Tabular Alumina, also known as Tabular Alumina, is a type of sintered alumina that is rapidly sintered at a temperature of 1925°C, slightly below the melting point of α-Al2O3 (2050°C), and the grains reach a completely recrystallized α-Al2O3 with a two-dimensional planar platelet shape and a microstructure characterized by more inter- and intracrystalline rounded closed pores.

The slab corundum was sintered in 1934 in a vertical kiln invented by Thomas S. Curtis and was produced commercially in 1935 after intermediate tests for use as a refractory and furnace lining material in the ceramic industry. During this period, Alcoa (now known as Ammann Aluminum) developed a series of slab corundum products made from low Na2O industrial alumina.

The development history of slab corundum in China

The history of the development of slab corundum in China can be roughly divided into four stages: the initial contact stage, the understanding development stage, the trial production stage, and the development and growth stage.

Initial contact stage

In the 1970s, WISCO 07 project used high alumina brick produced by American-made slab corundum as raw material, thus the domestic resistant material industry came into contact with slab corundum, with the start of construction of Baosteel, the introduction of some high-grade resistant material products production technology, such as sliding plate, continuous casting of three major parts, etc., due to production needs, must import slab corundum from Alcoa as its main raw material.

Understanding the development stage

In 1992, Alcoa gave Luoyang Refractories Research Institute a batch of granular material, after the in-depth analysis of the Institute, the plate corundum only had a more thorough understanding. Alcoa then introduced the product into China and promoted its application. Due to the technical control of Alcoa, it was difficult for domestic enterprises to obtain its production technology. In order to promote the development of national industry, China Refractories Industry Association attached great importance to the development of sintered corundum, and the "Eighth Five-Year Plan" and "Ninth Five-Year Plan" were taken as important issues to be tackled. The domestic research institutes and production units also started continuous exploration, from the 1990s, Professor Shen Jiyao's group of Tianjin University and the former Mehekou Grinding Wheel Factory technicians conducted experiments on the electrofusion method and passed the technical appraisal, but due to the limitations of the use of technology did not achieve the expected purpose, the product performance, physical and chemical indicators do not meet the requirements of use, and therefore did not form the market supply.

Trial production stage

At the same time, Shandong Aluminum built a 200mm diameter vertical kiln to test the production of sintered slab corundum, and in 1996, Jinan Pingyin Lunai New Material Factory built a 400mm diameter vertical kiln to produce sintered slab corundum on the basis of Shandong Aluminum's test.

Ltd. built a production line with an annual capacity of 4,000 tons of sintered slab corundum in 2001, based on extensive research and study, with Luoyang Refractories Research Institute and Shaanxi Metallurgical Design Institute as the main partners, together with Zhang Huiyou and other technical personnel from Jinan Pingyin Lunai New Material Factory, and produced products to meet the requirements of users in September 2002, unveiling a new era of sintered slab corundum. In September 2002, we produced the products to meet the requirements of customers, which opened the prelude of mass production of sintered plate corundum.

Development and growth stage

After the successful commissioning of sintered slab corundum production in Hanzhong Qingyuan New Materials Co. Ltd. invested in building one slab corundum production line every year from 2009 to 2011, and now the capacity of slab corundum reaches 40,000 tons/year. Through nearly 10 years of research and development, we have realized the industrialization, scale and localization of sintered plate corundum.

The basic process of slab corundum production

Ball milling

Bayer lightly sintered alumina powder is used as raw material, and continuous ball milling is carried out to achieve a certain fineness and specific surface area, which helps sintering and densification of alumina powder.

Balling

The finely ground powder is formed into balls using ball forming discs or cylinders. The formed billet balls need to have a certain strength to avoid breaking during transportation to the dryer. The problems such as high water content of semi-finished balls, easy delamination and drying difficulties in the ball forming process are properly solved by corresponding process optimization design.

Drying

The formed billet balls enter the dryer, and about 15% (w) of the moisture is removed by drying with the counter-current hot air in the vertical kiln. However, the temperature inside the vertical kiln should be strictly controlled to avoid cracks and delamination inside the billet balls, and even lumping and furnace blocking, which eventually cause interruption of ball flow operation and decrease of drying quality.

Sintering

After the billet balls are dried, they enter the shaft kiln. The sintering temperature is 1900~1950℃. By controlling the temperature and flow rate of the hot air in the shaft kiln, a fully developed and sintered slab corundum structure is obtained. After sintering, after cooling, picking (picking out over-fired and under-fired products), inspection (testing the physical and chemical indexes of the completely sintered products), crushing and sieving, products of different grain sizes can be obtained.

The microstructure diagram of the plate corundum produced by Zhejiang Zili Co. It can be seen that: the corundum grain size at low magnification is around 50~200μm, the crystal contains a large number of micron-sized pores, and the grains grow in a step-like manner, which makes the slab corundum have excellent thermal shock stability, thus it is used in the refractory industry on a large scale.

Problems.

1. Unstable color appearance

Because the industrial alumina contains some trace MgO, CuO, affected by the atmosphere in the furnace, the kiln material sometimes appears yellowish, and lavender, and foreign companies from the appearance of the product has a significant gap. This is related to the domestic kiln control level, and it is difficult to solve in a short time.

2、Sintered spherical material layering ratio

However, the relationship between the speed of the ball forming machine, the amount and speed of the water added, the amount and speed of the mother ball, and the amount and speed of the powder added has not been explored, and it is difficult to ensure that the layering phenomenon occurs during the ball forming process. In addition, the way of drying the spheres also affects. From the production of pellet material in each production plant, the proportion of layered material is much, which is the most urgent problem to solve.

3、The risk of overcapacity exists

In recent years, the production capacity has increased rapidly, some large refractory production plants, there are plans to start their own plate corundum production line. If there is no major change in the production conditions of white corundum, the market space can no longer bear about 300,000 tons of plate corundum production capacity.

With the change of economic situation, some plate corundum production plants are bound to raise the banner of price war to seize the market.