Method for Producing High-Purity Calcium

Abstract

A high-purity calcium and method of producing same are provided. The method includes performing first sublimation purification by introducing calcium starting material having a purity, excluding gas components, of 4N or less into a crucible of a sublimation vessel, subjecting the starting material to sublimation by heating at 750 C. to 800 C., and causing the product to deposit or evaporate onto the inside walls of the sublimation vessel; and then, once the calcium that has been subjected to first sublimation purification is recovered, performing second sublimation purification by introducing the recovered calcium again to the crucible to the sublimation vessel, heating the recovered calcium at 750 C. to 800 C., and causing the product to similarly deposit or evaporate on the inside walls of the sublimation vessel thereby recovering calcium having a purity of 4N5 or higher.

Claims

1. High-purity calcium having a purity of 4N5 or higher produced by a process comprising the steps of: charging calcium starting material having a purity, excluding the gas components, of 4N or less into a crucible of a sublimation vessel; performing first sublimation purification by heating at 750 C. to 800 C. so that calcium is sublimated and deposits (evaporates) onto the inner side wall of the sublimation vessel; recovering the calcium purified by the first sublimation purification; charging the calcium into a crucible of a sublimation vessel again; performing second sublimation purification by heating at 750 C. to 800 C. so that the calcium is sublimated and deposits (evaporates) onto the inner side wall of the sublimation vessel; and recovering the calcium having a purity of 4N5 or higher.

2. The high-purity calcium according to claim 1, wherein the high-purity calcium contains less than 5 ppm of each transition metal element.

3. The high-purity calcium according to claim 1, wherein the high-purity calcium contains less than 1 ppm of each transition metal element.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0020] FIG. 1 is a schematic explanatory diagram of a sublimation apparatus.

DETAILED DESCRIPTION

[0021] In the method of producing high-purity calcium of the present invention, a starting material of calcium having a purity, excluding the gas components, of 4N or less is charged into a crucible of a sublimation vessel. Subsequently, first sublimation purification is performed by heating the starting material at 750 C. to 800 C. and thereby allowing the sublimated calcium to deposit (evaporate) onto the inner side wall of the sublimation vessel. The calcium purified by the first sublimation purification is cooled and is then recovered.

[0022] Subsequently, the recovered calcium is charged into a crucible of a sublimation vessel again. The sublimation vessel may be different from or the same as that used in the first sublimation purification. Second sublimation purification is performed by heating the recovered calcium at 750 C. to 800 C. again and thereby allowing calcium to deposit (evaporate) onto the inner side wall of the sublimation vessel. As a result, calcium having a purity of 4N5 or higher can be recovered.

[0023] The temperature for sublimation, 750 C. to 800 C., is a temperature slightly lower than the melting point, 839 C., and is controlled for adjusting the sublimation rate of calcium. A temperature lower than 750 C. decreases the efficiency of sublimation purification, whereas a temperature exceeding 800 C. causes contamination of impurities. Accordingly, the temperature is adjusted within the above-mentioned range. As a result, the sublimation rate of calcium can be controlled to be 0.25 to 0.75 g/cm.sup.2/h. This rate is suitable for sublimation purification of calcium.

[0024] The sublimation vessel used is usually made of thermostable stainless steel. Calcium which is purified by sublimation purification and deposits (evaporates) to this sublimation vessel is recovered. The degree of vacuum in the sublimation vessel during the sublimation purification is kept to be high, i.e., 110.sup.4 Pa or more, to accelerate the sublimation and remove highly vaporizable impurities contained in calcium. The process of the present invention can achieve a yield of 80% or more based on the calcium starting material. In addition, the content of each transition metal element in the recovered high-purity calcium can be reduced to less than 5 ppm and further to less than 1 ppm.

[0025] Thus, high-purity calcium having a purity of 4N5 or higher can be provided. In addition, the content of each transition metal element in this high-purity calcium can be reduced to less than 5 ppm and further to less than 1 ppm.

EXAMPLES

[0026] Examples will now be described. The examples are intended to facilitate understanding and do no limit the present invention. That is, other examples and modifications within the technical idea of the present invention are encompassed in the present invention.

Example 1

[0027] Calcium starting material (3.5 kg) having a purity of 99.9% (3N) containing impurities shown in Table 1 was charged in a crucible at the bottom of a vertical sublimation vessel shown in FIG. 1. Table 1 also shows variation in the starting material. The degree of vacuum in the sublimation vessel was in an order of magnitude of 110.sup.4 Pa. The vacuum processing was achieved by rough pumping with a rotary pump and fine pumping with a cryopump. The heating of the crucible was controlled within the following range.

