Forget what you thought you knew about diamonds. For ages, diamonds were believed to be formed in the mantle, around 100 miles (160 KM) below the Earth’s surface, where massive pressure and time acts as a perfect recipe. What if I told you that brilliance can now be synthesized in labs?
Enter lab-grown diamonds – They possess the same chemical, optical, and physical properties as their mined counterparts. The only difference is in their origin story. Instead of being mined from the depths of the Earth, they are nurtured in a controlled lab environment. This isn't science fiction; it's a true episode that we are going to binge-watch in this blog.
The Brilliant Seed: Raw Material of Lab-Grown Diamonds
Similar to how you plant a seed to grow a tree, lab-grown diamonds begin with a small fragment of diamond known as a ‘seed’. Picture it as a blueprint, the basis of everything that is fascinating.
The Source: The seeds are usually obtained from previously lab-grown or mined diamonds. You could call it diamond inception! The seeds provide the crystalline structure which will be attached by new carbon atoms and stitched together to form a huge diamond.
Material Needed for HPHT and CVD: Both CVD and HPHT share an interesting commonality: the core raw material needed is the same.
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Diamond Seed: As mentioned, a small diamond seed is crucial. The quality and orientation of this seed can influence the final lab-grown diamond.
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Carbon Source: This is where the methods diverge slightly, but fundamentally, both methods require a source of pure carbon.
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HPHT: Uses elemental carbon. This is often in the form of graphite, which is a pure form of carbon.
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CVD: Uses carbon-rich gases, such as methane, in a gaseous state.
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Essentially, both methods are about providing carbon atoms in the right conditions so they organize themselves onto the diamond seed and replicate the natural diamond crystal structure.
High-Pressure High Temperature (HPHT): Replication of Earth’s Recipe
Consider trying to recreate the Earth’s mantle in a laboratory; that is essentially what the HPHT method achieves. It is violence disguised as intelligence, simulating the mind-boggling pressures and extreme heat which serve as the birthing place of natural diamonds.
What is the HPHT Method?
Diamonds can be made using numerous methods, but some people prefer the HPHT or High Pressure/Heat treatment style. This technique replicates the extreme low intervals of Earth’s surface where natural diamonds are situated. A carbon source is transformed into a diamond by applying immense pressure and heat. Think of it as a pressure cooker, but way more magnified with astonishing control.
Process Of HPHT Lab Grown Diamond:
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Understanding the Process: At the lowest point of a growth cell lies a diamond seed. Contained within this cell is the source of carbon, which is usually graphite, a metallic solvent catalyst, and the seed itself which is deep below. This catalyst is the magic wand; it reduces the temperature and pressure parameters necessary for diamond growth to something feasible in a laboratory.
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Increasing Pressure and Temperature: The HPHT machine contains the growth cell. There are mainly two varieties of HPHT machines:
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Belt Press- It squeezes the growth cell with hydraulic pressure.
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Cubic Press- It brings forth pressure from multiple directions at the same time.
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Split Sphere (BARS) Press- These have the capability of reaching even higher pressures, 5-6 GPa (gigapascals). That means 50,000-60,000 times the atmospheric pressure at sea level! The temperature increases to around the range of 1300-1600 °C (2372-2912 °F).
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Dissolving and Recrystallization: The carbon source gets dissolved in the metallic solvent catalyst under extreme conditions. This carbon-rich solvent is then moved to the diamond seed with lower temperatures.
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Cooling and Extraction: In between two and six weeks are necessary for the machine’s growth process to be complete. After that, the lab’s diamond crystal is retrieved after being cooled down.
Treatments for HPHT Diamonds:
Due to the presence of nitrogen impurities, HPHT-grown diamonds tend to have a yellowish and brownish tint during the growth process. To improve their appeal, these diamonds are sometimes treated with color-enhancing methods, such as:
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HPHT Annealing (Type IIa Diamonds): One other method of removing color from lab-grown diamonds of a specific type is through the further HPHT treatment, which ironically is called HPHT annealing. In this process, the defects within the nitrogen of the diamond crystal are altered, thus removing the color of the diamond.
Advantages of HPHT Diamonds:
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Established Technology: In comparison to the other methods of lab-grown diamond techniques, HPHT is a more established and efficient method of production.
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Larger Sizes: In contrast to CVD methods, HPHT is more efficient when attempting to create diamonds of larger sizes and certain colors.
