Aluminum‐enhanced alkali diffusion from float glass to PVD‐sputtered silica thin films

Interdiffusion processes between aluminum enriched PVD‐sputtered silica thin films and industrial float soda‐lime silicate glass substrates are quantitatively studied using SIMS analysis. Heat treatments are performed at temperatures close or above the glass transition temperature of the float glass. Aluminum doping of the film is shown to strongly increase the migration of alkali from the glass substrate to the silica thin film. In particular the final alkali content in the film exhibits a linear scaling with the aluminum concentration. An interdiffusion process is evidenced between bulk alkali ions and protons originating from a significant water content in the as‐deposited silica film. Experimental measurements of sodium concentration are shown to be consistent with a simple thermodynamic model based on the equilibration of the activity of sodium between the film and the glass substrate.     

Electric Fields Obviate Constrained Sintering

The phenomenon of constrained sintering, where large rigid inclusions of alumina have been shown to significantly reduce the rate of sintering of titania [Bordia and Raj (1988) J. Am. Ceram. Soc. 71, 302–310], is shown to subside nearly completely during flash sintering carried out under modest electrical fields. The result is explained by a different mechanism for volumetric and shear deformation under electric fields. It is proposed that vacancy and interstitials generated within the grains migrate to grain boundaries and pores to produce both volumetric and shear strain at equal rates, since, in this way, the diffusion distance for both modes of deformation becomes the same. In conventional sintering, where transport occurs from one interface to another, the diffusion distance for shear is twice as far as for densification, which retards sintering should it become controlled by shear deformation, as seen in constrained sintering.     

熔铸耐火材料抗盖板玻璃熔体侵蚀行为研究

本文以熔铸耐火材料为研究对象进行抗盖板玻璃熔体侵蚀试验,采用化学分析、岩相分析和电子显微镜能谱分析等测试分析方法,对比研究钠钙玻璃熔体、高铝玻璃熔体和锂铝玻璃熔体对熔铸耐火材料的侵蚀行为。结果表明,玻璃熔体中的碱金属离子向耐火材料中的玻璃相扩散,导致玻璃相黏度降低,同时耐火材料中刚玉相溶解,斜锆石分散,主体结构遭到破坏,并形成界面层。界面层内存在富铝含锆的玻璃相,由于高铝玻璃和锂铝玻璃氧化铝含量高,表面张力大,界面层内的玻璃相聚集在试样周围且扩散慢,从而阻止了侵蚀的发展。玻璃熔体的侵蚀速率为钠钙玻璃熔体＞高铝玻璃熔体＞锂铝玻璃熔体。     

Experimental Observations of Substrate Fracture Caused by Residually Stressed Films

Model systems for studying thin-film cracking consisting of thin plates of alumina and soda-lime glass were diffusion bonded to silica substrates at high temperature. Upon slow cooling, substrate fracture was induced by residual stresses from the thermal and elastic mismatch of the film and substrate. In particular, multiple substrate cracks formed parallel to the interface. The observed crack paths closely followed predictions based on a zero mode II stress intensity. Crack depths were found to be strongly dependent on the relative substrate thickness and the Young's modulus ratio.     

Promotion of Attack on Glass and Silica by Citrate and Other Anions in Neutral Solution

The observation that essentially neutral solutions of sodium citrate attacked sulfur-treated soda-lime glass bottles of generally high chemical resistance much more than was anticipated led to a general investigation. It has been found that neutral solutions of sodium citrate attack silicate glasses and silica with a severity similar to that of substantially alkaline solutions. This effect was observed for both soda-lime and borosilicate glasses and also for vitreous, crystalline, and amorphous forms of silica. The effect of citrate becomes perceptible at a pH of about 5 and increases rapidly with pH up to 7.6. Solutions of higher pH were not studied. Solutions of certain other complex-forming anions show the effect on sulfur-treated soda-lime glass containers in varying lesser degrees. Although the active anions studied are complexing agents for alkaline earths and aluminum, it was observed that citrate had more action on a fused silica container than on containers made of certain glasses containing calcium and aluminum. Therefore a digestive action on silica and the Si–O–Si structure of glasses is to be recognized. Fluoride, the only anion tested that forms previously known complexes with silicon, had slightly less action on sulfur-treated bottles than citrate. The results suggest that soluble silicon complexes are formed at pH values in the region of 7 by citrate and some of the other organic anions studied.     

