High temperature sintering processes of selective laser sintered Al2O3/ZrO2/TiC ceramics were studied. The effects of the sintering temperature and the sintering time on the relative density, strength and fracture toughness of Al2O3/ZrO2/TiC ceramics were investigated. The results showed that the sintering temperature and sintering time had a great effect on the relative density and the mechanical properties of Al2O3/ZrO2/TiC ceramics. The mechanical strength increased from 120MPa to 360MPa and KIC increased from 3.7 J/m2 to 6.9 J/m2 when the sintering temperature increased from 1400ºC to 1600ºC, however, the mechanical strength decreased rapidly from 370MPa to 330MPa and KIC decreased from 6.9 J/m2 to 6.1 J/m2 when the sintering time increased from 30min to 90min. Furthermore, the addition of TiC and ZrO2 in the Al2O3 matrix significantly improved mechanical strength and fracture toughness of the Al2O3 matrix ceramics.
DOI : 10.2298/SOS0901035B Anahtar Kelimeler :
high-temperature sintering, Al2O3/ZrO2/TiC ceramic, fracture toughness, strength, the relative density
Cilt: 41 Sayı: 1 Sayfa: 35 - 41
Hydroxyapatite/poly-L-lactide (HAp/PLL) composite biomaterial can be obtained by different processing methods. Three-dimensional blocks of HAp/PLLA composite biomaterial with mechanical characteristics close to the natural bone tissue can be obtained by hot pressing procedure. Effects of synthesis and compacting on the structure and characteristics of the HAp/PLLA composite biomaterial were studied in this work. Using wade angle X-ray structural analyses (WAXS), differentially scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared (IR) spectroscopy, the changes occurring in the material during synthesis and hot pressing were monitored. Surface microstructure was analyzed by scanning electronic microscopy (SEM) coupled with electron-dispersion analysis (EDX). The results obtained indicate a possible decrease in the degree of crystallinity with hot pressing time increase. A block of HAp/PLLA composite biomaterial with 1.6 times lower crystallinity of the polymer phase was obtained by hot pressing in a given time interval with a maximum of 60 minutes. Results of TG analysis show that PLLA stability decreases with increasing hot pressing time, and vice versa. IR study proved that neither destructive changes in constituents nor formation of new phases occurred during hot pressing.
The possibility of characterization of aluminium powders using a horizontal coherer has been considered. Al powders of known dimension were treated with a high frequency electromagnetic field or with a DC electric field, which were increased until a dielectric breakdown occurred. Using a multifunctional card PC-428 Electronic Design and a suitable interface between the coherer and PC, the activation time of the coherer was measured as a function of powder dimension and the distance between the coherer electrodes. It was also shown that the average dimension of powders of unknown size could be determined using the coherer.
DOI : 10.2298/SOS0201101N Anahtar Kelimeler :
coherer, dimension of powders, dielectric breakdown
Cilt: 34 Sayı: 1 Sayfa: 101 - 108
A powder mixture of Bi2O3 and TiO2, both monoclinic, was mechanochemically treated in a planetary ball mill in air atmosphere for different time, using zirconium balls as the milling medium. Mechanochemical reaction leads to the gradual formation of an amorphous phase. After 1 h of milling the starting oxides were transformed fully a nanocrystalline Bi4Ti4O12 phase. With increasing the milling time from 3 to 12h, the particle size of formed Bi4Ti3O12 did not reduced significantly. That was confirmed by IR and TEM analysis. The electron diffraction pattern indicates that Bi4Ti3O12 crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis. After milling for various times the powders were compacted by pressing and isothermal sintering. The dielectric permittivity of the sintered samples significantly depends on the milling time. Sample milled for 12 h and subsequently sintered at 1000°C for 24 h exhibit a hysteresis loop, confirming that the synthesized material possesses ferroelectric properties.
