Yüzey işlemleri öncesi cam yüzeyine uygulanan çözeltilerin etkileri
Yüzey işlemleri öncesi cam yüzeyine uygulanan çözeltilerin etkileri
Dosyalar
Tarih
2021
Yazarlar
Canbazoğlu, Semin
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Lisansüstü Eğitim Enstitüsü
Özet
Cam yüzeyinin kimyasal ve fiziksel özelliklerinin detaylı bir şekilde bilinmesi önemlidir. Yüzeydeki atomların enerjisi yüksektir ve koordinasyonlarını en üst düzeye çıkararak enerjilerini minimize etmeye çalışırlar. Bunun yolu da cam yüzeyine uygulanan işlemler ve/veya cam yüzeyinin maruz kaldığı ortam sayesinde cam yüzeyinden bazı bileşenlerin uzaklaşması ve/veya cam yüzeyine bazı bileşenlerin fiziksel veya kimyasal adsorpsiyonudur. Bunun sonucu olarak yüzeyin kimyasal ve fiziksel özellikleri değişebilmekte; yüzey, korozyona uğrayabilmekte, yüzeye uygulanacak kaplamanın yapışması olumsuz etkilenebilmekte ve en sonunda kaplamanın özellikleri değişebilmektedir. Camın korozyon mekanizmasının belirlenebilmesi ve gerekli önlemlerin alınıp korozyon direnci yüksek kaplama yüzeylerinin elde edilebilmesi gerekmektedir. Düz cam yüzeyi, kalay banyosundan çıktıktan hemen sonra, soğutma sırasında ve özellikle depolama ve nakliye sırasında havadaki nem ile temas eder. Camla temas eden su, özellikle Na+ ve Ca2+ katyonlarının yüzeye difüzyonuna neden olur. Soda kireç silika camında bulunan bu alkali iyonlar, yüzey hidrasyonu ile yüzeyde sodyum hidroksit ve/veya sodyum karbonat oluşumuyla sonuçlanan iyon değişimini içerir, bu da sulu çözeltinin pH değerini arttırarak camın yüzey reaktivitesini artırır ve SiO2 ağ yapının çözünmesine, dolayısıyla korozyon, optik özellik ve mekanik mukavemetin bozulmasına neden olabilir. Kimyasal veya mekanik mukavemeti arttırmak için alkalilerin yüzey bölgesinden uzaklaştırılması amacıyla cam yüzeyinin kaplanmasından önce etkili yıkama işlemleri uygulanmaktadır. Tez çalışmasının ilk kısmında, kaplama uygulamaları öncesinde, yüzeyden alkalilerin uzaklaştırılması için cam yüzeyine uygulanan farklı ön temizleme işlemlerinin etkisi incelenmiştir. Bu amaçla, yüzey liçleme hücresi kullanılarak düzcam yüzeylerinden çözeltilere geçen alkali miktarının sıcaklığa bağlı değişimi, yüzey kompozisyonu, bağ yapısı, yüzey morfolojisi ve yüzey gerilimi analizleri gerçekleştirilmiştir. Çalışmanın ikinci kısmında, soda kireç silikat cam yüzey temizliğinin, iyon değişimi yoluyla basma gerilmesi tabakasının oluştuğu kimyasal temperleme işlemine etkisi incelenmiştir. Ön işlem uygulanmış ve uygulanmamış numunelerin yüzey kompozisyonları, bağ yapıları, yüzey morfolojileri incelenmiş, kimyasal temperleme işleminden sonra numunelerde meydana gelen ağırlık değişimleri, iyon değişim miktarları, yüzey basma gerilmesi ve tabaka derinliği, kırılma yükü analizleri gerçekleştirilmiştir. Kimyasal temperleme işlemi, difüzyon temelli iyon değişim reaksiyonlarına dayanır. Alkali oksit içeren cam, camsı geçiş sıcaklığının altında, eriyik alkali tuz banyosuna daldırılmasıyla harici çekme gerilmesine karşı bir artık basma gerilme tabakası oluşturulur. Bu durum, cam yüzeyindeki küçük çaplı alkali iyonların, daha büyük çaplı alkali iyonlarla değiştirilmesiyle elde edilir. Yüzeyde oluşan basma gerilmesi camın mekanik olarak dayanımının artmasına neden olur. Kimyasal temperleme işlemi için temizleme işlemi uygulanmamış, deiyonize su ve asidik çözeltilerle temizlenen cam yüzeyler, eriyik KNO3 banyosunda belirli süre ve sıcaklıkta iyon değişimine tabi tutulmuştur. Cam yüzeyinin ön temizlenmesiyle elde edilen sıkıştırılmış tabakanın derinliği arasındaki ilişki yüzey gerilmesi analiziyle incelenmiş ve birim yüzey alanı başına toplam yer değiştiren iyon miktarı ile ilişkilendirilmiştir. Ön temizleme işlemi, işlem uygulanmamış numunelere kıyasla kimyasal temperleme sonrasında potasyum yüzey konsantrasyonu değişerek yüzey stres profillerine ve tabaka derinliğine etki etmektedir. Bu bulgu, kimyasal temperleme için camın optimum ön işlem koşullarının belirlenmesi gerekliliğini ortaya koymaktadır. Uygun yüzey temizleme işlemleriyle, halka-üstü halka çift eksenli bükme testlerinde, kimyasal temperlenmiş camlar için daha yüksek kırılma yüklerinin elde edildiği tespit edilmiştir.
