Specific heat in superconductors

Specific heat is a powerful tool to investigate the physical properties of condensed materials.Superconducting state is achieved through the condensation of paired electrons,namely,the Cooper pairs.The condensed Cooper pairs have lower entropy compared with that of electrons in normal metal,thus specific heat is very useful in detecting the low lying quasiparticle excitations of the superconducting condensate and the pairing symmetry of the superconducting gap.In this brief overview,we will give an introduction to the specific heat investigation of the physical properties of superconductors.We show the data obtained in cuprate and iron based superconductors to reveal the pairing symmetry of the order parameter.

Fluctuating specific heat in two-band superconductors

Theory of thermal fluctuations in two-band superconductors under an essentially homogeneous magnetic field is developed within the framework of the two-band Ginzburg-Landau theory. The fluctuating specific heat is calculated by using the optimized self-consistent perturbation approach and the results are applied to analyze the thermodynamic data of the iron-based superconductors Ba（1-x）KxFe2As2 with x -0.4, which have been suggested to have a two-band structure by recent experiments. We estimate the fluctuation strength in this material and find that the specific heat is described well with the Ginzburg number Gi = 4 · 10^-4. The influence of interband coupling strength is investigated and the result of the two-band Gaussian approximation approach is compared.

Characteristic of specific heat capacity of NiTi alloy phases

The specific heat capacity of NiTi alloy at constant pressure using MDSC (Modulated differential scanning calorimeter) was determined. It was found that the variation tendencies of the specific heat capacity for different phases are different. The fitting equations of the specific heat capacity for martensite and austenite phases were presented. Then, a reason, based on thermodynamic point of view, was proposed to explain the difference of the specific heat capacity between martensitic and austenitic phases. Finally, compared with the specific heat capacity of pure Ni and Ti, it was found that the specific heat capacity of NiTi alloy is inherent to that of pure Ti. When the specific heat capacity of NiTi alloy is calculated by Neuman Kopp, in the temperature region of phase transformation and the temperature higher than 400 K, the results are not desirable.[

Theoretical Study on the Effect of Multiband Structure on Critical Temperature and Electronic Specific Heat in SmOFeAs Iron Pnictide Superconductor

In the present theoretical work, superconducting order parameter (∆) and electronic specific heat (Ces) of SmOFeAs iron pnictide (IP) superconductor has been studied using multiband (MB) model of IP superconductors. Attempt has been made to use the MB structure of IP superconductors and expressions for critical temperature (Tc) and Ces are obtained, calculations being made for one, two and three bands of SmOFeAs. It has been found that MB results are close to the experimental value of Tc for this compound. Ces calculations show jump of 1.5 × 10-5 eV/atom K, 4 × 10-5 eV/atom K and 4 × 10-5 eV/atom K for one, two and three band models respectively. The study brings out the importance of MB structure in IPs, highlighting the fact that increasing the number of bands, increases Tc. The specific heat jump (∆C) does not correspond to the BCS value, thereby proving that IPs are unconventional in nature.

THE STRUCTURAL PHASE TRANSITION NEAR 210 K OF Bi-BASED SUPERCONDUCTORS

Recently, systematic investigations on Bi-based superconductors were carried out by means of ultrasonic measurements, thermal analysis, specific heat experiments and X-ray diffraction measurements. It was found for the first time that a possible structural phase transition occurs near 210 K in these systems. All the samples used were of single phase

工质线性变比热对内可逆Rallis循环功率效率性能的影响

应用有限时间热力学理论建立工质比热随温度线性变化时内可逆Rallis循环模型,导出循环的功率(P)和效率(η)的解析式。通过数值算例分析循环增压比(λ)、压缩比(ε)、预胀比(ρ)、传热损失(B)和工质比热随温度线性变化系数(k_(1))对P与膨胀比(σ)、η与σ以及P与η特性曲线的影响。结果显示:循环P-σ和η-σ特性曲线为类抛物线型,循环P-η特性曲线为扭叶型;存在最佳的膨胀比σ_(P)和σ_(η),分别使P和η达到最大值(P_(max)和η_(max));随着ε和λ的增大,P_(max)、σ_(P)、η_(max)、σ_(η)、η_(max)对应的功率(P_(η))和P_(max)对应的效率(η_(P))单调递增;随着ρ的增大,P_(max)、η_(max)、σ_(η)和P_(η)单调递增,σ_(P)不变,η_(P)单调递减;随着B和k1的增大,η_(max)和η_(P)单调递减,σ_(η)和P_(η)单调递增。将所得结论与恒比热内可逆Rallis循环的结论进行对比,结果显示:随ρ的增大,σ_(P)不变,恒比热时σ_(P)单调递增;η_(P)单调递减,恒比热时η_(P)单调递增。通过分析可知工质比热变化对Rallis循环性能的影响较为明显,所得结论对该循环的应用有一定参考意义。

三氟乙烷的气相音速测量与热力学性质研究

采用球型腔体声学共振法测量了新型制冷剂三氟乙烷 (HFC143a)的气相音速 ,得到了压力在 2 0 0～ 80 0kPa范围内 ,温度分别为 2 93 61、30 2 96、313 19和 32 3 18K时的 4条等温线共 2 8个音速数据 .根据实验数据 ,由热力学关系式得到了HFC143a的理想气体比定压热容和第二音速维里系数等热力学性质 ,同时根据现有的高精度实验数据拟合了HFC143a的理想气体比热方程 .温度、压力和气体音速测量的不确定度分别为± 14mK、2 0kPa和± 0 0 0 37% .

