Basic trend in the development of equipment for the preparation of carbon fibres

Khimtekstil'mash NPO (Chernigov). Translated from Khimicheskie Volokna, No. 5, pp. 30–33, September–October, 1993.     

Effects of heat treatment temperatures on microstructures and mechanical properties of the chopped carbon fibres SiC composites

ABSTRACT

A simple wet papermaking technique was used to fabricate chopped carbon fibre paper (C_sf-paper) with random fibre orientation and self-supporting network structures in this work. The C_sf-papers were laminated layer by layer and further infiltrated with PyC interface and SiC matrix via chemical vapour infiltration (CVI) to obtain C_sf/SiC composites. The effects of heat treatment temperatures on microstructures, phase composition, and mechanical properties were investigated. Results showed that the C_sf-paper has played a good self-supporting role and its fibres form a completely random fibre orientation in 2D plane. The fibres almost remained undamaged and unbroken during the CVI. Proper heat treatment could improve the mechanical properties. At 1200°C, the maximum values of flexural strength and Young's modulus reached about 306 MPa and 196.5 GPa, respectively. Meanwhile, compared with tape casting, reaction sintering and spark plasma sintering, composites fabricated by wet papermaking and CVI can improve the mechanical properties.     

化工设备设计中焊后热处理的分析

热处理能够很好地完善金属本身的材质,延长金属设备使用的时间。但是,热处理还有很多薄弱的环节。在化工设备设计中,热处理的方式主要有以消除应力为主要目的的焊后热处理、降低材料中氢含量的焊后消氢处理以及提升材料性能的恢复材料性能热处理。阐述焊后热处理的定义及目的,并对化工设备设计中焊后热处理提出可行方案。     

Structure of carbon fibres

Conclusions -- Carbon fibres have been examined as carbon band oriented amorphous-crystalline polymers.-- Characteristic regions in the formation of the structure of carbon fibres have been established, plus the interconnection between structural parameters.-- The components of preferential orientation of carbon fibres have been marked out, and a systematization of orientation in the transverse section of fibres has been presented.-- The character of change in axial component of texture with change in treatment temperature has been given, plus the connection between it and the elasticity and strength of fibres.-- A characteristic has been proposed for evaluating the activity of the surface of carbon fibres.Combustible Minerals Institute. Translated from Khimicheskie Volokna, No. 3, pp. 26–29, May–June, 1991.     

Optimization of stabilization and carbonization treatment of PAN fibres and structural characterization of the resulting carbon fibres

The properties of carbon fibres made from PAN are controlled by the heat treatment cycles during stabilization and carbonization. Optimum conditions can be derived by simple but time-consuming trials. The paper presents an indirect laboratory method, which is based on TMA and DSC measurements during the stabilization period. Results from this method contribute additionally to the explanation of the various simultaneously occurring chemical reactions, mainly dehydrogenation, intra- and intermolecular cyclization.Shrinkage measurements during stabilization under time linear heating show the start and end of the chemical stabilization reactions. The optimum stabilization conditions are derived from the shrinkage behavior as a function of the heating rate. As the stabilization is strongly affected by the heat of reaction, DSC measurements contribute to the accuracy but also to the explanation of the results from the TMA method.These stabilization conditions were applied for the preparation of carbon fibres which are characterized by mechanical and physical methods.     

浅谈化工设备设计中焊后热处理问题

对化工设备设计的焊后热处理问题提出了几条切实可行的方案和手段。希望对广大化工设备设计工作者有促进和提高作用。     

Appearance and development of polyconjugated structures in heat treatment of polyacrylonitrile fibres

The changes in the electrophysical and paramagnetic characteristics of PAN fibres during their heat treatment are similar to the corresponding changes in heat treatment of other polymer [10]; the character of these changes allows tracking the appearance and development of a polyconjugated structure in heat treatment of PAN fibres with the characteristic mobility of the -electrons and ability to form paramagnetic centers.Avtor Scientific and Industrial Association, Mytishchi. Translated from Khimicheskie Volokna, No. 6, pp. 13–16, November–December, 1993.     

Fabrication of carbon fibres from wet-spun commercial polyacrylonitrile fibres

The possibility of fabricating carbon fibre from commercial PAN fibres for textile applications was demonstrated. It is necessary to make some changes in the temperature—time conditions for total completion of the thermal stabilization process. Better strength of the carbon fibres, equal to 1401 MPa, was attained in conducting thermal stabilization cycle B. __________ Translated from Khimicheskie Volokna, No. 5, pp. 31–33, September–October, 2006.     

