Preparation,Structure and Properties of Mesophase-pitch Based Carbon Foams and Composites

Author:Liu He Guang

Supervisor:li tie hu

Database:Doctor

Degree Year:2017

Download:127

Pages:120

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Carbon foam prepared from mesophase pitch is a kind of novel carbon materials,which possesses three-dimensional sponge-like foam structure.Due to its excellent features,such as light weight,high strength,controllable thermal conductivity,high temperature resistance,corrosion resistance,electromagnetic shielding and high electrical conductivity,this kind of foam materials shows wide potential in numerous fields,such as electrical conduction,absorption,thermal protection,thermal conduction and electromagnetic protection,etc.Herein,carbon foams were prepared using mesophase pitches obtained from thermal polycondensation treatment of economic coal tar pitches,via foaming,carbonization process and graphitization process.The present work revealed the effect of mesophase pitch’s feature on the foam structure of resultant carbon foam.And the preparation of composite materials based on carbon foam was investigated,as well as the influence of different additive on the structure and performance of carbon foam.In addition,the potential application of the obtained composite based on carbon foam in various fields,such as thermal insulation,electrical conduction,thermal conduction and electromagnetic interference shielding,were discussed respectively.The research contents can be summarized as follows.Different mesophase pitches were synthesized under the same pressure and soaking time using medium coal tar pitch as raw material,via thermal polycondensation method.And the corresponding carbon foams were also prepared using the obtained mesophase pitches using foaming and carbonization process.The results showed that the content of secondary quinoline insoluble(QI)increased with the increase in the temperature.However,the foam structure could not be obtained at a poor secondary QI content.When the amount of secondary QI content is enough to form foam structure,the foam size increased firstly and then decreased with the increase of the secondary QI content,and the compressive strength of carbon foams decreased firstly and then increased.High temperature coal tar pitches were modified using boric acid and cinnamaldehyde(CMA)as agents,and mesophase pitches were obtained via thermal polycondensation treatment of modified coal tar pitches.Then carbon foams were prepared from mesophase pitches via foaming and carbonization process.The results showed that the performance and structure of modified coal tar pitches were totally different with the original coal tar pitches.And the mesophase pitches prepared from modified coal tar pitches possessed higher mesophase content than that of original coal tar pitches,exhibiting different properties with mesophase from original coal tar pitched.In addition,compared with carbon foams from original coal tar pitches,carbon foams from modified coal tar pitches showed more ordered and well-organized foam structure,as well as the better foam size distribution and mechanical strength.Particularly,the compressive strength of carbon foam from modified coal tar pitch(using 3 g boric acid and 7 g CMA)reached a maximum of 21.27 MPa.Silica aerogel/carbon foam composite material was prepared using medium coal tar pitch and TEOS as starting materials,via impregnation method under ambient pressure and spontaneous foaming method,respectively.And the thermal insulation performance of the obtained composites was investigated.For the compsite obtained by impregnation method under ambient pressure,it showed that silica aerogel was successfully formed in the surface foam cells of the obtained carbo foam.The possessed a thermal conductivity of 0.169 W/m·K,exhibiting a better thermal insulation property than that of neat carbon foam(improved by 41.9%).Moreover,the compressive strength testing results indicated that the mechanical strength of carbon foam was not significantly affected by the silica aerogel located in the surface foam cell.With regarding to the composite obtained by spontaneous foaming method,the addition of silica aerogel had an obvious effect on the thermal insulation and mechanical performance.The thermal coductivites of composite firstly decreased and then increased with the increase of silica aerogel.When the additive amount of silica aerogel was 11 wt%,the thermal conductivity of composite reached a minimum of0.254W/m·K.Furthermore,the compressive strength of composite firstly increased and then decreased with the increase of silica aerogel amount.And the compressive strength of composite reached a maximum of 12.72 MPa,while the additive amount of silica aerogel was 8 wt%.Multi-walled carbon nanotube(MWCNTs)/carbon foam composite materials were synthesized using mesophase pitch and modified MWCNTs as precursors,via foaming,carbonization process and graphitization process.We studied the influence of MWCNTs additive content on the mechanical strength,thermal conduction and electrical conduction performance of carbon foams.The results exhibited that the foam structure of carbo foams was significantly influenced by the addition of MWCNTs.The compressive strength of the obtained composites increased firstly and then decreased with the increase of MWCNTs content,and the maximum was 11.72MPa.At the same time,the thermal conductivity of carbon foam also exhibited a same variation tendency with the increase in MWCNTs additive content.When the additive amount of mMWCNTs was 2 wt%,the thermal conductivity of the obtained composite reached a maximum of 25.01 W/m·K at room temperature.In addition,due to the excellent electrical conduction performance of MWCNTs,the electrical conductivity of the obtained composites increased continuously with the increase in MWCNTs additive content.And the electrical conductivity of the obtained composite reached a maximum of 28.89×10~3 S/m,as the additive amount of MWCNTs was 4wt%.Ni-Zn ferrite/carbon foam composite materials were prepared using mesophase pitch and Ni-Zn ferrite powder as precursors,by foaming and carbonization process.It was found that the electromagnetic interference shielding performance of carbon foams in X band frequency was reinforced by the addition of Ni-Zn ferrite.The total shielding effectiveness of the obtained composites increased with the increase in the additive amount of Ni-Zn ferrite,and it reached a maximum of 42dB as the additive amount of Ni-Zn ferrite was 15 wt%.Furthermore,the addition of Ni-Zn ferrite also had an influence on the mechanical strength of the obtained composites.The compressive strength of the obtained composites increased firstly and then decreased as the increase of Ni-Zn ferrite content.When the additive amount of Ni-Zn ferrite was 11 wt%,the compressive strength of carbon foam reached a maximum of 13.43MPa.