Epoxy based coatings on glass: strengthening mechanisms

Glass may be strengthened by epoxy coatings although the strengthening mechanisms remain unclear. Possible strengthening mechanisms are reviewed and are used to analyse strength data for both a solvent based and a water based coating system. The coatings either fill (solvent based coatings), or partially fill (water based coatings) surface cracks and it is shown that closure stresses arising from the thermal expansion mismatch of the coating within these cracks can account for the observed degrees of strengthening. It is also demonstrated that other suggested mechanisms such as flaw healing cannot fully account for the observed degree of strengthening.     

Characterization and chemical durability of 70Ph2SiO·30TiO2 coating prepared by the sol-gel process

70Ph₂SiO·30TiO₂ coatings on slide glass and phosphate glass substrates have been prepared by the sol-gel process. Experimental results on the characterization and chemical durability of the coatings are presented. It is shown that the coatings heated at 150°C have reasonably good acid and water resistance while their alkali durability is very poor. The XPS results are used to verify the different corrosion behaviors of the coating in pure water and 1N HC1 solutions. The chemical durability of phosphate glass can be significantly improved by this coating.     

Investigations on glass-to-mold sticking in the hot forming process

The sticking behavior of various mold materials and coatings for hot glass melt forming processes, like, e.g. glass container manufacturing, was investigated using a new testing procedure. The mold material specimens under test were subjected to frequent contact with hot viscous glass gobs in a pressing process with presetting well defined non-isothermal pressing parameters to simulate industrial working conditions. Three different glass compositions were used in this investigation, soda-lime silicate glass, lead crystal glass, and borosilicate glass. The sticking characteristics of the tested mold materials and coatings were described by two quantities, a ‘lower’ and an ‘upper’ sticking temperature, which are specific for each mold material and type of glass in the non-isothermal pressing process. The ‘lower’ sticking temperatures of uncoated mold materials were found to depend monotonically on the thermal effusivity (heat penetration coefficient) of the bulk mold materials. All of the coating materials applied to various substrate mold materials were found to reduce the ‘lower’ sticking temperature as compared to the uncoated materials. Most of the coating materials were found to reduce also the ‘upper’ sticking temperature.     

Influence of sol-gel coatings on crack initiation by vickers indentation in soda-lime glass

In this work an indentation technique was used to study the effect of the sol-gel coatings of soda-lime glasses on crack formation. The tendency of samples to develop radial cracks has been evaluated by measuring their number in correspondence with the Vickers impressions as a function of the applied load. Silica coatings of different thickness were obtained from alcoholic solutions of TEOS by the dipping technique on glass sheets with different degrees of surface hydration.

All the coated samples show a lower crackability compared with the uncoated ones. It was found that this parameter is influenced by layer thickness, heat treatment temperature and by the degree of galss surface hydration.     

钛合金基体上TiN涂层的残余热应力分析

采用有限元方法分析TiN涂层的残余热应力,研究钛合金基体和涂层厚度对TiN涂层热应力分布的影响.结果表明:基体内以拉应力为主,涂层内以压应力为主,在明锐界面靠近自由边界处出现了剪切应力奇异场;当涂层厚度增加时,涂层的径向应力逐渐减少,而剪应力先增加随后又趋于平稳;涂层的径向应力随基体厚度增加而增加,当基体厚度超过1 mm时增加变得平缓.     

Mechanical properties of optical glass fibers damaged by nanoindentation and water ageing

Mechanical properties of optical glass fibers are strongly influenced by cracks on glass surface. Cracks may be generated during manufacture and handling. The chemo-mechanical effect due to water may decrease the response of glass fibers because of surface degradation. In this work glass fibers were aged in a wet chamber at humidity of 85% in temperatures lower than 90 °C, during seven weeks. After being aged, the fibers were submitted to tension tests. The fracture loads were investigated by Weibull statistics. An increase in dynamic fatigue parameter was observed. Surface analysis by AFM indicated smooth surfaces. Small cracks on optical fiber glass surface were made by Vickers indentation and nanoindentation using a Berkovich indenter. A decrease on applied load to fracture indicates that the fiber was damaged by indentation. The influence of indentation load was investigated. As the deformation rate was very low during tension tests, the cracks grow during the test and the fiber fracture at loads lower than for not indented fibers. The effect of water and small indentation fracture on glass is discussed considering the surface damage induced by both methods. The size of the cracks from the different indentations and ageing are estimated.     

