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1

Multifunctional clustering based on the LEACH algorithm for edge-cloud continuum ecosystem

Paszkiewicz Andrzej, Ćwikła Cezary, Bolanowski Marek, Ganzha Maria, Paprzycki Marcin, Hodoň Michal

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2024

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Vol. 72, nr 1

art. no. e147919

EN

This paper introduces a novel approach to building network cluster structures, based on the modified LEACH algorithm. The proposed solution takes into account the multitasking of the network infrastructure, resulting from various functions performed by individual nodes. Therefore, instead of a single head, dedicated to a given cluster, a set of heads is selected, the number of which corresponds to the number of performed functions. Outcomes of simulations, comparing the classical and the multifunctional approach, are presented. The obtained results confirm that both algorithms deliver similar levels of energy consumption, as well as efficiency in terms of the number of individual nodes discharged.

2

Mathematical models of hydromechanics of multiphase flow with varying mass

Mamedov Gasim A., Abbasov Natiq M.

Nafta-Gaz

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2023

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R. 79, nr 11

709--715

EN

The paper discusses the mathematical model of hydromechanics of multiphase flows with varying mass. A multiphase flow is considered a continuum consisting of a set of a large number of different groups of particles. The derivation of motion equations and similarity criteria are given taking into account both the externally attached (or detached) mass and phase transitions within the medium. The equations of mass, momentum and energy transfer for individual phases and the medium as a whole are derived based on fundamental conservation laws. It was demonstrated that in the absence of sources (or flow-offs) of mass, momentum and energy, the known equations of single- and multi-phase flow hydromechanics follow as a special case from the obtained systems of motion equations and similarity criteria. The obtained motion equations are valid for the description of an ingredient of mixture and the medium as a whole, regardless of their physical and mechanical properties. Thermodynamic and rheological state equations, as well as expressions for heat flow, interfacial mass forces phase transitions, and heat exchange between phases can be used to close them. The implemented models make it possible to simulate both the stationary distribution of parameters along the wellbore during production and non-stationary processes that occur, for example, when the pump shaft speed changes during oil production. The developed approaches were implemented in the DataFlow software tool for analysis of the hydrodynamics of multiphase hydrocarbon flows, taking into account heat exchange with the rocks surrounding the well, and phase transitions in the fluid. Using the software package, test calculations were carried out to demonstrate the performance of the proposed and implemented models.

PL

W artykule omówiono model matematyczny hydromechaniki przepływów wielofazowych o zmiennej masie. Przepływ wielofazowy jest traktowany jako kontinuum składające się ze zbioru dużej liczby różnych grup cząstek. Wprowadzone równania ruchu i kryteria podobieństwa są podane z uwzględnieniem zarówno zewnętrznej dołączonej (lub odłączonej) masy, jak i przejść fazowych wewnątrz ośrodka. Równania transferu masy, pędu i energii dla poszczególnych faz i ośrodka jako całości otrzymano przy użyciu podstawowych praw zachowania. Wykazano, że w przypadku braku źródeł (lub wypływów) masy, pędu i energii, znane równania hydromechaniki przepływu jedno- i wielofazowego wynikają jako szczególny przypadek z otrzymanych układów równań ruchu i kryteriów podobieństwa. Uzyskane równania ruchu mają zastosowanie do opisu składnika mieszaniny i medium jako całości, niezależnie od ich właściwości fizycznych i mechanicznych. Do ich rozwiązania można wykorzystać termodynamiczne i reologiczne równania stanu, a także wyrażenia dotyczące przepływu ciepła, siły międzyfazowych masy, przejść fazowych i wymiany ciepła między fazami. Wdrożone modele umożliwiają symulację zarówno stacjonarnego rozkładu parametrów wzdłuż odwiertu podczas wydobycia, jak i procesów niestacjonarnych, które zachodzą na przykład podczas zmiany prędkości wału pompy w trakcie wydobycia ropy. Opracowane podejścia zostały zaimplementowane w oprogramowaniu DataFlow do analizy hydrodynamiki wielofazowych przepływów węglowodorów, z uwzględnieniem wymiany ciepła ze skałami otaczającymi odwiert oraz przejść fazowych w płynie. Za pomocą pakietu oprogramowania przeprowadzono obliczenia testowe w celu wykazania wydajności proponowanych i wdrożonych modeli.

