The aim of our study was to investigate how different thermal conditions affect the transformation temperatures of two hot-work steels with high thermal conductivity. We focused on two conditions: ...soft annealing, and quenching and tempering. Soft annealing results in a ferritic steel matrix with spherical carbides, while quenching and tempering result in a fully hardened and tempered martensitic matrix with secondary and tempering carbides. We analysed samples using a simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to determine the transformation temperatures. Controlled heating and cooling allowed us to observe the energy changes associated with the phase transformations. The equilibrium temperatures were calculated using the CALPHAD method. Our study investigated the influence of thermal conditions on different transformation temperatures, including solidus/liquidus temperatures, austenite solid transformation temperatures (A1 and A3), austenite solidification temperatures and bainite and/or martensite transformation temperatures. A DSC analysis was used to quantitatively measure the transformation temperatures and energy absorption during the endothermic processes (austenite solid transformation and melting) and to study the energy release during the exothermic processes (solidification and transformation). The results showed that soft annealing reduced the solidification interval and the solidus temperature, while energy absorption increased during melting. Conversely, quenching and tempering reduced the austenite solid transformation temperatures and energy release during solidification, including δ-ferrite solidification.
A drop calorimetry method was used to measure the partial and integral mixing enthalpies of Ag-Mg-Pd liquid solutions. The experiments were performed for six separate series of liquid alloys starting ...from the binary alloys with constant xAg/xMg ratios equal to 1/9, 1/3, 1/1, and 3/1 for (Ag0.10Mg0.90)1-xPdx and (Ag0.25Mg0.75)1-xPdx at 1116 K and (Ag0.50Mg0.50)1-xPdx and (Ag0.75Mg0.25)1-xPdx at 1279 K and xMg/xPd ratios of 9/1 and 4/1 for (Mg0.90Pd0.10)1-xAgx and (Mg0.80Pd0.20)1-xAgx at 1116 K. Then, using the thermodynamic properties of the binary systems in the form of the Redlich-Kister equations and the changes in mixing enthalpies provided by this study, the ternary interaction parameters were determined with the Muggianu model and our own software (TerGexHm). Based on the binary and ternary interaction parameters, the partial mixing enthalpies of Ag, Mg, and Pd were calculated for the same cross-sections where the measurements were conducted. These studies were the first step of an investigation of the Ag-Mg-Pd system before the calculation of the phase diagram for this ternary system.
The limiting enthalpy of the solution of liquid indium in liquid tin was measured at 723 K. The calorimetric method was applied to determine the standard enthalpy of the formation of intermetallic ...phases and alloys from the In-Li system. The measurements were done at 747 K and 756 K. The structures of prepared alloys were confirmed by the X-ray diffraction measurements. Besides that, the ab initio calculations allowed the modeling of the formation energies, the volume thermal expansion, the heat capacity under constant pressure, and the elastic properties of the intermetallic phases. The theoretical formation energies show good agreement with the experimental findings. The analysis of the phonon dispersion indicates an instability of the InLi phase in the Fd-3m space group. A further investigation on the atomic arrangement in the case of the equiatomic ratio is suggested.
Reakcijska kalorimetrija Horvat, Gordan
Kemija u industriji,
11/2015, Letnik:
64, Številka:
11-12
Journal Article, Paper
Recenzirano
Odprti dostop
U radu je dan sažet prikaz principa rada reakcijskih kalorimetara. Opisani su adijabatski kalorimetri te kalorimetri kondukcijskog i kompenzacijskog tipa. Uz kalorimetre zatvorenog tipa opisani su i ...kalorimetri perfuzijskog tipa. Iznesena je fizikalna osnovica načina mjerenja topline za svaki od navedenih tipova kalorimetara. Također su navedeni postupci kalibracije kalorimetara.
The aim of the study is to show the differences between the measured and estimated values of resting energy expenditure and any changes occurring after the 6-month weight loss intervention program.
