Crystallization Of Leucite Research Articles

Characterization of the Evolution with Temperature of the Structure and Properties of Geopolymer-Cordierite Composites

This work is part of a research project aimed at producing ceramic-like materials, without the need for an initial sintering, for potential applications in catalysis or filtration at temperatures up to 1000 °C. In that context, cordierite-derived materials were prepared from recycled cordierite powder (automotive industry waste) bonded with metakaolin-potassium silicate geopolymer. The principle is that these materials, prepared at temperatures below 100 °C, acquire their final properties during the high-temperature commissioning. The focus is on the influence of the K/Al ratio and cordierite fraction on the stability of the dimensions and porosity during heating at 1000 °C, and on the final Young’s modulus and coefficient of thermal expansion. Conventional and high-temperature XRD evidenced the absence of crystallization of the geopolymer binder and interaction with the cordierite filler during the heating stage when K/Al = 1 or 0.75. By contrast, crystallization of kalsilite and leucite, and diffusion of potassium ions in the structure of cordierite is evidenced for K/Al = 1.5 and 2.3. These differences strongly influence the shrinkage due to sintering and the final properties. It is shown that a K/Al ratio of 0.75 or 1 is favorable to the stability of the porosity, around 25 to 30%. Moreover, a low coefficient of thermal expansion of 4 to 4.5 × 10−6 K−1 and a Young’s modulus of 40 to 45 GPa is obtained.

The geochemistry of leucite-bearing lavas from early stages of the Somma-Vesuvius volcanic complex: Feeder systems and mantle enrichment processes in the Neapolitan district of the Roman Magmatic Province

The lavas of the Mt. Somma volcanic epoch were erupted during the early stage of the Somma-Vesuvius volcanic complex. These lavas are mildly differentiated with the presence of plagioclase-clinopyroxene-olivine- ± leucite-bearing rocks (leucite tephrites, leucite-bearing shoshonites, latites), also characterized by low in MgO, Cr and Ni, with a Sr-Nd-isotope range (87Sr/86Sr = 0.706865–0.707861; 143Nd/144Nd = 0.51244–0.51258) that overlaps with lavas of the late stage Vesuvius erupted after 1631 CE (late stage of the Somma-Vesuvius volcanic complex). Differentiation is dominated by closed-system processes, with fractional crystallization of clinopyroxene, calcic plagioclase, olivine, magnetite, and leucite. Open-system differentiation processes are subordinate and associated with limited interaction with crustal rocks. Oxygen isotopes on clinopyroxene and olivine phenocrysts (δ18O = 6.5–7.9 ‰) are higher than typical uncontaminated mantle magmas, suggesting a crustal contribution to the melt. Although open-system assimilation + fractional crystallization certainly took place, this process alone does not adequately reproduce the chemical and isotopic composition of the Mt. Somma ultrapotassic magmas. Therefore, a contribution from a recycled crustal component in the mantle source is required, but probably dominated by sediment-derived fluids and melts. The Mt. Somma lavas are characterized by distinctly different geochemical features compared to the mafic products of the neighboring volcanic areas (i.e., Phlegrean, Procida and Ischia volcanic fields), where the recycled crustal component is less pronounced.

High temperature behavior of sodium and potassium volcanic ashes-based alkali-activated materials (Mt. Etna, Italy)

Thermal performances at 1000 °C of volcanic ash-based alkali-activated materials by both sodium or potassium solutions have been tested. Once defined the feasibility for the potassium set, a multidisciplinary characterization including spectroscopic, thermal, mechanical, diffractometric before and after treatment and dilatometric analyses was applied. The formation kinetics of different networks was evaluated. A correlation between the high mechanical properties and the least amount of water was observed in non-treated samples. Treated samples at 1000 °C showed higher compressive strengths due to the crystallization of wollastonite, leucite and nepheline. Thermal stability was observed increased with the solid content in the potassium-based formulations.

