Cubic-Formation and Grain-Growth Mechanisms in Tetragonal Zirconia Polycrystal

The microstructure in Y₂O₃-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°–1500°C was examined to clarify the role of Y³⁺ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y₂O₃ concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grain-boundary faces in Y-TZP and Y³⁺ ions segregated at their grain boundaries over a width of ∼10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y³⁺ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y³⁺ ions segregating along the grain boundary, respectively.     

Grain-Growth Transition During Sintering of Colloidally Prepared Alumina Powder Compacts

When the grain size in partially sintered compacts of alumina was measured as a function of density, we found that the grain-growth behavior fell into two distinct regions. In the region where the porosity remained interconnected, grain growth was negligible; when the continuous pore network collapsed into isolated pores, grains grew rapidly. The transition in grain-growth behavior was observed at approximately 90% of theoretical density. A simple phenomenological method for obtaining the transition in grain growth is suggested. It is based on the idea that an abrupt increase in grain size should be accompanied by a significant decrease in the rate of sintering since the sintering rate changes as the third or fourth power of the grain size. The method consists of fitting the sintering data to an exponential function. The transition then appears as a change in the time constant for the exponential. The low rate of grain growth in the region where the pores are interconnected contradicts earlier work in the literature where significant grain growth during intermediate-stage sintering has been reported. This difference is explained in terms of the homogeneity of packing of our powder compacts, which were prepared by colloidal processing.     

Effect of Silver on the Sintering and Grain-Growth Behavior of Barium Titanate

Silver and its alloys frequently are used as electrode material for BaTiO₃-based dielectrics. In the present study, a small amount of fine silver particles have been intimately mixed with BaTiO₃ powder. The sintering and grain-growth behavior of the silver-doped BaTiO₃ in air are investigated. The solubility of silver in BaTiO₃, as revealed by lattice-parameter measurement, electrical measurement, and electron probe microanalysis, is <300 ppm. The densification of BaTiO₃ is slowed slightly by the addition of silver inclusions. However, the presence of a small amount (<0.3 wt%) of silver increases the amount and size of abnormal grains. When the silver content is >0.3 wt%, the grain growth of BaTiO₃ then is prohibited by the silver inclusions.     

Grain-Growth Kinetics for Alumina in the Absence of a Liquid Phase

The kinetics of grain growth in fully dense Al₂O₃ with and without MgO solute additions were measured for high-purity samples containing no liquid phases. The MgO was found to suppress the grain-boundary migration rate by a factor of 50. Compensating lattice defects are suggested to play a role in grain-growth inhibition. Implications of these results to the sintering of Al₂O₃ are discussed.     

Effect of External Electric Field on the Grain-Growth Behavior of Barium Titanate

The effect of an external electric field on the grain-growth behavior of acceptor Mg-doped, undoped, and donor Nb-doped BaTiO₃ ceramics was investigated. The acceptor-doped and undoped specimens showed enhanced grain growth at the positive-biased region. On the other hand, for the highly donor-doped specimens, grain growth was enhanced in the negative-biased region. The results have been explained in terms of defect polarization and the consequent change in the boundary potential. It has been suggested that liquid penetration into grain boundaries is critically dependent on the boundary potential.     

Grain-Growth Behavior during Stepwise Sintering of Barium Titanate in Hydrogen Gas and Air

To study the effect of oxygen partial pressure on grain growth in BaTiO₃, TiO₂-excess samples have been sintered in air with and without a prior H₂ heat treatment. Without prior H₂ treatment, abnormal grain growth occurs below and above the eutectic temperature ( T _e). An introduction of H₂ treatment before air sintering, however, increases the average grain size and suppresses the formation of abnormal grains during subsequent air sintering below and above T _e. This H₂ treatment effect has been explained in terms of a decrease of the driving force for the growth of faceted grains below a critical value for formation of abnormal grains. The observed grain-growth behavior under various atmospheres demonstrates the possibility of having various microstructures via control of oxygen partial pressure and initial grain size.     

