Properties Of Silica Gel Research Articles

Characterization of Surface Modification, Thermal Stability, and Metal Selectivity Properties of Silica Gel Phases‐Immobilized Dithiocarbamate Derivatives

Carbon disulphide was used to modify the surface of silica gel phases containing amine moieties for the formation of four phases-immobilized dithiocarbamate derivatives (I–IV). Characterization of the surface modification by the organic modifier was accomplished by several means of instrumental analysis. These include infrared, secondary ion mass spectrometry (SIMS), as well as, thermal desorption analysis for determination of the surface coverage values (1.051–1.501 mmol g−1). The thermal stability and structure characterization of the modified silica gel phases (I–IV), along with their mercury(II) adducts, were studied and evaluated on the basis of electron impact mass spectrometric analysis (EI‐MS). The results of this study proved higher thermal stability characters incorporated into the metal adduct compared to the free silica gel phase. The selectivity properties incorporated into the modified silica gel phases for binding and interaction with a series of bi‐ and trivalent metal ions were studied and evaluated by determination of the distribution coefficient and separation factor. The results of these evaluation processes were found to point out the higher selectivity and preference of these four phases for binding with mercury(II), copper(II), and cadmium(II) compared to other metal ions.

Chromatographic Properties of Silica Gel Packing Materials as Influenced by Polymeric Coating

Some chromatographic properties of microspheric silica gels coated with copolymer of polystyrene, p-divinylbenzene, and allyl alcohol were studied. The measurements were performed by reverse-phase high-performance liquid chromatography using modified C8 and C18 phases with secondary silanization with trimethylchlorosilane.

Adsorption properties of silica gel prepared from a decationized sol

In accordance with the IUPAC classification, the shape of the capillary condensation hysteresis and type of the sorption isotherms of the vapors of water and tetrachloromethane by silica gel are identified, the latter being prepared from a decationized silica sol in the presence of aluminum chloride. It is found that the adsorption and structural properties of the silica gel depend on the concentration of silicon(IV) oxide and Al/Si molar ratio, as well as on the type of the adsorbate used. It is shown that the effect of aluminum chloride is manifested mainly in the spatial rearrangement of the particles of silicon(IV) oxide into dense agglomerates followed by their aggregation with the conservation of internal porosity. This leads to the appearance of narrow slitlike mesopores and to a decrease in or the stabilization of the average pore radius.

Ozone Storage Oriented to Power Load Leveling

This paper investigates the ozone storing properties of silica gel. There are three kinds of storing technologies for ozone at present: First, ozone gas is stored at high pressure in a gaseous state. As ozone is used, it is discharged from the container. Second, silica gel (which stores ozone at low temperatures) is able to adsorb ozone. When the silica gel is heated, ozone becomes detached. Third, silica gel that is stored under high atmospheric pressure can adsorb ozone. To detach ozone, the atmospheric pressure is reduced. It has been found that it is unnecessary to change the temperature and pressure inside the container when removing ozone from silica gel. This means that ozone can be detached from silica gel using very little energy. This system is proposed for storing ozone in industry, and this system is effective for Power Load Leveling.

Silica and other materials as supports in liquid chromatography. Chromatographic tests and their importance for evaluating these supports. Part II

Reversed-phase chromatography is the method of choice for the analysis of basic compounds. However, because of the problems encountered with these compounds, “base deactivated” stationary phases have been developed. This review focuses on a major problem encountered by the chromatographer which is to effectively choose, for a particular separation, the appropriate reversed-phase packing. Often, columns of the same type but provided by various manufacturers vary in their chromatographic behaviour. It is known that differences in the purity of column packings, in the properties of silica gel supports and the density of silanols on the surface can be responsible for chromatographic differences. Unfortunately, in the case of “base deactivated” columns there is no universal test and chromatographic effects are compound dependent. The aim of this review is to describe the various chromatographic tests proposed in the literature for the differentiation of the many stationary phases on the market.

