Effect of Particle Size on Binary Reactions Common to the Y-Ba-Cu-O System

A systematic study has been conducted to determine the effects of particle size on the reaction paths leading to binary phases in the Y-Ba-Cu-0 system. Using dynamic X-ray diffraction (DXRD), three binary reaction sets with stoichiometries equal to that present in the Y-Ba-Cu high- T _c; superconductor and having two different particle sizes (nanometers and micrometers) were reacted in both air and helium environments. Results indicate that the absence of oxygen and carbon dioxide leads to lower reaction temperatures and to different products in the Y-Cu and Ba-Cu binaries. Particle size comparisons show not only a higher reactivity in the nanometer system, but also different products due to the diffusion limitations in the micrometer system. Comparisons between the binary and ternary reactivities point to the Ba-Cu binary as the most critical reaction system for assuring high-quality HTSC.     

Calcium Sulfate as a Possible Oxidant in “Green” Silicon‐based Pyrotechnic Time Delay Compositions

Chemical time delay detonators are used to control blasting operations in mines and quarries. Slow burning Si BaSO₄ pyrotechnic delay compositions are employed for long time delays. However, soluble barium compounds may pose environmental and health risks. Hence inexpensive anhydrous calcium sulfate was investigated as an alternative “green” oxidant. EKVI simulations indicated that stoichiometry corresponds to a composition that contains less than 30 wt‐% Si. However combustion was only supported in the range of 30–70 wt‐% Si. In this range the bomb calorimeter data and burn tests indicate that the reaction rate and energy output decrease with increasing silicon content. The measured burning rates in rigid aluminum elements ranged from 6.9 to 12.5 mm s⁻¹. The reaction product was a complex mixture that contained crystalline phases in addition to an amorphous calcium containing silicate phase. A reaction mechanism consistent with these observations is proposed.     

Influence of Particle Contact on the Estimation of Powder Reaction Kinetics of Binary Mixtures

To develop a quantitative representation of the interparticle reaction rate of binary powder, an investigation of several models has been undertaken, and their fit to experimental data for the Fe₂O₃V₂O₅ system has been performed by the present authors, as well as for the Al₂O₃Cu_O, Al₂O₃ZnO, MgOAl₂O₃, MgOFe₂O₃, and Fe₂O₃ZnO systems published previously. A concentric spherical model proposed recently shows a quantitative correlation between the reaction rate and the number of contact points between particles in unidirectional diffusion and counterdiffusion systems. The model is consistent with experimental data for the above systems. It is potentially useful for reaction-rate analysis of a wide range of powder systems in which particle sizes and the mixing ratio are varied independently. This is an improvement over previous unreacted core analyses such as the Jander and Ginstling–Brounshtein models.     

Binary and ternary copolymerization in the system vinylchloride — maleic anhydride — butadiene

With free radical initiation, the addition of small quantities of butadiene to vinylchloride considerably reduces the rate of polymerization in the initial stages. If maleic anhydride is added as third monomer equimolar to or in molar excess over butadiene, the polymerization rate increases again. The accelerating effect is not due to a DIELS -ALDER -reaction between butadiene and maleic anhydride. It results instead from modification of the copolymerization process, most probably in such a way that the retarding growth step is suppressed. Vinylchloride and butadiene, within the range investigated, react in accordance with the rules of conventional free radical copolymerization kinetics. The system butadiene-maleic anhydride exhibits a strong “tendency toward alternation”. Vinyl chloride and maleic anhydride, on the other hand, except at unsuitable monomer compositions, form copolymers in which vinyl chloride is present in a molar excess. The ternary system behaves accordingly. At suitable monomer compositions, vinyl chloride is incorporated in the polymer chains in molar excess and at a higher partial rate than in the absence of maleic anhydride. Reaction mechanisms are discussed in the light of recent results on Donor-Acceptor-complex controlled polymerization as published in the literature.     

