DE1483145B2 - - Google Patents

Description

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The invention relates to nickel carbonyl chambers, the steel inner walls of which

powder, d. H. on a powder which is nitrided on the surface by thermal.

Decomposition of gaseous nickel carbonyl in the surface nitriding of the steel decomposition

heated free space of a decomposition chamber can be generated in the usual way by heating in the chamber

will. 5 Contact with ammonia gas, for example through a

The production of nickel powder from carbonyl or passage of ammonia gas takes place,

has been following this procedure for a number of years, taking the chamber walls and the other interior

carried out, and it is well known that surfaces are brought to a temperature

plus the working temperature, the carbonyl concentration high enough for the formation of a surface

tration and the presence or absence of a layer of iron nitrite from the reaction of iron

thinning gas, for example carbon monoxide, which is with the ammonia. For this purpose there is one

Nickel powder in one or two different forms suitable temperature of 500 ° C, with heating

accrues. These are the so-called "A" carbonyl- at least 1 hour, for example 3 hours,

Nickel powder, which is made of discrete particles to carry with one. The effectiveness of nitriding can be seen in

irregular, stem-like surface, as well as being controlled in the manner that during the

the so-called "B" powder, which from the nitriding treatment together creates a test piece of steel

clusters of intertwined threads or chains of speaking composition in the decomposition

consists of interconnected particles, the chamber is inserted and then at 500 ⁰ C

in turn are individually irregular. The "B" -Pul- for 2 hours under carbon monoxide with a

ver has a low density and a micro-low content of gaseous nickel carbonyl

scopic - shape in the form of narrower, more spongy annealed. If there is no black coal

Floeken. The size of the agglomerations of particles, deposition of matter on the surface of the specimen

that form such a chain can form within wide limits, the nitriding treatment is sufficient,

vary. Although it is preferable to use nitriding as a

Regardless of the physical nature of the treatment before the introduction of the carbonyl into that of the powder, this must be carried out when it leaves the decomposition chamber, it can also be useful to carry out low carbon contents by introducing ammonia in, for example, 0.05 to 0, 08 weight percent. In doing so, the decomposition chamber has to be nitrided while the predominant part of the carbon lies in the preceding batch of nickel powder produced and the nickel particles are consequently heated either as graphite or as a chemical decomposition chamber. The full bound to the nickel before. The nickel powder is the effect of the treatment according to the invention, but almost always in a small amount, generally less than 0.1 percent by weight, preventing the formation of carbon-rich particles, but does not occur as long as the chamber walls are small with a very high carbon content, for example not fully nitrided. The inner wall of the zer-50 ° / ₀ or more, contaminated. The presence of such carbon-rich particles must of course initially be clean for many in order to carry out the nitriding treatment. Uses not very desirable. As soon as the actual nitriding ends, the carbon-rich particles, if the nickel has come, it can still be sintered in a thin layer according to a further powder, and the feature of the invention is advantageous to leave corresponding cavities. And when there is 40 nickel carbonyl, small amounts of ammonia are mixed in with this thin layer to create a protective coating. As a result, the nitrided steel is treated, its protective effect is retained as reduced, while in the case of porous parts, such as the content of bonded carbon in the nickel-based fuel cell electrodes, an uneven powder is reduced. It can be assumed that the latter pore distribution is the result. For this reason, the carbon monoxide hindrance effect must be removed before the carbon particles are sold or set on the newly formed surfaces of the nickel using the nickel powder. powder particles resulting from the formation of carbon, in the event that the carbon-rich particles of the is normally included in the particles. are larger than the nickel particles, they can be counteracted by water vapor, so that sieving is removed, but this must be ensured that this is essentially absent, not always all of these harmful particles bound distant. Carbon content of the nickel powder results from

The invention is based on the finding that if small amounts of oxygen, for example 0.01

the carbon-rich particles are less than 0.1 percent by volume of the amount of gas conveyed

mix decomposition of carbon monoxide on the 55 during the decomposition together with the ammo

Surfaces of the steel walls and inner steel arma- nia are introduced. The volume ratio of

Doors of the decomposition chamber form and that their ammonia is preferably oxygen

Education can then be wholly or partially prevented 4: 3. Regardless of whether oxygen is introduced

can if these surfaces are nitrided. will or not, is the amount of ammonia required

It was also found that both the 60 very low, i.e. That is, already 0.01 percent by volume of the

Formation of the carbon-rich particles as well as the amount of gas introduced into the decomposition chamber are in

Inclusion of carbon in the nickel particles is generally sufficient. To avoid contamination of the

other form due to the presence of water - gas leaving the chamber as low as possible

steam is promoted. Proceeding from these hold fast and the formation of a noticeable crowd

Positions the invention consists in nickel powder 65 water vapor as a result of the reaction of ammonia with

To prevent oxygen by way of thermal decomposition of gaseous gas, the amount of

Nickel carbonyl in the absence of water vapor introduced ammonia preferably no longer

and in the heated free space of a decomposition rate of 0.1% by volume. The presence of sour

substance promotes nitration of the nickel powder because of the formation of active nitrogen through the reaction between ammonia and oxygen, so that the nitrogen content of the nickel powder increases. In the process according to the invention, however, the ammonia concentration does not exceed 0.2 percent by volume, if oxygen is present, since otherwise the powder becomes spherulitic, according to the according to the invention However, the method should not be spherulitic. The method according to the invention can not only in the production of nickel powder by means of the thermal decomposition of gaseous nickel carbonyl be used in concentrated form, but also in form diluted with carbon monoxide, the carbon monoxide may be present in excess. In addition, according to the invention Process produces both "A" and "B" nickel powder with reduced carbon content will. The shape of the nickel particles is determined by the presence of ammonia alone in the decomposition chamber was not affected, but some smoothing of the irregularities of the particle surface was achieved then observed when both ammonia and oxygen were present and the Nitrogen content reached 0.01 weight percent.

