Water vapor volatilization and oxidation induced surface cracking of environmental barrier coating systems: A numerical approach

A numerical model is developed for surface crack propagation in brittle ceramic coatings, aiming at the intrinsic failure of rare-earth silicate environmental barrier coating systems (EBCs) under combustion conditions in advanced gas turbines. The main features of progressive degradation of EBCs in such conditions are captured, including selective silica vaporization in the top coat due to exposure to water vapor, diffusion path-dependent bond coat oxidation, as well as crack propagation during cyclic thermal loading. In light of these features, user-defined subroutines are implemented in finite element analysis, where surface crack growth is simulated by node separation. Numerical results are validated by existing experimental data, in terms of monosilicate layer thickening, thermal oxide growth, and fracture behaviors. The experimentally observed quasi-linear oxidation in the early stage is also elucidated. Furthermore, it is suggested that surface crack undergoes rapid propagation in the late stage of extended thermal cycling in water vapor and leads to catastrophic failure, driven by both thermal mismatch and oxide growth stresses. The latter is identified as the dominant mechanism of penetration. Based on detailed analyses of failure mechanisms, the optimization strategy of EBCs composition is proposed, balancing the trade-off between mechanical compliance and erosion resistance.     

The relationship between crystallization and break temperature of mould flux

ABSTRACT

Many researchers believe that crystallization is responsible for drastic viscosity changes near the break temperature of mould flux; however, there are no reasonable experimental data to support this view. In this study, the complete crystallization process is recorded in situ by inhibiting the volatilization of fluoride, and the relationship between viscosity change and crystallization near the break temperature is studied. Mould flux with a basicity of 0.65 had no break temperature, and no crystallization occurs within the temperature range of the viscosity test. The other three mould fluxes begin to crystallize before the break temperature, but the crystal volume fractions at the break temperature are different. The break temperature of mould flux is the crystallization temperature with a critical crystal volume fraction, which is related to the viscosity before the break temperature. The higher the viscosity, the smaller the critical crystal volume fraction. Therefore, break temperature?≤?initial crystallization temperature.     

Solution-Processed Organic Solar Cells with High Open-Circuit Voltage of 1.3 V and Low Non-Radiative Voltage Loss of 0.16 V

Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔV_non-rad) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (V_oc). Herein, OSCs are fabricated by adopting two pairs of D–π–A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (E_CT) as high as 1.70–1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔE_CT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10⁻³ and 1.0 × 10⁻³ are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔV_non-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high V_oc of 1.3 V. The ΔV_non-rad of 0.16 V and V_oc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far.     

粗金粉中金的氯浸-控制电位还原精炼

某冶炼厂氰化金泥还原得到的粗金产品纯度较低，采用氯浸-还原工艺对粗金进行了精炼提纯。在生产工艺中采用盐酸+氯酸钠对粗金进行氯浸溶解，用焦亚硫酸钠控制电位选择性还原浸出液中的金。采用补水-冷却使银和铅从氯浸液充分沉淀析出，通过调整pH值、改变焦亚硫酸钠添加方式、精确控制还原电位等方法，产品金锭达到IC-Au99.99标准。两年的生产实践创造了明显的经济效益。     

Simultaneous extraction of gold and zinc from refractory carbonaceous gold ore by chlorination roasting process

A novel process based on chlorination roasting was proposed to simultaneously recover gold and zinc from refractory carbonaceous gold ore by using NaCl as chlorination agent. The effects of roasting temperature, roasting time and NaCl content on the volatilization rates of gold and zinc were investigated. The reaction mechanism and the phase transition process were also analyzed by means of SEM, EDS and XRD. The results demonstrated that under the optimal conditions of NaCl content of 10%, roasting temperature of 800 °C, roasting time of 4 h and gas flow rate of 1 L/min, the rates of gold and zinc were 92% and 92.56%, respectively. During low-temperature chlorination roasting stage, a certain content of sulfur was beneficial to the chlorination reactions of gold and zinc; and during high-temperature chlorination roasting stage, the crystal structure of vanadium-bearing mica was destroyed, and the vanadium-containing oxides were beneficial to the chlorinating volatilization of gold and zinc. Eventually, the chlorinated volatiles of gold and zinc could be recovered by alkaline solution.     

