纳米ZnFe2O4气敏材料的结构和敏感特性研究

ＺｎＦｅ_２Ｏ_４是传统的铁氧体材料,近年来又发现具有良好的气敏性能．本文采用化学共沉淀法制备了纳米尺寸的ＺｎＦｅ_２Ｏ_４粉末,利用ＸＲＤ、ＸＰＳ、ＳＥＭ等手段研究了结构特性．以ＺｎＦｅ２Ｏ４纳米粉末为原料制备了厚膜气敏元件,测试了元件的气敏性能,并对气敏机理给予了解释．     

熔盐法合成SrBi2Ta2O9粉体

采用熔盐法合成了纯的 系层状结构的ＳｒＢｉ_２Ｔａ_２Ｏ_９粉体．采用ＸＲＤ和ＳＥＭ等手段对粉体的结构和形态进行了分析,并与固相法进行了比较,结果表明熔盐法所得粉体形状呈片状,无团聚现象．对影响粉体颗粒尺寸和形状的因素进行了考查,并对熔盐法合成ＳｒＢｉ_２Ｔａ_２Ｏ_９粉体的机理进行了讨论．     

水热合成羟基磷灰石纳米粉体的研究

采用ＣａＣＯ３和ＣａＨＰＯ_４·２Ｈ_２Ｏ的混合物为前驱物,通过水热合成得到晶粒完整、分散性好、端面粒度在１００ｎｍ以下的ＨＡ粉体,并借助ＸＲＤ和ＳＥＭ分析讨论了前驱物配比、水热温度、反应时间与物相组成、粒度变化和晶体形貌的关系．     

热处理对掺锑二氧化锡纳米导电粉粒度和性能的影响

SnO₂超细粉用作透明导电膜和导电涂料具有广阔的应用前景．以ＳｎＣｌ_４·５Ｈ_２Ｏ和ＳｂＣｌ_３为原料,在掺杂浓度Ｓｂ_２Ｏ_３∶SnO₂＝９∶１００(重量比)的条件下,采用共沉淀法制得了纳米级的SnO₂超细粉．运用差示扫描量热法－失重分析(ＤＳＣ－ＴＧ)、Ｘ射线衍射(ＸＲＤ)、透射电镜(ＴＥＭ)和紫外可见光光谱分析(ＵＶ)等观测手段对微粉末进行了表征,比较系统地研究了热处理工艺(温度、时间)对粉末颗粒度和电阻的影响规律,探讨了掺锑SnO₂导电粉的显色特性．     

ZrO2的加入对(CeO2)0.86(SmO1.5)0.14陶瓷性能的影响

探讨了添加 ＺｒＯ_２对 ＣｅＯ_２／Ｓｍ_２Ｏ₃体系电导率和力学性能的影响,并用 ＸＲＤ、ＳＥＭ等对材料的微观性能进行了试验分析．结果发现,添加 ＺｒＯ_２使材料的电导率降低,主要是因为ＺｒＯ_２的固清使得ＣｅＯ_２电解质材料的晶格常数减小,活化能增加造成的;添加 ＺｒＯ_２可提高材料的断裂强度,使材料断裂以穿晶断裂为主,其原因可能是ＺｒＯ_２的固溶强化了晶界;添加 ＺｒＯ_２促进了致密烧结,使晶界结合紧密．实验确定,外加 ２．５ｍｏｌ％ ＺｒＯ_２的 ＣｅＯ_２电解质具有适中的强度和电导率,可以作为电解质材料应用．     

R型六方铁氧体化学键性质和穆斯堡尔谱位移研究

利用电介质的平均能带模型计算了Ｒ型六方铁氧体ＢａＴｉ_２Ｆｅ_４Ｏ_１１和ＢａＳｎ_２Ｆｅ_４Ｏ_１１的化学键参数,得到ＢａＴｉ_２Ｆｅ_４Ｏ_１１的２a、４ｆ、４ｅ、６ｇ各晶位平均共价性分别为０．０６２、０．３５４、 ０．３０９、 ０．３６１; ＢａＳｎ_２Ｆｅ_４Ｏ_１１的相应晶位平均共价性分别为０．０６２、 ０．３５３、 ０．１８３、０．２５５．应用化学环境因子计算了^５７Ｆｅ、^１１９Ｓｎ在Ｒ结构中的穆斯堡尔同质异能位移。确定了^５７Ｆｅ,^１１９Ｓｎ的价态和占位情况．     

