JPS62185802A - Control of oxygen content of flocculated molybdenum powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the oxygen content of agglomerated molybdenum powders by controlled oxidation of the powders. In particular, the present invention provides the following methods: 0) by contacting the powder with a liquid oxidizing agent; (II) by heating the powder in the presence of a non-aggressive atmosphere with controlled relative amounts of water vapor; ) A method for introducing a controlled amount of atom into an agglomerated molybdenum powder by reducing a mixture of molybdenum powder and oxides of molybdenum.

Generally, flame spraying and plasma spraying are opposite techniques for coating metal surfaces (substrates) with various metals, ceramics, and cermets with protective and wear-resistant coatings. The piston ring world commonly employs molybdenum coatings for internal combustion engine rings.

In flame spray technology, an electric arc or an oxy-acetylene flame melts the ends of a continuous coil of molybdenum wire and a gas jets it onto the wear surface substrate of, for example, a cast iron piston ring, where the molten molybdenum is flattened. and solidify to form a coating in sequential layers. Due to the presence of excess m'ig coming from either the flame or the ambient air, or both, coatings produced by this technique typically contain about 7-8% oxygen in solid solution. It is also contained in various molybdenum oxides. The large amount of oxygen in molybdenum apparently hardens the coating.

In plasma spraying of molybdenum, there is usually minimal oxygen present in the sprayed coating due to the use of a plasma gas system that contains little oxygen ft. Rabbit, argon, helium, hydrogen, nitrogen or a combination of these gases (
All of these are used in thermal spray processes (which rarely contain oxygen tubes).Thus, the small amount of oxygen in the spray coating can inadvertently cause the exchange of molten particles by oxygen impurities in the plasma gas and ( or) by surface oxidation of the newly deposited coating. Oxygen levels in such pure molybdenum coatings are in the 1-2% range. The coating is softer than its flame sprayed counterpart.

Therefore, in order to obtain higher hardness, expensive methods such as flame spraying requiring wire gold or more expensive powders such as molybdenum-nickel based alloys must be used. It would be desirable to develop a process for producing molybdenum powder with a sufficiently high oxygen content to allow it to be used in a process to produce hard coatings.

Prior Art U.S. Pat. No. 4,144,388 discloses a molybdenum plasma spray powder and a purple enzyme-containing at.
Disclosed is a method for preparing molybdenum and molybdenum oxide powders having the following properties. This method uses molybdenum particles'l?
It involves passing an oxygen-containing powder through a plasma containing oxygen to produce an oxygen-containing powder.

SUMMARY OF THE INVENTION In accordance with the present invention, a controlled level of c1! is produced in an agglomerated molybdenum metal powder. 0) contacting the powder with a relatively dilute solution containing a sufficiently small amount of a solubilizing agent for a sufficient period of time to increase the oxygen content of the powder; The resulting partially oxidized molybdenum powder may then be removed from the production bath, or (ii) at a sufficient temperature in the presence of water vapor and a controlled non-oxidizing atmosphere to form the partially oxidized molybdenum powder. (iii) forming a relatively uniform mixture of an agglomerated powder consisting essentially of molybdenum and one or more oxygen-containing molybdenum compounds having an oxygen content of greater than about 10% by weight; and reducing the mixture at a temperature sufficient for a sufficient time to remove a portion of the enzyme therefrom and form a molybdenum powder having an oxygen content of less than about 10% by weight.

By the method of the present invention, the oxygen level in the molybdenum powder is controlled to make it suitable for use in plasma coating applications.

In certain applications where the use of controlled oxygen content molybdenum powder produced from the process of the invention is preferred, namely plasma spray applications to produce hard coatings, the desired oxygen content is between about 1 and 15%, preferably 10%. % or less, preferably 7 to 10%. At these lower levels, the hardness of the plasma coating is not compromised. Above this range, the integrity or bond strength of the coating is compromised.

First Embodiment In this embodiment, the molybdenum powder is pre-aggregated and sintered by well-known methods.

A preferred method of agglomerating molybdenum powder is disclosed in U.S. Pat.
No. 975.948. May 1, 1980
Several methods are also disclosed in the paper ``Properties of Oxygen-Containing Molybdenum Coatings'' presented at the Proceedings of the 9th International Thermal Spray Conference held in The Hague, Netherlands, from September 9-25.

A preferred molybdenum powder for use is Chemical and Metaradical from GTE Products Corporation.
It is sold by Division as 5A-101.

By this method, preferably substantially about 105 weight i1%
The oxygen content of conventional molybdenum powders, which is less than oxygen, can be increased to the desired level by combining the powder with a relatively dilute solution containing a sufficient amount of saponifying agent (preferably hydrogen peroxide) and an oxygen-containing tube. Increased by contact for a sufficient period of time. The oxidizing agent must be present in an amount sufficient to increase the oxygen to the desired level, and not in an excessive amount such that the reaction cannot be controlled. Dilute solutions of the oxidizing agent provide better control. and avoid overoxidation. The solution preferably has a concentration of about 1 to 10
Contains heavy arc oxidizer.

