The influence of mechanical activation on the properties of MgO-TiO2 electroceramics

Intenzivan razvoj elektronike najvećim delom zavisi od razvoja novih materijala, koji se pored strogo određenog sastava odlikuju i tačno određenom raspodelom defekata i primesa. Sa sve rasprostranjenijom primenom tehnike u svakodnevnom ljudskom životu javlja se sve veća potreba za novim materijalima koji zadovoljavaju sve strožije zahteve savremene tehnologije kako po pitanju karakteristika, tako i po pitanju funkcionalnosti a u novije vreme sve više i pitanje ekonomičnosti. Materijali koji imaju značajnu ulogu u savremenoj elektrotehnici su keramički materijali zbog svojih izuzetnih funkcionalnih svojstava. Pomenuta svojstva u najvećoj meri zavise od načina pripreme i obrade materijala. Elektronska keramika se najčešće dobija procesom sinterovanja. U najopštijem smislu, može se reći da sinterovanje predstavlja oblik kompaktiranja disperznih smeša materijala, ili ispresaka dobijenih njihovim hladnim oblikovanjem, na temperaturama nižim od temperature topljenja jedne od bazičnih komponenati, u cilju konsolidacije disperznog sistema i obezbeđivanja određenog skupa fizičko-hemijskih, mehaničkih i električnih svojstava. Aktuelnost i značaj istraživanja u oblasti proučavanja elektronskih keramika iskazuje i niz naučnih časopisa u stručnoj literturi. Među materijalima koji su od posebnog interesa zbog svoje primene u elektronici su svakako keramike na bazi titanata. Ubrzani razvoj mobilne telefonije kao i drugih telekomunikacionih sistema zahtevaju upotrebu dielektrika koji se koriste u mikrotalasnoj oblasti. Zbog svojih dobrih električnih svojstava magnezijum titanatna keramika se koristi u izradi mikrotalasnih frekventnih rezonatora i antena, u filterima i oscilatorima za aplikaciju u komunikacionim sistemima. Još se primenjuje za izradu integrisanih kola i aktuatora, a predstavlja i bazični materijal pri izradi višeslojnih kondenzatora. Uslove koji ovi materijali treba da zadovolje su prvenstveno što niže vrednosti dielektričnih gubitaka (tj. tangensa ugla gubitaka tgδ, odnosno što veći faktor dobrote Q) i visoke vrednosti dielektrične konstante. Navedena svojstva elektrokeramike zavise prvenstveno od uslova i načina pripreme polaznih komponenti. Postoji više različitih metoda za sintezu magnezijum titanata koji su do sada poznati iz literture. Među njima su najčešće korišćeni sol-gel tehnike, koprecipitacija, sprej piroliza. Od reakcija u čvrstoj fazi poslednjih godina najzastupljenija je metoda mehaničke aktivacije. Mehanička aktivacija je često korišćena tehnika promena fizičko-hemijskih svojstava disperznih sistema. Često je korišćena tehnologija za dobijanje prahova zbog svoje jednostavnosti i mogućnosti dobijanja većih količina materijala što utiče na nižu cenu konačno proizvedenih komponenti. Ovakvim tretmanom polaznih prahova dolazi do kontrolisane destrukcije materijala kao i do intezivnog prenosa mehaničke energije na prahove. Dobro je poznato da je reakciona sposobnost materijala posledica strukturnih svojstava. Stoga mehaničkom aktivacijom narušena prvobitna struktura sistema dovodi do ubrzavanja procesa sinteze i sinterovanja materijala u kojima se koristi aktivirani prah. U ovom radu smeša prahova je mehanički aktivirana u visoko energetskom planetarnom mlinu sa kuglama u različitim dužinama vremena. Cilj istraživanja je ispitivanje mikrostrukturnih svojstava polaznih i u različitim vremenskim periodima mehanički aktiviranih prahova, procesa generacije strukturnih defekata, formiranje i evolucija faznog sastava i mikrostrukture u procesu dobijanja funkcionalnih elektrokeramičkih materijala. Za formiranja dielektrika sa najboljim električnim svojstvima i najvećom gustinom određeno je optimalno vreme mehaničke aktivacije i temperatura sinterovanja. Takođe, ispitan je uticaj režima mehaničke aktivacije na temperaturu sinterovanja i utvrđen tok reakcije u čvrstoj fazi u izotermskim uslovima sinterovanja sistema MgO-TiO2

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 effects of Chinese population policy on the labor market

