Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

α-Alumina and spinel react into single-phase high-alumina spinel in <3 seconds during flash sintering

In situ X-ray diffraction measurements at the Advanced Photon Source show that α-Al₂O₃ and MgAl₂O₄ react nearly instantaneously and completely, and nearly completely to form single-phase high-alumina spinel during voltage-to-current type of flash sintering experiments. The initial sample was constituted from powders of α-Al₂O₃, MgAl₂O₄ spinel, and cubic 8 mol% Y₂O₃-stabilized ZrO₂ (8YSZ) mixed in equal volume fractions, the spinel to alumina molar ratio being 1:1.5. Specimen temperature was measured by thermal expansion of the platinum standard. These measurements correlated well with a black-body radiation model, using appropriate values for the emissivity of the constituents. Temperatures of 1600-1736°C were reached during the flash, which promoted the formation of alumina-rich spinel. In a second set of experiments, the flash was induced in a current-rate method where the current flowing through the specimen is controlled and increased at a constant rate. In these experiments, we observed the formation of two different compositions of spinel, MgO•3Al₂O₃ and MgO•1.5Al₂O₃, which evolved into a single composition of MgO•2.5Al₂O₃ as the current continued to increase. In summary, flash sintering is an expedient way to create single-phase, alumina-rich spinel.     

Finite element modeling of segmental chip formation in high-speed orthogonal cutting

An explicit, Lagrangian, elastic-plastic, finite element code has been modified to accommodate chip separation, segmentation, and interaction in modeling of continuous and segmented chip formation in highspeed orthogonal metal cutting process. A fracture algorithm has been implemented that simulates the separation of the chip from the workpiece and the simultaneous breakage of the chip into multiple segments. The path of chip separation and breakage is not assigned in advance but rather is controlled by the state of stress and strain induced by tool penetration. A special contact algorithm has been developed that automatically updates newly created surfaces as a result of chip separation and breakage and flags them as contact surfaces. This allows for simulation of contact between tool and newly created surfaces as well as contact between simulated chip segments. The work material is modeled as elastic/perfectly plastic, and the entire cutting process from initial tool workpiece contact to final separation of chip from workpiece is simulated. In this paper, the results of the numerical simulation of continuous and segmented chip formation in orthogonal metal cutting of material are presented in the form of chip geometry, stress, and strain contours in the critical regions.     

A neural network application for reliability modelling and condition-based predictive maintenance

Traditionally, decisions on the use of machinery are based on previous experience, historical data and common sense. However, carrying out an effective predictive maintenance plan, information about current machine conditions must be made known to the decision-maker. In this paper, a new method of obtaining maintenance information has been proposed. By integrating traditional reliability modelling techniques with a real-time, online performance estimation model, machine reliability information such as hazard rate and mean time between failures can be calculated. Essentially, this paper presents an innovative method to synthesise low level information (such as vibration signals) with high level information (like reliability statistics) to form a rigorous theoretical base for better machine maintenance.     

Characteristics of Ni-Ir and Pt-Ir hard coatings surface treated by pulsed Nd:YAG laser

The subjects of the presented paper are to develop a laser surface treatment technology for the protective coatings of glass-molding dies and to better understand the interaction between laser beam and materials coated on the die surface. A variety of alloy films, including Ir-25 at.% Pt, Ir-50 at.% Pt, Ir-75 at.% Pt, Ir-25 at.% Ni, Ir-50 at.% Ni, and Ir-75 at.% Ni compositions are deposited by the ion source assisted magnetron sputtering system (ISAMSS). A Cr layer that functioned as a buffer layer is deposited between the alloy film and die surface. After an alloy film and the buffer Cr layer were sequentially coated on tungsten carbide (WC) surface, Nd:YAG laser was directly applied in the writing process. The temperature profile of the film stack structure is simulated by ANSYS software. The surface roughness was analyzed by atomic force microscopy (AFM) to compare the coating surface roughness before and after the laser surface treatments. The treated coatings for oxidation prevention test were examined by energy dispersive x-ray spectrometry (EDS). Nanoindentation instrument was performed to evaluate microhardness and reduced modulus of the coatings. The cross-sectional structures between the hard coating layer and buffer layer were also inspected by a scanning electron microscope (SEM). The Pt-Ir and Ni-Ir film coatings are unable to withstand the working temperature over 1500 °C, which is considered for quartz molding process and hot embossing process. The films showed high roughness, low microhardness and low reduced modulus because the film oxidation occurred in a high working temperature process.     

