Sintering of Bimodally Distributed Alumina Powders

The densification of alumina powders prepared to have a bi-modal particle-size distribution with a coarse-to-fine particle-size ratio of ≊ 10 can be predicted to a first approximation if the densification of the fine and coarse powders is known. Deviations from model prediction were attributed to compositional heterogeneity. Microstructural observations of bimodal powders show that only the fine powder undergoes grain growth. Thus, the grain-size distribution becomes more uniform than the initial particle-size distribution.     

Humidity Sensing Property of NaCl‐Added Mesoporous Silica Synthesized by a Facile Way with Low Energy Cost

NaCl‐added mesoporous silica SBA‐15 was prepared by a simple grind method which needs low energy cost. Humidity sensing property was studied. Study results indicated that NaCl‐added material possesses higher humidity sensitivity. Its impedance changed more than four orders of magnitude when the relative humidity changed from 11% RH to 95% RH. From the viewpoint of economy, NaCl‐added SBA‐15 material which possesses high sensitivity and needs low energy cost is more suitable to be a promising humidity sensing material. Complex impedance spectra, the corresponding equivalent circuit, and bode diagrams were carefully analyzed to explore sensing mechanism.     

Quantitative computer reconstruction of particulate materials from microtomography images

Traditional particle-characterization techniques require particles to be dispersed from their original form, which destroys important morphologic information in materials such as aggregates or porous materials. X-ray computed microtomography provides a powerful tool for non-destructive analysis. However, robust techniques for comprehensive material characterization of these images have not been developed.In this paper we present a new algorithm for the computer analysis of particulate materials from high-resolution tomography images. The key aspect of the algorithm is the assignment of every solid-phase voxel in the image to its associated particle in a physically representative manner, which is in essence a particle-scale computer reconstruction of the material. Once this digital reconstruction is obtained, a vast amount of morphologic information can be extracted, including parameters obtained by traditional particle-analysis techniques (e.g., particle-size distribution and porosity) as well as parameters not usually available (e.g., spatial correlations in particle size, particle aspect ratios, surface areas, and orientations, particle contacts, particle coordination numbers, and more). Additionally, the computer reconstruction allows for complex manipulations such as the comparison of a specific parameter for two different particle-size classes within the material. The paper includes validation of the algorithm using computer-generated packings, as well as an example using microtomography data from a real material.     

Colloid Mills: Theory and Experiment

In a colloid mill utilizing a rotating and a stationary plate, a high shear field exists. Particles rotate, generating a lift force moving them to the rotating plate. When particles collide, a substantial energy transfer occurs because their surface velocities are opposite. A mathematical model has been developed relating the particle rotational speed to the parameters of the colloid mill such as gap size, speed, slip viscosity, and particle size distribution. A slurry of the material being ground is forced into the gap. Grinding is autogenous as a result of collisions between rotating particles. All of the material in the process stream is ground finer than the gap setting and grinding can be optimized by adjusting mill operating parameters. However, the mill is not able to grind the incoming stream to submicrometer sizes and there is molecular contamination from the surface of theB₄C cones.     

Impact of ammonia fiber expansion (AFEX) pretreatment on energy consumption during drying,grinding, and pelletization of corn stover

Pretreatment and densification of biomass can increase the viability of bioenergy production by providing a feedstock that is readily hydrolyzed and able to be transported over greater distances. Ammonia fiber expansion (AFEX?) is one such method targeted for use at distributed depots to create a value-added and densified feedstock for bioenergy use. However, the pretreatment process results in a high-moisture material that must be dried, further size reduced, and pelletized, all of which are energy-intensive processes. This work quantifies the energy consumption required to dry, grind, and densify AFEX-pretreated corn stover compared to non-pretreated stover and explores the potential of reduced drying as a means to conserve energy. The purpose of this work is to understand whether material property changes resulting from AFEX pretreatment influence the material performance in downstream formatting operations. Material properties, heat balance equations, and a rotary drum dryer model were used to model a commercial-scale rotary drum dryer for AFEX-pretreated corn stover, showing the potential to reduce dryer energy consumption by up to 36% compared to non-pretreated corn stover. Laboratory-measured grinding and pelleting energies were both very sensitive to material moisture content. Overall, the total energy required for drying, grinding, and pelleting amounts to a savings of up to 23 kWh/dry Mg for the AFEX-pretreated material when dried to a low moisture content, equating to up to 0.61 $/Mg savings for gas and electricity. Grinding and pelleting of high-moisture AFEX-pretreated stover was shown to be more costlier than the savings collected through reduced drying. Although the energy and cost savings shown here are modest, the results help to highlight operational challenges and opportunities for continued improvement.     