Glasses exhibit a variety of advantageous structural properties, including high stiffness, high hardness, visual transparency, forming ability, low cost production, reproducible sample surfaces and often high chemical durability. Numerous technological applications of glass depend on the quality of the surface. However, glasses are also inherently brittle, typically leading to relatively low values of usable strength. At the origin of this, there are practically unavoidable microscale defects which occur on the glass surface, for example, caused by inclusions or residues from glass manufacture, micro-cracks at the edges of a glass product which result from finishing or cutting processes, or the scratches caused by further handling and daily usage. Surface and subsurface damage of soda lime silica glass can affect the morphology, defect density, the strength and durability of the coating applied on the glass surface. It is essential to know the chemical and physical properties of the glass surface in detail. The atoms on the surface have high energy and try to minimize their energy by maximizing their coordination. The float glass surface comes into contact with moisture in the air immediately after leaving the tin bath, during cooling, and especially during storage and transportation. After storage or bulk transport, it is possible to find chemical surface changes on the glass that cannot be removed and the glass can no longer serve its intended purpose. The glass composition and environmental conditions such as moisture can play an important role in the initiation and propagation of surface defects. Water in contact with glass causes diffusion of especially Na+ and Ca2+ cations to the surface. Alkali ions in soda lime silica glass may increase the surface reactivity of the glass in humid environments and the compounds formed such as sodium bicarbonate, sodium carbonate, or sodium hydroxide increase the pH of the aqueous solutions. This causes deterioration of surface hydration, hence the SiO2 network structure. As a result, the chemical and physical properties of the surface can change; the surface may corrode, the adhesion of the coating to be applied to the surface may be negatively affected and eventually the properties of the coating may change. It is necessary to determine the corrosion mechanism of the glass and to take the necessary precautions to obtain coating surfaces with high corrosion resistance. The way of this is the removal of some compounds from the glass surface and/or physical or chemical adsorption of some components to the glass surface through the processes applied to the glass surface and/ or the environment to which the glass surface is exposed to. Effective washing processes are applied before coating the glass surface in order to remove alkalis from the surface area in order to increase chemical or mechanical resistance. The effect of pre-cleaning processes applied to the glass surface before surface treatments was examined. The surface cleaning processes of soda-lime-silicate float glasses before chemical strengthening where a compressive stress layer is introduced via ion exchange and the effect of different cleaning processes applied to the glass surface to remove alkali ions from the surface before low-e coating were examined in two sections. In the first part of the thesis study, the temperature-dependent change of the alkali amount passing into the solution from the flat glass surface was investigated by using a surface etching cell. At this stage, first of all, the analysis of the washing water used in the coating line of the flat glass production plant was made and the changes on the surface after it was applied to the glass were examined. At the same time, the surface characterizations of freshly produced glasses and waiting for different periods in the warehouse were made. Finally, the effect of the dealkalization process on the glass surface was investigated. The practical use of glass is limited by its fragility, which is often associated with statistical failure. There are various ways to increase the strength of glass; including modification of glass surfaces. In order to improve the mechanical properties of glass, glass surface treatments are typically applied, primarily including thermal or chemical strengthening processes. Especially the second process generates higher strength, often exceeding the GPa-range. It relies on ion-exchange reactions, whereby a compressive residual stress layer is generated to counteract external tensile stress. This is achieved by exchanging small-diameter alkali ions on the glass surface with larger-diameter alkali ions, often denoted as stuffing. In principle, chemically strengthened glass is obtained via immersing a glass product into a molten salt bath at temperatures below the strain point of the glass. Many parameters affect the ion-exchange process during the chemical strengthening and, thus, the primary target parameters, i.e., the magnitude of surface compression and the depth of the compression layer below the surface. First, the employed glass structure has to contain a high concentration of mobile ion species. Second, the process must be operated in the absence of stress relaxation, thus, at sufficiently low temperature. Strength predictions using the effective residual stress profile require consideration of flaw geometric characteristics and their conservation after ion-exchange. In the presence of severe flaws, even a very high surface compression may result in a non-significant strength variation after chemical strengthening. Strengthening glass via the introduction of surface compressive residual stress is often