The short version of Sublimation fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-08-06 and is reviewed periodically as new material appears.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
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.
| Property | Value | Notes |
|---|---|---|
| Process name | Lyophilization or freeze-drying | Both terms appear in technical standards and literature. |
| Phase transition | Sublimation | Solid ice becomes vapor without a liquid step. |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product temperature and equipment. |
| Typical product temperature | -40 °C to -10 °C | Measured during primary drying; formulation sets limits. |
| Water content after drying | 0.5-3% w/w | Target varies by material and stability needs. |
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 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.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
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.
== Challenges == Infrastructure and logistics remain constraints on the industry. The USDA has identified weak port infrastructure, limited cold-chain capacity, food-preservation and packaging limitations, transport logistics, complex customs procedures and high import tariffs among challenges affecting the food market and processing sector. International certification is another constraint for export-oriented processors. In 2025, the Centre for Policy Dialogue reported that about 12 percent of agro-processing firms met international food-safety certification standards, limiting access to some higher-value overseas markets.
Consider the case of a nuclide A that decays into another B by some process A → B (emission of other particles, like electron neutrinos νe and electrons e− as in beta decay, are irrelevant in what follows). The decay of an unstable nucleus is entirely random in time so it is impossible to predict when a particular atom will decay. However, it is equally likely to decay at any instant in time. Therefore, given a sample of a particular radioisotope, the number of decay events −dN expected to occur in a small interval of time dt is proportional to the number of atoms present N, that is
K2CO3 + CO2 + H2O → 2 KHCO3 CO2 de-scrubber: The above potassium carbonate solution (enriched with CO2) is then sent to the CO2 de-scrubber where CO2 is de-scrubbed by stepwise (usually two steps) flashing. The first step is done to remove the hydrocarbon gases, and the second step is employed to strip off CO2.
John Kampfner, author, broadcaster and commentator; executive director at Chatham House; has written and presented for Reuters, The Daily Telegraph; chief political correspondent at the Financial Times; political commentator for BBC's Today radio programme; political correspondent on Newsnight; was chair of the Clore Duffield Foundation, Council of King's College London; Chief Executive of the freedom of expression organisation Index on Censorship and established Creative Industries Federation; shortlisted for the Orwell Book prize. Efraim Karsh (born 6 September 1953) British-Israeli historian at King's College London; director of political studies Bar-Ilan University the Begin-Sadat Center for Strategic Studies).; former director of Middle East Forum; held posts at Harvard, Columbia universities, Sorbonne, London School of Economics, Helsinki University, International Institute for Strategic Studies, Kennan Institute for Advanced Russian Studies in Washington D.C., and Jaffee Center for Strategic Studies at Tel Aviv University; in 1989 joined King's College London; has contributed articles to The New York Times, The Los Angeles Times, The Wall Street Journal, The Times (London) and The Daily Telegraph. His book Palestine Betrayed argued that 1948 Palestinian expulsion and flight was "exclusively of their own making".
Sources: en.wikipedia.org
=== Reported end of outbreak: August–September 2022 === On 5 August 2022, the country reported that it had not seen a fever case for seven consecutive days, and that every fever case had recovered. On 8 August, plans were announced to convene the Supreme People's Assembly in September, moving its members out of isolation. A separate review meeting to discuss a "change in direction" in pandemic response was also announced. On 11 August, Kim Jong Un's sister, Kim Yo Jong, stated that her brother had had a fever, implying that he had COVID-19 at one point. She also blamed South Korea for the COVID-19 outbreak in the country, claiming that it sent contaminated anti-Pyongyang leaflets to spread the disease. North Korean media reports indicate that the population have resumed regular activity. On August 25, several sources told NK News that North Korea could possibly allow foreigners into North Korea for the first time since 2020, likely after the 20th National Congress of the Chinese Communist Party later in 2022. In September, however, Kim Jong Un flagged the first rollout of vaccines in November and warned that COVID-19 could reappear in the winter months. The mass vaccination program started in the border areas in late September, making North Korea the last country in the world other than Eritrea to have a mass vaccination program against COVID-19.
Su ji (素鸡, "vegetarian chicken"), either by being rolled up or by being pressed together and fried. Baiye jie (百叶结 "baiye knots"), by slicing into 2 cm × 10 cm slices and tying the slice up. Various dishes that roll other food items inside a piece of baiye.
=== PTFE filter === Polytetrafluoroethylene (PTFE) filter has wide operating temperature (−120 °C ~ 260 °C) with high air permeability. The resistance to high temperature makes PTFE filter paper suitable for use in autoclaves. It is often used to filter hot oils, strong solvents and collecting airborne particulates.
