Process for the synthesis of nanostructured metallic hollow particles and nanostructured metallic hollow particles

Abstract

A process for the synthesis of nanostructured metallic hollow spherical particles, in which the metal is deposited onto sacrificial masks formed in a polymeric colloidal solution by the electroless autocatalytic deposition method. Deposition releases only gaseous products (N.sub.2 and H.sub.2) during the oxidation thereof, which evolve without leaving contaminants in the deposit. The particulate material includes nanostructured metallic hollow spherical particles with average diameter ranging from 100 nm to 5 ?m and low density with respect to the massic metal. A process for compacting and sintering a green test specimen are also described.

Claims

1. A process of synthesis of nanostructured metallic hollow spherical particles with average diameter between 100 nm and 5 ?m, in which the metal is deposited onto sacrificial masks by electroless autocatalytic deposition process, comprising: I. dissolving at least one sacrificial mask forming a colloidal suspension of a polymer selected from polyether in a neutral or basic aqueous solution; wherein the polyether is polyethylene glycol, polypropylene glycol, polyvinyl acetate, or other molecules that repeat ethers on the chain; II. adding at least one metallic salt to the solution obtained in step (I); III. adding at least one soluble base to the solution obtained in step (II); and IV. adding hydrazine or a basic solution containing hydrazine; wherein the zeta potential of the colloidal suspension formed in step (I) by dissolving the at least one sacrificial mask should be negative, so that the metallic hydroxide particles formed in step (III) are adsorbed on the surface of the polymeric masks.

2. The process according to claim 1, wherein the sacrificial mask forming polymer comprises polyethylene glycol with average molecular mass between 1.000 and 20.000 u.

3. The process according to claim 1, wherein the sacrificial mask forming polymer comprises polyethylene glycol with molecular mass of 10,000 u.

4. The process according to claim 3, wherein the concentration of the sacrificial mask forming polymer in the solution obtained in step I ranges from 1.0?10-7 to 1.0?10-2 mol/L.

5. The process according to claim 4, wherein the concentration of the polyethylene glycol in the solution obtained in step I ranges from 1.0?10-6 to 1.0?10-4 mol/L.

6. The process according to claim 1, wherein the metallic salt added in step II comprises sulfates, chlorides, acetates, nitrates or mixtures thereof.

7. The process according to claim 6, wherein the concentration of the metallic salt in the solution obtained in step II ranges from 1.0?10-2 to 10.0 mol/L.

8. The process according to claims 1, wherein in that the concentration of the metallic salt in the solution obtained in step II ranges from 0.1 to 0.5 mol/L.

9. The process according to claim 1, wherein the soluble base added in step III is selected from: sodium hydroxide, potassium hydroxide, ammonium hydroxide or mixtures thereof.

10. The process according to claim 1, wherein the pH of the solution obtained in step III has a controlled value ranging from 7 to 14 or varies between these values during the reaction.

11. The process according to claim 10, wherein the pH of the solution obtained in step III has a value between 10 and 12.

12. The process according to claim 1, wherein the hydrazine or the basic solution containing hydrazine added in step IV is in the form of hydrate, sulfate or chloride.

13. The process according to claim 12, wherein the ratio between molar concentration of hydrazine and of metallic salt is higher than 1:4.

14. The process according to claim 1, wherein the ratio between the molar concentration of hydrazine and of metallic salt is of 4:1.

15. The process according to claim 1, wherein the synthesis takes place in an open vessel or by the reflux method.

16. The process according to claim 1, wherein the solutions described in steps I and II are subjected to ultrasound.

17. The process according to claim 1, wherein the precipitate obtained in step IV is subjected to calcination in an oven at a temperature ranging from 100? C. to 500? C. for removal of the polymeric mask.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1Process for forming the nanostructured metallic hollow particles with self-organizing masks of a homopolymer, which comprises the following steps: self-organizing mask of the homopolymer; the nanoparticles of the metallic hydroxide are adsorbed on the mask surface; the nanoparticles of the hydroxide are gradually reduce; final stage of the formation of the spherical porous metallic nanostructured crust, after removal of the mask.

(2) FIG. 2MEVEC images with magnification of 10000? (a) and 90000? (b) of nanostructured hollow spheres of Ni with average diameter of 550 nm, produced in Example 01.

(3) FIG. 3MEV image of the particles produced in Example 01 partly corroded in an aqueous solution of nitric acid (C=10%), evidencing their hollow nature.

(4) FIG. 4MEV image with magnification of 1000? (a) and 5000? (b) of fractured region of a green test specimen produced in Example 03.

(5) Examples of the present process of forming the nanostructured metallic hollow particles with self-organizing masks of homopolymer, and a preferred application of the particulate material for compacting and pre-sintering a green test specimen are presented, which do not have the objective of limiting the protection scope of the present invention, will be discussed as follows:

EXAMPLE 01

Process of Producing Particulate Material Containing Hollow Pure Ni Spheres

(6) All the steps of this procedure are carried out with the following solutions under stirring at 80? C.