表面活性剂在陶瓷超细粉体制备中的应用

表面活性剂是一类加入少量就能使物质性质发生很大变化的精细化工产品。陶瓷超细粉体的制备可分为长大法和细碎法,本文主要概述了表面活性剂在细碎法中作助磨剂,对长大法中颗粒团聚的改善等的机理和应用。     

煤的助磨机理及对水泥性能的影响

针对水泥厂的熟料粉磨效率低下 ,提出了以煤作为助磨剂的解决方案 .分析了煤的微观结构及其化学成分 ,从而较好的解释了煤的助磨机理 .同时通过实验检验了煤作为助磨剂对水泥性能的影响 ,并分析了影响的原因 .为工厂具体操作提供了有利的依据     

Genesis of the Barium Titanate Butterfly Twin

It has been discovered that the formation of the butterfly twin in barium titanate depends on both the average particle size and the particle-size distribution of the starting material. Maximum twin yields occur when the particles have an average size near 1μ with a rather sharp cutoff in the distribution in the large-particle region. All impurities act to decrease twin yield, principally because they interfere with stacking-fault formation which also is necessary for twinning to occur.     

Fluidized-bed electrowinning — I. General modes of operation

An analysis is presented of the changes in properties of a fluidized-bed cathode during continued electrowinning use. Control of the particle-size distribution in the bed is achieved by periodic withdrawal of powder equal in weight to the electrowon metal, plus a small fraction of original bed weight. The electrode is restored to its original weight by addition of a suitable quantity of the starting material. The analysis demonstrates that the fluidized electrode approaches a steady-state condition which depends primarily on the detailed schedule under which it is operated, with the initial bed material exerting only a minor influence. Suitable operating schedules are discussed.     

Characterization,properties, and processing of LaRC™ PETI‐5 as a high‐temperature sizing material. I. FTIR studies on imidization and phenylethynyl end‐group reaction behavior

The imidization and phenylethynyl end‐group reaction behavior of phenylethynyl‐terminated imide oligomers (LaRC™ PETI‐5) with a number‐average molecular weight of 2500 g/mol has been extensively interpreted in terms of the disappearance and appearance of several characteristic absorption peaks. Most characteristic FTIR absorption bands including the phenylethynyl end group occurring via imidization and cure during dynamic and isothermal heat treatments of LaRC™ PETI‐5 were clearly resolved and assigned in the present study. The results give some information on temperature‐ and time‐dependency of the cure of LaRC™ PETI‐5, which may be useful for determining the processing conditions necessary for use as a high‐temperature fiber‐sizing material. This study also measures the extent of imidization and the activation energy of cure reaction of this material.     

Factorial Design of Experiments in Ceramics, l

A factorial design of experiment is one in which a variable is evaluated at all levels of all other variables. This type of experiment was applied to the unit operations in body preparation and forming by extrusion. Drying and firing unit operations were not considered, and the variance due to these operations was minimized by duplication. The variables or factors were (1) particle-size distribution at three levels, (2) water of plasticity at two levels, (3) entrapped air at two levels, and (4) two replications. Analysis of variance was used to determine the significant effects. It was found that 95%. ₀f the total variance of the drying shrinkage was accounted for by the particle-size distribution, water of plasticity, and two interactions; 95% of the total variance of the dry modulus of rupture was accounted for by particle-size distribution, water of plasticity, entrapped air, and two interactions; 52% of the total variance of the firing shrinkage was accounted for by the particle-size distribution; 87% of the total variance of the fired modulus of rupture was accounted for by the particle-size distribution, water of plasticity, entrapped air, and three interactions. Since a tunnel kiln makes it possible to control the firing operation closely and with no changes in composition, close control of the particle-size distribution, water of plasticity, and entrapped air should make it possible to produce more uniform ware. The slope constants for the factors were also determined which show the most efficient path leading to the development of optimum conditions necessary for maximizing a desired property.     

Chromium powder as a reference material for the quality control of particle-size measurement by laser diffraction

Chromium is an important alloying element for aluminium melts. During aluminium cast house practice, chromium is mainly added to melts of aluminium in the holding furnace as tablets or minitablets (compressed compacts of chromium and aluminium powders). Particle-size analyses of chromium powder used as raw material can routinely be carried out by laser diffraction to assure correct packing. Factors affecting the laser diffraction analysis were studied by means of designed experiments in order to improve and control the quality of such particle-size measurements. Moreover, a laboratory reference material based on chromium powder was produced to assure the quality control of particle-size measurements. The material was carefully handled (collection, pre-treatment and preservation) and its homogeneity and term stability were verified. Laser diffraction analyses were validated against sieve-type measurements for the same material.     

有减水作用的新型高效陶瓷助磨剂研制

利用曼尼奇反应原理 ,制备了多胺基磷酸钠陶瓷助磨剂 ,采用红外光谱、差热分析等对合成的助剂进行了表征 ;此外 ,通过对氧化铁以及石英滑石等原料的助磨应用测试表明 :合成的助剂是一种高效陶瓷助磨剂 ,同时还具有减水作用。     

Kinetics of Solid-State Reactions of Particulate Ensembles with Size Distributions

Rate equations for solid-state reactions of monosized spheres cannot be applied directly to particulate ensembles with a distribution of sizes, such as are frequently encountered in practice. A method using experimental data for the overall extent of reaction as a function of time is proposed for identification of the reaction mechanism and computation of the rate constant and activation energy when the particle-size spectrum of the starting material is known. The method, which is based on comparison of the characteristic paths of the assumed reaction mechanisms with experimental data, may be applied to a wide range of solid-state kinetic models.     

