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1,1,1-trichloroethane
Also called methyl chloroform, a chlorinated organic hydrocarbon (an alkaline) which is a traditional solvent used in vapor degreasing.

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A

Acid
Aqueous solutions with a pH less than 7 (on scale of 1 to 14). Strongly acidic materials have a pH less than 3. Acidic compounds yield hydrogen ions (H+) into solution.

Additive
Chemicals including corrosion inhibitors, de-foamers, emulsifying agents, chelating agents, inhibiting agents, water softening agents, and other substances which may be added to a cleaning solution in order to optimize its performance.

Alcohols
A series of oxygenated 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, but are flammable and can form explosive mixtures with air. Their use requires caution and well-designed equipment.

Alkaline
Aqueous solutions with a pH greater than 7 (on scale of 1 to 14). Strongly alkaline materials have a pH greater than 10. Also called base.

Alkaline Cleaning
Aqueous cleaning performed at a pH greater than 7 using caustic silicates, phosphates, or other alkaline salts mixed with surfactants in water.

Anion
A negatively-charged molecule that contains more electrons than protons, due to a gain in the number (ionization) of electrons.

Aqueous
Water-based.

Aqueous Cleaning
Employment of water-based solutions, which may include suitable detergents, saponifiers, or other additives used to enhance solubility and removal of soils. Aqueous cleaners are acidic, neutral, or basic.

ASTM
American Society for Testing and Materials. A technical organization that develops standards for the performance and testing of materials.

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B

Base
The opposite of acid; same as alkaline (pH greater than 7). Basic compounds yield hydroxide ions (OH-) into solutions.

Builders
Additives to detergent formulations used to increase their effectiveness by sequestering metals, such as calcium and magnesium. Many builders, such as EDTA and phosphates, can cause environmental problems.

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C

Cascade rinse
The rinsing of products transferred through a series of rinse tanks, where rinse water flowed into the final rinse tank overflows to successive tanks to the initial rinse tank, so that the flow of water is countercurrent (opposite) the direction of product transfer. Allows for products to be exposed to increasingly cleaner water.

Cation
A positively-charged molecule that contains more protons than electrons.

Caustics
A strong alkaline. When used alone the term usually refers to caustic soda (sodium hydroxide, extremely corrosive) used in the manufacture of soap as well as a neutralizing agent for acids, and in aggressive cleaning solutions.

Cavitation
In ultrasonic, the expanding and collapsing (implosion) of air bubbles within a liquid, where the implosion results in energy transfer capable of dislodging contaminants from a substrate surface. In a pump, vacuum bubbles that implode in the suction side of the pump. This can damage the pump.

CFC-113 (Freon)
The common designation for the chlorofluorocarbon solvent 1,2,2-trichloro-1,1,2-trifluoroethane, a traditional solvent used in vapor degreasing.

Chelation
The concept of sequestering or "chelating" specific contaminants found on metal surfaces is not as complicated as it may seem. Chelants, according to ASTM-A-380, are "chemicals that form soluble, complex molecules with certain metal ions, inactivating the ions so that they cannot normally react with other elements or ions to produce precipitates or scale." This process is called Specific Ion Coupling, and results when the new molecules bind and hold unwanted metal ions, preventing them from re-depositing on the treated surface until they are removed through the effluent stream. The chemicals that we refer to as chelating agents work in aqueous solutions (such as Citric acid mixtures) to "enhance solubility of scales and certain other contaminants that even mineral acids do not attack." When properly applied, inter-granular attack, pitting, and other forms of corrosion are minimal.

Cold Cleaning
Direct immersion of parts into an organic solvent bath, with cleaning occurring by dissolving the contaminants into the solvent.

Conductivity
The ability of an aqueous solution to conduct electricity. Conductivity is the reciprocal of the resistance; the purer the water, the lower the conductivity, the higher the resistance. Ion-exchange, ultra filtration and reverse osmosis methods are used to produce low-conductivity ultra-pure water.

Corrosion
Natural oxidation of iron or other metals, including aluminum and stainless steels. Can only be slowed, not stopped, by corrosion inhibitors and passivation.

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D

Deionized (DI) Water
Water at increased purity due to the removal of ionic species. Deionization is performed by an ion-exchange process, where anions and cations are exchanged for H+ andOH-ions, or a membrane process such as reverse osmosis that filters out anions and cations. Conductivity measurement can indicate degree of purity.

