Improvement of Building Materials Performance by Sol-Gel Derived Coatings
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IMPROVEMENT OF BUILDING MATERIALS PERFORMANCE BY SOL-GEL DERIVED COATINGS
WOLFRAM BEIER* AND IVAN ODLERI* *
Schott Glaswerke, Hattenbergstraie 10, D-6500 Mainz, FRG Technical University Clausthal, Institute of Non-metallic Materials, ZehntnerstraBe 2a, D-3392 Clausthal-Zellerfeld, FRG
ABSTRACT Different multicomponent solutions have been developed by which building materials were coated. After drying and annealing, the coatings convert into silicate based glassy films. TEOS or fumed silica were used as silica carriers and by adding lead compounds also low melting compositions were prepared. In some cases it proved to be convenient to adjust the viscosity of the solutions by additions of suitable organic polymers. The heat treatment was done either in an electric furnace or by means of a special acetylene burner. The produced films can protect building materials against corrosion, may reduce the absorption and permeation of water or improve abrasion resistance.
INTRODUCTION Several papers have been published on forming refractories from ceramic powders by the use of alkyl silicates as binders [1]. There have been published also data on the production of refractory materials entirely by sol-gel techniques [2]. On the other hand, not very much work has been done to improve building materials (or even whole constructions) by protective films applied by sol-gel processes. Therefore, a study was initiated, in which the possibilities of applying silicate based sol-gel glass films on building materials, such ceramic brick or concrete was explored. For that, we developed solutions which can be applied on the surface to be protected and may converted into sodium borosilicate glasses or to other (lead oxide containing) multicomponent glasses upon heating. The latter ones resemble certain commercial glazes. The necessary thermal energy was supplied by an electric furnace (laboratory studies) or by an acetylene burner (semi-technical conditions).
COATING OF CERAMIC BRICKS The solutions to be used corresponded to the oxidic composition (in mol per cent) of 25Na2(O13B2aO62SiO2 (solution 1) and 15Na2(-35B203-50SiO2 (solution 2). As starting materials NaNO3, HaBO3 and tetraorthosilicate (TEOS) were employed. This set of relatively cheap compounds had already proved in [3] and [4].
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
468
Samples from the interior of ceramic bricks were prepared by wet sawing. After storing them for 3 days at 25"C in a drying oven they were coated with the solutions. This was done three times within 2 min by the use of a fine brush. After the coatings had gelled the specimens were annealed at 700 or 1000"C in an electric furnace. Fig. 1 shows the surface of the uncoated brick while in Figs. 2 and 3 samples are displayed which were coated with solution 1 and annealed. It appears, that glassy films have formed at both 700"C and 1000"C. This way most of the small pores became sealed. The bigger pores, on the other hand, remained open as seen in Fig. 4, however, their interior s
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