Titanyum Oksit İlaveli Alümina Zirkonya Kompozitlerinin Spark Plazma Sinterleme Yöntemi İle Üretimi Ve Karakterizasyonu
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Fen Bilimleri Enstitüsü
Institute of Science and Technology
Institute of Science and Technology
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Alüminyum oksit (Al2O3) seramikleri sahip olduğu yüksek sertlik ve mukavemet değerleri ile kimyasal dayanım, aşınma direnci ve biyouyumluluk özellikleri, yüksek teorik yoğunluklarda sinterlenmiş alumina esaslı seramiklerin dental uygulamalarda, kalça ve diz implantlarında kullanımına olanak sağlamaktadır. Ancak Al2O3’ün düşük kırılma tokluğu değeri, özellikle biyoseramik olarak kullanımını sınırlandırmakta, vücut içerisinde çatlak ilerlemesi kontrol edilemeyeceğinden ciddi bir risk oluşturmaktadır. Al2O3 seramiklerinin kırılma tokluğunu arttırmak amacıyla fiber, visker veya ikincil fazların ilave edilebileceği çeşitli çalışmalar ile belirlenmiştir. Zirkonyum oksit (ZrO2), alüminanın kırılma tokluğunu arttıran en önemli bileşenlerden biridir. Ancak biyomedikal implant olarak kullanılan ZrO2 esaslı seramik malzemelerin en önemli dezavantajlarından biri fizyolojik sıvılarla temas halinde olduklarında, tetragonalden monoklinik faza dönüşüm sonucu zamanla mukavemetlerindeki azalmadır. Tetragonal-monoklinik dönüşümü tersinir bir dönüşüm olup, hacim değişikliği (%4-5) ve kayma gerilimine (%14-15) neden olur. Zirkonyanın gösterdiği dönüşüm toklaşmasında tane boyutu ve boyut dağılımı da etkilidir. Stabilizörlerin katkısı ile yarı kararlı t-ZrO2 yapıdan, kararlı monoklinik (m-ZrO2) faza dönüşümü sağlayan itici güç azalır ve tetragonal faz mikroyapıda tutulur. Y2O3, tetragonal faz dönüşebilirliğinde olumlu etkiye sahip olması ve tokluğu sebebiyle zirkonya seramiklerinde kullanılan en popüler stabilizördür. Alümina ve YSZ seramiklerinin sahip oldukları üstün özellikler ile bir araya getirilen ve zirkonya ile toklaştırılmış alümina olarak adlandırılan malzemeler, pek çok yapısal uygulamada monolitik alümina veya zirkonya seramiklerine tercih edilmektedir. Yüksek yoğunluğa sahip alümina esaslı seramiklerin, hava veya farklı atmosfer ortamlarında, basınçsız sinterleme teknikleri kullanılarak üretilebilmeleri için uzun sinterleme sürelerine ihtiyaç duyulmaktadır. Bu da aşırı tane büyümesi ile sonuçlanmaktadır. Spark plazma sinterleme tekniği, alümina esaslı seramiklerin daha düşük sıcaklıklarda, kısa sürede sinterlenmesini mümkün kılmaktadır. SPS tekniğinde tek eksenli basınç altında, grafit kalıp ve numuneye direkt olarak darbeli akım uygulanır. Tane büyümesi, yüksek ısıtma hızları ile engellenebilir ve yüksek sıcaklıklarda densifikasyon hızlandırılır. Böylelikle, yüksek ısıtma hızları ve kısa proses süreleri ile mikroyapı kontrol edilebilir. Bu çalışmada, alümina, alümina-itriya stabilize zirkonya ve ağırlıkça %3 ve %5 TiO2 içeren alümina-itriya stabilize zirkonya kompozitleri farklı sıcaklıklarda, spark plazma sinterleme (SPS) tekniği kullanılarak üretilmiştir. Başlangıç tozları olarak Al2O3 (ortalama partikül boyutu 0,6 μm), 3 mol itriya stabilize ZrO2 (ortalama partikül boyutu 0,1 μm) ve TiO2 kullanılmıştır. Hammaddeler uygun oranlarda tartılarak, bilyalı değirmende, etanol ortamında 24 saat karıştırılmış ve kurutulmuştur. İç çapı 50 mm olan grafit kalıbın toz karışımı ile doldurulmasının ardından toz, spark plazma sinterleme tekniği ile sinterlenmiştir. Temizleme işlemlerinin kolaylaştırılması ve iletkenliğin arttırılması için punç ve toz arasına ve kalıp ve toz arasına grafit kağıt yerleştirilmiştir. SPS prosesi sırasında tek eksenli 40 MPa basınç ve darbeli doğru akım (12 ms/açık, 2 ms/kapalı) uygulanmıştır. Grafit kalıp yüzeyine odaklanmış optik pirometre sıcaklığı ölçmek ve ayarlamak için kullanılmış, akım manuel olarak ayarlanmıştır. SPS prosesi esnasındaki çekilme, grafit punçların yerdeğiştirme miktarından belirlenmiştir. Sinterlenen numuneler 50 mm çapında 5 mm kalınlığında, pelet formunda üretilmiştir. Üretim sonrasında grafik kağıdı uzaklaştırmak amacıyla kumlama yapılmıştır. Yoğunluk değerleri, Arşimet Prensibi ile belirlenmiş, Al2O3, YSZ ve TiO2’nin teorik yoğunlukları kullanılarak relatif yoğunluk değerlerine çevrilmiştir. Yaklaşık %99 relatif yoğunluğa sahip kompozitler elde edilmiştir. Faz analizleri, X ışını difraktometresi kullanılarak Cu-Kα radyasyonu ile, 20-80˚ arasında gerçekleştirilmiştir. Faz analizlerinde t-ZrO2, α-Al2O3’e ait karakteristik pikler gözlenmiş, ayrıca ikinci bir faz, ZrTiO4, oluşumu belirlenmiştir. Sinterlenen numunelerin kırık yüzey mikroyapı görüntüleri tarama elektron mikroskobu ile incelenmiştir. Alümina tane büyümesi hacimce %10 YSZ ilavesi ile belirgin şekilde engellenmiştir. Zirkonyanın ikinci faz olarak yapıda bulunması tane sınırı ilerlemesini