Jiarong LI
,
Shizhong LIU
,
Zhengang ZHONG
材料科学技术（英文）
The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min was performed with the finite element thermal analysis method. The calculated results were in accordance with the experimental ones. The results showed that with the increase of withdrawal rate the concave curvature of the liquidus isotherm was bigger and bigger and the temperature gradient of the castings decreased. No effects of withdrawal rate on the distribution of the temperature gradient of the starter and helical grain selector of the castings were observed at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min. The relatively high temperature gradient between 500°C/cm and 1000°C/cm in the starter and helical grain selector was obtained at three withdrawal rates. The study indicates the three dimensional solidification simulation by finite element method is a powerful tool for understanding solidification and predicting defects in single crystal investment castings.
关键词:
Single crystal
,
null
,
null
Jiarong LI
,
Shizhong LIU
,
Hailong YUAN
,
Zhengang ZHONG
材料科学技术（英文）
The three-dimensional solidification simulation of the investment castings of single crystal hollow turbine blade at the withdrawal rates of 2 mm/min, 4.5 mm/min and 7mm/min has been performed with the finite element thermal analysis. The calculated results are in accordance with the experimental ones. The results show that with the increase of withdrawal rate the concave curvature of the liquidus isotherm is larger and larger, and the temperature gradients of the blades increase. No effects of withdrawal rate on the distribution of the temperature gradients of the starter and helical grain selector of the blades are observed at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min. The relatively high temperature gradient between 500ºC/cm and 1000 ºC/cm in the starter and helical grain selector is obtained at three withdrawal rates.
关键词:
Single crystal
,
null
,
null
Jing YU
材料科学技术（英文）
Bridgman directional solidification of investment castings is a key technology for the production of reliable and highly efficient gas turbine blades. In this paper, a mathematical model for three-dimensional (3D) simulation of solidification process of single crystal investment castings was developed based on basic heat transfer equations. Complex heat radiation among the multiple blade castings and the furnace wall was considered in the model. Temperature distribution and temperature gradient in superalloy investment castings of single blade and multiple ones were investigated, respectively. The calculated cooling curves were compared with the experimental results and agreed well with the latter. It is indicated that the unsymmetrical temperature distribution and curved liquid-solid interface caused by the circle distribution of multiple turbine blades are probably main reasons why the stray grain and other casting defects occur in the turbine blade.
关键词:
Directional solidification
,
null
,
null
,
null
甄超
,
吴亭亭
,
Mohammad W. Kadi
,
Iqbal Ismail
,
刘岗
,
成会明
催化学报
doi:10.1016/S1872-2067(15)60981-0
光电化学电池(如染料敏化太阳能电池、量子点敏化太阳能电池以及光电化学水分解电池)是实现太阳能转化及存储的有效手段之一.其中,光电极是光电化学电池的核心组成部分,它集光吸收、光生电荷输运及转移等决定光转化效率的关键过程于一身,因此构筑高活性半导体光电极以实现高效太阳能转化利用引起研究者广泛关注.多孔TiO2纳米颗粒堆垛薄膜光阳极因具有大的比表面积,可提供更多的染料(量子点)担载和反应活性位点,在光电化学电池中表现出优异活性而被广泛研究.然而, TiO2纳米颗粒间大量存在的晶界对光生电荷有较强的散射作用,降低了光生电荷的收集效率.英国牛津大学Snaith研究小组利用模板辅助水热过程首次获得了(001)晶面占优的多孔单晶锐钛矿TiO2微米颗粒,这种多孔单晶TiO2微米颗粒在具有大比表面积的同时,其单晶结构还能有效去除晶界对电荷的散射作用,因而具有优异的电荷输运特性.利用这种多孔单晶TiO2微米颗粒组建的光阳极用于染料敏化太阳能电池中,展现出优异的太阳能光电转化性能.受该工作启发,各种形貌的多孔单晶TiO2微米颗粒作为光催化剂和光电化学分解水用光阳极材料被广泛研究,并表现出优异活性.在单晶微米颗粒堆垛成的薄膜光电极中,虽然单个单晶微米颗粒中晶界对电荷的散射作用被有效抑制,但是单晶颗粒间的晶界仍然存在并影响光生电荷的收集效率.为了彻底抑制晶界对光生电荷的散射作用,每个单晶颗粒都应该贯穿整个薄膜,例如一维TiO2纳米棒单晶阵列薄膜.虽然一维单晶阵列薄膜能够有效提高光生电荷的收集效率,但相对于多孔薄膜具有较小的比表面积,限制了担载染料(量子点)和反应位点的数量.为了增大TiO2单晶纳米棒阵列薄膜的比表面积,目前主要的手段包括调控纳米棒长径比、表面修饰TiO2纳米颗粒以及二次生长构建TiO2枝晶阵列.本文首次提出通过制备多孔单晶TiO2纳米棒单晶阵列薄膜来获得高比表面积和高光生电荷收集效率的光阳极,提高光电化学电池的效率.在透明导电薄膜(FTO)表面利用水热生长TiO2纳米棒阵列薄膜之前,预先在FTO基体上沉积一层SiO2球密堆模板, TiO2纳米棒单晶阵列在从FTO表面向上生长过程中,会将SiO2球模板包裹进TiO2纳米棒中,再通过碱溶液将SiO2球模板溶解,首次在FTO基体上原位生长出多孔单晶TiO2纳米棒阵列薄膜.将所得多孔单晶金红石TiO2纳米棒阵列薄膜作为光电化学分解水电池光阳极,其光电化学分解水活性相对于实心单晶金红石TiO2纳米棒阵列提高了2.6倍.多孔单晶金红石TiO2纳米棒阵列光阳极性能的提升可归因于：(1)多孔结构赋予多孔单晶金红石TiO2纳米棒阵列薄膜更大的比表面积,可提供更多的反应活性位点；(2)多孔结构能够有效缩短单晶金红石TiO2纳米棒中光生电荷体相输运距离,提高光生电荷的收集效率；(3)多孔结构通过对光多次反射吸收可有效增强光吸收,产生更多光生电荷参与水分解反应；(4)在制备过程中引入Si掺杂,导致多孔单晶金红石TiO2纳米棒带隙扩大了0.1 eV,带隙增大归因于导带位置负移0.1 eV,光生电子具有更强的还原能力,光电流起始电位相应负移约0.1 V.
关键词:
氧化钛
,
光阳极
,
多孔
,
单晶
,
纳米棒阵列
王冠伟
,
曹义明
,
袁淑娟
,
冯振杰
,
康保娟
,
鲁波
,
曹世勋
,
张金仓
低温物理学报
本文采用光学浮区法生长了HoFe0.95Mn0.05O3单晶样品,对其磁性和磁热效应进行了研究.研究表明,微量Mn的掺杂使HoFeO3的自旋重取向温度由58 K升高到102 K.磁化强度随温度变化和自旋重取向相变过程中的热滞现象共同说明,自旋重取向由原来HoFeO3中的Γ4(G,Fz)→Γ2(Gz,Fx)自旋重取向变为HoFe0.95 Mn0.05O3中的Γ4(G,Fx)→Γ1(Cx,Ax)的自旋重取向.磁熵计算表明,虽然在a轴方向得到了-16.7J/kg·K的磁熵变,HoFe0.95Mn0.05O3的磁熵变显示出明显的各向异性,但是微量Mn的掺杂并未对HoFeO3的磁熵造成明显的影响.
关键词:
HoFe0.95Mn0.05O3
,
单晶
,
自旋重取向
,
磁热效应
