Effects of ammonium nitrate and sodium sulfate solution on mechanical properties and structure of fly ash based geopolymers

Геополимери на бази три различита узорка електрофилтерског пепела изложени су дејству концентрованог раствора NH4NO3 (480 g/dm3) и раствора Na2SO4 (50 g/dm3) у периоду од 18 месеци. Промене механичких својстава геополимера испитиване су након 5 термина: 28, 90, 180, 365 и 540 дана. Промене у структури геополимера испитиване су методама рендгенске структурне анализе, електронске микроскопије, инфрацрвене спектроскопије и нуклеарне магнетне резонанце чврстог стања. Састав свеже припремљених раствора NH4NO3 и Na2SO4 и састав раствора након излагања узорака геополимера њиховом дејству у одређеном временском периоду анализиран је оптичким емисионим спектрометром са индукованом спрегнутом плазмом. Утврђено је да је утицај раствора NH4NO3 на механичка својства геополимера припремљених од три различита узорка електрофилтерског пепела био је врло сличан. До највећег смањења чврстоће на притисак (14‒23 %) дошло након првих 28 дана испитивања, након чега је уочена стагнација или благо побољшање чврстоће малтера геополимера. Анализе раствора NH4NO3 показале су да је током излагања геополимера дејству раствора дошло до излуживања алкалних (Na, K), земноалкалних (Ca, Mg) елемената и сумпора из структуре геополимера и пораста pH вредности раствора NH4NO3 на око 8. На основу детаљне карактеризације структуре геополимера, закључено је да је излагање узорака геополимера дејству раствора NH4NO3 довело до раскидања Si‒O‒Al веза у структури алумосиликатног гела геополимера. Попуњавање дефеката у структури, насталих раскидањем Si‒O‒Al веза, силицијумом и формирање структуре богатије силицијумом, заслужни су за уочену стагнацију или благо повећање чврстоће геополимера током тестирања у дужем временском периоду. Излагање геополимера дејству раствора Na2SO4 довело је до малог смањења чврстоће на притисак геополимера (око 10 %). До највећег смањења чврстоће на притисак порознијих узорака геополимера дошло је већ после првих 28 дана испитивања, док је у даљем току тестирања уочено повећање чврстоће. У случају малтера геополимера ниже порозности до значајнијег смањења чврстоће дошло је тек после 365 дана испитивања. Испитивање промена у саставу раствора Na2SO4 показале су да је током испитивања узорака геополимера дошло до дифузије сулфатних јона у структуру геополимера и излуживања натријума, калијума и силицијума из структуре у раствор, као и до пораста pH вредности раствора на око 12. На основу резултата испитивања структуре геополимера методама инфрацрвене спектроскопије и нуклеарне магнетне резонанце утврђено је да је смањење чврстоће геополимера током излагања дејству раствора Na2SO4 последица формирања дефеката у структури насталих раскидањем Si‒O‒Si веза и излуживањем Si.Geopolymers based on three different fly ash samples were exposed to concentrated (480 g/dm3) NH4NO3 solution and Na2SO4 solution (50 g/dm3) over a period of 540 days. Mechanical properties of the geopolymer samples were tested after five terms: 28, 90, 180, 365 and 540 days. Changes in the geopolymer structure were investigated using X-ray powder diffraction analysis, scanning electron microscopy, infrared spectrometry and nuclear magnetic resonance (27Al MAS NMR and 29Si MAS NMR). Compositions of NH4NO3 and Na2SO4 solutions were analyzed by optical emission spectroscopy. It was found that the effects of the concentrated NH4NO3 solution on the mechanical properties of the geopolymer samples based on three different fly ash samples were similar. The greatest decrease in compressive strength of the geopolymer samples was observed after the first 28 days of testing (14‒23 %). Analyses of the NH4NO3 solution showed that alkali (Na, K), alkaline earth (Ca, Mg) elements and sulfur were leached from the geopolymer structure, while the pH value of the solution increased to 8. Based on detailed structural characterization of geopolymer samples, it was concluded that exposure of the geopolymer samples to the concentrated NH4NO3 solution caused breaking of Si‒O‒Al bonds in aluminosilicate geopolymer gel. Structural defects formed by breaking of Si‒O‒Al bonds were reoccupied by silicon, forming more siliceous structure, which resulted in the subsequent fluctuation in compressive strength. Treatment with the Na2SO4 solution caused small decrease in compressive strength of the geopolymer samples (about 10 %). The strength of the more porous geopolymer samples decreased after the first 28 days of testing, while subsequent exposure to the sulfate solution caused an increase in strength of the samples. On the other hand, decline in strength of the less porous geopolymer samples was observed after 365 days of testing. Analyses of the sulfate solution showed that, in addition to diffusion of sulfate ions in the geopolymer structure and leaching of Na and K from the structure, treatment of the geopolymer samples with the Na2SO4 solution caused leaching of Si. The pH value of the sulfate solution reached the value of about 12 already after 28 days of testing. Investigation of the geopolymers structure by means of infrared spectroscopy and 29Si MAS NMR showed that exposure of the geopolymer samples to the Na2SO4 solution caused breaking of Si‒O‒Si bonds in aluminosilicate geopolymer gel structure and leaching of Si. Breaking of Si‒O‒Si bonds and formation of structural defects led to the observed strength decrease of the geopolymer samples

