TABLE OF CONTENTS
HPHT technology: what is it?
The term high pressure-high temperature (HPHT) is used to define the most advanced instrumentation with undisturbed wellbore temperatures greater than 300°F (150°C) and pore pressure gradients exceeding 0.8 psi/ft (0.18 atm/m) or requiring well control equipment at operating pressures in excess of 10,000 psi (680 atm).
HPHT technology was commercialized back in the 1950s for the manufacture of laboratory-produced diamonds or to enhance the color of natural diamonds.
How are HPHT diamonds made?
To create high-performance heat-treated diamonds in the laboratory, scientists place diamond seeds at the bottom of a synthesis machine. The internal parts are then heated to 1400°C and above to melt the solvent metal. The molten metal dissolves a high-purity carbon source, which is then transported to the small diamond seeds, where it precipitates and forms lab-created diamonds.
The carbon source
A carbon source is any carbon-containing molecule (carbohydrates, amino acids, fatty acids, carbon dioxide) that an organism uses to synthesize organic molecules. Since diamonds are essentially crystalline carbon, scientists can create them in the laboratory using sources such as graphite, diamond dust, cremation ash, and human hair, which is 45% carbon in chemical composition.
The extracted carbon is purified to the highest degree and transformed into scaled graphite, which is placed in a diamond synthesizer and over time it is transformed into lab-made diamonds.
The diamond seed
The production of laboratory-made diamonds requires a microscopic type of diamond (natural, high-pressure and high-temperature or chemical vapor deposition) as a crystalline seed. Atoms from a carbon source are continuously attached to the diamond seed crystals until a new diamond crystal structure is formed. Thicker crystals can be obtained by extending the growth time of the diamond synthesizer.
The HPHT apparatus
HPHT technology uses three main press designs to provide the pressures and temperatures required to produce laboratory-manufactured diamonds.
Belt press
The device uses its upper and lower anvils to provide pressure loads to the cylindrical internal cell. This internal pressure is radially limited by a pre-stressed steel band. The anvil also serves as an electrode to provide current to the compression cell. A variation of the belt press uses hydraulic pressure rather than steel straps to limit the internal pressure.
BARS press
The rod unit is considered to be the most compact, efficient, and economical of all diamond production presses. In the center of the rod unit, there is a ceramic cylindrical “synthetic capsule” with dimensions of about 2 cm³.
The cell is placed in a pressure-transfer material cube, e.g. chlorite ceramic, which is pressed in by an inner anvil made of carbide (e.g. tungsten carbide or VK10 carbide). The outer octahedral cavity is pressed in by eight steel outer anvils.
After installation, the entire assembly is locked in a disc-type barrel with a diameter of about 1 meter. The barrel is filled with oil, heated and pressurized, and the oil pressure is transferred to the central unit. The synthetic capsule is heated by a coaxial graphite heater and the temperature is measured with a thermocouple.
Toroid press
The device consists of two carbide parts (anvils) with a conical press mounted in a steel support ring. The sample assembly is placed in a hole in the central part of the gasket and compressed between the two anvils. The surface of each anvil holder has a circular groove concentric within its axis.
Under the applied force, the anvil holders move against each other, creating different tangential stresses in the anvil holder material near the groove and in the central part of the anvil holder. When the latter is effectively supported, the available pressure on the anvil seat is higher and the life of the anvil seat is longer.
Hydraulic cubic press
Cube presses have six anvils that provide pressure to all sides of the cube volume at the same time. Cube presses are usually smaller than belt presses and can reach the pressures and temperatures needed to make lab-created diamonds much faster. However, cube presses do not scale easily to larger volumes: the pressurized volume can be increased by using larger anvils, but this also increases the force required to achieve the same pressure on the anvil.
Properties of an HPHT lab-made diamond
The manufacturing process and the carbon source used to make the laboratory-fabricated diamonds determine the type and number of crystal defects in the diamond and ultimately affect its mechanical, physical, and optical properties.
Crystallinity
A perfect HPHT laboratory fabricated diamond crystal has a structure consisting of carbon atoms covalently bonded in a tetrahedral network of sp3 hybridization arranged in a long-range order, a structure called a diamond cubic lattice.
Hardness
Diamond is the hardest known natural material, defined on the Mohs scale of hardness as 10. Notably, some HPHT nanocrystalline diamonds are harder than any known natural diamond.
