Volumetric Properties of Lithium–Lead Melts

The density of liquid lithium and lithium–lead alloys (10.02 at.% Pb, 14.98 at.% Pb, 18.06 at.% Pb, 20.02 at.% Pb, 22.24 at.% Pb, 23.09 at.% Pb, 25.10 at.% Pb, 30.15 at.% Pb, 38.21 at.% Pb, 40.11 at.% Pb, 43.08 at.% Pb, 46.65 at.% Pb, 50.15 at.% Pb, 60.23 at.% Pb, 70.01 at.% Pb, 83.00 at.% Pb, and 84.30 at.% Pb) has been measured using the gamma-ray attenuation technique over the temperature range from the liquidus line to 1050 K. The position of the liquidus curve in the Li–Pb phase diagram has been clarified. The compositional dependencies of molar volume and volumetric thermal expansion coefficient of the Li–Pb liquid system have been constructed and discussed.     

聚醚砜改性对环氧树脂室温和超低温韧性及力学性能的影响

用聚醚砜对环氧树脂进行室温和超低温的增韧研究,测试了该环氧树脂体系在室温和超低温的断裂韧性、冲击强度、弯曲性能、拉伸性能和压缩性能。实验结果表明,在室温和液氮温度下,PES均能增加环氧树脂体系的断裂韧性(KIc),但在液氮温度下,KIc的增加程度小于室温。在室温下,PES改性树脂体系的冲击强度基本不变,而在液氮温度下则明显增大。在液氮温度下,增韧体系的弯曲、压缩和拉伸性能比室温有更显著的降低。在室温,增韧体系的强度降低10％～22％,而在液氮温度下则下降15％～32％。在室温,增韧体系的模量没有明显减小,而在液氮温度下则下降了15％～32％。     

A Computational Study of Soot Formation in Methane Air Co-Flow Diffusion Flame Under Microgravity Conditions

An in-house developed code has been used to predict soot formation in a methane air co flow diffusion flame at normal gravity and at lower gravity levels of 0.5 G, and 0.0001 G (microgravity). There is an augmentation of soot formation at lower gravity levels because of lower buoyancy induced acceleration leading to an increased residence time. The peak temperature at microgravity is reduced by about 50 K than that at normal gravity level. The axial velocity under normal gravity and reduced gravity show negative values (relatively small in magnitude) near the wall at axial height beyond 15 cm; but axial velocity is never negative in microgravity condition. Peak value of soot volume fraction at 0.5 G and microgravity multiplies by a factor of ～3 and ～7, respectively of that at normal gravity. The zone of peak soot volume fraction shifts away from the axis towards the wings, as gravity level is lowered. In comparison to soot volume fraction, the factors of amplification of soot number density at reduced gravity and at microgravity are comparatively lower at 1.2 and 1.5 of that at normal gravity respectively. On the other hand, mean soot particle sizes at reduced gravity and microgravity increase to 1.5 and 2 times of that at normal gravity respectively.     

Mechanical behaviour of polycrystalline BeO,Al2O3 and AlN at high pressure

The mechanical behaviour of various types of BeO, Al₂O₃, and AlN have been investigated at confining pressures up to 1.25 GPa, at 25° C, and at strain rates of 3 to 7×10^–5 sec^–1. The stress-strain data taken in uniaxial compressive-stress loading indicate the BeO aggregates undergo a transition from brittle fracture at low pressures to plastic flow at high pressures. Depending on the fabrication process, this transition pressure in BeO occurs at 0.4 to 0.7 GPa. Concurrently, the ultimate compressive strength of BeO increases from 1.0 to 1.9 GPa at 0.1 MPa pressure to over 4.0 GPa at 1.O GPa. Alumina remains brittle at all pressures up to 1.25 GPa; its strength increases from 4.5 GPa at 0.1 MPa pressure to over 6.0 GPa at 1.25 GPa. Aluminium nitride behaves similarly to BeO, having a brittle-ductile transition at 0.55 GPa. Its ultimate strength increases from 3.2 GPa at 0.1 MPa pressure to 4.7 GPa at 0.8 GPa. The distortional strain energy (proportional to the area under the stress-strain curve) absorbed by each material during compression at pressure was calculated and compared to available data from the literature. Alumina shows a degraded energy absorption with pressure, but both BeO and AlN yield a strongly enhanced performance at moderate pressures. Beryllium oxide and AlN thus appear to be promising structural materials for certain applications where high strengths and ductilities are required at moderate pressures.     

