Biodiesel from rapeseed oil,methanol and KOH. 2. Composition of solution of KOH in methanol as reaction partner of oil

The composition of the solutions of solid KOH in methanol has been measured by means of determinating the content of water in the equilibrium mixture. The dependence of the equilibrium reaction extent ζ¹ and the concentration equilibrium constant Kc on the ratio of the initial amounts of methanol and KOH containing 0.164 and 16.27 wt‐% of water are determined and theoretically described. The concentration of CH₃O¯ ions can be calculated with these results. This value is very important for the course of the alkaline catalyzed methanolysis of rapeseed oil to biodiesel, because the methoxide ions are the true catalyst of such a transesterification.     

Convex corners undercutting and rhombus compensation in KOH with and without IPA solution on (1 1 0) silicon

The present investigation introduces convex corners undercutting and results of rhombus compensation patterns in 40% aqueous KOH solution and in KOH saturated with isopropanol (IPA) solution. All experiments are carried out on (1 1 0) silicon at 70 °C. Undercuts take place on convex corners in both solutions. Moreover, the front etch planes governing undercut vary with solutions. Rhombus compensations are used to correct the undercut. Perfect acute corner without residue is obtained, and there are only some residue structures on both sides of obtuse convex corners in KOH with IPA solution, which are better results than those in pure aqueous KOH solution.     

山茶油脂肪酸甲酯化条件研究

油脂甲酯法是应用气相色谱法测定油脂脂肪酸组成一个必不可少预处理工序。该文报道对比研究KOH―甲醇溶液法、H2SO4―甲醇溶液法对山茶油进行甲酯化效果,着重探讨振荡温度、振荡时间、催化剂用量等因素对山茶油甲酯化效果影响规律,通过气相色谱法测定油酸峰面积及油酸甲酯转化率为考核指标,优化KOH―甲醇溶液法和H2SO4―甲醇溶液法甲酯化条件,并提出酸碱结合甲酯化新方法,研究结果表明,采用酸碱结合法对山茶油进行甲酯化效果优于KOH―甲醇溶液法和H2SO4―甲醇溶液法,对应用气相色谱法测定油脂脂肪酸组成具有实际指导意义。     

Preparation of activated biomass carbon from pine sawdust for supercapacitor and CO2 capture

Biomass based carbon has captured more and more attention because it is environmentally friendly and has properties of low cost and ideal sustainability. In this study, three kinds of activated biomass carbons (ie, ABC-700, ABC-800 and ABC-900) were first carbonized through pine sawdust pyrolysis and then activated using KOH under three different activation temperatures (ie, 700°C, 800°C and 900°C). The structure properties of the prepared activated biomass carbons were characterized by N₂-adsorption/desorption, SEM, TEM, XRD, Raman, XPS, TG and ultimate analysis. To clarify the activation mechanism, the gas products produced during KOH activation process were measured online with an ETG gas analyzer. The performance of the activated biomass carbons derived from pine sawdust for supercapacitor and CO₂ capture was then evaluated. The predominant gas products during the activation process are H₂ and CO. It indicates that the porous structure was created by using an enhanced etching reaction between carbon atoms and KOH. An increment of the activation temperature from 700 to 900°C results in the increase of surface area (from 1728.66 to 2330.89 m²/g) and total pore volume (from 0.671 to 1.914 cm³/g). Among the three samples, ABC-900 exhibits the maximal specific capacitance of 175.6 F·g⁻¹ and high energy density of 24.39 Wh·kg⁻¹ at the 0.5 A·g⁻¹. And the ABC-700 shows the maximal CO₂ capture capacity of 4.21 mmol/g and high selectivity of CO₂ over N₂ at 298 K and 1 bar. In addition, ABC-700 also has excellent stability and reproducibility after 15 times adsorption-desorption cycles. The unexceptionable electrochemical performance and adsorption capacity of the biomass-carbons show its broad application prospects in the field of supercapacitors and CO₂ capture.     

A periodic array of silicon pillars fabricated by photoelectrochemical etching

A periodic array of silicon pillars was photoelectrochemically fabricated using the two-step etching process with a n-type Si (1 0 0) substrate. Two key factors, backside illumination and anodic bias, were required to obtain a high-aspect ratio macropore array of silicon. It was found that the initial pore could be separated into two different pores when the applied anodic bias was greater than a certain critical value. The pore size of the macroporous silicon with a high porosity was increased by anisotropic etching in an alkaline solution. Due to destruction of the pore sidewalls, KOH etching allowed for the fabrication of silicon pillars on a large-scale wafer with an improved uniformity. The anisotropic etching behavior of KOH solution led to necking of the silicon pillars when the etching time exceeded 60 s.     

