DE1483146B1 - METHOD OF MANUFACTURING SPHAEROLITHIC NICKEL POWDER - Google Patents

Description

The invention relates to a method for producing spherulitic nickel powder by thermal decomposition of gaseous nickel carbonyl in the free space of a heated decomposition chamber.

The production of nickel powder by thermal decomposition of gaseous nickel carbonyl has been carried out on an industrial scale for many years (Kieffer - Hotop, "Pulvermetallurgie und Sinterwerkstoffe", 1943, pp. 12 to 26; "The Iron Age", September 8, 1960, p 105). It is generally known that the resulting powder can be obtained in one or two forms depending on the decomposition temperature, the carbonyl concentration and the presence or absence of diluting gases, for example carbon monoxide. These are the so-called "A" nickel carbonyl powder, which consists of discrete particles with an irregular and stalky surface, and the so-called "B" powder, which is composed of agglomerations of intertwined threads or chains of touching particles, which in turn are separate are irregular. The "B" powder has a low bulk density and a microscopic appearance in the form of small and spongy to sammenballungen. The size of the particle assemblies forming the chains fluctuates within very wide limits.

The invention is based on the finding that in the decomposition of nickel carbonyl to nickel powder in

ίο presence of active nitrogen that forms, d. H. of nitrogen formed in the decomposition chamber, by introducing at least 0.01 percent by weight Nitrogen in the powder, a remarkable and entirely unexpected change in the external Appearance of the individual particles of the resulting nickel powder occurs, the nickel particles are essentially spherulitic.

This way are among those prevalent in the manufacture of "A" powder without active nitrogen The discrete particles formed in the presence of active nitrogen do not decompose conditions more irregular and stalky, but smooth and essentially spherulitic. A similar change in shape of the individual nickel particles results when the decomposition conditions are chosen so that normal "B" powder would be produced in the absence of active nitrogen. The won product Although it still consists of interlocked chains or threads of individual particles, an investigation shows at very high magnification, for example with the electron microscope, that these chains are longer or form less strongly branched aggregates of intergrown spheres.

This change in shape is illustrated in the drawing, the electron microscope images typical powder. In the drawing shows

1 shows an agglomeration in a 4000-fold enlargement individual particles from the conventional "A" powder,

F i g. 2 in the same enlargement a similar agglomeration of nitrogen-containing particles from "A" nickel powder according to the invention,
F i g. 3, enlarged 4,500 times, shows part of a single aggregation of conventional "B" powder particles and

F i g. 4, magnified 6000 times, shows a similar "B" aggregation of nitrogen-containing powder according to the invention.

The in the F i g. 1 and 3 reproduced powders contain less than 0.01% nitrogen. The "A" powder of FIG. 2 contained 0.016% nitrogen, had a density of 2.97 g / cm ³ and a Fisher size of 5.5 microns, while the "B" powder of FIG. 4 contained 0.08% nitrogen and had a density of 0.69 g / cm ³ and a Fisher size of 2.6 microns.

In order to ensure that the external shape of the powder particles becomes spherulitic, it is necessary to Bring at least 0.01 weight percent nitrogen into the powder. Some change in the Usually irregular and columnar shape of the particles arises even with smaller ones Nitrogen content, but the particles gradually become more rounded as the nitrogen content increases and are essentially spherulitic at a nitrogen content of 0.01%. The nitrogen content can be up to 0.2 or 0.3% or even more,

3 4

but an increase over 0.01% causes no mold The nitrogen content of the resulting nickel powder ^s

change of the individual particles. grows with increasing ammonia concentration in the

Even if the nitrogen content is below 0.01%, the decomposition chamber. In general, wind at least

spherulitic form does not occur, 0.2 percent by volume of ammonia is still required to reduce 0.01%

it is not necessary to bring the nitrogen content of the finished nitrogen into the powder, whereby the ammo

powder reaches this value. niac concentration preferably at least 0.3%

Which is repeated in the description and claims. Nickel powder with spherulitic particles

