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1.
Steady-state sublimation vapour pressures of anhydrous bismuth tribromide have been measured by the continuous gravimetric Knudsen-effusion method from 369.3 to 478.8 K. Additional effusion measurements have also been made from 435.4 to 478.6 K by the torsion—effusion method. Based on a correlation of Δsub H 298 0 and Δsub S 298 0 , a recommended p(T) equation has been obtained for BiBr3(s) $$\alpha - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\alpha /T - 12.294log{\text{ }}T + 5.79112 \times 10^{ - 3} {\text{ }}T + 47.173$$ with Cα=(Δ subH 298 0 +20.6168)/1.9146×10-2 $$\beta - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\beta /T - 23.251log{\text{ }}T + 1.0492 \times 10^{ - 2} {\text{ }}T + 77.116$$ with Cβ=(Δ subH 298 0 +46.2642)/1.9146×10-2 where p is in Pa, T in Kelvin, Δ sub H 298 0 in kJ mol?1. Condensation coefficients and their temperature dependence have been derived from the effusion measurements.  相似文献   

2.
3.
The14C self-diffusion coefficients for both lattice (D lc * ) and grain boundary (D bc * ) transport in high purity CVDβ-SiC are reported for the range 2128 to 2374 K. The Suzuoka analysis technique revealed thatD bc * is 105 to 106 faster thanD bc * ; the respective equations are given by $$\begin{gathered} D_{I c}^* = (2.62 \pm 1.83) \times 10^8 exp\left\{ { - \frac{{(8.72 \pm 0.14)eV/atom}}{{kT}}} \right\}cm^2 sec^{ - 1} \hfill \\ D_{b c}^* = (4.44 \pm 2.03) \times 10^7 exp\left\{ { - \frac{{(5.84 \pm 0.09)eV/atom}}{{kT}}} \right\}cm^2 sec^{ - 1} \hfill \\ \end{gathered} $$ A vacancy mechanism is assumed to be operative for lattice transport. From the standpoint of crystallography and energetics, reasons are given in support of a path of transport which involves an initial jump to a vacant tetrahedral site succeeded by a jump to a normally occupied C vacancy.  相似文献   

4.
Improvements have been made in a differential dilatometer using the three-terminal capacitance detector. The dilatometer is of copper and has been calibrated from 1.5–34 K in an extended series of observations using silicon and lithium fluoride as low-expansion reference materials. The expansion of silver and gold samples has been measured relative to the dilatometer, while the calibrations themselves have been used to determine the expansion of copper relative to the reference materials. Analyses of six sets of observations indicate that below 12 K the linear expansion coefficient α of copper is represented by $$10^{10} \alpha = (2.1_5 \pm 0.1){\rm T} + (0.284 \mp 0.005){\rm T}^3 + (5 \pm 3) \times 10^{ - 5} T^5 K^{ - 1} $$ corresponding to respective electronic and lattice Grüneisen parameters γ e =0.9 3 and γ 0 1 =1.78. Measurements on oxygen-free silver yield $$10^{10} \alpha = (1.9 \pm 0.2){\rm T} + (1.14 \mp 0.03){\rm T}^3 + (2 \pm 2) \times 10^{ - 4} T^5 K^{ - 1} $$ below 7 K, whence γ e ? 0.9 7 , γ 0 1 =2.23. By contrast, silver containing ca. 0.02 at. % oxygen showed a much larger expansion at the lowest temperatures: below 7 K, 10 10 α ~ 7T+1.19T 3 . We have not been able to obtain an unambiguous representation for gold, but find a reasonable fit below 7 K to be $$10^{10} \alpha \simeq (1 \pm 0.5){\rm T} + (2.44 \mp 0.05){\rm T}^3 - (5 \pm 1) \times 10^{ - 3} T^5 K^{ - 1} $$ with γ 1 ? 2.94 and γ e ? 0.7 (free-electron value).  相似文献   

