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1.
基于经典结晶理论讨论了非晶合金的晶化动力学因素和晶化热力学因素对玻璃形成能力(GFA)的影响.分析表明,合金的等温转变(TTT)曲线“鼻尖”温度Tn对应的黏度与晶化阻力因子成正比;重新加热时晶化开始温度Tx对应的黏度与晶化驱动力因子成反比.由此得到了新的GFA参数ω0=(Tg-T0)/(Tx-T0)-(Tg-T0)/(Tn-T0),其中Tg为玻璃转变温度,T0为理想玻璃转变温度.统计结果显示,ω0与临界冷却速率具有较高的相关性,R2高达09626.进一步分析表明:新提出的ω0参数可以合理地解释过冷熔体的黏度、脆性、液相稳定性、热稳定性以及Trg、ΔTxγγm、ΔTrgαβδφ等参数与GFA的关系. 关键词: 块体非晶合金 黏度 脆性 玻璃形成能力  相似文献   

2.
陈东丹  张勤远  姜中宏 《物理学报》2010,59(8):5796-5802
研究了混合形成体效应对掺铒碲酸盐玻璃热力学稳定性、1.53 μm发光特性和上转换发光强度的影响.通过拉曼光谱测试,分析了WO3,Nb2O5,GeO2等氧化物对Er3+离子配位场结构,以及对发光谱的非均匀展宽机理的作用.结果表明,通过掺杂适当声子能量的网络形成体氧化物,不但可获得热力学稳定性较好的玻璃,还可有效降低Er3+离子4I11/2能级的寿命,在抑制Er3+离子在可见光波段的上转换发光的同时不致劣化其在1.53 μm的发光特性.本文制得的碲酸盐玻璃具有较大的受激发射截面((9.64—10.96)×10-21cm2)和荧光半高宽(FWHM)(50—67 nm),热力学稳定性良好,是一种理想的掺Er3+宽带有源光纤用基质玻璃. 关键词: 掺铒碲酸盐玻璃 混合形成体 1.53 μm发光 声子能量  相似文献   

3.
在CuZr二元大块金属玻璃的基础上,利用铜模吸铸方法制备出了添加Al组元的CuZr 基大块 金属玻璃.CuZr基大块金属玻璃在很宽的成分范围内有很强的玻璃形成能力,在Al含量从4% 到8%之间,CuZr基大块金属玻璃都可以做出直径至少5 mm的非晶样品.通过实验分析,解释 了CuZr基大块金属玻璃具有良好玻璃形成能力的物理机理.CuZr基金属玻璃组分简单、成本 低廉,有潜在的应用价值;同时,制备CuZr基金属玻璃的方法为开发新的大块金属玻璃体系 提供了一条切实有效的途经. 关键词: 大块金属玻璃 玻璃形成能力 CuZr基金属玻璃  相似文献   

4.
新型Pr基大块非晶及其特性研究   总被引:8,自引:0,他引:8       下载免费PDF全文
用铜模吸铸法获得了直径为5mm的一种新的Pr基大块非晶.与以往其他稀土-过渡金属(RE-TM)大块非晶不同的是,这种新的Pr基大块非晶具有明显的玻璃转变和稳定的过冷液相区,且其玻璃转变温度在目前已知的大块非晶中是最低的,Tg=409K.研究了该大块非晶的玻璃转变动力学,并给出了Kauzmann温度Tk、Vogel-Fulcher温度T0g及脆性参数m等重要参数. 关键词: 大块非晶 玻璃转变 脆性参数m  相似文献   

5.
研究了Nd60Al10Fe20Co10 大块金属玻璃 磁性随温度的变化关系,结果表明Nd60Al10Fe20Co10 在室温下 表现为永磁性,随着温 度的降低,矫顽力和磁滞回线形状都有很大的变化.交流磁化率在18 K左右出现尖峰而且峰 值温度随频率变化,表明该大块非晶体系中存在自旋玻璃态. 关键词: 大块金属玻璃 低温磁化率 自旋玻璃  相似文献   

6.
在大块非晶临界冷却速率的非等温转变计算模型基础上提出了基于成分连续变化计算黏度的合金系临界冷速模型. 依据此模型对Zr-Ni-Al-Cu四元合金的临界冷却速率进行了计算并预测了Zr66.67(NixAlyCuz)33.33合金系中容易形成非晶的成分范围. 计算值与实验值符合得较好. 计算结果表明,此合金系具有很强的非晶形成能力,特别是在靠近共晶点的中心区域,临界冷却速率小于100 K/s,为容易形成非晶的成分范围. 冷却过程中,在高于1000K温度区间,没有发生明显的结晶现象,而在980 K至870 K温度范围内,结晶分数快速增大,低于870 K时不再发生明显改变. 此外,分析了合金系中Al,Cu,Ni原子摩尔分数的变化对临界冷速的影响. 关键词: 大块非晶 黏度 临界冷却速率 非晶形成能力  相似文献   