Polyvinylpyrrolidone adhesion layer for increased uniformity and optical transmittance of silica nanoparticle antireflective coatings

The uniformity of silica nanoparticle antireflective coatings deposited from aqueous solutions on glass substrates is limited by the high surface tension and low evaporation rate of water. In this work, thin films of polyvinylpyrrolidone (PVP) were utilized as an adhesion layer to increase the uniformity and optical transmittance of silica nanoparticle coatings. The increase in adhesive force caused by the presence of the PVP layer was measured using atomic force microscopy (AFM). The micro- and nanoscale uniformities of silica nanoparticle films with and without PVP adhesion layers were characterized using scanning electron microscopy and AFM. It was found that a thin PVP adhesion layer provides the adhesion required to form uniform films of silica nanoparticles. Solar weighted transmittance of 97.6% over a wavelength range of 330–1000 nm was achieved with soda-lime glass substrates coated on both sides.     

Ab inito and FTIR Studies of HfSiCNO Processed from the Polymer Route

The reactions between polysilazane and hafnium‐butoxide precursors are followed from the liquid, to the cross‐linked, and finally to the ceramic state by infrared spectroscopy. We find evidence of formation of Hf–N bonds in the liquid state, and Hf–O–Si bonds in the cross‐linked polymer state. Results from ab inito calculations for the ceramic state are presented. They show that Hf behaves like Si, forming bonds with C, N, and O in proportion of the Hf/Si ratio in the compounds. The average values of such bonds formed by Hf, relative to silicon, are 11.2, 17.8, and 24.4%, which is in reasonable agreement with the overall Hf/Si ratio in the samples (8%, 15% and 22%). It is concluded that it is appropriate to express the composition of these compounds in terms of the Hf/Si ratio. The X‐ray data that show the emergence of weak diffraction peaks for monoclinic HfO₂ when the Hf/Si ratio is 0.22, but not at lower concentrations of Hf [K. Terauds and R. Raj, J. Am. Ceram. Soc., 96 , 2117–2123 (2013)].     

Improved hydrothermal aging performance of glass fiber-reinforced polymer composites via silica nanoparticle coating

The long-term exposure to a hot and humid environment severely damages the bonding integrity of fiber-reinforced polymer composites and thus significantly degrades their mechanical performances. In this work, we aim to develop an improvement procedure for effectively enhancing the bonding strength in glass fiber-reinforced polymers (GFRPs). Glass fibers were coated with a thin layer of silica nanoparticles of different concentrations by the use of the evaporative deposition method. Micromorphological comparisons in terms of scanning electron microscope imaging demonstrate significant improvements on the surface roughness of glass fibers. With the coated glass fibers, GFRP composite laminates were designed, molded through the vacuum-assisted resin infusion technique, and experimentally tested for quantitatively studying their hydrothermal aging performance. The water absorption tests conducted for three exposure temperatures suggest that both the water diffusion rate and the equilibrium water content can be effectively reduced due to the introduction of the silica coating. With increased exposure temperatures, however, the desired reductions become much less significant. A so-called water-channel diffusion mechanism along fiber/resin interfaces was proposed to explain the coupling effects of silica coating and exposure temperature. Reductions of water diffusion rate and equilibrium water content were expected to slow down the hydrothermal aging performance of GFRPs. For this purpose, both uniaxial tensile test and three-point bending test were subsequently performed on GFRP specimens that have been subjected to different coating concentrations, exposure temperatures, and exposure durations. When compared with untreated GFRP specimens, both experiments demonstrate that the residual strength and stiffness can be effectively promoted through coating a thin layer of silica nanoparticles on glass fiber surfaces. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48652.     

Comment on: “Effect of particle size on the optical properties of lead zirconate titanate nanopowders” [J. Am. Cream. Soc. 2018;101:5335–5345]

In a recent paper [J Am Ceram Soc. 2018;101:5335-5345], Pakizeh and Moradi studied the structural, morphological, and optical properties of lead zirconate titanate nanopowders. The refractive index and extinction coefficient of samples were calculated based on reflectance and phase angle between the incident and reflected signals for a particular wavenumber. The authors used the Beer-Lamber equation to calculate the reflectance spectra. It is shown in this comment that they have used a wrong relation to calculate the reflectance, and consequently, calculated results based on the reflectance, such as refractive index, extinction coefficient, real and imaginary parts of dielectric constant, LO and TO phonon modes are incorrect.     

