首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 78 毫秒
1.
用示差扫描量热法和电阻测量研究高温时效对Cu-Zn-Al-Mn合金相变的影响。实验结果表明,刚制备的试样在第一次升温的DSC测量发一在130℃附近有一个放热峰,该峰可能与正交晶系的9R贝氏体形成之前溶质原子产生析出有关。  相似文献   

2.
Cu-Zn-Al合金中贝氏体相变对形状记忆效应的影响   总被引:1,自引:0,他引:1  
本文采用一种精确测量形状记忆效应(SME)和观察不同时期显微组织的方法,研究了Cu-26(wt)%Zn-4(wt)%Al合金,在800℃淬火后重返母相区130℃、150℃和170℃时效的变化规律.实验结果表明,淬火马氏体进入母相区时效初期形状记忆回复率迅速升高,达到一个最大值后随时效时间而下降,显示出时效过程中马氏体稳定化效应的消除和贝氏体相变的发展这两种不同机制对SME所引起的相反效果,即马氏体稳定化的消除增强着SME而贝氏体相变的发生却恶化着SME.贝氏体在晶界的析出对SME已颇为有害,而当贝氏体在晶内形成时SME将激烈恶化.  相似文献   

3.
β—环糊精的热稳定性及分解动力学研究   总被引:2,自引:0,他引:2  
β—环糊精的DSC曲线表明:β—CD在265~370℃之间有一大的吸热峰,温度超过370℃时转化为放热峰;吸热峰对应着β—CD失去结构水(分解过程),而放热峰表明是碳与氧反应生成二氧化碳的过程(氧化过程).本文用等温热重法和线性升温热重法在氮气气氛中研究β—CD的分解过程,运用判断机理的三步判别法对实验数据分析证明:该过程是受三维扩散机理(D4)控制.其热分解过程的表观活化能E=168.79kJ/mol,频率因子A=1.1250×1013min-1.  相似文献   

4.
用DSC(差示扫描量热法)研究三羟甲基乙烷CH3C(CH2OH)3(PG)和三羟甲基丙烷CH3CH2-C(CH2OH)3(TMP)二元系的混合物的贮热性能.PG和TMP具有固-固转变特性,其纯组分的转变温度分别为83℃和55℃附近.研究结果表明,随着PG浓度的增加,低温峰变小,高温峰形变大.尤其是在DSC测试中当第一次加热至固-固相变转化结束后,冷却至室温,再第二次加热,进行DSC测试,发现绝大多数PG/TMP二元系出现明显的唯一峰,且倾向高温峰方向,这表明TMP对该体系的低温贮热不利  相似文献   

5.
用离子交换法合成了杂多阴离子柱撑阴离子粘土ZnAl-SiW11和ZnAl-SiW11Z(Z=Co2+,Ni2+,Cu2+).XRD和IR测定结果表明,这些层柱化合物的通道高度是1.46×10-7cm,层间阴离子保持它们的Keggin结构.它们在空气中热分解序列为:ZnAl-SiW11Ni(347℃)>ZnAl-SiW11Co(341℃)>ZnAl-SiW11Cu(335℃)>ZnAl-SiW11(329℃)>ZnAl-(290℃),在沸腾水溶液中稳定存在的pH值范围是3.6~7.5.  相似文献   

6.
Cu—Zn—Al合金中贝氏体相变对形状记忆效应的影响   总被引:3,自引:1,他引:3  
本文采用一种精确测量形状记忆效应(SME)和观察不同时期显微组织的方法,研究了Cu-26(wt)%Zn-4(wt)%Al合金,在800℃淬火后重返母相区130℃、150℃和170℃时效的变化规律。实验结果表明,淬火马氏体进入母相区时效初期形状记忆回复率迅速升高,达到一个最大值后随时效时间而下降,显示出时效过程中马氏体稳定化效应的消除和贝氏体相变的发展这两种不同机制对SME所引起打反效果,即马氏体稳  相似文献   

7.
藉助于X-射线衍射(XRD)谱和热重(TG)分析,研究了纳米Co2TiO4的热稳定性。结果表明在第一次升温测量的差示扫描量热(DSC)曲线上存在两个吸热峰(P1,P2峰)和一个放热峰(P3峰),再次升温测量时,这些峰均消失了。研究表明,这些峰分别起因于物理脱附、化学脱附、相变和晶粒长大。  相似文献   

8.
本文报道用晶体场理论对新型稀磁半导体Zn_(1-x)Co_xSe和Zn_(1-x)Co_xS中Co ̄(2+)离子不同能级间的跃迁进行计算的结果。与实验观测结果进行了比较,获得了相应的晶场参量D_q,Racah静电参量B,C和自旋-轨道耦合参数λ。本文对Zn_(1-x)Co_xSe和Zn_(1-x)Co_xS分别指认了观测到的Co ̄(2+)离子能级间的跃迁。对较低能级部分,实验结果与理论计算符合较好。  相似文献   

9.
本文用铅笔芯制成的电极(PCE),与玻碳电极(GCE)比较,研究了Zn(Ⅱ)的阶梯循环伏安法(CSV)、阶梯阳极溶出伏安法(ASSV)和差分脉冲阳极溶出法(ASDPV)等的伏安特性。实验指出,PCE与GCE有相似的伏安特性曲线,且具有较好的重视性和选择性。由于PCE较GCE的结构疏松,电极表面积较大,故PCE的灵敏度RGCE高。其阳极溶出法的最低检出限可达到5×10-6mol·L-1的Zn(Ⅱ),Zn(Ⅱ)的浓度在3.6×10-4~8×10-6mol·L-1范围内与峰电流呈良好的线性关系。  相似文献   

10.
以自制Zr(OC3H7)4和Y(CH3COO)3为原料,应用溶胶-凝胶法(Sol-Gel)制备了YSZ(ZrO2-9mol%Y2O3)凝胶和超细粉末.研究了Sol-Gel形成机理以及pH值对胶凝时间和凝胶结构的影响.通过TG-DTA、XRD等分析手段,研究了从干凝胶到YSZ超细粉末过程中的反应机理.实验证明:反应可分为3个阶段,钇稳定立方相ZrO2的合成温度在470℃左右  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.
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   

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.
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   

16.
AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…  相似文献   

17.
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   

18.
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   

19.
正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-  相似文献   

20.
We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号