bluuebunny/crossref_metadata_2025 huggingface dataset:
Mesophase structure of some flexible chain polymers
Authors: Antipov E. M. , Kulichikhin V. G. , Platé N. A.
Published: December 2004

The mesophase structures of some flexible chain polymers, which do not contain mesogenic groups, but are able to form thermodynamically equilibrium mesomorphic states, were studied by means of the X‐ray analysis, the differential scanning calorimetry, and other methods. The mesophase polyethylene in bicomponent polymer blends, mesomorphic ultra‐high molecular weight polyphosphazenes, and membrane polyvinylorganosilanes were investigated. The scheme of polymer phase transitions is discussed. Besides conformational disordering, the step‐by‐step loss of different levels of the positional order (i.e. the multiple‐step character of melting) of flexible, semiflexible, and stiff chain polymers is deduced and illustrated by examples from the authors' experience and from the literature.
Thermophysical characterization of heterocyclic polymer networks
Authors: Privalko Valery P. , Kramarenko Victor Yu.
Published: December 2004

Heterocyclic networks obtained by copolymerization of epoxy oligomer (ER) with different amounts of hexamethylene diisocyanate (HMDI) were characterized by IR‐spectra, PVT measurements in the temperature interval 320 to 470 K and pressure range 15 to 90 MPa, and heat capacity in the temperature interval 150 to 470 K. Experimental data are discussed in terms of the variation of characteristic parameters of the Frenkel‐Hirai‐Eyring hole model with relative proportion of three‐arm, six‐membered isocyanourea heterocyles and two‐arm, five‐membered oxamolidone rings which changed with HMDI/ER ratio.
Strain‐induced crystallization of poly(ethylene terephthalate)
Authors: Jabarin Saleh A.
Published: December 2004

The fabrication of poly(ethylene terephthalate), PET, into fibers, films, and containers usually involves molecular orientation caused by molecular strain, which may lead to stress‐ or strain‐induced crystallization (SIC). The SIC of PET was studied by the methods of birefringence, density, thermal analysis, light scattering, and wide‐angle X‐ray. The development of crystallinity is discussed in relation to the rate of crystallization, the residual degree of orientation, and stress relaxation. The experimental procedure involves stretching samples at temperatures above the glass transition temperature, Tg, to a given extension ratio and at a specific strain rate of an Instron machine. At the end of stretching, the sample is annealed in the stretched state and at the stretching temperature for various periods of time, after which the sample is quickly quenched to room temperature for subsequent measurements. During stretching, the stress strain and the stress relaxation curves are recorded. The results indicate that the SIC of annealed, stretched PET can proceed in three different paths depending on the residual degree of orientation. At a low degree of residual orientation, as indicated by the birefringence value, annealing of stretched PET leads only to molecular relaxation, resulting in a decrease of birefringence. At intermediate orientation levels, annealing causes an initial decrease in birefringence followed by a gradual increase and finally a leveling off of birefringence after a fairly long period of time. At higher orientation levels, annealing causes a rapid increase in birefringence before leveling off. The interpretation of the above results is made using the measurements of light scattering, differential scanning calorimetry, and wide‐angle X‐ray. The rate of the SIC of PET is also discussed in terms of specific data analysis.
Assessment of oxidative thermal degradation of crosslinked polyethylene and ethylene propylene rubber cable insulation
Authors: Anandakumaran K. , Stonkus D. J.
Published: December 2004

This paper presents procedures to monitor oxidation degradation of two commonly used cable insulations, crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR). Since the techniques described require only micro specimens, deterioration of cable insulation can be monitored without destroying the function of the cable. The techniques described are melting point, crystallinity, infrared carbonyl absorbance, gel content, relative hardness, and differential scanning calorimetry (DSC) oxidation induction time. The techniques were applied following accelerated aging over a period in excess of two years. The results from the micro specimens were directly related to embrittlement and the decrease in ultimate elongation. The previous thermal history of XLPE was determined using DSC melting peak analysis.
Phase separation and mechanical properties of poly(methyl methacrylate)/polycarbonate blends
Authors: Kodama Minekazu
Published: December 2004

Dynamic mechanical properties, tensile properties, and scanning electron microscopy of blends of poly(methyl methacrylate) and polycarbonate were investigated after phase separation above their cloud point temperature by annealing in a hot press. The dynamic mechanical properties show that phase separation proceeds more distinctly for the blends annealed at higher temperature and for longer time. The scanning electron micrographs show that the morphology of phase separated blends varies with the conditions of heat treatment. The tensile properties of phase separated blends deteriorate on account of the coarsening of the brittle dispersed phase over the optimum size and the occurrence of voiding during the heat treatment.
Analysis of the packing stage of a viscoelastic melt
Authors: Nguyen Ky T. , Kamal Musa R.
Published: December 2004