...We included 33 healthy adults aged 25-49 years with an average body mass index 29.1±2.7 kg/m 2 for female and 29.8±2.8 kg/m
for male. The measured resting energy expenditure was obtained by indirect calorimeter MedGem® Microlife and estimated resting energy expenditure by the Harris-Benedict equation, the Mifflin-St Jeor equation, the Owen equation, the Wright equation, and by the Tanita body composition analyser. All measurements and calculations were carried out before and after the 6-month intervention. Results were compared using paired t-tests. P value less than 0.05 was considered statistically significant.
A comparison of the measured resting energy expenditure of female subjects with the estimated resting energy expenditure using the Harris-Benedict equation, the Mifflin-St Jeor equation and the Wright equation showed a statistically significant difference. A comparison of the measured resting energy expenditure of male subjects with the estimated resting energy expenditure using the Harris-Benedict equation and the Wright equation showed a statistically significant difference. There was a significant difference in the measured resting energy expenditure and estimated resting energy expenditure using Tanita.
We concluded that the most comparable equation for our sample was the Owen's equation. After losing weight, the measured resting energy expenditure has decreased, which must be taken into account in further diet therapy.
U ovom radu istražena je kinetika izotermne kristalizacije i kristalna struktura mješavina termoplastičnog poliuretana i polipropilena (TPU/PP) te termoplastičnog poliuretana i polipropilena uz ...dodatak talka (TPU/PP/T) različitog sastava (80/20, 50/50 i 20/80) diferencijalnom pretražnom kalorimetrijom (DSC). Kristalizacija je proučavana u području temperatura od 116 °C do 132 °C. Ustanovljeno je da je kristalizacija brža za mješavine TPU/PP/T. Kinetika izotermne kristalizacije opisana je pomoću Avramijeve jednadžbe. Utjecaj različite izotermne temperature proučavan je usporedbom vrijednosti kinetičkih parametara kao što su Avramijev eksponent, n, kinetička konstanta brzine kristalizacije, k, i polovično vrijeme kristalizacije, t1/2. Dobiveno je da se Avramijev eksponent kreće u rasponu od 1,18 do 2,31. Ti rezultati ukazuju na dvodimenzijski rast kristalnih jedinica.
Kinetika izotermne kristalizacije pokazala je da se dodatkom talka povećava kristalište i raste konstanta brzine kristalizacije, k, mješavina TPU/PP. Za dane temperature kristalizacije, polovično vrijeme kristalizacije, t1/2, mješavina TPU/PP/T niže je od pripadajućih vrijednosti kod mješavina TPU/PP.
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A mixture of phosphoric and sulfuric acid was used to investigate the dissolution kinetics of phosphate ore by Differential Reaction Calorimetry (DRC). The effect of the solid-to-iquid ratio, ...concentration, stirring speed, particle size and temperature of the reaction is examined. It was established that the dissolution rate increased with stirring speed and particle size. However, rising the olid-to-iquid ratio, temperature and concentration decreased the dissolution rate. It was determined that the dissolution rate fits in the first order of the pseudo-homogeneous reaction model. Two negative values of apparent activation energies were found in the range of 25 to 60?C. The experimental data were tested by graphical and statistical methods and it was found that the following models were best fitted for the experimental data and an empirical equation for the process was developed. -ln (1 ? x) = 2,2 E-09((S/L)0.75C -0.461G0.447(SS) 0.471exp (2671/T)t. T? 40?C -ln (1 ? x) = 2,2 E-09((S/L)0.75C -0.461G0.447(SS) 0.471exp (6959/T)t. T > 45?C
nema
Identification and characterization of different forms of methotrexate were carried out by crystallization from different solvents. Five different forms of the drug were obtained. Appearance of a ...desolvation endotherm in the DSC accompanied by mass loss in TGA for forms I, II, IV and V showed these forms to be acetonitrile solvate hydrate (form I), trihydrate (forms II and IV) and dimethylformamide solvate (form V), respectively. However, the desolvation peak was absent in form III (obtained from methanol) indicating the absence of any solvent of crystallization. This form was found to be partially crystalline by its XRPD pattern. Solution calorimetry was further used to differentiate between the forms as they differ in lattice energy, resulting in different enthalpies of solution. The dissolution and solubility profiles were correlated with the enthalpy of solution and subsequently with crystallinity of all the forms; the least endothermic form (form III) had the highest dissolution rate.
