Influence of mixing on nucleation and crystal growth kinetics of borax in dual impeller batch crystallizer

Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim miješalima na kinetiku kristalizacije dinatrijevog tetraborat dekahidrata (boraksa) tijekom njegove šaržne kristalizacije kontroliranim hlađenjem. Proces je provođen u kristalizatoru volumena 15 dm3, u kojem je omjer visine stupca matične otopine i promjera kristalizatora iznosio 1.3 što je zahtijevalo uvođenje drugog miješala u sustav. Miješanje se provodilo korištenjem triju različitih konfiguracija dvaju miješala: PBT-PBT, SBT-SBT te PBT-SBT. Za svaku primjenjenu konfiguraciju miješala detaljno je ispitan utjecaj brzine vrtnje, promjera miješala, udaljenosti donjeg miješala od dna te međusobne udaljenosti dvaju miješala na mehanizam i brzinu nukleacije, kinetiku rasta kristala boraksa te granulometrijske karakteristike finalnog produkta. U radu je također analiziran i utjecaj brzine hlađenja matične otopine na kinetiku ispitivanog procesa. Da bi se dobio potpuniji uvid u hidrodinamička zbivanja u ispitivanom sustavu, pri svim uvjetima miješanja je određeno vrijeme homogenizacije te je vizualizirana struktura toka kapljevine fotografiranjem tokova kao i simulacijom istih uporabom programskog paketa Visimix 2000 Turbulent. Primjenom Mersmannovog nukleacijskog kriterija je utvrđeno da je pri svim ispitivanim parametrima miješanja nukleacija započela primarnim heterogenim mehanizmom. Za definirani mehanizam su određene brzine nukleacije čime je sagledan utjecaj parametara miješanja i brzine hlađenja na ovu veličinu. Priroda sveukupnog toka suspenzije, definirana strukturom toka kapljevine, intenzitetom konvekcijskog toka te smičnim naprezanjima u zoni oko miješala, također se odražava i na promjenu linearne veličine kristala. Na temelju tih podataka su izračunate brzine te određeni parametri rasta kristala. Korištenjem Mersmannovog modela je pokazano da se pri svim ispitivanim uvjetima provedbe procesa rast odvija integracijskim mehanizmom. Hidrodinamički uvjeti se u konačnici odražavaju i na svojstva finalnog produkta procesa kristalizacije. Granulometrijska analiza prosijavanjem ukazuje na pojavu sekundarne nukleacije i aglomeracije pri određenim uvjetima provedbe procesa. Ukoliko je pak u bilo kojem od ispitivanih sustava bilo osigurano stanje intermedijalne suspenzije, aglomeracija je bila manje izražena. Najpravilniji kristali uz najužu raspodjelu veličina sepak dobivaju primjenom SBT-SBT konfiguracije miješala. Primjena različitih parametara miješanja se odrazila i na utrošak snage miješanja. Najveći utjecaj na ovu veličinu, pri svim ispitivanim konfiguracijama, ima brzina vrtnje miješala, a potom promjer korištenih miješala. S obzirom na navedeno, zaključuje se kako je pri odabiru uvjeta provedbe kristalizacije boraksa kontroliranim hlađenjem u šaržnim kristalizatorima s dvama miješalima neophodno detaljno ispitati utjecaj operacije miješanja na sve stupnjeve kristalizacijskog procesa. Kako parametri miješanja bitno utječu na kinetiku nukleacije i rasta kristala sasvim jasno da oni određuju i karakteristike finalnog produkta kristalizacije. Pravilnim odabirom konfiguracije dvaju miješala i podešavanjem uvjeta miješanja moguće je dobiti produkt željenih karakteristika uz minimalne energetske troškoveThe aim of this research was to investigate the influence of mixing in a dual impeller system on crystallization kinetics of borax in a batch cooling crystallizer. Crystallization was conducted in 15 dm3 crystallizer of tank diameter to liquid height ratio equal to 1.3. This aspect ratio required the use of a second impeller which was mounted on the same shaft. Stirring was conducted by using three different impeller configurations: PBTPBT, SBT-SBT and PBT-SBT. For each of the configurations listed before, an influence of impeller speed, size and position in the vessel on nucleation and crystal growth kinetics, as well as on the granulometric properties of the final product was analyzed in detail. In this work an influence of cooling rate was investigated as well. In order to gain a complete insight into the hydrodynamics of the crystallizer, mixing time was measured and the fluid flow was visualized, using the streak photograpy