MONITORING FATIGUE OF A NICKEL-BASE SUPERALLOY AT POSITIVE AND NEGATIVE STRESS RATIOS USING AN OPTICAL SYSTEM

Abstract— This paper describes the use of an optical crack monitoring system designed to examine the growth behaviour of short/long fatigue cracks in Waspaloy at room and elevated temperature. Its use at 19 and 500°C is demonstrated at stress ratios of 0.1 and -1. Fatigue crack formation was associated with slip band cracking at both R = 0.1 and R = -1. At 19°C short crack growth at R = -1 and R = 0.1 could not be normalized by adopting a positive stress approach. The compressive part of the fatigue cycle at R = -1 contributed to short crack growth at 19°C and long crack growth at 500°C.     

Superconducting properties of the composite-processed Nb3Sn superconductor with the Cu-Sn-Zn matrix

Effects of the Zn addition to the Cu-Sn matrix of the Nb₃Sn composite tape have been investigated by measuring the matrix work-hardening behaviour, the rate of Nb₃Sn layer formation and the pertinent superconducting properties. The Zn addition drastically enhances the diffusion rate of Nb₃Sn formation at each Sn level in the matrix examined, leading to sufficient superconducting properties even at a low Sn level of 3.5 at. %; a sample containing 3.5 at. % Sn and 15 at. % Zn in the matrix exhibits a critical temperature and critical current density comparable with those of samples at a Sn level of 7 at. %. The upper critical field obtained for a sample with the 6 at. % Cu-6 at. % Sn-4 at. % Zn matrix beyond 200 kOe. The work-hardening of the composite matrix is found to be essentially a function of Sn level, and insensitive to the Zn addition.     

Phase transformation during alternating aging at 473 K and at 773 K in the plasma-sprayed yttria stabilized zirconia coating

The phase transformation of plasma-sprayed 6 mass % yttria-stabilized zirconia coatings was investigated during alternating aging under two conditions, at 473 K in saturated steam pressure and at 773 K in air. Prior to the aging, the samples were annealed at 773 K and 1073 K in order to control stress relief. Selection of the annealing temperatures caused distinct differences in the phase transformation. After the first aging at 473 K, the monoclinic phase fraction in the coatings annealed at 773 K was found to be greater than that of the coatings annealed at 1073 K. In the coatings annealed at 773 K, the decrease of the monoclinic phase fraction was observed after aging at 473 K in each cycle, while the coatings annealed at 1073 K showed an increase of monoclinic phase fraction.     

PbTe热电材料的氧化行为

研究了热电材料ＰｂＴｅ在高温（７００～９００Ｋ）氧分压为０．０１～１００ｋｐａ时的氧化行为，发现氧化物均为Ｐｂ－Ｔｅ－Ｏ的三元化合物随温度及氧分压的变化有规律性地分布，在高温低氧分压条件下，试样质量减少，生成Ｐｂ３ＴｅＯ５或者Ｐｂ５ＴｅＯ７而在低温高氧分压条件下，试样质量增加，生成ＰｂＴｅＯ３或者ＰｂＴｅＯ３／Ｐｂ２ＴｅＯ４。     

Laser-induced fluorescence of green plants. 3: LIF spectral signatures of five major plant types

A technique amenable to remote sensing use which utilizes laser-induced fluorescence (LIF) properties of plants has been successfully used in the laboratory to identify five major plant types. These included herbaceous dicots, herbaceous monocots, conifers, hardwoods, and algae. Each of these plant types exhibited a characteristic LIF spectra when excited by a pulsed N2 laser emitting at 337 nm. Although monocots and dicots possess common fluorescence maxima at 440, 685, and 740 nm, they could be differentiated from one another by using the ratio of the square of the fluorescence intensity at 440 nm to the nonsquared intensity at 685 nm, i.e., (440)2/685. In all cases, monocots yielded a significantly higher ratio. Conifers have fluorescence maxima at 440, 525, and 740 nm but none at 685 nm. Hardwoods exhibited fluorescence at 440, 525, 685, and 740 nm. Algae had very low fluorescence at 440 nm, no fluorescence at 525 nm, and fluorescence maxima at 685 and 740 nm. For algae, the ratio of the fluorescence intensity at 685 nm to that at 740 nm was much greater than that for monocots, dicots, and hardwoods. The potential use of the LIF technique for individual species identification is suggested.     

Radiance Temperatures (in the Wavelength Range 527 to 1500 nm) of Palladium and Platinum at Their Melting Points by a Pulse-Heating Technique

The radiance temperatures (at seven wavelengths in the range 527 to 1500 nm) of palladium and platinum at their respective melting points were measured by a pulse-heating technique. The method, based on rapid resistive self-heating of a specimen from room temperature to its melting point in less than 1 s, used two high-speed pyrometers to measure specimen radiance temperatures every 0.5 ms during the heating and melting period. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for each metal as determined by averaging the results for several specimens at each wavelength are as follows. Based on uncertainties arising from pyrometry and specimen conditions, the expanded uncertainty (two-standard deviation level) is about ±7 K for the reported values in the range 527 to 900 nm and about ±8 K for the reported values at 1500 nm.     

