Dynamite Diamond

Diamond may be formed by direct conversion of graphite with explosion-produced shock waves. Alternatively, the explosive can itself provide the carbon source (e.g. by dynamite detonation) to form diamond. In this case, the dynamite may decompose to form carbon and compressed gas. Due to the presence of instantaneous pressure and temperature, the carbon network in dynamite may rearrange to form diamond. However, such diamond particles, being extremely small, are immediately liquefied by the high temperature. The "diamond shower" is soon quenched to form nanodiamond particles. This process was originally developed by Russian in 1980s (e.g. by Russian Alta I).

The explosive may also be used to generate strong shock waves that can collapse graphite to form microscopic conglomerates of nano-crystalline diamond particles (see the other chapter). This process was pioneered by du Pont scientists in 1960s.

Dynamite derived graphite is mostly 3-10 nm in size (Fig. 6.1) that often form clusters with much larger sizes (e.g. one order of magnitude larger).

Dynamite formed diamond is not completely transformed. The nano-sized diamond core may be covered by non-diamond carbon residues that may resemble bucky balls or carbon onions (Fig. 6.2). The surface may also be adhered with carbon soot that may shed the light of the dynamite origin.

The dynamite diamonds contain various impurities (Figs. 6.3 and 6.4) so its density (e.g. 2.8-3.1 g/cc) is lower than true diamond (3.5 g/cc). One example is with 87 wt.% of carbon, 10 wt.% of oxygen, 2 wt.% of nitrogen.

Diamond Nanotechnology: Synthesis and Applications by James C Sung & Jianping Lin

Copyright © 2009 by Pan Stanford Publishing Pte Ltd

www.panstanford.com

978-981-4241-36-6

Figure 6.1. A 3.5 nm nanodiamond containing about 4000 carbon atoms.
Figure 6.2. The onion rings of nanodiamond. The core may account for 1/2-3/4 by weight.
Figure 6.3. The HRTEM resolution of dynamite nanodiamond. Source: Courtesy of David Hsu.
Figure 6.4. Dispersed dynamite nanodiamond. Source: Courtesy of Yu-Fen Tseng.

6.1 NANODIAMOND CHARACTERISTICS

Nanodiamond particles may form clusters or agglomerates to become much larger collectives. The former may be due to the surface charges that are opposite to one another (Fig. 6.5). The latter can be produced by milling of shock wave compacted aggregates.

6.2 HIGH SURFACE AREAS

The nanodiamond particles derived from dynamite have very high specific surface areas. In fact, due to the small size of carbon atoms, nanodiamond particles possesses the highest proportion of surface atoms of all materials with the similar size (Table 6.1).

Because nanodiamond can be extremely small, the number of particles per carat may be enormous. For example, if diamond is about 3 ¡m in size, each carat may have hundred thousands (105) particles. If the diamond size is reduced to about 100 nm, the same carat may contain hundreds trillions (1014) particles.

6.3 THE EXPLOSION PROCESS

The convert of dynamite to form nanodiamond was pioneered by Russians in 1980s. The dynamite used to make nanodiamond particles must contain high carbon/oxygen ratio (e.g. oxygen content less than 6 wt.%). It is typically a mixture of TNT with a pressure enhancer such as RDX (e.g. one to one ratio). RDX may be replaced

X ftttis T X fto* rfli

Figure 6.5. Nanodiamond clusters (left) and nanodiamond agglomerates (right). The bottom diagrams compare the X-ray diffraction patterns of the two origins of nanodiamond. Note that the dynamite derived nanodi-amonds contained much of non-diamond materials. However, the shock wave formed aggregates included some amount of hexagonal diamond (lonsdaleite).

X ftttis T X fto* rfli

Figure 6.5. Nanodiamond clusters (left) and nanodiamond agglomerates (right). The bottom diagrams compare the X-ray diffraction patterns of the two origins of nanodiamond. Note that the dynamite derived nanodi-amonds contained much of non-diamond materials. However, the shock wave formed aggregates included some amount of hexagonal diamond (lonsdaleite).

by more explosive HMX, PETN, or even BTF (oxygen free dynamite). During the explosion, pressure may reach 20 GPa for a duration of a fraction of one micro (10-6) second; and temperature could exceed 3000°C. Although carbon (graphite and diamond included) will not melt at this temperature, but the decomposed carbon atoms are highly active and their combination of non-carbon atoms (e.g. H, O, N) greatly reduced the melting point. Consequently, these atoms are attracting one another to form atomic scaled liquid.

