Differences in surface failure modes of soda lime silica glass under normal indentation versus tangential shear: A comparative study on Na+/K+-ion exchange effects

The effects of exchanging Na⁺ with K⁺ on the mechanical and mechanochemical properties of a soda lime silica (SLS) glass were investigated. It is known that replacing smaller modifier ions with bigger ions in the silicate glass network, at temperatures below the glass transition (T_g), produces a compressive stress in the subsurface region that enhances resistance to mechanical damages. This study found that when Na⁺ ions in SLS are exchanged with K⁺ ions at 400°C, the hardness, indentation fracture toughness, and crack initiation load of the surface are increased, which is consistent with the chemical strengthening effect. However, the resistance to mechanochemical wear in a near-saturation humidity condition (relative humidity RH = 90%) is deteriorated. When K⁺ ions are exchanged back with Na⁺ ions at 350°C, the wear resistance in high humidity conditions is recovered. These results indicate that the improvement of mechanical properties under indentation normal to the surface is irrelevant with the resistance to mechanochemical wear under tangential shear at the surface. Based on the analysis of the surface chemical composition, silicate network structure, and hydrogen-bonding interactions of hydrous species in the subsurface region, it is proposed that the leachable Na⁺ associated with non-bridging oxygen and subsurface hydrous species in the silicate network play more important roles in the mechanochemical wear of SLS at high RH.     

Differences in indentation and wear behaviors between the two sides of thermally tempered soda lime silica glass

Thermal tempering is an industrial process widely used to make soda lime silica (SLS) glass panels stronger and tougher. During the tempering process, the upper and bottom sides of the glass may experience different cooling rates, and thus, their properties could be different. This study characterized changes in surface composition and subsurface glass network structures as well as indentation and wear resistance properties of the air- and tin-sides of 6-mm-thick SLS window panels faced toward the upper and sliding roller sides during thermal tempering. The results showed that although the chemical and structural differences detected with X-ray photoelectron spectroscopy and specular reflection infrared spectroscopy are subtle, there are large differences in nanoindentation behaviors and mechanochemical wear properties of the SLS glass surface. The findings of this study provide further insights into the performance difference between the air- and tin-sides of the SLS glass panel treated with thermal tempering.     

Synergy between surface mechanochemistry and subsurface dissolution on wear of soda lime silica glass in basic solution

The polishing of oxide glass in aqueous solution is sensitive to not only the mechanical conditions applied by abrasives but also the chemistry of solution. This study elucidates the synergistic interactions of mechanical and chemical effects—especially, the synergetic effects of surface mechanochemical wear and subsurface dissolution are studied by measuring the material removal rate of soda lime silica (SLS) glass upon rubbing with a Pyrex glass ball in noncorrosive (neutral pH) in corrosive solutions (pH 10 and 13 NaOH) as a function of sliding speed. Based on the synergetic model of surface wear and subsurface dissolution, it is found that the mechanochemical surface reaction dominates the wear behavior of SLS glass in neutral and pH 10 solution conditions; the wear of SLS glass in pH 10 is enhanced, compared to the neutral pH case, due to the presence of OH^- ions at the sliding interface. In the case of pH 13, the dissolution of the densified subsurface region, which is formed due to interfacial friction during the surface wear, becomes significant, further enhancing the material removal yield. The finding provides an insight for designing an efficient polishing process in manufacturing of oxide glass materials with a good surface finish.     

Atomistic understanding of surface wear process of sodium silicate glass in dry versus humid environments

Understanding surface reactions of silicate glass under interfacial shear is critical as it can provide physical insights needed for rational design of more durable glasses. Here, we performed reactive molecular dynamics (MD) simulations with ReaxFF potentials to study the mechanochemical wear of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules. The effect of water molecules on the shear-induced chemical reaction at the sliding interface was investigated. The dependence of wear on the number of interfacial water molecules in ReaxFF-MD simulations was in reasonable agreement with the experimental data. Confirming this, the ReaxFF-MD simulation was used to find further details of atomistic reaction dynamics that cannot be obtained from experimental investigations only. The simulation showed that the severe wear in the dry condition is due to the formation of interfacial Si_substrate–O–Si_{counter_surface} bond that convey the interfacial shear stress to the subsurface and the presence of interfacial water reduces the interfacial bridging bond formation. The leachable sodium ions facilitate surface reactions with water-producing hydroxyl groups and their key role in the hydrolysis reaction is discussed.     

