Shuangling Jin

Effects of Heat-Treatment Temperature and Binder Content on the Microstructure and Thermal Conductivity of Graphite Flake-Carbon Composites

In this work, graphite flake-carbon composites were fabricated from natural graphite flake and spinning pitch by a hot-pressing technique at 500°C and 10 MPa. The X-ray pole figure measurements show that the orientation degree of graphitized composite is higher than that of hot-pressed and carbonized composite and presents a descending tendency from 74.4 to 71.2% when the pitch content increases from 4 to 14 wt.%. A reducing trend of d002 and an increasing tendency of the average crystallite diameter (La), crystallite stack height (Lc) and degree of graphitization (g) can also be observed when pitch fraction increases from 4 to 16 wt.%. The apparent density and thermal conductivity in the direction perpendicular to the hot-pressing direction of graphitized composite with 16 wt.% of binder all achieve maximum values, 1.930 g/cm3 and 485 W/m K, respectively.

Effect of carbonization temperature on microwave absorbing properties of polyacrylonitrile-based carbon fibers

ABSTRACT The pre-oxidized fibers were carbonized at the temperature ranging from 400 to 1300 °C for 1 h. The microwave absorption properties of carbon fibers (CFs) were examined in the frequency range of 2–18 GHz. It is found that the reflection loss characteristics are highly sensitive to the carbonization temperature. At a thickness of 2 mm, the CFs obtained at 710 °C exhibit the best microwave absorbing ability with a maximum reflection loss of −22.9 dB at 15 GHz, and a bandwidth exceeding −10 dB in the range 12.4–18 GHz. Results indicate that dielectric loss in cooperation with better matched characteristic impedance results in the excellent microwave absorption of CFs. Low temperature makes ϵ′ and ϵ″ too small to consume the energy of microwave, while over high temperature makes ϵ′ and ϵ″ too large to transmit the microwave into the CFs.

Facile preparation of TiO2/C nanocomposites as anode materials for lithium-ion batteries

ABSTRACT TiO2/C nanospheres with diameter of 300–400 nm were synthesized by controlled thermal decomposition of titanium glycolate spheres in inert atmosphere. The effect of the calcination temperature and atmosphere on the structure and composition of the product are investigated. The products obtained by calcination of the precursor in nitrogen at 500°C consist of anatase and rutile nanoparticles, and amorphous carbon that is in situ generated from the organic components of glycolate precursor. When used as anode material for lithium-ion batteries, the as-prepared TiO2/C nanocomposite delivers a capacity of 166 mAh/g after 250 charge/discharge cycles at a current rate of 0.2 C and give a good rate capability. The native carbon not only improves the local conductivity but also prevents the aggregation and growth of TiO2 nanoparticles during calcination, allowing efficient electronic conductivity and Li ion diffusion.

Synthesis and characterization of Al 2 O 3 -C hybrid aerogels by a one-pot sol-gel method

Abstract Al 2 O 3 -C hybrid aerogels were prepared by a one-pot sol-gel method, supercritical n-hexane drying and carbonization using Al(NO 3 ) 3 ·9H 2 O as the Al 2 O 3 source, resorcinol (R) and furfural (F) as carbon precursors, and propylene oxide (PO) as a gelation initiator. The effects of the Al 2 O 3 contents, the R+F concentrations and the PO/Al molar ratios on the porosity of the hybrid aerogels were investigated using a constant R/F molar ratio of 0.5. It was found that the hybrid aerogels are all mesoporous with an average pore size below 20 nm. The crystalline structure of Al 2 O 3 is γ -type, but its diffraction peaks are quite broad. The hybrid aerogels are monolithic when the Al 2 O 3 content is below 5.31 wt% with an R+F concentration of 10 g/100 mL. The mesopore volume and size, BET surface area and external surface area all increase with increasing PO/Al molar ratio under otherwise identical conditions. The volume shrinkage decreases, carbonization yield increases and the density of the hybrid aerogel exhibits a maximum with an Al 2 O 3 content of 4.93 wt%. The size and volume of the mesopores, and the external surface area decrease with the increasing R+F concentration at PO/Al ratios of 5 and 6, but increase with increasing R+F concentration at a PO/Al ratio of 4.

