However, there are also some problems in directly bonded magnesia-chrome bricks:

(1) The magnesia-chrome brick will react with the cement clinker on the firing zone of the cement kiln to produce low-melting substances, such as: at 1335 °C, C12A7 will be formed, At 50, it will generate C4AF. At 1500°, it will generate CMS. At 1575, it will generate C3MS, and these low melting point mineral phases will penetrate into the

The depth of the refractory brick makes it difficult to form a thicker kiln skin layer on the surface of the refractory brick. As a result, the chemical corrosion resistance of refractory bricks becomes poor, and the application time changes. short.

(2) When the cement port is inspected inside and outside the dry oxidizing gas, monovalent Cr3+ is oxidized to form hexavalent cr6+, and then the front chrome brick will be severely corroded by sulfate, from.

The Cr6+ compounds are converted into water-soluble substances, and these substances containing hexavalent chromium ions will be discharged to the outside along with the refractory bricks and exhaust emissions after use.

noodle. As we all know, hexavalent Cr6+ compounds are highly toxic, which will seriously pollute the environment, cause serious harm to organisms, and even cause cancer.

(3) When the cement rotary kiln is in a reducing atmosphere inside and outside the kiln, O can undergo a reduction reaction with the magnesia chromite in the magnesia-chromium brick to generate magnesia ashite. and three

Assuming that the reducing atmosphere inside the cement rotary kiln body is converted into an oxidizing atmosphere, the internal structure of the refractory brick body will be completely disintegrated, reducing the use of refractory bricks.

between.

(4) Most of the kiln skin components of cement kilns using magnesia-chrome bricks are dicalcium sulfate. When the kiln body is cooled, B-C2S becomes V-C2S, resulting in the kiln skin becoming powdery

Eventually peeling off, shortening the application time of magnesia-chromium bricks.

With the strengthening of environmental protection policies, people's environmental awareness is also constantly improving. It is required to stop using it all over the world. In view of this situation, it is proposed to

The new idea of chrome-free. Although chrome-free refractories for cement kilns have been proposed for many years, chrome-free refractory bricks that can replace magnesia-chrome bricks now rely on

Of course not developed. Some researchers in the refractory industry, in order to achieve the recycling of materials, reduce the emission of harmful gases, and prolong the use time

For different purposes, it has always changed the properties of magnesia-chrome bricks:

(1) The content of chromium in the magnesia-chrome bricks required to be used is low

(2) After the magnesia-chrome brick is recycled and reused, a spinel crystallization will be formed on the surface, thereby enhancing the strength of the castable [3] reducing the magnesia-chrome brick

The discharge of waste bricks reduces the degree of environmental pollution:

(3) Using relatively strong reducing substances such as FeS04, MnS04, etc., the reduction reaction occurs with the used magnesia-chrome bricks, and the highly toxic Cr^ is converted into non-toxic

It seems that this reduction method is not only expensive, but also the synthesis process is very complicated, and it cannot be put into large-scale industrial production.

(4) By adding additives to the magnesia chrome brick, such as nano Fe203, Al203ZrO2, etc., the high temperature properties of the magnesia chrome brick body can be enhanced

It can improve the binding energy of the material, promote sintering, and reduce the apparent porosity of the magnesia-chrome brick body.