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1

Physical Properties and Microstructural Characterization of Mechanically Alloyed and Sintered W-2wt%B₄C-xwt%C (x=0, 0.25, 0.5, 1) Composites

100%

Sönmez S., Öveçoğlu M.

Acta Physica Polonica A

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2017

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vol. 131

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issue 1

193-196

EN

Mechanical alloying processes were carried out in a Spex mixer/mill to synthesize W-2wt% B₄C-xwt% C (x=0, 0.25, 0.5, 1) powders for durations of 1 and 9 h in argon atmosphere. Mechanically alloyed powders were consolidated into green compacts by uniaxial cold press under 500 MPa and solid phase sintered at 1770°C under hydrogen and argon atmospheres for 1 h and 5 h. Effects of milling duration as well as C addition on the microstructural and mechanical properties of the sintered W-2wt% B₄C-xwt% C composite samples were investigated. The microstructural and mechanical characterizations of the sintered samples were carried out by scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction, and Vickers hardness analyses. Density measurements and hardness measurements of the sintered samples were also carried out.

2

The Effect of Mechanical Alloying on the Microhardness and Fracture Toughness of BaTiO_3

61%

Ertuğ B., Çetiner B., Sadullahoğlu G., Gökçe H., Erkmen Z., Öveçoğlu M.

Acta Physica Polonica A

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2013

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vol. 123

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issue 2

188-190

EN

In this work, the effects of mechanical alloying on the mechanical properties of BaTiO_3 were investigated. In order to examine the milling conditions and sintering parameters on the solid state formation of BaTiO_3, X-ray diffraction technique was used. After mechanical alloying process, nanosized powder mixtures were produced. Sintering temperatures were 600, 700, 800, 900, 1000, and 1200C and sintering duration was 1 h. Besides X-ray diffraction examinations, mechanical properties of the BaTiO_3 samples were determined by Vickers microhardness test.

3

An Investigation on the Mass Attenuation Coefficients of W-VC-C and W-VC-TiC-C Composites for Gamma Radioisotopes

61%

Tuğrul A., Demir E., Yılmaz O., Sönmez S., Öveçoğlu M., Büyük B.

Acta Physica Polonica A

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2016

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vol. 129

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issue 4

724-727

EN

In this study, tungsten-vanadium carbide-graphite and tungsten-vanadium carbide-titanium carbide-graphite composites (W-VC-TiC-C) which can be used in high-tech equipment were investigated against different gamma radioisotopes. The composite materials were produced via mechanical alloying method in two groups; one of them includes 93% tungsten (W), 6% vanadium carbide (VC) and 1% graphite (C) which was synthesized during three different alloying times (6, 12, 24 hours). Other group of the samples were composited as 91% tungsten, 6% vanadium carbide (VC), 2% titanium carbide (TiC) and 1% graphite (C) which has also three different alloying times (6, 12, 24 hours). Gamma transmission technique was used in the experiments to investigate the gamma attenuation properties of the composite materials. Linear and mass attenuation coefficients of the samples were determined in the experiments and theoretical mass attenuation coefficients were calculated using widely acknowledged XCOM computer code. The experimental mass attenuation coefficients and calculated theoretical results were compared and evaluated with each other. Results showed that gamma attenuation coefficients of the composite materials dependent on alloying time. It can be concluded that increasing the tungsten ratio causes higher linear attenuation coefficient which decreases with increasing gamma energies.

4

Characterization Investigations of W-Ni Matrix Composites Reinforced with TiB_2 and La_2O_3

61%

Gökçe H., Balcı Ö., Ağaoğulları D., Demirkan Ö., Genç A., Öveçoğlu M., Duman İ.

Acta Physica Polonica A

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2013

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vol. 123

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issue 2

309-312

EN

W-1 wt% Ni (W1Ni) matrix composites reinforced with TiB_2 and La_2O_3 particles were fabricated via mechanical alloying and activated sintering methods. Powder blends with compositions of W1Ni-2 wt% TiB_2-x wt% La_2O_3 (x = 0.5, 1) were mechanically alloyed for 6 and 12 h. The results showed that increase in mechanical alloying duration to 12 h causes the decline of grain sizes of the W-Ni matrix to nanoscales. TiB_2/La_2O_3 particles have a significant effect on the density/microhardness values and wear amounts of the sintered samples.

