Dynamics of electrocrystallization of dendritic zinc deposits in galvanostatic and potentiostatic modes

In the work the dynamics of growth of zinc dendritic deposits in the galvanostatic and potentiostatic modes from an electrolyte containing 0.3 mol/L of ZnO, and 4 mol/L of NaOH has been studied. It has been shown that in galvanostatic conditions decrease in the elongation rate of dendrites and change in the deposit structure from dendritic to compact accompanied by increasing density and decreasing through-thickness porosity are observed. In potentiostatic conditions dendrites grow at a constant rate and the structure of the deposit varies little. The results have been confirmed by electron microscopic studies of morphology of zinc particles

Atomisation of molten Zinc

Zinc dust is produced by an atomisation process in which air at 17 atmospheres pressure is directed through a narrow annular nozzle surrounding a stream of molten zinc. Industrially, it is important to control the size distribution of zinc particles. It is therefore necessary to understand the features of the process, guided where appropriate by simple mathematical models and estimates. This report examines qualitative features using simple models for number of drops produced, estimates for air speed and swirl, heat transfer in the molten zinc and droplets, and droplet collisions and stability. Results from a literature survey are presented. At this stage, the construction of more elaborate mathematical models for the process is not warranted; rather, we expect that better understanding of the process requires an experimental program involving flow visualisation

Zinculose: A New Fibrous Material with Embedded Zinc Particles

In this paper, we report a simple and inexpensive procedure to make a composite material of cellulose fibers with embedded zinc micoparticles. This fibrous material is produced by sedimentation and is referred to as “Zinculose”. Zinculose increases the surface contact area between a sample fluid and zinc microparticles. The effect of different parameters including fiber content, zinc content, water volume, applied weight and its duration on the thickness of produced Zinculose were investigated. Results show that thickness depends on the amount of initial fiber and zinc while other parameters investigated had little to no effect. Measured porosity values for Zinculose ranged between 0.699 and 0.843. Characterization of flow in Zinculose exhibits a linear relationship between distance and the square root of time which is a distinctive feature of capillary driven flow in porous media. This is an important quality that allows Zinculose to be easily incorporated into any paper-based microfluidic device that requires a sample to flow and interact with zinc microparticles without disrupting the flow path between different sections of the device. An application is presented in which a strip of Zinculose is used to convert nitrate to nitrite. With the use of Zinculose in a paper-based microfluidic device, a conversion efficiency of 27% nitrate to nitrite was achieved. This represents a 36% enhancement over what has been previously published when zinc microparticles were not embedded within the fibers of the paper channel

An X-ray tomographic study of rechargeable Zn/MnO2 batteries

We present non-destructive and non-invasive in operando X-ray tomographic investigations of the charge and discharge behavior of rechargeable alkaline-manganese (RAM) batteries (Zn-MnO2 batteries). Changes in the three-dimensional structure of the zinc anode and the MnO2 cathode material after several charge/discharge cycles were analyzed. Battery discharge leads to a decrease in the zinc particle sizes, revealing a layer-by-layer dissolving behavior. During charging, the particles grow again to almost their initial size and shape. After several cycles, the particles sizes slowly decrease until most of the particles become smaller than the spatial resolution of the tomography. Furthermore, the number of cracks in the MnO2 bulk continuously increases and the separator changes its shape. The results are compared to the behavior of a conventional primary cell that was also charged and discharged several times.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Performance of Zinc-Rich Epoxy Primers Containing Carbon Nanotubes on the Corrosion Protection of Carbon Steel in Simulated Concrete Pore Environments

The performance of zinc-rich epoxy primers containing carbon nanotubes (CNT-ZRPs) on the corrosion protection of carbon steel in simulated concrete pore solutions contaminated with chloride ions was investigated. The research project was divided in two main sections; in the first part of this project, the author studied the influence of zinc content on the corrosion protection mechanism of carbon nanotubes/zinc rich epoxy primers on carbon steel under exposure to a simulated concrete pore solution. Based on the zinc content, three mechanisms of corrosion protection were identified. The CNT-ZRP with 60 wt. % Zn exhibited good barrier protection during the entire immersion period as a result of the highly cross-linked character of the epoxy binder. In contrast, the CNT-ZRP with 70 wt. % Zn afforded short-term sacrificial protection to the metallic substrate followed by intermediate barrier protection. Furthermore, it was found that the presence of CNTs in the coating system with 70 wt. % Zn, enhanced the electrical contact between the zinc particles and the carbon steel surface, allowing to provide sacrificial protection to the steel substrate. In addition, CNTs increased the barrier properties of the coating, suggesting that CNTs blocked micropores and defects in the material, hindering the diffusion of electrolyte throughout the coating. Finally, an extended galvanic protection was provided for the CNT-ZRP with 80 wt. % Zn. Insoluble zinc corrosion products were found inside the material and at the coating surface, as a result of the galvanic protection process and a self-corrosion process of the zinc particles. These mechanisms of corrosion protection were characterized quantitatively by electrochemical techniques such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and localized electrochemical impedance spectroscopy (LEIS) and high-resolution techniques such as scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In the second part of the research project, the influence of chloride concentration in the simulated concrete pore solution on the corrosion performance of these coating systems was investigated. The corrosion protection mechanisms for the different coating systems were similar to the ones described above, however, the effect of different chloride concentrations in the simulated concrete pore solution was noticeable; it was found that concrete pore environments with low chloride concentration allowed passivation of the carbon steel surface and formation of solid zinc corrosion products. In contrast, simulated concrete pore solutions with high chloride concentration led to breakdown of the passive layer, blister formation, and dissolution of zinc corrosion products previously formed during the sacrificial protection process

