The short version of Primary drying fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2025-09-20 and is reviewed periodically as new material appears.
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.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
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 low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
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.
| Property | Value | Notes |
|---|---|---|
| Physical state | Solid, porous cake or powder | Depends on formulation and container |
| Typical storage temperature | 2–25 °C, protected from moisture | Some materials require colder conditions |
| Solubility class | Usually readily soluble after reconstitution | Not an intrinsic chemical property |
| Common analytical method | Karl Fischer titration | Used for residual moisture |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilisation is a spelling variant |
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.
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.
==== Carbohydrates ==== Felines are natural carnivores and do not intentionally consume large quantities of carbohydrates. The domestic cat's liver has adapted to the lack of carbohydrates in the diet by using amino acids to produce glucose, which fuels the brain and other tissues. Studies have shown that carbohydrate digestion in young kittens is much less effective than that of a mature feline with a developed gastrointestinal tract. Highly digestible carbohydrates found in commercial kitten food provide additional energy and fiber to stimulate the immature gut tissue. Soluble fiber such as beet pulp is commonly used as a stool hardener and has been shown to strengthen intestinal muscles and thicken the gut mucosal layer, helping to prevent diarrhea.
== See also == Phragmen's voting rules – a ballot load balancing method analogous to the idea of Archimedes' principle. Ship stability – Archimedes's theory of displacement of fluid is a core principle of ship stability. List of eponymous laws
On November 11, 1911, Louis Upton (1886–1952), who worked as an insurance salesman, and his uncle, Emory Upton, who owned a machine shop, founded the Upton Machine Company. Following a failed business venture, Lou acquired a patent to a manual clothes washer. He approached Emory to determine if he could add an electric motor to the design. With the aid of a $5,000 investment from retailing executive Lowell Bassford, they began producing electric motor-driven wringer washers. Soon after its founding, Lou's younger brother Fred joined the company. Their first customer, the Federal Electric division of Commonwealth Edison, ordered 100 machines, but a fault in the gear transmission led the customer to threaten their return. After the machines were recalled and repaired, Federal Electric doubled the order. They remained a customer for three years, then they began producing their own washers. The loss of Federal Electric forced Upton to diversify until, in 1916, they landed Sears, Roebuck & Co. as a customer. Sears began selling two types of Upton wringer washers under the "Allen" brand, one for $54.75 and a deluxe model for $95. Sales grew quickly, and in 1921 Sears appointed Upton as their sole supplier of washers. To avoid becoming over-reliant on Sears, Upton began marketing a washer under their own brand name. The increasing volume of sales led Upton to merge with the Nineteen Hundred Washer Company of Binghamton, New York in 1929, adopting the name Nineteen Hundred Corporation. The company was relatively unaffected by the Great Depression.
Sources: en.wikipedia.org
== Methodology == Category 1: Stability (weighted 25% of total) Prevalence of summary offense Prevalence of violent crime Threat of terrorism Threat of war Threat of civil disorder Category 2: Healthcare (20%) Availability of private health care Quality of private healthcare Availability of publicly funded health care Quality of publicly funded health care Availability of over-the-counter drug World Bank's general health care indicators Category 3: Culture & Environment (25%) Humidity, temperature rating Discomfort of climate to travelers Transparency International's level of corruption Social or religious restrictions Level of censorship Sporting availability from 3 sport indicators Cultural availability from 4 cultural indicators Food and drink from 4 cultural indicators Consumer goods and services from product availability Category 4: Education (10%) Availability of private education Quality of private education World Bank's state school indicators Category 5: Infrastructure (20%) Street network quality Public transport quality International transportation service quality Availability of good quality housing Energy provision quality Water provision quality Telecommunications quality
In a study with 17 volunteers, blood and saliva samples were collected before and at 15, 30, 60 and 240 min after ingesting 1 g of paracetamol. Detection from stimulated saliva and plasma with PA-MS provided a reliable result that can aid in making timely treatment decisions. Moreover, participants' views of blood and saliva sampling procedures were assessed qualitatively, showing a preference for non-invasive sampling.
