What are the roles of ceramic additives?

The role of ceramic additives is mainly reflected in two aspects.

One is as a process additive, such as improving processing conditions, speeding up the operating rate of equipment, simplifying the process, etc..
The second is as a functional additive, such as the addition of the product has some specific functions. Different ceramic additives have different roles, including uncoagulation, slow coagulation, coagulation, plasticization, plasticizing, bonding, suspension, defoaming, leveling, corrosion, wetting, powder surface modification, grinding and promote drying, sintering, etc.

How to choose the right ceramic additives?

Ceramic additives are generally introduced in the form of additive, the use of the following principles should be followed.

(1) clear use of additives to solve the problem.
(2) To understand the interaction of additives with each raw material component.
(3) When a variety of additives are mixed, pay attention to their interactions.
(4) Pay attention to the amount of additives used and adjust it reasonably according to the actual situation to meet their production characteristics.
(5) To ensure that the quality of additives is stable, so that they do not deteriorate and fail during storage or use.
(6) To consider the stability of additives at a certain temperature.

Ceramic additives family members at a glance

Dispersants

Ceramic dispersant is a type of ceramic additive, also known as diluent or decoagulant. In the preparation process of wet molding of high-performance ceramics, ceramic suspensions are required to have high solids content, stability and good rheology in order to provide conditions for obtaining high-performance ceramics with complex shapes, small shrinkage of the firing body, uniform bulk density and stable properties after molding. Therefore, dispersant is an additive that assists in controlling the rheological properties of the slurry.
There are many kinds of dispersants, and according to the different dispersing media, dispersants can be divided into water-based dispersants and oil-based (non-aqueous media) dispersants, while the former includes ionic (including cationic and anionic), non-ionic, mixed type, etc.
Oil-based dispersants include organic small molecule dispersants and polymer dispersants, of which polymer dispersants are also called hyperdispersants, which were first researched and developed to solve the problem of dispersion of pigment particles in organic media, and polymer dispersants are also the most actively researched high-performance dispersants, especially in the field of ceramics. According to the composition, ceramic dispersants can also be divided into inorganic dispersants, organic dispersants, polymeric dispersants and composite dispersants, etc.

Enhancers

In the production of ceramics, ceramic reinforcing agents can be added to compensate for their poor plasticity and improve the strength of the raw ceramic. Ceramic enhancers can greatly enhance the strength of the billet without affecting the flow of the slurry, improve the bonding properties of the powder, and reduce the breakage caused by the billet during transportation and production. The principle of ceramic enhancer is that it can bridge between ceramic particles, cross-linking, and the formation of irregular mesh structure, while the surface of the particles are wrapped will also make the particles between the hydrogen bonding and greatly enhance the strength of the product.

Abrasives

The crushing of raw materials is an essential process in the preparation of ceramics, but currently it is still a high energy consumption and low efficiency process. Improving the efficiency of fine grinding of raw materials is of great practical significance to save energy and reduce consumption and improve production efficiency. A grinding aid is a substance that can improve the efficiency of crushing. Under the same conditions, a small amount of grinding additives can make the crushing efficiency increased exponentially, a variety of powder equipment and dry and wet operations (such as ball mills, vibration, airflow mill) are available it, it not only improves the crushing efficiency, while the average particle size of the powder is also significantly reduced.

Plasticizer

Plasticity refers to the deformation of the blank under stress, after the stress is removed to maintain the shape of the same performance. Ordinary ceramics are commonly used clay and bentonite to improve plasticity. Advanced ceramics and some glaze paste need to use organic plasticizers, commonly used organic plasticizers are organic alcohols and esters, such as glycerol, ethylene glycol, triglyceride acetate, dibutyl phthalate, dibutyl phthalate, butyl stearate, and various cellulose derivatives.

