Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
  • C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
  • C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
  • C22C32/0042—Matrix based on low melting metals, Pb, Sn, In, Zn, Cd or alloys thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/059—Making alloys comprising less than 5% by weight of dispersed reinforcing phases

Definitions

• ABSTRACT OF THE DISCLOSURE discloses a process for producing dispersion strengthened lead by mixing a small amount of a refractory oxide powder, such as alumina, with lead powder in an oxidizing atmosphere so as to coat the lead particles with lead oxide and thereby inhibit agglomeration thereof, while obtaining a substantially uniform dispersion of the refractory oxide.
• the mixture may be subjected to chemical reduction of the lead oxide preferentially, while avoiding significant reduction of the refractory oxide and the so reduced powder mixture may be subjected to a forming process to amalgamate the lead particles into a coherent matrix with the refractory oxide dispersed throughout.
• This invention relates to the production of dispersion strengthened lead and of lead powder from which the same can be made.
• lead powder having its constituent particles coated with lead oxide is subjected to a forming process which subjects the powder particles to shear deformation so that their oxide coatings become fragmented and dispersed, a coherent dispersion strengthened lead product can be obtained which exhibits considerably increased strength as compared with ordinary lead.
• a particularly effective forming process is extrusion, carried out at room temperature or at some higher temperature below the melting point of the lead in the powder.
• the production of dispersion strengthened lead in this manner is relatively simple and economic.
• the presence of the free lead oxide which is not a refractory material in the generally accepted sense, tends to impart some susceptibility to corrosion, so that in this respect the product may be less good than ordinary lead.
• the oxide coatings in general have a certain amount of lead carbonate associated with them and this can result in a tendency for the product to swell (due to liberation of carbon dioxide from the carbonate) at elevated temperatures.
• Dispersion strengthening of various metals by the incorporation of dispersed refractory oxides such as alumina, silica and magnesia is a well known technique and attempts have been made to use it for dispersion strengthening of lead by mixing such refractory oxide with lead powder prior to extrusion or other forming process.
• these attempts have met with only limited success, in part due to the difficulty of mixing the lead powder and refractory oxide to a satisfactory degree of dispersion while avoiding premature agglomeraiton of the lead particles due to their inherent softness and pliability.
• a process for the production of dispersion strengthened lead comprises the steps of intimately mixing lead powder and a minor proportion of a refractory oxide powder in an oxidizing,
• oxygen, atmosphere such as to coat the lead particles with lead oxide and thereby inhibit agglomeration thereof by a pressure welding effect while obtaining a substantially uniform dispersion of the refractory oxide, subjecting the mixture to a reduction process for chemically reducing the majority of the lead oxide preferentially with respect to the refractory oxide by reason of the greater stability of the latter, and subjecting the so reduced powder mixture to a forming process to amalgamate the lead particles into a coherent matrix with the refractory oxide dispersed throughout.
• the reduction process must be performed below the melting point of lead (so as to retain the powder form) reduction of all the lead oxide and simultaneously of lead carbonate tending to be present with it is not readily practicable.
• the presence of only a small amount of lead oxide and lead carbonate in the powder mixture when subjected to the forming process and therefore in the final product means that the susceptibility of the final product to corrosion and swelling may be correspondingly small.
• a refractory oxide powder consisting of particles of submicron size
• the lead powder particles may in the majority have an average size of about 50 microns or less.
• a ratio of about *:1 between the average lead particle size and average refractory oxide particle size has been found to give good results but this is not limiting and better results may be obtainable with a different ratio, especially if lead powder of significantly smaller particle size becomes readily obtainable.
• ballmilling in which the lead particles would be particularly prone to amalgamate if it were not for the presence of the oxidizing atmosphere, the charge of balls in the mill subjects the oxide coated lead particles to severe deformation and in doing so punches the alumina particles into the lead, thus producing a particularly homogeneous mix from which an extruded product with a more uniform refractory oxide distribution is obtained.
• the mixed powders were all subjected to chemical reduction by hydrogen in order to eliminate the majority of the lead oxide originally present on the lead powder and subsequently produced during the mixing process.
• extensive lead oxide reduction could be achieved by subjection of oxidised lead powder at about 300 C. to a stream of purified dry hydrogen for 24 hours. Consequently the powder mixtures were given this treatment.
• the reduced powder mixtures were in each case cooled to room temperature in hydrogen and then rapidly transferred (so as to avoid re-oxidation of the lead) to an extrusion press by which the subsequent forming process was to be performed.
• a charge of about 100 grams of powder was required to fill the extrusion press.
