Chemical elements
    Physical Properties
    Chemical Properties
    PDB 158d-1ajq
    PDB 1ak9-1ayk
    PDB 1ayo-1bg7
    PDB 1bg9-1byh
    PDB 1byn-1c8q
    PDB 1c8t-1cq1
    PDB 1cq9-1daq
    PDB 1dav-1dva
    PDB 1dvi-1el1
    PDB 1ela-1f4n
    PDB 1f4o-1fkq
    PDB 1fkv-1fzd
    PDB 1fze-1g9i
    PDB 1g9j-1gr3
    PDB 1gsl-1h5h
    PDB 1h5i-1hn4
    PDB 1hny-1i9z
    PDB 1ia6-1iyi
    PDB 1iz7-1jc2
    PDB 1jc9-1jui
    PDB 1jv2-1kck
    PDB 1kcl-1kvx
    PDB 1kvy-1led
    PDB 1lem-1lqd
    PDB 1lqe-1may
    PDB 1mbq-1mxe
    PDB 1mxg-1nfy
    PDB 1ng0-1nwg
    PDB 1nwk-1o3g
    PDB 1o3h-1om7
    PDB 1om8-1p7v
    PDB 1p7w-1pva
    PDB 1pvb-1qdo
    PDB 1qdt-1qq9
    PDB 1qqj-1rin
    PDB 1rio-1s10
    PDB 1s18-1scv
    PDB 1sdd-1su4
    PDB 1sub-1tf4
    PDB 1tf8-1top
    PDB 1tpa-1ujb
    PDB 1ujc-1uyy
    PDB 1uyz-1v73
    PDB 1v7v-1w2k
    PDB 1w2m-1wua
    PDB 1wun-1xkv
    PDB 1xmf-1y3x
    PDB 1y3y-1yqr
    PDB 1yr5-1zde
    PDB 1zdp-2a3x
    PDB 2a3y-2arb
    PDB 2are-2bd2
    PDB 2bd3-2bu4
    PDB 2bue-2c6g
    PDB 2c6p-2cy6
    PDB 2cyf-2dso
    PDB 2dtw-2eab
    PDB 2eac-2fe1
    PDB 2ff1-2fwn
    PDB 2fws-2gjp
    PDB 2gjr-2hd9
    PDB 2hes-2i6o
    PDB 2i7a-2ivz
    PDB 2iwa-2j7g
    PDB 2j7h-2jke
    PDB 2jkh-2kuh
    PDB 2kxv-2o1k
    PDB 2o39-2ovz
    PDB 2ow0-2pf2
    PDB 2pfj-2pyz
    PDB 2pz0-2qu1
    PDB 2qua-2re1
    PDB 2rex-2tmv
    PDB 2tn4-2vcb
    PDB 2vcc-2vqy
    PDB 2vr0-2w3i
    PDB 2w3j-2wlj
    PDB 2wm4-2wzs
    PDB 2x0g-2xmr
    PDB 2xn5-2z2z
    PDB 2z30-2zn9
    PDB 2zni-3a51
    PDB 3a5l-3ahw
    PDB 3ai7-3bcf
    PDB 3bdc-3bx1
    PDB 3bxi-3ch2
    PDB 3chj-3d34
    PDB 3d3i-3djl
    PDB 3dng-3e4q
    PDB 3e5s-3eqf
    PDB 3eqg-3faq
    PDB 3faw-3fou
    PDB 3foz-3gci
    PDB 3gcj-3gwz
    PDB 3gxo-3hjr
    PDB 3hkr-3i4i
    PDB 3i4p-3io6
    PDB 3ior-3k5m
    PDB 3k5s-3kqa
    PDB 3kqf-3lei
    PDB 3lek-3lum
    PDB 3lun-3mip
    PDB 3mis-3n7b
    PDB 3n7x-3nvn
    PDB 3nx7-3owf
    PDB 3ox5-3prq
    PDB 3prr-3sg5
    PDB 3sg6-3u39
    PDB 3u43-3vpp
    PDB 3zqx-4awy
    PDB 4awz-4dtu
    PDB 4dtx-4eoa
    PDB 4epz-5apr
    PDB 5bca-8tln
    PDB 966c-9rnt

Preparation of Calcium

The methods by which the problem of the separation of metallic calcium has been attacked may be divided into two classes -
  1. Electrolysis of a fused compound.
  2. The displacement of calcium from its compounds by a more electropositive metal.
Only the first has risen to the dignity of a commercial process, and that not to any great extent, owing to the limited use to which the metal has hitherto been put.

