Activity–Composition Relations in MnCr2O4–CoCr2O4 Solid Solutions and Stabilities of MnCr2O4 and CoCr2O4 at 1300°C

Phase equilibria in the system MnO–CoO–Cr₂O₃ were investigated at 1300°C under controlled oxygen partial pressures by using the gas equilibration technique. The CoO activities in various phase assemblages of the system were measured by determining the partial pressures of oxygen in the gas phase for coexistence with metallic cobalt. The activity data revealed that at 1300°C, MnO–CoO and MnCr₂O₄–CoCr₂O₄ solid solutions exhibit mild positive departures from ideal behavior. The activities in the stoichiometric spinel solutions were found to be in good agreement with those predicted from a model based on cation distribution equilibria. The standard free energy of formation of the compound CoCr₂O₄ from its oxide components at 1300°C was determined as −37 636 J/mol, while that for MnCr₂O₄ was found as −44 316 J/mol.     

A Process for Increasing the Free Fat Content of Spray-dried Whole Milk Powder

Exposing spray‐dried whole milk powder to high shear and elevated temperature in a twin‐screw continuous mixer increased the free fat content. The effects of operating conditions (powder feed rate, processor screw speed, and process temperature) on lactose crystallinity, particle size distribution, color, and moisture content of spray‐dried whole milk powder were investigated using response surface methodology. Exposure to elevated temperatures and high shear: (a) increased the free fat to more than 80%, (b) crystallized the lactose, (c) reduced the average volume‐based particle size, and (d) broadened the particle size distribution. The raw whole milk powder with creamy‐white color turned into an oily paste with bright‐yellow color. Processing enhanced the functional properties of spray‐dried whole milk powder for milk chocolate manufacture.     

Development of a liquid extraction method and comparison with dynamic thermal stripping–thermal desorption (DTS–TD) method: sorption of D‐limonene by flexible packaging films

The sorption of D ‐limonene into polymeric structures in contact with food simulant liquids (ethanol and acetic acid solutions) was determined using two methods, liquid extraction (LE) and dynamic thermal stripping–thermal desorption (DTS–TD). The polymeric films studied were PP (polypropylene), PE/nylon/EVOH/PE (polyethylene/nylon/ethylene vinyl alcohol/polyethylene) and metPET/VA EVA/LLDPE (metallized polyethylene terephthalate/ethylenevinyl acetate/linear low density polyethylene). Our assessment showed that both LE and DTS–TD techniques are valuable procedures. LE was evaluated as an alternative method with the advantage of being a simplified process. It was possible to measure the amount of D ‐limonene in the polymers using both methods. Correlation between methods was >82% and for the single layer polymers >92%. The respective sorption values obtained by the two methods were also found to be in good agreement. LE is simple and rapid to perform and, in general, gives slightly lower results compared to DTS–TS sorption tests conducted with adequate food simulants. The results indicate that the liquid extraction method is an excellent technique for the determination of sorbate concentration in polymeric structures. Copyright © 2004 John Wiley & Sons, Ltd.     

Microplane Model M5f for Multiaxial Behavior and Fracture of Fiber-Reinforced Concrete

Despite impressive advances, the existing constitutive and fracture models for fiber-reinforced concrete (FRC) are essentially limited to uniaxial loading. The microplane modeling approach, which has already been successful for concrete, rock, clay, sand, and foam, is shown capable of describing the nonlinear hardening–softening behavior and fracturing of FRC under not only uniaxial but also general multiaxial loading. The present work generalizes model M5 for concrete without fibers, the distinguishing feature of which is a series coupling of kinematically and statically constrained microplane systems. This feature allows simulating the evolution of dense narrow cracks of many orientations into wide cracks of one distinct orientation. The crack opening on a statically constrained microplane is used to determine the resistance of fibers normal to the microplane. An effective iterative algorithm suitable for each loading step of finite element analysis is developed, and a simple sequential procedure for identifying the model parameters from test data is formulated. The model allows a close match of published test data on uniaxial and multiaxial stress–strain curves, and on multiaxial failure envelopes.     

Longitudinal-bending mode micromotor using multilayer piezoelectric actuator

Longitudinal-bending mode ultrasonic motors with a diameter of 3 mm were fabricated using stacked multilayer piezoelectric actuators, which were self-developed from hard lead zirconate titanate (PZT) ceramic. A bending vibration was converted from a longitudinal vibration with a longitudinal-bending coupler. The motors could be bidirectionally operated by changing driving frequency. Their starting and braking torque were analyzed based on the transient velocity response. With a load of moment of inertia 2.5 x 10(-7) kgm2, the motor showed a maximum starting torque of 127.5 microNm. The braking torque proved to be a constant independent on the motor's driving conditions and was roughly equivalent to the maximum starting torque achievable with our micromotors.     

Formation of WC powders using carbon coated precursors

This paper deals with the formation of tungsten carbide from carbon coated tungstic oxide precursors. This study makes use of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscopy (TEM). DSC and TGA data for both coated and mixed 17.2 wt% carbon containing tungstic oxide demonstrate the superiority of the coated precursor in the formation of tungsten carbide, as conversion is initiated at lower temperature. XRD patterns of products from each 100°C isotherm from 900–1400°C, inclusive, illustrate the formation as it proceeds through lower oxides into tungsten then carburizes into tungsten carbide for both the mixed and coated samples.