微晶泡沫玻璃的制备及力学性能研究

以废旧阴极射线管为主要原料,SiC为发泡剂,采用烧结法制备了微晶泡沫玻璃。通过DTA,XRD,SEM等分析手段,研究了发泡剂用量,升温速率,降温速率,保温时间对试样力学性能的影响。结果表明,所制备的微晶泡沫玻璃的主晶相为Pb,次晶相为Pb3O4,Al6Si2O13,抗压强度为6.28MPa,抗折强度为2.1MPa。     

The nonlinear optical properties of silver nanoparticles decorated glass obtained from sintering mesoporous powders

Silver nanoparticles (Ag NPs) have excellent third-order nonlinear optical properties but it is still difficult to obtain silica glass containing Ag NPs with homogenous dispersion and small particle size. Herein, silica glass with homogenously distributed Ag NPs in its matrix was derived from sintering a famous type of mesoporous silica (FDU-12) encapsulated with Ag NPs (Ag NPs/FDU-12) through Spark Plasma Sintering (SPS) technique. Benefited from the low-temperature sintering property of the Ag NPs/FDU-12 powders (~930°C within 5 min), the Ag NPs can be directly trapped in the derived silica glass with small particle size (<3.0 nm) and without mass loss. The as-prepared Ag NPs/glass showed a typical reverse saturable absorption curve, which is measured via the Z-scan method by using a 532 nm nanosecond laser. The nonlinear coefficient and imaginary third-order susceptibility were calculated as 11.46 cm/GW and 2.22 × 10⁻¹² esu, respectively, indicating the excellent third-order nonlinear optical properties of the Ag NPs/glass. This study demonstrates a great potential for preparing silica glasses functionalized with well dispersed ultrafine functional particles, which is appealing in photonic field.     

Computation of sintering stress and bulk viscosity from microtomographic images in viscous sintering of glass particles

Sintering stress and bulk viscosity were derived as functions of relative density from microtomographic images in viscous sintering of glass particles. Three methods were proposed to estimate the sintering stress from relative density, specific surface area, and average of curvature on pore surface, which were directly measured by X‐ray microtomography. The surface energy method gave valid value in the final stage of sintering, while the mixed method gave better estimation in the intermediate stage. For the initial stage of sintering, the sintering stress was calculated from the average contact radius and the average coordination number observed by X‐ray microtomography. The sintering stress at the final stage increased in free sintering, but it decreased in constrained sintering due to pore coarsening. The bulk viscosity was calculated from the shrinkage rate and the sintering stress.     

Development of high‐definition aqueous polyvinylpyrrolidone photoresists for cathode ray tubes

Aqueous photoresists that are capable of higher resolutions than are currently employed by the cathode ray tube (CRT) industry were developed by combining photoactivators, which activate at shorter UV wavelengths with polyvinylpyrrolidone (PVP). Two photoactivators were synthesized: 4,4′‐diazido‐2,2′‐biphenyl disodium disulfonate (DABP), which has a maximum absorbance at 264 nm, and 4,4′‐diazido‐2,2′‐biphenylethane disodium disulfonate (DABPE), which has a maximum absorbance at 258 nm. The PVP/DABP and PVP/DABPE photoresists successfully imaged a pattern with resolution as small as 4.4 μm with photoactivator concentrations greater than 20% of the PVP concentration. Addition of silane and emulgen greatly improved the performance of the photoresists with more uniform coatings of thicknesses of up to 1.4 μm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1637–1644, 2006     

Preparation of bulk‐nanostructured UO2 pellets using high‐pressure spark plasma sintering for LWR fuel safety assessment

Nuclear fuel undergoes a significant restructuration during its lifetime in the nuclear reactor. Especially at the rim of the pellet, large UO₂ grains disintegrate into a nanosized material. In this paper, we focus on the preparation of bulk UO₂ with grain sizes below 100 nm to investigate the physico‐chemical properties of this so‐called “high burn up structure” (HBS). Preparation of bulk nanocrystalline materials is a challenge that can be overcome using the high‐pressure spark plasma sintering (HP SPS) technique. In‐house developed HP SPS with 500 MPa applied pressure was used for compaction of 11 nm UO₂ powder obtained by oxalate conversion. The procedure yielded dense (>90%) compacts with grain size as low as 34 nm for samples sintered at 800°C.     