RDX的比热容、热力学性质及绝热至爆时间

应用Micro-DSCⅢ微热量仪测定了RDX的比热容，得到了二次方温度方程，298．15K时RDX的标准摩尔比热容为251．17J·mol^-1·K^-1。运用Gaussian 03W程序的DFT—RB3LYP／6—311＋＋G^＊＊方法对RDX在280～350K的温区内进行比热容理论计算。结果表明，理论值低于实测值，偏差在12．72％～15．94%。用测得的比热容方程计算了298．15K为基础的RDX的热力学函数，并得到了绝热至爆时间为3．10～3．19s。

3，4-二硝基呋咱基氧化呋咱的比热容、热力学性质、绝热至爆时间及热感度概率密度分布

应用Micro-DSCm微热量仪对3，4-二硝基呋咱基氧化呋咱（DNTF）进行比热容测定，得到了DNTF比热容随温度变化的线性方程定压cp=0．31064＋2．109×10^-3T（285K〈T〈345K），298．15K时DNTF的标准摩尔比热容为293．10J／（mol·K）．运用Gaussian 98W程序的DFT—RB3LYP／6—31＋G（d）方法对DNTF在285～345K的温度范围内进行了比热容理论计算．用测得的比热容方程计算了298．15K为基础的DNTF的热力学函数，得到了绝热条件下DNTF的绝热至爆时间为103．7s．推导了含能材料热感度概率密度函数的表达式，构建了DNTF的热感度概率密度分布图．

二甲醚热力学性质的计算

利用现有的二甲醚气相状态方程、饱和气液密度方程、蒸气压方程、理想气体定压比热容等方程,计算得到了二甲醚的饱和液体熵和饱和气体熵.从气相维里方程出发,结合Clapeyron方程计算得到了二甲醚的饱和蒸发焓.采用偏差函数法及陈则韶教授提出的饱和液体焓推算公式,计算出了二甲醚的饱和气液焓和临界焓值.最后,开发了二甲醚热力学性质的计算程序,并得到了从235 15K至临界点的二甲醚饱和热力学性质表,计算结果的精度在±2%内,可为工程实际应用提供服务.

毛竹竹材几个热力学特性参数的测试与分析

采用闪光法和比较法及直线法分别测量了毛竹竹材沿垂直竹纤维方向的几个热力学特性参数:热扩散率α、比热Cp及竹材密度ρ,并根据公式λ=418.68αCpρ得出其另一个重要的热力学特性参数——导热系数λ.结果表明:竹材的热扩散率α与竹材生长的方向和高度的关系不大;导热系数λ、热扩散率α、比热均Cp在温度为70℃左右时具有最大值.这一结果对竹材的热处理加工具有一定的指导意义.

纳米晶体铁的低温热容和热稳定性

用等离子体法制备的纳米晶体铁由ＸＲＤ和ＳＥＭ等方法测定其晶粒尺寸的平均值为８７ｎｍ．用绝热量热方法在７９～３７１Ｋ温区精确测定了其低温热容、测量结果比大晶粒Ｆｅ的热容值有明显的增强．在 ８０～３００Ｋ温区之间增强热容为８％～１４％．差示扫描量热（ＤＳＣ）在高温区的研究结果则表明，纳米晶体 Ｆｅ在４００～７００Ｋ温区有一个宽的放热峰，对应于非平衡晶格缺陷所引起的含释放．８５０Ｋ观察到一个放热峰，是纳米晶体铁从α相向α＋γ相转变所引起的．

内可逆四热源吸收式热变换器的基本优化关系及其性能分析

应用内可逆四热源吸收式热变化器循环模型,分析热变换器受传热不可逆性影响时的基本性能。导出了牛顿传热定律下循环的比泵热率和泵热系数的基本优化关系以及工质的最佳工作温度和传热面积的最佳分配关系。由此讨论了循环的各种优化性能,并通过数值算例,得出循环参数对循环特性的影响规律。所得结果对实际四热源吸收式热变换器的优化设计具有一定指导意义。

换热器系统的热力学性能评价

引入可用能损率这一指标对串联组合的换热器系统的热力学性能进行了分析和评价 ,得到了换热器系统可用能损率的一般计算式 ,讨论了换热器系统的总流动趋势、冷热流体热容量流率比、传热单元数及单台换热器的流型。

