WO1997048651A2

WO1997048651A2 - Method of making ultrafine materials including metals, ceramics, and diamonds

Info

Publication number: WO1997048651A2
Application number: PCT/US1997/010633
Authority: WO
Inventors: Shengzhong Liu; Pravin Mistry
Original assignee: QQC Inc
Current assignee: QQC Inc
Priority date: 1996-06-20
Filing date: 1997-06-20
Publication date: 1997-12-24
Anticipated expiration: 1998-12-20
Also published as: WO1997048651A3

Abstract

A method of making ultrafine materials including metals, ceramics, and diamonds is disclosed. The general steps for producing these materials include: introducing at least one precursor material having a high absorption coefficient into a reaction sytem (12); providing at least one energy source (16) to rapidly dissociate and ionize said precursor material so as to produce an ultrafine material; and cooling (18) the ultrafine materials to prevent agglomeration.

Description

METHOD OF MAKING ULTRAFINE MATERIALS INCLUDING METALS, CERAMICS, AND DIAMONDS

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to silicon carbide powders. More particularly, this invention relates to the low-cost production of ultrafine silicon and diamond materials by directing energy at reactants in a vacuum chamber. The synthesized materials are optionally stabilized by a cooling medium.

2. Discussion A need exists for commercially producing ultrafine (ultrafine- grained, typically about 1 -1000 nm in grain diameter) materials on a large scale. Applications of ultrafine materials generally include treating military wastes, air cleaning, military personnel protection against chemical weapons, joining materials and bonding materials. Properties (characteristics) of ultrafine materials include large surface area (e.g., relative to volume), high reactivity, low melting point, and utility as

catalysts.

Although research on ultrafine materials is relative recent, it has been experimentally demonstrated that ultrafine particles possess many

unique properties, such as extremely large surface area, significantly lower melting points, novel mechanical, thermal, optical, magnetic, electronic and chemical characteristics. Moreover, these properties are often improved over those of conventional coarse-grained (i.e., non-

ultrafine) materials for many applications. The large surface area is a critical property for chemical and physical adsorption, catalysis and many chemical reactions. Greatly enhanced chemical reactivity has been demonstrated with ultrafine materials.

Ultrafine materials such as silicon, silicon carbine, or diamonds have great utility as corrosion-resistant, wear-resistant, erosion-resistant, and heat-resistant articles or coatings. Their potential uses are considerable However, production costs related to the manufacture of such materials remain prohibitive.

Examples of the production and use of ultrafine silicon and silicon-like materials are set forth in: United States Patent No. 5,332,601

issued July 26, 1994 for METHOD OF FABRICATING SILICON CARBIDE

COATINGS ON GRAPHITE SURFACES; United States Patent No 4,788,018 issued November 29, 1988 for METHOD FOR PRODUCING HIGH-DENSITY SINTERED SILICON CARBIDE; United States Patent No. 4,735,923 issued April 5, 1988 for EROSION-RESISTANT SILICON

CARBIDE COMPOSITE SINTERED MATERIALS; United States Patent

No. 4,690,790 issued September 1 , 1987 for SILICON NITRIDE/SILICON CARBIDE COMPOSITION AND ARTICLES THEREOF; United States

Patent No. 4,681 ,861 issued July 21 , 1987 for SILICON CARBIDE

SINTERED BODY AND PROCESS FOR PRODUCTION THEREOF;

United States Patent No. 4,676,940 issued June 30, 1987 for PLASMA ARC SINTERING OF SILICON CARBIDE; United States Patent No.

