Starting from scratch
"Prior to the 20th century, high-pressure research was a blank," says Mao. Pressure, temperature, and elemental composition are considered the three dimensions of materials science, because these factors determine the nature of materials. In the past, researchers focused on the effects of temperature and chemical composition, but the variable of pressure was ignored, mainly because past laboratory techniques could not create a high-pressure environment. Even if high pressures could have been attained, it would have been impossible to observe and verify what changes were occurring in the materials.
It is only in the past 30 years that it has been possible to attain adequately high pressures, and the only in the last ten that adequate measuring instruments have been available. Thus one can say this is a new science of the 21st century.
As Mao Ho-kwang puts it, "When you add the variable of pressure into the mix, it's like science has to start all over again."
Take water, for example. Water can have three states--solid, liquid, or gas--depending upon temperature. If you add pressure, however, synergistic effects are produced, and water can be changed into at least 20 states, such as plasma.
To take another familiar example: under high pressure, graphite, a commonly occurring form of carbon, turns into diamond. But it is less often considered how radically different the two substances are: the former is soft, the latter hard; the former is black, the latter crystalline and translucent; the former conducts electricity, the latter insulates (at normal pressures).
Using high pressure, Mao has even discovered the only known room-temperature liquid metal apart from mercury: sodium. Under high pressure the melting point of sodium falls to below room temperature, so it remains in a liquid state.
If the discoveries of basic high-pressure research could be carried over into the normal-pressure environment, the result would be the creation of materials that could be extraordinarily valuable in a variety of endeavors. Energy is a case in point.
It is estimated that petroleum and natural gas reserves will be exhausted within 50 years, so it is already urgent to find alternative energy sources. One focus of research is on using hydrogen to make fuel.
Hydrogen (H) is the most common element in the universe, and water (H2O) is the most common compound, meaning that you can get hydrogen just by breaking up water. Thus hydrogen can be considered inexhaustible. The problem is how to turn it into fuel. For instance, the technical problems of pumping it into cars like gasoline have thus far remained instractable.
Though hydrogen-powered cars were developed a long time ago, liquid hydrogen evaporates, while gaseous hydrogen requires vast amounts of storage space, and if the gaseous form explodes, it is highly dangerous. Based on Mao Ho-kwang's research, however, when hydrogen and water are combined under high pressure to form a compound, the water becomes a cage trapping the hydrogen inside, forming a substance like ice. When you release the high pressure, and return the compound to normal pressure and temperature, the hydrogen is released and can be burned. This is known as "flammable ice."
Through high-pressure research, Mao has found a safe and efficient way to store and release hydrogen. This new technology already has been patented in the US, though there is still a considerable way to go before it can be commercialized.
The synthetic diamonds produced in Mao's lab are nearly colorless and transparent.