3

Selected magnesium compounds as possible inhibitors of ammonium nitrate decomposition

Hoffmann Józef, Kaniewski Maciej, Nieweś Dominik, Hoffmann Krystyna

Polish Journal of Chemical Technology

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2020

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Vol. 22, nr 2

1--8

EN

Ammonium nitrate (AN) is considered to be a very hazardous and difficult to handle component of mineral fertilizers. Differential thermal analysis coupled with thermogravimetry and mass spectrometry was used to determine the possible inhibiting effect of selected magnesium compounds on thermal decomposition of AN. Each additive was mixed with AN to create samples with AN:magnesium compound mass ratios of 4:1, 9:1 and 49:1. Most of analyzed compounds enhanced thermal stability of ammonium nitrate, increasing the temperature of the beginning of exothermic decomposition and decreasing the amount of generated heat. Magnesium chloride hexahydrate was determined to accelerate the decomposition of AN while magnesium sulphate, sulphate heptahydrate, nitrate hexahydrate together with magnesite and dolomite minerals were defi ned as inhibiting agents.

4

The influence of self-doping of stibnite ore with impurities on the preparation, heat capacity, magnetic and transport properties of tetrahedrite Cu12Sb4S13

Chen Yuqi, Li Liang, Zhang Qianjun, Zhang Congzheng, Hirai Shinji

Materials Science Poland

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2020

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Vol. 38, No. 3

484-492

EN

Stibnite mineral (mainly Sb2S3) has been employed for the synthesis of tetrahedrite Cu12Sb4S13 bulk material by spark plasma sintering. High purity Cu12Sb4S13 can be quickly obtained by two sintering procedures at temperatures from the range of 420 °C to 440 °C for 1 h. Appropriate reduction of Cu content (Cu12+xSb4S13, x ⩽ –0.05) or CuS content (Cu12−ySb4S13−y, y = 0.1 or 0.3) was beneficial to fabricate Cu12Sb4S13. The secondary resintering improved the purity of Cu12Sb4S13 material. The first-order magnetic phase transformation with magnetic hysteresis effect was confirmed by the behavior of susceptibility, heat capacity and resistivity. The magnetization showed a linear increase with increasing field (up to 7 T) and non-saturation behavior was observed. The impurities in stibnite mineral Sb2S3 had a weak influence on the transformation temperature but affected the low-temperature magnetization value (~0.15, close to natural tetrahedrite). Similar transformation was observed by the analysis of heat capacity. The properties such as electrical resistivity, Seebeck coefficient and thermal conductivity were also measured for Cu11.9Sb4S13 and Cu11.9Sb4S12.9. The maximum figure of merit ZT of Cu11.9Sb4S12.9 was 0.22 at 367 K.

5

Phase Transitions and Electrochemical Corrosion Behaviors of Ti50Ni50-xCux Shape Memory Alloys for Metallic Biomaterials

Lee Kwangmin, Rho Sanghyun

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 4

1303--1306

EN

TiNi alloys have excellent shape memory properties and corrosion resistance as well as high biocompatibility. This study investigated the effects of copper addition on the phase transitions and electrochemical corrosion behaviors of Ti50Ni50-xCux alloys. TiNi, Ti50Ni47Cu3, Ti50Ni44Cu6, and Ti50Ni41Cu9 alloys were prepared using vacuum arc remelting followed by 4 h homogenization at 950°C. Differential scanning calorimetry and X-ray diffraction analyses were conducted. The corrosion behaviors of the alloys were evaluated using potentiodynamic polarization test in Hank’s balanced salt solution at a temperature of 36.5 ± 1°C. The TiNi alloy showed phase transitions from the cubic B2 phase to the monoclinic B19’ phase when the alloy was thermally cycled. The addition of copper to the TiNi alloy played a major role in stabilizing the orthorhombic B19 phases during the phase transitions of Ti50Ni50-xCux alloys. The shifts in the corrosion potential toward the positive zone and the low corrosion current density were affected by the amount of Cu added. The corrosion resistance of the TiNi alloy increased with increasing copper content.

