Ankara-bala Alçıtaşı Yataklarının Jeolojisi Ve Jeokimyası İle Alçının Teknolojik Parametrelerinin Araştırılması

Abstract

Bu çalışmanın amacı, çok eski zamanlardan beri bilinene alçıtaşı, hemihidrat ve anhidritin incelenmesidir ve hemihidratın en önemli kullanım alanı inşaat sektörüdür ve bu amaçla ilk kullanımı 1917 yılına kadar gitmektedir. Hemihidratın inşaat sektöründe kullanımı beraberinde pek çok avantajlar içermektedir. Bunların başında alçıpan olarak kullanımında ısı izolasyonu, ses yalıtımı gelmektedir ve bu özellikler bugünkü inşaat sektöründe oldukça önemlidir. Türkiyede alçıtaşı yatakları oldukça kolay madencilik koşullarına sahiptirler. Çok geniş alanlardan alçıtaşı madenciliği yapılabilmekte ve hemihidrat üretilebilmektedir. Fakat bu malzeme çok büyük avantajları olmasına rağmen inşaat sektöründe yeterli olarak kullanılmamaktadır. Bir diğer uygulama alanı olarak da dişçilikte kullanımını sayabiliriz. Bazı ülkelerde alçıtaşı kireç elde edilmesinde hammadde olarak kullanılmaktadır. Ayrıca daha çok paris plasteri adı verilen ve endüstride daha çok stucco olarak bilinen kalsine olmuş alçı eldesindede alçıtaşı kullanılmaktadır. Kimyasal olarak alçıtaşı, çift sulu sülfattır formülü ise CaS04.2H20'dir. Bünyedeki suyun uzaklaştırılmasına kalsinasyon denilir. Bu işlem iki ana basamaktan oluşur; CaS04.2H20 - CaS04.l/2H20+l/2H20 CaS04. 1/2 H20 - CaS04+ 1/2 H20 Bu reaksiyonlar tersinir reaksiyonlardır, fakat 100 °C sıcaklık civarında meydana gelmezler. Bu işlemler sonucunda bünyedeki su yarım molekül atılır ve hemidrat elde edilir, formülü ise CaS04.l/2H20'dir. Alçıtaşının eldüstrideki kullanımında daha çok geciktirici ve hızlandırıcılar kullanılmaktadır ve kristalizasyon üzerinde etkileri büyüktür. Daha çok endüstriyel uygulamalarda sitratlar ve tartaritler geciktirici olarak kullanılmakta, hızlandırıcı olarak ise potasyum sülfat, sodyum klorit yaygın olarak kullanılmaktadır.