The synthesis of active silicate phases by combined sol gel and high-temperature selfpropagating wave method, is described in this paper. They show a significant decrease of setting time and good mechanical properties, which are very important for its potential application in endodontic practice. Particularly, process of hydration of calcium silicate phases is carefully analyzed, from the aspect of phase changes during their soaking in water for 1, 3, 7 and 28 days. XRD and FTIR methods were used for phase analysis of all samples, while morphological characteristics and chemical composition of the given phases were investigated by SEM and EDS. [Projekat Ministarstva nauke Republike Srbije, br. 172026]
Organic modification of mineral clay using the monomer ethenyl acetate was performed. The exchange of inorganic interlayer clay cations was achieved using the cationic surfactant Genamine CTAC and Asepsol. Aiming to investigate the influence of organic modifications on adsorptive clay properties, dried composites of clay/ethenyl acetate, with different percentages of clay were soaked in distilled water. The influence of the temperature on the adsorptive properties of organoclays was also followed. The adsorptive properties of the obtained composites of organoclays with Luviskol, Carbopole and purine were investigated along with their capability for removing Pb2+ from water in charged systems. [Projekat Ministarstva nauke Republike Srbije, br. TR 34020, br. 172047 i br. 174007]
DOI : 10.2298/SOS1303363S Anahtar Kelimeler :
ethenyl acetate, adsorption, waste water
Cilt: 45 Sayı: 3 Sayfa: 363 - 376
Five porous cordierite-mullite ceramics with similar porosity and different neck characteristics were prepared from Al(OH)3, magnesite, silica and clay using an in-situ pore-forming technique. The phase composition, pore and neck characteristics and strength of the porous ceramics were investigated by an X-ray diffractometer (XRD), a scanning electron microscopy (SEM) and a microscopy measured method, etc. The experimental results showed that Al(OH)3 content had a significant effect on the pore size distribution and neck characteristics (neck size distribution, total value of neck size and phase composition) and then affecting the strength. With an increase in Al(OH)3 content, the median pore size decreased, the total length of necks and the uniformity of neck size increased, also the mullite content of necks increased, resulting in the increase of strength of the porous cordierite-mullite ceramics. When the Al(OH)3 content was 64.9 wt%, the porous cordierite-mullite ceramics had the best performance of high apparent porosity of 45.1 % and high compressive strength of 55.9 MPa.
This study is focused on the behaviour of fired-clay brick from the area around Beruas (Malaysia) that is known for it brick industries. The firing temperatures were set from 800°C to 1250°C and soaking time was fixed for an hour. The effects of firing temperature on the phase changes, microstructure, compressive strength, water absorption and porosity of the bricks were investigated. Test results indicate that the optimum firing temperature was found to be 1200°C. The percentage of porosity significantly reduces from 39.33% to 5.87% when sintered from 1000°C to 1250°C. Bricks sintered at 1200°C exhibited the highest strength of 89.5 N/mm2. The effect of firing temperature significantly improved the microstructure in terms of porosity and the quality of physical properties of fired-clay bricks.
This paper presents the results of tests of physical-mechanical, durability and microscopic properties of geopolymer mortar mixtures based on fly ash and ladle slag. The mixtures are alkali-activated using sodium silicate and sodium hydroxide solution. Firstly, the effects of different fly ash (class „F“) particle sizes on the characteristics of the mortar mixtures were examined when binder and alkali activator were cured at 95ºC for 24 h, also pozzolanic activity and strength activity index were investigated. After that, fly ash ground of optimal particle sizes (0,09 mm) was replaced with ladle slag, 0 to 20% of the mass, the replacement steps being 5%. The specimens having dimensions 4x4x16 cm were then cured in ambient conditions, and the effects of replacement of a part of fly ash with ladle slag were determined by testing water absorption, flexural and compressive strength, freeze-thaw resistance, sulfate attack, ultrasound velocity, FT-IR spectroscopy and leaching of heavy metals. According to the test results of compressive strength resistance of geopolymer mortars exposed to sulfate solution, the mortar made with fly ash and ladle slag showed better resistance to sulfate attack than the mortar made with fly ash only.