ZrO2-Si3N4陶瓷复合材料中的化学不相容性

ＺｒＯ_２与Ｓｉ_３Ｎ_４之间存在化学反应生成ＺｒＮ或氧氮化锆,ＺｒＯ_２也可能被氮稳定形成氨稳定的ＺｒＯ_２本文对ＺｒＯ_２－Ｓｉ_３Ｎ_４陶瓷复合材料中的化学不相容性及抑制措施进行了综述．     

Ba0.7Sr0.3TiO3薄膜的制备、结构及性能研究

研究了一种以乙二醇为稳定剂的新的ＢＳＴ前驱液,用ｓｏｌ－ｇｅｌ法在Ｐｔ／Ｔｉ／ＳｉＯ_２／Ｓｉ（１００）基底上成功地制备出具有优良电学性能的Ｂａ_０．７Ｓｒ_０．３　ＴｉＯ_３薄膜．乙二醇的加入有效地增加了前驱液的稳定性,并降低薄膜的结晶温度．利用ＸＲＤ、ＤＴＡ等技术分析了凝胶热处理过程中相变化情况及薄膜厚度与成相的关系．厚度 ２００ｎｍ,Ｏ_２气氛中 ７００℃处理 １５ｍｉｎ后的 ＢＳＴ薄膜具有良好的介电性能,１００ｋＨｚ时介电常数ε＞４００,介电损耗 Ｄ＜０．０２;Ｐ—Ｅ电滞回线说明薄膜具有良好的铁电性能,剩余极化只约为１．４μＣ／ｃｍ^２,矫顽场强 Ｅ_ｃ约为 ４８ｋＶ／ｃｍ．     

由SiO2/3Y-TZP包裹复合粉体制备ZrSiO4/3Y-TZP细晶陶瓷

对湿化学法制备的ＳｉＯ_２／３Ｙ－ＴＺＰ包裹复合粉体进行了热压烧结研究,并利用Ｘ射线衍射和透射电镜表征了烧结体的物相和显微结构．在低于１３００℃,复合粉体发生瞬时粘性烧结,材料密度迅速提高;随着烧结温度的升高,ＳＩＯ_２和ＺｒＯ_２发生反应生成ＺｒＳｉＯ_４．在１５００℃热压条件下,制备了平均晶粒尺寸为３５０ｎｍ的ＺｒＳｉＯ_４／３Ｙ－ＴＺＰ细晶复相材料．我们认为,在烧结过程中形成的第二相ＺｒＳｉＯ_４,特别是ＳｉＯ_２包裹层对抑制基体晶粒长大起主要作用．     

流态化CVD包硅的Fe3O4的氧化行为

采用流态化ＣＶＤ包硅技术制得了表面均匀包覆ＳｉＯ₂的Ｆｅ_３Ｏ_４磁粉．对该包硅Ｆｅ_３Ｏ_４磁粉的氧化机理和动力学进行了研究．结果表明,氧化反应机理符合三维球对称扩散模型,氧化反应活化能随包硅量的增加而增加,流态化ＣＶＤ包硅能提高Ｆｅ_３Ｏ_４磁粉的抗氧化作用在于粒子表面形成了均匀的ＳｉO₂保护层．     

纳米WS_2粉末在发动机模拟台架中的实验研究

采用多能场复合作用下的湿式粉碎法制备出纳米WS2粉末,并加入到发动机润滑油中制备成纳米WS2润滑剂.在自行研制的发动机模拟实验台架上考察了该润滑剂在发动机上的实际应用效果,分析了纳米WS2粉末对发动机润滑油摩擦学性能的影响,研究了其在减少发动机内部磨损和降低发动机油耗方面的效果,最后对比分析了全配方纳米WS2汽机油与2种国外品牌汽机油的性能.结果表明,纳米WS2粉末可以显著延长发动机润滑油的使用寿命和换油周期,并能使发动机活塞环的磨损量减少27.6%,发动机油耗降低13%～28%;同时,全配方纳米WS2汽机油在摩擦学性能、减少活塞环磨损以及降低发动机油耗方面均优于国外品牌汽机油.     

