Un metal (del griego μέταλλον métallon , "mina, cantera, metal") es un material que, recién preparado, pulido o fracturado, muestra un aspecto brillante y conduce la electricidad y el calor relativamente bien. Los metales son típicamente maleables (se pueden martillar en láminas delgadas) o dúctiles (se pueden estirar en alambres). Un metal puede ser un elemento químico como el hierro ; una aleación como el acero inoxidable ; o un compuesto molecular tal como nitruro de azufre polimérico .
En física, un metal se considera generalmente como cualquier sustancia capaz de conducir electricidad a una temperatura del cero absoluto . [1] Muchos elementos y compuestos que normalmente no se clasifican como metales se vuelven metálicos bajo altas presiones. Por ejemplo, el yodo no metálico se convierte gradualmente en un metal a una presión de entre 40 y 170 mil veces la presión atmosférica . Del mismo modo, algunos materiales considerados metales pueden convertirse en no metales. El sodio , por ejemplo, se convierte en un no metal a una presión de poco menos de dos millones de veces la presión atmosférica.
En química, dos elementos que de otra manera calificar (en física) como metales- frágil arsénico y antimonio -son comúnmente en vez reconocidos como metaloides debido a su química (predominantemente no metálicos para el arsénico, y equilibradas entre metalicidad y nonmetallicity para el antimonio). Alrededor de 95 de los 118 elementos de la tabla periódica son metales (o es probable que lo sean). El número es inexacto ya que los límites entre metales, no metales y metaloides fluctúan ligeramente debido a la falta de definiciones universalmente aceptadas de las categorías involucradas.
En astrofísica, el término "metal" se utiliza de forma más amplia para referirse a todos los elementos químicos de una estrella que son más pesados que el helio , y no solo a los metales tradicionales. En este sentido, los primeros cuatro "metales" que se acumulan en los núcleos estelares a través de la nucleosíntesis son el carbono , el nitrógeno , el oxígeno y el neón , todos los cuales son estrictamente no metales en química. Una estrella fusiona átomos más ligeros, principalmente hidrógeno y helio, en átomos más pesados durante su vida. Usado en ese sentido, la metalicidad de un objeto astronómico es la proporción de su materia compuesta por los elementos químicos más pesados. [2] [3]
Los metales, como elementos químicos, comprenden el 25% de la corteza terrestre y están presentes en muchos aspectos de la vida moderna. La fuerza y la resistencia de algunos metales ha llevado a su uso frecuente en, por ejemplo, edificio de gran altura y el puente de la construcción , así como la mayoría de los vehículos, muchos aparatos electrodomésticos , herramientas, tuberías, y las vías del ferrocarril. Los metales preciosos se utilizaron históricamente como moneda , pero en la era moderna, los metales de acuñación se han extendido a al menos 23 de los elementos químicos. [4]
Se cree que la historia de los metales refinados comienza con el uso del cobre hace unos 11.000 años. El oro, la plata, el hierro (como hierro meteórico), el plomo y el latón también se usaban antes de la primera aparición conocida del bronce en el quinto milenio antes de nuestra era. Los desarrollos posteriores incluyen la producción de formas tempranas de acero; el descubrimiento del sodio , el primer metal ligero, en 1809; el auge de los aceros aleados modernos ; y, desde el final de la Segunda Guerra Mundial, el desarrollo de aleaciones más sofisticadas.
Propiedades
Forma y estructura
Los metales son brillantes y lustrosos , al menos cuando están recién preparados, pulidos o fracturados. Las láminas de metal más gruesas que unos pocos micrómetros parecen opacas, pero la hoja de oro transmite luz verde.
El estado sólido o líquido de los metales se origina en gran medida en la capacidad de los átomos metálicos involucrados para perder fácilmente sus electrones de la capa externa. En términos generales, las fuerzas que mantienen en su lugar los electrones de la capa exterior de un átomo individual son más débiles que las fuerzas de atracción sobre los mismos electrones que surgen de las interacciones entre los átomos en el metal sólido o líquido. Los electrones involucrados se deslocalizan y la estructura atómica de un metal puede visualizarse efectivamente como una colección de átomos incrustados en una nube de electrones relativamente móviles. Este tipo de interacción se llama enlace metálico . [5] La fuerza de los enlaces metálicos para diferentes metales elementales alcanza un máximo alrededor del centro de la serie de metales de transición , ya que estos elementos tienen una gran cantidad de electrones deslocalizados. [n 1]
Aunque la mayoría de los metales elementales tienen densidades más altas que la mayoría de los no metales , [5] existe una amplia variación en sus densidades, siendo el litio el menos denso (0,534 g / cm 3 ) y el osmio (22,59 g / cm 3 ) el más denso. El magnesio, el aluminio y el titanio son metales ligeros de gran importancia comercial. Sus respectivas densidades de 1,7, 2,7 y 4,5 g / cm 3 se pueden comparar con las de los metales estructurales más antiguos, como el hierro en 7,9 y el cobre en 8,9 g / cm 3 . Por tanto, una bola de hierro pesaría tanto como tres bolas de aluminio de igual volumen.
Los metales son típicamente maleables y dúctiles, y se deforman bajo tensión sin romperse . [5] Se cree que la naturaleza no direccional de la unión metálica contribuye significativamente a la ductilidad de la mayoría de los sólidos metálicos. Por el contrario, en un compuesto iónico como la sal de mesa, cuando los planos de un enlace iónico se deslizan uno al lado del otro, el cambio de ubicación resultante desplaza los iones de la misma carga en estrecha proximidad, lo que resulta en la división del cristal. Este cambio no se observa en un cristal unido covalentemente , como un diamante, donde se produce la fractura y la fragmentación del cristal. [6] La deformación elástica reversible en metales puede describirse mediante la Ley de Hooke para restaurar fuerzas, donde la tensión es linealmente proporcional a la deformación .
El calor o fuerzas mayores que el límite elástico de un metal pueden causar una deformación permanente (irreversible), conocida como deformación plástica o plasticidad . Una fuerza aplicada puede ser una fuerza de tracción (tracción), una fuerza de compresión (empuje) o una fuerza de corte , flexión o torsión (torsión). Un cambio de temperatura puede afectar el movimiento o desplazamiento de defectos estructurales en el metal, tales como límites de grano , puntos vacantes , dislocaciones de líneas y tornillos , fallas de apilamiento y gemelos en metales cristalinos y no cristalinos . Puede producirse deslizamiento interno , fluencia y fatiga del metal .
Los átomos de las sustancias metálicas se organizan típicamente en una de las tres estructuras cristalinas comunes , a saber, cúbico centrado en el cuerpo (bcc), cúbico centrado en la cara (fcc) y hexagonal compacto (hcp). En bcc, cada átomo se coloca en el centro de un cubo de otros ocho. En fcc y hcp, cada átomo está rodeado por otros doce, pero el apilamiento de las capas es diferente. Algunos metales adoptan diferentes estructuras según la temperatura. [7]
- Estructura cristalina cúbica centrada en el cuerpo, con una celda unitaria de 2 átomos, como se encuentra en, por ejemplo, cromo, hierro y tungsteno
- Estructura de cristal cúbico centrada en la cara, con una celda unitaria de 4 átomos, como se encuentra, por ejemplo, en aluminio, cobre y oro.