The packing stage starts at the end of mold filling. During this stage, additional material is forced into the mold to compensate for the shrinkage during subse‐quent cooling. Underpacking results in molded parts with dimensional variation. Overpacking causes flash at the parting lines, stick during ejection, and excess residual stresses resulting in warpage. The packing stage is thus extremely important in the determination of the final quality of the product. Despite its importance, analysis of the packing stage has been relatively ignored, particularly the viscoelastic effect. In this work, the analysis of the isothermal packing stage is presented for a Maxwell fluid. A set of governing equations is derived for a two‐dimensional mold and solved using the Galerkin finite element method. In addition to the distribution of velocity and pressure, the model predicts the stresses in the planar direction, which could be used for subsequent calculation of the residual stresses.
Controlling morphology of polystyrene/poly(vinyl methyl ether) blends undergoing spinodal decomposition process by photo‐crosslinks
Authors: Tran‐Cong Q. , Imura M. , Soen T. , Shibayama M.
Published: December 2004

The morphology developing during the spinodal decomposition process of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends was successfully controlled by photo‐crosslink reactions between PS chains. The crosslink reaction was carried out by taking advantage of the photodimerization of anthracene moieties that are labeled on PS chains. Effects of photo‐crosslinks on the morphology induced by temperature jumps (T‐jump) from the one‐phase region into the spinodal region were examined under several experimental conditions such as T‐jump depths and irradiation times. It was found that the concentration fluctuations developing during the spinodal decomposition process were efficiently frozen upon irradiation using a XeF excimer laser as well as a mercury (Hg) lamp. Furthermore, these ordered structures are quite stable upon annealing. These results demonstrate that the morphology developing during the spinodal decomposition process can be well controlled by easily accessible light sources such as high pressure mercury lamps. Thus the photo‐crosslink reaction described in this work can provide the basis for a potential technique to design multiphase polymer materials with controllable ordered structures.
Liquid crystal polymer/polyethylene blends for thin film applications
Authors: Hsu T. C. , Lichkus A. M. , Harrison I. R.
Published: December 2004

A series of liquid crystal polymer/polyethylene (LCP/PE) blends have been studied to determine the potential of such a system to produce a high modulus film material which retains fabrication and low temperature characteristics of some current PE films. The subject of liquid crystalline polymer blends has been the focus of significant attention for the last decade due to the novel rheological and mechanical properties of this class of polymers. It has been demonstrated that if an LCP blend is processed under elongational flow conditions, the partially ordered LCP meso‐phase intermediate allows the development of an oriented fibrillar morphology which is retained upon solidification. In this study, blown films of blends of 5 and 15% LCP in PE have been produced which show an enhancement in modulus over the neat PE matrix. These results are discussed in terms of processing conditions, LCP reinforcement aspect ratio, fibril diameter, and LCP/PE modulus ratio.
Stress analysis around a three‐dimensional craze in glassy polymers
Authors: Xiao Z. M. , Pae K. D.
Published: December 2004

Stress analysis around a three‐dimensional craze and a three‐dimensional craze containing a penny‐shaped crack has been made. The craze is treated as a transversely isotropic, oblate spheroid embedded in an isotropic glassy polymer. The craze is assumed to consist of primary fibrils and cross‐tie fibrils, such that a penny‐shaped crack may form at the central regime of the craze. The craze surface stress, the stress field near the craze tip outside the craze region, and the stress intensity factor in the crack tip are determined by using Eshelby's equivalent inclusion method. Numerical values of the fracture toughness and the stress needed to sever a craze fibril at the crack tip are calculated and the results appear to be in good agreement with the data given in the literature.
Melt blending of ultra high molecular weight and high density polyethylene: The effect of mixing rate on thermal, mechanical, and morphological properties
Authors: Tinçer T. , Coşkun M.
Published: December 2004

The blends of two different ultra high molecular weight polyethylenes (UHMWPE) and high density polyethylene (HDPE) were prepared in melt at different compositions and mixing rates in Brabender Torque Rheometer. The temperature build‐up due to the internal friction during melt blending was recorded and evaluated with respect to the change in the torque. The temperature at maximum torque was considered the fusion point temperature of the UHMWPE in the blend. This fusion point temperature was found to depend on the composition, mixing rate, and molecular weight. The effect of mixing rate on the mechanical properties (measured as yield and tensile strengths and elongation at break), thermal oxidative degradation and melting behavior were studied. The morphology of the blends were investigated by optical microscopy.
Rheokinetic studies for the reaction injection molding of polydicyclopentadiene
Authors: Ng Hendra , Manas‐Zloczower Ica , Shmorhun Mark
Published: December 2004

