In many fields of modern industry, refractories play an indispensable role, and sintered mullite is one of the best. With its excellent physical and chemical properties and wide application prospects, sintered mullite is favored in the field of high temperature technology. In this paper, the characteristics, application, quality control, packaging and transportation of sintered mullite will be discussed in depth, in order to provide comprehensive reference for practitioners in related industries.

I. Introduction of sintered mullite

Sintered mullite is a kind of high-temperature sintered product with mullite as the main mineral phase. Mullite is a kind of aluminosilicate mineral with complex crystal structure, and its chemical formula is 3Al₂O₃·2SiO₂. The production process of sintered mullite usually involves the steps of selecting raw materials, fine processing and high temperature sintering to ensure that the products have high purity, low impurity content and excellent physical and chemical properties.

II. Characteristics of sintered mullite

With its unique mineral composition and crystal structure, sintered mullite shows a series of excellent properties, which make it perform well in high temperature environment.

(1) high mullite phase content

The mullite phase content of sintered mullite is usually high. For example, the mullite content of the products with the four grades M45, M47, M60 and M70 mentioned in this paper reaches 55%, 65%, 78% and 78% respectively. High mullite phase content means that the material has better high-temperature stability and thermal shock resistance, because mullite crystal structure can remain relatively stable at high temperature and is not easy to undergo phase transformation or decomposition.

(2) Low porosity

Low porosity is another characteristic of sintered mullite. The porosity of the four grades mentioned in this paper is controlled at a low level, such as the maximum porosity of M45 and M47 grades is 2.0%, and the maximum porosity of M60 and M70 grades is 2.8%. Low porosity means high compactness of the material, which can effectively reduce heat transfer and gas penetration, thus improving the corrosion resistance and permeability resistance of the material. In high temperature environment, sintered mullite with low porosity can better resist slag erosion and gas oxidation, and prolong the service life of the material.

(3) High fire resistance

The fire resistance of sintered mullite is very high, and the fire resistance of the four grades mentioned in this paper is 1750℃, 1790℃, 1820℃ and 1850℃ respectively. High fire resistance means that the material can maintain structural stability at extremely high temperatures without melting or deformation. This enables sintered mullite to meet the needs of many high-temperature industrial applications, such as glass melting furnaces, ceramic firing kilns, iron and steel smelting furnaces, etc. These equipments need to withstand extremely high temperatures during operation, and sintered mullite can provide reliable fire protection for these equipments.

(4) Good thermal shock resistance

Sintered mullite has good thermal shock resistance, can maintain structural integrity under the condition of rapid temperature change, and is not easy to crack or peel off. This characteristic is mainly due to the low thermal expansion coefficient of mullite crystal structure and the uniform microstructure inside the material. In practical application, for example, in the places where the temperature changes frequently, such as the feeding port and the discharging port of the glass furnace, the sintered mullite can withstand frequent temperature fluctuations, ensure the normal operation of the equipment, reduce the number of downtime and maintenance caused by thermal shock damage, and thus improve production efficiency and economic benefits.

(5) Low creep at high temperature

High-temperature creep refers to the slow deformation of materials under high temperature and stress. The high temperature creep of sintered mullite is small, which means that the shape and size of the material can remain relatively stable under high temperature environment and will not be obviously deformed due to long-term stress. This characteristic is very important for some high-temperature parts that need accurate size and shape, such as ceramic molds and glass molds. The mould made of sintered mullite can maintain good dimensional accuracy at high temperature, ensure the quality and consistency of products and reduce production costs.

(6) high bulk density and high hardness

The bulk density of sintered mullite is high, and the bulk densities of the four grades mentioned in this paper are 2.55 g/cm³, 2.64 g/cm³, 2.78 g/cm³ and 2.80 g/cm³ respectively. High bulk density means that the material contains more substances per unit volume, thus having higher strength and wear resistance. At the same time, sintered mullite also has high hardness, which makes it show good wear resistance in the face of mechanical impact and wear. For example, in ceramic production, grinding balls and grinding discs made of sintered mullite can effectively grind ceramic raw materials, and have less self-wear and long service life, thus improving production efficiency and product quality.

(7) Uniform expansion

Sintered mullite can expand uniformly during high-temperature heating, which is very important for some high-temperature equipment that needs to accurately control the dimensional change. For example, in the crown and furnace wall of glass melting furnace, sintered mullite can expand uniformly, avoiding structural stress concentration and damage caused by local uneven expansion. Uniform expansion can also ensure the sealing performance of equipment in the process of high temperature operation, prevent gas leakage and heat loss, and improve the energy utilization efficiency and operation safety of equipment.

(8) Good chemical resistance

Sintered mullite has good chemical resistance and can resist the erosion of many chemicals. This is mainly due to the stability of its chemical composition and the compactness of its crystal structure. In glass melting furnace, sintered mullite can resist the corrosion of alkali metal oxides in glass melt; In ceramic production, it can resist the chemical action of acidic or alkaline substances in ceramic raw materials. Good chemical corrosion resistance enables the sintered mullite to run stably in a complex chemical environment for a long time, reducing the material damage and equipment maintenance cost caused by chemical corrosion.

III. Application of sintered mullite

As a high-performance refractory, sintered mullite is widely used in many industrial fields, especially in the field of high-temperature technology.

(1) Glass industry

In glass melting furnace, sintered mullite is widely used to manufacture key parts of the furnace, such as the crown, pool wall, liquid hole and so on. These parts need to withstand the erosion of high-temperature glass liquid and the impact of temperature change. Sintered mullite is an ideal material choice because of its high refractoriness, low porosity, good thermal shock resistance and chemical corrosion resistance. For example, the fire resistance of M70 grade sintered mullite is as high as 1850℃, which can meet the requirements of high temperature operation of glass melting furnace. At the same time, its low porosity and chemical corrosion resistance can effectively resist the corrosion of alkali metal oxides in glass melt, prolong the service life of the furnace and reduce the production cost.