5.
Measurements of the heat capacity and electrical resistivity of POCO AXM-5Q1 graphite in the temperature range 1500–3000 K by a subsecond-duration pulse-heating technique are described. The results for heat capacity may be represented by the relation $$C_{{\text{p }}} = 19.438 + 3.6215 \times {\text{10}}^{{\text{ - 3}}} {\text{ }}T - 4.4426 \times {\text{10}}^{{\text{ - 7}}} {\text{ }}T^2$$ where C p is in J · mol?1 · K?1 and T is in K. The results for electrical resistivity vary with the density (d) of the specimen material and, therefore, are represented by the following relations: for d=1.709, $$\rho = 1084.6 - 1.9940 \times {\text{10}}^{{\text{ - 1}}} {\text{ }}T + 1.6760 \times {\text{10}}^{{\text{ - 4 }}} T^{2{\text{ }}} - 2.0310 \times {\text{10}}^{{\text{ - 8 }}} T^3$$ and for d= 1.744, $$\rho = 943.1 - 1.3836 \times {\text{10}}^{{\text{ - 1}}} {\text{ }}T + 1.3776 \times {\text{10}}^{{\text{ - 4 }}} T^{2{\text{ }}} - 2.0310 \times {\text{10}}^{{\text{ - 8 }}} T^3$$ where ρ is in μΩ · cm, T is in K, and d (at 20°C) is in g · cm ?3. The maximum uncertainties in the measured properties are estimated to be 3% for heat capacity and 1 % for electrical resistivity.  相似文献   

6.
On the basis of Lee–Low–Pines unitary transformation, the influence of magnetic field and LO phonon effects on the energy of spin polarization states of strong-coupling bipolarons in a quantum dot (QD) is studied by using the variational method of Pekar type. The variations of the ground state energy $E_0$ and the first excited state the energy $E_1$ of bipolarons in a two-dimensional QD with the confinement strength of QDs $\omega _0$ , dielectric constant ratio $\eta $ , electron–phonon coupling strength $\alpha $ and cyclotron resonance frequency of the magnetic field $\omega _{c}$ are derived when the influence of the spin and external magnetic field is taken into account. The results show that both energies of the ground and first excited states ( $E_0$ and $E_1)$ consist of four parts: the single-particle energy of electrons $E_\mathrm{e}$ , Coulomb interaction energy between two electrons $E_\mathrm{c}$ , interaction energy between the electron spin and magnetic field $E_\mathrm{S}$ and interaction energy between the electron and phonon $E_{\mathrm{e-ph}}$ ; the energy level of the first excited state $E_1$ splits into two lines as $E_1^{(1+1)}$ and $E_1^{(1-1)}$ due to the interaction between the single-particle “orbital” motion and magnetic field, and each energy level of the ground and first excited states splits into three “fine structures” caused by the interaction between the electron spin and magnetic field; the value of $E_{\mathrm{e-ph}}$ is always less than zero and its absolute value increases with increasing $\omega _0$ , $\alpha $ and $\omega _c$ ; the effect of the interaction between the electron and phonon is favorable to forming the binding bipolaron, but the existence of the confinement potential and Coulomb repulsive energy between electrons goes against that; the bipolaron with energy $E_1^{(1-1)}$ is easier and more stable in the binding state than that with $E_1^{(1+1)}$ .  相似文献   

7.
A new generalized correlation is presented for the low-pressure gaseous viscosity of fluorocarbon refrigerants. The following empirical equation is obtained based on the most reliable experimental data for 16 fluorocarbons: $$\eta \xi = \left( {0.5124T_r - 0.0517} \right)^{0.82} Z_c ^{ - 0.81}$$ where η is the viscosity in μPa·s and ξ is the viscosity parameter defined using the critical temperature T c in K, the critical pressure P c in MPa, and the molar mass M in g·mol?1 as follows: $$\xi = T_c ^{1/6} M^{ - 1/2} P_c ^{ - 2/3}$$ The applicable ranges are 0.6<T r<1.8 and 0.253<Z c<0.282. The availability of the correlating equation for both pure fluorocarbons and their mixtures has been investigated based on the experimental data of these authors and those in the literature. It is found that the present correlation is useful for the prediction of the viscosity of pure fluorocarbons and their binary mixtures at atmospheric pressure with mean deviations less than 1.6%.  相似文献   

8.
The dynamic spin susceptibility $\chi^{+,-}_{\mathrm{total}}(\omega,{\bf q})$ that takes into account the interplay of localized and itinerant charge carriers exhibits a diffusive-like, extremely narrow and sharp symmetric ring of maxima at very small wave vectors: $|{\bf q}|=q_{0}$ where q 0ω/J≈10?6 with the Nuclear Magnetic Resonance (NMR) frequency ω and the superexchange coupling constant J together with the peak at the antiferromagnetic wave vector Q=(π,π). The calculated plane copper 63(1/T 1) and oxygen 17(1/T 1) nuclear spin-lattice relaxation rates from carrier-free right up to optimally doped La2?x Sr x CuO4 are in good agreement with experimental data.  相似文献   

