What is calcium carbide for metallurgy and Why Do We Use Them?

Cal­ci­um car­bide is a chem­i­cal com­pound of cal­ci­um and car­bon, and is a white crys­talline sub­stance when pure. It is ob­tained from the re­ac­tion

Read more

Ca + 2C &#; CaC&#;

Calcium carbide

[Wikimedia]

Cal­ci­um car­bide has great prac­ti­cal sig­nif­i­cance. It is also known as cal­ci­um acetylide.

The chem­i­cal char­ac­ter­is­tics of cal­ci­um car­bide

Cal­ci­um car­bide is not volatile and not sol­u­ble in any known sol­vent, and re­acts with wa­ter to yield acety­lene gas and cal­ci­um hy­drox­ide. Its den­si­ty is 2.22 g/cm³. Its melt­ing point is °C, and its boil­ing point is °C. Since the acety­lene that forms upon con­tact with wa­ter is flammable, the sub­stance is list­ed in haz­ard class 4.3.

Cal­ci­um acetylide was first ob­tained by Ger­man chemist Friedrich Wöh­ler in when he heat­ed an al­loy of zinc and cal­ci­um with coal. The sci­en­tist de­scribed the re­ac­tion of cal­ci­um car­bide with wa­ter. Cal­ci­um car­bide re­acts vig­or­ous­ly with even mere traces of &#;&#;O, re­leas­ing a large amount of heat. If there is an in­suf­fi­cient quan­ti­ty of wa­ter, the re­sult­ing acetylide spon­ta­neous­ly com­busts. Cal­ci­um acetylide re­acts vi­o­lent­ly with aque­ous so­lu­tions of al­ka­lis and di­lut­ed non-or­gan­ic acids. These re­ac­tions re­lease acetylide. With its strong re­duc­tive prop­er­ties, CaC&#; re­duces all met­al ox­ides to pure met­als or turns them into car­bides.

It is eas­i­er to ob­tain cal­ci­um car­bide from its ox­ide than from cal­ci­um it­self, as the ox­ide is re­duced at tem­per­a­tures above °C. The met­al and car­bon com­bine:

CaO + 3C &#; CO&#; + CaC&#;

The re­ac­tion takes place in an elec­tric arc fur­nace, where a mix­ture of un­slaked lime and coke or an­thracite is heat­ed. The tech­ni­cal prod­uct is grey due to the pres­ence of free car­bon, cal­ci­um ox­ide, phos­phide, sul­fide, and oth­er chem­i­cal com­pounds. CaC&#; com­pris­es 80-85% of the prod­uct by mass.

Use of cal­ci­um car­bide

In the past, cal­ci­um car­bide was used in car­bide lamps, where it served as a source of acety­lene flame. Nowa­days these lamps are still used to pow­er light­hous­es and bea­cons, and also in cave ex­plo­ration. CaC&#; also serves as a raw ma­te­ri­al in the de­vel­op­ment of chem­i­cal tech­nolo­gies, most no­tably syn­thet­ic rub­ber. Cal­ci­um car­bide is also used to make vinyl chlo­ride, acety­lene black, acry­loni­trile, acetic acid, ace­tone, eth­yl­ene, styrene, and syn­thet­ic resins.

The old miner carbide lamp

[Deposit Photos]

In met­al­lur­gy, cal­ci­um car­bide is used to de­ox­i­dize met­als and re­duce their oxy­gen and sul­fur con­tent (desul­fu­ra­tion). Cal­ci­um car­bide is used to man­u­fac­ture pow­dered car­bide, a plant growth reg­u­la­tor. 3,000 kW/h of elec­tric­i­ty is re­quired to ob­tain one ton of CaC&#;. For this rea­son, the man­u­fac­ture of the sub­stance is only prof­itable when elec­tric­i­ty costs are low. At the same time, the pro­duc­tion of cal­ci­um car­bide world­wide is con­stant­ly in­creas­ing.

Cal­ci­um car­bide &#; re­ac­tion with wa­ter

When cal­ci­um car­bide re­acts with wa­ter, acety­lene is re­leased:

2H&#;O + CaC&#; &#; C&#;H&#;&#; + Ca(OH)&#;

Acety­lene is an in­dus­tri­al sub­stance with an un­pleas­ant smell, which is caused by the im­pu­ri­ties it con­tains (NH&#;, H&#;S, PH&#;, and oth­ers). In its pure form, acety­lene is a col­or­less gas with a char­ac­ter­is­tic faint smell, and it dis­solves in wa­ter.