The given nitrogen contents relate to the ammonia concentrations of 1 ° / ₀

Bulk of the powder. or more educated, but such a high level of

As a result of the endothermic reaction in the case of the decomposition monia concentration, pure waste. The sour tongue are the conditions in an externally heated substance concentration is preferably at least Decomposition chamber not uniform everywhere. From this 0.15 percent by volume. The volume ratio of Amer gives that a monia produced according to the invention to oxygen can vary within wide limits Nickel powder with an average ken. However, it is preferably 3: 4 to 4: 1; of at least 0.01% nitrogen, even individual parts have the best nitriding effect and thus the largest host or contains agglomerations of particles, the economy with regard to the expensive ammonia a higher or lower nitrogen content is considered in the case of an ammonia-oxygen volume own the average. A ratio of 4: 3 was achieved. High concentrations of Special noted that when separating into a coarse ammonia and oxygen, i. H. each about about aggregated fraction and a fine fraction, 20 0.5%, should also be avoided if a for example, by sieving with a 150 mesh low carbon powder BSS sieve, the nitrogen content of the fine fraction should be, because of the ammonia with the reaction relatively high and that of the coarse fraction of the oxygen in the decomposition chamber is relatively low and can be below 0.01%. The water vapor increases the carbon content of the nickel particles of the coarse fraction are still increased by spheruloid powder. For this reason, the thical form, and it can be assumed that they adhered to the production of nickel powder with low carbon hot chamber walls and, due to the very substance content, introduced into the decomposition chamber strong heating have lost nitrogen. Furthermore, no more gases than traces of water vapor escaped keep the nitrogen of the spherulitic powder after.

of the invention by heating at moderate temperature. Numerous experiments have been carried out to obtain the

doors, for example at 250 ⁼ C, and the effect of a change in the procedural

an essentially nitrogen-free spherulitic flow factors on the properties of the accruing

"A" or "B" powder can be produced. to determine the nickel powder. The results of this

The invention relates to a method for experiments are shown in Tables I to IV. Production of the spherulitic nickel powder, at 35. In these experiments, gaseous carbon was used a mixture of ammonia and oxygen monoxide with 7 percent by volume nickel carbonyl (175 g for the formation of active nitrogen during the decomposition of nickel per cubic meter) in an externally heated is used. These gases presumably react with mild steel walls and a in the decomposition chamber Decomposition chamber in the presence of the decomposing diameter of 254 mm at a flow settling end Karbonyls and the newly formed 40 speed of 2000 l / h through an inlet in the Nickel particles introduced according to the equation upper part of the chamber. Dry

Ammonia gas and oxygen were added to the gas stream at the inlet as specified in

₃ + 3U ₂ = 6hl ₂ L> - 4IN. Tables introduced. The temperature measurement takes place

45 at a point halfway between the chamber

Since active nitrogen is required, it is important to have the wall and chamber axis as well as three-quarters of the

that it is formed in the decomposition chamber. Dem- chamber height.

According to the introduction of gaseous molecular results in Table I results

Neither allow the effect of varying amounts of nitrogen in the decomposition chamber

Result, and also the sole introduction of am- 50 ammonia and acid added to the carbonyl

moniak remains unsuccessful. When using substance with an ammonia-oxygen volume increase

Ammonia and oxygen can be used in any ratio of 4: 3 and a chamber temperature of

conventional form, for example as air, at-290 ° C. With all powders produced

be directed. was it the "A" type. The average-

The process conditions under which the "A" and nitrogen content of the nickel powder increased with it "B" nickel powder in a decomposition chamber from increasing amounts of the ammonia-oxygen mixed gaseous form Nickel carbonyl can be produced gases. The four powders No. 1 to 4 with the highest are well known. Thereby conditions lead to nitrogen contents consisted of smooth and spherical lower which nucleation is very strong, to lithic particles according to the invention. The others Formation of "B" powder, while at lower 60 three powders all had nitrogen contents that Number of germs forms "A" powder. The high germ levels were below the critical minimum of 0.01%. the Generation index is determined by high temperature, tall particles of No. 5 powder containing 0.009% nitrogen Carbonyl concentration and high throughput favored a rough surface, while the particles Stigt, while a low nucleation number due to the powder no. 6 with 0.002% nitrogen is irregularly low Temperature, low carbonyl concentration 65 were moderate, but less stalky than usual and a low throughput is promoted. The same “A” powder and powder no. 7, the one without ben conditions are typical when decomposing into counter ammonia and oxygen use of ammonia and oxygen. represented irregular and stalky "A" powder.

