Utilization of accelerating rate calorimetry for the characterization of energetic materials at MRC-mound

The technique of Accelerating Rate Calorimetry (ARC) was used to investigate the thermal stabilities of energetic materials used in production and manufacturing at MRC-Mound. Plots of heat rate versus temperature, along with temperature and pressure versus time plots, were determined for selected secondary explosives and one model compound. Analyses of these data were used to derive zero-order kinetic parameters, time-to-explosion plots, and approximate critical explosion temperatures.     

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

Second-order non-linear optical studies on CdS microcrystallite doped lead silicate glasses

Second-order non-linear optical effect of CdS microcrystallite doped lead silicate glass is investigated in this paper. The second harmonic generation (SHG) from the base glass and CdS microcrystallite doped glasses were observed, and the effects of the heat treatments and the thermal poling temperature on the crystallization of CdS and second-order harmonic (SH) intensity were discussed, respectively. It is indicated that samples doped with CdS microcrystallite showed larger SH intensity than that of the base glass. Longer heat treatment time, higher heat treatment temperature and thermal poling temperature cannot get a good SH intensity in glasses.     

Nd3+/Yb3+共掺La2O3-TiO2-ZrO2微晶玻璃的制备及上转换发光研究

利用气悬浮方法制备了Nd³⁺/Yb³⁺共掺La₂O₃-TiO₂-ZrO₂前驱体玻璃, 通过热处理获得了微晶玻璃。通过DTA对前驱体玻璃的热稳定性进行了研究。利用光致发光谱, TEM和EDS对微晶玻璃进行了表征分析, 并研究了热处理对上转换发光的影响。结果表明: 玻璃转变温度和析晶起始温度分别为799℃和880℃. 在980 nm激光激发下, 样品发射出中心位于497, 523, 545, 603和657 nm处的五条发光带。热处理后样品上转换发光强度提高, 经过880℃保温50 min热处理的微晶玻璃显示了最强的上转换发光, 在545 nm处的发光强度是前驱体玻璃的11倍, 这是由于在微晶玻璃基质中存在致密柱状晶和Nd³⁺离子在晶体中富集造成的。     

Heat Capacity and Thermodynamic Properties of Poly(chlorotrifluoroethylene) from 2.5 to 620 K

Heat capacities and thermodynamic properties of a number of poly(chlorotrifluoToethylene) samples subjected to various thermal treatments, to achieve crystallinities ranging from approximately 10 to 90%, have been studied from 2.5 to 370 K by automated adiabatic calorimetiy and from 250 to 620 K by differential scanning calorimetry. Small heat capacity discontinuities in the temperature range from 320 to 350 K were observed in all samples with crystallinities greater than 40%. Spontaneous adiabatic temperature drifts associated with these anomalies were prasitive (exothermic) for quenched samples and negative (endothermic) for annealed samples. Therefore these anomalies were believed to be associated with a relaxation phenomenon similar to that of a glass transition. For highly quenched low crystallinity films, a much larger heat capacity discontinuity of greater than 15% was observed, amidst a crystallization exotherm. In addition to the above phenomena, annealing of the sample at any temperature between 240 to 400 K would produce a shift in the population distribution of crystallites from reorganization or melting and recrystallization. As a result, the apparent heat capacity became somewhat lowered at the annealing temperature and somewhat raised at about 20 K above the annealing temperature.     

Crystal growth and optical properties of CdS-doped lead silicate glass

The crystal growth and optical properties of CdS microcrystallite-doped lead silicate glass is investigated in this paper. The existence of CdS nanocrystals was confirmed via X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results reveal that a two-stage heat-treat procedure can produce a better size distribution of CdS nanocrystals than a one-stage heat-treat procedure in glasses. The second harmonic generation (SHG) from the base glass and CdS microcrystallite doped glasses was observed, and the effects of the heat treatments and the thermal poling temperature on the crystallization of CdS and second-order harmonic (SH) intensity were discussed, respectively. It is indicated that samples doped with CdS microcrystallite showed larger SH intensity than that of the base glass. Use of a higher thermal poling temperature than the glass transformation temperature does not result in a good SH intensity in glasses.     