taken as a way to prevent sub-critical crack growth. For chemically strengthened glass, there are two important conditions; when the size of the surface flaw is larger than the depth of the compressive stress layer and the flaw is accessible by water vapor, the tip of the flaw is permanently under tensile stress. When a flaw is generated after chemical strengthening, the strength loss occurs locally, eventually associated with further subcritical growth of the defect. The interfacial energy between a glass surface and molten salt, the phase boundary reaction barrier and the adsorption enthalpy at the glass surface are related to the surface quality; all these properties play an important role in the ion-exchange process. Effective and controlled cleaning treatment for reproducible glass surfaces prior to ion-exchange is therefore important to ensure process homogeneity by maintaining the contamination level on the surface at a minimum, constant level. Such a cleaning step before ion- exchange may involve ultrasonic treatment in demineralized water and ethanol or conventional washing with demineralized water followed by gently swabbing. However, the quantitative effects of such cleaning treatments on subsequent chemical strengthening process have not been reported as to yet. The second part of the study was focused on the effect of surface cleaning treatments of soda-lime-silicate float glasses before chemical strengthening where a compressive stress layer is introduced via ion exchange. The aim of the study is to elucidate the effect of surface cleaning on chemical strengthening by ion-exchange. For this purpose, as-received and cleaned glass surfaces were subjected to two different treatments using demineralized water and acidic solutions. Ion exchange process was applied to the prepared samples in a molten salt bath at a certain temperature and time. Precleaning treatment leads to a relative enhancement of the potassium surface concentration following chemical strengthening as compared to the uncleaned samples, also reflecting in altered surface stress profiles and case depth. The surface properties of uncleaned (as-received condition) and cleaned flat glass samples were characterized before and after chemical strengthening. The relationship between glass surface cleaning pre-treatment and the depth of the achieved compressive layer was then studied by surface stress analysis and related to the total amount of exchanged ions per unit surface area. These observations provide guidance for optimal pretreatment conditions of glass for chemical strengthening. Appropriate cleaning treatments can result in higher achievable fracture loads of subsequently chemically tempered glasses in ring-on-ring biaxial bending tests.
Glasses exhibit a variety of advantageous structural properties, including high stiffness, high hardness, visual transparency, forming ability, low cost production, reproducible sample surfaces and often high chemical durability. Numerous technological applications of glass depend on the quality of the surface. However, glasses are also inherently brittle, typically leading to relatively low values of usable strength. At the origin of this, there are practically unavoidable microscale defects which occur on the glass surface, for example, caused by inclusions or residues from glass manufacture, micro-cracks at the edges of a glass product which result from finishing or cutting processes, or the scratches caused by further handling and daily usage. Surface and subsurface damage of soda lime silica glass can affect the morphology, defect density, the strength and durability of the coating applied on the glass surface. It is essential to know the chemical and physical properties of the glass surface in detail. The atoms on the surface have high energy and try to minimize their energy by maximizing their coordination. The float glass surface comes into contact with moisture in the air immediately after leaving the tin bath, during cooling, and especially during storage and transportation. After storage or bulk transport, it is possible to find chemical surface changes on the glass that cannot be removed and the glass can no longer serve its intended purpose. The glass composition and environmental conditions such as moisture can play an important role in the initiation and propagation of surface defects. Water in contact with glass causes diffusion of especially Na+ and Ca2+ cations to the surface. Alkali ions in soda lime silica glass may increase the surface reactivity of the glass in humid environments and the compounds formed such as sodium bicarbonate, sodium carbonate, or sodium hydroxide increase the pH of the aqueous solutions. This causes deterioration of surface hydration, hence the SiO2 network structure. As a result, the chemical and physical properties of the surface can change; the surface may corrode, the adhesion of the coating to be applied to the surface may be negatively affected and eventually the properties of the coating may change. It is necessary to determine the corrosion mechanism of the glass and to take the necessary precautions to obtain coating surfaces with high corrosion resistance. The way of this is the removal of some compounds from the glass surface and/or physical or chemical adsorption of some components to the glass surface through the processes applied to the glass surface and/ or the environment to which the glass surface is exposed to. Effective washing processes are applied before coating the glass surface in order to remove alkalis from the surface area in order to increase chemical or mechanical resistance. The effect of pre-cleaning processes applied