method and by simulation in Visimix 2000 Turbulent. Using the Mersmann's nucleation criterion, it was determined that the primary heterogeneous nucleation was a dominating mechanism in all experiments conducted in this research. Based on the nucleation mechanism, the rate of nucleation was calculated in order to analyze the influence of mixing parameters and cooling rate on this value. The nature of the overall fluid flow, defined by the flow pattern, the intensity of the overall convection fluid flow and shear stress in the zone around the impeller/s, is reflected on the size of the growing crystal as well. From the change of values of linear crystal size in process time, growth rates and growth parameters were determined. By using the Mersmann’s model, it was determined that the growth rate was governed by the integration mechanism at all process conditions examined. Applied mixing parameters ultimately determined on the properties of the final product of crystallization. Granulometric analysis by sieving showed that both secondary nucleation and agglomeration were present at certain process conditions. But, ifintermedial suspension state was achieved, agglomeration was less pronounces regardless of the impeller configuration. By far, the most regularly shaped crystals were obtained by using the SBT-SBT impeller configuration. Hydrodynamic conditions in the vessel, generated by different mixing parameters reflected the power consumption as well. Impeller speed and size have the biggest influence on this value. Considering the stated, it can be concluded that it is of the essence to investigate the influence of dual impeller mixing on the process of batch cooling crystallization in detail. Since mixing parameters determine the nucleation and crystal growth kinetics it is clear that, at the same time, they determine the properties of the final product of crystallization. Therefore, by choosing the suitable dual impeller configuration and by adjusting the mixing conditions, it is possible to obtain a product of wanted characteristics with minimal energy cos

Učinkovitost recipročnih instrumenata pri reviziji endodontskih ispuna na bazi bioaktivnih i epoksidnih punila

Objective: To compare the effectiveness of reciprocating instruments in removing gutta-percha and bioactive-based (BioRoot RCS and MTA Fillapex) and epoxy resin-based (AH Plus) sealers from root canals based on filling residues and the time required for root canal revision. Material and methods: Root canals of 90 teeth were instrumented with Reciproc R40. All root canals were obturated using the single-cone technique with Reciproc R40 gutta-percha and with one of the selected sealers. Samples with oval, straight canals were used and randomly divided into three groups: (i) filled with AH Plus sealer and gutta-percha (n=30); (ii) filled with MTA Fillapex and gutta-percha (n=30); (iii) filled with BioRoot RCS and gutta-percha (n=30). Each group was divided into two subgroups (n=15) according to the retreatment instrument used (Reciproc M-Wire R25/R40 or Reciproc blue RB25/RB40). Root canals were longitudinally split and analyzed with a stereomicroscope at 15 × magnifications in the coronal, middle, and apical third. Computational analyses were performed with the Image J software. Data were compared using the Kruskal-Wallis test and Mann-Whitney U test. Results: While no statistically significant differences in the residual material surface were found for Reciproc Blue, Reciproc M-Wire showed significantly higher residual material surface for AH Plus and MTA Fillapex compared to BioRoot RCS. For AH plus. Residual material surface was significantly lower for Reciproc Blue than for Reciproc M-Wire. In contrast, BioRoot RCS showed a significantly higher residual material surface for Reciproc Blue. Conclusions: Calcium silicate-containing sealers were more retrievable compared to AH Plus, with fewer sealer remnants and shorter retreatment time. Retreatment with Reciproc M-Wire instruments was superior to Reciproc blue instruments in retreatment of BioRoot RCS. However, none of the sealers were removed completely.Cilj: Željela se usporediti učinkovitost instrumenata Reciproc u uklanjanju gutaperke i endodontskog punila na bazi bioaktivnih (BioRoot RCS i MTA Fillapex) i epoksidnih smola (AH Plus) iz korijenskih kanala na temelju ostataka punjenja i vremena potrebnog za reviziju korijenskog kanala. Materijal i metode: Korijenski kanali 90 zuba instrumentirani su Reciprocom R 40. Svi su zabrtvljeni tehnikom jednoga štapića gutaperke s Reciproc R 40 gutaperkom i jednim od punila. Svi uzorci imali su ovalne, ravne kanale te su nasumično podijeljeni u tri skupine: (i) ispunjeni punilom AH Plus i gutaperkom (n = 30); (ii) ispunjeni MTA Fillapexom i gutaperkom (n = 30); (iii) ispunjeni BioRoot RCS-om i gutaperkom (n = 30). Svaka je skupina podijeljena u dvije podskupine (n = 15) prema instrumentu koji se rabio za reviziju (Reciproc M-Wire R25/R 40 ili Reciproc blue RB 25/RB 40). Korijenski kanali uzdužno su prerezani i analizirani stereomikroskopom pri povećanju od 15 puta u koronalnoj, srednjoj i apikalnoj trećini. Računalne analize obavljene su u programu Image J. Podatci su uspoređeni Kruskal-Wallisovim i Mann-Whitneyjevim U testom.Rezultati: Iako nisu pronađene statistički značajne razlike u površini zaostalog materijala za Reciproc blue i Reciproc M-Wire, nakon revizije instrumentom Reciproc M-Wire uočena je znatno veća površina neuklonjenog ispuna na bazi AH Plusa i MTA Fillapexa u usporedbi s BioRoot RCS-om. Kod ispuna na bazi AH plusa površina zaostalog materijala bila je znatno niža nakon revizije instrumentom Reciproc blue nego nakon Reciproc M-Wireom. Suprotno tomu, BioRoot RCS imao je znatno veću površinu zaostalog materijala nakon revizije instrumentom Reciproc Blue. Zaključci: U usporedbi s brtvilima na bazi AH Plusa, brtvila koja sadržavaju kalcijev silikat bilo je lakše ukloniti i bila je pronađena manja površina neuklonjenog punila poslije revizije, a vrijeme potrebno za taj postupak bilo je kraće. Instrumenti Reciproc M-Wire bili su bolji od Reciproc bluea pri reviziji BioRoot RCS-om. No ni jedno punilo nije potpuno uklonjeno

Ružička days : International conference 16th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: open lecture (1), chemical analysis and synthesis (3), chemical and biochemical engineering (8), food technology and biotechnology (8), medical chemistry and pharmacy (3), environmental protection (11) and meeting of young chemists (2)

Influence of mixing on nucleation and crystal growth kinetics of borax in dual impeller batch crystallizer

Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim miješalima na kinetiku kristalizacije dinatrijevog tetraborat dekahidrata (boraksa) tijekom njegove šaržne kristalizacije kontroliranim hlađenjem. Proces je provođen u kristalizatoru volumena 15 dm3, u kojem je omjer visine stupca matične otopine i promjera kristalizatora iznosio 1.3 što je zahtijevalo uvođenje drugog miješala u sustav. Miješanje se provodilo korištenjem triju različitih konfiguracija dvaju miješala: PBT-PBT, SBT-SBT te PBT-SBT. Za svaku primjenjenu konfiguraciju miješala detaljno je ispitan utjecaj brzine vrtnje, promjera miješala, udaljenosti donjeg miješala od dna te međusobne udaljenosti dvaju miješala na mehanizam i brzinu nukleacije, kinetiku rasta kristala boraksa te granulometrijske karakteristike finalnog produkta. U radu je također analiziran i utjecaj brzine hlađenja matične otopine na kinetiku ispitivanog procesa. Da bi se dobio potpuniji uvid u hidrodinamička zbivanja u ispitivanom sustavu, pri svim uvjetima miješanja je određeno vrijeme homogenizacije te je vizualizirana struktura toka kapljevine fotografiranjem tokova kao i simulacijom istih uporabom programskog paketa Visimix 2000 Turbulent. Primjenom Mersmannovog nukleacijskog kriterija je utvrđeno da je pri svim ispitivanim parametrima miješanja nukleacija započela primarnim heterogenim mehanizmom. Za definirani mehanizam su određene brzine nukleacije čime je sagledan utjecaj parametara miješanja i brzine hlađenja na ovu veličinu. Priroda sveukupnog toka suspenzije, definirana strukturom toka kapljevine, intenzitetom konvekcijskog toka te smičnim naprezanjima u zoni oko miješala, također se odražava i na promjenu linearne veličine kristala. Na temelju tih podataka su izračunate brzine te određeni parametri rasta kristala. Korištenjem Mersmannovog modela je pokazano da se pri svim ispitivanim uvjetima provedbe procesa