1. Dispersoids in Al-Mg-Si alloy AA 6086 modified by Sc and YFranc Zupanič, Sandi Žist, Mihaela Albu, Ilse Letofsky-Papst, Jaka Burja, Maja Vončina, Tonica Bončina, 2023, izvirni znanstveni članek Ključne besede: aluminijeve zlitine, toplotna obdelava, mikrostruktura, disperzoidi, dilatometrija, trdota, aluminium alloy, heat treatment, microstructure, dispersoids, dilatometry, DSC, hardness
Objavljeno v DKUM: 05.04.2024; Ogledov: 183; Prenosov: 38
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2. Primerjava metod konstruiranja faznih diagramov trdno-tekoče binarnih zmesi organskih spojin : diplomsko delo univerzitetnega študijskega programa I. stopnjeJure Konjar, 2023, diplomsko delo Opis: V diplomskem delu smo primerjali eksperimentalne in računske metode konstruiranja binarnih faznih diagramov trdno-tekoče organskih spojin. Za primerjavo metod smo analizirali tri različne binarne sisteme organskih spojin: benzojska kislina + dimetil tereftalat, (-)-mentol + miristinska kislina in kofein + nikotinska kislina. Temperature faznih prehodov smo eksperimentalno določili s termično analizo z metodo diferenčne dinamične kalorimetrije. Na podlagi dobljenih rezultatov smo izrisali binarne fazne diagrame. Eksperimentalno določene podatke smo primerjali z izračuni enačbe stanja ravnotežja trdno-tekoče. Za izračun aktivnostnih koeficientov v enačbi stanja smo uporabili štiri različne aktivnostne modele: idealni, UNIFAC, UNIFAC (Dortmund) in UNIFAC-LLE. Pri izračunih smo uporabljali različne metode določanja aktivnostnih koeficientov s kombinacijo programov Aspen Plus ter ALAMO Modeling Tool.
Ključne besede: binarne mešanice, fazni diagrami, ravnotežje trdno-tekoče, organske spojine, DSC, modeliranje
Objavljeno v DKUM: 11.09.2023; Ogledov: 607; Prenosov: 40
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3. Akumulacija senzibilne toplote s fazno spremenljivimi snovmi : diplomsko delo visokošolskega strokovnega študijskega programa I. stopnjeAndraž Papež, 2019, diplomsko delo Opis: V prvem delu diplomskega dela so predstavljene teoretične osnove akumulacije toplote in opis delovanja fazno spremenljivih snovi (FSS). Prikazana je njihova razdelitev ter našteti osnovni kriteriji, ki jih moramo poznati pri izbiri FSS materiala. Opisani so pogosti problemi, ki so značilni za določeno vrsto FSS, ter kako se lahko le-tem izognemo. V teoretičnem delu so prav tako na kratko opisane metode za določevannje termičnih lastnosti in predstavljene so še vrste latentnih akumulatorjev toplote z izmenjavo toplote na notranjih površinah.
V drugem delu smo preučevali vpliv števila ciklov obratovanja fazno spremenljive snovi na termične lastnosti izbranega FSS materiala, in sicer magnezijevega klorida heksahidrata. FSS smo segrevali do 160 ºC in ohlajali do 50ºC za 30 faznih sprememb. Temperaturo tališča in izgubo mase smo določili z TGA/DSC1 analizo. Ugotovili smo, da se temperatura tališča in temperatura kristalizacije minimalno spreminjata. Potrdili smo dejstvo, da pride do nekongurentnega taljenja in do podhlajevanja, kar predstavlja največji problem. Prav tako smo ugotovili, da izguba mase po vsaki fazni spremembi ne vpliva na temperaturo tališča. Izkazalo se je, da je magnezijev klorid heksahidrat ugoden FSS material za akumulacijo toplote, še posebno, če upoštevamo dejstvo, da je problem podhlajevanja možno zmanjšati. Na koncu smo želeli prikazati še, kako bi izgledal FSS akumulator toplote, ki je tipa s prenosnikom toplote.
Ključne besede: akumulacija toplote, fazno spremenljive snovi, termična stabilnost, TGA/DSC analiza, magnezijev klorid heksahidrat, FSS akumulator toplote
Objavljeno v DKUM: 10.10.2019; Ogledov: 1201; Prenosov: 127
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4. Povečanje varnosti na morju s primerno uporabo telekomunikacijskih tehnologijUrška Čakš, 2018, delo diplomskega projekta/projektno delo Opis: V zaključnem delu so predstavljeni načini komuniciranja posadke s svetom sredi morja, na območjih izven dosega telefonskega signala. Pri plovbi je v primeru nesreč, nevarnosti ali hudih neviht najpomembnejša varnost in zaščita človeških življenj. Namen naloge je predstaviti radijske komunikacije, ki so v uporabi v pomorstvu. V nalogi so predstavljene tudi različne naprave za klice v sili. Zaključno delo podaja priporočila uprabe telekomunikacijske opreme za različne vrste pomorskih plovil za zagotavljanje večje varnosti človeških življenj na morju glede na namen in območja plovbe.
