Preparation and characterization of doubly substituted microwave absorbing material by sol-gel technique for super high frequency applications

Rare earth Dy~(3+)and divalent Mn~(2+)elements substituting W-type hexagonal ferrites Ba_(1-x)Dy_xZn_2Fe_(16-y)Mn_yO_(27)(x=0,0.02,0.06,0.1 and y=0,0.1,0.3,0.5)were prepared by sol-gel method.The thermo-gravimetric analysis(TGA)and differential scanning calorimetry(DSC)was carried out to find the temperature at which single phase can be obtained.XRD patterns indicate the presence of the single phase for all the synthesized samples with the absence of any extra peak due to unreacted material and secondary phases.The occurrence of absorption bands at low wave numbers(563 and 446 cm~(-1)),can be assigned to the stretching vibration of metal and oxygen ions in FTIR spectra,which also confirms the single hexagonal phase for prepared material.The grains are of platelet like structure,which enhances the microwave absorption properties of hexagonal ferrites.The synthesized material exhibits the minimum reflection loss of-20.9 dB at 11.8 GHz frequency,which reflects the applications of this material in super high frequency devices.The microwave conductivity of the material increases with frequency.     

Influence of thermal-decomposition temperatures on structures and properties of V2O5 as cathode materials for lithium ion battery

Submicron spherical V2O5 particles with a uniform size and a lower crystallinity were successfully synthesized by a chemical precipitationthermal decomposition technique using the commercial V2O5 powders as starting material. The crystal structure and grain morphology of samples were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM), respectively. Electrochemical testing such as discharge–charge cycling(CD) and cyclic voltammetry(CV) were employed in evaluating their electrochemical properties as cathode materials for lithium ion battery. Results reveal that the crystallinity and crystalline size of V2O5 particles increased when the thermal-decomposition temperature increased from 400 ℃ to 500 ℃, and their adhesiveness was also synchronously increased. This indicate that the thermaldecomposition temperature palyed a significant influence on electrochemical properties of V2O5 cathodes. The V2O5 sample obtained at 400 ℃ delivered not only a high initial discharge capacity of 330 m A h g-1and also the good cycle stability during 50 cycles due to its higher values ofα in crystal structure and better dispersity in grain morphology.     

重力场条件下砂岩突出倾向性

通过对永川煤矿砂岩物理力学性质的实验研究,得出了突出砂岩的特征,并据此研究了该矿-350m水平砂岩突出倾向性,提出了重力场条件下砂岩突出倾向性的判据. 研究表明:突出的砂岩具有孔隙率大、气孔容积大的物理特征和杨氏模量较低、强度低、不易产生塑性变形的力学特性;岩石和瓦斯突出发动过程与冲击地压特征具有一致性,可以用研究冲击地压的理论来研究砂岩突出倾向性问题;砂岩突出受多种因素影响,力学因素是主导因素. 在"三准则"理论基础上,建立了用能量准则、强度准则和冲击倾向性准则评价砂岩突出倾向性的方法.     

含氟二胺合成及其聚酰亚胺薄膜性能研究

为改善聚酰亚胺薄膜的透明性和溶解性,通过Williamson醚化反应较高产率地合成出高纯度的2,2-双[4-(4-氨基-2-三氟甲基苯氧基)苯基]丙烷,该含氟二胺与3,3’,4,4’-联苯四酸二酐(BPDA)在溶剂中缩聚得到聚酰胺酸,热亚胺化得到玻璃化转变温度Tg为350.2℃、在氮气中10%热失重温度为539.8℃、紫外截止波长为390 nm的含氟透明聚酰亚胺,并合成了联苯二酐/二苯醚二胺薄膜BPDA-ODA,通过对两种薄膜热稳定性、透光率、溶解性能的比较发现,在聚酰亚胺分子结构中引入氟原子,在不改变其热稳定性的前提下,可明显改善聚酰亚胺的透明性和溶解性。     