Investigation on sol–gel silica coatings for the protection of ancient glass: Interaction with glass surface and protection efficiency

To hinder the phenomenon of weathering of ancient stained glass, the present work proposes the application of sol–gel coatings to the glass surface. Previous investigations [1], [2], [3], [4], [5] and [6], in fact, show that sol–gel silica coatings do not change the appearance of artistic glasses when deposited on their surface. Moreover, the film thickness is so small (around 200 nm) and its composition and structure so compatible with that of the original glass, that the characteristics of the coating and original glass are not distinguishable. In this work, several recipes used to produce sol–gel coatings have been tested in order to understand their behavior when adopted for covering ancient weathered glass. The coatings are made of sol–gel silica prepared with two different catalysts: H⁺, Pb²⁺ and without catalyst. All the investigated samples show a good adhesion of the coating to the glasses used to simulate the behavior of ancient artefacts. The sol–gel silica coatings have been studied before and after accelerated ageing to test the resistance of the protective coatings to weathering. Another important index to test of the efficiency of the sol–gel coatings for the protection of an ancient glass is the lead ion mobility. In ancient stained glass, in fact, this element is present in the metallic lead network, in the grisaille paintings and constitutes a main component of many glass tesserae. The action of water on this highly mobile ion involves the degradation of the glass itself and the release of the ion in the rain solution. Ageing tests show the efficiency of H⁺ and Pb²⁺ catalyzed coatings and the inefficiency of the non-catalyzed sol–gel layers.     

Critical parameters in the processing of engineered stress profile glasses

A new approach to chemical strengthening is to move the maximum residual compression below the glass surface. With appropriate processing, this approach leads to strengthening and a decrease in the strength variability. This improvement in mechanical reliability is accomplished by introducing stable crack growth into the glass, which leads to multiple cracking of the glass surface prior to failure. In the current study, a fracture mechanics analysis is presented that uses a simple form for the stress profile. By determining the effect of this stress profile on the apparent fracture toughness of the material, it is possible to identify the conditions when spontaneous cracking occurs, the stress for the onset of multiple cracking and the ultimate strength of the glass. In particular, it is shown there is an important interplay between the depth of the maximum compression, the stress gradient and the magnitude of the maximum compressive stress. The current analysis is then used to define a strategy for the processing of glasses with engineered stress profiles.     

Strengthening of soda-lime-silica glass by surface treatment with sol–gel silica

In this study, the failure resistance of soda-lime-silica glass was increased by surface treatment with sol–gel silica. Samples annealed and ion-exchanged in KNO₃ for 24 h at 450 °C were considered. Sol–gel silica coating was carried out by dipping the glass samples into a sol suspension prepared by hydrolysis of Si(OEt)₄ in ethanol/water solution. The deposited layer was consolidated in air for 24 h and subjected to mild thermal treatment at 300 °C for 1 h. The surface treatment increased the fracture resistance of annealed glass of about 35 MPa; conversely, ion-exchanged specimens showed an average increase of about 90 MPa. The strengthening effect induced by the surface treatment was attributed to the reduction of the effective crack length generated by the silica coating. The different strength increase between annealed and ion-exchanged samples is discussed in terms of fracture toughness which, for ion-exchanged glass, is not constant, due to the presence of the surface residual stresses and thus the reduction of the crack length due to the silica coating determines a higher strength increase than for annealed glass.     

Influence of the dipping coating procedure on the mechanical strength of soda-lime glass rods

In order to investigate the effect of sol-gel coatings on the mechanical behavior of a high strength glass substrate, HF etched glass rods were used.

Coatings with different compositions (SiO₂, ZrO₂ and 20%ZrO₂---80%SiO₂) and different thicknesses were produced to study the influence of these parameters on strength.

Functions of integral probability versus strength were used to analyze data.

Coated glass rods exhibit higher strength in comparison with uncoated control rods that have undergone the same treatment. It seems evident that there is an effect of composition on strengthening. SiO₂ coated rods displayed higher strength.

A lowering in strength at thickness higher than 0.2 μ was observed, independently of composition.

The effect of a saturated Ca(OH)₂ solution was also studied.     

Preparation of CeO2-TiO2 coatings by the sol-gel process

Yellow coatings have been prepared from titanium tetraisopropoxide and cerium chloride by the sol-gel dip-coating process, and the transmittance, chromaticity, thickness and acidic durability of the coating films produced on glass or aluminum were studied. The effects of the pH of the solution on the preparation of the transparent and homogeneous coating films were studied by adding the alkali or acid, and as a result transparent and homogeneous yellow coating films were prepared by dipping the substrate in a solution containing acetic acidic solution. The acidic durability of the aluminum foil was improved by dip-coating the brilliant yellow CeO₂-TiO₂ coating three times.     

