Fine Blend Research Articles

Microstructure evolution of fine-grain Fe–Cu composites during heat treatment in hydrogen

The microstructure evolution of Fe–30% Cu fine-grain composites during sintering of fine particle blends and during heat treatment of the high-density specimens up to 1130°C was investigated. The metal powder blends with particle sizes less than 0.1 μm were prepared by mechanical alloying technique. The quantitative analysis of microstructure was carried out. The microstructure of solid-state sintered composites was practically identical for all specimen treatment conditions and featured a high degree of dispersity and uniformity. Very fast coarsening of the microstructure took place at the temperature 1130°C during sintering powder blends and during heating of the high-density specimens. The mechanism of microstructure transformation is discussed. The solid-state treating Fe–30% Cu materials have high hardness and good conductivity after hardening. These characteristics impair immediately when the copper liquid-phase appears.

Relationships Between Mixing Method, Microstructure and Strength of Nr:Br Blends

Abstract Much published literature on the way in which phase morphology and filler distribution affect blend properties is contradictory or confusing. Experiments were carried out to elucidate the relationships and to determine whether the use of compatibilizers or special mixing techniques might have a beneficial effect on natural rubber:butadiene rubber (NR:BR) blend properties. NR:BR blends were prepared using both a masterbatch method and a single-stage mixing method. A cure system which gave an even distribution of crosslinks between the phases was used. The morphology, tensile strength and tear strength properties of the blends were measured. Results indicated a high degree of compatibility with fine textured blends (domain sizes < 1µm) being quickly and easily produced, even from masterbatches of very different viscosities. Strength properties of these fine textured masterbatch blends could be predicted by applying the simple rule of mixtures to properties of individual compounds mixed under the same conditions. Although in particular situations a coarse morphology could result in high tear resistance values, for most applications a fine textured morphology gives the most satisfactory overall tensile and tear strength properties. For blends mixed in a single-stage process, development of a fine textured morphology was much quicker than that of filler dispersion. For NR:BR blends containing an optimum cure system it was concluded that the mixing cycle should be chosen to optimize filler dispersion and that use of a compatibilizer will not significantly shorten the mixing cycle or improve the properties of the blend.

Experimental investigation of the morphology development of polyblends in corotating twin-screw extruders

Compounding extruders are still designed based on experience and time-consuming experimental examinations. This work investigates the morphology development of incompatible polyblends along a mixing zone at the end of a corotating twin-screw extruder. During the process, the samples are taken from the running extruder using special barrel plates. These samples are subsequently examined by means of scanning electron microscopy (SEM). This method allows sampling in less than 1 min and thus extremely fast and almost unaffected. The experimental investigation of the morphology development improves the knowledge about the factors essentially influencing the blending process. It also allows the verification as well as improvement of theoretical models. Polyblends of polypropylene (PP) and polyamide (PA) with 7.5, 15, and 30 wt % PA were examined. As well as the relevance of the mass percentage of the dispersed phase, the influence of the screw geometry, the screw speed, the melt temperature, the melt throughput, and the pressure profile was investigated. Apart from the melt throughput, all varied factors show an influence on the resulting blend morphology that may not be neglected. However, the changes of the mean particle sizes in the observed mixing zones are only gradual (mean particle size ≈ 1–4 μm), which can be attributed to the extremely fine blend morphology already existing during or after the melting. That means that the application of “classic melting zones” generally already produces finely dispersed blend morphologies, thus proving the essential importance of the melting zones regarding the development of the blend morphology. Consequently, the mean particle sizes, calculated by means of quantitative image analyses of SEM micrographs in the mixing zones following the homogenizing section only slightly depend on the compounding conditions (screw speed, melt throughput, screw geometry, melt temperature, and pressure profile). However, the direct visual analysis of the SEM images, especially in the first parts of the mixing zones, shows the simultaneous existence of large PA6 particles in the PP matrix. In addition, a downstream unification of the particle size distribution can be observed. Especially the number and size of the coarser particles decreases in the mixing zones. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 708–721, 2000

Fine dispersed blends for compatibilizers for laminates of immiscible polymers

Blends of high-density polyethylene (HDPE) and isotactic polypropylene (iPP) are used to increase the strength of adhesive bonds between the immiscible polymers HDPE and iPP. Melt blended as well as solution blended material is examined for its suitability to compatibilize the interface between the bonded members. Two standard test methods, the T-peel test and the tensile test, are applied to determine the strengths of adhesive joints. Laminated samples for the peel-tests as well as specimens subjected to the tensile tests were prepared at a temperature exceeding the melting temperature of both homopolymers. TEM and LVSEM examinations were performed for characterizing the morphology of the interface with the aim to determine the parameters which significantly influence the blends' adhesive properties. The bonding strengths obtained with the blended material are discussed with respect to the morphologies of the interfaces, the degree of dispersion in the blend, and the bonding mechanisms.