6

Phase transition, microstructural evolution and mechanical properties of Ti–6Al–4V and Ti–6.5Al–3.5Mo–1.5Zr–0.3Si joints brazed with Ti–Zr–Ni–Cu filler metal

Yang Zhenwen, Chen Yuhan, Niu Shiyu, Wang Ying, Han Yajing, Cai Xiaoqiang, Wang Dongpo

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

353--367

EN

Ti–6Al–4V (TC4) and Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) joints were achieved via Ti–37.5Zr–15Ni–10Cu (wt%) filler metal when the brazing temperature was in the range from 950 °C (below β-transus) to 1040 °C (above β-transus) for 10–60 min. The role of brazing parameters in the microstructure evolution as well as mechanical properties of both base alloys and brazed joints was studied. The research analysis suggested that the typical interfacial microstructure was divided into five characteristic zones including reaction phases of α-Ti, β-Ti and (Ti, Zr)2CuNi. With the holding time prolonged, the sectionalized structure transformed into lamellar Widmanstätten structure in the brazing seam at the temperature of 950 °C, and the optimized shear strength reached 616 MPa at 950 °C for 60 min. Nevertheless, when increasing the brazing temperature to 1000 °C, the joint shear strength tended to be stable as the holding time exceeded 20 min due to the elemental homogenization, and the shear strength reached 627 MPa for the holding time of 20 min. Tensile test results showed that the mechanical properties of both TC4 and TC11 alloys were dramatically degraded at the heat treatment temperature of 1000 °C owning to the drastic grain coarsening and phase transition. Additionally, the plastic strain of TC4/TC11 joint brazed at 1000 °C for 20 min was 1.66%, while that of joint brazed at 950 °C for 60 min reached 2.01%. The variation in mechanical properties of base alloys as well as brazed joints under different thermal conditions revealed that the optimized temperature for brazing of titanium alloys was lower than β-transus with a long time.

7

Rheological properties of road bitumens modified by natural asphalt

Gajewski M., Horodecka R.

Roads and Bridges - Drogi i Mosty

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2018

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Vol. 17, no. 2

93--109

EN

The paper presents comprehensive results of the performance and non-standard rheological tests of chosen paving-grade bitumens modified by adding natural asphalt. It has been demonstrated that standard performance tests give the same classification rating to bitumens that have considerably different rheological properties. In such situations it is indispensable to test visco-elastic properties (complex shear modulus test) and visco-elastic-plastic properties (using tests with repeated stress pulse, such as MSCR). Additionally, a test used for indirect determination of so-called distinct phase transitions was carried out as part of this research. Although phase transitions are not distinct in the case of bitumen binders, the temperature corresponding to the maximum value of the imaginary part of the complex stiffness modulus can be treated as an important parameter from the point of view of thermodynamics and rheology. The benefits of modification of binders by addition of natural asphalts are clearly evident in the standard binder/aggregate bond strength test. Conversely, the respective non-standard tests failed to demonstrate the advantages of paving-grade bitumens modified with natural asphalt until MSCR and phase transition tests were carried out to this effect.

PL

W pracy przedstawiono kompleksowe wyniki badań funkcjonalnych oraz niestandardowych badań reologicznych wybranych asfaltów drogowych zmodyfikowanych dodatkiem asfaltu naturalnego. Wykazano, że w przypadku normowych badań funkcjonalnych asfalty o istotnie różnych właściwościach reologicznych są klasyfikowane jednakowo. W takich sytuacjach konieczne są badania cech lepko-sprężystości (badania zespolonych modułów ścinania) oraz badania cech lepko-sprężysto-plastyczności (badania przy powtarzalnym impulsie naprężeniowym, tj. np. badanie MSCR). Dodatkowo przeprowadzono badanie, które pośrednio jest używane do wyznaczania tzw. wyraźnych przejść fazowych. W przypadku lepiszczy asfaltowych przejścia fazowe nie są wyraźne, jednak temperatura odpowiadająca maksymalnej wartości części urojonej zespolonego modułu sztywności może być traktowana jako parametr istotny z punktu widzenia termodynamiki i reologii. Zalety modyfikacji lepiszcza asfaltem naturalnym są wyraźnie widoczne w normowym badaniu przyczepności do kruszyw. Z kolei w przypadku badań niestandardowych dopiero badanie MSCR i badanie przejść fazowych pozwoliły na wykazanie zalet asfaltów drogowych modyfikowanych asfaltem naturalnym.

8

Physico-chemical properties of fine-grained powder in Al2O3-ZrO2-Y2O3-CeO2 system produced by combined method

Smyrnova-Zamkova M. Y., Ruban O. K., Bykov O. I., Dudnik O. V.

