Miscellany

Jai Ganesh · 2025-03-30 23:26:43

2401) Metalloid

Gist

What are Metalloids? Metalloids can be defined as chemical elements whose physical and chemical properties fall in between the metal and non-metal categories. Boron, germanium, silicon, antimony, As, tellurium and pollanium are the seven most widely recognized metalloids.

Summary

A metalloid, in chemistry, an imprecise term used to describe a chemical element that forms a simple substance having properties intermediate between those of a typical metal and a typical nonmetal. The term is normally applied to a group of between six and nine elements (boron, silicon, germanium, As, antimony, tellurium, and possibly bismuth, polonium, astatine) found near the center of the P-block or main block of the periodic table. There is no single property which can be used to unambiguously identify an element as a metalloid. Since most metalloids tend to display semiconducting properties in at least one of their allomorphic modifications, the class might reasonably be extended to also include gray silicon (which, unlike white silicon, is a semiconductor rather than a metal) and the graphite form of carbon (which, unlike the diamond form, is a semimetal rather than an insulator). Chemically, metalloids correspond to atoms having intermediate electronegativities and an ability to display a range of both positive and negative oxidation states in their compounds.

Details

A metalloid is a chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. The word metalloid comes from the Latin metallum ("metal") and the Greek oeides ("resembling in form or appearance"). There is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature.

The six commonly recognised metalloids are boron, silicon, germanium, As, antimony and tellurium. Five elements are less frequently so classified: carbon, aluminium, selenium, polonium and astatine. On a standard periodic table, all eleven elements are in a diagonal region of the p-block extending from boron at the upper left to astatine at lower right. Some periodic tables include a dividing line between metals and nonmetals, and the metalloids may be found close to this line.

Typical metalloids have a metallic appearance, may be brittle and are only fair conductors of electricity. They can form alloys with metals, and many of their other physical properties and chemical properties are intermediate between those of metallic and nonmetallic elements. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate or hybrid properties, became widespread in 1940–1960. Metalloids are sometimes called semimetals, a practice that has been discouraged,[2] as the term semimetal has a more common usage as a specific kind of electronic band structure of a substance. In this context, only As and antimony are semimetals, and commonly recognised as metalloids.

Definitions:

Judgment-based

A metalloid is an element that possesses a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals, and which is therefore hard to classify as either a metal or a nonmetal. This is a generic definition that draws on metalloid attributes consistently cited in the literature. Difficulty of categorisation is a key attribute. Most elements have a mixture of metallic and nonmetallic properties, and can be classified according to which set of properties is more pronounced. Only the elements at or near the margins, lacking a sufficiently clear preponderance of either metallic or nonmetallic properties, are classified as metalloids.

Boron, silicon, germanium, As, antimony, and tellurium are commonly recognised as metalloids. Depending on the author, one or more from selenium, polonium, or astatine are sometimes added to the list. Boron sometimes is excluded, by itself, or with silicon. Sometimes tellurium is not regarded as a metalloid. The inclusion of antimony, polonium, and astatine as metalloids has been questioned.

Other elements are occasionally classified as metalloids. These elements include hydrogen, beryllium, nitrogen, phosphorus, sulfur, zinc, gallium, tin, iodine, lead, bismuth, and radon. The term metalloid has also been used for elements that exhibit metallic lustre and electrical conductivity, and that are amphoteric, such as As, antimony, vanadium, chromium, molybdenum, tungsten, tin, lead, and aluminium. The p-block metals,[33] and nonmetals (such as carbon or nitrogen) that can form alloys with metals or modify their properties have also occasionally been considered as metalloids.

Criteria-based

The elements commonly recognised as metalloids, and their ionization energies (IE); electronegativities (EN, revised Pauling scale); and electronic band structures (most thermodynamically stable forms under ambient conditions).

No widely accepted definition of a metalloid exists, nor any division of the periodic table into metals, metalloids, and nonmetals; Hawkes questioned the feasibility of establishing a specific definition, noting that anomalies can be found in several attempted constructs. Classifying an element as a metalloid has been described by Sharp[40] as "arbitrary".

The number and identities of metalloids depend on what classification criteria are used. Emsley recognised four metalloids (germanium, As, antimony, and tellurium); James et al. listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, moscovium, and livermorium). On average, seven elements are included in such lists; individual classification arrangements tend to share common ground and vary in the ill-defined margins.

