Research on the Development of Artificial Products

About the author: Zhang Daobiao, the first and second vice-chairmen of insurance institute of china Artificial Products Professional Committee, the third senior consultant, the former director and researcher of the Crystal Research Office of Shanghai Institute of Silicate, China Academy of Sciences.

I research and development of artificial products

The research of artificial products has a history of 6700 years, which began with the production of lead-containing glass gems by Egyptians in the15th century. At first, because the technology has not been fully developed (until the end of 19), its progress is relatively slow, mainly colorless and colored glass products. Since August Vernay, a Frenchman, first synthesized rubies and sapphires by flame melting in 1902, the development of artificial products entered a new stage. By 1907, the annual output of ruby synthesized by flame melting will reach 5 million carats, which is a milestone turning point. Subsequently, successfully synthesized gems were displayed one after another, and the development of artificial products entered a rapid stage.

1908 first synthesized single crystal. By 1920, amorphous single crystals have been mass-produced and used in electronic industry. At the same time, some colored crystals have been grown and industrialized.

Colorless, red and blue spinels were synthesized by 1920.

Rutile single crystal was synthesized in 1948.

1955 was used to synthesize strontium titanate single crystal. In the same year, General Electric Company of the United States synthesized fine-grained (0. 15mm) diamond crystals for the first time. Since then, they have been devoted to the research of big diamonds. 1970 successfully synthesized gem-grade diamonds for the first time.

1960, artificial colorless green yttrium aluminum garnet (YAG) was successfully developed. Subsequently, artificial gadolinium gallium garnet crystals (GGG) and synthetic emeralds were developed.

In the years after 1960, the flux method and hydrothermal method were developed to synthesize large emerald crystals and ruby crystals.

1976, the Soviet Union synthesized a cubic zirconia gem, which is a good substitute for diamonds. After successful development, it was put into production, developed rapidly and formed an industry.

In the late 1980s, Calhag Company of the United States successfully developed a glass imitation gold emerald cat's eye. Then it developed rapidly in China and formed the glass cat's eye industry, with an annual output of nearly1200 t.

By the 1980s, all the important gems in the world could be synthesized artificially. The raw material manufacturing, crystal growth methods and processes of these artificial crystals have successively established supporting production conditions, especially the synthetic gems related to science and technology, economy and national defense have reached a certain production scale. Such as artificial diamond, artificial sapphire, artificial crystal, artificial cubic zirconia, artificial crystal glass and its products have all formed industrialization of different scales, which has promoted the scientific and technological progress and economic development of the country.

Artificial YAG, artificial GGG, artificial strontium titanate and synthetic gem crystals such as lithium niobate, lithium tantalate and rutile are mainly used in electronic technology and laser technology; In terms of decoration, since synthetic cubic zirconia was put on the market in large quantities, their role as imitation diamonds has gradually decreased, because the price-performance ratio of these gem crystals is far lower than that of synthetic cubic zirconia, so they have faded out of the gem market. However, their applications in electronic technology and photoelectron technology are still developing rapidly, and people are still exploring and synthesizing many new crystals.

Although many precious gems have been synthesized, according to the quality index of gems, they are still unsatisfactory, because there is still a big gap between them and natural gems in lithofacies structure, growth stripes, bubbles, inclusions and so on, and it is easy to distinguish that they are artificial products and do not have enough taste of natural gems.

Second, the research progress of artificial products in recent ten years.

In recent ten years, the research work in artificial products is basically divided into two categories: one is used for decoration; The other type is used in science and technology engineering series. The research of decorative artificial products is basically around improving the quality of various synthetic gems, focusing on the simulation and approximation of natural gems; It is used in the research of gemstones in science and technology engineering series, focusing on improving purity, crystal structure integrity and large-size single crystal, and emphasizing the functional characteristics of gemstones. These two kinds of research are quite different in research contents and objectives, technical routes and equipment. This paper mainly discusses the research progress of decorative artificial products.

1. Great progress has been made in synthesizing diamonds.

1970 American general electric company successfully synthesized large-particle synthetic diamonds for the first time. Later, Britain, Russia, South Africa and Switzerland also announced the synthesis of gem-grade large-particle diamonds, but they failed to enter the market because of low production efficiency and high cost, and were only experimental products. After more than 20 years of equipment improvement and growth technology improvement, Gemesis Company of the United States has successfully developed the equipment and technology that can stably produce yellow diamonds and blue diamonds with the size of 1 ~ 2 carats (Figure 1), and put it on the market with a monthly output of 600 carats. The waist of each diamond is engraved with Gemesis manufacturing and number by laser to protect consumers' rights and interests. South Africa and Russia also announced that they can produce 1 ~ 4 carats of rhubarb diamonds and blue diamonds (Figure 2) and put them on the market. The successful research and development of this stable mass-produced gem-grade diamond synthesis process marks a breakthrough in the synthesis of gem-grade diamonds and breaks the old concept that the cost of synthesizing gem-grade diamonds is too high to enter the market in the past. In the future, there will be a large supply of artificial gemstone diamonds.