- Estructura cristalina hexagonal compacta, con una celda unitaria de 6 átomos, como se encuentra, por ejemplo, en titanio, cobalto y zinc.
La celda unitaria para cada estructura cristalina es el grupo más pequeño de átomos que tiene la simetría general del cristal, y a partir del cual se puede construir toda la red cristalina por repetición en tres dimensiones. En el caso de la estructura cristalina cúbica centrada en el cuerpo que se muestra arriba, la celda unitaria está formada por el átomo central más uno-ocho de cada uno de los ocho átomos de las esquinas.
Eléctrica y Térmica
La estructura electrónica de los metales significa que son relativamente buenos conductores de electricidad . Los electrones en la materia solo pueden tener niveles de energía fijos en lugar de variables, y en un metal los niveles de energía de los electrones en su nube de electrones, al menos hasta cierto punto, corresponden a los niveles de energía a los que puede ocurrir la conducción eléctrica. En un semiconductor como el silicio o en un no metal como el azufre, existe una brecha de energía entre los electrones de la sustancia y el nivel de energía en el que puede producirse la conducción eléctrica. En consecuencia, los semiconductores y los no metales son conductores relativamente pobres.
Los metales elementales tienen valores de conductividad eléctrica de 6,9 × 10 3 S / cm para el manganeso a 6,3 × 10 5 S / cm para la plata . Por el contrario, un metaloide semiconductor como el boro tiene una conductividad eléctrica de 1,5 × 10 −6 S / cm. Con una excepción, los elementos metálicos reducen su conductividad eléctrica cuando se calientan. El plutonio aumenta su conductividad eléctrica cuando se calienta en el rango de temperatura de alrededor de -175 a +125 ° C.
Los metales son relativamente buenos conductores de calor . Los electrones en la nube de electrones de un metal son muy móviles y pueden transmitir fácilmente la energía vibratoria inducida por el calor.
La contribución de los electrones de un metal a su capacidad calorífica y conductividad térmica, y la conductividad eléctrica del propio metal se pueden calcular a partir del modelo de electrones libres . Sin embargo, esto no tiene en cuenta la estructura detallada de la red de iones del metal. Tener en cuenta el potencial positivo causado por la disposición de los núcleos de iones permite considerar la estructura de la banda electrónica y la energía de enlace de un metal. Son aplicables varios modelos matemáticos, siendo el más simple el modelo de electrones casi libres .
Químico
Los metales suelen tender a formar cationes a través de la pérdida de electrones. [5] La mayoría reaccionará con el oxígeno en el aire para formar óxidos en varias escalas de tiempo (el potasio se quema en segundos mientras que el hierro se oxida durante años). Otros, como el paladio , el platino y el oro , no reaccionan en absoluto con la atmósfera. Los óxidos de metales son generalmente básicos , a diferencia de los de los no metales , que son ácidos o neutros. Las excepciones son en gran parte óxidos con estados de oxidación muy altos como CrO 3 , Mn 2 O 7 y OsO 4 , que tienen reacciones estrictamente ácidas.
Pintar , anodizar o enchapar metales son buenas formas de prevenir su corrosión . Sin embargo, se debe elegir un metal más reactivo en la serie electroquímica para el revestimiento, especialmente cuando se espera que el revestimiento se astille. El agua y los dos metales forman una celda electroquímica , y si el recubrimiento es menos reactivo que el metal subyacente, el recubrimiento en realidad promueve la corrosión.
Distribución de la tabla periódica
En química, los elementos que generalmente se consideran metales en condiciones normales se muestran en amarillo en la tabla periódica a continuación. Los elementos restantes son metaloides (B, Si, Ge, As, Sb y Te se reconocen comúnmente como tales) o no metales. La astatina (At) generalmente se clasifica como un no metal o un metaloide, pero algunas predicciones esperan que sea un metal; como tal, se ha dejado en blanco debido al estado inconcluso del conocimiento experimental. Es probable que los otros elementos que muestran propiedades desconocidas sean metales, pero existen algunas dudas para el copernicio (Cn) y el oganesson (Og).
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | dieciséis | 17 | 18 | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Grupo → | ||||||||||||||||||||||||||||||||
↓ Periodo | ||||||||||||||||||||||||||||||||
1 | H | Él | ||||||||||||||||||||||||||||||
2 | Li | Ser | B | C | norte | O | F | Nordeste | ||||||||||||||||||||||||
3 | N / A | Mg | Alabama | Si | PAG | S | Cl | Arkansas | ||||||||||||||||||||||||
4 | K | California | Carolina del Sur | Ti | V | Cr | Minnesota | Fe | Co | Ni | Cu | Zn | Georgia | Ge | Como | Se | Br | Kr | ||||||||||||||
5 | Rb | Sr | Y | Zr | Nótese bien | Mes | Tc | Ru | Rh | Pd | Ag | CD | En | Sn | Sb | Te | I | Xe | ||||||||||||||
6 | Cs | Licenciado en Letras | La | Ce | Pr | Dakota del Norte | Pm | Sm | UE | Di-s | Tuberculosis | Dy | Ho | Er | Tm | Yb | Lu | Hf | Ejército de reserva | W | Re | Os | Ir | Pt | Au | Hg | Tl | Pb | Bi | Correos | A | Rn |
7 | P. | Real academia de bellas artes | C.A | Th | Pensilvania | U | Notario público | Pu | Soy | Cm | Bk | Cf | Es | Fm | Maryland | No | Lr | Rf | Db | Sg | Bh | Hs | Monte | Ds | Rg | Cn | Nueva Hampshire | Florida | Mc | Lv | Ts | Og |
Metal Metaloide No metal Propiedades desconocidas El color de fondo muestra la tendencia metal-metaloide-no metal en la tabla periódica |
Aleaciones
Una aleación es una sustancia que tiene propiedades metálicas y que está compuesta por dos o más elementos, de los cuales al menos uno es un metal. Una aleación puede tener una composición variable o fija. Por ejemplo, el oro y la plata forman una aleación en la que las proporciones de oro o plata se pueden ajustar libremente; el titanio y el silicio forman una aleación Ti 2 Si en la que la proporción de los dos componentes es fija (también conocida como compuesto intermetálico ).
La mayoría de los metales puros son demasiado blandos, frágiles o químicamente reactivos para su uso práctico. La combinación de diferentes proporciones de metales como aleaciones modifica las propiedades de los metales puros para producir características deseables. El objetivo de hacer aleaciones es generalmente hacerlas menos frágiles, más duras, resistentes a la corrosión o tener un color y brillo más deseables. De todas las aleaciones metálicas que se utilizan en la actualidad, las aleaciones de hierro ( acero , acero inoxidable , hierro fundido , acero para herramientas , acero aleado ) constituyen la mayor proporción tanto en cantidad como en valor comercial. El hierro aleado con varias proporciones de carbono produce aceros de bajo, medio y alto carbono, con niveles de carbono crecientes que reducen la ductilidad y la tenacidad. La adición de silicio producirá hierros fundidos, mientras que la adición de cromo , níquel y molibdeno a los aceros al carbono (más del 10%) da como resultado aceros inoxidables.