Influence of the Drying Technique on the Structure of Silica Gels

In the present research the influence of drying technique on the structural properties of silica gels prepared by different routes was studied. The silica aquagels were obtained by hydrolysis of tetraethylorthosilicate Si(OEt)4 (TEOS) under base- or acid-catalyzed conditions or by the gelation of SiO2 sol prepared by the fast hydrolysis of Na2SiO3 aqueous solutions in the presence of HCl. The drying techniques employed were freeze-drying as compared to conventional thermal drying at 80°C. Properties of resulting xerogels and cryogels were studied by N2 adsorption at 77K, DTA and SEM. It was shown that the structural changes during both freeze-drying and conventional drying are strongly influenced by the structure of initial aquagel.

The variation of the hydration properties of silica gel during its carbonization by pyrolysis of acetyloacetone and Ti, Zn acetyloacetonates

The hydration properties of different silica gels containing carbonaceous patches and other components (TiO2, Zn2SiO4) on the surface were studied by1 H NMR spectroscopy method with bulk freezing. The materials were synthesised on the basis of mesoporous silica gel the surface of which was covered with a carbon layer by the high temperature pyrolysis of acetylacetone. The formation of titanium dioxide and zinc silicate on the surface of parent silica gel was performed by pyrolysis of acetylacetonates of suitable metals. It was established that above 80% of the adsorbed water is bonded with the oxide component of the materials surface. The carbon component of the surface is localised mainly in the most narrow mesopores. The interfacial free energies, characteristic decay lengths and Hamaker constants at the solid/water interface were determined for these materials. The minimal value of interfacial free energy was found for the most hydrophobic carbosil sample.

Effect of drying on properties of silica gel

Viscoelastic properties and permeability of a silica gel have been followed during the course of drying. The modulus and viscosity of the network rise by several orders of magnitude, and exhibit power-law dependence on the density of the gel. An aerogel was prepared from an undried gel, and its modulus was found by hydrostatic compression in a mercury porosimeter. Pore size distribution of the aerogel was determined by nitrogen sorption before and after compression. The bulk modulus of the aerogel was very close to that of the wet gel at low densities, but at higher densities the wet gels were more rigid that the compressed aerogels. This difference is attributed to aging of the wet gels in the pore liquid (water). The final shrinkage of the wet gels was greater than expected, based on the viscoelastic properties and the calculated capillary pressure, and the difference is attributed to accelerated viscoelastic relaxation of the network under high capillary stresses. The permeability decreases by almost four orders of magnitude as the gel contracts and pore size inferred from the permeability ( r w) decreases in direct proportion to the pore volume. The pore size measured by nitrogen desorption ( r BT) agrees closely with r w, as expected on theoretical grounds. For compliant aerogels, the nitrogen desorption process causes substantial compression of the gel, because of the capillary pressure exerted by liquid nitrogen. In such cases, the true pore size and pore volume can be estimated, given knowledge of the elastic modulus of the network; the corrected value of r BT agrees well with r w. At high densities r w was about 0.5 nm smaller than r BT, and this discrepancy is probably caused by neglect of the existence of a relatively immobile layer of water of that thickness on the surface of the network.

The influence of grafted functional groups on the adsorption properties of silica

The adsorption properties of silica gel with grafted aminopropyl and guanidinoethanethiol (GET) groups were studied by the techniques of adsorption under static conditions and gas chromatography. It was shown that molecules capable of forming hydrogen bonds are adsorbed on all modified samples more weakly than on the initial silica gel. The grafting of GET radicals on the surface results in a noticiable increase in the dispersion interaction with adsorbed molecules. Calculation of the contributions of molecular groups to the constant of adsorption equilibrium showed that the thermodynamic characteristics of adsorption on aminosilochromes and aminosilicas with a polymeric layer of the modifying agent have similar values. Such adsorbents can be used for investigation of polar compounds, including organic bases.

