共查询到20条相似文献,搜索用时 78 毫秒
1.
2.
3.
4.
5.
用一维1H、13C NMR谱、DEPT 13C NMR谱、选择性远程DEPT 13C NMR、1H-1H COSY和13C-1H COSY二维核磁共振技术研究了南海海绵Dysidea fragilis中的两个倍半萜herbadysidolide(1)和furodysinin lactone(2),确认了化学结构,并对其13C NMR和1H NMR谱进行了归属.药理活性试验表明:1和2具有一定的心血管活性. 相似文献
6.
7.
8.
9.
10.
11.
聚丙烯腈热裂解产物的ESR和固体13C NMR研究 总被引:3,自引:0,他引:3
用电子自旋共振(ESR)和固体13C NMR研究了聚丙烯腈(PAN)在不同裂解温度(TP)下的结构变化,当TP从250℃增加到600℃,ESR信号线形没有变化,g值与TP无关,ΔHPP减小,自旋浓度(NS)开始增加,TP进一步升高,NS又减少.13C NMR谱指出在不同TP下谱峰发生很大变化,与另文报道的红外及X-射经衍射结果一致,随TP升高,PAN逐渐脱去小分子形成具有环化共轭结构的产物. 相似文献
12.
简要介绍了核磁共振(NMR)方法在煤炭组成及热解过程分析中的应用. 目前用于煤炭分析的NMR方法主要包括固体NMR和液体NMR. 从检测手段来看,以13C NMR和1H NMR方法较多,15N NMR, 19F NMR和31P NMR也在煤炭的分析中发挥了重要作用. 其中用于区分和选择性检测不同官能团的NMR谱编辑方法的发展, 进一步推进了NMR在煤炭化工中的应用. 相似文献
13.
Dong Zeng Shengteng Hu Alan N. Sayre Hamid Sarv 《Proceedings of the Combustion Institute》2011,33(2):1707-1714
The secondary reactions of volatile compounds, including coal tar and light gases, accounts for a great portion of soot formation and the subsequent heat release and pollutant emissions in the combustion zone. While coal primary pyrolysis has been extensively studied over the last few decades and several network pyrolysis models has been developed to describe this process, coal secondary pyrolysis is still not well understood. The Babcock and Wilcox Company has been investigating coal secondary pyrolysis in order to develop a comprehensive mechanism for inclusion in predictive computational fluid dynamics and coal combustion models. Supportive experiments were carried out in an entrained-flow reactor. Tar was extracted from the pyrolysis byproducts of seven coals of widely-distributed rank at temperatures ranging from 923 to 1473 K, and analyzed by 13C NMR. Tars formed from higher rank coals generally demonstrated higher sooting propensities. This rank-dependent sooting propensity is associated with tar’s chemical structure properties. With increased heat treatment severity, tar molecules lose a substantial amount of aliphatic attachments, and the average size of substitution per cluster decreases. Compared to tars formed from high-rank bituminous coals, those formed from low-rank sub-bituminous coals have a larger attachment portion, higher averaged substitution, and higher oxygen-containing functional groups. These differences contribute to the higher cracking propensity observed for low-rank coal tars. 相似文献
14.
Porous ceramic materials of SiC were synthesized from carbon matrices obtained via pyrolysis of natural cork as precursor. We propose a method for the fabrication of complex-shaped porous ceramic hardware consisting of separate parts prepared from natural cork. It is demonstrated that the thickness of the carbon-matrix walls can be increased through their impregnation with Bakelite phenolic glue solution followed by pyrolysis. This decreases the material’s porosity and can be used as a way to modify its mechanical and thermal characteristics. Both the carbon matrices (resulted from the pyrolysis step) and the resultant SiC ceramics are shown to be pseudomorphous to the structure of initial cork. Depending on the synthesis temperature, 3C-SiC, 6H-SiC, or a mixture of these polytypes, could be obtained. By varying the mass ratio of initial carbon and silicon components, stoichiometric SiC or SiC:С:Si, SiC:С, and SiC:Si ceramics could be produced. The structure, as well as chemical and phase composition of the prepared materials were studied by means of Raman spectroscopy and scanning electron microscopy. 相似文献
15.