碘化亚铜微晶掺杂硼硅酸盐玻璃的制备及其电致二阶非线性光学效应

采用可分相的Na2－Al2O3－B2O3－SiO2系为基础玻璃，以CuO／SnO、NaI为原料；分别引入Cu 、I－，成功地制备出CuI微晶掺杂硼硅酸盐玻璃·通过X射线粉末衍射（XRD）和高分辨透射电镜（HRTEM）分析观察到了玻璃中的晶相及其分布；由玻璃的室温透射光谱研究了玻璃的热处理条件与光吸收性的关系．首次报道了该半导体微晶掺杂玻璃中的电致二次谐波发生，并讨论了该效应的机理．     

A Numerical Model to Explain Experimental Results of Effective Thermal Conductivity Measurements on Unsaturated Soils

Effective thermal conductivity measurements on unsaturated soils by means of the probe method (thermal conductivity probe, TCP) often present a nonlinear trend of \(\Delta T\) versus ln (\(\tau \)). Three different slopes are present in the plots, while a homogeneous material should present only one. Being soils composite structures made of different phases (solid earth, liquid water and air), a possible explanation is the presence of phenomena other than pure conduction, such as water evaporation and vapor migration through the soil structure. A numerical model based on finite differences has been developed to simulate these phenomena. The model takes into account several factors including heat conduction, heat storage due to thermal capacity, water evaporation and water diffusion through a porous medium. Results show that two of the three slopes can be successfully simulated by the model, confirming the interpretation of the phenomena. However, the third slope from the experimental data is lower than the model’s slope, likely indicating the presence of other phenomena not yet taken into account, such as capillarity.     

Al2O3和P2O5共同掺杂的SiO2玻璃的溶胶-凝胶法制备及其光学性质研究

以磷酸三乙酯、硝酸铝和正硅酸乙酯为原料，采用溶胶－凝胶法成功地制备了掺杂有Ａｌ２Ｏ３和Ｐ２Ｏ５的ＳｉＯ２玻璃。通过热分析和表面分析研究了凝胶向玻璃的转化过程，解释了热处理过程中的碳化现象，确定了热处理的适宜温度和时间。研究了掺杂有Ａｌ２Ｏ３和Ｐ２Ｏ５的ＳｉＯ２玻璃的光学性质。     

Investigations into the thermodynamics of polypeptide interaction with nonpolar ligands

In this paper, we describe a general procedure to evaluate the thermodynamics of the interaction between polypeptides and hydrophobic ligands in the presence of aquo-organic solvent mixtures. These studies address experimental requirements for the determination of the linear free energy relationships, derivation of partition coefficients or other extrathermodynamic parameters such as contact areas, or assessment of the conformational changes that may occur when polypeptides or proteins interact with immobilized nonpolar ligands. Not unexpectedly from thermodynamic arguments, the trends and magnitudes of free energy parameters, such as the enthalpy of association, as previously derived in many studies from gradient elution reversed-phase high-performance liquid chromatographic (RP-HPLC) measurements are often different from the data for the same parameters derived from equilibrium binding or microcalorimetric determinations. To reconcile these divergencies and to more closely examine the thermodynamic basis of the interaction of polypeptides with nonpolar ligands, the dependency of the logarithmic capacity factor, ln k', on temperature, T, for several polypeptides (bombesin, beta-endorphin, glucagon) have been investigated using a n-butylsilica and acetonitrile-water or methanol-water mixtures of defined solvent compositions. With low-pH, acetonitrile-water mixtures, the van't Hoff plots, i.e., the plots of ln k' versus 1/T, were nonlinear over the range of T = 278-358 K, although within a narrow temperature range, e.g., from T = 278-308 K, the experimental data for these polypeptides could be approximated by a linear relationship. This nonclassical van't Hoff behavior was associated with interactive processes that involved temperature-dependent enthalpic, entropic, and heat capacity changes. In contrast, with low-pH, methanol-water mixtures, the van't Hoff plots showed dependencies that were essentially linear over the range of T = 278-358 K. The slopes of the van't Hoff plots with acetonitrile-water and methanol-water mixtures at a defined T value and solvent composition were significantly larger than those found for the corresponding experiments carried out under gradient elution RP-HPLC conditions. From these plots of ln k' versus 1/T, the changes in the apparent enthalpy of association (delta H++assoc) and the apparent entropy of association (delta S++assoc) for the interaction of these polypeptides with the solvated n-butyl ligands at different T and solvent compositions have been determined. For these polypeptides, both delta H++assoc and delta S++assoc exhibited linear dependencies on the volume fraction, phi, of the organic solvent over a narrow range of T, but the slopes of these plots were dependent on the T range examined. The dependencies of the slope term, S, and the intercept term, ln ko, derived from the plots of ln k' versus phi as a function of T, have also been investigated. A new relationship linking the S values with delta H++assoc and delta S++assoc as a function of T and phi has been derived and validated. In addition, the relationship between S, delta H++assoc, delta S++assoc, the apparent change in heat capacity, delta C++assoc, and the accessible surface area, delta Atot, of these polypeptides has been examined, thus providing a linkage of these thermodynamic and extrathermodynamic parameters to the partition coefficient, P, and the molecular properties of these polypeptides. The results confirm that entropy-enthalpy compensation effects participate in the interaction of polypeptides with hydrophobic ligands. This investigation has confirmed that the use of solvent-water mixtures of defined composition, rather than the more convenient practice of using gradient elution methods, is essential if thermodynamically consistent values of the binding affinities and partition coefficients are to be quantitatively derived. (ABSTRACT TRUNCATED)     

