Stability Constants Determination of Mandelate Complexes of Cobalt(II), Nickel(II) and Zinc(II)

Stability constants of mandelate (2-phenyl-2-hydroxyacetate) complexes of cobalt(II), nickel(II) and zinc(II) were determined. potentiometrically using glass and quinhydrone electrodes at 25.0 ± 0.1 aC and ionic strength 2 mole dm" (sodium perchlorate). The numerical values of stability constants were evaluated from experimental data by a computer program based on a weighted least squares method

Development of polymer nanocomposites based on layered double hydroxides

Opisana je priprava i karakterizacija polimernih nanokompozita na osnovi slojevitih dvostrukih hidroksida (LDH). Pripravljen je novi razred punila na osnovi tetrakalcijeva aluminata hidrata, modificiranog benzoatnim (LDH-B) ili undecenoatnim (LDH-U) anionima. Punila su karakterizirana metodama rendgenske difrakcije (XRD) i infracrvene spektroskopije (FTIR) i potvrđena je ugradnja organskih aniona kao modifikatora i povećanje međuslojnog razmaka u odnosu na izvorno punilo. Punila su umješavana u polistirensku (PS), poli(metil-metakrilat)nu (PMMA) ili kopolimernu (SMMA) matricu metodom dvostupanjske in-situ radikalske polimerizacije u masi. Dobiveni prozirni kompozitni filmovi PS/LDH-B, odnosno SMMA/LDH-B karakterizirani su metodama XRD i FTIR, koje uz transmisijsku elektronsku mikroskopiju upućuju na to da kod PS/LDH-B nastaju potpuno raslojeni, a kod SMMA/LDH-B interkalirani nanokompoziti. Rezultati toplinske analize ukazuju na povišenje staklišta kod PS/LDH-B te poboljšanje toplinske postojanosti kod uzoraka PS/LDH-B i SMMA/LDH-B, u usporedbi s čistim polimerima.Polymeric nanocomposites are commonly considered as systems composed of a polymeric matrix and - usually inorganic - filler. The types of nanofillers are indicated in Fig. 1. Beside wellknown layered silicate fillers, recent attention is attracted to layered double hydroxide fillers (LDH), mainly of synthetic origin. The structure of LDH is based on brucite, or magnesium hydroxide, Mg(OH)2 and is illustrated in Fig. 2. The modification of LDHs is commonly done by organic anions, to increase the original interlayer distance and to improve the organophilicity of the filler, keeping in mind their final application as fillers for, usually hydrophobic, polymer matrices. We have used the modified rehydration procedure for preparing organically modified LDH. The stoichiometric quantities of Ca33Al2O6, CaO and benzoic (B) (or undecenoic (U)) acid were mixed with water and some acetone. After long and vigorous shaking, the precipitated fillers were washed, dried and characterized. X-ray diffraction method (XRD) has shown the increase of the original interlayer distance for unmodified LDH (OH–-saturated) of 0.76 nm to the 1.6 nm in LDH-B or LDH-U fillers (Fig. 3). Infrared spectroscopy method (FTIR) has confirmed the incorporation of benzoic anion within the filler layers (Fig. 4). For the preparation of LDH-B and LDH-U composites with polystyrene (PS), poly(methyl methacrylate) (PMMA) and copolymer (SMMA) matrices, a two-step in situ bulk radical polymerization was selected (Table 1 for recipes, azobisisobutyronitrile as initiator), using conventional stirred tank reactor in the first step, and heated mold with the movable wall (Fig. 6) in the second step of polymerization. All the prepared composites with LDH-U fillers were macroscopically phase-separated, as was the PMMA/LDH-B composite. PS/LDH-B and SMMA/LDH-B samples were found to be transparent and were further examined for deduction of their structure (Fig. 5) and thermal properties. FTIR measurements showed that there is some filler present in the nanocomposites (Fig. 7). XRD measurements pointed to the disturbance of the characteristic layered structure of the filler in the obtained composites (Fig. 8). Transmission electron microscopy (TEM) images showed that the filler was not homogeneously dispersed within the matrix (Fig. 9). However, the dispersion was quite good, and a high degree of exfoliation was obtained for PS/LDH-B composites (Fig. 10); the predominantly intercalated structure was found for SMMA/LDH-B composites (Fig. 11). Thus, in both cases nanocomposites were prepared. The thermal characterization by the differential scanning calorimetry (DSC) showed the increase of glass transition point of 10 °C for PS/LDH-B nanocomposite with intermediate (w = 2.5 or 5.0 %) filler content (in comparison with neat PS), a feature that is characteristic for exfoliated nanocomposites. No such increase was obtained for SMMA/LDH-B nanocomposites. The thermal degradation in the inert nitrogen atmosphere was studied by thermal gravimetric analysis (TGA) method. The improvement of thermal stability of PS/LDH-B in comparison with neat PS was found only for the nanocomposites with intermediate (w = 2.5 or 5.0 %) filler content (Fig. 12), again proving the exfoliated structure. The half-weight loss temperature of SMMA/LDH-B nanocomposites continuously increases with the increase of filler content (Fig. 13), a feature that is characteristic for intercalated nanocomposites. In conclusion, the described methods were found satisfactory for preparing the exfoliated nanocomposites of LDH-B and PS. New organic modifiers are to be sought, if exfoliated nanocomposites of SMMA and PMMA matrices are to be prepared. Further investigation will include the deduction of mechanical properties of prepared materials

