The key difference between mercury cell and diaphragm cell is that a mercury cell usually needs a higher voltage and more energy compared to a diaphragm cell.
We can use mercury cells, diaphragm cells, and membrane cells to produce chlorine and caustic soda on an industrial scale. In all methods, the basis is to electrolyze sodium chloride solution.
CONTENTS
1. Overview and Key Difference
2. What is a Mercury Cell
3. What is a Diaphragm Cell
4. Mercury Cell vs Diaphragm Cell in Tabular Form
5. Summary – Mercury Cell vs Diaphragm Cell
What is a Mercury Cell?
A mercury cell or mercury battery is an electrochemical battery that is non-rechargeable. We can categorize it as a primary cell and is also known as mercuric oxide battery, button cell, and Ruben-Mallory. Typically, a mercury battery uses a reaction between mercuric oxide and zinc electrodes in an alkaline electrolyte. The voltage of the mercury cell is 1.35 volts when the discharge of the cell remains practically constant. Here, the capacity is much greater than the zinc-carbon battery of the same size. Even in the past, these batteries have been used as button cells for watches, hearing aids, cameras, and calculators.
The cathode of the mercury cell is typically either pure mercury(II) oxide or a mixture of mercury(II) oxide with manganese dioxide. However, mercuric oxide is a non-conductor. Therefore, we need to mix graphite with it to prevent the collection of mercury into large droplets. Besides, the anode of this cell is basically made of zinc, and it separates from the cathode via a layer of paper of a porous material that is soaked with electrolyte. We call this a salt bridge. Moreover, the electrolyte of the mercury cell is either sodium hydroxide or potassium hydroxide.
When considering the electrical features of a mercury cell, if the cathode is mercuric oxide, those cells have a very flat discharge curve which can hold the voltage at 1.35 V until the last 5% of the life of the cell. Moreover, the voltage remains within 1% for several years at light load. On the other hand, mercury cells with the mercuric oxide and manganese dioxide cathode have 1.4 V output and a more sloped discharge curve.
What is a Diaphragm Cell?
A diaphragm cell is an electrolytic cell useful in producing sodium hydroxide and chlorine from sodium chloride brine. A diaphragm cell involves the flowing of the brine solution (that is introduced into the anode) from the anode area to the cathode area via the permeable diaphragm. In this process, the anode area is separated from the cathode area via a permeable diaphragm. However, the diaphragm cell shows less energy efficiency, low environmental friendliness, and low purity of the product. In comparison to this cell, the membrane cell is an optimized process.
Generally, a diaphragm cell is made from a porous mixture of asbestos and polymers. The solution inside the cell can seep through this material from the anode compartment to the cathode compartment. We can use this cell to get chlorine from the electrolyzing of sodium chloride solution. The anode is usually titanium, and the cathode is steel. Chlorine comes from the anode, while hydrogen comes from the cathode. Furthermore, the solution coming out from the cathode is a sodium hydroxide solution that is contaminated with sodium chloride. In order to make sure the liquid flow only occurs from anode to cathode, the anode compartment always has more liquid.
What is the Difference Between Mercury Cell and Diaphragm Cell?
Mercury cell and diaphragm cell are two of three major cells that we can use to manufacture chlorine as well as caustic soda. The key difference between mercury cell and diaphragm cell is that a mercury cell usually needs a higher voltage and more energy compared to a diaphragm cell. A mercury cell typically has a zinc anode and a cathode made of either pure mercury(II) oxide or a mixture of mercury(II) oxide with manganese dioxide. A diaphragm cell, on the other hand, has a titanium anode and a steel cathode.
The below infographic presents the differences between mercury cell and diaphragm cell in tabular form for side-by-side comparison.
Summary – Mercury Cell vs Diaphragm Cell
Mercury cells and diaphragm cells are two cells we can use to manufacture chlorine and caustic soda. The key difference between mercury cell and diaphragm cell is that a mercury cell usually needs a higher voltage and more energy compared to a diaphragm cell.
Reference:
1. “Diaphragm Cell and Membrane Cell.” The Diaphragm and Membrane Cells for the Manufacture of Chlorine. Chem Guide.
Image Courtesy:
1. “Mercury battery2” By SVG derivative by Rehua, original by Ted Ankara College Library and Information Center – English Wikipedia (Copyrighted free use) via Commons Wikimedia