Would you like to know why a snow crystal is a beautiful hexagon?

Crystallization—a familiar natural phenomenon with which you can also enjoy experiments—

A crystal is defined as a solid where atoms or molecules periodically arrange. It might sound difficult, but the crystallization is a familiar phenomenon and nothing special.

For example, I believe many people have made ice in a freezer. Ice is a crystal of water. Snow, icicles, and frost columns in soil are also crystals of water.

We cleverly use crystals to adopt them to foods and daily tools. The grains of salt and sugar are crystals. Quartz clocks use the accurate oscillation generated by a quartz crystal. Semiconductors, essential to electronic equipment, use silicon crystals.

We can also observe and enjoy how a crystal grows using familiar tools at home.

For example, I believe many people have made crystals of salt in class. You might have been a little surprised when beautiful cube crystals were made just by evaporating salt water you made.

Recently, some people place a storm glass in their rooms as an interior design piece. A storm glass is a clean glass container that contains a solution. In the solution, crystals are formed, and the form of crystals slowly changes to various forms.

We can also enjoy the crystallization of bismuth crystal. The phenomenon of bismuth crystallization occurs by heating and melting a metal called bismuth, and cooling it. Although caution must be taken as this experiment is carried out at high temperatures, some people do this at home.

Observing a crystal that changes to a unique form, which is a stepped form, is amazing and interesting. It is beautiful when the oxide film formed on the surface of the crystal turns to various colors of the rainbow. Bismuth crystal is a popular crystal well known by many people who love minerals and science experiments.

As described above, I think making crystals by yourself and observing the change in crystallization are enjoyable.

Furthermore, crystallization may arouse your curiosity, such as for why a crystal changes into that kind of form. The desire to understand the reason becomes the first step to the world of science.

Understand the fundamental principle of crystals to unveil the secret of crystallization

The storm glass was originally used as an instrument for forecasting weather in 19th century Europe. At that time, people thought that the form of a crystal changed in accordance with weather conditions.

Because of this, it seems that some people today think that they could predict an earthquake using a storm glass by exercising a wealth of imagination. But, in reality, the storm glass cannot help us forecast earthquakes nor the weather.

The reason is that only temperature influences crystals in a solution tightly contained in a glass container. In other words, crystals in the solution change the form in accordance with the change in temperature. It is quite a simple phenomenon that can be simply explained in science by crystal growth.

Although it is a simple phenomenon, predicting what form a crystal will become at what temperature is actually difficult. As the temperature changes from hour to hour, a crystal can grow or dissolve in accordance with the temperature. Components of a crystal in a solution are taken in when the crystal is growing and are emitted when the crystal is dessolving. Therefore, the concentration of the component in a solution differs depending on the location, and also changes depending on the time (mass transfer in a solution).

Furthermore, innumerable crystals exist in a solution. When crystals grow as the temperature drops, a situation where the crystals compete to growth in the solution, which makes the understanding of the form and the speed of growth of a crystal more complicated.

You may think that the storm glass is a mystical, special material with many mysteries. But this is not true.

The storm glass is not that special because the basic process of the formation of ordinary salt crystals is the same. Na (sodium) ion and Cl (chloride) ion dissolved in saltwater need to be gathered; therefore, the mass transfer is still the important process.

The concentration of ions (salinity) around crystals decreases as salt crystals begin to form. At this time, a transfer, in which salinity travels from the thick side to the thin side, is occurring in the saltwater. When several salt crystals form and grow in saltwater, crystals naturally scramble for salinity in the saltwater, which makes the understanding of the speed of growth and form of each crystal complicated.

Thus, in general, when you think of how the form and speed of the growth of a crystal is determined, you will think about them while imaging the transfer of heat and mass.

Of course, a crystal structure (how atoms and molecules are arrayed) is important when thinking about the form of a crystal. In addition to the structure, understanding the basic principle of the transfer of heat generated around the crystal and mass can give you a way of appreciating the form and the growth process of a crystal, which is not only beautiful and wonderful. It may stimulate your thoughts on what the ambient environment and conditions of forming a crystal are.

Crystal research on problems concerning the global environment and energy resources

When you carry out an experiment, such as crystallization, it is important to understand correctly the phenomenon that occurred in front of you without prejudice.

For example, I was asked how to make ice for making good shaved ice. The reason why ice made in a freezer at home is not so good is probably that we use tap water containing impurities, such as chlorinated lime. The crystal of ice itself is pure H2O. However, impurities are trapped in a lump of ice like the air dissolved in water is trapped as a bubble.

We carried out an experiment making shaved ices. We made a clear and clean ice with no bubbles using mineral water and made white cloudy ice with innumerable bubbles using the carbonated mineral water .

Many people predict that clear ice is good. But it is felt that shaved ice made from ice with lots of bubbles is better as it provides a softer food texture and melts in your mouth more smoothly.

Of course, ‘good’ is an individual feeling and cannot be explained from the crystal science viewpoint. But we can explain the reason why shaved ice made from ice full of bubbles provides a softer food texture. The shaved ice has a large surface area as the ice is full of holes due to bubbles and is easy to melt when you put it in your mouth.

If you shake off a preconception and accurately accept the fact presented in front of you, you can explain the causal relation simply.

I am also carrying out research on methane hydrate, which is a crystal formed by methane, a main component of natural gas, and water.

Methane hydrate, which is formed under the ocean floor, has various forms. It can be granular, needle-shaped, layered, or massive. Why does methane hydrate grow in various forms?

We have carried out hydrate crystal growth experiments in a model of soil and have finally drawn the “diagram of forms of a hydrate crystal”, in which the causal relation of the forms is charted. This diagram considers how much mass required for crystallization exists in the surrounding area, how easily it can be collected, and the principle of generating frost columns as it is crystallization in the ground in the same manner as when other crystals are formed.

I believe that the research on the formation and generation of methane hydrate will become research related to problems of the global environment and energy resources. But the starting point is, as explained above, a curiosity about the phenomenon of familiar various crystals, including the crystals of ice and salt.

Through this curiosity, we can discover that there are basic common principles and that one image of a crystal shows the time evolution of a crystal to reach that point like the annual rings of a tree.

Difficult knowledge and numerical formulas are not necessarily required to reveal these things. Junior high school students and high school students can think and understand them using their knowledge obtained in their respective stages of education.

The same thing can be said of adults. Treasure your curiosity to ask why and think it over based on your knowledge. I believe that curiosity will broaden your world and help you foster your logical thinking.

* The information contained herein is current as of May 2021.
* The contents of articles on Meiji.net are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.

Information noted in the articles and videos, such as positions and affiliations, are current at the time of production.