Reactions Between Ingredients in Binary Silicate Glasses

It is demonstrated that the density of binary glasses upon variation of the molar content of the modifier in their compositions obeys a parabolic dependence, whose parameters can be used to estimate the extent and type of reactions between the components. The reaction parameters in glasses that are prone to liquation are lower by an order of magnitude and have the negative sign.     

Reactions in solid particles—A reappraisal of models

Models such as the Ishida–Wen, or even more commonly the shrinking core models (Ginstling–Brounshtein being an important example), have long been used in the analyses of reactions in particles, particularly in solid–solid systems. There have been a few analyses of the validity of the assumptions made in these models, but to date, no comparison has been undertaken of these models against a general model to delineate their regions of applicability in the parameter space. In this article, we present a general unsteady‐state model that subsumes the earlier models as special cases. Nondimensionalization leads to the identification of two governing parameters in the model, a diffusion‐reaction parameter, and a relative abundance parameter. By solving the general model and comparing the solutions with those of the approximate models in the parameter space, conditions under which the approximate models apply, and the errors that result from their application in other situations, have been identified. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3161–3166, 2012     

The Critical Energy of Direct Initiation in Liquid Fuel‐Air and Liquid Fuel‐RDX Powder‐Air Mixtures in a Vertical Detonation Tube

Multiphase cloud detonation is an important but complex process, which has not been fully understood yet. Direct experimental data about the critical initiation energy (CIE) and pressure/velocity revolution of high explosive powder‐based multiphase cloud detonation is not available in the literature. In this paper, propylene oxide (PO), petroleum ether (PE), isopropyl nitrate (IPN), and a mixture of PE/IPN were individually dispersed to form a cloud in a 200 mm×5400 mm vertical detonation tube. Subsequently, this cloud was directly ignited by a high explosive. The critical initiation energy of various mist/air mixtures was measured by the up and down method. Meanwhile, the pressure history was recorded by six sensors along the detonation tube. RDX powder was added to the system and sprayed simultaneously with the liquid fuel to form a three‐phase gas‐liquid‐solid explosive cloud. The detonation pressure and velocity of all three‐phase cases significantly increased while the corresponding critical initiation energy decreased compared to the liquid‐air analogs. The CIE data were found to have a “U”‐shaped curve relationship to the fuel‐air ratio in two‐ and three‐phase systems, the minimum is always on the fuel‐rich side.     

香料接触过敏—化妆品中香料过敏反应的追踪（英）

介绍了两种用来测试皮肤过敏的过敏测试剂－混合香料和秘鲁香脂的组成以及对湿疹患者和普通人群的皮肤过敏测试试验。结果表明,对化妆品成份过敏者中,大部分是对其中香料过敏,混合香料作过敏指示剂较秘鲁香脂更接近实际。建议对香料严重过敏者不要使用含香料的产品,轻度过敏者,不要直接用于皮肤,可用于衣服和头发等。生产者最好把产品中易过敏成份樯识于产品说明书上。     

Enhanced Particle Removal in Fluorinated Liquids—An Application in Nuclear Decontamination

An experimental cleaning system has been developed to demonstrate the decontamination of model electronic circuit boards by this cleaning process. The media used in this process are a wash solution of a high molecular weight fluorocarbon surfactant in a perfluorinated carrier liquid which results in enhanced particle removal, followed by a perfluorinated carrier liquid rinse. The perfluorinated liquids of interest, which are recycled in the process, are inert, nonflammable, generally safe to use, and do not present a hazard to the atmospheric ozone layer. The cleaning experiments were performed at the MIT Nuclear Reactor Laboratory. The radioactive particles removed from the circuit boards were captured by 0.22 μm filters with a filtration efficiency of 99.5% per stage. Compatibility tests were performed on these model electronic circuit boards. The results obtained show that neither the process fluids used nor the maximum level of the ultrasonic agitation applied harmed the circuit boards or the circuit components. All the circuit boards used in these tests were still functional after the cleaning experiments. A three log reduction in contamination was obtained in 1 hour. These data indicate that this process, once implemented on a large scale, will offer users in the nuclear industry a practical and cost effective means of decontaminating and recovering a wide variety of tools and instruments.     

