Synthesis of Mullite Powders Through a Suspension Combustion Process

This work reports on the synthesis of mullite powders by a suspension combustion process. Aluminum nitrate, as a source of Al, and a colloidal silica suspension, as a source of Si, are used as reagents, and urea serves as the fuel. This colloidal suspension allows a complete mixing of the reactants, thus promoting a core-shell reaction to produce the mullite. The powders obtained need to be treated at a high temperature to form the mullite. However, when ammonium nitrate is also added as a combustion aid, the mullite phase is directly obtained without any further treatment. A chemical reaction involving all these compounds is proposed, and the thermodynamic parameters are calculated in order to predict the temperature reached during the combustion process. The addition of ammonium nitrate reduces the temperature of the reaction by ca. 150°C. Once the conditions for the combustion reaction are optimized, the Al/Si ratio is modified in an attempt to obtain monophasic mullite.     

PS/ABS复合粉末选择性激光烧结工艺参数的实验研究

针对选择性激光烧结件力学性能和尺寸精度差的问题,通过机械混合法制备了聚苯乙烯/丙烯腈-丁二烯-苯乙烯塑料(PS/ABS)的复合粉末。在预热温度85℃、8层网格支撑等条件下,采用单因素实验法研究激光功率、扫描速度、扫描间距和单层厚度对烧结件强度和相对误差的变化规律,并用正交试验对工艺参数进行优化。结果表明,烧结件的弯曲强度随着激光功率的增加而提高,随扫描速度、扫描间距和单层厚度的增加而降低。Z向尺寸相对误差随着激光功率的增加而增大,随着扫描速度、扫描间距和单层厚度的增加而减小;由极差分析可知,激光功率对PS/ABS烧结件弯曲强度和Z向尺寸相对误差的影响最大;最优的工艺参数组合为:激光功率30 W、扫描速度1 200 mm/s、扫描间距0.32 mm和单层厚度0.26 mm,此时烧结件的弯曲强度为7.85 MPa,Z向尺寸相对误差为1.30%。     

Experimental Study of Aerosol Filtration by the Granular Bed Over a Wide Range of Reynolds Numbers

The collection performance of granular bed filters consisting of uniform spheres with diameters of 0.5–2.0 mm was experimentally studied by using monodisperse aerosol particles ranging from 0.02 to 2 μm in diameter at superficial velocity from 0.4 to 120 cm/s. Based on the experimental data, prediction equations of collection efficiency due to individual mechanical collection mechanisms were obtained, elucidating the influence of the Reynolds number on the particle collection. Furthermore, by assuming the additivity of the individual mechanical collection efficiencies, a prediction equation applicable to the wide range of filtration conditions is proposed.     

超临界体系相行为实验测定方法研究进展

超临界相行为研究及其实验测定是超临界流体技术领域发展的基础和重要研究内容之一,从超临界相行为测量的意义和基本原理出发,对相行为及临界参数实验测定方法作了综述,主要介绍了可视观察法、光谱色谱法、脉冲加热法等测定方法,并对其优缺点和适用范围作了点评,最后对其未来发展方向做了展望。     

Experimental Research of the Effects of Superfine Aluminum Powders on the Combustion Characteristics of NEPE Propellants

The combustion behavior of grading aluminum powders containing superfine aluminum powder (SAl) in NEPE propellant has been studied by several kinds of experimental techniques. The results indicate that the usage of grading aluminum powders containing SAl can effectively improve the combustion characteristics of NEPE propellant and the combustion efficiency of aluminum. The reason is that SAl has the different combustion and thermochemical properties from those of generally powdered aluminum (Al). SAl is inclined to burn in a single step, hence greatly increasing the heat released during the thermal decomposition of NEPE propellant.     

Dynamic Features of Combustion of Polydisperse Aluminum Powders in a Gas

The results of a mesh analysis of aluminum powders are considered. It is shown that the particle mass distributions are nearly normal or lognormal. The differences in the combustion dynamics between powders consisting of polydisperse particles and particles of the same sizes are studied. It is established that these differences are manifested only in the late stage of combustion and are due to the presence of a coarse particle fraction in the powder.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 78–83, July–August, 2005.     

