Hot embossing of moth eye-like nanostructure array on transparent glass with enhanced antireflection for solar cells

Antireflection (AR) silicon and glass surfaces are necessarily required for solar cells, because a reflective silicon solar cell with a glass covering will reflect a percentage of sunlight. In this work, we demonstrate a universal and scalable net-shape nanofabrication method for broadband nanostructured AR surface on transparent glass, intended for solar cell applications. Moth eye-like glass nanopillars with various diameters were successfully fabricated by a combination of precision hot embossing and ultrasonic vibration demolding process. The morphologies of nanopillars were detected to characterize different profiles formed by glass flow at elevated temperatures. Facile optical experiments were designed and conducted to measure the AR performance at varying wavelengths and angle of incidences and the proposed nanostructures exhibit excellent AR property. Additionally, a feasible optical modeling is developed and compared with the measurement to evaluate the theoretical optical behaviors of glass nanostructures based on their embossed shapes. The inexpensive and environmental hot embossing method with ultrasonic vibration demolding is expected to create AR glass nanostructured surfaces for widespread applications such as solar cells, displays and laser systems.     

Fabrication of superhydrophobic surfaces on a glass substrate via hot embossing

This study developed a new hot pressing process to prepare superhydrophobic surfaces with controllable shape and size on a glass substrate. Microstructures were fabricated on tungsten carbide mold via picosecond laser processing. Microgroove structures were reproduced on glass during the hot embossing process and SiO₂ nanoparticles laid on the mold were also embedded into the glass surface under the action of heat and pressure to provide nanostructures. The contact angle of the superhydrophobic glass surface reached up to 161.8°, and the sliding angle was only 3°. The structures and chemical composition of superhydrophobic glass surface were identified by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), and Fourier transformed infrared (FTIR) spectroscopy. The 3D laser scanning microscopy result showed the height (20 μm) of the microgroove structures, while white light interferometry revealed the surface roughness (Ra 2.725 μm). The superhydrophobic glass surface demonstrated satisfactory temperature resistance and chemical stability through temperature and acid and alkali solution immersion tests. The surface exhibited certain mechanical stability by friction and wear test. This work provides a new hot embossing method for solving the problem of structural consistency and mass production of superhydrophobic glass, and will have great application prospects in the engineering field.     

Speed effect on the material behavior in high-speed scratching of BK7 glass

Scratch tests are often performed at a speed that is significantly lower than the real application like machining and grinding. However, brittle materials like BK7 behave very differently under high-speed conditions due to the more promising temperature and stain rate effects Therefore, it is important to study its material behavior under high-speed condition. In this study, single scratch tests and consecutive scratch tests were performed on BK7 under scratch speeds of 1, 5 and 20 m/s, which were much higher than the traditional scratch tests. The surface morphology as well as the subsurface cracks of the scratch grooves was inspected under AFM and FIB-SEM. The thermal effect that caused the changes in ductile-brittle transition (DBT) and scratch morphology was simulated and explained by a thermal-stress coupled finite element analysis. Finally, the changes in material removal behavior as well as the crack initiation mechanism due to speed effect was revealed.     

Recent progress in Japan on hot gas cleanup of hydrogen chloride, hydrogen sulfide and ammonia in coal-derived fuel gas

The present review paper highlights on the recent progress in Japan on the hot gas cleanup of HCl, H₂S and NH₃ in raw fuel gas for coal-based, combined cycle power generation technologies. It has been shown that NaAlO₂, prepared by mixing Na₂CO₃ solution with Al₂O₃ sol, can reduce HCl in an air-blown gasification gas from the initial 200 ppm to < 1 ppm at 400 °C, and it is tolerable for 200 ppm H₂S. With regard to the removal of H₂S, studies on the stability and durability of ZnFe₂O₄ sorbent in a simulated fuel gas have indicated the presence of an optimal operation temperature from the viewpoint of the suppression of both vaporization of metallic Zn and carbon formation from CO. High-performance TiO₂-supported ZnFe₂O₄, which can decrease 1000 ppm H₂S to < 1 ppm at 450 °C and 1 MPa, has been developed by the homogeneous precipitation method using a mixture of SiO₂ sol and an aqueous solution of Zn and Fe nitrates, followed by mixing with TiO₂. Although this sorbent is regenerable and durable, the sorption ability should be improved in a syngas-rich fuel gas from an O₂-blown gasifier. A novel method to prepare carbon-supported ZnFe₂O₄ and CaFe₂O₄ by impregnating the corresponding nitrate solution with brown coal has been proposed, and the large desulfurization capacity of almost 100% has been achieved in the removal of 4000 ppm H₂S around 450 °C. The present authors have demonstrated that an Australian limonite rich in α-FeOOH is practically feasible as the catalyst material for the decomposition of 2000 ppm NH₃ in a syngas-rich gas of 25 vol.% H₂/50 vol.% CO at 750 °C, because small amounts of H₂O and CO₂ added to the gas can work efficiently for inhibiting carbon deposition from the CO.     