Aim of this study; gpysum, hemihydrate and anhydrite were all known and used from early times. One of the most important usage of hemihydrate is in the building industry and it is used firts time for this purpose in 1917, in England. Besides ease and speed; using hemihydrates in buildings as plaster-board have lots of advantages such as heat isolation, sound and moisture arrangement which are, in fact, very important factors in today's building industry. In Turkey, extensive gypsum deposits are present having easy mining conditions. Gypsum mined from this deposits and hemihyrate produced from gypsum are consumed in various areas. But this material has not enoughly been used in building industries together with above mentioned advantages, in spite of building deficiency in Turkey. On the other hand, hemihydrate used for dental application is important. This study was under taken to check the viability of the technique described in the patent literature as a process and also to check the physical and chemical properties of the product in view of the existing information obtained by other investigators on the basis of lab. scale studies. The study, it is hoped would provide a basis leading to a higher interest in the subject in this country. Gypsum is known to have been used by architects, builders and sacientest for more than five thousand years. The Egyptians used it more than three thousand years before Christ in building the great pyramid of Cheops in the fourth dynasty of Egypt. The walls of the tombs were plastered with gypsum, and murals telling the life and times of the Pharaoh entombed therien were painted upon this plaster base. Thus for more than fifty centuries gypsum rock has been made into plaster and used to surface the walls of places, to be cast into decorative objects or even to finish wood paneling upon which such great artists as Leonardo da Vinci created some of their enduring masterpcieces. Besides the use in soil treatment and for building, gypsum also find many other applications. A major use is in the production of Portland cement. As a filler it is used in paints, paper, baking powders and textiles. It is also employed in the production of sulfiricacid, in yeast manufacture, water treatment and the brewing of beer. In some countries it is used as the raw material for making lime. However, its greatest use is for the production of calcined gypsum or plaster of Paris, commonly called ' stucco ' in the industry. Stucco has numerous uses which depend upon its reservision to gypsum when mixed with sufficient water to form a plastic mix of suitable consistenecy to be poured, pressed or molded into any desired shape or form. It is used in wallboard, lath, sheathing board, tile, building plasters, dental plasters, orthopedic plasters and molding plasters. Chemically, gypsum is mainly calcium sulfate dihydrate, CaS04.2 H20. In its pure form it is a snow whitecrystalline material with a sp gr of 2.31 - 2.33 and a Mohs hardness of 1.5 -2.0. Gypsum is pratically insoluable in most organic solvents and does not cause organic reactions. It is slighty soluable in water, having a maxsimum solubity of 2. 1 g/ liter at about 40 °C. Above and below this temperature its solubility decreaces to manima of 1.8 g/liter at about 0 °C and 1.9 g/liter in the range of 70 - 90 °C. treaces of electrlytes and variations in pH greatly affect the solubity of gypsum in water. Abundant suplies of gypsum are found in nature in a variety of forms, shapes and colors. Commercialy the mst important form are rock gypsum, alabester, selenite, satin spar and gypsite. A related mineral, anhyrite, consisting mainly of anhydrous calcium sulfate. CaSC«4, also appers in nature as adense crystalline rock. Usually white, it is sometimes tited grey, blue or pink. It has a sp gr of 2.8 - 2.9 and a Mohs hardness of 3.0 - 3.5. Nature anhyrite has practically the same solubility as gypsum in water but is less reactive and does not hydrate readly. The most useful property of gypsum is its ability to lose its water of hydration at elevated temperatures and then recombine with water at low temperatures to form the orginal dihydrate. This unique process is the basis for most of the commercial uses of gypsum and gypsum products. The process of removing the water of hydration from gypsum is called calcination. XI This process takes places in two chemical stages for which the major reactions are: CaS04.2H20 - CaS04.1/2 H20 + V2 H20 CaS04.I/2H20 - CaS04 + V2 H20 These reactions require the addition of heat to drive off the water ot hydrations and are reversible in the presence of water or water vapor. The reverse reaction will not occur at temperatures above 100 °C, however and hemihidrate, CaS04. Vi H^ and anhyrite. CaS04 can be produced from gypsum while in contact with water. Whwn gypsum is completely dehydrated at temperatures below 300 °C a higly active anhydrous form of calsium sulfate is obtained. This form called, solublty anydrite, has a great affinity for water and is widely esed as a desiccant. It is used in laboratories and throughout industry under the trade name Derierite. Complete dehydration of gypsum at temperatures above 532 °C produces with anhydrous calcium sulfate with thermodinamic properties identical to those of the naturally occuring anhydrite. This form is generally called insoluable anhydrite or dead burned gypsum. In most commercial calcining processes hemihiydrate is the major product. The material, plaster of Paris or stucco, readly reacts with water at normal atmospheric temperatures to form gypsum. Gypsum deposits are located in Nort America, South America, Europa, Asia, Africa and Australia. Calcining of gypsum is carried out by either of two processes. The mineral is powdered and heated in kettles or it is crushed and heated in rotary kilns. The kettle process is carried out in vertical cylindrical vessels with heavy steel bottoms convex upward, and with horizontal flues to allow the combustion gasses to pass througgh the body charge. The mas is gradually heated while being agitated and is dumped when the temperature is about 160 or 220 °C. The material produced by heating to 160 °C is called first settle stucco and is essentall calcium sulfate hemihdrate. That produced by hetaing to 220 °C is called second settle stucco and is primarily soluable anhyrite. The rotary klin process is a continuos process for the manufacture of calcined gysum. Xll Basically a rotary kiln consists of a long, sligtly inclined cylinder with gypsum fed to one end made to pass throuugh the kiln by its rotary motions. The klin is heated by oil, gas or coal. Gypsum as specified by ASTM C 22-50 ( 1965 ) must contain at least 70 wt % calcium sukfate dihyrate. There are no other uniform specifications for unprocessed gypsum and specifications for processe gypsum and gypsum products vary widely are usually subject to contract agreements. In generaly the nature of impurities present is more citical than the total quantity of impurities. This is so because most commercial uses of gypsum depend upon its ability to calcine and rehyrate. Thus the presence and cocentration of chemicals that greatly affect this property are critical. For this reason, hydroscopic materials are generally not desired in unprocessed gypsum Gypsum formulated for industrial use often contains accelerators or retardes. Many substances are used these purposes. Generally retardes are dispersing or deflocculating agents. Those most commonly used are based on hyrolyzed keratinous materials. Citrates or tartarates are often used as retardes in industrial plasters. Accelerators are most often coagulating or settling agent. Potassium sulfate, sodium chloride, and alum are commonly used for this purpose. Specifications for many building plasters are given by definition. Descriptions of some of the more common types of plaster follow: Gypsum ready - mixed plaster: a calcined gpysum mixwe at the mill wiyh a mineral aggregate. It is designed to function as abase for various finish coats and is often called ' base coat plaster '. It generally contains two to three cubic feet of mineral aggregates to 100 pounds of stucco. Gypsum neat plaster: hemihydrate mixed at the mill with other ingredients to control working qualty and settling time. It may be fibered or unfibered. Mineral aggregates are added onthe job. Neat plaster contains at least 66.0 wt % hemihydrate. Gypsum wood-fibered plaster: stucco containing wood fiber as an aggregate. It contains at least 66.0 wt % calcium sulfate hemihydrate. Xlll Gypsum bond plaster: stucco with ingredients that control working qualty and settin time so as to adapt it for application as a bonding coat over monolithic concrete. Gauging plaster: a plaster prepared for mixing with lime putty to be generally used for a finish coat. It may contain other materials to control setting time and working qualty but must contain at least 66.0 wt % calcium sulfate hemihydrate. Molding Plaster:. a plaster containing at least 80. Wt % calcined gypsum used for making interior embllishment and cornices. Basic terms used in connections with gpysum and gypsum products are fallow; Gypsum: calsium sulfate dihydrate. Anhydrite: natural anhydrous calsium sulfate. Soluable anhydrite: anhydrous calsium sulfate produced bu calcination below 300 °C. Insoluable anhydrite: anhydrous calcium sulfate produced by calcination above 532 °C. Stucco: calcium sulfate hemihdrate produced by partial calcination at 160 °C. Calcination: process to remove the water of hydration of gypsum. Setting: process of recombination with water to form the dihydrate. Plaster: calcined gypsum mixed with other ingredients to control set and for working quality. Set plaster: plaster in which the calcined gypsum has rehydrated to the dihydrate Aggregate: any inert material used as filler in plaster. Retarder: material added to calcined gypsum to slow up the rate of hydration.