Short-Time Drying of Beatsensitwe, Biologically Active Pulps and Pastes

Tomato concentrate and baker's yeast suspension were dried in the laboratory scale Mechanically Spouted Bed dryer with inert packing. Due to a large contact surface provided by the inert particles, very fast drying process can be achieved, ifthe thickness of the wet coating formed on the surface of the inert packing is film-like. The diffution resistance can be then considered negligible and drying can be performed at “quad-constant” rate. Derived fiom hydrodynamic characteristics the contact time between hot air and the wet coating is very short, therefore gentle drymg process can be performed. The quality of the dried yeast was controlled by counting the living cells (relative viabilny) and by measurement of the dough rise time. During continuous drying of thermoplastic tomato pure the “case hardening” periods could be shortened and tomato powder with insignificant quality loss was produced.     

Surface tension studies of additives in acrylic resin-based powder coatings using the Wilhelmy balance technique

A modified Wilhelmy balance technique using thin fibers as solid probes has been applied to study the effect of silicone additives in acrylic resin-based powder coatings on the surface tension of non-reactive binder systems. By measuring the temperature dependence of the surface tension in the temperature range between 140 and 180°C, it could be shown that the silicone additives investigated had a very different surface activity in the molten acrylic resin. Due to the high accuracy of the measuring technique and the good reproducibility of the experiments the influence of different additive concentrations on the surface tension was detectable even at very low concentrations (below 1 wt.%).

Compared to the pure powder coating binder which has a surface tension of about 30 mN/m the values decreased between 2–15 mN/m depending on the type of the silicone additive. In addition, the temperature coefficient −(dγ/dT) of the surface tension of the binder melt was changed. In the case of two additives, the surface tension of the powder coating and its temperature coefficient were lowered considerably. This effect of additives is desirable to reach good wetting and leveling of the powder coating.     

Influence of additives on interfacial phenomena during film formation of powder coatings

Film formation of powder coatings is illuminated from a physico-chemical point of view. Significant parameters influencing the film formation of powder coatings are surface (wetting) tension and viscosity of the polymer melt formed during the film formation process. A newly developed measuring device for the investigation of wetting at elevated temperatures is presented. This device allows systematic investigations of the temperature dependence of the wetting tension of powder coating binder systems. By combining analytical and surface tension measurements, it is possible to gain new information about the mechanism of action of additives in these melts. Hohe Stra?e 6, D-01069 Dresden, Germany.     

涂层表面形貌形成过程模拟与分析

表面涂层形貌形成过程的定量描述对涂层质量控制效果的提升至关重要,建立了集成蒙特卡罗（Monte Carlo）和计算流体力学（CFD）的混合方法模拟复杂的海量液滴沉积成液膜及其随后的流平过程,并系统研究油漆液滴平均直径、黏度、密度以及表面张力对涂层表面粗糙度、流平速度以及流平时间的影响。模拟结果表明,油漆液滴平均直径增大,涂层初始表面粗糙度增大,流平速度减小,流平时间延长;黏度增大,涂层的初始和最终表面粗糙度增大,流平速度减小,流平时间延长;密度减小,涂层初始表面粗糙度增大,初始流平速度增大,流平时间稍微缩短,对最终表面粗糙度影响不大;表面张力增大,涂层流平速度增大,流平时间缩短,对涂层最终表面粗糙度影响很小。     

Fracture Mechanics of aV-peel Adhesion Test - Transition from a Bending Plate to a Stretching Membrane

A linear elastic solution is proposed for a “V-peel” adhesion test for a thin film adhered to a rigid substrate. The mechanical responses of a stiff plate-like coating under pure bending, a semi-flexible film under mixed bending and stretching, and a flexible membrane-like film under pure stretching are discussed. For delamination to occur, the mechanical energy release rate is shown to be G = χ(Fw₀/2bl) with χ a numerical constant varying from 3/2 for a plate-like disc to 3/4 for a thin flexible membrane.     