Detergent
A surfactant compound containing both hydrophilic and hydrophobic groups, designed to render oils and greases soluble in water. Cleaning is performed upon attachment of the soils to the hydrophobic groups, and emulsification of the detergent-soil mixture in water. Builders and other additives enhance a detergent's cleaning capacity.

Drag
The cleaning process frequently uses successive tanks for liquid-based cleaning. Drag is the liquid that is carried from the first tank to the second along with the material being cleaned.

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E

Electropolishing
While electropolishing does create a visually bright and shiny surface prior to installation, the micro-finish and passive layer that is developed by electropolishing is destroyed by heat during installation welding. The heat-affected zones (HAZ) of welds are noted for their straw color or "heat tint," which is indicative of the breakdown of the passive layer. Passivity must be chemically restored to all weld areas prior to placing a system into operation, or rouging and contamination will result.

Furthermore, cleanliness resulting from electropolishing cannot be maintained over time in corrosive environments due to the dissimilar metallurgical make-up of milled alloys. In addition to primary constituents, milled alloys contain various inclusions such as sulfides, aluminum, manganese, and others, which act as contaminants by diffusing or leeching through the base metal, the metal phase, and even the passive layer, and ultimately into the media stream. These unwanted inclusions must be removed by chelation during passivation, or product contamination and corrosion will result.

Emulsion
A stable phase that results upon mixture of what would otherwise be separate insoluble phases due to the presence of an emulsifying agent that lowers the surface tension between phases. Mayonnaise and some salad dressings are stable emulsions formed from a mixture of oils and water.

Emulsion cleaning
Removal of organic soils from a substrate through use of an emulsion comprised of an alkaline cleaning agent, such as a detergent, and an organic solvent.

Existing System Passivation:
Existing systems also benefit from passivation through the elimination of process application residues. Corrosion occurs due to metal salts in product, galvanic corrosion due to dissimilar metallurgy and oxygen depletion cells. Migrational corrosion from rouge (pre-rust) resulting from extreme temperatures and improper pumping system practices may appear; in addition, corrosion due to compromised systems is often observed. Cleaning and passivation of these systems will remove the residues and control corrosion of the system.

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F

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G

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H

H²O²
Hydrogen peroxide. A strong oxidizing chemical used in particle removal chemistries, organic residue oxidation, and for sanitizing hardware by eliminating biological growth and killing live microorganisms (bacteria and fungi).

H²SO⁴
Sulfuric acid is a corrosive acid used in cleaning; commonly used for heavy organic removal and cleaning carbon steel.

Halogenated
A chemical compound containing any combination of chlorine, fluorine, or bromine.

HCL
Seehydrochloric acid.

HEPA Filter
High-efficiency particle air filter, used for filtration of fine air particles (0.3 microns or greater in size at 99.97% efficiency) from an air stream.

HF
Hydrofluoric Acid. A corrosive acid used in etching and cleaning. Commonly used for the removal of metals, silica, or thin oxides of glass.

Hydrocarbons
Organic chemicals containing only carbon and hydrogen atoms. Can be classified as aliphatic hydrocarbons or aromatic hydrocarbons. Substances such as oils, gasoline and greases are hydrocarbons.

Hydrochloric acid (HCl)
A corrosive acid used in particle removal chemistries. Commonly found in SC-2 or HPM solutions used for metallic removal. HCl is used to dissolve rust or other metal oxides in carbon steel piping or vessels.

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I

Immersion Cleaning
Direct immersion of a dirty substrate into the cleaning fluid. Performed by dissolving the contaminants into the cleaning fluid, the cleaning approach may be enhanced by the use of heating, ultra sonics, or spray agitation methods.

Inhibitors
Agents that retard any adverse chemical reaction of an aqueous cleaner and the substrate. They are commonly used to slow down the corrosion process of iron substrates and for non-ferrous substrates at high pH (strongly alkaline) or low pH (acid solutions).

Inorganic
Compounds including water, hydrogen, oxygen, carbon dioxide, nitrogen, sulfur, phosphorus, calcium, magnesium and other metals which are not based on organic carbon.

Insoluble
Not soluble. Materials that do not dissolve within each other or within a cleaning solution, but exist as separate phases. See solubility.

