Authors:J. Rincon, M. Romero, C. Díaz, V. Balek and Z. Malek
The silica waste originating from a geothermal power plant in Mexico was investigated with the aim of finding its applicability
as a raw secondary material for ceramics production. The thermal behaviour of the original silica waste (containing NaCl and
KCl from marine brine) and of the purified silica was characterized by means of DTA/TG, emanation thermal analysis (ETA) and
thermodilatometry (TD). The reactivity of the purified silica waste mixed with CaCO3 (1.8 mass%) was characterized by means of ETA, DTA and TG. The microstructures and phase compositions of the final products
prepared by heating in air were tested by means of X-ray diffraction and of scanning electron microscopy coupled with electron
probe X-ray microanalysis. The thermal analysis methods allowed determination of the optimal conditions for thermal treatment
of the silica waste in order to obtain partly sintered porous materials for use as refractory bricks.
Authors:V. Lobanov, A. Chuiko, N. Burlaenko, V. Klymenko, V. Tertykh, V. Yanishpolskii and M. Teretz
Kinetics of the monoethanolamine vapor adsorption on the surface of silica previously deposited onto quartz plate was examined
by the piezoelectric microweighing. With the assumptions which are in accord with the experimental data, the kinetic equation
of the process was obtained and thus the adsorption and desorption constants were found. The structure of the possible adsorption
complexes was studied in the framework of the quantum-chemical MNDO method and the conclusion was made that the two-center
adsorption of the monoethanolamine on the silica surface proceeds as a two-stage process with the participation of both functional
groups. The bonding is mainly effected owing to the proton-acceptor properties of amine groups.
Commercial humic acid (HA) was anchored onto silica gel (SiAPTS) previously modified with 3-aminopropyltrimethoxysilane (APTS).
HA was anchored onto SiAPTS through two routes: adsorption and covalent chemical immobilization onto the surface. The adsorption
occurred by adding SiAPTS to HA in an aqueous solution, producing SiHA1, while chemical immobilization was performed by reacting
HA suspended in N,N-dimethylformamide with SiAPTS, to yield SiHA2. The infrared spectra confirm HA immobilization using both
procedures and the termogravimetric results showed that the anchored compounds have significantly thermal stability increased.
While natural HA presents a thermal stability up to 200C, the anchored compound presents a thermal stability near to 750C.
Calorimetric measurements of adsorption for the surfactant (benzyldimethyldodecylammonium bromide) and its polar head-group
(benzyltrimethylammonium bromide) from aqueous solutions on two different silica surfaces (hydrophilic and hydrophobic one)
allow a more detailed picture of the subsequent stages of the adsorption process to be drawn. It is possible to determine
more precisely a boundary between the adsorption of individual molecules and the formation of surface aggregates. The local
disruption of the structure of the interfacial water molecules by surfactant cations gives an endothermic contribution to
the total enthalpy of displacement. This contribution depends on the length of alkyl chain as well as on the type and the
origin of solid surface.
Authors:Oana Ştefănescu, Corneliu Davidescu, Mircea Ştefănescu and Marcela Stoia
In this paper we present a study regarding the obtaining of iron oxides embedded in silica matrix, using a modified sol-gel
method. This method consists in the formation, inside the silica matrix, of some Fe(III)-carboxylate compounds, resulted in
the redox reaction between Fe(NO3)3 and diol.
We have synthesized four gels, starting from tetra-ethyl orthosilicate, Fe(NO3)3·9H2O and different diols: ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol, for a final composition 50% Fe2O3/50% SiO2. The obtained gels have been thermally treated at 130°C, when the redox reaction Fe(NO3)3-diol took place with formation of the precursors in the xerogels pores. The thermal decomposition of all four precursors
took place up to 300°C.
The samples obtained by annealing at 300, 500, 700°C of the four xerogels lead to crystalline phases inside the amorphous
silica matrix. γ-Fe2O3/SiO2 may be obtained as unique phase depending on the diols nature. The formation of the precursors inside the silica matrix and
the evolution of the crystalline phases were analyzed by thermal analysis, FTIR spectrometry and XRD.
Authors:L. Zane Miller, Jeremy L. Steinbacher, Tania I. Houjeiry, Ashley R. Longstreet, Kendra L. Woodberry, B. Frank Gupton, Banghao Chen, Ron Clark and D. Tyler McQuade
Monodisperse silica microcapsules are typically fabricated using hard templating methods. Though soft templating methods are known, none yet provides a fast and easy method to produce monodisperse capsules. Herein, we describe a mesofluidic strategy whereby monodisperse droplets of reactive silica precursors are formed using a snap-off mechanism via a T junction. Both the mesofluidic system and the composition of the reactive silica formulation are critical features. Using solid- and solution-state 29Si nuclear magnetic resonance, scanning electron microscopy, and optical microscopy, we have developed models for why some formulations form exploding capsules, why some capsules contain crystalline materials, and why some capsules have thin or thick walls.
Thermogravimetry, differential thermal analysis, and IR spectroscopy were used to investigate the process of thermal destruction
of adsorbed polydimethylsiloxane (PDMS) in air. The disperse adsorbents were pristine fumed silica and modified fumed silica
whose surface contained oxygen compounds of phosphorus.
It was shown that under the given experimental conditions the thermal destruction of PDMS on the fumed silica surface was
accompanied by the complete transformation of the adsorbed PDMS to SiO2. In the case of phosphorus-containing silica, the thermal destruction proceeded in a different way. It was found that at
140–300C depolymerization of the siloxane chains of a certain part of the adsorbed polymer took place with the concurrent
removal of volatile products of the reaction. However, the remaining part of the adsorbed PDMS interacted with the modified
silica surface to form chemisorbed dimethylsilyl structures. The thermal destruction of the chemisorbed fragments of PDMS
in air was initiated at 400C or above for both types of silica investigated.
Authors:V. Tertykh, V. Yanishpolskii and O. Panova
The reaction conditions and component ratios were established for the attachment of 4-(2-pyridylazo)resorcinol (PAR), 1-(2-pyridylazo)-2-naphthol
(PAN) and 8-hydroxyquinoline (8-HQ) to the silica surface by means of a single-stage Mannich reaction. The modified sorbents
that were synthesized were characterized by an adsorption method, and DRIFT and UV spectroscopies. The concentrations of PAR,
PAN and 8-HQ grafted to the silica surface that were attained were 2.810−5, 8.510−5 and 2.710−4 mol g−1, respectively.
The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined.
A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s.
The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.