Marina Aghayan

Tallinn University of Technology | TTU · Department of Materials Engineering

The irruption of additive manufacturing techniques opens the possibility to develop three-dimensional structures with complex geometries and high precision. In the current investigation a newly designed composite combining silicon (30, 40 and 50 wt%) with a bioactive glass and printed into scaffolds was obtained, using a direct selective laser melt...

Engineered bone tissue or scaffold is a potential alternative to the common use of bone grafts due to limitless supply and no disease transmission. We present a novel way to manufacture the highly efficient bioceramics combining osteoinductive and bioactive elements using additive manufacturing through selective laser melting without polymer based...

The catalytic effect of metal oxide/alumina whiskers (CeO 2 , Mn 3 O 4 , NiO, Co 3 O 4 , Fe 2 O 3 , Cr 2 O 3 /AW) was evaluated on their ability to drive the nitridation of silicon and to generate mesoporous fibrous silicon networks. Silicon powder with different particles size along with the catalyst was nitridized at 1300 °C for 5 h in nitrogen a...

Mesoporous networks with a special distribution of functional centers are an important class of high performance materials for catalysts, bioscaffolds, energy conversion and storage systems. Methods of fabrication allowing to control over special distribution of the functional sites of required phases and designed morphology are still of a great ch...

Additive manufacturing is gaining increasing attention as it provides cost-effective and waste-less production of materials with multi-axis geometries. Selective laser sintering of ceramics is very challenging in terms of poor sinterability caused by low thermal shock resistance and insufficient electron conductivity blocking absorption of laser be...

Difficulties in sintering refractory ceramics limit their potential high-demanding applications. Selective laser sintering/melting of ceramics is extremely challenging due to poor sinterability of refractories caused by a low thermal shock resistance and an insufficient electron conductivity blocking absorption of laser electron beam energy, etc. H...

The development of p-type transparent semiconductors with large optical bandgaps and high electrical conductivity is needed for a wide range of applications in optoelectronics and solar cell technologies. The experimental techniques currently used are limited to complex procedures and time consuming processing. In this work, we propose a versatile,...

In the present paper we report the synthesis, structural characterization and catalytic properties of alumina nanofibers supported Ni-CeO2 catalyst (Ni-CeO2/ANF) in pre-reforming of propane as a main component of liquefied petroleum gas. Ni-CeO2/ANF catalyst was prepared via template-assisted wet-combustion synthesis. High dispersion and uniform di...

Efficient capture and recycling of CO2 enable not only preventing global warming but also to supplying useful low-carbon fuels. The catalytic conversion of CO2 into organic compound is a promising recycling approach which opens new concepts and opportunities for catalytic and industrial development. Here we report about template-assisted wet-combus...

A novel wet-combustion method is developed to functionalize mesoporous network of alumina nanofibers. The wet-combustion method includes coating the nanofibers with the solution of the precursors of dopants mixed with fuels, followed by dissociation/oxidation of the precursors in a combustion mode. Due to the high temperature of the flame and short...

Nickel aluminate spinel (NiAl2O4) has received attention as a catalyst solid support due to its stability, strong resistance to acids and alkalis and high melting point. The properties and quality of the catalysts are heavily affected by crystal size, morphology, phase homogeneity and surface characteristics of the materials, which themselves are d...

In this study, a novel approach to processing electrically conductive and comparatively cost-effective ceramics by incorporation of the graphene coated oxide ceramic nanofibers into alumina matrix is presented. The conductive fillers are produced by chemical vapour deposition of a few-layered graphene shells on a dielectric substrate of alumina nan...

Ceramic materials have become of high industrial importance in some applications as their properties outperform ones of metallic components. However, use of ceramics is limited due to the difficulties in shaping. Electrically conductive ceramics can be machined by Electro-Discharge Machining (EDM) irrespective of its hardness or strength. In this s...

Graphene has attracted tremendous research interest in recent years owing to its exceptional properties. We report the remarkable ability to transform an insulating material, such as Al2O3, into a highly conductive material by filling the matrix with alumina nanofibers encapsulated by multi-layered graphene. The fibers of 7 nm in diameter were cove...

