Yuehua Cui

Size-dependent thermal oxidation of copper: single-step synthesis of hierarchical nanostructures

Thermal oxidation of copper is a simple and scalable method to produce copper oxide nanowires. We report for the first time the formation of nanowires on copper powder during thermal oxidation and the resulting nanowire coverage that is dependent on the initial particle size. Systematic thermogravimetric analysis (TGA) and in situ X-ray diffraction (XRD) studies of thermal oxidation of particles of different sizes provide insights into the size-dependent process and evolution of the various phases of copper and copper oxide with time. Furthermore, we find that a large void is formed within these particles after oxidation and propose a mechanism based on the Kirkendall effect. The unique tunability of hierarchical features and hollow interior can be used to create new scalable structures for applications in a variety of areas including thermal management and catalysis.

Superhydrophobic polymer surface via solvent-induced crystallization

We report on a rapid, single-step method to produce large-area superhydrophobic surfaces via acetone-induced phase transformation of polycarbonate. Crystallization of the polymer leads to the formation of a hierarchical structure composed of microporous spherulites covered with nano-fibrils, and resulted in superhydrophobic wetting behavior. A systematic study of the dependence of surface morphology on the acetone treatment time was conducted to optimize the treatment time and to elucidate the structure formation mechanism. The resulting surfaces exhibit high contact angles, low contact angle hysteresis, and complete dewetting during droplet impact. Theoretical analysis of the wetting and anti-wetting pressures shows that the nano-scale morphology is critical for achieving droplet impact resistance. This simple phase transformation approach could be more broadly applied to other solvent-polymer systems for fabricating large-area hierarchical surface textures.

Effects of Promoter La2O3 and Supports on Kinetic Parameters of Dissociation Activation of Methane over Ni-Based Catalysts

Abstract The influence of MgAl 2 O 4 and α-Al 2 O 3 supports, and La 2 O 3 promoter on the methane dissociation was studied by pulsing methane over catalysts Ni/α-Al 2 O 3 (A), Ni/La 2 O 3 /α-Al 2 O 3 (A-L), Ni/MgAl 2 O 4 (M), and Ni/La 2 O 3 /MgAl 2 O 4 (M-L). In these unsteady pulse reactions, the carbon species coverage on the catalysts was kept less than 100% and the information about methane dissociation on the fresh Ni active sites was disclosed. Kinetic parameters for the methane dissociation over these catalysts were obtained under reaction conditions free from heat and mass transfer limitations. The methane dissociation activation energy ( E a ) on catalysts A, A-L, M, and M-L is 90.9, 111.8, 79.5, and 85.9 kJ/mol, respectively. The E a values on catalysts M and M-L are lower than those on catalysts A and A-L. The La 2 O 3 promoter increases the E a of methane dissociation. There is a compensation effect between the activation energy and the pre-exponential factor in the methane dissociation on the Ni-based catalysts, which reduces the influence of the supports and promoter on the methane dissociation.

Scalable manufacturing of hierarchical nanostructures for thermal management

Thermal oxidation of copper is a simple and scalable method to produce copper oxide nanowires. We report for the first time the formation of nanowires on copper powder during thermal oxidation and the resulting nanowire coverage that is dependent on initial particle size. Systematic thermogravimetric analysis (TGA) and in-situ x-ray diffraction (XRD) studies of thermal oxidation of particles of different sizes provide insights into the size-dependent process and evolution of the various phases of copper and copper oxide with time. Furthermore, we find that a large void is formed within these particles after oxidation and propose a mechanism based on the Kirkendall effect. Using this new size-dependent oxidation process, we demonstrate the simple and scalable creation of new hierarchical structures for applications in thermal management, including electronics cooling and boiling.

Kinetic depressing the deposition of carbon species on ni-based catalysts: La2o3 adjusts the reaction rates of CO2 higher than CH4 by tuning the ea and pre-exponential factor

The same amount of CH 4 and CO 2 was pulsed through the catalysts Ni/a-Al 2 O 3 (A) and Ni/La 2 O 3 /α-Al 2 O 3 (AL) in 773-873 K to study the deposition rates of carbon species CH x (0≤x≤3) under the kinetic conditions. The pulse tests provided the possibility of non-deposition of carbon species on the catalyst AL. After elimination of the contribution of CO 2 rates in RWGS, the deposition of carbon species can be avoided on the catalyst AL for the reforming of equal molar of CH 4 and CO 2 under the kinetic conditions in 773-873 K.