Nanograin magnetoresistive manganite coatings for EMI shielding against directed energy pulses

Two magnetoresistive manganites, La_0.83Sr_0.17MnO₃ and La_0.7Sr_0.3MnO₃, are synthesized by the environmentally friendly “deposition by aqueous acetate solution (DAAS)” technique. The manganite film has a grain size of 100 nm, and can be processed as thinly as 0.03 μm per layer, while the powder form has a crystallite size of 40 nm. These magnetoresistive materials are shown to be effective and inexpensive electromagnetic interference (EMI) shield for the extremely low frequency (ELF) EM fields. The electrical resistance of manganites is very sensitive to external influences, such as temperature and electromagnetic fields. Both permeability (μ) and conductivity (σ) of manganites tend to increase with increasing applied magnetic field. The manganites have been shown to “react” to field increases in a way that is particularly useful for shielding EMI field fluctuations (e.g., due to current or voltage spikes).

The manganite properties, e.g., crystal structure, film morphology, radiation absorption and reflection, electrical resistivity, and magnetization, etc., have been measured. The ceramic manganites have a metal–insulator transition at 300 K or higher, and are suitable for a room temperature operation. A thin film (approx. 0.1 μm) of La_0.83Sr_0.17MnO₃ was fabricated on a quartz tube or refractory ceramic fiber blanket. Using this thin manganite film, the EMI shielding effectiveness for the measured E-field attenuation is similar to that of a 25 μm thickness of copper tube, aluminum foil, and silver–nickel particle-dispersed paper. The silver–nickel impregnated paper has an EMI shielding effectiveness of 35 dB at 10 kHz, and 15 dB at 60 Hz (or frequency above 1 MHz). The ceramic manganites are chemically inert, thermally stable, and mechanically flexible. They provide low cost EMI shielding against directed energy pulses and may serve as a “signature reduction” barrier.     

Stress measurements in high-shear granulators using calibrated “test” particles: application to scale-up

Granulation is a process by which fine powders are agglomerated into larger particles using a liquid binder. In high-shear granulation the powder–binder mix experiences intense agitation inside a mixing vessel as binder is dispersed and granules form and strengthen under the influence of shear and compacting forces in the device.

It is an implicit assumption that in a “high shear” mixer, large forces are transmitted to the powder and this results in a short and efficient granulation process. Owing to these desirable characteristics, high-shear granulation was adopted by several industries including pharmaceuticals and detergents where the process is used almost exclusively. In the work reported here, we attempt to measure shear forces in a moving powder inside a mixer-granulator. The method is based on previous numerical simulations [Powder Technology 110 (2000) 59] and experiments [Journal of Fluid Mechanism 347 (1997) 347] where we showed that at equilibrium between stresses in the mixer and the yield strength of the particles, granules attain a characteristic elongated shape. The measuring method adopted is indirect in the sense that pellets with well-defined mechanical properties were used to interrogate forces inside the granulating vessel at the point where they attain their characteristic elongated shape. We subsequently used the condition of equal shear forces in the device as a scale-up criterion so as to preserve the magnitude of stresses at both scales and thereby to expose forming granules to similar forces in both the small- and large-scale machines.

We found that shear forces in a “High-Shear” mixer-granulator with a vertical axis (Fielder) are actually not always high. The mixer has the potential to produce high shear forces but these forces are transmitted to the powder mass only if the powder is sufficiently cohesive or becomes cohesive due to binder addition. Shear forces in the granulator are strongly wet-mass-dependent and they increase rapidly as soon as a “granulation limit” is achieved, i.e., at the point where granules start to form in the shearing powder mass. We found that granulators with geometrically similar bowls can be scaled to generate comparable shear forces by decreasing the impeller rotational speed of the large machine by the factor (D/d)ⁿ, where D and d are the impeller diameters of the large and small machine, respectively, and n is a scaling index that depends on impeller geometry but not on wet mass properties. For the equipment studied in this work, the coefficient n was obtained as 0.80<n<0.85. We also propose an improved granulation process in which dry powders are pre-wetted before introduction into the main granulating device. This scheme has the potential to produce larger shear forces during wetting and binder introduction and thereby improve homogeneity and consequently final granule properties.     