Interfacial Contact and Bonding in Autohesion IV—Experimental Verification of Theory

A two-stage theory of autohesion, consisting of contact establishment as the first and bond formation as the second stage has been proposed previously. The shape of surfaces and their viscoelastic deformation are the controlling factors.

An experimental verification of the theory is obtained by performing bonding and tensile breaking tests on known cylindrical and “flat” surfaces. The test pieces are compression-molded polystyrene. Bonding is done at known temperatures, under known contact loads, and for known lengths of time. The experimental results agree well with those predicted by the theory.     

Photodegradation of Cotton Cellulose I—Reactions Sensitised by Anthraquinone Sulphonates

The mechanism of photodegradation of cotton cellulose sensitised by sodium anthraquinone-1- and -2-su!phonates (A) has been examined. Measurements of diffuse reflectance indicate that the sensitisers are present in monodisperse form on the cotton cellulose and interact, on irradiation (λ, 365 nm), to give the corresponding anthrahydroquinones (AH₂). A hydrogen-abstraction reaction, involving the nπ*-excited state (A*), leads to the formation of the semiquinone (AH·), which produces the anthrahydroquinone, probably by a further abstraction process: A* + Cell → AH· + Cell radical The accompanying decrease in degree of polymerisation of the cotton cellulose is equivalent to the production of AH₂. The photoinduced changes in the sensitiser and substrate are first-order in sensitiser concentration. Oxygen and water vapour are necessary for the cyclic regeneration of the sensitiser, which proceeds at the same rate for both 1- and 2-sulphonates. However, sodium anthraquinone-2-sulphonate is 16 times more efficient as a sensitiser than the 1-sulphonate, a result which is in agreement with the quantum yields for the production of AH₂ from these sensitisers in solution.     

Role of Particle Dissolution in the Stability of Binary Yttria-Silica Colloidal Suspensions

The stability of yttria-silica binary aqueous colloidal suspensions is examined as a function of time. It has been observed that initially stable silica particles go through a flocculation period and then restabilize. This phenomenon is attributed to slow dissolution and the specific adsorption of trivalent yttrium cation and its hydroxo complexes on the surface of silica. Furthermore, it is shown that the kinetics of flocculation and restabilization can be controlled by pH adjustment.     

振动流化床中双组分颗粒流化特性的研究

本文研究了内径为１４８ｍｍ振动圆柱床中等密度和不等密度的双组分颗粒流化特性,考察了不同振动强度对双组分颗粒的床层空隙率、最小流化速度及相图的影响,给出了床层空隙率和最小流化速度的计算式,此计算值与实验值基本相符,且对振动流化床的实际操作和工程设计起到一定的指导作用。     

Experimental Methods in Chemical Engineering: Particle Size Distribution by Laser Diffraction—PSD

Particle size is the top cited physical property researchers report in The Canadian Journal of Chemical Engineering and among the top properties in all science disciplines. ^[1] Techniques to measure particle size distribution (PSD) include physical operations like sieving and sedimentation, and spectroscopic techniques like laser diffraction image analysis based on optical and electron microscopy, and elecro‐zone instruments. Here we concentrate on laser diffraction analysis (LDA) and review its basic principles, operations, limitations, uncertainties, and mention how it compares to other techniques. LDA is an instantaneous, user‐friendly, convenient, and non‐destructive method to assess PSD of inorganic powders. It measures the scattering angle and intensity of light after it passes through diluted particle dispersions suspended in either a gas or liquid. The Mie theory is an exact solution to resolve the diffraction intensity of light caused by particles that applies to while the Fraunhoffer approximation applies only to particles greater than 20 m. The 95 % confidence interval of five measurements of 56 m and 0.1 m irregularly shaped polyhedrons was . Based on a bibliometric analysis of LDA of the top 10 000 cited articles in 2016 and 2017, the major research clusters are: particle measurement, powder behaviour, pharmacy, comminution, and adsorption. Future work will continue to introduce more laser sources, combine multiple technologies, implement mobile light sources (dynamic light scattering), and better define characterize irregularly shaped particles.     

