sublimation comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2025-09-26. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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 formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
| 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 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.
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 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.
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.
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.
=== Pharmacodynamics === Ephenidine and related diarylethylamines have been studied in vitro as treatments for neurotoxic injuries, and are antagonists of the NMDA receptor (Ki = 66.4 nM for ephenidine). Ephenidine also possesses weaker affinity for dopamine and norepinephrine transporters (379 nM and 841 nM, respectively) as well as σ1R (629 nM) and σ2R (722 nM) binding sites.
Chloral hydrate is a geminal diol with the formula Cl3C−CH(OH)2. It was first used as a sedative and hypnotic in Germany in the 1870s. Over time it was replaced by safer and more effective alternatives but it remained in use in the United States until at least the 1970s. It sometimes finds usage as a laboratory chemical reagent and precursor. It is derived from chloral (trichloroacetaldehyde) by the addition of one equivalent of water.
All meitnerium isotopes are extremely unstable (radioactive); in general, heavier isotopes are more stable than the lighter. The most stable known isotope, 278Mt (half-life 4.5 seconds), is also the heaviest known. The unconfirmed 282Mt is even heavier and seems to have a longer half-life, 67 seconds. With a half-life of 0.8 seconds, the next most stable known isotope is 270Mt. 276Mt and 274Mt have half-lives of 0.62 and 0.64 seconds respectively. 277Mt, created as the final decay product of 293Ts for the first time in 2012, was observed to undergo spontaneous fission, half-life 5 milliseconds. Preliminary data analysis considered the possibility that this fission is instead from 277Hs, for it also has a half-life of a few milliseconds, and could come from undetected electron capture somewhere in the decay chain. This possibility was later deemed very unlikely based on observed decay energies of 281Ds and 281Rg and the short half-life of 277Mt, although there is still some uncertainty of the assignment. Regardless, the rapid fission of 277Mt and 277Hs is strongly suggestive of a region of instability for superheavy nuclei with N = 168–170. The existence of this region, characterized by a decrease in fission barrier height between the deformed shell closure at N = 162 and spherical shell closure at N = 184, is consistent with theoretical models.
== Interaction with juvenile hormone == Juvenile hormone is synthesised in the corpora allata. In every insect tested, at least one of the three types of Allatostatin inhibits the biosynthesis of juvenile hormone. This is achieved by paracrine release of Allatostatin from neurons in the brain which terminate in the corpora allata. The signal is transduced by GPCR receptors, but the intracellular pathway is not yet known. Other amine and neuropeptide neurotransmitters may also inhibit juvenile hormone biosynthesis.
=== Alternative medicine === In countries such as China, herbs used alone or with antithyroid medications are used to treat hyperthyroidism. Very low quality evidence suggests that traditional Chinese herbal medications may be beneficial when taken along with routine hyperthyroidism medications; however, there is no reliable evidence to determine the effectiveness of Chinese herbal medications for treating hyperthyroidism.
Sources: en.wikipedia.org
=== Eosin === Eosin is most often used as a counterstain to haematoxylin, imparting a pink or red colour to cytoplasmic material, cell membranes, and some extracellular structures. It also imparts a strong red colour to red blood cells. Eosin may also be used as a counterstain in some variants of Gram staining, and in many other protocols. There are actually two very closely related compounds commonly referred to as eosin. Most often used is eosin Y (also known as eosin Y ws or eosin yellowish); it has a very slightly yellowish cast. The other eosin compound is eosin B (eosin bluish or imperial red); it has a very faint bluish cast. The two dyes are interchangeable, and the use of one or the other is more a matter of preference and tradition.
=== Poultry === Mature chickens show signs three weeks after being fed a deficient diet. In young chicks, it can appear before two weeks of age. Onset is sudden in young chicks, with anorexia and an unsteady gait. Later on, locomotor signs begin, with an apparent paralysis of the flexor of the toes. The characteristic position is called "stargazing", with the affected animal sitting on its hocks with its head thrown back in a posture called opisthotonos. Response to administration of the vitamin is rather quick, occurring a few hours later.
