Ultrasonic Synthesis and Processing of Nanodiamonds

By AZoNano

Table of Contents

Introduction
     Nanodiamonds
Synthesis of Nanodiamonds by Ultrasonication
Synthesis of Diamond Micro-crystals by Ultrasonication
Dispersion of Nanodiamonds Using High Power Ultrasound
Functionalization of Nanodiamonds
Conclusion
About Hielscher

Introduction

Nanodiamonds

Nanodiamonds are a unique form of carbon nanomaterials that exhibit special properties, such as large surface, lattice structure, and distinct magnetic and optical characteristics. They are used in a number of applications and are also called as ultradispersed diamonds or detonation diamonds. The characteristics of ultradispersed particles make nanodiamonds suitable for producing innovative materials with amazing functions. In the soot, the diamond particles measure approximately 5 nm.

Owing to their zeta-potential, the nanodiamond grains are not stable and therefore they tend to form aggregates. Nanodiamonds are used in heat sinks, cutting and polishing tools, and abrasives. They are also used as drug carrier for pharmaceutical active components.

With the help of ultrasonication, nanodiamonds can be produced from graphite. Additionally, in order to create a polishing agent, nanodiamonds that tend to form aggregates can be uniformly dissolved in liquid media.

Synthesis of Nanodiamonds by Ultrasonication

The development of diamonds is a vital research field with respect to commercial and scientific interests. High-pressure-high-temperature (HPHT) is the standard method used for producing micro-crystalline and nano-crystalline diamond particles.

Through this technique, the preferred process pressure of tens of thousands of temperatures and atmospheres of over 2000 K are created to manufacture the major part of industrial diamonds. In order to convert graphite into diamond, high temperatures and pressures are needed. Also, to increase the yield of diamond, catalysts are generally utilized. High power ultrasound can be used to meet these requirements.

Ultrasound in liquids produces extreme effects. When liquids are sonicated at high intensities, the sound waves that travel into the liquid media tend to cause alternating low-pressure and high-pressure cycles, with rates depending on the frequency. During the low-pressure cycle, ultrasonic waves of high intensity produce tiny vacuum bubbles or voids in the liquid.

Moreover, the implosion of the cavitation bubble causes liquid jets of about 280 m/s velocity. It is apparent that micro- and nano-crystalline diamonds can be produced in the field of ultrasonic cavitation.

Synthesis of Diamond Micro-crystals by Ultrasonication

Study indicates that it is possible to synthesize diamond micro-crystals through ultrasonication of graphite suspension in organic liquid at room temperature and atmospheric pressure. The cost of micro and nanodiamonds synthesized through this technique is projected to be competitive with the HPHT technique.

This makes ultrasound an effective option for producing micro and nanodiamonds, particularly as the manufacturing process of nanodiamonds can be improved by further analyses.

Figure 1. SEM images of the ultrasonically synthesized diamonds: pictures (a) and (b) display the sample series 1, (c) and (d) show the sample series 2

A number of parameters like temperature, pressure, amplitude, concentration, and cavitation fluid must be precisely checked to identify the spot of ultrasonic nanodiamond synthesis. With the positive results obtained with nanodiamonds synthesis, additional cavitation generated by ultrasound provides a possibility for producing other vital compounds, like carbon nitride and cubic boron nitride.

Moreover, there is a possibility to synthesize diamond nanorods and nanowires from multi-walled carbon nanotubes under ultrasonic irradiation.

Dispersion of Nanodiamonds Using High Power Ultrasound

In order to exploit the unique properties of nanodiamonds, deagglomeration and uniform particle size distribution in the medium are important. Ultrasonic dispersion and deagglomeration are a result of ultrasonic cavitation.

When liquids are exposed to ultrasound, the sound waves that travel into the liquid promote alternating low-pressure and high-pressure cycles. This causes mechanical stress on the attracting forces between particular particles.

Hence, ultrasound is suitable for dispersing and milling of micron and sub micron-size particles.

Functionalization of Nanodiamonds

For the functionalization of nano-sized particles, the particle surface must be available for chemical reaction. In other words, a fine and uniform dispersion is needed since the well-dispersed particles are enclosed by a molecular layer attracted to the surface of the particle.

In order to get new functional groups to the surface of nanodiamonds, this boundary layer needs to be eliminated. Ultrasonics can be used for this purpose.

Also, experiments using the Bead-Assisted Sonic Disintegration (BASD) process have demonstrated positive results for the surface funcionalization of nanodiamonds. Therefore, beads have been utilized to apply the ultrasonic cavitational forces onto the nanodiamond particles. The desagglomeration occurs as result of the interparticular collision between the ZrO2 beads and nanodiamond particles.

Figure 2. Graphic of the in situ deagglomeration and surface functionalization of nanodiamonds

Conclusion

In view of better availability of particle surface for chemical reactions, BASD or ultrasonic pre-treatment for dispersion purposes can be used. Through ultrasonic dispersion and deagglomeration, chemical reactions can continue more completely. For the mechanochemical BASD treatment, a solvent with low viscosity and high boiling point should be used to prevent boiling bubbles.

About Hielscher

Hielscher Ultrasonics is a family business, located in Teltow near Berlin (Germany). The main emphasis of its activities is the conception, development and production of ultrasonic devices for the use in laboratory and industrial applications. Technological innovations together with the realization of new ultrasound based processes substantiated the company growth and its market acceptance.

Today, ultrasonic devices made by Hielscher Ultrasonics are being used in laboratories and production plants on all continents across the world. More than 70% of the total sales is based on export. Almost every second device is supplied to customers outside Europe. Hielscher Ultrasonics integrates the ultrasonic devices into complex ultrasonic systems, such as wire cleaning systems, too. The systems are produced to meet the customers requirements in terms of power, extended range of accessories and steady state proof equipment.

Hielscher USA, Inc. is the representative for Hielscher ultrasonic equipment in the North American market. It is located in Ringwood, NJ.

This information has been sourced, reviewed and adapted from materials provided by Hielscher.

For more information on this source, please visit Hielscher.

Date Added: Mar 5, 2013 | Updated: Jun 11, 2013
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