Determination of the Isoelectric Point of Planar Oxide Surfaces by a Particle Adhesion Method

A particle adhesion method for the determination of the isoelectric point (iep) of planar oxide surfaces in aqueous media is described. The experiment consists in measuring the rate of deposition of latex particles as a function of pH. We have measured the iep of fused silica, soda-lime silicate glass and thin films of different metal oxides: tin, aluminum, iridium and tungsten. We find our results in good agreement with data from the literature obtained with other experimental techniques.     

Al与SiO2玻璃反应的显微组织结构及其演变

Ａｌ与ＳｉＯ２玻璃之间的反应分为２个阶段;在反应初期,得到Ａｌ／Ａｌ２Ｏ３复合组织,数量居多的Ａｌ２Ｏ３以颗粒形式存在,Ａｌ分布于Ａｌ２Ｏ３间,被还原出来的Ｓｉ在冷却时于Ａｌ中以颗粒形式析出;随反应时间延长,显微组织演变为Ａｌ与Ａｌ２Ｏ３互为网络的复合结构,Ａｌ２Ｏ３网络以更为细小的颗粒组成,研究表明,在反应得到的复合组织前沿存在过渡层,Ａｌ在过渡层中存在一定浓度梯度。     

Formation of an Alkali Diffusion Barrier and Stain-Resistant Glass Surface

As it is well known, the structures of silica and soda-lime-silica glasses are subjected to alkali ion diffusion. This diffusion can lead to staining of the glass surface, thus detrimentally affecting its optical functions. In this work, an effective alkali diffusion barrier layer is created by boron diffusion into the top 10 to 50-nm thick layer of glass surface. In this layer, alkali mobility is electrochemically arrested by a coordination change of boron. As a result, the glass surface stays pristinely clear, even under sustained exposure to hot and humid conditions. Structural studies indicate that when three-coordinated boron diffuses into a pre-existing glass network, it converts nonbridging oxygens, associated with alkali ions, into bridging oxygens by changing its coordination from 3 to 4. This forces alkali ions to change their bond association from nonbridging oxygens to the charge sphere of boron due to the required charge neutrality. This new bond arrangement immobilizes the alkali ions at these sites. As a result of the alkali ion immobilization, and the reduction in nonbridging oxygens in the network, the glass surface becomes resistant to nucleophillic attack, as well as resistant to stain formation, and crystallization.     

EFFECT OF FLUORINE AND PHOSPHORUS PENTOXIDE ON PROPERTIES OF SODA-DOLOMITE LIME-SILICA GLASS*

The effect of the substitution of fluorine for silica on the viscosity, liquidus temperature, and chemical durability of a typical soda-lime glass is shown. The effects of substituting P₂O₅ for (a) silica and (b) dibasic oxides in two typical soda-lime glasses are also described.     

Electrical conductivity of hexagonal Ba(Ti0.94Ga0.06)O2.97 ceramics

Impedance spectroscopy is used to estimate the bulk conductivity, σ_b, of hexagonal (6H)-Ba(Ti_0.94Ga_0.06)O_2.97 ceramics in air, N₂ and 5%H₂/95%N₂ between 400 and 1000 °C. Isothermal plots of log σ_b vs log pO₂ in the temperature range between 700 and 1000 °C show the presence of a p–n transition with slopes of ∼−1/4 and +1/4 in the n- and p-type regions indicating that the conductivity obeys the ‘extrinsic’ model proposed by Smyth and co-workers for undoped and acceptor-doped cubic BaTiO₃-based materials [J. Am. Ceram. Soc. 64 (1981) 556; J. Am. Ceram. Soc. 65 (1982) 167]. The activation energy E_a for oxidation in the p-type region to produce free holes is similar for 6H-Ba(Ti_0.94Ga_0.06)O_2.97 and cubic BaTiO₃-based ceramics with an estimated value from σ_b data of ∼0.8 eV. The band gap for 6H-Ba(Ti_0.94Ga_0.06)O_2.97 ceramics is ∼3.2 eV.     

Diffusion study of rare-earth oxides into silica layer for environmental barrier coating applications

The effect of exposure temperature and time on the diffusion rate of rare-earth oxides applied on silicon carbide fiber-reinforced SiC ceramic matrix composites (SiC/SiC CMCs) have been investigated. Knowledge on diffusion mechanism between the deposited rare-earth (RE) slurry and silica layer is necessary to understand the process governing EBCs formation and their properties. SEM/EDS analysis were used to study the effect of microstructure on diffusivity. The diffusion coefficient increases with increasing sintering temperature and time. The measured diffusion coefficients of the RE-coating into silica layer were in the order of 10^?15-10^-17 m²/s revealing an overall good adhesion on the SiC/SiC CMCs.     

