US3694186A - Thermal decomposition of nickel carbonyl - Google Patents

Abstract

THE CARBON CONTENT OF NICKEL FORMED BY THE THERMAL DECOMPOSITION OF NICKEL CARBONYL IS REDUCED BY CARRYING OUT THE DECOMPOSITION IN THE PRESENCE OF NITROUS OXIDE (N2O), ADVANTAGEOUSLY AT 260*C. OR ABOVE. ADVANTAGEOUSLY A DECOMPOSER WITH NITRIDED STEEL WALLS IS USED. THE PRESENCE OF N2O DURING THE DECOMPOSITION OF NICKEL CARBONYL ALSO INHIBITS THE CONTAMINATION OF THE NICKEL PRODUCED WITH IRON.

Description

United States Patent 3,694,186 THERMAL DECOMPOSITION OF NICKEL CARBONYL David Myers Llewelyn, Clydach, Swansea, Wales, assignor to The International Nickel Company, Inc., New York,

Filed July 2, 1971, Ser. No. 159,471 Claims priority, application Great Britain, July 7, 1970, 32,961/ 70 Int. Cl. B22f 9/00 US. Cl. 75-.5 AA 7 Claims ABSTRACT OF THE DISCLOSURE The carbon content of nickel formed by the thermal decomposition of nickel carbonyl is reduced by carrying out the decomposition in the presence of nitrous oxide (N 0), advantageously at 260 C. or above. Advantageously a decomposer with nitrided steel walls is used. The presence of N 0 during the decomposition of nickel carbonyl also inhibits the contamination of the nickel produced with iron.

This invention relates to the production of metallic nickel, and more particularly to the production of metallic nickel by the thermal decomposition of nickel carbonyl.

Nickel carbonyl has been decomposed to metallic nickel in various ways. For example, nickel carbonyl is passed over nickel pellets heated above the decomposition temperature of the carbonyl to deposit the nickel on the surface of the pellets so that they increase in size. Decomposition of nickel carbonyl in the hot free space of a decomposer leads to the formation of nickel powder having variously shaped particles according to the conditions used. Another process is to decompose the carbonyl on the surface of hot powder particles, which can be of nickel or of other materials that are to be coated with nickel, in the form of a fluidized bed or a suspension of powder in a stream of carbonyl-containing gas.

Nickel produced by the thermal decomposition of nickel carbonyl contains a small amount of carbon, which increases with the temperature of decomposition. This carbon is probably formed by the decomposition of carbon monoxide according to the equation:

Some of the carbon is generally combined with with the deposited nickel as a nickel carbide, but in this specification references to the carbon content of the nickel include free (graphitic) carbon.

It has now been discovered that the carbon and iron content of carbonyl nickel can be reduced by carrying out the decomposition in the presence of nitrous oxide (NO). The reduction of the carbon content becomes more pronounced as the temperature of decomposition is increased.

' It is an object of the present invention to provide a process for thermally decomposing nickel carbonyl to produce carbonyl nickel powder having low carbon contents.

Another object of the present invention is to provide a process for thermally decomposing nickel carbonyl to produce carbonyl nickel powder having low iron contents.

The invention also contemplates providing a process for producing carbonyl nickel powder having low carbon and iron contents.

It is a further object of the invention to provide a process for increasing the rate of thermal decomposition ice of nickel carbonyl without increasing the carbon content of the product.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates the decomposition of nickel carbonyl. A decomposing zone is established and is heated to a temperature high enough to decompose nickel carbonyl but below the temperature at which substantial carbon formation will occur during decomposition of nickel carbonyl. Nickel carbonyl and nitrous oxide are fed to the heated decomposing zone so that nickel carbonyl is decomposed in the presence of nitrous oxide to produce metallic nickel with a low carbon content.

The decomposing zone is normally established within a decomposer made of mild steel, and it has previously been found that it is a great advantage to nitride the walls, e.g., by heating the vessel in the presence of ammonia (advantageously, ammonia is admitted to the decomposing zone and heated to about 500 C. for at least one hour). If this is done the formation of black carbonaceous particles is largely prevented. It has been found, however, that nitrous oxide does not nitride the decomposer walls, so advantageously the walls are nitrided in a previous operation.

The process can be carried on in the temperature range of 230 C. to 350 C. Below 230 C. so small a proportion of the carbonyl is decomposed to powder that the process is not practicable on an industrial scale. Above 350 C. a high proportion of filamentary aggregates are formed. Advantageously, the process is conducted at temperatures above about 260 C. because the effects of nitrous oxide in minimizing carbon production become more pronounced at temperatures above 260 C.

The amount of nitrous oxide can vary within wide limits. As little as 10 parts per million of the carbonylcontaining gases, or even 1 p.p.m., is effective, and the concentration may be as high as 1500 p.p.m. or even more without any of the advantages being lost. However, larger amounts than 1500 p.p.m. or even 1000 p.p.m., besides increasing the cost, also create problems in purifying the gases for further use, and advantageously the amount of nitrous oxide added is kept as low as possible, e.g., to 250 p.p.m. or even less.

The use of nitrous oxide will now be considered in more detail in relation to the production of carbonyl nickel powder, that is to say powder made by the thermal decomposition of nickel carbonyl vapour in the hot free space of a decomposer.

Numerous tests were performed using a laboratory decomposer 10 inches in diameter having mild-steel walls that were externally heated in use. In all the tests carbon monoxide gas containing from 7% to 9% of nickel carbonyl was fed into the decomposer through an inlet at the top at a rate (unless otherwise specified) of 2000 litres/hour. The nitrous oxide, when used, was injected into the gas stream at a measured rate at room temperature. The temperature at the inlet to the decomposer was maintained at about 50 C. by water-cooling.

