Basic Shaped Refractories...

Basic Shaped Refractories  Basic shaped refractories are those refractories which have resistance to corrosive reactions with chemically basic slags, dusts and fumes at elevated temperatures. They are both MgO and CaO based refractories or in combination between them or in combination between MgO and Cr2O3. These refractories belong to MgO- CaO equilibrium system as shown in Fig 1. Fig 1 MgO-CaO equilibrium system  Broadly basic refractories falls into one of the following five compositional categories (Fig 2). Products based on dead burned magnesite (DBM) or magnesia. These products are known as magnesite bricks. Products based on DBM or magnesia in combination with chrome containing materials such as chrome ore. Chrome containing magnesite bricks with about 5 % to 15 % Cr2O3 are known as magnesite chrome bricks while those with 15 % to 30 % chromium are called chrome magnesite bricks. DBM or magnesia in combination with spinel. In these basic bricks magnesia-rich spinel (MgO.Al2O3) replaces chrome ore. These bricks are called magnesite spinel bricks. DBM or magnesia in combination with carbon. These bricks are known as magnesite carbon bricks. Dolomitic products. These bricks are known as sintered dolomite bricks. Fig 2 Categories of basic shaped refractories based on composition  Basic refractories are characterized by an extremely high refractoriness and good resistance to basic slags. Compared to fireclay bricks they do not have glassy phase. These refractories have low resistance both to thermal shocks and creep at temperatures close to 1500 deg C. The chemical-physical characteristics together with a very high thermal capacity and thermal conductivity make basic refractories ideal refractories for steel making processes. Hence basic refractories received increased importance with the introduction of basic oxygen steel making process. One of the more important types of magnesite bricks are those which have low...

Magnesia

Magnesia Magnesia or magnesium oxide (MgO) is a white hygroscopic solid mineral that occurs naturally as periclase. It forms magnesium hydroxide in the presence of water [MgO + H2O = Mg(OH)2], but this reaction can be reversed by heating magnesium hydroxide to separate moisture. Magnesium (Mg) is the eighth most abundant element and constitutes about 2 percent of the crust of the earth. It is the third most plentiful element dissolved in seawater, with a concentration averaging 0.13 %. Although magnesium is found in over 60 minerals, only dolomite, magnesite, brucite, carnallite, and olivine are of commercial importance. Magnesium and magnesium compounds are produced from seawater, well and lake brines and bitterns, as well as from the above mentioned minerals. Magnesite (MgCO3), the naturally occurring carbonate of magnesium (Mg) is one of the key natural sources for the production of magnesia (MgO) and subsequently fused magnesia. It is the world’s  largest source of magnesia. It contains a theoretical maximum magnesia content of 47.6 %. It occurs in two distinct physical forms namely (i)  macro-crystalline and (ii) crypto-crystalline. Crypto-crystalline magnesite is generally of a higher purity than macro-crystalline ore, but tends to occur in smaller deposits than the macro-crystalline form. The word magnesite literally refers only to the natural mineral, but common usage applies this name to three other types of materials, dead burned magnesia (DBM), electro fused magnesia and calcined magnesia also called caustic calcined magnesia. Often magnesia word is replaced by magnesite in these products. These products of magnesite often differ mainly in density and crystal development that results from different levels of heat application. The three products of magnesite are shown in Fig 1. Fig 1 Products of magnesite  Magnesia is an alkaline earth metal oxide. Magnesium oxide is normally produced by the calcinations of...