In this blog post, we explore why foam glass is manufactured in a manner similar to pancakes and examine its advantages as a building material, such as its thermal insulation properties and durability.
Sweet and fluffy pancakes are a beloved brunch item enjoyed by people of all ages. The appeal of pancakes can also be found in their simple ingredients and preparation process. To make pancakes, you add a little baking powder to white flour, sugar, and melted butter. Crack an egg into this mixture and mix well to create a thick, white batter. Maintaining the right consistency is crucial, as batter that’s too thin won’t rise properly. Additionally, the ratio of flour to baking powder must be just right for the batter to rise evenly, ensuring the pancakes stay soft and fluffy. Pour the batter onto a low heat and flip when bubbles start forming on one side. The moment bubbles appear is crucial; missing this point can cause the batter to burn or fail to rise.
The main component of this baking powder is sodium bicarbonate (NaHCO₃). During the mixing process and again during baking, a reaction occurs where carbon dioxide is released from the sodium bicarbonate. The carbon dioxide bubbles then cause the batter to rise, resulting in fluffy, soft pancakes. If pancakes don’t rise well, it’s often because the batter is too thick or there isn’t enough baking powder to produce sufficient carbon dioxide. Conversely, adding too much can cause the pancakes to rise excessively and collapse.
Foam Glass is the application of this baking technique to glass. Foam Glass is a black glass resembling a porous sponge. Its manufacturing principle closely mirrors the pancake-making process. First, a very small amount of manganese oxide (MnO₂, Mn₂O₃, Mn₃O₄, etc.) and carbon powder is mixed into powdered glass. This powder mixture, akin to pancake batter, is then placed into a device called a Heating Microscope and baked at extremely high temperatures. During this process, the temperature must be raised to approximately 800°C or higher, sufficient for the glass powder particles to fuse together. At this high temperature, the manganese oxide decomposes. From manganese’s perspective, this is a reaction where it loses oxygen, so we use the opposite term of oxidation and say the manganese is reduced. The oxygen gas molecules that have left the manganese now find a new home with carbon atoms. The oxygen then forms a new covalent bond, recombining with carbon to become carbon dioxide gas molecules. This process, where an oxygen molecule briefly forms before becoming carbon dioxide, is similar to how a small pancake puffs up after baking. The cross-sectional area of the mixture powder, containing various additives mixed with fine glass powder, expands by about 1.5 times, transforming into spherical foam glass.
Foam glass can be applied to roofs, building exteriors, and various gas and liquid transport pipes. One of its greatest advantages is its low thermal conductivity. The pores inside foam glass primarily contain carbon dioxide gas molecules, and carbon dioxide has lower thermal conductivity than other gas molecules like air or carbon monoxide. The carbon dioxide gas trapped within foam glass blocks heat transfer from the outside. It helps keep buildings cool in summer and warm in winter. Additionally, foam glass is highly resistant to pests and water penetration from the outside, comparable to cement. This is another important characteristic foam glass possesses as a building material. Moreover, foam glass possesses appropriate characteristics for building materials, such as low density and resistance to burning well during a fire.
Thinking back to pancakes, when we eat them, we seek pancakes that aren’t burnt, aren’t too dry, are moderately moist, and are fluffy. Similarly, when manufacturing foam glass, appropriate ratios, temperatures, and times are required. What factors determine these optimal conditions? The most significant factor is the ratio of closed pores to open pores. Consider basalt, which has numerous pores. The pores on the very surface are connected to the outside; we call these open pores. Conversely, pores well-trapped within the foam glass are called closed pores. The thermal conductivity of foam glass and its resistance to water penetration are determined by the proportion of these closed pores. In other words, there should be many closed pores where carbon dioxide can be well-trapped, and few open pores through which water and other causes of corrosion can enter. However, the problem is that when baking foam glass, the higher the heating temperature, the more actively manganese dioxide decomposes, increasing the proportion of open pores. This is similar to how pancakes become excessively dry and crumbly when baked at too high a temperature. Furthermore, prolonged heating at high temperatures causes the pores holding the gas to enlarge, leading two pores to merge into one large pore. This weakens the strength of the walls supporting the pores, resulting in foam glass with progressively poorer durability.
The quality of foam glass also varies depending on the type of gas inside the pores. Manganese oxide decomposes into manganese and oxygen gas. Subsequently, the oxygen gas must immediately combine with carbon powder to form carbon dioxide with an oxygen-to-carbon ratio of 2:1. Occasionally, an unsuitable 1:1 ratio produces carbon monoxide instead. However, carbon monoxide conducts heat twice as effectively as carbon dioxide, increasing the foam glass’s thermal conductivity. Therefore, good foam glass requires adding only the appropriate amount of carbon powder to capture the maximum amount of carbon dioxide gas.
The glass powder used in foam glass production is made by recycling glass that would otherwise be discarded. This includes recycling LCD glass used in computers, flat-screen TVs, and digital cameras, as well as CRT glass containing mercury, which is classified as a hazardous material. Currently, glass accounts for 7-10% of total solid waste in the United States and the United Kingdom. Recycling is crucial because if this glass is landfilled or incinerated, it can cause significant environmental harm. In Europe, thanks to well-designed recovery systems, over 75% of glass is recycled, and various recycling technologies are being developed. Building on such systems, foam glass transforms difficult-to-dispose-of glass waste into high-value construction materials using very inexpensive additives: carbon and manganese oxide. Foam glass can be considered a practical, environmentally friendly technology with infinite potential.