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Certain Colors More Easily Achieved: In comparison to other methods, HPHT is far easier in several processes and can produce stronger yellows and intense pinks with the correct doping methods.
Disadvantages of HPHT Diamonds:
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Higher Energy Consumption: Because pressure and temperature must be maintained at extremes, HPHT machines require a lot of energy which leads to CVD being a more energy efficient option.
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Metallic Inclusions: The demetallization of the solvent catalyst is not always complete, and traces of metallic inclusions can get lodged deep within the stone. They are usually invisible to the naked eye, but gem material laboratories can identify them.
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Cost of Equipment: Since HPHT equipment is costly and sophisticated, it affects the overall expenses incurred in production.
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Chemical Vapor Deposition (CVD): The Cutting Edge in Diamond Synthesis
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CVD is a more modern and sophisticated method when compared to the brute-force approach known as HPHT. Picture constructing a diamond the way high-tech 3D printers do – atom by atom, layer by layer.
The Process of CVD:
In a vacuum chamber, diamonds are formed using a carbon gas mixture under moderately high temperatures while the gas is in a vacuum. Imagine it as a sumptuous dance of carbon atoms settling on a seed to develop a bigger crystal.
Process of CVD Diamond Growth:
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Setup of Vacuum Chamber: In a vacuum chamber, a tiny seed of diamond is placed. This chamber is filled with gases that contain carbon, usually methane along with hydrogen.
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Energy Activation: Energy is injected to get the gases active; here are some common forms of doing this:
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Microwaves: Microwave plasma CVD (MPCVD) is really common.
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Hot Filament: CVD gets gated with a hot filament (HFCVD) which has heated filaments that split the gas molecules.
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Deposition of Carbon: The source of energy shatters carbon-containing gases into individual atoms. The carbon atoms float downwards and fall onto the diamond seed. Controlled environments with specific mixtures of gas facilitate these carbon atoms to bond in a perfect diamond crystal structure, which increases the size of the diamond by adding layers one upon the other.
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Carbon Growth Over Time: Growth of diamond through CVD is relatively slower than HPHT. It, however, gives greater control over the purity and size of the diamond. Nature has taken its time to create a gem-quality diamond of significant size. It can take several weeks.
CVD Diamond Treatments:
Just like HPHT diamonds, CVD diamonds can be slightly brown or grayish due to defects formed during the growth phase. In order to improve their appearance, treatments are generally performed and are reliable:
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Annealing: Heat treatment performed in a controlled atmosphere does wonders to remove color from most CVD diamonds, turning them colorless or almost colorless.
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Irradiation and Annealing: For fancy colored diamonds (for instance, pink and blue ones), certain colors can be induced by irradiation followed by annealing.
CVD Diamond Benefits:
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Lower Price: CVD diamonds are noticeably cheaper as they are created in a lab.
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Higher Purity: Unlike the HPHT diamonds which are filled with inclusions and other impurities leading to lower clarity, it is possible for CVD diamonds to be of higher clarity.
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Increased Energy Efficiency: Compared to HPHT, CVD processes are less energy consuming.
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Better Control Over Growth: A finer control over the diamond growth process translates to better control over other characteristics, such as color.
Disadvantages of CVD Diamonds:
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Historically Smaller Sizes: In the past, CVD made it difficult to grow very large diamonds. However, this gap is being rapidly closed with new technological advancements.
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Post Growth Treatment More Common: There are more post growth treatments of CVD diamonds than other types, for instance, annealing to achieve colorless or near colorless diamonds. This increases the processing time.
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Birefringence (strain): Some CVD diamonds may have slight strain patterns that are detectable under polarized light. While these patterns are not visible to the naked eye, they do not pose any structural damage or weakness.
CVD VS HPHT: The Diamond Duel
So, which method reigns supreme? It's not about one being "better" than the other, but rather understanding their nuances.
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The Verdict?
Both HPHT and CVD are impressive technologies that create amazing diamonds. The veteran HPHT, does well in larger sizes and some color categories, while the newer CVD excels in purity and energy consumption. The determination of which method is 'best' is fundamentally dependent on the characteristics expected from the specific diamond being grown.
The exciting truth is that lab-made diamonds are changing the diamond market for the better as they provide a stunning, ethical, and less harmful to the environment substitute for mined diamonds. Whether forged in the 'pressure cooker' of HPHT, or layered atom by atom in CVD, lab-grown diamonds showcase the remarkable ability of humans and offer a dazzling outlook of the world of jewelry to come.