A single quantitative criterion such as electronegativity is commonly used,[46] metalloids having electronegativity values from 1.8 or 1.9 to 2.2. Further examples include packing efficiency (the fraction of volume in a crystal structure occupied by atoms) and the Goldhammer–Herzfeld criterion ratio. The commonly recognised metalloids have packing efficiencies of between 34% and 41%. The Goldhammer–Herzfeld ratio, roughly equal to the cube of the atomic radius divided by the molar volume, is a simple measure of how metallic an element is, the recognised metalloids having ratios from around 0.85 to 1.1 and averaging 1.0. Other authors have relied on, for example, atomic conductance or bulk coordination number.

Jones, writing on the role of classification in science, observed that "[classes] are usually defined by more than two attributes". Masterton and Slowinski used three criteria to describe the six elements commonly recognised as metalloids: metalloids have ionization energies around 200 kcal/mol (837 kJ/mol) and electronegativity values close to 2.0. They also said that metalloids are typically semiconductors, though antimony and As (semimetals from a physics perspective) have electrical conductivities approaching those of metals. Selenium and polonium are suspected as not in this scheme, while astatine's status is uncertain.

In this context, Vernon proposed that a metalloid is a chemical element that, in its standard state, has (a) the electronic band structure of a semiconductor or a semimetal; and (b) an intermediate first ionization potential "(say 750−1,000 kJ/mol)"; and (c) an intermediate electronegativity (1.9–2.2).

Additional Information

The four major properties of metalloids are as follows:

- They are solids

- They have a metallic luster

- They are brittle

- They are semiconductors

What types of properties do metalloids display?

Metalloid element properties include a mixture of properties of both metals and nonmetals. While some characteristics (such as their metallic luster) are similar to metals, others (such as their brittleness) are similar to nonmetals.

Where are the metalloids on the periodic table?

The metalloids are located along a slanted line between the metal elements and nonmetal elements of the periodic table. They span from Group 13 to Group 16, 17, or 18 based on what criteria of classifying metalloid elements is being used.

How many metalloids are on the periodic table?

There are six elements generally accepted to be metalloids. However, based on the classification criteria being used, the exact number may vary, ranging from six to nine elements.

To summarize:

Metalloid is derived from the Latin metallum (“metal”) and the Greek oeides (“resembling in form or appearance”). A metalloid represents a chemical element exhibiting properties that are intermediate between those of metals and nonmetals. Or we can say they are a mixture of metals and nonmetals. Elements classified as metalloids are frequently highlighted in what is known as the “Metalloid Stair Step” because when colored differently from the other elements, this group of elements resembles a staircase.

The six most often recognized examples of metalloids cover boron, silicon, germanium, As, antiimony, and tellurium. And there are five elements, such as carbon, aluminum, selenium, polonium, and astatine are seldom categorized into metalloids. All eleven elements can be found on the standard periodic table. They are located in a diagonal region of the p-block ranging from boron at the upper left to astatine at the lower right. On some periodic tables, metalloids can be found near the dividing line between metals and nonmetals.

Metalloids have a metallic look, yet they are brittle and only electrical conductors with a level of intermediate to good. Chemically, they mainly act like nonmetals. They can combine with metals to make alloys. The majority of their other chemical and physical properties tend to be intermediate. Metalloids are often too brittle to be used in structural applications. However, metalloids and their compounds are always employed in alloys, biological agents, catalysts, flame retardants, glasses, optical storage, optoelectronics, pyrotechnics, semiconductors, and electronics.

Jai Ganesh · 2025-04-01 00:02:15

2402) Nonmetal

Gist

The 17 nonmetal elements are: hydrogen, helium, carbon, nitrogen, oxygen, fluorine, neon, phosphorus, sulfur, chlorine, argon, selenium, bromine, krypton, iodine, xenon, and radon.

Summary:

What is an example of a nonmetal element?

An example of a nonmetal element is helium. Helium is a noble gas which possesses very nonmetallic characteristics such as high electronegativity and high ionization energy. However, helium is exceptionally nonreactive and is not found in compounds like most metals are found in. Helium is also a gas at room temperature.

What is a nonmetal definition?

The definition of nonmetals is a classification of elements that possess particular chemical and physical properties such as the following:

* High electronegativity.

