Thinner than a cicada's wing and finer than a hair - this metal can be used in industry as well as for food and medicine?

1. Gold Leaf

1.1 Characteristics of gold foil

Gold is the most ductile metal. Gold can be made into very thin sheets, called gold foil. How thin can gold foil be? Surprisingly, it can be as thin as 0.1 µm, which means it can be as thin as one ten-thousandth of a mm. Using a 1 cm3 block of gold, you can make a gold foil with an area of ​​100 m2. You must all know the cicada, right? The cicada wing is the cicada's wing, and the phrase "as thin as a cicada wing" is often used to describe something very light and thin. But according to measurements, the thickness of a cicada wing is about 0.12 mm, which means that you need 1,200 sheets of gold foil stacked together to make it as thick as a cicada wing. It's incredible! The thickness of gold foil can of course be adjusted, that is, within a certain range, its thickness can be freely varied.

When the gold foil is so thin, it is transparent. Through this gold foil, you can see the scenery on the other side. Generally speaking, the scenery you see through a red glass will be red. So what color is seen through the transparent gold foil? Is it gold? No! Incredibly, it is green. This is because gold has a strong ability to reflect yellow and red light, and most of these colored lights are reflected. Therefore, even red leaves will magically turn green when viewed through gold foil (Figure 1). A long time ago, this characteristic was used to determine whether gold is real or fake: the material to be determined is made into foil. Then look through it to see if the scenery on the other side is green. If it is real gold, then what you see should be green, otherwise it is not real gold.

Another way to distinguish the authenticity of gold foil is by its thickness. Real gold foil is much thinner than imitation gold foil, and will break if touched by hand, while imitation gold foil is much thicker than real gold foil and will not break if touched by hand. Also, real gold is not afraid of fire, and you can tell the authenticity of gold foil by burning it. The main raw material of imitation gold foil is copper, which will generate copper oxide and turn black when burned, while real gold foil will not.

Figure 1: Looking at red leaves through gold foil

There is an even simpler way to determine whether an object is real gold. Just use a broken bowl to scratch the object to be judged. If the object is really gold, the scratch color will be gold. But if it is a metal other than gold, it will generally be a black scratch. Bowls are everywhere, you can find a bowl and scratch a gold ring around you. Of course, who will be responsible for destroying the gold ring?

We can also judge the approximate pure gold content of gold foil by naked eyes. There is a saying that 9 is red, 8 is yellow, and 7 is blue, that is, the gold content of more than 90% is red, the content of 80% is yellow, and the content of 70% is blue.

1.2 Preparation of gold foil

The production process of gold foil is unique and requires high technical requirements. It has been handmade since ancient times. The production process of gold foil is recorded in "The Exploitation of the Works of Nature": "When making gold foil, after it becomes a thin skin, it is wrapped in black gold paper and beaten with a hammer."

Gold leaf is made by tapping the thin gold sheet to make it gradually stretch due to its good ductility. However, this is not a simple tapping. The thin gold sheet is placed between papers and stacked about 100 times. A specialized gold leaf master taps it with a hammer, and the gold sheet gradually stretches and becomes thinner, and finally becomes the beautiful gold leaf of the desired thickness (Figure 2). The question is - what paper is used? The principle of tapping gold to make it gradually thinner is simple, but the paper holding the gold leaf is very special. This paper, called 萡紙, is generally a square with a side length of 30 cm, but it is definitely not ordinary paper. It is a special paper that is soaked in special water for more than half a year and then taken out and dried before use. This water contains special substances, and each gold leaf master has a special ancestral secret recipe. Once prepared, this paper can be reused many times, but of course its function will gradually decline. When it is no longer usable, it can be cut into a certain size and used for actors' makeup. Some people have also used high-quality copy paper to conduct experiments. Although they used this copy paper to clamp gold foil and then hit it, it can make it thinner, but many irregular holes will appear, and what is obtained is not gold foil. Therefore, if special paper is not used, beautiful gold foil cannot be made.

Figure 2 Production of gold foil

Ancient civilizations in the world all have superb skills in making gold foil. The earliest discovery of gold foil production was in the Nile River Basin of ancient Egypt. Artifacts unearthed from the tombs of ancient Egyptian pharaohs prove that Egypt mastered the gold foil processing technology very early. Gold foil products were found in a tomb in the Sahara of Africa dating back to 1500 BC, and images of gold foil were found on the excavations of Egyptian tombs in 1450 BC. In Europe, gold foil processing industries already existed in Hamburg, Vienna and other places in the Middle Ages.