The effect of fluxing agents and heat treatment on the leucite crystallization in bio glass–ceramic composites

The effect of fluxing agents and heat treatment on the leucite crystallization in bio glass–ceramic composites

Formation of ceramics from K-activated FeOx-(Al2O3)-SiO2 inorganic polymers: Effect of Al/K and Si/K molar ratio

The high-temperature transformations and crystallization of K-based inorganic polymers made from FeO-SiO2 and FeO-SiO2-Al2O3 iron-rich model slags were investigated, with particular focus on the effect of the Al/K and Si/K molar ratios. Upon firing to 1100 °C, the main crystalline phases were hematite and (iron) leucite. Addition of corundum decreases the crystallization rate of leucite. Increasing the Al/K molar ratio increased the thermal stability due to the substitution of Al3+ for Fe3+ in leucite. The Si/K molar ratio impacted the crystallization of leucite. Upon firing to 1100 °C and 1350 °C there was a linear correlation between the amount of leucite and the Si/K molar ratio. Higher Si/K molar ratio resulted in ceramics with higher glass content and lower thermal stability. Thus, the phase assemblage can be adjusted by changing the amount of activator.

Enhanced mechanical and thermal properties of fly ash-based geopolymer composites by wollastonite reinforcement

The present study investigated the mechanical and thermal properties of geopolymer composite. The geopolymer composite was prepared by mixing fly ash and wollastonite with the alkaline activator, which was 6 M KOH:K2SiO3 in a mass ratio of 1:1 and a solid:liquid mass ratio of 3:2. The compressive strength at 28 days of geopolymer was 33.3 MPa and possessed the highest strength of 38.3 MPa when 30 wt% wollastonite was added. The flexural strength presented differently whereby it increased from 2.1 MPa to 6.8 MPa. It increased remarkably up to 200% with the addition of 50 wt% wollastonite. The geopolymer composites were exposed to high temperatures at 800℃ to 1100°C for 2 h. Cracks were reduced since 20 wt% wollastonite was added. A high percentage of wollastonite presented excellent thermal stability. The total weight loss of the geopolymer composite at temperatures of 30℃ to 1400°C was minimized. It decreased from 25% to 12% when 50 wt% wollastonite was added, and the dilatometric data resulted in a dimensional change of almost zero. The phase development of the geopolymer composites at high temperatures showed the crystallization of leucite, kalsilite, calcium silicate, calcium aluminium silicate, and calcium aluminium oxide, which were the high temperature stable phases. The results indicated that wollastonite reinforced fly ash-based geopolymer composites are promising for use in high temperature applications.

Microstructure Evolution Mechanism of Geopolymers with Exposure to High-Temperature Environment

The investigation on geopolymers has intrigued broad interests in the past decades, due to the requirements for the recycling of aluminosilicate solid wastes, such as red mud, slags, sludges and demolished concrete. Previous studies have demonstrated the feasibility of reusing this Aluminosilicate as a resource to prepare cementitious materials and indicated their promising properties at ambient temperature. However, when this material was exposed to high temperatures, especially above 1000 °C, the microstructure evolution mechanisms were not systematically investigated. In this study, the microstructural evolution process of metakaolin-based K geopolymer (molar ratio of K:Al:Si was 1:1:4) is investigated. The crystalized leucite originated from the geopolymer precursor was detected above 1000 °C. The SEM results indicate that the microstructure of the geopolymer before heating was composed of non-reacted metakaolin with a typical layered structure and reacted amorphous binder phase. As the geopolymer heated to 1000 °C, the microstructure of the geopolymer changed to a porous structure with an average pore size from 10 to 30 μm. When the heating temperature reached 1100 °C, the pores started to close along with the leucite crystallization process. As the heating temperature reached 1200 °C, most of the pores were closed. The TEM results show that the microstructure of the geopolymer, after being heated to 1400 °C, was composed of an amorphous glassy phase and crystallized leucite phase. The crystallized leucite grains originated from the nano-sized crystal nuclei, with an average size of 2–3 nm. The TEM-EDS results indicate that the chemical composition of the glassy phase was complicated. It varied from area to area because of the movement and uneven distribution of K.