Effect of calcium on dissolution and precipitation reactions of amorphous silica at high alkalinity

A better understanding of silica dissolution–precipitation reactions at high pH aqueous solutions allows for promotion of favorable (e.g., pozzolanic) reactions and mitigation of deleterious (e.g., alkali-silica) reactions in concrete. In this paper, the kinetics and products of silica glass dissolution are studied as a function of solution pH, temperature, and availability of calcium. It was observed that dissolution rate versus time increases linearly with pH and reaches a maximum at pH = 14, with slower dissolution at higher alkalinities. In solutions with similarly high pH, but saturated with portlandite, glass dissolution is significantly slower. This is due to formation of a dense, low porosity, and strongly bonded C–S–H layer on the surface of glass, which serves as a barrier against diffusion of OH⁻ and alkali ions towards the substrate glass. This protective layer forms only when Ca is abundant and portlandite saturation can be maintained on a local scale.     

Evaluating the role of composition and local structure on alkali out-diffusion in glasses for thin-film solar cells

The presence of alkali ions has reportedly improved the performance of CIGS/CZTS–based thin-film solar cells. The out-diffusion of the alkali ion, in particular, Na, from the glass substrate offers a facile scalable route of supplying the alkali ions during the growth of the absorber layer. In this work, we demonstrate the diffusion of different alkali ions (Li/Na/K) from composition tuned glasses with intentionally incorporated excess alkali ions into a thin Mo film, typically used as a bottom electrode in solar cells. We also evaluate the physical, mechanical, and thermal properties of the glasses for suitability as a substrate in thin-film deposition. The out-diffusion of alkali ions to the overlayer is found to be critically influenced by the composition and the local structure of the glasses. The Na ions exhibit the highest extent of diffusion among the alkali ions present in glass substrates, while that for the K-ions is the lowest. For the glasses with mixed alkali ions, the presence of Li facilitated the out-diffusion of Na, whereas K ions appear to inhibit the same. Differently with the existing reports, we show that the activation energy and the presence of Ca ions as additional modifiers play a crucial role in the transport mechanism of the ions. In addition, the synthesized glasses exhibit hardness of the order 5-7 GPa, density ~2.55 g cm^-3. The glass transition temperature lies between 535 and 580°C and the coefficient of thermal expansion 8.5-10 ppm/K, which is highly suitable for use as substrates in thin-film solar cells.     

General formula for bending beam determination of case II diffusion in polymer-containing bilayer structures

An exact formula has been presented to correlate the bending curvature cariation ratio, Ω, of any given bilayer structure comprising a solvent-swellable polymer layer with diffusion time, t, under case II diffusion. The formula can be used to determine the diffusion front velocity, v, for layered structures comprising a thick polymer film on a thin substrate or vice versa when subjected to solvent diffusion. According to this formula, there is little effect from plasticization or swelling in the transverse direction on the diffusion curve of Ω vs. t if the polymer layer to be investigated is relatively thin and its intrinsic hygroscopic strain ratio is less than unity. By using this model, the diffusion of N-methyl pyrollidinone (NMP) in a 18-μm rodlike pyromellitic dianhydride p-phenylene-diamine (PMDA-PDA) polymide film, coated on a 75-μm silicon substrate, is found to be case II with a diffusion front velocity of 1.84 × 10^-7 cm/s. © 1995 John Wiley & Sons, Inc.     

Theoretical Model of Phosphorus Incorporation in Silica in Modified Chemical Vapor Deposition

Based on experiment, a theoretical model is developed of phosphorus incorporation in modified chemical vapor deposition. In the glass formation stage of this process, gas-phase reaction of silicon tetrachloride and phosphorus oxychloride generates submicrometer particles of phosphorus-doped silica. These particles deposit in a thin porous soot layer which is then viscously sintered. Equations for thermal and dopant transport through the soot voids and particles during sintering predict that gradients in each layer are due to inhibited diffusion of dopant through the gaseous voids of the soot, not to gas-phase gradients. Thermal gradients create variations in gas and solid diffusion and dopant solubility which enhance concentration gradients. These results apply to viscous sintering of glasses produced by flame hydrolysis and sol-gel processes.