In Asia, Japan has exquisite gold leaf manufacturing skills and produces excellent products. The main production area is Kanazawa City in Ishikawa Prefecture. The Kinkakuji Temple in Kyoto, Japan is completely covered with gold leaf (Figure 3). In 1950, a monk in the temple set a fire and burned down the Kinkakuji Temple. It was repaired in 1955, but the thickness of the gold leaf used at that time was not sufficient, resulting in ultraviolet rays penetrating the gold leaf and damaging the paint inside. Therefore, it was covered with gold leaf again in 1987. The thickness of the gold leaf used this time was 5 times the thickness of the original gold leaf. 200,000 pieces of gold leaf with a side length of 4.8 cm were used, and a total of about 20 kg of gold was used. The total cost reached 740 million yen (about 45 million yuan).

Figure 3 Kinkakuji Temple covered in gold foil

In China, gold foil is a traditional Chinese handicraft. It originated in the Eastern Jin Dynasty, matured in the Southern Dynasties, and became popular in the Song, Qi, Liang, and Chen dynasties. Nanjing is the birthplace of Chinese gold foil. Today, Nanjing is the world's largest gold foil production center. In May 2006, Nanjing's gold foil forging technique was listed as the first batch of national intangible cultural heritage by the State Council.

1.3 Application of gold foil

Gold foil has a wide range of uses, involving various fields such as Buddhism, classical gardens, high-end architecture, medical care, and cultural undertakings. Among them, gilding Buddha statues, carved beams and painted buildings, plaques and couplets, and decoration are the most common uses of gold foil.

1.3.1 Edible

According to research, adding a small amount of gold foil to edible wine has health functions such as detoxification and beauty care. In recent years, gold foil meals, gold foil wine, gold foil water, gold foil candy, and gold foil cakes have been launched one after another. It is especially popular in Japan and Southeast Asia. In 1983, the World Health Organization officially included gold in the category of food additives, and China's eighth category of new food resource materials - minerals and trace elements clearly includes "gold foil". At present, many domestic companies have produced "gold foil wine" (Figure 4).

Figure 4 Gold Foil Wine

1.3.2 Medical use

The medical value of gold foil has a long history. my country's famous Chinese patent medicines, such as Tongrentang's "Niuhuang Angong Pills", "Niuhuang Qingxin Pills", "Niuhuang Jiangya Pills", "Wuji Baifeng Pills", "Dahuo Luo Dan" and other precious Chinese patent medicines, all use gold foil in the formula or are wrapped in gold foil. Medical books of all dynasties record: "Eating gold can calm the spirit, strengthen the bone marrow, and clear the evil spirits of the five internal organs." "It can treat children's shock and injury, five internal organs' shock and loss of will, and calm the heart and soul." In the history of modern medicine, gold began to be used to treat immune diseases. Scientific research has also found that gold has strong antioxidant properties. Therefore, in today's highly developed modern medicine, gold foil is still a popular "golden elixir" at home and abroad. In my country, there are also folk remedies that use gold foil to calm children's shock. In modern surgery, gold foil is used to treat skin burns and surgical sutures.

1.3.3 Crafts

Craft gifts with gold foil veneer can integrate decoration, art appreciation and treasure collection. This kind of craft gifts can not only reflect the luxury of gold, but also have a relatively low cost compared to pure gold products. It can be as brilliant and eternal as gold, and can also maintain the essence of art. At present, the field of gold foil crafts has emerged in a bright and colorful situation. Such as gold foil paintings (Figure 5), gold image cards, gold foil business cards, gold foil photos, crystal gold foil ornaments, ceramic glaze gold foil paintings, etc.

Figure 5 Gold leaf painting

1.3.4 Beauty

There have been records of using gold foil for beauty since ancient times. In the poem "The Ballad of Mulan", "I comb my hair by the window, and apply gold foil on my face in front of the mirror", the gold foil is gold foil. In modern society, using gold foil to develop cosmetics has become a fashion in the beauty industry at home and abroad. It is said that gold foil treated with nano-materials will carry negative ions and generate microcirculation energy, which can clean dirt accumulated on the skin, promote skin metabolism, activate cell vitality and skin elasticity, and make the skin healthy and translucent.

