Organic-inorganic hybrid superhydrophobic surfaces using methyltriethoxysilane and tetraethoxysilane sol-gel derived materials in emulsion

By applying alkaline-catalyzed co-hydrolysis and copolycondensation reactions of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) in organic siloxane modified polyacrylate emulsion (OSPA emulsion), we are able to demonstrate the potential for developing a sol-gel derived organic-inorganic hybrid emulsion for a superhydrophobic surface research. TEOS and MTES derived sol-gel moieties can be designed for a physical roughness and hydrophobic characteristic (Si-CH₃) of the hybrid superhydrophobic surface, while OSPA emulsion can be endowed for good film-forming property. The effect of formulation parameters on superhydrophobicity and film-forming property was analyzed. The water contact angle (WCA) on the sol-gel derived hybrid film is determined to be 156°, and the contact angle hysteresis is 5° by keeping the mole ratio of TEOS:MTES:C₂H₅OH:NH₃·H₂O:AMP-95 at 1:4:30:10:0.63 and the mass percentage of OSPA emulsion at 25%. The nanoparticle-based silica rough surface is observed as the mole ratio of MTES/TEOS at 4:1. The sol-gel derived organic-inorganic hybrid emulsion shows remarkable film-forming property when the mole ratio of MTES/TEOS reaches or exceeds 4:1. With the primer coating, the performance of superhydrophobic film achieve actual use standard. It reveals that this new procedure is an effective shortcut to obtain a superhydrophobic surface with potential applications.     

双极结型晶体管的集电结反向雪崩击穿特性

通过气体放电产生更高浓度的低温等离子体要求具有纳秒上升沿和纳秒脉宽的高重频快脉冲,而目前被广泛使用的MOSFET和IGBT都无法满足这些参数要求,而双极结型晶体管(BJT）的集电极与发射极之间的雪崩击穿过程具有快导通、快恢复、高稳定性等优点,适合作为小型Marx发生器的自击穿开关。文中对用多种型号的BJT进行击穿特性比较测试实验,发现可以通过改变BJT的门极和发射极的并联电阻来调节其雪崩击穿电压,实现一定范围的工作电压。雪崩击穿恢复特性实验表明,当击穿电流衰减到低于维持电流时,BJT就会开始恢复绝缘而关断,通过改变电路中的参数以控制击穿电流的变化就可以控制BJT的雪崩击穿导通时间（即导通脉宽）。将这些结论应用到实际电路中,可获得上升沿5 ns、脉宽为10 ns、幅值2 kV、重复频率高达100 kHz的纳秒快脉冲,可用于激发高浓度低温等离子体。     

Strong correlation effects and new phase transition at high pressure-low temperature in La0.5Ba0.5FeO3

The physical properties of La_0.5Ba_0.5FeO₃ perovskite have been investigated. The resistivity and magnetism change at around the charge disproportionation temperature. The ferromagnetic cluster-glass state appears when . Under 5 kbar pressure a new phase transition at 5.5 K is found in the magnetization measurement. The transition temperature increases with the increase of the applied pressure. It is suggested that this transition is induced by the spin state transition from to with the pressure increase.     

Preparation of hybrid film with superhydrophobic surfaces based on irregularly structure by emulsion polymerization

A superhydrophobic surface originated from quincunx-shape composite particles was obtained by utilizing the encapsulation and graft of silica particles to control the surface chemistry and morphology of the hybrid film. The composite particles make the surface of film form a composite interface with irregular binary structure to trap air between the substrate surface and the liquid droplets which plays an essential role in obtaining high water contact angle and low water contact angle hysteresis. The water contact angle on the hybrid film is determined to be 154 ± 2° and the contact angle hysteresis is less than 5°. This is expected to be a simple and practical method for preparing self-cleaning hydrophobic surfaces on large area.     