Dicyclopentadiene (DCPD) based liquid engineered resins are emerging among the newest commercial reaction injection molding (RIM) systems. Since the filling stage is coupled with chemical reaction, an understanding of the chemorheological changes is critical for establishing moldability criteria. An adiabatic reactive viscometry technique which involves the simultaneous measurement of viscosity and temperature changes was used to investigate the chemorheological changes during the adiabatic copolymerization of a DCPD based RIM system. The influence of impingement mixing conditions and initial material temperature on the reaction kinetics, rheology, as well as the resulting final physical properties of the system were investigated. The “apparent gel time” under adiabatic conditions is estimated from the intersection of the tangents to the initial and final portions of the viscosity curve. An autocatalytic kinetic model with an Arrhenius rate constant was used to model the reaction kinetics.
The effects of physical aging on the brittle fracture behavior of polymers
Authors: Arnold J. C.
Published: December 2004

The effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, have been studied. Properties examined were creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking in ethanol. Fractured samples were examined both optically and by scanning electron microscopy to determine the degree of crazing. It was found that a longer physical aging time produced shorter lifetimes in all cases. The main reason for this is the reduction in craze strength caused by a reduced toughness due to physical aging. A long aging time was found to delay craze formation, but once formed, these crazes were much less stable than those formed with a short aging time. The effects of aging are important on failure prediction criteria and on testing methodologies, and the implications are discussed.
A preliminary investigation of flash formation during injection molding of polyphenylene sulfide and liquid crystalline polymer blends
Authors: Shonaike G. O. , Yamaguchi S. , Ohta M. , Hamada H. , Maekawa Z. , Nakamichi M. , Kosaka W. , Toi K.
Published: December 2004

Flashing in pure polyphenylene sulfide (PPS) and a blend containing PPS and liquid crystalline polymer (LCP) during injection molding was investigated by differential scanning calorimetry and scanning electron microscopy. The shape of the flash was observed by use of a projector. Flashing was detected in pure PPS and 90/10 PPS/LCP blend but was not found in other compositions, including pure LCP. The DSC thermograms of the flash revealed both exothermic and endothermic peaks at around 120° and 285°C. The first peak, known as crystallization temperature on heating, occurred as a result of early crystallization of PPS. The observed double peaks indicated that the degree of crystallinity was lower in the flash than in the molded part. The morphological studies revealed the presence of LCP fibrils in the skin region and droplets in the core region of 90/10 PPS blend. The absence of flash was attributed to the diameters of the fibrils and droplets, which were found to increase with increasing LCP component.
Modeling the dielectric response of unsaturated polyester resin during cure
Authors: Alperstein D. , Narkis M. , Siegmann A.
Published: December 2004

The dielectric relaxation of unsaturated polyester resin during cure was modeled using a modified Williams–Watts decay function. The dielectric response was studied using dielectric measurements coupled with two dynamic mechanical measurement methods. It was found that the variation of the relaxation time during cure is a WLF process using Tg (α) (α‐conversion) as the varied temperature. It was shown that this process fits the Williams‐Watts decay function Φ(t)=exp(‐(t/τ)β) where τ‐relaxation time and β‐empirical parameter are time dependent. It was found that τ obeys a time dependent power law rule and β depends linearly on log(time). Using this modified decay function, it was shown that the experimental dielectric response measured during cure agrees well with the computed response. Relaxation times above and below the dielectric measurement system capability were computed thus, demonstrating the capability of yielding the entire relaxation times spectrum during cure, out of a single limited frequency dielectric measurement.
Effect of the pressure drop rate on cell nucleation in continuous processing of microcellular polymers
Authors: Park Chul B. , Baldwin Daniel F. , Suh Nam P.
Published: December 2004

Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth.
Morphology and mechanical properties of liquid crystalline copolyester and polyester elastomer blends
Authors: Jang Sang Hee , Kim Bong Shik
Published: December 2004

Blends of a polyester elastomer (PEL) having a hard segment of polyester (PBT) and soft segment of polyether (PTMG) and a liquid crystalline copolyester (LCP), poly(benzoate‐naphthoate), were prepared in a twin‐screw extruder. Specimens for mechanical testing were prepared by injection molding. The morphology of the LCP/PEL blends was characterized under different processing conditions. To determine what conditions were necessary for the development of a fibrillar morphology of LCP, we have studied the effect of processing method (extrusion and injection molding), injection molding temperature (below and above the melting point of LCP), and gate position in the mold (direct gate and side gate). SEM studies revealed that some extensional flow was required for the fibrillar formation of LCP and the fibrillar structure of LCP was controlled by the processing method. The morphology of the blends was found to be affected by their compositions and processing conditions. SEM studies revealed that finely dispersed spherical domains of LCP were formed in the PEL matrix and the inclusions were deformed in fibrils from the spherical droplets with increasing LCP content and injection temperature. The mechanical properties of the LCP/PEL blends were also found to be affected by their compositions and processing conditions. The mechanical properties of LCP/PEL blends were very similar to those of polymeric composite. An attempt was made to correlate the structure of the blends from the scanning electron microscope with the measured mechanical properties. All of the aspects of the morphology were possible to explain in terms of the mechanical properties of the blends. A DSC study revealed that the crystallization of PEL was accelerated by the addition of LCP in the matrix and a partial compatibility between LCP and PEL was predicted. The rheological behavior of the LCP/PEL blends was found to be very different from that of the parent polymers, and significant viscosity reductions were observed in the blend consisting of only 5 wt% of LCP.
The effect of curing of unsaturated polyester resin on the dynamic relaxation time
Authors: Alperstein D. , Narkis M. , Siegmann A. , Binder B.
Published: December 2004

