Fast Fourier Transform IR Characterization of Epoxy GY Systems Crosslinked with Aliphatic and Cycloaliphatic EH Polyamine Adducts

The use of fast FT-IR spectroscopy as a sensitive method to estimate a change of the crosslinking kinetics of epoxy resin with polyamine adducts is described in this study. A new epoxy formulation based on the use of polyamine adducts as the hardeners was analyzed. Crosslinking reactions of the different stoichiometric mixtures of the unmodified GY250 epoxy resin with the aliphatic EH606 and the cycloaliphatic EH637 polyamine adducts were studied using mid FT-IR spectroscopic techniques. As the crosslinking proceeded, the primary amine groups in polyamine adduct are converted to secondary and the tertiary amines. The decrease in the IR band intensity of epoxy groups at about 915 cm(-1), as well as at about 3,056 cm(-1), was observed due to process. Mid IR spectral analysis was used to calculate the content of the epoxy groups as a function of crosslinking time and the crosslinking degree of resin. The amount of all the epoxy species was estimated from IR spectra to changes during the crosslinking kinetics of epichlorhydrin

Effects of the acrylic polyol structure and the selectivity of the employed catalyst on the performance of two-component aqueous polyurethane coatings

Two kinds of aqueous acrylic polyols (single step and multi step synthesis type) have been investigated for their performance in the two-component aqueous polyurethane application, by using more selective catalysts. The aliphatic polyfunctional isocyanates based on hexamethylen diisocyanates have been employed as suitable hardeners. The complex of zirconium, commercially known as K-KAT(R)XC-6212, and manganese (III) complexes with mixed ligands based on the derivative of maleic acid have been used as catalysts in this study. Both of the aqueous polyols give good results, in terms of application and hardness, when elevated temperatures and more selective catalysts are applied. A more selective catalyst promotes the reaction between the isocyanate and polyol component. This increases the percentage of urethane bonds and the degree of hardness in the films formed from the two components of aqueous polyurethane lacquers. The polyol based on the single step synthesis route is favourable concerning potlife and hardness. The obtained results show that the performance of the two-component aqueous polyurethane coatings depends on the polymer structure of the polyols as well as on the selectivity of the employed catalyst

zaštita opreme od korozije u sistemu za pasterizaciju mleka

In the course of the pasteurization treatment of milk and dairy products the temperature of the technological process is kept at a constant value. The regulation of the temperature is carried out by means of technological water that comes from certain pools cooled to the temperature of 5ºC. the water heated in the process of pasteurization is sent back through steel pipes to the pool where it is cooled to the working temperature. the pools for water cooling are fitted with a bundle of pipes made of plain carbon steel that corrode over the time. the protection of pipes against corrosion is possible to be performed in two ways: by use of inhibitors and by cathodic protection. The application of either method depends on a number of factors. It is cheaper to protect new pipes from corrosion using inhibitors, whereas pipes already attacked by corrosion are more efficiently protected against further corrosion by applying the cathodic protection.U toku postupka pasterizacije mleka i mlečnih proizvoda temperatura tehnološkog procesa održava se na konstantnoj temperaturi. Regulacija temperature se vrši pomoću tehnološke vode koja dolazi iz bazena rashlađena do temperature od 5°C. zagrejana voda iz procesa pasterizacije vraća se cevima u bazen gde se pomoću tečnog amonijaka hladi do radne temperature. U bazenima za hlađenje tehnološke vode nalazi se snop cevi od običnog čelika kroz koji prolazi tečni amonijak, a koje vremenom počinju da korodiraju. Zaštita cevi od korozije je moguća na dva načina: primenom određenih inhibitora korozije i primenom katodne zaštite. Koji će od ova dva načina da bude primenjen zavisi od više faktora. Za nove cevi je jeftinija zaštita od korozije primenom inhibitora. za cevi koje su već u upotrebi ili je kod njih počela korozija, primena katodne zaštite je efikasniji postupak dalje zaštite od korozije

The Influence of the Addition of Polyacrylic Hydrogel on the Content of Proteins, Minerals and Trace Elements in Milk Protein Solutions