• the powder was compacted and extruded in a single direct operation to produce a wire of 0.100 inch diameter.
• the extrusion ratio was 40:1 and no lubrication was used.
• the extrusion was performed at a rate of about 11% feet per minute at room temperature, but the temperature of the extrudate was about 60 C. because of the severe deformation involved.
• Agglomerations of alumina would tend to be broken up by these two processes although any tendency for such agglomerations to form due to build up of electrostatic charges of the alumina particles would be minimised by the presence of the metallic lead. This would assist in dissipating such charges, especially in the case of the ball milling machine with its metal container as compared with the blender with its insulating glass container.
• Creep tests were conducted on samples of material made from a mixture of lead powder and 1% alumina by weight ball-milled reduced and extruded in accordance with the invention. This particular material had a tensile strength of 5500 lb./in. and elongation of 14%. Some of these creep tests were performed at room temperature (20 C.) and others at 80 C. For comparison, similar tests were performed on samples of pure lead at room temperature. The tests were stress-rupture tests, which consist in applying a fixed stress to a specimen at a fixed temperature and determining the time required under these conditions to bring about fracture of the specimen. The total elongation which had occurred was also measured after fracture. The results are given in the following table, in which a plus sign (-1-) indicates that at the time stated fracture had not occurred and the test was still continuing.
• the present invention also includes a process for producing as a vendible product in its own right, a lead powder mixture suitable for the manufacture of dispersion strengthened lead by extrusion or other forming process preceded by chemical reduction, which powder production process consists in mixing lead powder and a refractory oxide powder in an oxidising atmosphere preferably in a ball-milling apparatusto produce an intimate mixture of the refractory oxide powder dispersed through the lead powder with the lead particles coated with lead oxide. It is contemplated that powder so prepared, being reasonably stable, may be kept for substantial periods before use for the production of dispersion strengthened lead by chemical reduction and subsequent forming.
• the invention further contemplates within its scope lead oxide coated lead powder with a minor proportion of refractory oxide powder particles intimately dispersed therein in an amount preferably between 0.1 and 10 vol. percent inclusive, with at least a substantial proportion of the refractory oxide particles embedded in the lead particles, and also dispersion strengthened lead comprising a lead matrix with a substantially uniform dispersion of sub-micron alumina particles as the principal dispersion strengthening agent and a lead oxide content less than 1 wt. percent PbO and preferably less than 0.5 wt. percent, the alumina content being preferably between 0.1 and 10 vol. percent inclusive.
• the lead may contain antimony in amounts as high as about 0.8%.
• a process for the production of dispersion strengthened lead comprising the step of intimately mixing lead powder and about 0.1 to 10% by volume of a refractory oxide powder in an oxidizing atmosphere so as to coat the lead particles with lead oxide and thereby inhibit agglomeration thereof by a pressure welding effect while obtaining a substantially uniform dispersion of the refractory oxide, subjecting the mixture to a reduction process for chemically reducing the lead oxide preferentially with respect to the refractory oxide by reason of the greater stability of the refractory oxide, and subjecting the so reduced powder mixture to a forming process to amalgamate the lead particles into a coherent matrix with the refractory oxide dispersed throughout.
• a process as] claimed in claim 1 wherein the reduction process consists in subjecting the mixed powders to a temperature of about 300 C. in a stream of dry hydrogen for about 24 hours to give a residual lead oxide content of less than 1.0% PbO by weight.
• a process as claimed in claim 1 wherein the forming process consists in extruding the reduced mixed powders.
• a process for producing a lead powder mixture suitable for making dispersion strengthened lead by subsequent chemical reduction followed by forming comprising the step of mixing lead powder and about 0.1 to 10% by volume of a refractory oxide powder in an oxidizing atmosphere to produce an intimate mixture of the refractory oxide powder dispersed through the lead powder with the lead powder particles coated with lead oxide.
• a process as claimed in claim 4 wherein the mixing step consists in ball milling the lead powder and the refractory oxide powder together.
• a powder mixture for the production of dispersion strengthened lead by chemical reduction and subsequent forming of the powder comprising lead oxide coated lead powder particles with about 0.1 to 10% by volume of refractory oxide powder particles intimately dispersed therein with refractory oxide particles embedded in the lead particles.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Powder Metallurgy (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Cosmetics (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=10159306

Family Applications (1)

Country Status (4)

Cited By (27)

Families Citing this family (1)

Citations (8)

• 1965
  • 1965-05-19 GB GB21225/65A patent/GB1122823A/en not_active Expired
• 1966
  • 1966-05-12 SE SE6563/66A patent/SE304865B/xx unknown
  • 1966-05-12 US US549449A patent/US3416918A/en not_active Expired - Lifetime
  • 1966-05-18 DE DE19661533156 patent/DE1533156A1/de active Pending

Patent Citations (8)

Also Published As

Similar Documents