Ključne besede: GMDSS, VHF, MF/HF, DSC, EPIRB, PLB, SART, AIS
Objavljeno v DKUM: 07.02.2019; Ogledov: 1158; Prenosov: 116
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5. Constitutive modeling and computer methods in geotechnical engineeringChandrakant Desai, 2010, izvirni znanstveni članek Opis: Computer methods are in the forefront of the procedures for analysis and design for geotechnical problems. Constitutive models that characterize the behavior of geologic materials and interfaces/joints play a vital role in the solutions obtained by using computer methods or any other solution procedure. The literature on both constitutive and computer models is wide; attention in this paper is devoted to the disturbed state concept (DSC) for constitutive modeling and the finite element method for computer solutions. The disturbed state concept, a unified and hierarchical approach, provides a unified framework for characterization of the behavior of geologic materials and interfaces/joints. Important factors such as elastic, plastic and creep responses, stress paths, volume change (contraction and dilation), disturbance (softening and damage or stiffening), thermal effects, partial saturation and liquefaction can be included in the same DSC framework. Because of its hierarchical nature, simplified models for specific applications can be derived from the DSC. It has been applied successfully for defining behavior of many geologic materials and interfaces/joints.
Procedures for the determination of parameters for the DSC models based on laboratory tests have been developed. Various models from the DSC have been validated at the specimen level with respect to laboratory test data. They have been validated at the practical boundary value problem level by comparing observed behavior in the field and/or simulated problems in the laboratory with predictions using computer (finite element) procedures in which DSC has been implemented; these have been presented in various publications by Desai and coworkers, and are listed in the References. Three typical examples of such validations at the practical problem level are included in this paper. It is believed that the DSC can provide unified and powerful models for a wide range of geomechanical and other engineering materials, and interfaces/joints.
Ključne besede: constitutive modeling, disturbed state concept, DSC, geologic materials, interfaces/joints
Objavljeno v DKUM: 11.06.2018; Ogledov: 924; Prenosov: 106
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6. The curing of diallylterephthalate determination of the kinetic triplet A, Ea,app, ƒ(α) using the isoconversional methodDušan Klinar, Janvit Golob, Matjaž Krajnc, 2003, izvirni znanstveni članek Opis: Allyl polymers are important materials for the production of high performance ophthalmic lenses by free-radical bulk polymerization in the casting process. Isoconversional model-free analysis was applied to the isothermal and nonisothermal curing of diallylterephthalate performed by DSC at different sets of heating rates. The results of the kinetic analysis in a form of kinetic triplet $(Ea, A, ƒ(α))$ present the variation of the Arrhenius parameters with the calculation method, reaction extent, process mode and heating rates applied. This variation is a sign of the complex and multi-step reaction mechanism. Such a mechanism was approximated with one step $(1-α)^n$ reaction model. With the isokinetic relationship - IKR (compensation effect) in the form of $lnA=aEa,app+b$ it was found out that the isothermal and nonisothermal IKR lines converge to different singular points. From the correlation procedure with the experimental data isothermal narrowest point – NPI was selected as a common point. The curing process in the isothermal and nonisothermal process conditions, respectively, was successfully simulated with the obtained kinetic parameters. The possible alternative reaction paths and the partial diffusion control of the curing process are the reasons for the limiting usage of the model-free kinetic analysis method. This method was mainly used as a preliminary step for further analysis with other methods.
Ključne besede: DSC, DAT, curing kinetics, compensation effect
Objavljeno v DKUM: 29.08.2017; Ogledov: 1505; Prenosov: 109
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7. Synthesis, crystal structure and magnetic properties of a new hydroxylammonium fluoroferrateBrina Dojer, Matjaž Kristl, Zvonko Jagličić, Amalija Golobič, Marta Kasunič, Mihael Drofenik, 2012, izvirni znanstveni članek Opis: This paper reports on the synthesis of a new hydroxylammonium fluoroferrate, with the formula $(NH_3OH)_3FeF_6$, obtained after dissolving iron powder in hydrofluoric acid and adding solid $NH_3OHF$. This new compound has been characterized by chemical and thermal analysis, single-crystal X-ray diffraction, and magnetic measurements. The title compound crystallizes trigonal, R3c, with cell parameters a = 11.4154(2) Å, c = 11.5720(2) Å, Z = 6. The structure consists of $NH_3OH^+$ cations and isolated $FeF_6^{3–}$ octahedra in which the central ion lies on a threefold axis. The oxygen and nitrogen atoms of the hydroxylammonium cations are donors of hydrogen bonds to fluoride anions, resulting in a network of hydrogen bonds between counterions. The effective magnetic moment $µ_{eff}$ = 5.8 BM was calculated and perfectly matches the expected value of high-spin Fe(III) ions. The thermal decomposition of the compound was studied by TG, DSC, and X-ray powder diffraction.