Ion
An atom or group of atoms that is not electrically neutral but instead carries a positive or negative electric charge.

Ion-exchange
Replacement of inorganic ions (positive cations and/or negative anions) with other ions as a result of adsorption onto a resin with subsequent desorption of ions into solution. Ion-exchange resins can be used to remove heavier metals from wastewater.

Isopropanol
An alcohol solvent which can be used in manual and co solvent cleaning processes. Also known as isopropyl alcohol or IPA. It is also used to help dry hardware and systems that have been aqueous cleaned and rinsed with water. IPA accomplishes this by combining with the residual water and then evaporating from the surface (along with the water).

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J

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M

Manual Cleaning
Contact cleaning performed by hand using swabs, cloths, or aerosol sprays. See solvent wiping.

Material Safety Data Sheet (MSDS)
A document which lists the physical and chemical properties, acute and chronic hazards, routes of exposure, emergency procedures, as well as handling, storage, and disposal information pertinent to any chemical used in the workplace.

Media
The substance which performs the cleaning action. Can be aggressive, non-aggressive, or peening (spherical). See aggressive cleaning, nonabrasive media, and shot peening.

Megasonic Cleaning
Used primarily for particle removal in situations where ultrasonic cavitation may be too aggressive for the substrate material. Megasonic is generally performed at frequencies between 700 KHz and 1.2 MHz. See ultrasonic cleaning.

Membrane Filtration
Micro filtrations, ultra filtration, reverse osmosis, and similar filter treatment processes which utilize thin-film polymer materials to separate contaminants from wastewater.

Micro Filtration
Separation of solids to 0.1 micron through use of a polymer membrane. Often applied as a pre-filter for ultra filtration.

Mineral Acid
Inorganic acids which dissociate at nearly 100 percent in aqueous solution and have a pH of approximately 1. Hydrochloric, nitric, phosphoric, and sulfuric acids are typical mineral acids.

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N

Neutral Cleaners
Include alcohols and other water-soluble surfactant formulas that function in a pH range of 6 to 8. Used in applications that require low alkalinity, they generally cause less foaming than alkaline cleaners. They are especially useful on aluminum and copper components.

Neutralization
Refers to the addition of an acid to a base, or vice versa, in order to obtain a neutral solution (pH of 6 to 8 on scale of 1 to 14). Neutralization reactions are generally performed with indicators that change color at the neutral endpoint (equivalence point).

New System Passivation:
Passivation of new systems is an important part of the "start-up" phase of construction. As previously discussed, newly fabricated and electropolished piping and vessels may have a very shiny appearance, but inclusions in the metal can present major problems in the future.

New Stainless Steel contains a host of impurities, largely because much of it is recycled from lower grade alloys by adding substances such as chromium, nickel and molybdenum, among others to improve the heat/corrosion resistance of the steel. During the reconstitution process, aluminum is also added to deoxidize the "melt" or decrease porosity. These inclusions must be removed from high purity systems or corrosion will result.

Another impurity frequently found in mechanically polished stock is residual abrasive material left in the surface from the mechanical finishing procedures that precede electropolishing.

This abrasive material can consist of up to 15% iron oxide, and might be more appropriately termed "rouge pending" or "rouge initiator". Another favorite mechanical finishing abrasive is corundum or aluminum oxide. Because it is so hard, these materials get embedded in the stock surface and provide sites for severe pitting to begin. To further complicate matters, welding operations create a crystalline structure of corrosion cells and carbon inclusions that are present in the heat affected zone. Anytime heat tint is present, the passive layer has been comprised. Dust and other forms of debris which may exist in proximity to the system being fabricated can contaminate. Grinding, cutting and deburring of dissimilar metals, such as structural (carbon) steel which then accidentally contacts the micro-finished surface, can begin corrosion before construction is even completed.

The benefits of pre-operational passivation include removal of residues, heat tint, scales, inclusions, residual abrasives, free iron and other metallic dusts, galvanic corrosion and moisture cells, and migrational oxidation. A collateral benefit is lower carbon content of the stainless surface following chelation.

NH⁴OH
Also known as Ammonium Hydroxide or Aqua Ammonia. A corrosive base chemical used in particle removal chemistries. Commonly found in SC-1 and APM solutions used for light organic removal, and also to buffer passivation solutions.