In recent years, a range of computer simulation models leading to a better understanding of liquid phase sintering phenomena, have been developed with the aim of simulating the detailed evolution of microstructure during grain growth. Some liquid phase sintered materials show both macrostructural and microstructural effects associated with gravity force. Therefore we will develop a numerical procedure for the estimation of how much gravity will influence domain (two-dimensional particle representation) growth, domain boundary migration and solid skeleton formation due to gravity induced segregation during liquid phase sintering. The method used for the simulation of a gravity field will be based on the settling procedure. Gravity induced settling will be separated into two stages - Free Settling and Skeletal Settling. Isolated solid phase domains fall under gravity and slide down over the already settled domains (free settling). During settling they make point contacts with each other. Necks between them then form and start to grow until the equilibrium dihedral angle between the domain boundaries and the liquid is established. Thus a solid skeleton forms and skeletal settling of a connected solid structure takes place. .
The fine defective structure of silicon carbide powders obtained from silicic acid-saccharose, aerosil-saccharose, aerosil-carbon black, and hydrated cellulose-silicic acid gel systems was investigated. The relation between IR absorption characteristics and the microstructure of SiC particles obtained from different starting materials was established. The numerical relationship between the lattice parameter a and the frequency νTO is presented.
Low energy Ag ions were implanted into silicon and annealed at different temperatures in order to generate plasmonic active silicon hybrids. It was found that as the ion fluence of irradiation was increased, a monotonic decrease in the absorption spectra in the ultraviolet region occurs, due to amorphization and macrostructuring of the Si surface. At the same time, the optical spectra are characterized by a strong band after implantation presenting the contribution of the surface plasmon resonance (SPR) of Ag nanoparticles. After heat treatment at 500 and 600ºC, the SPR peak shifts to lower wavelengths, as compared to as implanted samples, whereas the plasmon position shifts to higher wavelengths for annealing at 700°C. This observation can be explained by either an out-diffusion of Ag or by stress relaxation and recrystallization of silicon. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 45005]
DOI : 10.2298/SOS2002207M Anahtar Kelimeler :
silicon, ag nanoparticles, thermal treatment, ion beam implantation, spr peak
Cilt: 52 Sayı: 2 Sayfa: 207 - 217
The equilibrium between solid and 1iquid phases in sintered composite materials has been studied. It is shown that closed surfaces, which bound dispersed phases, influence the mechanical equilibrium between these phases. An expression is derived for a dihedral angle in composite materials, which includes values of surface tensions at the phase interfaces as well as parameters of a composite equilibrium structure (phase composition, particle contiguity and coefficients of a particle geometry).
DOI : 10.2298/SOS0402081L Anahtar Kelimeler :
thermodynamics, dihedral angle, composite material
Cilt: 36 Sayı: 2 Sayfa: 81 - 86
Titanium dioxide nanopowder samples consolidated by method of cold uniaxial compaction at 200 MPa and conventionally sintered in air at 1300°С with isothermal tempering during 60 minutes or spark-plasma sintering at 1300°С and 30 MPа were studied using the method of light combination scattering spectroscopy (Raman spectroscopy) and scanning electron microscopy. The samples were found to differ significantly in terms of color, density, phase composition and microstructure.
The aim of this work was analysis of isothermal sintering of zinc titanate ceramics doped with MgO obtained by mechanical activation. Mixtures of ZnO, TiO2 and MgO (0, 1.25 and 2.5%) were mechanically activated 15 minutes in a planetary ball mill. The powders obtained were pressed under different pressures and the results were fitted with a phenomenological compacting equation. Isothermal sintering was performed in air for 120 minutes at four different temperatures. Structural characterization of ZnO-TiO2-MgO system after milling was performed at room temperature using XRPD measurements. DTA measurements showed different activation energies for pure and doped ZnO-TiO2 systems. Thus addition of MgO stabilizes the crystal structure of zinc titanate.