Otras aleaciones metálicas importantes son las de aluminio , titanio , cobre y magnesio . Las aleaciones de cobre se conocen desde la prehistoria (el bronce dio su nombre a la Edad del Bronce) y tienen muchas aplicaciones hoy en día, sobre todo en el cableado eléctrico. Las aleaciones de los otros tres metales se han desarrollado relativamente recientemente; debido a su reactividad química requieren procesos de extracción electrolítica . Las aleaciones de aluminio, titanio y magnesio se valoran por sus elevadas relaciones resistencia-peso; el magnesio también puede proporcionar blindaje electromagnético . [ cita requerida ] Estos materiales son ideales para situaciones en las que una alta relación resistencia-peso es más importante que el costo del material, como en la industria aeroespacial y algunas aplicaciones automotrices.
Las aleaciones especialmente diseñadas para aplicaciones muy exigentes, como los motores a reacción , pueden contener más de diez elementos.
Categorías
Los metales se pueden clasificar según sus propiedades físicas o químicas. Las categorías descritas en las subsecciones siguientes incluyen metales ferrosos y no ferrosos ; metales quebradizos y refractarios ; metales blancos; metales pesados y ligeros ; y metales básicos , nobles y preciosos . La tabla de elementos metálicos de esta sección clasifica los metales elementales según sus propiedades químicas en metales alcalinos y alcalinotérreos ; transición y post-transición metales; y lantánidos y actínidos . Son posibles otras categorías , según los criterios de inclusión. Por ejemplo, los metales ferromagnéticos , aquellos metales que son magnéticos a temperatura ambiente, son el hierro, el cobalto y el níquel.
Metales ferrosos y no ferrosos
El término "ferroso" se deriva de la palabra latina que significa "que contiene hierro". Esto puede incluir hierro puro, como hierro forjado , o una aleación como el acero . Los metales ferrosos suelen ser magnéticos , pero no exclusivamente. Los metales no ferrosos (aleaciones) carecen de cantidades apreciables de hierro.
Metal quebradizo
Si bien casi todos los metales son maleables o dúctiles, algunos (berilio, cromo, manganeso, galio y bismuto) son frágiles. [8] El arsénico y el antimonio, si se admiten como metales, son frágiles. Los valores bajos de la relación entre el módulo de elasticidad volumétrico y el módulo de corte ( criterio de Pugh ) son indicativos de fragilidad intrínseca.
Metal refractario
En ciencia de materiales, metalurgia e ingeniería, un metal refractario es un metal que es extraordinariamente resistente al calor y al desgaste. Los metales que pertenecen a esta categoría varían; la definición más común incluye niobio, molibdeno, tantalio, tungsteno y renio. Todos tienen puntos de fusión superiores a 2000 ° C y una gran dureza a temperatura ambiente.
- Cristales de niobio y un cubo de niobio anodizado de 1 cm 3 para comparar
- Cristales de molibdeno y un cubo de molibdeno de 1 cm 3 para comparar
- Un solo cristal de tantalio, algunos fragmentos cristalinos y un cubo de tantalio de 1 cm 3 para comparar
- Varillas de tungsteno con cristales evaporados, parcialmente oxidados con deslustre de colores, y un cubo de tungsteno de 1 cm 3 para comparar
- Monocristal de renio, una barra refundida y un cubo de renio de 1 cm 3 para comparar
metal blanco
Un metal blanco es cualquiera de los metales de color blanco (o sus aleaciones) con puntos de fusión relativamente bajos. Dichos metales incluyen zinc, cadmio, estaño, antimonio (aquí se cuenta como un metal), plomo y bismuto, algunos de los cuales son bastante tóxicos. En Gran Bretaña, el comercio de bellas artes utiliza el término "metal blanco" en los catálogos de subastas para describir artículos de plata extranjeros que no llevan las marcas de la British Assay Office, pero que, no obstante, se consideran plata y tienen un precio acorde.
Metales pesados y ligeros
Un metal pesado es cualquier metal o metaloide relativamente denso . [9] Se han propuesto definiciones más específicas, pero ninguna ha obtenido una aceptación generalizada. Algunos metales pesados tienen usos específicos o son notablemente tóxicos; algunos son esenciales en cantidades mínimas. Todos los demás metales son metales ligeros.
Metales básicos, nobles y preciosos
En química , el término metal base se usa informalmente para referirse a un metal que se oxida o corroe fácilmente , como reacciona fácilmente con ácido clorhídrico (HCl) diluido para formar un cloruro metálico e hidrógeno . Los ejemplos incluyen hierro, níquel , plomo y zinc. El cobre se considera un metal base ya que se oxida con relativa facilidad, aunque no reacciona con el HCl.
El término metal noble se usa comúnmente en oposición al metal base . Los metales nobles son resistentes a la corrosión u oxidación , [10] a diferencia de la mayoría de los metales base . Suelen ser metales preciosos, a menudo debido a la rareza percibida. Los ejemplos incluyen oro, platino, plata, rodio , iridio y paladio.
En alquimia y numismática , el término metal base se contrasta con metal precioso , es decir, aquellos de alto valor económico. [11] Un objetivo de los alquimistas desde hace mucho tiempo fue la transmutación de metales básicos en metales preciosos, incluidos metales de acuñación como la plata y el oro. La mayoría de las monedas de hoy están hechas de metales básicos sin valor intrínseco ; en el pasado, las monedas frecuentemente derivaban su valor principalmente de su contenido de metales preciosos .
Químicamente, los metales preciosos (como los metales nobles) son menos reactivos que la mayoría de los elementos, tienen un alto brillo y una alta conductividad eléctrica. Históricamente, los metales preciosos fueron importantes como moneda , pero ahora se los considera principalmente como bienes de inversión e industriales . El oro , la plata , el platino y el paladio tienen cada uno un código de moneda ISO 4217 . Los metales preciosos más conocidos son el oro y la plata. Si bien ambos tienen usos industriales, son más conocidos por sus usos en el arte , la joyería y la acuñación . Otros metales preciosos incluyen los metales del grupo del platino : rutenio , rodio , paladio, osmio , iridio y platino, de los cuales el platino es el más comercializado.
La demanda de metales preciosos está impulsada no solo por su uso práctico, sino también por su función como inversiones y reserva de valor . [12] El paladio y el platino, a partir del otoño de 2018, se valuaron en aproximadamente tres cuartas partes del precio del oro. La plata es sustancialmente menos costosa que estos metales, pero a menudo se considera tradicionalmente un metal precioso a la luz de su papel en la acuñación y la joyería.
Metales de válvula
En electroquímica, un metal de válvula es un metal que pasa corriente en una sola dirección.