Effect of heat treatment on synthetic carbon precursors

Carbonaceous materials obtained from polyethyleneterephthalate (PET), a potential precursor for polymer-based carbon, were studied after heat treatment at 750, 900 and 1200 °C in an inert atmosphere. The carbon content increases to more than 95% (w/w) already at the lowest temperature applied. The surface area decreases from 242 to 14.7 m²/g between 750 and 1200 °C, causing also a reduced pore volume and the conversion of open to closed pores. The pore structure exhibits a gate effect. The carbon matrix contains both amorphous and semicrystalline regions. The spatial extent of the latter can be described by a Maxwellian distribution with a maximum of 12 Å at the lowest and 17 Å at the highest temperature values. Increasing the temperature from 900 to 1200 °C does not increase the size of these domains but yields a more ordered carbon skeleton. In the WAXS spectrum a flat diffuse peak about 3.5-4.0 Å corroborates that the graphitic domains are of colloidal size. The immersional wetting enthalpies determined in water, methanol and benzene indicate that the surface has an amphoteric character and that the carbon structure and surface chemistry are strongly affected by the heat treatment processes.     

High-strength high-modulus carbon fibres

Translated from Khimicheskie Volokna, No. 3, pp. 5–8, May–June, 1991.     

Microstructure of activated carbon fibres

Conclusions Quantitative data have been obtained on the elements of ACF microstructure and its genesis during the process of carbon fibre oxidation.The use of model concepts has made it possible to considerably expand the informativeness of the adsorption method of investigating ACF microstructure.The anisotropic ordered structure of carbon fibres makes it possible to synthesize adsorbents having a micro- or micro- and mesoporous structure with practically complete absence of macropores.On the basis of graphic dependences obtained, it is possible to predict the preparation of ACF with assigned properties.Translated from Khimicheskie Volokna, No. 6, pp. 14–16, November–December, 1987.     

Thermal conversion of carbon fibres/polysiloxane composites to carbon fibres/ceramic composites

The aim of this work is to investigate the thermal conversion of carbon fibres/polysiloxane composites to carbon fibres/ceramic composites. The conversion mechanism of four different resins to the ceramic phase in the presence of carbon fibres is investigated. The experiments were conducted in three temperature ranges, corresponding to composite manufacturing stages, namely up to 160 °C, 1000 °C and finally 1700 °C.The study reveals that the thermal conversion mechanism of pure resins in the presence of carbon fibres is similar to that without fibres up to 1000 °C. Above 1000 °C thermal decomposition occurs in both solid (composite matrix) and gas phases, and the presence of carbon fibres in resin matrix produces higher mass losses and higher porosity of the resulting composite samples in comparison to ceramic residue obtained from pure resin samples. XRD analysis shows that at temperature of 1700 °C composite matrices contain nanosized silicon carbide. SEM and EDS analyses indicate that due to the secondary decomposition of gaseous compounds released during pyrolysis a silicon carbide protective layer is created on the fibre surface and fibre–matrix interface. Moreover, nanosized silicon carbide filaments crystallize in composite pores.Owing to the presence of the protective silicon carbide layer created from the gas phase on the fibre–matrix interface, highly porous C/SiC composites show significantly high oxidation resistance.     

Anchorage of carbon nanotubes grown on carbon fibres

A novel reinforcing material based on the concept of an uniform 3-dimensional distribution of carbon nanotubes directly grown on yarns of carbon fibres has been developed. This material shows a potential for applications in polymeric matrix composites, combining the properties of carbon nanotubes with those of a traditional reinforcement.In view of the dipping process of the CNT coated fibres into a polymeric matrix, a good anchorage of CNT to the fibre surface is mandatory. Carbon fibres coated with metallic clusters and CNT were immersed into different liquids (deionised water, ethanol, n-butanol, acetone) and processed with different treatments (immersion, magnetic stirring, centrifugation and ultrasonic bath) in order to test their behaviour in different stressing environments. The morphological features of the samples were characterised by SEM both before and after the tests, demonstrating a good adhesion of the three-component material, which was not destroyed even after the most aggressive test.