Formulas for evaluating the stabilization time of sluggish measuring instruments

Conclusions In this article formulas are suggested for calculating the stabilization time in ranges of 0<1 and 1.04<. These formulas are universal, they have a higher precision than has been hitherto obtained and they reflect the actual nature of the relationship between t_s and .Translated from Izmeritel'naya Tekhnika, No. 11, pp. 58–60, November, 1966.     

Thermodynamic properties of iron doped beta″-alumina by e.m.f. measurements with beta-alumina electrolytes

Thermodynamic studies of the non-stoichiometric iron doped beta-alumina (ID) phase were carried out by electrochemical measurements coupled with coulometric titration using the cell Na_liq/Li-alumina/ID. Hot pressing and glass sealing techniques were developed and employed to obtain a suitable and stable Li-alumina/ID interface. The equilibrium e.m.f. of the cell was determined as a function of sodium concentration over the temperature range 444 to 523 K. The range of sodium concentrations over which the ID phase is stable was also determined. The relative partial molar thermodynamic quantities of sodium, , , and in ID alumina as a function of sodium concentration were obtained from cell e.m.f. data.     

Thermodynamic investigations of liquid Bi-Na and Sn-Na alloys by coulometric titration using β″-alumina

The following double galvanic cell was assembled and the thermodynamic properties of liquid Bi-Na and Sn-Na alloys, and the ion selectivity of -alumina during coulometric titration, were investigated. Mo, Na(I)¦-alumina¦M-Na(I), Mo [I] M-Na(I)¦-alumina¦Au + Au₂Na, Mo [II] (M = Bi or Sn) where M-Na(1) and Au + Au₂Na were used as the common electrode and reference electrode, respectively. Sodium was coulometrically titrated through the -alumina electrolyte of cell I both ways, and the EMFs were measured. It was found that no ion-exchange reaction occurs between the liquid alloys and the -alumina, and only Na was transferred in the -alumina during coulometric titrations. The thermodynamic properties of liquid Sn-Na and Bi-Na alloys were found to be in agreement with the literature.     

On the calculation of second virial coefficients for nonspherical molecules

A self-consistent scheme is given for the calculation of the contributions of nonspherical molecular interactions to second virial coefficients. The usual longrange nonspherical interactions, which are asymptotically valid only at large separations, are modified by damping functions that render them valid at small separations as well. Numerical tables of new auxiliary functions J _n ^D (T^*) are given for 6n30 and 0.5T ^*10. These are designed to be used in the identical statistical-mechanical formalism for the second virial coefficient that had been developed for the undamped long-range nonspherical interactions.     

Compressibility measurements of β- and β″ -alumina

The compressibilities of the a- and c-axes for sodium - and -aluminas were determined up to 10 GPa from the pressure dependence of powder X-ray diffraction measured at room temperature using synchrotron radiation as an X-ray source. Powders of sodium - and -aluminas which were prepared from grinding synthesized single crystals were used as the specimens for X-ray diffraction. The compressibilities of - and -aluminas are 1.5 ± 0.2 ×10^–12 and 1.7 ± 0.2 × 10^–12 Pa^–1 for the a-axis and 2.9 ± 0.2x10^–12 and 1.6 ± 0.2 ×10^–12 Pa^–1 for the c-axis, respectively. For the c-axis, the compressibility of -alumina is larger than that of -alumina. This experimental fact is explained by the different stacking of oxygen layers and the different content in sodium ion between - and -aluminas.     

A scaled equation of state for real fluids in the critical region

A scaled equation of state is proposed for real fluids in the critical region which incorporates asymmetry with respect to the critical isochore. In the range of reduced densities 0.65(/ _c)1.4 and for reduced temperatures (T/T _c)1.2, the equation represents P-V-T data for steam within the experimental accuracy.     