== Guest appearances == Several celebrities or future celebrities made uncredited appearances, either as part of the main storyline or in brief segments; among these were Richard Sanders who later gained fame playing Les Nessman on WKRP in Cincinnati. Ordinary citizens were interviewed by the kids in selected segments of some episodes in a "man on the street" format.
In the case of children and young people, especially if they are socially disadvantaged, research suggests that it is important that healthcare providers listen to and discuss their feelings and life situation to help them engage with diabetes services and self-management. To this end, treatment programs such as the Cognitive Behavioural Therapy - Adherence and Depression program (CBT-AD) have been developed to target the psychological mechanisms underpinning adherence.
Sources: en.wikipedia.org
=== In insects === Tyrosinase has a wide range of functions in insects, including wound healing, sclerotization, melanin synthesis and parasite encapsulation. As a result, it is an important enzyme as it is the defensive mechanism of insects. Some insecticides are aimed to inhibit tyrosinase.
Communist revolution erupted in the Americas in this period, including revolutions in Bolivia, Cuba, El Salvador, Grenada, Nicaragua, Peru and Uruguay. The Cuban Revolution (1953–1959) led by Fidel Castro and Che Guevara deposed the military dictatorship (1952–1959) of Fulgencio Batista and established the Republic of Cuba, a state formally recognised by the Soviet Union. In response, the United States launched a coup against the Castro government in 1961. However, the CIA's unsuccessful Bay of Pigs invasion (17 April 1961) by anti-communist Cuban exiles impelled the Republic of Cuba to side with the Soviet Union in the geopolitics of the bipolar Cold War. The Cuban Missile Crisis (22–28 October 1962) occurred when the United States opposed Cuba being armed with nuclear missiles by the Soviet Union. After a stalemate confrontation, the United States and the Soviet Union jointly resolved the nuclear-missile crisis by respectively removing United States missiles from Turkey and Italy and Soviet missiles from Cuba. Both Bolivia, Canada and Uruguay faced Marxist–Leninist revolution in the 1960s and 1970s. In Bolivia, this included Che Guevara as a leader until being killed there by government forces. In 1970, the October Crisis (5 October – 28 December 1970) occurred in Canada, a brief revolution in the province of Quebec, where the actions of the Marxist–Leninist and separatist Quebec Liberation Front (FLQ) featured the kidnap of James Cross, the British Trade Commissioner in Canada; and the killing of Pierre Laporte, the Quebec government minister.
=== Women with cancer === In women with cancer, radiation therapy and chemotherapy can damage the ovarian reserve. In such cases, a pre-treatment AMH is useful in predicting the long-term post-chemotherapy loss of ovarian function, which may indicate fertility preservation strategies such as oocyte cryopreservation. A post-treatment AMH is associated with decreased fertility. Granulosa cell tumors of the ovary secrete AMH, and AMH testing has a sensitivity ranging between 76 and 93% in diagnosing such tumors. AMH is also useful in diagnosing recurrence of granulosa cell tumors.
Lidocaine/prilocaine is a topical anesthesia which can be used to numb the skin for medical or cosmetic purposes; it is a eutectic mixture of equal quantities (by weight) of lidocaine and prilocaine. A 5% emulsion preparation, containing 2.5% each of lidocaine/prilocaine, is marketed by APP Pharmaceuticals under the trade name EMLA (an abbreviation for Eutectic Mixture of Local Anesthetics). As a spray, it is marketed under the name Tempe (topical eutectic-like mixture for premature ejaculation) (PSD502) that can be used by men to help with premature ejaculation. The spray is manufactured by Plethora Solutions and branded as Fortacin in the UK and Recordati in the EU.
Sources: en.wikipedia.org
Conventional drying uses heat to evaporate liquid water, often at temperatures that can degrade sensitive materials. Lyophilization freezes the material first and then removes water by sublimation under vacuum. This avoids prolonged exposure to liquid water and high heat.
Lowering pressure reduces the boiling point of water and allows ice to sublimate at temperatures below freezing. Vacuum also limits convective heat transfer, so heat is usually supplied by shelves or radiation. The pressure must stay below the vapor pressure of ice at the product temperature.
The cycle typically includes freezing, primary drying, and secondary drying. Freezing solidifies water and sets the pore structure; primary drying removes bulk ice; secondary drying removes bound water. Some cycles add annealing or pre-freezing steps.
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.