Welder using an acetylene torch

Wanding are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

[Deposit Photos]

A sim­ple ex­per­i­ment can be used to demon­strate the re­ac­tion of cal­ci­um car­bide with wa­ter: pour wa­ter into a 1.5 L bot­tle, quick­ly add sev­er­al pieces of cal­ci­um car­bide, and close the bot­tle with a stop­per. As a re­sult of the en­su­ing re­ac­tion be­tween cal­ci­um car­bide and wa­ter, acety­lene col­lects in the bot­tle as pres­sure builds. As soon as the re­ac­tion stops, place a burn­ing piece of pa­per in the bot­tle &#; this should trig­ger an ex­plo­sion ac­com­pa­nied by a fiery cloud. As the walls of the bot­tle can burst as a re­sult of the re­ac­tion, this ex­per­i­ment is dan­ger­ous, and should only be con­duct­ed with strict ob­ser­vance of safe­ty pre­cau­tions.

Warn­ing! Do not at­tempt these ex­per­i­ments with­out pro­fes­sion­al su­per­vi­sion! Look here for ex­per­i­ments with flame you can safe­ly do at home

To demon­strate the re­ac­tion of cal­ci­um car­bide with wa­ter, the ex­per­i­ment can be re­peat­ed in mod­i­fied form &#; us­ing a six-liter bot­tle. In this case, the com­po­nents must be weighed with pre­ci­sion, be­cause the greater the ra­dius of the bot­tle, the less the con­tain­er can with­stand high pres­sure (as­sum­ing iden­ti­cal ma­te­ri­al and wall thick­ness). A bot­tle with a large ca­pac­i­ty has a large ra­dius, but its walls are ap­prox­i­mate­ly the same &#; ac­cord­ing­ly, it is less re­sis­tant to pres­sure. To pre­vent it from ex­plod­ing, the amount of cal­ci­um car­bide must be cal­cu­lat­ed be­fore­hand. Cal­ci­um has a mo­lar mass of 40 g/mol, while car­bon&#;s is 12 g/mol, so the mo­lar mass of cal­ci­um car­bide is around 64 g/mol. Ac­cord­ing­ly, 64 g of car­bide will yield 22.4 L of acety­lene. The vol­ume of the bot­tle is 6 L, and the pres­sure has risen by ap­prox­i­mate­ly 4 at­mos­pheres.

The bot­tle must with­stand five at­mos­pheres: to con­duct the ex­per­i­ment, we take around 64 g of cal­ci­um car­bide and about 0.5 L of wa­ter. Place a piece of car­bide in­side a small bag. Push the bag into the bot­tle, then quick­ly close the bot­tle with the stop­per. The re­ac­tion of cal­ci­um car­bide with wa­ter con­tin­ues for sev­er­al min­utes, the bot­tle swells up and the process is ac­com­pa­nied by loud bangs, but the bot­tle should with­stand this.

Ball-and-stick model of the undecane molecule

[Wikimedia]

Af­ter the re­lease of acety­lene is com­plete, place a hot rag soaked in hen­de­cane on the bot­tle stop­per, then move away to a max­i­mum safe dis­tance. You will soon see a bright yel­low flash, and a foun­tain of flame up to 4 me­ters high will rise out of the bot­tle. This will burn the stop­per and warp the bot­tle, but the bot­tle should re­main in­tact. This ex­per­i­ment must be con­duct­ed in the open air, far away from flammable and ex­plo­sive ob­jects. Be sure to ob­serve all rel­e­vant safe­ty pre­cau­tions.

Desulfurization (direct)

In modern steelmaking operations, the need for lower sulfur steels demanded by modern continuous casting operations and specialty applications has increased calcium carbide's appeal as a hot metal desulfurizer.

As late as , most blast furnace iron was desulfurized in the torpedo car as shown above. In the integrated steel mill, this practice has now been largely replaced by the use magnesium to remove an initial amount of sulfur in the transfer ladle, and the use of carbide as a steel ladle deoxidizer and slag conditioner to obtain the final sulfur specification.

In ductile iron foundries, liquid iron must be desulfurized before specialized inoculation treatments can be employed. This desulfurization is frequently performed by feeding granular forms of calcium carbide onto the surface of the liquid iron, which is contained in specially designed mixing units.

Purity and particle size are the key parameters for optimum effectiveness in these applications. Particle sizing is carefully selected to provide maximum contact with carbide particles without incurring excessive dust losses.

Carbide Industries manufactures three standard sized products for ductile iron desulfurization, generally within the range of 8 to 80 US-mesh (2.5 to 0.2 mm). In addition, two patented specialty products are available to meet specific customer requirements. These specialized products are formulated to help eliminate the retention of unreacted carbide in the resulting desulfurization slags and also to minimize slag odor.

For subsurface injection, a powdered carbide is manufactured by ball milling selected sizes of carbide to less than 140 US-mesh (<105 microns). The milled carbide can then be custom blended with a wide range of other powder additives, such as lime, limestone, and fluorspar to meet customer specified formulations. The milled carbide is treated with special additives to significantly improve flow characteristics.

Because of their reactivity, calcium carbide powders are manufactured, mixed, loaded, and transported in either 20 ton pressure differential trailers or 90 ton railcars, under an inert nitrogen atmosphere.

For more information, please visit calcium carbide for metallurgy.