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81.
《Ceramics International》2019,45(11):13958-13963
In this paper, Hot Pressing Flowing Sintering (HPFS) was successfully applied to the consolidation of silicon nitride ceramics at low sintering temperature. Fine-grained α/β-Si3N4 with high density was fabricated by HPFS at 1550 °C. The low temperature densification process was based on the hot pressing flow enhanced particle rearrangement mechanism. The shear stress which generated in the flowing process helped enhance the particle rearrangement with the lubrication of the liquid phase, which lead to collapse of the pores. The densification process was finished with minimum grain growth. Meanwhile, the rod-like β-Si3N4 nuclei was textured during the flowing process. The (101)/(210) ratio of β-Si3N4 was 0.09 on the plane perpendicular to the hot-pressing direction. The Vickers hardness and flexural strength of the sintered sample was 19.59 ± 0.36 GPa and 1022 ± 138 MPa, respectively. 相似文献
82.
83.
Hyune‐Jea Lee Robert C. Roberts Do Jin Im Se‐Jun Yim Heejin Kim Ji Tae Kim Dong‐Pyo Kim 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(50)
High‐resolution 3D‐printed stainless steel metal microreactors (3D‐PMRs) with different cross‐sectional geometry are fabricated to control ultrafast intramolecular rearrangement reactions in a comparative manner. The 3D‐PMR with circular channel demonstrates the improved controllability in rapid Fries‐type rearrangement reactions, because of the superior mixing efficiency to rectangular cross‐section channels (250 µm × 125 µm) which is confirmed based on the computational flow dynamics simulation. Even in case of very rapid intramolecular rearrangement of sterically small acetyl group occurring in 333 µs of reaction time, the desired intermolecular reaction can outpace to the undesired intramolecular rearrangement using 3D‐PMR to result in high conversion and yield. 相似文献
84.
The dynamic cellular facility layout problem (DCFLP) is a well-known NP-hard problem. It has been estimated that the efficient design of DCFLP reduces the manufacturing cost of products by maintaining the minimum material flow among all machines in all cells, as the material flow contributes around 10–30% of the total product cost. However, being NP hard, solving the DCFLP optimally is very difficult in reasonable time. Therefore, this article proposes a novel similarity score-based two-phase heuristic approach to solve the DCFLP optimally considering multiple products in multiple times to be manufactured in the manufacturing layout. In the first phase of the proposed heuristic, a machine–cell cluster is created based on similarity scores between machines. This is provided as an input to the second phase to minimize inter/intracell material handling costs and rearrangement costs over the entire planning period. The solution methodology of the proposed approach is demonstrated. To show the efficiency of the two-phase heuristic approach, 21 instances are generated and solved using the optimization software package LINGO. The results show that the proposed approach can optimally solve the DCFLP in reasonable time. 相似文献
85.
本文报道了8种新的芳氨基硫脲类化合物即1-(2'羧基苯基)-4-烷基氨基硫脲的电子轰击质谱。结果表明,该类化合物具有较强的分子离子峰M^+,分子离子的断裂以N-N键和C-N键的断裂为主,并伴随六员环和四员环过渡态氢重排,生成的碎片离子继续脱去水分子或其它小分子,从而产生一系列特征离子,包括骨架重排离子。4-位N上的取代烷基对谱图有一定的影响。 相似文献
86.
双酚A生产中母液裂解和重排的研究 总被引:1,自引:0,他引:1
对双酚A生产过程母液裂解重排系统,分别在第二裂解器和母液罐中加催化剂的两种不同工艺条件下,研究了温度对裂解重排反应的影响和精馏去除裂解产物中杂质的办法。试验结果表明,提高裂解温度可提高裂解回收率;在裂解气相产物冷凝前通过精馏可有效去除其中的色满等杂质;在母液罐或第二裂解器中加催化剂两种工艺下裂解重排反应无明显差别 相似文献
87.
以苯酚和邻甲酚为起始原料,合成了一个新型链状手性Schiff碱配体(5,5-亚甲基一双-[(R,R)-{N-(3-甲基水杨醛)-N-(3’,5’-双-叔丁基-2’-羟基苯乙酮)/-1,2-二苯乙二胺]),并对其进行表征。在邻甲酚的羟基邻位甲酰化过程中,用三乙胺代替六甲基磷酰三胺(HMPA)定位,取得了较好的效果。通过对传统的Fries重排进行研究和改进,以较高的产率合成了新的中间体(3,5-二叔丁基-2-羟基苯乙酮)。 相似文献
88.
89.
G. D. Yadav D. V. Satoskar 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1997,69(4):438-450
The rearrangement of epoxides over acidic and superacidic catalysts leads to several products with selectivity to the desired aldehyde depending upon the nature of the catalyst surface and the reaction conditions. This paper reports the studies with 1,2-epoxyoctane as a model compound, over several catalysts such as sulphated zirconia and zeolites, and dodecatungstophosphoric acid, phosphoric acid and ZnCl2 supported on silica, clay and carbon. The typical products of rearrangement are aldehyde, allylic alcohols, furan and aldol. A mechanism for the formation of these species is given. H3PO4/SiO2, dodecatungstophosphoric acid supported on K-10 clay and ZSM-5 were found to be efficient under different conditions. A kinetic model is presented. © 1997 SCI. 相似文献
90.
A facile synthesis of two novel diisocyanates containing methylene groups and preformed imide structure is described. Furthermore, six thermally stable and soluble polyimides were synthesized by polycondensation of these two diisocyanates with pyromellitic dianhydride (PMDA), 3, 3 ′,4, 4 ′‐benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene‐2,2‐bis‐(phthalic anhydride) (6FDA) in N,N ‐dimethyl acetamide. All monomers and polymers were characterized by conventional methods and their physical properties such as solution viscosity, solubility properties, thermal stability and thermal behaviour were studied. © 1999 Society of Chemical Industry 相似文献