9.
Having estimated the critical driving force associated with martensitic transformation,ΔG α→M, as $$\Delta G^{\alpha \to M} = 2.1 \sigma + 900$$ whereσ is the yield strength of austenite atM s, in MN m?2, we can directly deduce theM s by the following equation: $$\Delta G^{\gamma \to {\rm M}} |_{M_S } = \Delta G^{\gamma \to \alpha } + \Delta G^{\alpha \to M} = 0.$$ The calculatedM s are in good agreement with the experimental results in Fe-C, Fe-Ni-C and Fe-Cr-C, and are consistent with part of the data in Fe-Ni, Fe-Cr and Fe-Mn alloys. Some higher “M s” determined in previous works may be identified asM a,M s of surface martensite or bainitic temperature. TheM s of pure iron is about 800 K. TheM s in Fe-C can be approximately expressed as $$M_S (^\circ {\text{C}}) = 520 {\text{--- }}\left[ {{\text{\% C}}} \right]{\text{ }}x 320.$$ In Fe-X, the effect of the alloying element onM s depends on its effect onT 0 and on the strengthening of austenite. An approach for calculation of ΔG γ→α in Fe-X-C is suggested. Thus dM s/dx c in Fe-X-C is found to increase with the decrease of the activity coefficient of carbon in austenite.  相似文献   

10.
In the context of a numerical experiment, it is shown that the switching wave described by the reaction-diffusion equation can be delayed at a medium inhomogeneity with a thickness Δ and amplitude Δβ for a finite time τ = τ(Δβ, Δ) up to a complete stop at it (τ = ∞). Critical values Δβ c and Δ c corresponding to the autowave stop are found. The similarity laws \(\tau \sim (\Delta _c - \Delta )^{ - \gamma _\Delta } \) and \(\tau \sim (\Delta \beta _c - \Delta \beta )^{ - \gamma _\beta } \) are established, and the critical indices and are found. The similarity law is established for critical values of amplitude and width of the inhomogeneity corresponding to the autowave stop Δβ c ~ Δ c where δ ≈ 1.  相似文献   

11.
Using the multiphase equilibration technique for the measurement of contact angles, the surface and grain-boundary energies of polycrystalline cubic ZrO2 in the temperature range of 1173 to 1523 K were determined. The temperature coefficients of the linear temperature function obtained, are expressed as $$\frac{{{\text{d}}\gamma }}{{{\text{d}}T}}({\text{ZrO}}_{\text{2}} ){\text{ }} = {\text{ }} - 0.431{\text{ }} \times {\text{ }}10^{ - 3} {\text{ }} \pm {\text{ }}0.004{\text{ }} \times {\text{ }}10^{ - 3} {\text{ Jm}}^{ - {\text{2}}} {\text{ K}}^{ - {\text{1}}} $$ and $$\frac{{{\text{d}}\gamma }}{{{\text{d}}T}}({\text{ZrO}}_{\text{2}} - {\text{ZrO}}_{\text{2}} ){\text{ }} = {\text{ }} - 0.392{\text{ }} \times {\text{ }}10^{ - 3} {\text{ }} \pm {\text{ }}0.126{\text{ }} \times {\text{ }}10^{ - 3} {\text{ Jm}}^{ - {\text{2}}} {\text{ K}}^{ - {\text{1}}} $$ respectively. The surface fracture energy obtained with a Vickers microhardness indenter at room temperature is found to be γ F=3.1 J m?2.  相似文献   

12.
Measurements are described of specific heat capacity and electrical resistivity of a 2-2-3 T-50 carbon-carbon composite in the temperature range 1500–3000 K by a subsecond duration pulse heating technique. The results are represented by the relations 1 $$C\rho = 1.691 + 2.598{\text{x10}}^{{\text{ - 4}}} T - 2.691{\text{x10}}^{{\text{ - 8}}} T^2 $$ 2 $$\rho = 733.0 + 6.594{\text{x10}}^{{\text{ - 2}}} T$$ where c p is in J · g?1 · K?1, ρ is in ΜΩ · cm, and T is in K. Inaccuracy of specific heat capacity and electrical resistivity measurements is estimated to be not more than ±3%.  相似文献   