Copper oxide-doped alumina nanofibres were fabricated by the solution combustion method. The bundled alumina nanofibres were impregnated with a copper nitrate–glycine (oxidizer–fuel) solution and heat-treated in an open-air environment at 400 °C for 30 min. The microstructure and phase composition of the final product were characterized by XRD, SEM...

Graphene has attracted tremendous research interest in recent years owing to its exceptional properties. We report the remarkable ability to transform an insulating material, such as Al 2 O 3 , into a highly conductive material by filling the matrix with alumina nanofibers encapsulated by multi-layered graphene. The fibers of 7 nm in diameter were...

In this study alpha-alumina thin films have been deposited continuously onto novel gamma-alumina nanofibers with 7 nm in diameter and 5 cm in length. This selective alpha phase deposition on gamma phase was carried out by a one-step solution combustion process using aluminum nitrite as the precursor of aluminum and urea as a fuel. Effect of the fue...

Non�isothermal siliconizing in Si�-clad Mo wires has been studied over a wide range of heating rates Vh and silicon layer thicknesses δSi. At T = 1000–1600°C, the reaction was found to proceed in two stages: by Mo(s) + Si(s) mechanism (stage I) and by Mo(s) + Si(l) mechanism (stage II). For sufficiently thin silicon layers, non�isothermal Mo–Si rea...

Non�isothermal siliconizing in Si clad Mo wires has been studied over a wide range of heating rates Vh and silicon layer thicknesses δSi. At T = 1000–1600°C, the reaction was found to proceed in two stages: by Mo(s) + Si(s) mechanism (stage I) and by Mo(s) + Si(l) mechanism (stage II). For sufficiently thin silicon layers, non-isothermal Mo–Si reac...

Effect of alumina nanofibers covered with graphene (ANF-C) on zirconia sinterability and properties was studied in the present work. The nanofibres of aspect ratio of 107 were covered with several nanolayers of graphene by thermal chemical vapor deposition technique and were used as reinforcements in zirconia matrix. ANF-Cs were shown to be the pro...

A novel type of alumina nanofibers (ANF) and alumina nanofibers covered with graphene (ANFC) has been used for fabrication of alumina composites with improved mechanical properties. Al 2 O 3 –1.5 wt. % ANF and Al 2 O 3 – 1,9 wt. % ANFC composites were consolidated by sinter/HIP technology at 1400 ºC in argon atmosphere under 20 bar pressure. It was...

A novel type of alumina nanofibers has been used for fabrication of the alumina toughened zirconia composites and the effect of different sintering techniques on the characteristics of the material was studied. ZrO2-10 vol% Al2O3 composite was consolidated by spark plasma sintering (SPS) in a temperature range from 1000 degrees C to 1200 degrees C...

Macrokinetic features and mechanism of Mo-Si reaction in conditions of rapid heating on a single particle level (Mo/Si diffusion couple) were studied by high-speed scanning electrothermography. The experiments were conducted in the temperature-time conditions (T = 1000–1600°C, t = 0.01–3.0 s) comparable to those of combustion synthesis of molybdenu...

The possibility to obtain biphasic HA/TCP composite by solution combustion synthesis method using urea and glycine as fuels was investigated. Calcium nitrate was taken as a source of calcium, and diammonium hydrogen phosphate served as a source of phosphate ions. Nitric acid and nitrate ions were used as oxidizers. The effect of the nature of fuel...

The influence of the quantity of urea on the synthesis of calcium aluminate by solution combustion method was studied. It was shown that the amount of urea has a big influence on morphological characteristic and phase composition of the combustion products. The sintering behavior of the combustion products, before and after milling, was studied by...

Fine boron nitride powders were synthesized by combining direct nitridation of boron with carbothermic reduction of boron oxide. It has been established that the heat released in direct nitridation of boron can be utilized to carry out carbothermic reduction of boron oxide in a mode of self-sustained combustion. Intermediate gaseous products were f...