U radu je provedena identifikacija i karakterizacija pet različitih formi metotreksata dobivenih kristalizacijom iz različitih otapala. Desolvatacijska izoterma u DSC popraćena gubitkom mase u TGA za forme I, II, IV i V ukazuje da su te forme solvati s acetonitrilom: hidrat (forma I), trihidrat (forma II i IV) i solvat s dimetilformamidom (forma V). Međutim, desolvatacijski pik je odsutan u formi III (dobivenoj iz metanola) što ukazuje na odsutnost otapala u kristalnoj formi. Ta forma je parcijalno kristalna i pokazuje odgovarajući XRPD uzorak. Energija kristalne ćelije je za različite forme različita, što ima za posljedicu različite entalpije otapanja te omogućava primjenu kalorimetrije otopine za diferencijaciju formi. Topljivost je korelirana s entalpijom otopine i kristaliničnosti svih formi. Najmanje endotermna forma (forma III) je najbolje topljiva.
Oksidacija masti je jedna od osnovnih reakcija koja utječe na pad
kvalitete maslaca i masla kako s gledišta proizvođača tako i s gledišta potrošača navedenih proizvoda, kao i proizvoda s njihovim ...sadržajem. Obzirom da je većina produkata reakcije oksidacije masti štetna po zdravlje potrošača, nedovoljno praćenje kvalitete jestivih masti i proizvoda koji ih sadrže dovelo bi do rizika po zdravlje potrošača, a i do financijskih gubitaka proizvođača. Pri procjeni oksidacione stabilnosti masti do danas su korištene standardne kemijske metode, odnosno određivanje karakterističnih brojeva (jodni, kiselinski, peroksidni, anisidni itd.) čiji proces zahtijeva upotrebukemikalija i dugo traje. Međutim analiza pomoću diferencijalne skenirajuće kalorimetrije (DSC) pokazuje da se jednostavnim načinom u vrlo kratkom vremenu, može utvrditi oksidaciona stabilnost maslaca i masla. Provedena su laboratorijska istraživanja mogućnosti primjene diferencijalne skenirajuće kalorimetrije (DSC) pri praćenju oksidacione stabilnosti maslaca i masla, kako u svježem stanju tako i već upotrijebljenom za prženje. Dobiveni rezultati komparirani su s promjenom jodnog broja određenog standardnom metodom. Postignuti rezultati potvrđuju opravdanost i mogućnost primjene diferencijalne skenirajuće kalorimetrije pri praćenju oksidacione stabilnosti maslaca i masla.