Overpotential controls the morphology of electrolytically produced copper dendritic forms

The morphologies of copper dendritic forms obtained in both potentiostatic and galvanostatic regimes of electrolysis with various amounts of the electricity were analyzed by the scanning electron microscopy (SEM) technique. Irrespective of amount of passed electricity, 3D (three dimensional) pine-like dendrites with sharp tips were formed in the potentiostatic regime of electrolysis. On the other hand, the amount of passed electricity had a strong effect on the shape of the 3D pine-like dendrites formed in the galvanostatic regime of electrolysis. Dendrites with sharp tips were formed with smaller amount of passed electricity, while dendrites with globular tips were formed with larger amounts. The change in the shape of the galvanostatically synthesized 3D pine-like dendrites was explained by comparison with copper deposits obtained potentiostatically at overpotentials that corresponded to the final overpotentials during galvanostatic regime of electrolysis for the analyzed amounts of electricity. Based on the similarity of the obtained morphologies at the macro level, it was concluded that the overpotential plays a crucial role in the formation of the electrolytically synthesized dendrites and that the controlled conditions of electrolysis could represent a suitable way for a synthesis of spherical Cu particles by electrolysis

Effect of Milling Time on Mechanical Properties of Anorthite Obtained by Thermal Transformation of Ca-LTA Zeolite

Anorthite ceramics was fabricated from calcium exchanged Na-LTA zeolite. The powder compacts of Ca-LTA zeolite were sintered at different temperatures ranging between 1100 and 1400°C. It was found that the temperature of 1100°C was sufficiently high to trigger formation of anorthite which stayed stable even at temperature as high as 1400°C. The highest relative density and the lowest open porosity were measured in samples sintered at 1200°C for 3 h. The effect of milling time of Ca-LTA zeolite precursor on density, microstructure and mechanical properties of samples sintered at 1200°C for 3 h was investigated. The particle size refinement appeared to be beneficial in accelerating densification process and improving mechanical properties. The density, compressive strength and hardness of anorthite ceramics obtained from non-milled precursor were measured to be 70.5 %TD, 64 MPa and 1.45 GPa, respectively. On the other side the anorthite ceramics obtained from 24-hour-long milled zeolite precursor had density of 83.9 %TD, compressive strength of 101 MPa and hardness of 3.44 GPa

Permanent disposal of Cs ions in the form of dense pollucite ceramics having low thermal expansion coefficient