Electrolytic Methods of Calcium Preparation

Davy electrolysed a paste of calcium oxide mixed with the red oxide of mercury, using a platinum anode and a mercury cathode. An amalgam was formed from which distillation in a current of hydrogen failed to remove the mercury completely. Several subsequent investigators attempted the separation by similar methods with more or less success.

The experiments of Bcfrchers and Stockem first made possible the production of metallic calcium on a large scale. They electrolysed used calcium chloride, avoiding a temperature above the melting-point of calcium at the cathode because the molten metal dissolves in calcium chloride, producing the subchloride Ca2Cl2. The product obtained round the cathode submerged below the surface of the liquid, was spongy, brittle, and not very pure.

Redlich and Suter obtained a much more compact product by a device which has been adopted in the commercial production of calcium at Bitterfeld by the firm of Siemens and Halske. Calcium chloride, sometimes mixed with calcium fluoride to reduce the temperature of fusion, is used. As calcium burns in air above 800° C., this forms the limit beyond which the temperature must not be allowed to rise. The cathode, a cooled iron rod just touching the surface of the liquid, is gradually raised as electrolysis proceeds, drawing with it the solid calcium protected by a layer of the fused salt. This contact cathode tends to prevent the formation of a " metallic fog," or suspension of finely divided metallic calcium. The current density required at the cathode is about 100 amp. per sq. cm. The metal is obtained in the form of irregular cylinders weighing 200 to 300 grm. The following percentage analysis of Bitterfeld calcium has been given: Ca 97.75, Mg 0.89, Si 0.84, Fe 0.14, Al 0.37. It may, however, reach a purity of 99.3 – 99.6 per cent. Further purification of the commercial product may be effected by distillation in a high vacuum.

Subsequent study of the electrolytic separation of the metal has been mainly concerned with the relative merits of the submerged and contact cathodes, and with the desirability or otherwise of adding another electrolyte to the calcium chloride. Goodwin 5 at first adopted a submerged cathode of wrought iron passing through the bottom of a furnace of Acheson graphite, the walls of which formed the anode. Eventually he replaced this by the contact electrode employed at Bitterfeld, and that appears to be the most satisfactory method.

Goodwin used fused calcium chloride alone for the bath, but Moldenhauer and Andersen used potassium chloride in place of the calcium fluoride of the commercial process, and with a current density of 60-110 amp. per sq. cm. obtained metallic calcium practically free from potassium, with a current efficiency of 75-90 per cent. Brace concluded that pure, completely dehydrated calcium chloride is better than any admixture with another electrolyte. He also found that careful control of the temperature is necessary, and can be secured by varying the separation and degree of immersion of the anodes. Almost the entire charge of the electrolyte should be molten, only a small portion at the sides and bottom of the graphite container being allowed to remain solid.

Wohler described the conditions under which the metal may be prepared on a laboratory scale. He used a mixture of 100 parts of calcium chloride with 12 parts of calcium fluoride, melting at 660° C., and contained in an iron vessel. The cathode was an iron wire of 8 mm. diameter, and a current of 40 amp. at 38 volts was supplied, giving a density of 100 amp. per sq. cm. of cathode surface.

It is also possible to obtain calcium by electrolysis of a concentrated solution of calcium chloride, instead of the fused salt, using a mercury cathode. The amalgam may then be distilled.

Chemical Methods of Calcium Preparation

These consist essentially in the replacement of calcium in its salts by a more electropositive metal. In the first attempts, in which, for example, calcium iodide was heated with sodium, or with sodium and zinc, or calcium iodide was replaced by a mixture of potassium iodide and calcium chloride, the pure product was never obtained.

Moissan succeeded in getting rid of excess of sodium by utilising the fact that, although it dissolves calcium at red heat, the two metals are not miscible at crystallising-point, and the sodium can be removed by treatment with absolute alcohol, leaving the calcium untouched in the form of brilliant white crystals of 98.9 – 99.2 per cent, purity. It was necessary to avoid contact with oxygen, hydrogen, or nitrogen, and to use pure salts. The fact that the process required sodium and large quantities of absolute alcohol prevented its use commercially.

The difficulties of the displacement method are due largely to the circumstance that, although calcium is less electropositive than sodium at ordinary temperatures, at a temperature of about 800° C., or even lower, it will liberate sodium from its compounds, due either to the greater volatility of sodium at higher temperatures, or to calcium becoming more electropositive than sodium. It will not, however, replace potassium. At bright red heat a mixture of calcium and potassium is obtained.

Other reducing agents have been suggested in place of sodium - for example, magnesium, carbon, and aluminium. Methods have also been proposed for the direct production of calcium alloys, but these will be referred to later.
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