TABLE-US-00001 TABLE 1 Ca analytica value (Example) First Residue in first Second Variation in raw material Raw material sublimation sublimation sublimation Weight Min Max 3.5 kg 3.0 kg 0.25 kg 2.8 kg Li 0.17 Te 5.4 0.35 0.15 <0.05 <0.05 Li Be <0.05 <0.05 <0.05 <0.05 <0.05 Be B 0.05~0.08 <005 <0.05 <0.05 <0.05 B F 1~4 <1 <1 <1 <1 F Na 0.76~97 0.33 0.51 <0.05 <0.05 Na Mg 4.5~240 52 7.9 <0.05 <0.05 Mg Al <0.05~90 14 5.8 110 <0.05 Al Si 0.06~140 15 6.4 135 <0.05 Si P <0.05~0.06 <0.05 <0.05 <0.05 <0.05 P S 0.19~3.1 0.21 2 1 <0.05 S Cl 40~2400 ~2100 ~160 ~30 ~50 Cl K 0.5~2.5 <0.5 1.1 <0.5 <0.5 K Ca Ca Sc <0.01 <0.01 <0.01 <0.01 <0.01 Sc Ti <0.05~5.3 0.57 0.58 1.4 <0.05 Ti V <0.01~0.09 0.09 <0.01 0.07 <0.01 V Cr <0.05~0.8 0.56 0.36 0.6 <0.05 Cr Mn 7.1~42 26 0.48 0.77 0.09 Mn Fe 1.4~75 5 1.3 64 <0.05 Fe Co <0.05~0.52 <0.05 <0.05 <0.05 <0.05 Co Ni <0.1~1.1 <0.1 <0.1 <0.1 <0.1 Ni Cu 30~850 95 4.6 380 <2 Cu Zn <0.1~2.4 <0.1 <0.1 <0.1 <0.1 Zn Ga <0.05 <0.05 <0.05 <0.05 <0.05 Ga Ge <0.5 <0.5 <0.5 <0.5 <0.5 Ge As =<50 =<50 =<50 =<50 =<50 As Se =<10~100 =<10 =<10 =<10 =<10 Se Br <0.5 <0.5 <0.5 <0.5 <0.5 Br Rb <0.05 <0.05 <0.05 <0.05 <0.05 Rb Sr =<160~3500 =<47 =<830 =<420 =<230 Sr Y <0.1 <0.1 <0.1 <0.1 <0.1 Y Zr <0.05 <0.05 <0.05 <0.05 <0.05 Zr Nb <0.1 <0.1 <0.1 <0.1 <0.1 Nb Mo <0.5 <0.5 <0.5 <0.5 <0.5 Mo Ru <1 <1 <1 <1 <1 Ru Rh <0.1 <0.1 <0.1 <0.1 <0.1 Rh Pd <0.5 <0.5 <0.5 <0.5 <0.5 Pd Ag <0.5 <0.5 <0.5 <0.5 <0.5 Ag Cd <5 <5 <5 <5 <5 Cd In <0.5 <0.5 <0.5 <0.5 <0.5 In Sn <0.5 <0.5 <0.5 <0.5 <0.5 Sn Sb <0.1 <0.1 <0.1 <0.1 <0.1 Sb Te <0.5 <0.5 <0.5 <0.5 <0.5 Te I <1 <1 <1 <1 <1 I Cs <0.5 <0.5 <0.5 <0.5 <0.5 Cs Ba 2.3~110 8.5 17 33 22 Ba La <0.05 <0.05 <0.05 <0.05 <0.05 La Ce <0.05 <0.05 <0.05 <0.05 <0.05 Ce Pr <0.05 <0.05 <0.05 <0.05 <0.05 Pr Nd <0.05 <0.05 <0.05 <0.05 <0.05 Nd Sm <0.05 <0.05 <0.05 <0.05 <0.05 Sm Eu <0.05 <0.05 <0.05 <0.05 <0.05 Eu Gd <0.05 <0.05 <0.05 <0.05 <0.05 Gd Tb <0.05 <0.05 <0.05 <0.05 <0.05 Tb Dy <0.05 <0.05 <0.05 <0.05 <0.05 Dy Ho <0.05 <0.05 <0.05 <0.05 <0.05 Ho Er <0.05 <0.05 <0.05 <0.05 <0.05 Er Tm <0.05 <0.05 <0.05 <0.05 <0.05 Tm Yb <0.05 <0.05 <0.05 <0.05 <0.05 Yb Lu <0.05 <0.05 <0.05 <0.05 <0.05 Lu Hf <0.05 <0.05 <0.05 <0.05 <0.05 Hf Ta <5 <5 <5 <5 Ta W <0.1 <0.1 <0.1 <0.1 <0.1 W Re <0.05 <0.05 <0.05 <0.05 <0.05 Re Os <0.05 <0.05 <0.05 <0.05 <0.05 Os Ir <0.05 <0.05 <0.05 <0.05 <0.05 Ir Pt <0.05 <0.05 <0.05 <0.05 <0.05 Pt Au <1 <1 <1 <1 <1 Au Hg <0.1 <0.1 <0.1 <0.1 <0.1 Hg Ti <0.05 <0.05 <0.05 <0.05 <0.05 Ti Pb <0.05~1.1 <0.05 1.9 3.8 <0.05 Pb Bi <0.05 <0.05 <0.05 <0.05 <0.05 Bi Th <0.005 <0.005 <0.005 <0.005 <0.005 Th U <0.005 <0.005 <0.005 <0.005 <0.005 U C 35~150 48 55 100 40 C N <10~120 13 <10 <10 <10 N O 100~1200 120 80 2000 100 O S <10 <10 <10 <10 <10 S H 23~48 23 30 50 30 H