Interfacial Contact and Bonding in Autohesion V—Bonding of “Flat” Surfaces

All surfaces, when viewed under the microscope, are found to be rough. When the so-called “flat” surfaces are bonded together, the initial contact is only at the high points in the surface. This contact increases with time and the rate of contact establishment is a function of surface roughness and the viscoelastic properties of the material.

A surface study of the “flat” compression-molded surface is made. The profiles are generated by tracing the surface with a stylus. The Interference Microscope is used to study the region in the vicinity of an asperity.

The surfaces are approximated to be composed of simple spherical segments. The deformation is conceived of as a two-stage process. The first stage of easy deformation controls the initial bond strength. The initial bond strength predicted by theory agrees well with experiment.     

气固流化床中大差异双组份颗粒分级特性的实验研究

为解决清洁汽油生产工艺中存在的能量利用问题,需开发一种能使两种温度不同的催化剂直接混合换热,然后实现催化剂再次分离的组合流化床再生器.在一套φ500 mm×7000 mm的大型冷模装置上对密度相近、粒径差异较大的双组份颗粒形成的气固流化床中稀、密相间颗粒分级特性进行了系统的实验研究,结果表明表观气速、混合颗粒平均停留时间以及混合进料浓度是影响颗粒分级的主要因素,停留时间阈值可用于表征气体分布板形式对分级的影响.利用实验数据回归得到了分级效率的经验模型,模型计算值与实验值吻合较好.     

Coloring Properties of Various High‐Nitrogen Compounds in Pyrotechnic Compositions

Strontium salts are widely used in red flame pyrotechnic compositions, usually combined with perchlorate salts as oxidizer. The potential environmental impact of perchlorate could be avoided by using high‐nitrogen compounds. Therefore, the following nitrogen‐rich strontium salts were prepared and characterized: strontium tetrazolate pentahydrate ( 1 ), strontium 1‐methyl‐5‐nitriminotetrazolate monohydrate ( 2 ), and strontium 1‐(2‐chloroethyl)‐5‐nitriminotetrazolate monohydrate ( 3 ). Their combustion behavior and both color intensity and purity were investigated in pyrotechnics. These results were compared with the US Army in‐service signal formulation.     

Manganese as Fuel in Slow‐Burning Pyrotechnic Time Delay Compositions

Manganese metal was evaluated as a fuel for slow‐burning delay compositions press‐filled in aluminium or compaction‐rolled in lead tubes. Oxides of antimony, bismuth, copper, manganese and vanadium were considered as oxidants. Measured burn rates for binary mixtures varied between 5 and 22 mm s⁻¹ but slower burning ternary and quaternary compositions were also found. The addition of fumed silica to the Mn/MnO₂ system had little effect on the propagation rate but a low level addition of hollow glass sphere significantly reduced the burn rate. Mn MnO₂ mixtures showed reliable burning over a wide stoichiometric range. In this system the fuel and the oxidant share a common metal. They combine to form the more stable intermediate oxide (MnO) releasing considerable quantities of heat in the process.     

Application of Amorphous Boron Granulated With Hydroxyl‐ Terminated Polybutadiene in Fuel‐Rich Solid Propellant

Amorphous boron powder granulated with HTPB, whose particle diameter could be controlled, was prepared by mechanical mill method. It was found that amorphous boron powder could be granulated with HTPB binder to form B‐HTPB particles, whose median particle diameter (d₅₀) and specific surface area are in the range of 125.0–431.0 µm and 0.02–0.1 m² g⁻¹, respectively. The B‐HTPB particles could be dispersed in the HTPB binder with relatively low viscosity compared with direct addition of amorphous boron powder to the HTPB binder. The experimental results showed that the content of boron particles in a fuel‐rich propellant could be increased by addition of B‐HTPB particles and the combustion characteristics of the fuel‐rich solid propellant could be improved.