Uncommon K-foiditic magmas: The case study of Tufo del Palatino (Colli Albani Volcanic District, Italy)

Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the aH2O < 1 and high CO2 activity in the melt, as testified by the CO3 in the clinopyroxene melt inclusions, by the early crystallization of CO3-bearing apatite and by the high CO2 activity in the free volatile phase that led to crystallization of calcium carbonate in the scoria clast vesicles. The K-foiditic magmas plot on the Cpx + Lc + melt divariant surface of the Ol-Cpx-Lc-Mel-H2O-CO2, P ≥ 0.2 GPa and T ≤ 1100 °C. The assimilation of cold carbonate by hot magmas is an important open-system process allowing the establishment of aH20 < 1 condition in the volatile-rich, Colli Albani magma chambers where the stability fields of the olivine and phlogopite are reduced in favor of clinopyroxene and leucite. Trace element modelling indicates large amount of carbonate assimilation (~12.4 wt%) involved in the differentiation process that origins the K-foiditic magmas starting from a K-rich, phonotephritic parental magma. The large amount of assimilate carbonate is consistent with the peculiar distribution of the latent heat across the crystallization interval of the phonotephritic parental magma. The isenthalpic assimilation process is very efficient in the phonotephritic magma because the crystallization of clinopyroxene and leucite in equilibrium with a K-foiditic melt proceeds over a relatively large temperature interval (>200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district.

Microstructural Characterization and Microhardness of Leucite Glass-Ceramics Synthesized from Sarawak Sand Reserves.

The purpose of this study was to evaluate the effect of varying the sintering temperature and holding time on the crystallization and microhardness of the SiO2 – Al2O3 –K2O glass system using SiO2 from Sarawak sand reserves. A starting glass composition of SiO2 (from Sarawak sand), Al2O3, K2O, Na2O, CaO, LiO and TiO2 was prepared by conventional melt quenching technique followed by ball milling. The glass powder was pressed under pressure into disk-shaped compacts with 2 mm thicknesses and 14 mm diameters. The samples were then subjected to differing heat treatment schedules of 750°C, 800°C and 850°C with 1, 3 and 6 hours holding times. They were characterized by X-ray Diffraction (XRD), Scanning electron microscopy (SEM) and Vickers microhardness. XRD showed the crystallization of tetragonal leucite with minor secondary sanidine phases. SEM showed the formation irregular shaped and non-uniformly dispersed crystals. The hardness values showed an increasing trend with longer holding time at temperatures of 750°C and 800°C. This pattern was inversed for sintering temperature 850°C. In conclusion, sintering temperatures and holding time combinations influenced the crystallization and microhardness values of leucite glass ceramics produced from Sarawak sand silica.

Electrical conductivity and thermal analyses studies of phase evolution in the illite – CaCO3 system

Mixture of a purified illitic clay (>90 wt% of illite, Northeastern Hungary) and CaCO3, in laboratory grade, was studied with respect to the high-temperature crystallization of anorthite and leucite mineral phases. The prepared samples were subjected to thermal analyses – differential scanning calorimetry (DSC) and thermodilatometry (DIL), and microstructure was characterized by scanning electron microscopy. The phase composition of the samples after firing was determined by the help of XRD measurement. Among anorthite and leucite (which were present as dominant mineral phases), gehlenite was found in the fired samples. Crystallization temperatures were determined from DSC peaks (940 °C and 1070 °C for gehlenite/anorthite and leucite crystallization, respectively). The samples exhibited a steep contraction as the low-viscosity glassy phase appeared and the anorthite/gehlenite started to crystallize. The crystallization temperatures were confirmed by the temperature dependence of the loss tangent, which exhibited two maxima at 940 °C and 1070 °C. Thus, during crystallization, the contribution of the ions to the conductivity was hindered by their cooperative migration to occupy new sites.