Kinematics of four-wheel-steering vehicles

In this paper, we review some aspects of the kinematical theory of four-wheel-steering (4WS) vehicles and present some new results and conclusions that we came across during our research on the subject. In a first paragraph, we compare the turning radius of two-wheel-steering (2WS) and 4WS vehicles and draw some interesting conclusions on the manoeuvring ability of either of them. In a second paragraph, we present a general kinematical analysis of 4WS vehicles by considering either the simplified two-wheel (bicycle) model or the more complete four-wheel model. In this analysis, we assume the sideslip angles of the wheels as non-negligible and we derive the general formulae relating the steering angles of the wheels to the geometrical data of the vehicle. By taking as zero the steering angles of the rear wheels, we derive from the above relations the well-known formulae of Ackermann–Jeantaux that are valid for 2WS vehicles.     

Comparison of a vehicle equipped with Electronic Stability Control (ESC) to a vehicle with Four Wheel Steering (4WS)

Electronic Stability Control (ESC) and Four Wheel Steering (4WS) have been used to control the yaw rate and sideslip angle of automobiles, in order to improve stability and prevent accidents. The scope of this paper is to compare the behaviour of a vehicle equipped with no control systems, to a vehicle equipped with ESC, a vehicle equipped with 4WS and a vehicle equipped with a combination of ESC and 4WS in a series of simulated tests, using an adequate vehicle and driver model. The operating parameters of the control systems and the driver model have been optimised by using an evolution strategy. According to the results, the vehicle equipped with 4WS performed better in open-loop tests, while the vehicle equipped with ESC performed better in closed-loop tests where the vehicle is controlled by the driver model. The vehicle equipped with a combination of ESC and 4WS has achieved consistently better results in all our tests and has shown that the use of 4WS systems can augment the operation of ESC system and achieve a better safety level for future vehicles.     

High-resolution electron microscopy study of mesoporous dichalcogenides and their hydrogen storage properties

In this work, we report a detailed investigation on the surface topology of ordered mesoporous WS(2) nanoarrays nanocast from the silica SBA-15 template. Using a high-resolution scanning electron microscopy (HRSEM) technique, we acquire distinguishably clear images of the WS(2) surface. A large number of small nanorods are found to be evenly distributed among the nanowire arrays, supporting their ordered mesostructures. Based on these observations, tunnel-like connecting pores are proposed to have a similar distribution in the mother mesoporous silica SBA-15 template. Interestingly, we observe the atomic crystal lattices of the layered WS(2) on the HRSEM image. To the best of our knowledge, this is the first time that atomic crystal lattices have been directly observed using a SEM technique. In addition, both materials show good adsorption-desorption capabilities with hydrogen, and the maximum amount of hydrogen that can be taken up is 0.34 wt% for mesoporous WS(2) and 0.52 wt% for mesoporous MoS(2) at a pressure of 10 bar, indicating that both are potential hydrogen storage materials.     

一种基于代理的动态服务组合方法

Web服务是现代网络流行的技术之一,而BPEL4WS的流程建模工具又是基于Web服务wsdl的,该文提出的在BPEL4WS中引入AgentService是对BPEL4WS运行模式的改进,提出在BPEL4WS中引入AgentService之后,不仅减少了流程模板的编制,而且增加了与用户的交互性.     

Fullerene-like WS(2) nanoparticles and nanotubes by the vapor-phase synthesis of WCl(n) and H(2)S

Inorganic fullerene-like (IF) nanoparticles and nanotubes of WS(2) were synthesized by a gas phase reaction starting from WCl(n) (n = 4, 5, 6) and H(2)S. The effect of the various metal chloride precursors on the formation of the products was investigated during the course of the study. Various parameters have been studied to understand the growth and formation of the IF-WS(2) nanoparticles and nanotubes. The parameters that have been studied include flow rates of the various carrier gases, heating of the precursor metal chlorides and the temperature at which the reactions were carried out. The best set of conditions wherein maximum yields of the high quality pure-phase IF-WS(2) nanoparticles and nanotubes are obtained have been identified. A detailed growth mechanism has been outlined to understand the course of formation of the various products of WS(2).     