13.
Cyanide-bridged Fe-Co complex [Fe(Tp)(CN)3]2Co(bpe)?5H2O (1?5H2O; Tp = hydro-tris(pyrazolyl)borate; bpe = 1,2-bis(4-pyridyl)ethane) shows temperature- and light- induced metal-to-metal charge transfer (MMCT) involving spin state changes between magnetic $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{HS}}$ (HS = high spin, LS = low spin) state and nonmagnetic $\mathrm{Fe}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}$ state, while the dehydrated material 1 does not show any MMCT and holds $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{HS}}$ state. We have investigated the magnetic properties of each spin state in 1 and 1?5H2O by means of magnetization and ESR measurement under pulsed high magnetic field. At low temperature below T N, in both 1 and 1?5H2O, the saturation magnetization in the induced ferromagnetic phase is well explained by S and g values derived from the magnetic susceptibility study. In the ESR of 1, we observed characteristic modes corresponding to a spin excitation in the induced ferromagnetic phase where its temperature dependence shows an evolution of spin correlation in the $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{HS}}$ state at low temperature. We further found that the similar ESR modes grow in the light-induced state of 1?5H2O. The results strongly suggest that the light-induced magnetization in 1?5H2O is driven by a light-induced MMCT, which involves transition of spin multiplicity from the nonmagnetic $\mathrm{Fe}^{\mathrm{II}}_{\phantom{\mathrm{II}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}$ to the magnetic $\mathrm{Fe}^{\mathrm{III}}_{\phantom{\mathrm{III}}\mathrm{LS}}\mbox{--}\mathrm{Co}^{\mathrm{II}}_{\phantom{\mathrm{\mathrm{II}}}\mathrm{HS}}$ pair.  相似文献   

14.
The anomalous magnetic properties of Pr ions in the PrBa2Cu3O6+x system are investigated at low temperature. Measurements of the specific heat C P(T) and the magnetic susceptibility χ(T) are performed on ceramic samples in the tetragonal structure with x=0.44 and x=0. Two new magnetic transitions are observed below the Néel temperature of the Pr antiferromagnetic ordering $T_{\mathrm{N}}^{\mathrm{Pr}} \sim 9\mbox{--}10~\mathrm{K}$ . The first one is observed at the low-critical temperature T cr~4–5?K and the second one is observed at $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}} \sim 6\mbox{--}7~\mathrm{K}$ , respectively. Assuming that ΔC P(T) can be used to represent the Pr contribution to the specific heat C P(T), the data are well fitted for T<T cr by using the development of ΔC P(T)/TA(T 2)?3/2 γ+M(T 2) 1 +m(T 2) 2 . The values of the electronic coefficient Δγ are found much lower than all previous results obtained in compounds of the orthorhombic structure, and this is, in good agreement with the insulating character of our non-superconducting samples. The high values obtained for the coefficient M, permits us to confirm the existence of strong Pr–Pr exchange interactions. Some non-linear effects attributed to the values of the coefficient m are revealed and discussed in terms of the previous Pr–Cu coupling with a spin reorientation phase transition of both spin sublattices around $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}}$ . The appearance of a weak ferromagnetic tendency in the magnetic susceptibility analysis below T cr, could be associated with the reordering of the Pr subsystem.  相似文献   

15.
For high-hardness materials, particularly for ceramics, the relationship of hardness to load is revealed very strongly. An equation is proposed for conversion of Vickers hardness from one load to another: $$HV = HV_1 \left( {\frac{P}{{P_1 }}} \right)^{1 - 2/n}$$ where HV and HV1 are the hardness with loads on the indentor of P and P1 respectively. The parameter n is determined from the equation P = const dn, where d is the indentation diagonal. The parameter n may also be determined on the basis of a normalized curve of the value of HV/E (E is Young's modulus). The physical nature of the relationship of hardness to load is discussed and the hardness \(HV_{d_f }\) is introduced with a fixed indentation diagonal df (and not with a fixed load) calculated using the equation $$HV_{d_f } = HV\left( {\frac{d}{{d_f }}} \right)^{2 - n}$$ . The introduction of \(HV_{d_f }\) makes it possible to unify measurement of microhardness for different materials at different temperatures. Curves are given simplifying conversion of hardness from one load to another and determination of the hardness \(HV_{d_f }\) .  相似文献   

16.
The Galitskii approach to the calculation of self-energies is used to find the energy barrierΔE opposing the penetration of electrons into He, Ne, and Ar. To second order in thes-wave scattering lengtha, it is found that $$\Delta {\text{E = (2}}\pi \hbar ^2 {\text{na/m)}}\left\{ {{\text{1 + 2a}}\pi ^{{\text{ - 1}}} \int_0^\infty {{\text{dk[1 - S(k)]}}} } \right\}$$ wheren is the fluid number density,m is the electron mass, andS(k) is the fluid static structure factor. Typical barrier energies for4He and3He are 0.97 and 0.67 eV.  相似文献   