Effect of field-annealing on magnetostriction and tunneling magnetoresistance of Co/AlOx/Co/IrMn junctions

The magnetostriction (λ_s) and tunneling magnetoresistance (TMR) of two Co/AlO_x/Co/IrMn MTJ systems that were deposited on Si(1 0 0) and glass substrate were examined at RT and field-annealing with various thicknesses of AlO_x. One structure was a Si(1 0 0)/Ta/Co/AlO_x/Co/IrMn/Ta system, and the other was a glass/Co/AlO_x/Co/IrMn system. The experimental results reveal that, in the Si(1 0 0)/Ta/Co/AlO_x/Co/IrMn/Ta system, the ratio of TMR is maximal under the field-annealing condition, and is optimal at an AlO_x thickness of 26 Å as well as in the RT condition. EDS analysis demonstrates that, these results are related to the distribution of Co and O atoms, because the oxidation of AlO_x is most extensive at a thickness of 26 Å. In the glass/Co/AlO_x/Co/IrMn system, λ_s does not significantly vary under the RT condition; however, λ_s is maximized (?20 ppm) by field-annealing at an AlO_x thickness of 17 Å. The abundance of Co and O in the system dominates the behavior of λ_s, according to EDS analysis. Finally, the minimum value of λ_s and the maximum ratio of TMR are ?8 ppm and 60%, respectively, at an AlO_x thickness of 26 Å under the field-annealing condition.     

A Novel Technique for Synthesizing Nanoshell Hollow Alumina Particles

A novel and versatile synthesis route has been developed to fabricate hollow Al₂O₃ microspheres with nanoporous shell structures. The method involves a preferential "implantation" of Al species into polymeric template particles to form a core–shell structure in solvent. The template cores can then be removed by thermal pyrolysis to form hollow interiors. This unique "implantation" process allows for synthesis of monodisperse hollow spheres with a nonaggregated character. The implantation of Al species is confirmed by electron spectroscopy for chemical analysis/Auger analysis in depth profiles. The shell structure changes from amorphous to γ-Al₂O₃ at 900°C; because of which, the shell is nanoporous in structure. The porous shell then transforms to α-Al₂O₃ as temperature is further raised above 1000°C. Transmission electron microscopy examination reveals a uniform shell thickness of ca. 20–40 nm, and grain growth appears to be constrained by the thin shell walls at 1100°C, leading to void formation at the triple grain junctions.     

Effect of polyvinylpyrrolidone on morphology and structure of In2O3 nanorods by hydrothermal synthesis

Indium oxide (In₂O₃) nanorods were hydrothermally synthesized from aqueous InCl₃ solution in urea with addition of polyvinylpyrrolidone (PVP) as a steric stabilizer. Indium hydroxide, In(OH)₃, was precipitated at 60 °C and was changed into a transient InOOH phase upon calcination at 250 °C in air. X-ray diffractometry revealed that the existence of PVP delays the phase transformation of InOOH. Cubic-structured In₂O₃ phase was then formed when temperature was raised to 350 °C, regardless of the PVP concentration. The In(OH)₃ phase without the PVP showed a rod-based, flower-like morphology of polycrystalline character. Minor addition of the PVP, i.e., 0.1–2 wt.%, resulted in a pronounced evolution in morphology from the three-dimensional, flower-like form to discrete, one-dimensional nanorods aligned in planar form. Both the flower-like and discrete nanorod morphologies were preserved after heat treatments at 250 and 350 °C. This reveals that the morphological change is attributable to preferential adsorption of the PVP molecules on the In(OH)₃ crystallite surface, so that the aggregate attachment responsible for the multipod growth is inhibited.     

The comparison between the polyol process and the impregnation method for the preparation of CNT-supported nanoscale Cu catalyst

Carbon nanotubes (CNTs) are relatively potential materials for catalyst supports. CNT-supported Cu catalysts were prepared by an impregnation method and a polyol process. The catalytic activity was examined under different reaction atmospheres, Cu contents, and sizes of supports for CO oxidation. The experimental results showed that the active phase on the catalyst prepared by the impregnation method (10–20 nm) was smaller than that on the catalyst prepared by the polyol process (30–50 nm). Furthermore, the smaller active phase showed better performance for CO oxidation. Therefore, catalysts prepared by the impregnation method had a lower activation energy (57.47 kJ mol^?1) than those prepared by the polyol process. The optimum CNT-supported Cu catalyst prepared by the impregnation method using 10–20 nm CNTs had a Cu content of 13.4 wt.%, and a CO conversion of 33% achieved at 125 °C with a total space velocity of 1.56 × 10⁵ h^?1.