Enhanced performance of Al₂O₃–SiC–C castables via in-situ formation of multi-reinforced phases by introducing surface treated composite metal powders

Al2O3–SiC–C (ASC) castables were prepared with bauxite and silicon carbide as major raw materials and introducing large amount of surface treated composite metal powders (STCMPs) as antioxidant. Their comprehensive properties were greatly improved attributed to the in situ formation of multi-reinforced phases including carbide silicon whiskers and mullite fibers in the matrix. Compared with the corresponding samples without STCMPs, the high temperature modulus of rupture of those with 6 wt% STCMPs calcined in air increased by 47.3% and with 8 wt% STCMPs calcined in reducing atmosphere increased by 220%. The retained CMOR ratio of the sample with 6 wt% STCMPs calcined in reducing atmosphere was high up to 50% after 5 cycles thermal shocks. Moreover, the oxidation index and slag erosion index of samples with 6 wt% STCMPs were decreased by 45% and 74%. This work provides a new perspective for the preparation of ASC castables with excellent high-temperature performance.</p

Honeycombed activated carbon with greatly increased specific surface by direct activation of glucose for supercapacitors

In the production of activated carbons (ACs), glucose as a precursor is prone to producing the graphitic char intermediates after carbonization, which are difficult to be activated in the subsequent activation. In order to obtain a desirable specific surface area, either twice activation after carbonization or hydrothermal treatments of glucose before activation is applied. In this research, the direct activation of glucose has been executed to produce honeycombed ACs via deoxygenation of the glucose precursor in the KOH aqueous solution for appropriate time at room temperature. It is found that when glucose is subjected to the alkaline circumstance, dehydration and polymerization reactions increase the C/O ratio while the degradation and oxidation decrease the C/O ratio. The AC from the deoxygenated product with the highest C/O ratio has a superior specific surface area of 1912 m2 g−1 which is much higher than 130 m2 g−1 for the AC by the conventional two-step method. The Honeycombed morphology and the specific surface increased by one order of magnitude lead to good performance of 268 F g−1 in the KOH and 24.5 Wh kg−1 in the KBr electrolyte

Effects of pore widening vs oxygenation on capacitance of activated carbon in aqueous sodium sulfate electrolyte

The commercial activated carbon has a relatively low specific capacitance in the Na2SO4 electrolyte, which hinder the development of asymmetrical supercapacitors with high voltage. Re-activation and oxidative etching methods were applied to change the pore structure of activated carbon, respectively, to study the capacitive behavior of carbon in the Na2SO4 electrolyte. The pore distributions combining with capacitive properties deduce that 0.85 nm is the threshold diameter of the ion-accessible micropores for hydrated Na+ and SO42−. The specific capacitances of both the carbon materials by re-activation and oxidative etching methods are increased by 40 %, in comparison with the commercial activated carbon. The enhanced capacitive performances of the carbon materials were mainly attributed to the increased ion-accessible specific surface area and pseudocapacitance, respectively. The oxidative etching is a more facile and economical method for practice application. Combining with MnO2 as the positive electrode, the asymmetrical supercapacitor with a high voltage of 1.8 V exhibits a maximum specific cell capacitance of 50 F g–1 and specific energy of 22.5 Wh kg–1

Molecular level one-step activation of agar to activated carbon for high performance supercapacitors

Activated carbon was synthesized by a simple one-step calcination of deoxygenated agar in a hot KOH aqueous solution, in which KOH plays both deoxidant and activation agent. The deoxygenation course omits high temperature carbonization in the conventional technology and leads to molecular level activation of agar in subsequent one-step calcination. The one-step activated carbon has superior specific surface area of 1672 m2 g−1 and total pore volume of 0.81 cm3 g−1. It also shows a maximum specific capacitance of 226 F g−1 in the KOH electrolyte, which is 1.4 times as high as that for the activated carbon by the conventional two-step method. This study provides potentially economical and effective means for the production of commercial activated carbon with high porosity for supercapacitors

Investigation on Application Prospect of Refractories for Hydrogen Metallurgy: The Enlightenment from the Reaction between Commercial Brown Corundum and Hydrogen

Hydrogenous environments put forward new requirements to refractories for the hydrogen metallurgy field. The temperature and impurities in refractories played an important role in stability. A commercial brown corundum with many impurities was adopted as a raw material, thermodynamic calculations and reduction experiments of the brown corundum by high-purity hydrogen (99.99%) were accepted to investigate the stability of the oxides. The weight loss and mass fraction were tested to estimate the stability of the oxides in the brown corundum. XRD and SEM were used to analyze the mineral compositions and microstructures. The results showed that: the thermodynamic stability of the oxides in the brown corundum under high-purity hydrogen was in the order of Al2O3 &gt; CaO &gt; MgO &gt; SiO2 &gt; TiO2 &gt; Fe2O3 at temperatures lower than 1400 &deg;C. Obvious weight loss appeared after heating at 1400 &deg;C for 8 h. The content of CaO did not decline after reduction even at 1800 &deg;C, owing to the formation of hibonite (CaAl12O19), high-purity Al2O3 and CaAl12O19 -based refractories had the prospect for lining materials in the hydrogen metallurgy field, owing to their excellent chemical stability under hydrogenous environments

Improved Mechanical Properties of Alumina Ceramics Using Plasma-Assisted Milling Technique

In order to improve the mechanical properties of alumina ceramics, dielectric barrier discharge plasma-assisted milling (DBDPM) was employed to activate alumina powder. The effect of the plasma-assisted milling technique on the grinding behavior of alumina powder, as well as the microstructure and properties of fabricated alumina ceramic, was investigated in detail. Attributed to the great thermal stress induced via plasma heating, DBDPM showed significantly higher grinding efficiency than the common vibratory milling technique. Moreover, the lattice distortion of alumina grains occurred with the application of plasma, leading to an improved sintering activity of the produced alumina powders. Therefore, compared with the common vibratory milling technique, the fabricated alumina ceramics exhibited smaller grain sizes and improved mechanical properties when using alumina powder produced via the DBDPM method as the starting material

Simultaneous enhance of the thermal shock resistance and slag-penetration resistance for tundish flow-control refractories: The role of microporous magnesia

As the low thermal shock and slag-penetration resistance of the magnesia castables cause the premature failure of tundish flow-control devices leading to the pollution of steel, the microporous magnesia with high closed porosity and intergranular CaZrO3 phase was utilized for simultaneously enhancing the high-temperature performance. The thermomechanical stress and slag corrosion tests indicated that since the micro-closed pores effectively relieved the thermal stress and CaZrO3 absorbed massive crack-propagation energy, the cold modulus of rupture and residual strength ratio respectively reached 14.4 MPa and 73.4% after thermal shock cycles, nearly half higher than that of the fused magnesia based castables. Meanwhile, the synergistic effect of micro-closed pores and intergranular CaZrO3 phase significantly reduced the slag-wettability, improved the interfacial energy and dihedral angle, leading to the decline of slag penetration indice (decreased by ∼34.8%). This study suggests a potential approach to generate new magnesia based castables in tundish for making clean steel