Processing and characterization of cobalt nanowires-growth characteristics and thermal characterization of cobalt nanowire modified nanofluid

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Ali Imran Shiave (Creator)
Institution
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/
Advisor
LaJeunesse LaJeunesse

Abstract: Cobalt (Co) 1-D nanostructures commonly known as nanowires, based on one of five ferromagnetic materials have attracted interest from researchers because of their potential applications in various fields. In particular, novel and suitable methods to grow nanowires that are simple, scalable, cheap and environmentally benign are also of great interest. Various approaches have been employed to grow metal nanowires; however, each process has their own set of advantages and disadvantages. Template Assisted electrodeposition (TAE) of nanowire growth in which solid templates act as a scaffold for the growth of the nanowire, is recognized as the best approach to grow pure metal nanowires for several reasons. The TAE process is simple to adopt, scalable, and cheap. TAE allows for the generation of a broad range of nanowire morphologies and sizes as the templates control the nanowire dimensions during synthesis; the growth of nanowires is governed by the dimensions of the template’s nano-channels. However, there are many challenges in this process as even a minor change in any processing conditions i.e. bath temperature, solution pH, mechanical conditions/agitation, current density, etc. can and will change the properties of formed nanowires. This high sensitivity of the nanowire synthesis process is why it is necessary to determine and define the relationship between various processing conditions and their effect on nanowire properties and characteristics. Another major problem with TAE nanowire fabrication is the polycrystalline natures of yielded nanowires. Although some research groups have shown that it is possible to growsingle-crystalline nanowires using this approach, the conditions and factors that controlcrystallinity still remain unclear.1-D nanostructures (that are composed of a metal, a metal oxide, or a non-metal)possess completely different properties compared to the same bulk materials and areuseful in different applications. Metallic nanowires offer superior properties e.g. thermal,electrical, and mechanical when compared to nanowires composed of metal oxides ornon-metals. Metallic materials have higher thermal conductivities than most materials(apart from some exceptions such as diamond) and have been used for decades forefficient thermal transport; metal nanowires are no different and have a similar set ofproperties that provide enormous potential in electronic and sensor applications whichrequire thermal transport and management. This is especially true in our current world ofminiaturization, where effective and efficient heat transport and transfer mechanisms arecritical. From small electronic devices to giant industrial machinery, improved capacityfor the dissipation of thermal energy results in better performance. Conventional coolantsi.e. water, ethylene glycol, and oil are currently being used in heat transfer andtemperature management applications although thermal conductivity of these fluids ispoor. If incorporated successfully, metal nanowires can offer a potential solution to thisproblem. Metal based nanofluids will play an important role in efficient heat transfer.However, current work with nanofluids (both metal and non-metal), have only involvedthe use of 0-D nanostructures and there has been little work done with 1-D nanowirebased fluid materials. The major challenge in using 1-D nanostructure based nanofluidshas been the difficulty of stabilizing 1-D nanofluids. Heat transfer nanofluids that are notwell stabilized will lead to settlement of added nano level constitutes thus clogging the heat transfer channels. Metallic nanofluid, composed of ferromagnetic metals such as iron, cobalt, and nickel offers several advantages beyond a more efficient heat transfer media. Further, due to the ferromagnetic nature of cobalt, a cobalt nanofluid has several advantages including a more efficient cleaning process for the clogged channels which could overcome the problems posed by sedimentation easily.Cobalt (Co) 1-D nanostructures commonly known as nanowires, based on one of five ferromagnetic materials have attracted interest from researchers because of their potential applications in various fields. In particular, novel and suitable methods to grow nanowires that are simple, scalable, cheap and environmentally benign are also of great interest. Various approaches have been employed to grow metal nanowires; however, each process has their own set of advantages and disadvantages. Template Assisted electrodeposition (TAE) of nanowire growth in which solid templates act as a scaffold for the growth of the nanowire, is recognized as the best approach to grow pure metal nanowires for several reasons. The TAE process is simple to adopt, scalable, and cheap. TAE allows for the generation of a broad range of nanowire morphologies and sizes as the templates control the nanowire dimensions during synthesis; the growth of nanowires is governed by the dimensions of the template’s nano-channels. However, there are many challenges in this process as even a minor change in any processing conditions i.e. bath temperature, solution pH, mechanical conditions/agitation, current density, etc. can and will change the properties of formed nanowires. This high sensitivity of the nanowire synthesis process is why it is necessary to determine and define the relationship between various processing conditions and their effect on nanowire properties and characteristics. Another major problem with TAE nanowire fabrication is the polycrystalline natures of yielded nanowires. Although some research groups have shown that it is possible to grow single-crystalline nanowires using this approach, the conditions and factors that control crystallinity still remain unclear. 1-D nanostructures (that are composed of a metal, a metal oxide, or a non-metal) possess completely different properties compared to the same bulk materials and are useful in different applications. Metallic nanowires offer superior properties e.g. thermal, electrical, and mechanical when compared to nanowires composed of metal oxides or non-metals. Metallic materials have higher thermal conductivities than most materials (apart from some exceptions such as diamond) and have been used for decades for efficient thermal transport; metal nanowires are no different and have a similar set of properties that provide enormous potential in electronic and sensor applications which require thermal transport and management. This is especially true in our current world of miniaturization, where effective and efficient heat transport and transfer mechanisms are critical. From small electronic devices to giant industrial machinery, improved capacity for the dissipation of thermal energy results in better performance. Conventional coolants i.e. water, ethylene glycol, and oil are currently being used in heat transfer and temperature management applications although thermal conductivity of these fluids is poor. If incorporated successfully, metal nanowires can offer a potential solution to this problem. Metal based nanofluids will play an important role in efficient heat transfer. However, current work with nanofluids (both metal and non-metal), have only involved the use of 0-D nanostructures and there has been little work done with 1-D nanowire based fluid materials. The major challenge in using 1-D nanostructure based nanofluids has been the difficulty of stabilizing 1-D nanofluids. Heat transfer nanofluids that are not well stabilized will lead to settlement of added nano level constitutes thus clogging the heat transfer channels. Metallic nanofluid, composed of ferromagnetic metals such as iron, cobalt, and nickel offers several advantages beyond a more efficient heat transfer media. Further, due to the ferromagnetic nature of cobalt, a cobalt nanofluid has several advantages including a more efficient cleaning process for the clogged channels which could overcome the problems posed by sedimentation easily. My dissertation focuses on several areas critical to synthesis, characterization of cobalt nanowires, and application of metallic nanofluids, specifically cobalt nanowire based nanofluid. In my research (1) I have developed a protocol for the synthesis of cobalt nanowire and successfully synthesized Co nanowire using template-assisted electrodeposition technique; (2) I have defined and understood morphological and structural effects of various deposition parameters i.e. bath temperature, current density; (3) I have proposed and established growth models for these nanowires and the associated mechanisms of growth; (4) I have prepared stabilized Cobalt nanowire based nanofluids in an aqueous medium; (5) I have determined effective thermal conductivity of a cobalt-nanowire nanofluid that are composed of different levels of nanowire concentration and (6) I have demonstrated the application and showed the efficacy of a cobalt-nanowire nanofluid in simple heat exchanger set up.

Additional Information

Publication
Dissertation
Language: English
Date: 2020
Keywords
Characterization, Cobalt, Electrodeposition, Nanofluid & Colloid, Nanowire Synthesis, Processing
Subjects
Nanowires $x Electric properties
Nanofluids $x Thermal properties
Cobalt $x Thermal properties

Email this document to