1.3.5 Architecture

The gilding technique can make a small amount of gold play the effect of making the main body with gold, so it is widely used in antique buildings, modern buildings, gold-lettered plaques, etc. Famous gilded buildings in China include: Tiananmen Square in Beijing, the Great Hall of the People, CCTV, Oriental Pearl Tower in Shanghai, Potala Palace in Tibet (Figure 6), etc.

Figure 6 Potala Palace

2. Gold thread

2.1 Characteristics of gold wire

Gold's excellent ductility can also be demonstrated in wire drawing. 1 gram of gold can be drawn into a gold wire 66 km long and less than 1 µm in diameter. With 600 grams of gold, such a thin wire can wrap around the earth. The thickness of a male hair is generally 0.08~0.4 mm, that is, between 80~400 µm. The diameter of the gold wire can be less than one percent of a human hair. If calculated only by the cross-sectional area, it would take about 10,000 thin gold wires tied together to be equivalent to one hair!

As an important raw material, gold wire must have the following important properties: good mechanical properties and electrical conductivity; appropriate breaking force; suitable size; clean surface without pollution and damage. Moreover, when used as bonding gold wire (Figure 7), it is not good to be too soft or too hard. Too soft gold wire will lead to the following adverse consequences: (1) arch wire drooping; (2) unstable ball shape; (3) ball neck is easy to shrink; (4) gold wire is easy to break. Too hard gold wire will lead to the following adverse consequences: (1) holes are punched in chip electrodes or epitaxy; (2) gold ball neck is broken; (3) alloy formation is difficult; (4) arch wire arc is difficult to control. Taking bonding gold wire as an example, its preparation method and application are explained.

Figure 7 Bonding wire

2.2 Preparation of gold wire

One of the main uses of gold wire is as bonding wire. The production methods of bonding wire mainly include melting and casting process, wire drawing process, annealing process, performance testing, winding, etc. By optimizing the process, refining the process, and improving the equipment, the product quality of the material can be improved, the product yield rate can be increased, industrial production can be realized, and the production cost can be reduced.

First, it is necessary to obtain ultra-high purity gold raw materials. In the past, 99.99% gold was generally used as raw material to produce gold materials or prepare alloys. When used as bonding wire, it had certain defects in stability, weldability and semiconductor properties. Using 99.999% gold as raw material to prepare gold products not only enhances its electrical properties, but also strictly controls impurity elements to reduce interference factors and improve the reliability of gold products.

The main methods for preparing high-purity gold include chemical reduction separation, dissolution extraction and electrolytic refining.

Chemical reduction separation method. Generally, more than 99.9% gold is used as raw material, and the production of 99.999% gold is achieved by dissolving it in aqua regia, driving out nitrate with hydrochloric acid, and controlling the Au3+ concentration in the solution, the amount of reducing agent oxalic acid, the reduction time and the temperature.

Dissolution extraction method. Usually, 99.99% gold is prepared with aqua regia solution or electrolytic solution making method to prepare a relatively pure chloroauric acid solution, which is then extracted with ether, and then reduced with sulfur dioxide after back extraction to obtain pure gold with a grade of ≥99.999%.

Electrolytic refining method. With gold (≥99.9%) as the anode and an inert material that is not corroded by the electrolytic medium as the cathode, when power is turned on, the gold at the anode mainly undergoes the Au→Au3+ + 3e dissolution reaction, while the cathode mainly undergoes the Au3+ + 3e→Au precipitation reaction. The cell voltage and cathode current density are strictly controlled so that only gold is precipitated at the cathode, while other metal ions are not precipitated, so that the gold precipitated at the cathode is purified.

Obtaining uniform gold casting structure is also the key to preparing high-performance gold wire. For example, the intermediate alloy can be prepared by leak casting-quenching method, and then added to the parent metal liquid, so that the alloying speed is fast and the dispersion is good, and the ingot structure with uniform distribution of strengthening elements is obtained.

There are two methods for preparing alloy ingots for bonding wire: vacuum melting and casting and continuous casting. Now most alloy bars are prepared by continuous casting, which can improve the yield rate of ingots. For example, a vertical medium-frequency induction vacuum continuous casting furnace is used for continuous casting, and intermittent casting is used to suppress the formation of columnar crystals, which is conducive to the formation of equiaxed crystals. While meeting the ductility of the ingot, a certain strength can be achieved, which can better meet the processing of ultra-fine wires, improve the yield rate of gold wires and the consistency between batches, and meet the requirements of batch and large-scale stable production.