Table 6.1. Surface atoms of small diamond particles.

Size

Atom

Surface Atom

Weight

Particle

Surface Area

(Number)

(%)

(gm)

(#/Carat)

(m2/gm)

1 nm

143

92%

1.8x10"

21

1.1 x1020

1705

2 nm

1147

23%

1.5x10"

20

1.4x1019

852

5 nm

1.8x104

3.7%

2.3x10"

19

8.7x1017

341

10 nm

1.4x105

0.9%

1.8x10"

18

1.1x1017

170

50 nm

1.8x107

3.7x10-2%

2.3x10"

16

8.7x1014

34

100 nm

1.4x108

9.2x10-3%

1.8x10"

15

1.1x1014

17

500 nm

1.8x1010

3.7x10-4%

2.3x10"

-13

8.7x10"

3

1 ßm

1.4X1011

9.2x10-5%

1.8x10"

12

1.1x1011

2

10 ßm

1.4x1014

9.2x10-7%

1.8x10"

"9

1.1x108

0.2

50 ßm

1.8x1016

3.7x10-8%

2.3x10"

-7

8.7x105

3.4x10"2

100 ßm

1.4x1017

9.2x10-9%

1.8x10"

"6

1.1x105

1.7x10"2

500 ßm

1.8x1019

3.7x10-10%

2.3x10"

"4

8.7x102

3.4x10-3

1 mm

1.4x1020

9.2x10-11%

1.8x10"

-3

1.1x102

1.7x10"3

These liquid clusters can be quenched by pouring in water, CO2, or N2 to preserve diamond-like nano-particles. Because the quenching effect is more pronounced with water, the diamond yield is higher than using gas as coolant (Fig. 6.6).

During the process of detonation, the nanodiamond particles so formed have a melting point that is actually below the detonation temperature. As a result, nanodiamond formed droplets of liquid that are soon frozen by super cooling to become defect ridden diamond particles (Figs. 6.7 and 6.8).

Due to the rapid vitrification of the super cooled liquid of diamond, the particle size distribution is rather tight for detonated nanodiamond (Fig. 6.9).

A design sketch of the explosion assembly is shown in Fig. 6.10.

During the detonation, the pressure may surge momentarily to 30 GPa, and temperature can rise above 2000°C. During the few microseconds when pressure and temperature are the highest, non-oxidized carbon atoms are squeezed to form nanodiamond. The region where non-carbon atoms are concentrating will form carbon soots.

One example of detonation is to mix TNT with solids composed of C,H,N,O atoms and subject the charge to detonation. The detonation produces N2, H2O, CO2 and solid carbon at a pressure

Dynamite Chemical Structure
Figure 6.6. Various dynamite molecular structures that may form nanodiamond after detonation in oxygen deficient.
Figure 6.7. The diamond yield as a function of dynamite composition.
Figure 6.8. The detonation pressures and temperatures of dynamite and the melting point of diamond as a function of temperature.
Figure 6.9. The nucleation and growth rate of nanodiamond condensed from super cooled liquid of diamond.

\ \ p®3!

m • |

I

i

W^j I

Figure 6.10. Some examples of detonation device.

of about 30 GPa, and about 3000°C. The explosion is immediately quenched with gas (e.g. CO2 or N2) or water. Even so, the surface of nanodiamond remain hot enough (>1600)°C that it immediately back converted to form carbon onions. In addition, the carbon on the surface that has not converted to diamond could be packed around the carbon onions to form carbon black, bucky balls, and carbon nano tubes. The nanodiamond so formed is centered at 5 nm with a size spread that may be as tight as 5 A.

The soot can be purified by boiling in benzene to remove organic materials. Subsequent acid treatment can eliminate metal contaminants (e.g. boiling in 18% HCl for 1 h). The cleaned residue may be dipped in a 200°C solution of 6 HOO4 and 1 HNO3 and stir for 2 h. Finally, the product is washed and rinsed in distilled water. The nanodiamond so recovered may still contain a significant amount of non-carbon elements. For example, the following amounts of impurities were found, 10 wt.% of oxygen, 2 wt.% of nitrogen, and 1 wt.% of hydrogen.