rast odvija integracijskim mehanizmom. Hidrodinamički uvjeti se u konačnici odražavaju i na svojstva finalnog produkta procesa kristalizacije. Granulometrijska analiza prosijavanjem ukazuje na pojavu sekundarne nukleacije i aglomeracije pri određenim uvjetima provedbe procesa. Ukoliko je pak u bilo kojem od ispitivanih sustava bilo osigurano stanje intermedijalne suspenzije, aglomeracija je bila manje izražena. Najpravilniji kristali uz najužu raspodjelu veličina sepak dobivaju primjenom SBT-SBT konfiguracije miješala. Primjena različitih parametara miješanja se odrazila i na utrošak snage miješanja. Najveći utjecaj na ovu veličinu, pri svim ispitivanim konfiguracijama, ima brzina vrtnje miješala, a potom promjer korištenih miješala. S obzirom na navedeno, zaključuje se kako je pri odabiru uvjeta provedbe kristalizacije boraksa kontroliranim hlađenjem u šaržnim kristalizatorima s dvama miješalima neophodno detaljno ispitati utjecaj operacije miješanja na sve stupnjeve kristalizacijskog procesa. Kako parametri miješanja bitno utječu na kinetiku nukleacije i rasta kristala sasvim jasno da oni određuju i karakteristike finalnog produkta kristalizacije. Pravilnim odabirom konfiguracije dvaju miješala i podešavanjem uvjeta miješanja moguće je dobiti produkt željenih karakteristika uz minimalne energetske troškoveThe aim of this research was to investigate the influence of mixing in a dual impeller system on crystallization kinetics of borax in a batch cooling crystallizer. Crystallization was conducted in 15 dm3 crystallizer of tank diameter to liquid height ratio equal to 1.3. This aspect ratio required the use of a second impeller which was mounted on the same shaft. Stirring was conducted by using three different impeller configurations: PBTPBT, SBT-SBT and PBT-SBT. For each of the configurations listed before, an influence of impeller speed, size and position in the vessel on nucleation and crystal growth kinetics, as well as on the granulometric properties of the final product was analyzed in detail. In this work an influence of cooling rate was investigated as well. In order to gain a complete insight into the hydrodynamics of the crystallizer, mixing time was measured and the fluid flow was visualized, using the streak photograpy method and by simulation in Visimix 2000 Turbulent. Using the Mersmann's nucleation criterion, it was determined that the primary heterogeneous nucleation was a dominating mechanism in all experiments conducted in this research. Based on the nucleation mechanism, the rate of nucleation was calculated in order to analyze the influence of mixing parameters and cooling rate on this value. The nature of the overall fluid flow, defined by the flow pattern, the intensity of the overall convection fluid flow and shear stress in the zone around the impeller/s, is reflected on the size of the growing crystal as well. From the change of values of linear crystal size in process time, growth rates and growth parameters were determined. By using the Mersmann’s model, it was determined that the growth rate was governed by the integration mechanism at all process conditions examined. Applied mixing parameters ultimately determined on the properties of the final product of crystallization. Granulometric analysis by sieving showed that both secondary nucleation and agglomeration were present at certain process conditions. But, ifintermedial suspension state was achieved, agglomeration was less pronounces regardless of the impeller configuration. By far, the most regularly shaped crystals were obtained by using the SBT-SBT impeller configuration. Hydrodynamic conditions in the vessel, generated by different mixing parameters reflected the power consumption as well. Impeller speed and size have the biggest influence on this value. Considering the stated, it can be concluded that it is of the essence to investigate the influence of dual impeller mixing on the process of batch cooling crystallization in detail. Since mixing parameters determine the nucleation and crystal growth kinetics it is clear that, at the same time, they determine the properties of the final product of crystallization. Therefore, by choosing the suitable dual impeller configuration and by adjusting the mixing conditions, it is possible to obtain a product of wanted characteristics with minimal energy cos

