Adsorption capacities of Shungite - a Russian Mineral

Shungite, a carbon-rich rock of the Precambrian age widespread over Russia, attracts much attention due to possibilities of application in various industrial and medical fields. Carbon acts as an efficient catalyst of hydrogenation at low temperatures, as an adsorbent and filter in water purification processes, and as a multifunctional filler of polymeric and inorganic binders. The presence of the starting components α-SiO2, Fe2O3, carbon C, α-Al2O3, γ-Al2O3, and CaCO3 has been determined by XRD measurement. Particle size distribution of the initial powder indicates large agglomerates with size of 10 microns and larger, confirmed by SEM also. In a batch test, the influence of shungite mass, contact time and temperature on adsorption efficiency of amlodipine, medicament used to treat high blood pressure and coronary artery disease, has been investigated. This material showed moderate adsorption capacity of 54.95 mg/g at 10 mg/l initial amlodipine concentration. The concentrations of amlodipine were determined using UVVIS spectrometry

Properties of 3Y-TZP zirconia ceramics with graphene addition obtained by spark plasma sintering

In this study the influence of graphene addition on the microstructure, phase composition, mechanical, and electrical properties of 3Y-TZP ceramics was investigated. Blends of pure 3Y-TZP and with addition of 1 − 4 vol% graphene were prepared by mixing and milling, and they were consolidated by spark plasma sintering (SPS). Addition of 3 vol% graphene is necessary to overcome the percolation threshold and obtain electrically conductive composites. However, rising the graphene contents obstructs sinterability. Hence, flexural strength, Young's modulus, and hardness decrease with increasing the graphene content, and the fracture resistance reaches an intermediate maximum at 2 vol% graphene. Graphene lamellae are oriented orthogonally to the pressing direction. They evidently provide some energy dissipation by crack deflection. TZP-graphene interfaces are very weak. Thus, crack bridging can be neglected. © 2018 Elsevier Ltd and Techna Group S.r.l.This is the peer-reviewed version of the article: Obradović, N., Kern, F., 2018. Properties of 3Y-TZP zirconia ceramics with graphene addition obtained by spark plasma sintering. Ceramics International 44, 16931–16936. [https://doi.org/10.1016/j.ceramint.2018.06.133

Influence of Mechanical Activation on Electrical Properties of Ceramic Materials in VHF Band

Mechanical activation is commonly used as a pre-sintering process in order to enhance the reactivity of materials, reduce the particle size, increase diffusion rates, accelerate the reaction, and lower the sintering temperature. The mechanical activation can affect the final electrical and mechanical characteristics. In this paper we consider the influence of the mechanical activation on the permittivity and the loss tangent. We outline methods for evaluation of these parameters, with emphasis on our coaxial-chamber technique for measurements in the VHF band

Electrical properties of mechanochemicaly activated cordierite ceramics

Three-component oxide mixture was prepared containing MgO+Al2O3+SiO2 in a 2:2:5 ratio with addition of 10% Bi203. Mixtures were mechanically activated in range from 5 to 240 minutes in a mill with ceramic balls, and sintered at range from 1173-1573 K. In order to determine the structure transformations, sintered products were analyzed by the XRD method. The goal of presented research was to find the possible correlation between process parameters and functional properties of the cordierite-based ceramic materials. Quantitative measures of the functional sample properties, capacity (Cc) and electrical resistance (RJI) as well as of dielectric loss (tgd) were used. The results obtained proved that there is a correlation between mechanical activation and properties of cordierite ceramics

Structural analyses of sintered MT and BZT ceramics

Development of dielectric materials is increasing with a rapid progress in mobile and satellite communications systems, where magnesium titanates find their place owing to good dielectric properties. Recently it has been established that, these materials, which are based on binary magnesium titanates (MgTi03 and Mg2Ti04) can be applied in MW engineering. These materials differ extremely low dielectric loss in the microwave range and high dielectric constant. On the other hand, barium-titanate compounds have attracted great attention for their specific microwave properties, as well. They were commonly used as parts of resonators, filters and multilayer ceramic capacitors, in the microwave region. The crystal phase with the structure BaZn2Ti40 11 is present in various commercial microwave dielectric materials based on barium-titanate compounds. Taking all this into account, in this article, the influence of mechanical activation of the MgO-Ti02 and BaCOr ZnO-Ti02 systems on phase composition, crystal structure and microstructure before and after sintering process, has been reported

Isothermal sintering of BZT ceramics

Starting mixtures of BaCO3 •ZnO and Ti02 were mechanically activated for 0,5, 10,20.40 and 80 minutes in a planetary ball mill. The powders obtained were sintered isothermally to temperatures between 1000 and 1300 °C. The phase composition of powders and sintered samples were followed by X-ray analyses. Also, the changes in microstructures were detected using SEM

The additive influence on sintering of zno-tio2 system according to triad “synthesis-structure-properties”