(2) Ceramic industry

In ceramic production, sintered mullite can be used to make ceramic molds, kiln furniture, nozzles and other parts. Ceramic molds need to maintain good dimensional accuracy and shape stability at high temperature to ensure the quality and consistency of ceramic products. The characteristics of sintered mullite, such as high bulk density, high hardness and low creep at high temperature, make it an ideal material for manufacturing ceramic molds. For example, the sintered mullite with M60 grade has a bulk density of 2.78 g/cm³ and high hardness, which can maintain the shape and dimensional accuracy of the mold at high temperature and improve the quality and production efficiency of ceramic products. In addition, the kiln furniture and nozzles made of sintered mullite can also run stably in high temperature environment, reducing the production interruption caused by material damage.

(3) Iron and steel industry

In iron and steel smelting furnace, sintered mullite can be used to make furnace lining, taphole and other parts. These parts need to withstand the erosion and mechanical impact of high temperature slag. The high refractoriness, low porosity and good chemical resistance of sintered mullite enable it to run stably in the harsh environment of iron and steel smelting furnace for a long time. For example, the fire resistance of M47 grade sintered mullite is 1790℃, which can meet the requirements of high temperature operation of iron and steel smelting furnace. At the same time, its low porosity and chemical resistance can effectively resist the erosion of slag, prolong the service life of furnace lining and reduce the cost of steel production.

(4) Other industrial fields

Sintered mullite is also widely used in other industries that need high-temperature refractories, such as petrochemical, electric power, building materials and other industries. In the field of petrochemical industry, sintered mullite can be used to manufacture the lining material of catalytic cracking unit, which can resist the corrosion and chemical corrosion of high temperature oil and gas. In the power industry, sintered mullite can be used to make lining materials for high temperature furnaces, which can ensure the structural stability and operational safety of the furnace body. In the building materials industry, sintered mullite can be used to manufacture parts such as kiln car and kiln wall of tunnel kiln, which can improve the service life and production efficiency of kiln.

IV. Quality control of sintered mullite

In order to ensure the quality of sintered mullite, production enterprises usually establish a perfect quality control system. The quality inspection items mentioned in this paper include particle size distribution, chemical analysis, physical properties, mineral composition and pH value.

(1) particle size distribution

Particle size distribution is one of the important factors affecting the properties of sintered mullite. Reasonable particle size distribution can improve the compactness and strength of materials and improve the construction performance of materials. In the production process, the ideal particle size distribution can be obtained by accurately controlling the grinding and screening process of raw materials. For example, for sintered mullite used for the crown of glass melting furnace, larger particles are needed to improve the corrosion resistance and thermal shock resistance of the material; For sintered mullite used in ceramic molds, smaller particles are needed to ensure the construction performance and dimensional accuracy of the material.

(2) Chemical analysis

Accurate control of chemical composition is the key to ensure the properties of sintered mullite. The chemical composition of sintered mullite mentioned in this paper includes Fe₂O₃, SiO₂, TiO₂, KO, Na₂O, MgO and CaO. Through chemical analysis, it can be ensured that the content of each chemical component in the product meets the standard requirements. For example, the content of Fe₂O₃ will affect the reduction resistance and corrosion resistance of materials, and the content of SiO₂ will affect the fire resistance and thermal shock resistance of materials. Strictly controlling the content of chemical components can ensure the stability and reliability of sintered mullite in different application fields.

(3) Physical performance test

Physical performance test includes the detection of bulk density, porosity, fire resistance, thermal shock resistance, high temperature creep and other items. These test items can comprehensively evaluate the performance indexes of sintered mullite and ensure that the products can meet the needs of different application fields. For example, through the test of bulk density and porosity, the compactness and erosion resistance of materials can be evaluated; Through the tests of fire resistance and thermal shock resistance, the stability and reliability of materials in high temperature environment can be evaluated. Through the test of high temperature creep, the deformability of materials under high temperature and stress can be evaluated. Strict physical performance testing can effectively screen out unqualified products and ensure the quality of products.

V. Packaging and Transportation of Sintered Mullite

The packaging and transportation mode of sintered mullite is of great significance for ensuring product quality and reducing transportation cost. The packaging methods mentioned in this paper include 25kg plastic woven bags or kraft paper bags in large bags of 1000-1500kg, and 25kg plastic woven bags or kraft paper bags in trays and covered with plastic films. These packaging methods can effectively protect sintered mullite from damage during transportation, and are convenient for loading, unloading and storage.

In terms of transportation, it is mentioned that a 20-foot container can carry 24 tons and a 40-foot container can carry 28 tons. This standardized container transportation mode can improve transportation efficiency, reduce transportation costs and facilitate international logistics transportation. As an important refractory, sintered mullite has a wide market demand. It can be transported to customers all over the world conveniently by container transportation to meet the needs of industrial production in different regions.

VI. Conclusion

As a high-performance refractory, sintered mullite has been widely used in glass, ceramics, steel and other industrial fields because of its excellent properties such as high mullite phase content, low porosity, high refractoriness, good thermal shock resistance, small high-temperature creep, high bulk density and high hardness, uniform expansion and good chemical corrosion resistance. Through strict quality control system, including particle size distribution, chemical analysis, physical performance test, mineral composition analysis and pH value detection, the quality stability and reliability of sintered mullite can be ensured. Reasonable packaging and transportation methods can effectively protect the safety of products during transportation, reduce transportation costs and improve market competitiveness. With the continuous development of high-temperature industry and the improvement of environmental protection requirements, sintered mullite has a broad market prospect and will play a more important role in future industrial production.