The gold wire gradually becomes thinner during the multiple drawing processes, and finally meets the requirements for use. Figure 8 is a schematic diagram of metal wire drawing. During the wire drawing process, the gold wire is generally heated to 300~600℃ for annealing. After annealing, it is directly wound on the take-up reel for winding. At this time, the bonding gold wires are prone to self-diffusion bonding effect, resulting in the next process to use the wire cannot be released, resulting in wire breakage, and reducing the product yield. In order to prevent the bonding gold wire from sticking after annealing, a cooling circulation device can be set between the annealing furnace and the take-up reel, which can better solve the bonding gold wire after continuous online annealing. The phenomenon of adhesion is caused by winding on the same take-up reel, thereby improving the product yield.

Figure 8 Schematic diagram of metal wire drawing

Through the combined effect of trace elements and the optimal alloying element design, the bonding wire can be alloyed, processed thin and low-cost, and the bonding strength and performance in high temperature and vibration environments can be improved. Usually, trace elements are added to refine the grains and strengthen the alloy. For example, by adding 0.0005%~0.001% of Be (bismuth), 0.001%~0.003% of Ce (cerium), 0.0008%~0.002% of Cu (copper) or Ge (germanium) to gold with a content (mass fraction) ≥99.996%, a bonding wire with high strength, low arc, high product yield and long winding length of the take-up reel can be obtained. Adding 0.0003%~0.0008% Ca (calcium), 0.002%~0.004% Cu (copper), 0.0005%~0.0015% Ge (germanium) can obtain bonding wires with high strength and low arc length. The addition of trace elements Be (bismuth) and Sm (samarium) can improve the tensile strength and elongation of bonding wires. In addition, adding trace amounts of W (tungsten), Re (rhenium), Pt (platinum), Y (yttrium), Mg (magnesium), Ir (iridium), La (lanthanum), etc. to the bonding wire can make the wire have better strength and plasticity.

2.3 Application of gold wire

2.3.1 Bonding wire

In recent years, with the rapid development of the semiconductor industry, the degree of integration of integrated circuits has become higher and higher, the size of circuit boards has become smaller and smaller, the number of electrodes on the device has increased, the electrode spacing has become narrower, and the package has become smaller and smaller accordingly. The objective requirement is that the bonding wire used as the lead has high strength, low arc length and very high arc stability (Figure 9).

Figure 9 The distance between electrodes on circuit boards is getting narrower

Bonding is an important step in the production of integrated circuits. It is the operation of connecting the circuit chip to the lead frame. Bonding wire is a fine metal wire inner lead used to achieve electrical connection between the input/output bonding points of the circuit inside the chip and the internal contact points of the lead frame when assembling semiconductor devices and integrated circuits. The quality of bonding directly affects the performance of integrated circuits. Bonding wire is one of the five basic materials in the overall IC packaging material market. It is an inner lead material with excellent electrical, thermal and mechanical properties and excellent chemical stability. It is an important structural material for manufacturing integrated circuits and discrete devices.

Gold has very high electrical conductivity and excellent corrosion resistance. Therefore, it can be used for high-energy power transmission, such as high-current wires, circuit boards for 3C products, etc.

Gold bonding wire is an inner lead material with excellent electrical, thermal, mechanical properties and chemical stability. Gold bonding wire is mainly used for packaging of integrated circuits (ICs) and discrete semiconductor devices, such as diodes (such as LEDs) and transistors. Discrete semiconductor devices have a wide range of applications. Among them, discrete devices with high power, high current, high reverse voltage, high frequency, high speed, high sensitivity, low noise and other characteristics have a broad application space. The industry uses a huge amount of gold bonding wire.

Another important application area of ​​gold bonding wire is IC packaging. Gold bonding wire for IC is the foundation of the IC industry and determines the development level of the integrated circuit industry. The development level of the IC industry also reflects the production capacity and technical level of gold bonding wire.

The most commonly used conductive wire material for VLSI wire bonding is gold wire. Bonding gold wire refers to high-purity gold alloy wire with a purity of 99.99% and a wire diameter of 18 to 50 µm.

