Spontaneous Precipitation in the System Uranyl(2+ )nitrate Potassium Hydroxide - Phosphoric Acid - Water

The precipitation system U02(NOs)2-KOH-H3P04-H20 (at 298 K) aged for 1 day and for 30 days is examined ([U02(NOs)2] = = 1 · 10-a mol dm-3, [KOH] varied from 1 · 10-6 to 6 · 10-1 mol dm-3, [H3P04] from 2 · 10-4 to 6 · 10-1 mol dm-3 and 1.5 <pH< 11.5). The precipitation and phase boundaries are determined. The solid phases U02HP04 · 4 H20(s) and (U02)s(P04)2 · 8 H20 are stable at [KOH] < 1 · 10-3 mol dm-3, 1.5 <pH < 4.0. Uranates precipitate at pH > 9.5. The stability region of KU02P04 · 3 H20(s) is found at high concentrations of KOH and H3P04. X-ray diffraction pattern of this compound is given. According to the precipitation boundary after 30 days (equilibrium conditions) the solubility product of KU02P04 · 3 H20 is determined: log ([K+] · · [U022+] [P043-]) = -- 26.28 (at I =0 mol dm-3)

Identification and Characterization of Alkaline Uranyl(2 +) Phosphates

The spontaneous precipitation in the systems U02(N03)2- -MOH-HaP04--H20 and U02(N03)2-MNOa-H3P04- H20 (M = = Li, Na, K, Rb, Cs) is examined. The formation of alkaline- uranyl(2+) phosphates polyhydrates is detected: M[U02P04] · · n H20 (n = 4 for M = Li, n = 3 for M = Na, K, Rb and n = 2.5 for M =Cs). The X-ray powder patterns of these compounds are determined and compared with that of H30[U02P04] · 3 H20. A close structural relation within this series is observed. The size of the alkaline ionic species in the particular compound affects the content of crystalline water in the unit cell

The tribological performance of hardfaced/ thermal sprayed coatings for increasing the wear resistance of ventilation mill working parts

During the coal pulverizing, the working parts of the ventilation mill are being worn by the sand particles. For this reason, the working parts are usually protected with materials resistant to wear (hardfaced/thermal sprayed coatings). The aim of this study was to evaluate the tribological performance of four different types of coatings as candidates for wear protection of the mill’s working parts. The coatings were produced by using the filler materials with the following nominal chemical composition: NiFeBSi-WC, NiCrBSiC, FeCrCTiSi, and FeCrNiCSiBMn, and by using the plasma arc welding and flame and electric arc spraying processes. The results showed that Ni-based coatings exhibited higher wear resistance than Fe-based coatings. The highest wear resistance showed coating produced by using the NiFeBSi-WC filler material and plasma transferred arc welding deposition process. The hardness was not the only characteristic that affected the wear resistance. In this context, the wear rate of NiFeBSi-WC coating was not in correlation with its hardness, in contrast to other coatings. The different wear performance of NiFeBSi-WC coating was attributed to the different type and morphological features of the reinforcing particles (WC)

Reduction in Pathogenic Biofilms by the Photoactive Composite of Bacterial Cellulose and Nanochitosan Dots under Blue and Green Light

In this study, nanochitosan dots (ChiDs) were synthesized using gamma rays and encapsulated in bacterial cellulose (BC) polymer matrix for antibiofilm potential in photodynamic therapy. The composites were analyzed for structural changes using SEM, AFM, FTIR, XRD, EPR, and porosity measurements. Additionally, ChiD release was assessed. The results showed that the chemical composition remained unaltered, but ChiD agglomerates embedded in BC changed shape (1.5–2.5 µm). Bacterial cellulose fibers became deformed and interconnected, with increased surface roughness and porosity and decreased crystallinity. No singlet oxygen formation was observed, and the total amount of released ChiD was up to 16.10%. Antibiofilm activity was higher under green light, with reductions ranging from 48 to 57% under blue light and 78 to 85% under green light. Methicillin-resistant Staphylococcus aureus was the most sensitive strain. The new photoactive composite hydrogels show promising potential for combating biofilm-related infections

The Impact of One Heat Treated Contact Element on the Coefficient of Static Friction

The subject of the paper includes theoretical considerations, the conducting of experimental tests, and the analysis of exposed test results related to determination of the coefficient of static friction of previously heat-treated contact pairs. One contact element is previously, before the procedure of determining the coefficient of static friction, heated at temperatures in the range of ambient temperature to 280°C and then cooled down to ambient temperature. The results of experimental tests of five different materials show that depending on the heat treatment of one contact element, there is a significant decrease in the coefficient of static friction. The authors of the paper consider that the reasons for the decreasing coefficient of static friction are related to oxide formation and changes in the surface layer of the contact element which is previously heat-treated