Surface and Structural Properties of Silica Gels Used in High Performance Liquid Chromatography

Abstract Complete nitrogen adsorption-desorption isotherms were measured over the entire pressure range including the region of very low pressures for a series of silica gels used in high performance liquid chromatography. In addition to standard characterization of the silicas studied, which included the evaluation of the specific surface area and the total pore volume, the experimental adsorption isotherms were used to calculate the adsorption energy distributions and the pore volume distributions by employing an advanced numerical algorithm based on the regularization method. For most silica samples studied, the resulting energy distributions are similar indicating that their surface properties are analogous. For some silicas, which are able to chemisorb greater amounts of water as shown by supplementary thermogravimetric studies, the adsorption energy distributions are different. Analysis, of the resulting pore volume distributions for most silicas studied, shows a relatively narrow range of mesopores...

Controlled-porosity glasses as alternative adsorbents to silica gel for HPLC

The paper deals with the use of controlled-porosity glasses (CPGs) as adsorbents for HPLC. The physicochemical and chromatographic properties of small-pore CPGs are compared to the analogous properties of silica gels. The results show good correlation between them and suggest the possibility of application of CPGs as adsorbents for liquid chromatography.

Effect of preparation pH on properties of silica gel

AbstractSilica gels were obtained by drying the silica hydrogels formed at pH values between 1 and 4 at 100°C. The bulk density of the 2–3 mm diameter fraction decreased from 0·62 g cm−3 to 0·20 g cm−3 as the preparation pH increased from pH 3 to pH 3·65. The apparent density of silica gels was between 1·43 and 1·95 g cm−3. Isotherms for the adsorption of water vapour on samples prepared at different pH values showed hysteresis in all cases. Thermogravimetry analysis showed that the amount of bound water was in the range of 4·4 to 5·5% on a dry weight basis. Specific heats were determined by a differential scanning calorimetry method using a sapphire standard and were between 0·82 and 0·97 J g−1 K1.

Mechanical Properties of Silica Alcogels and Aerogels.

ABSTRACTThe mechanical properties of silica gels (alcogels and aerogels) are measured by three point bending. The elastic moduli (E,G) and the fracture strength (σ) are investigated as functions of the concentration of silicon precursor, the catalysing conditions, and the aging time.Elastic moduli and strength follow scaling laws as a function of the bulk density of the solid. The scaling exponents are discussed in terms of percolation theory.The evolution of the mechanical properties is also followed during the steps of the gel to glass transformation:- hypercritical drying- oxidation of the organic groups-densification heat treatmentAt each step of the process the increases of the elastic moduli and σ are related to the gel structure. During the hypercritical drying flexible “dead ends” in the network can condense and form new links. The connectivity is also enhanced by the removal of the organic groups creating siloxane bonds. Finally densification leads to a material having mechanical properties identical to those of conventional vitreous silica.

Titration of H2SO4/SiO2-mounted catalysts in cyclohexane with pyridine based on a new acidity function considering the effect of physisorption sites

A spectroscopic and visual titration of H2SO4/SiO2-mounted catalysts in cyclohexane with pyridine has been carried out by applying a new acidity function S′A in which the strength and amounts of acid and physisorption sites are taken into consideration. The S′A function is defined by S′A= pβI+ pKP, I+ log([PI]/[AI]) for a surface on which a kind of acid site and a kind of physisorption site exist, where pβI is the basic strength of a Hammett indicator and KP, I represents the equilibrium constant of the indicator for physisorption; [PI] and [AI] are the amounts of the indicator adsorbed on physisorption and acid sites, respectively. The physical properties of silica gel used here as the carrier were estimated based on the adsorption isotherm of pyridine and several indicators. It was revealed through simulation of the base titration system based on the S′A function that the strength and amounts of physisorption sites influence the estimate of acid strength distribution by the titration method, and that existence of strong physisorption sites often makes the titration impossible. The results of the improved spectroscopic titration showed that acid sites equal to the amount of sulphuric acid exist on the mounted catalyst. The strength of these sites was estimated by analysing the obtained S′A curve and was expressed in terms of the equilibrium constant for pyridine adsorption. At the same time, the relative strength of several indicators on the catalyst was determined. From the results of the improved visual titration, it was revealed that acid sites that correspond to the amount of sulphuric acid exist on each of the three kinds of mounted catalyst. It was pointed out that the physical meaning of the strength and amount of acid sites obtained by the conventional method is very obscure.

