Materials for Powder Metallurgy - Iron Powder

The manufacturing industry of metal powder, as the basic raw material for powder metallurgy, has also actively adjusted its product structure. The output of powder has developed steadily, the quality has been further improved, and the variety has increased. Ultrafine iron powder is one of the basic raw materials for the powder metallurgy industry. Due to its large specific surface area and activity, it has special properties such as electricity, magnetism, light, catalysis, adsorption and chemical reaction.

Therefore, ultrafine iron powder has a wide range of uses, mainly used in powder metallurgy, manufacturing mechanical parts, production of friction materials, anti-friction materials, superhard materials, magnetic materials, lubricants and other products. Secondly, ultrafine iron powder is widely used in chemical industry, cutting, heating materials, welding rods, etc. In recent years, iron powder has also had broad application prospects in many fields such as electromagnetics, biology, medicine, optics, metallurgy, etc.

Production method of iron powder:

1. Pig iron powder: It is made by crushing the leftover materials from cast iron or metal processing industry. Its carbon content is about 2-4%. It is an alloy powder of iron and is usually used in sewage treatment industry; it uses the galvanic cell reaction to decolorize sewage.
2. Reduced iron powder: The production method of reduced iron powder is through chemical reduction method, that is, using carbon monoxide to reduce the iron oxide phosphorus produced during steel rolling. The elemental iron powder produced by this method is called "reduced iron powder". Because it has good interstitial degree and sponge-like microstructure, it is also called "sponge iron powder". The iron content is generally more than 96.0%. It can be used in chemical reduction, powder metallurgy and other industries, but due to the high iron oxide content, the density of the pressed product is usually only 5.8g/cm3, the hardness is relatively large, and it is difficult to process it again.
3. Electrolytic iron powder    The high-purity iron produced by electrolyzing scrap steel in an aqueous solution of iron sulfate is called "electrolytic iron powder". This elemental iron powder has very high purity, very fine particles, irregular shape, and large surface area. Studies have shown that the chemical activity and human absorption rate of this elemental iron powder are the highest among all kinds of iron powders. However, due to the high production cost, this elemental iron powder is difficult to popularize.
4. Hydroxyl iron powder    Hydroxy iron powder is a compound Fe-OH formed by iron and hydroxyl groups. Its physical properties are round particles. It is the smallest among all kinds of elemental iron powders, but its interstitial density is very low. It can be used in the desulfurization process in industry with good desulfurization effect. It can replace ZnO in certain situations. Its cost is lower than ZnO and its desulfurization effect is better. However, due to the high production cost, this elemental iron powder has not yet been widely used.
5. Atomized iron powder
(1) Water atomized iron powder: divided into two production processes: low carbon steel liquid water atomization method and QMP method
(2) Use high-pressure gas to impact the liquid iron water flow, but the gas atomized iron powder further oxidizes the iron powder. After atomization cooling, it must be reduced again before it can be deoxidized and the finished product. Compared with gas atomized iron powder, there is an additional reduction process. Now most of them are water atomized iron powder.

So what kind of cargo is iron powder, and what are its dangerous characteristics?
What precautions should be taken during sea transportation? Let's take a look at it together. Dangerous goods express reduced iron powder is a kind of gray or black powder mainly containing elemental iron, and its particle size is usually less than 1mm, commonly known as "double absorbent". It is generally made by reducing iron oxides (ferroferric oxide, iron concentrate, etc.) using solid or gas reducing agents (coke, charcoal, anthracite, water gas, converted natural gas, decomposed ammonia, hydrogen, etc.). It is divided into five grades according to particle size: coarse powder, medium powder, fine powder, microfine powder and ultrafine powder. Iron powder composed of particles with a particle size of 150-500μm is coarse powder, with a particle size of 44-150μm is medium powder, 10-44μm is fine powder, 0.5-10μm is ultrafine powder, and less than 0.5μm is ultrafine powder.

The main uses of reduced iron powder are: ① As the raw material of powder metallurgy products, the consumption accounts for about 60-80% of the total iron powder consumption; ② As the raw material of welding rods, adding 10-70% iron powder to the coating can improve the welding process of the welding rod and significantly improve the deposition efficiency; ③ As a spray agent for flame cutting, when cutting steel products, spraying iron powder into the oxygen-acetylene flame can improve the cutting performance, expand the range of cutting steel types, and increase the thickness that can be cut; ④ It can also be used as a reducing agent in organic chemical synthesis, a carrier for copier ink, etc. Its reducing and adsorption properties are used to treat industrial solid waste and industrial wastewater; it is also widely used in the production process of lithium battery materials in the new energy industry.

Production process of reduced iron powder
Reduced iron powder is usually produced by iron ore reduction method and atomization method.
1. Iron ore reduction method is generally generated by reducing ferric oxide in a hydrogen or carbon monoxide gas flow under high heat conditions. The reduced iron powder produced by this process has irregular particles, low looseness and poor compressibility, but is cheap and is often used in large-scale applications such as structural parts, welding rods, and metal cutting. It is divided into primary reduced iron powder (direct reduced iron powder) and secondary reduced iron powder according to the purity requirements.
2. Atomization method (water mist, gas mist) The most widely used are gas atomization and water atomization. When atomizing iron powder, the iron metal raw material is first melted into liquid (generally overheated 100~150℃), and then it is atomized into fine droplets when it passes through the nozzle and meets the high-speed airflow or water flow. The atomized droplets are quickly solidified into reduced iron powder in the closed atomization cylinder.

There is no impurity mixed in the production process of atomized iron powder, high purity, good compressibility, and controllable particle morphology and particle size. It is often used in high-demand areas such as high-density mechanical parts. The main danger of iron powder is self-heating. Reduced iron powder is easy to react with water or air to release heat and self-heat. The self-heating reaction is very slow at room temperature. When the temperature reaches above 200℃, the reaction speed is significantly accelerated, generating a large amount of heat and hydrogen. If the ambient temperature continues to rise or there is a large amount of moisture, it is very easy to spontaneously combust. When there is water or humid water vapor in the cargo hold, the reduced iron powder is easy to react with water to release hydrogen and heat, and when the volume ratio of hydrogen and air exceeds 4%, a violent explosion may occur. In particular, when it encounters salty water or comes into contact with seawater, the reaction will intensify.

Flammable reduced iron powder will react with oxygen in the air under appropriate conditions, that is, it will catch fire and burn, releasing a lot of heat. Reduced iron powder particles have a large specific surface area and are highly active. Its danger increases as its particle size decreases. In production, the smallest iron powder particle can be processed into 1~5 microns. Generally speaking, -200 mesh (less than 75 microns) is more dangerous and easier to burn.

Inhalation hazard: The main hazard of reduced iron powder in the production and storage stages is inhalation. Inhalation of excessive iron powder or iron oxide smoke and dust for a short period of time will irritate the respiratory tract and cause pharyngitis, coughing, shortness of breath, weakness, fatigue, chills, sweating, muscle and joint pain; long-term exposure and excessive inhalation will cause iron deposition in the lungs, spleen, and lymphatic system; inhalation of dust will cause color spots in the lungs; therefore, when reducing iron powder is produced or used for a long time, there must be a dust removal and exhaust system in the closed places where the reduced iron powder is produced and used, and individuals must have complete respiratory protection equipment.