Cobalt

Pourret, Olivier; Faucon, Michel‐Pierre

doi:10.1007/978-3-319-39193-9_271-2

Cited by 5 publications

(2 citation statements)

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“…Zinc is the second-most abundant metal in organisms and close to half the world population is deficient in zinc [5]. Likewise, cobalt is essential in the coenzyme cobalamin (Vitamin B12), acting as a dietary supplement as a factor against pernicious anemia [6].To be consistent, researchers should only use well-accepted definitions. In the case of "heavy metal", this term should be replaced by "metal", "metalloid", or "trace metal".…”

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On the Necessity of Banning the Term “Heavy Metal” from the Scientific Literature

Pourret

2018

Sustainability

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Keywords: heavy metal; trace metal elements; metal; metalloid Many terms are increasingly improperly used by scientists. The term "heavy metal" is increasingly used, especially in multidisciplinary studies. Even if a debate exist as recently outlined by Ali and Khan [1] or Pourret and Bollinger [2], in 1980 Nieboer and Richardson [3] had already proposed the replacement of this nondescript term by biologically and chemically significant classification. Moreover, according to the International Union of Pure and Applied Chemistry, the term "heavy metal" is considered imprecise at best, and meaningless and misleading at worst [4]. The Union discourages the use of this term. Indeed, no standardized definition of this term currently exists. Nevertheless, nothing has really changed: the term is still widely used by part of the scientific community. Taking a journal like Sustainability as an illustrative example: 45 articles out of 7849 published that used the term "heavy metal" in their title or keywords were published these last five years (as determined from the mdpi website, using "heavy metal*" search, data accessed on July 26, 2018), including three review papers. Moreover, three special issues considering the "heavy metal" term in their topic were also proposed.As a reviewer and now as an editor of Sustainability, I have the responsibility to spread the word and this letter is an effective demonstration of why this term should be removed from our vernacular. Among the numerous testimonies I collected and exchanges I experienced with colleagues after the publication of the letter co-written with my colleague Jean-Claude Bollinger [2], and more generally with the scientific community, the major reason for the persistence of the use of the term "heavy metal" is mostly due to the ignorance of Nieboer and Richardson's proposition [3]. The term "heavy metal" is based on categorization by density (and some metals have a relatively low density, e.g., zinc). It is often used as a group name for metals and metalloids (i.e., arsenic) that are associated with contamination and potential toxicity. However, the assumption that all so-called "heavy metals" and their compounds have relatively high toxicity are not always supported by facts: chromium and its alloys can be used securely in medicine (e.g., prostheses), even though chromate is recognized as a carcinogen [4]. The "heavy metals" list is not clearly defined and often mixes metals and metalloids without clear definition. Eventually, the pejorative connotation of "heavy" associated with the toxicity of metal induces a kind of fear amongst society. Nonetheless, metals are not always toxic and some are in fact essential: a given metal can be essential and toxic, depending on the dosage and exposure levels and the receiving organism/population. Even the presence of some metals at relatively low levels in the environment are needed for life. Take the examples of zinc and cobalt. Zinc is the second-most abundant metal in organisms and close to half the world population is d...

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On the Necessity of Banning the Term “Heavy Metal” from the Scientific Literature

Pourret

2018

Sustainability

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“…However, it was not isolated as a metallic until around 1735. The discovery of the metal has been credited to a Swedish chemist, Georg Brandt [77]. Therefore, carbon content plays an important role in dictating the structure and mechanical properties of the alloys as the alloys derive their strength from the formation of carbide phases [79].…”

Section: Cobalt and Cobalt-based Superalloysmentioning

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The Effects of Composition and Heat Treatment on the Microstructure and Performance of Cobalt-based Alloys for Molten Zinc Applications