[0028] The heating temperature was 770 C. in a steady state and was normally controlled within a range of 750 C. to 800 C. The sublimation rate was 0.64 g/cm.sup.2/h in a steady state and was normally controlled within a range of 0.25 to 0.75 g/cm.sup.2/h. A sublimation rate lower than this range increases the variation in sublimation rate and causes to decrease the efficiency; on the other hand, a sublimation rate higher than this range is apt to give a low purity.

[0029] As described above, 3.5 kg of the calcium starting material was used. The first sublimation gave 3.0 kg of an adhered (deposited) product onto the inner side wall of the sublimation vessel. This analytical value is also shown in Table 1. The residue of the first sublimation was 0.25 kg, and the loss was 0.25 kg. The analytical values of the residue in the first sublimation are also shown in Table 1. The values were Mg<0.05 wt ppm, Fe: 64 wt ppm, and Cu: 380 wt ppm. The amount of the residual copper was high. In the first sublimation, the starting material shape was prone to be unstable, and the sublimation rate was also prone to be unstable.

[0030] Subsequently, the calcium starting material (3.0 kg) deposited in the first sublimation was charged in a crucible at the bottom of a vertical sublimation vessel shown in FIG. 1. As a result, 2.8 kg of calcium was recovered. Accordingly, the yield was 80%, obtained by 2.8/3.5=80. The amounts of impurities in calcium after the second sublimation are also shown in Table 1. As obvious from the amounts of impurities shown in Table 1, high-purity calcium was provided. As shown in Table 1, it is demonstrated that since the amount of Cu present in calcium as starting material largely varies, sublimation purification is required to be performed twice. The amounts of Sr and Ba are relatively high as analytical values of calcium. However, since the properties of these elements are similar to those of calcium, these elements do not substantially cause any problem in use of calcium as a reducing agent. The conditions for the first and second sublimation were the same.

Comparative Example 1

[0031] The same calcium starting material as that in Example 1 was sublimated only once at 750 C. at a sublimation rate of 0.50 g/cm.sup.2/h to obtain a deposited product on the inner side wall of the sublimation vessel. Other conditions were the same as those in Example 1. As a result, as shown in the analytical results shown in Table 2, the amounts of impurities were generally greater than those in Example 1; the amounts of Fe and Cu were apparently large, and thus the object of the present invention could not be achieved.

TABLE-US-00002 TABLE 2 Sublimation rate (g/cm.sup.2/h) 0.50 Temperature ( C.) 750 First sublimation Li <0.05 Sn <0.5 Be <0.05 Sb <0.1 B 0.07 Te <0.5 F <1 I <1 Na 0.31 Cs <0.5 Mg 8 Ba 38 Al 1.1 La <0.05 Si 1.6 Ce <0.05 P <0.05 Pr <0.05 S 1.5 Nd <0.05 Cl ~550 Sm <0.05 K <0.5 Eu <0.05 Ca Gd <0.05 Sc <0.01 Tb <0.05 Ti 0.55 Dy <0.05 V <0.01 Ho <0.05 Cr 0.22 Er <0.05 Mn 0.95 Tm <0.05 Fe 4.1 Yb <0.05 Co <0.05 Lu <0.05 Ni <0.1 Hf <0.05 Cu 17 Ta <5 Zn <0.1 W <0.1 Ga <0.05 Re <0.05 Ge <0.5 Os <0.05 As =<140 Ir <0.05 Se =<110 Pt <0.05 Br <0.5 Au <1 Rb <0.05 Hg <0.1 Sr =<1200 Tl <0.05 Y <0.1 Pb 0.8 Zr <0.05 Bi <0.05 Nb <0.1 Th <0.005 Mo <0.5 U <0.005 Ru <1 C 90 Rh <0.1 N <10 Pd <0.5 O 300 Ag <0.5 S <10 Cd <5 H 15 In <0.5

Comparative Example 2

[0032] The same calcium starting material as that in Example 1 was sublimated once at 850 C. at a sublimation rate (evaporation rate) of 4.0 g/cm.sup.2/h to obtain a deposited product on the inner side wall of the sublimation vessel. Other conditions were the same as those in Example 1. As a result, as shown in the analytical results in the left side of Table 3, the amounts of impurities were generally greater than those in Example 1; the amounts of Si, Ti, Mn, Fe, Cu, As, Sr, and Ba were apparently large, and thus the object of the present invention could not be achieved.

