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An Introductory Guide to Sintering

Introduction

Sintering refers to the formation of a solid mass material by heat and pressure and not melting it to the liquefaction point. During the process, atoms of materials diffuse across particle boundaries and fuse into a single piece. The process of sintering naturally occurs in mineral deposits. It is the process that’s used to manufacture materials like metals, sintered plastic, and ceramics, and a pe filter

As the sintering temperature is below the melting point of the material, it is usually used for high melting point materials, for example, tungsten and molybdenum. In this article, we give you a complete guide to the sintering process.

What is the Sintering Process?

Sintering can be defined as a heat treatment procedure in which loose materials are exposed to high pressure and temperature to form a compact piece. It is similar to ice cubes sticking together in a water glass as a result of the temperature difference between water and ice.

The pressure and heat needed for sintering are less compared to the melting point of the material. 

How Does it Work?

In the same way that materials have melting points, they also have desirable sintering points. This is the temperature at which the pressure and heat are just enough to decrease the porous spaces between the particles of the materials. It squeezes loose materials together to form a solid lump.

In electrical conductivity and minerals, pressure and heat are naturally used. Sintering increases the property of materials. It also has a positive impact on material strength, translucency, integrity, and electrical connectivity.

Types of sintering

There are many types of sintering, and they are categorized based on the specific sintering process or material that is being joined.

Ceramic Sintering

This is a type of sintering usually used in manufacturing ceramic objects, for instance, tile. Since some raw materials for making ceramics have a lower plasticity index and more affinity for water than clay, they require adding organic additives before sintering. Ceramic sintering leads to shrinkage after reaching the transition temperature and after the consolidation of the powder structure. This is what reduces porosity. The high temperatures, coupled with electrical currents and high pressure, drive the process. Pressure is the most important additional factor, but this is not to say that pressureless sintering is impossible. To achieve pressureless sintering, the manufacturers use graded metal-ceramic plus a nanoparticle sintering aid through a technology called bulk molding.

Metallic Powder Sintering

Sintering can be applied to most metals, especially if they are pure and placed in a vacuum that makes contamination impossible. During the process of sintering metal powders, protective gas should be used under atmospheric pressure. Sintering usually causes the overall volume of the material to decrease because of the increase in density and the fact that the material fills the void before the atoms move along the borders and smooth the walls via surface tension.

When at least one of the materials is in the liquid state, it is called liquid state sintering. Metallic powder sintering is also called powder metallurgy and it is used for making carbide and tungsten carbide. There are many uses for sintered metal powder like making heat pipes, shotgun shells, bearings, and jewelry. Also, sintering is regarded as one of the most viable methods for where materials involved have high melting points.

Plastic Sintering

Plastic sintering is used for items requiring specific material porosity. This includes applications like control of gas and fluid flows and filtration units. Other uses of sintered plastic are whiteboard marker nibs, inhaler filters, and packaging material linings. They are also the base materials in snowboards and skis.

Liquid Phase Sintering

The liquid phase sintering technology is used where materials being used are difficult to sinter. It involves adding an additive to the powder due to be sintered. The additive will melt, causing the liquid to be pulled into the pores. Also, this causes the rearranging of the grains into a more favorable packing arrangement. In situations where the particles are closer together and capillary pressures are high, the atoms dissolve and precipitate in lower chemical potential areas. It is akin to grain boundary diffusion. And like other types of sintering, the additive must melt before sintering occurs.

Permanent Liquid Phase Sintering

It works similarly to the regular liquid phase sintering method only that it encourages capillarity to draw liquid into open pores that lead to improved packing and grain movement.

Transient Liquid Phase Sintering (TLPS)

It is a process for forming bulk materials and is used to make metals, ceramics, and metal matrix ceramic materials. The materials should be soluble in the liquid wetting the solid to create a high diffusion rate. 

Where is Sintering Used?

The main benefit of sintering is to enhance material properties. These include strength, translucency, thermal, and electrical conductivity. Sintered plastics also have a wide range of industrial applications. Sintering has been around for centuries where it was previously used for making almost any type of metal or ceramic product.

Modern applications of include manufacturing steel parts, tungsten wiring, magnetic materials, self-lubricating bearings, electrical contacts, medical products, dental products, porous metals, and cutting tools, to mention but a few.

Spark Plasma Sintering

Spark plasma sintering utilizes an electric field and pressure to improve the density of metallic powder and ceramic powder compacts. Through the use of hot pressing and an electric field to enhance densification, spark plasma sintering makes it possible to use lower sintering temperatures and also cuts processing time. But don’t be fooled by the name of the process. According to research, no plasma has been used. This has led to other names like Direct Current Sintering, Field Assisted Sintering Technique, and Electric Field Assisted Sintering.

Conclusion

Sintering has many applications. It strengthens sintered plastic and also improves thermal and electric conductivity. Also, it is the method used to create a high-quality pe (Polyethylene) filter. It is often used where the material has incredibly high temperatures. There are several types of sintering techniques and these apply to different materials and situations.


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