A study of the solid-state polymerization of trithiane

The temperature dependence of the rate of solid-state polymerization of trithiane was investigated in conjunction with calorimetric measurements of the heat capacity of the irradiated monomer as a function of temperature. It was found that the rate of change of entropy with temperature exhibited a maximum at about 175° C. The curve of per cent polymerization versus isochronal, post-irradiation polymerization temperature also peaked at some 175° C. Finally, the existence of a crystalline phase-transition in the monomer at about 194° C was discovered by DSC and was confirmed by X-ray powder diffraction and by optical microscopy. Two models which may interrelate this set of phenomena are suggested.This work was supported by a grant from the National Science Foundation.     

Sn对Ge-Se-Te玻璃结构与光学特性的影响

采用熔融淬冷法制备了系列Ge₃Se₅Te₂Sn_x(x=0、0.4、0.8、1.2、1.6、2.0, mol%)硫系玻璃。采用X射线衍射(XRD)图谱、差示扫描量热曲线(DSC)、可见/近红外光谱、傅里叶红外(FTIR)光谱、显微拉曼光谱等手段对玻璃的物化性能及结构进行表征, 研究发现Sn的引入导致Ge-Se-Te玻璃系统物化性能的变化: 玻璃的转变温度T_g降低、红外截止波长发生红移, 并有效地降低了杂质吸收峰对样品红外透过率的影响。利用Philips网络约束理论计算的玻璃平均配位数及拉曼光谱的变化, 讨论了引入Sn对Ge-Se-Te玻璃的影响。     

Studies of RbF-BeF2 glasses by differential scanning calorimetry

The heat capacity, softening temperature, and crystallization temperature of RbF-BeF₂ (10, 15, 18, 22, and 27 mol % RbF) glasses were measured by differential scanning calorimetry. The results lend support to the view that RbF-BeF₂ glasses are diphasic. The glasses studied are shown to contain fragments of (BeF₃) _n ^-n fluoroberyllate chains and to be close in many aspects to KF-BeF₂ glasses.     

Inverse ductile–brittle transition in metallic glasses?

There is evidence that metallic glasses can show increased plasticity as the temperature is lowered. This behaviour is the opposite to what would be expected from phenomena such as the ductile–brittle transition in conventional alloys. Data collected for the plasticity of different metallic–glass compositions tested at room temperature and below, and at strain rates from rate 10^?5 to 10³ s^?1, are reviewed. The analogous effects of low temperature and high strain rate, as observed in conventional alloys, are examined for metallic glasses. The relevant plastic flow in metallic glasses is inhomogeneous, sharply localised in thin shear bands. The enhanced plasticity at lower temperature is attributed principally to a transition from shear on a single dominant band to shear on multiple bands. The origins of this transition and its links to shear bands operating ‘hot’ or ‘cold’ are explored. The stress drop on a shear band after initial yielding is found to be a useful parameter for analysing mechanical behaviour. Schematic failure mode maps are proposed for metallic glasses under compression and tension. Outstanding issues are identified, and design rules are considered for metallic glasses of improved plasticity.     