Crystallization pathways in glass-ceramics by sintering cathode ray tube (CRT) glass with kaolin-based precursors

The crystallization mechanisms for the formation of glass-ceramics by sintering CRT glass with kaolin-based precursors were investigated by quantitatively determining the crystalline and amorphous phases in the products. Amorphization of sintered products was observed in CRT/kaolinite and CRT/mullite glass-ceramics systems at 700–900?°C. With the increase of temperature, the crystallochemical formation of lead feldspar and orthoclase was detected. Orthoclase was found to be the major crystalline phase in both CRT/kaolinite and CRT/mullite systems at 1000–1100?°C. When the temperature increased to 1000–1100?°C, lead feldspar was formed as the only crystalline phase to host Pb. The leaching tests suggested that the glass-ceramic product sintered by CRT/kaolin-based precursors has stronger resistance against acid attack because of the incorporation of lead into lead feldspar crystal protected by glass matrix. The incorporation of CRT glass into glass-ceramics provides a promising strategy for reducing the environmental hazard of CRT glass.     

Rapid manufacturing of silica glass parts with complex structures through stereolithography and pressureless spark plasma sintering

This paper reports a method for preparing silica glass by pressureless spark plasma sintering (PL-SPS), which can rapidly manufacture silica glass parts with complex structures by coupling with stereolithography 3D printing technology. The rapid sintering process and microstructure evolution of silica glass prepared by PL-SPS were mainly investigated. The experimental results showed that the sintering temperature and dwelling time were the main factors affecting the PL-SPS of silica glass. The microstructure evolution indicated that the densification rate of the sample was very fast from 1250 °C to 1300 °C, and the interlayer defects caused by the printed layer thickness could be healed in the final stage of densification. Like conventional pressureless sintering, silica glass with a relative density of more than 99% and a visible-light transmittance of more than 90% could also be obtained through PL-SPS, but the entire working time was shortened from 22.53 h to 0.49 h.     

Phosphor‐in‐glass thick film formation with low sintering temperature phosphosilicate glass for robust white LED

Phosphor‐in‐glass (PiG) thick film was fabricated on a borosilicate glass substrate using a conventional screen printing method and employing phosphosilicate glass to allow low‐temperature sintering. The vehicle content and sintering temperature were optimized to form a thick film with a thickness of ~50 μm. Commercial yellow (Y₃Al₅O₁₂:Ce³⁺) and red (CaAlSiN₃:Eu²⁺) phosphors were successfully incorporated within the glass matrix and then sintered at 550°C. Color‐tunable white LEDs were achieved using the PiG thick films as a color converter by varying the glass to phosphor (GtP) ratio. The high luminous efficacy of up to ~120 lm/W and high color rendering index of up to 89 in combination with the thermal quenching property prove the practical feasibility of the PiG thick films for high‐power/high‐brightness LED applications.     

X‐ray tomography of feed‐to‐glass transition of simulated borosilicate waste glasses

High‐level waste feed composition affects the overall melting rate by influencing the chemical, thermophysical, and morphological properties of a cold cap layer that floats on the molten glass where most feed‐to‐glass reactions occur. Data from X‐ray computed tomography imaging of melting pellets comprised of a simulated high‐aluminum feed reveal the morphology of bubbles, known as the primary foam, for various feed compositions at temperatures between 600°C and 1040°C. These feeds were formulated to make glasses with viscosities ranging from 0.5 to 9.5 Pa s at 1150°C, which was accomplished by changing the SiO₂/(B₂O₃+Na₂O+Li₂O) ratio in the final glass. Pellet dimensions and profile area, average and maximum bubble areas, bubble diameter, and void fraction were evaluated. The feed viscosity strongly affects the onset of the primary foaming and the foam collapse temperature. Despite the decreasing amount of gas‐evolving components (Li₂CO₃, H₃BO₃, and Na₂CO₃), as the feed viscosity increases, the measured foam expansion rate does not decrease. This suggests that the primary foaming is not only affected by changes in the primary melt viscosity but also by the compositional reaction kinetic effects. The temperature‐dependent foam morphological data will be used to inform cold cap model development for a high‐level radioactive waste glass melter.     

Surface modification of ultra‐high‐molecular‐weight polyethylene. I. Characterization and sintering studies

We performed surface modification of ultra‐high‐molecular‐weight polyethylene (UHMWPE) through chromic acid etching with the aim of improving the performance of UHMWPE's composites with poly(ethylene terephthalate) fibers. In part I of this study, we evaluated the effects of chemical modification on the surface properties of UHMWPE with X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements. The thermal properties, rheology, and sintering behavior of the modified UHMWPE were compared to those of the base material. XPS and FTIR analysis confirmed the presence of carboxyl and hydroxyl groups on the surface of the modified powders. The substitution of polar groups into the backbone of the polymer decreased its contact angles with water and hexadecane and increased its surface energy, as evidenced by contact angle measurements. The modified UHMWPE was more crystalline than the base resin and less prone to thermal degradation. Although the rheological properties were virtually identical, the modified powders sintered more readily, presumably due to their higher surface energy, which suggested enhanced processability by compression molding. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Characterization and thermal degradation of protective layers in high‐rating fire‐resistant glass