Provider: - Institution: - Data provided by Europeana Collections- Although thermally induced transformations of framework aluminosilicates provide unique method for synthesis of materials with ...advanced properties, conversion mechanism is not explained yet because of the complexity of the process. Because of the small unit cell (Na12Si12Al12O4827H2O) and well known framework structure and extra-framework cation distribution, zeolite Na-LTA represents ideal model for investigation of changes in the short, middle and long range order, in the processes of zeolite thermal transformation into stuffed derivatives of SiO2 polymorphs. Even though investigations showed that Na-LTA zeolite is not pure from crystallographic point of view and, depending on synthesis procedure, contains different amounts of Na, Al and Si inclusions inside α and β cages, there are no data regarding catalytic influence of these species on the mechanism of thermal conversions. Presented thesis surmises results of investigations of the influence of Na, Al and Si inclusion species on the mechanism of Na-LTA thermally induced transformations into carnegieite and nepheline polymorphs. The first chapter of thesis deals with Na-LTA synthesis procedure with different amounts of Na, Al and Si inclusions. The influence of small variations of Na2O:Al2O3:SiO2 ratio in initial reaction mixture on stoichiometry of synthesized Na-LTA zeolites and crystal grain morphology is described. Refluxing treatment at 100 ºC is suggested as method for removing extra-framework species remained after synthesis process, which does not induce amorphization or other structural changes of zeolite. The second chapter of the thesis is focused on the investigation of the influence of Na, Al and Si inclusions on zeolite Na-LTA thermal stability and conversion into carnegieite and nepheline polymorphs. Special attention is dedicated to the investigation of the mechanism of zeolite Na-LTA transformation into low-temperature carnegieite, which is presented with different conversion routes in the literature. In one aspect Na-LTA zeolite transforms directly into low-temperature carnegieite: Na-LTA → low-temperature carnegieite, while in the other, unfolds through amorphous phase: Na- LTA →Amorphous phase → low-temperature carnegieite. XRPD, DTA and IR investigations showed that Na, Al and Si inclusions catalyze zeolite Na-LTA transformation into low-temperature carnegieite, without the possibility of detection of amorphous phase, inducing rapid breaking and formations of bonds, whereby the rate of transformation increases with increasing Al content. On the other hand, in the case of reflux treated Na-LTA zeolite with ideal stoichiometry, thermal transformation into low-temperature carnegieite is preceded by collapse of LTA framework and formation of stable amorphous phase, which subsequently crystallized into low-temperature carnegieite. Characterization of amorphous NaAlSiO4 phase by IR and Raman spectroscopy showed the presence of four- and six-membered tetrahedral rings, which lead to conclusion that by the collapse of zeolite into amorphous phase, relicts of LTA frameworka are retained. This can can be used as a starting point in synthesis of perfect glasses. On higher temperatures, formation conditions of nepheline structures by reconstructive phase transformations of low-temperature carnegieite were investigated. Because of the various nepheline polymorphs with diverse symmetry, formation conditions of different nepheline structures are current problem in mineralogy. Investigation showed that Na, Al and Si inclusion species in Na-LTA zeolite, induce transformation of low-temperature carnegieite into mixture of monoclinic trinepheline and basic hexagonal nepheline, while in the process of thermally induced transformation of reflux treated samples with ideal stoichiometry, pure basic hexagonal nepheline was formed. Also, conditions of thermal conversion of monoclinic trinepheline into basic hexagonal nepheline were investigated. Intermediate phase of nepheline (“ABABAB…”) structure type, which could not be identified according to known nepheline phases, was synthesized in the presence of Na and Si inclusion species. Differences in the short and middle range order between hightemperature NaAlSiO4 polymorphs, formed by thermal conversion of Na-LTA with different stoichiometry, were ascribed to the influence of Na, Al and Si inclusions in zeolite cages.By this investigation we propose that Na-LTA is the example of much wider problem of non-stoichiometry influencing the course of zeolite thermal transformation route and can be extended to other zeolite types containing various extra-framework cations.