Microwave hydrothermal synthesis of WO3(H2O)0.333/CdS nanocomposites for efficient visible-light photocatalytic hydrogen evolution

WO₃(H₂O)_0.333/CdS (WS) nanocomposites are obtained via a rapid microwave hydrothermal method, and they are served as visible light-driven photocatalysts for the H₂ generation. By using Pt as the cocatalyst, the WS nanocomposite with 70 wt.% CdS reaches the H₂ evolution rate of 10.32 mmol·g⁻¹·h⁻¹, much quicker than those of WO₃(H₂O)_0.333 and CdS. The cycling test reveals the good photocatalytic stability of the WS nanocomposite. The carrier transfer mechanism of WS nanocomposites can be explained by the Z-scheme mechanism. The existence of the Z-scheme heterojunction greatly helps to separate photogenerated carriers and thus improves the photocatalytic activity. The present work provides a rapid synthesis method for preparing Z-scheme heterojunction photocatalysts, and may be helpful for the green production of hydrogen.     

硅烷KH570与聚甲基丙烯酸甲酯改性WS_2固体润滑涂层的性能

为提高WS_2固体润滑涂层的性能,先以甲基丙烯酰氧基三甲氧基硅烷(KH570)改性WS_2颗粒,再在颗粒表面以甲基丙烯酸甲酯(MMA)原位合成聚甲基丙烯酸甲酯(PMMA)进行二次改性,并制备了WS_2固体润滑涂料涂层。采用扫描电子显微镜对涂层微观结构进行表征,采用摩擦磨损试验评价了固体润滑涂层的摩擦学性能,并采用数码相机观察磨痕的形貌。结果表明:KH570改性WS_2固体润滑涂层耐磨性能显著提高,摩擦系数也随KH570用量降低显著减小;MMA原位合成二次改性增加了涂层摩擦系数,但MMA与WS_2质量比为7∶50时,二次改性WS_2固体润滑涂层磨损量仅为纯WS_2涂层的31%。     

WS2软涂层刀具的材料优选及涂层制备

运用有限元软件分析了不同基体材料和过渡层的基体表面WS2软涂层的残余热应力。结果表明弹性模量和热膨胀系数等参数是影响涂层残余热应力大小的主要因素。采用中频磁控溅射、多弧离子镀外加离子束辅助沉积工艺制备了4种WS2软涂层刀具并对其性能进行了测试,分析结果符合有限元计算的结论,发现残余热应力对WS2软涂层刀具的性能产生很大的影响,并发现Zr过渡层能有效促进WS2Ⅱ型织构的生长。     

Quasi-freestanding,striped WS2 monolayer with an invariable band gap on Au(001)

Revealing the structural/electronic features and interfacial interactions of monolayer MoS2 and WS2 on metals is essential to evaluating the performance of related devices.In this study,we focused on the atomic-scale features of monolayer WS2 on Au(001) synthesized via chemical vapor deposition.Scanning tunneling microscopy and spectroscopy reveal that the WS2/Au(001) system exhibits a striped superstructure similar to that of MoS2/Au(001) but weaker interfacial interactions,as evidenced by experimental and theoretical investigations.Specifically,the WS2/Au(001) band gap exhibits a relatively intrinsic value of ～ 2.0 eV.However,the band gap can gradually decrease to ～ 1.5 eV when the sample annealing temperature increases from ～370 to 720 ℃.In addition,the doping level (or Fermi energy) of monolayer WS2/Au(001) varies little over the valley and ridge regions of the striped patterns because of the homogenous distributions of point defects introduced by annealing.Briefly,this work provides an in-depth investigation into the interfacial interactions and electronic properties of monolayer MX2 on metal substrates.