The CureVac COVID-19 vaccine (abbreviated CVnCoV) was a COVID-19 vaccine candidate developed by CureVac N.V. and the Coalition for Epidemic Preparedness Innovations (CEPI). The vaccine showed inadequate results in its Phase III trials with only 47% efficacy. In October 2021 CureVac abandoned further development and production plans for CVnCoV and refocused efforts on a cooperation with GlaxoSmithKline.
Sources: en.wikipedia.org
== Heavy-duty vehicles == U.S. National Highway Traffic Safety Administration regulations only apply to vehicles under 10,000 pounds. For heavy-duty vehicles (Classes 7 and 8, gross vehicle weight greater than 26,000 pounds), which are central to fleet management, most of the above-mentioned systems don't work well, requiring the development of other systems. The US Department of Transportation has commissioned several studies to find systems that work on the heavy-duty market specifying some goals that were needed in this market. The SAE has tried to disseminate best practices since legal regulations for heavy vehicles has been lagging.
A report by demographer William Frey suggests that as of 2019, 50.9% of Generation Z is white, 13.8% is black, 25.0% Hispanic, and 5.3% Asian. 29% of Generation Z are children of immigrants or immigrants themselves, compared to 23% of Millennials when they were at the same age. As of 2019, 13.7% of the U.S. population is foreign-born, compared to 9.7% in 1997, when the first members of Generation Z had their birth cries. Indeed, according to the Pew Research Center, in spite of the diminished flow of immigrants to the United States following the Great Recession, Generation Z is the most ethnically diverse yet seen. 52% of this generation is white. 25% is Hispanic. 14% is black, and 4% is Asian. Approximately 4% is multiracial, and this number has risen rapidly between 2000 and 2010. More specifically, the number of Americans who identify as mixed white and black has grown by 134% and those of both white and Asian extraction by 87%. For comparison, 44% of Millennials, 40% of Generation X, and 28% of the Baby Boomers identify as non-white. Research by the demographer Bill Frey suggests that at the national level, Hispanics and Asians are the fastest-growing racial minority groups in the United States while the number of Caucasians under the age of 18 has been declining since 2000. Overall, the number of births to Caucasian women in the United States dropped 7% between 2000 and 2018. Among foreign-born Caucasian women, however, the number of births increased by 1% in the same period.
Numerous beetles in the Nicrophorus genus are obligately necrophagous, for example Nicrophorus americanus and N. vespilloides. Many other beetles are facultative necrophages including checkered beetles, dermestid beetles, diving beetles, scarab beetles, silphine beetles and water scavenger beetles. Types of carrion eaten include wildlife, livestock and poultry carcasses, livestock viscera and human bodies.
Politico contributed to reinforcing the AI Cold War narrative. In 2020, the paper argued that because of the increasing AI capabilities of China, the US and other democratic countries have to create an alliance to stay ahead of China. Former Google chief executive Eric Schmidt, together with Graham T. Allison alleged in an article in Project Syndicate that, in the context of the COVID-19 pandemic, the AI capabilities of China are ahead of the US in most critical areas. Scientists who have immigrated to the U.S. play an outsize role in the country's development of AI technology. Many of them were educated in China, prompting debates about national security concerns amid worsening relations between the two countries. Policy and technology experts have pointed to concerns about unethical use of AI which would be primarily associated with China. Ethics would therefore constitute a major ideological divide in the upcoming AI Cold War. Fears around disrupting supply chains and a global semiconductor shortage are linked to Taiwan's critical role in the production of semiconductors. 70% of semiconductors are either produced in Taiwan or transfer through Taiwan, where TSMC, world's largest chipmaker is headquartered. The PRC does not recognize the sovereignty of Taiwan and trade restrictions by the US on companies selling semiconductors to the PRC have disrupted in the past the commercial relationships between TSMC and Huawei.
Sources: en.wikipedia.org
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.
Reduced pressure keeps the solvent below its triple point, allowing ice to become vapor without melting. Vacuum also helps remove water vapor from the product chamber. The exact pressure is chosen with the formulation and equipment.
Residual moisture is water that remains in the dried solid after secondary drying. It is often measured by Karl Fischer titration, near-infrared spectroscopy, or thermogravimetry. Acceptable levels depend on the material and its stability profile.
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.