Ispitana je mogućnost uporabe poliakrilnog hidrogela za uklanjanje iona teških metala iz otopina koncentrata proteina mlijeka, koncentrata proteina sirutke i albumina iz goveđeg seruma. Dobiveni rezultati pokazuju da bubrenje gelova u ovim otopinama različito utječe na udjel proteina i koncentraciju mineralnih tvari i elemenata u tragovima. Ukupan udjel proteina i koncentracija fosfora povećali su se nakon bubrenja hidrogela u otopinama koncentrata proteina mlijeka i proteina sirutke, bez promjene u sastavu proteina. Osim toga, smanjio se udjel proteina u otopini albumina iz goveđeg seruma. U otopini se proteina mlijeka nakon bubrenja hidrogela koncentracija natrija nije promijenila, dok se u otopini proteina sirutke znatno povećala. Koncentracija se kalcija i magnezija u otopinama koncentrata proteina mlijeka i proteina sirutke nakon bubrenja hidrogela smanjila za 20,3-63,4 %, ovisno o uzorku i mineralnoj tvari. Tijekom bubrenja hidrogela u svim je analiziranim uzorcima koncentracija cinka ostala nepromijenjena, dok su se one Fe, Cu, Mn, Ni i Pb znatno smanjile. Iz dobivenih se rezultata može zaključiti da se dodatkom poliakrilnog hidrogela otopinama koncentrata proteina mlijeka i proteina sirutke bitno smanjuje koncentracija teških metala, bez utjecaja na proteinski sastav otopina. Dobiveni bi se rezultati mogli primijeniti za razvoj novih tehnoloških procesa za uklanjanje iona teških metala iz mliječnih proizvoda.Solutions of milk protein concentrate, whey protein concentrate and bovine serum albumin (BSA) were treated with polyacrylic hydrogel to establish whether the hydrogel could be used for decontamination of heavy metal ions from milk protein-based products. The obtained results indicated that swelling of hydrogel in these solutions had different effects on their mineral, trace element and total protein content. Total protein and phosphorus content increased in milk protein concentrate and whey protein concentrate solutions after swelling of hydrogel without changes in their protein compositions. On the other hand, the protein content in BSA solution decreased after swelling. The content of Na did not change in milk protein concentrate solution, whereas it significantly increased in whey protein concentrate solution after hydrogel swelling. The content of Ca and Mg was reduced after the swelling in milk protein concentrate and whey protein concentrate solutions for 20.3–63.4 %, depending on the analysed sample and the mineral. The content of Zn did not change during swelling, whereas the content of Fe, Cu, Mn, Ni and Pb significantly decreased after hydrogel swelling in all analysed samples. According to the obtained results, the addition of polyacrylic hydrogel to milk and whey protein concentrate solutions can significantly decrease the content of heavy metal ions without affecting their protein composition. Therefore, this work could be useful in developing a new technological process for heavy metal purification of milk protein-based products

Synergetic electrocatalytic effect of d metals for the hydrogen evolution reaction on gold substrates

An electrocatalytic method developed previously for the depolarization of the hydrogen evolution reaction (HER) on graphite, iron, steel, nickel and titanium substrate surfaces was employed to improve the polarization characteristics of gold. The combination of two d metals from two branches of Balandin's "volcano" curve for the HER creates a marked electrocatalytic effect, particularly for molybdenum and cobalt which are added in situ as their anionic or complex species during the electrolytic process. The alloy activity appears to be shifted to potential values that are representative of precious metals and even exceeds these values at higher current densities; the shift is more than 700 mV over the current density range important for similar industrial applications. The synergetic electrocatalytic effects and the improvements in the polarization are illustrated by linear potential sweep voltammograms and steady state Tafel lines. The duration (the lifetime) of the electrocatalytic coating was about 4 months with simple reactivation by means of the in situ addition of negligible amounts of cheap and available cobalt and molybdenum species

Katodna zaštita armirano-betonskih konstrukcija na objektima vodovoda i kanalizacije

