Solvents are used in most manufacturing processes. They are one of the most common sources of air pollution found emanating from stationary sources. Getting familiar with these terms will help with all of your environmental compliance efforts.

Solvents Glossary


Acute toxicity: The short-term toxicity of a product in a single dose. Can be divided into oral, cutaneous, and respiratory toxicities.
Adsorption: Adsorption is a surface phenomenon that some products exhibit, whereby they form a physicochemical bond with substances. Not to be confused with absorption.
Aerosol spray: A means of atomizing liquids by propelling them from a pressurized container by a soluble gas.
Alcohols: A series of hydrocarbon derivatives with at least one hydrogen atom replaced by an -OH group. The simplest alcohols (methanol, ethanol, n-propanol, and isopropanol) are good solvents for some organic soils, notably rosin, but are flammable and can form explosive mixtures with air: their use requires caution and well-designed equipment.
Anion: A negatively charged ion.
Aqueous cleaning: Cleaning parts with water to which may be added suitable detergents, saponifiers, or other additives.
Azeotrope: A mixture of chemicals is azeotropic if the vapor composition is identical to that of the liquid phase. This means that the distillate of an azeotrope is theoretically identical to the solvents from which it is distilled. In practice, the presence of contaminants in the solvent slightly upsets the azeotropy.
Biocide: An additive that destroys biological contaminants.
Biodegradable: Products in wastewater that can easily be broken down or digested by, for example, sewage treatment.
BOD: Biochemical oxygen demand, the amount of oxygen consumed by bacteria and other microorganisms.
Buffer: A solution that minimizes changes in hydrogen ion concentration that would otherwise occur as a result of a chemical reaction.
Buffering agent: Drives an acidic or alkaline solution to neutral.
Carbon tetrachloride: A chlorocarbon solvent with a high ODP (about 1.1) used primarily as a base material for the production of other chemicals. It is also considered toxic and is a probable human carcinogen (classified as a B2 carcinogen by US EPA). Its use is strictly regulated in most countries.
Cation: A positively charged ion.
CFC: Chlorofluorocarbon.
CFC-112: 1,1,2,2-tetrachloro-1,2-difluoroethane.
CFC-113: A common designation for the most popular CFC solvent, 1,1,2-trichloro-1,2,2-trifluoroethane, with an ODP of approximately 0.8.
CFC-113a: An isomer of CFC-113; 1,1,1-trichloro-2,2,2-trifluoroethane.
Chelation: Chelation is the solubilization of a metal salt by forming a chemical complex or sequestering. One way of doing this is with ethylenediaminetetra-acetic acid (EDTA) salts, which have a multidentate spiral ligand form that can surround metallic and other ions.
Chlorocarbon: An organic chemical composed of chlorine and carbon, e.g., carbon tetrachloride.
Chlorofluorocarbon: An organic chemical composed of chlorine, fluorine, and carbon atoms, usually characterized by high stability contributing to a high ODP.
Chronic toxicity: The long-term toxicity of a product in small, repeated doses. Chronic toxicity can often take many years to determine.
Cleaning: The removal of soil or unwanted matter from a surface to which it clings.
Closed cup (CC): A method used to determine the flashpoint of a liquid or volatile solid.
COD: Chemical oxygen demand, a test that measures the potential capacity for a microorganism to react with oxygen.
Colloid: A substance that remains suspended in a solution or fails to settle out of solution.
Composite: A resin combined with another material such as glass fiber in such a way that the resulting product has improved physical properties.
Curd: To cause to become viscous or thickened into a coherent mass.
Conformal coating: A protective material applied in a thin, uniform layer to all surfaces of a printed wiring assembly including components.
Defluxing: The removal of flux residues after a soldering operation. Defluxing is a part of most high-reliability electronics production.
Detergency: Lifting soil from a surface by displacing it with surface active materials that have a greater affinity for the surface than they do for the soil.
Detergent: A product designed to render, for example, oils and greases soluble in water, usually made from synthetic surfactants.
Dry cleaning: A common term for cleaning garments in organic solvents as opposed to water.
Electrolytes: Compounds that conduct an electric current by the movement of ions.
Emulsifier: An aqueous additive used to keep soils dispersed throughout the cleaning fluid.
Eutrophication: The enrichment of water with nutrients that increase plant growth.
Fatty acids: The principal part of many vegetable and animal oils and greases, also known as carboxylic acids which embrace a wider definition. These are common contaminants that solvents are used to remove. They are also used to activate fluxes.
Flammable: Anything that will ignite easily and burn rapidly. The National Fire Protection Association and the Department of Transportation (DOT) define flammable liquids as those having a flash point less than 100 F and a vapor pressure of not over 40 psia at 100 F.
Flash Point: The temperature at which a liquid or volatile solid gives off vapor sufficient to form an ignitable mixture near the surface of the liquid or within the test vessel.
Flux: An essential chemical employed in the soldering process to facilitate the production of a solder joint. It is usually a liquid or solid material, frequently based on rosin.
