Key Difference – Local Action vs Polarization
The terms local action and polarization are used to name two types of defects in batteries. These are found in simple electric batteries. These defects reduce the practical value and performance of these cells (or batteries). Local action of a battery is the internal loss of battery due to local currents that flow between different parts of a plate. These local currents are produced by chemical reactions. Polarization is the termination of the cell reaction in the battery due to the collection of hydrogen gas around the positive electrode. The key difference between local action and polarization is that local action can be minimized using pure zinc whereas polarization can be minimized using a depolarizer such as manganese oxide
CONTENTS
1. Overview and Key Difference
2. What is Local Action
3. What is Polarization
4. Side by Side Comparison – Local Action vs Polarization in Tabular Form
5. Summary
What is Local Action?
The local action of a battery is the deterioration of the battery due to currents that are flowing from and to the same electrode. A battery contains one or more electrochemical cells. These electrochemical cells have external connections to power electrical devices. There are two terminals in a battery; positive terminal or the cathode and negative terminal or the anode. Batteries convert chemical energy into electrical energy.
There are electrodes and electrolytes inside a battery. The electrolyte contains anions and cations that are required to keep the continuous current flow inside the battery. The redox reactions take place when the electrolyte provides electrons to create a current. But, sometimes certain defects can take place inside a battery, such as reducing the performance and value of the battery. Local action is one such defect.
The local action is the discharge of current by a battery even when it is not connected to an external power device due to the impurities present. These impurities can create potential differences between some portions of the electrode. It is a type of a self-discharge.
For example, when a zinc electrode is used, there can be impurities embedded such as iron and lead. These impurities can act as a positive electrode when compared to zinc electrode and zinc act as a negative electrode. Then, when the cell is not in use, electric currents flow through these electrodes, eventually resulting in the deterioration of the cell.
Figure 01: A Battery
Local action can be minimized using a pure zinc electrode that has no impurities embedded in it. But it is a very expensive option. Therefore, a cheaper option is used where zinc is alloyed with mercury to produce zinc amalgam. The process is called amalgamation.
What is Polarization?
Polarization is a defect that occurs in simple electric cells due to the accumulation of hydrogen gas around the positive electrode. In simple cells, hydrogen gas is evolved as a result of chemical reactions taking place inside the cell. When this hydrogen gas is collected around the positive electrode, eventually it causes the insulation of positive electrode from the electrolytic solution. This process is known as polarization.
The polarization of a battery reduces the practical value and performance of a cell. Therefore, it is considered as a cell defect. To minimize the polarization, a depolarizer can be used since it can react with hydrogen gas produced in the cell. A common depolarizer is manganese oxide. It reacts with hydrogen gas producing water as a byproduct.
What is the Difference Between Local Action and Polarization?
Local Action vs Polarization |
|
| The local action of a battery is the deterioration of the battery due to currents that are flowing from and to the same electrode. | Polarization is a defect that occurs in simple electric cells due to the accumulation of hydrogen gas around the positive electrode. |
| Process | |
| In local action, embedded impurities in a zinc electrode can act as positive electrodes and create electric currents between zinc and this positive electrode. | Hydrogen gas produced in chemical reactions inside the battery can get accumulated around the electrodes and result in insulation. |
| Cause | |
| Caused by impurities in electrodes like iron and lead. | Caused by hydrogen gas produced by chemical reactions. |
| Minimization | |
| Can be minimized using pure zinc. | Can be minimized using a depolarizer such as manganese oxide. |
Summary – Local Action vs Polarization
Local action and polarization are two types of defects discussed under batteries. The key difference between local action and polarization is that local action can be minimized using pure zinc whereas polarization can be minimized using a depolarizer such as manganese oxide
Reference:
1.“Defects of a simple Electric Cell.” Defects of a simple Electric Cell ~, Available here
2.“Battery (Electricity).” Wikipedia, Wikimedia Foundation, 22 Feb. 2018. Available here
Image Courtesy:
1.’Panasonic-PP3-9volt-battery-crop’ (CC BY-SA 2.5) via Commons Wikimedia