固定床传热中的参数估值传热参数中的床高效应

本文试验测定了固定床的传热数据,计算和分析表明,床高效应反映了加热段进口热边界层对传热参数的影响,不能通过在传热 模型中引入轴向导热项或采用抛物线型进口边界条件获得补偿;轴向导热项对拟合传热参数以及模拟床层内的温度场均无意义,因此拟均相模型应该采用ＰＦ模型的形式。要想到可靠的传热参数,必须通过不同床高下的传热 数据来获得传热参数的渐近值。     

Evaluation of Elution Parameters for Cesium Ion Exchange Resins

Abstract

Cesium ion exchange is one of the planned processes for treating and disposing of waste at the U.S. Department of Energy Hanford Site. Radioactive supernatant liquids from the waste tanks will undergo ultrafiltration, followed by cesium ion exchange using a regenerable organic ion exchange resin. Two resins, SuperLig^®644 and a resorcinol‐formaldehyde resin, are being evaluated for cesium removal and cesium elution characteristics. The main purpose of this study is to optimize the cesium elution to provide a resin that, after undergoing elution, would meet the U.S. Department of Energy/Office of River Protection Project‐Waste Treatment Plant processing and resin disposal criteria. Columns of each resin type were loaded to greater or equal to 90% breakthrough with a Hanford waste stimulant and eluted with nitric acid. The temperature, flow rate, and nitric acid concentration were varied to determine the optimal elution conditions. Temperature and eluant flow rate were the most important elution parameters. As would be predicted based upon kinetic consideration alone, decreasing the eluant flow rate and increasing the temperature provided the optimal elution conditions. Varying the nitric acid concentration did not have a significant effect on the elution completion; however, elutions performed using both high acid concentration (1 M) and elevated temperature (45°C) resulted in resin degradation, causing gas generation and resin bed disruption.     

Sintering and Grain-Growth Kinetics of MgAl2O4

The sintering and grain-growth kinetics of finely divided MgAl₂O₄ were determined from 1300° to 1600°C for densities up to 96% of theoretical. These results show that sintering is governed by volume diffusion and that the temperature dependence of the diffusivities is 157 exp [(-118 kcal/mol)/ RT ] cm²/s. Grain growth follows the expression ( G ²- G ₀²)= Kt , where K =51.3 exp [(-110 kcal/mol)/ RT ] cm²/s.     

Evaluation of Supercritical Fluid Extraction Model Parameters by Monte-Carlo Methods

Theoretical Foundations of Chemical Engineering - The problem of evaluation of model parameters for supercritical fluid extraction of oil from ground plant materials with high initial oil contents...     

基于模糊综合评判的整体压裂裂缝参数优化

考虑启动压力梯度,建立了整体压裂三维油水两相数学模型和压裂方案模糊综合评判优选模型。利用建立的数学模型对油水井压裂进行单一裂缝参数影响因素分析,在此基础上,利用正交试验设计方法设计整体压裂试验方案,采用模糊综合评判法进行多目标优化,从而得到最合理裂缝参数组合。该研究方法综合考虑了各参数之间的交互影响,可以优化出与井网、储层合理匹配的人工裂缝参数。研究成果为低渗透油藏整体压裂的合理、高效开发提供技术支持与保障。     

Evaluation of Thermodynamic Parameters for Separation of Hexavalent Chromium by Fly Ash

Abstract

Kinetics and thermodynamic parameters of Cr⁶⁺ separation by fly ash from aqueous solution has been evaluated. It was found that the separation process is partly diffusion controlled and endothermic in nature. The mass transfer coefficient increases with an increase in temperature. The activation energy and change of enthalpy were also evaluated and found to be 17.5 kJ/mol and 14.47 kcal/mol, respectively. The free energy of the process was small but positive, and it decreases with an increase of temperature. The change of entropy was found to be small and remains unchanged over the 30 to 50°C temperature range. This process follows the Langmuir isotherm model where Q _o and b were also determined at different temperatures.     

应用统计分析和化学动力学参数评价生物制品的稳定性

目的应用统计分析和化学动力学参数评价生物制品的稳定性。方法以重组乙型肝炎疫苗为例,拟合其效力随时间衰减的回归直线,由其95%置信曲线预测制品的有效期。根据阿伦尼乌斯方程,从较高温度下效力衰减的速率常数估算较低温度下的速率常数。由衰减速率常数计算制品的半衰期,并用于稳定性评估。结果通过对稳定性数据的统计分析能预测有效期和失活速率常数等化学动力学参数能有效地反映制品稳定性的变化。结论应用统计分析和化学动力学参数研究生物制品的稳定性,可以在设定的置信区间下预测制品的有效期,缩短临床前稳定性研究所需的时间,并对生产变更可能导致的稳定性变化进行可靠的评估。     

厌氧发酵产氢关键影响因素考察与优化

通过单因素实验方法研究发酵液初始pH值、NH⁺₄、Fe²⁺、Mg²⁺浓度以及厌氧活性污泥的热处理条件对厌氧发酵产氢的影响。归纳得到最适宜产氢条件为:厌氧活性污泥在90 ℃下热处理 40 min,调节发酵液初始pH值至8.0 并添加3.00, 0.10和0.03 g/L的(NH₄)₂SO₄, FeSO₄和MgSO₄。在该最适宜条件下得到较高纯度（体积分数为0.80）的氢气630 mL,1 mol葡萄糖可产氢气2.62 mol。实验表明厌氧发酵是较为高效的产氢方式。     

