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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
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In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Chrome plating (less commonly chromium plating) is a technique of electroplating a thin layer of chromium onto a metal object.[1] A chrome plated part is called chrome, or is said to have been chromed. The chromium layer can be decorative, provide corrosion resistance, facilitate cleaning, and increase surface hardness. Sometimes a less expensive substitute for chrome, such as nickel, may be used for aesthetic purposes.
Chromium compounds used in electroplating are toxic. In most countries, their disposal is tightly regulated. Some fume suppressants used to control the emission of airborne chromium from plating baths are also toxic, making disposal even more difficult.
The preparation and chrome plating of a part typically includes some or all of these steps:
There are many variations to this process, depending on the type of substrate being plated. Different substrates need different etching solutions, such as hydrochloric, hydrofluoric, and sulfuric acids. Ferric chloride is also popular for the etching of nimonic alloys. Sometimes the component enters the chrome plating vat while electrically live. Sometimes the component has a conforming anode made from lead/tin or platinized titanium. A typical hard chrome vat plates at about 0.001 inches (25 μm) per hour.
Some common industry specifications governing the chrome plating process are AMS 2460, AMS 2406, and MIL-STD-1501.
Hexavalent chromium plating, also known as hex-chrome, Cr6+, and chrome(VI) plating, uses hexavalent chromium (CrVI) as the main ingredient. Hexavalent chromium plating solution is used for both decorative and hard plating, as well as bright dipping of copper alloys, chromic acid anodizing, and chromate conversion coating.[3]
A typical hexavalent chromium plating process is:
The activation bath is typically a tank of chromic acid with a reverse current run through it. This etches the work-piece surface and removes any scale. In some cases, the activation step is done in the chromium bath. The chromium bath is a mixture of chromium trioxide and sulfuric acid, the ratio of which varies greatly between 75:1 to 250:1 by weight. This results in an extremely acidic bath (pH 0). The temperature and current density in the bath affect the brightness and final coverage. For decorative coating the temperature ranges from 35 to 45 °C (100 to 110 °F), but for hard coating it ranges from 50 to 65 °C (120 to 150 °F). Temperature is also dependent on the current density, because a higher current density requires a higher temperature. Finally, the whole bath is agitated to keep the temperature steady and achieve a uniform deposition.[3]
One functional disadvantage of hexavalent chromium plating is low cathode efficiency, which results in bad throwing power. This means it leaves a non-uniform coating, with more on edges and less in inside corners and holes. To overcome this problem the part may be over-plated and ground to size, or auxiliary anodes may be used around the hard-to-plate areas.[3] Hexavalent chromium is also considerably more toxic than trivalent chromium, rendering it a major health risk both in manufacturing and disposal if not handled with care.[4]
Trivalent chromium plating, also known as tri-chrome, Cr3+, and chrome(III) plating, uses chromium sulfate or chromium chloride as the main ingredient. Trivalent chromium plating is an alternative to hexavalent chromium in certain applications and thicknesses (e.g. decorative plating).[3]
A trivalent chromium plating process is similar to the hexavalent chromium plating process, except for the bath chemistry and anode composition. There are three main types of trivalent chromium bath configurations:[3]
The trivalent chromium-plating process can plate the workpieces at a similar temperature, rate and hardness, as compared to hexavalent chromium. Plating thickness ranges from 5 to 50 μin (0.13 to 1.27 μm).[3]
The functional advantages of trivalent chromium are higher cathode efficiency and better throwing power. Better throwing power means better production rates. Less energy is required because of the lower current densities required. The process is more robust than hexavalent chromium because it can withstand current interruptions.[3]
One of the disadvantages when the process was first introduced was that decorative customers disapproved of the color differences. Companies now use additives to adjust the color. In hard coating applications, the corrosion resistance of thicker coatings is not quite as good as it is with hexavalent chromium. The cost of the chemicals is greater, but this is usually offset by greater production rates and lower overhead costs. In general, the process must be controlled more closely than in hexavalent chromium plating, especially with respect to metallic impurities. This means processes that are hard to control, such as barrel plating, are much more difficult using a trivalent chromium bath.[3]
Divalent chromium plating is done from liquids comprising Cr2+ species. Such solutions were avoided prior to ca. 2020, because of air-sensitivity and hydrogen evolution from aqueous Cr2+ solutions. In the 2020s, it was discovered that chromous chloride has ca. 4.0 M solubility in water at room temperature (i.e. with H2O:Cr molar ratio around 14:1), and such liquids behave like supersaturated electrolytes with a reduced propensity toward hydrogen evolution. The best quality bright deposits are produced at relatively high current density of 20 mA/cm2.[5]
Decorative chrome is designed to be aesthetically pleasing and durable. Thicknesses range from 2 to 20 μin (0.05 to 0.5 μm), however, they are usually between 5 and 10 μin (0.13 and 0.25 μm). The chromium plating is usually applied over bright nickel plating. Typical base materials include steel, aluminium, plastic, copper alloys, and zinc alloys.[3] Decorative chrome plating is also very corrosion resistant and is often used on car parts, tools and kitchen utensils.[citation needed]
Thin dense chrome (TDC) differs from decorative chrome.[6] While decorative chrome is applied primarily for aesthetic purposes with thin layers that provide a shiny finish, TDC, such as Armoloy, focuses on enhancing surface performance. It delivers wear resistance, corrosion protection, and hardness without adding significant thickness. TDC also avoids the microcracking associated with decorative chrome, making it ideal for industrial applications where durability and friction reduction are necessary. Thin dense chrome is commonly used in precision tools, aerospace, medical, and food processing equipment.