* High ionization energy.

* Poor conductor of electricity and heat.

* Relatively low boiling point.

* Matte, nonmetallic appearance, and usually brittle as a solid.

What are the nonmetals on the periodic table?

Nonmetals are typically found toward the top right of the periodic table of elements. This excludes hydrogen, which is all the way in the top left of the periodic table. Nonmetals exhibit nonmetallic characteristics and are poor conductors of heat and electricity, and typically have high ionization energy and electronegativity. Nonmetals include the following elements:

Hydrogen
Helium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
Silicon
Phosphorous
Sulfur
Chlorine
Argon
Germanium
As
Selenium
Bromine
Krypton
Antimony
Tellurium
Iodine
Xenon
Radon.

Details

In the context of the periodic table a nonmetal is a chemical element that mostly lacks distinctive metallic properties. They range from colorless gases like hydrogen to shiny crystals like iodine. Physically, they are usually lighter (less dense) than elements that form metals and are often poor conductors of heat and electricity. Chemically, nonmetals have relatively high electronegativity or usually attract electrons in a chemical bond with another element, and their oxides tend to be acidic.

Seventeen elements are widely recognized as nonmetals. Additionally, some or all of six borderline elements (metalloids) are sometimes counted as nonmetals.

The two lightest nonmetals, hydrogen and helium, together make up about 98% of the mass of the observable universe. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—make up the bulk of Earth's atmosphere, biosphere, crust and oceans.

Industrial uses of nonmetals include in electronics, energy storage, agriculture, and chemical production.

Most nonmetallic elements were identified in the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, a basic classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then about twenty properties have been suggested as criteria for distinguishing nonmetals from metals.

Definition and applicable elements

Nonmetallic chemical elements are often described as lacking properties common to metals, namely shininess, pliability, good thermal and electrical conductivity, and a general capacity to form basic oxides. There is no widely accepted precise definition; any list of nonmetals is open to debate and revision. The elements included depend on the properties regarded as most representative of nonmetallic or metallic character.

Fourteen elements are almost always recognized as nonmetals:

Hydrogen
Nitrogen
Oxygen
Sulfur
Fluorine
Chlorine
Bromine
Iodine
Helium
Neon
Argon
Krypton
Xenon
Radon

Three more are commonly classed as nonmetals, but some sources list them as "metalloids", a term which refers to elements regarded as intermediate between metals and nonmetals:

Carbon
Phosphorus
Selenium

One or more of the six elements most commonly recognized as metalloids are sometimes instead counted as nonmetals:

Boron
Silicon
Germanium
As
Antimony
Tellurium

About 15–20% of the 118 known elements are thus classified as nonmetals.

Additional Information

A nonmetal, in physics, is a substance having a finite activation energy (band gap) for electron conduction. This means that nonmetals display low (insulators) to moderate (semiconductors) bulk electrical conductivities, which increase with increasing temperature, and are subject to dielectric breakdown at high voltages and temperatures. Like metals, nonmetals may occur in the solid, liquid, or gaseous state. However, unlike metals, nonmetals display a wide range of both mechanical and optical properties, ranging from brittle to plastic and from transparent to opaque.

From a chemical point of view, nonmetals may be divided into two classes: 1) covalent materials, which contain atoms having small sizes, high electronegativities, low valence vacancy to electron ratios, and a pronounced tendency to form negative ions in chemical reactions and negative oxidation states in their compounds; 2) ionic materials, which contain both small and large atoms. Ions may be formed by adding electrons to (small, electronegative atoms) or by extracting electrons from (large, electropositive) atoms. In ionic materials, nonmetals exist either as monatomic anions (e. g., F-in NaF) or as constituents of polyatomic anions (e.g., N and O in the NO3-`s in NaNO3). When in the form of simple elemental substances, about 25 or 22% of the known elements form nonmetals at normal temperatures and pressures, including all of the elements in the S-block of the periodic table and approximately 58% of those in the P-block.

Jai Ganesh · Yesterday 00:00:44

2303) Water wheel

Gist

A waterwheel is also called a turbine. Water-powered grist mill in Tennessee. Three types of waterwheels are tha horizontal waterwheel, overshot vertical waterwheel, and undershot vertical waterwheel. In the horizontal waterwheel, water flows from an aqueduct or pipe from the side of the wheel and onto the wheel.