Ciclo vital
Formación
Metales en la corteza terrestre: | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
abundancia y presencia o fuente principal, en peso [n 2] | |||||||||||||||||||
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | dieciséis | 17 | 18 | ||
1 | H | Él | |||||||||||||||||
2 | Li | Ser | B | C | norte | O | F | Nordeste | |||||||||||
3 | N / A | Mg | Alabama | Si | PAG | S | Cl | Arkansas | |||||||||||
4 | K | California | Carolina del Sur | Ti | V | Cr | Minnesota | Fe | Co | Ni | Cu | Zn | Georgia | Ge | Como | Se | Br | Kr | |
5 | Rb | Sr | Y | Zr | Nótese bien | Mes | Ru | Rh | Pd | Ag | CD | En | Sn | Sb | Te | I | Xe | ||
6 | Cs | Licenciado en Letras | Lu | Hf | Ejército de reserva | W | Re | Os | Ir | Pt | Au | Hg | Tl | Pb | Bi | ||||
7 | |||||||||||||||||||
La | Ce | Pr | Dakota del Norte | Sm | UE | Di-s | Tuberculosis | Dy | Ho | Er | Tm | Yb | |||||||
Th | U | ||||||||||||||||||
Más abundante (hasta 82 000 ppm) | |||||||||||||||||||
Abundante ( 100 - 999 ppm) | |||||||||||||||||||
Poco común (1 a 99 ppm) | |||||||||||||||||||
Raro ( 0,01 - 0,99 ppm) | |||||||||||||||||||
Muy raro ( 0,0001 - 0,0099 ppm) | |||||||||||||||||||
Los metales que quedan de la línea divisoria se producen (o se obtienen) principalmente como litófilos ; los de la derecha, como calcófilos, excepto el oro (un siderófilo ) y el estaño (un litófilo). |
- Esta subsección trata de la formación de los metales elementales de la tabla periódica, ya que estos forman la base de los materiales metálicos, como se define en este artículo.
Los metales que se encuentran en las proximidades del hierro (en la tabla periódica) se producen en gran medida mediante la nucleosíntesis estelar . En este proceso, los elementos más ligeros, desde el hidrógeno hasta el silicio, experimentan sucesivas reacciones de fusión dentro de las estrellas, liberando luz y calor y formando elementos más pesados con números atómicos más altos. [13]
Los metales más pesados generalmente no se forman de esta manera, ya que las reacciones de fusión que involucran tales núcleos consumirían energía en lugar de liberarla. [14] Más bien, ellos se sintetizan en gran parte (de elementos con un número atómico inferior) por la captura de neutrones , con los dos modos principales de esta captura repetitiva siendo el s-proceso y el proceso r . En el proceso s ("s" significa "lento"), las capturas singulares están separadas por años o décadas, lo que permite que los núcleos menos estables se desintegran beta , [15] mientras que en el proceso r ("rápido"), las capturas suceden más rápido de lo que los núcleos pueden descomponerse. Por lo tanto, el proceso-s toma un camino más o menos claro: por ejemplo, los núcleos estables de cadmio-110 son bombardeados sucesivamente por neutrones libres dentro de una estrella hasta que forman núcleos de cadmio-115 que son inestables y se desintegran para formar indio-115 (que es casi estable, con una vida media30 000 veces la edad del universo). Estos núcleos capturan neutrones y forman indio-116, que es inestable, y se desintegra para formar estaño-116, y así sucesivamente. [13] [16] [n 3] Por el contrario, no existe tal ruta en el proceso r. El proceso s se detiene en el bismuto debido a la corta vida media de los dos elementos siguientes, polonio y astato, que se descomponen en bismuto o plomo. El proceso r es tan rápido que puede saltarse esta zona de inestabilidad y crear elementos más pesados como el torio y el uranio. [18]
Metals condense in planets as a result of stellar evolution and destruction processes. Stars lose much of their mass when it is ejected late in their lifetimes, and sometimes thereafter as a result of a neutron star merger,[19][n 4] thereby increasing the abundance of elements heavier than helium in the interstellar medium. When gravitational attraction causes this matter to coalesce and collapse new stars and planets are formed.[21]
Abundance and occurrence
The Earth's crust is made of approximately 25% of metals by weight, of which 80% are light metals such as sodium, magnesium, and aluminum. Nonmetals (~75%) make up the rest of the crust. Despite the overall scarcity of some heavier metals such as copper, they can become concentrated in economically extractable quantities as a result of mountain building, erosion, or other geological processes.
Metals are primarily found as lithophiles (rock-loving) or chalcophiles (ore-loving). Lithophile metals are mainly the s-block elements, the more reactive of the d-block elements. and the f-block elements. They have a strong affinity for oxygen and mostly exist as relatively low density silicate minerals. Chalcophile metals are mainly the less reactive d-block elements, and the period 4–6 p-block metals. They are usually found in (insoluble) sulfide minerals. Being denser than the lithophiles, hence sinking lower into the crust at the time of its solidification, the chalcophiles tend to be less abundant than the lithophiles.
On the other hand, gold is a siderophile, or iron-loving element. It does not readily form compounds with either oxygen or sulfur. At the time of the Earth's formation, and as the most noble (inert) of metals, gold sank into the core due to its tendency to form high-density metallic alloys. Consequently, it is a relatively rare metal. Some other (less) noble metals—molybdenum, rhenium, the platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum), germanium, and tin—can be counted as siderophiles but only in terms of their primary occurrence in the Earth (core, mantle and crust), rather the crust. These metals otherwise occur in the crust, in small quantities, chiefly as chalcophiles (less so in their native form).[n 5]
The rotating fluid outer core of the Earth's interior, which is composed mostly of iron, is thought to be the source of Earth's protective magnetic field.[n 6] The core lies above Earth's solid inner core and below its mantle. If it could be rearranged into a column having a 5 m2 (54 sq ft) footprint it would have a height of nearly 700 light years. The magnetic field shields the Earth from the charged particles of the solar wind, and cosmic rays that would otherwise strip away the upper atmosphere (including the ozone layer that limits the transmission of ultraviolet radiation).
Extraction
Metals are often extracted from the Earth by means of mining ores that are rich sources of the requisite elements, such as bauxite. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines. In some cases, the sale price of the metal/s involved make it economically feasible to mine lower concentration sources.
Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.
When a metal ore is an ionic compound of that metal and a non-metal, the ore must usually be smelted—heated with a reducing agent—to extract the pure metal. Many common metals, such as iron, are smelted using carbon as a reducing agent. Some metals, such as aluminum and sodium, have no commercially practical reducing agent, and are extracted using electrolysis instead.[22][23]
Sulfide ores are not reduced directly to the metal but are roasted in air to convert them to oxides.
Uses
Metals are present in nearly all aspects of modern life. Iron, a heavy metal, may be the most common as it accounts for 90% of all refined metals; aluminum, a light metal, is the next most commonly refined metal. Pure iron may be the cheapest metallic element of all at cost of about US$0.07 per gram. Its ores are widespread; it is easy to refine; and the technology involved has been developed over hundreds of years. Cast iron is even cheaper, at a fraction of US$0.01 per gram, because there is no need for subsequent purification. Platinum, at a cost of about $27 per gram, may be the most ubiquitous given its very high melting point, resistance to corrosion, electrical conductivity, and durability. It is said to be found in, or used to produce, 20% of all consumer goods. Polonium is likely to be the most expensive metal, at a notional cost of about $100,000,000 per gram,[citation needed] due to its scarcity and micro-scale production.
Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, and railroad tracks.
Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.
The thermal conductivity of metals is useful for containers to heat materials over a flame. Metals are also used for heat sinks to protect sensitive equipment from overheating.
The high reflectivity of some metals enables their use in mirrors, including precision astronomical instruments, and adds to the aesthetics of metallic jewelry.
Some metals have specialized uses; mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Radioactive metals such as uranium and plutonium are used in nuclear power plants to produce energy via nuclear fission. Shape memory alloys are used for applications such as pipes, fasteners and vascular stents.
Metals can be doped with foreign molecules—organic, inorganic, biological and polymers. This doping entails the metal with new properties that are induced by the guest molecules. Applications in catalysis, medicine, electrochemical cells, corrosion and more have been developed.[24]
Recycling
Demand for metals is closely linked to economic growth given their use in infrastructure, construction, manufacturing, and consumer goods. During the 20th century, the variety of metals used in society grew rapidly. Today, the development of major nations, such as China and India, and technological advances, are fuelling ever more demand. The result is that mining activities are expanding, and more and more of the world's metal stocks are above ground in use, rather than below ground as unused reserves. An example is the in-use stock of copper. Between 1932 and 1999, copper in use in the U.S. rose from 73 g to 238 g per person.[25]
Metals are inherently recyclable, so in principle, can be used over and over again, minimizing these negative environmental impacts and saving energy. For example, 95% of the energy used to make aluminum from bauxite ore is saved by using recycled material.[26]
Globally, metal recycling is generally low. In 2010, the International Resource Panel, hosted by the United Nations Environment Programme published reports on metal stocks that exist within society[27] and their recycling rates.[25] The authors of the report observed that the metal stocks in society can serve as huge mines above ground. They warned that the recycling rates of some rare metals used in applications such as mobile phones, battery packs for hybrid cars and fuel cells are so low that unless future end-of-life recycling rates are dramatically stepped up these critical metals will become unavailable for use in modern technology.
Interacciones biologicas
The role of metallic elements in the evolution of cell biochemistry has been reviewed, including a detailed section on the role of calcium in redox enzymes. [28]
One or more of the elements iron, cobalt, nickel, copper and zinc are essential to all higher forms of life. Molybdenum is an essential component of vitamin B12. Compounds of all other transition elements and post-transition elements are toxic to a greater or lesser extent, with few exceptions such as certain compounds of antimony and tin. Potential sources of metal poisoning include mining, tailings, industrial wastes, agricultural runoff, occupational exposure, paints and treated timber.
Historia
Prehistory
Copper, which occurs in native form, may have been the first metal discovered given its distinctive appearance, heaviness, and malleability compared to other stones or pebbles. Gold, silver, and iron (as meteoric iron), and lead were likewise discovered in prehistory. Forms of brass, an alloy of copper and zinc made by concurrently smelting the ores of these metals, originate from this period (although pure zinc was not isolated until the 13th century). The malleability of the solid metals led to the first attempts to craft metal ornaments, tools, and weapons. Meteoric iron containing nickel was discovered from time to time and, in some respects this was superior to any industrial steel manufactured up to the 1880s when alloy steels become prominent.[citation needed]
- Native copper
- Gold crystals
- Crystalline silver
- A slice of meteoric iron
- Oxidised lead
nodules and 1 cm 3 cube - A brass weight (35 g)
Antiquity
The discovery of bronze (an alloy of copper with arsenic or tin) enabled people to create metal objects which were harder and more durable than previously possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were harder and more durable than their stone and copper ("Chalcolithic") predecessors. Initially, bronze was made of copper and arsenic (forming arsenic bronze) by smelting naturally or artificially mixed ores of copper and arsenic.[29] The earliest artifacts so far known come from the Iranian plateau in the 5th millennium BCE.[30] It was only later that tin was used, becoming the major non-copper ingredient of bronze in the late 3rd millennium BCE.[31] Pure tin itself was first isolated in 1800 BCE by Chinese and Japanese metalworkers.
Mercury was known to ancient Chinese and Indians before 2000 BCE, and found in Egyptian tombs dating from 1500 BCE.
The earliest known production of steel, an iron-carbon alloy, is seen in pieces of ironware excavated from an archaeological site in Anatolia (Kaman-Kalehöyük) and are nearly 4,000 years old, dating from 1800 BCE.[32][33]
From about 500 BCE sword-makers of Toledo, Spain were making early forms of alloy steel by adding a mineral called wolframite, which contained tungsten and manganese, to iron ore (and carbon). The resulting Toledo steel came to the attention of Rome when used by Hannibal in the Punic Wars. It soon became the basis for the weaponry of Roman legions; their swords were said to have been "so keen that there is no helmet which cannot be cut through by them."[citation needed][n 8]
In pre-Columbian America, objects made of tumbaga, an alloy of copper and gold, started being produced in Panama and Costa Rica between 300 and 500 CE. Small metal sculptures were common and an extensive range of tumbaga (and gold) ornaments comprised the usual regalia of persons of high status.
At around the same time indigenous Ecuadorians were combining gold with a naturally-occurring platinum alloy containing small amounts of palladium, rhodium, and iridium, to produce miniatures and masks composed of a white gold-platinum alloy. The metal workers involved heated gold with grains of the platinum alloy until the gold melted at which point the platinum group metals became bound within the gold. After cooling, the resulting conglomeration was hammered and reheated repeatedly until it became as homogenous as if all of the metals concerned had been melted together (attaining the melting points of the platinum group metals concerned was beyond the technology of the day).[34][n 9]
- A droplet of solidified molten tin
- Mercury being
poured into a petri dish - Electrum, a natural alloy of silver and gold, was often used for making coins. Shown is the Roman god Apollo, and on the obverse, a Delphi tripod (circa 310–305 BCE).
- A plate made of pewter, an alloy of 85–99% tin and (usually) copper. Pewter was first used around the beginning of the Bronze Age in the Near East.
- A pectoral (ornamental breastplate) made of tumbaga, an alloy of gold and copper
Middle Ages
Copper for the craftsman cunning at his trade.
"Good!" said the Baron, sitting in his hall,
"But Iron—Cold Iron—is master of them all."
from Cold Iron by Rudyard Kipling[35]
Arabic and medieval alchemists believed that all metals and matter were composed of the principle of sulfur, the father of all metals and carrying the combustible property, and the principle of mercury, the mother of all metals[n 10] and carrier of the liquidity, fusibility, and volatility properties. These principles were not necessarily the common substances sulfur and mercury found in most laboratories. This theory reinforced the belief that all metals were destined to become gold in the bowels of the earth through the proper combinations of heat, digestion, time, and elimination of contaminants, all of which could be developed and hastened through the knowledge and methods of alchemy.[n 11]
Arsenic, zinc, antimony, and bismuth became known, although these were at first called semimetals or bastard metals on account of their immalleability. All four may have been used incidentally in earlier times without recognising their nature. Albertus Magnus is believed to have been the first to isolate arsenic from a compound in 1250, by heating soap together with arsenic trisulfide. Metallic zinc, which is brittle if impure, was isolated in India by 1300 AD. The first description of a procedure for isolating antimony is in the 1540 book De la pirotechnia by Vannoccio Biringuccio. Bismuth was described by Agricola in De Natura Fossilium (c. 1546); it had been confused in early times with tin and lead because of its resemblance to those elements.