Figure 1 Gemesis Company Synthetic Rhubarb Diamond and Synthetic colored diamond.

Fig. 2 Large diamonds synthesized by Derbyl Company in South Africa.

In the synthesis of industrial-grade diamonds, all countries are striving to improve the quality and output. As the saying goes, "Without Jin Gangzuan, we wouldn't be engaged in porcelain work." Industrial-grade diamonds are widely used in all kinds of cutting tools, cutting tools and geological drilling tools, and the output of synthetic industrial-grade diamonds has also become one of the symbols to measure the industrial level of a country. At present, the industrial grade diamond synthesized in China ranks first in the world, with an annual output of 654.38+0.2 billion Dockwra, although the quality needs to be improved.

Growth of diamond and diamond films by CVD chemical vapor deposition

In recent ten years, CVD chemical vapor deposition has been very active in growing diamonds. American Apollo company can grow not only single crystal thick film but also single crystal diamond by using CVD homoepitaxy technology, and has polished 0.25 carat diamond (Figures 3 and 4). With the increase of thick film deposition thickness, large single crystal diamond will become a reality in the near future, which is a very attractive new technology.

Fig. 3 Apollo CVD diamond synthesis furnace.

Fig. 4 0.25 carat diamond synthesized by CVD method of Apollo company.

2. Large particle synthesis in moissanite.

In recent ten years, the synthetic large single crystal of silicon carbide has developed rapidly. It is an important material for the third generation wide band gap semiconductor substrate, and it is also an essential substrate material for the production of high voltage, high temperature, low power consumption and high power devices, which has been valued and supported by the state. At present, mass production of (75 ~ 80) mm× 50 mm ingots is mainly used in semiconductor industry. Some of them do not meet the IT requirements and will inevitably flow to the GEM industry. It can polish beautiful synthetic moissanite imitation diamond, which is closer to diamond than synthetic cubic zirconia and more popular. This is a new member of synthetic gemstones since 1996, and it is a major new progress in synthetic gemstones. However, due to the high requirements of crystal growth technology and small output per furnace, the cost performance of synthetic cubic zirconia is far less than that of synthetic cubic zirconia, and the dominant position of synthetic cubic zirconia in diamond-like will not change in the near future.

3. Hydrothermal synthesis of ruby, starlight and emerald.

In the past ten years, there have been a lot of hydrothermal synthesis of rubies, starlight gems and emeralds in the laboratory, and they have never stopped. Firstly, for better simulation, the growth of ruby synthesized by flame melting method and Czochralski method was studied by hydrothermal method at high temperature and high pressure. Hydrothermal method mainly simulates the metallogenic conditions of natural gemstones, using natural gemstone wafers as seeds (which is different from the spontaneous nucleation of rubies grown by flux method). The grown large ruby crystal not only has hexagonal growth stripes, but also has the illusion of natural gem phase structure. These crystals can polish 5-8 carats or even larger red gem ring. Russia, the United States, India, Switzerland and many other countries have continuously listed hydrothermal rubies and yellow sapphires. Now, some companies are planning to build 70 ~ 100 mm corrosion-resistant high-pressure shafts, and plan to plant 50 ~ 60 mm rubies, and gradually develop more simulated and natural rubies, blue-yellow sapphires and starlight sapphires. And create the ability of mass production. The outlook is optimistic.

Similarly, the hydrothermal growth and synthesis of emeralds is also very successful. The United States, Swiss, Russian and China can all grow large emeralds. At present, the market demand is not strong, and it is difficult to pull them. Therefore, the growth of emerald crystals by hydrothermal method is slow and has not been put into mass production.

4. Colorless sapphire was prepared by melt pulling method, melt kyropoulos method method and melt heat exchange method.

At present, the research and development of colorless sapphire in various countries is advancing by leaps and bounds. Because of its high infrared transmittance, high strength and high temperature resistance, it has a good application space in national defense industry and can be used as window material and missile hood. Gallium nitride (GaN) coated substrate in optoelectronic technology is an important material in semiconductor lighting engineering. The quality requirements reach IT level, and the demand is great. Related companies in many countries are developing it. At present, colorless sapphire single crystals with a diameter of 1.20 ~ 200 mm can be grown by Czochralski method. Colorless sapphire with a diameter of 200 ~ 250 mm and a weight of 25 ~ 30kg can be grown by kyropoulos method (Figure 5). The world's largest sapphire was grown by heat exchange method, with a diameter of 34 cm and a weight of 68 kg (Figure 6). Although many domestic companies are actively developing large-diameter sapphire crystals and have made great progress, there is no mass production scale at present, and the substrates for LED are basically imported.

5. Long afterglow artificial luminous gems.

The artificial luminous gem with long afterglow was successfully developed by Beijing Hualong Yang Ya Company on 1996 and named "Qinglong Luminous Gem", which has been patented by China, the United States, South Korea and other countries. Excellent performance, no radioactivity, high afterglow brightness and long aging time, superior to natural "night pearl". Artificial luminous jade in green, blue-green, milky white, red and purple has been developed, and large pieces of artificial luminous jade can be used to carve large handicrafts. At present, it has been produced in large quantities, which is in short supply and is expected to form industrialization.