The effect of hot curing of unsaturated polyester resin on the dynamic relaxation time was studied using dielectric measurements along with two dynamic mechanical measurement methods. It was found that the dynamic response during cure was a material frequency dependent property and did not depend on the measurement method. All relaxation times, measured during cure, by all three measurement methods used, converged to a single equation: τ(t)av=atbwheret= curing time,a, b=constants. The increase of the relaxation time during cure followed the same trend as a friction factor, which was found to increase with conversion. The crosslinking density was found to increase slowly with conversion, while the relaxation time increased exponentially. These two different modes of behavior during cure explain the high resolution of dynamic measurements as a cure monitoring tool, which can easily detect small curing changes. This behavior of the relaxation time was explained by the sharp rise of activation energy due to a parallel decrease of free volume at high conversion.
Effect of extensional viscosity and wall quenching on modeling of mold fillings
Authors: Moller James C. , Lee Daeyong , Kibbel Bradley W. , Mangapora Leslie
Published: December 2004

A combined finite element and finite difference approach has been developed to include the capability to model fluid and thermal transport for the filling of a die cavity by a fluid that has differing sensitivities to extensional and shear deformation rates. This is referred to here as a dual viscosity fluid. For the case of mildly convergent or divergent quasi two‐dimensional flows, a viscosity model is described that has such a dual‐viscosity character and in which shear and extension rate sensitivities are nearly separated. Filling simulation results can be generated rapidly in a modest computational environment. The range of cavities and molding materials that may be modeled realistically is widened by the inclusion of a dual viscosity model. The effect of wall quenching (freezing) increased with decreasing filling rate, while the effect of dual viscosity increased with increasing filling rate.
Principal directions as a basis for the evaluation mixing
Authors: Bigio David I. , Conner James H.
Published: December 2004

Measures of mixing for laminar flow are developed from basic principles of continuum mechanics for infinitesimal rates of stretch. The entire analysis is performed from the basis of the eigenvalues and principal directions of the appropriate flow tensors. Measuring the rate of line growth, where the line marks the interface between two miscible fluids, in terms of the major eigenvalue provides a direct measure of the maximum rate of mixing. Two efficiency measures for mixing are derived in terms of the eigenvalues and their directions. The creation efficiency of the magnitude of the major eigenvalue as a function of the energy input into the flow field is evaluated. The orientation of the interface to the principal direction qualifies the mixing efficiency in laminar flow. The new theory is used to analyze two‐dimensional and three‐dimensional channels. The results demonstrate not only the continuum measures for mixing but also extend our present understanding on mixing and provide future directions.
The self‐wiping co‐rotating twin‐screw extruder as a polymerization reactor for methacrylates
Authors: Jongbloed H. A. , Kiewiet J. A. , Van Dijk J. H. , Janssen L. P. B. M.
Published: December 2004

The self‐wiping co‐rotating twin‐screw extruder was studied as a reactor for two polymerizations in bulk: the homopolymerization of n‐butylmethacrylate and the copolymerization of n‐butylmethacrylate with 2‐hydroxypropylmethacrylate. The influence of the extrusion parameters on the product was analyzed. With both reactions, conversions up to 95% were obtained. Nevertheless, a significant difference was observed in the working domain of both polymerizations, in which a stable reactive extrusion process could be attained wherein the discharge rate is constant and equals the feed rate. In the case of the relatively fast copolymerization, both the throughput and the screw rotation rate could be raised without endangering the stability of the process. This was not the case for the homopolymerization studied. It was determined that the stability of the process depends on the reaction velocity and the product viscosity. Within the boundaries of the working domain, the molecular weight could be influenced by adjustments of the extrusion parameters.
Polymer research in korea
Authors: Lee Youngchul
Published: December 2004

This special issue is dedicated to the current and rapidly growing polymer research in Korea. The isue contains a grouping of typical research studies from Korea. The set is not inclusive, as there are many fine additional research programs under way in Korea. A brief history and comments on several aspects of Korean polymer research may provide a perspective.
Determination of fracture toughness in rubber modified glassy polymers under impact conditions
Authors: Bernal Celina R. , Frontini Patricia M.
Published: December 2004

This paper analyzes the applicability of simple indirect methods for determining the impact fracture toughness of ductile polymers. Commercial rubber‐modified thermoplastics were assayed. Tests were carried out in a Charpy impact pendulum on sharp notched samples at room temperature and at 80°C. Specimens of different geometric relationship, were considered. Thickness, side grooving and span effects were investigated. Reslts appear to be geometrically and strain rate independent.

