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Protectosil® 851 was used in the restoration of the Charlottenburg gate in Berlin
At the boundary between Berlin's Charlottenburg and Tiergarten districts stands the Charlottenburg Gate, an ornate neo-baroque structure dating from the early twentieth century. Situated between Ernst-Reuter-Platz and the Siegessäule on the Strasse des 17. Juni, it forms a counterpart to the Brandenburg Gate on the opposite side of the Tiergarten. Following the extensive restoration of the actual structure last year, the Berlin restoration firm Opus is now taking in hand the two 22 meter high candelabra that stood on the Charlottenburg side of the gate before they were destroyed in the Second World War. Before the year ends, the two columns will be restored to their previous splendor. Originally of tufa, the candelabra will be reconstructed by Opus using a concrete mix that allows replication of the ocher color of the stone. And the concrete also conceals other surprises: An oligomeric alkylsilane that Evonik has developed for the construction industry will, by its water-repellent action, ensure the durability of the restored candelabra. Employees of the integrated silicon production facility in the Inorganic Materials Business Unit have succeeded in developing oligomeric alkylsilanes to the extent that they open up entirely new possibilities for the construction and filler industries. For this achievement the team has now received Evonik's Innovation Award for 2009 in the New Products category. The Inorganic Materials Business Unit is a globally active supplier of functional silanes, with a total of four production sites in the Europe, North America, and Asia Regions. The business unit works in close conjunction with strategic customers and develops together with them optimized silanes that help open up new market opportunities. Inorganic Materials pools product know-how in its Protectosil® and Dynasylan® functional silanes. Protectosil® offers solutions for water repellents, protection against graffiti and corrosion, and surface protection for a variety of materials including concrete, sandstone, granite, and stucco. The Dynasylan® brand, on the other hand, has for more than 50 years stood for silanes that help improve product properties in a widely diverse range of industries, from paints and coatings through sealants and fillers to pharmaceuticals.
The construction industry needs high-performance chemicals that are easy to process at construction sites. For a wide variety of substrates, water repellent action is the most important requirement because this is the only way of preventing corrosion in reinforced concrete, alkali-silica reactions, or sulfate attack. Corrosion of rebars is one of the major causes today for failure of concrete structures. A tragic example from the U.S. is the bridge carrying the Interstate 35 Highway in Minnesota, which collapsed on August 1, 2007. The filler industry also needs water repellents as cost-effective but high performance dispersants that should have a very low content of volatile organic compounds. These are used primarily for manufacturing window frames and plastic films. The oligomeric alkylsilane that Evonik obtains from a synthesis of organofunctional chlorosilanes is the base product for the new development, which allows new and improved applications in the construction and filler industries. The employees of the business unit have produced three grades, which have different physical properties; there is also one customizable grade.
The products are Dynasylan® 9896 and Protectosil® 266. Dynasylan® 9896, aimed at the filler industry(fig.1), has a significantly lower volatile organic compound content than the monomeric silanes that are frequently used as dispersants. This is important for processing and also, from a broader viewpoint, because of increasing public concern in both Europe and the U.S. about hazardous gas emissions from organic compounds, with intense political debate on appropriate limits. Dynasylan® 9896 has a high boiling point and is thus suitable even for applications where high safety requirements must be met. The surface of a treated filler can be modified even at relatively high temperatures without affecting the water-repellent action. Protectosil® 266 on the other hand is an oligomeric alkylsilane serving as an impregnating agent for absorbent mineral facade construction materials. It is competitive with the silicone-based products that have so far dominated this market segment. As an aqueous emulsion, the product has the names Protectosil® WS 610 and WS 630, and as a powder Protectosil® DRY CIT. All the three are virtually free of volatile organic compounds. They allow the concrete cover of rebars to be thinner; this reduces the required quantity of concrete, a construction material whose production is known to be highly energy intensive. 35 years of corrosion protection for concreteAs early as 2008, Evonik received an award for Protectosil® DRY CIT at DEUBAU, Germany's most important trade show for the construction industry. The organic sheath of the powder system dissolves in the cement mix, releasing the active components where they are needed. The components bind covalently to the concrete in a chemical reaction, which explains the remarkable durability of the corrosion protection(fig.2). Tests confirm that Protectosil® DRY CIT remains effective for at least 35 years(fig.3, 4). In contrast, the corrosion control formulations available on the market are often good for only a few years.
The Buda Castle in Budapest (Hungary) was restored in 2008. Since then, Protectosil® WS 630 has been protecting the walls against moisture. (Photo: Das kleine Atelier – Fotolia)
The fourth grade of the oligomeric alkylsilane is a customizable solution: Protectosil® 60 SK can be rapidly adapted for new customer requirements, for example, by the use of suitable catalysts, so that the water-repellent action of the product can be fully developed even on substrates of lower alkalinity(fig.5). Ever since the market launch of the oligomeric alkylsilanes, the products have enjoyed increasing popularity among customers, thanks to their excellent property profile. In none of the grades could the oligomeric alkylsilane be used directly after its generation as a by-product in the synthesis of organofunctional chlorosilanes; various refining steps and extensive tests were necessary. With the powder grade, for example, a problem arose on mixing the product with concrete, when large quantities of air were introduced; the project team had to find a suitable defoamer that could be added to the powder. Silane systems have long been used for their water repellent action. They also have excellent corrosion inhibiting properties. Until now, however, they have always had the disadvantage of a high volatile organic substance content due to the alkoxy groups of the silanes. With their oligomerized alkylsilanes, the project team has succeeded in reducing these unwanted emissions by up to 85 percent, making an important contribution toward a healthier environment.
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