to the glass surface before surface treatments was examined. The surface cleaning processes of soda-lime-silicate float glasses before chemical strengthening where a compressive stress layer is introduced via ion exchange and the effect of different cleaning processes applied to the glass surface to remove alkali ions from the surface before low-e coating were examined in two sections. In the first part of the thesis study, the temperature-dependent change of the alkali amount passing into the solution from the flat glass surface was investigated by using a surface etching cell. At this stage, first of all, the analysis of the washing water used in the coating line of the flat glass production plant was made and the changes on the surface after it was applied to the glass were examined. At the same time, the surface characterizations of freshly produced glasses and waiting for different periods in the warehouse were made. Finally, the effect of the dealkalization process on the glass surface was investigated. The practical use of glass is limited by its fragility, which is often associated with statistical failure. There are various ways to increase the strength of glass; including modification of glass surfaces. In order to improve the mechanical properties of glass, glass surface treatments are typically applied, primarily including thermal or chemical strengthening processes. Especially the second process generates higher strength, often exceeding the GPa-range. It relies on ion-exchange reactions, whereby a compressive residual stress layer is generated to counteract external tensile stress. This is achieved by exchanging small-diameter alkali ions on the glass surface with larger-diameter alkali ions, often denoted as stuffing. In principle, chemically strengthened glass is obtained via immersing a glass product into a molten salt bath at temperatures below the strain point of the glass. Many parameters affect the ion-exchange process during the chemical strengthening and, thus, the primary target parameters, i.e., the magnitude of surface compression and the depth of the compression layer below the surface. First, the employed glass structure has to contain a high concentration of mobile ion species. Second, the process must be operated in the absence of stress relaxation, thus, at sufficiently low temperature. Strength predictions using the effective residual stress profile require consideration of flaw geometric characteristics and their conservation after ion-exchange. In the presence of severe flaws, even a very high surface compression may result in a non-significant strength variation after chemical strengthening. Strengthening glass via the introduction of surface compressive residual stress is often taken as a way to prevent sub-critical crack growth. For chemically strengthened glass, there are two important conditions; when the size of the surface flaw is larger than the depth of the compressive stress layer and the flaw is accessible by water vapor, the tip of the flaw is permanently under tensile stress. When a flaw is generated after chemical strengthening, the strength loss occurs locally, eventually associated with further subcritical growth of the defect. The interfacial energy between a glass surface and molten salt, the phase boundary reaction barrier and the adsorption enthalpy at the glass surface are related to the surface quality; all these properties play an important role in the ion-exchange process. Effective and controlled cleaning treatment for reproducible glass surfaces prior to ion-exchange is therefore important to ensure process homogeneity by maintaining the contamination level on the surface at a minimum, constant level. Such a cleaning step before ion- exchange may involve ultrasonic treatment in demineralized water and ethanol or conventional washing with demineralized water followed by gently swabbing. However, the quantitative effects of such cleaning treatments on subsequent chemical strengthening process have not been reported as to yet. The second part of the study was focused on the effect of surface cleaning treatments of soda-lime-silicate float glasses before chemical strengthening where a compressive stress layer is introduced via ion exchange. The aim of the study is to elucidate the effect of surface cleaning on chemical strengthening by ion-exchange. For this purpose, as-received and cleaned glass surfaces were subjected to two different treatments using demineralized water and acidic solutions. Ion exchange process was applied to the prepared samples in a molten salt bath at a certain temperature and time. Precleaning treatment leads to a relative enhancement of the potassium surface concentration following chemical strengthening as compared to the uncleaned samples, also reflecting in altered surface stress profiles and case depth. The surface properties of uncleaned (as-received condition) and cleaned flat glass samples were characterized before and after chemical strengthening. The relationship between glass surface cleaning pre-treatment and the depth of the achieved compressive layer was then studied by surface stress analysis and related to the total amount of exchanged ions per unit surface area. These observations provide guidance for optimal pretreatment conditions of glass for chemical strengthening. Appropriate cleaning treatments can result in higher achievable fracture loads of subsequently chemically tempered glasses in ring-on-ring biaxial bending tests.
Açıklama
Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2021
Anahtar kelimeler
Cam,
Glass,
Cam yapımı,
Glass manufacture,
İyon değişimi,
Ion exchange,
Difüzyon,
Diffusion