Sublimation (phase transition): Difference between revisions

Revision as of 22:23, 6 May 2021

Revision as of 06:08, 7 October 2021

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===Carbon dioxide===

[[File:Dry Ice Vapor (17490553041).jpg|thumb|[[Dry ice]] subliming in air]]

Solid [[carbon dioxide]] ([[dry ice]]) sublimes everywhere along the line below the triple point (e.g., at the temperature of −78.5 °C (194.65 K, {{convert|194.65|K|F|disp=output only}}) at [[atmospheric pressure]], whereas its melting into liquid CO₂ can occur only along the line at pressures and temperatures above the triple point (i.e., 5.2 atm, −56.4 °C).{{citation needed}}

===Water===

[[Snow]] and [[ice]] sublime, although more slowly, at temperatures below the freezing/[[melting point]] temperature line at 0&nbsp;°C for partial pressures below the triple point pressure of 612 Pa (0.0006 atm).<ref>{{cite journal |last=Fassnacht |first=S. R. |year=2004 |title=Estimating Alter-shielded gauge snowfall undercatch, snowpack sublimation, and blowing snow transport at six sites in the coterminous USA |journal=Hydrol. Process |doi=10.1002/hyp.5806 |bibcode=2004HyPr...18.3481F |volume=18 |issue=18 |pages=3481–3492}}</ref> In [[freeze-drying]], the material to be dehydrated is frozen and its water is allowed to sublime under reduced pressure or vacuum. The loss of snow from a [[snowfield]] during a cold spell is often caused by sunshine acting directly on the upper layers of the snow. [[Ablation]] is a process that includes sublimation and erosive wear of [[glacier ice]].{{citation needed}}

===Naphthalene===

[[Naphthalene]], an organic compound commonly found in pesticides such as [[mothball]]s, sublimes easily because it is made of non-polar molecules that are held together only by [[Van der Waals force|van der Waals]] intermolecular forces. Naphthalene is a solid that sublimes at [[standard conditions for temperature and pressure|standard atmospheric temperature]]<ref>

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For even higher purification efficiencies, a [[temperature gradient]] is applied, which also allows for the separation of different fractions. Typical setups use an evacuated glass tube that is heated gradually in a controlled manner. The material flow is from the hot end, where the initial material is placed, to the cold end that is connected to a pump stand. By controlling temperatures along the length of the tube, the operator can control the zones of re-condensation, with very volatile compounds being pumped out of the system completely (or caught by a separate [[cold trap]]), moderately volatile compounds re-condensing along the tube according to their different volatilities, and non-volatile compounds remaining in the hot end.

Vacuum sublimation of this type is also the method of choice for purification of organic compounds for use in the [[organic electronics|organic electronics industry]], where very high purities (often > 99.99%) are needed to satisfy the standards for consumer electronics and other applications.{{citation needed}}

==Historical usage==

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{{Main|Dye-sublimation printer}}

Dye-sub printing is a digital printing technology using full color artwork that works with polyester and polymer-coated substrates. Also referred to as digital sublimation, the process is commonly used for decorating apparel, signs and banners, as well as novelty items such as cell phone covers, plaques, coffee mugs, and other items with sublimation-friendly surfaces. The process uses the science of sublimation, in which heat and pressure are applied to a solid, turning it into a gas through an endothermic reaction without passing through the liquid phase.{{citation needed}}

In sublimation printing, unique sublimation dyes are transferred to sheets of “transfer” paper via liquid gel ink through a piezoelectric print head. The ink is deposited on these high-release inkjet papers, which are used for the next step of the sublimation printing process. After the digital design is printed onto sublimation transfer sheets, it is placed on a heat press along with the substrate to be sublimated.{{citation needed}}

In order to transfer the image from the paper to the substrate, it requires a heat press process that is a combination of time, temperature and pressure. The heat press applies this special combination, which can change depending on the substrate, to “transfer” the sublimation dyes at the molecular level into the substrate. The most common dyes used for sublimation activate at 350 degrees Fahrenheit. However, a range of 380 to 420 degrees Fahrenheit is normally recommended for optimal color.{{citation needed}}

The end result of the sublimation process is a nearly permanent, high resolution, full color print. Because the dyes are infused into the substrate at the molecular level, rather than applied at a topical level (such as with screen printing and direct to garment printing), the prints will not crack, fade or peel from the substrate under normal conditions.{{citation needed}}

==See also==