Impurities and Inclusions
Metallic inclusions are a common feature of many HPHT lab-created diamonds unless they are prevented from forming during growth or are physically removed during faceting. They consist primarily of cubic γ-(FeNi), face-centered cubic (FeNi)23C6, rhombohedral Fe3C, and hexagonal Ni3C, which are formed by the reaction of molten catalysts entrapped or entrapped melts with contaminants in the diamond at the growth front.
HPHT laboratory fabricated diamonds are attracted to magnets because the flux metal alloys used to make the diamonds contain elements such as cobalt, nickel, and iron.
Thermal conductivity
Unlike most electrical insulators, diamond is a good conductor of heat because of its strong covalent bonding and very low phonon scattering. In fact, laboratory-prepared single-crystal diamond rich in 99.9% isotopic carbon has the highest thermal conductivity of any known solid at room temperature: 3320 w/(m-K).
HPHT lab-made diamond manufacturers
Since the commercialization of HPHT technology in the early 1950s, many manufacturers have entered the market with different types of lab-made diamonds, ranging from standard lab-made diamonds for luxury goods, cremation or funeral-related lab-made diamonds for souvenirs, and finally lab-made diamonds for weddings.
Notably, the market has undoubtedly become more competitive, to the point that even natural diamond companies like De Beers have moved to create their own lab-made diamond brands as an investment in a lucrative industry.
CVD technology: what is it?
The chemical vapor deposition (CVD) technique was born in the 1980s and mimics the process of diamond formation in interstellar gas clouds. This technique uses smaller machines and less pressure than the HPHT method.
Notably, the CVD technique produces diamonds of the highest chemical purity (Type IIA), which are extremely rare in nature, and the stones are not as magnetic as HPHT diamonds.
How are CVD diamonds made?
In the CVD process, a thin piece of diamond seed (usually HPHT-produced diamond) is placed in a sealed chamber and heated to about 800 degrees Celsius. The chamber is then filled with a carbon-rich gas (usually methane) and other gases. The gas is then ionized into a plasma using microwaves, lasers, or other special processes. The ionization breaks the molecular bonds in the gas and pure carbon atoms attach to the diamond seeds, which slowly form crystals.
The “Thin” diamond seed
The interface is extremely important in the growth of diamonds using the CVD process. According to industry experts, crystal seeds containing at least 26 carbon atoms are required for true crystal growth.
Thin diamond seeds are planted on a surface and exposed to a plasma that either dissolves the seeds or makes them grow. The competition between the two processes of growth determines the final size of the diamond crystal.
The carbon-rich gas mixture
Chemical vapor deposition techniques involve heating a mixture of hydrocarbons (usually methane) and hydrogen in a vacuum chamber at very low pressure. Under normal circumstances, heating this mixture at such low pressure would produce graphite or some other non-diamond form of carbon. However, in the CVD growth chamber, some of the hydrogens are converted to atomic hydrogen, which is a more stable environment for diamond formation.
The atomic hydrogen reacts with a primitive hydrocarbon gas (methane) to form a highly reactive hydrocarbon. When this decomposes, it releases hydrogen to form pure carbon, which in this case is the lab-created diamond.
The CVD apparatus
CVD devices make it easy to grow diamond films on large-area substrates and control the properties of the final product. Modern chemical vapor deposition devices are available with low-pressure chemical vapor deposition (LPCVD) and ultra-high vacuum chemical vapor deposition (UHVCVD) operating systems.
High temperature / low pressure sealed chamber
Low-pressure deposition systems typically operate in the pressure range of 0.1 to 10 Torr. Substrates are introduced into the transfer station using a load lock arrangement and FOUP protocol. Once the transfer station is evacuated to vacuum, a robotic processor transfers the substrate from the center chamber to the process chamber. The process chamber is sealed and the substrate is passed through CVD for thin film deposition.
When the process is complete, the substrate is either transferred to another process module (i.e., gate stack treatment, annealing, etc.) or to a cooling module before being transferred back to the transfer station where it is removed from the system.
Properties of a CVD lab-made diamond
The physical properties of CVD synthetic diamonds fall well within the range of natural diamonds in terms of hardness, thermal conductivity, strength, and so forth. Therefore, when cut into gemstone form, CVD synthetics exhibit the same brilliance and fire as natural diamonds and are just as hard and durable.
Crystallinity
A diamond can be a single, continuous crystal or it can be composed of many smaller crystals (polycrystals). Large, clear monocrystalline diamonds are commonly used as gemstones. Polycrystalline diamond (PCD) consists of many tiny particles that are easily visible to the naked eye through intense light absorption and scattering; these particles are not suitable for making gemstones and are used in industrial applications such as mining and cutting tools.