Thermal Poling of Soda‐Lime Silica Glass with Nonblocking Electrodes—Part 1: Effects of Sodium Ion Migration and Water Ingress on Glass Surface Structure

It is generally well known that not only the sodium itself, but also the non‐bridging oxygen (NBO) sites associated with sodium ions are largely responsible for the surface reactivity of soda‐lime‐silica (SLS) glass. Thermal poling can modify the distribution of sodium in the subsurface region. In this work, a commercial SLS float glass was thermally poled using nonblocking electrodes in air. The Na⁺?depleted anode surface and the Na⁺?gradient cathode surface were characterized using a variety of methods to find the compositional, structural and morphological effects of thermal poling. Of particular significance is the use of nondestructive vibrational spectroscopy methods, which can lead to new and improved understanding of water interactions with sodium and its sites in the glass. It was found that during thermal poling, the Na⁺?depleted glass network on the anode side undergoes condensation reactions of NBO sites accompanied by the increase in concentrations of silanol (SiOH) groups and molecular water species. In contrast, silanol and water species do not increase and the silicate network change is negligible in the Na⁺?gradient cathode side. Vibrational sum frequency generation (SFG) spectroscopy analysis revealed the difference in distributions of hydrous species in the Na⁺?depleted and Na⁺?gradient surfaces. The structural information of the thermally‐poled surfaces provides critical insights needed to understand the mechanical and mechanochemical properties of the Na⁺?concentration modified SLS glass surfaces reported in the Part 2 companion paper.     

Thermal Poling of Soda‐Lime Silica Glass with Nonblocking Electrodes—Part 2: Effects on Mechanical and Mechanochemical Properties

The mechanical and mechanochemical properties of soda lime silica (SLS) glass surfaces can vary with the sodium ion (Na⁺) concentration in the subsurface region. Changes in these properties were studied upon modification of Na⁺ concentrations in the SLS glass by thermal poling. In Part‐1, it is found that the Na⁺‐depleted and Na⁺‐gradient layers could be formed at the anode and cathode sides, respectively. Here in Part‐2, we show that Na⁺ ions play a pivotal role in the mechanochemical wear property upon lateral shear stress. The Na⁺‐depleted glass wear more readily as relative humidity (RH) increases, while Na⁺‐gradient glass becomes resistant to wear at high RH. It is also found that the Na⁺‐gradient glass surface has a higher elastic modulus and hardness with very little change in fracture toughness compared to the pristine surface. The Na⁺‐depleted glass surface shows a lower elastic modulus and hardness; but its fracture toughness is significantly improved, which might be due to a larger densification capacity of Na⁺‐depleted layer.     

Modeling birefringence in SiO2 glass fiber using surface stress relaxation

The retardance of silica glass fibers was evaluated using photoelastic techniques. Here, surface birefringence in glass fibers is shown to be a consequence of surface stress relaxation for as-received fibers drawn from Suprasil II. The surface features of the birefringent fibers were compared to a model of the residual axial stress profile resulting from a diffusion-controlled surface stress relaxation. Additionally, a uniform birefringence in the fiber equivalent to a constant tensile stress was recognized and attributed to structural anisotropy produced during fiber drawing. The contribution of structural anisotropy to the observed birefringence remained constant as the surface features were successively etched away. Surface compressive stress generation was also observed, as retardance corresponding to a surface compressive stress was found to increase with applied tensile stress during short heat treatments. Significant features of the retardance profile in as-received silica glass fibers, with a thin surface compressive stress layer and compensating interior tensile stress, agreed with the residual stress profiles predicted by the surface stress relaxation model after correcting for this observed structural anisotropy.     