Composites Theory and Practice

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2018

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R. 18, nr 4

234--240

EN

At present due to the emergence of new methods of synthesising starting powders and their consolidation, Al2O3-based high-strength ceramic materials toughened by ZrO2 (ZTA) are widely used as structural materials for various purposes. It is known that the material properties depend on the properties of the starting powders. Combined methods of powder preparation essentially extend the possibility to vary the powder properties. The purpose of this work is to produce a fine-grained powder of the composition (mol%) 58.5 α-Al2O3 - 41.5 ZrO2 (Y2O3, CeO2) by a combined method (hydro-thermal synthesis in an alkaline medium/mechanical mixing). The resultant fine-grained powder was heat-treated at 400, 550, 700, 850, 1000, 1150, 1300, and 1450°C with holding for 2 hours at each temperature. The properties of the synthesized powders were characterized by differential thermal analysis (DTA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and specific surface measurements (BET). The microstructural and phase analyses were conducted by petrographic study. The powder morphology varies continuously topologically. The agglomerates after mechanical mixing had an irregular shape up to 1450°C. A tetragonal solid solution based on ZrO2 (T-ZrO2) and α-Al2O3 was identified in the powder after mechanical mixing. T-ZrO2, as well as a monoclinic solid solution based on ZrO2 (M-ZrO2) and α-Al2O3 were identified after heating at 1450°C. The research results will be used for the microstructural design of ZTA composites.

PL

Obecnie, dzięki pojawieniu się nowych metod syntezy proszków wyjściowych i ich konsolidacji wysoko wytrzymałe materiały ceramiczne na bazie Al2O3 hartowane przez ZrO2 (ZTA) są szeroko stosowane jako materiały konstrukcyjne do różnych celów. Wiadomo, że właściwości materiału zależą od właściwości wyjściowych proszków. Połączone metody przygotowania proszku w istotny sposób rozszerzają możliwość zmiany właściwości proszku. Celem tej pracy jest wytworzenie drobnoziarnistego proszku o składzie (% mol) 58,5 α-Al2O3 - 41,5 ZrO2 (Y2O3, CeO2) metodą łączoną (synteza hydrotermiczna w środowisku alkalicznym/mieszanie mechaniczne). Uzyskany drobnoziarnisty proszek poddano obróbce cieplnej w temperaturze 400, 550, 700, 850, 1000, 1150, 1300 i 1450°C z utrzymywaniem przez 2 godziny w każdej temperaturze. Właściwości zsyntetyzowanych proszków scharakteryzowano za pomocą różnicowej analizy termicznej (DTA), skaningowej mikroskopii elektronowej (SEM), dyfrakcji rentgenowskiej (XRD) i specyficznych pomiarów powierzchni (BET). Za pomocą badań petrograficznych przeprowadzono analizy mikrostrukturalne i fazowe. Morfologia proszku zmienia się w sposób ciągły topologicznie. Aglomeraty po mechanicznym mieszaniu miały nieregularny kształt do temperatury 1450°C. Tetragonalny stały roztwór oparty na ZrO2 (T-ZrO2) i α-Al2O3 został zidentyfikowany w proszku po mechanicznym mieszaniu. T-ZrO2, jak również jednoskośny stały roztwór na bazie ZrO2 (M-ZrO2) i α-Al2O3 otrzymano po ogrzewaniu w temperaturze1450°C. Wyniki badań zostaną wykorzystane do mikrostrukturalnego projektowania kompozytów ZTA.

9

Analysis of the Thermal Behaviour of CL-20, Potassium Perchlorate, Lithium Perchlorate and Their Admixtures by DSC and TG

Zhang J.-J., Guo X.-J., Jiao Q.-J., Zhang H.-L., Li H.

Central European Journal of Energetic Materials

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2018

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Vol. 15, no. 1

115--130

EN

The thermal decomposition characteristics of CL-20, potassium perchlorate (KP), lithium perchlorate (LP), a CL-20/KP mixture, and a CL-20/LP mixture were studied using thermogravimetry-differential scanning calorimetry (TG-DSC). The DSC curves for KP exhibited three endothermic peaks and one exothermic peak. The first two endothermic peaks correspond to the rhombic-cubic transition and the fusion of KP, respectively, the third indicates the fusion of KCl, while the exothermic peak is attributed to the decomposition of KP. The DSC curves obtained from LP showed four endothermic peaks and one exothermic peak. The first two endothermic peaks indicate the loss of adsorbed water and water of crystallization, while the third and fourth are associated with the fusion of LP and LiCl, respectively; the exothermic peak is due to the decomposition of LP. The presence of KP had little effect on the thermal decomposition of CL-20 while the addition of LP increased the temperature at which CL-20 exhibits an exothermic peak. In addition, the thermal decomposition of LP appeared to be catalyzed by the presence of CL-20.

