Zhang Daobiao
About the author: Zhang Daobiao, the first and second vice-chairman of the Artificial Gemstone Professional Committee of China Jewelry Association, the third senior consultant, former Shanghai Silicate Research of the Chinese Academy of Sciences Director and researcher of the Institute of Crystallography Research.
1. Research and development history of artificial gemstones
The research on artificial gemstones has a history of six to seven hundred years since the production of leaded glass gemstones in Egypt in the 15th century. In the beginning, because science and technology had not yet fully developed (until the end of the 19th century), its progress was relatively slow, and colorless and colored glass products were still the main products. Since Auguste Verneuil in France first synthesized rubies and sapphires using the flame fusion method in 1902, the development of artificial gemstones has entered a new stage. By 1907, the flame fusion method for synthesizing rubies could produce 5 million carats per year, marking a milestone turning point. Successfully researched synthetic gemstones were revealed one after another, and the development of artificial gemstones entered a stage of rapid progress.
Single crystal crystal was synthesized for the first time in 1908. By 1920, single crystal crystal without double crystals was being mass-produced for the electronics industry. At the same time, some colored crystals were also grown and industrialized.
Colorless, red and blue spinels were synthesized in 1920.
Rutile single crystal was synthesized in 1948.
Strontium titanate single crystal was synthesized in 1955. In the same year, General Electric Company of the United States synthesized fine-grained (0.15mm) diamond crystals for the first time. In the future, they continued to study large diamonds. In 1970, gem-quality diamonds were successfully synthesized for the first time.
In 1960, artificial colorless and green yttrium aluminum garnet (YAG) was successfully developed. Subsequently, artificial gadolinium gallium garnet crystals (GGG) and synthetic chrysoberyl were developed.
In the years after 1960, the flux method and hydrothermal method were developed to synthesize large-grain emerald crystals and ruby ??crystals.
In 1976, the Soviet Union synthesized large cubic zirconia gemstones, which were a better substitute for diamonds. After successful development, they were quickly put into production and developed rapidly, forming an industry.
In the late 1980s, glass imitation chrysoberyl cat's eye was successfully developed by the American company Calhag. Subsequently, it developed rapidly in my country and formed a glass cat's eye industry with an annual output of nearly 1,200t.
As of the 1980s, all important precious gemstones in the world could be synthesized artificially. Supporting production conditions have been established for the raw material manufacturing of these artificial gem crystals, crystal growth methods and processes, especially synthetic gemstones related to science and technology, economy and national defense have a certain production scale. For example, synthetic diamonds, synthetic sapphires, synthetic crystals, synthetic cubic zirconia, artificial crystal glass and their products have formed industrialization of different scales, promoting the country's scientific and technological progress and economic development.
Gem crystals such as artificial YAG, artificial GGG, artificial strontium titanate and synthetic lithium niobate, lithium tantalate and rutile are mainly used in electronic technology and laser technology; in terms of decoration, since the synthesis of cubic zirconia in large quantities After being launched on the market, their role as imitation diamonds gradually decreased, because these gem crystals are much less cost-effective than synthetic cubic zirconia, so they have faded out of the gem market. However, their application in electronic technology and optoelectronic technology is still developing rapidly, and people are constantly exploring and synthesizing many new crystals.
Although many precious gems have been synthesized, the quality indicators of gems are still unsatisfactory because they are not consistent with the petrographic structure, growth stripes, bubbles and inclusions of natural gems. The gap is still relatively large, it is easy to tell that it is a man-made product, and it does not have enough taste of natural gems.
2. Research progress on artificial gemstones in the past decade
In the past decade, the research work on artificial gemstones has been basically divided into two categories: one is for decoration; It is used in science and technology engineering series.
Research on artificial gemstones for decoration is basically focused on improving the quality of various synthetic gemstones, focusing on simulating and approaching natural gemstones; research on gemstones used in scientific and technological engineering series focuses on improving purity, crystal structure integrity and large size A single crystal emphasizing the functional properties of the gemstone. These two types of research are very different in terms of research content and goals, technical routes and equipment. This article mainly discusses the research progress of artificial gemstones for decoration.
