Although diamond mining does not leave as much toxic chemical waste as the extraction of precious metals, it involves the creation of deep pits, which means disturbing the soil and possibly cutting down the forest at the site of the deposit. All these factors can lead to changes in the ecosystem and should be considered. So based on our experience and ecological trends, we decided to focus first on synthetic diamond production analysis with the two most popular methods: HPHT and MPCVD, and then consider diamond mining.
This estimation of labor input is applicable to (near-) colorless medium-sized rough diamonds and will be significantly different for the production of either “dark” nitrogen-rich or small diamonds (). The presence of nitrogen in the HPHT chamber can significantly enhance the speed of growth, as nitrogen readily replaces carbon (С) and produce solid solution. Growing many smaller diamonds in a chamber requires less time than growing larger ones. One press can produce small-sized diamonds in days, or medium-sized ones in weeks. The total mass of diamonds will depend on the graphite mass at the beginning of each cycle. Therefore, more nitrogen and a smaller target size result in greater productivity for an HPHT press, but the resulting diamonds are generally small, yellowish to dark brown in color, and are, therefore, less economically attractive to producers. We, therefore, focus on nitrogen-free (near-) colorless medium-sized diamonds, which are well-priced and are generally in more demand.
Taking all of this into consideration, we arrived at the following simple calculations for Russian based ( Eq. (1) ) and Chinise based companies ( Eq. (2) ), respectively:
The core personnel, who are responsible for the entire process, are the operators, engineer-technologists, and chemists. They reload and launch the presses approximately once every 12 days, and control all the parameters during the process, including pressure and temperature; they also mix metal powders (iron with cobalt, nickel, and other additives) with graphite and the initial diamond seed(s). They extract the newly created diamonds at the end of the synthesis operation and use strong acids to remove them from the metal medium. This group of staff accounts for the main core competence () of the operation and an inexperienced operator/technologist/chemist would reduce the performance dramatically. Other staff play supporting roles in the HPHT team, each focusing on a particular function that maintains the process. These roles include highly skilled engineers, suppliers, and administrators. Each role is important to ensure that the HPHT process runs on the 24/7 regime. Typically, these professionals work 40 h per week.
Chapter 1 - the core competence of the corporation∗ ∗reprinted by permission of harvard business review, May–June 1990, pp. 79–91. Copyright (1990 by the resident and fellows of harvard business college, all rights reserved.
This table shows approximately 32 people are needed to support a 30-press HPHT array, operating on a 24/7 regime, and growing approximately 700 carats of gem-quality average-sized (near-) colorless diamonds per week.
An example of people distribution in an array of 30 HPHT presses is presented in Table 1
Our calculation considers a typical HPHT array consisting of 30 modern HPHT presses comprising two models, with working cylinder diameters of 750 mm and 850 mm, respectively. The yearly productivity of each press according to data of NDT company is approximately 1200 carats of jewelry-size colorless and near-colorless (D-J according to Gemology Institute of America classification (“”)) diamonds. The total productivity of a 30-press HPHT array is therefore nearly 700 carats per week if the machines are working on a 24/7 regime. In case of Chinise companies, yearly productivity of each press is approximately 2400 carats. The total productivity of a 30-press HPHT array is therefore nearly 1380 carats per week if the machines are working on a 24/7 regime.
HPHT presses are typically assembled into an array, to optimize water-cooling, energy supply, and operational services. The total number of presses in one array varies widely between different manufactures. China-based market leaders use arrays of hundreds of presses, while quality-focused EU, Russia, and Ukraine “art-growers” use arrays of only a few presses. After visiting many HPHT facilities we arrived at a simple estimation: on average, one person is required to operate each press.