[A comparative cephalometric study of cases with normal occlusion and malocclusions]

Autori su izvršili kefalometrijsko ispitivanje 60 slučajeva, koji su bili podeljeni u tri grupe: 20 slučajeva pravilne okluzije, 20 slučajeva nepravilnosti klase II odeljenje 1, i 20 slučajeva nepravilnosti klase III. Cilj ispitivanja bio je da se odrede prosečne vrednosti raznih kefalometrijskih promera za slučajeve sa pravilnom okluzijom i da se one uporede sa vrednostima koje su odredili strani autori. Osim toga, analizirajući slučajeve sa nepravilnostima klase II od. 1 i klase III, autori su želeli da provere da li telerendgenografska ispitivanja potvrđuju kliničku dijagnozu. Za ovaj rad odabrani su sledeći uglovi: SNA, SNB, AN Bi, međuvilični, mandibular- ni, nagib gornjih sekutića, nagib donjih sekutića i međusekutićni. Dobijeni rezultati su obrađeni statistički, i određene su srednje vrednosti i standardna devijacija za svaki posmatrani ugao. Upoređivanjem dobijenih srednjih vrednosti za pravilnu okluziju sa srednjim vrednostima koje su dali engleski, nemački i američki autori, nađene su izvesne razlike. Upoređivanjem slučajeva pravilne okluzije sa slučajevima nepravilnosti ll/l i III klase, nađeno je da kefalometrijska analiza potvrđuje kliničku dijagnozu. Autori su iz ovoga zaključili da je potrebno izvršiti šira ispitivanja jugoslovenskog stanovništva sa pravilnom okluzijom radi određivanja prosečnih vrednosti raznih kefalometrijskih promera, kao i da telerendgenografska analiza slučajeva pravilne okluzije, nepravilnosti klase ll/l i nepravilnosti klase III potvrđuje kliničku dijagnozu.The athors made a cephalometric examination ot 60 cases, consisting of three groups: 20 cases of normal occlusion, 20 cases of Class II div. 1 malocclusion and 20 cases of Class II malocclusion. Their intention was to find the mean values of different cephalometric measures in cases with normal occlusion, and to compare these value with those of foreign authors. Analyzing the cases of Class II div. 1 and Class III malocclusions, the authors wanted also to check up whether cephalometric examinations confirm clinical diagnosis. For this purpose following angles were measured: SNA, SNB, ANB, intermaxillary planes angle, gonial angle, the inclination of upper incisors, the inclination of lower incisors and the interincisal angle. All the data were statistically analyzed, and both the mean values and standard deviations for each observed angle were found. The comparison between the mean values in normal occlusion cases in this analysis and those of English, German and American authors was made, and it was found that they do not correspond to each other. The comparison made between cases of normal occlusion and of malocclusions showed that the cephalometric analysis confirms the clinical diagnosis. The authors concluded that it would be necessary to undertake some wide investigation of Yugoslav citizens with normal occlusion in order to establish the mean values of different cephalometric measures

Kinetics and mechanism of sphalerite leaching by sodium nitrate in sulphuric acid solution

Interest for application of hydrometallurgical processes in a processing of complex sulphide ores and concentrates has increased in recent years. Their application provides better metal recoveries and reduced emission of gaseous and toxic ageneses in the environment. The kinetics and mechanism of sphalerite leaching from complex sulphide concentrate with sulphuric acid and sodium nitrate solution at standard conditions was presented in this paper. The influences of temperature and time on the leaching degree of zinc were investigated and kinetic analysis of the process was accomplished. With temperature increasing from 60 to 90°C, the zinc leaching increased from 25.23% to 71.66% after 2 hours, i.e. from 59.40% to 99.83% after 4 hours. The selected kinetic model indicated that the diffusion through the product layer was the rate-controlling step during the sphalerite leaching. The activation energy was determined to be 55 kJ/mol in the temperature range 60-90°C. XRD, light microscopy and SEM/EDX analyses of the complex concentrate and leach residue confirmed formation of elemental sulphur and diffusion-controlled leaching mechanism

Repair of a damaged turbocharger

The turbocharger is among the highest quality assemblies for modern internal combustion engines. Its contribution to engine operation is immeasurable – it increases the power output of the engine while indirectly reducing fuel consumption. Like all devices, turbochargers require quality maintenance as they are susceptible to failure. Faulty turbochargers are either repaired or replaced with new ones. Repair ensures substantial financial savings. The paper presents the consequences of damage to the turbocharger and the process of its repair