Rheological behavior of ethylene–vinyl acetate copolymer and fabrication of micropyramid arrays by roll‐to‐roll hot embossing on its thin films

Films of ethylene–vinyl acetate (EVA) copolymer with different vinyl acetate (VA) contents were adopted as flexible substrates for fabrication of micropyramid arrays by roll‐to‐roll (R2R) hot embossing at roller temperatures 40–80 °C. An empirical relationship between rheological behavior of EVA in rubbery state and demolding performance of the films was explored. Dependence of average forming height of micropyramid arrays on VA content and roller temperatures was investigated. Our study showed that both viscosity and relaxation behavior of EVA can be related to the ultimate forming height of micropyramids. The relationships can provide references for experimental research and industrial manufacture on R2R hot embossing. Retroreflection of micropyramid arrays was observed and transmittances of the two sides of embossed films were studied. Transmittances of the VA28 film embossed at 60 °C were 97.9% (the embossed side) and 41.8% (the smooth side), which showed potential applications in reflective film and antireflective film fields. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45228.     

Research progress of hot gas filtration,desulphurization and HCl removal in coal-derived fuel gas: A review

The present review paper highlighted on the recent progress of hot gas filtration, desulphurization and HCl removal in coal-derived fuel gas for combined cycle power generation (IGCC) or molten carbonate fuel cells (MCFC) technologies. As a critical process in the gasification system, hot gas filtration in the particulate control device (PCD) was introduced with enhanced understanding of equipment and operation, filter element and failsafe material properties, and gasification ash characteristics. The issues associated with the commercialization of hot gas filtration were also addressed, and some novel systems and methods were also discussed. The hot gas desulphurization in coal-derived fuel gas has concentrated on developing regenerable sorbents including the single and composite oxides of Zn, Fe, Cu, Mn and other species, and the reduction of metal oxides in the highly reducing atmosphere followed by vaporization of elements can be a problem for reactivity and regeneration. With regard to the removal of HCl, the studies have indicated sorbents prepared by pelletizing the powders of naturally available alkali metal and alkali earth metal substances can rapidly react with HCl vapor and reduce the HCl vapor concentration to less than 1 ppmv, and some sorbents lab-made have very high chlorine capacity. The sorbents based hot gas cleaning also has some challenges. Kinetics studies showed that unreacted shrinking core (USC) can be applied to the modeling of H₂S and HCl removal by sorbents at high temperature, and the surface chemical reaction and reactant diffusion by product layers between solid sorbents and gases were very important mechanisms. The paper also proposed and discussed a rational concept for the simultaneous removal of multiple contaminants including ash, H₂S and HCl, which will offer a possible cost reduction by two or more processes in a single vessel for hot gas cleaning.     

Effects of reduction of metal oxide sorbents on reactivity and physical properties during hot gas desulphurization in IGCC

In this study, the changes of physical properties and reactivity of the metal oxide sorbents were investigated under the reducing conditions of coal gas. Metal oxide sorbents are converted into metal sulphides as a result of reaction with H₂S in synthesis gas. This could cause the reduced reactivity of sorbents if the metal oxides were converted into metallic elements due to the reduction by either hydrogen or carbon monoxide. In this experiment, the changes of physical properties and reactivity of the metal oxides were investigated over the temperature range 480-700 °C. It is confirmed that the reactivity of sulphidation and the reduction of metal oxide increased with increasing temperature. Even though the sulphur capacity of the sorbents in the early stage was high, it reduced rapidly due to the progressive reduction of metal oxides as the sulphidation/regeneration process was repeated. The reduction of metal oxide and the extent of reduction were verified by measuring the amount of oxygen consumed and the amount of SO₂ produced during the regeneration of sulphidated sorbents with the aids of a gas analyser. It was concluded that the reactivity of the metal oxide sorbents was influenced by reduction with coal gas at high temperature.     