A promising method for removal of Cs ions from water and their incorporation into stable crystal structure ready for safe and permanent disposal was described. Cs-exchanged X zeolite was hot-pressed at temperature ranging from 800 to 950 °C to fabricate dense pollucite ceramics. It was found that the application of external pressure reduced the pollucite formation temperature. The effect of sintering temperature on density, phase composition and mechanical properties was investigated. The highest density of 92.5 %TD and the highest compressive strength of 79 MPa were measured in pollucite hot-pressed at 950 °C for 3 h. Heterogeneity of samples obtained at 950 °C was determined using scanning electron microscopy. The pollucite hot-pressed at 950 °C had low linear thermal expansion coefficient of ∼4.67 × 10−6 K−1 in the temperature range from 100 to 1000 °C. © 201

Morfologija prahova Ni-Mo-O legura istaloženih elektrohemijskim postupkom iz rastvora amonijum sulfata

The electro deposition of the Ni-Mo-O alloy powders from ammonium sulfate containing electrolytes of different Ni/Mo ions concentration ratios was investigated by the polarization measurements. In all electrolytes similar polarization curves were obtained, characterized by two inflection points Point A, the beginning of the electro deposition process and point B, a moment when the powder electro deposition is controlled by the hydrogen bubbles formation. The morphology of the electrodeposited Ni-Mo-O alloy powders was investigated using SEM. At Ni/Mo ratios higher or equal to 1/1 two types of particles were detected in the powder deposits: spongy-type particles (100 - 200 μm) with flat nodular surface and presence of cavities and agglomerates of similar dimensions characterized by the presence of cracks and cavities, with the nodular surface that is not flat, but is covered by the freshly formed dendrites. At Ni/Mo ratios of 1/3 the contribution of the amorphous-compact deposit is significant, while on top of this deposit rounded dendrite and compact outgrowths were detected.Elektrohemijsko taloženje prahova Ni-Mo-O legura ispitivano je snimanjem polarizacionih dijagrama u sulfatno-amonijačnim elektrolitima pri različitim odnosima Ni/Mo. Sve polarizacione krive okarakterisane su prisustvom dve prelomne tačke (A i B) na dijagramu. Tačka A odgovara početku taloženja Ni-Mo-O legure, dok tačka B reflektuje momenat kada je ukupna elektrohemijska reakcija kontrolisana brzinom formiranja mehurova gasovitog vodonika pri čemu se sa povećanjem koncentracije MoO4 2- jona u elektrolitu potencijal početka taloženja (tačka A) pomera ka negativnijim vrednostima. Morfologija čestica prahova ispitivana je skenirajućom elektronskom mikroskopijom (SEM). Prahovi istaloženi na staklastom ugljeniku iz elektrolita sa Ni/Mo ≥ 1/1 okarakterisani su prisustvom dve vrste čestica: sunđeraste čestice veličine 100 - 200 μm relativno glatkih površina sa jasno izraženim rupama i aglomerati sličnih veličina na kojima su prisutne jasno izražene naprsline i rupe, čija površina nije glatka i pokriveni su novo stvorenim grozdovima dendritičnog taloga. Za čestice praha istaloženog iz elektrolita koji sadrži odnos jona Ni/Mo = 1/3 karakteristično je da je udeo kompaktnog taloga značajan u poređenju sa ostalim prahovima, na kome se mogu registrovati dva tipa loptastih izraslina: manje kompaktne izrasline sa jasno definisanim dendritima i znatno kompaktnije izrasline. Kod prahova istaloženih na elektrodi od Ni, pored vrsta čestica koje su registrovane pri taloženju prahova na elektrodi od staklastog ugljenika, može se videti da se deo kompaktnog taloga praktično sastoji iz slojevitih struktura koje su posledica favorizovanog epitaksijalnog rasta taloga na srodnim podlogama

Morfologija prahova Ni-Mo-O legura istaloženih elektrohemijskim postupkom iz rastvora amonijum sulfata

