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1.
Multi-step reaction processes are frequently encountered in the synthesis of pharmaceuticals, separate study on each step however is easily neglected. Herein, we separately investigated two reaction steps for the synthesis of an intermediate (DTG-6) of an anti-HIV drug dolutegravir (DTG) in microreactors. The first step (i.e., deprotection of DTG-4) was optimized to achieve a high DTG-5 yield (i.e., 96.7%) in the microreactor after the parametric screening on the DTG-4 concentration, methanesulfonic acid loading, molar ratio of reaction components, and so forth. Reaction kinetics was revealed based on substantial experimental data and mechanism cognition. Validation experiments showed the accuracy of this reaction kinetics. After thoroughly understanding this deprotection step, we combined it with the following annelation step in a cascade microreactor system for the two-step synthesis of DTG-6 with a much higher yield even at a remarkably shorter residence time compared with literature reports, thus indicating efficient process intensification.  相似文献   
2.
Mechanical properties of glasses can be significantly increased by inducing surface crystallization of a low coefficient of thermal expansion phase. In this work, we produced surface crystallized lithia-alumina-silica glass-ceramics with different crystallized layer thicknesses and analysed the resulting residual stresses and their effect on mechanical properties. The residual stress magnitude was estimated by analytical and experimental methods, as well as numerical modeling. The surface compressive stress reached 390 MPa and 490 MPa, as given by the analytical and experimental determination, respectively. These stresses prevented radial cracking in microhardness and scratch tests. The best glass-ceramic achieved a Vickers hardness of 7.5 GPa and fracture strength of 680 ± 50 MPa in a ball-on-three-ball test. These glass-ceramics are translucent, providing 50–60% transmittance over the visible wavelength spectrum (1.3 mm-thick-sample). This study unveiled the causes of improved mechanical properties and validates the concept that surface crystallization is a valuable technique for developing high strength glass-ceramics.  相似文献   
3.
《Ceramics International》2022,48(10):14349-14359
The influence of heat-treatment temperatures (700 °C, 900°C, 1200 °C) on the phase, physical properties, crystallization rate, and in vitro properties of the solution combustion synthesized silicon-doped calcium phosphates (CaPs) were investigated. The thermodynamic aspects (enthalpy, entropy, and free energy) of the synthesis process and the crystallographic properties of the final samples were first predicted and then confirmed using density functional theory (DFT). Results demonstrated that the crystallization rate was controlled by the fuel(s) type (glycine, citric acid, and urea) and the amounts of Si4+ ions (0, 0.1, 0.4 mol). The highest calculated crystallization rate values of the un-doped, 0.1, and 0.4 mol Si-doped samples were 64%, 22%, 38%, respectively. The obtained results from the DFT simulation revealed that crystal growth in the direction of c-axis of hydroxyapatite (HAp) structure could change the stability of (001) surface of (HAp). Also, the computational data confirmed the adsorption of Si–OH groups on the (001) surface of HAp during the SCS process with an adsorption energy of 1.53 eV. AFM results in line with DFT simulation showed that the observed change in the surface roughness of Si-doped CaPs from 2 to 8 nm could be related to the doping of Si4+ ions onto the surface of CaPs. Besides, the theoretical and experimental investigation showed that crystal growth and doping of Si4+ ions could decrease the activation energy of oxygen reduction reaction (ORR). Furthermore, the results showed that the crystallized HAp structure could have great potential to efficiently reduce oxidative stress in human body.  相似文献   
4.
Recovery of hydrogen (H2) from H2-containing gas mixtures has great significance for energy conservation, cost reduction and benefit increase. However, the common separation methods have the ubiquitous problem due to phase equilibrium principle and results in the conflict between H2 concentration and H2 recovery rate in the product gas. Consequently, an innovative conception of hydrate-membrane coupling approach is proposed in this work. In the separation process, hydration and membrane permeation two separation driving forces coexist to achieve the aim of strengthening mass transfer kinetics. H2 and non-H2 components (hydrocarbons) are synchronously and directionally selected by membrane and hydrate to improve different phase compositions. Therefore, the gas in feed side could keep relatively high two separation driving forces (H2 fugacity and hydrocarbons fugacity). The results show that the coupling method could synchronously increase both the concentration and the recovery rate of H2 in the product gas. At the same time, the volume and concentration of the hydrocarbons in hydrate both increases effectively. It indicates that hydrate and membrane separation methods support each other in the separation process. The hydrate-membrane coupling method fundamentally solves the issue of the decreasing driving force resulting from single separation method and phase equilibrium relationship.  相似文献   
5.
以铜阳极泥为原料,研究了在空气气氛下硫酸化焙烧蒸硒过程的影响规律和动力学,通过硫酸化焙烧蒸硒实验,研究了影响蒸硒过程的主要因素和控制过程,得到了焙烧蒸硒过程的动力学方程,可为优化铜阳极泥硫酸化焙烧蒸硒工艺提供理论指导。试验结果表明,铜阳极泥硫酸化焙烧蒸硒效果受焙烧温度和焙烧时间的影响较大,但受空气流速和酸矿比的影响较小。在焙烧温度723K、焙烧时间20min、空气流速为200L/h、酸矿比为0.75的较优条件下,蒸硒渣中硒含量由8.50%降至0.24%,硒挥发率为96.54%。蒸硒过程受化学反应动力学控制,表观活化能为42.509 kJ/mol。  相似文献   
6.
