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Porous anorthite (CaAl2Si2O8) ceramics, suitable for thermal insulation in buildings, were obtained using waste seashells as a source of CaO, kaolin as a source of Al2O3 and SiO2 and banana peel as a pore former. Changing the volume of banana peel as well as the processing temperature was found to be an effective approach to control the thermo-mechanical properties of the obtained anorthite ceramics. The sintering of powder compacts containing up to 30 wt% banana peel at temperatures ranging from 1100 to 1200 °C resulted in anorthite ceramics possessing up to 45% open porosity, a compressive strength between 13 and 92 MPa, a bulk density between 1.87 and 2.62 g/cm3 and thermal conductivity between 0.097 and 3.5 W/mK. It was shown that waste materials such as seashells and banana peel can be used to obtain cost-effective thermal insulation in buildings.

Praseodymium doped calcium hydroxyapatite (PrHAP) nanopowder was synthesized by the co-precipitation method and characterized by X-Ray Diffraction, Fourier Transform Infrared, and Fluorescence Spectroscopy. Characterization studies from XRD and FTIR spectra showed that obtained crystals are monophase hydroxyapatites and that the sample particles are of nano size. A fluorescence study has shown that PrHAP particles have fluorescent emission under UV‐ Visible excitation. These results may open new avenues for developing bioactive materials for bone regeneration and fluorescent probes for bio-imaging applications.

This paper presents the technological process for obtaining basalt-stainless steel composite materials and testing their physical and mechanical properties. The phases of the technological process consist of: milling, homogenization, pressing, and sintering to obtain composite materials with improved fracture toughness. Andesite basalt from the deposit site "Donje Jarinje", Serbia, was used as a matrix in the composites, while commercial austenitic stainless steel 316L in the amount of 0-30 wt.% was used as a reinforcement. Although the increase of 316L amount caused a continuous decrease in the relative density of sintered samples, the relative density of sample containing 30 wt.% of 316L was above 94%. The 316L grains, which possess a larger coefficient of thermal expansion than the basalt matrix, shrinking faster during cooling from sintering temperature resulting in the formation of compressive residual stress in the basalt matrix surrounding the spherical steel grains. The presence of this stress activated toughening mechanisms such as crack deflection and toughening due to compressive residual stress. The addition of 20 wt.% of reinforcing 316L particles increased the fracture toughness of basalt by more than 30%. The relative density of these samples was measured to be 97%, whereas macrohardness was found to be 6.2 GPa.

In modern industry, there is an increasing demand for environmentally friendly and light structural materials with good physical and mechanical properties, produced from cheap natural raw materials available in large quantities. One of the materials that meet the mentioned criteria is basalt. Basalt is a natural igneous rock of volcanic origin, created by the pouring of magma on the Earth's surface, the amount of which is significant in the territory of Serbia. Since basalt does not exhibit toxic, carcinogenic, or mutagenic effects, it is in the true sense a non-hazardous material and belongs to the group of eco-friendly materials. In this research, andesite basalt aggregate from the "Donje Jarinje" site, in Serbia, was used to obtain high-density glass-ceramic materials. High-density glass-ceramic materials were obtained by powder metallurgy process, which consisted of the following methods: dry grinding, homogenization, cold uniaxial and isostatic powder pressing and sintering in the air. In order to achieve a high-density of the materials, the green compacts were sintered in the temperature range from 1040 to 1080 °C. After confirming that the highest density materials were achieved at the sintering temperature of 1060 °C, the sintering time was optimized in the time interval from 30 to 240 min. After the experimental test, the optimal sintering parameters for obtaining high-density glass-ceramic material at the temperature of 1060 °C for 60 min were achieved, whose relative density is 99.50%, and hardness is 6.70 GPa. The characterization of andesite basalt powder was performed using the laser light diffraction method, scanning electron microscopy and X-ray diffraction method, while the characterization of sintered glass-ceramic materials was performed using the Archimedes method, X-ray diffraction method, optical light microscopy and Vickers hardness test. The results of this research confirmed that by applying powder metallurgy and sintering in the air, high-d