The electro deposition of the Ni-Mo-O alloy powders from ammonium sulfate containing electrolytes of different Ni/Mo ions concentration ratios was investigated by the polarization measurements. In all electrolytes similar polarization curves were obtained, characterized by two inflection points Point A, the beginning of the electro deposition process and point B, a moment when the powder electro deposition is controlled by the hydrogen bubbles formation. The morphology of the electrodeposited Ni-Mo-O alloy powders was investigated using SEM. At Ni/Mo ratios higher or equal to 1/1 two types of particles were detected in the powder deposits: spongy-type particles (100 - 200 μm) with flat nodular surface and presence of cavities and agglomerates of similar dimensions characterized by the presence of cracks and cavities, with the nodular surface that is not flat, but is covered by the freshly formed dendrites. At Ni/Mo ratios of 1/3 the contribution of the amorphous-compact deposit is significant, while on top of this deposit rounded dendrite and compact outgrowths were detected.Elektrohemijsko taloženje prahova Ni-Mo-O legura ispitivano je snimanjem polarizacionih dijagrama u sulfatno-amonijačnim elektrolitima pri različitim odnosima Ni/Mo. Sve polarizacione krive okarakterisane su prisustvom dve prelomne tačke (A i B) na dijagramu. Tačka A odgovara početku taloženja Ni-Mo-O legure, dok tačka B reflektuje momenat kada je ukupna elektrohemijska reakcija kontrolisana brzinom formiranja mehurova gasovitog vodonika pri čemu se sa povećanjem koncentracije MoO4 2- jona u elektrolitu potencijal početka taloženja (tačka A) pomera ka negativnijim vrednostima. Morfologija čestica prahova ispitivana je skenirajućom elektronskom mikroskopijom (SEM). Prahovi istaloženi na staklastom ugljeniku iz elektrolita sa Ni/Mo ≥ 1/1 okarakterisani su prisustvom dve vrste čestica: sunđeraste čestice veličine 100 - 200 μm relativno glatkih površina sa jasno izraženim rupama i aglomerati sličnih veličina na kojima su prisutne jasno izražene naprsline i rupe, čija površina nije glatka i pokriveni su novo stvorenim grozdovima dendritičnog taloga. Za čestice praha istaloženog iz elektrolita koji sadrži odnos jona Ni/Mo = 1/3 karakteristično je da je udeo kompaktnog taloga značajan u poređenju sa ostalim prahovima, na kome se mogu registrovati dva tipa loptastih izraslina: manje kompaktne izrasline sa jasno definisanim dendritima i znatno kompaktnije izrasline. Kod prahova istaloženih na elektrodi od Ni, pored vrsta čestica koje su registrovane pri taloženju prahova na elektrodi od staklastog ugljenika, može se videti da se deo kompaktnog taloga praktično sastoji iz slojevitih struktura koje su posledica favorizovanog epitaksijalnog rasta taloga na srodnim podlogama

Uticaj režima elektrolize na morfologiju i strukturu dendrita bakra

Comparative analysis of morphological and structural features of copper dendrites obtained by potentiostatic and galvanostatic regimes of electrolysis was made. The 3D (three dimensional) pine-like dendrites composed from stalk and corncob-like forms as branches, with the sharp tips of both stalk and branches, were obtained by the potentiostatic regime of electrolysis with all analyzed amounts of passed electricity. On the other hand, with increasing the amount of the passed electricity the shape of 3D pine-line dendrites obtained by the galvanostatic regime of electrolysis changed than those with the sharp tips of stalk and branches to those which the tips finished globules. Comparing with Cu deposits obtained at overpotentials which belonged to different types of electrodeposition control, it is concluded that overpotential at the end of passed amount of the electricity plays crucial role in the final shape of galvanostatically produced Cu dendrites. Irrespective of the shape of Cu dendrites, crystallites of copper were random oriented in the both types of dendrites.Napravljena je uporedna analiza morfoloških i strukturnih karakteristika dendrita bakra dobijenih potenciostatskim i galvanostatskim režimima elektrolize. Trodimenzionalni (3D) dendriti nalik stablu bora izgrađeni od stabla i grana koje nalikuju klipovima kukuruza, sa oštrim vrhovima, su bili dobijeni potenciostatskim režimom elektrolize sa svim analiziranim količinama propuštenog naelektrisanja. Na drugoj strani, sa povećanjem količine propuštenog naelektrisanja oblik 3D dendrita dobijenih galvanostatskim režimom elektrolize se menjao od onih sa oštrim vrhovima i stalka i grana do onih čiji vrhovi su se završavali globulama. Poređenjem sa talozima bakra dobijenim na prenapetostima koje su pripadale različitim tipovima kontrole procesa elektrohemijskog taloženja, zaključeno je da prenapetost na kraju propuštene količine naelektrisanja igra presudnu ulogu u krajnjem obliku galvanostatski proizvedenih Cu dendrita. Bez obzira na oblik Cu dendrita, kristaliti bakra su bili slučajno orijentisani u oba tipa dendrita.XII YuCorr International Conference, September 13-16, 2021, Tara Mountain, Serbia, [http://sitzam.org.rs/YUCORR/

