41 research outputs found
Synthesis of TiAl-based intermetallics with nanocrystalline structure by mechanical alloying and hot isostatic pressing: Microstructure stability and properties
No full textTwo fully dense nanocrystalline TiAl-based compacts, Ti-47.5Al-3Cr and Ti-48Al-2Nb-2Cr, were synthesized by hot isostatic pressing (HIP'ing) from mechanically alloyed (MA'd) powders. Microstructure evolution and phase transformations after MA'ing, HIP'ing, and following annealing were studied. Formation of amorphous phases was detected in both powders after 15 hour MA'ing. During HIP'ing, crystallization of the amorphous phases occurred and very fine equiaxed gamma-TiAl grains were formed. The grain size decreased when the temperature of HIP'ing was decreased, and it was 42 nm after HIP'ing at 725 °C. Grain growth occurred during annealing of the HIP'd alloys, which could be described by a single thermally activated process limited by a permanent pinning force. The activation energy of the grain growth was close to the activation energy for lattice diffusion of Ti in TiAl. Microhardness decreased with the annealing time and followed the Hall-Perch dependence on the grain size
Sinthesis of TiAl-Based Intermetallics with Nanocrystalline Structure by Mechanical Alloying and Hot Isostatic Pressing: Microstructure and Properties
No full textSilicon carbide nanorods and ceramics from wood
No full textJapanese cedar carbonized at 700degreesC was vacuum infiltrated with tetraethylorthosilicate (TEOS), and heated for 30 min at 1400, 1600 and 1800degreesC by electric pulse heating. The microstructure was investigated by X-ray diffraction and electron microscopy. Extra peaks in the XRD scans could be traced back to beta-SiC. Preliminary Auger analysis indicated an increase of the Si signal in pore walls. This was considered together with SEM images in agreement with the concept of a reaction layer covering the pore walls. Moreover, a large number of nanorods were present inside the pores. TEM analysis confirmed them to be SiC nanorods grown along the direction
Chemical degradation of restorative materials
No full textThe chemical environment is an important aspect of the oral environment that could have an appreciable influence on restorative materials. The effects of chemical media on surface roughness, Vickers hardness and weight loss of a ceramic material, a hybrid ceramic resin, an ormocer and a posterior composite were investigated. The specimens were made for each material and were stored in artificial saliva at 37degreesC for 24 h. The weight of the specimens were recorded and then randomly divided into two groups and stored in the following chemicals for 2 weeks at 37degreesC: 0.02 N citric acid and 0.02 N lactic acid. After conditioning, the specimens were weighed again and subjected to Vickers hardness and surface roughness tests. The specimens were also examined in the scanning electron microscopy (SEM). All results were analyzed statistically. After a 2 week storage period, there was a significant weight loss in P60(TM) stored in citric acid and Admira(TM) stored in lactic acid. Vickers hardness values of all materials except Finesse were increased significantly (p<0.05)
Compositional modifications in humidity sensing MgAl2O4 ceramics
No full textThe MgAl2O4 powders were synthesized using the mixed oxide technique. The powders were doped with Na+ ion to modify the sintering behavior and the response characteristics of the spinel ceramics. The variations in electrical impedance were determined at room temperature under relative humidity (RH) values ranging from 21 to 98%. The effect of Na2O addition and sintering temperature on the microstructure and humidity sensitivity of MgAl2O4 were investigated
Evaluation of porcelain surface treatments and agents for composite to porcelain repair
No full textThe purpose of this study was to investigate the effects of Nd:YAG laser, air abrasion and acid-etching on the porcelain surface and repairment. Ten standard cylindrical specimens were made for each preparation (Finesse(TM) Dentsply). The specimens were lased for five seconds at a fluence of 80 mJ and a frequency of 20 Hz; air abraded for five seconds with 50 micron Al-oxide (Lit 60 psi); and acid etched with % 9,6 hydrofluoric acid for 120 seconds. The specimens were examined in the scanning electron microscopy (SEM) before and after the Nd:YAG laser, air abrasive and acid-etching. After silane coupling agent was applicated, two flowable restorative materials (Admira Flow(TM), Voco; Tetric Flow(TM), Vivadent) were bonded to the porcelain surfaces. Each group was stored in distilled water at 37degreesC for one day before the determination of shear bond strengths. A shear bond strength machine with 50 kg load cell and a 0.5 mm/min crosshead speed was used. The results were analyzed statistically. There was a significance between the shear bond strenth values of Admira Flow(TM) and Tetric Flow(TM) in the lased group (p<0.05)
Mechanical properties of ceramics and composite resins
No full textWe investigated the mechanical properties of certain dental restorative materials to assess their durability. This study determines the flexural strength of a ceramic material (Finesse(TM), Dentsply), a hybrid ceramic resin (Estenia(TM), Kuraray), an ormocer (Admira(TM), Voco) and a posterior composite resin (Solitaire2(TM), Heraeus Kulzer). The specimens were fabricated from the various restoratives. Flexural strength was determined in 4-point bending. Scanning electron microscopy (SEM) was used to examine and compare surface topography of the fractured and nonfractured surfaces. The results were analyzed statistically. The flexural strength values of Estenia(TM) samples were significantly higher compared to those of Admira(TM) and Finesse(TM) (p<0.006)
Fabrication and mechanical behavior of calcium-phosphate in situ coating on Ti6Al4V substrates
No full text8th Conference of the European-Ceramic-Society -- JUN 29-JUL 03, 2003 -- Istanbul, TURKEYIn this work, in situ coating techniques of biocompatible metal (Ti(6)Al4V ELI alloy) implants with calcium hydroxyapatite, HA, (Ca-10(PO4)(6)(OH)(2)) were investigated. The bioceramic coating of HA on the surface of titanium alloy substrate was prepared in Synthetic/Simulated Body Fluids (SBF) with different immersion time and chemical composition at constant temperature 37 degreesC and pH 7.4. The coating surface characterization of HA was performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of HA layer thickness and chemical composition on the mechanical properties of the resulting coatings was also determined. Adhesive strength of coatings was measured according to the standards ASTM F 1044-99.Turkish Ceram Soc, European Ceram So
Silicon carbide nanorods and ceramics from wood
No full textJapanese cedar carbonized at 700degreesC was vacuum infiltrated with tetraethylorthosilicate (TEOS), and heated for 30 min at 1400, 1600 and 1800degreesC by electric pulse heating. The microstructure was investigated by X-ray diffraction and electron microscopy. Extra peaks in the XRD scans could be traced back to beta-SiC. Preliminary Auger analysis indicated an increase of the Si signal in pore walls. This was considered together with SEM images in agreement with the concept of a reaction layer covering the pore walls. Moreover, a large number of nanorods were present inside the pores. TEM analysis confirmed them to be SiC nanorods grown along the direction.</p
Textured ZnO-Based varistors via templated grain growth
No full text8th Conference of the European-Ceramic-Society -- JUN 29-JUL 03, 2003 -- Istanbul, TURKEYWOS: 000223059700072Textured ZnO-based varistors were produced by using templated grain growth technique (TGG). Rod-like ZnO particles which used as templates in TGG were synthesized by homogeneous precipitation method from the 0.01 M zinc nitrate and 0.0125 M hexamethylenetetramine (HMT) solutions at 90degreesC. The templates were aligned by tape casting of ZnO based aqueous slurries. A modified tape caster with a comb blade was used for the tape casting process. Texture development in the green and sintered samples was investigated by x-ray diffractometer (XRD) and scanning electron microscope (SEM).Turkish Ceram Soc, European Ceram So