Modeling and Optimization of Jet Milling

The energy efficiencies of the acceleration nozzles of ejector and pneumatic jet mills are compared. Mathematical models are proposed for the acceleration of a two-phase mixture in the nozzle and the jet, and a procedure is put forward for optimizing subsonic nozzles and open-loop jet mills. The gas-dynamic perfection of the nozzles of pneumatic jet mills is assessed, and the initial particle-size range where the mill efficiency is highest is determined.     

An analytical approach to relating powder characteristics and rheological properties of powder injection molding feedstocks

This study quantitatively analyzes the relationship between the material structure (powder characteristics) and flow properties of highly filled compounds. The model parameters are the powder particle-size distribution and its volume fraction in a compound. The simulated material structure is developed using the Hard Spheres Model, from which the structural functions in terms of the statistical distribution of inter-particle distances and the histograms of effective volumes of groups of close particles are calculated. A close similarity between simulated and real functions was obtained. The results obtained imply that numerical modeling might serve as a reliable and sensitive approach for analyzing the influence of powder particle-size distribution on the ability to process highly filled compounds.     

E-90-P COMPARATIVE TEST OF HAMMER MILL PULVERIZER AND DRY PAN FOR CRUSHING STREATOR SHALE1

In the machines as described below the following points are discussed: (1) the grinding action, (2) energy consumption per ton ground, (3) capacity to produce fines six-mesh and under, (4) to determine the operating characteristics of the hammer mill. The conclusions given are: (1) The dry pan will not grind shale chunks larger than 15 inches maximum diameter, nor chert nodules of any size. The hammer mill grinds easily in one operation all chunks small enough to go through the 20 × 42-inch hopper opening and all chert nodules. (2) The energy consumption of the dry pan as compared to the hammer mill in kw. hrs. per ton of fines through six-mesh is approximately as 1.40 to 1.25. (3) The maximum capacity of the Frost %foot dry pan with 1/4-inch screen plate openings was known to be approximately 25 tons through six-mesh per hour. The maximum capacity of the 30 × 42-inch Williams hammer mill as reached in these tests with hand feeding was found to be 56 tons total feed and 42 tons through six-mesh per hour. This figure could have been greatly exceeded if the material could have been fed more rapidly. The dry pan tailings coarser than six-mesh compared to the hammer mill tailings of the same coarseness are as 40 to 25%. (4) The hammer mill is more efficient than the dry pan in practically all respects if properly set up and operated, but it is easily possible to secure less efficient results from the hammer mill, particularly if the feeding is not properly regulated.     

碳含量对LiFePO4/C复合正极材料性能的影响

Olivine-type LiFePO4/C composite cathode materials were synthesized by a solid-state reaction method in an inert atmosphere. The glucose was added as conductive precursors before the formation of the crystalline phase. The effects of glucose content on the properties of as-synthesized cathode materials were investigated. The crystal structure and the electrochemical performance were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, laser particle-size distribution measurement and electrochemical performance testing. The material has a single crystal olivine structure with grain-sizes ca. 100-200 nm. SEM micrographs and the corresponding energy dispersive spectrometer （EDS） data confirm that the carbon particulates produced by glucose pyrogenation are uniformly dispersed among the LiFePO4 grains, ensuring a good electronic contact. Impedance spectroscopy was used to investigate the ohmic and kinetic contributions to the cell performance. It is found that increasing the carbon content leads to a reduction of the cell impedance due to the reduction of the charge transfer resistance. The galvanostatically charge and discharge tests show that the material obtained by adding 10% C （by mass） gives a maximum discharge capacity of 140.8mA·h·g^-1 at the same rate （C/10）. The material also displays a more stable cycle-life than the others.     

Combined puncture and cutting of elastomer membranes: A fracture energy approach

Resistance to puncture or cutting by pointed blades is an important property of elastomer membranes and glove materials, making it necessary to define a fundamental criterion for measuring this resistance. However, the intrinsic properties controlling puncture/cutting crack propagation are still unidentified. This study has established a simple criterion describing the relationship between true fracture energy and the puncture/cutting process. Several samples of neoprene and nitrile rubber materials 1.6 mm and 3.2‐mm thick were tested using three pointed blades having tip angles of 22.5°, 35°, and 56°. It was found that both friction energy and true fracture energy contributed to global applied energy. True fracture energy, which is useful for in‐depth study of the puncture/cutting process, was independent of material thickness, blade geometry, and blade lubrication. Furthermore, friction energy was approximately twice as great as true fracture energy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44945.