A waterwheel is a mechanical device for tapping the energy of running or falling water by means of a set of paddles mounted around a wheel. The force of the moving water is exerted against the paddles, and the consequent rotation of the wheel is transmitted to machinery via the shaft of the wheel.

Summary

A waterwheel, is a mechanical device for tapping the energy of running or falling water by means of a set of paddles mounted around a wheel. The force of the moving water is exerted against the paddles, and the consequent rotation of the wheel is transmitted to machinery via the shaft of the wheel. The waterwheel was perhaps the earliest source of mechanical energy to replace that of humans and animals, and it was first exploited for such tasks as raising water, fulling cloth, and grinding grain.

A brief treatment of waterwheels follows.

The combination of waterwheel and transmission linkage, often including gearing, was from the Middle Ages usually designated a mill. Of the three distinct types of water mills, the simplest and probably the earliest was a vertical wheel with paddles on which the force of the stream acted. Next was the horizontal wheel used for driving a millstone through a vertical shaft attached directly to the wheel. Third was the geared mill driven by a vertical waterwheel with a horizontal shaft. This required more knowledge and engineering skill than the first two, but it had much greater potential. Vertical waterwheels were also distinguished by the location of water contact with the wheel: first, the undershot wheel; second, the breast wheel; and third, the overshot wheel. These waterwheels generally used the energy of moving streams, but tidal mills also appeared in the 11th century.

Each type of mill had its particular advantages and disadvantages. Relatively little is known of their development before the Middle Ages, but certain of their characteristics suggest an order of appearance within the context of the complexity of construction and the possibilities for utilization.

The simple vertical wheel required little extra structure, but the force and rate of power takeoff were dependent upon stream characteristics and wheel diameter. Since change of power direction was not involved, this wheel proved most useful in raising water, utilizing, for instance, a string of pots worked by a chain drive.

The horizontal-wheel mill (sometimes called a Norse or Greek mill) also required little auxiliary construction, but it was suited for grinding because the upper millstone was fixed upon the vertical shaft. The mill, however, could only be used where the current flow was suitable for grinding.

The geared vertical-wheel mill was more versatile. Construction was relatively simple if the wheel was of the undershot kind, because the wheel paddles could be simply dipped in the stream flow, whether it was river, tide, or man-built millrace. A millwright could choose his gear ratio to match power utilization with rate of stream flow, and the wheel could be mounted in a bridge arch or on a barge anchored in midstream. Vitruvius described the first geared vertical wheel for which we have good evidence. This mill is also of major significance because it was the first application of gearing to utilize other than muscle power. This mill had an undershot wheel and, unlike the breast or overshot wheels, did not make use of the weight of falling water.

Mills with geared breast and overshot wheels required more auxiliary construction, but they allowed the most generalized exploitation of available water power. A major construction problem was locating a mill where the fall of water would be suited to the desired diameter of the wheel. Either a long millrace from upstream or a dam could be used.

Little is known of the details of geared-mill development between the time of Vitruvius and the 12th century. An outstanding installation was the grain mill at Barbegal, near Arles, France, which had 16 cascaded overshot wheels, each 7 feet (2 metres) in diameter, with wooden gearing. It is estimated that this mill could meet the needs of a population of 80,000.

Even though the highly adaptable, geared mill, with its widely diversified stream-flow conditions, was used in the Roman Empire, historical evidence suggests that its most dramatic industrial consequences occurred during the Middle Ages in Western Europe. After the 13th century the overshot waterwheel appears to have become more common than the undershot wheel.

The geared mill of the Middle Ages was actually a general mechanism for the utilization of power. The power from a horse- or cattle-powered mill was small compared to that from overshot water-wheels, which usually generated two to five horsepower.

Details

A water wheel is a machine for converting the kinetic energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a large wheel (usually constructed from wood or metal), with numerous blades or buckets attached to the outer rim forming the drive mechanism. Water wheels were still in commercial use well into the 20th century, although they are no longer in common use today. Water wheels are used for milling flour in gristmills, grinding wood into pulp for papermaking, hammering wrought iron, machining, ore crushing and pounding fibre for use in the manufacture of cloth.

Some water wheels are fed by water from a mill pond, which is formed when a flowing stream is dammed. A channel for the water flowing to or from a water wheel is called a mill race. The race bringing water from the mill pond to the water wheel is a headrace; the one carrying water after it has left the wheel is commonly referred to as a tailrace.