聚乙烯醇－双快水泥自硬砂的抗爆热性和抗变形性

本文探讨了爆热温度、爆热时间、型砂放置时间对聚乙烯醇－双快水泥自硬砂抗爆热性和抗变形性的影响，以便进一步掌握这种自硬砂的性能和应用。     

南极产低温蛋白酶菌株Marinobacter sp.R2的发酵条件及酶学性质研究

从南极海域沉积物中筛选到一产蛋白酶的菌株R2，经细菌学形态特征鉴定及16S rDNA序列分析鉴定，该菌株属于海杆菌属(Marinobacter)．生长特性研究表明该菌株属于兼性嗜冷菌，其最适生长温度为10～15℃．R2菌株能利用多种碳源产酶，最适产酶温度为20℃．粗酶液经硫酸铵盐析、DEAE cellulose-52柱层析进行初步分离纯化后进行酶学性质的研究．该菌株所分泌蛋白酶的最适作用温度为20℃，最适pH值为9～10，对热敏感．是典型的低温碱性蛋白酶．Ca^2 、Mn^2 、Cu^2 对该蛋白酶有较为明显的激活作用，而Cd^2 、Co^2 则能抑制酶活．高浓度的变性剂、PMSF、AEBSF和EDTA都能抑制该蛋白酶，表明该酶属于丝氨酸蛋白酶，且金属离子对酶活性中心构象有关键性的影响．     

表面活性剂与水溶性吲哚方酸菁染料光谱性能

测定了四种吲哚方酸菁染料在阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）,阴离子表面活性剂十二烷基硫酸钠（SDS）和非离子表面活性剂曲拉通（TX－100）水溶液中的吸收发射光谱,结果表明：这些吲哚类方酸菁染料可以与胶束发生有效的相互作用,在表面活性剂溶液中,随着胶束的形成,染料的最大吸收和发射光谱都发生红移．     

TaAgN复合膜显微结构、力学性能和摩擦性能的研究

采用非平衡反应磁控溅射法制备了TaAgN复合膜。利用X射线衍射仪、CSM纳米压痕测试仪和摩擦磨损测试了复合膜的显微结构、力学性能和摩擦性能。结果显示,TaAgN复合膜由面心立方结构的TaN相和底心斜方结构的Ta₄N相组成。随着Ag靶功率的增加,硬度H、弹性模量E、弹性恢复W_e和H³/E²值均呈先升高后降低的趋势,最大值分别为34 GPa,394 GPa,57%和250 MPa。随着Ag靶功率的增加,TaAgN复合膜室温下的平均摩擦因数呈降低趋势。当Ag靶功率为25 W时,随着温度的升高,TaAgN复合膜的平均摩擦因数逐渐减小。     

微米级二硫化钼作为添加剂的润滑油性能研究

将表面改性后的微米级二硫化钼添加至基础油中,利用MRS-10W型和M-2000型试验机,对所制备润滑油的摩擦学性能进行测定.结果表明,基础油中添加含量为1.5%的微米级二硫化钼后,润滑油的最大无卡咬载荷提高了15.5%,摩擦副之间的摩擦系数降低了33.1%,磨损量减少了43.5%.     

乙醇-乙酸二元体系汽液平衡的热力学性质

用新型泵式沸点仪测定了在101.325kPa下乙醇-乙酸二元体系在不同液相组成时的沸点,用过量自由能函数Q,采用间接法由Tpx推算了乙醇-乙酸二元体系的汽相平衡组成y.汽相的非理想性用截至第二项的维里系数的状态方程求出汽相混合物中组分逸度系数.二元体系活度系数的关联分别用W ilson模型、NRTL模型、M argu-les模型和Van Laar模型进行关联,用最小二乘法求出了它们的液相活度系数模型参数.所得的液相活度系数来计算二元体系的过量吉布斯自由能函数GE/RT.计算的泡点温度与实验所测得的沸点温度吻合良好,由面积积分法检验这些模型参数计算的二元体系相平衡数据得到很好的热力学一致性.