Investigation Of Effects Of Alum And Potassium Sesquicarbonate On The Fire Characteristics Of Flexible Polyurethane Foam

Applications of polyurethane foam polymer [52]

Polyurethane foams, used for almost 40years, offer a wide variety of products suitable for various applications.

Polyurethane foams are also used as adhesives, automobile seats, tennis grips, electronic components, abrasion resistance etc.

Alum

Alum is referred to as specific chemical compound and a class of chemical compounds. The specific compound is the hydrated aluminum potassium sulfate with the formula KAl(SO4)2 . 12H2O. The wider class of compounds known as alums have related stoichiometry, AB (SO4)2. 12H20 [54].

Crystal chemistry of the alums

Double sulphates with the general formula A2SO4. B2 (SO4)3 . 24H2O are known where A is a monovalent cation such as sodium, potassium, rubidium, thallium or a compound cation such as ammonium (NH4+), methylammonium (CH3NH3+), hydroxylammonium (HONH3+), etc. B is a trivalent metal ion such as aluminium, chromium, titanium, manganese, gallium, ruthenium, etc. The specific combinations of univalent cation, trivalent cation and anion depends on the sizes of the ions. Alums crystallize in one of the three different crystal structures. These classes are caused , – β – and γ – alums,

Origin of alum

The word “alum” is derived from the latin word “alumen” and was found naturally in the earth. Different substances were distinguished by the name of “alumen” but they were all characterized by a certain degree of astringency and were all employed in dyeing and medicine. One specie was a liquid which was apt to be adulterated but when pure it had the property of blackening when added to pomgranate juice. Another kind of alum called “ schistos” by the Greeks forms white threads upon the surface of certain stones. From the name schistos and the mode of formation there can be little doubt that this species was the salt which forms spontaneously on certain salty minerals as alum slate and bituminous shale and which consist chiefly of sulphates of iron and aluminium. Native alumen from melos appears to have been a mixture mainly of alunogen (Al2 (SO4)3 . 17H2O) with alum and other minor sulphates [55].

The western desert of Egypt was a major source of alum substitutes in antiquity. These evaporites were mainly FeAl2(SO4)4 . 22H2O, MgAl2 (SO4)4 . 22H2O etc.

The presence of sulphuric acid in potassium alum was known to the alchemists since the time of Jabir Ibn Hayyan (Geber) who discovered sulphuric acid in the 8th century. J.H Pott and Andreas Marggrai demonstrated that alumina was another constituent.

Tobern Bergman observed that the addition of potash or ammonia made the solution of alumina in sulphuric acid crystallize and that potassium sulphate is frequently found in alum.

In 1797, L.N. Vanguelin published a dissertation demonstrating that alum is a double salt composed of sulphuric acid, alumina and potash. Soon after, J. A. Chaptal published the analysis of four different kinds of alum namely, Roman alum, Levant alum, British alum and alum manufactured by himself. This analysis led to the same result as vanguelin.

Production of alum

Alum from alunite

In order to obtain alum from alunite, it is calcined and then exposed to the action of air for a considerable time. During this exposure it is kept continually moistened with water so that it ultimately falls to a very fine powder. This powder is then dissolved with hot water, the liquor decanted and the alum allowed to crystallize. The alum schist's employed the manufacture of alum are mixtures of iron pyrite, aluminium silicate and various bituminous substances and are found in upper Bohemia, Belgium and Scotland. These are either roasted or exposed to the weathering action of the air. In the roasting process, sulphuric acid is formed and acts on the clay to form aluminium sulphate. The mass is now systematically extracted with water and a solution of aluminium sulphate of specific gravity 1.16 is prepared. This solution is allowed to stand for some time and is then evaporated until ferrous sulphate crystallizes on cooling; it is then drawn off and evaporated until it attains a specific gravity of 1.40. it is now allowed to stand for some time, decanted from any sediment and finally mixed with the calculated quantity of potassium sulphate well agitated, and the alum is thrown down as a finely divided precipitate of alum meal.

Alum from clay or bauxite

Here, the material is gently calcined then mixed with sulphuric acid and heated gradually to boiling; it is allowed to stand for some time, the clear solution drawn off, mixed with potassium sulphate and allowed to crystallize. When cryolite is used for the preparation of alum, it is mixed with calcium carbonate and heated. By this means, sodium aluminate is formed, it is then extracted with water and precipitated either by sodium bicarbonate or by passing a current of carbon dioxide through the solution. The precipitate is then dissolved in sulphuric acid, the requisite amount of potassium sulphate added and the solution allowed to crystallize.

Types of alum [56]

Soda alum

Sodium alum Na2SO4. Al2(SO4)3. 24H2O mainly occurs in nature as the mineral mendozite. It is very soluble in water and extremely difficult to purify. In the preparation of this salt, it is preferable to mix the component solutions in the cold and to evaporate them at a temperature not exceeding 60â—¦C. soda alum is used in the manufacture of baking powder.

Ammonium alum

Ammonium alum, NH4Al(SO4)2 . 12H2O a white crystalline double sulphate of aluminium is used in water purification, vegetable glues, porcelain cements, natural deodorants, fire proofing textiles etc.