Kuzey ve Batı Anadolu bentonitlerinin kalıp kumu özelliklerine etkisinin incelenmesi
The Investigation of the effect of north and west anatolian bentonites on casting mold sand properties
- Tez No: 21776
- Danışmanlar: PROF. DR. NİYAZİ ERUSLU
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 183
Özet
ÖZET Bentonit, temel içeriği montmorillonit olan bir kil çeşitidir. Bentonit endüstrinin birçok dalxnda geniş bir kullanım alanxna sahibtir. Türkiye'de ticari önemi olan, Kuzey ve Batı Anadolu bentonitlerinden Ordu ili Ünye ilçesi, Çanakkale ili Ay vacık ilçesi Ahmetçe köyü ve Çankırı ili Kurşunlu ilçesi ve Eldivan ilçesi Hacıbey köyündeki bentonit yataklarına ait bentonitlerin, fiziksel ve kimyasal özellikleri ince lenmiş, döküm endüstrisinde bentonitlerin döküm kalıp ku muna etkileri araştırılmıştır. Kuzey ve Batı Anadolu bentonitlerinin çoğunun 0.5jım. altında tane boyutunda olduğu ve yoğunluklarının da 2.7- 2. 8 gr/cm arasında olduğu tespit edilmiştir. Çankırı ve Ordu bentonitlerinin en fazla şişme (17- 18 katı) gösterdiği, Çanakkale bentonitinin ise 10 katı- şişme gösterdiği gözlenmiştir. En yüksek camlaşma sıcak lıkları Ordu (KH-6) ve Çankırı (Ç-3) bentonitlerinde tes- bit edilmiştir. Ordu ve Çanakkale bentonitlerinin benzer DTA eğrisi gösterdiği ve pik değerlerinin montmorillonit mineraline uyduğu, Çankırı ilinin ise illite uyduğu belirlenmiştir. X-ışınları analizinde Ordu bentonitlerinde montmorillo nit yanında illit mineraline de rastlanılmıştır. Ordu (KH-3, KH-6) bentoni tinde kalsit minerali de belirlen miştir. Çanakkale bentonitinde ise, montmorillonit ya nında kuvars minerali bulunmuştur. Çankırı bentonitle rinde Na-montmorillonit, beidellit ve kuvars tesbit e- dilmiştir. viı
Özet (Çeviri)
THE INVESTIGATION OF THE EFFECT OF NORTH AND WEST ANATOLIAN BENTONITES ON CASTING HOLD SAND PROPERTIES SUMMARY Bentonite is basically a kind of montmorillonite group clay mineral. The term bentonite was first sug gested by W.C.Knigth (1898) in describing a clay mineral found in Wyoming, USA. There have been a number of definitions proposed for bentonite based on mineralogy, origin, and end-uses. The acceptance of these defi nitions can vary from country to country. A suitable and popular definition for bentonite as an industrial mineral has been a clay consisting essentially of min erals of smectite clay mineral group, whose physical properties are dictated by the dominant mineral, and regardless of origin and occurunce. Bentonite is a very fine grained material capable of ion exchanging, which contains montmorillonite group clay minerals. It forms naturally by devitrification of volcanic based rock, alteration of acid based volcanic based rock. It can capable of forming alkaline gel. Bentonite must has a property of swelling at least five times to have a commercial value. A bentonite capable of swelling ten or twenty times, is accepted as a quality one. The swelling property disappears completely above 600°C. Basically bentonites are divided into two groups which are Na-bentonites that swell well in water, and Ca-bentonites that swell less. They are also grouped according to their exchangable cations. Non-swelling type bentonites contain Ca-ions as changable cations. Some of the Ca-bentonites are naturally active, others can become active by acids and are called“activated bentonite”. Ca-bentonites can be converted into Na-bentonites by replacing Ca ion with Na ion. The bentonite formed by this way is termed as synthetic bentonite. Na is the cation which can be changed in swelling type bentonites. For this reason they are called as Na-bentonites. Vlli!The first usage of bentonite has been in the petro leum exploratery in 1940. The industrial usage has began in 1960. The bentonites in the north of Middle Anatolian regions, are Na -bentonites which have applica tions in pelletizing of iron ores in foundary and ex ploratery tower muds. Bentonite has a widespread application in many fields of industry. They are used as binders in metal lurgy for the preparation of casting molds sands and for pelletizing and agglomeration. In the food industry they are used as floculation agent for catching unwanted par ticles in the alcoholic drinks, which give them dimmy appearance. They are also used as fulling element in medicine industry as lighter for butters. They can be utilized for improving and the plasticity of ceramic paste, and for uniform mixing of that paste. In addition to that they also decrease the amount of freezing cracks. With the addition of 1% bentonite to Portland cement, mechanical properties improve the freezing time shorten. In the civil engineering, bentonite is utilized because of its water absorption. The binding property of bentonite is utilized in dam construction. It has an importance in fertilizer industry for providing the wetty environment necessary for growing the plants. Since bentonite keeps water in its structure, it gives usage in fire extinguishers. The swelling type Na-bentonites have been found in Çankırı, Tokat, Çorum, Nevşehir, Kütahya, Çanakkale, Ordu. The deposites found in Tokat, Çankırı and Ordu are the most important ones. The reserves found in Tokat in Reşadiye is expected to have 1.5 million tonage capacity. The reserves found in Çankırı in Eldivan, Çerkez and Kurşunlu are expected to have 3-5 million tonage capacity. The theory of the bonding mechanism in clay-bonded green sands is of great importance for foundry tech nology. According to the Grim bond strength theory, the green strength of clay-bonded molding sands is largely determined linking the grains in a compacted sand, which Grim described as wedge-shaped blocks at the grain contact points. Bentonite-bonded sand grains have, according to Grim, a smooth and uniform envelope. The theory assumes IXthat bentonite particles break down without any diffi culty into very fine elementary platelets during sand preparation and become deposited on top of each other in a uniform arrangement. A typical characteristic, according to Grim' s optical microscope investigations, is