Waterwheels were used for various purposes from things such as agriculture to metallurgy in ancient civilizations spanning the Hellenistic Greek world, Rome, China and India. Waterwheels saw continued use in the post-classical age, like in medieval Europe and the Islamic Golden Age, but also elsewhere. In the mid- to late 18th century John Smeaton's scientific investigation of the water wheel led to significant increases in efficiency, supplying much-needed power for the Industrial Revolution. [ Water wheels began being displaced by the smaller, less expensive and more efficient turbine, developed by Benoît Fourneyron, beginning with his first model in 1827. Turbines are capable of handling high heads, or elevations, that exceed the capability of practical-sized waterwheels.

The main difficulty of water wheels is their dependence on flowing water, which limits where they can be located. Modern hydroelectric dams can be viewed as the descendants of the water wheel, as they too take advantage of the movement of water downhill.

Types

Water wheels come in two basic designs:

* a horizontal wheel with a vertical axle; or
* a vertical wheel with a horizontal axle.

The latter can be subdivided according to where the water hits the wheel into backshot (pitch-back), overshot, breastshot, undershot, and stream-wheels. The term undershot can refer to any wheel where the water passes under the wheel[9] but it usually implies that the water entry is low on the wheel.

Overshot and backshot water wheels are typically used where the available height difference is more than a couple of meters. Breastshot wheels are more suited to large flows with a moderate head. Undershot and stream wheel use large flows at little or no head.

There is often an associated millpond, a reservoir for storing water and hence energy until it is needed. Larger heads store more gravitational potential energy for the same amount of water so the reservoirs for overshot and backshot wheels tend to be smaller than for breast shot wheels.

Overshot and pitchback water wheels are suitable where there is a small stream with a height difference of more than 2 metres (6.5 ft), often in association with a small reservoir. Breastshot and undershot wheels can be used on rivers or high volume flows with large reservoirs.

Additional Information

Water wheels are found next to areas of moving water such as rivers or canals. They harness the moving water to generate power or electricity; this can be called hydro-power.

There are three different types of water wheel that you could see, this includes:

* overshot
* undershot
* breastshot.

The main difference between the three types is where the water hits the paddles attached to the wheel - either from above, below or the middle.

Jai Ganesh · Today 00:30:16

2304) Amalgam

Gist

An amalgam is an alloy, or a mixture, of mercury with one or more other metals, often used in dentistry for fillings and in gold extraction.

Summary

An amalgam is an alloy of mercury and one or more other metals. Amalgams are crystalline in structure, except for those with a high mercury content, which are liquid. Known since early times, they were mentioned by Pliny the Elder in the 1st century ad. In dentistry, an amalgam of silver and tin, with minor amounts of copper and zinc, is used to fill teeth.

A sodium amalgam is formed during the manufacture of chlorine and sodium hydroxide by the electrolysis of brine in cells wherein a stream of mercury constitutes the negative electrode. Reaction of the amalgam with water produces a solution of sodium hydroxide and regenerates the mercury for reuse.

Fine particles of silver and gold can be recovered by agitating their ores with mercury and allowing the resultant pasty or liquid amalgam to settle. By distillation of the amalgam, the mercury is reclaimed, and the precious metals are isolated as a residue.

Amalgams of silver, gold, and palladium are known in nature. Moschellandsbergite, silver amalgam, is found at Moschellandsberg, Ger.; Sala, Swed.; and Isère, France. Gold amalgam occurs in California, U.S., Colombia, and Borneo.

Details

An amalgam is an alloy of mercury with another metal. It may be a liquid, a soft paste or a solid, depending upon the proportion of mercury. These alloys are formed through metallic bonding, with the electrostatic attractive force of the conduction electrons working to bind all the positively charged metal ions together into a crystal lattice structure. Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum. Gold-mercury amalgam is used in the extraction of gold from ore, and dental amalgams are made with metals such as silver, copper, indium, tin and zinc.

Important amalgams:

Zinc amalgam

Zinc amalgam finds use in organic synthesis (e.g., for the Clemmensen reduction). It is the reducing agent in the Jones reductor, used in analytical chemistry. Formerly the zinc plates of dry batteries were amalgamated with a small amount of mercury to prevent deterioration in storage. It is a binary solution (liquid-solid) of mercury and zinc.

