Compressive strength and hydrolytic stability of fly ash based geopolymers

The process of geopolymerization involves the reaction of solid aluminosilicate materials with highly alkaline silicate solution yielding an aluminosilicate inorganic polymer named geopolymer, which may be successfully applied in civil engineering as a replacement for cement. In this paper we have investigated the influence of synthesis parameters: solid to liquid ratio, NaOH concentration and the ratio of Na2SiO3/NaOH, on the mechanical properties and hydrolytic stability of fly ash based geopolymers in distilled water, sea water and simulated acid rain. The highest value of compressive strength was obtained using 10 mol dm-3 NaOH and at the Na2SiO3/NaOH ratio of 1.5. Moreover, the results have shown that mechanical properties of fly ash based geopolymers are in correlation with their hydrolytic stability. Factors that increase the compressive strength also increase the hydrolytic stability of fly ash based geopolymers. The best hydrolytic stability of fly ash based geopolymers was shown in sea water while the lowest stability was recorded in simulated acid rain. [Projekat Ministarstva nauke Republike Srbije, br. 172054 i Nanotechnology and Functional Materials Center, funded by the European FP7 project No. 245916

Mutations in the PAH gene: A Tool for population genetics study

Fenilketonurija je urođena metabolička bolest prouzrokovana mutacijama u genu za fenilalanin hidroksilazu (PAH). U srpskoj populaciji je identifikovano 19 različitih PAH mutacija. PAH mutacije korišćene su kao molekularni markeri za populaciono-genetičko istraživanje. Niska vrednost homozigotnosti PAH gena (0,10) ukazuje na heterogenost fenilketonurije u Srbiji i odražava brojne migracije u regionu jugoistočne Evrope. U skladu sa tim, osmišljena je strategija molekularne dijagnostike fenilketonurije za Srbiju. U cilju rasvetljavanja porekla najčešće mutacije koja uzrokuje fenilketonuriju u Srbiji, L48S, urađena je haplotipska analiza PCR-RFLP metodom. Naši rezultati sugerišu da je L48S mutacija poreklom iz više populacija sa različitim genetičkim karakteristikama. .Phenylketonuria (PKU), an inborn error of metabolism, is caused by mutations in the phenylalanine hydroxylase (PAH) gene. In the Serbian population, 19 different PAH mutations have been identified. We used PAH mutations as molecular markers for population genetics study. The low homozygosity value of the PAH gene (0.10) indicates that PKU in Serbia is heterogeneous, reflecting numerous migrations throughout Southeast Europe. The strategy for molecular diagnostics of PKU was designed accordingly. To elucidate the origin of the most common (L48S) PKU mutation in Serbia, we performed haplotype analysis by PCR-RFLP. Our results suggest that the L48S mutation was imported into Serbia from populations with different genetic backgrounds

Surface hydrophobization of handmade paper

U ovom radu su predstavljene mogućnosti povećanja hidrofobnosti površine papira nanošenjem slojeva hidrofobnog materijala na njegovu površinu. Ispitane su dve različite tehnike nanošenja stearinske kiseline, šelaka i cink-hidroksida na površinu papira. Hidrofobnost je ispitana modifikovanom metodom po Kobu, merenjem ugla kvašenja i vremena zadržavanja kapi. Prisustvo sredstava za hidrofobizaciju potvrđeno je FTIR spektroskopijom. Utvrđeno je da se, primenjenim metodama nanošenja, mnogo bolji rezultati dobijaju sa stearinskom kiselinom nego sa šelakom.The paper shows the possibilities of increasing the hydrophobicity of the paper surface by applying layers of hydrophobic material to the surface. Various application techniques and the following substances were tested: stearic acid, shellac and zinc-hydroxide. Hydrophobicity was tested using the modified Cobb method, measuring the contact angle and drop retention time. The presence of hydrophobizing agents was confirmed by FTIR spectroscopy. It was found that the methods of applying the hydrophobizing agent, used in this work, give much better results with stearic acid, compared to shellac. This manuscript presents novel possibilities of increasing paper surface hydrophobicity by applying layers of hydrophobic material to the surface. Various layer application techniques were examined, as well as substances including: stearic acid, shellac and zinc-hydroxide. Hydrophobicity was tested using the modified Cobb method, measuring the contact angle and drop retention time. The presence of hydrophobizing agents was confirmed by FTIR spectroscopy. Based on the results achieved, it can be concluded that the methods of applying the hydrophobizing agent, used in this work, give much better results with stearic acid, compared to shellac

Surface hydrophobization of handmade paper

U ovom radu su predstavljene mogućnosti povećanja hidrofobnosti površine papira nanošenjem slojeva hidrofobnog materijala na njegovu površinu. Ispitane su dve različite tehnike nanošenja stearinske kiseline, šelaka i cink-hidroksida na površinu papira. Hidrofobnost je ispitana modifikovanom metodom po Kobu, merenjem ugla kvašenja i vremena zadržavanja kapi. Prisustvo sredstava za hidrofobizaciju potvrđeno je FTIR spektroskopijom. Utvrđeno je da se, primenjenim metodama nanošenja, mnogo bolji rezultati dobijaju sa stearinskom kiselinom nego sa šelakom.The paper shows the possibilities of increasing the hydrophobicity of the paper surface by applying layers of hydrophobic material to the surface. Various application techniques and the following substances were tested: stearic acid, shellac and zinc-hydroxide. Hydrophobicity was tested using the modified Cobb method, measuring the contact angle and drop retention time. The presence of hydrophobizing agents was confirmed by FTIR spectroscopy. It was found that the methods of applying the hydrophobizing agent, used in this work, give much better results with stearic acid, compared to shellac. This manuscript presents novel possibilities of increasing paper surface hydrophobicity by applying layers of hydrophobic material to the surface. Various layer application techniques were examined, as well as substances including: stearic acid, shellac and zinc-hydroxide. Hydrophobicity was tested using the modified Cobb method, measuring the contact angle and drop retention time. The presence of hydrophobizing agents was confirmed by FTIR spectroscopy. Based on the results achieved, it can be concluded that the methods of applying the hydrophobizing agent, used in this work, give much better results with stearic acid, compared to shellac

