In this blog post, we will look at the principles of metal diffusion technology and how it could have been applied to the design of the Titanic, a symbol of early 20th century technology, and what changes it could have brought about.
On April 10, 1912, a ship that departed from Southampton, England, struck an iceberg and sank with its hull split in two. Of the approximately 2,200 passengers, 1,500 went down with the ship in this tragic event involving the famous Titanic. The Titanic was considered the pinnacle of technology at the time and was known as the “unsinkable ship.” However, despite its reputation, the Titanic sank on its maiden voyage. People at the time may have thought it was just an accident, but the sinking of the Titanic was a clear example of the limitations of modern technology.
What would have happened if the hull of the Titanic had been stronger? Perhaps the tragedy of hitting an iceberg and sinking could have been avoided. Not only that, but the movie Titanic, starring Leonardo DiCaprio, would not have been made. This movie remains a masterpiece of the century and has deeply moved many people. Without the sinking of the Titanic, we would not have had the various emotions and memories that we experienced through this movie. This is a good example of how a page of history can influence art and culture.
However, if the person who built the Titanic had been more knowledgeable about the diffusion of metals, the Titanic might not have sunk. If the diffusion phenomenon had been understood and the strength of the metal had been adjusted appropriately, the tragedy of the Titanic as we know it today would not have occurred.
When we hear the word “diffusion,” we often think of the smell of perfume spreading in the air or a drop of ink mixing with water. In fact, some dictionaries describe diffusion as a phenomenon in which molecules spread from areas of high concentration to areas of low concentration due to differences in density or concentration in gases or liquids. This explanation provides an important basis for understanding the phenomenon of diffusion, but diffusion in solids such as metals has a more complex mechanism. The fact that diffusion occurs in solids that appear to be solid and do not flow like water or air may seem a little strange. However, although it is not visible to the naked eye, diffusion in metals occurs frequently and is an important factor in determining the properties and performance of the metal products we use.
Car motors, gears, and steel plates used in airplane and ship hulls are made of alloys. Even stainless steel kitchen utensils found in kitchens across the country are made of alloys rather than pure metals to increase their strength. One of the most common methods used to make these alloys is metal diffusion. Metal diffusion is the movement of atoms that occurs when two different substances come into contact with each other through their boundaries. During this process, new alloys are formed, and the properties of the metal are changed and strengthened.
There are two main mechanisms of metal diffusion: vacancy diffusion and interstitial diffusion. First, let’s learn about vacancy diffusion. Metals are aggregates of atoms connected to each other by metallic bonds. Even metals that appear smooth and solid on the surface have empty spaces, or voids. Vacancy diffusion refers to the diffusion of atoms through these empty spaces. When a metal atom moves to an empty space next to it, the space it occupied becomes empty, and the atom next to it moves into the empty space, causing diffusion. This process occurs relatively slowly but causes significant changes in the microstructure of metals.
The second mechanism, interstitial diffusion, is often found in metals with large differences in atom size, unlike vacancy diffusion. It is a process in which small atoms move into the spaces between large atoms. Compared to vacancy diffusion, where the probability of movement is low due to the small amount of empty space (voids) relative to the number of atoms, the diffusion rate is relatively fast. When a room is almost completely filled with golf balls and ping pong balls of similar sizes, this can be called vacancy diffusion. When a room is filled with bowling balls and ping pong balls of significantly different sizes, this can be called interstitial diffusion. Imagine how the balls would move in each situation. Interstitial diffusion, which occurs between atoms of significantly different sizes, is mainly found at the interface between gases and solids.
Diffusion is a phenomenon affected by time. Therefore, phenomena that occur over time can be divided into two cases: steady-state diffusion and nonsteady-state diffusion. The factor that distinguishes steady-state diffusion from nonsteady-state diffusion is the diffusion flux. Here, diffusion flux refers to the amount of mass diffused per unit time and unit area in the direction perpendicular to the interface between metals or between metals and gases. Suppose that metals A and B are in contact with each other. If the amount of atoms from A moving toward B and the amount of atoms from B moving toward A are equal during the same time, the sum of the diffusion fluxes is zero, and this is called steady-state diffusion. In steady-state diffusion, the amount of atoms moving in each direction is the same, so diffusion actually occurs, but it appears as if no diffusion is occurring. Conversely, nonsteady-state diffusion refers to the state that we most commonly see. The amount of atoms diffusing in one direction is greater than the amount diffusing in the opposite direction, so even when the amount of atoms diffusing in the opposite direction is taken into account, the diffusion flux is not zero. For example, if three atoms of A move toward B per unit time and per unit area, and five atoms of B move toward A, the diffusion flux will be 2 in the direction of A. Outwardly, it will appear that only two atoms of B are moving toward A.
So far, we have learned how diffusion occurs in metals. Metals are indispensable in our lives, and their importance is growing day by day. From steel plates used in large ships, airplanes, and automobiles to smartphone cases and kitchen utensils that we easily encounter in our daily lives, metals are permeated in almost all aspects of our lives. Isn’t it amazing that metals, which appear to be hard and static, are actually actively diffusing? Even at this moment, metals are constantly diffusing to become stronger and new alloys. Understanding the dynamic properties of metals will not only deepen our understanding of everyday life, but also play an important role in future technological developments.