Mechanochemical Wear of Soda Lime Silica Glass in Humid Environments

The mechanochemical wear of multicomponent glasses was studied under controlled humidity conditions using a reciprocating ball‐on‐flat tribometer. For dry conditions, the surfaces were extensively damaged by scratching for all of the glasses, while for humid conditions the wear behavior varied with the glass composition suggesting a chemical effect on scratch behaviors of glass surfaces. The wear of soda lime silica (also called sodium calcium silicate) glass was suppressed with increasing humidity, while the borosilicate and barium boroaluminosilicate glasses showed an increase in wear volume with increasing humidity. The unique humidity dependence of the observed mechanochemical wear of soda lime silica glass supports the hypothesis that hydronium ion formation in the sodium‐leached sites of the soda lime glass enhances its wear resistance.     

An Overview of the Strengthening of Glass Fibers by Surface Stress Relaxation

Pristine glass fiber is well known to become mechanically weaker when heat-treated in the presence of water vapor. However, recently, the same fiber was found to become stronger if heat-treated while held under a subcritical tensile stress at a temperature below the glass transition temperature. The added strength was attributed to the formation of a surface compressive layer on the glass created by a surface stress relaxation process that occurred while being held under the tensile stress in air. Silica glass fibers with strengths estimated to be ~7–8 GPa were produced, exceeding the ~5.5 GPa strength of fresh optical fiber commonly reported at room temperature in air. Similar degrees of strengthening, a 20–30% improvement, have been observed previously for E-glass and is reported here for the first time for soda-lime silicate glasses. This process is a new glass strenthening method that may be applied to all oxide glasses and is not subject to the same constraints as currently available methods.     

高速公路钢纤维混凝土的性能研究

结合高速公路的实际需要,研究了钢纤维掺量对混凝土性能的影响.在此基础上,研究了粉煤灰掺量对混凝土性能的影响.研究结果表明:钢纤维对于混凝土抗压强度、抗拉强度、抗折强度、磨损量存在一个最佳掺量,其最佳掺量分别是1.5％、2.0％、2.0％、2.5％.当钢纤维掺量为2.0％时,粉煤灰对于混凝土抗拉强度、抗折强度、磨损量存在一个最佳掺量,其最佳掺量分别是15％、10％、15％,但粉煤灰掺量对混凝土抗压强度影响不大.     

Wet Erosive Wear of Alumina Densified with Magnesium Silicate Additions

A study was made of the wet erosive wear of polycrystalline alumina of mean grain size >1 μm, containing up to 10 wt% of magnesium silicate sintering aid. For pure polycrystalline alumina, the dominant wear mechanism was grain-boundary microfracture, leading to partial or complete grain removal. In the case of the liquid-phase-sintered materials, wear rates could be as low as 25% of those of pure alumina of the same mean grain size, and the main material removal mechanism was transgranular fracture combined with tribochemical wear. The use of Cr³⁺ photoluminescence line broadening showed much higher levels of local stress in the magnesium silicate-sintered materials (∼450 MPa) than in the pure-alumina materials (∼200 MPa). Grain-boundary compressive hoop stresses, caused by the thermal expansion mismatch between a continuous magnesium silicate film and the alumina grains, provided an explanation for the improved wear resistance of the alumina sintered with magnesium silicate.     

Utilization of Flyash as Filler Material in Hybrid Polyester Composites for Improved Thermo-Mechanical and Erosion Wear Behavior

The present work was carried out for the utilization of major quantities of flyash as filler material in the short fiber reinforced polyester resin composites in various engineering and structural applications. The incorporation of flyash modifies the hardness, tensile, flexural, impact and damping behavior of the composites. It is observed that hardness, flexural modulus and impact strength of flyash filled composites increases with increase in the flyash filler contents. Whereas, with the addition of flyash contents it is observed that there is decrease in tensile strength and flexural strength. But beyond the 10 wt.-% flyash filler addition in the composite the flexural strength increases. At the end, the erosion wear behavior of all the composites has been studied by Taguchi experimental design. It is found that unfilled glass polyester composite suffers greater erosion loss as compare to particulate filled glass polyester composites. The eroded surface morphology is examined by SEM and the related erosion wear mechanism is discussed in detail.     