10

Phase Transition and Plasticity Enhancement of Ti-Cu-Based Bulk Metallic Glasses

Wang L., Wang X., Zhang G., Sun X.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 1

387--391

EN

In this paper, we report the complex crystallization kinetics of phase transition happening in Ti-Cu-based bulk metallic glasses (BMGs), which play significant roles in the glass formation with respect to their low reduced glass transition temperatures, Trg. The first exothermic event just occurs when annealing the BMG samples in the supercooled liquid region, leading to the Avrami exponent deviating from conventional modes affected by the residual amorphous phase. For Ti43Cu43Ni7Zr7 BMG, the plasticity can be improved by pre-annealing at a sub-Tg temperature of 623K (≈50K below Tg) for 0.5 hour, however, deteriorated by 1 hour annealing, which could be related to the change in stability of this BMG against crystallization with different pre-annealing times.

11

Synthesis and characterization of γ-glycine – a nonlinear optical single crystal for optoelectronic and photonic applications

Latha A. A., Anbuchezhiyan M., Kanakam C. C., Selvarani K.

Materials Science Poland

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2017

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Vol. 35, No. 1

140--150

EN

A single crystal of gamma-glycine (GG), a polymorph of glycine, was synthesized by crystallization. The single crystal of GG was grown from an aqueous solution. The morphology of GG was studied in order to assess its growth facets. The good quality single crystals were subjected to X-ray diffraction studies to reveal their structure. The FT-IR spectral analysis was carried out to confirm the presence of expected functional groups. The UV-Vis analysis was done for GG single crystals to determine the optical transparency and band gap. Simultaneous TG-DTA analysis was employed to understand the thermal and physicochemical stability of the title compound. The mechanical stability and laser stability of GG single crystal were studied using Vickers microhardness test and laser induced damage threshold on different planes of the crystal to reveal its anisotropic nature. The dielectric measurement was carried out as a function of frequency and the results were discussed. The existence of second harmonic generation (SHG) of the title compound was confirmed by Kurtz-Perry powder technique. The SHG effective nonlinearity and particle size dependence of GG powder sample were compared with a standard reference material: potassium dihydrogen phosphate (KDP).

12

Percolation Transitions and Fluid State Boundaries

Woodcock L. W.

Computational Methods in Science and Technology

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2017

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Vol. 23, No. 3

281--294

EN

Percolation transitions define gas- and liquid-state limits of existence. For simple model fluids percolation phenomena vary fundamentally with dimensionality (d). In 3d the accessible volume (VA) and excluded volume (VE = V --VA) percolation transitions occur at different densities, whereas in 2d they coincide. The region of overlap for 3d fluids can be identified as the origin of a supercritical mesophase. This difference between 2d and 3d systems vitiates the hypothetical concept of “universality” in the description of critical phenomena. Thermodynamic states at which VA and VE, for a spherical molecule diameter , percolates the whole volume of an ideal gas, together with MD computations of percolation loci for the penetrable cohesive sphere (PCS) model of gas-liquid equilibria, show a connection between the intersection of percolation loci, and the 1st-order phase-separation transition. The results accord with previous findings for square-well and Lennard-Jones model critical and supercritical fluid equilibria. Percolation loci for real liquids, e.g. CO2 and argon, can be determined from literature thermodynamic equation-of-state data, and exhibit similar supercritical gas- and liquid-state bounds. For these real fluids the mesophase bounds extend to low density and pressures and appear to converge onto the Boyle temperature (TB) in the low-density limit.

13

Ocena możliwości zastosowania różnych metod badawczych do określenia stabilności termodynamicznej wybranych materiałów PCM z grupy hydratów o niskiej temperaturze przemiany fazowej

Komerska A., Ksionek D., Rosiński M.

