# US 8,540,797 B2 · Process for preparation of nano ceramic-metal matrix composites and apparatus thereof

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- Number: US 8,540,797 B2
- Document ID: US8540797B2
- Status: Granted
- Kind: B2
- Application number: 13/056,503
- Filed: 2008-07-29
- Published: 2011-12-29
- Granted: 2013-09-24
- Earliest claimed: 2008-07-29
- Assignees: Indian Institute of Science
- Applicants: Rishi Raj; Mirle Krishnegowda Surappa; Sudarshan
- Inventors: Rishi Raj; Mirle Krishnegowda Surappa; Sudarshan
- Web page: https://patentgrep.com/patent/US8540797B2

## CPC

- C22C 1/1068: {Making hard metals based on borides, carbides, nitrides, oxides or silicides}
- F27B 14/04: adapted for treating the charge in vacuum or special atmosphere
- F27B 14/06: heated electrically, e.g. induction crucible furnaces with or without any other source of heat (F27B14/04 takes precedence)
- F27D 27/00: Stirring devices for molten material (charging or discharging liquid or molten material F27D3/14)
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- F27B: FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27D: DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE

## Abstract

A method to introduce ceramic particles into liquid metal through the polymeric precursor route by cross-linking organic precursor into a hard polymer, which is added to the liquid melt for in-situ pyrolysis of the organic into the ceramic phase. The starting material, the organic, for the above process can be in the form of a liquid or a solid. If it is a solid it is usually dissolved into a solvent to create a liquid form. The organic is then cross linked either directly by a thermal process, by adding a catalyst, or by the well known sol-gel process into a hard polymer. It is this hard polymer which is then pyrolyzed into a high temperature ceramic material by the process outlined above.

## Claims

### Claim 1

A process for preparation of nano-ceramic metal-matrix composites, said process comprising steps of cross-linking organic precursors to obtain organic polymers, inserting the organic polymers into a metal melt to produce a dispersion of organic polymers within the metal melt; carrying out pyrolysis of said organic polymers by raising the metal melt temperature to a level where the polymer pyrolyzes in-situ into a ceramic phase.

### Claim 2 (depends on 1)

The process as claimed in claim 1, wherein the organic precursors used in said method are in liquid or a solid form.

### Claim 3 (depends on 1)

The method as claimed in claim 1, wherein the organic precursor is cross-linked by thermal process by adding a catalyst, by sol-gel process or by other conventional processes.

### Claim 4 (depends on 1)

The method as claimed in claim 1, wherein the polymer is pyrolyzed at high temperature ranging between 300° C. to 1000° C.

### Claim 5 (depends on 1)

The method as claimed in claim 1, wherein the pyrolysis is carried out in a controlled environment, wherein the controlled environment is an inert environment containing argon or nitrogen in order to preserve the desired chemical composition of an end product.

### Claim 6 (depends on 1)

The process as claimed in claim 1, wherein hydrogen released during pyrolysis from of the polymer is flushed by bubbling nitrogen or argon through the melt.

### Claim 7 (depends on 1)

The method as claimed in claim 1, wherein the melting point of the metal is below the pyrolysis temperature.

### Claim 8 (depends on 1)

The process as claimed in claim 1, wherein the organic-polymer comprises elements selected from the group consisting of Si, O, C, N and a combination thereof, and wherein the organic polymer is selected from the group consisting of polysilazanes, silsesquioxanes and mixtures thereof.

### Claim 9 (depends on 1)

The process as claimed in claim 1, wherein the cross-linked polymer added to the liquid melt ranges from 1% to 70% by volume with respect to the metal.

### Claim 10 (depends on 1)

The process as claimed in claim 1, wherein the temperature is raised to the pyrolysis temperature of the polymer ranging from 800-1200° C., for a period of 1 h up to 8 h.

### Claim 11 (depends on 1)

The process as claimed in claim 1, wherein the organic polymer is added in liquid form by injecting it directly into the liquid melt.

### Claim 12 (depends on 1)

The process as claimed in claim 1, wherein said process is employed to produce nanoscale ceramic composites of aluminum matrices, where the intermetallic and ceramic phases created by said process consist of Al, Mg, Si, N, C and O.

### Claim 13 (depends on 1)

The process as claimed in claim 1, wherein the organic-polymer is added to facilitate mixing at a melt temperature of 660-800° C. for Mg, where the melt is protected by an argon gas purge.