高分子网络凝胶法制备氧化物纳米陶瓷粉体

以Al2O3和Y2O3纳米陶瓷粉体的制备为例,研究了高分子网络凝胶法制备氧化物纳米陶瓷粉体的过程及其影响因素.制备了颗粒尺寸小于20nm的Al2O3和Y2O3粉体,分析了网络凝胶机理和胶体的热失重过程.对粉体进行煅烧发现氧化铝的最佳煅烧温度为1100℃;氧化钇的最佳煅烧温度为850℃.单体和网络剂的摩尔比例对粉体粒度有一定影响当单体和网络剂的比例为51时,所制备的纳米颗粒尺寸细小,均匀;当比例偏离51较大时,团聚比较严重,且一部分颗粒尺寸长大,造成颗粒尺寸分布不均匀.     

碳热还原氮化法制备AlN超细粉体新工艺

为降低碳热还原氮化法制备AlN粉体的反应温度,减小粉体粒径、缩短反应时间,以勃母石(γ-AlOOH)为铝源、蔗糖为碳源,采用碳热还原氮化法在不同温度下制备了AlN超细粉体,用XRD、TEM等方法分析了所制备粉体的物相组成与形貌.结果表明:在1 480℃、流通氮气氛中保温1 h可制备出平均粒径为350 nm的AlN粉体,大幅度降低了反应温度,缩短了反应时间;在高温下,γ-AlOOH分解成Al2O3,部分Al2O3被碳还原成气态铝和铝的低价氧化物(Al2O3,AlO),它们与氮气直接反应生成AlN和中间相AlON,随后中间相AlON也发生反应生成AlN.     

Ag-CuO钎料空气反应钎焊AlN陶瓷接头组织及性能

采用Ag-Cu O钎料实现了Al N陶瓷与自身的空气反应钎焊。研究了Cu O含量、钎焊温度和预氧化温度对界面组织及力学性能的影响规律,分析了连接机理。当钎料成分为Ag-6 mol%Cu O,在1000℃/5 min的钎焊参数下,Al N/Ag-Cu O/Al N接头可获得最高的抗剪切强度为13.9 MPa。采用SEM、EDS及XRD对其接头界面显微组织、断口形貌及成分进行了分析。典型接头界面组织结构为Al N/Cu Al_2O_4/Cu O/Al N+Ag+Cu O/Cu O/Cu Al_2O_4/Al N。然而,在该条件下无法获得无缺陷的接头。为了降低残余热应力获得无缺陷的接头,对Al N陶瓷采用预氧化处理,在Al N陶瓷表面形成一层Al_2O_3层。当预氧化参数为1 000℃/5 h时,Al N陶瓷表面的Al_2O_3层厚度约为10μm。采用成分为Ag-6 mol%Cu O的钎料,在1 000℃/5min的钎焊参数下,对预氧化后的Al N陶瓷进行连接,获得了无缺陷的接头,接头典型界面显微组织为Al N/Al_2O_3/Cu Al_2O_4/Cu O/Ag+Al_2O_3/Cu O/Cu Al_2O_4/Al_2O_3/Al N。接头的抗剪切强度最高为22.6 MPa,与未氧化的Al N陶瓷接头相比提升了62.6%。接头进行抗剪切测试时,断面主要出现在Al N陶瓷母材。     

等离子喷涂用纳米Al2O3/TiO2团聚粉体的制备

采用喷雾造粒技术制备出纳米Al2O3/TiO2团聚粉体,使用高温电炉通过三种不同制度进行了烧结;测定了其松装密度与流动性,用X射线衍射方法分析了其相组成,用扫描电镜分析了团聚粉体的形貌,并进行了等离子喷涂试验.结果表明:两步烧结法所得纳米团聚粉体的致密度与结合强度高,适于等离子喷涂,可以获得高质量的纳米涂层.     

共沉淀法制备纳米CuO/Al2O3复合粉体

以NH4 HCO3为沉淀剂、CuSO4和NH4Al(SO4)2为母液,采用共沉淀法制备CuO/Al2O3复合粉体,用激光粒度分析仪、扫描电镜、X射线衍射仪等研究了母液浓度、沉淀剂浓度、反应温度、pH值等工艺条件对粒径和粒度分布的影响.结果表明:通过控制反应条件,可获得粉体粒径较小、分布较窄的纳米CuO/Al2O3复合粉体;最佳工艺参数为反应温度55℃,pH值为7,CuSO4浓度为0.095 mol/L,NH4Al(SO4)2质量浓度为1.67 g/L,NH4HCO3浓度为1.52 mol/L,得到的纳米复合粉体的粒径在60 nm左右.     

碳热/硼热还原法制备ZrB_2-SiC复合粉体

以氧化锆、氧化硅、氧化硼及活性炭为原料,采用碳热/硼热还原法制备了ZrB_2-SiC复合粉体,并对合成过程进行了热力学分析,研究了反应温度以及活性炭含量对复合粉体物相组成和显微结构的影响。结果表明:在1 400~1 450℃温度范围可以合成ZrB_2-SiC复合粉体;提高反应温度有利于合成ZrB_2-SiC复合粉体,经1 450℃保温3h反应可以得到较纯的ZrB_2-SiC复合粉体;活性炭过量50%和75%(物质的量分数)条件下制备的复合粉体的物相组成基本相同。     

沉淀包裹法制备Cu/α-Al2O3纳米复合粉体

以纳米Al2O3、CuSO4·5H2O和纳米铝粉为原料,采用非匀相沉淀工艺获得了纳米铜包裹α-Al2O3复合粉体;研究了反应温度和pH值对复合粉体成分及性能的影响;利用XRD、XPS、TG/DSC、Zeta电位和TEM等方法对复合粉体的成分、热学特性以及形貌特征进行了表征.结果表明采用反应温度为40℃、保温4 h的工艺条件,可以获得纳米铜颗粒包裹Al2O3纳米复合粉体,铜颗粒呈球形,尺寸为10 nm左右.     