Sintering additives

The sintering temperature of advanced ceramics such as alumina and silicon nitride tends to be high, which consumes a lot of energy and requires high equipment requirements. Therefore, it is very important to reduce the sintering temperature of ceramics. There are many ways to reduce the sintering temperature of ceramics, such as reducing the particle size of ceramic powder, using special sintering processes, adding sintering aids, etc. Compared with other methods, the addition of sintering additives has the advantages of low cost, good effect and simple process, and is currently the most effective method of low temperature sintering.

In practice, a single sintering additives often can not meet the requirements of both sintering and electromechanical properties, in general, a single additive to reduce the sintering temperature at the same time will lead to a reduction in ceramic properties, therefore, the use of a variety of different additives to form a composite additive than the use of one of the additives alone is more common.

Porosity agents

Porogenic agent, refers to the molding in the blank occupies a certain volume, in the firing, processing and will be removed, and make the volume occupied by the pores of a class of substances, also known as porous agent, pore-forming agent, etc..

Adding porogenic agents in the raw material into the pore is one of the most common methods of preparing porous ceramic materials, which can greatly improve the porosity of porous ceramics, to overcome the shortcomings of the porosity of the pore structure formed by the stacking of ceramic particles bonded low porosity. In addition, the size, shape and distribution of the pores can be adjusted by controlling the content of the porogenic agent, the size, shape and distribution of the porogenic particles.

Foaming agent

Like porogenic agents, foaming agents are often used to prepare porous ceramics. The process involves adding organic or inorganic chemicals that form volatile gases when heated and treated to ceramic raw materials to produce foams that result in a porous structure after firing. The blowing agent can be mixed with ceramic powder, and when sintering, the blowing agent then releases gas in the body of the blank to produce pores, thus obtaining porous ceramics, such as mixing CaCO3 with ceramic powder, and during sintering, CaCO3 releases CO2 gas due to thermal decomposition, leaving pores in the ceramic body; or the blowing agent can be mixed with ceramic slurry to produce a large number of bubbles through chemical reaction.

Porous ceramic materials with high porosity can be prepared by using the process of adding gas blowing agent to form pores, and the porosity can reach more than 95%. The shape, composition and density of ceramic products can be easily controlled, which is especially suitable for preparing porous ceramics with closed pores, and the pore size of the gas pores can be easily controlled.

Lubricant

In the water-based cast system, it can improve the wettability of water on ceramic powder and the dispersion uniformity of slurry, shorten the mixing time and improve the surface properties of plain billets. Lubricants are generally some solvent-soluble surfactants, such as: glycerol triglycerides, sulfonates and phosphates, etc.

Homogenizer

It can improve the mutual solubility of slurry components and prevent the formation of crust on the surface of slurry, such as cyclohexanone.

Defoamer

In the process of ball milling and stirring, harmful air bubbles may be generated in the slurry, and generally the elimination of air bubbles is accomplished by the joint action of defoamer and mechanical stirring. At present, the commonly used defoamers include mineral type defoamer, polyether type defoamer and silicone type defoamer.

Flocculant

In order to prevent the slurry from forming over-density precipitation reagent, the flocculant used for flow forming is affected by pH, which can be counteracted by adjusting the pH close to the isoelectric point to the dispersant.

Summary

Ceramic additives are an important member of the family of chemical additives, belonging to an important category of fine chemicals, its quality and application is directly related to the improvement of product quality, performance and processing technology. The promotion of the use of new additives in the ceramic industry, to improve product quality, increase production and reduce energy consumption will play a very big role, especially for reducing energy consumption and promote the green work of the ceramic industry will also play a positive role.


Reference Sources
[1] Zhang, Haifeng. Research and application of multifunctional composite ceramic additives
[2] Lin L. et al. Application and development trend of ceramic additives in the ceramic industry
[3] Qin Wei. Introduction to the application and development status of ceramic additives
[4] Sun Shilai et al. The development and application of ceramic additives
[5] Xie Yuzhou et al. Research progress of cast molding technology
Article source: Shanchuan Powder Network

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