engelleyerek alümina tane büyümesinin önüne geçmiştir. Vickers mikrosertlik (Hv) değerleri 9,8 N yük altında belirlenmiştir. Al2O3-YSZ kompozitlerinin sertliğinde, YSZ hacimce %10’dan %30’a çıkarıldığında azalma gözlenmiştir. Bu etki itriya ile stabilize edilen zirkonyanın alümina ile kıyaslandığında dana düşük sertliğe sahip olması ile açıklanabilir. Ağırlıkça %3 ve %5 TiO2 ilavesi ise Al2O3-YSZ kompozitlerinin sertliğini düşürmüştür. Bu etki ise ZrTiO4 oluşumuna dayandırılabilir. Kırılma tokluğu (K1C) mikrosertlik ölçüm cihazı kullanılarak, 19,6 N yük altında, indentasyon çevresinde oluşan çatlakların uzunluklarından hesaplanmıştır. Al2O3’ün kırılma tokluğu %30 YSZ ilavesi ile 2,8 MPa•m1/2’den 4,2 MPa•m1/2’ ye yükselmiştir. Hücre kültürü testlerine göre osteoblast hücreleri Al2O3-YSZ ve Al2O3-YSZ-TiO2 kompozitleri bulunan kültür ortamında büyümeye devam etmiş, kompozitlerin hücreler ile olumlu veya olumsuz herhangi bir etkileşime girmediği gözlenmiştir.
A biomaterial can be simply defined as a synthetic material used to replace part of a living system or to function in intimate with living tisssue. When biomaterials are implanted into the body, two factors will determine the fate of the biomaterials. One is tissue response to the biomaterials, i.e. physico-chemical properties, cytotoxicity, and chemical compositions. The other is the change in biomaterial properties after implantation, i.e. body fluid erosion, and enzyme degradation. Bioceramics is a large class of inorganic nonmetallic materials. It is widely used in repairing and replacing skeletal and hard tissues such as hip-joints, teeth, and bone due to its antimicrobial activity and resistance to pH change, acid and base solutions, and high temperatures. At the same time, bioceramics generally show better tissue responses than polymers or metals. Most bioceramics do not release their components into the human body unless they are designed to be bioresorbable. High density, high strength alumina and zirconia are often considered bioinert ceramics. Due to their excellent corrosion resistance, high wear resistance, and good biocompatibility, the major application of alumina or zirconia is in total hip joint and knee replacements. High density sintered alumina based ceramics, Al2O3, are widely used for dental and orthopedic implants such as total hip and knee replacement prostheses. Their widespread use is based on a combination of good strength, high wear and chemical resistance, and good biocompatibility. However, slow crack growth resulted in a failure of alumina ceramic component with time in service. In order to increase the toughness of alumina, many techniques have been investigated based on the addition of fibers, whiskers and hard particulates. Zirconia (ZrO2) has been known to enhance the toughness of alumina. A major drawback of zirconia ceramics is their strength reduction, due to an unfavorable tetragonal (t) to monoclinic (m) martensitic phase transformation, with time when they are in contact with physiological fluids. The t-m transform is a reversible martensitic transformation, associated with a large temperature hysteresis (around 200˚C), a finite amount of volume change (4-5%) and a large shear strain (14-15%), which leads to crumbling of the sintered part made of pure zirconia during cooling. It has been found that zirconia shows transformation toughening is influenced by the grain size and grain size distribution. The tetragonal phase in zirconia ceramics can be obtained by using stabilizers. Yttria is the most popular stabilizer used for zirconia ceramics for its excellent mechanical properties, wear properties, and a good effect on tetragonal phase transformability. Advantages of combined high hardness of alumina with highly fracture resistant yttria stabilized zirconia (YSZ) make Al2O3-YSZ system as an alternative choice to alumina and zirconia monolithic ceramics for structural and functional applications. Titania is a ceramic material, which is generally used as a white pigment or catalyst in manufacturing industries. In recent years, TiO2 have become a topic of extensive biological investigations. TiO2 ceramics are promising for implant applications. The functions of additives for alumina and zirconia have been often aimed to lower the sintering temperature, tailor the microstructure, or improve the product properties. For example, the addition of TiO2 has been reported to promote the sintering alumina and zirconia. However, the addition of titania to zirconia tends to result in the formation of zirconium titanate, depending on the mixing homogeneity and sintering temperature. Al2O3 ceramics are normally densified by pressureless sintering in air or different atmospheres, resulting in a long sintering period to obtain