Handbook of Industrial Diamonds

Volume 1, Superabrasives and Diamond Syntheses

James Sung

• Publisher: Jenny Stanford Publishing
• Year: 2021
• eBook ISBN: 9781000400878
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Mechanics

Every year, the world consumes more than 10, 000 tons of diamond superabrasives, which are indispensable for fields such as construction, metals, ceramics, automobiles, semiconductors, computers, and cellular phones. In fact, the per capita consumption of superabrasives may be used as an indicator of a country's industrial activities.

This volume presents several aspects of superhard materials, especially diamond superabrasives and their manufacture, properties, and applications, and introduces several new designs of ultrahard materials that may be harder than diamond. It discusses diamond's connection with the origin of life, in particular, the origin of the first RNA. In addition, it throws light on the concept of diamond quantum computers with neutrons of the carbon-13 isotope as quantum bits. This innovation may maintain quantum coherence with minimal interference without using complicated cryogenic cooling. Hence, it can be a robust design for future quantum computers. For those interested in the depth of the quantum mechanical world, a chapter elaborates the history of life and humanity in light of the evolution of quantum universes.

Chapter 1

High-Pressure Synthesis of Saw Diamond

Every diamond maker can make grind diamond. Very few can make saw grits, particularly with size coarser than 40 mesh.

1.1 The Technology Barrier for Growing Saw Diamond

Modern civilization has been greatly aided by the widespread use of industrial diamonds. In particular, the construction of building materials (e.g., concrete, granite, marble) may not proceed without using of diamond saws, drill bits, grinding wheels, and polishing pads. With the aid of these diamond tools, we can now live comfortably in a revitalized stone age.

The world consumption of industrial diamonds has been increasing steadily, and it exceeded 400 metric tons (2 billion carats) in 2002. Almost all industrial diamonds used are synthetic, and among them the saw grits account for more than half of the quantity produced (about half made in China), with an annual sales of over $600 millions.

The per capita consumption of stone for the world is about 8 kg of primary materials (16 kg of quarried stone) and 8 m² of finished products. For industrialized countries, the per capita consumption is more than each person’s body weight. It may be of interest to note that each carat (0.2 g or 0.05 cm³) of diamond can cut about 10,000 cm² of a hard stone (e.g., granite, about 10 times for marble). This cutting area may be equivalent to about 100 cm³ of the stone processed; hence, the diamond/stone ratio is about 0.5 PPM, that is about what the diamond abundance in a kimberlite pipe. Moreover, the diamond saws used to cut the stone contain about 5% (20 concentration) in volume of diamond grits. This ratio (about 1 carat/ cm³) is also similar to the average yield of high-grade saw diamond synthesized in a high-pressure reaction cell.

Saw diamond has the largest grit size (20 to 50 mesh, or 1 mm to 0.25 mm) of all industrial diamonds. It also possesses the highest degree of perfection. Almost all abrasive grains are rough on surfaces and they also contain numerous flaws and impurities, but saw diamond crystals are in generally euhedral with fully grown crystallographic faces, and their interiors often contain very little defects or inclusions (Fig. 1.1).

Such perfection of diamond grits is required because of its size and application. Saw grits cut stones at high speed, and they break the stone by brutal force. Hence, their impact strength is critical to maintain the integrity. In contrast, smaller grits (e.g., in a grinding wheel) work their way by scratching the object gradually, so they are more relying on hardness to penetrate the material than on toughness to smash the work piece.

The small diamond grits can be grown in a high-pressure reaction volume in minutes, and their less stringent crystal conditions can tolerate the inadvertent excursion of pressure and temperature. But for growing large saw grits consistently to a high degree of perfection would require the meticulous control of pressure and temperature for more than half an hour. This is a very sophisticated technology, so very few diamond synthesizers can master.

The manufacturing processes for saw grits have been highly guarded industrial secrets. Although over 20 countries and over 500 companies (China has the majority) are producing industrial diamonds worldwide, only three companies in the world are capable of making high-grade saw diamonds. They are General Electric (the author was the responsible manager in the late 1970s and early 1980s) of the U.S.A., De Beers of South Africa, and Iljin Diamond (the author designed the plant and provided initial technology in the late 1980s) of Korea.

Figure 1.1 The premium saw grit possesses euhedral crystal shape (top). The crystal is cubo-octahedral (bottom with its shape that tends to be more octahedral when it is growing at a higher temperature. In the bottom diagram, the fastest direction of diamond growth (the largest size of the crystal) is measured by α = √3V(111)/V(100), where V is the growth rate in the direction perpendicular to the particular face.

The most advanced technologies in growing saw grits today employ stringent controls on the uniformity of raw materials (e.g., graphite, catalyst), and the steadiness of synthesis processes (e.g., pressure, temperature). The state-of-art of diamond technology is such that the high-pressure compressed reaction volume can be more than 200 cm³ (e.g., using a press capacity of 5000 tons or more). Each cubic centimeter of the compressed reaction cell may grow up to 3 carats of diamond (17% of volume utilization) in the compressed state—the graphite to diamond conversion rate of up to 30%. However, because the diamond distribution inside reaction cell is still random, about 1/3 of the crystals grow with flaws on outside (e.g., rough surface) and inside (e.g., metal inclusions); hence, they are not desirable in size or quality for commercial applications.

High-pressure diamond synthesis is a field that can be entered with ease, but mastered with difficulty. Many companies make diamond in the first year of investment but struggle in decades afterward trying to survive. Examples of the ones that did not make include Synthetic Diamond Technology, Valdiamant, Superhard in the United States; Baoding Bada-Winter, Asia Diamond in China; and other companies in France, Italy, Malaysia, and India.

Diamond superabrasives are like other industrial commodities that come with a hierarchy of grades and prices. All diamond makers can make low-grade products (low strengths and small sizes), but only a few can produce high-grade ones. The most premium diamond superabrasives are high-grade saw grits for cutting stone (e.g., granite) and concrete. The saw grits are well-crystallized single crystals with limited amounts of flaws (surface roughness or metal inclusions).

Saw grits are relatively large (0.3 mm to 1 mm) in size. Hence, it would require ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• 1. High-Pressure Synthesis of Saw Diamond
• 2. Diamond Grit
• 3. Diamond Saws
• 4. Micron and Nanom Diamond
• 5. Active Braze-Coated Diamond
• 6. Diamond Grinders
• 7. Cubic Boron Nitride
• 8. Diamond Pad Dresser
• 9. Polycrystalline Diamond
• Appendix
• Index