4,437,217 issued March 20, 1984 for COMPOSITE CERAMIC HEAT

EXCHANGE TUBE, United States Patent No 4,332,295 issued June 1 ,

1982 for COMPOSITE CERAMIC HEAT EXCHANGE TUBE, United States

Patent No 4,327,186 issued April 27, 1982 for SINTERED SILICON

CARBIDE-TITANIUM DIBORIDE MIXTURES AND ARTICLES THEREOF;

United States Patent No 4,158,687 issued June 19, 1979 for METHOD FOR PRODUCING HEAT-RESISTANT COMPOSITE MATERIALS REINFORCED WITH CONTINUOUS SILICON CARBIDE FIBERS, United States Patent No 4,117,565 issued October 3, 1978 for CHROMIUM BASE ALLOY COMPOSITE MATERIALS REINFORCED WITH

CONTINUOUS SILICON CARBIDE FIBERS AND A METHOD FOR PRODUCING THE SAME, and United States Patent No. 3,850,689 issued

November 26, 1974 for PROCEDURES FOR COATING SUBSTRATES WITH SILICON CARBIDE However, among the shortcomings of prior art techniques for making ultrafine silicon and silicon-like materials is that they are both time-consuming and expensive. What is needed is a cost and time effective method for making ultrafine materials.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved technique for making ultrafine materials.

A further object of the present invention is to provide a technique for producing ultrafine silicon materials at a low cost.

Still a further object of the present invention is to provide a technique for producing ultrafine silicon carbide materials at a low cost.

An additional object of the present invention is to provide a technique for producing ultrafine diamond materials at a low cost.

Yet a further object of the present invention is to provide a technique for producing ultrafine silicon carbide-diamond composite materials at low cost.

Still an additional object of the present invention is to provide a technique for making ultrafine SiC materials and SiC-diamond materials with a C0₂ laser from silane or ethylene precursors or from precursors containing both silane and ethylene. These materials have considerable

commercial value. For example, SiC is very hard and light in weight and has excellent resistance to wear, corrosion and erosion. It is also stable at high temperatures, and thus is particularly suitable for engine and exhaust systems, as a barrier coating, and as a surface treatment technique including ion implantation, carburising, and siliconising.

These and other objects are achieved by the provision of a

method of making ultrafine materials including metals, ceramics, and diamonds according to the present invention. In general, the steps for producing these materials include: (1) introducing at lest one precursor material having a high absorption coefficient into a reaction system; (2) providing at lest one energy source to rapidly dissociate and ionize said precursor material so as to produce an ultrafine material; and (3) cooling the ultrafine materials to prevent agglomeration.

The steps set forth above are only illustrative, and a method of making ultrafine materials including metals, ceramics, and diamonds may have varied steps.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiments which make reference to the drawings of

which: Figure 1 is a diagrammatic view of the apparatus for employing the general method of the present invention;

Figure 2 is a flowchart illustrating a preferred set of steps to be taken in the production of ultrafine silicon materials; Figure 3 is a flowchart illustrating the first preferred set of steps to be taken in the production of ultrafine silicon carbide materials;

Figure 4 is a flowchart illustrating the second preferred set of steps to be taken in the production of ultrafine silicon carbide materials;

Figure 5 is a flowchart illustrating the third preferred set of steps to be taken in the production of ultrafine silicon carbide materials;

Figure 6 is a flowchart illustrating the first preferred set of steps to be taken in the production of ultrafine diamond materials;

Figure 7 is a flowchart illustrating the second preferred set of steps to be taken in the production of ultrafine diamond materials;

Figure 8 is a flowchart illustrating the third preferred set of steps to be taken in the production of ultrafine diamond materials;

Figure 9 is a flowchart illustrating the first preferred set of steps

to be taken in the production of ultrafine silicon carbide-diamond composite materials; and Figure 10 is a flowchart illustrating the second preferred set of

steps to be taken in the production of ultrafine silicon carbide-diamond composite materials.

DETAILED DESCRIPTION OF THE PREFERRED

EMBODIMENTS OF THE PRESENT INVENTION

The method of making ultrafine materials including metals, ceramics, and diamonds according to the present invention generally involves a series of steps including (1 ) introducing at least one precursor material having a high absorption coefficient into a reaction system; (2) providing at lest one energy source to rapidly dissociate and ionize said precursor material so as to produce an ultrafine material; and (3) cooling the ultrafine materials to prevent agglomeration. Variations of these general steps may be employed to produce different ultrafine materials, as set forth below, however a suggested apparatus for accomplishing the general steps of the preferred method

is set forth in Figure 1. Again, this is an exemplary figure, and variations of this general apparatus are possible. The apparatus of Figure 1 , generally illustrated as 10, includes a reaction system 12 (which may be an enclosure), a source for one or more reactants 14, an energy source 16, a cooling media 18, and a vacuum system or similar system 20 for creating a vacuum within the system 12 as may be desired for the particular reaction at hand. The energy source 16 may be a laser of the C0₂ or excimer type.