1. Synthetic diamonds have made great progress
Large-grained synthetic diamonds were successfully synthesized for the first time in 1970 by the General Electric Company of the United States. Later, countries such as the United Kingdom, Russia, South Africa, and Switzerland also It has been announced one after another that they have synthesized large gem-quality diamonds, but due to low production efficiency and high cost, they have not been able to enter the market and are only experimental products. After more than 20 years of improving equipment and improving growth technology, the American company Gemesis has successfully developed equipment and technology that can stably produce 1 to 2 carats of yellow diamonds and blue diamonds (Figure 1). The production volume of 600 carats is put on the market, and the Gemesis manufacturing and number are laser-engraved on the waist of each diamond to protect the rights and interests of consumers. South Africa and Russia have also successively announced that they can produce large 1-4 carat yellow and blue diamonds (Figure 2) and bring them to the market. The successful development of this stable and mass-produced gem-grade diamond synthesis process marks a breakthrough in synthetic gem-grade diamonds, breaking the old concept that synthetic gem-grade diamonds are too expensive to enter the market. In the future, synthetic large gem-quality diamonds will be available in larger quantities.
Figure 1 Gemesis Company synthesizes large yellow diamonds and synthetic colored diamonds
Figure 2 Large diamonds synthesized by Debyer Company in South Africa
In the process of synthesizing industrial-grade diamonds On the other hand, all countries have made great efforts to improve quality and output. As the saying goes, "If you don't have diamonds, you can't do porcelain work." Various cutting tools, cutting and grinding tools, and geological drilling tools all use industrial-grade diamonds in large quantities, and synthetic industrial-grade diamonds are used in large quantities. Diamond production has become one of the indicators of a country's industrial level. Although the quality of industrial-grade diamonds synthesized in our country still needs to be improved, the output ranks first in the world, with an annual output of more than 1.2 billion carats.
CVD chemical vapor deposition method to grow diamonds and diamond films
In the past decade, CVD chemical vapor deposition method has been very active in growing diamonds. The American Apollo company uses CVD homoepitaxial technology to not only It can grow thick films of diamond single crystals, and can also grow single crystal diamonds, and has polished 0.25 carat diamonds (Figure 3, Figure 4). As the deposition thickness of thick films increases, large single crystal diamond blocks will become a reality in the near future, which is an attractive new technology.
Figure 3 Apollo's CVD furnace for synthetic diamonds
Figure 4 Apollo's CVD synthetic 0.25 carat diamond
2. Large particle synthetic moissanite ( Moissanite)
For more than ten years, synthetic silicon carbide large single crystal has developed rapidly. It is an important material for the third generation semiconductor substrate with wide bandgap and is an important material for the production of high voltage, high temperature resistance, Substrate materials necessary for low power loss and high-power devices have received national attention and support. At present, crystal ingots of (75~80) mm×50mm are mass-produced, mainly used in the semiconductor industry. Some of the crystal ingots do not meet IT-level requirements and will inevitably go to the gem industry. It can polish beautiful synthetic moissanite imitation diamonds, which are closer to diamonds than synthetic cubic zirconia and are more popular among people. This is a new member of synthetic gemstones since 1996. It is a major new development in synthetic gemstones. However, due to the high requirements of crystal growth technology and the small output of a single furnace, the cost performance of imitation diamonds is far inferior to that of synthetic cubic zirconia. It will not be used in the near future. Changing the dominance of synthetic cubic zirconia for imitation diamonds.
3. Hydrothermal synthesis of rubies, synthetic star gems and synthetic emeralds
The hydrothermal synthesis of rubies, synthetic star gems and synthetic emeralds has been carried out in the laboratory for more than ten years The work on Gem is a lot, on and off, and never stops.