Y xBayCuzO7− δ solid solutions

Y_xBa_yCu_zO_7– ceramics forming at isobaric conditions were studied by x-ray diffraction analysis, dynamic magnetic measurements and potentiometric titration. It was established that compositions: 0.8 x 1.2 y=2, z=3; x-1, 1.8 y 2.2, z=3; x=1, y=2, 2.7 z 3.4: are in the homogeneity range of 123. It was found that compositions with nonstoichiometric cations rations have minimum T_c.     

Crystal growth of thin-plate β-alumina by liquid transport

Single crystals of -alumina (Na₂0.11Al₂O₃) were grown by liquid transportat 1030–1150 °C and for durations of 4–140 h, using an Na₃AlF₆ solvent and - or -alumina as the nutrient. The maximum size of -alumina crystal grown using a small platinum crucible was 1.1 cm in length and 0.6 mm in thickness. On the other hand, a single crystal 1.8 m long and 0.7 mm thick was grown using a large crucible. These grown single crystals were hexagonal, thin platelike, and very transparent. Screw dislocation-like patterns were observed on the surfaces of grown -alumina single crystals; each pattern showed a right-handed rotation. Small crystals on a matrix crystal grew spirally about the c-axis and formed a new, flat surface on the matrix crystal, evidently an intrusive twin. The angle between the two inclined crystals was 2.9–2.8 °. The twin face seemed to be w(14, 14, 3). The growth rates of -alumina single crystals treated for less than 12 h using large and small crucibles were 3.3 × 10^–1 and 4.0 × 10^–1 mm h^–1, respectively. For treatment ranging from 12 to 40 h growth rates were 1.1 × 10^–1 and 1.5 × 10^–1 mm h^–1 for the large and small crucible, respectively; rates for 40–100 h treatment were 0.3 × 10^–1 mm h ^–1 for both crucibles. The grown -alumina single crystals had fairly good crystallinity. The growth mechanism of the -alumina single crystal can be estimated from transport through liquid film in the crucible, i.e. a creeping phenomenon.     

An electron microscopic investigation of oxides related to ß-alumina

High resolution electron microscopic (HREM) investigation of potassium-alumina and the related gallate and ferrite has revealed that whereas the aluminate and gallate are highly disordered, consisting of random sequence of and units, the ferrite is more ordered. The aluminate and gallate are sensitive to electron beam irradiation exhibiting beam-induced damage similar to sodium-alumina. Significantly, the ferrite is beamstable, the difference in behaviour amongst these related oxides arising from the different mechanisms by which alkali metal nonstoichiometry is accommodated. Barium hexaaluminate and hexaferrite are both highly ordered; specimens prepared by the barium borate flux method exhibit a new 3a×3a superstructure of the hexagonal magnetoplumbite cell.Contribution No. 241 from the Solid State and Structural Chemistry Unit.     

Method for heat transfer calculation using isothermal coordinates

Equations for steady-state heat transfer are considered in curvilinear coordinates. The equations are shown to be simplest when one of the families of coordinates are isotherms. Conditions are obtained for which these coordinate systems and some exact solutions of the heat conduction equations must satisfy.Notation a ₁, a₂, ..., a_n coefficients determining the temperature dependence of thermal conductivity (see formula (8)) - f() function of the -coordinate (see formula (4)) - H ₁,H ₂,H ₃ coefficients of the first differential form (Lamé coefficients) (see formula (2)) - n number of a term of the series in formula (8) - q heat flux - Q power of volume heat release - x, y, z Cartesian coordinates - , , general curvilinear orthogonal coordinates - ₁, ₂ coordinates of the boundary surfaces on which the temperatures are prescribed - x ₀₁ thermal conductivity att=0 - () function of the -coordinate (see formula (4)) - () -function determining temperature distribution in the case of constant heat flux along the coordinate lines Scientific-Research and Design-Technological Institute of Machine Manufacture, Scientific-Production Subbranch Novator, Kramatorsk, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 4, pp. 651–659, July–August, 1995.     