Experiments and modeling for thermal conductivity of graphite nanoplatelets/carbon composites

ABSTRACT In this work, the graphite nanoplatelets/carbon composites were fabricated from graphite nanoplatelets and pitch powders by a hot-pressing technology followed by carbonization and graphitization. The XRD and pole figure results show that the incorporation of pitch induces the decrease of size (La) and orientation degree of graphitic crystallites, while the in-plane thermal conductivity of graphitized sample is increased with the increasing pitch content up to 6 wt.%, achieving a maximum value of 405 W/m K. The pitch binders are filled into the voids to bridge two or more graphite nanoplatelets particles together to form extra thermal paths, which makes a great contribution to the enhancement of thermal conductivity. A thermal conductivity model for the graphitized composites is constructed based on a bridging mechanism, and the predicted results fit well with the experimental results.

Synthesis of alumina aerogels from AlCl3·6H2O with an aid of acetoacetic-grafted polyvinyl alcohol

AbstractAlumina aerogels are prepared from the cheap AlCl3·6H2O precursor by the sol-gel method using acetoacetic-grafted polyvinyl alcohol (acac-PVA) as a template and dispersing agent, and propylene oxide as a gelation initiator. The acac-PVA has a high dispersing ability for Al3+ ion through complexation interaction and increases the content of AlCl3·6H2O in sols to as high as 37 wt%, leading to the formation of wet gels without precipitate and crack, and little shrinkage. As-prepared alumina aerogels have high density, high mechanical strength, high mesoporosity, and high-surface area. The shrinkage in supercritical drying processes is greatly reduced. The specific surface area increases and pore size decreases with increasing the content of the acac-PVA in sols. The acac-PVA also acts as a template that provides nucleation sites for boehmite AlOOH particles and inhibits their growth. An excess content of the acac-PVA isolates secondary particles, weakens the interaction between them, and therefore decreases the Young’s modulus. Coarsening is not alleviated obviously after removal of the acac-PVA by high-temperature treatment in air, and the fine primary particles grow into nanorods with diameters of 10–20 nm and lengths of 30–70 nm. HighlightsAcetoacetic group is grafted on polyvinyl alcohol via esterification reaction with a -OH conversion of about 80%.Acetoacetic group on polyvinyl alcohol forms complex with Al3+ and Al-clusters to obtain AlCl3·6H2O sols with a high concentration.The shrinkage of gels in sol-gel and supercritical drying steps are decreased significantly via an aid of the acetoacetic-grafted polyvinyl alcohol.The resulting aluminum aerogels have a high density, high mechanical strength, and high mesoporosity.

Adsorption of thiophene, dibenzothiophene, and 4,6-dimethyl dibenzothiophene on activated carbons

Four activated carbons (ACs) activated by different activation methods from different precursors were heat-treated at 600℃ to decrease surface oxygen functional groups and to separate the effect of pore texture from surface chemistry on their sulfur adsorption performance. The ACs and the heat-treated ones were used as adsorbents for thiophene (T), dibenzothiophene (DBT), and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) for model fuels with or without a competing benzene. The correlations of surface functional groups and pore textures to their adsorption capacities for T, DBT and 4,6-DMDBT were investigated. Results indicated that the heat treatment not only decreased surface oxygen content, but also caused a pore texture modification. The adsorption isotherms can be well fitted by the Langmuir–Freundlich single solute isotherm. The sulfur adsorption capacity of ACs after the treatment for T, DBT, and 4,6-DMDBT has a good linear relationship with the pore volume of pores within 0.536–1.090, 0.536–1.179, and 0.679–1.268 nm, respectively. The decreased percentage of surface oxygen of ACs by the heat treatment is correlated linearly with the decreased percentage of the sulfur adsorption capacity for all the thiophenic compounds. Micropore filling via the π–π interaction is the dominant adsorption mechanism of thiophenic compounds for both the untreated and heat-treated ACs. Surface oxides contribute to the thiophenic adsorption by a cooperative interaction of the π–π interaction and the acid–base interaction between the basic sulfur atom and the acidic carbon atoms linked with oxygen in graphene edges. A flat adsorption is the most possible geometry in the adsorption of thiophenic compounds.