固化温度及固化剂种类对模拟PBX浇注炸药力学性能的影响

测试了端羟基聚丁二烯-异佛尔酮二异氰酸酯-三苯基铋（HTPB-IPDI-TPB）和端羟基聚丁二烯-六亚甲基二异氰酸酯三聚体-亚乙基二胺（HTPB-HDI-trimer-DABCO）两种黏结剂在不同固化温度下对模拟PBX浇注炸药的力学性能的影响。实验结果表明,随着固化温度的升高,HTPB-IPDI-TPB和HTPB-HDI-trimer-DABCO制备的模拟PBX浇注炸药药柱的力学性能增强。固化剂IPDI和HDI-trimer对药柱的机械性能有较大影响,与含IPDI炸药相比,含HDI-trimer的炸药药柱的剪切强度在35 ℃增大50.27%,45 ℃增大34.30%,55 ℃增大44.83%;抗拉强度在35 ℃降低82.66%,45 ℃降低78.73%,55 ℃降低82.22%;抗压强度在35 ℃增大54.85%,45 ℃增大45.25%,55 ℃增大53.38%。HDI-trimer形成三维网状结构降低了药柱的抗拉强度。     

Radiance temperatures (at 658 and 898 nm) of niobium at its melting point

Radiance temperatures (at 658 and 898 nm) of niobium at its melting point were measured by a pulse-heating technique. A current pulse of subsecond duration was imparted to a niobium strip and the initial part of the melting plateau was measured by high-speed pyrometry. Experiments were performed with two techniques and the results do not indicate any dependence of radiance temperature (at the melting point) on initial surface or system operational conditions. The average radiance temperature at the melting point of niobium is 2420 K at 658 nm and 2288 K at 898 nm, with a standard deviation of 0.4 K at 658 nm and 0.3–0.6 K at 898 nm (depending on the technique used). The total uncertainty in radiance temperature is estimated to be not more than ±6 K. The results are in good agreement with earlier measurements at the National Institute of Standards and Technology (USA) and confirm that both radiance temperature and normal spectral emissivity (of niobium at its melting point) decrease with increasing wavelength in the region 500–900 nm.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Effect of Cu on the Spinodal Decomposition of AlZn Alloy with Symmetrical Composition

1. IntroductionThe spinodal decomposition, as a method ofmaking ultra-fine microstructure, has recently beenadverted[1~3]. The Al-Zn binary system is the basis ofsome practically important systems among Al-based lightalloys, and a typical example with spinodal decomposi-tion. However, being different from others such as Cr-W with broad temperature range, the miscibility gapof the Al-Zn system remains stable at higher tempera-tures (277~350°C)[4]. The discontinuous precipitation ofthe β Z…     

Comparison of fluorescence spectra of Yb:Y3Al5O12 and Yb:YAlO3 single crystals

Yb:Y₃Al₅O₁₂ (Yb:YAG) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 25 at.%, 50 at.%, 100 at.% and Yb:YAlO₃ (Yb:YAP) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 30 at.% were grown by the Czochralski process. The fluorescence spectra of these crystals and the effects of self-absorption on the shape of the fluorescence spectra were studied. Through comparing the fluorescence spectra of Yb:YAG and Yb:YAP, all results indicate that the effects of self-absorption on the fluorescence spectra of Yb:YAP are remarkably stronger than that of Yb:YAG at the same Yb concentration.     

Neutral points of skylight polarization observed during the total eclipse on 11 August 1999

We report here on the observation of unpolarized (neutral) points in the sky during the total solar eclipse on 11 August 1999. Near the zenith a neutral point was observed at 450 nm at two different points of time during totality. Around this celestial point the distribution of the angle of polarization was heterogeneous: The electric field vectors on the one side were approximately perpendicular to those on the other side. At another moment of totality, near the zenith a local minimum of the degree of linear polarization occurred at 550 nm. Near the antisolar meridian, at a low elevation another two neutral points occurred at 450 nm at a certain moment during totality. Approximately at the position of these neutral points, at another moment of totality a local minimum of the degree of polarization occurred at 550 nm, whereas at 450 nm a neutral point was observed, around which the angle-of-polarization pattern was homogeneous: The electric field vectors were approximately horizontal on both sides of the neutral point.     