The industrial requirements in the 21st century are environmentally friendly and light construction materials with good physical-mechanical properties manufactured from cheap natural raw materials available in large quantities. One of these materials is basalt. Basalt is a natural igneous rock of volcanic origin, with a significant amount in Serbia. Basalt belongs to the group of non-hazardous and eco-friendly materials. Andesite basalt aggregate from the "Donje Jarinje" site, Serbia, was used as the starting natural raw material for obtaining the glass-ceramic material. The aggregate is from 2 to 5 mm in size. The aggregate was milled in the tungsten-carbide vibrating cup mill for 30 min to obtain a fine powder for synthesis. The homogenization of andesite basalt powder and binder was carried out in the mortar and pestle for 10 min. The paraplast was used as a binder with a content of 0.6 wt.%. After that, uniaxial pressing of the powder at a pressure of 50 MPa was performed. A forming green compact, cold isostatic pressing was performed with a pressure of 230 MPa to increase its density. The sintering was carried out at the temperature of 1060 °C for 60 min in the air. The sintered glass-ceramic sample was a relative density of 99.5%, a macrohardness of 6.7 GPa and a fracture toughness of 2.2 MPa·m1/2 [1]. The andesite basalt powder was characterized using the laser light diffraction method, X-ray diffraction method and scanning electron microscopy. Sintered glassceramic material was characterized using the X-ray diffraction method, Archimedes principle, scanning electron and optical light microscopy and the Vickers hardness test. The glass-ceramic material obtained by sintering andesite basalt powder could be used for various industrial applications in the civil engineering, mechanical, chemical, and petrochemical industries, as well as for the making of containers to store nuclear waste.

It is well known that geopolymers are a new group of binder materials of alumosilicate origin. Geopolymers are made by the reaction of precursor aluminosilicate materials with alkaline activator solutions. The current research relates to a low-cost and eco-friendly procedure, suitable of being implemented in two easy steps. The first step is the production of a solid phase based on fly ash (Obrenovac, Serbia) and eggshell ash as waste materials rich in calcium. The second step is alkali activating the solid phase using an alkaline activator (a mixture of NaOH and Na2SiO3) and procedures in proper laboratory conditions. Four samples with different eggshell ash content were synthesized. The concentration of used NaOH was 12 mol dm−3. The structural properties of all investigated samples were analyzed by XRD (X-ray diffraction), DRIFT (diffuse reflectance infrared Fourier transform), SEM (scanning electron microscopy) and UV/Vis spectroscopy analysis. XRD determined the amorphous halo with the presence of quartz as the crystal phase in all of the investigated samples. These results were confirmed by DRIFT analysis. The morphology of the samples was determined by SEM analysis. UV/Vis showed that the material could be a potential adsorbent.

The effect of zircon (ZrSiO4) on the physico-chemical and mechanical properties of geopolymer/zircon composites was examined in this study. Four geopolymer/zircon composites containing 10, 20, 30 and 40 wt.% zircon were prepared from metakaolin with alkali activators. Characterization of the obtained geopolymers was performed by X-ray diffraction (XRD), Scanning electron microscope (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). XRD results did not confirmed the formation of interconnected phases between added zircon, starting aluminum silicates and alkali activators. Compressive strength of prepared geopolymer was examined. The maximum obtained compressive strength of 70.15 MPa was measured in sample containing the smallest fraction of zircon, i.e., 10 wt.%. Addition of larger amount of zircon (20 wt.%) hinders the progress of geopolymerization reaction and consequently decreases compressive strength.

In the present study, andesite basalt originated from the deposit site “Donje Jarinje”, Serbia, was examined as a potential raw material for high-density ceramics production. The production of high-density ceramics included dry milling, homogenization, cold isostatic pressing and sintering in the air. To determine the optimal processing parameters the sintering was conducted at 1040, 1050, 1060, 1070 and 1080°C, and afterwards the sintering duration was varied from 30 to 240min at the optimal sintering temperature of 1060°C. Characterization of the starting and sintered materials included the estimation of particle size distribution, density, hardness and fracture toughness complemented with X-ray diffraction, optical light microscopy, scanning electron microscopy and energy dispersive spectroscopy analysis. Phase transformations did not occur during processing in the investigated temperature range from 1040 to 1080°C. The obtained research results showed that 99.5% of relative density and the highest hardness and fracture toughness values of 6.7GPa and 2.2MPa•m1/2, respectively, were achieved for the andesite basalt sintered at 1060°C for 60min in the air. The results of the present study confirmed that the sintered andesite basalt can be used as a high-density ceramic material for various industrial applications.