Precipitate strengthening mechanisms in magnesium zinc alloy single crystals

The mechanical behaviour of Mg-5.1 wt % Zn alloy single crystals was studied in the 4.2 to 300° K temperature range. Quenched crystals have activation energies and volumes best associated with the cutting of small clusters of Zn atoms by dislocations. Fully hardened crystals contain fine ₁ and occasional ₂ precipitates with an average ₁ interparticle spacing of 330 to 660 Å. Strengthening in these crystals is mainly ascribed to the cutting of ₁ particles by dislocations. In the overaged condition ₁, ₂ and equilibrium particles are present and lead to a considerable temperature-dependence unusual for an overaged condition. Analysis of this temperature-dependence suggests that below 77° K the relatively easy cutting of ₁ particles by dislocations takes place in addition to the cutting of ₂ and particles. Above 77° K the difficult cutting of ₂ and particles alone controls the deformation, ₁ being more easily cut with the aid of thermal fluctuations.     

The K2O·Al2O3-Al2O3 system

The phase relationships in the system K₂O · AL₂O₃-Al₂O₃ between 1200 and 1700° C have been experimentally established. The homogeneity range of potassium -alumina is limited by the 83 and 91 mol % Al₂O₃ compositions. The eutectic point between the K₂O-Al₂O₃ and -alumina was found to be at 1450° at about 62 mol % Al₂O₃ composition. An X-ray diffraction pattern analysis of potassium -alumina is shown.     

Fermi liquid behaviour of the viscosity of3He-4He mixtures

We have investigated³He-⁴He mixtures at³He-concentrations 0.98%x9.5% by the vibrating wire technique in the temperature range 1 mKT 100 mK and at pressures 0 bar p 20 bar. In the degenerate regime of the mixtures the Landau theory of Fermi liquids predicts a temperature dependence of the viscosity proportionalT ^–2. We report on the first observation of this behaviour at 3 mKT 10 mK for all investigated concentrations and pressures. At temperatures below about 20 mK slip corrections had to be taken into account due to the increase of the quasiparticle mean free path at very low temperatures. The low-temperature cut-off in T ² = constant indicates the transition into the ballistic regime of the mixtures, where the mean free path of the quasiparticles exceeds the radius of the vibrating wire. Our results for the pressure dependence of the viscosity as well as for its magnitude show substantial differences from predictions based on pseudopotential theory. However, a calculation of with the quasiparticle interaction potential of recent solubility measurements in mixtures agrees well with our experimental data, in particular the pressure independence of .     

Ionic conductivity of Na,K and Ag β″-alumina-ZrO2 composites

Composite samples of Na -alumina with 15 vol % Zr0₂ stabilized with 4.5 wt % Y₂O₃ were fabricated using two sintering schedules. K and Ag -alumina composites were prepared from the Na -alumina composite by ion exchange. The ionic conductivities of the Na, K, and Ag composites at 300 °C were 1.3×10^–1, 5.9×10^–2 and 6.8×10^–3 S cm^–1, respectively. K _1c for the K composite was as high as 3.7 MPam^1/2.     

Relations between specific heat discontinuities and Ginzburg-Landau parameters for superfluid 3He

We show that the value of the ratio ₅/₂₄ deduced from specific heat experiments is extremely sensitive to the coefficient of the quadratic term in the Ginzburg-Landau functional. A strong coupling calculation of this coefficient implies that the experimental value of ₅/₂₄ is more than three times larger than previously believed.This work was supported in part by the National Science Foundation through Grant DMR7826530.     

Structural transformation during sintering and annealing of beta alumina

Changes in the phase content, microstructure and lattice parameter are observed in stabilized/ alumina specimens following extended sintering and annealing treatments. The resulting state is dependent on composition of the starting powder and on temperature and duration of heat treatment; the kinetics of transformation between and alumina are generally slow and certain/ ceramics remain in a metastable state even after a prolonged high temperature anneal. Following post-sinter heat treatment, splitting of X-ray diffraction peaks reveals a segregation of the phase into two components of differing lattice parameter. With sintering schedules of a long duration the splitting may even be present in the as-fired condition as recently reported by Harbach [1]. The splitting is attributed to a structural change resulting from the expulsion of Na₂O from supersaturated grains.     