Our observations revealed that the common modern HPHT presses are highly productive, producing approximately 1200 carats per year, as confirmed by the published data of the Russia-based company New Diamond Technology (NDT), which is one of the global technological leaders in the HPHT area (). The ability to grow approximately 1200 carats per year, using commercially-available HPHT presses, is very important in our further calculations of labor input which depends on press productivity (). However, each manufacturer for a set HPHT process has its own recipe with its own temperature and pressure modes and correspondingly its own performance. Moreover, as technology develops, the data changes rapidly and in most cases this information is kept confidential. The leading manufacturers of cubic presses on an industrial scale are currently Chinese companies. Using their upgraded HPHT press, it is possible to synthesize on average up to 200 carats of diamonds per month, respectively about 2400 carats per year, depending on the technology, size of synthesized crystals and quantity of initial seed diamonds. (“”)
Tiny diamond seeds are initially placed into the mix in the chamber and later become the centers of nucleation. However, if the aim is to produce only powder-like diamonds, no seeds are needed. A powerful hydraulic system shown in Figure 1 pressurizes the chamber, up to 6 GPa, and an internal heating controller supports temperatures of approximately 1500 °C ().
The HPHT method reflects the natural process of diamond formation under high pressure and temperature (). Central to the HPHT process is a chamber that contains a mix of iron, cobalt, nickel, and graphite (which acts as the source of carbon).
3.2 MP CVD
The MP CVD method of growing diamonds is very different from the HPHT method and does not replicate a natural process. It uses methane-hydrogen plasma, instead of an iron-based graphite melt, and takes place in a low vacuum inside a CVD chamber. The CVD method allows for the creation of complicated crystal structures for jewelry, optics and electronics and precise control of all relevant synthetic parameters.
Glyavin et al., 2020 Glyavin M.
Sabchevski S.
Idehara T.
Mitsudo S. Gyrotron-based technological systems for material processing—current status and prospects. Vikharev et al., 2006 Vikharev A.L.
Gorbachev A.M.
Kozlov A.V.
Koldanov V.A.
Litvak A.G.
Ovechkin N.M.
Radishev D.B.
Bykov Yu.V.
Caplan M. Diamond films grown by millimeter wave plasma-assisted CVD reactor. Ando et al., 2002 Ando Y.
Yokota Y.
Tachibana T.
Watanabe A.
Nishibayashi Y.
Kobashi K.
Hirao T.
Oura K. Large area deposition of ⟨100⟩-textured diamond films by a 60-kW microwave plasma CVD reactor. Diamond and related materials, 12th European conference on diamond, diamond- like materials, carbon nanotubes. Horino et al., 2006 Horino Y.
Chayahara A.
Mokuno Y.
Yamada H.
Fujimori N. High-rate growth of large diamonds by microwave plasma chemical vapor deposition with newly designed substrate holders. Silva et al., 2009b Silva F.
Hassouni K.
Bonnin X.
Gicquel A. Microwave engineering of plasma-assisted CVD reactors for diamond deposition. We have already mentioned the disadvantages of HF and DC CVD, related to the risk of impurity. Such impurities are undesirable for electronic and optic projects, which is why we limit our analysis to MP CVD, where plasma is usually created by a magnetron (gyrotron-supported CVD reactors are also used, but are not very common ()). CVD reactor magnetrons operate on specific frequencies of 915 MHz () or 2.45 GHz (). As the authors of this study have no experience using 915 MHz magnetrons, we have limited our discussion to the 2.45 GHz MP CVD method. In the CVD process, the speed of diamond deposition, and therefore the productivity, depends to a large extent on the plasma density (), though many other parameters must also be taken into consideration. If all other parameters are equal (including magnetron power and the inner pressure of the CVD chamber), the main difference between the two magnetron frequencies is the plasma distribution. A 915-MHz magnetron results in a larger plasma “spot” than a 2.45-GHz magnetron.
4 is a widely used source of carbon in the CVD process, although some researchers have successfully used other carbon-based gasses ( Kitaura et al., 2015 Kitaura R.
Miyata Y.
Xiang R.
Hone J.
Kong J.
Ruoff R.S.
Maruyama S. Chemical vapor deposition growth of graphene and related materials. 2 ), with only a small fraction of methane, just enough to support deposition ( The labor input for the CVD process is also correlated with the mix of gasses that are used. Methane CHis a widely used source of carbon in the CVD process, although some researchers have successfully used other carbon-based gasses (). Such process has one major disadvantage in that it is explosive, which demands more attention when working to avoid any risk to staff. This fact is important for labor input, as someone experienced should be responsible for methane supply. On average, the plasma in the CVD reaction is based on hydrogen (H), with only a small fraction of methane, just enough to support deposition ( Figure 2 ). Although hydrogen is even more explosive than methane, modern hydrogen stations can work automatically on a 24/7 regime and do not require a lot of staff attention, and one hydrogen station can easily support an array of CVD reactors.
