Correlation between IR peak position and bond parameter of silica glass: Molecular dynamics study on fictive temperature (cooling rate) effect

The fictive temperature of glass is a consequence of its thermal history (cooling rate, primarily) and has a direct effect on physical and chemical properties of the glass. But, it is not easy to measure. The ability to nondestructively and spectroscopically measure it at room temperature would be of great benefit. Although empirical correlations have been established between fictive temperature and selected absorption peaks in the infrared spectra of silica glass, the fundamental understanding for this correlation has not been reported. Here, we use molecular dynamics simulations to show that the blue shift in the Si–O–Si asymmetric stretching peak of pure silica glass, which is known to correlate with a decrease in fictive temperature, can be attributed to a decrease in the average length of the Si–O bond in the silica network, not changes in the density or the Si–O–Si bond angle. The decrease in density at higher fictive temperatures of silica is associated with a decreased population of 5‐ and 6‐membered rings and broadening of the ring‐size distribution, and an increase in the average Si–O–Si bond angle.     

Effects of fictive temperature on the leaching of soda lime silica glass surfaces

The fictive temperature of glass characterizes the glass network structure and its thermal history, and thereby can influence ion and water transport in the glass surface. In this study, IR specular reflectance (SR), refractive index, and density measurements were used to characterize and confirm the effects of glass sample processing, especially the fictive temperature/thermal‐history variations. The subsequent acid leaching of these glasses created leached surface layers due to interdiffusion and reaction of hydrous species in the surface; the hydrogen depth profiles obtained with secondary ion mass spectrometry (SIMS) confirmed enhanced leaching with increasing fictive temperature. Attenuated total reflectance (ATR) in the mid‐ and near‐IR indicated increases in both SiOH and H₂O species with increasing fictive temperature. The relative intensities and shapes of the ATR peaks were found to vary between the samples suggesting that speciation of the hydrous reaction products (eg, strong and weakly hydrogen‐bonded OH) is also influenced by the original fictive temperature of the glass, but could not be quantitatively determined.     

Adsorption reactions of carboxylic acid functional groups on sodium aluminoborosilicate glass fiber surfaces

Multicomponent silicate glasses are ubiquitous in modern society as evidenced by their inclusion in applications ranging from building materials and microelectronics to biomedical implants. Of particular interest in this study is the interface between multicomponent silicate glasses and adhesive polymers. These polymeric systems often possess a variety of different organic functional groups. In this study, we selected acetic acid as a probe molecule representative of the carboxylic acid functional group found in many adhesives. We have used Fourier transform infrared spectroscopy (FT-IR) and NMR to study the interaction of acetic acid with the surface of sodium aluminoborosilicate continuous glass fibers. Methods were developed that enable analyses to be carried out without damaging or altering the pristine as drawn fiber surface. While dosing the surface of fumed silica with acetic acid resulted in the formation of silyl ester groups, analogous dosing of sodium aluminoborosilicate glass fibers resulted in the formation of carboxylate species, principally coordinated to sodium, while silyl ester groups were not observed.     

In-situ identification of material batches using machine learning for machining operations

Journal of Intelligent Manufacturing - In subtractive manufacturing, differences in machinability among batches of the same material can be observed. Ignoring these deviations can potentially...     

Nitrogen Coordination in Oxynitride Glasses

Soda-silica and soda-lime-silica glasses were prepared with varying amounts of Si₃N₄, to produce oxynitride glasses with nitrogen contents up to 3.23 mol%. The glasses were analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, and evidence for the formation of tricoordinated nitrogen groups in the glasses was obtained.     

Effect of carbon monoxide partial pressure on the high-temperature decomposition of Nicalon fibre

The high-temperature equilibrium partial pressures of the predominant gaseous species over Nicalon were determined thermochemically. It was calculated that the most prevalent gaseous species in equilibrium with Nicalon at 1300 °C is carbon monoxide. Subsequently, fibres of Nicalon (NLM 202) were heat treated at 1300 °C in various partial pressures of carbon monoxide gas and analysed via single filament strength testing, scanning electron microscopy, X-ray diffraction, and scanning Auger microscopy. The heat treatments in carbon monoxide had a significant effect on the strength retention and composition of the fibres (75% retained) compared to the treatments in argon where only 25% of the initial strength was retained. The Auger analysis revealed that the treatment in argon evolved carbon and oxygen from the fibre while in carbon monoxide atmospheres a carbon layer was deposited on the fibre surface. X-ray diffraction showed that grain growth had not occurred in any of the heat treatments. This study shows the important role of thermochemical reactions in the strength degradation of Nicalon, and its possible relationship to the formation of carbon surface/interface layers.     

甘蔗栽培地沉积物中分离出的腐殖质的光谱表征

腐殖质有很重要的环境属性,它通过和金属物质的相互作用而影响其运输、积累和吸收。在本项研究中,用于表征的沉积物中的腐殖质来自圣保罗的第三大甘蔗栽培区,这个地区生产的甘蔗约占巴西全国甘蔗总产量的60%。根据国际腐植酸学会提出的碱抽提方法可以将腐殖质提取出来,然后通过红外光谱、紫外可见光谱和分子荧光光谱对其进行表征。从红外光谱中获得的腐殖质的特征带以及从紫外可见光谱中分析所得的E4/E65的结果均表明腐殖质分子结构的聚合度很高。在分子荧光发射光谱中显示的主要是芳香结构的特征带。分子荧光光谱的同步检测图则显示腐殖质在400 nm处的荧光强度最大,而在此处含有五个芳香环的多环芳烃的荧光强度恰好也是最大。因此,实验结果表明腐殖质分子有很高的聚合度,并且其芳香性大于脂肪性。     

Mechanical characterization of materials at small length scales

A review on the mechanical characterization of materials at small length scale is presented. The focus is on the different micro- and nanoscale testing techniques, the variety of materials investigated by the scientific and industrial communities and the mechanical quantities identified by such methodologies.     

Fabrication and characterization of microwell array chemical sensors

Microwell arrays have been fabricated on the distal face of coherent fiber-optic bundles. A typical microwell array comprises approximately 3,000 individual optical fibers that were etched chemically. Individual microwells were 1 to 14-microm deep with approximately 22-microm widths and were filled partially with a chemical sensing (polymer + dye) layer to produce a microwell array sensor (MWAS). MWASs were fabricated using a technically expedient, photoinitiated polymerization reaction whereby a approximately 2 to 10-microm thick pH-sensitive or O2-sensitive sensing layer was immobilized inside each microwell. The pH-sensing layer comprised fluorescein isothiocyanate-dextran conjugate immobilized in a photopolymerizable poly(vinyl alcohol) membrane. The O2-sensing layer comprised a ruthenium metal complex entrapped in a gas-permeable photopolymerizable siloxane membrane. pH and PO2 were quantitated by acquiring luminescence images using an epifluorescence microscope/charge-coupled device imaging system. The pH-sensitive MWAS displayed a pKa of approximately 6.4 and a response time of approximately 2.5 s. The O2-sensitive MWAS behaved according to a nonlinear Stern-Volmer model with a maximum I0/I of approximately 4 and a response time of approximately 2.5 s. MWASs are advantageous in that suitably sized samples such as single biological cells can be co-localized with the sensing matrix in individual microwells.     

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.