Fire‐resistant glass products are considered to have better performance against fire. They are developed to replace conventional glass products. However, the smoke emitted from these products can be potentially harmful during fires and cause injuries or even deaths. Six samples of insulating glass available in the local market were selected. A variety of techniques, including X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric FTIR, pyrolysis–gas chromatography–mass spectrometry and tubular furnace coupled FTIR spectroscopy, were employed. According to the test results, there are two types of protective layers of the fire‐resistant glass. One consists of water, water‐soluble salt and polyamide with possible presence of alcohols, and the other consists of water metal silicates with possible presence of carboxylate and alcohols. Gases emitted from the protective layers heated in air, in argon and in vacuum are similar. Water vapor, carbon dioxide and hydrogen chloride are the main components of the gases emitted. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

The goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide (ITO) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing (HP) or spark plasma sintering (SPS). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy (IS), SEM, and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO. Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP. This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.     

Preparation and characterization of low molecular weight silk fibroin by high‐temperature and high‐pressure method

A low molecular weight silk fibroin powder (LMSF) was prepared through high temperature (200°C) and high pressure (20 kgf/cm²), without any addition of chemicals. The carbonized adducts produced during this process were then removed by treatment with activated charcoal. The yield of LMSF by this preparation method was over 60% after the removal of carbonized adducts by using activated charcoal. Amino acid analysis showed an observable decrease in contents of serine and tyrosine in LMSF prepared by this method, as compared to those prepared by neutral salt. The molecular weight of this LMSF was also observably decreased with an increase in the reaction time. From the measurements of differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), thermal properties of LMSF through high temperature and high pressure were also decreased as compared to those produced by neutral salts. In addition, wide‐angle X‐ray diffraction (WAXD) patterns showed that the crystallinity of LMSF differed from that of the original silk fibroin. It can be said that the preparation method of LMSF in this study is a simple, economical, and environmentally compatible process with many advantages. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2890–2895, 2002     

Experimental investigation into the selective laser sintering of high‐impact polystyrene

High‐impact polystyrene (HIPS) was used as selective laser sintering (SLS) material. The sintering parameters and the properties of sintered parts were investigated. The results show that sintered parts, which have good dimensional accuracy and good mechanical properties, can be fabricated with wide ranges of laser energy and bed temperature. To apply HIPS parts as functional parts, a reinforcement method, in which the sintered HIPS parts were postprocessed by infiltrating with epoxy resin, were suggested. The properties of the parts after postprocess were also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optimization of a gadolinium‐rich oxyhalide glass scintillator for gamma ray spectroscopy

A transparent gadolinium‐rich oxyhalide glass scintillator was developed for gamma ray spectroscopy with an energy resolution of 14.0% at 662 keV. To the best of our knowledge, this is the highest energy resolution reported for a glass‐based scintillator. The high gadolinium content facilitated a scintillator density of 4.4 g/cm³. The high fluorine and bromine incorporation is advantageous for better uniformity and a good light output of ~3200 Ph/MeV. The peak emission at 431 nm with a FWHM of 90 nm, resulting from the fast Ce³⁺ transitions, yielded pulse‐height spectra with distinctive peaks from 122 keV to 1.33 keV for gamma radiation from different nuclides.     

Alcohol dehydrogenase in non‐aqueous media using high‐pressure technologies: reaction set‐up and deactivation determination

BACKGROUND: The demand for enantiomerically pure molecules is growing continuously and biocatalysis is a powerful technique for their production. In this work, the catalyst was an enzyme combined with its coenzyme, NADP. High pressure technology, a second clean technology, was applied as well. Dense gases are promising solvents for biocatalysis. They have been investigated extensively as reaction media for lipase‐catalysed reactions, but seldom for reactions, catalysed with alcohol dehydrogenases, as in this work. RESULT: The production of optically pure R‐1‐phenylethanol from acetophenone was investigated. The NADP‐dependent alcohol dehydrogenase from Lactobacillus brevis (LBADH) was used as a catalyst. The hydrogenation was performed with isopropanol as a co‐substrate in different conditions: dense propane with LBADH and NADP co‐immobilized on glass beads and in the biphasic system water/dense propane. The obtained R‐1‐phenylethanol was enantiopure. The conversions were up to 90%. Deactivation of LBADH was also measured in these media. CONCLUSION: Protocols were successfully developed for the testing of alcohol dehydrogenase activity in dense gases. Enantioselectivity of LBADH is excellent in those media but it deactivated quickly. An LBADH‐catalysed reaction was performed in a dense gas for the first time. Copyright © 2010 Society of Chemical Industry     

Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high‐density polyethylene blends

The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (T_g) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, T_g of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while T_g of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of T_g of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry     

A low sintering temperature glass based on SiO2–P2O5–ZnO–B2O3–R2O system for white LEDs with high color rendering index