Ciepłownictwo, Ogrzewnictwo, Wentylacja

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2017

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T. 48, nr 5

187--191

PL

Wykorzystanie materiału fazowo zmiennego w budownictwie wymaga zbadania wielu jego właściwości fizykochemicznych. Aby zapewnić powtarzalność pracy i wysoką efektywność energetyczną systemu akumulatora ciepła, materiał PCM musi charakteryzować się przede wszystkim stabilnością termodynamiczną. W artykule przedstawiono wyniki badań stabilności termodynamicznej trzech komercyjnych materiałów PCM należących do grupy hydratów. Badania doświadczalne przeprowadzono dwiema powszechnie stosowanymi metodami badawczymi: metodą różnicowej kalorymetrii skaningowej DSC oraz metodą analizy termicznej prostej. Pozwoliło to na porównanie wyników badań uzyskanych przy zastosowaniu obu procedur laboratoryjnych oraz ich ocenę w badaniach stabilności termodynamicznej hydratów.

EN

The potential use of the phase change material in the building construction sector requires a deep investigation of the thermophysical properties of the PCM. In order to achieve repeatable and constant operational parameters as well as high energy efficiency of the heat storage, the PCM must maintain its thermal properties over many working cycles. This paper presents results of an experimental investigation of the thermodynamic stability of three commercial phase change materials, classified as salt hydrates. The measurements were conducted with the use of two commonly used methods: differential scanning calorimetry (DSC) and simple thermal analysis. This approach enabled to compare results obtained from both laboratory procedures as well as the method evaluation in determination of the salt hydrates thermal stability.

14

Zmiany strukturalne w stali konstrukcyjnej wywołane epizodami jej nagrzewania i stygnięcia podczas pożaru

Maślak M., Żwirski G.

Bezpieczeństwo i Technika Pożarnicza

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2017

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Vol. 48, iss. 4

34--52

PL

Cel: Celem artykułu jest krótkie omówienie podstawowych zagrożeń wynikających z epizodów nagrzewania i stygnięcia stali konstrukcyjnej podczas pożaru, które mogą warunkować ewentualne dalsze użytkowanie elementów nośnych z niej wykonanych. Zagrożenia te wiążą się na ogół z termicznie indukowanymi i trwałymi zmianami obserwowanymi w mikrostrukturze stali wystudzonej po zakończeniu ekspozycji na ogień, z reguły niedostrzeganymi wizualnie podczas klasycznej inwentaryzacji przeprowadzanej po pożarze, której celem jest ocena stanu technicznego obiektu. Metody: Struktura artykułu pozwala prześledzić kolejne, potencjalne formy zmian mikrostruktury stali konstrukcyjnej, najpierw inicjowane monotonicznym wzrostem temperatury tego materiału, a następnie mniej lub bardziej gwałtownym jego stygnięciem. W pierwszej kolejności omówiono skutki rozrostu ziaren ferrytu, w drugiej kolejności – efekty częściowej przemiany perlitu w austenit, a w końcu – zagrożenia determinowane zainicjowaniem w fazie chłodzenia przemiany bainitycznej i/lub martenzytycznej. Na tym tle podjęto dyskusję na temat konsekwencji ewentualnego powierzchniowego odwęglenia, a także możliwego wystąpienia zjawisk grafityzacji i/lub sferoidyzacji ziaren cementytu. Wyniki: Wykazano, że zmieniające się w czasie, a przy tym niekontrolowane oddziaływanie wysokiej temperatury pożaru na stal konstrukcyjną z dużym prawdopodobieństwem prowadzi do wystąpienia w tym materiale niekorzystnych przemian strukturalnych, które z reguły skutkują drastycznym zmniejszeniem się jego efektywnej ciągliwości skojarzonym z wyraźnym zwiększeniem się jego twardości. Taki zestaw cech stali w przypadku dalszego jej użytkowania po pożarze nieuchronnie implikuje dużą jej podatność na kruche pękanie, a co za tym idzie – znaczne ryzyko nagłego i niespodziewanego zniszczenia wykonanych z niej elementów. Wnioski: Klasyczna inwentaryzacja przeprowadzana po pożarze w celu oceny deformacji stalowego ustroju nośnego, uzupełniona jedynie o eksperymentalną weryfikację parametrów wytrzymałościowych charakteryzujących taką stal, nie wystarcza, by dostatecznie wiarygodnie wnioskować o przydatności tych elementów do ich dalszego użytkowania pod obciążeniem. Taka ocena musi być bowiem bezwzględnie poszerzona co najmniej o aposterioryczne badania mikrostruktury rozpatrywanego materiału oraz o próby pozwalające na sprawdzenie jego popożarowej twardości i udarności.