研究剪切流动下共混物相行为规律的实验方法

从实验原理、仪器设备、分析方法等方面,介绍了在开展剪切流动对共混物相行为影响研究中应用的实验方法,并着重介绍了包括应用最广泛的二维小角激光散射流变法在内的实时测试的各种实验方法,为不断改进和完善此类研究的实验手段提供了参考。     

研究G-四链体与其配体相互作用的技术方法概述

近年来以G-四链体DNA为药物靶点的研究引起了人们的广泛关注,G-四链体与其配体相互作用的研究方法也多种多样.本文对研究G-四链体形成的结构,配体与G-四链体结合能力,配体与G-四链体结合模式等三个方面的技术方法进行了综述.     

Combustion of Agglomerated Ultrafine Aluminum Powders in Air

It is shown experimentally that agglomeration of ultrafine aluminum powders decreases their reactivity during nonisothermal oxidation in air. Under normal and low pressures, the concentration of bound nitrogen in combustion products is lower for agglomerated powders than for unagglomerated powders, and under high pressures (>120 kPa), it is higher for agglomerated powders. Key words: ultrafine powder, aluminum, agglomeration, combustion, reactivity, aluminum nitride.     

Combustion Prevention of Iron Powders by a Novel Coating Method

The effectiveness of a novel coating method in providing fine iron powder particles with a protective barrier against rapid oxidation was systematically studied. Particles were individually coated with an alumina‐based (Al₂O₃) ultra‐thin film using the Atomic Layer Deposition method. The oxidation resistance of the coating layer was found to be greatly dependent on the film thickness. Furthermore, for each film thickness there was a corresponding temperature above which the film drastically lost its protective effectiveness, primarily due to cracking caused by the thermal expansion mismatch between the particle and the alumina film. This problem was largely overcome when, instead of Al₂O₃, the protective film was generated from alternating layers of Al₂O₃/ZnS to ensure that the thermal expansion properties of the resultant film matched that of iron. The technique employed in this study is quite robust and can be adapted for combustion prevention in other types of metal powders.     

Influence of Process Parameters on the Morphology of Spray‐Dried BaCl2 Powders

Spray‐drying is an effective method for producing powder aggregates with controlled size and morphology. Here, we report on a systematic study aimed at determining how spray‐drying parameters such as nozzle temperature, gas flow, salt concentration and solution feed rate, influence the characteristics of BaCl₂ granules prepared from aqueous solutions. We correlate the granule characteristics to these conditions through the use of processing maps and modeling. It is found that well‐dispersed, high density and spherical aggregates, which are favorable for subsequent powder compaction and sintering, can be obtained within a limited range of processing conditions.     

生物活性炭滤池工艺参数试验研究

生物活性滤池的工艺参数直接影响其处理效果和成本,本文分析探讨了炭床高度和空床接触时间对生物活性炭滤池净水效果的影响,认为空床接触时间是决定性因素,合理确立了生物活性炭滤池的相关工艺参数。     

多目标质量压气机实验叶片注射成型工艺参数优化

为获得综合质量较高的发动机低速实验台所用树脂叶片,提出并研究了叶片多目标质量优化方法。以叶片翘曲量、收缩率、残余应力为优化目标,模具温度、熔体温度、注射时间、保压时间、保压压力、冷却时间为优化变量,模拟叶片成型过程,获得不同参数组合下的翘曲量、收缩率以及残余应力数据,并基于回归分析建立工艺参数与各质量目标间的映射关系;然后通过层次分析法计算各质量目标的权重,进而建立叶片注射成型多目标质量优化数学模型,最后基于遗传算法对叶片注塑工艺参数进行优化。实验验证表明,优化的工艺参数可显著提高叶片成型质量。     

Empirical Likelihood for a Long Range Dependent Process Subordinated to a Gaussian Process

This article develops empirical likelihood methodology for a class of long range dependent processes driven by a stationary Gaussian process. We consider population parameters that are defined by estimating equations in the time domain. It is shown that the standard block empirical likelihood (BEL) method, with a suitable scaling, has a non‐standard limit distribution based on a multiple Wiener–Itô integral. Unlike the short memory time series case, the scaling constant involves unknown population quantities that may be difficult to estimate. Alternative versions of the empirical likelihood method, involving the expansive BEL (EBEL) methods are considered. It is shown that the EBEL renditions do not require an explicit scaling and, therefore, remove this undesirable feature of the standard BEL. However, the limit law involves the long memory parameter, which may be estimated from the data. Results from a moderately large simulation study on finite sample properties of tests and confidence intervals based on different empirical likelihood methods are also reported.     