By controlling the contact time, the amount and dilution of the oxidant solution, and the molybdenum to oxidant ratio, the degree of oxidation can be controlled.

When hydrogen peroxide is used, it is preferred to have about 2 to 5 moles of oxidizing agent present per mole of molybdenum.

The resulting partially oxidized molybdenum powder is separated from the bath liquor by any standard technique such as filtration.

EXAMPLE Twit Molybdenum powder (type 5A-101 from GTB) about 7J dried and having a particle size of -200-+525 mesh and containing about cL 2% oxygen by weight
'! , for about 2 hours with a solution containing about 6 CC of 30% hydrogen peroxide in 150 cc of deionized water. The resulting partially oxidized molybdenum powder was filtered and dried. Analysis of this powder revealed an oxygen content of approximately 18'Ijt! It was jk%.

In this method as well, the molybdenum powder is preliminarily agglomerated and sintered using known methods. The preferred agglomeration method and preferred molybdenum powder used follow the first embodiment.

This method reduces the oxygen content of conventional molybdenum powders, which is preferably less than about α05% by weight of oxygen.
Augmentation may be achieved by heating the agglomerated and sintered powder in the presence of water vapor and a non-oxidizing atmosphere at a sufficient temperature for a sufficient period of time.

The amount of non-oxidizing atmosphere is controlled to produce molybdenum molybdenum molybdenum powder.

Heating may be accomplished by standard methods of heating residual powders. A preferred method is the use of a single-converter calciner (Calciner) or a fluidized bed furnace.

The heating temperature is generally about 700 to 900°C, and about 750°C.
~850°C is preferred. The heating time depends on the temperature and type of equipment used. For example, the slope of the rotary kiln section can be adjusted to vary the residence time of the powder.

Water is introduced into the furnace to provide the necessary moisture for the process.

A preferred non-oxidizing atmosphere is nitrogen. By controlling the storm of non-oxidizing components in the furnace atmosphere, the degree of oxidation and thus the enzyme content of the molybdenum powder is controlled. The amount of non-oxidizing gas can be increased or decreased by controlling the flow rate. For example, when the flow rate of the non-oxidizing atmosphere (eg, nitrogen) is reduced, the #1 content of partially butyrated molybdenum produced is increased.

The resulting partially oxidized molybdenum powder consists of substantially spherical grains. The oxygen content of this powder ranges from about 3 to 15% by weight.

X-right analysis of the partially oxidized powder revealed the presence of molybdenum, molybdenum dicondensate, and occasionally molybdenum dioxide. Unwanted molybdenum trioxide can be eliminated without destroying other desirable properties of the powder by dissolving it using an ammonia solution.

Alternatively, if the rjN content is too high, the powder can be subjected to standard reduction methods to reduce the oxygen content.

EXAMPLE A molybdenum powder (Type 5 from GTE Corporation) which is blast dried and coated on a particle size range of 1200 to +525 mesh.
A-101 was fed at about 12 Km/hr into a 6" diameter rotary furnace under a nitrogen atmosphere at a temperature of about 800°C.

Water was injected into a separate funnel at a rate of approximately 20-50 cc/min to provide the necessary moisture for the oxidation process. The resulting powder is in the form of substantially spherical brown particles and about 2.4~
2. It had a bulk density of a 77 /cc.

The above procedure was carried out with varying nitrogen flows.

The oxygen content of the produced powder is shown below along with the nitrogen flow rate: Mountain ft Weight % 02 2.0 5.2115
5.841, 4
8.6112 14.29 Nitrogen style versus generated powder 0 elementary weight f! The attached drawing is a plot of the percentage relationship.

It can be seen that a direct correlation exists between the nitrogen flow rate and the percent oxygen in the oxidized powder. As the nitrogen flow rate decreases, the degree of oxidation, as indicated by weight percent oxygen, increases.

Oxygen-containing molybdenum compounds are used here. As the acid-based molybdenum compound, molybdenum dioxide, molybdenum oxide, or ammonium paramolybdate may be used.

Any agglomerated mixture of molybdenum and oxygen-containing molybdenum compounds may be used as long as the oxygen content of the mixture exceeds about 10% by weight.

A typical composition of the mixture to be agglomerated consists essentially of about 40% molybdenum, about 50% molybdenum dioxide, and about 10% molybdenum trioxide, expressed in weight percent, and an oxygen content of about 15.8% by weight. It is.

The mixture of molybdenum and oxygen-containing compound(s) may be agglomerated by any of several well known methods.