A low sintering temperature glass based on the SiO₂–P₂O₅–ZnO–B₂O₃–R₂O (R=K and Na) system was studied as a matrix for embedding phosphors to fabricate color tunable white LEDs. The proposed system, which uses no heavy‐metal elements and can be sintered at 500°C, incorporates thermally weak commercial phosphors such as CaAlSiN₃:Eu²⁺ to produce phosphor‐in‐glasses (PiGs). Changing the mixing ratio of glass to phosphors affected the photo‐luminescence spectra and color coordinates of the PiGs when mounted on a blue LED. The color rendering index (CRI) and color correlated temperature (CCT) of the LEDs were also varied with the mixing ratio, providing color tunable white LEDs. A high CRI, up to 93, as well as highly improved thermal stability were obtained, along with a low sintering temperature compared to other glass systems, suggesting the practical feasibility of the proposed system.     

Modification of high‐performance polymer composite through high‐energy radiation and low‐pressure plasma for aerospace and space applications

In this investigation, attempts are made to modify a high‐performance polymer such as polybenzimidazole (PBI) (service temperature ranges from ?260°C to +400°C) through high‐energy radiation and low‐pressure plasma to prepare composite with the same polymer. The PBI composites are prepared using an ultrahigh temperature resistant epoxy adhesive to join the two polymer sheets. The service temperature of this adhesive ranges from ?260°C to +370°C, and in addition, this adhesive has excellent resistance to most acids, alkalis, solvents, corrosive agents, radiation, and fire, making it extremely useful for aerospace and space applications. Prior to preparing the composite, the surface of the PBI is ultrasonically cleaned by acetone followed by its modification through high‐energy radiation for 6 h in the pool of a SLOWPOKE‐2 (safe low power critical experiment) nuclear reactor, which produces a mixed field of thermal and epithermal neutrons, energetic electrons, and protons, and γ‐rays, with a dose rate of 37 kGy/h and low‐pressure plasma through 13.56 MHz RF glow discharge for 120 s at 100 W of power using nitrogen as process gas, to essentially increase the surface energy of the polymer, leading to substantial improvement of its adhesion characteristics. Prior to joining, the polymer surfaces are characterized by estimating surface energy and electron spectroscopy for chemical analysis (ESCA). To determine the joint strength, tensile lap shear tests are performed according to ASTM D 5868–95 standard. Another set of experiments is carried out by exposing the low‐pressure plasma‐modified polymer joint under the SLOWPOKE‐2 nuclear for 6 h. Considerable increase in the joint strength is observed, when the polymer surface is modified by either high‐energy radiation or low‐pressure plasma. There is further significant increase in joint strength, when the polymer surface is first modified by low‐pressure plasma followed by exposing the joint under high‐energy radiation. To simulate with spatial conditions, the joints are exposed to cryogenic (?196°C) and high temperatures (+300°C) for 100 h. Then, tensile lap shear tests are carried out to determine the effects of these environments on the joint strength. It is observed that when these polymeric joints are exposed to these climatic conditions, the joints could retain their strength of about 95% of that of joints tested under ambient conditions. Finally, to understand the behavior of ultrahigh temperature resistant epoxy adhesive bonding of PBI, the fractured surfaces of the joints are examined by scanning electron microscope. It is observed that there is considerable interfacial failure in the case of unmodified polymer‐to‐polymer joint whereas surface‐modified polymer essentially fails cohesively within the adhesive. Therefore, this high‐performance polymer composite could be highly useful for structural applications in space and aerospace. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1959–1967, 2006     

Chemical grafting of metallocene‐catalyzed functional polypropylene copolymer on glass substrates through surface modification

This work deals with surface modification of soda‐lime glass slides which, by itself, does not have hydroxyl groups at the surface. So, a glass surface pretreatment is needed, to create hydroxyl groups onto it, before carrying out the polypropylene (PP) grafting reaction. Different acid/base pretreatments were performed to develop an adequate concentration of superficial hydroxyl groups. Subsequently, a metallocenic polymerization (propylene‐α olefin graft reaction, catalyzed by EtInd₂ZrCl₂/methylaluminoxane), was carried out to provide graft‐PP chains chemically linked to the glass surface. The surface so modified can be further functionalized and tailored for different applications, including polymer composites. The pretreatment conditions that best preserved homogeneity and caused less damage to the glass surface resulted from a step of contact with dilute HF/NH₄F buffer, a washing step with distilled water, and a final exposure to KOH. After the propylene copolymerization was performed, part of the graft copolymer formed remained chemically bonded to the glass slide surface. The presence of grafted PP at the surface was confirmed by SEM, FTIR, and EDAX characterization, even after the physically adsorbed polymer was excluded by a severe solvent extraction treatment. From these results, the copolymerization of a hydroxy α‐olefin, grafted on a MAO‐pretreated glass slide, is foreseen as a possible way to graft polymers onto inorganic solids. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008