Local surface damage and material dissolution in 45S5 bioactive glass: Effect of the contact deformation

Bioactive glasses react with the human physiological solution in control of their biofunctionality. The stress state in bioactive glasses determines the chemomechanical reaction and their biofunctionality. Using the microindentation technique, the effect of the indentation deformation on the surface damage and material dissolution of 45S5 bioglass was investigated. The indentation-induced local surface damage, including ring cracks and radial cracks, was revealed before and after the immersion tests in phosphate buffer solution (PBS). There existed a critical load for the formation of the radial cracks, which emanated from the periphery of the outmost ring crack. The growth of the radial cracks in the PBS solution displayed the stress-corrosion behavior with the crack-growth speed being a linear function of the indentation load. Fast dissolution occurred at the edges of the surface-damaged zone due to stress-assisted dissolution under the action of local tensile stress, which was different from the dissolution behavior of stress-free 45S5 bioglass.     

Performance and durability of octadecyltrichlorosilane coated borosilicate glass

While a coating may alter the surface properties and the performance of a material, it is unclear if these thin barrier layers can effectively inhibit environmentally-assisted cracking processes. In this research a nanoscale, hydrophobic film of octadecyltrichlorosilane was applied to bulk borosilicate glass rods. The resistance of the coated and uncoated rods to environmentally-assisted cracking was then evaluated in a room temperature, deionized water environment. While the coating procedure did not damage the glass surface or affect the probability of completing a successful test, it did not provide protection the glass samples against environmentally-assisted cracking. Analytical models based on linear elastic fracture mechanics suggest that the coating thickness must be on the order of the crack mouth opening displacement for the barrier layer to be effective. This finding suggests that nanoscale barrier coatings are best suited for micron and nanometer-scale substrates when superior structural performance is required.     

Coloured coatings containing mixed transition metal oxides

Glass coloured coatings of M_nO_m---N_pO_q---SiO₂ (M, N = Fe, Co, Ni, Mn, Cr) prepared on soda-lime-silica flat glasses by the sol-gel route using the dip-coating technique.

The optical properties of these films were investigated by spectrophotometry and the optical parameters obtained allowed the colouration mechanism acting in each case to be determined as well as a comparison to be made with the parameters on the single TMO coloured films. Colour coordinates were calculated in every case.

On the other hand coatings have been prepared consisting of two different single TMO films. The corresponding mixed coatings were compared with these double films, showing different behaviours and widening the colour spectrum of glass TMO coatings.     

Study of the mechanical properties of two organic–inorganic hybrid systems: GPTMS/colloidal silica and GPTMS/TEOS

This work investigates the mechanical properties of different scratch resistant coatings, namely, a mixture of 3-glycidoxypropyltrimethoxysilane (GPTMS) with either colloidal silica particles or tetraethoxysilane (TEOS). Coatings were prepared by the hydrolysis and the condensation of the precursor's alkoxide (sol–gel process) with thermally catalyzed polymerization of epoxy ring of GPTMS. Dip deposition techniques were used on silicon substrate.The nanoindentation technique was used to analyze the force required to indent the coating with a diamond tip. At low forces, this technique, based on indentation depth, predicts the hardness and the elastic modulus of the coating, while at higher forces, cracks appear. Another analysis based on geometric approach, namely, the crack length, allows the determination of both coating and interface toughness.     

Bioactive coatings deposited on titanium alloys

One of the ways to minimise corrosion products release from metallic implants to the surrounding tissue consists in applying a protective coating which may be functionalised with a bioactive material, able to generate a natural bonding to the living tissue. This work describes the development of a double layer coating obtained by the sol–gel technique containing bioactive glass, glass–ceramic or hydroxyapatite particles in hybrid methyl-triethoxisilane (MTES) and tetraethilorthosilicate (TEOS) sol on titanium alloy (ASTM F 67). Samples were electrochemically evaluated in a simulated body fluid (SBF). The application of the coating on the titanium alloy shows an improvement in the corrosion resistance in the tested period of time. This improvement could be due to the reaction of the particles with the physiological medium, which nucleates the formation of calcium phosphate crystals, and blocks the porosity of the coating.     