Escott¹

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The purpose of this research was to identify and develop cobalt-based superalloys for journal bearing applications by improving the stability and service life of submerged galvanising pot hardware. To achieve this goal the mechanical properties and chemical resistance of four cast cobalt superalloys were investigated. The alloys were subjected to three heat treatments which included a high temperature annealing treatment, a solution treatment and additional age hardening, and a plasma nitriding treatment. The heat-treated alloys were examined and compared to untreated samples to identify any microstructural changes or improvements in material performance. Four commercially available cobalt-based superalloys were identified for analysis including three cast CoCrW alloys and one cast CoCrMo Tribaloy. It was identified that increasing the carbon and tungsten content, with the CoCrW alloys, increased the area fraction of chromium and tungsten carbide phases in addition to increasing the concentration of alloying elements retained in solid solution. Both factors contributed to increased material hardness. The substitution of tungsten with molybdenum and the absence of carbon, with the CoCrMo Tribaloy, replaced the formation of eutectic carbides with a primary Laves phase that dominated the Tribaloys microstructure. This provided the CoCrMo alloy with enhanced hardness properties compared to the CoCrW alloys. The untreated alloys were submerged in a molten zinc alloy bath containing 0.35wt.% Al in a series of static immersion tests where the alloys were submerged for times ranging between 1-4 weeks. All the materials reacted with the molten zinc bath resulting in the diffusion of bath species into the alloys microstructure as well as the leaching of alloying elements into the bath. With each alloy, molten metal ingress preferentially occurred in the cobalt rich solid solution phase whereas the carbide and Laves phases were more resistant to bath reactivity. The high area fraction of Laves phase and increased molybdenum concentrations retained in eutectic solid solution with the T-800 Tribaloy, provided the alloy with enhanced chemical resistance to the bath in comparison to the CoCrW alloys. The improved chemical resistance reduced the depth of diffusion and reduced the quantity of cobalt-aluminide formation at the alloys surface. A plasma nitriding treatment resulted in the formation of a nitrogen rich diffusion layer at the surface of each of the alloys. Increasing the treatment temperature or treatment time produced a thicker diffusion layer with increased concentrations of nitrogen. The formation a nitride layer significantly improved the surface hardness of each of the alloys where increased material hardness correlated with a thicker diffusion layer. The plasma treated samples were dip tested in a molten zinc bath containing 0.35wt.% Al. The formation of the nitride diffusion layer improved the long-term chemical performance of the alloys where reduced zinc and aluminium diffusion depths were recorded with the CoCrW alloys after 4-weeks of testing. The nitride treatment generally improved the surface integrity of the alloys where increased levels of alloying elements were retained within the matrix diffusion layer after prolonged bath exposure and each alloy experienced less material loss. There was also a noticeable reduction in the quantity of cobalt-aluminide phases at the alloy’s surfaces. An annealing heat treatment slightly changed the morphology of the alloy’s microstructure where phase precipitation within the solid solution phase occurred in addition to low levels of carbide dissolution. Small improvements in material hardness were recorded with the CoCrW alloys whereas the annealing treatment had detrimental effects on the hardness properties of the CoCrMo alloy. Using the nano-properties of the matrix to calculate the mean H/E ratio it was predicted that the wear performance of the matrix of the WT-4 and WT-12 alloys were slightly improved by the annealing process. A solution treatment significantly changed the microstructure morphology of the WT-6 and WT-12 alloys. The solution treatment resulted in extreme coarsening of the chromium and tungsten carbides with the WT-12 alloy and coarsening of the chromium carbides and the precipitation of tungsten rich phases with the WT-6 alloy. Low levels of carbide dissolution were also recorded. A drop in material hardness was recorded with both alloys after the solution treatment. Additional aging treatments did not significantly alter the alloys microstructures further but precipitation within the matrix occurred. This coincided with significant improvements in the hardness properties of both alloys. Calculating the mean H/E ratio of the matrix phase in both alloys estimated that no improvements in matrix wear resistance occurred with WT-6 alloy whereas an improvement with the WT-12 matrix was calculated.

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Investigating Cobalt in Soil-plant-animal-human system: Dynamics, Impact and Management

Banerjee¹,

Bhattacharya²

2021

J Soil Sci Plant Nutr

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Cobalt

Abstract: Cobalt (chemical symbol, Co) is a d-block transition metal, bluish-white.

Cited by 5 publications

References 19 publications

On the Necessity of Banning the Term “Heavy Metal” from the Scientific Literature

On the Necessity of Banning the Term “Heavy Metal” from the Scientific Literature

The Effects of Composition and Heat Treatment on the Microstructure and Performance of Cobalt-based Alloys for Molten Zinc Applications

Investigating Cobalt in Soil-plant-animal-human system: Dynamics, Impact and Management

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