Ovim tehničkim rešenjem pokazano je da je moguća brza i kvalitetna izrada keramičkog zavrtnja sa unapred zadatim dimenzijama, mašinskom obradom ispresaka kao etapom u izradi gotovog keramičkog proizvoda. Keramički zavrtanj izrađen mašinskom obradom ispresaka, nalazi primenu u mnogim oblasitma tehnike, naročito u kritičnim uslovima primene. U ovom tehničkom rešenju detanjno je opisan postupak izrade delova keramičkog zavrtnja, vijka i navrtke. Kvalitetna i jednostavna izrada vijka i navrtke, omogućena je mašinskom obradom ispresaka zahvanjujući primeni metilmetakrilata (MMA) u pripremi keramičkog praha alumine. U prisustvu MMA ostvaren je odličan kvalitet mašinske obrade ispresaka od alumine do forme vijka i navrtke sa preciznim dimenzijama koje su uvećane za predviđeni procenat skupljanja ispreska od alumine tokom sinterovanja.

In this paper, raw natural metakaolin (MK, Serbia) clay was used as a starting material for the synthesis of geopolymers for thermal treatment. Metakaolin was obtained by calcination of kaolin at 750 °C for 1 h while geopolymer samples were calcined at 900 °C, which is the key transition temperature. Metakaolin was activated by a solution of NaOH of various concentrations and sodium silicate. During the controlled heat treatment, the geopolymer samples began to melt slightly and coagulate locally. The high-temperature exposure of geopolymer samples (900 °C) caused a significant reduction in oxygen, and even more sodium, which led to the formation of a complex porous structure. As the concentration of NaOH (6 mol dm−3 and 8 mol dm−3) increased, new semi-crystalline phases of nepheline and sanidine were formed. Thermal properties were increasingly used to better understand and improve the properties of geopolymers at high temperatures. Temperature changes were monitored by simultaneous use of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The loss of mass of the investigated samples at 900 °C was in the range of 8–16%. Thermal treatment of geopolymers at 900 °C did not have much effect on the change in compressive strength of investigated samples. The results of thermal treatment of geopolymers at 900 °C showed that this is approximately the temperature at which the structure of the geopolymer turns into a ceramic-like structure. All investigated properties of the geopolymers are closely connected to the precursors and the constituents of the geopolymers.

Comprehensive study on effect of YAG amount on densification, creep resistance and mechanical properties of Al2O3-YAG composite pressureless sintered at 1600 o C was conducted. The main goal was to optimize the amount of YAG in order to fabricate a composite with improved creep resistance and sufficiently good mechanical properties. The composite was made by mixing a commercially available Al2O3 powder with fine YAG powder obtained by glycine-nitrate combustion synthesis. Increased driving force for sintering of fine YAG powder allowed fabrication of dense Al2O3-YAG composite containing up to 30 vol% YAG. The presence of YAG was found to be effective in improving creep resistance as well as mechanical properties of Al2O3-YAG composite such as hardness and elastic modulus. While fracture strength of the composite can be as high as that of monolithic Al2O3 (~ 300 MPa), fracture toughness of composite decreased continuously as the YAG content increased. The decrease was ascribed to transgranular fracture of both YAG and Al2O3 grains in samples containing larger amounts of YAG. The proper balance between fracture toughness and creep resistance was found in composite containing 18 vol% YAG which had considerably improved creep resistance accompanied by a relatively small decrease in fracture toughness which reached value of ~ 3 MPa·m1/2. Hardness and elastic modulus were found to be 15 GPa and 371 GPa, respectively.

The effect of Ca2+ amount and sintering temperature on mechanical properties of geopolymer-brushite (GPB) binders was investigated. Brushite and raw abandoned kaolinite clay thermally transformed into metakaolin were used for GPB synthesis. The complete phase and structural analyses were performed by X-ray powder diffraction, and Fourier transforms infrared spectroscopy (FT-IR). The pore-filling effect as a consequence of Ca2+ ions incorporation into the hybrid geopolymer networks improved the compressive strength. On the other hand, the chosen biscuit sintering at 800 and 900oC caused the phase transformation of brushite into calcium pyrophosphate, which negatively affected the compressive strength of such materials. The obtained results indicate that the usage of relatively high sintering temperatures is not always the necessary step for producing geopolymer-based types of cement with prominent mechanical properties.

