Gas tight sintered material for high temperature sublimation setups

Fine powders of WC, TaC and TaC with W and WC additives were cold-isostatically pressed to ceramic discs and pressurelessly sintered at temperatures up to 2100 °C in a second step. Afterwards, the discs were tested as crucible lid under typical AlN growth conditions. The prepared discs should be gas tight and ensure a better alignment of the thermal expansion coefficients of TaC lid and AlN.Ceramic discs densified by this method reveal a relative density up to 97%. The TaC ceramic discs without additives show a microstructure with grain sizes in the range of 10-200 μm after sintering. The grain enlargement could be reduced by W and WC additives in the range of 1-5 wt.%. The results show that the AlN boules adhere only to WC lids and tungsten containing lids with W contents higher than or equal to 3 wt.%.     

Anisotropy and thermal stability of hot-forged BICUTIVOX oxygen ion conducting ceramics

The oxygen ion conductivity of ultra dense, hot forged Bi₄(Me_xV_1−x)₂O₁₁ (BIMEVOX) ceramics is reported for the first time. A novel approach to electrode preparation, including laser trenching, was developed to perform 4-probe impedance spectroscopy and determine conductivity of small bar-shaped samples with high accuracy and precision. Hot forged (HF) Bi₄(Cu_0.05Ti_0.05V_0.90)₂O₁₁ (BICUTIVOX) ceramic, with modest preferred orientation (11%), exhibits anisotropy by a factor of 2 in its conductivity. Brick layer model (BLM) analysis of complex impedance plots reveals that the relative contribution of grains and grain boundaries to the total resistance is direction dependent, in the low temperature γ′ phase. The total ionic conductivity of BICUTIVOX, prepared either by hot-forging or conventional sintering, appears to be stable with thermal aging and cycling. Anisotropy in the thermal expansion of polycrystalline BIMEVOX ceramics is also reported.     

Preparation of the thermally stable conducting polymer PEDOT - Sulfonated poly(imide)

We describe the template polymerization of EDOT with sulfonated poly(amic acid) (SPAA), resulting in a stable conducting polymer aqueous dispersion, PEDOT-SPAA, with particle size ca. 63 nm. In films of PEDOT-SPAA, the sulfonated poly(amic acid) template undergoes imidization within 10 min at temperatures greater than 150 °C, resulting in PEDOT-sulfonated poly(imide) (PEDOT-SPI) with 10-fold conductivity enhancement. This material is highly thermally stable as compared to PEDOT-PSS. Thermal stability is necessary for many processing applications of conducting polymers, including annealing for OPVs and melt-processing of polycarbonate for device encasement. Isothermal TGA experiments were run at 300 °C for PEDOT-PSS and PEDOT-SPAA and we found that PEDOT-SPAA had a smaller slope for degradation. Annealing of films at 300 °C for 10 min caused the conductivity of PEDOT-PSS films to be unmeasurable (<1 × 10⁻⁵ S/cm), while those of PEDOT-SPAA increased 6-fold. Secondary doping of the PEDOT-SPAA system with additives commonly used for PEDOT-PSS was also investigated.     

TPLIB－94 69群截面库的研制

介绍了ＴＰＬＩＢ－９４６９群截面库的研制。此载面库可供ＴＰＦＡＰ和ＣＡＲＭＰ等热中子反应堆物理计算程序使用。     

High-strength AlN ceramics by low-temperature sintering with CaZrO3–Y2O3 co-additives

Aluminum nitride (AlN) ceramics with the concurrent addition of CaZrO₃ and Y₂O₃ were sintered at 1450-1700 °C. The degree of densification, microstructure, flexural strength, and thermal conductivity of the resulting ceramics were evaluated with respect to their composition and sintering temperature. Specimens prepared using both additives could be sintered to almost full density at relatively low temperature (3 h at 1550 °C under nitrogen at ambient pressure); grain growth was suppressed by grain-boundary pinning, and high flexural strength over 630 MPa could be obtained. With two-step sintering process, the morphology of second phase was changed from interconnected structure to isolated structure; this two-step process limited grain growth and increased thermal conductivity. The highest thermal conductivity (156 Wm⁻¹ K⁻¹) was achieved by two-step sintering, and the ceramic showed moderate flexural strength (560 MPa).     

Effect of hydrogen donors on polymer degradation

The thermal decomposition of hydrocarbon macromolecules, including polymers in solution, is influenced by the presence of hydrogen donors. Depending on the particular polymer, hydrogen donors may increase, decrease, or have no effect on degradation rate. We investigated the concentration effect of the hydrogen- (H-)donor, 6-hydroxy tetralin, on degradation of polystyrene (2 g/l) dissolved in mineral oil at 275°C. The time evolution of the molecular weight distribution (MWD) was determined by gel permeation chromatography of samples from the batch reactor. The data indicated that the H-donor decreases the polystyrene degradation rate. This is in contrast to the H-donor (tetralin) enhancement of degradation for poly(styrene–allyl alcohol) dissolved in a 1-butanol solution at 150°C. Because the reaction mechanism for polymer degradation involves radicals, we have developed continuous-distribution mass balances for polymers and radicals in the elementary reactions by treating molecular weight as a continuous variable. Based on reactions for initiation–termination, propagation–depropagation and H-abstraction, the model describes the various H-donor effects through relative values of rate coefficients.     

The role played by dopant ions for the production of broadband white light emission from metal oxide nano-powders under laser diode excitation

We report on the role played by dopant ions to create broadband white light emission from metal oxide nano-powders. Y₂O₃ was doped with different rare earth ions (Nd³⁺, Er³⁺, Yb³⁺) and Cr³⁺ ion to investigate their role on the production of white light emission. We have determined that the dopant ions have a facilitator but not a decisive role on the production of the white light emission by doing measurements such as reflectance, white light emission, excitation power dependency and color quality parameters. All measurements showed that the production of white light does not depend on the amount and the type of the dopant ions.     

Crystallization and thermal expansion behavior of lithium zinc silicate sealing glass

Effect of heat treatment schedule on the crystallization and thermal expansion behavior of a lithium zinc silicate glass system was investigated by differential scanning calorimeter (DSC), X-ray diffraction, and linear thermal expansion test. Two well-defined crystallization exothermic peaks were observed from the DSC trace. According to the apparent activation energies and avrami parameter values calculated from the two crystallization exothermal peaks, the first crystallization exothermal peak was attributed to a combining surface and internal crystallization behavior, while the second one was found to be internal crystallization. Additionally, the phase evolution and the thermal expansion behavior with increasing heat treatment temperature were found to be closely related. Interestingly, it was found in comparison with previous reports that addition of CaO varies the phase composition of the resulting glass–ceramic in an opposite way to K₂O and the deep rooted reason has been discussed which may cast light on the modulation of properties of glass–ceramic involved crystalline phase of quartz or cristobalite. At last, average thermal expansion coefficient of 7.99–15.38×10⁻⁶ K⁻¹ in the temperature range of 25–400 °C has been obtained with different heat treatment schedules.     

能量守恒定律在制冷循环过程中的解析

能量守恒定律是自然界普遍存在的定律之一,本文通过内能概念,利用能量守恒定律从微观上解释蒸气压缩式制冷的各个过程,从而为我们理解蒸气压缩式制冷原理提供了一个新思路。