KOH亚熔盐法分解钛铁矿

以KOH亚熔盐为反应介质,研究了KOH浓度、反应温度与时间、搅拌速率和碱/矿比等因素对钛铁矿在KOH亚熔盐体系中分解率的影响. 结果表明,反应温度、反应时间及KOH浓度为主要影响因素,提高反应温度及KOH浓度均有利于钛铁矿在KOH亚熔盐中的分解,但当反应温度超过260℃时,钛铁矿的分解率又随反应温度的升高而降低;在KOH浓度80%(w)、搅拌速度700 r/min、反应温度260℃、碱/矿质量比5、反应时间180 min的条件下,钛铁矿在KOH亚熔盐中的分解率超过95%. 此外,钛铁矿在KOH亚熔盐中的分解符合未反应收缩核模型,受界面化学反应控制.     

Single Unit-Cell Layered Bi2Fe4O9 Nanosheets: Synthesis,Formation Mechanism,and Anisotropic Thermal Expansion

As an important multiferroic material, pure and low-dimensional phase-stable bismuth ferrite has wide applications. Herein, one-pot hydrothermal method was used to synthesize bismuth ferrite. Almost pure Bi₂Fe₄O₉, BiFeO₃, and their mixture were successfully obtained by controlling the KOH concentration in the hydrothermal solutions. The as-prepared Bi₂Fe₄O₉ products were crystalline with Pbam space group, had nanosheet morphology, and tended to aggregate into nanofloret or random stacking. Each Bi₂Fe₄O₉ nanosheet was a single crystal with (001) plane as its exposed surface. Single unit-cell layered Bi₂Fe₄O₉ nanosheets had a uniform thickness of 1 nm. The surface energies of various (100), (010), and (001) planes were 3.6–4.0, 5.6–15.1, and 1.7–3.0 J m⁻², respectively, in the Bi₂Fe₄O₉ crystal. The formation mechanism and structural model of the as-prepared single unit-cell layered Bi₂Fe₄O₉ nanosheets have been given. The growth of Bi₂Fe₄O₉ nanosheets was discussed. Thermal analysis showed that the Bi₂Fe₄O₉ phase was stable up to 1260 K. The thermal expansion behavior of the Bi₂Fe₄O₉ nanosheet was nonlinear. The thermal expansion coefficients of the ultrathin Bi₂Fe₄O₉ nanosheets on the a-, b-, c-axes, and on the unit-cell volume V were determined, showing an anisotropic thermal expansion behavior. This study is helpful for the controllable synthesis of ultrathin Bi₂Fe₄O₉ nanosheets.     

Activated carbon from Water Hyacinth as electrocatalyst for oxygen reduction reaction in an alkaline fuel cell

Water Hyacinth is an invasive aquatic plant with an excellent carbon source with heteroatoms. Activated carbon is a viable choice as an electrocatalyst for fuel cell applications. Based on the plant's leaves, stem, and root, we got activated carbons using KOH at 730 °C with N₂. The samples, named WH_LA730, WH _SA730, and WH_RA730, were examined as electrocatalysts for oxygen reduction reaction in 0.5 M KOH. The high surface area and nitrogen content in the activated carbon provided a good electrochemical activity. The potential reaction for WH_SA730 was at 0.9 V and 0.85 V for WH_RA730. Both samples showed a promising activated carbon for the alkaline fuel cell compared to WH_LA730.     

铝在碱性电解液中的阳极行为

用电化学方法研究了Al(99.999%￣99.5%)在4mol/LKOH溶液中的阳极行为,结果表明:杂质(Fe,Si,Cu)含量递增,铝的传递电阻变小、腐蚀速度增大,达到稳定开路电位所需时间延长,但50℃时商业铝Al99.82%的极化程度最小,在-1.224V下有400mA/cm2大电流产生;温度升高而铝阳极的活化作用随之增强,但腐蚀也加剧;铝电极在5mmol/LNa2SnO3 4mol/LKOH中的浸泡时间为20min较适合;添加剂Na2SnO3对铝的腐蚀抑制、电化学性能改善都产生有利影响,其最佳浓度为5mmol/L。