The high absorption coefficient allows the precursor material to effectively absorb the energy and create an explosion or a rapid reaction including disassociation and ionization to produce a variety of ultrafine materials. In addition, an inert gas may be introduced for: (a) transferring

energy to the precursor material; (b) acting as a buffer to optimize the reaction; (c) cooling the ultrafine material to prevent agglomeration; and/or (d) transporting the ultrafine material to a collection system. In addition to the metals, ceramics, and diamonds produced by this general reaction, non-metals may result, as well as a great variety of ultrafine composite materials. However, the composition of the end product naturally depends upon the selected precursor. Accordingly, several precursor materials as well as several processes are provided to produce a variety of ultrafine end products.

The method of the present invention may be undertaken in an enclosure, in a vacuum, or in an ambient environment. Laser energy may be used, and as two of the preferred components of the precursors, silane and ethylene, are known to be among the most effective absorbents for C0₂ (10.6 μm) laser energy, this type of laser is preferred, although other lasers are usable as required for most effectively energizing the selected precursor, the latter being determined by the sought-after product. Accordingly, and for example, it is possible to synthesize ultrafine SiC powders and SiC-diamond composites with C0₂ laser energy. Furthermore, by adjusting the silane:ethylene ratio, one may get SiC powder, or SiC-diamond composites with different compositions.

1. Preferred Precursors. Energy Sources, And Methods

By varying the type of precursor, the energy source, and the material-producing steps, a variety of materials may be produced as set forth below. Of course, the following combinations are exemplary, and it is conceivable that other combinations may be employed to

accomplish the production of ultrafine materials such as metals, ceramics, and diamonds. Figures 2 through IQ disclose the various exemplary combinations. a. Ultrafine Silicon Materials

A single preferred process is disclosed for producing ultrafine silicon materials. The steps of this process are set forth in Figure 2. At

Step 30, silane is introduced into an enclosure preferably having a vacuum formed therein, afterwhich energy, preferably in the form of a laser beam produced by a C0₂ laser, is directed to the silane at Step 32 to produce an ultrafine material The produced material is allowed to cool at Step 34.

b. Ultrafine Silicon Carbide Materials

Three preferred processes are disclosed for producing ultrafine silicon carbide materials, and the steps of these processes are set forth in Figures 3, 4, and 5

With respect to the process set forth in Figure 3, a silane- and ethylene-containing precursor material is introduced into an enclosure preferably having a vacuum formed therein at Step 40 Thereafter, energy in the form of a laser beam produced by a laser such as a C0₂ laser is directed to the precursor material to produce an ultrafine product at Step 42 At Step 44 the produced material is allowed to cool

With respect to the process set forth in Figure 4, a first material containing toluene is introduced into the enclosure and a second precursor material containing silane is introduced into the enclosure preferably having a vacuum formed therein, both of these introductions occurring at Step 50 The carbon to silicon ratio is about 1. The energy

source for dissociation and tonization of the toluene is preferably a KrF

excimer laser radiating at 248 nm The energy source for dissociation and tonization of the silane is preferably a C0₂ laser These energy sources are directed to the precursors at Step 52. The produced material is allowed to cool at Step 54.

With respect to the process set forth in Figure 5, a first precursor

material is ablated from a silicon material (e.g., Si wafer) at Step 60. Thereafter, the first precursor material is reacted with a second precursor material containing carbonaceous gases to produce an ultrafine material at Step 62. The silicon to carbon ratio is about 1. The

material is thereafter allowed to cool in Step 64. This example does not require a vacuum. c. Ultrafine Diamond Materials

Three preferred processes are disclosed for producing ultrafine diamond materials. The steps of these processes are set forth in Figures 6, 7 and 8.