(7) One dissolves 1.0 mg of polyethylene glycol (PEG 10000) in 15 ml of distilled water for 30 min.

(8) The mixture is taken to an ultrasound bath for 10 min.

(9) 3,000 g of nickel sulfate (NiSO.sub.4.6H.sub.2O) are dissolved in 15 ml of distilled water and mixed with the preceding solution.

(10) 0.460 g of sodium hydroxide (NaOH) are dissolved in 10 ml of distilled water and mixed with the solution of item (c).

(11) 0.460 g of sodium hydroxide (NaOH) are dissolved in 10 ml of distilled water and then 2.44 ml of hydrazine hydrate (N.sub.2H.sub.4.H.sub.2O) are added.

(12) The solution of item (e) is then added slowly to the solution obtained in item (d).

(13) The reaction begins to take place about 10 minutes after the reducing agent has been added (item f). Then, it is possible to observe an intense evolution of gases. In a little more than 20 minutes, the evolution of gases stops and the powder accumulates on the bottom of the container, leaving the remaining solution almost transparent. The final pH of the solution remains between 10 and 11.

(14) The precipitate is washed with water and ethanol, with the aid of a magnet to decant the powder.

(15) The final product is calcined in an oven under vacuum at 150? C. for 5 h.

(16) The particulate material obtained in Example 01 is a black, magnetic, fine, loose powder, formed by rugous spherical hollow particles of pure Ni with average diameter of 550 nm.

(17) The yield of the synthesis is of 90%, on average, calculated by considering the number of nickel moles in the final product divided by the number of moles present in the reactants ion the beginning of the synthesis.

(18) The average density of the nanostructured metallic hollow particles obtained in this example is of approximately 3.5 g/cm.sup.3.

(19) FIG. 2 shows images of electronic scanning microscopy of the particulate material, and FIG. 3 shows images of the particulate material partly digested by nitric acid.

EXAMPLE 02

Process of Producing Hollow Pure Pd Spheres

(20) All the steps of this procedure are carried out with the solutions under magnetic stirring and at 80? C.

(21) 0.300 g of palladium chloride (PdCl.sub.2) and 3 ml of ammonium hydroxide (NH.sub.4OH 28%) are dissolved in 22 ml of distilled water with stirring for 20 min.

(22) 1.0 mg of polyethylene glycol (PEG 10000) is dissolved in 15 ml of water and added to the PdCl.sub.2 solution.

(23) The mixture is taken to an ultrasound bath for 10 min.

(24) 3 ml of ammonium hydroxide NH.sub.4OH (28%) and 0.2 ml of hydrazine (N.sub.2H.sub.4.H.sub.2O (99%)) are added in 17 ml of distilled water and then mixed to the mother solution.

(25) The reaction occurs immediately after the reducing agent has been added (item d), making the solution black. The final pH of the solution remains between 10 and 11.

(26) The precipitate is washed with water and ethanol, with the aid of a centrifuge to decant the powder.

(27) The final product is calcined in an oven under vacuum at 150? C. for 5 h.

(28) The particulate material obtained in Example 02 is a black, non-magnetic, fine and lose powder, formed by spherical hollow particles of pure Pd with average diameter of 250 nm.

(29) The average yield is of 85%, calculated by considering the number of palladium moles in the final product divided by the number of moles present in the reactants in the beginning of the synthesis.

EXAMPLE 03

Preparation of a Green Test Specimen with the Product of Example 01 Through Powder Metallurgy

(30) The material obtained in Example 01 is mixed to 2% by mass of paraffin in a Becker. Cycloexane is added until it wets the whole powder to dissolve the paraffin, causing it to involve the particles. With the powder still wet, the Becker is inclined and axially rotated at a moderate velocity for about 15 minutes, until most of the organic solvent evaporates, leaving the particles covered with paraffin and agglomerating them, due to collisions between them during the rotation of the Becker. After the granulation process, the powder is dried for 24 h in a vacuum desiccator.

(31) After granulation, the material is compacted in a hand-operated press with a double-effect compaction die, applying 100 MPa pressure.

(32) With the objective to extract the organic ligand and to provide the green test specimen with more resistance to green, the latter is subjected to a pre-sintering process in standard-mixture atmosphere (95% N.sub.2/5% H.sub.2). Using a heating rate of 10? C./min, initially one ra ises it to a level of 500? C. for 30 min in order to remove the paraffin and then to a level of 700? C. for 40 minutes to pre-sinter the material.

(33) Preferred examples of embodiment having been described, one should understand that the scope of the present invention embraces other possible variations, being limited only by the contents of the accompanying claims, which include the possible equivalents.