- Arsenic, sealed in a container to prevent tarnishing
- Zinc fragments and a 1 cm 3 cube
- Antimony, showing its brilliant lustre
- Bismuth in crystalline form, with a very thin oxidation layer, and a 1 cm 3 bismuth cube
The Renaissance
The first systematic text on the arts of mining and metallurgy was De la Pirotechnia (1540) by Vannoccio Biringuccio, which treats the examination, fusion, and working of metals.
Sixteen years later, Georgius Agricola published De Re Metallica in 1556, a clear and complete account of the profession of mining, metallurgy, and the accessory arts and sciences, as well as qualifying as the greatest treatise on the chemical industry through the sixteenth century.
He gave the following description of a metal in his De Natura Fossilium (1546):
Metal is a mineral body, by nature either liquid or somewhat hard. The latter may be melted by the heat of the fire, but when it has cooled down again and lost all heat, it becomes hard again and resumes its proper form. In this respect it differs from the stone which melts in the fire, for although the latter regain its hardness, yet it loses its pristine form and properties.
Traditionally there are six different kinds of metals, namely gold, silver, copper, iron, tin and lead. There are really others, for quicksilver is a metal, although the Alchemists disagree with us on this subject, and bismuth is also. The ancient Greek writers seem to have been ignorant of bismuth, wherefore Ammonius rightly states that there are many species of metals, animals, and plants which are unknown to us. Stibium when smelted in the crucible and refined has as much right to be regarded as a proper metal as is accorded to lead by writers. If when smelted, a certain portion be added to tin, a bookseller's alloy is produced from which the type is made that is used by those who print books on paper.
Each metal has its own form which it preserves when separated from those metals which were mixed with it. Therefore neither electrum nor Stannum [not meaning our tin] is of itself a real metal, but rather an alloy of two metals. Electrum is an alloy of gold and silver, Stannum of lead and silver. And yet if silver be parted from the electrum, then gold remains and not electrum; if silver be taken away from Stannum, then lead remains and not Stannum.
Whether brass, however, is found as a native metal or not, cannot be ascertained with any surety. We only know of the artificial brass, which consists of copper tinted with the colour of the mineral calamine. And yet if any should be dug up, it would be a proper metal. Black and white copper seem to be different from the red kind.
Metal, therefore, is by nature either solid, as I have stated, or fluid, as in the unique case of quicksilver.
But enough now concerning the simple kinds.[36]
Platinum, the third precious metal after gold and silver, was discovered in Ecuador during the period 1736 to 1744, by the Spanish astronomer Antonio de Ulloa and his colleague the mathematician Jorge Juan y Santacilia. Ulloa was the first person to write a scientific description of the metal, in 1748.
In 1789, the German chemist Martin Heinrich Klaproth was able to isolate an oxide of uranium, which he thought was the metal itself. Klaproth was subsequently credited as the discoverer of uranium. It was not until 1841, that the French chemist Eugène-Melchior Péligot, was able to prepare the first sample of uranium metal. Henri Becquerel subsequently discovered radioactivity in 1896 by using uranium.
In the 1790s, Joseph Priestley and the Dutch chemist Martinus van Marum observed the transformative action of metal surfaces on the dehydrogenation of alcohol, a development which subsequently led, in 1831, to the industrial scale synthesis of sulphuric acid using a platinum catalyst.
In 1803, cerium was the first of the lanthanide metals to be discovered, in Bastnäs, Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger, and independently by Martin Heinrich Klaproth in Germany. The lanthanide metals were largely regarded as oddities until the 1960s when methods were developed to more efficiently separate them from one another. They have subsequently found uses in cell phones, magnets, lasers, lighting, batteries, catalytic converters, and in other applications enabling modern technologies.
Other metals discovered and prepared during this time were cobalt, nickel, manganese, molybdenum, tungsten, and chromium; and some of the platinum group metals, palladium, osmium, iridium, and rhodium.
Light metals
All metals discovered until 1809 had relatively high densities; their heaviness was regarded as a singularly distinguishing criterion. From 1809 onwards, light metals such as sodium, potassium, and strontium were isolated. Their low densities challenged conventional wisdom as to the nature of metals. They behaved chemically as metals however, and were subsequently recognised as such.
Aluminum was discovered in 1824 but it was not until 1886 that an industrial large-scale production method was developed. Prices of aluminum dropped and aluminum became widely used in jewelry, everyday items, eyeglass frames, optical instruments, tableware, and foil in the 1890s and early 20th century. Aluminum's ability to form hard yet light alloys with other metals provided the metal many uses at the time. During World War I, major governments demanded large shipments of aluminum for light strong airframes. The most common metal in use for electric power transmission today is aluminum-conductor steel-reinforced. Also seeing much use is all-aluminum-alloy conductor. Aluminum is used because it has about half the weight of a comparable resistance copper cable (though larger diameter due to lower specific conductivity), as well as being cheaper. Copper was more popular in the past and is still in use, especially at lower voltages and for grounding.
While pure metallic titanium (99.9%) was first prepared in 1910 it was not used outside the laboratory until 1932. In the 1950s and 1960s, the Soviet Union pioneered the use of titanium in military and submarine applications as part of programs related to the Cold War. Starting in the early 1950s, titanium came into use extensively in military aviation, particularly in high-performance jets, starting with aircraft such as the F-100 Super Sabre and Lockheed A-12 and SR-71.
Metallic scandium was produced for the first time in 1937. The first pound of 99% pure scandium metal was produced in 1960. Production of aluminum-scandium alloys began in 1971 following a U.S. patent. Aluminum-scandium alloys were also developed in the USSR.
- Sodium
- Potassium pearls under paraffin oil. Size of the largest pearl is 0.5 cm.
- Strontium crystals
- Aluminum chunk,
2.6 grams, 1 x 2 cm - A bar of titanium crystals
- Scandium, including a 1 cm 3 cube
The age of steel
The modern era in steelmaking began with the introduction of Henry Bessemer's Bessemer process in 1855, the raw material for which was pig iron. His method let him produce steel in large quantities cheaply, thus mild steel came to be used for most purposes for which wrought iron was formerly used. The Gilchrist-Thomas process (or basic Bessemer process) was an improvement to the Bessemer process, made by lining the converter with a basic material to remove phosphorus.
Due to its high tensile strength and low cost, steel came to be a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.
In 1872, the Englishmen Clark and Woods patented an alloy that would today be considered a stainless steel. The corrosion resistance of iron-chromium alloys had been recognized in 1821 by French metallurgist Pierre Berthier. He noted their resistance against attack by some acids and suggested their use in cutlery. Metallurgists of the 19th century were unable to produce the combination of low carbon and high chromium found in most modern stainless steels, and the high-chromium alloys they could produce were too brittle to be practical. It was not until 1912 that the industrialisation of stainless steel alloys occurred in England, Germany, and the United States.