6.4 NANODIAMOND PROPERTIES

Due to the presence of diamond structure, nanodiamond is super-hard that may penetrate hard materials such as ceramics (Fig. 6.11).

The hardness of diamond may be compared with other materials in relative and absolute scales as follows.

Figure 6.11. The schematic that contrasts the atomic sizes and their structures of various materials. Diamond is superhard due to its small carbon atoms with strong covalent bonds.

It is interesting to note that superhard diamond may be as slippery as the soft Teflon. This is because while Teflon's softness is due to its weak bonds between molecules, the slippery of diamond does not come from the yielding of chemical bonds, but the lack of reaction on smooth surface of diamond (Figs. 6.12 and 6.13).

6.5 NANODIAMOND APPLICATIONS

The properties of dynamite formed diamond-like carbon particles are compared with other diamond micron powder as listed in Table 6.2.

One example of explosive derived nanodiamond is shown in Table 6.3.

Figure 6.12. The scale of hardness for various materials.

Steel

V

V

/Graphite

DiamondX

/ Teflon

Figure 6.13. The frictional coefficient as a function of hardness.

Table 6.2. Properties of diamond micron powder

Making Method

Crushed Grain

Shock Wave

Explosive

Size Structure

Microns Single

Microns

Derivative

Crystal

Polycrystals

Nanometers

Diamond-like

Carbon

Density (g/cm3)

3.5

3.4

3.2

Packing Density

0.7

0.5

0.3

(g/cm3)

Purity (C%)

100

99

90

Specific Surface

<10

30

Table 6.3. Nanodiamond characteristics

Application

Polishing

Lubrication

Size

Composition

Bulk density Surface area Oxidation threshold (air) Graphitization in

0.7 gm/cm3 350-390 m2/gm 450

1100

vacuum

The explosive derived nanodiamond can be used for ultra polishing of eye glasses, contact glasses, hard drive (nickel layer), magnetic ferrite, optical and laser components, diamond knives, gem stones, etc. The surface finish may attain a super smoothness of Ra < 0.2 nm.

Another major application is in lubrication coating on engine components, such as piston-cylinder, crane shaft, gears box, pumping components, etc. For the application of engine oil additive, 0.02% addition may reduce 30% of surface friction; and 0.1%, more than 50%. Normally, an abrasive particle can scratch the moving parts of an engine is the size of the particle is in the same magnitude

Table 6.4. The abrasion resistance enhancement by plating with nanodiamond

Coating

Increase in Wear-Resistance, N-Fold where N

Cr

2-12

Ni

5-9

Cu

9-10

Au

2-6

Ag

4-12

Sn

2-4

AI

10-13

of the gap between two moving parts, but for nanodiamond particles, their sizes are much smaller than the gap, so they will not scratch either part. Instead, these particles may be embedded on the wall of the moving part and become the hard facing component. As a consequence, they can protect the engine parts from further mechanical wear or chemical erosion. In addition, the opposing moving parts are now sliding against the hard facing that has a much lower frictional coefficient than any metal component. As the motion of the engine part will receive much less drag, less energy (e.g. gasoline) is needed to power the engine.

Another application of nanodiamond is to be the ingredient of composite hard facing for metal parts. Thus, by dispersing nan-odiamond in an ordinary electrolyte, the electro deposited metal will incorporate nanodiamond in its matrix. Hence, nanodiamond may be co-deposited by electroplating of gold, nickel or chromium. The coated surface will be much harder and it is highly resistant to chemical corrosion. For example, by dispersing nano-diamond in an electrolyte (e.g. 2.5 g/liter) for Ni plating, 5-9 times increase of wear resistance may be expected. For gold plating with nanodi-amond, the thickness may be halved to retain the same appealing luster, but it may come with a 10-fold increase of wear resistance (Table 6.4). Alternatively, nanodiamond may be blended in with copper plating to form a highly thermal conductive heat spreader (e.g. for CPU or laser diode applications).