Hardness
The hardness of a laboratory-made diamond depends on its purity, crystal integrity, and orientation. It is worth noting that nanocrystalline diamond produced by CVD technology has a hardness of 30% to 75% of that of monocrystalline diamond and the hardness can be controlled depending on the specific application.
Impurities and inclusions
Each diamond contains atoms other than carbon in concentrations that can be detected by analytical techniques; when these atoms come together, they form macroscopic phases called inclusions. Black non-diamond carbon is the most common inclusion in CVD diamonds.
Thermal conductivity
The thermal conductivity of CVD diamond ranges from a few tens of W/m-K to 2000 W/m-K, which is related to defects, and grain boundary structure. As with CVD-grown diamonds, the grains grow with increasing film thickness, resulting in a gradient of thermal conductivity along the film thickness direction. Unlike most electrical insulators, pure diamond is an excellent heat conductor because it has strong covalent bonds in the crystal.
CVD lab-made diamond manufacturers
CVD lab-produced diamonds are preferred among manufacturers over HPHT lab-produced diamonds because of the technology's ability to grow diamonds over large areas and on a variety of substrates, coupled with the fine control of chemical impurities and the subsequent performance of the diamonds produced.
There are many dealers that make lab-grown diamonds, like Rolary™. Italian company Rolary™ is known for producing exquisite jewelry with lab-grown diamonds. Their slogan is "Accessible lab diamond jewelry that will accentuate your shine forever".
Rolary™ wants everyone to be able to enjoy the beauty of diamonds. Their scientists develop all of their products in-house and continually enhance and invest in their HPHT and CVD technology. Rolary™ strives to offer magnificent lab-grown diamonds at affordable pricing by using cutting-edge technology.
Machine learning (AI) changing diamond manufacturing
Machine learning is a subset of artificial intelligence (AI) that deals with computer algorithms that are automatically improved through experience. The effects of this technology extend all the way from helping manufacturers optimize their production processes and improve diamond production efficiency, to grading and daily sales of diamonds.
More flexibility In the diamond pipeline
The journey of a diamond from the mine to the store is long and difficult. It involves the use of a wide range of technologies, multiple specialized technologists, different manufacturing and polishing processes, various stages of the sales funnel, and other standard procedures. However, thanks to artificial intelligence, these processes are constantly being automated and streamlined to suit the socioeconomic climate.
Using AI-based technology to quickly and easily grade diamonds
Advanced scanning and imaging technology combined with machine learning-based grading algorithms allow diamond grading to be performed anywhere, anytime, without the need for extensive laboratory infrastructure. A popular example of this technology is Sarin Light - a grading standard based on actual measurements of a diamond's light properties. This cloud-based technology can assess a diamond's brilliance (reflected light), sparkle (flash), fire (burst of color), and photo symmetry in less than a minute.
Optimize manufacturing time
In order to maximize the quality of polished diamonds, manufacturers often turn to gemological laboratories for assistance. In many cases, the manufacturer may even send the diamond to the gemological laboratory multiple times for repeated grading and analysis. This stretches the production line, making the process longer, more costly, more cumbersome, and less efficient.
Fortunately, the use of artificial intelligence eliminates all this repetition, considering that diamond grading can be done anywhere and the results are immediate.
Your 3D digital jewelry experience
Two techniques have historically defined jewelry making: handcrafting and dewax casting. Both methods require a great deal of technical expertise, are time intensive, and mistakes in the process that can be costly. However, today's jewelers are able to use artificial intelligence software tools to digitally create intricate designs and print out high-resolution 3D jewelry patterns. This eliminates the need for time-consuming manual labor, and the designs themselves are easy to save, modify and recreate when needed.
Artificial intelligence is also used to create 360-degree animations that showcase jewelry models online in a way similar to the real-life viewing experience.
3D jewelry imaging with verto
Verto's artificial intelligence jewelry imaging service uses the camera on your mobile device and a special calibration table to help you create state-of-the-art, high-resolution 3D models of your jewelry. This technology enables users to display individual items from multiple views, change colors with a single click, and even display entire collections on a real model.
Lab-made diamonds are increasingly popular today because of the emotional attachment people have to each piece. Production technology allows people to create their own unique stones from scratch, or personalize them with meaningful details.
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