inorganic chemistry - Melting and boiling point comparison - Chemistry Stack Exchange
The very term "covalent compounds" is confusing, so you may just as well stop using it. The elementary substances you specified are covalent. Tantalum is a chemical element with symbol Ta and atomic number Previously known as . Tantalum's high melting point of °C (boiling point °C) is exceeded among the Structure-property relations in nonferrous metals. But since water fills a smaller volume when it's liquid, rather than solid, it will go to a lower melting point -- allowing more solid to become liquid. Answered by.
There are many species of tantalum minerals, only some of which are so far being used by industry as raw materials: Tantalite has the same mineral structure as columbite FeMn Ta, Nb 2 O 6; when there is more tantalum than niobium it is called tantalite and when there is more niobium than tantalum is it called columbite or niobite.
The high density of tantalite and other tantalum containing minerals makes the use of gravitational separation the best method.
Vanadium - Element information, properties and uses | Periodic Table
Other minerals include samarskite and fergusonite. Tantalum producers in with Rwanda being the main producer The primary mining of tantalum is in Australiawhere the largest producer, Global Advanced Metalsformerly known as Talison Mineralsoperates two mines in Western Australia, Greenbushes in the Southwest and Wodgina in the Pilbara region. The Wodgina mine was reopened in January after mining at the site was suspended in late due to the global financial crisis.
Some other countries such as ChinaEthiopiaand Mozambique mine ores with a higher percentage of tantalum, and they produce a significant percentage of the world's output of it.
Tantalum is also produced in Thailand and Malaysia as a by-product of the tin mining there. During gravitational separation of the ores from placer deposits, not only is cassiterite SnO2 found, but a small percentage of tantalite also included. The slag from the tin smelters then contains economically useful amounts of tantalum, which is leached from the slag. Beginning in and throughthe major sources of tantalum production from mines dramatically shifted to the DRC, Rwanda, and some other African countries.
Coltanthe industrial name for a columbite — tantalite mineral from which niobium and tantalum are extracted,  can also be found in Central Africawhich is why tantalum is being linked to warfare in the Democratic Republic of the Congo formerly Zaire.
According to an October 23, United Nations report,  the smuggling and exportation of coltan has helped fuel the war in the Congo, a crisis that has resulted in approximately 5. Ethical questions have been raised about responsible corporate behavior, human rights, and endangering wildlife, due to the exploitation of resources such as coltan in the armed conflict regions of the Congo Basin.
Melting and Boiling Point
First, the mineral is crushed and concentrated by gravity separation. This is generally carried out near the mine site. Refining[ edit ] The refining of tantalum from its ores is one of the more demanding separation processes in industrial metallurgy.
The chief problem is that tantalum ores contain significant amounts of niobiumwhich has chemical properties almost identical to those of Ta. A large number of procedures have been developed to address this challenge.
In modern times, the separation is achieved by hydrometallurgy.
Tantalum - Wikipedia
This step allows the tantalum and niobium to be separated from the various non-metallic impurities in the rock. Although Ta occurs as various minerals, it is conveniently represented as the pentoxide, since most oxides of tantalum V behave similarly under these conditions.
A simplified equation for its extraction is thus: This simple procedure allows the removal of most metal-containing impurities e. Separation of the tantalum from niobium is then achieved by lowering the ionic strength of the acid mixture, which causes the niobium to dissolve in the aqueous phase. It is proposed that oxyfluoride H2[NbOF5] is formed under these conditions. Subsequent to removal of the niobium, the solution of purified H2TaF7] is neutralised with aqueous ammonia to precipitate hydrated tantalum oxide as a solid, which can be calcined to tantalum pentoxide Ta2O5.
Instead of requiring the input oxide and output metal to be in liquid form, tantalum electrolysis operates on non-liquid powdered oxides. The initial discovery came in when Cambridge University researchers immersed small samples of certain oxides in baths of molten salt and reduced the oxide with electric current.
The cathode uses powdered metal oxide. The anode is made of carbon. Tantalum is not solderable. Grinding tantalum is difficult, especially so for annealed tantalum. In the annealed condition, tantalum is extremely ductile and can be readily formed as metal sheets.
The primary decay products before 48Ti are element 21 scandium isotopes and the primary products after are element 23 vanadium isotopes. Because of its high oxidation state, titanium IV compounds exhibit a high degree of covalent bonding. Unlike most other transition metals, simple aquo Ti IV complexes are unknown.
Oxides, sulfides, and alkoxides The most important oxide is TiO2, which exists in three important polymorphs ; anatasebrookiteand rutile.
All of these are white diamagnetic solids, although mineral samples can appear dark see rutile. They adopt polymeric structures in which Ti is surrounded by six oxide ligands that link to other Ti centers.
The term titanates usually refers to titanium IV compounds, as represented by barium titanate BaTiO3. With a perovskite structure, this material exhibits piezoelectric properties and is used as a transducer in the interconversion of sound and electricity. Star sapphires and rubies get their asterism star-forming shine from the presence of titanium dioxide impurities.
Ti3O5, described as a Ti IV -Ti III species, is a purple semiconductor produced by reduction of TiO2 with hydrogen at high temperatures,  and is used industrially when surfaces need to be vapour-coated with titanium dioxide: They are industrially useful for depositing solid TiO2 via the sol-gel process.
Titanium isopropoxide is used in the synthesis of chiral organic compounds via the Sharpless epoxidation. Titanium forms a variety of sulfides, but only TiS2 has attracted significant interest.
It adopts a layered structure and was used as a cathode in the development of lithium batteries. Because Ti IV is a "hard cation"the sulfides of titanium are unstable and tend to hydrolyze to the oxide with release of hydrogen sulfide. Halides Titanium tetrachloride titanium IV chloride, TiCl4  is a colorless volatile liquid commercial samples are yellowish that, in air, hydrolyzes with spectacular emission of white clouds.
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Via the Kroll processTiCl4 is produced in the conversion of titanium ores to titanium dioxide, e. A notable example is titanium III chloride TiCl3which is used as a catalyst for production of polyolefins see Ziegler-Natta catalyst and a reducing agent in organic chemistry.
Organometallic complexes Main article: Organotitanium chemistry Owing to the important role of titanium compounds as polymerization catalyst, compounds with Ti-C bonds have been intensively studied. The most common organotitanium complex is titanocene dichloride C5H5 2TiCl2.