CARBIDE

Carbide – a ripening and health effect.

Introduction
At the rate of RM 2/- a dozen, death is being sold now-a-days in our markets. My request for everybody is to be vigilant. Friends, we all love bananas and we eat a lot of them, but the bananas available in the market are forced ripe by dipping in water mixed with Carbide. The consumption of these bananas is 100% sure to cause Cancer or some other infection in the stomach. Therefore, such type of bananas are to be avoided. But, how does one recognize the bananas ripened with the help of Carbide? Bananas which are ripened naturally are dark yellow and there are small black spots here and there on the bananas and the stalks are black. While those which are forced ripe with Carbide are lemon yellow and their stalks are green and more over they are clear yellow without any black spots. Now, what is Carbide and how is it harmful? Carbide is a chemical which if mixed with water, emits heat and the heat emitted by a Close tank mixed with Carbide is even more than that emitted by a LPG Cylinder, so> much so it can be used for Gas Cutting (which means the calorific value is so high that it can replace LPG gas). In the same way, when the bunch of bananas are dipped in the water mixed with Carbide, the gas gets absorbed into the bananas and they get ripe. However, the banana vendors are not that literate and so they do not know the exact proportion of Carbide to be used for a dozen of bananas. As a result they end up using excess quantity of Carbide which gets absorbed into the bananas and ultimately enters our stomach. Due to this excess use of Carbide, Tumors can be formed in our digestive system. So, next time you purchase bananas, make sure you select the naturally ripened ones.

Ripening agents
Ripening agents speed up the ripening process.
They allow many fruits to be picked prior to full ripening, which is useful, since ripened fruits do not ship well. For example, bananas are picked when green and artificially ripened after shipment by being gassed with ethylene.[1] A similar method used in parts of Asia was to cover a bed of slightly green-harvested mango and a few small open containers of clumps of calcium carbide with a plastic covering. The moisture in the air reacted with the calcium carbide to release the gas acetylene, which has the same effect as ethylene. Ethylene is not emitted by the plant naturally, and cannot activate the ripening of nearby fruits, rather, it used as a hormone within the plant.
Calcium carbide is used for ripening the fruit artificially in some countries. Industrial-grade calcium carbide may contain traces of arsenic and phosphorus, and, thus, use of this chemical for this purpose is illegal in most countries. Calcium carbide, once dissolved in water, produces acetylene,[2] which acts as an artificial ripening agent. Acetylene is believed to affect the nervous systemby reducing oxygen supply to brain; however, it has been shown that, in practice, acetylene is not sufficiently reactive to affect consumers
Catalytic Generators are used to produce ethylene gas, simply and safely. Ethylene sensors can be used to precisely control the amount of gas.
Covered fruit ripening bowls are commercially available to increase fruit ripening.[3] The manufacturers claim the bowls increase ethylene and carbon dioxide gasses around the fruit which promote ripening.
Climacteric fruits are able to continue ripening after being picked, a process accelerated by ethylenegas. Non-climacteric fruits can ripen only on the plant and, thus, suffer from short shelf-lives

CARBIDE
a carbide is a compound composed of carbonand a less electronegative element. Carbides can be generally classified by chemical bonding type as follows: (i) salt-like, (ii)covalent compounds, (iii) interstitial compounds, and (iv) "intermediate" transition metal carbides. Examples includecalcium carbide, silicon carbide, tungsten carbide (often called simply carbide), and cementite[1], each used in key industrial applications.
Salt-like carbides
Salt-like carbides are composed of highly electropositive elements such as the alkali metals, alkaline earths, and group 3 metals including scandium, yttrium and lanthanum. Aluminium from group 13 forms carbides, but gallium, indium and thallium do not. In these materials feature isolated carbon centers, often described as "C4−"; two atom units, "C22−" in the acetylides and three atom units "C34−" in the sesquicarbides.[1] These formal anion C4–, sometimes called methanides (or methides) because they hydrolyse to give methane gas. The naming of ionic carbides is not consistent and can be quite confusing.

Methanides
Methanides in general chemical context refers to any compound that decomposes in water, producingmethane. However, according to IUPAC systematic naming conventions, it refers solely to the hypothetical CH3- anionic species. It is a useful simplification to describe methyl compounds, with relatively large bond polarity between the carbon and non-hydrogen atom, as containing the anionic species. In truth most such compounds, if not all, are, in fact, highly polar covalent, not ionic. Other compounds described as methanides in the general context contain various ratios of hydrogen down to no hydrogen at all. Two such examples which, can be called methanides, are aluminium carbide, andberyllium carbide.



