This is a working overview of sublimation, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-06. Anything still debated is marked as such rather than presented as settled.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
A freeze-dryer consists of a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. Vials, ampoules, or bulk trays hold the product during the cycle. The condenser traps water vapor as ice at a temperature lower than the product. Cycle development balances shelf temperature, chamber pressure, and time. Scale-up can be difficult because heat and mass transfer change with equipment size, so process analytical tools and conservative validation are often used.
Lyophilization is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
Freezing is the first stage and sets the ice structure that later becomes the pore network. The formulation is cooled below its freezing point, often with a controlled ramp, and solutes concentrate as ice forms. Primary drying then lowers chamber pressure and supplies heat to sublime the ice. The product temperature must stay below its collapse or eutectic temperature to prevent structural loss. Secondary drying raises the temperature modestly to remove bound water and achieve a low residual moisture.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
The process relies on the phase diagram of water, where the triple point marks the conditions at which ice, liquid water, and vapor coexist. By maintaining pressure below this point, typically around 0.01 to 0.1 millibar, sublimation becomes the dominant mechanism. Formulations often include excipients such as sugars or polymers that act as lyoprotectants and bulking agents. These additives help preserve the structure of the active ingredient and prevent collapse during drying. The choice of excipient and freezing rate influences the final cake morphology and stability.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
Lyophilization, also known as freeze-drying, is a process that removes water from a material by freezing it and then reducing pressure to allow ice to sublimate directly into vapor. The method begins with a freezing step that solidifies the water content. Next, primary drying lowers the pressure below the triple point of water, enabling sublimation without passing through a liquid phase. A final secondary drying step removes bound water through desorption. This sequence produces a dry, porous cake that can be reconstituted later.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
== History == The test was invented in 1897 by the Polish pathologist Edmund Biernacki. In some parts of the world the test continues to be referred to as Biernacki's Reaction (Polish: odczyn Biernackiego, OB). In 1918, Dr. Robert Fåhræus noted that ESR differed only during pregnancy. Therefore, he suggested that ESR could be used as an indicator of pregnancy. In 1921, Dr. Alf Vilhelm Albertsson Westergren used ESR to measure the disease outcome of tuberculosis. He defined the measurement standards of ESR, which are still being used today. Robert Fåhræus and Alf Vilhelm Albertsson Westergren are eponymously remembered for the 'Fahraeus-Westergren test' (abbreviated as FW test; in the UK, usually termed Westergren test), which uses sodium citrate-anti-coagulated specimens.
require that the partial double bond be broken, so that the activation energy is roughly 80 kJ/mol (20 kcal/mol). However, the activation energy can be lowered (and the isomerization catalyzed) by changes that favor the single-bonded form, such as placing the peptide group in a hydrophobic environment or donating a hydrogen bond to the nitrogen atom of an X-Pro peptide group. Both of these mechanisms for lowering the activation energy have been observed in peptidyl prolyl isomerases (PPIases), which are naturally occurring enzymes that catalyze the cis-trans isomerization of X-Pro peptide bonds. Conformational protein folding is usually much faster (typically 10–100 ms) than cis-trans isomerization (10–100 s). A nonnative isomer of some peptide groups can disrupt the conformational folding significantly, either slowing it or preventing it from even occurring until the native isomer is reached. However, not all peptide groups have the same effect on folding; nonnative isomers of other peptide groups may not affect folding at all.
== Safety profile == Apart from procedural pain, some common post-treatment adverse events (AEs) of MNs include temporary discomfort, erythema (skin redness), and edema. Pinpoint bleeding, itching, irritation, and bruising are also possible in some cases. However, most of the adverse side effects are not long-lasting and could be resolved spontaneously within 24 hours after the treatment, making MNs a rather safe tool. Photoprotection and minimal exposure to chemicals irritants are often advised for an effective recovery and lowered chance of skin inflammation. Severe risks may be possible if there are technical errors during the procedure. For example, the usage of non-sterile tools might result in post-inflammatory hyperpigmentation, systemic hypersensitivity, local infections, etc. Moreover, if excess pressure is used over a bony prominence, it could lead to "Tram-track scarring". But this could be avoided by using smaller needles and prevent over-pressurizing on top of these areas. In addition, if the patient is allergic to the either the drug used or the material of MNs, contact dermatitis is possible. Therefore, clinicians should be cautious towards patients with high risks of allergy.