ABS and high impact polystyrene samples exhibited a whitening effect due to craze formation through the whole fracture surface, indicating that stable crack propagation was occurring. Medium impact polystyrene, however, exhibited combined stable and unstable crack propagation mode, displaying shiny and dull zones on the surfaces of the broken samples. Data were analyzed following the corrected elastic and the Jc methods. The fit quality was evaluated by statistical analysis. In addition, two new methods were tried: the methods proposed by Vu‐Khanh and De Charentenay for semiductile behavior and by Vu‐Khanh for ductile behavior. The equivalencies between the different critical parameters that arose from the methods are compared and analyzed.
Dynamics of liquid‐liquid mixing: A 2‐zone model
Authors: Janssen Jos M. H. , Meijer Han. E. H.
Published: December 2004

The development of multiphase liquid‐liquid morphologies during mixing at small Reynolds numbers has been modeled. The mixing process is divided into (i) stretching of dispersed drops. (ii) breakup of the liquid threads formed, and (iii) coalescence of the final droplets upon collision. Rules and criteria of the distinct processes are presented and combined to a general 2‐zone mixing model simplifying the flow field into a sequence of alternating “strong and weak zones.” In a “strong zone,” dispersed drops and threads are stretched unless their radius is too small; meanwhile, the stretching threads might break up into droplets. In the subsequent “weak zone,” the remaining threads may disintegrate while any drops present may coalesce. After passing a number of zones, stretching, breakup, and coalescence lead to a dynamic equilibrium that could be considered as the “final” morphology. Using the 2‐zone mixing model, the influence of material parameters and processing conditions on the morphology has been studied. Interestingly, increasing either viscosity (dispersed or continuous phase) yields a finer morphology due to the delay of thread breakup, allowing for further stretching and suppression of coalescence.
A hybrid numerical technique to model 3‐D flow fields in resin transfer molding processes
Authors: Friedrichs B. , Güçleri S. I.
Published: December 2004

A hybrid two‐/three‐dimensional solution technique is presentedto model 3‐D flow fields in resin transfer moeling using Darcy's low. The 3‐D flow field is only solved for regions where all three velocity components are significant, thus largely reducing the number of unknowns. Elsewhere, the commonly used 2‐D approximation for flow in thin gaps between plates is employe.d The method is applied to regions where the flow splits, such as T‐joints. Because of the uncertainties associated with an accurate determination of the permeability in these regions, a simplified decompled procedure is procesed, which reduces the computational complexity. In this procedure, the flow front is advanced using the 2‐D formulation. The 2‐D formulation also provides the boundary conditions for the subsequent computation of the 3‐D flow field without feedback of flow field information to the 2‐d model. The governing equations are solved using boundary fitted coordinate systems (BFCS) together with the finite difference method (FDM). Numerical as well as algebraic grid generation and domain decomposition are employe dto generate grids that always concide with the continuously deforming and enlarging flow domain. Results that include the trackingof numerical tracer particles to visualize the three‐dimensionality of the flow field are presented for isothermal flow of a Newtonian fluid through a T‐joint. This detailed flow field description is expected to form the basis for a rather accurate simulation of quantitities that largely depend on the fluid particle pathlines, such as the degree of cure. The method is also extendable to shear‐thinning fluids as well as to 3‐D flow in the vicinity of the flow front.
Curing reaction of saturated aliphatic polyester modified unsaturated polyester resins
Authors: Liu S. B. , Yang J. F. , Yu T. L.
Published: December 2004

Two series of unsaturated polyesters (UPE from isophthalic acid, fumaric acid, and propylene glycol) were prepared. In series‐A resins, UPEs wee thickened with isocyanate‐terminated saturated aliphatic polyestes, i.e., an isocyanate‐terminated polycaprolactone diol (PE‐di‐OL), through reaction of the isocyanate group with the hydroxyl group of the UPE. In series‐B resins, the UPEs were mixed with saturated aliphatic polyesters i.e., PE‐di‐OL. The curing reaction of these two series of UPEs with styrene was studied by using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The DSC data show that for a fixed PE‐di‐OL molecular weight, the curing reaction rate of series‐A UPE is faster than that of series‐B UPE. The variation of microgel size during curing ws studied by GPC. These results revealed that microgel formation has a great effect on the kinetics of cure for the unsaturated polyester‐styrene system. The curing of these two series of UPEs is found to strongly depend on the compatibility of the components in the curing system.
Fundraising, culture, and the U.S. perspective
Authors: Wagner Lilya
Published: December 2004