TABLE-US-00003 TABLE 3 Sublimation rate (g/cm.sup.2/h) 4.0 Sublimation rate (g/cm.sup.2/h) 4.0 Tmeperature ( C.) 850 Temperature ( C.) 850 First sublimation Second sublimation Li <0.05 Sn <0.5 Li <0.05 Sn <0.5 Be <0.05 Sb <0.1 Be <0.05 Sb <0.1 B <0.05 Te <0.5 B 0.45 Te <0.5 F 2.1 I <1 F <1 I <1 Na <0.2 Cs <0.5 Na 0.21 Cs <0.5 Mg 1.7 Ba 43 Mg 2.9 Ba 29 Al 0.82 La <0.05 Al 0.13 La <0.05 Si 4.2 Ce <0.05 Si 0.37 Ce <0.05 P <0.05 Pr <0.05 P <0.05 Pr <0.05 S 2.8 Nd <0.05 S 0.42 Nd <0.05 Cl ~3600 Sm <0.05 Cl ~740 Sm <0.05 K <0.5 Eu <0.05 K <0.5 Eu <0.05 Ca Gd <0.05 Ca Gd <0.05 Sc <0.01 Tb <0.05 Sc <0.01 Tb <0.05 Ti 6.8 Dy <0.05 Ti <0.05 Dy <0.05 V <0.01 Ho <0.05 V <0.01 Ho <0.05 Cr 0.13 Er <0.05 Cr <0.05 Er <0.05 Mn 3 Tm <0.05 Mn 0.41 Tm <0.05 Fe 6.7 Yb <0.05 Fe 0.16 Yb <0.05 Co <0.05 Lu <0.05 Co <0.05 Lu <0.05 Ni 0.32 Hf <0.05 Ni <0.1 Hf <0.05 Cu 150 Ta <5 Cu 5.1 Ta <5 Zn <0.1 W <0.1 Zn <0.1 W <0.1 Ga <0.05 Re <0.05 Ga <0.05 Re <0.05 Ge <0.5 Os <0.05 Ge <0.5 Os <0.05 As =<110 Ir <0.05 As =<20 Ir <0.05 Se =<90 Pt <0.05 Se =<100 Pt <0.05 Br <0.5 Au <1 Br <0.5 Au <1 Rb <0.05 Hg <0.1 Rb <0.05 Hg <0.1 Sr =<670 Tl <0.05 Sr =<560 Tl <0.05 Y <0.1 Pb 3.1 Y <0.1 Pb 3.9 Zr <0.05 Bi 0.14 Zr <0.05 Bi 0.15 Nb <0.1 Th <0.005 Nb <0.1 Th <0.005 Mo <0.5 U <0.005 Mo <0.5 U <0.005 Ru <1 C 100 Ru <1 C 120 Rh <0.1 N <10 Rh 0.1 N <10 Pd <0.5 O 230 Pd <0.5 O 130 Ag <0.5 S <10 Ag <0.5 S <10 Cd <5 H 35 Cd <5 H 210 In <0.5 In <0.5

Comparative Example 3

[0033] The same calcium starting material as that in Example 1 was sublimated twice at a first heating temperature of 850 C. at a sublimation rate (evaporation rate) of 4.0 g/cm.sup.2/h and then at a second heating temperature of 850 C. at a sublimation rate (evaporation rate) of 3.7 g/cm.sup.2/h to obtain a deposited product on the inner side wall of the sublimation vessel. Other conditions were the same as those in Example 1. As a result, as shown in the analytical results in the right of Table 3, the amounts of impurities were generally greater than those in Example 1; the amounts of Mg, Al, Si, Fe, Cu, and Pb were apparently large, and thus the object of the present invention could not be achieved.

[0034] The present invention relates to recovery of calcium having a purity of 4N5 or higher by performing sublimation purification twice and has an excellent effect of stably providing highly purified calcium. The purified calcium can be used not only in production of high-purity lanthanum but also as a reducing agent for other rare earths, a desulfurizing or deoxidizing agent for metals, or a getter for high-vacuum pumps.