Sublimation raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-12-02 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.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
| 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. |
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.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
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.
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.
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 process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
Mitchell had designed an excellent seaplane for the 1931 Schneider Trophy, but the British government would not fund this excellent design - the Supermarine S.6B, leaving Lucy, Lady Houston, married to Sir Robert Houston, 1st Baronet, to fund the project entirely herself, from a request of the Royal Aero Club; the 230 mph Type 224 led to the 265 mph Type 425, with a 650 hp Goshawk engine; R-R proposed a 27-litre engine, derived from their R engine, in 1934; this new engine led R.J. Mitchell to propose the 350 mph Type 300 with the 1000 hp Merlin engine, and a £10,000 contract was offered for this aircraft to be ready by October 1935; the Hawker Hurricane was a monoplane Hawker Fury; 310 Spitfires were ordered; military historian Corelli Barnett and how later versions of the Spitfire took three times the man hours of the Bf 109; Sir Peter Masefield; 19 Squadron, led by Iliffe Cozens, converted from the Gloster Gauntlet to the Spitfire in August 1938; in the Battle of Britain, thirty Spitfires had the 20mm cannon fitted; the second movement - Fortune plango vulnera of Carmina Burana and the Messerschmitt Bf 109 at RAF Boscombe Down; Spitfire pilot Laddie Lucas; around 350 Spitfires entered US service.
== Receptor targets == Most neuropeptides act on G-protein coupled receptors (GPCRs). Neuropeptide-GPCRs fall into two families: rhodopsin-like and the secretin class. Most peptides activate a single GPCR, while some activate multiple GPCRs (e.g. AstA, AstC, DTK). Peptide-GPCR binding relationships are highly conserved across animals. Aside from conserved structural relationships, some peptide-GPCR functions are also conserved across the animal kingdom. For example, neuropeptide F/neuropeptide Y signaling is structurally and functionally conserved between insects and mammals. Although peptides mostly target metabotropic receptors, there is some evidence that neuropeptides bind to other receptor targets. Peptide-gated ion channels (FMRFamide-gated sodium channels) have been found in snails and Hydra. Other examples of non-GPCR targets include: insulin-like peptides and tyrosine-kinase receptors in Drosophila and atrial natriuretic peptide and eclosion hormone with membrane-bound guanylyl cyclase receptors in mammals and insects.
E300 ascorbic acid (approved for use as a food additive in the UK, US Canada, Australia and New Zealand) E301 sodium ascorbate (approved for use as a food additive in the UK, US, Canada, Australia and New Zealand) E302 calcium ascorbate (approved for use as a food additive in the UK, US Canada, Australia and New Zealand) E303 potassium ascorbate (approved in Australia and New Zealand, but not in the UK, US or Canada) E304 fatty acid esters of ascorbic acid such as ascorbyl palmitate (approved for use as a food additive in the UK, US, Canada, Australia and New Zealand) The stereoisomers of Vitamin C have a similar effect in food despite their lack of efficacy in human scurvy. They include erythorbic acid and its sodium salt (E315, E316).
Sources: en.wikipedia.org
=== Occurrence === All berkelium isotopes have a half-life far too short to be primordial. Therefore, any primordial berkelium − that is, berkelium present on the Earth during its formation − has decayed by now. On Earth, berkelium is mostly concentrated in certain areas, which were used for the atmospheric nuclear weapons tests between 1945 and 1980, as well as at the sites of nuclear incidents, such as the Chernobyl disaster, Three Mile Island accident and 1968 Thule Air Base B-52 crash. Analysis of the debris at the testing site of the first United States' first thermonuclear weapon, Ivy Mike, (1 November 1952, Enewetak Atoll), revealed high concentrations of various actinides, including berkelium. For reasons of military secrecy, this result was not published until 1956. Nuclear reactors produce mostly, among the berkelium isotopes, berkelium-249. During the storage and before the fuel disposal, most of it beta decays to californium-249. The latter has a half-life of 351 years, which is relatively long compared to the half-lives of other isotopes produced in the reactor, and is therefore undesirable in the disposal products. The transuranic elements up to fermium, including berkelium, should have been present in the natural nuclear fission reactor at Oklo, but any quantities produced then would have long since decayed away.
Duterte also received criticism after he threatened to order the military in mid-2017 to bomb Lumad schools, which he and the military suspected to shelter rebels and teach subversion. Additionally, the military and the NTF-ELCAC were denounced after they cited clandestine recruitment activities by the communist rebels within university campuses nationwide, notably in both state-run University of the Philippines and Polytechnic University of the Philippines. Several human rights organizations called on the succeeding Bongbong Marcos administration to abolish the NTF-ELCAC due to continued red-tagging allegations; the calls, however, were later rejected by Marcos.
== Early life == Pickston was born in Oldham, Lancashire, and grew up in Shaw, Lancashire, where she was raised by her grandfather, William Fawcett. Her father, Paul Fawcett, worked for British Telecom during her early years. Pickston attended Rishworth School. Her mother, whose surname is Yachan, is Thai.
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.
Freezing only converts liquid to solid. Lyophilization adds vacuum and controlled warming so frozen solvent sublimes, leaving a dry porous solid. The two steps are related but not interchangeable.