Concrete is a widely used material in the construction industry. It is obtained by mixing cement as a binding agent and inert or only partly reactive aggregates as fillers. In order to increase its bearing power concerning extension it is fitted with steel elements as armature. It is usually believed that the concrete provides the steel armature, embedded into it, with the protection against the corrosion regarding the high alkalinity that takes place during the hydration reactions and which retains as the solution in the concrete pores. Regardless of the aforesaid the corrosion of the steel armature in the concrete occurs due to the effect of a number of factors including the contamination of the concrete by chlorine ions, carbonation of the concrete and the like. As a consequence of this corrosion the formation of corrosion products that are in terms of volume much bigger than the in-built metal takes place and that results in the additional stress to extension of the material of the concrete. As the concrete is weak to strains by extension these forces lead to the occurrence of cracks, detachment and braking away of the concrete cover layer from the armature. Further corrosion that can endanger the lifetime of the entire structure develops on the in-built armature. This problem occurs with the reinforced concrete constructions such as bridges, dams and suchlike. Therefore it is by all means necessary to protect additionally the steel armature in the concrete against the effects of the corrosion. .Beton je veoma raširen kao materijal u građevinarstvu. Dobija se mešanjem cementa kao vezivnog sredstva i inertnih ili samo delimično reaktivnih agregata kao punila. Za povećanje njegove nosivosti s obzirom na istezanje u njega se ugrađuju čelični elementi kao armatura. Normalno se smatra da beton pruža zaštitu čeličnoj armaturi koja je u njega ulivena od korozije s obzirom na jaku alkalnost do koje dolazi u toku hidratacionih reakcija i koja se zadržava kao rastvor u porama betona. Bez obzira na izloženo do korozije čelične armature u betonu dolazi usled delovanja više faktora, uključujući kontaminaciju betona hlornim ionom, karbonacijom betona i sl. Usled ove korozije dolazi do stvaranja korozionih produkata koji su zapreminski mnogo veći od ugrađenog metala što dovodi do dodatnog naprezanja na razvlačenje materijala betona. Kako je beton slab na opterećenja, razvlačenjem ove sile dovode do pojave naprslina, odvajanja i otpadanja betonskog prekrivnog sloja sa armature. Na izloženoj armaturi dolazi do dalje korozije, koja može ugroziti vek trajanja cele strukture. Ovaj problem se javlja kod armirano-betonskih konstrukcija kao što su mostovi, brane i sl.

Interactive supported electrocatalysts and spillover effect in electrocatalysis for hydrogen and oxygen electrode reactions

The aim of the present paper has been to introduce the electron conductive and d-d-interactive individual and composite hypo-d-oxides of the increased altervalent capacity, or their suboxides (Magneli phases,), as catalytic supports and therefrom provide: (i) The Strong Metal-Support Interaction (SMSI) effect, and (ii) the Dynamic spillover interactive transfer of primary oxides (M-OH) for further electrode reactions, and thereby advance the overall electrocatalytic activity. The d-band has been pointed out as the bonding, adsorptive and catalytic orbital. In the same context, the phenomenon and significance of the d-d-correlations both in heterogeneous catalysis and electrocatalysis are displayed and inferred. Since hypo-d-oxides feature the exchange membrane properties, the higher the altervalent capacity, the higher the spillover effect. Potentiodynamic experiments have shown that the reversible peak of the primary oxide growth on Pt, Ru and Au supported upon hypo-d-oxides and suboxides becomes distinctly increased in the charge capacity and shifts to remarkably more negative potential values, so that it starts even within the range of H-adatoms desorption, while its rfeduction extends until and merge with the UPD of hydrogen atoms. With wet tungstenia doped titania supported Pt catalyst in membrane cells these peaks dramatically increase in their charge capacity and reversibly become shrunk with a decreased moisture content in the feeding inert gas mixture, and vice versa. Such distinct potentiodynamic scans, in conjunction with some broaden complementary kinetic electrocatalytic improvements rising from the same hypo-d-oxide and/or suboxide interactive support effects, have been proved to be the best and comparable experimental evidence for the spillover effect of primary oxides

Some specific potentiodynamic behaviour of certain aldehydes and monosaccharides - Some simple and some specific aldehydes

