement materials. Two types of normalized CEM I and CEM II Portland cement mortars were carbonated at 20°C, 65% relative humidity and 20% of CO₂ concentration for 32 days. The pore size distributions determined from the water sorption showed a reduction in microporosity and a slight increase in the mesoporosity. The pores clogging due to formation of calcium carbonate was highlighted by the reduction of the quantity of adsorbed water and the decrease in the hysteresis isotherms. We also studied the coupling effect between carbonation and humidification-drying cycles. The results of this study also indicated that the humidification-drying cycles coincide only from the second cycle because of a difficult evacuation of water during desorption, even at low humidity.

Abstract: Silica gel, a material that is produced from the condensation polymerisation of silicic acid, contains surface silanol groups formed during the condensation. The silanol groups on the surface are mostly of free and vicinal silanol groups. These silanol groups can be modified in several different ways. Thermal treatment and hydrothermal treatment can be carried out to alter the concentration proportions between free and hydrogen bonded silanol groups on the surface. They can also be chemically treated with suitable chlorosilanes to modify the silanol groups into polar or non polar materials that can be used in separation science.This article explores the chemical nature of silanol groups on the surfaces of different materials. Near infrared reflectance spectroscopy was used as the instrumental technique in this study. The silanol groups classifications were made by analyzing the near infrared spectra obtained during the adsorption of water molecules. Absorption of the combination frequencies of water molecules in the region 5500- 5000 cm ^-1 were used in characterizing the silanol groups on the surfaces. Second derivative technique was employed in the resolution and detailed analysis of these absorptions.The study reveals that the materials contain free, vicinal and gem silanol groups. Silica gel contains free and vicinal silanol groups, thermally treated silica gel contains fewer vicinal silanol groups compared to the base silica gel, and hydrothermally treated silica gel contains higher concentrations of vicinal silanol groups compared to the base silica gel. Furthermore, the chemically modified silica gel contains vicinal or geminal silanol groups depending on the type of functionality introduced.

Abstract: The objective of this work was to examine the influence of carbonation on the water vapor adsorption desorption isotherms of cement materials. Two types of Portland mortars, which were CEM I and CEM II, were carbonated at 20°C, 65% relative humidity and 20% of CO₂ concentration. The pore size distributions were determined from the water adsorption method. We also studied the coupling effect between carbonation and humidification-drying cycles. The results showed a reduction in microporosity and a small increase in the mesoporosity. The pores clogging due to formation of calcium carbonate was highlighted by the reduction of the quantity of adsorbed water and the decrease in the hysteresis isotherms. The results of this study also indicated that the humidification-drying cycles coincide only from the second cycle because of a difficult evacuation of water during desorption, even at low humidity.

Abstract: The objective of this work was to examine the microstructural changes caused by the carbonation of normal mortar. Samples were prepared and subjected to accelerated carbonation at 20°C, 65% relative humidity and 20% CO₂ concentration. The evolutions of the pore size distribution and the specific surface area during carbonation were calculated from the adsorption - desorption isotherms of water vapour and nitrogen. Conflicts observed in the results showed that the porous domains explored by these two methods are not the same due to the difference in molecular sizes of nitrogen and water. These two techniques therefore help to complementarily evaluate the effects of carbonation. The study also helped to explain why results in the literature diverge greatly on the influence of carbonation on specific surface area.