# Presentation: 147824

## Welding of Small Parts Using Nanocomposite Thermites 

- Ann Cannella
- New Jersey Institute of Technology
- Mentor: Dr. Dreizin

**Notes:**
This summer I worked at New Jersey Institute of Technology under the mentorship of Dr. Ed Dreizin.  There, I studied the welding of small parts using nanocomposite thermites.  

## Thermites

- Compositions of mixed metal (typically Al) and metal oxide
- 2Al+Fe2O3 → 2Fe+Al2O3+heat.
- Reactions release large quantities of heat, molten iron, and aluminum oxide
- Difficult to ignite
- Self-sustaining only for a large amount of thermite mixture
- Used traditionally for large scale welding

- Example of Traditional Welding

- http://www.ameco.net/images/products/thermite_welding_tns.jpg

**Notes:**
Thermites are compositions that consist of mixed metal (typically Al) and metal oxide. When such compositions react, they release a large quantity of heat.  A thermite reaction, also called aluminothermic reaction can be described as: 2Al0 + Fe2O3 → 2Fe0 + Al2O3 + heat. The products of this thermite reaction are molten iron and aluminum oxide.  In joining applications, molten iron can be used as a filler and the energy released in the thermite reaction can be used to preheat the parts being joined.  However, practical applications of thermites are limited.  Thermite reactions are typically difficult to ignite and they become self-sustaining only for a large amount of thermite mixture.  Thus, thermites reactions have been used for large scale welding, such as for rails for railroads. 

## Nanocomposites 

- Mixture of two or more materials blended on the scale of one billionth of a meter.
- Produced by mechanical milling
- Large reactive surface areas
- React more rapidly and more intensely than larger sized composites

**Notes:**
A nanocomposite is a mixture of two or more materials (referred to as components) blended on the scale of one billionth of a meter and is remarkably homogeneous.  It can be produced by mechanical milling of the component powders.  If the components can chemically react with one another, the materials are called reactive nanocomposite materials.  Nanocomposites have effectively very large reactive surface areas. Thus, they react more rapidly and more intensely than larger-sized composites or powder mixtures because of the more intimate mixing between the reactive components, for example, fuel and oxidizer. 

## Objective

- Identify conditions for the thermite welding suitable for joining small parts
- Vary
- Composition
- Mixture density
- Scale of mixing between components

**Notes:**
Like I stated previously, thermite reactions are typically difficult to ignite and they become self-sustaining only for a large amount of thermite mixture.  However, reducing particle size allows the thermites to burn faster and release heat rapidly enough. Therefore, homogeneous nanocomposites of aluminum copper oxide were made and then used in an attempt to weld two metallic parts together. 

## Nanocomposite Thermites

- Al-CuO prepared using Arrested Reactive Milling (ARM)
- Blends of varying ratios of Al-CuO and Al or Al-Cuo and Cu prepared in an ultrasonic bath

- Shaker Mill

- Crest Ultrasonics

**Notes:**
Samples of aluminum copper oxide were synthesized using a shaker mill by a process known as Arrested Reactive Milling (ARM).  Arrested Reactive Milling is a ball-milling process in which an initial blend of powders is repeatedly intermixed until the particles are bonded.  Blends of varying ratios of aluminum copper oxide and aluminum or aluminum copper oxide and copper were prepared using an ultrasonic machine.  

## Tests 

- Powerstat Variable Autotransformer

- Copper plates pressed in copper wedge

- Tungsten Wire (diameter .2mm)

**Notes:**
The powders were pressed between two copper plates using a copper wedge.  They were then ignited using a series circuit.    

## Results 		  	

- Textolite boards covered by copper foil were used as parts to be joined
- A series of experiments with different compositions prepared and performed
- ARM powder of 2Al+3CuO
- Added Al powder
- Added Cu powder
- Mixed Al and CuO powders
- Bonding of molten copper to the copper foil observed in some experiments, but no joining was achieved
- Reaction was
- too quick: copper boils and vapor repels joining parts
- too slow: does not propagate

**Notes:**
None of the tests yielded the desired results.  The thermite reaction was either too quick or too slow.  The thermites were not dense enough and therefore future work should press them into a denser form, such as pellets.  The pellets should then be ignited with laser to ensure a sufficient amount of heat is present for ignition.     

## Future Work

- Press powders into pellets
- Remove porosity
- Reduce reaction temperature to avoid Cu boiling
- Reduce amount of filler by making thin pellets
- Use laser to ignite thermites
- Overcome ignition difficulties for dense pellets