Thermal Properties of Epoxy Resin/Layered Double Hydroxide Intercalated Nanocomposites

Pripravljen je Ca-Al slojeviti hidroksid (LDH) modifi ciran benzoatnim anionima (Ca4Al2(OH)12(C6H5COO)2 · x H2O, LDH-B) modifi ciranom metodom rehidratacije, tj. dodavanjem benzojeve kiseline i CaO u smjesu vode i acetona, kojom se trikalcijev aluminat (Ca3Al2O6) pretvara u konačni slojeviti hidroksid. Interkalacija benzoatnih aniona unutar LDH slojeva potvrđena je rendgenskom difrakcijom (XRD), spektroskopijom u infracrvenom području (FTIR) i termogravimetrijskom analizom (TGA). Interkalirani nanokompoziti na osnovi epoksidne smole i LDHB pripravljeni su in situ polimerizacijom, uz polioksipropilen diamin kao umreživalo. Uzorci s različitim udjelom LDH-B (5, 10 i 15 phr) ispitivani su XRD-om, FTIR-om, TGA-om, razlikovnom pretražnom kalorimetrijom i transmisijskom elektronskom mikroskopijom (TEM). Rendgenska difrakcija pokazala je nastajanje interkaliranih nanokompozita, a TEM analiza potvrdila raspršenje LDH-B unutar matrice i nastajanje interkalirane strukture, uz djelomično raslojavanje u nanokompozitu s 5 phr punila. Toplinska analiza pokazala je smanjenje početne temperature degradacije u usporedbi s nemodifi ciranim epoksidnim polimerom, dok se ostatak pri 1000 °C povećao, posebice kod djelomično raslojenog nanokompozita. Staklište se snizuje u usporedbi s nemodificiranim epoksidnim polimerom, što upućuje na slabije umreživanje epoksidne matrice.Ca-Al layered double hydroxide (LDH) modifi ed by the incorporation of benzoate anions (Ca4Al2(OH)12(C6H5COO)2 · x H2O, LDH-B) was prepared by a variation of the rehydration method, by adding benzoic acid and CaO into a mixture of water and acetone used to convert tricalcium aluminate (Ca3Al2O6) into fi nal layered structure. Intercalation of benzoate anions within LDH layers was confi rmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Intercalated nanocomposites based on an epoxy resin and LDH-B were prepared by in situ polymerisation, with poly(oxypropylene) diamine as a curing agent. Nanocomposites prepared with different contents of LDH-B (5, 10 and 15 phr) were characterised by XRD, FTIR, TGA, differential scanning calorimetry and transmission electron microscopy (TEM). The XRD results indicated formation of intercalated nanocomposites, and TEM analysis confi rmed that LDH-B was dispersed within the matrix forming an intercalated structure, which becomes partially exfoliated in the nanocomposite with 5 phr fi ller. Results of thermal analysis showed detrimental infl uence on initial degradation temperature in comparison to the neat crosslinked epoxy, while residue at 1,000°C increases, especially for the partially exfoliated nanocomposite. The glass transition temperature decreases in comparison with the neat crosslinked epoxy, indicating poorer crosslinking of the epoxy matrix