Table I.

Flow rate NH ₃ /H O ₂ concentration O ₂ Size according to
Fisher in Properties of nickel powder Chemical composition N ₂ , ° / o attempt
No. in 20th 15th in percent by volume 0.75 micron Schütt
weight in C,% 0.13 16 12th NH ₃ 0.6 4.10 g / cm ³ 0.075 0.14 1 12th 9 1 0.45 4.56 2.12 0.047 0.065 2 8th 6th 0.8 0.3 5.10 2.21 0.034 0.035 3 4th 3 0.6 0.15 5.28 2.8 0.029 0.009 4th 1.6 1.2 0.4 0.06 5.20 3.09 0.033 0.002 5 - 0.2 - 4.36 2.87 0.035 <0.001 6th 0.08 3.66 2.39 0.039 7th - 1.99

An increase in the chamber temperature leads to the formation of "B" powder. This is shown in Table II for ammonia and oxygen flow rates of 4 and 3 l / h and in Table III for twice the flow rate (8 l / h NH ₃ and 6 l / h oxygen). In each case there is a pronounced conversion from "A" to "B" powder

290-320 ⁰ C. The average nitrogen content of the powder according to Table II was too low to be in accordance with the invention, and thus the particles were irregular, although they were not acicular. The powders of Table III all consisted of smooth and spherulitic particles according to the invention.

Table II

attempt Chamber temperature Size according to properties of nickel powder Type composition N ₂ ,% No. in Τ Fisher in microns Bulk weight in Chemical "B" C,% 0.007 2.35 g / cm ³ "A" 0.12 0.009 8th 320 5.20 0.65 "A" 0.033 0.005 5 290 5.70 2.87 "A" 0.031 0.006 9 260 6.04 2.81 0.050 10 230 2.91

Table III

attempt Chamber temperature Size according to properties of nickel powder Type composition N ₂ , · /. No. Y _n ³ P Fisher in microns Bulk weight in Chemical "B" C,% 0.02 111 V- 1.55 g / cm ³ "A" 0.072 0.035 11th 320 5.28 0.31 "A" 0.029 0.06 4th 290 6.12 3.09 "A" 0.031 0.026 12th 260 6.22 3.26 0.028 13th 230 3.29

The results in Table IV illustrate the effect of different ratios of ammonia to oxygen at a constant temperature of 290 ^° C.

Table IV

Flow O ₂ volume Properties of nickel powder Size according to Bulk weight in Chemical composition N ₂ , »/" VCXaULH
No. speed in l / h 2 relationship Fisher in microns g / cm ³ C,% <0.001 NH ₃ 12th NH ₃ : O ₂ 3.02 1.19 0.062 0.031 14th 0 6th 0 4.22 2.51 0.033 0.035 15th 8th 6th 2: 3 5.28 3.09 0.029 0.026 4th 8th 6th 4: 3 4.04 2.29 0.032 0.032 16 24 6th 4: 1 4.26 2.60 0.027 0.031 17th 36 0 6: 1 3.59 2.09 0.033 0.002 18th 48 8: 1 4.2 2.42 0.035 19th 8th 00

In this series of tests, Tests Nos. 14 and 19 produced a conventional, irregular and columnar "A" powder which was essentially nitrogen free, from which it follows that the admixture of either ammonia or oxygen alone does not produce any particular effects. All the others Powders possessed the spherulitic of the invention

Form and proved that the ammonia-oxygen ratio can be changed within wide limits. Provided that the decomposition only takes place with such low levels of ammonia and oxygen, The nickel powders according to the invention have that no appreciable amounts of water vapor arise a lower carbon content in the

7 8

Nickel particles as nickel powder made under the same 2.96 g / cm ³ and 0.03% carbon

Conditions established in the absence of ammonia and containing 0.015% nitrogen in a loose layer

and usually 0.05 to 0.08% carbon of about 0.5 mm thickness for 15 minutes at HOO ⁰ C

fabric included. Carbonyl nickel powder contains sintered. The sintered plate obtained in this way possessed

habitable a very small amount, generally 5 a porosity of 28%, while a corresponding

less than 0.01 percent by weight, particles with a very plate of ordinary "A" powder have a porosity

high carbon content, which was extremely un- of 51%.

is desired and, for example, de-spherulitic "B" powder is particularly suitable

must be removed. The formation of this carbon for the manufacture of electrodes for batteries

rich particles can in the process according to the io as well as from other sintered moldings because it is better

Invention can be prevented by having the flow properties than the conventional one

Settlement in a chamber with surface nitrided »B« powder.

