Preparation of Electrically Fused Magnesium Oxide from Calcined Magnesite for Use in Electrothermics

U današnje vrijeme postoji velika potreba za materijalima koji mogu podnijeti oksidacijske uvjete na vrlo visokim temperaturama. Pogodan materijal za takvu primjenu je elektrolučno taljeni magnezijev oksid (MgO), s talištem 2825 °C, koji je od velike važnosti za proizvodnju visoko vatrostalnih materijala. Kristali MgO dobiveni iz taline pravilnije su građe, s manje strukturnih pogrešaka u usporedbi s kristalima koji nastaju sinteriranjem na nižim temperaturama. Cilj rada priprava je vrlo čistog elektrolučno taljenog MgO iz kalciniranog magnezita za uporabu u elektrotermiji. U istraživanjima su upotrijebljeni uzorci magnezita (MgCO3) iz ležišta Strezovce, Kosovo, za pripravu vrlo čistog MgO taljenog u peći za elektrolučno taljenje u Kosovskoj Kamenici. Nakon priprave granuliranog taljenog MgO, pri čemu su kontrolirani atmosfera, temperatura i trajanje obrade, određeni su parametri optimalne toplinske obrade i mikrotvrdoća. Na temelju izvedenih istraživanja može se zaključiti da je, uz optimalne uvjete u svim fazama postupka, iz kalciniranog magnezita ležišta Strezovce moguća priprava taljenog MgO za primjenu u elektrotermiji, koji je kvalitetom usporediv s MgO dostupnim na svjetskom tržištu.Nowadays, there is a great need for materials that can withstand oxidative environment at very high temperatures. The most important material for such use is electrically fused MgO with melting point 3098 K and of great importance in the production of high-heat-resistant materials. MgO crystals obtained from melt have a regular structure, with few structural faults, compared to MgO crystals, which are formed at lower temperatures by sintering process. The goal of this work is the preparation of pure electrically fused MgO for use in electrothermics, from calcinated magnesite. Because the Republic of Kosovo possesses grade magnesite (MgCO3), in this research for preparation of pure fused MgO in the electromelting furnace in Kosovska Kamenica samples of Strezovce magnesite deposit were used. After granulated fused MgO preparation, the optimum heat treatment and hardness were determined under controlled atmosphere, temperature range, and total time. Based on the research presented in this paper, it can be concluded that under optimal conditions at all stages, from calcined magnesite deposits of Strezovce, Republic of Kosovo, possible is the preparation of fused MgO for use in electrothermics, of quality comparable to MgO, which is available on the world market

Preparation of Highly Pure Aluminium Oxide (α-Al2O3) Ceramic for Extrusion Moulding

S obzirom na izuzetno široku primjenu aluminijev oksid (Al2O3) najvažniji je materijal iz skupine oksidne keramike. Najvažnija svojstva aluminij-oksidne keramike visoka su čvrstoća i tvrdoća, temperaturna stabilnost, velika otpornost na abraziju, otpornost prema djelovanju agresivne okoline (osim ograničene otpornosti prema lužinama) i korozijska postojanost pri povišenim temperaturama. Zbog navedenih svojstava aluminij-oksidna keramika primjenjuje se u sljedećim područjima: industriji sanitarija za brtvene elemente, elektrotehnici za izolacijske dijelove, proizvodnji elektroničkih podloga, strojogradnji i graditeljstvu za dijelove otporne na trošenje, kemijskoj industriji za dijelove otporne na koroziju, visoke temperature, paru, taline i trosku, mjernoj tehnici za zaštitne cijevi termoelemenata za mjerenja pri visokim temperaturama, medicini za implantate te za visokotemperaturnu primjenu poput sapnica za plamenike te nosače grijača. U radu je opisano dobivanje aluminij-oksidne (α-Al2O3) keramike visoke čistoće za oblikovanje ekstrudiranjem, kvalitetom usporedive s uzorcima dostupnim na svjetskom tržištu. Proizvodnja obuhvaća sljedeće postupke: dobivanje α-Al2O3, pripravu keramičkog praha, pripravu keramičke mase, ekstrudiranje, sušenje, sinteriranje i ispitivanja proizvoda.Aluminium oxide (A2O3) is the most important material from the group of oxide ceramics due to the extremely wide range of applications. The most important properties of aluminium oxide ceramics are high strength and hardness, temperature stability, high resistance to abrasion, resistance to aggressive work environment (except limited alkali resistance) and corrosion resistance at elevated temperatures. Due to these properties, aluminium oxide is used in the following areas: sanitation industry for sealing elements, electrical insulating parts, electronics substrates, engineering and construction of wear resistant parts, chemical industry for parts that are corrosion, high-temperature steam, and molten slag resistant, thermocouple measurements at high temperatures, medical implants and high temperature applications, such as nozzle and heater mounts. This paper describes the process of preparation of highly pure aluminium oxide (α-Al2O3) ceramics for extrusion moulding, quality comparable to the world market. The production includes the following operations: obtaining α-Al2O3, preparation of ceramic powders, preparation of ceramic mass, extruding, drying, sintering, product testing

Hepatitis B virus prevalence and vaccine antibody titers in children HIV exposed but uninfected in Botswana.

BackgroundBotswana introduced the HBV vaccine at birth for all newborns in 2000. To the best of our knowledge, since the introduction of HBV vaccination, there have been limited data for vaccine response to HBV and its impact on early childhood HBV infections among children HIV exposed but uninfected in Botswana.AimsTo determine the prevalence of hepatitis B surface antigen (HBsAg) and HBV vaccine response in 18 months old children HIV exposed but uninfected in Botswana.MethodsStored plasma samples from 304 children at 18 months of age and 287 mothers from delivery were tested for HBsAg. Mothers with positive HBsAg had HBV DNA level tested, and their HBV genotypes were determined by amplifying a 415-base pair (bp) region of the surface gene. Plasma samples from children exposed to HIV were tested for hepatitis B surface antibody (anti-HBs) titers.ResultsNo children (0 of 304) were positive for HBsAg at 18 months while 5 (1.74%) of 287 HIV-positive mothers were HBsAg positive. Four of the HBsAg positive mothers were infected with genotype A1, while 1 was infected with genotype E. The median anti-HBs titer in children was 174 mIU/mL [QR: 70, 457]. Three (1.1%) of 269 children had an inadequate vaccine response (ConclusionNo HBsAg positivity was identified in a cohort of children HIV exposed but uninfected. The absence of HBsAg positives was associated with good HBV vaccine responses and low maternal HBsAg prevalence in Botswana