One preferred method involves forming a slurry of water, ammonia or ammonium hydroxide, molybdenum trioxide, molybdenum dioxide, and microfine (about 1-3 micron diameter) molybdenum particles. Ammonium paramolybdate is formed from molybdenum dioxide and ammonium hydroxide and acts as a binder in the system. The resulting slurry is then spray dried to remove its condensate and form a relatively uniform agglomerated mixture of substantially spherical particles. This method is described in US Pat. No. 4,973,948.

Another method of forming a relatively uniform agglomerated mixture is by first forming a slurry as described above. The slurry is continuously agitated to break up the material while the water is allowed to evaporate. The coarse wet temperature powder produced is 100 mesh M.
' and collected. Thereafter, the powder is further dried with gentle stirring. after that,
The final agglomerated mixture is sieved from the dry mixture.

Some preferred aggregation methods are disclosed in the aforementioned articles.

The resulting agglomerated mixture has some of the elements removed and about 10%
It is reduced at a sufficient temperature and for a sufficient period of time to form a molybdenum powder having an oxygen content of about 7 to 10%.

Reduction can be carried out in a standard furnace in a dry hydrogen atmosphere. Preferred temperatures are in the range of about 700-1000°C. The time depends on the temperature and the characteristics of the isthmus iJ. However, typical times are about 2-4 hours.

Reduction can be carried out in a fluidized bed or in a rotary kiln. The reduction conditions are adjusted to give the final new value oxygen content lit. The advantage of reduction using a fluidized bed or rotary kiln over static reduction is that bed depth problems are avoided and the reduction is more uniform. In fluidized beds or rotary kilns, the reduction of the agglomerates occurs from the outside to the inside, with the result that the metallic phase is always present on the outside. This results in more efficient melting of the agglomerates in one plasma coating, thus producing a harder coating.

Powders produced with controlled oxygen levels are used in plasma spray applications to produce coatings for piston rings and other materials.

EXAMPLE An aqueous slurry consisting of approximately 85% solids and ammonia was prepared. Solid content is approximately 11% molybdenum dioxide, approximately 52%
Made of molybdenum dioxide and about 36% molybdenum, its oxygen content was 16.6%. The amount of ammonia was about 87% of the molybdenum trioxide. The slurry was dried in a conventional drying oven to produce a relatively uniform agglomerated mixture of real*spherical particles. This mixture was reduced in dry hydrogen at 800° C. for approximately 2 hours to produce a free-flowing molybdenum spray powder with a #I element content of about 7-8%.

Although the invention has been described above, it is to be understood that many modifications may be made within the scope of the invention.

[Brief explanation of drawings]

The drawing is a graph plotting the relationship between the nitrogen flow rate and the m elementary weight % in the molybdenum fluoride powder in connection with the second real Ih school. Name of agent Motohiro Kurauchi Hiroshi Kazama ゛・ ■□ shi, - 0,40,8+,2 1.6 Ko, Ochi"7!;,
% (4,1,)

Claims (1)

Claims: 1) A method of introducing controlled levels of oxygen into an agglomerated molybdenum metal powder, comprising: (i) combining the powder with a relatively dilute solution containing a sufficient amount of an oxidizing agent; contacting for a sufficient time to increase the oxygen content and subsequently removing the resulting partially oxidized powder from the product solution, or (ii) a non-oxidizing atmosphere in a controlled amount to create water vapor and partially oxidized molybdenum powder. or (iii) heating the powder at a sufficient temperature for a sufficient period of time in the presence of a relatively uniform agglomerated powder consisting essentially of molybdenum and one or more oxygen-containing molybdenum compounds in an amount greater than about 10% by weight of oxygen. forming a mixture having a content of Molybdenum powder oxygen introduction method. 2) In case (i), the powder is contacted with a solution containing about 1 to 10% by weight of oxidizing agent, with about 2 to 5 moles of oxidizing agent being present per mole of molybdenum. The method described in paragraph 1. 3) The method according to claim 2, wherein the oxidizing agent is hydrogen peroxide. 4) In the case of (ii), the temperature is approximately 700 to 900°C
The method of claim 1 within the scope of. 5) The method according to claim 4, wherein the non-oxidizing atmosphere is nitrogen. 6) Oxygen content of partially oxidized molybdenum powder is about 3-15
6. A method according to claim 5, wherein the amount is % by weight. 7) In case (iii), the mixture contains molybdenum,
A method according to claim 1, consisting essentially of ammonium paramolybdate and molybdenum oxide. 8) In the case of (iii), the reduction temperature is about 700-1
The method according to claim 1, wherein the temperature is 000°C. 9) The oxygen content of the reduced molybdenum powder is about 7~
9. The method of claim 8, wherein the amount is 10% by weight.