How are synthetic diamonds made?

By means of Owais AliReviewed by Lexie HoekOctober 22, 2024

Synthetic or laboratory-grown diamonds are artificially created gemstones that have the same chemical composition and crystal structure as natural diamonds. They can be designed with specific optical and mechanical properties, making them valuable for jewelry and industrial applications.

Image credits: Roma Likhvan/Shutterstock.com

Diamonds are formed deep in the Earth’s mantle, about 250 kilometers below the surface, where enormous pressure (up to 10 GPa) and temperatures (around 2200 °C) compress carbon into diamonds over billions of years. This lengthy shaping process adds to its value, but the growing demand for diamonds in various applications makes alternatives necessary.

As a result, researchers have turned to synthetic diamonds, which offer a cheaper, sustainable and ethical option that meets the needs of the industry while reducing environmental impact.¹

What are lab-grown diamonds made of?

Lab-grown diamonds are chemically and structurally identical to natural diamonds, consisting of carbon atoms arranged in a crystal lattice. Unlike diamond alternatives such as cubic zirconia or moissanite, which only mimic the appearance of diamonds, synthetic diamonds are physically and optically real diamonds.

While natural diamonds take billions of years to form, synthetic diamonds can be created in just a few weeks. This rapid production, combined with lower costs and lower environmental impact, has fueled their popularity in both consumer markets and high-tech industries.

The two main methods for creating lab-grown diamonds are high-pressure-high-temperature (HPHT) and chemical vapor deposition (CVD). Both processes take place in controlled laboratory environments, allowing precise manipulation of conditions to achieve specific characteristics including size, color and clarity.^1,2

Method 1: High Pressure High Temperature (HPHT)

HPHT was the first industrial method used to produce synthetic diamonds. It mimics the conditions under which natural diamonds form in the earth.

This process involves placing carbon in a chamber with a diamond seed and a metal catalyst such as nickel, cobalt or iron, lowering the temperature required for diamond formation. The chamber is exposed to extreme pressures (up to 870,000 psi) and high temperatures (1,300 to 1,600 °C). Under these conditions, carbon dissolves in the metal catalyst and then crystallizes around the diamond seed, creating a synthetic diamond.³

Advantages and disadvantages of HPHT diamonds

HPHT diamonds are valued for their hardness and durability, making them ideal for high-pressure applications. For example, polycrystalline diamond (PCD), produced via the HPHT method, is a super-hard material commonly used in PDC drills. It offers exceptional hardness, wear resistance and improved penetration rates, making it ideal for demanding oil and gas drilling applications.

However, HPHT diamonds often contain metallic inclusions from the growth catalysts, which reduces their clarity and limits their use in high-end jewelry. The internal stress caused by the extreme forming conditions can also lead to stress in the crystal lattice, compromising its integrity for applications that require defect-free crystals.

Additionally, impurities such as nitrogen can result in color variations, such as yellow diamonds, which can be less desirable for jewelry and optical applications.^4.5

Industrial landscape of HPHT diamonds

Despite these challenges, HPHT remains a key method for the production of synthetic diamonds, especially for industrial applications.

Companies such as Hyperion Materials & Technologies use this technology to manufacture diamond-based composites such as Versimax™ and Compax™. These composites provide exceptional corrosion and wear resistance at high temperatures, along with high strength properties comparable to cobalt-sintered PCD and improved thermal stability.

These materials are widely used in metal forming, wire drawing, and high-pressure research environments, including geothermal studies. Their hardness and durability also make them essential in the mining and drilling sector, especially for oil and gas extraction.⁶

Method 2: Chemical Vapor Deposition (CVD)

The chemical vapor deposition (CVD) method offers an energy-efficient alternative to making synthetic diamonds, using gases instead of extreme pressure.