Non-Polar
Molecule lacking a permanent dipole moment, as a result of symmetry. Non-polar solvents tend to dissolve non-polar solutes (contaminants such as oils and greases): Like dissolves like. Methane, benzene, carbon tetrachloride, and carbon dioxide are examples of non-polar molecules. Water and Isopropanol, in contrast, are polar molecules. See polar.

Non-Volatile Residue
The inorganic material that remains on a substrate upon completion of the cleaning process.

Non-Volatile Residue analysis
Involves dissolution of residual contaminant in a solvent, with subsequent evaporation of solvent. The quantity of non-volatile residue can be determined by gravimetric means, which involves weighing the dried residue, or by instrumental methods for greater precision and accuracy.

N-Propyl Bromide
A brominated hydrocarbon serving as an alternate solvent, suggested for use in vapor degreasing, cold cleaning, ultrasonic, and manual cleaning applications.

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P

Particle Counting
Quantitative technique to detect particles of varying sizes. Subject to errors attributable to the non-spherical nature of many particles and the presence of bubbles in the sample.

Particles
Any solid pieces of foreign material on the surface of the substrate or in equipment environments.

Passivation
Passivation is the chemical treatment process by which the electrochemical condition of passivity is obtained on the surface of metal alloys. Passivity as it relates to austenitic stainless steel is the state in which chemical reactivity is minimized under special environmental conditions, such that the metal exhibits a very low corrosion rate.

Passivation Theory of Austenitic Stainless Steel:
Stainless steel surfaces are rendered passive by the formation of a surface film that is a "barrier" to corrosion. This "barrier" establishes a very slow, controlled equilibrium of anion and cation diffusion across it. This passive layer consists primarily of chromium oxides, hydroxides and iron compounds, which form on the outermost surface of the metal phase. Through diffusion, the passive layer constantly "fixes" or re-passivates itself under minimum corrosion conditions. Initial passive layer establishment is achieved through chemical treatments, which remove foreign inclusions and more reactive metal ions. This treatment enhances the effective concentration of chromium, nickel and molybdenum (in the case of 316-grade stainless steel) at the surface of the metal phase. Through an unknown mechanism, these three metals together affect the creation of a more homogenous chromium oxide/ iron oxide passive layer. The uniformity and stability of the film will vary depending upon the method of treatment. Passive layer thickness and stability is critical to system longevity and product purity.

Perchloroethylene
A chlorinated alkene solvent, 1,1,2,2-tetrachlorethene, commonly used in dry cleaning.

pH
A logarithmic scale (from 1 to 14) used to represent measured hydrogen ion (H+) concentration in order to determine the acidity, basicity, or neutrality of an aqueous solution. See acid, base.

Phosphates
Form neutral salts when combined with sodium or other cation. Used to a limited extent as builders in detergents in order to sequester hard water, provide alkalinity, peptize, suspend solids, and add bulk to cleaning compounds. Such usage has been limited, however, due to the effect of phosphates on eutrophication of natural water systems. Phosphates can also be used as a coating formed by certain metals upon reaction of phosphoric acid (i.e., iron phosphate, zinc phosphate).

Polar
A compound which possesses a net positive or negative dipole moment (a positive end and a negative end) due to charged groups or additional electron pairs within the molecule. Polar compounds include water, oxygen, ozone, acids, bases, salts and some substituted and oxygenated organic compounds. See non-polar.

PPB
Parts per billion. A measure of the concentration of a material within another, determined on a weight basis.

PPM
Parts per million. A measure of the concentration of one material within another, determined on a weight basis.

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. Precision cleaning is evaluated by the measurement of micron-sized particles and PPM (or mg/ft²) of residue contaminant.

Pre-Cleaning
A surface preparation step which precedes the actual cleaning or surface treatment of a substrate.

PSI
Pounds per square inch, a unit of pressure measurement.

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R

Reverse Osmosis
A membrane procedure which separates ionic species from aqueous solutions to produce water of extremely high purity. Applied pressure forces H+ and OH ions across a membrane that does not allow for passage of other ions. The purity of the water can be measured with a conductance meter.

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S

Scale
Layer of insoluble salts of calcium, magnesium carbonate, iron oxides, phosphates, or other contaminants which have been precipitated from water by heat or chemical reaction or have been left behind when water evaporates.