Morfologija prahova Fe-Ni legura elektrohemijski istaloženih iz citratno-sulfatnih rastvora

The electrochemical deposition of the Fe-Ni alloy powders from citrate-sulfate containing electrolytes of different Ni/Fe ions concentration ratios at pH 4.5 was examined by the polarization measurements. All polarization curves have a similar shape and are characterized by the presence of two inflection points. The first inflection point reflects the beginning of alloy deposition, while the second one (˜) corresponds to the moment when the cathode reaction becomes determined by the rate of hydrogen bubbles formation. The potentials of Fe-Ni alloys deposition at all investigated Ni/Fe ratios are more positive than those for pure metal powders deposition. As the Ni/Fe ratio decreases, the polarization curves are placed at slightly more positive potentials. The morphology of electrodeposited powder particles was investigated using scanning electron microscopy (SEM). A common characteristic of all Fe-Ni alloy powders is the presence of cone shaped cavities. Powder particles electrodeposited at the ratio Ni/Fe = 9/1 are mainly consisted of nodules of either very flat surface or rough surface, with well defined crystals detected only on a few particles. With the decrease of the Ni/Fe ratio, the presence of well defined crystals on the nodule surface becomes more pronounced. In the powder with the highest amount of Fe (Ni/Fe = 1/3), the whole surface of all particles is covered with crystals of different shapes.Elektrohemijsko taloženje prahova Fe-Ni legura ispitivano je snimanjem polarizacionih dijagrama u citratno-sulfatnim rastvorima pri različitom odnosu koncentracija Ni/Fe jona na pH 4,5. Sve polarizacione krive imaju sličan oblik i okarakterisane su prisustvom dve prevojne tačke na dijagramu. Prva prevojna tačka odgovara početku taloženja Fe-Ni legure, dok druga predstavlja momenat kada ukupna elektrohemijska reakcija postaje kontrolisana brzinom formiranja mehurova vodonika. Potencijali taloženja Fe-Ni legura pri svim ispitivanim odnosima Ni/Fe pozitivniji su od potencijala taloženja čistih metala, pri čemu se sa smanjenjem odnosa Ni/Fe polarizacione krive pomeraju ka malo pozitivnijim vrednostima potencijala. Morfologija čestica prahova ispitivana je korišćenjem skenirajuće elektronske mikroskopije (SEM). Zajednička karakteristika svih prahova Fe-Ni legura je prisustvo šupljina konusnog oblika. Čestice praha istaloženog pri odnosu Ni/Fe = 9/1 uglavnom su sastavljene od čvorića, glatke ili neravne površine, kod kojih se na pojedinim mestima mogu uočiti dobro definisani kristali. Sa smanjenjem odnosa Ni/Fe, prisustvo kristala na površini čvorića postaje sve izraženije, dok su kod praha sa najvećim sadržajem Fe (Ni/Fe = 1/3) na celoj površini čestica prisutni kristali različitog oblika

Influence of the Shape of Copper Powder Particles on the Crystal Structure and Some Decisive Characteristics of the Metal Powders

