Hygrothermal aging of rubber‐modified and mineral‐filled dicyandiamide‐cured DGEBA epoxy resin. III. Dielectric spectroscopy investigation

The effects of moisture absorption on the dielectric properties of a rubber‐modified, mineral‐filled, epoxy resin based on the diglycidyl ether of bisphenol A cured with dicyandiamide are reported. Samples of the resin were aged by immersing in deionized water, or 5% w/w NaCl solution, at elevated temperatures. Dielectric measurements were carried out over the frequency range 10^?1 to 6 × 10⁵ Hz. A featureless dielectric spectrum was observed with both real and imaginary dielectric permittivity increasing with the amount of absorbed water. The change in the dielectric properties with absorption of water was independent of presence of salt, temperature of exposure, and aging history, although a hysteresis of the hydration–dehydration process was observed at low frequencies. Two types of absorbed water were observed—water molecularly dispersed within the epoxy matrix and clustered water in spherical microcavities. The time dependence of the real dielectric permittivity measured at 10 kHz was found to closely resemble that of the water absorption, which allowed the activation energy of diffusion to be calculated from both dielectric and gravimetric data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1011–1024, 2002; DOI 10.1002/app.10368     

Energy-saving technologies of autoextractive distillation of an acetone-chloroform-n-butanol-dimethylformamide mixture

The autoextractive distillation of an azeotropic solvent mixture of acetone, chloroform, n-butanol, and dimethylformamide is considered. A set of flowsheets belonging to different structural classes is synthesized (flowsheets containing two-withdrawal columns and flowsheets involving complex columns with a single side section). The flowsheet that is optimal in energy consumption is revealed, and it is shown that flowsheets with coupled heat and material flows are more efficient than conventional ones.     

Investigation of Taimyrsk graphites for producing periclase-carbon ladle refractories

Conclusions The investigations showed that Taimyrsk graphite corresponds in chemical composition to foundry and crucible graphite.The content of crystalline graphite equals 13.0–26.3%. The characteristics of periclase carbon goods based on foundry and Taimyrsk graphites correspond to the demands placed on ladle refractories. The wear factors of these products in the slag belt of the lining of 350-tonne steel ladles are on practically the same level.Taimyrsk graphites may be used for the production of periclase-carbon ladle refractories in place of crucible or foundry graphite.L. N. Kurlyandskaya (Urals Geology Planning Association) and L. Ya. Osipova (All-Union Institute of Refractories) took part in this research.Translated from Ogneupory, No. 1, pp. 15–17, January, 1991.     

Service properties of chrome-plated surface of fibre-guiding equipment in the KV-III-250 KA machine

Conclusions The effect of the form of chromium-plated fibre-conducting equipment in the KV-III-250 KA machine on the properties of polycaproamide yarn of 187 tex linear density which has been treated with lubricant Teprém-6 is described.It is recommended to use worn-in stretch rolls with a matte surface for their lower stretch rolls; for the heat-plasticizers and other parts, where it is advisable to have a low coefficient of yarn friction, it is recommended to use a shiny-rough surface.Translated from Khimicheskie Volokna, No. 2, pp. 57–59, March–April 1984.     

Production and properties of zirconia ceramics

Conclusions A study was made of the effect of preliminary milling and the process temperature of a mixture of zirconium and yttrium hydroxides on the technical aspects of preparing large articles from partially stabilized zirconia.A procedure was developed for making such items from tetragonal zirconia, both by monoaxial pressing and by slip casting in gypsum molds. The main physicochemical and frictional properties of the materials were investigated.The material has been tested for pushers, piston units, inserts and gaskets, friction pairs of the gas distribution tract in internal combustion engines, and the axles of shafts for pumps handling corrosive media. The tests confirmed the workability of the material in friction pairs.Translated from Ogneupory, No. 2, pp. 6–9, February, 1991.     

Systematic Analysis of Viscoelastic-Plastic Properties of Marine Polymer Ropes

Fibre Chemistry - Methods of systematic analysis of the viscoelastic-plastic properties of marine polymer ropes are considered, which make it possible to qualitatively assess the operational and...     

Effect of heat exchange at the hot junction of a thermoelectric element on the optimum current-carrier density distribution along its branches

The optimum current-carrier density distribution along the height of the branches of a thermoelectric element is obtained, which ensures minimum temperature at the cold junction taking into account the heat transfer at the hot junction.Notation T absolute temperature - T temperature drop between the cold junction and the medium - q temperature gradient - n current-carrier density - u density gradient - a heat-transfer coefficient - x coordinate of the length - d height of the thermoelectric element - , , thermal conductivity, the electrical conductivity, and the thermoelectric coefficient respectively - j current density Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 1, pp. 125–130, July, 1984.     

Non-alloy Cr/Au Ohmic contacts in the technology of planar beam-lead GaAs <Emphasis Type="Italic">p-i-n</Emphasis> diodes

The characteristics of non-alloy Cr/Au ohmic contacts in planar beam-lead GaAs p-i-n diodes have been studied. The room-temperature reduced contact resistance in the structures studied was 2 × 10⁻⁶ Ω cm². The obtained parameters of p-i-n diodes allow these devices to be used as limiters in radar protection systems.