矩形翅片椭圆管束性能研究及场协同分析

利用CFD方法对空冷系统的基本换热元件矩形翅片椭圆管进行了数值模拟;与实验数据相比较,研究了其在不同迎面风速下的阻力特性与换热特性,拟合出了三排管对流换热系数和协同角随迎面风速的变化关系;并采用场协同原理分析讨论了温度梯度与速度矢量方向的夹角对矩形翅片椭圆管换热特性的影响;结果表明,随着夹角的增大,换热效率变低,以致换热量非线性增加。     

掺铒碲酸盐玻璃的热力学稳定性和光谱性质的研究

分析了掺Er³⁺碲酸盐玻璃的热力学稳定性能,研究了掺Er3+碲酸盐玻璃的吸收和荧光光谱性质;应用Judd-Ofelt理论计算了碲酸盐玻璃中Er3+离子的强度参数Ω(Ω₂=4.79×10^-20cm², Ω₄=1.52×10^-20cm²,Ω₆=0.66×10^-20_cm2),计算了离子的自发跃迁几率,荧光分支比;应用McCumber理论计算了Er3+的受激发射截面(σ_e=10.40×10^-21cm²)、Er³⁺离子⁴I_13/2→⁴I_15/2 发射谱的荧光半高宽(FWHM=65.5nm)及各能级的荧光寿命(⁴I_13/2能级为τ_rad=3.99ms);比较了不同基质玻璃中Er3+离子的光谱特性,结果表明掺铒碲酸盐玻璃更适合于掺Er³⁺光纤放大器实现宽带和高增益放大.     

Long-term mechanical behaviour of optical fibres coated with a u.v.-curable epoxy acrylate

Long-term strength tests have been performed on glass fibres drawn from both Suprasil rods and graded index pre-forms in a laser furnace and in a graphite resistance furnace and coated in both cases with a u.v.-curable epoxy acrylate. Results of stress-free ageing tests in humid environments over a period of 18 months show that the fibres weaken at a rate that depends not only upon humidity level but also upon which heating source is used for fibre drawing. The weakening phenomenon has been ascribed to stress-induced reactions between silica and adsorbed water at the glass-polymer interface which occur spontaneously during the tensile test (dynamic fatigue). Static fatigue tests in 90% r.h. show that the fatigure behaviour deviates from that predicted by the theories of Charles and of Charles and Hillig for uncoated glasses; specifically plots of log (stress) versus log (time-to-failure) and stress versus log (time-to-failure) show downward curvatures which become more pronounced as the applied stress is lowered. In the absence of fatigue data for uncoated fibres, however, it is not possible to determine whether such non-linear behaviour is brought about by the presence of the organic coating layer.     

自复叠制冷循环试验中的特殊现象讨论

在自复叠制冷循环中,经过大量的实验测试,发现在实验中存在气液分离器液体温度偏低、蒸发器出现换热系数过小以及蒸发器制冷量过小,但仍能循环等特殊的现象,这些现象在理论基础上无法解释。针对这些现象,进行了详细的描述,分析并结合实验数据给出一些见解与推测,这有助于对自复叠系统更加深入的研究。     

碘化亚铜微晶掺杂硼硅酸盐玻璃的制备及其电致二阶非线性光学效应

采用可分相的Ｎａ２－Ａｌ２Ｏ３－Ｂ２Ｏ３－ＳｉＯ２系为基础玻璃，以ＣｕＯ／ＳｎＯ、ＮａＩ为原料，分别引入Ｃｕ＾＋、Ｉ＾－，成功地制备出ＣｕＩ微晶掺杂硼硅酸盐玻璃。通过Ｘ射线粉末衍射（ＸＲＤ）和高分辨透射电镜（ＨＲＴＥＭ）分析观察到了玻璃中的晶相及其分布；由玻璃的室温透射光谱研究了玻璃的热处理条件下光吸收性的关系。首次报道了该半导体微昌掺杂玻璃中的电致二次谱波发生，并讨论了该效应的机理。     

Synthesis, structure and impedance spectroscopic analysis of [(Pb x Sr1?x )·OTiO2]–[(2SiO2·B2O3)]–7[BaO]–3[K2O] glass ceramic system doped with La2O3

Various compositions of glasses were prepared by melt quenching method in the glass ceramic 64[(Pb _x Sr_1?x )OTiO₂]–25[(2SiO₂·B₂O₃)]–7[BaO]–3[K₂O]–1[La₂O₃] (0.5?≤?x?≤?1) system doped with La₂O₃. Dielectric constant, ε_r versus temperature, T, plots revealed diffused peaks, while dielectric loss, D, versus T plots showed shifting in the peaks toward the higher temperature side similar to relaxor-like ceramics. Curie temperature was found to change systematically with changing the concentration of SrO. Impedance spectroscopy results indicated the contributions of polarization process relaxing in low frequency region attributed to polarizations at the crystal to glass interface and the glassy region.