First of all, in order to achieve more simulation and overcome the obvious arc-shaped growth stripes and string-shaped bubbles in rubies synthesized by the flame melting method and the Czochralski method, a high-temperature and high-pressure hydrothermal method was used to study the growth. The hydrothermal method mainly simulates the conditions of natural gemstone mineralization, using natural gemstone wafers as seeds (this is different from the spontaneous nucleation of rubies grown by the flux method). The large ruby ??crystals grown have both hexagonal growth stripes and the illusion of the petrographic structure of natural gemstones. These crystals can be polished to produce ruby ??rings of 5 to 8 carats or even larger. Many countries, such as Russia, the United States, India, and Switzerland, are constantly listing hydrothermal-method rubies and yellow sapphires. Now some companies are planning to build 70-100mm corrosion-resistant high-pressure axes to grow 50-60mm rubies, and are gradually developing more The prospect of simulating and closer to natural rubies, blue and yellow sapphires, star gemstones, etc., and creating mass production capabilities is optimistic.
Similarly, hydrothermal growth of synthetic emeralds has also been successful. Large emeralds can be grown in the United States, Switzerland, Russia and China. However, the current market demand is not strong and it is difficult to pull them. Therefore, the hydrothermal method of growing emerald crystals is progressing slowly and has not been put into mass production.
4. Use melt pulling method, melt soaking method and melt heat exchange method to develop colorless sapphire
At present, the research and development of colorless sapphire in various countries is advancing by leaps and bounds. It has the characteristics of high infrared transmittance, high strength and high temperature resistance. It has good application space in the defense industry and can be used as window materials and missile head covers; it is used as gallium nitride (GaN) coating in optoelectronic technology. Substrate is an important material in semiconductor lighting engineering. The quality requirements must reach IT level. The demand is huge and relevant companies in many countries are working hard to develop it. At present, the Czochralski method can be used to grow large single crystals of colorless sapphire with a diameter of 120 to 200 mm; the bubble method can be used to grow a colorless sapphire with a diameter of 200 to 250 mm and a weight of 25 to 30 kg (Figure 5); the heat exchange method has been used to grow the world's largest single crystal of colorless sapphire. The largest sapphire in the world has a diameter of 34cm and weighs 68kg (Figure 6). Although many companies in our country are actively developing large-diameter sapphire crystals and have made great progress, they do not yet have the scale for mass production, and substrates for LEDs are basically imported.
5. Synthetic long afterglow artificial luminous gems
Long afterglow artificial luminous gems were successfully developed by Beijing Hualong Yayang Company in my country in 1996 and named "Qinglong luminous gems" , has obtained invention patents from China, the United States, South Korea and other countries. It has excellent performance, no radioactivity, high afterglow brightness and long lasting effect, which is better than the natural "night pearl". Artificial luminous jade in colors such as green, blue-green, milky white, red and purple has been developed. Large pieces of artificial luminous jade can be used to carve large-scale crafts. At present, it has been mass-produced and the supply exceeds the demand, and it is expected to be industrialized.
6. Synthetic turquoise and malachite
The research and development of synthetic turquoise and malachite in the United States and Russia has never stopped. At present, the large pieces of malachite synthesized can weigh up to 8-10kg, and there is a certain market for making sculptures and furnishings.
7. Glass imitation gemstones
Although glass imitation gemstones are very old, they are also a type of imitation gemstones that are constantly advancing and developing with the times. Although it is a low- to mid-range imitation gemstone, today's glass jewelry and handicrafts are much more beautiful than those of more than ten years ago. The quality and taste of glass-imitation diamond "rhinestones" have been greatly improved, and their market share is not small. Especially today, when people's decoration concepts have changed, requiring fashion, high quality and low price, and frequent replacement of jewelry, novel glass products have become the first choice, such as Austrian Swarovski lead glass imitation crystal and imitation diamond decoration series Products, imitation gemstone jewelry of colored glass and rare earth glass, imitation opal jewelry, lead glass crafts, prizes, souvenirs and furnishings are all fashionable and very popular. Glass imitation gemstones have gained people's recognition and have developed rapidly in the past few years.
In recent years, breakthroughs have been made in the development of automated production lines for glass imitation diamonds. It not only promotes the industrial production of lead glass imitation diamonds, but will also significantly promote the processing industry of other artificial gemstones. effect.
