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Abstract. In the present research, phenol-formaldehyde resins were used instead of common surfactants for dispersing carbon nanotubes and graphene nanoplatelets in order to develop new composite materials. The use of such resins makes it possible to increase the concentration of nanoparticles in solution by approximately two orders of magnitude. The presence of reactive groups on the surface of the phenol-formaldehyde-resin-modified carbon nanotubes and graphene nanoplatelets promotes synthesis of a variety of composites. According to the experiments performed herein, the modification of the nanomaterials with the phenol-formaldehyde resin significantly improves their compatibility and provides good water-solubility. While dispersing in water, the aggregates of the carbon nanotubes disappear, giving rise to an ordered structure. Besides, they form stable colloidal solutions at slightly alkaline pH values, but coagulate when decreasing the pH. This effect allows for self-assembly of carbon and composite nanostructures from nanoparticles in solution due to pH adjustment. This enables easy synthesis of hybrid composite materials based on carbon nanotubes, graphene nanoplatelets and phenol-formaldehyde resins.

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Аннотация: Показано как протекает процесс в безводной серной кислоте поликонденсации гексаметилентетрамина. Предложен механизм протекающих превращений и структура образующихся продуктов. Для образующегося продукта предложено техническое название «аминокумулен». Найдены условия получения растворимого и нерастворимого продуктов поликонденсации гексаметилентетрамина. Исследованы спектральные свойства полученных продуктов. Показано, что растворимый аминокумулен является эффективным диспергатором и стабилизатором дисперсий углеродных нанотрубок и графеновых материалов.

The structural state of annular work pieces made of brass CuZn34Mn3Al2FeNi after hot forming at temperatures of 700 and 780 C is studied. Electron microprobe analysis of the material of rings shows the absence of any harmful impurities, low melting eutectics, silicides and nonmetallic inclusions on the ʹ-grain interfaces. Irregularity of the dynamic recrystallization process in the cross section of the rings has been revealed; namely, there are two zones differing in the amount of deformation. One area with minimal deformation and excessively large grain, the second -with the maximum deformation and small grain resulting from dynamic recrystallization. Determined that heating for stamping to 780 Cresults togrowth of βʹ-grains up to 0.3 mmin the area with minimal deformation, the grains boundaries are reinforced (on the borders -300 HV 0.2, and in the center of the grain -170 HV 0.2), which facilitates the emergence and rapid growth of cracks under the action of internal residual stresses formed during cooling of blanks. Lowering the temperature of heating for forging to 700 C reduces the size of the maximum βʹ-grains up to 0.15 mm, thus not detected hardening of their borders that helps to preserve the integrity of the rings after cooling.