3,3'-二氨基-4,4'-氧化偶氮呋咱的热分解行为及热力学性质

采用TG-DTG和DSC研究了3,3'-二氨基-4,4'-氧化偶氮呋咱(DAOAF)的热分解行为,运用Kissinger法和Flynn-Wall-Ozawa法计算了DAOAF的热分解动力学参数;利用DSC仪的连续比热容测定模式测定了DAOAF的比热容;根据比热容与热力学函数关系,计算了DAOAF以298.15 K为基准的热力学函数在253~373 K温区的焓、熵和吉布斯自由能函数值。结果表明,DAOAF是一种熔融分解型含能材料,DAOAF热分解的平均活化能和指前因子分别为152.23 kJ·mol^(-1)和1012.53s^(-1)。得到比热容随温度变化的关系式cp(J·g^(-1)·K^(-1))=0.00303T+0.17235(253 K<T<373 K),298.15 K时DAOAF的标准摩尔热容为228.05 J·mol^(-1)·K^(-1)。

3,5-二氨基-1,2,4-三唑苦味酸盐的比热容、热力学性质及爆速爆压的估算

目的研究三唑类含能离子化合物3,5-二氨基-1,2,4-三唑苦味酸盐(C8N8H8O7,简称DAT.PA)的比热容,热力学性质及爆速、爆压。方法比热容测定采用Micro-DSCⅢ微热量仪中的连续比热容测定模式;运用Gaussian 03W程序的DFT-RB3LYP/6-31g*方法对DAT·PA在283～353K的温度范围内进行了比热容理论计算;根据热力学基本方程计算以298.15 K为基础DAT.PA的热力学函数;采用氮平衡方程研究化合物的爆速和爆压。结果得到DAT.PA比热容方程为Cp(J/g·K)=-0.233 7+6.005 6×10-3T-5.396 9×10-6T2(283K<T<353K),298.15K下,标准摩尔比热容为353.285J/mol·K。计算得到化合物的爆速爆压值分别为982.48 m/s和36.07GPa。结论化合物基本物化参数及性能参数的测量及估算,为其在含能材料领域的应用提供必要的基础数据。

微纳米RDX炸药的连续比热容、热力学性质和热分解动力学

为了分析不同粒径RDX的热性能,在温度288~353K下,采用μSC量热法测试了粒径分别为1μm、500nm、100nm的微纳米R D X炸药的连续比热容,由比热容随温度的变化曲线拟合得到了温度二次方的Cp表达式,并依据热力学定律计算获得了不同粒径RDX的热力学参数;采用DSC分别测试了3种粒径RDX的热分解性能,获得热分解规律曲线,并用Kissinger法计算了不同粒径RDX的分解动力学参数。结果表明,μSC量热法测试连续比热容简便并且数据准确。微纳米RDX的比热容、熵和焓均随着温度的升高而增加,但吉布斯自由能降低;焓和吉布斯自由能随粒径的下降而下降,但熵随着粒径的下降而增加;与微米RDX相比,两种纳米RDX的熵和吉布斯自由能随粒径的变化不大,这两种热力学函数显示了纳米与微米材料之间的不同;纳米与非纳米RDX熔融态分解的动力学参数虽有不同,但它们都服从同一"动力学补偿效应"。

工质变比热和传热损失对内可逆矩形循环性能的影响

用有限时间热力学理论和方法分析空气标准矩形循环,由数值计算给出了存在传热损失和工质变比热时循环功与压缩比、效率与压缩比以及功和效率的特性关系,并分析了传热损失和工质变比热对循环性能的影响特点,通过分析可知传热和变比热特性对矩形循环性能有较大影响。

ATO的DFT研究、热力学性质及绝热至爆时间(英文)

用DFT法在B3LYP/6-311G＊＊水平上对作为结构单元的4-氨基-1,2,4-三唑-5-酮（ATO）进行了理论研究,评述了它的布居分析及稳定性。运用Micro-DSC微热量仪对ATO的比热容进行了测定,拟合得到其比热容与温度的关系式为Cp=1.482915-6.209699×10^-3T＋1.699017×10^-5T2（J·g^-1·K^-1）和298.15K时标准摩尔热容114.18J·mol^-1·K^-1。根据热容与热力学函数关系,计算得到了ATO以298.15K为基准在283~353K温区的焓、熵和吉布斯自由能。根据热容关系式及其热分解参数估算其绝热至爆时间为408.05s。

二乙酸·二(4-氨基-1,2,4-三唑)合锌(Ⅱ)配合物的制备、晶体结构、比热容及热力学性质

利用4-氨基-1,2,4-三唑(4-ATZ)的乙醇溶液与乙酸锌的甲醇溶液合成了标题化合物Zn(4-ATZ)_2(CH_3COO)_2,并培养出单晶,通过X射线单晶结构分析法测定晶体结构,晶体属于正交晶系,空间群为Aba2,晶胞参数为:a=0.767 32(7)nm,b=1.66444(16)nm,c=1.09040(11)nm,V=1.3926(2)nm^3,D_c=1.936 g·cm^(-3),Z=4,F(000)=720,R_1=0.0246,wR_2=0.0675。运用Micro-DSCⅢ微热仪测定配合物的比热容,在283～353 K时,比热容随温度呈二次方关系,其关系式为:C_p/(J·g^(-1)·K^(-1))=-2.021915+1.749228×10^(-2)T-2.358752×10^(-5)T^2,298.15 K时配合物的标准摩尔比热容为385.62 J·mol^(-1)·K^(-1)。