In the first set of tests the decomposer temperature (measured half-way between the axis and the wall) was maintained at 290 C. and the concentration of the nitrous oxide was varied. Table I below shows the concentration of the carbonyl by volume, the amount of nitrous oxide introduced (in parts per million), the particle size of the powder as measured in the Fisher sub-sieve sizer, and the bulk density of the powder and the carbon content of the powder. The first three tests, A, B and C are given by way of comparison. Tests A and B were carried out in the decomposer before its walls were nitrided. Test C was carried out with the walls of the decomposer in a nitrided condition, and so were the other tests described in this specification. All the powders produced had a nitrogen content less than 0.001% and consisted of discrete particles having a spiky appearance when exam- The effect of varying the temperature on the iron content of the nickel powder produced is shown by the results set forth in Table IV.

ined microscopically under high magnification. 5 TABLE Iv TABLE I N Temp tifiiiii 1? $3353? 1 N o ibe ehconce n- Fisher Bulk C.) (p.p.m.) (percent) tration tration size density Test No. (percent) (p.p.m.) (microns) (g./0c.) C(percent) l0 fig 9.0 4. 47 2.47 0.057 230 1, 000 0.011 7. 0 a. 66 1. 99 0. 039 260 0. 010 8.0 4. 37 2.41 0.029 200 125 0.004 7. 0 a. 53 2. 05 0. 020 260 1, 000 0. 004 8. 0 a. 91 2. 0. 020 290 0. 014 7. 5 4. 47 2. 0. 020 290 125 0. 014 8.0 4.32 2.34 0.022 15 290 00 0.007 8.5 4. 47 2. 0. 020 320 0. 015 9. 0 4. 5 2. 4s 0. 020 320 125 0. 01a 8. 5 5. a 2. 5e 0. 010 320 1, 000 0. 014

This table shows that at all the nitrous oxide concentrations used there was a marked reduction in the carbon 20 The results in Tables III and IV show that at 260 C. content of the powder. the iron content is reduced to a remarkably low level. It

The eifect of varying the temperature of decomposrappears that the concentration of nitrous oxide required tion is shown by the results in Table II. All the tests were to bring about a significant improvement increases as the carried out with the walls of the decomposer in the nidecomposition temperature increases. trided condition. 25 Although the present invention has been described in TABLE II Carbonyl N20 eoncenconcen- Fisher Bulk tration tration size density 0 (percent) (p.p.m.) (microns) (g./cc.) (percent) It will be seen that while the carbon content of the conjunction with preferred embodiments, it is to be underpowders increases as the decomposition temperature 18 stood that modifications and variations may be resorted increased, in each case the presence of nitrous oxide durto w thout departing from the spirit and scope of the ining the decomposition lowered the carbon content. The ventron, as those skilled in the art will readily understand. shape and nitrogen content of the powder particles I 1Ch modifications and variations are considered to be formed at 250 c. and 320 c. were similar to that of wlthln pu and scope of the invention and pthose formed at 290 0., though the particle size was pended'clalmsgreater at 260 C. and smaller at 320 C. I (3181111! A further advantage of using nitrous oxide is that its A pr thermally decomposing nickel presence during the decomposition of nickel carbonyl bonYl Whlch P a l Shmg a decomposing zone, appears to inhibit the contamination of the nickel proheatlng the decomposlpg Zone t0 a temperature high duced with iron. This effect is shown by the results in enough to (16009113056 mckel Y the t m- Table'III, which set forth the iron contents of nickel pow- Pemtul'e f Whlch carbon formation vvlll Occur during ders formed by the decomposition at 290 C. of nickel 9 P of nickel f y i feedlllg the mcarbonyl containing traces of iron carbonyl, using the P 5 11100118 OXIdo in Small but efl'ective amounts same decomposer with nitrided steel walls as in the previto n llmml ze the decomposltlon of Carbon m noxide and ous tests, with and without the presence of nitrous oxide feedmg nickel o y t0 the heated decomposing Z0116 in the concentrations shown. In each case the concentrato decompose the nickel CaIbOHYI t0 metallic el With tion of nickel carbonyl was in the range 7-9% by volume, a low carbon content the balance of the gas being carbon mon id 0 2. The process as descr1bed in claim 1 wherein the decomposingrone 1s the free space of a reactor and the free space is maintained at a temperature between about 230 C. and 350 C. to produce carbonyl nickel powder. 3. The process as described in claim 2 wherein the free TAB III space of the reactor is bounded by nitrided mild steel N10 walls.

ggg gg g 4. The process as described in claim 1 wherein the con- Test No (p.p.rn.) (percent) centration of nitrous oxide in the carbonyl-containing gas M14 is between about 1 part per million and 1,500 parts per 0.015 million. 8:85: 5. The process as described in claim 4 wherein the 0. 015 carbonyl-containing gas contains between about 10 parts 8:83}, per nullion and 1,000 parts per million nitrous oxide 0.005 to produce carbonyl nickel powder with low carbon con- 6 6. The process as described in claim 4 wherein the References Cited 1:10:32 fghcglyat :dgegorgposed at a temperature between UNITED STATES PATENTS 7. The process as described in claim 6 wherein the 2,844,456 4/1958 Llewelyn 75 0-5 AA nickel carbonyl is decomposed at a temperature of at 6 least about WAYLAND W. STALLARD, Prlmary Exammer