7.
潘杰云  张辰  何法  冯庆荣 《物理学报》2013,62(12):127401-127401
利用混合物理化学气相沉积法(HPCVD)在MgO(111)衬底上制备了干净的MgB2超导超薄膜. 在背景气体压强, 载气氢气流量以及沉积时间一定的情况下, 改变B2H6的流量, 制备得到不同厚度系列的MgB2超导薄膜样品, 并测量了其超导转变温度 Tc, 临界电流密度Jc等临界参量. 该系列超导薄膜沿c轴外延生长, 表面具有良好的连接性, 且有很高的超导转变温度Tc(0) ≈ 35-38 K和很小的剩余电阻率ρ(42 K) ≈ 1.8-20.3 μΩ·cm-1. 随着膜厚的减小而减小, 临界温度变低, 而剩余电阻率变大. 其中20 nm的样品在零磁场, 5K时的临界电流密度Jc ≈ 2.3×107 A/cm2. 表明了利用HPCVD在MgO(111)衬底上制备的MgB2超薄膜有很好的性能, 预示了其在超导电子器件中广阔的应用前景. 关键词: MgO(111)衬底 2超薄膜')" href="#">MgB2超薄膜 混合物理化学气相沉积  相似文献   

8.
崔晓  徐保臣  王知鸷  王丽芳  张博  祖方遒 《物理学报》2013,62(1):16101-016101
以1at% Ag元素分别等量替代Zr57Cu20Al10Ni8Ti5金属玻璃的各个组元,利用差示扫描量热升温分析获得不同试样的热力学参数,并结合不同尺寸(Φ8,Φ10,Φ12)吸铸试样的X-射线衍射分析结果,考察、验证元素替代后合金的实际玻璃形成能力及热稳定性的变化规律.经比较发现,Ag替代Ti元素,其玻璃形成能力显著提高(直径实际增大4 mm),同时热稳定性也明显改善,且临界冷却速率也明显降低,而Ag替代其他组元却无明显规律.针对玻璃形成能力的相关数据比较分析表明,本文结果未显示符合其Inoue的尺寸准则,混合焓判据也未显示出明显符合的现象.通过对堆垛密度的计算发现,1 at% Ag替代Ti元素后使金属玻璃体系内部的堆垛密度增加.通过动力学分析,从晶化激活能、晶化反应速率常数两方面探讨了元素替代对玻璃形成能力和热稳定性的作用机理.  相似文献   

9.
陈艺灵  张辰  何法  王达  王越  冯庆荣 《物理学报》2013,62(19):197401-197401
通过混合物理化学气相沉积法 (hybrid physical-chemical vapor deposition, HPCVD), 在(000l) SiC 衬底上制得一系列从10 nm到8 μm的MgB2超导膜样品, 并对它们的形貌、超导转变温度Tc 和临界电流密度Jc与膜厚度的关系进行了研究. 观察到Tc随膜厚度增加上升到最大值后, 尽管膜继续增厚, 但Tc值保持近乎平稳, 而Jc则先随膜厚度增加上升到最高值后, 继而则随膜的厚度的增加而下降. MgB2膜的Tc(0)和Tc(onset)值与膜厚的关系基本一致, Tc(0)在膜厚为230 nm处达到最大值Tc(0)=41.4 K, 而Jc(5K,0T)在膜厚为100 nm时达到最大值, Jc (5 K, 0 T)=2.3×108A·cm-2, 这也说明了我们能用HPCVD方法制备出高质量干净MgB2超导膜. 本文研究的超导膜厚度变化跨度非常大, 从10 nm级的超薄膜到100 nm级的薄膜, 再到几微米的厚膜, 如此TcJc对膜厚度变化的依赖就有了较完整、成体系的研究. 并且本文的工作对MgB2超导薄膜制备的厚度选取具有实际应用意义. 关键词: 2超导膜')" href="#">MgB2超导膜 混合物理化学气相沉积法 厚度 临界电流密度  相似文献   