full densification. Also, abnormal grain growth occurs during sintering process. Spark plasma sintering (SPS) makes possible to densify Al2O3 based composites at a lower temperature and in a shorter times compared with conventional techniques. In the SPS technique, a pulsed direct current passes through graphite punch rods and dies simultaneously with a uniaxial pressure. The grain growth can be suppressed by rapid heating and the densification is accelerated at high temperature. Furthermore, the microstructure can be controlled by a fast heating rate and shorter processing times. In this study, alumina, alumina-yttria stabilized zirconia composites containing 3 and 5 mass% TiO2 were prepared using spark plasma sintering (SPS) technique at different temperatures. Al2O3 (an average particle size of 0.6 μm), 3 mol yttria stabilized ZrO2 (an average particle size of 0.1 μm) and TiO2 powders were used as starting materials. The raw materials were weighed in appropriate quantities, ball milled in ethanol for 24 h and then dried. A graphite die 50 mm in inner diameter was filled with the mixture, followed by sintering using spark plasma sintering apparatus. A graphitic sheet was placed between the punches and the powder, and between the die and the powder for easy removal and better conductivity. A uniaxial pressure of 40 MPa and pulsed direct current (12 ms/on, 2 ms/off) were applied during the entire SPS process. The pulsed direct current flows through the graphite die, the punches and the powder. Relative density values of the samples studied, the microstructure and phase analysis was performed after sintering in a vacuum under 40 MPa pressure and with temperature range of 1350°C and 1400°C for 5 min. Afterwards, microhardness and fracture toughness were measured and cell culture tests were carried out by the immersed samples in the simulated body fluid solution, nearly equal to human blood plasma. An optical pyrometer, focused on a small hole at the surface of the graphite die, was used to measure and adjust the temperature. The current was controlled manually. Linear shrinkage of the specimens during SPS process was continuously monitored by displacement of the punch rods. The sintered specimens were in the form of pellets 50 mm in a diameter and 5 mm thick and characterized after sand-blasted in order to remove graphitic sheet. The bulk densities of the speciments were determined by the Archimedes’ method and converted to relative density using theoretical densities of Al2O3, YSZ and TiO2. Fully dense composites with a relative density of approximately 99% were obtained. The value of theoretical density depends on the composition and calculated using theoretical densities and volume fractions of Al2O3 (3.97 Mg/m3), YSZ (6.05 Mg/m3) and TiO2 (4.20 Mg/m3). The crystalline phases were identified by X-ray diffractometry in the range of 20-80˚ with Cu Kα radiation. In phase analysis, the characteristic peak of t-ZrO2, α-Al2O3 were identified. A second phase, ZrTiO4 was also identified. The microstructure of fracture surfaces of the sintered specimens were observed by scanning electron microscopy. The grain growth of alumina was inhibited significantly by the addition of 10 vol% yttria stabilized zirconia. The presence of zirconia as a second phase could be beneficial with respect to inhibition of grain growth. Fine zirconia particles could have a pinning effect of grain boundaries of alumina which inhibited the grain boundary migration. Vickers hardness (HV) was measured under load of 9.8 N. The hardness of Al2O3-YSZ composites decreased when YSZ content from 10 to 30 vol%. This effect could be associated with the lower hardness of 3 mol% yttria stabilized zirconia compared to that of alumina. The hardness of Al2O3-YSZ composites significantly decreased with the addition of 3 and 5 mass% TiO2. This effect could be associated with the form of ZrTiO4. Fracture toughness (K1C) was evaluated by a microhardness tester, under load of 19.6 from the half length of a crack formed around the indentations. The fracture toughness of Al2O3 increased from 2.8 MPa•m1/2 to 4.2 MPa•m1/2 with the addition of 30 vol% yttria stabilized zirconia. Cell viability and alkaline phosphates in the presence of 85A15Z, 85A15Z3T, and 85A15Z5T samples were studied against controls. Cell viability/proliferation was not prevented by the presence of samples. Cell viability in the presence and absence of samples increased within the first 3 days and the similar increase ratio was observed when samples compared to control. When alkaline phosphatase activities were measured at the end of the incubation period, materials did not obstruct alkaline phosphate production. The cell culture test (cell viability and alkaline phosphatese tests) showed that Al2O3-YSZ ceramics containing %15 YSZ with 3 and 5 mass% TiO2 have good biocompability and there was no unaccepted observation as a function of titania content. Moreover, Al2O3-YSZ-TiO2 composites containing 3-5 mass% TiO2 showed almost same cell viability and alkaline phosphatese activity compared control and also better than without TiO2.