The main characteristics of bonding gold wire are as follows: (1) It has a tensile strength and elongation force that can withstand the stress during packaging. (2) It has good ball-forming properties to facilitate welding. (3) The surface of the gold wire is free of scratches, dirt, dust and other adhesions, so that there is sufficient bonding strength between the gold wire and the semiconductor chip, and between the gold wire and the lead frame. (4) It can prevent the wire from getting stuck as the length of the gold wire increases. (5) The diameter of the gold wire must be highly accurate and there must be no curling on the surface. (6) There is no ripple in the solder joint during welding.

The development direction of gold bonding wire. At present, there are two main development directions of gold bonding wire:

(1) In order to achieve alloying of bonding wire, thinning of wire, low cost, and improving bonding strength and performance in high temperature and vibration environments, trace elements are usually added to gold. The added elements in gold wire tend to be diversified and traceable. Trace added elements have a significant impact on the performance of gold wire and play a decisive role in bonding performance and yield. The amount of trace elements added must be strictly controlled and cannot deviate from the allowable range, otherwise it will be counterproductive.

(2) In order to improve the thinness, bondability and cost reduction of bonding wires, companies such as Japan's Tanaka Electronics, Sumitomo Metal Mining and Germany's Heraeus have successively developed new high-performance fine alloy wires, such as Au-Ag, Au-Ni, Au-Sn, Au-Cu, etc., which are now entering the stage of promotion and application.

At present, the domestic gold bonding wire for small and medium-sized ICs and discrete devices has been basically solved, while the gold bonding wire for large-scale and ultra-large-scale ICs still needs to be imported in large quantities. With the rapid development of my country's microelectronics industry, the technical requirements for gold wires are also very high. For example, thinner bonding wires are required for narrow spacing and long distance bonding. Therefore, higher and higher requirements are put forward for the technical indicators of gold bonding wires. The demand for high-purity, high-temperature, ultra-fine and ultra-long gold wires is growing rapidly, and its development potential is huge and the prospects are broad. However, most of the current demand for such gold wires by enterprises depends on imports, and domestic gold wires cannot meet the requirements in terms of quality or quantity. Japan's gold wire types, quality and output are ranked first in the world. There is still a large gap between the domestic gold bonding wire industry and developed countries. At present, the domestic gold bonding wire processing urgently needs to form a large-scale, efficient and high-quality production situation.

2.3.2 Gold thread embroidery

Gold can be made into gold thread for embroidery. Goldwork is an embroidery technique that uses metal thread. The thread used is not limited to gold. It can even be said that pure gold is rarely used. It is just that the word "gold thread" is in the name. Generally speaking, goldwork uses alloy threads of gold, silver, copper or other metals to create.

The process of gold thread embroidery is that the silk is first stretched and fixed on the frame, and then the craftsman draws the pattern lines. Then, the embroidery master uses the ancient technique of gold thread embroidery to twist the gold thread into a spiral gold thread with an embroidery needle, and then patiently embroiders the complex composition details one by one on the silk, thus creating an exquisite work of art. Figure 10 is an example of contemporary gold thread embroidery work.

Figure 10 Contemporary gold thread embroidery works

Gold thread embroidery has a history of more than 2,000 years. It first appeared in China, and then this technology gradually spread, taking root in India, the Middle East, ancient Babylon, Egypt, Africa, and European countries.

In Europe, gold thread embroidery technology appeared and became popular after the 11th century, and the technical level reached its peak in the middle of the 13th century. During this period, gold thread embroidery was widely used in church clothing and church hanging decorations. Pope Innocent IV had a special liking for gold thread embroidery, so he suggested that the monks and nuns of the Cistercian Order purchase gold thread embroidery gowns and recruited embroiderers who specialized in gold thread embroidery. At the end of the 13th century, the transaction of gold thread embroidery works once exceeded that of other types of embroidery works, which was a prosperous period for gold thread embroidery. These works use gold thread, silver thread and gold-plated thread as the main thread materials, and are supplemented with pearls, semi-precious stones and other materials for decoration, so a complete and exquisite gold thread embroidery work is very valuable for collection and expensive.

In the early 15th century, the technique of gold thread embroidery developed rapidly, soon surpassing other embroidery techniques and being widely used. This technique uses different colored silk threads to create pairs of gold threads. The works preserved today are usually portraits or narrative scenes.