DOI : 10.2298/SOS0703241O Anahtar Kelimeler :
Pressing, Sintering, ZnO-TiO2 system
Cilt: 39 Sayı: 3 Sayfa: 241 - 248
The paper reports on some experimental results obtained from the production of glass-ceramics containing gold tailings powder (GTP). Frits particle sintered technology was used to prepare glass ceramic products. SiO2, CaO, ZnO, BaO and B2O3 were selected to adjust the composition of the glass. Based on the results of differential thermal analysis (DTA), the nucleation and crystallization temperature of parent glass samples with different schedule were identified, respectively. X-ray diffraction (XRD) analysis of the produced glass-ceramics materials revealed that the main crystalline phase was β-wollastonite. With the increasing of CaO content, the intensity of crystal diffractive peaks also increases. The formation of β-wollastonite crystal could be accelerated by the increasing of CaO. The glass-ceramics with fine microstructure showed better physical, mechanical properties and chemical resistance. Overall results indicated that it was a feasible attempt to produce glass-ceramics for building and decorative materials from waste materials. The amount of GTP used in the glass batches was more than 65 wt% of the whole raw.
The author considers potential lines in the formation of mesostructures in cemented carbides, analyzes the existing technologies of the formation thereof, describes physical and mechanical properties of cemented carbides with mesostructure and shows the efficiency of such cemented carbides in metal working and rock destruction tools.
DOI : 10.2298/SOS1102161L Anahtar Kelimeler :
cemented carbide, hard metal, structure, mesostructure
Cilt: 43 Sayı: 2 Sayfa: 161 - 173
The family of bismuth titanate, Bi4Ti3O12 (BIT) layered-structured ferroelectrics materials is attractive from the viewpoint of their application as electronic materials such as dielectrics, piezoelectrics and pyroelectrics, because they are characterized by good stability of piezoelectric properties, a high Curie temperature and a good resistance vs temperature. Bismuth titanate (Bi4Ti3O12) powders can be prepared using different methods, depending if the creation will be film coating or ceramics. The structure and properties of bismuth titanate materials show a significance dependence on the applied synthesis method. In this review paper, we made an attempt to give an approach to analyzing the structure, synthesis methods and properties of bismuth titanate ferroelectrics materials. .
Inverse opal zirconia is useful in many ways because of their ability to combine several chemical and physical properties. In this research, polystyrene template was fabricated by self-assembly method and inverse opal zirconia was prepared by colloidal crystal-templating method. The process of preparation of inverse opal zirconia as well as effects on morphology and phase of as-prepared inverse opal zirconia were studied. The results showed precursor ratio of zirconium acetate and methanol, mass ratio of polystyrene templates and precursor and dipping times had remarkable influence on morphology of inverse opal zirconia. When the precursor ratio was 1:1; the mass ratio was 1:15 and dipped once, much better morphology of inverse opal zirconia was obtained. The mass ratio, sintering temperature and holding time had significant effect on crystallization of zirconia. Pure phase zirconia could be obtained when sintered at 600 oC, holding time was 2h and the mass ratio was 1:1. A distinguished single stop band in the visible region of the spectrum and unique structural color were observed in inverse opal zirconia, which will make this material promising candidate for novel pigment.
DOI : 10.2298/SOS1803387L Anahtar Kelimeler :
inverse opal, Zirconia, crystal-templating, structural color
Cilt: 50 Sayı: 3 Sayfa: 387 - 394
The copper matrix has been dispersion strengthened with 3wt.%Al2O3 by mechanical alloying. Commercial alumina powder with an average particle size of 0.75mm was used for alloying. The mechanical alloying process was performed in a planetary ball mill up to 20h in air. After milling all powders were treated in H2 at 4000C for 1h, and finally hot pressing was used for compaction (800oC, 3h, Ar). Structure observations revealed a lamellar structure (Al2O3 particles largely restricted to interlamellar planes between adjacent copper lamellae) accompanied also by structure refinement. These structural changes were mostly completed in the early stage of milling, and retained after compaction. Micro hardness was found to progressively increase with milling time. So, after 5h of milling the micro hardness of the Cu+3twt%Al2O3 compact was 1540MPa, i.e. 2.5 times greater than for the as-received electrolytic copper powder (638MPa) compacted under identical conditions, while after 20h of milling it was 2370 MPa. However after exposing the tested compact at 800oC up to 5h, the achieved hardening effect vanished.
