Can old mobile phones be refined into gold? Yes, it is true!

When we mention gold, we often think of gold bracelets, gold chains, gold bars, etc. In fact, in addition to being used as jewelry and currency, gold is also an indispensable material in industry and high-tech industries. For example, many components in smartphones use gold. So, what are the main applications of gold in industry? Why does it have great scientific and technological value?

Beautiful decoration made of gold

1. Characteristics of gold

Gold (Au) is a precious metal. It is very valuable because of its harsh formation conditions and low content on earth. The density of gold is 19.3g/cm³ (at 20℃), the hardness is relatively low, and it can be scratched with a fingernail. It has a metallic luster and has a good decorative effect. The melting point of gold exceeds 1000℃ and the boiling point is 2808℃.

Natural Gold

Source: usgs

Gold is chemically very stable, resistant to acid and alkali corrosion (usually only soluble in aqua regia), and will not change color or oxidize when heated to high temperatures. In addition, it has excellent electrical conductivity, thermal conductivity and ductility . One ounce (the international unit of measurement for gold, approximately equal to 28 grams) of gold can be drawn into a thin wire tens of thousands of meters long, and can be beaten thin into a gold foil with a thickness of only microns. It is precisely because of these physical and chemical properties of gold that it is widely used in jewelry processing, electronics, chemicals, medicine and other industries.

2. Ideal material for electronic devices

Modern life is inseparable from a variety of electronic products. Mobile phones and computers have become "necessities of life" for many people. These sophisticated electronic devices are assembled from a large number of electronic components and circuit boards, which are connected by countless wires, connectors, welding points, switches, etc. This requires the use of metal materials with good conductivity, and the stability of voltage must be ensured as much as possible to reduce obstacles to the flow of current. Gold has become a good choice and plays a very important role in ensuring the reliability of electronic devices.

Source: pixnio

First of all, we have to mention the "mother of electronic products" - printed circuit boards. There are many thin copper wires distributed on the circuit board. The copper solder joints are easily oxidized in the air, which will cause poor contact and affect the performance of the circuit board. Therefore, gold is often plated on the surface of the copper as a protective layer. In addition, when the circuit board is immersed in the etching solution for too long, the copper wire may fall off, and the gold coating has extremely fine porosity, which can protect the metal parts from corrosion.

Since gold is expensive, pure gold is usually only plated on high-end printed circuit boards.

Source: szfux.com

On the edge of the circuit board that is inserted into the matching connector, you will also see many golden contacts arranged in finger shapes. Because their surfaces are gold-plated, they are called "gold fingers". The main function of gold fingers is signal connection and conduction, so they must have good electrical conductivity, oxidation resistance, wear resistance, and corrosion resistance. Since pure gold will wear out at a very fast speed during friction contact, the "gold" in gold fingers is generally a gold compound.

Source: A shopping website

Gold is also commonly seen in switches. Taking a relay (an automatic electrical switch) as an example, the size of the contact resistance between the contacts directly affects the service life of the contacts, especially in small relays, because the control current and the contact surface of the contacts are small, conductivity is particularly important, so gold is plated on the contact surface. Gold increases the conductivity of electronic components, can carry very low voltages, and minimizes the resistance at the contact point. It is also very reliable under extreme conditions of low current and low potential. In addition, unlike platinum or palladium, gold does not catalyze the decomposition of organic vapors, avoiding the formation of poorly conductive organic polymer films on the metal contact surface.

However, the softness of gold makes it easily damaged by dust particles and foreign matter. Dust particles can easily become embedded under even slightly closed contacts, which can interfere with good contact between components. To overcome this disadvantage, alloying technology is widely used.

With the rapid development of electronic products, people require products to be "lighter and thinner", which makes the size of electronic devices smaller and smaller. In a limited space, in order to connect various components, the diameter of the wire also becomes smaller. For some ultra-fine pitches, if copper, aluminum and other metals are used to make wires, they are very easy to break. Gold has excellent ductility and can be pulled into extremely fine gold wires while still maintaining its performance.

3. Gold is playing a big role in space

As we mentioned before, gold is the most ductile metal. When gold is made into an extremely thin film (only a few molecules thick), it has special uses. The high reflectivity of gold film to infrared radiation makes it have heat insulation properties. Plating gold film on the surface of spacecraft and space suits can form an ideal reflective film to protect spacecraft and space suits from excessive solar radiation. At the same time, gold film can transmit light from the yellow to blue range of the visible light spectrum and ultraviolet rays. Its transparency is similar to that of glass. Plating gold on the goggles of astronauts' helmets can be both heat-insulating and will not block vision.

Gold can also act as a solid lubricant, that is, a layer of gold is applied to the surface of steel, iron, etc. We know that aerospace parts have complex structures and precise designs, such as the antenna system on artificial satellites, solar cell sailboard mechanisms, and the drive mechanism of light-sensing instruments. The close cooperation between various parts requires the support of bearing materials. Due to the harsh environment in space, higher requirements are placed on the performance of bearing materials and grease. Gold solid lubricants are very stable, soft, and have a low friction coefficient, which reduces the wear of parts and can make up for the lack of performance of general lubricants.

The James Webb Space Telescope's primary reflector also uses a gold coating. It is an infrared telescope whose operating temperature needs to be kept below -223.2°C. The gold coating not only improves the reflectivity of infrared light and isolates heat, but also increases its durability.

The James Webb Space Telescope's gold-coated mirror

Source: NASA/Jet Propulsion Laboratory-Caltech

4. Application of gold in the medical field

When the size of gold is reduced to the nanometer level - gold nanoparticles, its properties will change strangely. Gold nanoparticles have the advantages of large specific surface area, easy surface modification, and good biocompatibility (the degree of compatibility of the material with the human body after implantation), which makes gold nanoparticles have a wide range of application scenarios in the medical field.

First, it is used in the field of photothermal therapy for cancer. Cancer seriously threatens human health, and existing clinical treatments such as chemotherapy and radiotherapy have strong side effects. The unique photothermal effect of nanogold provides a new idea for the treatment of cancer - photothermal therapy. Photothermal therapy uses photothermal materials to efficiently convert light energy into heat energy, thereby raising the temperature of tumor tissue to kill tumor cells. It has the advantages of precise spatial positioning and less damage to cell tissues around the affected area. Through local infrared irradiation, nanogold particles perform efficient photothermal conversion and have good biocompatibility. Therefore, they are highly anticipated in the photothermal treatment of cancer.

Several cancer treatments

Source: Baidu Encyclopedia

In addition, gold nanoparticles are also very good drug carriers. Many drugs cannot be used directly due to their poor water solubility and pH sensitivity, and require carriers to transport them to the site of action. Encapsulating drug ingredients with gold nanoparticles to regulate their release rate and biopermeability in the body can greatly improve the utilization rate of drugs. In addition, this drug delivery system can also endow its carrier with pH responsiveness, targeting and other characteristics by loading various functional molecules. In the future, it is expected to be widely used in drug delivery.

Gold nanoparticles (AuNPs) are tightly linked to cells

Source | "Reversibly Modulating the Blood–Brain Barrier by Laser Stimulation of Molecular-Targeted Nanoparticles"

Seeing this, are you amazed at the excellent performance of gold in different fields? With the development of society, the use of gold in industry, technology, medicine and other fields is increasing. I believe that in the near future, gold will bring more benefits to everyone.