7.
摘要:DP1180钢相变动力学方程的构建,有利于其力学性能的精准调控。利用Gleeble 3500对DP1180钢进行相变点测定,结合切线法、金相 硬度法研究了DP1180钢在冷却过程中的显微组织演变规律,绘制连续冷却转变曲线(CCT),并基于相变产物对相变动力学方程(JMAK方程)进行了修正。结果表明:冷速为0.5~1℃/s时,组织为铁素体(F)和贝氏体(B);冷速为2℃/s时,有马氏体(M)出现;冷速为10℃/s时,组织为贝氏体(B)和马氏体(M);冷速大于20℃/s时,组织以马氏体(M)为主;显微硬度随冷速的增加而升高;基于不同相变产物对n值的影响规律,对传统JMAK方程进行修正,构建了基于相变产物的相变动力学方程,预测精度得到提升。  相似文献   
8.
In this study, the Bayan Obo rare earth concentrates mixed with Na2CO3 were used for roasting research. The phase change process of each firing stage was analyzed. The kinetic mechanism model of the continuous heating process was calculated. This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis. Using X-ray diffraction (XRD), Fourier infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, the reaction process and the existence of mineral phases were analyzed. The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics. The phase transition results show that carbonate-like substances first decompose into fine mineral particles, and CaO, MgO, and SiO2 react to form silicates, causing hardening. Further, REPO4 and NaF can directly generate CeF3 and CeF4 at high temperatures, and a part of CeF4 and NaF forms a solid solution substance Na3CeF7. Rare earth oxides calcined at a high temperature of 750 °C were separated to produce Ce0.6Nd0.4O1.8, Ce4O7, and LaPrO3+x. Then, BaSO4, Na2CO3, and Fe2O3 react to form barium ferrite BaFe12O19; the kinetic calculation results show that during the continuous heating process, the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440–524 °C, and the reaction order n reaches the maximum, which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy. The mechanism function is F(α) = [?ln (1?α)]1/3. The reaction order n reaches the minimum in the temperature range of 680–757 °C, and the apparent activation energy E is large. The difficulty of the reaction increases during the final stage. The reaction mechanism function is F(α) = [1?(1?α)1/3]2. Observing the entire reaction stage, the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion (spherical symmetry).  相似文献   
9.
通过测试水泥浆体的凝结时间、抗压强度、电阻率,同时结合水化产物分析及热力学模拟,研究了不同掺量钢渣粉对硫铝酸盐水泥水化行为的影响规律。结果表明,随着钢渣粉质量掺量的增大,初凝时间呈先延长后缩短的趋势,且在掺量为20%时达到最大值。在28 d龄期内,掺入钢渣粉的水泥硬化浆体抗压强度均小于未掺入钢渣粉的硬化浆体,但在龄期达到60 d和90 d时,掺入40%钢渣粉试样的抗压强度均大于未掺入钢渣粉的试样。钢渣粉与硫铝酸盐水泥复合浆体的电阻率在水化初始阶段随着钢渣粉掺量的增大而增大,在水化后期(约3 h后)则随钢渣粉掺量的增大而减小。在1 d龄期内,钢渣粉掺量为40%的试样中的钢渣粉发生了水化反应,使得水泥浆体在减速期的水化速率最大。由热力学模拟结果可知:在钢渣粉掺量为40%的试样中,C2S在10 h后开始进行水化反应,C2ASH8则在168 h后开始生成;当钢渣掺量大于15%时,随着钢渣粉掺量的增大,钙矾石和铝胶的生成量逐渐减少,C2ASH8的生成量逐渐增多。  相似文献   
10.
《Ceramics International》2022,48(9):11988-11997
We have studied peculiarities in the formation of single-crystalline barium titanate (BaTiO3) nanorods from a glycolate-mediated complex via a single-step hydrothermal process under different supersaturation (SR) conditions. X-ray diffraction (XRD) showed the formation of pure BaTiO3 with an SR of above 19. The tetragonality for the BaTiO3 (c/a) reached 1.013 at SR = 19–29 and dropped to 1.010 for SR = 39. According to the transmission electron microscopy (TEM) and XRD analyses, the rod-shaped particles exhibited single crystallinity and crystal growth along the [001] plane. With scanning electron microscopy (SEM), the morphological evolution from a plate-shaped intermediate precursor (SR = 6–9) to a rod-shaped product with an aspect ratio of 6–9 (SR = 19–29), and to non-polar material with an irregular structure (SR = 39), was observed. The negative slope, linear dependence of the particles’ width and length on the supersaturation level in the range SR = 19–39 was established for the first time. The replacement of the prevailing crystallization mechanism from in-situ topotactic transformation into dissolution-precipitation above SR = 19 was observed. It was shown that with a simple regulation of the SR, the structural and morphological characteristics of the obtained BaTiO3 nanoparticle can be effectively tuned.  相似文献   
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