10.
在非等温转变理论以及非稳态形核理论基础上提出了计算大块非晶合金连续冷却转变曲线和 临界冷却速率的新模型,以用于评估合金的非晶形成能力. 依据此模型对Zr基和Pd基8种合金 进行了计算,计算结果与实验值符合较好. 计算结果表明,影响临界冷却速率的主要因素为 黏度、临界形核功和临界结晶分数. 随着黏度增大,临界冷却速率降低;随临界形核功增大 ,临界冷却速率急剧降低;随临界结晶分数增大,临界冷却速率起初降低较快,达到一定程 度后下降速率趋于缓慢. 关键词: 临界冷却速率 非晶形成能力 大块非晶 连续冷却转变曲线  相似文献   

11.
The temperature dependence of Gibb's free energy difference (ΔG), entropy difference (ΔS) and enthalpy difference (ΔH) between the undercooled melt and the corresponding equilibrium solid phases of bulk metallic glass (BMG) forming melts has been proved to be very useful in the study of their thermodynamical behavior. The present study is made by calculating ΔG, ΔS and ΔH in the entire temperature range Tm (melting temperature) to Tg (glass transition temperature) for three Zr-based samples of BMGs: Zr57Cu15.4Ni12.6Al10Nb5, Zr41.2Ti13.8Ni10Cu12.5Be22.5 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8. The study is made on the basis of Taylor's series expansion and a comparative study is also performed between the present result and the result obtained in the framework of expansions proposed by earlier workers, and also with the experimental results. An attempt has also been made to study the glass forming ability for BMGs.  相似文献   

12.
Enthalpy recovery is not only an important characteristic of physical aging of glass, but also a good tool to investigate the physical aging. Using differential scanning calorimeter (DSC), the enthalpy recovery of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass (BMG) was studied. The typical characteristics of enthalpy recovery of glass including the sub-T g peak and ‘overshot’ were found in BMG. The evolution of the sub-T g peak and ‘overshot’ were described by the free volume theory and Hodge’s model, respectively. It was found that the former failed to describe the enthalpy recovery in the BMG, while the latter could give a qualitative explanation. In combination with the dynamics in the BMG, the origin of the enthalpy recovery in the BMG was discussed. The results show that BMGs are an ideal material to investigate the physical aging. The further understanding of physical aging of BMGs is useful to clarify the nature of glass and improve the application and device of new types of BMGs. Supported by the National Natural Science Foundation of China (Grant No. 50671118)  相似文献   

13.
Changes of activation parameters, ΔH and ΔS, with σ constants of substituents in the phenol and aniline nucleophiles for their SNAr reactions in various solvents give the δΔH and δΔS reaction constants which are linearly related. The dependence obtained, δΔH versus δΔS, allow estimation of the contribution of changes of the internal enthalpy, δΔHint, to the enthalpy reaction constant, δΔH, which give a linear dependence on the Hammett reaction constants, ρ. The results obtained show that the substituent effects on the charge development in the transition state (TS) are governed by the magnitude of δΔHint. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

14.
The interaction of an amino-functionalized ionic liquid, 1-(2-aminoethyl)-3-butylimidazolium bromide ([NH2C2C4im]Br), with cytochrome c (cyt c) at pH 7.4 was investigated using fluorescence and UV-Vis absorption spectroscopic techniques. From the experimental results, it is found that cyt c has a strong ability to quench the intrinsic fluorescence of [NH2C2C4im]Br and the quenching mechanism is considered as a static quenching process. The binding constants and the number of binding sites (n) were calculated at different temperatures. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) were calculated by thermodynamic equations. According to the results, the values of ΔG, ΔH, and ΔS are all negative, suggesting that interaction between [NH2C2C4im]Br and cyt c is spontaneous and mainly driven by hydrogen bonding and van der Waals forces.  相似文献   

15.
Differential scanning calorimetry (DSC) has been employed to investigate the glass transition activation energy E g, thermal stability and glass-forming ability (GFA) of Se90In10? x Sb x (x = 0, 2, 4, 6, 8, 10) chalcogenide glasses. DSC runs were performed at six different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperature. The dependence of glass transition temperature T g on heating rate (α), as well as composition of Sb, has been studied. From the dependence of glass transition temperature on heating rate, the E g has been calculated on the basis of the Kissinger [Anal. Chem. 29 (1957) p.1702] and Moynihan [J. Phys. Chem. 78 (1974) p.267] models. Thermal stability has been monitored through the calculation of temperature differences T cT g, the stability parameter S, and the enthalpy released during crystallization H c. The GFA has been investigated on the basis of the Hruby parameter H r, which is strong indicator of GFA. Results for GFA are in good agreement with fragility index F i calculations, indicating that Se90In6Sb4 is an excellent glass-former.  相似文献   