Since heavy metal lead is toxic to the human body, high-lead glass jewelry will be strictly restricted. People are conducting research on cheap lead-free high-refractive index crystal glass and reducing the cost of rare earth glass, both of which are alternatives. Major measures regarding leaded glass should be taken seriously.
3. In-depth research and development of industrialized artificial gemstones
Synthetic diamonds, synthetic crystals, synthetic moissanite and synthetic large-size colorless sapphires are mainly used in science and engineering technology, and are related to The requirements of the gem industry are different and will not be discussed here.
1. Synthesis of rubies and sapphires by flame fusion method
Currently, the growth of rubies and sapphires by flame fusion method has reached a considerable scale. The world’s annual output reaches more than 1,000 tons, and China’s output is More than 300 tons, accounting for about 1/3 of world production. However, the quality of the crystals needs to be improved, and the production cost is still high. If we want to push the industry forward, we must make full use of the surplus hydrogen and oxygen gas energy in relevant chemical plants and strive to increase the daily output of a single furnace.
Using surplus hydrogen from chemical plants directly changes the problem of high power consumption. According to the past electrolysis of water to obtain hydrogen, 1100kW·h of electricity was needed to produce 1kg of ruby. Due to the increase in electricity prices, the production cost is very high. By switching to the surplus hydrogen from chemical plants, the electricity savings can be considerable. However, the purification of hydrogen must be improved, otherwise the quality and yield of gems will be affected.
The research and development content to increase the daily output of a single furnace refers to changing the equipment structure and production process. On the basis of the current daily output of 6 rubies of 70-80g in a single furnace, the diameter of the crystal should be slightly increased, and the length of the crystal should be lengthened. For example, the furnace should be enlarged to improve the heat preservation capacity of the furnace, appropriately expand the diameter of the gas nozzle and ensure the stability of the gas supply. properties, improve flame temperature distribution, increase raw material purity and fineness, etc. This is an important part of R&D work. It is a systematic engineering R&D. There is room for innovation. It is expected to improve crystal quality and increase the daily output of a single furnace by about 2 times. It can be seen that It has great potential and deserves attention, especially if the product must be closely integrated with market requirements.
2. In-depth research and development of synthetic cubic zirconia
Synthetic cubic zirconia has formed an industry in my country, and its current output ranks first in the world. Due to the relatively low market prices, manufacturers are under greater pressure.
At present, we should attach great importance to the research and development of new varieties with high added value and reduce the production of some low-value products. The color of the product is important. Emerald green, London blue, ocean blue and carmine red synthetic cubic zirconia are all very popular, and their prices are also higher, so new cubic zirconia colors that people like are developed. Zirconia is a topic that guides the continuous development of the production of synthetic cubic zirconia, because cubic zirconia has a high refractive index, large dispersion, high hardness, and is easy to produce on a large scale, especially with high cost performance, which is far beyond the comparison of other artificial gemstones. On this basis, the introduction of colors that people love will surely last forever.
Figure 7 Emerald YZrO2
Synthetic cubic zirconia production is a large consumer of electricity. The problem of electricity consumption has always troubled manufacturers, and the production plants have been moved to remote areas where low-cost electricity is available. In mountainous areas, this is a temporary solution, but it is not a long-term solution. Research on reducing power consumption per unit production is an issue that cannot be ignored. The power consumption in early production was about 200kW·h/kg crystal, and recently the power consumption has dropped to about 80kW·h/kg crystal. It is now expected to drop to less than 60 kW·h/kg crystal. Reducing power consumption is the comprehensive result of many factors. Equipment reform, especially the use of transistor high-frequency generators, plays an important role.
References
He Xuemei, Shen Caiqing.2005. Gemstone synthesis technology. Beijing: Chemical Industry Press.
Chandra P.Khattak, Frederick Schmid.2001 .Growth of wourd's largest sapphire crystals.Journal of crys-tal growth.225, 572～579.
Geology, 198B, Lesson 9: Synthetics and simulants.
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