ABSORPTION AND DESORPTION TO AND FROM LIQUID FILMS ON INCLINED PLANES

Two published theoretical models are examined and applied to experimental results for absorption and desorption. The system used was CO₂/H₂O and studies were made for liquid film flow down inclined planes. Experimental results give “Reduced” values of mass ransfer rates.

Interferometric studies give interfacial concentration, penetration and film depths, and take-up of carbon dioxide. In the case of desorption the interferograms are distorted by “deflections.”

All the experimental values for absorption and desorption differ from those calculated from theoretical models.

Desorption is not a mirror image of absorption, and it is approximately 75% of the transfer rate of absorption over a wide operating range.

A comparison is made of the behaviour of static pools and flowing liquid films.     

SINTERING KINETICS AND TRANSPORT PROPERTY EVOLUTION OF LARGE MULTI-PARTICLE AGGREGATES

Ultrafine (“nano”-) particles produced from highly supersaturated vapors or liquids are usually aggregated, often containing thousands of small 'primary' particles bound together in tenuous structures characterized by mass fractal dimensions less than 3. Such aggregates have large initial surface area but are metastable with respect to more compact configurations. Available restructuring mechanisms include surface energy driven coalescence, which, in the case of viscous flow at high gas temperatures, is ultimately able to obliterate all evidence of the original (“primary”) particles. We here exploit the notion that, provided an aggregate is sufficiently large, it can be treated like a spatially non-uniform porous medium, undergoing finite-rate surface energy driven viscous flow sintering leading to final collapse to a single dense sphere. For this purpose, after a D_ƒ ≌s const stage of sintering [associated with a corresponding increase in mean apparent primary particle ('grain') size], we use an extension of the sintering rate models of Mackenzie and Shuttleworth (1949) and Scherer (1977), treating the material of the restructuring aggregate to be a Newtonian viscous fluid. We predict and report here the time-dependent increase in fractal dimension, D_ƒ, and associated decreases in: aggregate outer (maximum) radius, mobility radius, and changes in accessible surface area with dimension-less time [real time in multiples of the characteristic sintering time, μ (R₁)_t=0/σ cr, where u is the material's viscosity (R_l)_t=0 is the effective initial grain radius and a the material surface tension]. In these units, we find that the total required coalescence time does not increase with N as sensitively as N^1/3 an important observation for processes involving very large aggregates. With validation and the indicated extensions, our pseudo-continuum methods are efficient enough to be used for estimating the morphological- and transport property-evolution of entire populations of restructuring aggregates, perhaps characterized by some non-separable probability density function pdf(N, D_ƒ,R₁,) locally, in non-isothermal combustion-synthesis reactors.     

On Multi-valued Surface Properties of PMMA Films

An apparent link between the surface properties of polar group-containing polymers, such as PMMA and Styrene/Acrylic copolymers, and the thermodynamic quality of solvents used in solutions from which the polymers were cast, was described in earlier papers.^1,2 In these polymers, significant variations have been observed in critical surface tensions(γ_c), and in the thermodynamic interaction parameters for selected vapor-polymer pairs, when the configuration of the polymer in solution was varied through the suitable selection of solvents of differing thermodynamic quality. The “solvent history” effect on surface properties of solid film was not detected however for non-polar polymers such as polystyrene (PS).^1,2 Apparently the distinct chain configurations adopted in solution by PMMA are carried over into the solid and result in different proportions of non-polar (backbone) and polar (side chain) moieties being located in the surface layer of the solid. Since only one surface state can correspond to a thermodynamic equilibrium, it may be expected that the film surface properties will change with time, as the thermodynamically preferred state is attained. As a consequence, use properties of these films should also display (initially) the “solvent history” effect, and should vary similarly with time. The present communication is concerned with these points.     

