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1.
以NH4Al(SO4)2·12H2O为原料,通过加入不同质量分数的葡萄糖合成α-Al2O3,研究了葡萄糖含量和预压处理对α-Al2O3粉体合成工艺和温度的影响。结果表明:葡萄糖的加入可以明显改变相变过程,降低合成温度。添加质量分数为30%的葡萄糖时,可在950℃合成单相α-Al2O3粉体,合成温度比不添加葡萄糖时低200℃左右;添加质量分数为75%的葡萄糖时,α-Al2O3的合成温度可进一步降低至900℃。添加葡萄糖可以降低α-Al2O3合成温度的主要原因有两个:一是葡萄糖氧化分解产生的热加速了NH4Al(SO4)2·12H2O的热分解,二是葡萄糖的添加使NH4Al(SO  相似文献   

2.
研究以K2CO3,Li2CO3和TiO2为反应原料合成层状钛酸盐K0.81Li0.27Ti1.73O4过程中合成条件对产物的影响. 结果表明: 反应温度在
1 000~1 200 ℃, 反应原料配比为n(K2CO3) ∶n(Li2CO3) ∶n(TiO2)=(0.405~0.42) ∶(0.135~0.165) ∶1.73时, 均可以得到产物K0.81Li0.27Ti1.73O4, 延长反应时间及升高反应温度均有利于产物的生成; 在1 200 ℃高温条件下, 使用刚玉坩埚为反应容
器时, 最佳的反应条件是: 反应温度为1 100 ℃, 反应原料配比为n(K2CO3) ∶n(Li2CO3) ∶n(TiO2)=0.405 ∶0.135 ∶1.73, 反应24 h.  相似文献   

3.
用水热法制备Li4Ti5O12@TiO2复合材料与同样方法制备的尖晶石型Li4Ti5O12进行对比.对2种材料采用扫描电子显微镜、X射线衍射仪、光电子能谱仪(XPS)进行表征;N2吸附-脱附曲线进行比表面积分析;恒电流充放电测试和电化学交流阻抗(EIS)技术进行电化学性能分析.结果表明Li4Ti5O12@TiO2和Li4Ti5O12均呈颗粒状,粒径分别约为50和70 nm.XPS分析显示Li4Ti5O12@TiO2中的Ti为+4价态.电化学测试结果显示Li4Ti5O12复合了锐钛型TiO2...  相似文献   

4.
采用PVC粘合成型技术对实验室合成的Li4Mn5O12粉体进行成型,制备出直径约为3.5mm的球形PVC-Li4Mn5O12复合材料,并通过SEM、孔径分布、吸附动力学和选择性测试等手段研究成型前后离子筛的形貌和吸附性能。结果表明:PVC-Li4Mn5O12复合样品中的离子筛仍为纳米棒;且球形离子筛具有较大的比表面积,在模拟卤水中对Li+具有良好的选择性吸附性能。  相似文献   

5.
以分析纯La(NO33·6H2为O、Sr(NO32、Co(NO32·6H2O和Fe(NO31·9H2O为原料,采用溶胶凝胶-自燃烧法制备了不同组成的La0.6Sr0.4Co1-xFexO3-δ(LSCF)超细粉体。采用X线衍射(XRD)和透射电子显微镜(TEM)对合成超细粉体的结构和形貌进行测定和表征。结果表明:溶胶凝胶-自燃烧法可一步合成粒径为30~70 nm的LSCF超细粉体,且随着Fe3+含量的增加,衍射峰值向低角度方向略有偏移。对超细粉体的烧结性能、热膨胀性能及电性能进行测试,结果表明:该粉体在1 100℃下烧结2 h,其相对密度达到97%。热膨胀系数随x(Fe3+含量)增加而增大,由x=0.1时的8.42×10-6K-1增大至x=0.5时的9.56×10-6K-1。直流四端子法电导测试表明:电导率随温度的升高(200~800℃)出现极大值,最大值可达950 S/cm,在500~700℃范围内,电导率均在200 S/cm以上,能够很好地满足中低温固体氧化物燃料电池对阴极材料的要求。  相似文献   

6.
立方尖晶石结构的Li2ZnTi3O8(LZTO)具有成本低和安全性高的优势,被认为是代替碳材料作为锂离子电池负极材料的理想选择。然而,Li+和Zn2+离子位于LZTO的四面体位点,在一定程度上阻碍了离子的迁移,导致LZTO电导率差,锂离子扩散系数低。LiAlO2的包覆有效避免了电极表面与有机电解质的接触,从而减少了副反应的发生。因此,本文采用简单的高温固相法合成了Li2ZnTi3O8@LiAlO2复合材料。结果表明:LiAlO2改性未改变LZTO的形貌和粒径,但是提高了其结构稳定性、锂离子脱嵌的可逆性和电化学活性,促进了锂离子的迁移。Li2ZnTi3O8@LiAlO2 (8wt%)在0.5 C、1 C、2 C、3 C和5 C时的充电容量分别为203.9、194.8、187.4、180.6和177.1 mAh·g?1,表现出良好的倍率性能。然而,在相同的倍率下,纯LZTO仅有134.5、109.7、89.4、79.9和72.9 mAh·g?1的容量。即使在较大的充放电倍率下,Li2ZnTi3O8@LiAlO2(8wt%)材料也表现出良好的循环性能。在5 C倍率循环150次后后,Li2ZnTi3O8@LiAlO2(8wt%)仍具有263.5/265.8 mAh·g?1的充放电容量。LiAlO2的引入增强了LZTO材料的电子导电性,使Li2ZnTi3O8@LiAlO2复合材料具有优异的电化学性能。  相似文献   