重度聚合物改性沥青蠕变恢复测试参数及评价准则

为了比较常规掺量SBS改性沥青与重度SBS改性沥青蠕变恢复行为之间的差异,采用多应力蠕变恢复试验作为两种改性沥青的评价方法,研究多应力蠕变恢复试验参数变化对高温蠕变恢复行为的影响.采用旋转烧瓶法替代传统的旋转薄膜烘箱试验(RTFO)以使得高粘度的重度改性沥青老化更加均匀.结果表明,与常规掺量SBS改性沥青相比,当采用MSCR试验评估重度改性沥青时,其不可恢复蠕变柔量低估了应变响应,从而导致高估重度改性沥青所能适用的交通水平.此外,重度改性沥青的永久应变具有很强的加载时间依赖性,采用较短的加载时间更有利于减轻重复蠕变恢复对试验结果的影响.最终推荐采用0.1 s的加载、0.9 s的卸载组合,同时以3.2 kPa下第10次蠕变恢复循环得到的Jnr值作为最终的评价参数.     

Evaluation of Ozone Pretreatment on Flux Parameters of Reverse Osmosis for Surface Water Treatment

This research details the effects of ozone pretreatment on flux of a reverse osmosis membrane. Initial tests were conducted to determine the effects of ozonation on solids removal, turbidity, and chemical oxygen demand concentrations using various doses on a simulated surface water. These initial tests showed that the best reduction of solids in the 2–5 microns range was at 0.30 mg/L of ozone. Next, a series of bench scale tests was run for 62.5 hours using a standard reverse osmosis system under constant pressure with three pre-ozonation doses and a no ozone baseline dose. Temporal models were developed using the flux data from these tests to determine the effects of operating hours and ozone dosage on flux. It was found that the laboratory data were not linear and followed power law models. Statistical analysis was used to determine the significance of each ozone dose on the four developed models. The change in flux over the 62.5 operating hours with an ozone dosage of 0.30 mg/L showed the lowest flux change. Last, the models were tested using Hermia's filtration models and resistance versus time data to determine the type of membrane fouling that existed. It was concluded that the major fouling was pore blockage. This work demonstrated that ozone pretreatment is effective prior to use with reverse osmosis since it shows a better solid and organic removal rate as well as decreased flux and resistance changes over time.     

Evaluation and Optimization of Effective Parameters on Zinc Sulfate Flotation by the Taguchi Method

In this research, optimization of effective parameters on zinc flotation of zinc sulfate obtained from the zinc sulfate process is investigated by the Taguchi method. Experiments were evaluated with regard to seven factors in two levels by a Taguchi L8 orthogonal array. The optimum conditions proposed by the model for zinc sulfate flotation tests are as follows: amount of collector and frother 100 g/t, flotation time of 30 min, pH = 9, S/L = 30/70, rotor speed = 1250 rpm and preparation time = 100 min. Under these conditions the zinc grade in the flotation product was 41.5 %, which is little different to the actual amount of 42 % from the flotation tests.     

Evaluation of Spectroscopic Parameters for Cobalt (II) Species Sorbed on Ion Exchangers

New spectral data for cobalt (II)-ligand-solvent systems is reported and spectroscopic parameters are evaluated for various tetrahedral and octahedral species sorted on ion exchangers.     

Degradation of Polyvinylpyrrolidone by Photocatalytic Ozonation and Evaluation of the Influence of Some Operational Parameters

Photocatalytic degradation of polyvinylpyrrolidone (PVP) by titanium dioxide and ozone in an annular reactor was investigated using a 125-W mercury vapor lamp as the light source. It was observed that the TiO₂/O₃/UV process presented a greater efficiency than the TiO₂/UV process. In fact, around 90% of the mineralization was obtained in 1 h of reaction, reflecting the synergistic effect of the combination of O₃ and TiO₂ under UV light, because the sum of the rate constants of the individual processes is less than the rate constant of the combined process. The effects of the initial PVP concentration, photocatalyst dosage, ozone input flow rate and pH on the PVP degradation rate were studied. In general, the results suggest that PVP can undergo a cross-linking process when the TiO₂/O₃/UV treatment is applied. The reaction rate was increased when the photocatalyst dosage was increased up to 2.0 g L^?1; however, increasing the initial PVP concentration led to a drop in the reaction rate. The efficiency also decreased at basic pH, because ozone is decomposed under alkaline conditions. In addition, it was noted that most of the nitrogen atoms of the macromolecules of PVP can be transformed into nitrate and ammonia during photocatalytic ozonation.