Comparative Study on Quality of Fuel Pellets from Switchgrass Treated with Different White-Rot Fungi

Fungal pretreatment of switchgrass using Phanerochaete chrysosporium (PC), Trametes versicolor 52J (TV52J), and the Trametes versicolor mutant strain (m4D) under solid-state fermentation was conducted to improve its pellet quality. For all three fungal strains, the fermentation temperature had a significant effect (p < 0.05) on pellet unit density and tensile strength. The p-values of the quadratic models for all the response variables showed highly significant regression models (p < 0.01) except for dimensional stability. In addition, 3.1-fold and 2.8-fold increase in pellet tensile strength were obtained from P. chrysosporium- and T. versicolor 52J-treated materials, respectively. Microstructural examination showed that fungal pretreatment reduced pores in the pellets and enhanced pellet particle bonding. Among the fungal strains, PC had the shortest optimum fermentation time (21 d) and most positive impact on the pellet tensile strength and hydrophobicity. Therefore, switchgrass pretreatment using PC has the potential for resolving the challenges of switchgrass pellet transportation and storage and reducing the overall pelletization cost. However, a detailed comparative technoeconomic analysis would be required to make definitive cost comparisons.

Sequential Processing of Cold Gas Sprayed Alloys by Milling and Deep Rolling

Cold gas spraying (CS) is a solid-state material deposition process which, in addition to the flexible repair of individual component areas, also enables the build-up of larger samples. The layers are created on a substrate by the impact-induced bonding of highly accelerated micrometer particles. Since melting does not occur, the material composition can be varied flexibly and independently of material-specific melting points. In this work, the influence of the described forming process on subsequent machining by milling and deep rolling is investigated. The process forces measured during milling and the surface topography after milling and deep rolling were influenced by the material composition and the CS-related properties, e.g., high material hardness or particle bonding. In contrast to prior assumptions, deep rolling was shown to have no influence on the determined hardness depth profile for the investigated materials. Future work will focus on additional analyses, such as the determination of half-widths, to obtain further insight on the material behavior.

Effect of Pre-Treatment on Substrates for Metal Coatings Fabricated by Low Pressure Cold Spray Technique

Low pressure cold spraying is an attractive technique for onsite metal coating fabrication due to its compactness and portability. However; the bonding strength of the coating prepared by low pressure cold spraying is generally low; which restricts the further applications in engineering and industrial fields. To improve the bonding strength; pre-treatment on substrate surface can be an effective procedure. In this study; a low-temperature plasma treatment was applied to a pretreatment technique; and the effect of the treatment on particle bonding was compared with that of a laser treatment. Copper coatings on aluminum and copper substrates were selected and studied as basic metal materials. The SEM observation results show that the particle adhesion rate significantly increases by the laser and plasma treatments; due to the removal of the native oxide films on the substrates. The particle bonding on the plasma-treated substrate reveals better interfacial adhesion with less gap compared with the laser-treated one. The pre-treatment by low-temperature plasma can be an attractive technique to assist the cold spraying process due to the oxide removal ability and no thermal effect which can apply a wide range of materials.

Breakage Strength of Wood Sawdust Pellets: Measurements and Modelling

Wood pellets are an important source of renewable energy. Their mechanical strength is a crucial property. In this study, the tensile strength of pellets made from oak, pine, and birch sawdust with moisture contents of 8% and 20% compacted at 60 and 120 MPa was determined in a diametral compression test. The highest tensile strength was noted for oak and the lowest for birch pellets. For all materials, the tensile strength was the highest for a moisture content of 8% and 120 MPa. All pellets exhibited a ductile breakage mode characterised by a smooth and round stress–deformation relationship without any sudden drops. Discrete element method (DEM) simulations were performed to check for the possibility of numerical reproduction of pelletisation of the sawdust and then of the pellet deformation in the diametral compression test. The pellet breakage process was successfully simulated using the DEM implemented with the bonded particle model. The simulations reproduced the results of laboratory testing well and provided deeper insight into particle–particle bonding mechanisms. Cracks were initiated close to the centre of the pellet and, as the deformation progressed, they further developed in the direction of loading.

Co(OH)2/TiO2 Nanotube Composite for High-Rate Performance Supercapacitor

The TiO2 nanotube arrays were prepared on Ti plate by anodizing technology, and then Co (OH)2 nanoparticles in-situ grew into TiO2 nanotubes with "Tube-particle bonding" nanocomposited structure. Co (OH)2 nanoparticles with a particle size of 40.5±8 nm were infiltrated in the TiO2 nanotube arrays, and the Co (OH)2 outside the tube presented a nanosheet structure. The specific capacitance of the Co (OH)2/TiO2 nanotube array composite reached 260 F/g at the current density~1 A/g. The capacity retention rate was 82.5 % after 2,000 cycles at the current density~5 A/g. The high-rate performance of the Co (OH)2/TiO2 nanotube array composite reached 210 F/g at the current density~10 A/g.