The last stable metallic elements
By 1900 three metals with atomic numbers less than lead (#82), the heaviest stable metal, remained to be discovered: elements 71, 72, 75.
Von Welsbach, in 1906, proved that the old ytterbium also contained a new element (#71), which he named cassiopeium. Urbain proved this simultaneously, but his samples were very impure and only contained trace quantities of the new element. Despite this, his chosen name lutetium was adopted.
In 1908, Ogawa found element 75 in thorianite but assigned it as element 43 instead of 75 and named it nipponium. In 1925 Walter Noddack, Ida Eva Tacke and Otto Berg announced its separation from gadolinite and gave it the present name, rhenium.
Georges Urbain claimed to have found element 72 in rare-earth residues, while Vladimir Vernadsky independently found it in orthite. Neither claim was confirmed due to World War I, and neither could be confirmed later, as the chemistry they reported does not match that now known for hafnium. After the war, in 1922, Coster and Hevesy found it by X-ray spectroscopic analysis in Norwegian zircon. Hafnium was thus the last stable element to be discovered.
- Lutetium, including a 1 cm 3 cube
- Rhenium, including a 1 cm 3 cube
- Hafnium, in the form of a 1.7 kg bar
By the end of World War II scientists had synthesized four post-uranium elements, all of which are radioactive (unstable) metals: neptunium (in 1940), plutonium (1940–41), and curium and americium (1944), representing elements 93 to 96. The first two of these were eventually found in nature as well. Curium and americium were by-products of the Manhattan project, which produced the world's first atomic bomb in 1945. The bomb was based on the nuclear fission of uranium, a metal first thought to have been discovered nearly 150 years earlier.
Post-World War II developments
Superalloys
Superalloys composed of combinations of Fe, Ni, Co, and Cr, and lesser amounts of W, Mo, Ta, Nb, Ti, and Al were developed shortly after World War II for use in high performance engines, operating at elevated temperatures (above 650 °C (1,200 °F)). They retain most of their strength under these conditions, for prolonged periods, and combine good low-temperature ductility with resistance to corrosion or oxidation. Superalloys can now be found in a wide range of applications including land, maritime, and aerospace turbines, and chemical and petroleum plants.
Transcurium metals
The successful development of the atomic bomb at the end of World War II sparked further efforts to synthesize new elements, nearly all of which are, or are expected to be, metals, and all of which are radioactive. It was not until 1949 that element 97 (berkelium), next after element 96 (curium), was synthesized by firing alpha particles at an americium target. In 1952, element 100 (fermium) was found in the debris of the first hydrogen bomb explosion; hydrogen, a nonmetal, had been identified as an element nearly 200 years earlier. Since 1952, elements 101 (mendelevium) to 118 (oganesson) have been synthesized.
Bulk metallic glasses
A metallic glass (also known as an amorphous or glassy metal) is a solid metallic material, usually an alloy, with disordered atomic-scale structure. Most pure and alloyed metals, in their solid state, have atoms arranged in a highly ordered crystalline structure. Amorphous metals have a non-crystalline glass-like structure. But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity. Amorphous metals are produced in several ways, including extremely rapid cooling, physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying. The first reported metallic glass was an alloy (Au75Si25) produced at Caltech in 1960. More recently, batches of amorphous steel with three times the strength of conventional steel alloys have been produced. Currently the most important applications rely on the special magnetic properties of some ferromagnetic metallic glasses. The low magnetization loss is used in high efficiency transformers. Theft control ID tags and other article surveillance schemes often use metallic glasses because of these magnetic properties.
Shape-memory alloys
A shape-memory alloy (SMA) is an alloy that "remembers" its original shape and when deformed returns to its pre-deformed shape when heated. While the shape memory effect had been first observed in 1932, in an Au-Cd alloy, it was not until 1962, with the accidental discovery of the effect in a Ni-Ti alloy that research began in earnest, and another ten years before commercial applications emerged. SMA's have applications in robotics and automotive, aerospace and biomedical industries. There is another type of SMA, called a ferromagnetic shape-memory alloy (FSMA), that changes shape under strong magnetic fields. These materials are of particular interest as the magnetic response tends to be faster and more efficient than temperature-induced responses.
Quasicyrstalline alloys
In 1984, Israeli chemist Dan Shechtman found an aluminum-manganese alloy having five-fold symmetry, in breach of crystallographic convention at the time which said that crystalline structures could only have two-, three-, four-, or six-fold symmetry. Due to fear of the scientific community's reaction, it took him two years to publish the results for which he was awarded the Nobel Prize in Chemistry in 2011. Since this time, hundreds of quasicrystals have been reported and confirmed. They exist in many metallic alloys (and some polymers). Quasicrystals are found most often in aluminum alloys (Al-Li-Cu, Al-Mn-Si, Al-Ni-Co, Al-Pd-Mn, Al-Cu-Fe, Al-Cu-V, etc.), but numerous other compositions are also known (Cd-Yb, Ti-Zr-Ni, Zn-Mg-Ho, Zn-Mg-Sc, In-Ag-Yb, Pd-U-Si, etc.). Quasicrystals effectively have infinitely large unit cells. Icosahedrite Al63Cu24Fe13, the first quasicrystal found in nature, was discovered in 2009. Most quasicrystals have ceramic-like properties including low electrical conductivity (approaching values seen in insulators) and low thermal conductivity, high hardness, brittleness, and resistance to corrosion, and non-stick properties. Quasicrystals have been used to develop heat insulation, LEDs, diesel engines, and new materials that convert heat to electricity. New applications may take advantage of the low coefficient of friction and the hardness of some quasicrystalline materials, for example embedding particles in plastic to make strong, hard-wearing, low-friction plastic gears. Other potential applications include selective solar absorbers for power conversion, broad-wavelength reflectors, and bone repair and prostheses applications where biocompatibility, low friction and corrosion resistance are required.
Complex metallic alloys
Complex metallic alloys (CMAs) are intermetallic compounds characterized by large unit cells comprising some tens up to thousands of atoms; the presence of well-defined clusters of atoms (frequently with icosahedral symmetry); and partial disorder within their crystalline lattices. They are composed of two or more metallic elements, sometimes with metalloids or chalcogenides added. They include, for example, NaCd2, with 348 sodium atoms and 768 cadmium atoms in the unit cell. Linus Pauling attempted to describe the structure of NaCd2 in 1923, but did not succeed until 1955. At first called "giant unit cell crystals", interest in CMAs, as they came to be called, did not pick up until 2002, with the publication of a paper called "Structurally Complex Alloy Phases", given at the 8th International Conference on Quasicrystals. Potential applications of CMAs include as heat insulation; solar heating; magnetic refrigerators; using waste heat to generate electricity; and coatings for turbine blades in military engines.
High entropy alloys
High entropy alloys (HEAs) such as AlLiMgScTi are composed of equal or nearly equal quantities of five or more metals. Compared to conventional alloys with only one or two base metals, HEAs have considerably better strength-to-weight ratios, higher tensile strength, and greater resistance to fracturing, corrosion, and oxidation. Although HEAs were described as early as 1981, significant interest did not develop until the 2010s; they continue to be the focus of research in materials science and engineering because of their potential for desirable properties.