- Iako termalno indukovane transformacije mrežnih alumosilikata daju jedinstven metod za formiranje novih faza sa poboljšanim osobinama, zbog kompleksnosti samog procesa, mehanizam konverzije još uvek nije u potpunosti razjašnjen. Usled male jedinične ćelije (Na12Si12Al12O4827H2O) i dobro proučene mrežne strukture i raspodele van-mrežnih katjona, zeolit Na-LTA predstavlja model supstancu za ispitivanje promena u uređenju na kratkom, srednjem i dugom dometu u procesu termalnih transformacija zeolita u popunjene derivate SiO2 polimorfa. Iako su još prva istraživanja pokazala da svaki sintetisan Na-LTA zeolit nije čist u kristalografskom smislu i u zavisnosti od uslova sinteze sadrži različite količine Na, Al i Si inkluzija unutar i kaveza, u literaturi ne postoje podaci o katalitičkom uticaju ovih vrsta na mehanizam termalne konverzije Na-LTA zeolita. Prezentovana teza sumira rezultate istraživanja uticaja Na, Al i Si inkluzija na mehanizam termalno indukovanih transformacija Na-LTA zeolita u karnegitske i nefelinske polimorfe. U prvom delu teze opisan je potupak sinteze Na-LTA zeolita sa različitim sadržajem Na, Al i Si inkluzija. Ispitan je uticaj variranja Na2O : Al2O3 : SiO2 odnosa u polaznoj reakcionoj smeši na stehiometriju sintetisanih Na-LTA zeolita i morfologiju kristalnih zrna. Kao postupak uklanjanja inkluzija zaostalih u Na-LTA zeolitima nakon sinteze, predložen je tretman refluksovanja Na-LTA zeolita na 100 ºC, koji ne izaziva amorfizaciju i dodatne strukturne promene u Na-LTA zeolitima. Drugi deo teze fokusiran je na ispitivanje uticaja Na, Al i Si inkluzija na termalnu stabilnost Na-LTA zeolita i njegovu konverziju u karnegitske i nefelinske polimorfe. Posebna pažnja je posvećena ispitivanju mehanizma fazne transformacije Na-LTA zeolita u nisko-temperaturni karnegit koji je u literaturi prezentovan dvema različitim šemama: kao direktna topotaktička transformacija Na-LTA → nisko-temperaturni karnegit i kao dvostepeni mehanizam Na-LTA → Amorfna faza → nisko-temperaturni karnegit. Metodama XRPD, DTA i IR spektroskopije je utvrđeno da Na i Al inkluzije podstiču fazni prelaz Na-LTA zeolita u nisko-temperaturni karnegit uz nemogućnost detekcije kolapsa LTA mreže u amorfnu strukturu, izazivajući brzo raskidanje i formiranje novih veza, pri čemu brzina termalne transformacije raste sa povećanjem sadržaja Al. Sa druge strane, u slučaju faznog prelaza refluksom tretiranih Na-LTA zeolita idealne stehiometrije u niskotemperaturni karnegit, utvrđen je kolaps LTA mreže u stabilnu amorfnu strukturu iz koje je zatim kristalisala faza nisko-temperaturnog karnegita. Karakterizacijom amorfne NaAlSiO4 faze infracrvenom i ramanskom spektroskopijom, utvrđeno je prisustvo četvoročlanih i šestočlanih tetraedarskih prstenova čime je zaključeno da su kolapsom zeolita u amorfnu fazu zadržani fragmenti LTA mreže, što može biti polazna osnova u sintezi „perfektnih“ stakala. Na višim temperaturama, ispitani su uslovi formiranja nefelinskih struktura, rekonstruktivnom faznom transformacijom nisko-temperaturnog karnegita, što je usled velikog broja nefelinskih polimorfa različite simetrije, veoma aktuelna problematika. Rezultati ispitivanja su pokazali da Na, Al i Si inkluzije u Na-LTA zeolitu uslovljavaju transformaciju nisko-temperaturnog karnegita u smešu monokliničnog trinefelina i osnovnog heksagonalnog nefelina, dok se u procesu termalno indukovanih transformacija refluksom tretiranih zeolita idealne LTA stehiometrije, formira faza čistog osnovnog heksagonalnog nefelina. Takođe, ispitani su uslovi termalne konverzije monokliničnog trinefelina u osnovni heksagonalni nefelin. U prisustvu Na i Si inkluzija sintetisana je intermedijerna faza nefelinskog („ABABAB...“) strukturnog tipa koja nije mogla biti identifikovana na osnovu poznatih nefelinskih struktura. Razlike u uređenju na kratkom i srednjem dometu visokotemperaturnih NaAlSiO4 polimorfa dobijenih termalnom konverzijom Na-LTA zeolita različite stehiometrije, pripisane su uticaju Na, Al i Si inkluzija u kavezima zeolita. Ovim istraživanjem predloženo je da Na-LTA zeolit predstavlja primer mnogo šireg problema uticaja nestehiometrije na tok i mehanizam termalno indukovanih transformacija zeolita, kao i da se isti zaključci mogu primeniti i na druge tipove zeolita koji sadrže različite van-mrežne katjone.- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
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