Steel walls is carried out. As is well known, as an example of the fluctuation in nitrogen content Steel, for example, by heating individual particles of the spherulitic nickel material for 3 hours Presence of ammonia to be nitrated. 15 powder became a powder with an average Thereafter, operation of the decomposition chamber leads to a nitrogen content of 0.013% and 0.022% coal production of nickel powder with admixture of substance according to the method of the invention at a Ammonia simultaneously causes a nitration of the inner chamber temperature of 240 ° C and an ammonia surface the chamber wall and ensures oxygen ratio of 4: 3 is generated. The accruing that these surfaces remain nitrided constantly. Velvet 20 powder was divided into a fine and a coarse fraction borrowed in Tables I and IV reproduced experiments by sieving with a 150-mesh sieve were divided in a decomposition chamber and a small amount (less than 1%) of the very out, the wall previously in the above coarse material on a 30-mesh sieve Way had been nitrided. left behind, discarded. The fine fraction, the 70%

In addition to their spherulitic shape, which makes up 25 of the total amount, possessed a bulk weight

Nickel powder according to the invention by a very of 3.42 g / cm ³ and contained 0.016% nitrogen as well

characterized by high purity and in particular by 0.022% carbon, while the coarse fraction

very low levels of sulfur and cobalt. Dem- (about 30% of the total amount) a bulk weight of

according to the "A" powder of Fig. 2 and which ^{possessed 1.87 g / cm 3} and contained only 0.005% nitrogen as well

"B" powder of FIG. 4 of the drawing contained less than 30 0.022% carbon. The nickel particles

0.0002% sulfur and less than 0.002% cobalt; however, both factions were spherulitic. In the

In general, the coarse fraction according to the invention contained the individual particles were strong

Nickel powder less than 0.0007% sulfur and less associated in dense piles and possessed

than 0.002% cobalt. good flow properties.

The spherulitic "A" and "B" powders after 35 It is obvious that the ratio of

the method according to the invention are particularly fine and coarse material depending on the conditions

suitable for powder metallurgical processes because it fluctuates in the decomposition chamber. The low one

compared to the conventional nickel powder temperature of the above embodiment

of the same type have improved sintering properties. led to the formation of an exceptionally large one

For example, a spherulitic "A" -pul- 40 amount of coarse powder sinters.

ver faster and results in sintered bodies, which are only such a coarse fraction as in the case of the pre-small Have pore volume and accrued for fuel-standing example is particularly suitable for cell electrodes and filters are very suitable. So powder metallurgical purposes because they became carbon a spherulitic powder which, as stated above, is not greater than the average of the described, at a temperature of 290 "C 20 l / h 45 whole powder, while a coarse fraction that Ammonia and 4 l / h oxygen and separated from ordinary nickel powder with a Fisher- size of 5.5 microns and a bulk density of an undesirably high carbon content.

1 sheet of drawings

) 209 537/77

COPY J

Claims (6)

Patent claims: 1. Process for the production of spherulitic nickel powder by thermal decomposition of gaseous nickel carbonyl in the free space of a heated decomposition chamber, characterized in that the decomposition in the presence of active nitrogen in such amounts are made that the resulting nickel powder has an average nitrogen content of at least 0.01%. 2. The method according to claim 1, characterized in that the decomposition at an ammonia-oxygen volume ratio from 3: 4 to 4: 1. 3. The method according to claim 2, characterized in that the decomposition at an ammonia-oxygen volume ratio of 4: 3 takes place. 4. The method according to claims 1 to 3, characterized in that it is in a decomposition chamber made of steel with a nitrided inner surface. 5. The method according to claim 1, characterized in that the resulting nickel powder in two Fractions divided and a fine fraction with a relatively high nitrogen content and a coarse fraction Fraction with relatively low nitrogen content is produced. 6. The method according to claims 1 to 4, characterized in that the resulting nickel powder is annealed to remove the nitrogen.