How to identify calcium-free silica bricks?

Calcium-free silica bricks are becoming more and more common on the top of glass furnaces, but their appearance is similar to ordinary silica bricks. How to pick it out at a glance? The following three methods can be used directly.

1.First look at the surface of “calcium-free silica bricks”: understand the physical properties

We can make a preliminary judgment by observing its physical properties.

First, lay the brick flat in natural light for comparison. Calcium-free silica bricks are closer to white or light gray in color because of their pure raw materials and few impurities. Ordinary silica bricks usually appear light yellow or yellowish brown in cross section because they contain impurities such as iron and titanium as well as calcium oxide mineralizers.

In addition, a comparison is made from a structural perspective. The crystal structure of the former is more uniform and dense, and the porosity is relatively low. If you touch its cross-section with your hand, you can feel a more delicate texture. In comparison, the latter may have a stronger sense of grain.

This difference in appearance and structure is the external manifestation of the different internal chemical composition.

2.Check the data again to know the chemical properties

The most fundamental way to identify the brick is to look at its chemical composition.

Calcium oxide is usually introduced as a mineralizer during the production process of ordinary silica bricks to promote the conversion of quartz to tridymite. Its content is generally between 2% and 3%.

In contrast, the core feature of calcium-free silica bricks is their extremely low calcium oxide content, which is usually required to be less than 0.1%.

Therefore, checking the material’s quality analysis report and confirming the CaO index is the first step to distinguish the two.

3.Key performance and application scenarios

Combining performance and application scenarios is an effective verification method to identify this type of brick.

The most outstanding properties of this brick are its extremely high refractoriness, as well as its excellent creep resistance and chemical corrosion resistance. Especially the resistance to alkaline atmosphere. These properties make it an ideal choice for glass melting furnaces, ceramic tunnel kilns, etc.

If you see refractory materials with a service life far exceeding that of ordinary silica bricks in a certain part of the furnace that requires extremely high material purity, such as a glass melting furnace, then it is very likely to be calcium-free silica bricks.

Therefore, understanding its application areas can in turn help us determine the true properties of the material.

In short, grasping these three points will basically help you choose the right calcium-free silica bricks. At the same time, when choosing refractory bricks, try to find a refractory brick supplier that can provide a full set of test data and has stable specification tolerance control, so that you can reduce rework in subsequent furnace construction.