Chrome containing refractory

Chromium containing refractories used in different high-temperature industrial kilns are considered to contain hexavalent chromium indiscriminately. But this view obviously lacks the support of experimental data.

Chromium containing refractories include magnesia chromium series, high chromium series and aluminum chromium series refractories. Magnesia chrome bricks are mainly used in industrial fields such as cement, steel and non-ferrous metal smelting, while high chrome refractories are suitable for coal gasifiers and high-performance alkali free glass melting pools.

Magnesia chrome refractories are mainly composed of MgO and Cr2O3, with periclase and magnesia chrome spinel as the main mineral components. Chrome ore is inert to steelmaking slag and compatible with other refractories, while the appearance of magnesia chrome materials improves the thermal shock resistance of magnesia materials. The international standard ISO1109 divides the magnesia chrome products according to the limit content of the main chemical components. The magnesia chrome brick: 55% ≤ MgO ＜ 80%; the chrome magnesia brick: 25% ≤ MgO ＜ 55%; the chrome brick: Cr2O3 ≥ 25%, MgO ≤ 25%. ASTMC455 divides magnesia chrome brick, chrome magnesia brick and chrome brick into 6 grades according to MgO content: 30, 40, 50, 60, 70 and 80, and the minimum content of corresponding MgO percentage is 25, 35, 45, 55, 65 and 75 respectively, and indicates that chrome brick is basically or completely made of chrome ore. Usually, the raw materials used to produce magnesia chrome products are mainly magnesia, chrome sand and synthetic magnesia chrome sand, sometimes a small amount of additives need to be added. The fused magnesia and sintered magnesia with different MgO content (generally more than 89%), together with refractory chrome ore, chrome concentrate, fused magnesia chrome sand or sintered magnesia chrome sand with different Cr2O3 content (sometimes a small amount of chrome green is added), produce many varieties and brands of magnesia chrome products. Nowadays, the most popular varieties for commodity exchanges include magnesia chrome bricks, recombined (semi recombined) magnesia chrome bricks, directly bonded magnesia chrome bricks and unburned magnesia chrome bricks.

The beginning of high chromium refractories began with the research of MgCr2O4 materials. The experiment shows that the high-purity Cr2O3 rich magnesium chromium material made of Cr2O3 and magnesia has formed a stoichiometric magnesia chrome spinel with a structure of large grain MgCr2O4 and Cr2O3 phases. The high chromium refractory is a compact material with strong bonding property and is resistant to the penetration and dissolution of coal slag. 1 Scope

This standard specifies the classification, technical requirements, test methods, quality assessment procedures, packaging, marking, transportation, storage and quality certificate of magnesia chrome bricks. This standard is applicable to fired magnesia chrome bricks for nonferrous smelting furnace, steel refining furnace, cement rotary kiln and other industrial kilns

2 Normative References

The following documents are indispensable for the application of this document. For dated references, only the dated versions are applicable to this document. For undated references, the latest version (including all amendments) is applicable to this document.

GB/T 2992.1 Shape and Dimensions of Refractory Bricks - Part 1: Common Bricks

GB/T 2997 Test Method for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products

GB/T 5070 Chemical Analysis Methods for Chromium containing Refractories

GB/T 5072 Test Method for Compressive Strength of Refractory Materials at Room Temperature

GB/T7321 Preparation of Shaped Refractory Products

GB/T 10325 Rules for Acceptance Sampling Inspection of Shaped Refractory Products

GB/T 10326 Dimension, Appearance and Section Inspection Method of Shaped Refractory Products

GB/T 16546 Packaging, Marking, Transportation and Storage of Shaped Refractory Products

GB/T 17912 Shape and Dimensions of Refractory Bricks for Rotary Kiln

GB/T 18257 Marking of Refractory Brick Hot Surface for Rotary Kiln

GB/T 20511 Classification Rules for Refractory Products

YB/T 370 Test Method for Load Softening Temperature of Refractory Products (Non differential temperature rise method)

YB/T376.1 Test method for fire resistance, medium frequency and thermal shock resistance (water quenching method)

YB/T376.2 Test Method for Thermal Shock Resistance of Refractory Products (Air Quenching Method)

3 Terms and Definitions GB/T 10325 and the following terms and definitions are applicable to this document

3.1 The direct bonded magnesia chrome brick refers to the refractory products made of high-purity magnesia and chrome concentrate as the main raw materials

3.2 The fused and rebonded magnesia chrome brick refers to the refractory products made of fused magnesia chrome sand as the main raw material

3.3 Electric fused semi re bonded magnesia chrome brick refers to the refractory products made of electric fused magnesia chrome sand and sintered magnesia chrome sand, chromite or pre reactive magnesia chrome sand

3.4 Ordinary magnesia chrome bricks refer to refractory products made of ordinary magnesia and ordinary refractory chrome ore.