Kinetics of catalytic hydrolysis of tetraethoxysilane by polycomponent solutions of neutral salts

Bessarabov, A. M.; Shalumov, B. Z.

doi:10.1007/bf02069196

Cited by 4 publications

(4 citation statements)

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“…12-quartz container, 13-MW screen. lead) and boric acid [8]. The hydrolyzates represent complex multicomponent liquid-phase systems containing the pmducts of inwmplete saponification of ethoxy p u p s , dissociation products of salts of alloying components that did not react with intermediate hydrolysis products of Si(0-El), and Ti(0-Bu),, ethyl alcohol, butyl alcohol and water.…”

Section: Methodsmentioning

confidence: 99%

“…A dummy lo@ of tap water flowing through a fluoroplanic spiral tube (8) with effective volume of 0.00Im1 war htalled in the chamber to avoid mismatch of the electric circuiu. 11-teflon stopper.…”

Section: Methodsmentioning

confidence: 99%

“…The chamber is slightly inclined toward one end and the slope of inclination can be precisely adjusted. The upper end of the chamber is connected with'the feeder of initial sol, the system for vapour condensation and discharge (8,15,16). and the water load (9) which prevents from reflecting not absorbed microwave energy back to the magnetron.…”

Section: Continuous Microwave Dryer and A Drying Processmentioning

confidence: 99%

“…(Figures 3 and 4) and according to the literature data [8]. The specific power of an electromagnetic energy absorbed in unit volume and transformed into the heat is found according to the equation:…”

Section: Design Calculationsmentioning

confidence: 99%

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Microwave Drying of Multicomponent Sols

Bessarabov¹,

Shimichev²,

Menshutina

1999

Drying Technology

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Extensive studies on microwave drying of multicomponent materials have been carried out in order to determine dielectric pmpenies of melalsiloxane sols, define the heating and drying characteristics of metalsiloxane sols and gels, develop the mathematical model of thermal processing, and design the continuous micmwave dryer that could be used in an industrial scale. INTRODUCTIONThe production of high purity multicomponent materials by thermal treatment of concentmted metalsiloxane sols is a highly challenging task for the fibre optics industry because of possible contamination of the end product when being in contact with metallic parts of the apparatus and the heat transferring agent. The most promising technology appears to be microwave drying because of: (i) non-contact heating, (ii) selective and volumetric heat generation with negligible temperature gradient, and (iii) negligible effect of thermal properties of the processed materials on the heating (drying) rates.Volumetric heat generation as a result of the ability of electromagnetic energy to penetrate a significant depth of the material to be processed is a distinctive feature of microwave drying. The heating and thus the moisture evaporation rates depend largely on Copyright 0 1999 by Marcel Dekker. Inc. Downloaded by [Northeastern University] at 16:26 27 December 2014 380 BESSARABOV, SHIMICHEV, AND MENSHUTINAthe applied power density and dielectric properties of the processed materials but do not depend on the rate of heat transfer to the evaporation h n t . Boiling of liquid moisture and other characteristic phenomena observed during microwave drying such as internal pressure build-up, evaporation-condensation phenomena, or D m y flow result also h m volumetric heat generation [I, 21. Although microwave heating has been found advantageous in numerous processes such as drying, curing, sintering, mineral processing, etc. [3,4] it has not been used so far in the technology of high-purity substances. Our exploratory trials on drying of various composite materials have revealed, however, that microwave processing of metalsiloxane sols can offer more pure and homogeneous products than traditional methods of heating. Moreover, syneresis of the resulting gel that greatly reduces product quality can practically be eliminated [5-71. In addition, water:alcohol based multiwmponent sols belong tb the class of lossy dielectrics in contrast to preferable materials of wnshuction such as quartz glass, fluoroplastics and most of ceramics. It allows design of the microwave apparatus with significant wall thickness without affecting the heating characteristics of the pmduct. All these features of microwave processing has driven the present studies aimed at M e r developing a technology that could be used in production of high-purity multicomponent materials. MATERIALS AND METHODThe heating and drying characteristics of metalsiloxane sols were studied in an experimental rig shown schematically in Figure 1. The metallic microwave cavity was custom built in the fonn of th...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Continuous Microwave Dryer and A Drying Processmentioning

confidence: 99%

Section: Design Calculationsmentioning

confidence: 99%

See 2 more Smart Citations

Microwave Drying of Multicomponent Sols

Bessarabov¹,

Shimichev²,

Menshutina

1999

Drying Technology

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Modeling heterogeneous liquid-phase processes in apparatus with intermittent agitators

Bessarabov¹

1996

Chem Petrol Eng

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The mathematical description of a process by the block-diagram method [1] starts with the construction of a hydrodynamic model. A large body of experimental data [2] shows that liquid overshoots, nonuniform velocity profiles, and other factors cause a deviation from ideal mixing, even on a laboratory scale and more so in large-capacity industrial equipment. However mixers are often assumed to be ideal in engineering calculations, which are sufficiently accurate for practical problems [3, 4]. The interaction between mixing and the processes occurring in the reactor can be considered to have two components: micromixing and macromixing [5].Today mixing processes in heterogenous systems are studied by determining the parameters which characterize both the homogeneity and the energy required to create homogeneous compositions [6]. Because one of the basic goals of mixing is to decrease temperature and concentration gradients, the flow structure created in the apparatus must have the most uniform velocity profile possible over the whole volume of the apparatus.A silicon-organic liquid ~ tetraethoxysilane, dispersed in water -is used in the industrial synthesis of polycomponent metal siloxane compositions for fiber optics. These processes are conducted under transient conditions in apparatus with disk agitators operating intermittently [7]. Research with this type of apparatus has been conducted on the effect of the hydrodynamics on the reaction kinetics and operational conditions for synthesizing metal siloxane compositions.The cohydrolysis kinetics of tetraethoxysilane and water-soluble salts of alloying components have been modeled by assuming a pseudohomogeneous process [8, 9]. In order to determine the limiting stage of heterogeneous hydrolysis of tetraethoxysilane, the change of concentration of the key component was calculated by various mathematical models [10] that considered the change in phase composition and the area of the interphase surface during the synthesis. Good correlation between experimental and calculated tetraethoxysilane concentrations was obtained by using a model that describes the diffusion of water through the boundary film of tetraethoxysilane droplets:(1)where S is the specific contact surface of the phases, m2/m3; r is the volumetric fraction of the dispersed phase; M is the initial molar ratio of reagents in the continuous and dispersed phases; X ~ and X ~ are the initial concentrations of the continuous and dispersed phases, mole/liter; X is the current concentration of tetraethoxysilane, mole/liter; and Kg is the mass transfer coefficient of reagent from the main flow to the outer surface of droplets of tetraethoxysilane, m/sec. During experimental research on a laboratory setup with a propeller mixer, hydrodynamic conditions were found that correspond to a value of the Weber criterion WeK: the synthesis rate of the polycomponent hydrolysis components did not increase as the mixer rotation rate was increased when n > 800 rpm. The hydrodynamic parameters, the specific phase contact su...

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Scientific fields and practical applications of sol-gel techniques in the Soviet Union

Shalumov¹

1992

Eurogel '91

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Kinetics of catalytic hydrolysis of tetraethoxysilane by polycomponent solutions of neutral salts

Cited by 4 publications

References 1 publication

Microwave Drying of Multicomponent Sols

Microwave Drying of Multicomponent Sols

Modeling heterogeneous liquid-phase processes in apparatus with intermittent agitators

Scientific fields and practical applications of sol-gel techniques in the Soviet Union

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