17.
The quasi-two-dimensional system in which magnetism is caused by spin density wave (SDW) with an anisotropic energy spectrum (with defined impurity concentration x) is examined. The wave vector $\vec{Q}$ is supposed to be different from 2k F and the umklapp scattering (U-processes) is taken into account. The system is placed in a magnetic field arbitrarily oriented with respect to the vector $\vec{M}_{Q}$ . The basic equations for order parameters $M_{Q}^{z}, M_{Q}', M_{z}, M^{\sigma}$ are obtained and the system of these equations is transformed taking into account the U-processes. The particular cases $( \tilde{H} \Vert \vec{M}_{Q} )$ and $( \tilde{H} \bot \vec{M}_{Q} )$ and the case of small arbitrarily oriented magnetic fields $\vec{\tilde{H}}$ are examined in detail. The conditions of the system transition to commensurable and incommensurable SDW state are analyzed. The phase diagram (T,x) at H=0 is traced. The influence of the magnetic field $\vec{\tilde{H}}$ on the temperature of magnetic transition is researched and the aspect of the phase diagram in magnetic field in the cases H z H σ =0 is presented. The longitudinal magnetic susceptibility χ which demonstrates that at x<x c the temperature behavior is similar to the case when the system has a gap, and at x>x c to a gapless case. At xx c in the dependence X (T) a local maximum appears. The influence of the energy spectrum anisotropy on the system’s properties is researched. Also the angular anisotropy of the quantity χ at different values of T and x is determined.  相似文献   

18.
A gas of spin 1/2 fermions with an interaction V+W = -|Λ|-1k,k′ g k,k′χ(k)χ(k′) $b_{\text{k}}^{\text{*}} b_{ - {\text{k}}}^{\text{*}}$ b k′ b -k′ - 2γ ∑kχ(k)n k+ n k-, where n = $a_{{\text{k}} \pm }^{\text{*}}$ a , b k = a k+ a k- and a , $a_{{\text{k'}}\sigma '}^{\text{*}}$ satisfy Fermi anticommutation relations, is investigated in the $d_{x^2 - y^2}$ -pairing case. W+V4 is nonzero only within a thin layer of one-fermion energies around the chemical potential μ, and χ(k) denotes the characteristic function of the corresponding range of momenta. Two cases are studied: 10 γ = 0, 20 γ = 0.10025 eV. In the first case the system exhibits a first order transition, in the second, the transition is second order. Temperature dependence of the system's thermodynamic functions is examined and compared with that of the s-pairing case.  相似文献   

19.
Chemical diffusion coefficients for chromium in austenitic and ferritic steels are determined using diffusion couples studied by electron probe microanalysis techniques. The average chemical volume diffusion coefficient, for the composition range 14 to 28 at % chromium, for ferritic AISI 446 in the temperature range 800 to 1000° C is: $$\tilde D = 0.15\left( {\frac{{ + 0.54}}{{ - 0.12}}} \right) \exp \left( {\frac{{ - 210( \pm 15)}}{{RT}}} \right) cm^2 \sec ^{ - 1} $$ and for austenitic AlSl 310 in the temperature range 800 to 1200°C is: $$\tilde D = 0.27\left( {\frac{{ + 1.04}}{{ - 0.22}}} \right) \exp \left( {\frac{{ - 246( \pm 16)}}{{RT}}} \right) cm^2 \sec ^{ - 1} $$ whereR is in kJ K?1 mol?1 Good agreement is found with existing data for ferritic steels but the data are more scattered in the austenitic case. Diffusion data from diffusion couples are thought to be more realistic than those obtained from tracer work for the purpose of predicting diffusion-controlled corrosion behaviour.  相似文献   

20.
Measurements of the heat capacity and electrical resistivity of nickel in the temperature range 1300–1700 K by a subsecond duration pulse heating technique are described. The results are expressed by the relations: $$\begin{gathered} C_p = 21.735 + 9.8200 \times 10^{ - 3} T \hfill \\ \rho = 18.908 + 2.3947 \times 10^{ - 2} T \hfill \\ \end{gathered} $$ whereC p is in J · mol?1·K?1,ρ is inμΩ·cm, andT is in K. Estimated maximum uncertainties in the measured properties are 3% for heat capacity and 1% for electrical resistivity.  相似文献   

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