X-ray,electrical conductivity and magnetic hysteresis studies of the chalcogenide system Zn1−xCuxCr2Se4

X-ray diffraction studies performed here indicated solid-solution formation between ZnCr₂Se₄ and CuCr₂Se₄, and all the compounds could be indexed on the basis of cubic spinel lattice. The compositions between 0 x 0.8 showed semi-conducting behaviour, while CuCr₂Se₄ (x=1.0) exhibited metallic conductivity. Seebeck measurements showd P-type behaviour for 0 x 1. Magnetic hysteresis indicated a ferromagnetic nature for all the compounds except ZnCr₂Se₄ (x=0). The shapes of/ _i plotted againstT exhibited single domain behaviour, and Curie temperatures showed an increase with increasing copper concentration.     

Elastodynamic parameters for dynamic interface fracture mechanics

Summary Dynamic extension of cracks running along curvilinear interfaces of brittle bimaterials subjected to mechanical crack surface loads and superimposed thermal strains acting along the ligament is considered. This paper especially addresses the provision and discussion of elastodynamic interface parameters in order to assess quantitatively the bimaterial fracture in view of the governing physical features: applied mechanical and thermal strain loading, existence of an interface, crack-tip velocity and curvature of the interface contour. By utilizing the linear theory of thermoelasticity and adopting Stroh's method of generalized complex potentials, from the corresponding boundary and continuity conditions vectorial Hilbert problems are derived. It is shown that the parameters of the eigenvalues and of the eigenvectors of the Hilbert problems can be interpreted as elastodynamic interface mechanics parameters reading (,v _p, _Hf , _Hf ). Generalized Dundurs parameters of dynamics (, ) and consequently an associated generalized Dundurs diagram of dynamics are proposed. While the aforementioned elastodynamic interface parameters (, ,v _p, _Hf , _Hf ) do not assume the interface to be damaged, interfaces with running interface cracks generally cause two additional interface parameters, denoted as bimaterial constants (, _Hf ), where the latter is specific to the curvature of the interface in conjunction with the velocity of the interface crack. However, the bimaterial constants (, _Hf ) can be traced back to interface parameters for an uncracked bimaterial, namely to (, _Hf ).     

The formation of NaMg2Al15O25 in an α-Al2O3 matrix and its effect on the mechanical properties of alumina

An in-situ sintering reaction was designed to produce lath-like \-alumina in an -alumina matrix in order to make alumina ceramics stronger and tougher. The reaction sequence to produce \-alumina (NaMg₂Al₁₅O₂₅) requires the formation of \-alumina (NaAl₁₁O₁₇) and spinel (MgAl₂O₄) at around 1100 dgC followed by a solid-state reaction of these two phases to give \-alumina at elevated temperatures; this reaction is complete at around 1600 °C. The in-situ sintering reaction produces near-theoretically dense alumina ceramics in which lath-like \-aluminas are homogeneously distributed. The bending strength and fracture toughness increase to 620 MPa and 5 MPam^1/2, respectively; these increases are thought to be due to the suppression of grain growth as well as the crack deflection and bridging associated with lath-like \-alumina.     

Thermal shock of ß-alumina with zirconia additions

Sodium-alumina electrolyte tubes were prepared from spray dried precursor powders with additions of 2, 5, 10 and 15 wt % ZrO₂ made by the sodium zirconate route. The thermal shock behaviour of ring segments cut from the tubes was examined by quenching into water at 0° C. At the 2% ZrO₂ level the dispersed ZrO₂ particle size was low, <0.5m, and the tetragonal phase was retained. For higher weight fractions, particle coarsening during the-alumina sintering schedule was extensive and the large particles transformed to monoclinic on cooling. At the 15% ZrO₂ level the-alumina had a slightly reduced strength and high resistance to thermal shock and to thermal shock damage, quenching into water from 800° C effecting only a 43% reduction in strength. These observations are consistent with the effects of microcracking in the vicinity of second phase ZrO₂ particles.