Photo-induced deformation behavior depending on the glass transition temperature on the surface of urethane copolymers containing a push-pull type azobenzene moiety

Urethane copolymers containing a push-pull type azobenzene moiety with the same dye content were synthesized to investigate the relationship between photo-induced deformation and molecular mobility. The copolymers exhibit different glass transition temperatures (T_g), from 46 to 143 °C, due to their different main chain structures. An indented nanostructure induced by the optical near field around the polystyrene microspheres and a surface relief grating (SRG) induced by exposure to a two-beam interference pattern were examined using films of copolymers. We found the dependency of the deformation efficiency on T_g was inverted depending on the irradiation power. The deformation depth increased with T_g under high power irradiation in both the indented nanostructure and the SRG forming experiments. In contrast, the deformation depth of the SRG decreased with increasing T_g under low power irradiation. The discovery of this inverted tendency suggests that, in addition to the molecular mobility, we should consider other factors in the deformation mechanism, such as the recovery of deformation, the degree of plasticization, and the thermal effects.     

Corrosion of alumina and mullite hot gas filter candles in gasification environment

Reliable fuel gas cleaning is required to meet environmental regulations as well as to prevent corrosion and erosion of downstream components. The aggressive process environment in biomass-gasification power generation systems or in biofuels production systems causes corrosion in the ceramic hot gas filter candles used to clean the fuel gas. Therefore, in order to improve the reliability and durability of filters, the influence of steam, ash, hydrogen sulfide, and alkaline metals on the corrosion processes was studied for alumina and mullite filter candles fabricated by Pall Schumacher. Exposure to these contaminants effects the chemical composition of the binder phases resulting in exchange of alkaline metals and alkaline earth metals. Analyses by energy dispersive X-ray spectroscopy demonstrate the negative effect of silicon containing binder phases. These effects are discussed and it is shown that the usage of silicon-free binder phases in hot gas filter candles for gasification processes is promising.     

Corrosion of silicon carbide hot gas filter candles in gasification environment

Reliable cleaning of the fuel gas is required to meet the environmental regulations and to prevent corrosion and erosion of downstream components. The aggressive process environment in biomass-gasification power generation systems or in biofuels production systems can cause corrosion in ceramic hot gas filter candles used to clean the fuel gas. Therefore, to improve the reliability and durability of filters, the influence of steam, ash, and alkaline (earth) metals on the corrosion processes was studied for silicon carbide filter candles fabricated by Pall Schumacher. Exposures with biomass and lignite ashes caused a macroscopically expansion as well as microstructural effects that were analysed by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. All effects are discussed and it is shown that the employment of silicon carbide filter candles in water vapour containing, alkali-rich gasification environment at high temperature is problematic.     

Numerical analysis of flow field in the hot gas filter vessel during the pulse cleaning process

The flow field is simulated for a ceramic filter vessel containing three candle filters which are arranged in the form of an equilateral triangle. Grids generated by GAMBIT are adopted for the simulations. The Reynolds stress model provided by FLUENT code is applied to evaluate gas flow and temperature field in the filter vessel. The temperature profiles in the ceramic candle filter cavity during the pulse cleaning process are analyzed under different operating conditions and for different lengths of candle filter. The evolution of radial velocity in the porous wall of the filters being cleaned and the normal working filters as well as around the filters is discussed. Sharp temperature change takes place in the top of the candle filter which is subject to thermal stress. The phenomenon of temperature increase during the pulse cleaning process has been carefully observed and interpreted based on the effect of gas compression. The simulated results show qualitative agreement with the experimental field observations with the filter vessel.     

The effect of confinement in nanoporous polymers on the glass transition temperature

The glass transition temperature (T_g) of nanoporous polyetherimide (PEI) and PEI thin films was investigated. The T_g decreased from its bulk value in both of these confined systems. Monte Carlo simulations were performed to calculate the nearest neighbor pore-to-pore distances in the nanoporous PEI. A quantitative analogy between the nanoporous PEI and PEI thin films is proposed through an equivalence of nearest neighbor pore-to-pore distances and thin film thickness. The effect of confinement is believed to be due to the interface regions, which possess higher chain mobility than the bulk. When these high mobility interface regions are sufficiently close together, the excess mobility at the interface region affects the dynamics of the system by restraining percolation of the slow domains resulting in the observed decrease in T_g.     