Volatilization of fluorine in a CaO–SiO2–CaF2-based system with the substitution of Na2O with K2O

Cuspidine-based systems are used to control the crystallization in mold fluxes, which is enabled by CaF₂ additions. However, excess CaF₂ increases the corrosion of casting machines. Therefore, Na₂O and K₂O are added to the mold flux system to ensure an optimized crystallization and lubrication ability of the flux with the CaF₂ content. This study investigated the effect of substituting Na₂O with K₂O on the volatilization of fluorine in a CaO–SiO₂–CaF₂-based slag system at high temperatures. The substitution of Na₂O with K₂O was performed at 5 mol% intervals. The volatilization was observed by thermogravimetric analysis under several isothermal conditions. The mass loss was measured at a heating rate of 5, 10, and 20 K/min. As the temperature increased, the volatilization of the mixed samples increased. The activation energy was calculated using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. A kinetic analysis of the volatilization of fluorine was conducted using the calculated parameters and several known kinetic models. Consequently, the volatilization of the Na-rich sample was controlled by chemical reactions and that of the K-rich sample was identified to be controlled by a phase-boundary-controlled reaction. These results suggest that the addition of mixed alkali oxide promote the volatilization during the early stages of the reaction. From the post-experimental composition analyses, the remaining Na and K in the samples suggested a different mechanism for the Na and K volatilization. The volatilization of Na increased with time, whereas K volatilized easily during the beginning of the reaction.     

质子酸催化合成α-氯代十二酸工艺研究

采用廉价的浓硫酸为催化剂,氧气为自由基捕集剂,以十二酸为原料,经氯化合成α-氯代十二酸。系统考察了反应温度、催化剂用量、氯气流量、氧氯比、反应时间等因素的影响,得到最佳工艺条件:十二酸20 g,在反应温度135℃、催化剂10%、氯气流量50 mL·min-1、vO2/vCl2=1∶2、反应时间3 h,可实现十二酸基本完全转化,目标产物α-氯代十二酸选择性达到94.5%。     

石蜡氯化反应异常停止的原因

氯化石蜡生产中因液氯质量问题引起反应终止,分析了影响液氯质量的因素（主要是液氯中硫酸、二氧化硫、铁的化合物、水分、光气及二氧化氯等含量超标）,提出了解决措施.     

顶空-气相色谱法在车用氯化聚氯乙烯制品总碳挥发量测试中的应用

采用顶空-气相色谱法测定氯化聚氯乙烯(CPVC)制品中有机挥发物总碳挥发量。通过对平衡温度、平衡时间以及颗粒大小的探索性试验,确定了本方法的最佳测试条件。以丙酮为外标物得到的标准曲线的线性相关系数为0.999 8,样品测试结果的相对标准偏差为1.36,加标回收率可达99.8%。     

石墨炉原子吸收光谱法测定奶粉中的六价铬

基于Cr(Ⅲ)与噻吩甲酰三氟丙酮(TTA)生成的络合物在石墨炉中的挥发性,建立一种前处理简单、灵敏度高的测定奶粉中六价铬的分析方法。对样品的消化方式、Cr(Ⅲ)与TTA络合的酸度、试剂的加入量、超声波水浴的温度和时间、静置时间与石墨炉挥发Cr(Ⅲ)的原子化条件进行探讨。结果表明,Cr(Ⅵ)在0.002~0.010mg·L-1浓度内呈良好线性关系(r=0.9995)。奶粉样品中Cr(Ⅵ)不同加入量的平均回收率为78%~93%,其相对标准偏差为3.8%~9.4%,检出限为0.4 mg·L-1。方法具有分析速度快、灵敏度高、干扰少、操作简便等特点,应用于奶粉中六价铬的测定获得了满意的结果。