EN

Aim: The aim of this article is to provide a brief review of the basic hazards which might affect the potential re-use of bearing members made of structural steel following exposure to heating and cooling episodes in a fire. These hazards generally involve thermally induced and permanent changes observed in the microstructure of the steel after the fire is extinguished, usually not seen during a standard post-fire inventory aimed at assessing the technical condition of the building. Methods: The article’s structure guides the reader through the successive potential forms of changes in the microstructure of structural steel, initiated by a monotonic increase in the temperature of the material, and followed by its more or less rapid cooling. The article first discusses the effects of ferrite-grain growth, then proceeds to a description of the effects of a partial pearlite-to-austenite transformation, and finally addresses the threats created by the initiation of a bainitic and/or martensitic transformation during the cooling phase. In this context, it discusses the consequences of potential surface decarburisation and the results of the possible occurrences of graphitisation and/or spheroidisation of cementite grains. Results: It has been shown that the time-varying and uncontrolled impact on structural steel of a high fire temperature is likely to lead to the occurrence of unfavourable structural changes in this material, which usually result in a dramatic decrease in the effective ductility, coupled with a marked increase in hardness. In structural members re-used after a fire, such a set of features inevitably implies the high vulnerability of this type of steel to brittle fracture, and, consequently, carries a significant risk of the sudden and unexpected destruction of the components made of it. Conclusions: The standard post-fire inventory of member deformations in the steel-bearing structure, supplemented only by the experimental verification of such steel-strength parameters, is not sufficient to reasonably conclude that these members are suitable for re-use under load. Such an assessment must be extended at least by a detailed study of the microstructure of the material under consideration, made a posteriori, and also by tests which allow the verification of its post-fire hardness and impact strength.

15

Barium oxide as a modifier to stabilize the γ-Al2O3 structure

Pakdeh S. G., Rasoolzadeh M., Moghadam A. S.

Polish Journal of Chemical Technology

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2016

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Vol. 18, nr 4

1--4

EN

This research concentrated on the structural stability of γ-alumina (γ-Al2O3 ) was investigated by a combination of differential thermal analysis, X-ray diffractometry and surface-area measurements. The γ –to– θ and then α phase transitions were observed as an exothermic peak at 1000°C–1400°C in the DTA curves. The role of barium oxide as a modifier to stabilize γ-Al2O3 structure has been investigated. XRD measurements show that after calcination at 1000°C for 2 h, a significant fraction of the pure γ-Al2O3 (BaO-free) transformed to θ-Al2O3 while that the transition phase in alumina samples modified by BaO have been reduced significantly. Barium oxide, eliminate pentacoordinated aluminum ions through coordinative saturation and alter these ions into octahedral cations and effectively suppressed the γ –to– α phase transition in Al2O3 , which concluded as improving the thermal stability and porous properties of the experimental samples.

16

VO2(B) conversion to VO2(A) and VO2(M) and their oxidation resistance and optical switching properties

Zhang Y.

Materials Science Poland

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2016

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Vol. 34, No. 1

169--176

EN

Vanadium dioxide VO2 has been paid in recent years increasing attention because of its various applications, however, its oxidation resistance properties in air atmosphere have rarely been reported. Herein, VO2 (B) nanobelts were transformed into VO2 (A) and VO2 (M) nanobelts by hydrothermal route and calcination treatment, respectively. Then, we comparatively studied the oxidation resistance properties of VO2 (B), VO2 (A) and VO2 (M) nanobelts in air atmosphere by thermo-gravimetric analysis and differential thermal analysis (TGA/DTA). It was found that the nanobelts had good thermal stability and oxidation resistance below 341 degrees C, 408 degrees C and 465 degrees C in air, respectively, indicating that they were stable in air at room temperature. The fierce oxidation of the nanobelts occurred at 426, 507 and 645 degrees C, respectively. The results showed that the VO2 (M) nanobelts had the best thermal stability and oxidation resistance among the others. Furthermore, the phase transition temperatures and optical switching properties of VO2 (A) and VO2 (M) were studied by differential scanning calorimetry (DSC) and variable-temperature infrared spectra. It was found that the VO2 (A) and VO2 (M) nanobelts had outstanding thermochromic character and optical switching properties.