An understanding of cultural elements that are critical in determining how fundraising is carried out in a particular society and country is vital for professionals who seek philanthropic support for their organizations.
The Characterisation of the Flow of Aerated Powders
Authors: Lloyd Philip J. , Webb Peter J.
Published: December 2004

This paper reviews the development of a new annular shear cell for the characterisation of aerated powders. The cell enables the measurement of the transmitted shear stress at degrees of aeration below fluidisation. Results are presented for three powders, Alumina, Phosphate Rock and Sodium Carbonate. These show a large reduction in shear stress for small quantities of air entrainment and a transition from normal coulomb‐solid flow to liquid‐type flow at high shear rates. This characterisation enables an explanation of the flooding phenomena experienced in powder handling processes.
Scattering of a Gaussian Beam by a Sphere Using a Bromwich Formulation: Case of an arbitrary location
Authors: Gouesbet Gérard , Maheu Bruno , Gréhan Gérard
Published: December 2004

A complete theory of Gaussian beam scattering by a sphere is exposed. It is a generalization of the Lorenz‐Mie Theory to the case of Gaussian beam illumination. The spherical, isotropic and homogeneous scatterer may be located anywhere with respect to the beam. The Bromwich Scalar Potentials are used to solve the scattering problem and expressions are obtained for the scattered field (both in the near field and far field regions), the scattered intensities and the phase angle. In the limit of special cases the expressions agree with previous works restricted to more particular problems.
Determination of the Fractal Dimension of the Irregular, Compressive Stress‐Strain Relationships of brittle, crumbly particulates
Authors: Peleg Micha , Normand Mark D.
Published: December 2004

The apparent fractal dimension of normalized rugged compressive force‐deformation curves of two types of brittle particulates was determined using the blanket algorithm. Although the shape of the original force‐deformation relationships of the individual specimens was irreproducible, the apparent fractal dimension of the normalized data was fairly constant and characteristic of the material. The applicability of the algorithm and the validity of the results were tested with computer simulated relationships generated with a set of Weierstrass functions whose fractal dimension was known a‐priori. It is demonstrated that as long as the resolution along the two axes is the same, the fractal dimension so calculated provides an absolute rather than a relative measure of the relationship's jaggedness.
Correction of the Effect of Particle Shape on the size distribution measured with a laser diffraction instrument
Authors: Heffels Camiel M. G. , Verheijen Peter J. T. , Heitzmann Daniel , Scarlett Brian
Published: December 2004

This paper gives a theoretical basis for calculating Fraunhofer diffraction patterns of arbitrary polyhedron particles. It is shown that this solution can be used for calculating a scatter matrix adapted to the particle shape in a straightforward manner. Some simulations were made to show the difference between the size distribution by volume obtained with a scatter matrix for spheres and with that for the appropriate shape. Finally, some experimentally measured signatures from platelets and rods are evaluated in order to show that the spherical equivalent diameter could be accurately retrieved.
Calculating Shape Factors from Particle Sizing Data
Authors: Barreiros Fatima M. , Ferreira Paulo J. , Figueiredo M. Margarida
Published: December 2004

It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials – glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) – were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.
On the Time‐Dependence of the Force in Tests of impact sensitivity
Authors: Wild R.
Published: December 2004

In order to characterize the small fall‐hammer of BAM (Bundesanstalt fur Materialprüfung) its mechanical properties were determined. Using the theory of the forces between two colliding bodies expressions were derived to describe the tester which were validated by the experimental measurements. I t was found that forces of up to 21 kN were transmitted to the anvil (for 1 kg weight dropping through 0,s m) and that the impact times ranged from about 150 f i s for the small weights to about 500 f i s for the large weights. It was also found that in addition to the expected kinetic energy dependence of the forces on the anvil there was also a dependence on the actual weight used.
A General Model for the Shock Initiation of Explosives
Authors: Walker F. E. , Wasley R. J.
Published: December 2004

A general model for the shock initiation of explosive reaction in chemical explosives is proposed. The model is based on the concepts of: (1) the kinetics of decomposition in which ions and free radicals produced by the shock wave shear forces initiate chain reactions that contribute to and accelerate the decomposition produced by the thermally activated molecules; (2) the formation of statistically random reaction sites whose number in a specific explosive is a direct function of the shock pressure as the shock transits the explosive; and (3) a critical‐ energy‐fluence requirement for initiation. This model appears to apply to explosive reaction in gases, liquids, and solids.
Thermal Decomposition of Hydrazinium Diperchlorate
Authors: Pai Verneker V. R. , Sharma A. N. , Jain S. R.
Published: December 2004