The Mechanical Behaviour of Polyimide/Copper Laminates Part 2: Peel Energy Measurements

The mechanical peel behaviour of laminates consisting of polyimide films adhered to copper foil using a modified acrylic adhesive has been studied over a wide range of test rates and temperatures. The laminates were prepared from polyimide films which had been subjected to either a “high-thermal history” or a “low-thermal history” treatment during the production of the film. The measured peel energies of the laminates could be superimposed to give a master curve of peel energy versus the reduced rate of peel test, Ra_T, where R is the rate of peel test and a_T is the time-temperature shift factor. The appropriate shift factors were a function of the test temperature and were mainly deduced from tensile tests conducted on the bulk adhesive. The “high-thermal history” laminates gave higher peel energies and the locus of failure of the laminates was mainly by cohesive fracture through the adhesive layer. At low values of log₁₀ Ra_T, i.e. Low rates of peel and high test temperatures, the “low-thermal history” laminates also failed in the adhesive layer and possessed similar peel energies to those measured for the “high-thermal history” laminates. However, at high log₁₀ Ra_T values, the peel energies measured for the “low-thermal history” laminates were lower and showed a wider scatter. These arose from a different locus of failure occurring in these “low-thermal history” laminates when tested under these conditions. Namely, it was found that most of these laminates failed in a weak boundary layer in the outer regions of the “low-thermal history” polyimide film.     

Transcrystalline Region of Polypropylene: Its Formation, Structure and Mechanical Properties

The question of the dominant factors in the production of a transcrystalline region (TCR), an “interphase,” in crystalline polymers on solidifying in contact with a substrate is investigated for isotactic polypropylene (PP) using polarization microscopy and scanning electron microscopy. Several uncoated substrates, and the same substrates coated with certain vacuum-evaporated metals and carbon, as well as surface replicas of these made with cellulose acetate, are compared as nucleating surfaces. It is concluded that TCR formation is not dependent on the species of substrates or their surface energy but on the geometrical morphology or surface roughness. In fact, the rough surface produced by abrasion with carborundum powder creates a TCR for every substrate used. An all-transcrystalline (TC) film of PP more than 300μm thick is obtained by hot pressing the PP between two sheets of PTFE. Wide-and small-angle X-ray analysis of the film reveals a “cross-hatch” structure of lamellae. Micro-beam X-ray analysis shows that three-dimensional crystal growth occurs up to 20-30μm from the interface and, thereafter, a one-dimensional TCR grows up to the mid-plane of the film from both sides. The stress-strain behavior of the various TC films are compared with spherilitic-crystalline and quenched amorphous films. The TC film is able to undergo up to 800% elongation in spite of its almost perfect crystallinity. The mechanism of deformation is discussed on the basis of X-ray observations.     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d_s and γ^d_l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d_s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^-2 K^-1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d_s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d_s and d(γ^d_s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

LIMITING FLUX IN ULTRAFILTRATION OF MACROMOLECULAR SOLUTIONS

The mass transfer equation describing the process of gel polarized ultrafiltration is solved using an integral method. A concentration profile is assumed to be an nth degree polynomial. In conventional integral method, “n”is arbitrarily assigned an integer value. In this paper we have taken the first moment of the convective diffusion equation to determine “n” as a function of the system parameters. The agreement between the closed form integral method solution and the exact numerical solution is excellent while the widely used film theory deviates considerably.     

Interface science for optimizing the size of oxidic nanoparticles in supported catalysts

In the present work we attempt to optimize the size of the supported “molybdenum oxide”/titania and “cobalt oxide”/γ-alumina nanoparticles formed after calcination by “selecting”, respectively, the proper mode of deposition and the local structure of the deposited species achieved upon the impregnation step of catalyst preparation. Concerning the first system, it was found that the disubstituted Mo inner sphere surface complexes, which are bound on the support surface stronger than the monosubstituded ones, resist more effectively to the sintering taking place during calcination where the above complexes are transformed progressively into MoO₃ supported nanoparticles. This leads to a catalyst with very small MoO₃ nanoparticles and thus with very high activity for the selective reduction of NO by NH₃. Concerning the “cobalt oxide”/γ-alumina catalysts, it was found that a relatively large (small) size of the supported nanocrystallites is imposed by the bulk deposition (formation of inner sphere surface complexes). A quite small size of the supported “cobalt oxide” nanocrystallites, not strongly interacted with the support surface, is imposed by the interface precipitation. This is the optimum supported phase for the complete oxidation of benzene.     

