ADVANCED MATERIALS & PROCESSES | JULY 2026 32 Many cultural heritage sites and historical monuments around the world have been suffering from environmental deterioration for a long time. To address this trend, the development of appropriate pro- tective coatings has become one of the most important issues in modern conservation. This article focuses on one novel solution—silicone-based inorganic coatings, especially those derived from alkoxysilanes. Two case studies, conducted by the authors, are introduced to demonstrate the effectiveness of the coatings on historical structures. INTRODUCTION Modern protective coatings are generally classified into two categories: organic coatings and inorganic coatings. Conventional organic coatings, such as acrylics, epoxies, and urethanes, are widely used because of their flexibility, strong adhesion, and ease of processing. However, when they are exposed to ultraviolet light, moisture, oxygen, and temperature fluctuations for a long time, their organic molecular structures gradually degrade through HOW SILICONE-BASED INORGANIC COATINGS HELP PROTECT CULTURAL HERITAGE AND HISTORICAL MONUMENTS Case studies on historical structures exposed to the natural environment show how a novel coating helps create a protective film with ceramic-like stability while preserving the original appearance. Hideyuki Kanematsu, FASM,* University of Osaka, Suita, Japan, and BEL Inc., Sakai, Osaka, Japan Akiko Ogawa, National Institute of Technology, Suzuka College, Suzuka, Japan Akira Suzuki, D&D K.K., Yokkaichi, Mie, Japan Takayoshi Nakano, University of Osaka, Suita, Japan *Member of ASM International photo-oxidation, chain scission, and hydrolysis. As a result, discoloration, cracking, and the loss of protective performance may occur over time. In contrast, inorganic coatings have been attracting increasing attention for applications requiring long-term durability and environmental resistance. Among various inorganic materials, those that are silicone-based have become particularly important. This is because they combine the flexibility of organic materials with the stability of inorganic networks. THE CHEMISTRY OF ALKOXYSILANE HYBRID COATINGS The fundamental structure of silicone materials is based on siloxane bonds, represented by the Si–O–Si linkage. The Si–O bond (approximately 452 kJ/mol) is significantly stronger than the C–C bond (approximately 347 kJ/mol) found in conventional organic polymers. Therefore, silicone- based materials show excellent resistance to heat, ultraviolet radiation, oxidation, and weathering. One important class of silicone- related materials is alkoxysilane-based resins. These materials contain alkoxy groups attached to silicone atoms. Although the term “silicone” usually refers to fully polymerized polysiloxanes, alkoxysilanes are their reactive precursors. Once cured, the resulting network is chemically continuous with silicone chemistry. Consequently, these coatings are often classified into the broader “silicone-based” family. When alkoxysilanes are exposed to moisture in air or on substrate surfaces, the alkoxy groups undergo a twostep reaction, classically known as the sol-gel process: Hydrolysis: ≡Si–OR + H₂O → ≡Si–OH + R–OH Condensation: ≡Si–OH + HO–Si≡ → ≡Si–O–Si≡ + H₂O Through this sequence, a dense inorganic or inorganic-organic hybrid network is gradually formed on the surface of the material and within the porous structure of the substrate. This moisture-curing mechanism is one of the key reasons why alkoxysilane-based systems are often described
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