Ključne besede: inorganic chemistry, crystallography, coordination compounds, synthesis, crystal structure, characterization of compounds, determination of the structure of compounds, X-ray diffraction, magnetic measurements, thermal analysis, TG, DSC, hydrogen bond, metal complexes, hydroxylammonium fluoromethalatehydroxylammonium, fluoroferrate
Objavljeno v DKUM: 25.08.2017; Ogledov: 2076; Prenosov: 77
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8. Synthesis and characterisation of hydroxylammonium fluorochromateMatjaž Kristl, Mihael Drofenik, Ljubo Golič, Amalija Golobič, 2003, izvirni znanstveni članek Opis: Reactions in the system $Cr – NH_3OHF – HF – H_2O$ were investigated. Green crystals of a new compound with the formula $(NH_3OH)_3CrF_6$ have been isolated from the water solution and characterized by chemical analysis. The compound crystallizes as triclinic, P-1, with cell parameters: a = 6.5461(2) Å, b = 6.9347(2) Å, c = 9.4072(3) Å, α = 86.772(1)°, β = 83.804(1)°, γ = 70.283(1)°. The effective magnetic moment, $µ_{eff}$ = 3.82 BM, was calculated from magnetic susceptibility measurements in the temperature range 80-290 K. The thermal decomposition of the compound was studied by TG and DSC analysis. $(NH_3OH)_3CrF_6$ decomposes above 125 °C in three steps and the residue has been identified by X-ray powder diffraction as $α – Cr_2O_3$.
Ključne besede: inorganic chemistry, structural chemistry, crystalline structure, coordination compounds, synthesis, inorganic reactions, thermal decomposition, characterization of compounds, TG, DSC, X-ray diffraction, chromium complexes, hydroxylammonium fluoro chromates, crystals
Objavljeno v DKUM: 25.08.2017; Ogledov: 1893; Prenosov: 119
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9. VPLIV NUKLEATORJEV NA LASTNOSTI POLIPROPILENAŽiga Kvar, 2016, magistrsko delo Opis: V magistrski nalogi smo proučevali vpliv α, β in kombinacije α/β nukleatorjev na reološke, termične in mehanske lastnosti polipropilen homopolimera (PPH) in polipropilen kopolimera (PPC). Reološke lastnosti smo opazovali z meritvami indeksa tečenja (MFI - melt flow index), termične lastnosti smo proučevali z diferenčno dinamično kalorimetrijo (DSC - differential scanning calorimetry), s trgalnim preizkusom smo proučevali mehanske lastnosti.
Nukleatorji so imeli večji vpliv na reološke lastnosti v primeru modifikacije PPC, na PPH je imel vpliv samo dodatek α/β - nukleatorja.
Z dodatkom nukleatorjev k PPH in PPC smo opazili povišanje temperature kristalizacije. Prav tako smo v primeru modifikacije PPC povišali stopnjo kristaliničnosti. Pri PPH smo z dodatkom β - nukleatorja opazili padec kristaliničnosti. Temperaturni pik taljenja se je, zaradi promocije β - kristalitov, v primeru β - nukleatorja znižal, ostali vzorci so imeli pik v področju α - kristalitov. Vzorec PPHα1 je povišal čas oksidativne razgradnje (OIT - oxidative induction time), vsi ostali opazovani vzorci so ga znižali.
Rezultati kažejo na povišanje togosti modificiranega PPH (razen v primeru β - nukleatorja) ter modificiranega PPC in zmanjšanje natezne trdnosti na meji plastičnosti (razen v primeru β - nukleatorja) za oba modificirana PP. Opazili smo povezanost trdote s togostjo; β - nukleator je v PPH znižal togost in povišal trdoto. Pri modifikaciji PPC so vsi nukleatorji povišali trdoto.
Ključne besede: polipropilen, nukleator, kristalizacija, DSC, OIT
Objavljeno v DKUM: 14.10.2016; Ogledov: 2168; Prenosov: 237
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10. Analiza razgradnih produktov po kemijskem recikliranju poliamida 66Kaja Vrezner, 2016, diplomsko delo Opis: Veliko izdelkov iz plastične mase danes konča na odlagališčih. Kemijsko recikliranje je postopek, s katerim se želimo temu izogniti. Poliamid 6.6 smo reciklirali s postopkom hidrolize v nevtralnem in bazičnem mediju. Kot rezultat kemijskega recikliranja poliamida 6.6 smo želeli dobiti monomerne enote čim višje čistosti, zato smo v posamezen eksperiment vnašali čim manj kemikalij. Rezultate depolimerizacije smo spremljali z IR, RAMAN in 1H NMR spektroskopijo, kakor tudi z DSC analizo. Beležili smo tudi pH tekočega ostanka in maso trdnega ostanka. Opravljene analize so potrdile, da nam je uspelo vlakno PA 6.6 razgraditi na manjše oligomerne in tudi monomerne enote.
Ključne besede: Poliamid 6.6, recikliranje, hidroliza, IR spektroskopija, Raman spektroskopija, DSC termična analiza.
Objavljeno v DKUM: 05.10.2016; Ogledov: 1915; Prenosov: 1 |