A biomaterial can be simply defined as a synthetic material used to replace part of a living system or to function in intimate with living tisssue. When biomaterials are implanted into the body, two factors will determine the fate of the biomaterials. One is tissue response to the biomaterials, i.e. physico-chemical properties, cytotoxicity, and chemical compositions. The other is the change in biomaterial properties after implantation, i.e. body fluid erosion, and enzyme degradation. Bioceramics is a large class of inorganic nonmetallic materials. It is widely used in repairing and replacing skeletal and hard tissues such as hip-joints, teeth, and bone due to its antimicrobial activity and resistance to pH change, acid and base solutions, and high temperatures. At the same time, bioceramics generally show better tissue responses than polymers or metals. Most bioceramics do not release their components into the human body unless they are designed to be bioresorbable. High density, high strength alumina and zirconia are often considered bioinert ceramics. Due to their excellent corrosion resistance, high wear resistance, and good biocompatibility, the major application of alumina or zirconia is in total hip joint and knee replacements. High density sintered alumina based ceramics, Al2O3, are widely used for dental and orthopedic implants such as total hip and knee replacement prostheses. Their widespread use is based on a combination of good strength, high wear and chemical resistance, and good biocompatibility. However, slow crack growth resulted in a failure of alumina ceramic component with time in service. In order to increase the toughness of alumina, many techniques have been investigated based on the addition of fibers, whiskers and hard particulates. Zirconia (ZrO2) has been known to enhance the toughness of alumina. A major drawback of zirconia ceramics is their strength reduction, due to an unfavorable tetragonal (t) to monoclinic (m) martensitic phase transformation, with time when they are in contact with physiological fluids. The t-m transform is a reversible martensitic transformation, associated with a large temperature hysteresis (around 200˚C), a finite amount of volume change (4-5%) and a large shear strain (14-15%), which leads to crumbling of the sintered part made of pure zirconia during cooling. It has been found that zirconia shows transformation toughening is influenced by the grain size and grain size distribution. The tetragonal phase in zirconia ceramics can be obtained by using stabilizers. Yttria is the most popular stabilizer used for zirconia ceramics for its excellent mechanical properties, wear properties, and a good effect on tetragonal phase transformability. Advantages of combined high hardness of alumina with highly fracture resistant yttria stabilized zirconia (YSZ) make Al2O3-YSZ system as an alternative choice to alumina and zirconia monolithic ceramics for structural and functional applications. Titania is a ceramic material, which is generally used as a white pigment or catalyst in manufacturing industries. In recent years, TiO2 have become a topic of extensive biological investigations. TiO2 ceramics are promising for implant applications. The functions of additives for alumina and zirconia have been often aimed to lower the sintering temperature, tailor the microstructure, or improve the product properties. For example, the addition of TiO2 has been reported to promote the sintering alumina and zirconia. However, the addition of titania to zirconia tends to result in the formation of zirconium titanate, depending on the mixing homogeneity and sintering temperature. Al2O3 ceramics are normally densified by pressureless sintering in air or different atmospheres, resulting in a long sintering period to obtain full densification. Also, abnormal grain growth occurs during sintering process. Spark plasma sintering (SPS) makes possible to densify Al2O3 based composites at a lower temperature and in a shorter times compared with conventional techniques. In the SPS technique, a pulsed direct current passes through graphite punch rods and dies simultaneously with a uniaxial pressure. The grain growth can be suppressed by rapid heating and the densification is accelerated at high temperature. Furthermore, the microstructure can be controlled by a fast heating rate and shorter processing times. In this study, alumina, alumina-yttria