Other applications of nanodiamond include as mechanical reinforcement fillers (e.g. polymer/rubber matrix elastomers,

PTFE Teflon matrix lubricant, ceramic matrix composites); hydrogen storage medium for fuel cell battery; nucleation seeds for CVD deposition of diamond; feedstock for high pressure sintering of polycrystalline diamond, protein absorption, separation, etc.

6.6 CHINESE DYNAMITE DIAMOND

Although the West could develop and make advancements in technologies earlier, the Chinese have been notorious in overtaking the manufacturing capacity after learning the secret. Thus, the static high pressure processes for making mesh sized diamonds were perfected by GE Superabrasives and De Beers Industrial Diamond for decades, China became the largest diamond maker at the turn of this century. GE was forced to sell the superabrasives business that became Diamond Innovations. De Beers was compelled to reorganize the diamond business as Element Six. Despite these survival damage controls, Chinese diamond capacity continued to surge. Thus, in 2007, China made more than 80% of the world's industrial diamonds totaled about 1000 tons (five billion carats).

The dynamite diamond may not be immuned to Chinese glutted production. Although the technology was pioneered by Russians in 1960s, Chinese cracked the code in 1990s. Thus, several entities have been engaged in pilot production of dynamite diamonds (e.g. Lanzhou Institute of Chemical Physics of Chinese Academy of Sciences, Beijing Institute of Technology, The Second Artillery College, Southwest Institute of Fluid Physics, Northwest Instutte of Nuclear Technology). It is expected that China will dominate dynamite diamond production in the next decade. The following are summarized Chinese technologies that was presented by Annie Hui and Wang Guangzu at the Fifth Zhenzhou International Conference on Superhard Materials, September 5, 2008 (Table 6.5).

The process design parameters include ratios of dynamites, their geometry (size and shape), and loading methods (injection or pressing). The amount (about 10%) of detonation soots appears to be maximized with TNT=RDX. TNT provides the transformed nanodiamond while RDX generated formation pressure that controls the yield, and temperature that affects the size. Larger charges and premixing of nanodiamond seeds tend to increase the yield.

Table 6.5. Main attributes of dynamites

Properties

RDX

TNT

Scientific Name

Cyclotrimethylenet-

Trinitrotoluene

rinitramine

Colour

White Powder

Yellow Squamose

Crystals

Molecular Formula

C3H6N6O6

C7H5N3O6

Molecular Weight

222.1

227.13

Oxygen Balance

-0.216

-0.740

Crystal Density/g/cm3

1.816

1.654

Detonation Velocity m/s

8661

6928

(p = 1.765 g/cm3)

(p = 1.634 g/cm3)

Detonation Pressure/Gpa

32.6

19.1

(p = 1.765g/cm3)

(p = 1.634g/cm3)

Detonation Temperature/K

3700

3000

Detonation Heat/kJ/kg

5620

3000

(p = 1.77g/cm3)

(p = 1.62g/cm3)

Performance Ability

1.81

1.03

Calculated/kJ/g

Observed/kJ/g

1.716

1.06

Gas Products

908

690

Calculated/cm3/g

Measured

900

790

Melting Point/K

478

353.9

Weight of Carbon Content/%

16.22

37.00

Price/rmb/ton

23000

9000

The nanodiamond yield (Fig. 6.14) is also influenced by the type of protective atmosphere in the reaction chamber. CO2 seems to produce more nanodiamond than N2, Ar or He. Water or ice may also be used to quench the explosive products so the conversion to graphitic carbon may be minimized. The sealed metal container is the source of contamination so coating the inner side with a refractory metal or ceramics may reduce the amount of vaporized contaminants.

Size Distribution Nanodiamonds
Figure 6.14. Particle size distribution of nanodiamond from detonation soot.

Table 6.6. Product characteristics Item

Specific Surface Area (m2/g)

Particle Size (nm)

Shape

Dust Colour

Nanodiamond Content (%) Density (g/cm3) Pore Volume (cm3/g) Surface Functional Groups

Initial Oxidation Temperature (K) Hydrophilic Degree (Mj/mol. G)

Black Soot Grey Soot

Spherical or Banded Spherical Black Grey

3.05 - 3.3 1.314 -OH, -C=O, -CN -COOH -C -O-803 -3100

Chapter Seven

Was this article helpful?

0 -1

Responses

  • Adelbert
    What is the diffrences between diamond and dynamite?
    1 year ago

Post a comment