5

The Effect of Milling Time and Sintering Temperature on Crystallization of BaFe₁₂O₁₉ Phase and Magnetic Properties of Ba-Hexaferrite Magnet

52%

Sadullahoğlu G., Ertuğ B., Gökçe H., Altuncevahir B., Öztürk M., Topkaya R., Akdoğan N., Öveçoğlu M., Addemir O.

Acta Physica Polonica A

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2015

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vol. 128

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issue 3

377-382

EN

Barium hexaferrite samples were prepared by mechanical alloying using the stoichiometric amounts of BaCO₃ and Fe₂O₃ precursors followed by heat treatment applied in the temperature range 700-1150°C. It was found that the high energy ball mill with a milling rate enabled to obtain powders with the finer particles at the reduced milling time mechanical alloying of the initial powders linked to the formation of barium hexaferrite phase. The exothermic reaction peaks corresponding to the formation of BaFe₁₂O₁₉ phase shift from 928°C to 793°C for the increased milling time up to 6 h. This was resulted in improved magnetic properties that the Mₛ value of the as-blended sample sintered at 800°C rised from 31.16 emu/g to 53.46 emu/g after milling for 6 h. The saturation magnetization and remanence values of the samples mechanically alloyed for 3 h and sintered at 1150°C also increased to 63.57 emu/g and 31.26 emu/g, respectively, more than for 800°C and 900°C. The increase in the annealing temperature favours the formation of BaFe₁₂O₁₉ phase in the samples.

6

Bioceramic Production from Sea Urchins

52%

Ağaoğullari D., Kel D., Gökçe H., Duman I., Öveçoğlu M., Akarsubaşi A., Bılgıç D., Oktar F.

Acta Physica Polonica A

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2012

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vol. 121

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issue 1

23-25

EN

Bioceramic nanopowders, currently one of the most demanding challenges for producing new biomaterials, have been tackled only when starting from chemical reagents. There are few studies aiming at producing hydroxyapatite nanopowders from naturally derived raw materials, such as nacre shells. Natural species of sea origin, such as corals and nacres, always attract special interest in biomaterials science and technology. Nacre shells are made up of pure aragonite crystallized in an organic matrix. The most common way to transform aragonite structures to hydroxyapatite is via hydrothermal transformation under very high pressure. However, such ways can be very dangerous if the equipment is worn. Ultrasonic and hotplate methods are apparently very safe. This work proposes a new approach for developing highly bioactive fine powders of Ca-phosphates (which can be used afterwards to build up hydroxyapatite-based bioceramic bone-scaffolds) from sea urchins via the above mentioned methods. The suspended raw powders were put on a hotplate (i.e. ultrasound). The temperature was set to 80C for 15 min and then, equivalent (to the amount of CaCO_3 in the sea urchins) amount of H_3PO_4 was added drop by drop into the solution. The reaction continued for 2 h. Then, to evaporate the liquid part, the mixture was put into an incubator at 100C for 24 h and the resultant dried sediment was collected. X-ray diffraction analysis identified various calcium phosphate phases, predominantly monetite, and tricalcium phosphate as a secondary phase. The worldwide availability and the low cost of all kinds of nacre and sea urchin shells, along with their biological-natural origin are attractive features conferring to them a high potential for preparing calcium phosphate materials for uses in biomedicine. Heart urchin, used in this study, can be an ideal candidate for producing bioceramic particles.

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Physical Properties and Microstructural Characterization of Mechanically Alloyed and Sintered W-2wt%B₄C-xwt%C (x=0, 0.25, 0.5, 1) Composites

The Effect of Mechanical Alloying on the Microhardness and Fracture Toughness of BaTiO_3

An Investigation on the Mass Attenuation Coefficients of W-VC-C and W-VC-TiC-C Composites for Gamma Radioisotopes

Characterization Investigations of W-Ni Matrix Composites Reinforced with TiB_2 and La_2O_3

The Effect of Milling Time and Sintering Temperature on Crystallization of BaFe₁₂O₁₉ Phase and Magnetic Properties of Ba-Hexaferrite Magnet

Bioceramic Production from Sea Urchins