Faced with high levels of poverty, China introduced its "one-child policy" in 1980 and began economic and systemic reforms that led to the country's strong economic development. Thanks to the improvement in the average standard of living, certain socioeconomic aspects related to women's employment, the pursuit of higher education, delays in childbirth, and the number of children have changed. These changes have not only reduced the number of children being born and led to population aging, but have also affected the labour market. The aim of this paper is to determine the effects of Chinese population policy on selected labour market indicators: labour force by age and sex in rural/urban areas, the labour force participation rate, and the unemployment rate. Research results from 2010 to 2020 show the growth of the labour force, while the unemployment rate has been growing since 2018. It is noticeable that the number of workers in the labour force is growing in cities, while it is declining in rural areas. On the other hand, the unemployment rate is lower in rural areas, while the growth of unemployment is evident in urban areas. The research shows that the long-term implementation of this population policy has resulted in a larger number of men, leading to greater participation of men in the labour force. Despite measures to improve the position of women at work, women's social security is still not guaranteed, and it is more difficult for women to decide to expand their families. As China has ambitious plans for economic development, defining adequate population and social policies is crucial for their implementation

INVESTMENT FUNDS WITH LEGAL PERSONALITY – A TRUE RIVAL TO MUTUAL FUNDS?

Investment funds come in a large variety of legal forms, investment techniques, target investors, redemption rights, and others. It is often said that there are no two investment funds that are the same. The focus of this article is the legal form in which they come. Authors shall analyze the position of investors in funds with legal personality in order to discuss differences in comparison to investors in mutual funds. On the EU level only the UCITS funds are harmonized, while alternative investment funds are left to national regulations. The aim is to discuss whether the legal status of investment funds is a real yardstick for determining the crucial investor’s rights such as redemption rights and relations between the investors and fund managers. In order to provide answer authors shall compare funds in jurisdictions that are comparable and often serve as role models, as well as those in which the fund industry is most developed, followed by the Croatian perspective. Finally, the authors shall contribute to the discussion of how can traditional types of companies such as joint-stock or limited liability companies be integrated into the capital market law arena, serving as a vessel to investment funds

High-accuracy quasistatic numerical model for bodies of revolution tailored for RF measurements of dielectric parameters

We have developed rotationally symmetrical coaxial chambers for measurements of dielectric parameters of disk-shaped samples, in the frequency range from 1 MHz to several hundred MHz. The reflection coefficient of the chamber is measured and the dielectric parameters are hence extracted utilizing a high-accuracy quasistatic numerical model of the chamber and the sample. We present this model, which is based on the method-of-moments solution of a set of integral equations for composite metallic and dielectric bodies. The equations are tailored to bodies of revolution. The model is efficient and accurate so that the major contribution of the measurement uncertainty comes from the measurement hardware

Structural characterization of mechanically activated MgO-TiO2 system

In this article the influence of ball miling process on structure of MgO-TiO2 system was investigated. The mixtures of MgO-TiO2 powders were mechanically activated in a planetary ball mill for the time period from 0 to 120 minutes. The influence of mechanical activation on the lattice vibrational spectra was studied by Raman spectroscopy at room temperature. Structural investigations have been performed on produced powders. Nitrogen adsorption method was used to determine the BET specific surface area and pore size distribution. Unusual results have been obtained: specific surface area continuously decreased up to 40 minutes of activation and increased after that, reaching its minimun value of 5.5 m2/g. The Raman spectra of activated powders have shown that anatase modes have been decreasing in intensity and broadening as the time of activation extended. Also, the additional modes attributed to TiO2 II, srilankite and rutile phases started to appear as a consequence of activation

Adsorption capacity of wollastonite based adsorbents with porous structure controlled with different progeny agents

Porous wollastonite (WL) based adsorbents were fabricated by a pressureless sintering process by using low molecular weight poly(methyl methacrylate) (PMMA), nanocellulose (NC) and yeast as the pore forming agents. WL based adsorbents were synthesized in two step process. In the first step, calcium carbonate and methylhidrogen cyclosiloxane were mixed with isopropyl alcohol, dried and calcined at 250 °C. Second step included WL mixing with porogen, followed by controlled calcination and on that way the sintered materials with randomly distributed pores were obtained. The effectiveness of the synthesis steps as well as material properties, i.e., the pore morphology were determined by FTIR analysis and scanning electron microscopy (SEM), respectively. The pore morphology and adsorption capacity was changed dramatically by changing the pore forming agent. The highest adsorption capacity was obtained when NC was used as the pore forming agent. Obtained materials showed moderate adsorption capacities of 10.56, 8.42 and 11.33 mg/g with respect to As5+, Cr6+ and phosphate, respectively. The con centrations of heavy metal ions were determined by using Ion chromatography coupled with mass spectrometry (ICP-MS)