=== Recognition of scientific advances === Coleman and Friedman have been awarded numerous prizes acknowledging their roles in discovery of leptin, including the Gairdner Foundation International Award (2005), the Shaw Prize (2009), the Lasker Award, the BBVA Foundation Frontiers of Knowledge Award and the King Faisal International Prize, Leibel has not received the same level of recognition from the discovery because he was omitted as a co-author of a scientific paper published by Friedman that reported the discovery of the gene. The various theories surrounding Friedman's omission of Leibel and others as co-authors of this paper have been presented in a number of publications, including Ellen Ruppel Shell's 2002 book The Hungry Gene. The discovery of leptin also is documented in a series of books including Fat: Fighting the Obesity Epidemic by Robert Pool, The Hungry Gene by Ellen Ruppel Shell, and Rethinking Thin: The New Science of Weight Loss and the Myths and Realities of Dieting by Gina Kolata. Fat: Fighting the Obesity Epidemic and Rethinking Thin: The New Science of Weight Loss and the Myths and Realities of Dieting review the work in the Friedman laboratory that led to the cloning of the ob gene, while The Hungry Gene draws attention to the contributions of Leibel.
The numbers 1.930 and 0.537 are phenomenological; these specific values provide a fairly good fit to the data. The product Re√fD (called the "friction Reynolds number") can be considered, like the Reynolds number, to be a (dimensionless) parameter of the flow: at fixed values of Re√fD, the friction factor is also fixed. In the Kármán–Prandtl resistance equation, fD can be expressed in closed form as an analytic function of Re through the use of the Lambert W function:
Sources: en.wikipedia.org
== Safety == The safety of ketosis from low-carbohydrate diets is often called into question by clinicians, researchers and the media. A common safety concern stems from the misunderstanding of the difference between physiological ketosis and pathologic ketoacidosis. There is also continued debate whether chronic ketosis is a healthy state or a stressor to be avoided. Some argue that humans evolved to avoid ketosis and should not be in ketosis long-term. The counter-argument is that there is no physiological requirement for dietary carbohydrates, as adequate energy can be made via gluconeogenesis and ketogenesis indefinitely. Alternatively, the switching between a ketotic and fed state has been proposed to have beneficial effects on metabolic and neurologic health. The effects of sustaining ketosis for up to two years are known from studies of people following a strict ketogenic diet for epilepsy or type 2 diabetes; these include short-term adverse effects leading to potential long-term ones. However, literature on longer term effects of intermittent ketosis is lacking.
=== Modern method === Deep-frozen stomachs are milled and put into an enzyme-extracting solution. The crude rennet extract is then activated by adding acid; the enzymes in the stomach are produced in an inactive form and are activated by the stomach acid. The acid is then neutralized and the rennet extract is filtered in several stages and concentrated until reaching a typical potency of about 1:15,000; meaning 1 g of extract can coagulate 15 kg of milk. One kilogram of rennet extract has about 0.7 g of active enzymes – the rest is water and salt and sometimes sodium benzoate (E211), 0.5%–1.0% for preservation. Typically, 1 kg of cheese contains about 0.3 mg of rennet enzymes.
Ion exchange is a reversible interchange of one species of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid. Ion exchange is used in softening or demineralizing of water, purification of chemicals, and separation of substances. Ion exchange usually describes a process of purification of aqueous solutions using solid polymeric ion-exchange resin. More precisely, the term encompasses a large variety of processes where ions are exchanged between two electrolytes. Aside from its use to purify drinking water, the technique is widely applied for purification and separation of a variety of industrially and medicinally important chemicals. Although the term usually refers to applications of synthetic (human-made) resins, it can include many other materials such as soil. Typical ion exchangers are ion-exchange resins (functionalized porous or gel polymer), zeolites, montmorillonite, clay, and soil humus. Ion exchangers are either cation exchangers, which exchange positively charged ions (cations), or anion exchangers, which exchange negatively charged ions (anions). There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously. However, the simultaneous exchange of cations and anions is often performed in mixed beds, which contain a mixture of anion- and cation-exchange resins, or passing the solution through several different ion-exchange materials.
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.
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.