Modeling of reactive synthesis in consolidated blends of fine Ni and Al powders

A model is proposed to describe the kinetics of reactive synthesis of NiAl from consolidated Ni–Al fine powder blends for various synthesis heat treatments. The presence of interfacial oxide in the blend and heat exchange between the sample and the environment have been taken into account to simulate the evolution of temperature and phase composition in the blend. A good agreement was obtained between the model calculations and experimental results. The effect of interfacial oxides and of various external parameters (heating rate, heat exchange conditions, powder size, etc.) on the synthesis kinetics was investigated. The model allows to explain the difference in reaction paths (self-propagating synthesis or solid state synthesis) observed in consolidated powder blends, as well as to describe the shape of the differential thermal analysis signal. Based on the results, the disagreement in previously reported data on growth kinetics of aluminides in diffusion structures with different characteristic diffusion distances is discussed.

Low-maintenance AlternativeTurfgrass

Thirteen materials and two controls were evaluated for 3 years at two locations for color, cover, and overall rating as acceptable turf or lawn. 10' × 16' plots were maintained at 2”, 4”, and no mowings; two, one or no fall fertilizations; with no pesticide or irrigation. Best color ratings were the fine fescues; best cover a traditional mix of Kentucky bluegrass, fine fescues and perennial ryegrass (Sunnylawn mix); dryland ecology mix and fleur de lawn;best overall rating was Sunnylawn mix, fine fescue blend, and Ram I. Materials evaluated included: 378 and 45-3 buffalograss; `Alma' bluegrama;”No Mow”; 'Azay' sheep fescue; 'Discovery' hard fescue;dwarf sheep fescue; fine fescue blend; fleur de lawn; Dryland Ecology Mix; native grass and forb mix; Flowers and Flowers Elite;Super Short Mix; creeping alfalfa; Sunnylawn mix and `Ram I' KBG were used as controls.

The strategic presidency: hitting the ground running

Perfectly timed to anticipate possible election of a new president in 1996, second edition of James Pfiffner's Strategic Presidency provides most complete and authoritative volume on presidential transitions from JFK to Bill Clinton. First published in 1988, it is now more valuable than ever with addition of new chapters on Bush and Clinton transitions and numerous other revisions that greatly update volume. When book first appeared eight years ago, it was hailed by American Political Science Review as an important new work following in the path that Richard Neustadt long ago blazed in his classic book, Presidential Power. Immediately recognized for its contributions to scholarship, it also popularized a new phrase, the strategic presidency, which has since become an essential part of lexicon in presidential studies. As this book makes clear, to accomplish his policy objectives, a new president must always first get control of government. Thus White House must organize itself; establish a cabinet; recruit presidential appointees; confront entrenched career bureaucracy; and formulate a legislative agenda. The supreme challenge of this transitional period, Pfiffner argues, is that all of this must be done in a very compressed time frame and under extreme pressure of press scrutiny and unrealistically high public expectations. Even so, he also shows that systematic preparation during this period can maximize a president's opportunity at beginning of a term. Contrary to much conventional advice, Pfiffner contends that a newly elected president's best opportunity for achieving policy goals is at beginning of term. Even if a honeymoon atmosphere does not prevail, Congress is likely to be more receptive to presidential initiatives in early months of a term, and public opinion is likely to decline after several months in office. That's why it's so important for presidents to hit ground running. Like first edition, new one provides a concise guide for scholars and presidential aides and will be widely adopted for courses on modern presidency. With its fine blend of insider perspective, illuminating anecdotes, and user-friendly political analysis, it will also appeal to general readers.

Dense CoAl-based alloys with improved ductility: Solid-state synthesis and microstructure control

Dense single- and multiphase B2 CoAl-based intermetallics were synthesized from fine elemental Co-Al blends by a completely solid-state processing route at temperatures as low as 800 °C. To ensure full density of the final product, a moderately high external pressure (≤500 MPa) was applied during the solid-state reactive synthesis. Microstructure and mechanical properties of the materials obtained were investigated employing X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and microhardness and compression testing. To improve the room-temperature ductility, an attempt was made to control the microstructure of hyperstoichiometric CoAl alloysvia solution treatment with subsequent aging. At the early stages of aging, fine Widmanstatten precipitates of Co were formed; the coarsening of Co dispersions during long or higher temperature anneals resulted in the pronounced compressive ductility of the overaged samples. In addition to general precipitation, cellular precipitation was observed in CoAl alloys with a high Co content. The relatively coarse equilibrium cellular precipitates were found to rapidly overgrow the fine metastable Widmanstatten Co plates, causing rapid overaging of these alloys. The lattice parameter of hyper-stoichiometric CoAl was found to decrease linearly with increasing Co content.