Anorthite ceramics was fabricated from calcium exchanged Na-LTA zeolite. The powder compacts of Ca-LTA zeolite were sintered at different temperatures ranging between 1100 and 1400°C. It was found that the temperature of 1100°C was sufficiently high to trigger formation of anorthite which stayed stable even at temperature as high as 1400°C. The highest relative density and the lowest open porosity were measured in samples sintered at 1200°C for 3 h. The effect of milling time of Ca-LTA zeolite precursor on density, microstructure and mechanical properties of samples sintered at 1200°C for 3 h was investigated. The particle size refinement appeared to be beneficial in accelerating densification process and improving mechanical properties. The density, compressive strength and hardness of anorthite ceramics obtained from non-milled precursor were measured to be 70.5 %TD, 64 MPa and 1.45 GPa, respectively. On the other side the anorthite ceramics obtained from 24-hour-long milled zeolite precursor had density of 83.9 %TD, compressive strength of 101 MPa and hardness of 3.44 GPa.

Cordierite-acicular mullite composites containing 0, 25, 50, 75 and 100 wt% of mullite were fabricated from waste MoSi2 and commercial powders of Al2O3 and spinel (MgAl2O4). Careful oxidation of pulverised waste MoSi2 rendered a precursor mixture of MoO3 and amorphous SiO2, which served as pore forming agent and SiO2 source, respectively. Evaporation of MoO3 at ∼750 °C allowed production of highly porous cordierite-mullite ceramic composite after sintering in air at 1350 °C for 4 h. The combination of equiaxed cordierite grains and elongated (prism-like) mullite grains, resulted in unique microstructure with open porosity between 53.3 and 55.6 vol% which makes the obtained composite convenient for application as diesel particulate filter material. The presence of mullite affected four key thermo-mechanical properties which determine the thermal shock resistance of cordierite-mullite composite. The best thermal shock resistance was measured in composite containing 75 wt% of mullite. It was a result of improved thermal conductivity (1.081 W/mK) and bending strength (3.62 MPa) and relatively low values of coefficient of thermal expansion (3.8 × 10−6 K−1) and elastic modulus (2.27 GPa).

This paper outlines the production of an inorganic polymer/geopolymer using a metakaolin by an environmental friendly, energy saving, clean technology to conserve natural environment and resources. The influence of alkali activation, i.e. different concentration of NaOH as a component of alkali activator mixture on the process of geopolymerization of metakaolin is investigated. Also, process of aging time of geopolymer is followed by several analytical methods. The structure of metakaolin and metakaolin based geopolymers and their physicochemical properties were studied using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and after 28 days scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was applied for the surface characterization of the samples. A shift of the Si-O or Si-O-X (X=Al, Si, Na...) bands as the molarity of activator increasing during geopolymerization process was observed by FTIR. Mass spectra of geopolymers were characterized by MALDI TOF mass spectrometer. Structural reorganization of geopolymer samples occurs during the curing/aging in accordance with a geopolymerization mechanism.

This paper outlines the production of an inorganic polymer/geopolymer using a metakaolin by an environmental friendly, energy saving, clean technology to conserve natural environment and resources. The influence of alkali activation, i.e. different concentration of NaOH as a component of alkali activator mixture on the process of geopolymerization of metakaolin is investigated. Also, process of aging time of geopolymer is followed by several analytical methods. The structure of metakaolin and metakaolin based geopolymers and their physicochemical properties were studied using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and after 28 days scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was applied for the surface characterization of the samples. A shift of the Si-O or Si-O-X (X=Al, Si, Na...) bands as the molarity of activator increasing during geopolymerization process was observed by FTIR. Mass spectra of geopolymers were characterized by MALDI TOF mass spectrometer. Structural reorganization of geopolymer samples occurs during the curing/aging in accordance with a geopolymerization mechanism.