Fig. 5 Large-size sapphire crystal grown by melting kyropoulos method.

95 mm in diameter and 1 10 mm in height.

Fig. 6 growth of sapphire with a diameter of 34 cm by heat exchange method

6. Synthetic turquoise and malachite

The research and development of synthetic turquoise and malachite in the United States and Russia has been uninterrupted. At present, the synthetic malachite can reach 8 ~ 10 kg, which has a certain market for carving decorative parts.

7. glass imitation gems

Although the glass imitation gem is very old, it is also a kind of imitation gem that keeps pace with the times and develops constantly. Although it is a low-grade imitation gem, the glass ornaments and handicrafts nowadays are much more beautiful than those ten years ago. The quality and taste of "rhinestones" made of glass imitation diamonds have been greatly improved, and the market share is not small. Especially in today's changing decoration concept, fashion, high quality, low price, frequent replacement of accessories and novel glass products are the first choice. For example, Swarovski lead glass imitation crystal and imitation diamond decorative series products, colored glass and rare earth glass imitation gem ornaments, imitation opal ornaments, lead glass handicrafts, prizes, souvenirs and furnishings are all fashionable and very popular. Glass imitation gems have been recognized by people and developed rapidly in recent years.

In recent years, breakthrough has been made in the research and development of the automatic production line of glass imitation diamond, which not only promotes the industrial production of lead glass imitation diamond, but also greatly promotes other processing industries of artificial products.

Because heavy metal lead is toxic to human body, high lead glass ornaments will be strictly restricted. People are studying cheap lead-free high refractive index imitation crystal glass to reduce the cost of rare earth glass, which is an important measure to replace lead glass and should be paid attention to.

Third, the deepening of R&D in industrial man-made products.

Synthetic diamonds, synthetic crystals, synthetic moissanite, and synthetic large-size colorless sapphires are mainly used in scientific and technological projects, which are different from the requirements of the gem industry, and will not be discussed here.

1. Synthesis of Ruby and Sapphire by Flame Melting

At present, the ruby and sapphire grown by flame melting method have reached a considerable scale, with the annual output in the world reaching more than 1 1,000 tons, and that in China is more than 300 tons, accounting for about13 of the world output. However, the crystal quality needs to be improved, and the production cost is still high. In order to promote the development of industry, we must make full use of the surplus hydrogen and oxygen energy of related chemical plants and strive to increase the daily output of a single furnace.

The utilization of residual hydrogen in chemical plants directly changes the problem of high electricity consumption; According to the past, electrolytic water production 1kg ruby needs1100 kw h electricity, and the production cost is very high due to the increase of electricity price. Switching to the residual hydrogen in chemical plants can save a lot of electricity. However, the purification of hydrogen must be improved, otherwise the quality and output of gems will be affected.

The research and development content of increasing the daily output of a single furnace refers to changing the equipment structure and production technology. Based on the current daily output of six rubies of 70 ~ 80g per furnace, the crystal diameter is slightly increased and the crystal length is lengthened. For example, make the furnace bigger, improve the heat preservation capacity of the furnace, appropriately expand the diameter of the gas nozzle and the stability of gas supply, improve the flame temperature distribution, and improve the purity and fineness of raw materials. This is an important content of research and development, and it is a systematic engineering research and development. There is room for innovation, which is expected to improve the crystal quality, and the daily output of a single furnace is increased by about 2 times, showing potential.

2. Further research and development of cubic zirconia synthesis.

Synthetic cubic zirconia has formed an industry in China, and its output ranks first in the world at present. Because the market price is relatively low, manufacturers are under great pressure.

At present, we should pay attention to the research and development of new varieties with large added value and reduce the production of some low-value products. The color of the product is very important. The synthetic cubic zirconia of emerald, London blue, navy blue and carmine is very popular and the price is high. Therefore, the research and development of cubic zirconia with a new color that people like is a subject to guide the continuous development of synthetic cubic zirconia production, because cubic zirconia has high refractive index, large dispersion and high hardness, which is easy for mass production, especially high cost performance, which is far from being compared with other artificial products. On this basis, people can introduce their favorite colors.

Fig. 7 emerald YZrO2

The production of synthetic cubic zirconia is a big power consumer, and the power consumption problem has been puzzling manufacturers. Moving the production plant to a remote mountainous area with low electricity cost is a temporary feasible solution, but it is not a long-term solution. How to reduce the power consumption per unit area is a problem that cannot be ignored. The power consumption of early production was about 200 kW h/kg crystal, and recently it was reduced to about 80 kW h/kg crystal. Now it is expected to be lower than 60 kW h/kg crystal. Reducing power consumption is the comprehensive result of many factors, and the transformation of equipment, especially the use of transistor high frequency generator, plays an important role.

refer to

He, Shen. 2005. Gemstone synthesis technology. Beijing: Chemical Industry Press.

Frederick schmid Chandra Kartak Growth of the world's largest sapphire crystal. Journal of crystal growth, 225, 572~579.

Geology, 198B, lesson 9: synthetic materials and analog materials.

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