Influence of mixing on nucleation and crystal growth kinetics of borax in dual impeller batch crystallizer

Cilj rada je bio ispitati utjecaj hidrodinamičkih uvjeta u kristalizatoru s dvama turbinskim miješalima na kinetiku kristalizacije dinatrijevog tetraborat dekahidrata (boraksa) tijekom njegove šaržne kristalizacije kontroliranim hlađenjem. Proces je provođen u kristalizatoru volumena 15 dm3, u kojem je omjer visine stupca matične otopine i promjera kristalizatora iznosio 1.3 što je zahtijevalo uvođenje drugog miješala u sustav. Miješanje se provodilo korištenjem triju različitih konfiguracija dvaju miješala: PBT-PBT, SBT-SBT te PBT-SBT. Za svaku primjenjenu konfiguraciju miješala detaljno je ispitan utjecaj brzine vrtnje, promjera miješala, udaljenosti donjeg miješala od dna te međusobne udaljenosti dvaju miješala na mehanizam i brzinu nukleacije, kinetiku rasta kristala boraksa te granulometrijske karakteristike finalnog produkta. U radu je također analiziran i utjecaj brzine hlađenja matične otopine na kinetiku ispitivanog procesa. Da bi se dobio potpuniji uvid u hidrodinamička zbivanja u ispitivanom sustavu, pri svim uvjetima miješanja je određeno vrijeme homogenizacije te je vizualizirana struktura toka kapljevine fotografiranjem tokova kao i simulacijom istih uporabom programskog paketa Visimix 2000 Turbulent. Primjenom Mersmannovog nukleacijskog kriterija je utvrđeno da je pri svim ispitivanim parametrima miješanja nukleacija započela primarnim heterogenim mehanizmom. Za definirani mehanizam su određene brzine nukleacije čime je sagledan utjecaj parametara miješanja i brzine hlađenja na ovu veličinu. Priroda sveukupnog toka suspenzije, definirana strukturom toka kapljevine, intenzitetom konvekcijskog toka te smičnim naprezanjima u zoni oko miješala, također se odražava i na promjenu linearne veličine kristala. Na temelju tih podataka su izračunate brzine te određeni parametri rasta kristala. Korištenjem Mersmannovog modela je pokazano da se pri svim ispitivanim uvjetima provedbe procesa rast odvija integracijskim mehanizmom. Hidrodinamički uvjeti se u konačnici odražavaju i na svojstva finalnog produkta procesa kristalizacije. Granulometrijska analiza prosijavanjem ukazuje na pojavu sekundarne nukleacije i aglomeracije pri određenim uvjetima provedbe procesa. Ukoliko je pak u bilo kojem od ispitivanih sustava bilo osigurano stanje intermedijalne suspenzije, aglomeracija je bila manje izražena. Najpravilniji kristali uz najužu raspodjelu veličina sepak dobivaju primjenom SBT-SBT konfiguracije miješala. Primjena različitih parametara miješanja se odrazila i na utrošak snage miješanja. Najveći utjecaj na ovu veličinu, pri svim ispitivanim konfiguracijama, ima brzina vrtnje miješala, a potom promjer korištenih miješala. S obzirom na navedeno, zaključuje se kako je pri odabiru uvjeta provedbe kristalizacije boraksa kontroliranim hlađenjem u šaržnim kristalizatorima s dvama miješalima neophodno detaljno ispitati utjecaj operacije miješanja na sve stupnjeve kristalizacijskog procesa. Kako parametri miješanja bitno utječu na kinetiku nukleacije i rasta kristala sasvim jasno da oni određuju i karakteristike finalnog produkta kristalizacije. Pravilnim odabirom konfiguracije dvaju miješala i podešavanjem uvjeta miješanja moguće je dobiti produkt željenih karakteristika uz minimalne energetske troškoveThe aim of this research was to investigate the influence of mixing in a dual impeller system on crystallization kinetics of borax in a batch cooling crystallizer. Crystallization was conducted in 15 dm3 crystallizer of tank diameter to liquid height ratio equal to 1.3. This aspect ratio required the use of a second impeller which was mounted on the same shaft. Stirring was conducted by using three different impeller configurations: PBTPBT, SBT-SBT and PBT-SBT. For each of the configurations listed before, an influence of impeller speed, size and position in the vessel on nucleation and crystal growth kinetics, as well as on the granulometric properties of the final product was analyzed in detail. In this work an influence of cooling rate was investigated as well. In order to gain a complete