Razdvajanje faza u sustavu La0.5Sr0.5MnO3 Andreja Žužić; Jelena Macan
Kemija u industriji; časopis kemičara i tehnologa Jugoslavije,
11/2022, Letnik:
71, Številka:
11-12
Journal Article
Recenzirano
Odprti dostop
Perovskiti su tema brojnih znanstvenih istraživanja zbog svojih primjenskih svojstava, kao što su električna vodljivost, feromagnetičnost i reduktivnost. Svojstva perovskita dodatno se mogu ...poboljšati dopiranjem te formiranjem strukturnih defekata. Cilj ovog rada bio je istražiti mogućnost pripreme stroncijem dopiranog lantanova manganita kemijske formule La0,5Sr0,5MnO3 postupkom koprecipitacije. Dio materijala žaren je na 1200 °C/2h, a dio je prešan u tabletu i sinteriran na istim uvjetima. Iako je rendgenska difrakcijska (PXRD) analiza žarenog praha ukazivala na nastanak čiste faze, morfološkom analizom lomne površine tablete uočene su dvije faze. Energijski razlučujuća rendgenska spektrometrija pokazala je da je svjetlija faza SrMnO3, dok je tamnija La0,76Sr0,24MnO3. Tableta je usitnjena te analizirana PXRD-om. Iako su se maksimumi poklapali sa standardnom rendgenskom karticom faze La0,5Sr0,5MnO3, Rietveldovom metodom utočnjavanja potvrđen je udio Sr od 0,24 i nastanak faze La0,76Sr0,24MnO3. Ostatak stroncija dodanog tijekom sinteze kristalizirao je u SrMnO3 fazu. Time je potvrđeno da je supstitucija moguća do određene mjere nakon koje postoji opasnost od izdvajanje nove faze, pogotovo ako je uzorak pripremljen u obliku tablete.
All COVID-19 prevention strategies include regular use of surface disinfectants and hand sanitisers. As these measures took hold in Croatia, the Croatian Poison Control Centre started receiving phone ...calls from the general public and healthcare workers, which prompted us to investigate whether the risk of suspected/symptomatic poisonings with disinfectants and sanitisers really increased. To that end we compared their frequency and characteristics in the first half of 2019 and 2020. Cases of exposures to disinfectants doubled in the first half of 2020 (41 vs 21 cases in 2019), and exposure to sanitisers increased about nine times (46 vs 5 cases in 2019). In 2020, the most common ingredients of disinfectants and sanitisers involved in poisoning incidents were hypochlorite/glutaraldehyde, and ethanol/isopropyl alcohol, respectively. Exposures to disinfectants were recorded mostly in adults (56 %) as accidental (78 %) through ingestion or inhalation (86 %). Fortunately, most callers were asymptomatic (people called for advice because they were concerned), but nearly half reported mild gastrointestinal or respiratory irritation, and in one case severe symptoms were reported (gastrointestinal corrosive injury). Reports of exposure to hand sanitisers highlighted preschool children as the most vulnerable group. Accidental exposure through ingestion dominated, but, again, only mild symptoms (gastrointestinal or eye irritation) developed in one third of the cases. These preliminary findings, however limited, confirm that increased availability and use of disinfectants and sanitisers significantly increased the risk of poisoning, particularly in preschool children through accidental ingestion of hand sanitisers. We therefore believe that epidemiological recommendations for COVID-19 prevention should include warnings informing the general public of the risks of poisoning with surface and hand disinfectants in particular.
Strontium and lanthanum manganites are nowadays the subject of extensive research because of their promising electrical and magnetic properties. Strontium manganite, SrMnO3, was successfully prepared ...by citrate-nitrate autocombustion (CNA) and by the coprecipitation method. These methods were then applied to synthesis of strontium doped lanthanum manganites, La1-xSrxMnO3 (x = 0, 0.1, 0.2 and 0.3). The optimal phase formation conditions were determined by thermogravimetry and differential scanning calorimetry. Crystallization of precursors and calcined powders was studied by X-ray diffraction. Powders, in which pure manganite phase was obtained, were also analyzed by permanganate titration with Mohr’s salt in order to determine oxygen nonstoichiometry. Oxygen stoichiometry was achieved in SrMnO3 powders obtained by the CNA method and calcined at 1000 °C as well as in powders obtained by the coprecipitation method and calcined at 1200 °C. La1-xSrxMnO3 phase was oxygen stoichiometric for x = 0.3 while decreasing of x resulted in cation deficiency, i.e. oxygen excess. Oxygen deficit was achieved for x = 0.09 upon calcination at 1200 °C. The obtained results were confirmed by thermogravimetry and the Rietveld refinement analysis.
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•Sr-manganites and Sr-doped La-manganites were successfully prepared.•Two synthesis methods were used: autocombustion and coprecipitation.•A simple volumetric method for routine analysis of oxygen content was developed.•Obtained powders might be suitable for magneto-resistance applications.
Sr-doped CaMnO3 and BaMnO3 were prepared by autocombustion (CNA) and coprecipitation and investigated as catalysts for catalytic oxidation of benzene, toluene, ethylbenzene and o-xylene mixture in a ...fixed-bed reactor. Ethylbenzene and o-xylene were completely removed by all prepared catalysts. Toluene was completely removed by BaMnO3 and Ba0.5Sr0.5MnO3 catalysts prepared by CNA synthesis, while conversions of ∼98% or higher were obtained for all the other prepared catalysts. The highest benzene conversion of 86.43% at 723 K was obtained for the Ba0.7Sr0.3MnO3 catalyst prepared by CNA synthesis. The differences in catalytic activities can be ascribed to Sr-doping, oxygen nonstoichiometry and morphological differences.