Safety and protection from fire and/or explosion in physiotherapy

Ovim radom opisuju se vrste potencijalnih opasnosti od požara i/ili eksplozije te načini raščlanjivanja i prosuđivanja mogućih ugroženosti ili razine rizika od tih opasnosti pri obavljanju fizioterapeutske djelatnosti. Posebna pozornost posvećena je predočavanju znakovitih uzroka požara i eksplozija, te svih praktičnih izvora energije paljenja. U radu je prikazan pregled vrsta i obilježja zapaljivosti požarno i eksplozijski potencijalno opasnih tvoriva i tvari, držanih ili rabljenih u sklopu svih prostora ustanova u kojima se provodi fizioterapeutska djelatnost. Radom su prikazani neki lako mogući uzroci nastanka požara i/ili eksplozije u sklopu takvih prostora zbog nepoštovanja tehničkih smjernica, preporuka i zakonskih propisa s ciljem da se iskoriste spoznaje o uočenim rizicima kako bi se oni smanjili na najmanju moguću mjeru.This paper addresses the types of potential fire and/or explosion threats as well as ways of classifying and evaluating possible danger or risk level stemming from those threats when administering physiotherapeutic treatment. Special attention has been paid to identifying significant causes of fires and explosions as well as to all ignition sources. Furthermore, the paper provides an overview of the types and characteristics of potentially combustible and explosive substances which are stored or used within all healthcare institutions that provide physiotherapeutic treatment. In addition, the paper presents possible fire and/or explosion occurrence scenarios, which may occur due to failure to comply with technical guidelines, recommendations and legal regulations, with the intent to raise awareness of perceived hazards and reduce them to a minimum

On the Stability of Formato, Acetato, Propionato, Butyrato, Glycolato and Chloroacetato Complexes of Cobalt, Nickel, Copper, Zinc, Cadmium and Lead

Stability constants of formato, acetato, propionato, butyrato, glycolato and chloroacetato complexes of cobalt, nickel, copper, zinc, cadmium and lead have been determined by the potentiometric method. The change of concentration of hydrogen ions in the monocarboxylate buffer has been measured. Stability constants have been obtained by means of a digital computer applying the Gauss Z programme devised by R. S. Tobias. On the basis of these results as well as the results obtained in the former investigations by the polarographic and spectrophotometric method, the stability of the investigated monocarboxylato complexes has been discussed and the corresponding orders of stability were established