insight into the hydrodynamics of the crystallizer, mixing time was measured and the fluid flow was visualized, using the streak photograpy method and by simulation in Visimix 2000 Turbulent. Using the Mersmann's nucleation criterion, it was determined that the primary heterogeneous nucleation was a dominating mechanism in all experiments conducted in this research. Based on the nucleation mechanism, the rate of nucleation was calculated in order to analyze the influence of mixing parameters and cooling rate on this value. The nature of the overall fluid flow, defined by the flow pattern, the intensity of the overall convection fluid flow and shear stress in the zone around the impeller/s, is reflected on the size of the growing crystal as well. From the change of values of linear crystal size in process time, growth rates and growth parameters were determined. By using the Mersmann’s model, it was determined that the growth rate was governed by the integration mechanism at all process conditions examined. Applied mixing parameters ultimately determined on the properties of the final product of crystallization. Granulometric analysis by sieving showed that both secondary nucleation and agglomeration were present at certain process conditions. But, ifintermedial suspension state was achieved, agglomeration was less pronounces regardless of the impeller configuration. By far, the most regularly shaped crystals were obtained by using the SBT-SBT impeller configuration. Hydrodynamic conditions in the vessel, generated by different mixing parameters reflected the power consumption as well. Impeller speed and size have the biggest influence on this value. Considering the stated, it can be concluded that it is of the essence to investigate the influence of dual impeller mixing on the process of batch cooling crystallization in detail. Since mixing parameters determine the nucleation and crystal growth kinetics it is clear that, at the same time, they determine the properties of the final product of crystallization. Therefore, by choosing the suitable dual impeller configuration and by adjusting the mixing conditions, it is possible to obtain a product of wanted characteristics with minimal energy cos

Efficacy of Reciprocating Instruments in Retreatment of Bioactive and Resin-Based Root Canal Sealers

Objective: To compare the effectiveness of reciprocating instruments in removing gutta-percha and bioactive-based (BioRoot RCS and MTA Fillapex) and epoxy resin-based (AH Plus) sealers from root canals based on filling residues and the time required for root canal revision. Material and methods: Root canals of 90 teeth were instrumented with Reciproc R40. All root canals were obturated using the single-cone technique with Reciproc R40 gutta-percha and with one of the selected sealers. Samples with oval, straight canals were used and randomly divided into three groups: (i) filled with AH Plus sealer and gutta-percha (n=30); (ii) filled with MTA Fillapex and gutta-percha (n=30); (iii) filled with BioRoot RCS and gutta-percha (n=30). Each group was divided into two subgroups (n=15) according to the retreatment instrument used (Reciproc M-Wire R25/R40 or Reciproc blue RB25/RB40). Root canals were longitudinally split and analyzed with a stereomicroscope at 15 × magnifications in the coronal, middle, and apical third. Computational analyses were performed with the Image J software. Data were compared using the Kruskal-Wallis test and Mann-Whitney U test. Results: While no statistically significant differences in the residual material surface were found for Reciproc Blue, Reciproc M-Wire showed significantly higher residual material surface for AH Plus and MTA Fillapex compared to BioRoot RCS. For AH plus. Residual material surface was significantly lower for Reciproc Blue than for Reciproc M-Wire. In contrast, BioRoot RCS showed a significantly higher residual material surface for Reciproc Blue. Conclusions: Calcium silicate-containing sealers were more retrievable compared to AH Plus, with fewer sealer remnants and shorter retreatment time. Retreatment with Reciproc M-Wire instruments was superior to Reciproc blue instruments in retreatment of BioRoot RCS. However, none of the sealers were removed completely