The tendency for free carbon to form in the decomposition chamber increases as the chamber temperature is increased. The temperature in the decomposition chamber therefore preferably does not exceed 310 ^° C. and is advantageously not more than 300 ^° C _.;

The method according to the invention is illustrated by the results of a series of experiments, in which gaseous nickel carbonyl has eleven times its volume in carbon monoxide (nickel carbonyl concentration 7 to 9 percent by volume) in an externally heated decomposition chamber with walls made of cast steel and a diameter of 254 mm at a flow rate of 2000 l / hour over an inlet port was introduced in the head of the chamber. This was dry ammonia gas and Oxygen is added to the gas stream introduced into the chamber in contents as shown below the table below. The internal temperature

ao was in three quarters of the height and in half the radius measured; in all experiments it was 290 ° C during the TSe temperature of the chamber wall, which was measured by means of a thermocouple located on the inside of the wall, for example

as was 400 ^° C.

attempt
No. Flow rate
l / h O ₂ concentration
Volume percentage
Nickel- ^ rr _T - size
(Fishing
Classification) properties
space
weight d < 7oN ₂ NH ₅ _ carbonyl - - micron g / cm ³ <0.001 1 _ - 9 0.4 0.06 4.47 2.47 <0.001 2 - - 7th 0.08 0.15 3.66 1.99 0.002 3 8th 1.2 7th 0.2 - 4.2 2.42 0.002 4th 1.6 3 7th 0.1 - 4.36 2.39 0.009 5 4th - 7th 0.05 - 5.20 2.87 0.003 6th 2 - 9 0.025 - 5.92 3.02 0.004 7th 1 - 9 0.0125 0.075 6.20 2.82 0.005 8th 0.5 - 9 0.0125 0.075 6.26 2.74 0.004 9 0.25 1.5 9 0.025 0.075 5.83 2.73 0.004 10 0.25 1.5 9 0.05 0.075 4.58 2.41 • 0.004 11th 0.5 1.5 9 0.1 0.0375 4.28 2.18 0.004 12th 1 1.5 9 0.1 0.019 5.10 2.36 0.006 13th 2 0.75 9 0.1 0.0095 4.86 2.25 0.006 14th 2 0.38 9 0.1 5.58 2.92 0.004 15th 2 0.19 9 5.42 2.48 0.003 16 2 9 5.62 2.91 as nickel powder
Chemical together
settlement ⁰ IoC 0.057 0.039 0.035 0.035 0.033 0.026 0.029 0.028 0.028 0.022 0.020 0.025 0.019 0.020 0.020 0.016

Before the start of the test series, the inner wall of the steel decomposition chamber was clean and nitride-free. The reproduced in the table test results show that, without addition of ammonia or oxygen, the carbon content of the nickel powder 0.057 ° / ₀ while the nitrogen content was insignificant (Experiment 1) was. However, the powder contained a small amount of black carbon-rich particles. The chamber wall was then nitrided by passing in 5 l / hour (0.25 percent by volume) ammonia gas for three hours, with nickel carbonyl being decomposed as before. Further tests (tests 2 to 16) were then carried out without any admixture, with ammonia and with ammonia and oxygen. Care was taken to ensure that all the gases introduced were dry. In each of the experiments 2 to 16 carried out according to the method according to the invention, the nickel powder obtained was free from black, carbon-rich particles. The carbon content of the powder produced with the admixture of ammonia was lower than that under similar conditions without ammonia after the chamber walls were nitrided, and the carbon contents in the presence of ammonia and oxygen were even lower. The slightly higher carbon contents of the nickel powder from experiments 3 ^ is 5 result from a lower carbonyl concentration.

The resulting when using ammonia and oxygen powder had higher nitrogen contents, wherein the particles of the experiment 5, containing 0.009 ° / ₀ nitrogen, were mainly spherulitic and having round surfaces.

In all experiments, type "A" nickel powder was produced. The nickel produced according to the invention

powder completely dissolved in hydrochloric acid, giving a clear solution of nickel chloride, while the Powder from Experiment 1 left an insoluble carbon sludge. .

Claims (4)

Patent claims: 1. Process for producing non-spherical -'-. litbjschem nickel powder, which is essentially free of carbon particles is due to the thermal decomposition of gaseous nickel carbonyl, thereby characterized in that the process is carried out in a steel reaction chamber nitrided inner surface to the exclusion of. Steam is carried out. 2. The method according to claim 1, characterized in that the gaseous nickel carbonyl Ammonia is added. 3. The method according to claim 2, characterized in that the gaseous nickel carbonyl wherein the amount of ammonia and oxygen is regulated so that the resulting nickel powder contains less than 0.01 ° / ₀ nitrogen, oxygen is also admixed. 4. The method according to claim 2 or 3, characterized in that the walls of the decomposition chamber be nitrated during the decomposition of nickel carbonyl in the presence of ammonia in a preliminary process.