A grid nesting method for large-eddy simulation of planetary boundary-layer flows

A method for performing nested grid calculations with a large-eddy simulation code is described. A common numerical method is used for all meshes, and the grid architecture consists of a single outer or coarse grid, and nested or fine grids, which overlap in some common region. Inter-grid communication matches the velocity, pressure and potential temperature fields in the overlap region. Resolved and sub-grid scale (SGS) turbulent fluxes and kinetic energy on the fine grid are averaged to the coarse grid using a conservation rule equivalent to Germano's identity used to develop dynamic SGS models. Simulations of a slightly convective, strong shear planetary boundary layer were carried out with varying surface-layer resolutions. Grid refinements in the (x, y, z) directions of up to (5, 5, 2) times were employed. Two-way interaction solutions on the coarse and fine meshes are successfully matched in the overlap region on an instantaneous basis, and the turbulent motions on the fine grid blend smoothly into the coarse grid across the grid interface. With surface-layer grid nesting, significant increases in resolved eddy fluxes and variances are found. The energy-scale content of the vertical velocity, and hence vertical turbulent fluxes, appear to be most influenced by increased grid resolution. Vertical velocity spectra show that the dominant scale shifts towards higher wavenumbers (smaller scales) and the magnitude of the peak energy is increased by more than a factor of 3 with finer resolution. Outside of the nested region the average heat and momentum fluxes and spectra are slightly influenced by the fine resolution in the surface layer. From these results we conclude that fine resolution is required to resolve the details of the turbulent motions in the surface layer. At the same time, however, increased resolution in the surface layer does not appreciably alter the ensemble statistics of the resolved and SGS motions outside of the nested region.

Ultra-fine cements for special applications

Recent development in the application of ultra-fine cement and particle-size distribution-controlled cement are described, focusing on the Japanese experience. They are modified by mixing other fine blending components, organic materials, and admixtures. Their uses are diversified not only in soil and rock grouting, and filling and selling of crack in concrete, but also in peat soil hardening, materials of cement for high performance concrete, and adhesives for bonding insulators with metal fillings.

Newfoundland in the North Atlantic world, 1929-1949

Neary draws material from both public and private sources in the United Kingdom, Canada, the United States, and Newfoundland. Following a brief summary of major developments in Newfoundland before 1929, he gives an account of the tumultuous events that led to the demise of responsible self-government and the establishment of a British-appointed Commission of Government in 1934. He details and evaluates the major policies of the commission during three distinct phases: the continuing hard times of the 1930s, the boom years of the Second World War, and the period of post-war adjustment. The reasons for constitutional change are examined and Neary explains clearly why Newfoundland became a province of Canada in 1949. Through a fine blending of domestic and international history, he reveals the intricate connections between events in Newfoundland and in the rest of the North Atlantic World, providing a balanced view which takes into account constitutional, political, economic, and social developments. He acknowledges the role of British, Canadian, and American policymakers in determining the course of events in Newfoundland and illuminates the role that Newfoundlanders themselves played at a critical time in their history.

Restructured Pork from Hot-Processed Sow Meat: Effect of Particle Size and Blend Ratio

A 2 × 3 factorial arrangement of treatments was used to investigate the effect of grind size and blend ratio on quality and sensory traits of restructured pork manufactured from hot-processed sow meat. Two blend ratios: [1. 50% through a 3.2mm plate (FG)/50% tenderized muscle chunks (TMC); 2. 40% FG/60% TMC] were used in combination with three different sizes of TMC. The TMC portion was prepared by: grinding once through a kidney plate (K), grinding twice through a kidney plate (KK), or grinding once through a kidney plate followed by grinding through a 10 mm plate (K10). The six treatments were: 50FG/50K, 50FG/50KK, 50FG/50K10, 40FG/60K, 40FG/60KK, and 40FG/60K10. There were no differences (P>.05) for cooking loss, juiciness, connective tissue, or flavor scores; however, restructured steaks from the 40FG/60K treatment were more cohesive (P<.05) than the steaks from the 50FG/50KK, 50FG/50K10, and 40FG/60K10 treatments. Restructured steaks from the 40FG/60K treatment had greater shear values (P<.05) than steaks from the 50FG/50KK treatment which had greater shear values (P<.05) than steaks from the 50FG/50K10 and 40FG/60K10 treatment. Restructured steaks from the 50FG/50K10 treatment had greater tensile strength (P<.05) than those from the 50FG/50KK treatments. It was determined that a 50% chunks/50% fine ground blend ratio in combination with any of the three grind sizes would be best suited for use in commercial processing operations. This ratio is the more practical ratio to obtain from the sow carcass, and no added product quality is achieved by the use of a 60% chunks/40% fine ground ratio.

Effects of the particle sizes of expansive clinker on strength-expansion characteristics of type K expansive cements

In tests conducted on blended Type K expansive cements, it was observed that in fine blends, the main expanding particles (C 4A 3S) and sulfates deplete faster compared to identical coarser blends because the fine blends have a larger number of expansive sites. This can decrease the expansion time and susceptibility to abnormal behavior, i.e. “double-curvature expansion” and “strength-drop” phenomena. Observations suggest that the mechanism of formation of ettringite crystals is topochemical.