stabilized zirconia composites containing 3 and 5 mass% TiO2 were prepared using spark plasma sintering (SPS) technique at different temperatures. Al2O3 (an average particle size of 0.6 μm), 3 mol yttria stabilized ZrO2 (an average particle size of 0.1 μm) and TiO2 powders were used as starting materials. The raw materials were weighed in appropriate quantities, ball milled in ethanol for 24 h and then dried. A graphite die 50 mm in inner diameter was filled with the mixture, followed by sintering using spark plasma sintering apparatus. A graphitic sheet was placed between the punches and the powder, and between the die and the powder for easy removal and better conductivity. A uniaxial pressure of 40 MPa and pulsed direct current (12 ms/on, 2 ms/off) were applied during the entire SPS process. The pulsed direct current flows through the graphite die, the punches and the powder. Relative density values of the samples studied, the microstructure and phase analysis was performed after sintering in a vacuum under 40 MPa pressure and with temperature range of 1350°C and 1400°C for 5 min. Afterwards, microhardness and fracture toughness were measured and cell culture tests were carried out by the immersed samples in the simulated body fluid solution, nearly equal to human blood plasma. An optical pyrometer, focused on a small hole at the surface of the graphite die, was used to measure and adjust the temperature. The current was controlled manually. Linear shrinkage of the specimens during SPS process was continuously monitored by displacement of the punch rods. The sintered specimens were in the form of pellets 50 mm in a diameter and 5 mm thick and characterized after sand-blasted in order to remove graphitic sheet. The bulk densities of the speciments were determined by the Archimedes’ method and converted to relative density using theoretical densities of Al2O3, YSZ and TiO2. Fully dense composites with a relative density of approximately 99% were obtained. The value of theoretical density depends on the composition and calculated using theoretical densities and volume fractions of Al2O3 (3.97 Mg/m3), YSZ (6.05 Mg/m3) and TiO2 (4.20 Mg/m3). The crystalline phases were identified by X-ray diffractometry in the range of 20-80˚ with Cu Kα radiation. In phase analysis, the characteristic peak of t-ZrO2, α-Al2O3 were identified. A second phase, ZrTiO4 was also identified. The microstructure of fracture surfaces of the sintered specimens were observed by scanning electron microscopy. The grain growth of alumina was inhibited significantly by the addition of 10 vol% yttria stabilized zirconia. The presence of zirconia as a second phase could be beneficial with respect to inhibition of grain growth. Fine zirconia particles could have a pinning effect of grain boundaries of alumina which inhibited the grain boundary migration. Vickers hardness (HV) was measured under load of 9.8 N. The hardness of Al2O3-YSZ composites decreased when YSZ content from 10 to 30 vol%. This effect could be associated with the lower hardness of 3 mol% yttria stabilized zirconia compared to that of alumina. The hardness of Al2O3-YSZ composites significantly decreased with the addition of 3 and 5 mass% TiO2. This effect could be associated with the form of ZrTiO4. Fracture toughness (K1C) was evaluated by a microhardness tester, under load of 19.6 from the half length of a crack formed around the indentations. The fracture toughness of Al2O3 increased from 2.8 MPa•m1/2 to 4.2 MPa•m1/2 with the addition of 30 vol% yttria stabilized zirconia. Cell viability and alkaline phosphates in the presence of 85A15Z, 85A15Z3T, and 85A15Z5T samples were studied against controls. Cell viability/proliferation was not prevented by the presence of samples. Cell viability in the presence and absence of samples increased within the first 3 days and the similar increase ratio was observed when samples compared to control. When alkaline phosphatase activities were measured at the end of the incubation period, materials did not obstruct alkaline phosphate production. The cell culture test (cell viability and alkaline phosphatese tests) showed that Al2O3-YSZ ceramics containing %15 YSZ with 3 and 5 mass% TiO2 have good biocompability and there was no unaccepted observation as a function of titania content. Moreover, Al2O3-YSZ-TiO2 composites containing 3-5 mass% TiO2 showed almost same cell viability and alkaline phosphatese activity compared control and also better than without TiO2.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2012
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2012
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2012
Konusu
Spark Plazma Sinterleme, Al2O3, ZrO2, TiO2, Spark Plasma Sintering, Al2O3, ZrO2, TiO2