Calcium Aluminate Cement Hydration Model

U ovome radu istražen je utjecaj temperature (ϑ = 5 - 20 °C) i vodocementnog masenog omjera (mH/mAC = 0,4; 0,5 i 1,0) na rano razdoblje hidratacije uzoraka komercijalnog aluminatnog cementa uporabom diferencijalnog mikrokalorimetra. Kemijski vezana voda u hidratiziranim uzorcima određena je termogravimetrijskom metodom. Rano razdoblje hidratacije opisano je pojednostavljenim stehiometrijskim modelom koji je temeljen na stehiometriji reakcija hidratacije glavnih minerala: monokalcijeva aluminata, majenita i feritne faze. Ukupni proces hidratacije nakon razdoblja indukcije uspješno je opisan predloženim kinetičkim modelom u obliku sume otpora pojedinačnih mehanizama: nukleacije i rasta kristala, interakcije na granici faza i prijenosa tvari. Ustanovljeni veliki utjecaj vodocementnog omjera na ukupno razvijenu toplinu hidratacije aluminatnog cementa, odnosno na stupanj hidratacije, ukazuje na važnost vode kao limitirajućeg reaktanta koji rano usporava hidrataciju. Stoga je predloženim kinetičkim modelom interakcija opisana bimolekulskom reakcijom vode i cementa, a prijenos tvari je opisan relativno prema mjerodavnomu reaktantu. Primjenom predloženog kinetičkog modela istražen je utjecaj temperature i vodocementnog omjera na mjerne veličine izdvojenih mehanizama procesa hidratacije.Calcium aluminate cement (AC) is a very versatile special cement used for specific applications. As the hydration of AC is highly temperature dependent, yielding structurally different hydration products that continuously alter material properties, a good knowledge of thermal properties at early stages of hydration is essential. The kinetics of AC hydration is a complex process and the use of single mechanisms models cannot describe the rate of hydration during the whole stage. This paper examines the influence of temperature ϑ=5–20 °C) and water-to-cement mass ratio (mH /mAC = 0.4; 0.5 and 1.0) on hydration of commercial iron-rich AC ISTRA 40 (producer: Istra Cement, Pula, Croatia, which is a part of CALUCEM group), Figs 1–3. The flow rate of heat generation of cement pastes as a result of the hydration reactions was measured with differential microcalorimeter. Chemically bonded water in the hydrated cement samples was determined by thermo-gravimetry. Far less heat is liberated when cement and water come in contact for the first time, Fig. 1, than in the case for portland cement (PC). Higher water-to-cement ratio increases the heat evolved at later ages (Fig. 3) due to higher quantity of water available for hydration. A significant effect of the water-to-cement ratio on the hydration rate and hydration degree showed the importance of water as being the limiting reactant that slows down the reaction early. A simplified stoichiometric model of early age AC hydration (eq. (8)) based on reaction schemes of principal minerals, nominally CA, C12A7 and C4AF (Table 1), was employed. Hydration kinetics after the induction period (ϑ < 20 °C) had been successfully described (Fig. 4 and Table 2) by a proposed model (eq. (23)) which simultaneously comprised three main mechanisms: nucleation and growth, interaction at phase boundary, and mass transfer. In the proposed kinetic model the nucleation and growth is proportional to the amount of reacted minerals (eq. (18)), the interaction at phase boundary was described by a bimolecular consumption of both reactants (eq. (19)), cement and free water, while the mass transfer mechanism was described relative to the limiting reactant (eq. (21)). Increasing temperature from 5 to 20 °C decreases the rate of nucleation and growth (NR) (Fig. 6), increases the rate of interaction (I) according to Arrhenius law (E12 ≈43 kJ mol-1) (Fig. 7), and increases the rate of mass transfer (k) linearly (Fig. 8)

Layered double hydroxides as nanofillers for polymers

U posljednjih desetak godina osobitu pozornost privlače slojeviti hidroksidi (e. layered double hydroxides, LDH) kao potencijalna nanopunila za polimere. Osnovni anorganski slojevi LDH pozitivno su nabijeni te predstavljaju komplement negativno nabijenim slojevitim silikatima i omogućuju uvođenje različitih aniona kao modifikatora u strukturu punila. Ve}ina istraženih slojevitih hidroksida sintetskog je podrijetla i stoga visoke čistoće, što im je prednost u usporedbi s prirodnim punilima. Svojstva slojevitih hidroksida mogu se mijenjati u širokom rasponu, prikladnim izborom metalnih kationa i protuaniona. Ovaj rad daje pregled novijih istraživanja slojevitih hidroksida – nanopunila za polimere, uključujući postupke priprave i karakterizacije te načine ugradnje u polimerne matrice.Over the past decade, special attention has been paid to layered double hydroxides (LDH) as potential nanofillers for polymers. Basic inorganic layers of LDHs are positively charged; thus they complement the negatively charged silicate layers and may serve as a route for the introduction of anionic functionalities as modifiers in the filler structure. Most of the investigated LDHs are of synthetic origin and consequently of high purity, which presents an advantage in comparison with naturally occurring fillers. The properties of LDHs may be varied in a wide range by the adequate choice of metal cations and counteranions. This paper gives an overview of the recent investigations into layered double hydroxides as polymer nanofillers, and describes the filler synthesis and characterization procedures as well as procedures for the incorporation of fillers within polymer matrices