Acetylides
Several carbides are assumed to be salts of the acetylide anion C22– (also called percarbide), which has a triple bond between the two carbon atoms. Alkali metals, alkaline earth metals, and lanthanoid metals form acetylides, e.g., sodium carbide Na2C2, calcium carbide CaC2, and LaC2.[1] Lanthanoids also form acetylides with formula M2C3. Metals from group 11 too tend to form acetylides, such ascopper(I) acetylide and silver acetylide. Carbides of the actinide elements, which have stoichiometry MC2 and M2C3, are also described as salt-like derivatives of C22–.
The C-C triple bond length ranges from 109.2 pm in CaC2 (similar to ethyne), to 130.3 pm in LaC2 and 134 pm in UC2. The bonding in LaC2 has been described in terms of LaIII with the extra electron delocalised into the antibonding orbital on C22−, explaining the metallic conduction.[1]
Sesquicarbides
The polyatomic ion C34–, sometimes called sesquicarbide, is found in Li4C3, Mg2C3. The ion is linear and is isoelectronic with CO2.[1] The C-C distance in Mg2C3 is 133.2 pm.[2] Mg2C3 yieldsmethylacetylene, CH3CCH, on hydrolysis which was the first indication that it may contain C34–.
Covalent carbides
The carbides of silicon and boron are described as "covalent carbides", although virtually all compounds of carbon exhibit some covalent character. Silicon carbide has two similar crystalline forms, which are both related to the diamond structure.[1] Boron carbide, B4C, on the other hand has an unusual structure which includes icosahedral boron units linked by carbon atoms. In this respectboron carbide is similar to the boron rich borides. Both silicon carbide, SiC, (carborundum) and boron carbide, B4C are very hard materials and refractory. Both materials are important industrially. Boron also forms other covalent carbides, e.g. B25C.
Interstitial carbides
The carbides of the group 4, 5 and 6 transition metals (with the exception of chromium) are often described as interstitial compounds.[1] These carbides have metallic properties and are refractory. Some exhibit a range of stoichiometries, e.g. titanium carbide, TiC. Titanium carbide and tungsten carbide are important industrially and are used to coat metals in cutting tools.[3]
The longheld view is that the carbon atoms fit into octahedral interstices in a close packed metal lattice when the metal atom radius is greater than approximately 135 pm:[1]
 When the metal atoms are cubic close packed, (ccp), then filling all of the octahedral interstices with carbon achieves 1:1 stoichiometry with the rock salt structure, (note that in rock salt, NaCl, it is the chloride anions that are cubic close packed).
 When the metal atoms are hexagonal close packed, (hcp), as the octahedral interstices lie directly opposite each other on either side of the layer of metal atoms, filling only one of these with carbon achieves 2:1 stoichiometry with the CdI2 structure.
The following table[1][3] shows actual structures of the metals and their carbides. (N.B. the body centred cubic structure adopted by vanadium, niobium, tantalum, chromium, molybdenum and tungsten is not a close packed lattice.) The notation "h/2" refers to the M2C type structure described above, which is only an approximate description of the actual structures. The simple view that the lattice of the pure metal "absorbs" carbon atoms can be seen to be untrue as the packing of the metal atom lattice in the carbides is different from the packing in the pure metal.
Metal Structure of pure metal Metallic
radius (pm) MC
metal atom packing MC structure M2C
metal atom packing M2C structure Other carbides
titanium
hcp 147 ccp rock salt
zirconium
hcp 160 ccp rock salt
hafnium
hcp 159 ccp rock salt
vanadium
cubic body centered 134 ccp rock salt hcp h/2 V4C3
niobium
cubic body centered 146 ccp rock salt hcp h/2 Nb4C3
tantalum
cubic body centered 146 ccp rock salt hcp h/2 Ta4C3
chromium
cubic body centered 128 Cr23C6, Cr3C,
Cr7C3, Cr3C2
molybdenum
cubic body centered 139 hexagonal hcp h/2 Mo3C2
tungsten
cubic body centered 139 hexagonal hcp h/2
For a long time the non-stoichiometric phases were believed to be disordered with a random filling of the interstices, however short and longer range ordering has been detected.[4]
Intermediate transition metal carbides
In these carbides, the transition metal ion is smaller than the critical 135 pm, and the structures are not interstitial but are more complex. Multiple stoichiometries are common, for example iron forms a number of carbides, Fe3C, Fe7C3 and Fe2C. The best known is cementite, Fe3C, which is present in steels. These carbides are more reactive than the interstitial carbides, for example the carbides of Cr, Mn, Fe, Co and Ni all are hydrolysed by dilute acids and sometimes by water, to give a mixture of hydrogen and hydrocarbons. These compounds share features with both the inert interstitials and the more reactive salt-like carbides.[1]
Molecular carbides


The complex [Au6C(PPh3)6]2+, containing a carbon-gold core.
Metal complexes containing Cn fragments are well known. Most common are carbon-centered clusters, such as [Au6C(PPh3)6]2+. Similar species are known for the metal carbonyls and the early metal halides. Even terminal carbides have been crystallized, e.g., CRuCl2(P(C6H11)3)2.
Impossible carbides
Some metals, such as lead and tin, are believed not to form carbides under any circumstances.[5] There exists however a mixed titanium-tin carbide, which is a two-dimensional conductor.[6] (In 2007, there were two reports of a lead carbide PbC2, apparently of the acetylide type; but these claims have yet to be published in reviewed journals.