Semi-Aqueous
Cleaning processes which involve washing with an organic solvent and rinsing with water (inorganic solvent). Surfactants and other chemicals are commonly added in order to lower the surface tension between the solvent and the substrate contaminants.

Silicates
Soluble or insoluble compounds that contribute emulsifying power and alkalinity, and act as corrosion inhibitors. Insoluble silica, a component of sand, is used in semiconductor manufacture, while soluble silicates are used in powder or granular form as ingredients of metal cleaning compounds.

Snow (CO²) Cleaning
Precision cleaning method whereby carbon dioxide (CO²) passed through a specialized nozzle exits as a solid and a vapor. Surface contaminants removed include organic oils, fluxes, fingerprints, and fine fibers and particles.

Solubility
The ability of a substance to dissolve in another substance. Materials are generally classified as insoluble, slightly soluble, partially soluble, or completely soluble. Solubility can be quantified as grams per liter or as a weight percent.

Solvent
Liquid substance, especially an organic compound, used to dissolve other substances.

Solvent Wiping
A hydrocarbon or chlorinated solvent applied by some absorbent material, usually a cloth or rag. See manual cleaning.

Stabilizers
Additives to solvents which are used to avoid by-product reactions with light, air, and water. Common types include metal stabilizers that pacify a surface by forming an oxide coating, anti-oxidants which minimize solvent reaction with oxygen, and acid acceptors which react with the acid formed due to the moisture effects on halogenated solvents.

Substrate
Soiled or oily item or component which is subjected to cleaning methods.

Surface Tension
The behavior of a liquid on a surface that is dependent on the intermolecular forces that cause the liquid to contract. Surface tension of a liquid sphere on a surface can be measured as a contact angle, which approaches zero as the surface tension is reduced and the liquid wets the surface.

Surfactant
Short for surface-active agent. Additives commonly used to reduce the surface tension between hydrophobic soils and an aqueous cleaning solution.

Suspended Solids
Solids which exist dispersed as a separate phase within a liquid, though not dissolved. Can be separated by filtration methods. Wastewater treatment often involves precipitation of suspended solids.

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T

Terpenes
Naturally occurring organic compounds typically found in essential oils and citrus oils, used as cleaning agents in semi-aqueous systems. D-limonene, a hydrocarbon, is the most commonly used terpene in precision cleaning applications; some terpenes contain oxygen.

Transducer
An electronic device used in ultrasonic that converts an electric signal into ultrasonic waves within a fluid medium.

Trichloroethylene
A chlorinated organic hydrocarbon (an alkene) which is a traditional solvent used for metals cleaning.

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U

Ultra Filtration
Filtration via semi-permeable membrane of particles in the 0.001 to 0.1 micron size range.

Ultrasonic Cleaning
Sonic frequencies between 20 and 400 KHz, emitted through a transducer, cause expansion of air bubbles in a liquid until they collapse within a region of high pressure. This cavitation results in an energy transfer capable of dislodging contaminants from a substrate surface.

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V

Vapor Pressure
The pressure exerted by a vapor above a substance (generally a liquid), caused by evaporation of that substance. Corresponds with the molecular weight of the substance. Lower boiling (more volatile) chemicals generally have a higher vapor pressure.

Vapor-Phase Cleaning
Sometimes called vapor degreasing, a cleaning process (usually with a solvent) in which the final rinse of the parts being cleaned is achieved by condensing solvent vapors on the parts suspended above a heated vat of solvent.

Volatile Organic Compound
Constituents that will evaporate at room temperature and which, by a photochemical reaction in the troposphere, will potentially cause atmospheric oxygen and nitrogen to be converted into smog.

Volatility
The tendency of a substance to evaporate (convert from a liquid into a gas). The lower a liquid's boiling point, the greater its volatility.

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W

Water Break Test
Qualitative test for assessing substrate cleanliness, whereby the degree of cleanliness is determined by dipping or spraying the part with clean water (usually deionized or distilled) and noting the time it takes for rinse water to break. If the water breaks into beads, the part can be considered contaminated; if the water sheets and flows off evenly, it is clean.

Weir Overflow
The method of rinsing substrates in a tank by which the solution is made to flow over a weir or dam carrying away the foreign material.

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