Preparation And Study Of Solar Reflection Coatings Based On Potassium Silicate

Various buildings exposed outdoors absorb solar radiation and cause high surface temperatures,leading to aging,deformation,and damage.Solar reflective coatings are widely studied and applied as an efficient and direct method to solve solar radiation hazards.However,most solar reflective coatings currently use organic materials as the main component.Solar reflective coatings based on organic materials have a limited service life due to the poor durability of organic components against acids,alkalis,and U-V rays.Potassium silicate(K₂O·n Si O₂)is a colorless,transparent,viscous liquid with good film-forming properties and chemical stability.However,coatings based on K₂O·n Si O₂ are prone to cracking and peeling in specific application scenarios and require improved adhesive strength and flexibility.Mechanical activation converts part of the mechanical energy into internal energy of the material,reduces particle size and crystallinity,changes particle morphology,and increases reactivity.Fiber toughening is an effective way to improve the flexibility of materials,reducing the load on the materials and prevent the propagation of cracks.Therefore,in this study,K₂O·n Si O₂was used as the film-forming substance to prepare solar reflective coatings based on potassium silicate.The adhesive strength of the coatings was improved through mechanical activation,polyester fiber toughening was used to improve the flexibility of the coatings,and the feasibility of quantitative characterization of the flexibility of the coatings was explored through small punch testing.In this study,three groups of coatings(T5H1,T5H1.5,and T5H2,where T5H1 refers to Ti O₂:H₂O=5:1 and T5H1.5 and T5H2 are the same)were prepared by using K₂O·n Si O₂ as film-forming material,Ti O₂ as pigment,Al PO₄ as curing agent and water as dispersion medium.Eight samples of Al PO₄ were prepared according to different mechanically activated times(A0,A2.5,A5,A10,A20,A40,A80,A160,where A0 referred to Al PO₄ mechanically activated for 0 min,others as well).Four groups of coatings(C0%F,C0.3%F,C0.6%F,C0.9%F,where C0%F refers to coatings with 0 wt.%fiber admixture,others as well)were prepared by incorporating short-cut dispersion-treated PET fibers to improve the flexibility of the coatings.The coatings were characterized by UV/VIS/NIR spectrophotometer for solar reflectance.The water resistance and alkali resistance of the coating ware characterized according to GB 1733-93 and GB/T 9265-2009.The chemical composition and microstructure of the coatings were characterized by XRD,SEM and FTIR.The mechanical properties of the coating were characterized by the universal material mechanics testing machine and hardness tester.Fluorescence microscope was used to characterize the uniformity of fiber dispersion in the coating.The flexibility of the coating was characterized by the flexibility test of the shaft rod method and the small punch testing.The UV/VIS/NIR spectrophotometer reflectance spectra of the coatings showed that the solar reflectance of the coatings exceeded 90%.SEM results showed that the porosity of the coatings was 39.08%,35.61%and 34.37%,respectively,with T5H1.5 not only having the most uniform distribution of pores but also the lowest porosity.The water resistance test results showed that the water-resistance of all three coatings meets the requirements of the GB/T10222-88 for water resistance of coatings.The mechanical test results showed that the adhesive strength of the three groups of coatings T5H1>T5H1.5>T5H2,with the exception of T5H2,reached 0.49 MPa as required by the GB/T 16777-2008.The results of XRD and FTIR showed that the degree of polymerization of the Si-O-Si polymer in the coatings and the reaction of K₂O·n Si O₂with Al PO₄ increased with the order of T5H1,T5H1.5 and T5H2.The study of mechanical activation to enhance the adhesive strength of coatings showed that crystallite size and the absolute value of zeta potential of Al PO₄ gradually decreased during mechanical activation,while the particle size first decreased,reaching a critical grain size of 2.7?m at 40min,and then gradually increased.The SEM revealed that agglomeration occurred in A160,and that A0,A5 and A40 were well dispersed.The FTIR and XRD results of the coatings showed that mechanical activation increased the degree of polymerization of Si-O-Si due to the higher reaction degree between K₂O·n Si O₂and Al PO₄in the coatings,with C40 showed a higher reaction degree than that of C0,C5 and C160.The EDS and SEM results of the coatings showed that the uniformity of Si-O-Si distribution in C40 was the highest among the four coatings.The mechanical test results showed that mechanical activation increased the adhesive strength of the coatings,with C40 reaching a maximum value of 0.7MPa.The study of fiber toughened coatings showed that the PET fibers after the short-cut dispersion treatment could be uniformly dispersed in the coating.The UV/VIS/NIR spectrophotometer spectral reflectance results showed that the blending of PET fiber would not significantly reduce the solar reflectance of the coating.The chemical structure and phase analysis showed that fiber incorporation would reduce the water involved in the chemical reaction of the coating.And reduce the degree of polymerization of the coating Si-O-Si and the reaction degree of K₂O·n Si O₂with Al PO₄.The flexibility test results of the shaft rod method showed that the incorporation of PET fiber significantly improved the flexibility of the coating,and the flexibility was C0.6%F>C0.9%F>C0.3%F>C0%F.The load-displacement curve of the small punch testing showed that the failure mode of the specimen gradually changed from brittle fracture to ductile fracture with the addition of fibers,the flexibility of the coating was C0.6%F>C0.9%F>C0.3%F>C0%F,which was consistent with the flexibility test results of the shaft rod method.In summary,a new type of solar reflective coating based on potassium silicate using K₂O·n Si O₂ as the coating film-forming material,Ti O₂ as the pigment,Al PO₄ as the curing agent and water as the dispersion medium was prepared.The mechanical activation treatment of Al PO₄ could significantly improve the adhesive strength of the coating.The method of incorporating short-cut dispersed PET fibers improved the flexibility of the coating.The small punch testing results indicated that the small punch testing could quantitatively analyze the flexibility of the coating.