Microstructure and mechanical properties of tabular alumina composites with geopolymer binder at elevated temperatures

Alumina/geopolymer refractory composite was prepared using tabular alumina aggregates and metakaolin with micro silica and potassium hydroxide. The effect of different sized tabular alumina particles on the castables microstructure and mechanical properties has been evaluated. The composition was with 75 vol% tabular alumina and 25 vol% geopolymer as binder exhibited high mechanical strength at ambient temperature. By increasing temperatures, significant change happens in microstructure, strength and observation of dislocations in the composite. Liquid sintering initiated collapse of pores, strong bonds among particles and densification of the composites which are up to 1000 °C. The crystallization of leucite was observed in samples which are heated in 1200 °C. However, the residual stresses in the specimens due to the mismatch of thermal expansion of components (liquid phase, leucite and tabular alumina) diminished the strength at 1200 °C and transgranular fracture observed in some aggregates.

Formation Conditions of Leucite-Bearing Lavas in the Bolsena Complex (Vulsini, Italy): Research Data on Melt Inclusions in Minerals

Abstract—A melt inclusion study was carried out in the leucite-bearing tephriphonolite and phonolite lavas of the Bolsena complex in order to obtain direct data on the chemical composition of initial melts, their evolution, and their crystallization temperatures. It has been found that the initial melt for the considered rocks was of tephrite–basanite composition. Its crystallization began with the formation of clinopyroxene phenocrysts at 1205–1100 °C, then leucite and plagioclase crystallization took place at about 1120 °C and 1080–1060 °C, respectively. The initial tephrite–basanite melt was slightly enriched in volatile components (H2O, F, SO3, and Cl). During the crystallization of clinopyroxene, leucite, and plagioclase, the composition of the initial magma changed toward an increase in the contents of SiO2, Al2O3, and K2O and a decrease in the contents of FeO, MgO, and CaO, i.e., evolved toward phonolite. A similar evolution trend is typical of alkaline basic systems. The tephrite–basanite melt was probably the product of the crystallization differentiation of the parental mantle magma similar in composition to the leucite-bearing tephrite–basanite of the Montefiascone complex.

Geologia, Petrologia e Evolução Magmática das Rochas Alcalinas Félsicas da Ilha de Vitória, São Paulo, Brasil

This paper presents geological, petrographic, geochemical characteristics and radiometric ages for the felsic alkaline rocks of the Vitoria Island Intrusive Complex, Sao Paulo State, Brazil, and discusses its geochemical evolutionary processes. This intrusive body is about 3 km in diameter and the emerged island areas correspond to its northeastern border. The main intrusion is constituted by nepheline syenite at the central zone, nepheline-bearing syenite at the outer zone, syenite at the border, and quartz syenite at the contact zone with alkali feldspar represented by orthoclase. Clinopyroxene vary from hedenbergite, soda-augite to aegirine-augite, and some crystals have resorption shape and amphibole reaction rim. They are intruded by phonolite, trachyte and lamprophyre dykes. Based on the intrusion relation, the dykes are subdivided into two generations: the first one encompass a radial system and the second a parallel system with NE-SW orientation and sinistral displacement. The alkaline rocks vary from silica undersaturated to oversaturated, show peralkaline to peraluminous compositions and belong to the potassic series. The K-Ar ages for amphibole of the nepheline-bearing syenite and syenite are 89.58 ± 3.18 Ma and 84.35 ± 3.92 Ma, respectively. The rocks are strongly fractionated with high differentiation index (DI) of 88.15 in average, indicating mafic minerals fractionation. K 2 O/(K 2 O+Na 2 O) ratios are low, in average 0.51, in accordance to crystallization of pseudo leucite and potassic feldspar the last observed in thin sections.

