This is a working overview of Sublimation, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-01-17. Anything still debated is marked as such rather than presented as settled.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
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.
Lyophilization, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
| Property | Value | Notes |
|---|---|---|
| Primary phase change | Sublimation | Ice changes directly to vapor under reduced pressure |
| Typical chamber pressure | 0.01–0.5 mbar (1–50 Pa) | Below the triple point of water; product-specific |
| Typical product temperature during primary drying | −40 °C to −10 °C | Kept below collapse temperature |
| Typical residual moisture | 0.5–3% w/w | Target range varies by formulation and use |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilization is the US spelling |
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
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 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.
==== United Kingdom ==== From October 2011 as part of the Modernising Scientific Careers scheme, the route to accreditation as a medical physicist in England and Wales is provided by the Scientist Training Programme (STP). This scheme is a three-year graduate program provided by the National School of Healthcare Science. Entrants are required to have an undergraduate degree (first or upper second class honours) in an appropriate physical science prior to this three-year graduate program. The STP involves a part-time MSc in Medical Physics (provided by either King's College London, University of Liverpool or Newcastle University) in addition to practical training within the National Health Service. Assessment is provided by the completion of competencies and by a final assessment similar to the OSCE undertaken by other clinical staff. Completion of the STP leads to accreditation by the Institute of Physics and Engineering in Medicine (IPEM) and registration as a Clinical Scientist with the Health and Care Professions Council (HCPC). Prior to 2011 the training route in the United Kingdom was administered in two parts, and this scheme is still used in Scotland (known as the Scottish Medical Physics and Clinical Engineering Training Scheme (SMPCETS)). Part I involves limited clinical experience and a full-time MSc in medical physics. Part II involves exclusively clinical experience in which the candidate would produce a portfolio of experience and submit to the Academy for Healthcare Science which (in addition to a viva) would lead to professional accreditation by IPEM.
=== Working standards === Primary, calibration, and reference materials are only available in small quantities and purchase is often limited to once every few years. Depending on the specific isotope systems and instrumentation, a shortage of available reference materials can be problematic for daily instrument calibrations or for researchers attempting to measure isotope ratios in a large number of natural samples. Rather than using primary materials or reference materials, a laboratory measuring stable isotope ratios will typically purchase a small quantity of the relevant reference materials and measure the isotope ratio of an in-house material against the reference, making that material into a working standard specific to that analytical facility. Once this lab-specific working standard has been calibrated to the international scale the standard is used to measure the isotopic composition of unknown samples. After measurement of both sample and working standard against a third material (commonly called the working gas or the transfer gas) the recorded isotopic distributions are mathematically corrected back to the international scale. It is thus critical to measure the isotopic composition of the working standard with high precision and accuracy (as well as possible given the precision of the instrument and the accuracy of the purchased reference material) because the working standard forms the ultimate basis for accuracy of most mass spectrometric observations.
==== Germany ==== In Germany all of the major parties are loosely associated with research foundations that play some role in shaping policy, but generally from the more disinterested role of providing research to support policymakers than explicitly proposing policy. These include the Konrad-Adenauer-Stiftung (Christian Democratic Union-aligned), the Friedrich-Ebert-Stiftung (Social Democratic Party-aligned), the Hanns-Seidel-Stiftung (Christian Social Union-aligned), the Heinrich-Böll-Stiftung (aligned with the Greens), Friedrich Naumann Foundation (Free Democratic Party-aligned) and the Rosa Luxemburg Foundation (aligned with Die Linke). The German Institute for International and Security Affairs is a foreign policy think tank. Atlantic Community is an independent, non-partisan and non-profit organization set up as a joint project of Atlantische Initiative e.V. and Atlantic Initiative United States. The Institute for Media and Communication Policy deals with media-related issues. Transparency International is a think tank on the role of corporate and political corruption in international development.
==== Physical infrastructure ==== The destruction of physical infrastructure has represented high costs for several sectors of the economy, directly altering production and distribution networks. The costs generated by damage to the oil infrastructure have shown a substantial increase since 1990. This is mainly explained by the increase in attacks on oil pipelines by groups outside the law. According to data from Ecopetrol, between 1999 and 2003, the costs assumed by the hydrocarbon exploitation sector grew by approximately 59%, amounting to $817,654.5 million. This equates to 23.6% of the total royalties that Ecopetrol turned to 20 departments and 110 municipalities, destined to improve the quality of life of the inhabitants. For 2004, costs decreased substantially to $11,015.5 million. This is the first sector most affected by the terrorist actions of groups outside the law. The costs are mainly derived from the spilled oil, "[...] from the repair of the pipeline, from the environmental decontamination and from the oil stopped producing 60% of the total expenses incurred." During the 1999–2003 period, costs against electrical and telecommunications towers increased substantially, representing $134,871.2 million. This is equivalent to 5.4% of 2003 GDP for the electricity, gas, and water sector. On the other hand, according to data from the National Institute of Roads (INVÍAS), between 1993 and 1995, groups outside the law demolished 11 tolls and a bridge, and its reconstruction cost $378,476,248.