17

Electronic and structural properties of rare earth pnictides

Bhardwaj R.

Materials Science Poland

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2016

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Vol. 34, No. 1

45--52

EN

In the present paper structural and electronic properties of rare earth pnictides have been presented. The present calculation has been performed using self-consistent tight binding linear muffin tin orbital (TB-LMTO) method within the local density approximation (LDA). The studied compounds undergo a structural phase transition from NaCl-type structure to CsCl-type structure. The electronic band structure and density of states of the pnictides have been reported. The equilibrium lattice parameter a (A), bulk modulus B (GPa), number of f-states at the Fermi level Nf (states/Ry cell) and volume collapse of AmBi and CmBi have also been reported. The calculated equilibrium structural parameters are in good agreement with the available experimental results.

18

Effect of changing P/Ge and Mn/Fe ratios on the magnetocaloric effect and structural transition in the (Mn,Fe)2 (P,Ge) intermetallic compounds

Wlodarczyk P., Hawelek L., Zackiewicz P., Kaminska M., Chrobak A., Kolano-Burian A.

Materials Science Poland

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2016

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Vol. 34, No. 3

494--502

EN

The magnetocaloric effect in the Mn_xFe_2xPGe_y intermetallic compounds with the amount of Mn in the range of x = 1.05 to 1.17 and amount of Ge in the range of y = 0.19 to 0.22 has been studied. It was found that a higher Ge/P ratio causes an increase in Curie temperature, magnetocaloric effect at low field (up to 1 T), activation energy of structural transition and a decrease in thermal hysteresis, as well as transition enthalpy. Contrary to this observation, higher Mn/Fe ratio causes a decrease in Curie temperature, slight decrease of magnetocaloric effect at low magnetic field, and an increase in thermal hysteresis. Simultaneous increase of both ratios may be very advantageous, as the thermal hysteresis can be lowered and magnetocaloric effect can be enhanced without changing the Curie temperature. Some hints about optimization of the composition for applications at low magnetic fields (0.5 T to 2 T) have been presented.

19

Thermally Induced Polymorphic Transformation of Hexanitrohexaazaisowurtzitane (HNIW) Investigated by in-situ X-ray Powder Diffraction

Liu Y., Li S., Wang Z., Xu J., Sun J., Huang H.

Central European Journal of Energetic Materials

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2016

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Vol. 13, no. 4

1023--1037

EN

The ε→γ phase transition of HNIW induced by heat was investigated with in situ X-ray powder diffraction (PXRD). The effects of purity, particle size, insensitive additives and the time of isothermal heat treatment on the phase transition were evaluated. It was found that the phase transition is irreversible with changes in temperature, and the two phases can coexist in a certain temperature range. Moreover, the initial phase transition temperature increases with increasing purity and decreasing particle size of HNIW, and thus with the approximate crystal density. The addition of graphite and paraffin wax to HNIW as insensitive additives leads to a decrease in the initial phase transition temperature, but the addition of TATB does not affect the initial phase transition temperature. Thus, TATB is a suitable insensitive additive. Moreover, at the critical temperature, the isothermal time determined the efficiency of the ε- to γ-phase transition. This work lays the foundations for the choice of molding technologies, performance test methods, ammunition storage options, as well as the manufacture of HNIW-based explosive formulations.

20

The Microstructural Evolution in HMX Based Plastic-bonded Explosive During Heating and Cooling Process: an in situ Small-angle Scattering Study

Yan G., Tian Q., Liu J., Fan Z., Sun G., Zhang C., Wang Y., Chen B., Gong J., Zhou X., Yang Z., Nie F., Li J., Li X.

Central European Journal of Energetic Materials

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2016

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Vol. 13, no. 4

916--926

EN

The thermal damage in octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) based plastic-bonded explosive (PBX) was investigated using in situ small-angle neutron and X-ray scattering techniques. The microstructural evolution was quantitatively characterized by the model fitting parameters of total interfacial surface area (Sv) and void volume distribution. The Sv of HMX-PBX decreased markedly above 100 °C, indicating the movement of binder into the voids. After subsequent cooling to room temperature, the scattering intensity increased significantly with increasing storage time, and a new population of voids with average diameter of 20 nm was observed, accompanied by the gradual phase transition of HMX from δ- to β-phase. The experimental results implied that serious damage within the HMX-PBX was developed during storage after heating.