Photoelectronic behaviors of self-assembled ZnSe/ZnS/L-Cys quantum dots synthesized at low temperature

The photogenerated carriers’ transport and microstructure of self-assembled core–shell ZnSe/ZnS/L-Cys quantum dots (QDs), which was synthesized at room temperature, are studied via the surface photovoltaic and transient photovoltaic techniques, X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet–visible absorption spectra. The results suggest that the ZnSe nanocrystals prepared at room temperature prefer to nucleate at (111) and (220) faces, and grow a shell–ZnS at (220) face rather than at (311) face. The quantum well depth in some interface space charge region (SCR) of the QDs prepared at room temperature is smaller than that prepared at 90 °C. The evolution of the band bending from a depletion layer to an accumulation layer may occur in the graded-band-gap and at the side of the interface SCR, as compared the QDs with p-type photovoltaic characteristic synthesized at room temperature to that at 90 °C. This electron structural shift may be ascribed to the reduced quantum well depth and then an obvious resonance quantum tunneling of the QDs synthesized at room temperature.     

Radiance Temperatures (in the Wavelength Range 530 to 1500 nm) of Nickel at Its Melting Point by a Pulse-Heating Technique

The radiance temperatures (at seven wavelengths in the range 530 to 1500 nm) of nickel at its melting point were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring specimen radiance temperatures every 0.5 ms. Melting of the specimen was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for nickel, as determined by averaging the results at each wavelength for 25 specimens, are: 1641 K at 530 nm, 1615 K at 627 nm, 1606 K at 657 nm, 1589 K at 722 nm, 1564 K at 812 nm, 1538 K at 908 nm, and 1381 K at 1500 nm. Based on uncertainties arising from pyrometry and specimen conditions, the combined uncertainty (two standard-deviation level) is about ± 6 K for the reported values in the range 530 to 900 nm and is about ± 8 K for the reported value at 1500 nm.     

Significance of water/solid ratio and temperature on the physico-mechanical characteristics of hydrating 4CaO.Al2O3.Fe2O3

Tetracalcium alumino-ferrite in paste form, at water/solid (W/S) ratios of 0.3, 0.4, 0.5 and 1.0, and in pressed form at effective water/solid ratios of 0.13 and 0.08 has been hydrated for up to 45 days at temperatures of 23 and 80° C. Some prehydrated samples have also been subjected to autoclave treatment at 216° C. Of all the samples studied, that hydrated at a W/S=0.13 at 80° C indicated the highest ratio of cubic phase to hexagonal phase; that hydrated at a W/S=0.08 at 23° C showed the lowest.Thermograms gave evidence of the formation of hexagonal phases, although X-ray diffraction patterns did not. The specific surface area values depended on the degree of hydration and the nature of the product, autoclaved samples giving the lowest values. During the four days of hydration the specimen hydrated at 80° C expanded more than that hydrated at 23° C, but after that time the rates of expansion were reversed: that of the sample hydrated at 80° C was much lower than that of the sample hydrated at 23° C. Microstructural examination of the material formed at higher temperatures and lower water/solid ratios indicated a closely welded, continuous network of cubic phase. Such a structure yields a product of higher strength than that of a loose structure formed at higher water/solid ratios. A reasonably linear relation was found between porosity and logarithm of microhardness.     

不同退火温度下铁基薄带介观结构的AFM研究

用原子力显微镜(AFM)观测了铁基合金(Fe73.5Cu1Nb3Si13.5B9)薄带断口的介观结构.通过对310℃退火样品的观测,可以发现薄带的贴辊面区(SRFA)和自由面区(FFA)存在着非常明显的结构差异;而540℃退火样品的AFM观测结果则显示这种差异并不明显.将310℃和540℃退火的样品在HF酸溶液中进行腐蚀,获得不同腐蚀深度的腐蚀表面,再用AFM观测其表面形貌,则发现:在310℃退火样品的腐蚀表面,自由面和贴辊面形貌各自随腐蚀深度的变化而变化,并且两表面形貌之间在腐蚀前期有差异,但后期无明显不同;而540℃退火样品的两个腐蚀表面,则不存在这样的变化和差异.该观测结果与薄带断口观测到的介观结构相符合.造成这种结构差异的原因是经不同温度退火后,薄带内部残留的内应力不同.     

Radiance Temperatures (in the Wavelength Range 521 to 1500 nm) of Rhenium and Iridium at Their Melting Points by a Pulse-Heating Technique

The melting-point radiance temperatures (at seven wavelengths in the range 521 to 1500 nm) of rhenium and iridium were measured by a pulse-heating technique. The method is based on rapid resistive self-heating of the specimen from room temperature to its melting point in less than 1 s and on simultaneously measuring the specimen radiance temperature every 0.5 ms with two high-speed pyrometers. Melting was manifested by a plateau in the radiance temperature-versus-time function for each wavelength. The melting-point radiance temperatures for a given specimen were determined by averaging the measured temperatures along the plateau at each wavelength. The melting-point radiance temperatures for each metal were determined by averaging results for several specimens at each wavelength. The results are as follows. Based on estimates of the random and systematic errors arising from pyrometry and specimen conditions, the expanded uncertainty (two standard-deviation level) in the reported values is ±8K.