Chemical composition and bond structure of aerosol particles of amorphous hydrogenated silicon forming from thermal decomposition of silane

Aerosol particles of amorphous hydrogenated silicon resulting from thermal decomposition of silane were investigated by hydrogen evolution, IR-, EPR-, NMR spectroscopy, and transmission electron microscopy.

The experimental data show that aerosol particles contain to a various extent {SiH₂}_n polymer structures and two types of monohydride groups SiH- “clustered” and “dilute” monohydride groups. The hydrogen atoms of the “clustered” monohydride groups are located close to each other. The “clustered” monohydride groups are inaccessible to the ambient because they are embedded in the amorphous network. The “dilute” monohydride groups are relatively isolated from each other. The majority of “dilute” monohydride groups are open to the ambient. They are located on the surface of preferentially interconnected microchannels and microvoids.

Interaction between the “dilute” SiH groups and atmospheric oxygen results in formation of OSiH groups in which hydrogen and oxygen are bonded to a common silicon atom. Evidently, the interaction occurs throw the oxygen reaction with weak bonds associated with “dilute” monohydride groups. There is no interaction between oxygen and both “clustered” SiH groups and {SiH₂}_n chain because the former are inaccessible to atmospheric oxygen and the latter has presumably no weak bonds in the chains.     

Pretreatment of substrate surface for improved adhesion of diamond films on hard metal cutting tools

The d.c. plasma jet CVD process is one of the most promising coating processes used for the production of polycrystalline diamond films. In comparison with other CVD processes, its obtainable linear growth rates, in the range of 100 μm/h, are much higher than growth rates of microwave or hot filament CVD (1–10 μm/h).

One interesting application is the diamond coating of cutting tools. The main problem here is the poor adhesion of the films. Therefore, a mechanical or chemical pretreatment or intermediate layers are used to improve the adhesion.

In these investigations the influence of mechanical pretreatment by grinding and polishing with diamond powder of different grain sizes as well as chemical etching are examined on WC-Co hardmetals. Sputtered metallic interlayers of different thicknesses and arc-ion plated amorphous carbon films are deposited on these substrates, and diamond films were synthesized on these pretreated cutting tools by d.c. plasma jet CVD.

Adhesion and wear resistance of the diamond films have been examined by dry turning tests on very abrasive metal-matrix composites. Distinct improvement in adhesion of diamond coatings on hard metal substrates was achieved by two methods of substrate surface pretreatment: etching with Murakami's solution and following ultrasonically seeding with diamond particles or using an amorphous carbon film as intermediate layer.     

Reversible reactions within anodic oxide films on titanium electrodes

Evidence is presented for a reversible reaction occurring within the bulk of the surface oxide film on Ti electrodes at negative potentials.

High frequency impedance measurements give results characteristic of a bulk phenomenon and clearly distinguish the behaviour of filmed Ti electrodes from that of some other “valve” metals at low potentials.

The potential/pH dependences of the impedance minima are discussed in terms of various models for the reversible formation of a hydrated oxide in the bulk of the oxide film.     

Optimization of fluid dynamics for maximum fouling prevention

Experimental results with ultrafiltration of coloured solutions show, as a general rule, that “quo;gel formation”quo; develops as stripes in the flow direction on flat sheet membranes.

However, secondary flows in the bulk fluid cannot be detected with the experimental accuracy possible in Newtonian liquids.

An attempt to explain the phenomena important to ultrafiltration in laminar flow is made by theories explaining the phenomena by instability in the boundary layer at the membrane surface.     

The Contact Adhesion of Self-Adhesive Strain Gauges

Thin pieces of flexible polymers may be adhered to rigid substrates merely by pressing the two surfaces into intimate contact. The peel strength of the bond is poor, but the shear strength can be sufficiently high for strain gauge operation. This paper offers an explanation for the adhesion which can account quantitatively for the behaviour of various materials. Frictional phenomena, resulting from a normal force produced by the surface tension of a surface film, can explain why a gauge with a PVC body does not slip. With other polymers, other liquids or electrostatic effects may be of importance. Any surface “fluid” film of sufficiently high viscosity that viscous effects are important will behave as an integral part of the elastomer.