By the 19th century, gold embroidery began to play an important role in military and state or ceremonial dress. The gold embroidery patterns on these garments had very strict design specifications for different occasions, just like the official uniforms of ancient China, where different patterns represented different ranks or social status. The gold embroidery decorations were usually embroidered separately, then carefully cut out and embroidered onto the dress using pearl gold and silver thread or special metal thread.

In the 20th and 21st centuries, gold thread embroidery continued to be used in the military, celebrations and religion, such as the highest quality church supplies, special clothing for special occasions, etc. At the same time, with the development of technology, it has become easier to integrate gold thread embroidery with other embroidery techniques, which has also brought a broader creative space for gold thread embroidery.

Because gold thread embroidery works are extremely gorgeous and can bring quite brilliant effects when used, gold thread embroidery will continue to shine with its unique brilliance in the future.

3. Conclusion

Gold is not only the king of metals because of its nobleness and value retention, but also the champion in terms of its processing ductility. Gold foil with a thickness of only one thousandth of a cicada's wing and gold wire with a diameter of only one hundredth of a hair are widely used in many fields.

References:
[1] Saito Katsuhiro. へんなmetalすごいmetal. Japan: Technology Review Society, 2009

[2] Tang Rencheng. Gold Foil Gourmet. Food and Life, 2019(12):44

[3] Chen Yongtai, Xie Ming, Wang Song, et al. Research progress of precious metal bonding wire materials. Precious Metals, 2014, 35(3): 66 DOI: 10.3969/j.issn.1004-0676.2014.03.016

About the Author:

Jia Chengchang is a professor and doctoral supervisor at the University of Science and Technology Beijing. He graduated from the Department of Metal Materials of Beijing Iron and Steel Institute with a bachelor's degree in 1982. He received a master's degree from Tohoku University in Japan in 1987. He received a doctorate from Tohoku University in Japan in 1990. He was a postdoctoral fellow and chief engineer at Kanagawa Science City in Japan from 1990 to 1994. He has obtained more than 20 national invention patents. He has published more than 200 papers in domestic and foreign academic journals, including 76 papers retrieved by SCI and 127 papers retrieved by EI. A single article has been cited more than 100 times. He has compiled 15 academic monographs: "Composite Materials Tutorial", "Introduction to Ceramic Matrix Composite Materials", "Sintered Metal Oil-bearing Bearings", "Introduction to Metal Matrix Composite Materials", "Superhard Materials and Tools", "Metal Powder Gel Injection Molding", "Sintering Practice and Scientific Principles", "Professor Han Fenglin's Papers", etc. He has won the second prize of Science and Technology Progress of the Ministry of Education, the first prize of Excellent Textbooks of China Metallurgical Education Association, the first prize of National Teaching Achievement in Higher Education (participated), the first prize of Beijing Education and Teaching Achievement (participated), the second prize of Excellent Journal of China Nonferrous Metals Society, the Outstanding Worker of China Metal Society, the Outstanding Instructor of "Challenge Cup" National College Student Science and Technology Competition, the Outstanding Editorial Board Member of "Journal of Composite Materials" of Composite Materials Society, "I Love My Teacher - the Best Teacher in My Mind" of Beijing University of Science and Technology, Advanced Individual in Teacher Ethics, Outstanding Party Member, Advanced Worker, First Prize for Teaching Achievement, SCI Inclusion Award for Scientific Papers and other honors. Main social part-time jobs: Director of China Composite Materials Society, Honorary Director of Powder Metallurgy Branch of China Metal Society, Executive Director of Powder Metallurgy Branch of China Mechanical Engineering Society, Director of Powder Metallurgy and Ceramics Branch of China Nonferrous Metals Society, Honorary Director of Powder Metallurgy Branch of China Steel Structure Association, Distinguished Expert of China Nonferrous Processing Association, Director of Powder Branch of China Building Materials Industry Association, Distinguished Expert of Powder Metallurgy Branch of China Machinery Association, Editorial Board Member of Journal of Composite Materials, Member of Advisory Committee of Powder Metallurgy Technology, Editorial Board Member of Powder Metallurgy Industry, Editorial Board Member of China Molybdenum Industry, Editorial Board Member of Powder Metallurgy Materials Science and Engineering, Editorial Board Member of China Materials Science and Equipment, Guest Contributor of Metal World