=== Molecular and genetic changes === UVB rays are a primary mutagen that can only penetrate through the epidermal (outermost) layer of the skin and can cause DNA mutations. These mutations arise due to chemical changes within skin cells. These mutations may be clinically related to specific signs of photoaging, including wrinkling.
== References == Courtnall, Roy; Johnson, Chris (1999). The Art of Violin Making. London: Robert Hale. ISBN 0-7090-5876-4. Patrick Spielman. Gluing and Clamping: A Woodworker's Handbook. Sterling Publishing, 1986. ISBN 0-8069-6274-7 Weisshaar, Hans; Shipman, Margaret (1988). Violin Restoration. Los Angeles: Weisshaar~Shipman. ISBN 0-9621861-0-4.
Sources: en.wikipedia.org
The most difficult steps in synthesising berkelium were its separation from the final products and the production of sufficient quantities of americium for the target material. First, americium (241Am) nitrate solution was coated on a platinum foil, the solution was evaporated and the residue converted by annealing to americium dioxide (AmO2). This target was irradiated with 35 MeV alpha particles for 6 hours in the 60-inch cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley. The (α,2n) reaction induced by the irradiation yielded the 243Bk isotope and two free neutrons:
=== January === 2 January – Former Deputy Prime Minister Sir Nick Clegg announces he is standing down as Meta's president of global affairs after almost seven years. Twenty Labour Party councillors on Broxtowe Borough Council in Nottinghamshire have resigned from Labour in protest at the direction of the party under Keir Starmer and will sit as independents. Graham Sheldon resigns as leader of Oldham Council's Conservatives, and from the Conservative Party itself, after police were called to a heated council meeting on 18 December. Kemi Badenoch calls for a public inquiry into grooming gangs. 3 January – The UK government announces that the plans for reforms to social care in England may not be published until 2028, or later. Zoe Hughes, a transgender member of Exeter City council, quits the Labour Party in a row over transgender issues. 4 January – Reform UK leader Nigel Farage seeks to distance himself from Elon Musk's call for far-right activist Tommy Robinson to be released from prison. At Reform's East of England Conference in Chelmsford, Farage threatens to target Conservative leader Kemi Badenoch's North West Essex seat over her allegations his party's membership figures are weak, and seems to show that the party now has 170,000 members. 5 January – In a post on Twitter, Elon Musk says that Nigel Farage "doesn't have what it takes" to lead Reform UK, remarks that Farage says stem from a disagreement over Musk's support for far-right activist Tommy Robinson.
== Etymology == The word "cirrhosis" is a neologism derived from Greek: κίρρωσις; kirrhos κιρρός, meaning "yellowish, tawny" (the orange yellow colour of the diseased liver) and the suffix -osis, i.e., "condition" in medical terminology. While the clinical entity was known before, René Laennec gave it this name in an 1819 paper.
Nanotechnology provides methods to organizing materials such as molecules, polymers, building blocks, etc. to form precise nanostructures which have many applications. In the process and application of peptide self-assembly into nano tubes, the single-wall carbon nano tubes is an example which consists of a graphene sheet seamlessly wrapped to a cylinder. This produced in the outside flow of a carbon and yield by laser vaporization of graphite enriched by a transition metal. Nanoimprint lithography is a popular method to fabricate nanometer scale pattern. The patterns are made by mechanical deformation of imprint resist (monomer or polymer formulation) and subsequent processes. Then, it is cured by heat or ultraviolet light, and tight level of the resist and template is controlled at appropriate conditions depend on our purposes. In addition, nanoimprint lithography has high resolution and throughput with low cost. Disadvantages include increased time for templating procedures, a lack of standard procedures results in multiple fabrication methods, and the patterns that are able to be formed are limited.
Sources: en.wikipedia.org
=== Injury === The clinically important layer is the aponeurosis. Scalp lacerations through this layer mean that the "anchoring" of the superficial layers is lost and gaping of the wound occurs which would require suturing. This can be achieved with simple or vertical mattress sutures using a non-absorbable material, which are subsequently removed at around days 7–10.