Effect of copper-containing additives on properties of silicagel greases

Effect of copper-containing additives on properties of silicagel greases

Protein Loading Capacity and Textural Properties of Column Packings in Reversed-Phase HPLC

Abstract The relationship between the textural properties (pore size, pore volume and surface area) of reversed-phase silica gel packings for HPLC and the dynamic loading capacity of large biomolecules was studied by using silica gels manufactured by similar processes. Several silica gels whose unbonded pore diameters range from 100 to 250 A and whose pore volumes range from 1.0 to 1.4 ml/g have been prepared and characterized. The bonded phase is monomeric C18. The textural properties of the bonded silica gels are also presented and related to the properties of the unbonded silica gels. Chromatographic evaluation with typical proteins in an underload-to-overload condition was performed in order to relate the influence of textural properties of silica gel to loading capacity and resolution. The packings with larger pore size and pore volume produced better column performance and higher loading of proteins.

Qualitative IR spectral analysis of products absorbed from ditolyl methane coolant by silica gel and the absorption isotherms

The authors describe a technique for the qualitative analysis of a ditolyl-methane organic coolant and the solvent extraction and infrared spectroscopy of its constituent chemical and corrosion products. Adsorption isotherms and vibrational states are discussed and the solvent and sorptive properties of silica gel are evaluated.

Investigation of the adsorption properties of silica gel by using electron paramagnetic resonance

Investigation of the adsorption properties of silica gel by using electron paramagnetic resonance

The effect of heat-treatment of silica gel at high temperature

The effect of heat treatment on the properties of silica gel has been studied above 700°C, by means of dilatometry, thermogravimetry, surface area by BET method, optical and electron-scanning microscopy, and infrared spectroscopy. Silica gel of high surface area and containing Na cation impurity less than several hundred ppm shows abnormal shrinkage and then expansion at temperatures between about 800 and 1200°C. The surface area by BET N 2 method shows also sharp decrease and then increase corresponding to this volume change. This abnormal shrinkage was caused by bulk diffusion and produced closed cavities inside silica gel. The sharp decrease of the BET N 2 surface area resulted from the fact that the nitrogen molecule cannot migrate easily into these closed cavities. The pressure of steam enclosed or formed later in the closed cavities causes the shrunken gel to explode and a foamy light solid similar to plastic foam is produced. The thermal behavior of the infrared spectra of OH stretching vibration coincides with this change.

Influence of additives on lubricating and structural-mechanical properties of silica gel greases

1. Organic compounds that are added to improve the lubricity of silica gel greases will reduce the thickening effect of the silica gel [11]. 2. Mechanical working, heating, or prolonged storage will harden silica gel greases; the degree of mechanical or thermal hardening is less when additives are present (the aluminum arylcarbamate is an exception). The LZ-318 additive tends to harden greases during storage; replacement of the MVP oil by PES-3 fluid tends to reduce the hardening. When the grease hardens, there is a concomitant increase in colloidal stability [decrease in oil bleeding tendency]. 3. The ability of additives to reduce wear and increase the critical seizure load for silica gel greases depends on the nature of the dispersion medium and the frictional regime. An increase in severity of the frictional regime (an increase in sliding speed or replacement of the mineral oil by a silicone) tends to increase the lubricating effectiveness of chemically active additves such as LZ-318.