Hard chrome, also known as industrial chrome or engineered chrome, is used to reduce friction, improve durability through abrasion tolerance and wear resistance in general, minimize galling or seizing of parts, expand chemical inertness to include a broader set of conditions (such as oxidation resistance), and bulking material for worn parts to restore their original dimensions.[7] It is very hard, measuring between 65 and 69 HRC (also based on the base metal's hardness). Hard chrome tends to be thicker than decorative chrome, with standard thicknesses in non-salvage applications ranging from 20 to 40 μm,[8] but it can be an order of magnitude thicker for extreme wear resistance requirements, in such cases 100 μm or thicker provides optimal results. Unfortunately, such thicknesses emphasize the limitations of the process, which are overcome by plating extra thickness then grinding down and lapping to meet requirements, or to improve the overall aesthetics of the chromed piece.[3] Increasing plating thickness amplifies surface defects and roughness in proportional severity, because hard chrome does not have a leveling effect.[9] Pieces that are not ideally shaped in reference to electric field geometries (nearly every piece sent in for plating, except spheres and egg shaped objects) require even thicker plating to compensate for non-uniform deposition, and much of it is wasted when grinding the piece back to desired dimensions.[citation needed]
Modern engineered coatings do not suffer such drawbacks, which often price hard chrome out due to labor costs alone. Hard chrome replacement technologies outperform hard chrome in wear resistance, corrosion resistance, and cost. Hardness up to 80 HRC is not extraordinary for such materials. Modern engineered coatings applied using spray deposition can form layers of uniform thickness that often require no further polishing or machining. These coatings are often composites of polymers, metals, and ceramic powders or fibers as proprietary formulas protected by patents or as trade secrets, and thus are usually known by brand names.[10]
Hard chromium plating is subject to different types of quality requirements depending on the application; for instance, the plating on hydraulic piston rods are tested for corrosion resistance with a salt spray test.[citation needed]
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Most bright decorative items affixed to cars are referred to as "chrome", meaning steel that has undergone several plating processes to protect it from weathering and moisture but the term passed on to cover any similar-looking shiny decorative auto parts, including silver plastic trim pieces in casual terminology. Triple plating is the most expensive and durable process, which involves plating the steel first with copper and then nickel before the chromium plating is applied.
Prior to the application of chrome in the 1920s, nickel electroplating was used. In the short production run prior to the US entry into World War II, the government banned plating to save chromium and automobile manufacturers painted the decorative pieces in a complementary color. In the last years of the Korean War, the US contemplated banning chrome in favor of several cheaper processes (such as plating with zinc and then coating with shiny plastic).