Single phase MgAl2O4 was made from a one-to-one molar ratio of MgO and Al2O3 powders mixed using ball-milling. Mixtures of MgO and Al2O3 were subsequently treated in planetary ball mill for 30, 60, 90 and 120 minutes in air. The aim of this study was to examine phase composition, microstructure, and densification behavior of sintered specimens. After sintering in dilatometer at 1500°C, the powder was converted to single phase MgAl2O4. The results show that mechanical activation improved the densification behavior of MgAl2O4 sintered specimens, and it reduced the onset temperature for sintering by approx. 100°C. Based on dilatometer data, powders were subsequently densified at 1450°C by hot pressing. Almost аll specimens exhibited full density, while sample activated for 30 minutes showed the fastest densification rate. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172057, and Grant no. III 45007]
New nuclear glass-ceramics are extensively studied for the radioactive waste confinement, due to the double confinement conferred by the glass-ceramics. In this study, a glass-ceramic constituted by an aluminosilicate glass in the system: SiO2-Al2O3-CaO-MgOZrO2-TiO2, containing 2wt.% of Ca0.83Ce0.17ZrTi1.66Al0.34O7 zirconolite, has been synthesized by the discontinuous method. Cerium, an actinide surrogate is introduced both in the glass and ceramic phases. The synthesis is performed by a double melting at 1350°C, followed by a nucleation at 564°C, during 2 h, and a crystal growth at 1010°C during 3 h. Then effect of Ca/Mg ratio on the distribution of the crystalline network in the material was studied for Ca / Mg ratios ranging from 0.4 to 5.5. For the whole of the materials, Archimedes density is about 2.80 g/cm3. X-ray diffraction (XRD) analysis shows that the increase of Ca/Mg ratio leads to the increase of aluminosilicated crystalline phases with high Ca contents; the materials molar volumes remaining constant. The zirconolite phase is not affected by these additive aluminosilicated phases. The scanning electron microscopy analysis (SEM) coupled with energy dispersive X-ray (EDX) analysis confirmed these results; and shows the uniformity of distribution of the ceramics in the bulk of the materials.
The formation of different Mg-Al LDHs (Mg/Al = 2:1) under hydrothermal conditions (200°C; 4-24 h) was investigated in the 4MgCO3⋅Mg(OH)2⋅5H2O - γ-Al2O3/Al(OH)3 - H2O and Mg5(CO3)4(OH)2•4H2O - γ-Al2O3 - H2O systems. It was determined that chemical nature of the initial Mg containing components changes the formation mechanism of the synthesis products during isothermal curing. Magnesium aluminum hydroxide hydrate is crystallized by using 4MgCO3⋅Mg(OH)2⋅5H2O as starting material while hydroxide hydrate in the Mg5(CO3)4(OH)2•4H2O presence. The sequence of the compounds formation is presented. It should be noted that different modifications of Al containing components have only a slight influence on the meixnerite-type LDH hydrothermal synthesis. It was determined that after 45 min of sorption all Zn2+ ions are incorporated into the crystal structure of hydrotalcite. It should be underlined that crystallinity of the latter compound do not change during ion exchange experiments. Thus, the latter compound can be used as adsorbent for Zn2+ ion removal. Synthesized samples were characterized by powder X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis (STA) and scanning electron microscopy (SEM).
Mixtures of MgO-TiO2 were mechanically activated using high-energy planetary ball mill during 5, 10, 20, 40, 80 and 120 minutes. Sintering process was preformed in air at 1100o-1400oC for 2h. The decrease in powder’s particle size was noticed as the time of mechanical activation increased and confirmed by particle size analyzer. XRD analyses were performed in order to acquire the information about phase composition. Different ratio mixtures of MgTiO3 and Mg2TiO4 are present within all sintered samples. The effect of tribophysical activation on microstructure was investigated by scanning electron microscopy. The differential thermal gravimetric analysis has been performed in order to investigate thermal behaviour of the mixtures.