MAX phase alloys
MAX | M | A | X |
---|---|---|---|
Hf2SnC | Hf | Sn | C |
Ti4AlN3 | Ti | Al | N |
Ti3SiC2 | Ti | Si | C |
Ti2AlC | Ti | Al | C |
Cr2AlC2 | Cr | Al | C |
Ti3AlC2 | Ti | Al | C |
In a MAX phase alloy, M is an early transition metal, A is an A group element (mostly group IIIA and IVA, or groups 13 and 14), and X is either carbon or nitrogen. Examples are Hf2SnC and Ti4AlN3. Such alloys have some of the best properties of metals and ceramics. These properties include high electrical and thermal conductivity, thermal shock resistance, damage tolerance, machinability, high elastic stiffness, and low thermal expansion coefficients.[37] They can be polished to a metallic luster because of their excellent electrical conductivities. During mechanical testing, it has been found that polycrystalline Ti3SiC2 cylinders can be repeatedly compressed at room temperature, up to stresses of 1 GPa, and fully recover upon the removal of the load. Some MAX phases are also highly resistant to chemical attack (e.g. Ti3SiC2) and high-temperature oxidation in air (Ti2AlC, Cr2AlC2, and Ti3AlC2). Potential applications for MAX phase alloys include: as tough, machinable, thermal shock-resistant refractories; high-temperature heating elements; coatings for electrical contacts; and neutron irradiation resistant parts for nuclear applications. While MAX phase alloys were discovered in the 1960s, the first paper on the subject was not published until 1996.
Ver también
- Colored gold
- Ductility
- Ferrous metallurgy
- Metal theft
- Metallurgy
- Metalworking
- Properties of metals, metalloids and nonmetals
- Structural steel
- Transition metal
Notas
- ^ This is a simplified explanation; other factors may include atomic radius, nuclear charge, number of bond orbitals, overlap of orbital energies, and crystal form.[5]
- ^ Trace elements having an abundance equalling or much less than one part per trillion (namely Tc, Pm, Po, At, Ra, Ac, Pa, Np, and Pu) are not shown.
- ^ In some cases, for example in the presence of high energy gamma rays or in a very high temperature hydrogen rich environment, the subject nuclei may experience neutron loss or proton gain resulting in the production of (comparatively rare) neutron deficient isotopes.[17]
- ^ The ejection of matter when two neutron stars collide is attributed to the interaction of their tidal forces, possible crustal disruption, and shock heating (which is what happens if you floor the accelerator in car when the engine is cold).[20]
- ^ Iron, cobalt, nickel, and tin are also siderophiles from a whole of Earth perspective.
- ^ Another life-enabling role for iron is as a key constituent of hemoglobin, which enables the transportation of oxygen from the lungs to the rest of the body.
- ^ Bronze is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminum, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon.
- ^ The Chalybean peoples of Pontus in Asia Minor were being concurrently celebrated for working in iron and steel. Unbeknownst to them, their iron contained a high amount of manganese, enabling the production of a superior form of steel.
- ^ In Damascus, Syria, blade-smiths were able to forge knives and swords with a distinctive surface pattern composed of swirling patterns of light-etched regions on a nearly black background. These blades had legendary cutting abilities. The iron the smiths were using was sourced from India, and contained one or more carbide-forming elements, such as V, Mo, Cr, Mn, and Nb. Modern analysis of these weapons has shown that these elements supported the catalytic formation of carbon nanotubes, which in turn promoted the formation of cementite (Fe3C) nanowires. The malleability of the carbon nanotubes offset the brittle nature of the cementite, and endowed the resulting steel with a unique combination of strength and flexibility. Knowledge of how to make what came to called Damascus steel died out in the eighteenth century possibly due to exhausting ore sources with the right combination of impurities. The techniques involved were not rediscovered until 2009.
- ^ In ancient times, lead was regarded as the father of all metals.
- ^ Paracelsus, a later German Renaissance writer, added the third principle of salt, carrying the nonvolatile and incombustible properties, in his tria prima doctrine. These theories retained the four classical elements as underlying the composition of sulfur, mercury and salt.
Referencias
- ^ Yonezawa, F. (2017). Physics of Metal-Nonmetal Transitions. Amsterdam: IOS Press. p. 257. ISBN 978-1-61499-786-3.
Sir Nevill Mott (1905-1996) wrote a letter to a fellow physicist, Prof. Peter P. Edwards, in which he notes...I’ve though a lot about 'What is a metal?' and I think one can only answer the question at T =0 (the absolute zero of temperature). There a metal conducts and a nonmetal doesn’t.
- ^ Martin, John C. "What we learn from a star's metal content". John C. Martin's Homepage. Retrieved March 25, 2021.
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Otras lecturas
- Choptuik M. W., Lehner L. & Pretorias F. 2015, "Probing strong-field gravity through numerical simulation", in A. Ashtekar, B. K. Berger, J. Isenberg & M. MacCallum (eds), General Relativity and Gravitation: A Centennial Perspective, Cambridge University Press, Cambridge, ISBN 978-1-107-03731-1.
- Cox P. A. 1997, The elements: Their origin, abundance and distribution, Oxford University Press, Oxford, ISBN 978-0-19-855298-7
- Crow J. M. 2016, "Impossible alloys: How to make never-before-seen metals", New Scientist, 12 October
- Hadhazy A. 2016, "Galactic 'gold mine' explains the origin of nature's heaviest elements", Science Spotlights, 10 May 2016, accessed 11 July 2016.
- Hofmann S. 2002, On Beyond Uranium: Journey to the End of the Periodic Table, Taylor & Francis, London, ISBN 978-0-415-28495-0.
- Padmanabhan T. 2001, Theoretical Astrophysics, vol. 2, Stars and Stellar Systems, Cambridge University Press, Cambridge, ISBN 978-0-521-56241-6.
- Parish R. V. 1977, The metallic elements, Longman, London, ISBN 978-0-582-44278-8
- Podosek F. A. 2011, "Noble gases", in H. D. Holland & K. K. Turekian (eds), Isotope Geochemistry: From the Treatise on Geochemistry, Elsevier, Amsterdam, pp. 467–492, ISBN 978-0-08-096710-3.
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- Rehder D. 2010, Chemistry in Space: From Interstellar Matter to the Origin of Life, Wiley-VCH, Weinheim, ISBN 978-3-527-32689-1.
- Russell A. M. & Lee K. L. 2005, Structure–property relations in nonferrous metals, John Wiley & Sons, Hoboken, New Jersey, ISBN 978-0-471-64952-6
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- Wilson A. J. 1994, The living rock: The tory of metals since earliest times and their impact on developing civilization, Woodhead Publishing, Cambridge, ISBN 978-1-85573-154-7
enlaces externos
- ASM International (formerly the American Society for Metals)
- Strong as Titanium, Cheap as Dirt: New Steel Alloy Shines
- The Minerals, Metals & Materials Society Home Page