Development of multifunctional photoactive self-cleaning glasses

Glasses for architecture must have many functions in addition to their transparency. For example, the glasses with the functions, of self-cleaning, light control, UV reduction, anti-bacterial, energy conversion, and so on, will be used in buildings in the near future. This paper reviews some results on multifunctional photoactive glasses based on multi-layer coatings containing TiO₂ film and other functional coatings developed by us recently. The self-cleaning of glasses can be realized by coating the photoinduced super-hydrophilic nanoporous thin films based on TiO₂ photocatalysts via sol–gel route. A new method to enhance the photocatalytic activity of TiO₂ thin films direct coated on soda-lime glass was developed by treating the films in acidic solutions. The films also have good photoinduced anti-bacterial properties. The doping of a small amount of silver into the TiO₂ porous film can enhance its anti-bacteria effect without UV light irradiation. The TiO₂ thin films by appropriate heat-treatment can operate as self-cleaning glass in the visible light region. The UV reduction self-cleaning glasses are prepared by magnetron sputtering two layers of TiO₂–CeO₂ and TiO₂ thin films on soda-lime glasses. The TiO₂–CeO₂ thin films can cut all of UV light through adjusting the ratio of TiO₂ and CeO₂. The TiO₂/TiN/TiO₂ type multi-layer coated on glass substrate can act as low-E self-cleaning glass. The potential water-repellent coating based on TiO₂ is discussed finally.     

Effect of laser‐induced nanocrystallisation on the properties of electroless Ni‐P/Ni‐W‐P duplex coatings

This paper presents a comparative study of nanocrystallisation and the wear resistance of electroless plated Ni‐P/Ni‐W‐P duplex coatings with a single Ni‐W‐P coating before and after high‐ power diode laser treatment. Effects of the laser operating parameters on microstructures, in terms of crystallisation, porosity formation, phase transformation and grain growth, were investigated using scanning electron microscopy (SEM) with energy dispersive X‐ray spectroscopy (EDX) and quantitatively X‐ray Diffraction (XRD). Microhardness and wear behaviour of the coatings before and after laser treatment were evaluated by measurement of coating surface and cross‐section hardness as well as un‐lubricated friction and wear tests. The results revealed that in the case of laser treatment, the Ni‐P/Ni‐W‐P duplex coatings offered better wear resistance than the single Ni‐W‐P coating, while the as‐plated, single Ni‐W‐P coating showed better wear resistance than the Ni‐P/Ni‐W‐P duplex coatings. Adhesive wear mechanism prevails in the laser‐treated coatings when subjected to wear test against hardened steel material. The effects of microstructural characteristics in the coatings, in particularly the grain size of Ni₃P phase and the degree of crystallisation, on the adhesive wear behaviour have been investigated and found to be dominant besides the effect of hardness.     

TiAl过渡层对电弧离子镀沉积TiAlN膜层的影响

利用电弧离子镀,在不锈钢和SiCP增强2024铝基复合材料基底上沉积TiAlN薄膜.结果表明:TiAlN膜层直接沉积在不锈钢基底上,膜层呈[111]择优取向;然而,TiAlN膜层沉积在不锈钢基底的TiAl过渡层上,膜层呈[220]方向择优取向;并且随着过渡层从零开始增厚,TiAlN膜层的织构系数T(111)逐渐减小,而T(200)逐渐增大,但膜层一直以[220]方向择优取向,内应力的存在可能是膜层产生[220]方向择优取向的原因.在复合材料基底TiAl过渡层上沉积,随着负脉冲偏压的增加,TiAlN膜层的择优取向由[111]向[200]转变.在不锈钢基底上,没有TiAl过渡层时,膜层表面相对光滑,大颗粒较少;有了TiAl过渡层,表面大颗粒较多;TiAl过渡层不同沉积时间对膜层表面影响不大,颗粒尺寸相差无几.没有TiAl过渡层时,膜层结合强度很差,有了TiAl过渡层,结合强度明显增加,但结合强度的大小随过渡层沉积时间(厚度)变化.     

Crack bridging mechanism for glass strengthening by organosilane water-based coatings

We used an epoxysilane/aminosilane coating deposited from an aqueous solution to strengthen flat glass. We studied film formation, interfacial and mechanical properties of the film. The film is highly cross-linked with a 6 GPa Young’s modulus and good adhesion. Our results suggest that crack face bridging accounts for most of the 75% reinforcement in this system.