In this paper, we studied the effects of Er3+/Yb3+ concentration ratio on structural, morphological and luminescence properties of GdVO4:Er3+/Yb3+ green phosphors prepared by a high-temperature solid state method. The samples with different concentrations (between 0.5 to 2 mol%) of dopant Er3+ emitting ions and different concentrations (between 5 to 20 mol%) of sensitizer ions (Yb3+) were studied. The phosphors were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy. For all samples, XRD diffraction patterns confirmed a formation of a pure GdVO4 phase, while the SEM showed that the materials are comprised of chunks of deformed particles with an average diameter ranging from approximately 2 μm to 8 μm. Both, down-conversion and up-conversion emission spectra of GdVO4:Er3+/Yb3+ samples, under near UV and IR excitations, exhibit two strong emission bands in the green spectral region at 525 nm and 552 nm wavelengths corresponding to 2H11/2 →4I15/2 and 4S3/2 → 4I15/2 electronic transitions of Er3+ ions. The intensity of the green emission was changed by changing the Er3+/Yb3+ concentration ratio. This dual-mode luminescence makes these materials ideal as green phosphors for a wide variety of applications in the fields of bioanalysis and biomedical. [Projekat Ministarstva nauke Republike Srbije, br. 45020 i br. 172056]
Powdery nickel ferrite, NiFe2O4 has been obtained by soft mechanochemical synthesis in a planetary ball mill. Ni(OH)2 and Fe(OH)3 are used as initial compounds. This mixture was mechanically activated for 25h, uniaxial pressed and sintered at 1100°C for 2h. The phase composition of the sintered sample was analyzed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Raman spectroscopy. Morphologies were examined by scanning electron microscopy (SEM). The electrical DC/resistivity/conductivity at different temperatures was measured using a Source Meter Keithley 2410. An Impedance/Gain-Phase Analyzer (HP-4194) was used to measure the impedance spectra (100Hz - 10MHz) at different temperatures. [Projekat Ministarstva nauke Republike Srbije, br. III 45003 i br. III 45015]
Barium-Strontium-Titanate Ba0.77Sr0.23TiO3 was prepared from starting materials BaCO3, SrCO3 and TiO2 through solid-state reactions. Mixtures of these oxides are mechanically activated in a high-energy planetary ball mill at different time intervals from 0 to 120 minutes. In order to obtain information on phase composition, crystal structure was determent by X-ray diffraction. It was observed that after 80 minutes in process synthesis Ba0.77Sr0.23TiO3 started Thermal analyzes were performed in order to determine the characteristic temperatures of the processes that occur in the solid phase. Particle size distribution, together with electron microscopy scanning has given us very useful information about the morphology of the powder.
It is well known that alumina possesses good mechanical and chemical properties. Nanofibers having α - alumina structure was used as reinforcement for metal, polymer and ceramic matrix composites. In this study, three series of nanofibers were prepared. The first series was made from 10 % water solution of the aluminium chloride hydroxide/polyvinyl alcohol with a mass ratio of 5:1. The other two series were made with the addition of 1 wt.% of MgCl2 or 1 wt.% of FeCl3 regarding the aluminium chloride hydroxide content. Nanofibers were prepared using the electrospinning technique and they were characterized by the TGA/DTA, XRD and FESEM methods. It was proven that addition of FeCl3 into the initial spinning solution lowers the temperature for the corundum structure formation while the addition of MgCl2 results if the formation of mixed oxides that eases the sintering process. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR34011]
Modeling of the mechanical behavior of fiber-reinforced ceramic matrix composites (CMC) is presented by the example of Al2O3 fibers in an alumina based matrix. The starting point of the modeling is a substructure (elementary cell) which includes on a micromechanical scale the statistical properties of the fiber, matrix and fiber-matrix interface and their interactions. The numerical evaluation of the model is accomplished by means of the finite element method. The numerical results of calculating the elastic modulus of the composite dependance on the quantity of the fibers added and porosity was compared to experimental values of specimens having the same composition. [Projekat Ministarstva nauke Republike Srbije, br. ON174004 i TVH to project III45012]