The synthesis of SiC–Si–C materials by siliconizing porous carbon matrices has been considered, and a method of determining their phase composition has been devised. Preforms of two types have been siliconized, i.e., biomorphic carbon matrices prepared by wood pyrolysis and artificial porous graphites prepared by mixing and compacting carbon powders with an organic binder. The calculated phase compositions are in good agreement with microstructure metallographic examination data. 相似文献
16.
A. I. Shelykh B. I. Smirnov I. A. Smirnov A. R. de Arellano-Lopez J. Martinez-Fernandez F. M. Varela-Feria 《Physics of the Solid State》2006,48(2):216-217
In the temperature range 100–650 K, the linear expansion coefficient β was measured for the SiC/Si biomorphic composite, a new cellular ecoceramic fabricated from a porous cellular carbon matrix prepared through pyrolysis of wood (white eucalyptus) in an argon ambient with subsequent infiltration of molten Si into the channels of the matrix and the formation of 3C-SiC. The SiC/Si samples studied had an “excess” ~30% volume concentration of Si and a porosity of ~13–15%. The measurements were conducted on samples cut along (β∥) and across (β⊥) the tree growth direction. The measured values of β(T) of SiC/Si are compared with literature data available for the linear expansion coefficients of Si and 3C-SiC. 相似文献
17.
以聚碳硅烷(PCS)为原料,通过炉内成球技术制备SiC空心陶瓷微球,讨论辐照交联和高温碳化对SiC陶瓷微球化学成分、成键结构和表面特性的影响。结果表明,PCS在热处理过程中的失重率约为35%,其分解温度在400~800℃之间。微球经电子束辐照后会生成以Si—C—Si和Si一O一Si骨架结构为主的三维网络交联结构。碳化过程使Si—C_32键,Si—H键和C—H键断裂,生成以Si—C为主的无定形态Si(C。辐照的均化作用使高温热处理碳化的微球能够维持完好的球壳结构,且具有更好的表面粗糙度和平整性。 相似文献
18.
A. I. Shelykh B. I. Smirnov T. S. Orlova I. A. Smirnov A. R. de Arellano-Lopez J. Martinez-Fernandez F. M. Varela-Feria 《Physics of the Solid State》2006,48(2):229-232
The electrical resistivity ρ and the thermopower coefficient α of a SiC/Si biomorphic composite fabricated from a porous carbon matrix [prepared through pyrolysis of wood (white eucalyptus)] by infiltrating molten Si into the empty channels of the matrix were measured in the temperature ranges 100–950 and 100–750 K, respectively. Silicon reacts chemically with the carbon of the matrix to produce 3C-SiC, which, in combination with the excess Si unreacted with carbon, forms the SiC/Si biomorphic composite. The SiC/Si samples studied had a concentration of “excess” Si of ~30 vol % and a porosity of ~13–15 vol %. Measurements of ρ were carried out on samples cut either along (ρ∥) or across (ρ⊥) the tree growth direction, and α was measured on a sample cut along the tree growth direction. 相似文献
19.
L. S. Parfen’eva T. S. Orlova N. F. Kartenko N. V. Sharenkova B. I. Smirnov I. A. Smirnov H. Misiorek A. Jezowski J. Mucha A. R. de Arellano-Lopez J. Martinez-Fernandez F. M. Varela-Feria 《Physics of the Solid State》2006,48(3):441-446
The thermal conductivity κ and electrical resistivity ρ of a white-eucalyptus cellular carbon preform used to fabricate silicon-carbide-based (SiC/Si) biomorphic ceramics have been measured in the 5-to 300-K temperature interval. The carbon preform was obtained by pyrolysis (carbonization) of white-eucalyptus wood at 1000°C in an argon ambient. The κ(T) and ρ(T) relations were measured on samples cut along the tree growth direction. The experimental data obtained were processed. 相似文献
20.
《Composite Interfaces》2013,20(4):383-393
Two types of SiC fiber tows (Hi-Nicalon? and Hi-Nicalon S?) were coated with stabilized ZrO2 and composited using preceramic polymer impregnation pyrolysis to form SiC/SiCf minicomposites. Properties of the fiber/matrix interface in composites were investigated using the indentation method in which a pyramidal indenter was used to push on an individual fiber and cause sliding at the interface. The interfacial frictional stresses were determined from the force–displacement relation. The composites reinforced by the ZrO2-coated fibers have smaller interfacial frictional stresses than composites reinforced by the initial fibers and show fibers sliding relatively more easily with respect to the SiC matrix. 相似文献