U okviru ove doktorske disertacije detaljno i sistematski je proučen uticaj aditiva magnezijum oksida na sintezu i sinterovanje sistema ZnO-TiO2. Smeša prahova ZnO, TiO2, MgO (0, 1,25 i 2,50 masenih % MgO), mehanički je aktivirana mlevenjem u visokoenergetskom planetarnom mlinu u toku 15 minuta. Metodama skenirajuće elektronske mikroskopije i rendgenske difrakcije analizirane su strukturne promene u materijalu koje se dešavaju tokom mehaničkog tretmana. Diferencijalnom termijskom analizom određene su karakteristične temperature u intervalu 20-1100°C. Takođe je detaljno ispitan uticaj mehaničke aktivacije na presovanje prahova. Proučavano je sinterovanje u izotermskim uslovima na temperaturama 800, 900, 1000 i 1100°C, kao i reakciono sinterovanje u neizotermskim uslovima u temperaturnim intervalima od sobne do 800, 900, 1000 i 1100°C pomoću dilatometrijske analize. Rendgenostrukturnim proučavanjem uzoraka sinterovanih izotermski utvrđen je fazni sastav dobijenog materijala, a mikrostrukturne karakteristike skenirajućom elektronskom mikroskopijom. Analizom mikrostrukturnih parametara aktiviranih smeša utvrđeno je da se suštinske mikrostrukturne promene odigravaju uglavnom u kristalnoj strukturi ZnO. U toku mehaničkog dejstva dolazi do značajnog smanjenja veličine kristalita cink-oksida, povećanja gustine dislokacija i mikronaprezanja u njegovoj kristalnoj strukturi, dok kod titan-dioksida nije primećena takva pojava. Uticaj aditiva na reakciju u čvrstoj fazi između ZnO i TiO2 praćen je u izotermskim i neizotermskim uslovima. Predložen je mehanizam sinterovanja, utvrđeno je da se sa dodatkom aditiva temperatura početka reakcionog sinterovanja neznatno menja, reakcija formiranja spinela (cink-ortotitanata) se pomera ka višim temperaturama, ali se najveće zgušnjavanje nakon procesa sinterovanja, kako izotermskog tako i neizotermskog, dešava upravo kod smeše sa najvećom koncentracijom dodatog aditiva. Ispitivanjem električnih svojstava utvrđeno je da električna otpornost opada sa frekvencom i temperaturom sinterovanja ali i da raste sa dodatkom aditiva. Na samom kraju, zaključujemo da smo našim istraživanjima predstavljenim u ovoj doktorskoj disertaciji, definisali zavisnosti između sinteze i svojstava, koja direktno vezuje sintezu i strukturu odn. strukturu i svojstva, čime je dat i doprinos prognozi svojstava materijala.In this doctoral dissertation the influence of additive addition on the synthesis and sintering of zinc titanate, Zn2TiO4, was studied. The powder mixtures of ZnO, TiO2 and MgO (0, 1.25 and 2.50 weight % MgO) were mechanically activated by milling using a high-energy ball mill for 15 minutes. Structural changes of the material that occur during mechanical treatment were analyzed using the scanning electron microscopy and X-ray powder diffraction. The characteristics maximums in the temperature range 20-1100°C were determined using differential thermal analysis. Isothermal sintering on temperatures 800, 900, 1000 and 1100°C as well as non-isothermal reaction sintering at the same temperatures were studied. X-ray diffraction was employed to determine a phase composition of sintered samples. Scanning electron microscopy was used in order to determine the phase microstructure evolution. Analysis of microstructural parameters revealed that essential microstructural changes occur mainly in the crystal structure of ZnO. Mechanical activation caused significant reduction of zinc oxide crystallite size, and increase of dislocation density and microstrains in the crystal structure. These phenomena were not observed for titan dioxide. The influence of additive addition on solid state reaction between ZnO and TiO2 was studied in isothermal and non-isothermal conditions. It was established that MgO addition has no influence on sintering temperatures, that moves the temperature of the beginning of reaction to higher temperatures and lags the formation of spinel (zinc-titanate), but the highest densification, after isothermal as well as non-isothermal sintering, is observed within mixture with highest content of mentioned additive. The electrical resistivity data revealed a clear decrease with increasing sintering temperatures as well as slight increase with MgO addition. And finally, we can conclude that observed results presented within this doctoral dissertation gave dependences between synthesis and properties, which directly combine synthesis and structure as well as structure and properties

Reaction sintering of the 2ZnO-TiO2 system

Sintering kinetics of the mechanically activated ZnO-TiO2 system was studied. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill for different time intervals from 0 to 300 minutes. Formal phenomenological analyses were performed in order to describe the specimen’s behavior during isothermal sintering at 1100oC. Non-isothermal sintering was investigated by dilatometer measurements up to 1100oC with a constant heating rate. The Dorn method was applied in order to give information on the activation energy

Investigation of sintering kinetics of ZnO by observing reduction of the specific surface area

Reduction of the specific surface area of porous ZnO during the sintering process was studied. ZnO powder was sintered at temperatures from 673 K to 1173 K. The decrease in the specific surface area was observed as a function of temperature and sintering time. Two different models were involved in order to define the appropriate parameters. The Arrhenius equation was used to give information on the activation energy of sintering. The LSE method was applied for determining optimum parameter values

The Influence of Tribophysical Activation on Zn2TiO4 Synthesis

Poster presented at the Seventh Yugoslav Materials Research Society Conference - YUCOMAT 2005, Herceg Novi, Crna Gora, September 12-16, 2005