Ion-Exchanged Glass Laminates that Exhibit a Threshold Strength

Glass laminates, fabricated to include periodic thin layers containing biaxial compressive stresses, exhibit a threshold strength, i.e., a stress below which failure will not occur. Ion-exchange treatments in KNO₃ at 350°–450°C for periods of 3–72 h were used to create residual compressive stresses at the surface of soda lime silicate glass sheets. Wafer direct bonding of the ion-exchanged glass sheets resulted in glass laminates with thin layers of compressive stress adjacent to the glass interface and perpendicular to the laminate top surface. Critical strain energy release measurements of the bonded interface were used to optimize the bonding temperature/time to avoid significant relaxation of the stress produced by ion exchange. Stress profiles, determined via the wafer curvature measurement method, showed a residual compressive stress maximum of 328 MPa for an ion exchange temperature of 450°C. The threshold flexural strength of the ion exchanged glass laminates was determined to be 112 MPa after the introduction of indentation cracks with indent loads ranging from 1 to 5 kg. In contrast to similar ceramic laminates, where cracks either propagate across the compressive layer or bifurcate within the compressive layer, the cracks in the glass laminates were deflected along the interface between the bonded sheets.     

Hydronium Ions in Soda‐lime Silicate Glass Surfaces

The presence of leachable alkali ions, or their hydrated sites in the glass, is believed to be a determining factor for the interfacial water structure at the glass surface, influencing the surface properties of glass. The interfacial water structure on soda‐lime silicate glass in humid ambience at room temperature was analyzed with sum‐frequency‐generation (SFG) vibration spectroscopy, which can probe the interfacial water layer without spectral interferences from the gas phase water. The soda‐lime glass surface exposed to water vapor shows three sharp SFG peaks at 3200, 3430, and 3670 cm^?1 in SFG, which is drastically different from the SFG spectra of the water layers on the fused quartz glass surface and the liquid water/air interface. The sharp peak at 3200 cm^?1 is believed to be associated with the hydronium ions in the Na⁺‐leached silicate glass surface. The 3200 cm^?1 peak intensity varies with the relative humidity, indicating its equilibrium with the gas phase water. It is proposed that the hydronium ions in the Na⁺‐leached sites produce compressive stress in the silicate glass surface; thus the growth of hydronium ions with increasing humidity might be responsible for the increased wear resistance of soda‐lime glass surfaces in near‐saturation humidity conditions.     

Fabrication of DLC thin films with improved diamond-like carbon character by the application of external magnetic field

Diamond-like carbon (DLC) thin films were grown on Si-(100) substrates by a magnetically-assisted pulsed laser deposition (PLD) technique. The role of magnetic field on the structural, morphological, mechanical properties and deposition rate of DLC thin films has been studied. The obtained films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and nanoindentation techniques. It was found that the diamond-like character, thickness and deposition rate of the DLC films increase in the presence of magnetic field. The films deposited under magnetic field exhibit a denser microstructure and smoother surface with lower surface roughness. Meanwhile, the mechanical properties of the magnetically processed DLC thin films experience an improvement, relative to the conventionally processed ones. It seems that the DLC films deposited under magnetic field can be better candidate for hard and wear resistance coating applications.     

超细羟基硅酸镁粉体在磨损后钢表面的自修复特性(英文)

使用AMSLER摩擦磨损试验机进行摩擦磨损试验,研究超细羟基硅酸镁粉体作为润滑油添加剂在磨损后摩擦副表面的自修复特性。使用扫描电子显微镜、能谱仪和X射线光电子能谱分析了2种润滑油润滑下磨损后的45#钢环的表面形貌和化学组成。结果显示:经50h纯润滑油润滑后在45#钢表面出现了大量的划痕,而之后经50h含添加剂润滑油润滑后这些划痕被自修复膜所覆盖。这层自修复膜主要由Fe,O,Si,C和Mg构成,这表明粉体添加剂在摩擦磨损过程中可以向磨损的金属表面发生转移。自修复膜的形成原理是这些粉体可以吸附到钢的磨损后新鲜表面,之后在接触表面的剪切应力下铺展于磨损后金属表面。这层自修复薄膜可以明显提高金属摩擦副的抗磨损性能。     