In 2007, a Restriction of Hazardous Substances Directive (RoHS) was issued banning several toxic substances for use in the automotive industry in Europe, including hexavalent chromium, which is used in chrome plating. However, chrome plating is metal and contains no hexavalent chromium after it is rinsed, so chrome plating is not banned.[11]
Chrome-lining protects the barrel or chamber of arms from corrosion and makes these parts also easier to clean, but this is not the main purpose for lining a barrel or chamber. Chrome-lining was introduced in machine guns to increase the wear resistance and service life of highly stressed arms parts like barrels and chambers, allowing more rounds to be fired before a barrel is worn and needs to be replaced. The end of the chamber, freebore and leade (the unrifled portion of the barrel just forward of the chamber), as well as the first few centimeters or few inches of rifling, in rifles are subject to very high temperatures—as the energy content of rifle propellants can exceed 3500 kJ/kg—and pressures that can exceed 380 MPa (55,114 psi). The propellant gases act similarly as the flame from a cutting torch, the gases heating up the metal to red-hot state and the velocity tearing away metal. Under slow fire conditions, the affected areas are able to cool sufficiently in between shots. Under sustained rapid fire or automatic/cyclic fire there is no time for the heat to dissipate. The heat and pressure effects exerted by the hot propellant gases and friction by the projectile can quickly cause damage by washing away metal at the end of the chamber, freebore, leade and rifling. Hard chrome-lining protects the chamber, freebore, leade and rifling with a thin coat of wear resistant chrome. This significantly extends barrel life in arms that are fired for prolonged periods in full-auto or sustained rapid fire modes. Some arms manufacturers use Stellite-lining alloy as an alternative to hard chrome-lining to further increase the wear resistance and service life of highly stressed arms parts.[12][13]
Hexavalent chromium is the most toxic form of chromium. In the U.S., the Environmental Protection Agency regulates it heavily. The EPA lists hexavalent chromium as a hazardous air pollutant because it is a human carcinogen, a "priority pollutant" under the Clean Water Act, and a "hazardous constituent" under the Resource Conservation and Recovery Act. Due to its low cathodic efficiency and high solution viscosity, a toxic mist of water and hexavalent chromium is released from the bath. Wet scrubbers are used to control these emissions. The liquid from the wet scrubbers is treated to precipitate the chromium and remove it from the wastewater before it is discharged.[3]
Additional toxic waste created from hexavalent chromium baths include lead chromates, which form in the bath because lead anodes are used. Barium is also used to control the sulfate concentration, which leads to the formation of barium sulfate (BaSO4).[3]
Trivalent chromium is intrinsically less toxic than hexavalent chromium. Because of the lower toxicity it is not regulated as strictly, which reduces overhead costs. Other health advantages include higher cathode efficiencies, which lead to less chromium air emissions; lower concentration levels, resulting in less chromium waste and anodes that do not decompose.[3]
Maintaining a bath surface tension less than 35 dyn/cm is necessary to prevent plating solution from becoming airborne when bubbles rise to the surface and pop. This requires a frequent cycle of treating the bath with a wetting agent fume suppressant and confirming the effect on surface tension.[14] Usually, surface tension is measured with a stalagmometer or tensiometer. This method is, however, tedious and suffers from inaccuracy (errors up to 22 dyn/cm have been reported), and is dependent on the user's experience and capabilities.[15]
While they are effective for the control of toxic airborne chromium, many widely used wetting agent fume suppressants are toxic themselves because they contain perfluoroalkyl substances (PFAS), which are hazardous chemicals that can cause long-term health effects.[16] This makes electroplating one of the jobs with the highest risk of occupational exposure to PFAS, but not as high as firefighters using fluorinated aqueous film forming foams.[17] In addition to their detrimental effects on human health, PFAS are persistent pollutants that cause significant bioaccumulation and biomagnification, putting animals at the highest trophic level at the highest risk for toxic effects.[18] [19]
It has been known for over a century, that chromium electroplating is relatively easy from (di)chromate solutions, but difficult from Cr3+ solutions. Several theories have been proposed to explain this finding.
An earlier view suggested, that an active Cr3+ species (perhaps, with a ligand rather than water) forms initially from electroreduced Cr6+.[20][21] This active Cr3+ species can be reduced into metallic chromium relatively easy. However, the "active Cr3+" also undergoes within less than 1 second a transition into "inactive Cr3+", which is believed to be a polymeric hexa-aqua complex.[22] Some complexes of Cr3+ with ligand other than water can undergo relatively fast electroreduction to metallic chromium, and they are used in chromate-free chromium plating methods.[23][24]
A different school of thought suggests, that the main problem with chromium plating from Cr3+ solution is hydrogen evolution reaction (HER), and the role of chromate is to scavenge H+ ions in a reaction that competes with H2 evolution:
The shine of plated chrome depends on whether microscopic cracks in the plating are visible on the surface. The dull appearance of some chrome layers is due to continuous cracks that propagate through the whole plated metal layer, while bright deposits appear in the case of small microcracks that are confined to inner depth of the deposit. This HER side-reaction mechanism seems more acceptable by the electrochemistry community at present. Methods of plating chromium from Cr3+ solutions that rely on reversed current pulses have been commercialized (allegedly, to reoxidize the H2).[25][26][27]
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Chrome plating (less commonly chromium plating) is a technique of electroplating a thin layer of chromium onto a metal object. A chrome plated part is called chrome, or is said to have been chromed. The chromium layer can be decorative, provide corrosion resistance, facilitate cleaning, and increase surface hardness. Sometimes a less expensive substitute for chrome, such as nickel, may be used for aesthetic purposes. Chromium compounds used in electroplating are toxic. In most countries, their disposal is tightly regulated. Some fume suppressants used to control the emission of airborne chromium from plating baths are also toxic, making disposal even more difficult.