Bending strength and reliability of porcelains used in all-ceramic dental restorations

Abstract Four dental porcelains for covering zirconia were sintered (fired) at 910-960 °C and characterized, focusing in analyzing reliability, physical and mechanical properties. Samples with relative density close to 99% presented leucite crystallization apart from residual amorphous phase. Hardness between 491±23 and 575±32 HV was different among all ceramics. Fracture toughness between 1.13±0.11 and 1.42±0.25 MPa.m1/2 was statistically different. Bending strength results were not different for three porcelain groups (73±9 to 75±12 MPa), with the exception of one specific group (62±4 MPa). Weibull analysis indicated bending strength between 73 and 75 MPa, Weibull modulus (m) between 5.7 and 7.1, while the ceramic with strength of 60 MPa presented m=13.6. The use of classical theory of fracture mechanics associated to the results of properties obtained in this work indicated the critical failure size in these ceramics lays between 65 and 90 μm and the theoretical fracture energy of porcelains is approximately from 10.5 to 16.3 J/m. It was concluded that the porcelains had different behavior, and it seems that there is no clear relationship among the studied properties.

Crytallization and Properties of SiO&lt;sub&gt;2&lt;/sub&gt;-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-K&lt;sub&gt;2&lt;/sub&gt;O-ZrO&lt;sub&gt;2&lt;/sub&gt; Glass-Ceramics for Dental Applications

The aim of the study was to investigate the influence of ZrO2 on the crystallization and properties of leucite phase from K2O -Al2O3- SiO2 glass-forming melts. A starting glass composition of weight %; 60.7-63.2% SiO2, 16.6% Al2O3, 11.6% K2O, 5.10% Na2O, 2.5-5.0% ZrO2, 0.5% TiO2 and 0.5% LiO2 was melted in an electric furnace, followed by quenched in cool water to produce glass frit. Malaysian silica sand from Terengganu was used as the SiO2 source. The glass powders were ball milled and compressed to form 13mm diameter discs using cool isostatic pressing. The discs were sintered at 650°C, 700°C, 750°C, 800°C and 850°C for 1 hour and characterised using X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The results indicate that the amount of ZrO2 additive is one of the key factors controlling of leucite crystallization. The properties of sintered disc specimens were studied using three point bending, diametral and Vickers microhardness test. The results showed that the mechanical properties of leucite glass-ceramics increased as the amount of ZrO2 was increased.

Effect of process parameters on the physical properties of porous geopolymers obtained by gelcasting

Open cell geopolymer foams with a total porosity as high as 80vol% were produced by gelcasting, and the effect of processing (mixing speed, amount and type of surfactant) on some physical properties of the components was investigated. The data show that, as expected, the permeability increased while the compression strength decreased with increasing the amount of open porosity. No great statistically significant difference could be observed when using either one of the surfactants, but we can suggest that the use of Tween 80 as a surfactant is more amenable to the formation of interconnected cell structures and high levels of total porosity. The gas permeability data indicate that these foams perform similarly to granular filters and other ceramic foams produced by gelcasting. Heating the geopolymer foams to intermediate (700°C) or high (1200°C) temperature reduced the specific surface area, the total and the open porosity, due to the crystallization of leucite and partial viscous sintering.