固相法制备Al2(WO4)3粉体及其负热膨胀性能

以Al2O3和WO3为原料,采用固相反应法制备了负热膨胀性能的Al2(WO4)3粉体.用X射线粉末衍射和扫描电镜分别对粉体进行物相、晶体结构分析和形貌观察;通过热重-差热分析了粉体的热性能;采用热膨胀仪测定了热膨胀系数.结果表明:产物为高纯度正交晶系结构的Al2(WO4)3,形状规则,大小均匀,平均尺寸为0.6 μm×0.4 μm.从室温到熔点范围内,Al2(WO4)3粉体无相变,不发生分解,30～900 ℃的平均热膨胀系数为-1.56×10-6 K-1.     

Tb2TiO5-Dy2TiO5中子吸收材料的显微组织及性能

以Tb₄O₇粉、Dy₂O₃粉和TiO₂粉为原料,采用高能球磨、冷等静压和高温烧结工艺制备了Tb₂TiO₅-30%(质量分数)Dy₂TiO₅中子吸收材料,研究不同球磨时间(0~48 h)下混合粉体的微观结构,不同烧结温度(1 200~1 400℃)与时间(1~96 h)下烧结块体材料的微观结构、热物理性能和耐腐蚀性能。结果表明:混合粉体的晶粒尺寸随球磨时间的延长而减小,球磨12 h后即可获得均匀混合的纳米晶粉体,纳米晶混合粉体在1 300℃烧结96 h获得了具有高致密度正交晶体结构Tb₂TiO₅-Dy₂TiO₅块体材料;该块体材料在500℃的热导率和热膨胀系数分别为2.2 W·m^-1·K^-1和5.8×10^-6 K^-1,在360℃/18.6 MPa去离子水中的腐蚀速率变化很小,平均腐蚀速率为0.18 mg·dm^-2·h^-1,该块体材料具有较高的热导率、较低的热膨胀系数以及较好的耐高温水腐蚀性能,是控制棒用中子吸收材料较优的候选材料。     

相转移法制备纳米CoFe_2O_4粉体

采用相转移法制备了纳米CoFe2O4前驱体.运用差示扫描量热仪(DSC)研究了纳米CoFe2O4前驱体的热分解特性.利用XRD、TEM研究了不同煅烧温度对生成的纳米CoFe2O4成分、形貌和粒度的影响,探讨了相转移法的制备机理.结果表明:相转移法可有效控制成核速度,油相的成膜有效地实现了阻聚作用,400℃为最佳煅烧温度,所得到的CoFe2O4粉体呈规则的立方形链状分布,无明显团聚体,平均粒径为30 nm,且粒径分布窄.     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

考虑进油孔有限长滑动轴承油膜力的近似解析解

针对具有进油孔的有限长滑动轴承油膜力求解问题,采用变分原理和分离变量法,求得了有限长滑动轴承油膜压力分布的近似解析表达式。将油膜压力分布的近似解析表达式在油膜存在区域上进行积分,即得到了油膜力。将提出的计算有限长滑动轴承油膜力方法与无限长轴承模型、有限元方法的计算结果进行了比较,发现了提出的方法与有限元方法的计算结果很接近。最后,研究了进油孔位置和进油压力对油膜存在区域、油膜力等的影响,研究结果表明进油孔位置和进油压力对油膜存在区域和油膜力有较大的影响。     

Fifth International Summer School on Screw-Theory Based Methods in Robotics

正3-11 September,2014University of Bologna,Bologna,Italy www.summerscrews.org summerscrews2014.ing.unibo.it SUMMER 20SCREWS 14In 2014,our screw-theory school comes to the world's oldest university.In early September,Summer Screws'14 will gather six experts in the application of screw theory in robotics and up to 40 participants at the University of Bologna,Bologna,Italy.The school will teach attendees how to apply existing methods and empower them to develop new ones in their own research.The basic theoretical notions will be introduced in a rigorous manner,emphasizing examples,applications,and exercises.Scholarships are available.     

交通荷载作用下桥梁结构参数识别方法

应用动力节点加载法,将作用在桥梁上的交通荷载转化为等效节点荷载,再用两步构造法识别结构物理参数.第1步,用Newmark-β方法变换结构运动方程,并用结构的加速度响应求得变换空间内的位移、速度和加速度响应;第2步,基于最小二乘原理,构造出变换空间内求解结构参数的递推式,进行结构物理参数识别.数值模拟结果表明,在交通荷载作用下,该方法能够快速、准确地进行桥梁结构参数识别.     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

INDUSTRIAL ENGINEERING AND VISUALISATION-A PRODUCT DEVELOPMENT PERSPECTIVE

Taking the actual project of teaching and researching process for example, the relationship between the industrial engineering and product development is discussed. And use the novel visualization technology to support the industrial engineering and product development. How to use the new computer modeling and simulating technologies to support the product development and industrial engineering, is introduced especially. The support includes both domestic products and industrial systems. The visualization and computer technologies take a very important role in some system or multi-direction modeling, those technologies mentioned above can help the industrial engineers study the effect of design on the whole life circle, including the producing steps. So the engineers can avoid making the wrong decision which may cause bad effects on the whole industrial engineering.