This involves placing a diamond seed in a vacuum chamber filled with carbon-containing gases, such as methane, and heating the chamber to temperatures of 800 to 900 °C. The heat breaks down the gas molecules, allowing carbon atoms to deposit layer by layer on the diamond seed and gradually form a diamond crystal.

This method allows precise control over the diamond’s properties, including size, shape and clarity; However, it can take several days to weeks to grow depending on the desired size and quality of the diamond.³

Advantages and disadvantages of CVD diamonds

CVD diamonds are typically purer than HPHT diamonds, making them more suitable for high-end jewelry. Furthermore, the absence of metal catalysts results in fewer inclusions and impurities, increasing their suitability for optical applications.

Their lower internal voltage, defect-free nature and high thermal conductivity make them valuable for high-performance optics and semiconductor devices. Additionally, the CVD process enables the production of larger diamonds with tailored properties, useful in applications such as heat sinks in electronics or optical windows for high-power lasers.

However, the CVD process is slower than HPHT, requiring precise control over growth conditions, resulting in longer production times and higher costs, limiting mass production for industrial use.

Many CVD diamonds also have a brownish tint due to imperfections in the lattice, requiring post-production treatments to improve color, further complicating the process and increasing production costs.^4.5

Industrial landscape of CVD diamonds

Element Six, a subsidiary of De Beers Group, is at the forefront of CVD diamond production. It specializes in high-quality synthetic diamonds for various applications, including cutting tools, infrared optics and high-performance electronics. The CVD diamonds are designed for consistency and quality, making them ideal for industries that require precise material properties, such as aerospace.

Recently, SBQuantum (SBQ), a startup focused on transforming navigation in GPS-denied environments, used Element Six’s synthetic diamond to improve accuracy in challenging environments, such as the Arctic, where magnetic interference from structures is problematic.

The integration of these diamonds enabled SBQ devices to achieve low power consumption, drift suppression and high accuracy, improving their applications in geological surveys and underwater pipe detection.⁶

Conclusion

The production of synthetic diamonds using HPHT and CVD techniques has revolutionized the diamond industry and several high-tech sectors, making diamonds more accessible and sustainable while providing an ethical alternative to mined diamonds.

More from AZoM: Using synthetic diamond and tungsten carbide as engineering materials for fusion energy

References and further reading

1. Marinescu, I. D., Rowe, W. B., Dimitrov, B., and Ohmori, H. (2012). Abrasives and abrasives. Tribology of Abrasive Machining Processes (Second Edition). https://doi.org/10.1016/B978-1-4377-3467-6.00009-4
2. Butcher, A. (2024). Lab-grown diamond production methods. (Online). International Gem Society. Available at: https://www.gemsociety.org/article/lab-grown-diamond-production-methods/
3. D’Haenens-Johansson, UF., Butler, JE., Katrusha, AN. (2022). Synthesis of diamonds and their identification. Reviews in Mineralogy and Geochemistry. https://doi.org/10.2138/rmg.2022.88.13
4. Kasu, M. (2016). Diamond pitaxy: basics and applications. Advances in crystal growth and materials characterization. https://doi.org/10.1016/j.pcrysgrow.2016.04.017
5. Naamoun, M., Tallaire, A., Silva, F., Achard, J., Doppelt, P., Gicquel, A. (2012). Mechanism for the formation of etching pits induced on HPHT and CVD diamond crystals by H2/O2 plasma etching treatment. Physica Status Solidi (a. https://doi.org/10.1002/pssa.201200069
6. Hyperion materials and technologies. (2024). Hyperon – Advantages of diamond composite. (Online) Hyperion materials and technologies. Available at: https://www.hyperionmt.com/en/products/Wire-Dies/diamond-composite-advantages/
7. E6. (2020). Unlocking the next generation of quantum sensors. (Online) E6. Available at: https://e6-prd-cdn-01.azureedge.net/mediacontainer/medialibraries/element6/documents/guides/sbq-e6_case_study_june2020.pdf?ext=.pdf

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