The mechanism of the thermal decomposition of hydrazinium diperchlorate (HP‐2) has been investigated in the temperature range 100–200°C. l he decomposition can be represented by the chemical equations:

The solid state decomposition up to 180°C ensues with an activation energy of 23 kcal/mole whereas above 180°C in the molten state the activation energy is 35 kcal/mole.
Effect of Intentional Impurities, Aging, Particle Size and Pre‐Irradiation on the Thermal Decomposition of Hydrazinium Diperchlorate
Authors: Verneker V. R. Pai , Sharma A. N. , Jain S. R.
Published: December 2004

The effect of dopants, aging, particle size and pre‐irradiation on the thermal decomposition of hydrazinium diperchlorate (HP‐2) has been investigated. Data on the uptake of N2H6S04 indicate that these impurities are distributed homogenously in HP‐2. Anion vacancies have been found to sensitize the decomposition while cation vacancies desensitize. The mechanism of the decomposition has been discussed in terms of the migration of ionic species and electron transfer from CIO4− ion to N2H62+ ion.

The decomposition is found to desensitize with age. The aging effect is attributed to a decrease in anion vacancy concentration with age. Particle size does not seem to have any effect on the decomposition of HP‐2. Pre‐irradiation is found to affect the decomposition appreciably only when HP‐2 is irradiated for longer durations (> 1 hr), the effect being observed only during the later stages of the decomposition (01 > 0.3).
Simple and Rapid Determination of Small Amounts of Sulphate in Cellulose Nitrate
Authors: Dawoud Abdel‐Fattah , Soliman Adly A.‐W. , Saad H. A.
Published: December 2004

Oxidative decomposition of cellulose nitrate was brought about by simple wet‐ashing in a beaker with nitric acid and the digest‐residue was further oxidised with 30% hydrogen peroxide, followed by evaporation to dryness. Interferences arising from use of hydrogen peroxide were later avoided by digesting with nitric acid and Evaporation to dryness. Complete oxidation was achieved in approximately one hour. The digests allow rapid sulphate determination by the lead nitrate‐dithizone titration method. The method was greatly successful for analyzing both the unstabilized cellulose nitrates and those carefully stabilized materials.
The Tip Origin of a Shaped Charge Jet*
Authors: Carleone J. , Jameson R. , Chou Pei Chi
Published: December 2004

This study demonstrates that the pex portion of a typical 42° conically lined shaped charge is not being efficiently utilized. In fact, approximately 40% of the liner height at the apex end of the cone does not provide an efficient jet as far as penetration depth is concerned. In this paper, we present an experimental and theoretical study of the liner apex. First, a series of experiments were conducted in which liner apices were filled to various heights to inhibit the collapse of the apex portion of the liner. Next, a one‐dimensional analytical shaped charge model was used to simulate the filled cone experiments. From these experiments and calculations we have determined that approximately 30–40% of the cone height is used to produce a compact tip particle rather than a stretching jet. This indicates that i t may be possible to redesign the apex portion of the liner to achieve a more efficient use of liner height.
Thermal Reactivity of Methylammonium Nitrates
Authors: Jain S. R. , Rao M. V. , Pai Verneker V. R.
Published: December 2004

The reactivity of the mono‐, di‐ and trimethyl‐ammonium nitrates to heat has been studied using differential thermal analysis, thermogravimetry and mass spectral analysis. The decomposition temperature of these compounds increases in the order CH3NH3NO3 > (CH3)2NH2NO3 > (CH3)3NHNO3. The activation energies have been determined employing isothermal decomposition technique. Mass spectrometric investigation shows that the extent of decomposition increases with increasing substitution on the nitrogen atom. Possible reasons for such behaviour have been explored.
The State of the Detonation Products of Solid Explosives
Authors: Hornberg H.
Published: December 2004

The polytropic equation, together with the detonation relations, provides practicable values for all the quantities characterizing the detonation products of solid, high explosives apart from the temperature. Its application, however, is restricted to material at absolute zero, that is to solids possessing purely potential energy. Thus polytropic detonation products have the characteristics of solids although their state of aggregation is gaseous.

In fact the polytropic equation can be derived by assuming a solid under an internal, expansive pressure sufficient to break all atomic bonds. In terms of the Debye theory this represents an approximation which is valid in the absence of the thermal energy contribution from atomic vibrations. This requirement is satisfied by the detonation products of solid explosives of sufficiently high density since their heat of detonation is completely absorbed by the breakage of atomic bonds or the sublimation of the atomic lattice.