Potassium amalgam

For the alkali metals, amalgamation is exothermic, and distinct chemical forms can be identified, such as KHg and KHg2. KHg is a gold-coloured compound with a melting point of 178 °C, and KHg2 a silver-coloured compound with a melting point of 278 °C. These amalgams are very sensitive to air and water, but can be worked with under dry nitrogen. The Hg-Hg distance is around 300 picometres, Hg-K around 358 pm.

Phases K5Hg7 and KHg11 are also known; rubidium, strontium and barium undecamercurides are known and isostructural. Sodium amalgam (NaHg2) has a different structure, with the mercury atoms forming hexagonal layers, and the sodium atoms a linear chain which fits into the holes in the hexagonal layers, but the potassium atom is too large for this structure to work in KHg2.

Sodium amalgam

Sodium amalgam is produced as a byproduct of the chloralkali process and used as an important reducing agent in organic and inorganic chemistry. With water, it decomposes into concentrated sodium hydroxide solution, hydrogen and mercury, which can then return to the chloralkali process anew. If absolutely water-free alcohol is used instead of water, an alkoxide of sodium is produced instead of the alkali solution.

Aluminium amalgam

Aluminium can form an amalgam through a reaction with mercury. Aluminium amalgam may be prepared by either grinding aluminium pellets or wire in mercury, or by allowing aluminium wire or foil to react with a solution of mercuric chloride. This amalgam is used as a reagent to reduce compounds, such as the reduction of imines to amines. The aluminium is the ultimate electron donor, and the mercury serves to mediate the electron transfer.[5] The reaction itself and the waste from it contain mercury, so special safety precautions and disposal methods are needed. As an environmentally friendlier alternative, hydrides or other reducing agents can often be used to accomplish the same synthetic result. Another environmentally friendly alternative is an alloy of aluminium and gallium which similarly renders the aluminium more reactive by preventing it from forming an oxide layer.

Tin amalgam

Tin amalgam was used in the middle of the 19th century as a reflective mirror coating.

Other amalgams

A variety of amalgams are known that are of interest mainly in the research context.

Ammonium amalgam is a grey, soft, spongy mass discovered in 1808 by Humphry Davy and Jöns Jakob Berzelius. It decomposes readily at room temperature or in contact with water or alcohol.

* Thallium amalgam has a freezing point of −58 °C, which is lower than that of pure mercury (−38.8 °C) so it has found a use in low temperature thermometers.
* Gold amalgam: Refined gold, when finely ground and brought into contact with mercury where the surfaces of both metals are clean, amalgamates readily and quickly forms alloys ranging from AuHg2 to Au8Hg.
* Lead forms an amalgam when filings are mixed with mercury[citation needed] and is also listed as a naturally occurring alloy called leadamalgam in the Nickel–Strunz classification.

Dental amalgam

Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc. Amalgam is an "excellent and versatile restorative material" and is used in dentistry because it is inexpensive and relatively easy to use and manipulate during placement. It remains soft for a short time so it can be packed to fill any irregular volume, and then forms a hard compound. Amalgam possesses greater longevity when compared to other direct restorative materials, such as composite. However, this difference has decreased with continual development of composite resins.

Amalgam is typically compared to resin-based composites because many applications are similar and many physical properties and costs are comparable.

Dental amalgam has been studied and is generally considered to be safe for humans, though the validity of some studies and their conclusions have been questioned.

In July 2018 the EU, in consideration of the persistent pollution and environmental toxicity of amalgam's mercury, prohibited amalgam for dental treatment of children under 15 years and of pregnant or breastfeeding women.

Use in mining

Mercury has been used in gold and silver mining because of the convenience and the ease with which mercury and the precious metals will amalgamate. In gold placer mining, in which minute specks of gold are washed from sand or gravel deposits, mercury was often used to separate the gold from other heavy minerals.

After all of the practical metal had been taken out from the ore, the mercury was dispensed down a long copper trough, which formed a thin coating of mercury on the exterior. The waste ore was then transferred down the trough, and gold in the waste amalgamated with the mercury. This coating would then be scraped off and refined by evaporation to get rid of the mercury, leaving behind somewhat high-purity gold.

Mercury amalgamation was first used on silver ores with the development of the patio process in Mexico in 1557. There were also additional amalgamation processes that were created for processing silver ores, including pan amalgamation and the Washoe process.

