Effects Of Acid Treatment And Surface Coating On The Mechanical And Optical Properties Of Glass

According to the analog computation based on the chemical bond strength andstructure of glass，the theoretical flexural strength of the glass can reach up to10-15Gpa. however, the practical flexural strength of ordinary glass is only about50¹00MPa, less than1%of the theoretical value. the main reason is that there are lots offlaws in the glass surface, which causing stress concentration, resulting in asignificant decrease in strength of the glass. In this paper, the ordinary glass slideswere treated by the mixture of hydrofluoric acid and sulfuric acid, after treatment thesurface flaws were passivated and etched, the flexural strength of the glass wasimproved. But the surface after acid treatment is very fresh and easy to be scratched,which can reduce the glass strength again. Thus, the aluminum films with highhardness were prepared on the surface of the glass to improve the scratch resistanceof the sample. However, the refractive index of the alumina film is higher than theglass substrate, causing light transmittance of the sample was lower than the glass, sothe MgF₂films were prepared to improve visible light transmittance of the sample.In short, in this paper the mechanical properties and optical properties of the glasswere improved by acid treatment and surface coating technology.The main experimental results are as follows:（1） The content of HF and reaction time are the main factors affecting the flexuralstrength of glass. The content of HF affected greatest, while reaction temperature andthe content of H₂SO₄had little influence on the strength of the glass, which themain role of H2SO4is dissolving the poorly soluble product.（2） With ultrasonic-wave assisted, when the practical parameter were:22wt%forHF,25wt%for H₂SO₄, the reaction time was14min, the reaction temperature was25℃, the flexural strength of the acid-treated glass can reach up to239.26MPa,whichwas3.5times than the untreated glass （68.34MPa）（3） The transparent and stable alumina sol can be obtained aluminum by theprecursor aluminum nitrate when aluminum nitrate: ammonia: nitric acid=1:3:0.3（molar ratio） and the hydrolysis temperature was85℃（4） θ-Al₂O₃films prepared by sol-gel method after heat treatment at530℃, at this time microhardness of the sample increased approximately50%to1215.32HVthan the uncoated samples, anti-scratch properties of the sample were also improvedgreatly; flexural strength of the sample increased about9.5%.（5） Magnesium acetate and hydrofluoric acid were selected as start materials,ethanol as solvent. Typically, a molar ratio of magnesium acetate, ethanol and HF was1:50:2.3, after stirring at40℃for20h, transparent magnesium fluoride sol wasprepared. MgF₂films prepared by the sol-gel method can significantly improve thevisible light transmittance of the samples, compared to the aluminum film sampleswithout coated by magnesium fluoride films, the average antireflective effect can beachieved about7.5%in the visible band，the microhardness of the samples was1086.24HV.