•Alkaline-earth manganites are tested for aromatic compounds removal.•Removal (> 80%) of benzene, toluene, ethylbenzene and o-xylene is achieved.•Coprecipitation and combustion yield catalysts of similar specific surface area.•Catalysts prepared by combustion have higher reducibility and catalytic activity.
Influence of addition of alumina and preparation methods (sol-gel synthesis and mechanochemical preparation) on crystallization and morphology of yttria stabilised zirconia was examined. Presence of ...alumina was found to delay crystallization of zirconia, the effect being more pronounced at higher alumina content. The two oxides form easily distinguished separate phases. Milling lowers the crystallization temperatures of the sol-gel derived powders since nuclei are formed during the milling and smaller particle size allows easier removal of residual organic components. The milling results in crystallization of some monoclinic zirconia, both in sol-gel derived powders and in case of mechanochemical processing. There are no significant differences between the preparation methods in pore size and relative density of sintered tablets: powders obtained by mechanochemical processing and milled sol-gel derived powders both give tablets with homogeneous morphology. The advantage of sol-gel process is preparation of pure tetragonal zirconia phase without traces of monoclinic phase.
Nekoć su se agregiranje i samoudruživanje molekula povezivali prvenstveno s micelnim i koloidnim molekulskim sustavima. Međutim, razvoj supramolekulske kemije omogućio je mnogo dublje razumijevanje ...molekulskog samoudruživanja, a time i stvaranje raznolikih oblika i veličina, uz konstrukciju novih i očaravajućih molekulskih topologija. Cilj ovog dokumenta jest definirati više od 150 naziva vezanih uz agregiranje i samoudruživanje makromolekula. Popis je ograničen na najčešće nazive.
While obesity is recognisably associated with changes in heart rate variability (HRV), the association between skeletal muscle mass and HRV is less clear.
In this cross sectional study, we analysed ...the association of body fat (four parameters) and muscle mass (five parameters) with indicators of HRV activity.
Assessment of body composition and HRV was performed in n = 180 young-to-middle age healthy men exposed to high occupational physical activity, using the multi-frequency bioelectrical impedance device and the PPG-StressFlow® HRV photoplethysmography device, respectively.
Mean values of parameters of fat tissue were above normal/reference values. Muscle tissue indicators were higher or within the reference ranges. Fat tissue parameters were significantly higher in participants with lower parasympathetic nervous system (PNS) indicators. Weight-adjusted skeletal muscle index (wSMI) was significantly lower in men with reduced PNS parameters. Fat tissue parameters were negatively correlated with PNS parameters, while wSMI was positively correlated with PNS parameters.
Participants with higher fat mass and lower muscle mass had poorer parasympathetic activity. Since mean values of HRV parameters indicated mild parasympathetic dominance, we conclude that physical activity and consequently good muscle mass potentially compensated for the negative interaction between fat tissue and HRV.
Celotno besedilo
Dostopno za:
DOBA, FSPLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Objectives
To review recent epidemiological studies investigating carcinogenic or reprotoxic effects among hairdressers who seem to be at greater risk for systemic adverse effects of chemicals ...released from hair care products than consumers.
Methods
A systematic review according to the PRISMA‐P guidelines was performed and included studies published from 2000 to August 2021, in which cancer or adverse reproductive effects were diagnosed in 1995 and onward. Data were synthetized qualitatively due to the small number of studies, heterogeneity of study designs, outcomes, and methods.
Results
Four studies investigating cancer frequencies and six studies investigating effects on reproduction among hairdressers were identified. All were of good quality and with low risk of bias. Only one of the four studies found an increased risk of cancer reporting nine times higher odds for bladder cancer in hairdressers than the population‐based controls. Three other studies investigating bladder and lung cancer, and non‐Hodgins lymphoma did not find an increased risk in hairdressers. Regarding reprotoxic effects, numerous outcomes were investigated including menstrual disorders, congenital malformations, fetal loss, small‐for‐gestational age newborns, preterm delivery, and infertility. Increased risk was found for ventricular septal defect in newborns of fathers working as hairdressers. Furthermore, several indices of poor neonatal or maternal health were significantly associated with mothers working as hairdresser.
Conclusions
Despite the scarce evidence that hairdressers are at increased risk of carcinogenic or reprotoxic effects related to their trade, such health risks cannot be ruled out. Therefore, preventive efforts to diminish occupational exposures to hairdressing chemicals should be targeted.
Hairdressers are at high risk of developing occupational hand eczema. Opinions on the health and safety concerns of nonfood consumer products, such as cosmetics and their ingredients, consider the ...exposure of a “common consumer,” which may not account for occupational exposure of hairdressers. As a result, there is a parlous scenario in which serious safety concerns about occupational exposures are present. The purpose of this review is to compare the frequency of exposure to various types of hair cosmetic products among hairdressers and consumers. Database searches for this review yielded a total of 229 articles; 7 publications were ultimately included. The analysis showed that—dependent on the task—hairdressers were exposed 4 to 78 times more than consumers to a wide spectrum of hair cosmetic products used in their daily working life, ranging from shampoos, conditioners, oxidative and nonoxidative hair colors, to bleaching agents. The highest frequency was found for coloring hair with oxidative hair color. Consumer use frequency does not appear to be appropriate for representing hairdresser exposure. The current standards do not effectively address the occupational risks associated with hairdressers' use of cosmetics. The findings of this study should cause current risk‐assessment procedures to be reconsidered.
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