Performance of Zinc-Rich Epoxy Primers Containing Carbon Nanotubes on the Corrosion Protection of Carbon Steel in Simulated Concrete Pore Environments

The performance of zinc-rich epoxy primers containing carbon nanotubes (CNT-ZRPs) on the corrosion protection of carbon steel in simulated concrete pore solutions contaminated with chloride ions was investigated. The research project was divided in two main sections; in the first part of this project, the author studied the influence of zinc content on the corrosion protection mechanism of carbon nanotubes/zinc rich epoxy primers on carbon steel under exposure to a simulated concrete pore solution. Based on the zinc content, three mechanisms of corrosion protection were identified. The CNT-ZRP with 60 wt. % Zn exhibited good barrier protection during the entire immersion period as a result of the highly cross-linked character of the epoxy binder. In contrast, the CNT-ZRP with 70 wt. % Zn afforded short-term sacrificial protection to the metallic substrate followed by intermediate barrier protection. Furthermore, it was found that the presence of CNTs in the coating system with 70 wt. % Zn, enhanced the electrical contact between the zinc particles and the carbon steel surface, allowing to provide sacrificial protection to the steel substrate. In addition, CNTs increased the barrier properties of the coating, suggesting that CNTs blocked micropores and defects in the material, hindering the diffusion of electrolyte throughout the coating. Finally, an extended galvanic protection was provided for the CNT-ZRP with 80 wt. % Zn. Insoluble zinc corrosion products were found inside the material and at the coating surface, as a result of the galvanic protection process and a self-corrosion process of the zinc particles. These mechanisms of corrosion protection were characterized quantitatively by electrochemical techniques such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and localized electrochemical impedance spectroscopy (LEIS) and high-resolution techniques such as scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In the second part of the research project, the influence of chloride concentration in the simulated concrete pore solution on the corrosion performance of these coating systems was investigated. The corrosion protection mechanisms for the different coating systems were similar to the ones described above, however, the effect of different chloride concentrations in the simulated concrete pore solution was noticeable; it was found that concrete pore environments with low chloride concentration allowed passivation of the carbon steel surface and formation of solid zinc corrosion products. In contrast, simulated concrete pore solutions with high chloride concentration led to breakdown of the passive layer, blister formation, and dissolution of zinc corrosion products previously formed during the sacrificial protection process

Electronic and Ionic Conductivities Enhancement of Zinc Anode for Flexible Printed Zinc-Air Battery

Zinc-air battery is considered a promising candidate for future energy applications due to its high energy density, safety and low cost. However, poor battery performance and low efficiency of zinc utilization, resulted from passivation effect of the zinc anode, is a major challenge. Thus, in this work, investigation of electronic and ionic conductivities enhancement of the zinc anode for flexible printed zinc-air battery has been carried out. The anode was made from a zinc-based ink, prepared from a mixture of zinc and zinc oxide particles. Carbon black, sodium silicate (Na2SiO3) and bismuth oxide (Bi2O3) were investigated for implementation on the anode. The results showed that performance of the battery increased when carbon black was introduced into the anode as the presence of carbon black improved electronic conductivity of the anode. Again, the battery performed better when Bi2O3 orNa2SiO3 was introduced due to the formation of solid electrolyte interface (SEI) on the anode. The SEI inhibits passivation of zinc active surfaces and provides effective electrolyte access. The battery with Bi2O3 provided the best performance. The highest performance was observed when Bi2O3 content reached 26wt.%. No significant improvement was observed whenBi2O3 concentration increased higher than 26 wt.%.Zinc-air battery is considered a promising candidate for future energy applications due to its high energy density, safety and low cost. However, poor battery performance and low efficiency of zinc utilization, resulted from passivation effect of the zinc anode, is a major challenge. Thus, in this work, investigation of electronic and ionic conductivities enhancement of the zinc anode for flexible printed zinc-air battery has been carried out. The anode was made from a zinc-based ink, prepared from a mixture of zinc and zinc oxide particles. Carbon black, sodium silicate (Na2SiO3) and bismuth oxide (Bi2O3) were investigated for implementation on the anode. The results showed that performance of the battery increased when carbon black was introduced into the anode as the presence of carbon black improved electronic conductivity of the anode. Again, the battery performed better when Bi2O3 or Na2SiO3 was introduced due to the formation of solid electrolyte interface (SEI) on the anode. The SEI inhibits passivation of zinc active surfaces and provides effective electrolyte access. The battery with Bi2O3 provided the best performance. The highest performance was observed when Bi2O3 content reached 26 wt.%. No significant improvement was observed when Bi2O3 concentration increased higher than 26 wt.%