Sulphur poisoning of nickel-based hot gas cleaning catalysts in synthetic gasification gas II. Chemisorption of hydrogen sulphide

The effect of different components of gasification gas on sulphur poisoning of nickel catalysts were studied. In addition, the sulphur distribution and content of nickel catalyst beds were analysed to account the poisoning effect of sulphur on the activity of catalysts to decompose tar, ammonia and methane. The desorption behaviour of chemisorbed sulphur from the bed materials was monitored by temperature programmed hydrogenation (TPH). It was established that bulk nickel sulphide was active in decomposing ammonia in high-temperature gasification gas-cleaning conditions. The decomposing activity of methane was not affected by bulk nickel sulphide formation, but that of toluene was decreased. The activity of the catalyst regained rapidly when H₂S was removed from the gas. However, the conversion of ammonia was not regained at as high a level as before sulphur addition, most probably due to irreversible sulphur adsorption on the catalyst. The temperature increase could also be used to regenerate the catalyst performance especially in respect to methane and toluene. Sulphur adsorbed on nickel catalysts in different chemical states depends on the process conditions applied. At >900°C the sulphur adsorbed on the catalyst formed an irreversible monolayer on the catalyst surfaces, while at <900°C the adsorbed sulphur, probably composed of polysulphides (multilayer sulphur), was desorbed from the catalyst in sulphur-free hydrogen containing atmosphere. However, a monolayer of sulphur still remained on the catalyst after desorption. The enhanced effect of high total pressure on sulphur-poisoning of nickel catalysts could be accounted for the increased amount of sulphur, probably as a mode of polysulphides, adsorbed on the catalyst.     

Resistance to sulfur poisoning of hot gas cleaning catalysts for the removal of tar from the pyrolysis of cedar wood

In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H₂S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO₂/SiO₂ using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H₂S. Steam reforming Ni catalyst was effective for the tar removal without H₂S addition, however, the addition of H₂S deactivated drastically. In contrast, Rh/CeO₂/SiO₂ exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H₂S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO₂/SiO₂, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis.     

Sulphur poisoning of nickel-based hot gas cleaning catalysts in synthetic gasification gas: I. Effect of different process parameters

The effect of different process parameters on sulphur poisoning of nickel catalysts in tar (toluene), ammonia and methane decomposition was studied. Tests were carried out in a fixed-bed tube reactor at 800–1000°C at 5 and under 20 bar total pressure using a synthetic gasification gas mixture. In the same conditions, sulphur affected less the toluene and methane decomposing activity than the ammonia decomposing activity. Ammonia conversion was affected by the catalyst type but not by the nickel content of catalyst. When temperature was increased the effect of sulphur poisoning was decreased. At 20 bar pressure the poisoning effect of sulphur was stronger than at 5 bar pressure. To prevent sulphur poisoning of nickel catalysts in the tar and ammonia decomposition process at high pressure (20–30 bar), the catalyst process should operate at > 900°C. In addition, by decreasing the space velocity of the process the sulphur poisoning effect could be compensated in the test conditions.     

The effect of reactor temperature gradient on microstructures of sodium borosilicate glass powders produced by ultrasonic spray pyrolysis technique

Sodium borosilicate glass powders were produced by ultrasonic spray pyrolysis technique for three different reactor temperature gradients and the effect of the reactor temperature gradient on the microstructures of the powders produced was investigated. A three-zone ultrasonic spray pyrolysis system reactor in which the temperatures of each zone could be controlled separately was designed for this purpose. When the drying speed is high, early shell formation was observed in the aerosol droplets due to the difference of the drying speed between inner and outer parts and hollow powders were produced. In order to produce dense powder particles, shell formation on the aerosol droplet should be prevented, therefore drying speed should be decreased. The powders produced were glass-structured, spherical shaped and with smooth surfaces. The density of the hollow powder particle was 1.9 g/cm³ while the density of the dense particle was 2.5 g/cm³.     

