Most of the things that we observe around us generally exist in three primary forms or phases: solid, liquid, or gas. For instance, the water we drink is in the liquid phase, the ice we use to make shakes and smoothies is water in solid form, and the steam we use to cook dumplings is water in gaseous form. The phase of the matter is temperature-dependent, i.e., with the temperature change, every material changes its phase from one state to another. In other words, matter changes state when the energy is added or taken away from it. The atoms and molecules that make up the matter frequently move in random directions. Even in the solid-state, they do so, but not very often. When enough energy is added to the matter in the form of heat, the molecules and atoms begin to move more randomly, resulting in volume expansion and a decrease in the density of the matter. Therefore, if enough heat is added, a solid can become liquid, and a liquid can become gas. Sometimes, however, under specific temperature and pressure conditions, a substance can directly change its phase from the solid to the gas state without passing through the liquid state. This process is known as Sublimation. The variation of matter with respect to changes in pressure and temperature is given by something called a “phase diagram.”
In a phase diagram, “triple point” is a unique configuration of temperature and pressure where all the three phases of matter can coexist in thermal equilibrium. In other words, it corresponds to the lowest pressure at which the substance can exist as a liquid (intermediate state) for a given temperature. Below that temperature, when the pressure drops below the level of the solid phase, it transitions directly into the gas phase. One way to think about this is that if you want to have sublimation, you need to get the substance beneath the triple point by lowering the pressure. The consequence of this is that if the triple point is at high pressure, then sublimation is actually easier than melting the substance since the high pressures needed to turn them into liquids are typically a challenge to create. However, one should not confuse sublimation with the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid ammonium chloride into hydrogen chloride and ammonia is not sublimation but a chemical reaction. Similarly, the combustion of candles, containing paraffin wax, to carbon dioxide and water vapour is not sublimation but a chemical reaction with oxygen. In general, sublimation only attributes to the physical state change of the matter. Let’s discuss a few examples of sublimation in daily life:
1. Dry Ice
Carbon Dioxide usually exists as a gas in our environment. However, it can also exist in solid form as “Dry Ice.” Unlike its name, dry ice has little to do with frozen water. It is named so because it resembles normal ice and does not melt but evaporates, hence the term “dry ice.” It goes directly from a solid to gas by the sublimation process. At pressures below 5.13 atm and temperatures below −56.4 °C (216.8 K; −69.5 °F) (the triple point), CO2 changes from a solid to a gas with no intervening liquid form. It is used primarily as a cooling agent but is also used in fog machines at theatres for dramatic effects. Its advantages include providing a lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods where mechanical cooling is unavailable. However, it is advised to not deal with solid carbon dioxide wit bare hands as it can leave severe frostbites on the skin.
2. Water Cycle
In the water cycle, sublimation is most commonly used to explain the process of snow and ice turning into water vapour in the air without first melting into water. The opposite of sublimation is “deposition,” where water vapour changes directly to the ice, such as snowflakes and frost. Sublimation is not easy to see, at least not with ice. One way to see the effects of sublimation is to hang a wet shirt outside on a cold day. The ice in the shirt would finally disappear. When weather conditions such as low relative humidity and dry winds are present, sublimation happens more readily. It also happens at higher altitudes, where there is less air pressure than at lower altitudes. Energy is also needed, such as strong sunlight. If one had to choose a location on Earth where sublimation happens a lot, Mt. Everest’s south face would be a perfect choice. Low temperatures, strong winds, powerful sunshine, very low air pressure are just the necessary condition for sublimation to take place.
Every year, when the summer arrives, people put their warm out-of-season clothes in storage until next winter or autumn. Every time they do so, they also put tiny but notably pungent mothballs along with the clothes to protect them from moth. During the fall, when we take those clothes out again, we find the balls are significantly shrunk in size, but there is no residue on the clothes. This occurs because, in general, the mothballs we use are made of naphthalene, which can sublimate from solid to gas under normal room temperature conditions during the summer. The strong order of naphthalene prevents the insect from approaching the clothes and causing any harm. However, since naphthalene can catch fire easily, modern mothballs use 1,4-dichlorobenzene instead. Moreover, 1,4-dichlorobenzene mothballs can go under sublimation even at a lower temperature of 21-24 °C.
4. Dye-Sublimation Printing
Sublimation printing is becoming more and more popular nowadays. The best designed graphic apparel, home décor, and advertising displays use the dye sublimation process to achieve vibrant and everlasting graphics. It is a form of digital printing that uses specialized paper. The process uses the science of sublimation, not exactly but in the opposite sense. The heat and pressure are applied to a solid, turning it into a gas through an endothermic reaction without passing through the liquid phase. This process is known as “Deposition” or “Desublimation.” The artwork is transferred to an object in a gas state using a high-temperature heat press during the dye sublimation printing process. The inks then penetrate the fibres of the material and are permanently bonded to it and the result is a high-definition print with an extremely intricate level of detail. It differs from traditional printing methods because it bypasses the liquid step.
Solving a crime scene is never a cakewalk. Thanks to the scientific methods that justice can be brought based on concrete evidence. The criminal investigation includes means for developing and analyzing physical evidence from crime scenes. It is an applied science that involves the study of facts that are then used to inform criminal trials. Modern-day criminal investigations commonly employ many modern scientific techniques known collectively as forensic science. DNA is the gold standard for criminal evidence. But often, there is no DNA at the scene of a crime. Then, an old-fashioned fingerprint analysis can be used. A skilled analyst can identify an individual from a single good print because no two people have identical fingerprints. When people touch objects with their fingers, they may leave behind traces of skin oils. This oil outline the pattern of whorls on their fingers. One method for bringing latent prints into view is called iodine fuming. Under normal temperature and pressure conditions, iodine is a solid crystalline substance with a metallic lustre. However, it is volatile, meaning that it sublimes easily. Therefore, when its fumes are blown over a surface containing fingerprints, iodine will be trapped in the fatty acid secreted by fingertips, and dark colour prints will appear. Another sublimation process that helps in a criminal investigation is Dye sublimation. It is used to create digital watermarks on documents. This enables a forensic examiner to differentiate an authentic document from a forgery.
6. Perfume Tablets
We are all aware of the scented perfume tablets used for rendering a pleasant fragrance in the bathroom or wardrobe. These accessories are rich and charmingly scented, making for a beautiful and cautious gift. They give your home a subtle, personalized scent. They are made of 100% organic wax imbued with pure essential oils that enhance their effectiveness and longevity. Depending on the type of usage, one can last until 3-6 months after unpacking. Most of these tablets include camphor as a major ingredient for scent. Camphor can go under sublimation at room temperature. Therefore, these aromatic tablets appear to decrease in size over time.
7. Accretion of Matter in Space
Once in a while, most of us wonder how this solar system, planets, comets, moons, and other celestial objects came into existence? In astrophysics, the aggregation of particles into a large object by gravitationally attracting more matter, normally gaseous matter, to the accretion disk is known as the accretion of matter. Most astronomical objects, such as galaxies, stars, and planets, are formed by accretion processes. Planets form in protoplanetary discs of gas and dust that surround young stars. In the classical planet formation scenario, dust grains collide, stick together, and form larger and larger bodies. These molecular clouds are very cold, typically less than 50K, so that ices of many kinds may accrete onto grains. Dust particles in orbit around a star drift toward the central star by the Poynting-Robertson effect and pile up by sublimation.