Evolution and solar modulation of 7Be during the solar cycle 23

The modulation of ⁷Be-aerosols concentration due to solar activity during the cycle 23 is studied in the present research. For that purpose, was analyzed the differences in the long-term variation of geomagnetic and solar activity to assess the physical effects over the evolution of ⁷Be during the period 1996–2010. Furthermore, exploratory data analysis was applied to understand better the behavior of ⁷Be-aerosols in the surface atmosphere. This study shows that there is an inverse relationship among ⁷Be measured in the near ground air and solar activity. The modulation of ⁷Be-aerosols during the cycle 23 was divided in two steps. In the first stage, ascending phase, 1996–2002, the solar activity played an important role in the production rate of ⁷Be, r = ?0.75. However, during the descending phase, 2002–2009, the role of the solar activity was secondary, r = ?0.30, allowing that ⁷Be-aerosols reached the maximum concentration, 9.33 mBq m^?3 in August-09 when the solar activity was zero. Moreover, the remaining solar activity after the end of the ascending phase and the last important solar storm (December-06) caused the slowdown of ⁷Be production rate from 2001 to 2004 and the rupture of the seasonal behavior of ⁷Be in 2007, respectively. Finally, this research highlight the necessity to take into account the solar cycle phase, ascending or descending, to model studies of atmospheric process with ⁷Be as tracer since the contribution of the variables studied are so different in these stages.     

Evaluation of the effect of silicon on the carbonization process of Colombian semi-anthracites

The environmental impacts associated with the exploitation and transformation of fossil resources aggravate the planet's situation in terms of climate change. Due to this, this paper studies an alternative use of mineral coal as a precursor to obtaining new materials with different properties to the starting coals. The thermal degradation of two Colombian semi-anthracites is analyzed through the thermogravimetry (TG) technique coupled to a Fourier transform infrared spectroscopy (FTIR) equipment from room temperature (25 °C) to 900 °C, at a heating rate of 10 K min^?1 in an inert atmosphere. The catalytic effect of the addition of silicon to these samples before being subjected to a carbonization process is evaluated during this process. The results indicated that the primary reaction occurs in the temperature range between 400 and 680 °C, where the highest mass loss rate was observed. At the end of the heating process, the TG profile of the samples with silicon addition showed losses between 14.33 and 18.82% in mass, these values being slightly higher compared to the starting and demineralized samples. The release of water, light gases such as CO₂, CH₄, and species such as toluene, phenol and formic acid was identified in most of the samples. The presence of silica seems to favor the release of all these species, being more evident in one of the semi-anthracites studied. According to the results obtained, it is proved that the presence of silicon in samples subjected to carbonization processes has a catalytic effect that improves some characteristics of the new materials obtained, thus contributing to the use of carbon to get new materials.

     

Synthesis of nanometric β-barium metaborate powder from different borate solutions by ultrasound-assisted precipitation

In this study, the synthesis of barium metaborate powder (BaB₂O₄) was carried out by ultrasound-assisted precipitation using different borate solutions. Different solutions such as borax (Na₂B₄O₇, BD), boric acid (H₃BO₃, BA), and sodium metaborate (NaBO₂, SMB) were used in the synthesis and an ultrasonic immersion horn probe was used as the major source of ultrasound. The effect of reaction temperature and time, pH, and crystallization time on the BaB₂O₄ yield (%) was investigated. The ultrasound-assisted synthesis up to 90 % yield could be achieved using a 0.2 M BD solution at 80 °C, reacting for 5 min at pH 13 followed by 2 h of crystallization. Following crystallization, the obtained powder was heated up to 140, 250, 650, and 750 °C for 2.5 h, and it was shown that β-BaB₂O₄ nanometric powders were obtained after the 750 °C heat treatment.     

Thermoanalytical and dilatometric studies of the Al2O3–Cu–Mo hybrid composite

Journal of Thermal Analysis and Calorimetry - The present research is focused on the characterization of the composites from Al2O3–Cu–Mo system. The composites were prepared by slip...