Sulfur in chromia

The solubility of sulfur in chromia has been studied in H₂-H₂O-H₂S tagged with³⁵S at 973 and 1173 K at low oxygen and sulfur partial pressures typical for coal gasification-systems. For monocrystalline samples, it has been shown that sulfur-containing species are only present adsorbed on the surface of the specimens and can be removed by ultrasonic cleaning in acetone. The surface coverage after 4 weeks of exposure to H₂-H₂O-H₂S was between 2.8 and 19.3% of a monolayer. In polycrystalline chromia, sulfur was located only in pores and cracks of the sample. In dense, compact areas of the specimens the solubility of sulfur was below the detection limit of autoradiography, which was estimated to be better than 0.17 ppm.     

Silicon Nitride Derived from an Organometallic Polymeric Precursor: Preparation and Characterization

Partially crystalline Si₃N₄, with nanosized crystals and a specific surface area greater than 200 m²/g, is obtained by pyrolysis of a commercially available vinylic polysilane in a stream of anhydrous NH₃ to 1000°C. This polymer does not contain N initially. Crystallization to high-purity α-Si₃N₄ proceeds with additional heating above 1400°C under N₂. The changes in crystallinity, powder morphology, infrared spectra, and elemental compositions, for samples annealed from 1000° to 1600°C under N₂, are consistent with an amorphous-to-crystalline transformation. Although macroscopic consolidation and local densification occur at 1400°C, volatilization and accompanying weight loss limit bulk densification. The effect of temperature on specific surface area is examined and related to the sintering process. These results are applicable to pyrolysis, decomposition, and crystallization studies of ceramics synthesized by polymeric precursor routes.     

Good ergonomics and team diversity reduce absenteeism and errors in car manufacturing

Prior research suggests that ergonomics work design and mixed teams (in age and gender) may compensate declines in certain abilities of ageing employees. This study investigates simultaneous effects of both team level factors on absenteeism and performance (error rates) over one year in a sample of 56 car assembly teams (N = 623). Results show that age was related to prolonged absenteeism and more mistakes in work planning, but not to overall performance. In comparison, high-physical workload was strongly associated with longer absenteeism and increased error rates. Furthermore, controlling for physical workload, age diversity was related to shorter absenteeism, and the presence of females in the team was associated with shorter absenteeism and better performance. In summary, this study suggests that both ergonomics work design and mixed team composition may compensate age-related productivity risks in manufacturing by maintaining the work ability of older employees and improving job quality.     

Fabrication and characterization of machined 3D diffractive optical elements

The production of three dimensional blazed grating structures based on ultra-precision machining is an up-to-date issue. Hence, in the development of manufacturing technologies technology-related failure modes are generated due to structural variations. These failure errors must be recorded in cause and effect and then characterized by their type in order to achieve the optimum quality. This paper addresses the influence of processing parameters on the shape-persistence and hence on the grating quality and explains the possibility of detection and classification of them.     

Surface hydrolysis of filaments based on poly(trimethylene terephthalate) spun at high spinning speeds

The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180°C. Fiber weight loss increased with an increasing heat‐setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well‐developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 μm. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat‐setting temperature. A temperature of 180°C is the upper limit for heat‐setting PTT filaments but seems to be the most effective for making porous fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1724–1730, 2004     

Unsaturated para-linked aromatic LC polyesters: Thermotropic and lyotropic systems

Liquid-crystalline thermosets (LCT) are a new class of materials which combine typical properties of LC polymers with those of conventional thermosets. This article reports on the development of a lyotropic LC thermoset (LLCT) in which the solvent is a vinyl monomer. Such an LLCT is expected to have several advantages compared to conventional unsaturated polyester resins. The synthesis and characterization of a variety of novel substituted para-linked aromatic polyesters and copolyesters containing unsaturated fumaroyl units is presented. The thermal and liquid crystal properties were investigated. It is demonstrated that it is possible to prepare a lyotropic LC solution in styrene. These lyotropic solutions are capable of thermal crosslinking by the addition of a free-radical initiator. © 1995 John Wiley & Sons, Inc.     

Infrared heated μ-blistering,a new fabrication technology for HARMST

Polymeric replication technologies such as injection moulding or hot-embossing have gained wide acceptance in the microtechnological community, microthermoforming of thin polymer foils, also called μ-blistering, still remains relatively unknown. Although the general potentials of the µ-blistering have already been pointed out, little work has been carried out addressing its capability for high aspect ratio microstructuring. In the scope of this work we therefore demonstrate the feasibility of μ-blistering to obtain aspect ratios for free standing structures of up to 7 within a process cycle time of <4 min. The presented processing technology uniquely combines manufacturing of macro-, micro- and even nanoscopic feature sizes in a single process.