Etched Parallelogram Patterns with Sides Along <100> and <n10> Directions in 25 wt % TMAH

In this paper, we present and analyze etching of parallelogram patterns in the masking layer on a (100) silicon in 25 wt % TMAH water solution at the temperature of 80 0C. Sides of parallelogram islands in the masking layer are designed along and crystallographic directions. A 3D simulation of the profile evolution from these patterns during etching of silicon using the level set method is also presented. We determined all crystallographic planes that appear during etching in the experiment and obtained simulated etching profiles of these 3D structures. A good agreement between dominant crystallographic planes through experiments and simulations is obtained

Kontrolisan raspored integrisanih prepreka u silicijumskim mikrokanalima nagrizanim u 25 mas.% rastvoru tetrametilamonijum hidroksida

In this paper, fabrication of silicon microchannels with integrated obstacles by using 25 wt.% tetramethylammonium hydroxide (TMAH) aqueous solution at the temperature of 80 C is presented and analysed. We studied basic island patterns, which present union of two symmetrical parallelograms with the sides along predetermined crystallographic directions (2. Acute angles of the parallelograms were smaller than 45o. We have derived analytical relations for determining dimensions of the integrated obstacles. The developed etching technique provides reduction of the distance between the obstacles. Before the experiments, we performed simulations of pattern etching based on the level set method and presented evolution of the etched basic patterns for the predetermined crystallographic directions . Combination of basic patterns with sides along the and crystallographic directions is used to fabricate a matrix of two row of silicon obstacles in a microchannel. We obtained a good agreement between the experimental results and simulations. Our results enable simple and cost-effective fabrication of various complex microfluidic silicon platforms with integrated obstacles.U ovom radu je prezentovana i analizirana izrada silicijumskih mikrokanala sa integrisanim preprekama u vodenom rastvoru 25 mas.% tetrametilamonijum hidroksida (TMAH) na temperaturi od 80 oC. Proučavani su osnovni oblici maski koji predstavljaju uniju dva simetrična ostrva u obliku paralelograma čije su stranice duž unapred određenih kristalografskih pravaca (2. Oštri uglovi paralelograma su manji od 45˚. Izvedene su formule za izračunavanje dimenzija integrisanih prepreka. Razvijena je tehnika nagrizanja koja smanjuje rastojanje između prepreka. Pre eksperimenata izvršene su simulacije osnovnih oblika koje se baziraju na metodi implicitno definisanih nivoa (engl. level set method). Prezentovan je razvoj nagrizanih osnovnih oblika maski za unapred određene kristalografske pravce . Kombinacija osnovnih oblika maski čije su stranice duž kristalografskih pravaca i je iskorišćena za izradu dva reda matrice silicijumskih prepreka u mikrokanalu. Dobijeno je dobro slaganje između eksperimenata i simulacija. Dobijeni rezultati omogućavaju jednostavnu i jeftinu izradu različitih kompleksnih mikrofluidnih silicijumskih platformi sa integrisanim preprekama

Adsorption kinetics, equilibrium, and thermodynamics of Cu2+ on pristine and alkali activated steel slag

Two adsorbents, pristine electric arc furnace slag (EAFS) and alkali activated slag (AAS) were used for Cu2+ removal from aquatic solutions. Batch adsorption tests were conducted at various temperatures and initial Cu2+ concentrations, while solid to liquid ratio and pH of solution were kept constant. Pseudo-first-order and pseudo-second-order (PSO) kinetics models, Langmuir and Freundlich isotherm models, as well as intraparticle and Boyd's diffusion models were applied in order to investigate the adsorption process. It has been found that alkali activation of EAFS leads to an increase in the specific surface of slag and thus improves the sorption properties of EAFS. The adsorption of Cu2+ onto both adsorbents proceeds via PSO adsorption mechanism, film diffusion mainly controls the adsorption process, and Langmuir isotherm model fits well the experimental data. Results indicated a fast adsorption process which is spontaneous and endothermic in nature. Microstructural investigation of EAFS and AAS revealed morphological changes in metal loaded EAFS and AAS samples in comparison to unloaded adsorbents. X-ray powder diffraction analysis indicated that adsorption of Cu2+ onto both adsorbents occurs through formation of a Cu-complex

Durability of alkali activated slag in a marine environment: Influence of alkali ion

The durability of alkali-activated steel electric arc furnace slag (EAFS) in a marine environment was evaluated with respect to the chemical composition of the alkaline activator. Two different alkaline activators have been used: a mixture of NaOH and Na2SiO3 solutions (Na-activator), as well as a mixture of KOH and K2SiO3 solutions (K-activator). The obtained results gave the insight into the influence of alkaline activator chemistry on the compressive strength and durability of alkali-activated slag (AAS), which was exposed to the damaging seawater environment. The porosity of AAS was found to be the most important factor with regards to the strength and durability of these materials in marine environment. Sodium based alkali-activated slag (Na-AAS) displayed lower porosity and higher compressive strength compared to potassium based AAS (K-AAS). Lower porosity and thus a lower rate of water uptake by AAS matrix, i.e., the lower sorptivity was exhibited by the Na-AAS when compared to K-AAS. Hence, Na-AAS exhibited better durability in a marine environment