Effects of acid leaching treatment of soda-lime silicate glass on crack initiation and fracture

Water or acid soaking surface treatments have been shown to increase the mechanical strength of soda-lime silicate (SLS) glasses. This increase in strength has traditionally been attributed to effects related to residual stress or changes in fracture resistance. In this work, we report experimental data that cannot be explained based on the existing knowledge of glass surface mechanics. In dry environments, annealed and acid-leached SLS surfaces have comparable crack initiation stress and fracture stress as measured by Hertzian indentation and biaxial bending tests, respectively. Yet, in the presence of humidity, acid-leached surfaces have higher failure stress than the annealed surfaces. This apparent enhancement in the crack resistance of the acid-leached surface of SLS glass in humid environments supports the hypothesis that acid-leached surface chemistry can lower the transport kinetics of molecular water to critical flaws.     

Conducting glass fibers of giant thermosensitivity by cladding drawing

Strong and conducting glass fibers are produced from reduced graphene oxide and soda-lime-silica (rGO/SLS) glass by a novel process of cladding drawing. GO nanosheets are bound to the SLS glass particles through an electrostatic assembly and are well distributed in the hot-pressed rGO/SLS bulk composites. These bulks are subsequently BN-cladded, from which rGO/SLS fibers are drawn. Results confirm the rGO sheets are well dispersed inside the fibers and become wrinkled due to the contraction of glass matrix while cooling. Mechanical properties of as-prepared fibers have been greatly improved, with tensile strength two times that of pure SLS fibers. As rGO concentration increases, a conducting network of rGO sheets forms along the fibers, which can survive intensive wear. Thanks to the wrinkled configuration of rGO sheets, the conductivity of the composite fibers is extremely sensitive to temperature, nearly 25 times that of flat rGO sheets, making the fibers potential built-in temperature sensors.     

Alkali-activation of marble sludge: Influence of curing conditions and waste glass addition

The use of marble sludge as precursor for new alkali activated materials was assessed studying three different curing conditions (air, humid and water immersion, respectively), after an initial curing at 60 °C for 24 h, and two glass powder fractions additions (2.5 and 5.0 vol%). Microstructural, physical (drying shrinkage, Fourier transform-infrared (FT-IR) spectroscopy, X-ray spectroscopy (XPS)), thermal (differential thermal analysis – thermogravimetric analysis, DTA-TGA) and mechanical (flexural and compressive strength) properties were investigated. Air curing was the most favourable atmosphere for mechanical properties development because it promotes Si-O-Si polymerization and gel densification, as demonstrated by FT-IR and FE-SEM observations, respectively. Satisfactory mechanical properties were achieved (18 MPa and 45 MPa, for flexural and compressive strength, respectively) in particular for glass containing mixtures. Moreover, glass powder addition significantly reduced drying shrinkage of air-cured samples because it operated as a rigid aggregate in the matrix and strengthened the formed gel.     

锂铝硅玻璃的研究进展

与传统的钠钙硅玻璃和高铝玻璃相比,锂铝硅玻璃具有网络结构致密、弹性模量较高和适宜两步法化学钢化等特点,被视为第三代高强玻璃基板,可用作电子信息产品盖板、航空透明器件以及舰船、特种车辆的观察窗口等。目前,锂铝硅玻璃的研究主要涉及:(1)探究锂铝硅玻璃的“组成-结构-性能”本构关系,为设计优化高性能锂铝硅玻璃提供理论指导和性能预测;(2)改进现有溢流和浮法成型方法和装备,满足大尺寸、多厚度和高尺寸精度锂铝硅玻璃成型需要;(3)研究锂铝硅玻璃的两步法化学增强方法,解决表面压应力和应力层深度同步提升难题,显著提高玻璃强度、硬度和抗跌落性能。本文基于上述三个方面综述了锂铝硅玻璃的国内外研究进展。