Gold amalgam:

Gold extraction (mining)

Gold amalgam has proved effective where gold fines ("flour gold") would not be extractable from ore using hydro-mechanical methods. Large amounts of mercury were used in placer mining, where deposits composed largely of decomposed granite slurry were separated in long runs of "riffle boxes", with mercury dumped in at the head of the run. The amalgam formed is a heavy dull gray solid mass. The use of mercury in 19th century placer mining in California, now prohibited, has caused extensive pollution problems in riverine and estuarine environments, ongoing to this day. Sometimes substantial slugs of amalgam are found in downstream river and creek bottoms by amateur wet-suited miners seeking gold nuggets with the aid of an engine-powered water vacuum/dredge mounted on a float.

Gold extraction (ore processing)

Where stamp mills were used to crush gold-bearing ore to fines, a part of the extraction process involved the use of mercury-wetted copper plates, over which the crushed fines were washed. A periodic scraping and re-mercurizing of the plate resulted in amalgam for further processing.

Gold extraction (retorting)

Amalgam obtained by either process was then heated in a distillation retort, recovering the mercury for reuse and leaving behind the gold. As this released mercury vapors to the atmosphere, the process could induce adverse health effects and long term pollution.

Today, mercury amalgamation has been replaced by other methods to recuperate gold and silver from ore in developed nations. Hazards of mercurial toxic waste have played a major role in the phasing out of the mercury amalgamation processes. Mercury amalgamation is still regularly used by small-scale gold placer miners (often illegally), particularly in developing countries.

Amalgam probe

Mercury salts are, compared to mercury metal and amalgams, highly toxic due to their solubility in water. The presence of these salts in water can be detected with a probe that uses the readiness of mercury ions to form an amalgam with copper. A nitric acid solution of salts under investigation is applied to a piece of copper foil, and any mercury ions present will leave spots of silvery-coloured amalgam. Silver ions leave similar spots but are easily washed away, making this a means of distinguishing silver from mercury.

Additional Information

Dental amalgam, often referred to as “silver fillings,” has been a dentistry staple for over a century. These iconic silvery-gray restorations have filled cavities, restored damaged teeth, and saved countless smiles. However, dental amalgam has also faced its share of controversies and debates. In this article, we’ll explore the history, composition, benefits, concerns, and alternatives of dental amalgam to provide a comprehensive view of this commonly used dental material.

A Brief History

Dental amalgam’s history can be traced back to the early 19th century when the amalgamation of metals was a well-known concept. In 1819, the French chemist Louis Nicolas Vauquelin introduced the use of silver amalgam in dentistry. The basic idea was to mix powdered silver with mercury, creating a malleable and durable filling material. This revolutionary development allowed dentists to restore teeth with a more reliable and long-lasting solution compared to earlier methods like using tin and gold.

Composition of Dental Amalgam

Traditional dental amalgam is composed of a mixture of several metals, with the primary components being:

* Silver: Silver provides durability and strength to the amalgam filling.

* Tin: Tin aids in amalgam alloy formation and increases its workability.

* Copper: Copper improves resistance to corrosion and tarnishing.

* Mercury: Mercury serves as the binder, allowing the mixture to become pliable for filling cavities.

The Dental Restoration Process

Dental amalgam is renowned for its ease of use and durability. The process of placing a dental amalgam filling typically involves the following steps:

Preparation: The dentist removes decayed or damaged tooth structure, creating a clean cavity to be filled.

Mixing: The amalgam alloy is mixed with mercury, forming a soft, pliable material.

Filling: The mixed amalgam is carefully placed into the prepared cavity and shaped to match the natural contours of the tooth.

Hardening: Over time, the amalgam hardens and becomes a solid, long-lasting filling.

Benefits of Dental Amalgam

Dental amalgam has several advantages that have contributed to its continued use in dentistry:

Durability: Dental amalgam is exceptionally durable and can withstand the forces of biting and chewing over many years.

Cost-Effectiveness: Amalgam fillings are often more affordable than alternative materials, making them accessible to a broader range of patients.

Quick Placement: The placement of dental amalgam fillings is relatively quick and straightforward, making it a convenient option for both patients and dentists.

Versatility: Amalgam can be used in various dental situations, from small cavities to larger restorations.

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