Spatial patterns of greenhouse gas emission in a tropical rainforest in Indonesia

Spatial patterns of CO₂, CH₄, and N₂O flux were analyzed in the soil of a primary forest in Sumatra, Indonesia. The fluxes were measured at 3-m intervals on a sampling grid of 8 rows by 10 columns, with fluxes found to be below the minimum detection level at 12 points for CH₄ and 29 points for N₂O. All three gas fluxes distributed log-normally. The means and standard deviations of CO₂ and CH₄ fluxes calculated by the maximum likelihood method were 3.68 ± 1.32 g C m^–2 d^–1 and 0.79 ± 0.60 mg C m^–2 d^–1, respectively. The mean and standard deviation of N₂O fluxes using a maximum likelihood estimator for the censored data set was 2.99 ± 3.26 g N m^–2 h^–1. The spatial dependency of CH₄ fluxes was not detected in 3-m intervals, while weak spatial dependency was observed in CO₂ and N₂O fluxes. The coefficients of variation of CH₄ and N₂O were higher than that of CO₂. Some hot spots where high levels of CH₄ and N₂O were generated in the studied field may increase the variability of these gases. The resulting patterns of variability suggest that sampling distances of >10 m and > 20 m are required to obtain statistically independent samples for CO₂ and N₂O flux in the studied field, respectively. But because of weak or no spatial dependency of each flux, a sampling distance of more than 10 m intervals is enough to prevent a significant problem of autocorrelation for each flux measurement.     

Morphological effects on glass transition behavior in selected immiscible blends of amorphous and semicrystalline polymers

The effects uncompatibilized immiscible polymer blend compositions on the T_g of the amorphous polymer were studied in the systems polystyrene/polypropylene (PS/PP), polystyrene/high density polyethylene (PS/PE) and polycarbonate/high density polyethylene (PC/PE). In the two similar systems of PS/PP and PS/PE, the T_g of PS increased with decreasing PS percentage in the blends. This variation in glass transition is attributed to the polymer domain interactions resulting from the different morphologies of various blend compositions. Experiments were conducted to study these effects by preparing blends with various polymers that varied the relationship between the T_g of the amorphous polymer and the crystallization behavior of the semicrystalline polymer. Results show that the variation in amorphous component T_g with composition depends strongly on the physical state of the semicrystalline domains. Whereas the T_g of PS in PS/PE blends changed with composition, the T_g of PC in the PC/PE blend did not change with composition.     

Suppressing the effect of cullet composition on the formation and properties of foamed glass

The process of foaming glass is very dependent on the chemical composition of the glass. In this study we used a foaming-agent/oxidizing-agent couple and a crystallization inhibitor to foam cullets of flat, container and CRT-panel glass. Foamed glass with a density of 110–120?kg?m^–3, a thermal conductivity of 50–52?mW?m^–1 K^–1 and a homogeneous pore structure was obtained from a mixture of panel glass, 0.33?wt% carbon and 4.45?wt% Fe₂O₃. We also showed that it is possible to fabricate foamed glass with the same density or pore structure as mentioned above by adding up to 50?wt% container cullet or 70?wt% flat glass to the mixture. In the foamed samples with a low content of panel glass, crystals form, resulting in an increased open porosity, density and inhomogeneous pore structure. The crystallization can, however, be inhibited by adding calcium phosphate, so enabling the preparation of high-quality foamed glass from flat glass or flat/container-glass mixture. The pore gas is predominantly CO₂ and the pressure inside the pores is 0.36–0.47?bar. The reduced effect of the composition on the foaming process suggests that there is a great potential for stabilizing the production of foamed glass and ensuring the product's quality.     

表面活性剂在瓦斯水合物生成过程中的热力学作用

在实验研究基础上,结合表面活性剂水溶液中瓦斯水合物生成微观机理,提出了表面活性剂改变水合物生成热力学条件物理作用假说,认为表面活性剂胶束对溶于其中的气体分子和吸附于其周围的水分子的束缚作用,相当于降低了体系的温度.利用T40（0.001 mol·L^-1）、T40（0.002 mol·L^-1）、T40/T80（0.001 mol·L^-1）分别组成的3种气 液 煤 水合物反应体系实验测定了水合物生成时的相平衡参数,与同样温度和压力条件下相平衡计算值比较,结果表明,表面活性剂的加入有效地改变了水合物生成的热力学条件.例如,在T40/T80（0.001 mol·L^-1）实验体系中,当压力为22.67 MPa时,水合物生成相平衡温度为22.6℃,比纯水中提高2.1℃.