== Education == Brigitte Askonas was born to Czechoslovak parents, Jewish converts to Catholicism, who fled Austria after the Nazi takeover. Vienna-born Askonas studied biochemistry at McGill University (BSc, MSc) and carried out her postgraduate work in the school of biochemistry at the University of Cambridge where she was a student of Girton College, Cambridge and worked in Frederick Sanger's laboratory from 1948 to 1952. Her role models in the department included two distinguished scientists, Marjory Stephenson and Dorothy Needham, two of the first women to be elected to the Royal Society. She said they taught her that "good science gets recognition regardless of the sex of the scientist". Her PhD research was supervised by Malcolm Dixon.
As a result of tight advertising and marketing prohibitions, tobacco companies view packaging as a vital factor in displaying brand imagery and creating in-store presence at the point of purchase. Market testing shows the influence of this dimension in shifting the consumer's choice when the same product is displayed in alternative packaging. Companies have manipulated a variety of elements on packaging designs to communicate the impression of lower tar content or milder cigarettes, although the actual contents were the same. Some countries require cigarette packs to display warnings about the health impact of smoking. The United States was the first, later followed by other countries including Canada, most of Europe, the United Kingdom, Australia, Pakistan, India and Hong Kong. In 1985, Iceland became the first country to enforce graphic warnings on cigarette packaging. At the end of December 2010, new regulations in Canada increased the size of tobacco warnings to cover three-quarters of cigarette packaging. As of November 2010, 39 countries have adopted similar legislation. In February 2011, the Canadian government passed regulations requiring cigarette packaging to contain 12 new images to cover three quarters of the outside panel and eight new health messages on the inside panel with full color. As of April 2011, Australian regulations require all packaging to use a bland olive green that researchers determined to be the least attractive color, with 75% coverage on the front of the pack and all of the back consisting of graphic health warnings.
If SO3 is condensed above 27 °C, then α-SO3 forms, which has a melting point of 62.3 °C. α-SO3 is fibrous in appearance. Structurally, it is the polymer [S(=O)2(μ-O)]n. Each end of the polymer is terminated with OH groups. β-SO3, like the alpha form, is fibrous but of different molecular weight, consisting of a hydroxyl-capped polymer, but melts at 32.5 °C. Both the gamma and the beta forms are metastable, eventually converting to the stable alpha form if left standing for sufficient time. This conversion is caused by traces of water. Relative vapor pressures of solid SO3 are alpha < beta < gamma at identical temperatures, indicative of their relative molecular weights. Liquid sulfur trioxide has a vapor pressure consistent with the gamma form. Thus heating a crystal of α-SO3 to its melting point results in a sudden increase in vapor pressure, which can be forceful enough to shatter a glass vessel in which it is heated. This effect is known as the "alpha explosion".
Nucleic acid quaternary structure refers to the interactions between separate nucleic acid molecules, or between nucleic acid molecules and proteins. The concept is analogous to protein quaternary structure, but as the analogy is not perfect, the term is used to refer to a number of different concepts in nucleic acids and is less commonly encountered. Similarly to other biomolecules such as proteins, nucleic acids have four levels of structural arrangement: primary, secondary, tertiary, and quaternary structure. Primary structure is the linear sequence of nucleotides, secondary structure involves small local folding motifs, and tertiary structure is the 3D folded shape of nucleic acid molecule. In general, quaternary structure refers to 3D interactions between multiple subunits. In the case of nucleic acids, quaternary structure refers to interactions between multiple nucleic acid molecules or between nucleic acids and proteins. Nucleic acid quaternary structure is important for understanding DNA, RNA, and gene expression because quaternary structure can impact function. For example, when DNA is packed into heterochromatin, therefore exhibiting a type of quaternary structure, gene transcription will be inhibited.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
Yes, the terms are generally interchangeable. Lyophilization is more common in pharmaceutical and laboratory contexts, while freeze-drying appears widely in food science and general writing. Both describe removal of solvent by sublimation under vacuum after freezing.