Sources: en.wikipedia.org
Siuzdak has hundreds of papers and has authored two books: Mass Spectrometry for Biotechnology (1996) and The Expanding Role of Mass Spectrometry in Biotechnology (2003) as well as The Expanding Role of Mass Spectrometry in Biotechnology 2nd Ed. (2006).
290 aircraft; more than 20,000 employees; 5.2 million square feet of building space (about 90 football fields). the capacity to handle 115 packages per second (equivalent to 416,000 packages flowing through its facilities every hour);
=== Chemical intermediate === Glycerol is used to produce a variety of useful derivatives. Nitration gives nitroglycerin, an essential ingredient of various explosives such as dynamite, gelignite, and propellants like cordite. Nitroglycerin under the name glyceryl trinitrate (GTN) is commonly used to relieve angina pectoris, taken in the form of sublingual tablets, patches, or as an aerosol spray. Trifunctional polyether polyols are produced from glycerol and propylene oxide. Oxidation of glycerol affords mesoxalic acid. Dehydrating glycerol affords hydroxyacetone. Chlorination of glycerol gives the 1-chloropropane-2,3-diol:
Grade 1: Only some of the fibers in the ligament are torn, and the injured site is moderately painful and swollen. Function in the joint will be unaffected for the most part. Grade 2: Many of the ligament fibers are torn, and pain and swelling is moderate. The functionality of the joint is compromised. Grade 3: The soft tissue is completely torn, and functionality and strength on the joint is completely compromised. In most cases, surgery is needed to repair the damage.
=== Nervous system involvement === The original clinical criteria of MCTD stressed the absence of central nervous system (CNS) involvement. For instance, people with MCTD do not suffer serious problems such as cerebritis, psychosis, or seizures. However, roughly 25% of individuals have some form of CNS illness. The most common central nervous system manifestation is trigeminal (fifth cranial) nerve neuropathy, which may be a patient’s first symptom. Headaches are prevalent and are typically vascular in origin. Headaches can also be due to aseptic meningitis. Sensorineural hearing loss is frequently overlooked; however, it is estimated to occur in 50% of MCTD patients.
Sources: en.wikipedia.org
== Uses == Medical uses of cannabinoids include the treatment of nausea due to chemotherapy, spasticity, and possibly neuropathic pain. Common side effects include dizziness, sedation, confusion, dissociation, and "feeling high".
The musical forms of punk and hip hop both originated in the United States in the 1970s. The United States has the world's largest music market, with a total retail value of $15.9 billion in 2022, and is the largest exporter of music. Most of the world's major record companies are based in the U.S.; they are represented by the Recording Industry Association of America (RIAA). Mid-20th-century American pop stars, such as Frank Sinatra and Elvis Presley, became global celebrities and best-selling music artists, as have artists of the late 20th century, such as Michael Jackson, Madonna, Whitney Houston, and Mariah Carey, and of the early 21st century, such as Eminem, Britney Spears, Lady Gaga, Katy Perry, Taylor Swift and Beyoncé.
=== Regenerative research === The Healing Foundation Centre at the University of Manchester was opened in 2007. It was focused on understanding wound healing and tissue regeneration mechanisms, with notable discoveries including the identification of genes activated during tissue regeneration in animals. Additionally, the Scar Free Foundation co-funded the 3D BioFace project at Swansea University. This ongoing initiative employs 3D bioprinting technology to reconstruct facial cartilage, offering less invasive and more personalised solutions for patients requiring facial reconstruction, such as those with microtia or bosma arhinia microphthalmia syndrome.
=== North America === Tim Hortons originally was concentrated in Ontario and Atlantic Canada. However, the chain has expanded its presence into Quebec and western Canada. Its location in Iqaluit, Nunavut, was the northernmost store as of 2010. Its location in Pond Inlet, Nunavut is the northernmost store as of 2023.
Sources: en.wikipedia.org
Lyophilization relies on sublimation, so water moves from solid ice to vapor without becoming liquid. The material is frozen, pressure is reduced, and controlled heat is supplied. Vapor is captured on a cold condenser, leaving a dry porous solid.
The process has three main stages: freezing, primary drying, and secondary drying. Freezing sets the ice structure, primary drying removes free ice, and secondary drying removes bound water. Each stage uses specific temperature, pressure, and time settings.
No, it is a drying method rather than a sterilization method. Removing water can limit microbial growth, but it does not reliably kill microorganisms. Sterility must come from separate steps such as filtration, heat treatment, or aseptic processing.
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.