Greenhouse effect: A thermodynamic effect whereby energy absorbed at the earth's surface, which is normally able to radiate back into space in the form of long-wave infrared radiation, is retained by gases in the atmosphere, causing a rise in temperature. The gases in question are partially natural, but manmade pollution is thought to increasingly contribute to the effect. The same CFCs that cause ozone depletion are known to be "greenhouse gases," with a single CFC molecule having the same estimated effect as 10,000 carbon dioxide molecules.
Halons: Fire-extinguishing agents with high ODPs.
HCFC: Hydrochlorofluorocarbon.
HFC: Hydrofluorocarbon.
Hydrocarbon: An organic chemical composed only of hydrogen and carbon. Gaseous or volatile hydrocarbons are flammable.
Hydrocarbon/surfactant blend: A mixture of low-volatility hydrocarbon solvents with surfactants, allowing the use of a two-phase cleaning process. The first phase is solvent cleaning in the blend and the second phase is water cleaning to remove the residues of the blend and any other water-soluble soils. The surfactant ensures the water-solubility of the otherwise insoluble hydrocarbon. Terpenes are often used in this application.
Hydrochlorocarbon: An organic chemical composed of hydrogen, chlorine and carbon, e.g., trichloroethylene.
Hydrochlorofluorocarbon: An organic chemical composed of hydrogen, chlorine, fluorine, and carbon atoms. These chemicals are less stable than pure CFCs, thereby having generally lower ODPs.
Hydrolysis: A chemical reaction of a substance with water, leading to decomposition or other change of substance.
Hydrophilic: Water loving or having a strong affinity for water.
Hydrophobic: Water hating or having a strong aversion to water.
IARC: International Agency for Research on Cancer.
Immiscible: Incapable of mixing or obtaining homogeneity.
Ion: An atom or group of atoms that is not electrically neutral but instead carries a positive or negative electric charge.
Inert gas soldering: A soldering process done in a relatively oxygen-free atmosphere. The process greatly reduces oxidation of the solder, so that less flux is required, thereby easing or eliminating the need for cleaning.
Isopropanol: Also known as isopropyl alcohol.
Leaded surface mount: A surface mount component (SMC) whose external component connection consists of formed leads.
Leadless surface: A surface mount component (SMC) whose external mount component connection consists of metallized terminations that are an integral part of the component body.
Low-solids flux: A flux that contains little solid matter, thereby easing or eliminating the need for cleaning. See no-clean flux.
Lyophilic or lypophilic: Oil loving. Marked by a strong affinity between a dispersed phase and the liquid in which it is dispersed.
MEA: Monoethanolamine.
Metal cleaning: General cleaning or degreasing of metallic components or assemblies.
Methyl chloroform: See 1,1,1-trichloroethane.
Miscible: Capable of being mixed in any ratio without separation of two phases.
Monoethanolamine: A saponifier capable of eliminating rosin fluxes and (MEA) fatty acids.
No-clean flux: A flux whose residues do not have to be removed from an electronics assembly, therefore no cleaning is necessary. This type of flux is usually characterized by low quantities of residues.
Organic acid (OA): See water-soluble flux.
Ozone: A gas formed when oxygen is ionized by, for example, the action of ultraviolet light or a strong electric field. It has the property of blocking the passage of dangerous wavelengths of ultraviolet light. Although it is a desirable gas in the stratosphere, it is toxic to living organisms at ground level (see volatile organic compounds).
Ozone depletion: Accelerated chemical destruction of the stratospheric ozone layer by the presence of substances produced mostly by human activities. The most depleting species for the ozone layer are the chlorine and bromine free radicals generated from relatively stable chlorinated, fluorinated, and brominated products by ultraviolet radiation.
Ozone depletion potential (ODP): A relative index indicating the extent to which a chemical product may cause ozone depletion. The reference level of 1 is the potential of CFC-11 and CFC-12 to cause ozone depletion. If a product has an ozone depletion potential of 0.5, a given weight of the product in the atmosphere would, in time, deplete half the ozone that the same weight of CFC-11 would deplete. The ozone depletion potentials are calculated with mathematical models that take into account factors such as the stability of the product, the rate of diffusion, the quantity of depleting atoms per molecule, and the effect of ultraviolet light and other radiation on the molecules.
Ozone layer: A layer in the stratosphere, at an altitude of approximately 10 to 50 km, where a relatively strong concentration of ozone shields the earth from excessive ultraviolet radiation.
PCB: Printed circuit board. See printed circuit.
Pentafluoropropanol: A fluorinated alcohol.
Perchloroethylene: A perhalogenated chlorocarbon solvent used extensively in industrial degreasing and in dry cleaning.
Perhalogenation: An organic molecule is perhalogenated if all the parent hydrogen atoms in a hydrocarbon are replaced with halogen atoms (astatine, bromine, chlorine, fluorine or iodine). For example, carbon tetrachloride (CCl4) is perchlorinated methane (CH4). Chloroform (CHC13) is an example of a simple chlorinated methane, where only three of the hydrogen atoms have been replaced.
Photochemical reaction: A chemical reaction caused by light or ultraviolet radiation.
Photoresist: A photomechanical product, in the form of a liquid or a laminated dry film, used in the manufacture of printed circuits. Certain types require the use of large quantities of ozone-depleting hydrochlorocarbon solvents, mostly 1,1,1-trichloroethane and methylene chloride, for their processing.