Three different forms of Cu powder particles obtained by either galvanostatic electrolysis or a non-electrolytic method were analyzed by a scanning electron microscope (SEM), X-ray diffraction (XRD) and particle size distribution (PSD). Electrolytic procedures were performed under different hydrogen evolution conditions, leading to the formation of either 3D branched dendrites or disperse cauliflower-like particles. The third type of particles were compact agglomerates of the Cu grains, whose structural characteristics indicated that they were formed by a non-electrolytic method. Unlike the sharp tips that characterize the usual form of Cu dendrites, the ends of both the trunk and branches were globules in the formed dendrites, indicating that a novel type of Cu dendrites was formed in this investigation. Although the macro structures of the particles were extremely varied, they had very similar micro structures because they were constructed by spherical grains. The Cu crystallites were randomly oriented in the dendrites and compact agglomerates of the Cu grains, while the disperse cauliflower-like particles showed (220) and (311) preferred orientation. This indicates that the applied current density affects not only the morphology of the particles, but also their crystal structure. The best performance, defined by the largest specific surface area and the smallest particle size, was by the galvanostatically produced powder consisting of disperse cauliflower-like particles

Morfologija prahova Fe-Ni legura elektrohemijski istaloženih iz citratno-sulfatnih rastvora

The electrochemical deposition of the Fe-Ni alloy powders from citrate-sulfate containing electrolytes of different Ni/Fe ions concentration ratios at pH 4.5 was examined by the polarization measurements. All polarization curves have a similar shape and are characterized by the presence of two inflection points. The first inflection point reflects the beginning of alloy deposition, while the second one (˜) corresponds to the moment when the cathode reaction becomes determined by the rate of hydrogen bubbles formation. The potentials of Fe-Ni alloys deposition at all investigated Ni/Fe ratios are more positive than those for pure metal powders deposition. As the Ni/Fe ratio decreases, the polarization curves are placed at slightly more positive potentials. The morphology of electrodeposited powder particles was investigated using scanning electron microscopy (SEM). A common characteristic of all Fe-Ni alloy powders is the presence of cone shaped cavities. Powder particles electrodeposited at the ratio Ni/Fe = 9/1 are mainly consisted of nodules of either very flat surface or rough surface, with well defined crystals detected only on a few particles. With the decrease of the Ni/Fe ratio, the presence of well defined crystals on the nodule surface becomes more pronounced. In the powder with the highest amount of Fe (Ni/Fe = 1/3), the whole surface of all particles is covered with crystals of different shapes.Elektrohemijsko taloženje prahova Fe-Ni legura ispitivano je snimanjem polarizacionih dijagrama u citratno-sulfatnim rastvorima pri različitom odnosu koncentracija Ni/Fe jona na pH 4,5. Sve polarizacione krive imaju sličan oblik i okarakterisane su prisustvom dve prevojne tačke na dijagramu. Prva prevojna tačka odgovara početku taloženja Fe-Ni legure, dok druga predstavlja momenat kada ukupna elektrohemijska reakcija postaje kontrolisana brzinom formiranja mehurova vodonika. Potencijali taloženja Fe-Ni legura pri svim ispitivanim odnosima Ni/Fe pozitivniji su od potencijala taloženja čistih metala, pri čemu se sa smanjenjem odnosa Ni/Fe polarizacione krive pomeraju ka malo pozitivnijim vrednostima potencijala. Morfologija čestica prahova ispitivana je korišćenjem skenirajuće elektronske mikroskopije (SEM). Zajednička karakteristika svih prahova Fe-Ni legura je prisustvo šupljina konusnog oblika. Čestice praha istaloženog pri odnosu Ni/Fe = 9/1 uglavnom su sastavljene od čvorića, glatke ili neravne površine, kod kojih se na pojedinim mestima mogu uočiti dobro definisani kristali. Sa smanjenjem odnosa Ni/Fe, prisustvo kristala na površini čvorića postaje sve izraženije, dok su kod praha sa najvećim sadržajem Fe (Ni/Fe = 1/3) na celoj površini čestica prisutni kristali različitog oblika