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Thermal Treatment and Inorganic Particles Modification on Pitch of TiB2/C Composite Cathode for Aluminum Electrolysis

Author: ZuoJian
Tutor: LaiYanQing；LvXiaoJun
School: Central South University
Course: Non-ferrous metallurgy
Keywords: aluminium electrolysis TiB2/C composite cathode modified pitch thermal treatment inorganic particles
CLC: TQ522.65
Type: Master's thesis
Year: 2011
Downloads: 33
Quote: 0
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Abstract


This thesis is funded by the National High Technology Research and Development Program (863 program) and the National Science & Technology Pillar Program, aiming at developing satisfactory TiB2/C composite cathode material for aluminum electrolysis. In order to improve properties of composite cathode, binder pitches were modified by thermal treatment and inorganic particles. Effects of thermal treatment temperature, thermal treatment time, kinds and additive amount of inorganic particles on structure and properties of modified pitches and TiB2/C composite cathodes were investigated. The major results are summarized as follows:(1) With the increase of thermal treatment temperature and thermal treatment time, reaction yield of modified pitch decreased while their softening point, viscosity, coking value and apparent activation energy all increased. When thermal treatment temperature increased from 200℃to 400℃, the coking value and apparent activation energy increased from 60.62 wt.% to 84.89 wt.%. When thermal treatment time stretched from 0.5 h to 4.0 h, the coking value increased from 61.84 wt.% to 76.20 wt.%.(2) With the increase of additive amount of inorganic particles, both reaction yield and coking value of modified pitch increased. Compared with the contrast sample, softening point, viscosity and apparent activation energy of inorganic particles based modified pitches all decreased. When additive amount of inorganic particles increased from 2.5 wt.% to 15 wt.%, coking value of A12O3 particles based modified pitch increased from 62.44 wt.% to 67.14 wt.%, and that of TiB2 particles based modified pitch increased from 62.26 wt.% to 67.38 wt.%. When additive amount was 10 wt.%, apparent activation energy of TiB2 particles based pitch had a bigger decrease, compared to contrast sample, it was decreased by 6.29%。(3) With the increase of thermal treatment temperature and thermal treatment time, open porosity of modified pitch based TiB2/C composite cathode decreased while bulk density and compressive strength increased, however, both electrical resistivity and electrolysis expansion first decreased and then increased. When thermal treatment temperature increased from 200℃to 400℃, open porosity decreased from 34.35 vol.% to 27.22 vol.% while bulk density and compressive strength increased from 2.24 g/cm3 to 2.39 g/cm3 and from 24.23 MPa to 54.51 MPa, respectively. When thermal treatment time stretched from 0.5 h to 4.0 h, open porosity decreased from 35.11 vol.% to 29.50 vol.% while bulk density and compressive strength increased from 2.24 g/cm3 to 2.36 g/cm3 and from 25.77 MPa to 43.18 MPa, respectively. When pitch was modified at 300℃for 2 h, both electrical resistivity and electrolysis expansion of cathode reached the minimum, compared to contrast cathode, they were decreased by 13.63% and 28.57%, respectively.(4) With the increase of additive amount of inorganic particles, open porosity of cathode decreased while bulk density increased, but compressive strength first decreased and then increased. Meanwhile, electrical resistivity of A12O3 particles modified pitch based cathode also first decreased and then increased, but that of TiB2 particles modified pitch based cathode gradually decreased. Additionally, compared with contrast cathode, inorganic particles modified pitch based cathode had a lower electrolysis expansion. When additive amount of A12O3 particles increased from 2.5 wt.% to 15 wt.%, bulk density of cathode increased from 2.244 g/cm3 to 2.265 g/cm3 while open porosity decreased from 34.33 vol.% to 32.35 vol.%. When additive amount of TiB2 particles increased from 2.5 wt.% to 15 wt.%, bulk density increased from 2.254 g/cm3 to 2.302 g/cm3 while open porosity decreased from 34.28 vol.% to32.00 vol.%. When additive amount was 10 wt.%, TiB2 particles modified pith based cathode had the lowest electrolysis expansion, compared with contrast cathode, which was decreased by 20.51% while its electrical resistivity was decreased by 5.63% and its compressive strength was increased by 15.00%.

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