Pickling: The removal of oxides (rust) with acidic materials.
Polymers: Compounds of very high molecular weights that are made up of a large number of simple molecules which have reacted with one another.
POTW: Publicly owned treatment works, local water/sewage treatment facility.
Precision cleaning: Cleaning of high-precision mechanical parts and electronic sensory devices, as opposed to general metal cleaning. This is usually done under controlled atmospheres, notably in clean-rooms with low particle contamination.
Printed circuit: A printed circuit is an electronic component designed for interconnecting the other components. It usually consists of a metallic conductor pattern on an organic insulating substrate. After fabrication, it is known as a printed circuit board (PCB); after assembly where components are added, it is known as a printed wiring assembly (PWA).
PWA: Printed wiring assembly. See printed circuit.
Reflow soldering: A method of electronics soldering commonly used with surface mount technology, whereby a paste formed of solder powder and flux suspended in an organic vehicle is melted by the application of external heat.
Rosin: A solid resin obtained from pine trees which, in a pure form and usually with additives, is frequently used as a flux.
Rosin flux: A flux whose main constituent is rosin. There are several categories of rosin flux, often designated by the codes R (pure rosin), RMA (rosin, mild activation), RA (rosin, activated usually with free chloride ions), RSA (rosin, super activated), SA (synthetic resin, activated).
Saponifier: A chemical designed to react with organic fatty acids, such as rosin, some oils and greases, to form a water-soluble soap. This is a solvent-free method of defluxing and degreasing many parts. Saponifiers are usually alkaline and may be mineral (based on sodium hydroxide or potassium hydroxide) or organic (based on water solutions of monoethanolamine).
Saponification: The breaking down of oils into very fine droplets called colloids; to hydrolyze a fat with alkali to form a soap and glycerol.
SMC: Surface mount component.
SMD: Surface mount device.
SNAP: Significant New Alternatives Policy. Section 612 of the Clean Air Act Amendments of 1990 requires EPA to publish lists of acceptable and unacceptable alternatives for ozone depleting substances (ODSs). These lists are available from: SNAP Coordinator U.S. EPA 6205J 401 M St. SW Washington, DC 20460 (202) 233-9195
Solvent: Although not a strictly correct definition, in this context a product (aqueous or organic) designed to clean a component or assembly by dissolving the contaminants present on its surface.
Solvent containment: Means of preventing or reducing the emission of CFC or other solvents into the environment. This technique usually involves improving the design of the equipment in which the solvent is used and preventing losses.
Surface mount technology (SMT): A technique of assembling SMDs or SMCs on the surface of PCBs and PWAs, as opposed to wiring them through holes. Surface mount technology offers a number of important advantages, but also some disadvantages, such as difficulty in defluxing under certain types of SMD.
Surface mount component (device): A component (device) capable of being attached to a PCB by surface mount technology. The device may be either leaded or leadless.
Surfactant: A product designed to reduce the surface tension of water. Also referred to as tensio-active agents/tensides. Detergents are made up principally from surfactants.
Terpenes: Any of many homocyclic hydrocarbons with the empirical formula C10H16 and a characteristic odor. Turpentine is mainly a mixture of terpenes. Other common terpenes are pinene and limonene.
1,1,1-trichloroethane (TCA or MCF1,1,1-trichloroethane (TCA or MCF): A hydrochlorocarbon solvent with an estimated ODP of between 0.1 and 0.16. Also known as methyl chloroform.
TSDF: Treatment, storage, and disposal facilities.
Vapor phase cleaning: A cleaning process, usually with CFC-113 solvent or hydrochlorocarbon solvents, in which the final rinse of the parts being cleaned is achieved by condensing solvent vapors on the parts.
Vapor pressure: Total gas pressure at equilibrium due to a specific compound present as liquid and gas. For example, the pressure due to the evaporation of a solvent when as much has evaporated as the air can hold under current conditions.
Volatile organic compound (VOC): The environmental or legislated definition: Constituents that will evaporate at their temperature of use and which, by a photochemical reaction, will cause atmospheric oxygen to be converted into potential smog-promoting tropospheric ozone under favorable climatic conditions. Some areas classify a substance to be a VOC based on its vapor pressure. Scientific definition: Any hydrocarbon, except methane and ethane, with a vapor pressure equal to or greater than 0.1 mm Hg.
Water-soluble flux: A flux, which itself may be free from water, but whose residues after soldering may be entirely eliminated by a water wash. Such fluxes are usually very active so adequate defluxing is an essential part of their use. They are also known as organic acid (OA) fluxes or inorganic acid fluxes.
Wave soldering: Also known as flow soldering, a method of mass soldering electronics assemblies by passing them, after fluxing, through a wave of molten solder.
Wetting agents: Another name for surfactants.
Wetting: The action by which a cleaner penetrates and loosens the substrate-soil bond by lowering surface and interfacial tension.
Zeolite: A natural or synthetic hydrated aluminosilicate with an open three-dimensional crystal structure in which water molecules are held; often called molecular sieves.