SUMMARYThis paper reports an experimental investigation in designing a tree-shaped wind power system using piezoelectric materials. The proposed system has been designed to produce power if there is any wind strong enough to cause any bending in the energy converting elements, i.e. piezoelectric materials. Two different kinds of piezoelectric materials are used in this study to produce power by scavenging energy from the wind. The soft flexible one is used to make the leaf element, whereas the hard one is applied to the trunk portion of the tree requiring rather strong winds to generate any power. Although small, each leaf deems to play the role of a power producer as currents are continuously trickling down to a storage battery installed at the bottom of the system.

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The interaction forces between air bubbles and mineral surfaces were directly measured during the attachment process using an apparatus developed in our laboratory, and they are defined as the attachment forces. The attachment forces were measured between the air bubble and mineral surfaces modified with surfactants to have different hydrophobicities. Chalcopyrite and galena were used as the mineral surfaces, and their hydrophobicity was controlled by adsorbing xanthates with different hydrocarbon chain lengths. The hydrophobicity is represented by the static contact angle of water on the mineral surface. When the static contact angle was less than 90°, the attachment force increased considerably with increasing static contact angle of the surfaces, irrespective of the mineral type or the hydrocarbon chain length of the adsorbed xanthate. The hydrophobicity of the mineral surface is found to be the dominant factor determining the attachment force. The measured attachment forces agree well with those calculated based on the force balance model derived from the capillary force and Laplace pressure equation. Microflotation experiments to examine the relationship between the attachment force and flotation kinetics were carried out under the same conditions to control surface hydrophobicity. The variation in the flotation kinetic constants and attachment forces with the water contact angle are very similar. As a result, the attachment forces measured by the developed apparatus can provide quantitative information on the interaction between an air bubble and the mineral surface and can be used for predicting the flotation kinetics.

Co films were deposited by a remote plasma atomic layer deposition (ALD) method using either cyclopentadienylcobalt dicarbonyl [CpCo(CO) 2 ] or dicobalt octacarbonyl [Co 2 (CO) 8 ] as the Co precursor. The Co films deposited with the Co 2 (CO) 8 precursor showed a lower ALD process window (75 -110 C) and higher growth rate ($1:2 A ˚/cycle) than the Co films deposited with CpCo(CO) 2 which had a process window of 125 -175 C and a growth rate of $1:1 A ˚/cycle. The Co films deposited using CpCo(CO) 2 showed an oxygen content of less than 1% with both the H 2 and N 2 plasma and about 13% carbon with the N 2 plasma and about 7 -8% carbon with the H 2 plasma. In the case of Co 2 (CO) 8 , the carbon and oxygen contents were $15 and $2% with the H 2 plasma, and $8 and $21% with the N 2 plasma, respectively. The carbon impurities in the Co films deposited with CpCo(CO) 2 had a significant number of C-H bonds while Co-C bonds were dominant in the Co films deposited with Co 2 (CO) 8 . The retardation of silicide formation temperature up to 100 C for the Co films deposited with Co 2 (CO) 8 can be explained by high carbon content including Co-C bonds.

Cobalt thin films were deposited by a remote plasma atomic layer deposition (ALD) system with a metalorganic precursor of dicobalt octacarbonyl (Co2(CO)8) . To investigate the reaction kinetics and the characteristics of the Co films, we carried out experiments, varying parameters such as precursor flow rate and injection time, reactant gas flow rate, plasma power, and substrate temperature. The deposition rate of Co films was ∼1.2Å∕cycle in the ALD window of 75–110°C . The extent of impurity content such as oxygen and carbon was highly affected by plasma power. Two Co films deposited with a plasma power of 50 and 300W showed different compositional variations. The carbon content of the samples was about ∼22% and ∼15% , and oxygen content was about ∼15% and ∼2% , for deposition with plasma powers of 50 and 300W , respectively. The incorporation of impurities was caused by the incomplete decomposition of Co-CO and suppressed Co reaction on Si substrate, retarding silicide formation.

Herein, alumina foams were prepared from particle-stabilized foams, fabricated by direct foaming methods, that varied according to the concentration of sodium dodecyl sulfate (SDS). To confirm the formation mechanism of pore structures in alumina ceramic foams with varying SDS concentrations, the adsorption density, contact angle, ζ-potential, and surface tension of the alumina particles dispersed in SDS were analyzed. Additionally, model analysis was performed to confirm the interaction between alumina and air bubbles by applying the extended Derjaguin–Landau–Verwey–Overbeek model. The attachment of alumina particles to bubble surfaces at different SDS concentrations affected the pore structure of the ceramic foams; this confirmed that the attachment was significantly affected by the electrostatic interaction energy rather than hydrophobic interaction. Therefore, the pore size and connectivity of alumina foams could be controlled by varying the electrostatic interaction energy between alumina particles and air bubbles, which is determined by the SDS concentration.

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