Two-Photon Excitation Spectra of Various Fluorescent Proteins within a Broad Excitation Range

Two-photon excitation fluorescence laser-scanning microscopy is the preferred method for studying dynamic processes in living organ models or even in living organisms. Thanks to near-infrared and infrared excitation, it is possible to penetrate deep into the tissue, reaching areas of interest relevant to life sciences and biomedicine. In those imaging experiments, two-photon excitation spectra are needed to select the optimal laser wavelength to excite as many fluorophores as possible simultaneously in the sample under consideration. The more fluorophores that can be excited, and the more cell populations that can be studied, the better access to their arrangement and interaction can be reached in complex systems such as immunological organs. However, for many fluorophores, the two-photon excitation properties are poorly predicted from the single-photon spectra and are not yet available, in the literature or databases. Here, we present the broad excitation range (760 nm to 1300 nm) of photon-flux-normalized two-photon spectra of several fluorescent proteins in their cellular environment. This includes the following fluorescent proteins spanning from the cyan to the infrared part of the spectrum: mCerulean3, mTurquoise2, mT-Sapphire, Clover, mKusabiraOrange2, mOrange2, LSS-mOrange, mRuby2, mBeRFP, mCardinal, iRFP670, NirFP, and iRFP720.     

Combustion of Mixtures of Commercial Aluminum Powders and Ultrafine Aluminum Powders and Aluminum Oxide in Air

The paper studies the combustion of mixtures of commercial aluminum powders (ASD-1 and ASD-4) and ultrafine powders of Al and -Al₂O₃ in air. It is shown that the combustion of coarsely dispersed commercial powders is accompanied by binding of air nitrogen with formation of AlN and AlON. The combustion of mixtures proceeds in two stages with the possible formation of intermediate gaseous and liquid products. The processes of sintering and incomplete combustion play an important role in the combustion of mixtures of commercial powders and ultrafine powders of aluminum.     

气体注射控制参数对聚合物气辅共注成型过程影响的实验研究

为了建立气辅控制系统的控制模型,系统研究了气辅注射工艺参数对气辅共注成型过程的影响规律。研究表明,保压时间和气体注射延迟时间对气辅共注成型的气体穿透有较大影响,而对芯层熔体的穿透影响不明显。随着保压时间的延长,气体的穿透深度和穿透宽度均增加,而随着气体注射延迟时间的延长,气体穿透深度增大,穿透宽度减小。延长气体注射延迟时间有利于气体的穿透,但易出现指进现象和气体穿透流动的不稳定。     

层燃炉煤燃烧碳黑形成规律的实验研究

设计了可移动式-固定床块煤燃烧实验台,进行了层燃炉块煤燃烧碳黑生成规律的研究。结果表明,随着温度的升高,碳黑和焦油的生成量先增加后减少,呈马鞍形,这是碳黑、焦油形成过程与氧化过程相互竞争的结果,高温有利于减少碳黑的排放;随着气体停留时间的延长,碳黑和焦油的生成量减少;高挥发分煤不完全燃烧时,碳黑的生成量较高;随着氧量比的增大,碳黑和焦油的生成量逐渐减少;当氧量为理论燃烧煤所需氧量的0.9倍时,没有碳黑和焦油生成。     

Methods for Determining the Marangoni Numbers in Studying the Absorption in the Operation of a Heat Pump

It is analyzed whether or not experimental data on the surface tension of an aqueous lithium bromide solution with or without surfactants can be used to study the heat and mass transfer in the operation of the absorber of a heat pump. Examples of the erroneous determination of the Marangoni numbers under these conditions are given. A method for calculating the interfacial tension gradients and the Marangoni numbers is proposed. It is argued that it is necessary to perform additional experimental investigations for determining the interfacial tension under the conditions of equilibrium in the surfactant-containing aqueous lithium bromide solution-water vapor system at constant water vapor pressure.