The sublimation process in the course of the reaction also allows the Chapman‐Jouguet temperature of the detonation products to be determined from the equilibrium between the phases. In addition the fracture theory provides material data which assign a metallic character to the polytropic detonation products and indicate that they form a conducting plasma.
Is ammonium perchlorate in composite solid propellant under strain?
Authors: Pai Verneker V. R. , Kishore K. , Prasad G.
Published: December 2004

Thermal decomposition of ammonium perchlorate‐polystyrene propellant as a function of oxidizer loading has been found to behave in a fashion analogous to the thermal decomposition of ammonium perchlorate as a function of precompression pressure. It has been argued that the above behaviour of the propellant is due to the strain caused by the binder film on ammonium perchlorate contained in the propellant matrix. The presence of strain has been demonstrated independently by x‐ray diffraction peak and infrared peak broadening and strain energy measurements.
Thermal Decomposition of Ammonium Perchlorate containing a polymeric additive
Authors: Thomas T. J. , Nandi U. S.
Published: December 2004

Thermal decomposition of ammonium perchlorate (AP) containing different concentrations of a polymeric additive such as polyvinyl pyrrolidone (PVP) has been studied by the technique of differential thermal analysis (DTA). The decomposition products have been identified by means of a mass spectrometer. The results of these two experiments suggest strong interaction between AP and PVP in the solid state.
A Photographic Study of the Combustion Zones of burning double base propellant strands
Authors: Eisenreich N.
Published: December 2004

The combustion zones of doublebase propellant strands and their dependence on pressure were studied by different photographic techniques to get new information on the action of ballistic modifiers. Photos of short exposure time were taken from the foam, dark and flame zones. The extinguished burning surface was studied by optical and scanning electron microscopes. A detailed picture on the production of carbonaceous material on the burning surface was obtained.
Performance Optimization of Metallized Solid Propellants
Authors: Swaminathan V. , Rajagopalan S.
Published: December 2004

The object of this paper is to present a method for determining, for a typical metallized solid propellant system, the optimum combination of the reactants so as to arrive at a composition which can yield the maximum specific impulse. A direct approach of this kind for optimization of propellants does not appear to have been attempted so far. The optimization is sought to be carried out by expressing the theoretical specific impulse of the propellant under frozen flow conditions as a function of the different variables involved and maximizing the same, subject to the usual linear and non‐linear constraints of mass balance, mass action, pressure balance, energy conservation and entropy conservation. The gradient projection technique due to Rosen has been adopted for carrying out this optimization. The method was programmed on the IBM 360/Model 44 Computer in FORTRAN IV language and the results of the computations for a typical metallized solid propellant system are presented in the paper. The investigations reveal that the gradient projection technique can be a useful computational device for determining the optimum composition and the corresponding performance parameters of propellant systems containing a large number of reactants and products with or without condensed phases.
A Reappraisal of Silver Fulminate as a detonant
Authors: Collins P. H. , Holloway K. J.
Published: December 2004

The preparation and properties of silver fulminate have been examined to assess its potential for use as a primary explosive. It is an extremely effective detonant but does not appear promising as a stab‐sensitive material. It is concluded that its extreme sensitiveness and the hazards and difficulties associated with its preparation render it unsuitable for military applications. It does find commercial use in the manufacture of toys and crackers when it is normally handled exclusively in small quantities and in the wet state.
The relationship of Impact Sensitivity with Structure of Organic High Explosives. II. Polynitroaromatic explosives
Authors: Kamlet M. J. , Adolph H. G.
Published: December 2004

Impact sensitivities of organic high explosives are primarily functions of the rates of the thermal decomposition processes taking place in the temperature regimes generated under the impact hammer. For classes of explosives with similar decomposition mechanisms, there appear to be statistically significant linear relationships (sensitivity/composition trends) between logarithmic 50% impact heights and values OB100, a measure of oxidant balance. In addition, it is shown that polynitroaromatic explosives containing a C‐H linkage alpha to the aromatic ring are more sensitive as a class than explosives lacking such a linkage. These results are consistent with the finding that products of thermal decomposition of TNT indicate a preferred site of inter‐ and intramolecular oxidative attack to be at the alpha C‐H linkage.
The Double Pipe Test for Commercial Explosives I. Description and Results
Authors: Lownds C. M. , du Plessis M. P.
Published: December 2004

A new test for commercial explosives called the Double Pipe Test has been devised. A column of explosive is placed in the top pipe, simulating a borehole. This pipe rests on a thick‐walled witness pipe, which is dented by the action of the explosive. The arrangement of explosive and initiator in the top pipe is made to represent as closely as possible the practical use of the explosive. No special skill or instrumentation is needed to conduct the test, and scaling up to large charge diameters is easy. Results presented show that the test is very sensitive to variables such as type of initiator and degree of consolidation of the explosive. These and other aspects of explosive performance which are important in their practical use can readily be studied quantitatively with the Double Pipe Test.