Figure 3 Photo of growing process in CVD reactor after a few days of synthesis.
Technical Specifications|ARDIS 300, Technical Specifications|ARDIS 300 Liang et al., 2009 Liang Q.
Yan C.
Meng Y.
Lai J.
Krasnicki S.
Mao H.
Hemley R.J. Recent advances in high-growth rate single-crystal CVD diamond. Diamond and related materials. Silva et al., 2009a Silva F.
Achard J.
Brinza O.
Bonnin X.
Hassouni K.
Anthonis A.
De Corte K.
Barjon J. High quality, large surface area, homoepitaxial MPACVD diamond growth. Diamond and Related Materials. We observed that the average deposition rate of a 2.45-GHz MP CVD reactor is approximately 35 μm/h (sometimes exceeding 50 μm/h or 100 μm/h) (“”) especially at the end of the cycle, but much lower at the beginning (). Following this, 1–2 days of downtime is required to reload the reactor. Based on our observations, each reactor we studied was able to synthesize, on average, 7 carats per week in a single-crystal regime (illustrated in Figures 3 and 4 ). There is one curious advantage of CVD synthesis: the growth of the diamond can be observed ( Figure 3 ), which is impossible during the HPHT process.
Figure 4 Cubic-shaped recently synthesized MP CVD diamond with parasitic polycrystalline jacket. This process is, therefore, beyond the upstream stage and has been omitted from our calculations.
Our observations are based on a relatively small MP CVD array of only 5 reactors. However, to make the estimate of hourly labor input more realistic we have based our estimate on an array of 10 reactors, as we feel that is the optimal number for a CVD array. To clarify: despite there being a positive correlation between the number of reactors and business performance, a 10-reactor unit can be run by only 1 operator, and so it can be used as the building block to construct larger arrays.
• Clean the chamber via different protocols (for hydrogen and oxygen usage) to remove all parasitic layers. If this is not done, the diamond will be impure.
• Schermer et al., 1995 Schermer J.J. van Enckevort W.J.P. Giling L.J. Orientation dependent surface stabilization on flame deposited diamond single crystals. Input a correctly oriented diamond seed (the Miller index () should be {100} to maximize the speed of deposition), avoiding any pollution on its surface.
• Start the synthesis, carefully raising the temperature and controlling the hydrogen-methane mix and the pressure (less than 1 atm) in the resonator.
• Thumm, 2011 Thumm M. Progress on gyrotrons for ITER and future thermonuclear fusion reactors. Maintain the vital parameters during the whole cycle (which can last for days, weeks, or even months (if growing a polycrystalline diamond window for the International Thermonuclear Experimental Reactor (ITER) project ()).
• Slow down plasma in the reactor before stopping it.
• Extract the diamond and repeat the process. Each reactor requires servicing, including regular downtime, and all vital parameters must be controlled during the synthesis process. This means that an experienced member of staff is required to perform the following tasks:
All the tasks mentioned above require highly skilled professionals: there should be someone near the reactor throughout the 24/7 regime, one person should be responsible for the more complicated process of re-loading, and another person should manage all the processes, including the supply operations (e.g. methane delivery and the purchase of spare parts). Thus, if staff work 8-hour shifts, an array of up to 10 MP (or HF) CVD reactors requires at least 4 CVD operators, 1 senior grower (or head of the laboratory, in our terminology), and 1 administrator ( Table 2 ):
Table 2 The staff required to support an array of 10 2.45-GHz MP CVD reactors. Functionality Total Operators 4 Senior grower (head of the laboratory) 1 Administrator (supply, external operations) 1 Total 6
6∗40 h worked per week/70 carat = 3,43 h worked per carat (hw/ct), (3)
We use the same approximation as for the HPHT process, i.e., an average of one person per reactor. Therefore, our estimate of labor input required per carat for an array of 10 CVD reactors is as follows ( Eq. (3) ):