the absence of aggregates or coarse bentonite parti cles which have not been broken down during mixing. Bentonite bonded sands should posses high strength because the binder bridges are strong and free from zones of weakness as a result of the uniformity of the sand grain envelopes. By contrast, the binder bridges made up of other clay minerals will exhibit zones of weakness due to the presence of coarse aggregates, thus explaining the lower strength levels provided by kaolinite clays. The sand moisture can be contained in the water layers; surrounding the particles as layer water in the hydration shells of ions as hydration water. The bonding between particles through layer water should be designated as surface bonding and that through hydration water as bridge bonding. The surface bonding extends directly between contiguous particle surfaces and also through the strongly or weakly ordered network of rigid water. This bonding cannot be operative through liquid water. For this bonding the presence of adsorbed cations is not required. Bridge bonding comes about between neighboring particles through the hydration shell of their adsorbed cations which, as bridges of rigid water, can penetrate through liquid surface water and thus effect perceivable strengths. Hydration water is more strongly bonded to the cations as compared to layer water to the surfaces of the particles. Surface bonding is the strongest at temper point water content (clay:water ratio, 10:4) and falls three times the temper point condition to zero. Such high moistures cause, due to saturation of the force fields of clay particles, the presence of non- oriented, highly mobile water molecules, which make surface bonding inoperative. The effectiveness of bridge bonding is zero at temper point condition and reaches its highest value at three times temper point (clay:water ratio about 10:12). Only at still higher moisture contents will the bridge bonding decrease. According to investigations of Norris, up to a clay:water ratio of 10:3.7, montmorillonite swellsstepwise. Between the clay: water ratio of 10:3.7 and 10:11.0 clay particles overcome a potential threshold at approximately 20 Angstroms from the first to the second stage of swelling. At a clay:water ratio of 10:3.7, clay particles begin the swelling jump. With an increase in water content more particles overcome the potential threshold and at a clay:water ratio of 10:11.9 all clay particles are on the second swelling stage. From this moisture content, the swelling proceeds con tinuously. The water takeup in montmorillonites occurs first by filling the inner spaces of the layer packets without an observable swelling. Water fills the empty space in flake aggregates. Up from a clay:water ratio of 10:4 the primary particles surround themselves with water lay ers (inter crystal line swelling through water adsorption) and only then the clay becomes plastic. Therefore, the plasticity depends only in small part upon the inner- crystalline swelling. It depends more upon the inter- crystalline swelling, by the increase of distance between primary particles. The bentonite samples were subjected into investi gation in three parts; chemical analysis, physical analysis and investigation of the effects of bentonites on the properties of casting mold sands. The bentonite samples were subjected into investi gation i.e. X-ray diffraction analysis and chemical analysis in order to determine the mineralogical struc ture, and chemical composition. X-ray powder diffraction patterns of bentonite samples as air dried, glycolated and heat treated to 550 °C indicate that the major phases present are Na- monmtmorillonite and beidellite for Ordu Ünye province and Çanakkale bentonites, Na-montmorillonite and illite for Cankirx bentonites. The intense background were noted in all patterns. Differential Thermal Analysis (DTA) curves reveal all energy changes occuring in the bentonite on heating. The curves are, therefore, a function of the crystal structure, mineralogical nature, and chemical composi tion of bentonite. XIDehydroxylation loses for Ordu and Çanakkale bentonites are similar to that for montmorillonites from Wyoming. Dehydroxylation loses for Çankırı bentonites are fairly typical for illite from Le Puy en Velay, France. The grain size of bentonites which were investiga ted was observed to be below 0.5um. The density of the bentonites fall into the region of 2.7- 2.8 gr/cm Swelling index which is related to the capacity of the bentonite for holding water under rigid form. A high swelling index indicates a high resistance to expansion casting defects. The calcium bentonite has a low index whereas the sodium bentonite can give higher values. The swelling index (i.e. 17-18 times of its original volumes ) were observed for Çankırı and Ordu region bentonites. On the other hand, Çanakkale bentonite displays the swelling properties of 10 times of its original volumes. The bentonites coded KH-6 and Ç-3 was determined to have the highest melting point from the sintering experiments. Bentonites coded Ç-1 and Ç-2 were found to have the highest plasticity water from tablet experiments. The brittleness of Ç-1 and Ç-2 bentonites can be attributed to their high plasticity water content. The investigation of bentonite on the properties of mold sand were made by using sand with AFS number 75. The relationship of green compression strength, green shear strength, permeability and moisture percentage for the 5-15% bentonites added range have been investigated. The green compression strength, green shear strength at tain peak values from the bentonites belonging to Çankırı. They attain their maximum value at a water/bentonite of 2.5. For a given water /bentonite ratio, green compression strength and green shear strength rapidly increase with the increase in bentonite percentage, and tend to attain a steady value at higher bentonite percentage. Green permeability decreases with the increase in bentonite percentages. xi i
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