Porous nanostructures and method of fabrication thereof

• US 6,709,622 B2
• Filed: 03/11/2002
• Issued: 03/23/2004
• Est. Priority Date: 03/23/2001
• Status: Expired due to Fees

• Current Assignee: Ourtef Corporation
• Original Assignee: Hanh T. Nguyen, Romain Billiet
• Inventors: Billiet, Romain, Nguyen, Hanh T.
• Primary Examiner(s): Fiorilla, Christopher A.
• Application Number:
  US10/101,033
• Publication Number:
  US 20020167118A1
• Time in Patent Office: 743 Days
• Field of Search: 264/628, 264/432, 419/2
• US Class Current: 264/432
• CPC Class Codes: B22F 1/054 Nanosized particles
• CPC Class Codes: B22F 2009/043 by ball milling
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 3/1103 with particular physical characteristics
• CPC Class Codes: B22F 9/04 starting from solid material, e.g. by crushing, grinding or milling C22C1/1084 takes precedence; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C04B 2235/3225 Yttrium oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3246 Stabilised zirconias, e.g. YSZ or cerium stabilised zirconia
• CPC Class Codes: C04B 2235/5409 expressed by specific surface values
• CPC Class Codes: C04B 2235/5454 nanometer sized, i.e. below 100 nm
• CPC Class Codes: C04B 2235/6021 Extrusion moulding
• CPC Class Codes: C04B 2235/667 Sintering using wave energy, e.g. microwave sintering
• CPC Class Codes: C04B 2235/77 Density
• CPC Class Codes: C04B 35/00 Shaped ceramic products characterised by their composition porous ceramic products C04B38/00; ceramic articles characterised by particular shape, see the relevant classes, e.g. linings for casting ladles, tundishes, cups or the like B22D41/02; ceramic substrates for microelectronic semi-conductors H01L23/15; Ceramics compositions containing free metal bonded to carbides, diamond, oxides, borides, nitrides, silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides or sulfides other than as macroscopic reinforcing agents C22C; shaping of ceramics B28B; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products chemical preparation of powders of inorganic compounds C01; infiltration of sintered ceramic preforms with molten metal C04B41/51
• CPC Class Codes: C04B 35/486 Fine ceramics
• CPC Class Codes: C04B 35/6261 Milling
• CPC Class Codes: C04B 35/62625 Wet mixtures
• CPC Class Codes: C04B 35/63 using additives specially adapted for forming the products , e.g.. binder binders
• CPC Class Codes: C04B 35/632 Organic additives
• CPC Class Codes: C04B 35/634 Polymers C04B35/636 takes precedence
• CPC Class Codes: C04B 35/63408 : Polyalkenes
• CPC Class Codes: C04B 35/64 : Burning or sintering processes C04B33/32 takes precedence ; powder metallurgy B22F
• CPC Class Codes: C04B 38/0054 : the pores being microsized or nanosized
• CPC Class Codes: C04B 38/0058 : open porosity
• CPC Class Codes: C04B 38/045 : the dissolved-out substance being a monolitic element having approximately the same dimensions as the final article, e.g. a prepreg obtained by bonding together dissolvable particles C04B38/0022 takes precedence
• CPC Class Codes: C04B 38/0615 : the burned-out substance being a monolitic element having approximately the same dimensions as the final article, e.g. a porous polyurethane sheet or a prepreg obtained by bonding together resin particles C04B38/0022 takes precedence

Abstract

A method of fabricating nanostructures containing isotropically distributed, interconnected pores having cross-sectional diameters in the nanometer and Angstrom range by integrating the steps of attriting precursor nanometer-sized particulate materials, desorbing the exposed surfaces of the attrited nanoparticulates, adsorbing a surfactant on 25-50% of the desorbed surfaces and dispersing the surfactant-coated nanoparticulates in an organic matrix to form a homogeneous thermoplastic compound from which green nanostructures are formed, dewaxed and sintered to the desired degree of microporosity.

Claims

1. A method for producing a body having substantially uniform, isotropically distributed controlled open nanoporosity, comprising the steps of:

a. providing at least one type of sinterable precursor nanoparticulate material,

b. attriting a predetermined volume of said precursor nanoparticulate material or materials under a protective non-reactive fluid blanket having substantially higher density than that of water and breaking up any aggregates and mechanically removing any adsorbed volatiles, moisture, atmospheric gases or contaminants from the surface of said nanoparticulates or from the fresh surfaces generated during attrition,

c. separating any contaminants thus removed from the deaggregated nanoparticulates,

d. removing the protective fluid blanket from the decontaminated nanoparticulates using vacuum distillation,

e. desorbing the surface of the nanoparticulates by applying a sufficiently high vacuum,

f. allowing a predetermined volume of a suitable surfactant to adsorb onto the surface of the said desorbed nanoparticulates such that substantially 25-50% of the nanoparticulates'"'"' surface will be coated with a monolayer of said surfactant,

g. dispersing said surfactant-coated nanoparticulates in a predetermined volume of a suitable degradable organic thermoplastic binder to form a homogeneous thermoplastic compound,

h. shaping said thermoplastic compound into a green body,

i. extracting substantially all of the organic thermoplastic binder from said green body and sintering the thus obtained organic-free preforms to less than full density until the desired degree of open porosity is achieved.

2. The method of claim 1 wherein the method of sintering includes microwave sintering.

3. The method of claim 2 wherein the said nanoparticulate materials are selected from the class of metals and their alloys, ceramics and their alloys and mixtures of metals and ceramics and their alloys.

4. The method of claim 2 wherein the said degradable organic thermoplastic binder ingredients are selected from the class of polyolefins, waxes, plasticizers, greases, oils, surfactants and mixtures of these.

5. The method of claim 2 wherein the formation of aggregates is reduced or prevented.

6. The method of claim 2 wherein the pyrophoricity of nanoparticulates is controlled.

7. The method of claim 2 wherein excessive grain growth during sintering of green porous nanostructures is reduced or prevented.

8. The method of claim 2 wherein the fine-grained porous nanostructures have improved dimensional accuracy.

9. The method of claim 2 wherein the fine-grained porous nanostructures are produced by an economic manufacturing process which lends itself easily to automation and mass-production.

10. The method of claim 2, wherein said nanoparticulate materials are selected from the group consisting of metal oxides, carbides, borides, nitrides, silicides, aluminas, mullite, and zeolites.

11. The method of claim 1, wherein the fluid blanket is a nonaqueous organic heavy liquid.

12. The method of claim 1, wherein the fluid blanket has a low viscosity and low surface tension.

13. The method of claim 1, wherein attriting is interrupted or slowed down to allow dislodged gaseous contaminants to coalesce at or above the surface of the fluid blanket.

14. The method of claim 1, further comprising controlling the volume of the thermoplastic binder to control the amount of porosity of the body.

15. The method of claim 1, further comprising minimizing the volume of the thermoplastic binder.

16. The method of claim 1, further comprising controlling the number of estimated contact points between nanoparticles.