Art Deco, short for the French Arts décoratifs (lit. 'Decorative Arts'), is a style of visual arts, architecture, and product design that first appeared in Paris in the 1910s just before World War I and flourished internationally during the 1920s to early 1930s, through styling and design of the exterior and interior of anything from large structures to small objects, including clothing, fashion, and jewelry. Art Deco has influenced buildings from skyscrapers to cinemas, bridges, ocean liners, trains, cars, trucks, buses, furniture, and everyday objects, including radios and vacuum cleaners. The name Art Deco came into use after the 1925 Exposition internationale des arts décoratifs et industriels modernes (International Exhibition of Modern Decorative and Industrial Arts) held in Paris. It has its origin in the bold geometric forms of the Vienna Secession and Cubism. From the outset, Art Deco was influenced by the bright colors of Fauvism and the Ballets Russes, and the exoticized styles of art from China, Japan, India, Persia, ancient Egypt, and the Maya. In its time, Art Deco was tagged with other names such as style moderne, Moderne, modernistic, or style contemporain, and it was not recognized as a distinct and homogeneous style. During its heyday, Art Deco represented luxury, glamour, exuberance, and faith in social and technological progress. The movement featured rare and expensive materials such as ebony and ivory, and exquisite craftsmanship. It also introduced new materials such as chrome plating, stainless steel, and plastic. In New York, the Empire State Building, the Chrysler Building, and other buildings from the 1920s and 1930s are monuments to the style. The largest concentration of Art Deco architecture in the world is in Miami Beach, Florida. Art Deco became more subdued during the Great Depression. A sleeker form of the style appeared in the 1930s called Streamline Moderne, featuring curving forms and smooth, polished surfaces. Art Deco was an international style but, after the outbreak of World War II, it lost its dominance to the functional and unadorned styles of modern architecture, in particular what is now called the International Style.
Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium is valued for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating (electroplating with chromium) together comprise 85% of the commercial use. Chromium is also greatly valued as a metal that is able to be highly polished while resisting tarnishing. Polished chromium reflects almost 70% of the visible spectrum, and almost 90% of infrared light. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored. Industrial production of chromium proceeds from chromite ore (mostly FeCr2O4) to produce ferrochromium, an iron-chromium alloy, by means of aluminothermic or silicothermic reactions. Ferrochromium is then used to produce alloys such as stainless steel. Pure chromium metal is produced by a different process: roasting and leaching of chromite to separate it from iron, followed by reduction with carbon and then aluminium. Trivalent chromium (Cr(III)) occurs naturally in many foods and is sold as a dietary supplement, although there is insufficient evidence that dietary chromium provides nutritional benefit to people. In 2014, the European Food Safety Authority concluded that research on dietary chromium did not justify it to be recognized as an essential nutrient. While chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called "hexavalent chromium", is toxic and carcinogenic. According to the European Chemicals Agency (ECHA), chromium trioxide that is used in industrial electroplating processes is a "substance of very high concern" (SVHC).
The Dekochari or decoration charinko (デコチャリ or デコレーション・チャリンコ, dekochari or dekorēshon charinko) is a form of art bike indigenous to Japan dating back to the mid-1970s. "Deko" in Japanese is short for "decoration" and "chari" is slang for "bike". The dekochari was a response by children to the Dekotora ("tora" is short for "truck") craze which swept Japan after a series of movies called Truck Yaro was released. These movies featured giant trucks decked out in chrome and flashy lights. Unable to drive the chrome-plated flashing trucks, children instead built plywood boxes around their bikes and attached chrome plating and lights. Almost all current Dekocharis have elaborate light displays and many include hi-fi audio systems and cup-holders. There are currently several dekochari bike gangs in Japan, including the All Japan Hishyomaru fleet, the All Japan DC Club Ryumaki and the All Japan Kyokugenmaru Gang.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.