Three distinct potentiodynamic features have been scanned on cyclic voltammograms in the presence of simple (formaldehyde, acetaldehyde), and some specific (cinnam aldehyde, croton aldehyde, furfural and benzaldehyde) aldehydes: (a) anodic oxidation of aldehyde group proceeds as a direct heterogeneous reaction with weakly or reversibly adsorbed OH-adatomic group, or in overall, as an electrode kinetics similar to Volmer-Heyrovsky mechanism for hydrogen evolution (R-CHO + 2M-OH double right arrow R-COOH + H2O + 2M + 2e), which is practically the same as the Lamy mechanism; (b) as the result, the oxide growth upon Pt, Pd, Au electrode substrates becomes prevailingly or partially prevented and reflects in the proportionally reduced charge capacity for its desorption peak, and (c) the consequence of the latter represents the unusual, but sharply pronounced reverse current jump into anodic range with peaks of repeated aldehyde oxidation during reversal potential scans towards hydrogen evolving limits. Aldehyde reduction, except on Au and Hg, occurs as the heterogeneous catalytic reaction with adsorbed H-adatoms and appears competitive with hydrogen evolution, and while being for about two order of magnitude faster than H-adatom recombination, at lower current densities (about 10 mA cm(-2)) yields rather high current efficiencies (above 90%). Oxygen evolution proceeds along with aldehyde oxidation and only at rather high positive potentials prevails in both surface oxide formation and thereby reduced rate in carboxylic acid production. At extremely positive anodic potentials on Au electrode, there appears a distinct peak of carboxylic group oxidation with release of CO2, preceding oxygen evolution, or occurring along with the latter

Proces umrežavanja vodenih poliuretanskih sistema

The DSC method has been employed to monitor the kinetics of reticulation of aqueous polyurethane systems without catalysts, and with the commercial catalyst of zirconium (CAT®XC-6212) and the highly selective manganese catalyst, the complex Mn (III)-diacetylacetonemaleinate (MAM). Among the polyol components, the acrylic emulsions were used for reticulation in this research, and as suitable reticulation agents the water emulsible aliphatic polyisocyanates based on hexamethylendoisocyanate with the different contents of NCO-groups were employed. On the basis of DSC analysis, applying the methods of Kissinger, Freeman-Carroll and Crane-Ellerstein the pseudo kinetic parameters of the reticulation reaction of aqueous systems were determined. The temperature range of the examination was from 500C to 4500C with the heat rate of 0.50C/min. The reduction of the activation energy and the increase of the standard deviation indicate the catalytic action of the selective catalysts of zirconium and manganese. The impact of the catalysts on the reduction of the activation energy is the strongest when using the catalysts of manganese and applying all the three afore-said methods. The least aberrations among the stated methods in defining the kinetic parameters were obtained by using the manganese catalyst.DSC metodom praćena je kinetika umrežavanja vodenih poliuretankih sistema, bez katalizatora, sa komercijalnim katalizatorom cirkonijuma (KAT®XC-6212) i visokoselektivnim manganovim katalizatorom, kompleksom Mn(III) - diacetilacetonatomaleinatom (MAM). U ovom radu za umrežavanje od poliolnih komponenti korišćene su akrilne emulzije a kao pogodni umreživači koričćeni su vodoemulgujući alifatični poliizocijanati na bazi heksametilendiizocijanata sa različitim sadržajem NCO-grupa. Na osnovu DSC-analize, metodama Kissinger-a, Freeman-Carrollaa i Crane-Ellerstein-a, određeni su prividni kinetički parametri reakcije umrežavanja vodenih sistema. Temperaturni opseg ispitivanja koričćen je od 50 do 450oC sa brzinom grejanja od 0.5oC/min. Smanjenje energije aktivacije i povećanje standardne devijacije ukazuju na katalitičko dejstvo selektivnih katalizatora cirkonijuma i mangana. Učešće katalizatora u smanjenju energije aktivacije je najveće kod katalizatora mangana, korišćenjem sve tri bbbmetode izračunavanja kod ispitivanih uzoraka u odnosu na cirkonijumov katalizator. Najmanja odsupanja između pomenutih metoda u određvanju kinetičkih parametara dobijena su korišćenjem manganovog katalizatora