Nitrocellulose,or cellulose nitrate,has received considerable interest due to its various applications,such as propellants,coating agents and gas generators.However,its high mechanical sensitivity caused many accident...Nitrocellulose,or cellulose nitrate,has received considerable interest due to its various applications,such as propellants,coating agents and gas generators.However,its high mechanical sensitivity caused many accidents during its storage and usage in ammunition.In this work,two kinds of insensitive step ladderstructured nitrocellulose(LNC)with different nitrogen contents were synthesized.The products were characterized by FT-IR,Raman,XRD,SEM,elemental analysis,TGA,DSC,accelerating rate calorimeter analysis(ARC),and drop weight test to study their molecular structure,thermal characteristics and desensitization performance.Compared with raw nitrocellulose,LNC has a sharper exothermic peak in the DSC and ARC curves.The H50values of the two kinds of LNC increased from 25.76 to 30.01 cm for low nitrogen content and from 18.02 to 21.84 cm for high nitrogen content,respectively.The results show that the ladder-structure of LNC which provides regular molecular arrangement and a soft buffer made with polyethylene glycol could affect the energy releasing process of LNC and reduce the sensitivity of LNC.Insensitive LNC provides an alternative to be used as a binder in insensitive propellants formulation.展开更多
Because of the mixed grain and coarse grain structure, the long heat treatment cycle and large energy conservation in the heavy cylinder heat treatment process, the up ladder type and terraced type normalizing heat tr...Because of the mixed grain and coarse grain structure, the long heat treatment cycle and large energy conservation in the heavy cylinder heat treatment process, the up ladder type and terraced type normalizing heat treatment of heavy cylinder after rolling were put forward. The microstructure and mechanical properties of 2.25Cr1Mo0.25 V steel after the up ladder type normalizing, terraced type normalizing and isothermal type normalizing were studied. Experimental results show that： 1） For the grain refinement, the twice terraced type normalizing is better than the up ladder type and isothermal type normalizing, and the average grain size is 18 μm; 2） The yield strength, tensile strength and-30℃ charpy impact energy after twice terraced type normalizing are 681 MPa, 768 MPa and 181 J, respectively, and the mechanical properties are better than those of the up ladder type and isothermal type normalizing; 3） Compared with the isothermal type normalizing, the holding time of terraced type normalizing can be shortened by 30%, which greatly reduces the energy consumption.展开更多
An Estonian passenger ferry carrying 867 people sank in a storm off southwest Finland on September 28 and officials said fewer than 100 had been rescued. The Estonia, sailing from the Estonian capital of Tallinn to St...An Estonian passenger ferry carrying 867 people sank in a storm off southwest Finland on September 28 and officials said fewer than 100 had been rescued. The Estonia, sailing from the Estonian capital of Tallinn to Stockholm, sank with dramatic speed dragging hundreds of passengers and crew into the chilly Baltic Sea. A massive rescue effort was launched with ships and holicopters from Finland, Sweden and denmark.展开更多
The officer- selecting system is an important part of the administrative legal system of the ancient China. In the ancient times,there were different officer- selecting systems in China,such as the hereditary system,t...The officer- selecting system is an important part of the administrative legal system of the ancient China. In the ancient times,there were different officer- selecting systems in China,such as the hereditary system,the recommendatory system,the nine- rank system and the imperial examination system and so on. Different officer- selecting systems are reasonable and have some limitations at the same time. Besides,they own some realistic significance for the cadre- selecting system of the present.展开更多
基金supported in part by the National Natural Science Foundation of China(No.22075146)。
文摘Nitrocellulose,or cellulose nitrate,has received considerable interest due to its various applications,such as propellants,coating agents and gas generators.However,its high mechanical sensitivity caused many accidents during its storage and usage in ammunition.In this work,two kinds of insensitive step ladderstructured nitrocellulose(LNC)with different nitrogen contents were synthesized.The products were characterized by FT-IR,Raman,XRD,SEM,elemental analysis,TGA,DSC,accelerating rate calorimeter analysis(ARC),and drop weight test to study their molecular structure,thermal characteristics and desensitization performance.Compared with raw nitrocellulose,LNC has a sharper exothermic peak in the DSC and ARC curves.The H50values of the two kinds of LNC increased from 25.76 to 30.01 cm for low nitrogen content and from 18.02 to 21.84 cm for high nitrogen content,respectively.The results show that the ladder-structure of LNC which provides regular molecular arrangement and a soft buffer made with polyethylene glycol could affect the energy releasing process of LNC and reduce the sensitivity of LNC.Insensitive LNC provides an alternative to be used as a binder in insensitive propellants formulation.
基金Project(51305388)supported by the National Natural Science Foundation of ChinaProject(BJ2014055)supported by the Youth Talent Projects of Colleges in Hebei Province,ChinaProject(2016M590211)supported by China Postdoctoral Science Foundation
文摘Because of the mixed grain and coarse grain structure, the long heat treatment cycle and large energy conservation in the heavy cylinder heat treatment process, the up ladder type and terraced type normalizing heat treatment of heavy cylinder after rolling were put forward. The microstructure and mechanical properties of 2.25Cr1Mo0.25 V steel after the up ladder type normalizing, terraced type normalizing and isothermal type normalizing were studied. Experimental results show that： 1） For the grain refinement, the twice terraced type normalizing is better than the up ladder type and isothermal type normalizing, and the average grain size is 18 μm; 2） The yield strength, tensile strength and-30℃ charpy impact energy after twice terraced type normalizing are 681 MPa, 768 MPa and 181 J, respectively, and the mechanical properties are better than those of the up ladder type and isothermal type normalizing; 3） Compared with the isothermal type normalizing, the holding time of terraced type normalizing can be shortened by 30%, which greatly reduces the energy consumption.
文摘An Estonian passenger ferry carrying 867 people sank in a storm off southwest Finland on September 28 and officials said fewer than 100 had been rescued. The Estonia, sailing from the Estonian capital of Tallinn to Stockholm, sank with dramatic speed dragging hundreds of passengers and crew into the chilly Baltic Sea. A massive rescue effort was launched with ships and holicopters from Finland, Sweden and denmark.
文摘The officer- selecting system is an important part of the administrative legal system of the ancient China. In the ancient times,there were different officer- selecting systems in China,such as the hereditary system,the recommendatory system,the nine- rank system and the imperial examination system and so on. Different officer- selecting systems are reasonable and have some limitations at the same time. Besides,they own some realistic significance for the cadre- selecting system of the present.