With respect to the process as set forth in Figure 6, ethylene is

introduced as the precursor material into an enclosure preferably having a vacuum therein at Step 70. Thereafter, energy, preferably in the form of a beam from a C0₂ laser, is directed to the precursor material at Step 72 to produce an ultrafine material. Finally, the ultrafine material is allowed to cool at Step 74. With respect to the process as set forth in Figure 7, toluene is introduced as the precursor material into an enclosure preferably having a vacuum therein at Step 80. Thereafter, energy, preferably in the form of a beam produced by a KrF excimer laser, is directed to the precursor material at Step 82 to produce an ultrafine material. Finally, the produced ultrafine material is allowed to cool at Step 84. With respect to the process as set forth in Figure 8, benzene is introduced as the precursor material into an enclosure preferably having a vacuum therein at Step 90. Thereafter, energy, preferably in the form of a beam produced by a KrF excimer laser, is directed to the precursor material at Step 92 to produce an ultrafine material. Finally, the produced ultrafine material is allowed to cool at Step 94. d. Ultrafine Silicon Carbide-Diamond Composite Materials Two preferred processes are disclosed for producing ultrafine silicon carbide-diamond materials. The steps of these processes are set forth in Figures 9 and 10. With respect to the process as set forth in Figure 9, a precursor

material containing silane and ethylene is introduced into an enclosure

preferably containing a vacuum at Step 100. The carbon-to-silicon ratio is preferably greater than 1. Thereafter, energy, preferably produced by a C0₂ laser, is directed to the precursor material to produce an ultrafine material at Step 102. The produced material is thereafter allowed to cool

at Step 104. With respect to the process as set forth in Figure 10, a first precursor material containing silicon is ablated from a silicon substrate

(e.g. Si wafer) at Step 110. Thereafter, the first precursor material is

reacted with a second precursor material containing carbon at Step 112. The energy source for ablating the silicon substrate is preferably an excimer laser. The carbon to silicon ratio is greater than 1. This example does not require a vacuum.

2. Variations And Additional Processes

Other silicon-containing and carbon-containing powder materials may be used to replace silane and ethylene. Other lasers, radiation sources such as microwave, RF, etc. may be used to replace the C0₂ laser. Cooling, such as via inert gas, liquid nitrogen, water, etc. may be necessary to stabilize ultrafine powder materials.

To produce ultrafine nitride materials, ammonium, nitrogen and

other nitrogen-containing materials may be used as precursor materials.

To produce ultrafine boride materials, boranes and other boron- containing materials may be used as precursor materials. Selection energy source so that the precursor material can effectively absorb the radiation for creating rapid reactions to produce ultrafine materials. For example, radiation by C0₂ laser can be effectively absorbed by ammonium and boranes for creating rapid reactions to produce the ultrafine materials.

Furthermore, and in addition to the preferred methods set forth above, in a non-vacuum environment, use of a laser (preferably an

excimer laser) to ablate silicon (e.g. Si wafers) and react wfth carbon- containing gases to form SiC or SiC-diamond composites is possible. If nitrogen is fed, silicon nitride and/or its composites may be produced. More lasers may be used to ablate silicon and excite gases for the reactions. Another possible method is to use multiple energy sources or lasers. For example, one laser is absorbed strongly by one material and another laser is efficiently absorbed by another precursor, the combination produces the desired material, e.g. SiC, efficiently. It is known that silane absorbs C0₂ laser radiation very efficiently and benzene and toluene strongly absorbs 248 nm radiation of KrF based excimer laser. If silane and toluene are used as precursors and C0₂ and KrF lasers used for energy sources, SiC or SiC-diamond composite may be produced very effectively.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.

Claims

WE CLAIM:

1. A method of making ultrafine materials, comprising the steps of: introducing at least one precursor material having high absorption coefficient into a reaction system; providing at least one energy source to rapidly dissociate and ionize said precursor material so as to produce ultrafine materials; and cooling said ultrafine materials to prevent agglomeration.

2. An apparatus for making ultrafine materials, comprising: a reaction system; means for directing at least one precursor material having high absorption coefficient into said reaction system;

at least one energy source to rapidly dissociate and ionize said precursor material so as to produce ultrafine materials; and means for cooling said ultrafine materials to prevent agglomeration.