Effects of flux concentrations and sintering temperature on dental porcelain

In this study, samples of dental porcelain bodies have been made by using the materials collected from selected deposits employing different mixing proportions of clay, quartz and feldspar. Dental porcelain ceramics have been successfully fabricated by using the sintering technique together with some Na 2 CO 3 additive. The dental porcelain powder has been pressed into pellets at first and subsequently sintered at 700, 800, 900, 1000 and 1100 °C for 2 h. The physical and mechanical properties of the prepared samples have been investigated. The sintering behavior of the fired samples has been evaluated by bulk density, linear shrinkage, water absorption and apparent porosity measurements. This study includes the evaluation of the Vickers’s microhardness by microhardness tester. Phase analysis and microstructural study have been performed by XRD and optical microscope respectively. Optical properties have been investigated using UV-visible spectroscopy. Influence of firing conditions on leucite formation, densification and microstructural development of the sintered samples has been investigated. It has been found that the choice of sintering temperature is one of the key factors in controlling leucite crystallization in dental porcelain ceramics. It has also been found that the flux concentration of material and the effect of temperature on preparation of dental porcelain contribute to the firing shrinkage and hardness, which has been found to increase with the increase of treatment temperature.

Conduit- to Localized-scale Degassing during Plinian Eruptions: Insights from Major Element and Volatile (Cl and H2O) Analyses within Vesuvius AD 79 Pumice

Textural investigations of the AD 79 Vesuvius pumice emphasize the complexity of magma degassing and crystallization during the eruption, which emitted two types of pumice (white and gray) associated with different magma bodies of phonolitic and tephriphonolitic compositions respectively. These studies proposed that velocity gradients caused spatial variations in degassing within the ascending magma column at both the conduit and the localized scale. To validate this hypothesis, analyses of volatiles (Cl, H2O) and major elements in pumice glasses and melt inclusions were performed using high spatial resolution tools (microRaman spectrometry and electron microprobe) and combined with major element and volatile concentration profiles and maps. The results indicate that the melt phase differentiated through degassing-induced crystallization of leucite, and that the gray pumice magma was efficiently homogenized prior to degassing. Because Cl diffuses more slowly than H2O during fast ascent, it behaves as an incompatible element and can be used as a tracer of crystallization and H2O degassing. We emphasize the importance of strain localization in generating zones of preferential exsolution and permeable pathways for gases, and establish degassing scenarios that incorporate the effects of shear-zones.

In Situ Mechanical Properties of Chamotte Particulate Reinforced, Potassium Geopolymer

Geopolymers are an inorganic polymeric material composed of alumina, silica, and alkali metal oxides. Monolithic geopolymer is brittle and susceptible to dehydration cracking at elevated temperatures. The addition of a reinforcing phase not only improves strength and toughness but also maintains the structural integrity of the material at elevated temperatures. For this study, potassium‐based geopolymer (KGP) is reinforced with varying weight percent of chamotte particles. Chamotte is kaolinite grade clay calcined at 1350°C to produce 38% crystalline mullite, as well as metastable cristobalite and quartz. The chemical composition of the chamotte is almost identical to that of the metakaolin used to create the geopolymer, however, its crystalline nature prevents reactivity with the caustic potassium silicate solution and it remains as a particulate reinforcement. Flexural strength is evaluated at room temperature and in situ at elevated temperatures to just below the leucite crystallization temperature. Reinforcement with 25 wt% chamotte has shown a two‐fold increase in room‐temperature flexural strength. Flexural strength is also evaluated at room temperature after heating above the leucite crystallization temperature to determine if the chamotte aids in maintaining structural integrity during the volumetric contraction and destructive transformation from cubic to tetragonal symmetry upon forming leucite.

Fabrication of Superfine Leucite‐Reinforced Dental Material by Hydrothermal Precursor and Low‐Temperature Frit

A superfine leucite‐reinforced dental material was prepared by heat‐treating the mixture of hydrothermally derived leucite precursor and low‐temperature frit at 750°C. XRD and DSC results indicate that the low‐temperature frit can lower leucite crystallization temperature from 1027°C to 694°C. High‐temperature X‐ray diffraction of the dental porcelain demonstrates that there exists a temperature range in which leucite crystals are in the equilibrium of forming, ripening, and dissolving, and the size and content of leucite remain almost unchanged in the range. The average size of leucite in the dental porcelain prepared by the mixture of low‐temperature frit and the material is about 115 nm, which would benefit PFM's strength.