16.
Maleic acid-alt-styrene (MAaS) copolymer with number-average molecular weight [Mbar] n = 2500 was used as a compatibilizer in blends of poly(ethylene oxide) (PEO) and poly(styrene) (PS). PEO with weight-average molecular weight [Mbar] w = 105 (PEO100) and two PS samples with [Mbar] w = 9 × 104 and 4 × 105, respectively (PS90 and PS400, respectively) were used. A depression of the melting temperature T m of PEO in blends containing MAaS relative to pure PEO and PEO/PS blends was observed. The melting enthalpy ΔH m for the PEO/PS blends containing MAaS was lower than those of pure PEO and PEO/PS blends without compatibilizer. The crystallization kinetics of PEO and the blends were studied by differential scanning calorimetry (DSC) at different crystallization temperatures T c. Flory-Huggins interaction parameters χ12 for the blends were estimated. Their values are in good agreement with those obtained for similar systems and suggest that the free energy of mixing ΔG mix should be negative. Polarized optical microscopy shows differences in the macroscopic homogeneity of the blends containing compatibilizer that could be attributed to a compatibilization process.  相似文献   

17.
Heat capacities of the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its radical-ion salt NH4-TCNQ have been measured at temperatures in the 12-350 K range by adiabatic calorimetry. A λ-type heat capacity anomaly arising from a spin-Peierls (SP) transition was found at 301.3 K in NH4-TCNQ. The enthalpy and entropy of transition are ΔtrsH=(667±7) J mol−1 and ΔtrsS=(2.19±0.02) J K−1 mol−1, respectively. The SP transition is characterized by a cooperative coupling between the spin and the phonon systems. By assuming a uniform one-dimensional antiferromagnetic (AF) Heisenberg chains consisting of quantum spin (S=1/2) in the high-temperature phase and an alternating AF nonuniform chains in the low-temperature phase, we estimated the magnetic contribution to the entropy as ΔtrsSmag=0.61 J K−1 mol−1 and the lattice contribution as ΔtrsSlat=1.58 J K−1 mol−1. Although the total magnetic entropy expected for the present compound is R ln 2 (=5.76 J K−1 mol−1), a majority of the magnetic entropy (∼4.6 J K−1 mol−1) persists in the high-temperature phase as a short-range-order effect. The present thermodynamic investigation quantitatively revealed the roles played by the spin and the phonon at the SP transition. Standard thermodynamic functions of both compounds have also been determined.  相似文献   

18.
Variation of the activation parameters in the SN2, acyl‐transfer, SNAr, SNV, and AdN reactions offers a uniquely useful probe for the mechanistic features of these reactions in solution. New approach uses the substituent effects on the aromatic ring to the variation of the activation parameters, ΔH and ΔS, in the above reactions in the frameworks of the Hammett‐like equations in order to evaluate the resultant δΔH and δΔS reaction constants. Compensation relationships of δΔH versus δΔS allow one to estimate the contribution of changes of the internal enthalpy, δΔHint, to the enthalpy reaction constant, δΔH, that is inherent to bimolecular nucleophilic reactions and gives a single linear dependence on the Hammett ρ reaction constants for these reactions. The deviations from dependence of δΔHint versus ρ serve as useful points of interpretation of changes of the transition state structure or reaction mechanism. The results obtained show that the substituent effects in the substrates, nucleophiles, and leaving groups on the mechanistic features in bimolecular nucleophilic reactions are governed by the magnitude of δΔHint. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

19.
The heat capacity of [(C2H5)2NH2]2CuCl4 crystals, both nonirradiated and γ-irradiated to a dose of 107R, was studied in the temperature interval 90–330 K by adiabatic calorimetry. The temperature dependence of Cp(T) was found to have a peak-shaped anomaly in the region of the thermochromic phase transition (PT) at T = 322.7 K. Smoothened experimental heat capacity data were used to calculate the changes in the thermodynamic functions. The changes in the entropy and enthalpy of the thermochromic PT were determined to be ΔS = 42 J K?1 mol?1 and ΔH = 13653 J mol?1 for the nonirradiated crystals and ΔS = 39 J K?1 mol?1 and ΔH = 12120 J mol?1 for the irradiated crystals, respectively. Irradiation of a [(C2H5)2NH2]2CuCl4 crystal by γ rays to a dose of 107 R was shown to shift the PT point toward lower temperatures by ΔT ≈ 1.7 K.  相似文献   

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