7.
针对目前超临界溶剂热合成纳米磷酸铁锂(LiFePO4)的晶体生长机制及反应参数影响规律尚不明确的问题,采用超临界溶剂热合成方法在340~400℃反应温度下制备了平均粒径为68~85 nm的LiFePO4粉体,表征并分析了产物的晶体结构及粒径等性能,评估了超临界乙醇中纳米LiFePO4晶体生长过程表观活化能及生长机制,并建立了纳米LiFePO4晶体生长动力学。结果表明,纳米LiFePO4在超临界溶剂中的生长过程对其最终尺寸起主导作用,且生长过程受表面反应控制,符合多核控制的二阶生长动力学。纳米LiFePO4产物的电化学性能测试表明,在400℃下获得的样品在0.1C(C为电池充放电倍率)倍率下的初始放电比容量达到153.5 mA·h/g,放电倍率提高至5C时容量保持率为68.3%。在340℃反应温度下:所得产物中的杂质(Li3Fe2(PO4)3和Fe3...  相似文献   

8.
为了研究Gd2Zr2O7烧绿石的合成条件,以Gd2O3,ZrO2混合粉体为原料,在1 773 K的温度、3 GPa和5.2 GPa的压力及10~30 min的保温保压时间内,进行了高温高压实验。借助于XRD,SEM,IR等分析,对合成样品结构、形貌等进行表征,结果表明:在1 773 K的高温、5.2 GPa的高压和10 min的保温保压条件下可合成单一物相的Gd2Zr2O7立方烧绿石。为固化锕系核素的陶瓷基材合成及其固化体的制备提供了一种快速高效的方法。  相似文献   

9.
 采用高能球磨法在800℃保温2h预烧合成MgNb2O6粉体,研究了MgNb2O6陶瓷的相结构、显微结构和微波介电性能随烧结温度的变化关系。实验结果表明,高能球磨法有效促进MgNb2O6粉体的低温合成,降低MgNb2O6陶瓷的烧结温度。1220℃保温2h烧结MgNb2O6陶瓷,密度为4.80g/cm3,平均粒径为3.5μm,介电常数εr为19.7,品质因数(Q·f)为29444GHz的优良微波介电性能,MgNb2O6粉体有望成为新一代中温烧结高频微波介质基板材料。  相似文献   

10.
采用液相无焰燃烧法在500℃反应1 h,然后在600℃二次焙烧3、6、9 h和12 h制备了尖晶石型Li1.05Ni0.05Mn1.90O4正极材料.结果表明,不同二次焙烧时间制备的Li-Ni复合共掺材料没有改变LiMn2O4的尖晶石结构,随着焙烧时间的增加,颗粒尺寸增大,结晶性提高.二次焙烧时间为9 h的Li1.05Ni0.05Mn1.90O4样品的颗粒尺寸约为70~100 nm,具有优异的电化学性能,在1 C(1 C=148 mA·h·g-1)倍率,初始放电比容量为94.8 mA·h·g-1,400次循环后展现出72.15%的容量保持率;在5 C下初始放电比容量可达到89.7 mA·h·g-1,800次循环后,仍能维持70.79%的容量保持率.并且具有较小的电荷转移电阻和较低的表观活化能.Li-Ni复...  相似文献   

11.
Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.  相似文献   

12.
何延凌 《科技信息》2008,(4):258-258
Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women's language from these perspectives: pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women's language, more attention should be paid to language use in social context. What's more, the linguistic phenomena in a speaking community can be understood more thoroughly.  相似文献   

13.
There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.  相似文献   

14.
理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。  相似文献   

15.
The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3~4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰~ -7.8‰, PDB) and matrix dolomites (-6.6‰~ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084~0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078~0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.  相似文献   

16.
As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.  相似文献   

17.
王慧 《科技信息》2008,(10):240-240
Wuthering Heights, Emily Bronte's only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.  相似文献   

18.
The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.  相似文献   

19.
In the 19th century the society was controlled by men, and women were just appendants of them, they had not any rights and freedom. But Jane was an exception, she showed some characteristics of early feminist. Jane showed her characteristics of feminism in three aspects: rebellion, equality, and independence. These characteristics were helpful to her success, and feminism is the only way out for women of that time.  相似文献   

20.
1 Rise of studies on climate change's effects on biodiversity
Until the 1980s, climate change and biodiversity were studied as two independent disciplines for more than a century. In 1992, the Ecological Society of America's annual report named climate change, biodiversity, and the sustainable ecological system as the three major global environmental issues of the twenty-first century [1].  相似文献   

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