Stages Of Crystallization Research Articles

Porosity Formation in Thin Welded Joints of Al-MG-LI Alloys.

This work is about the study of the correlation of pore formation in welded joints of Al–MG–LI alloy with zirconium additives with the state of the base metal, thermal vacuum treatment, and welding technologies MIG and EBW. Metallographic analysis has been carried out, the phase composition of the alloy and weld metal has been investigated, and thermal cycles of welding have been calculated, allowing to estimate the residence time of metal in the alloying zone and weld metal in the liquid state. The nature of the allocation of strengthening fine-dispersed phases in the welded joints of the alloy has been determined. The regularity and character of pore formation in welded joints depending on the applicable thermal vacuum treatment (TVT) and welding technology have been revealed. It was established that TVT with subsequent hardening and aging has no effect on the phase composition of the alloy. However, this type of treatment contributes to the formation of a more homogeneous and uniform nature of the separation of fine-dispersed strengthening phases. It was revealed that the MIG technology (metal with and without TVT) is characterized by a large length of the fusion zone, the high residence time of metal in the fusion zone and weld metal in the liquid state, and the formation of pores. Phase formation in the temperature range of the beginning and end of the alloy crystallization occurs not only in the weld at the final stage of crystallization but also in the fusion zone, which may induce pore formation, whereas EBW welding shows the opposite trend and no pores. It was found that EBW technology prevents pore formation and makes it possible to obtain welded joints of 1420 Al alloys of the required quality.

Influence of annealing on mechanical properties of alloys of Al-REM-Ni(Fe)

Have been investigated the influence of annealing on the physicochemical properties of amorphous alloys based on aluminum. It has been established that: after annealing during 5, 15, 30, 45, 60 min at the temperature of the third stage of crystallization, an X-ray amorphous structure with an insignificant volume fraction of a disordered nanocrystalline phase forms. The temperature of annealing was determined from DSC-curves. In structural transformations under these conditions, the microhardness of the alloys increases to a maximum degree in these conditions. The optimal time limits of time heat treatment to improve the physicochemical properties of aluminum-based AMAs have been established.

GEOCHEMICAL CHARACTERISTICS OF THE MAIN ROCKS TYPES OF THE KORSUN'-NOVOMYRHOROD ANORTHOSITE-RAPAKIVI GRANITE PLUTON

The geochemical features of most distributed rocks from the Korsun'-Novomyrhorod Pluton are considered. The obtained data give reason to assume that the association of basic and intermediate rocks of the pluton was formed because of the differentiation of the primary melt, similar in composition to high alumina tholeiites. It can be inferred that anorthosites were the earliest rocks that appeared in the early stages of plagioclase crystallization. The chondrite-normalized patterns of REE from anorthosites are characterized by the classical distribution of REE for such rocks, with significant positive Eu-anomalies at low REE concentrations. Further evolution of the residual melts enriched by mafic components could lead to the formation of gabbro-anorthosites. Less distributed gabbronorites and norites were formed because of crystallization of residual melts after segregation of anorthositic and gabbro-anorthositic cumulates. Considering the high iron content in all types of rocks, the basic rocks crystallized from residual melts that were genetically related to anorthosites. But ore-bearing norites (Nosachiv-type), in contrast to most distributed basic rocks, had been formed in the early stages because of simultaneous accumulation of feldspar and ilmenite, followed by gravitational precipitation at lower levels of magmatic chambers. The genesis of monzonite-syenite rocks is more enigmatic. Their geochemical features very resemble those in gabbroic rocks, which gives reason to consider them as a result of residual melts crystallization after escaping from anorthositic and gabbronoritic bodies. Subsequent migration and protracted differentiation of such K-enriched melts could cause the appearance of the high-Fe syenites of the Velyka Vyska-type, enriched in REE, Y, Zr, partially Nb, and depleted in Sr and Ba. Although the geochemical characteristics of rapakivi show significant similarities to monzonitic rocks, their genesis remains problematic. It's worth noting that our findings are more consistent with continental crust melting caused by ascending intrusions of basic composition.

GEOCHEMICAL CHARACTERISTICS OF THE MAIN ROCKS TYPES OF THE KORSUN'-NOVOMYRHOROD ANORTHOSITE-RAPAKIVI GRANITE PLUTON

The geochemical features of most distributed rocks from the Korsun'-Novomyrhorod Pluton are considered. The obtained data give reason to assume that the association of basic and intermediate rocks of the pluton was formed because of the differentiation of the primary melt, similar in composition to high alumina tholeiites. It can be inferred that anorthosites were the earliest rocks that appeared in the early stages of plagioclase crystallization. The chondrite-normalized patterns of REE from anorthosites are characterized by the classical distribution of REE for such rocks, with significant positive Eu-anomalies at low REE concentrations. Further evolution of the residual melts enriched by mafic components could lead to the formation of gabbro-anorthosites. Less distributed gabbronorites and norites were formed because of crystallization of residual melts after segregation of anorthositic and gabbro-anorthositic cumulates. Considering the high iron content in all types of rocks, the basic rocks crystallized from residual melts that were genetically related to anorthosites. But ore-bearing norites (Nosachiv-type), in contrast to most distributed basic rocks, had been formed in the early stages because of simultaneous accumulation of feldspar and ilmenite, followed by gravitational precipitation at lower levels of magmatic chambers. The genesis of monzonite-syenite rocks is more enigmatic. Their geochemical features very resemble those in gabbroic rocks, which gives reason to consider them as a result of residual melts crystallization after escaping from anorthositic and gabbronoritic bodies. Subsequent migration and protracted differentiation of such K-enriched melts could cause the appearance of the high-Fe syenites of the Velyka Vyska-type, enriched in REE, Y, Zr, partially Nb, and depleted in Sr and Ba. Although the geochemical characteristics of rapakivi show significant similarities to monzonitic rocks, their genesis remains problematic. It's worth noting that our findings are more consistent with continental crust melting caused by ascending intrusions of basic composition.

Nanocrystallization of amorphous alloy Al87Ni8Dy5 induced by heat treatment

The aim was to investigate the characteristics of the short-range structure and the nanocrystallization kinetics of amorphous alloys in the heat treatment of amorphous alloys. On the basis of X-ray research it is established that at the first stage of primary crystallization (418–465 K) there is a simultaneous nucleation and three-dimensional growth of Al-nanocrystals. Within temperature range 465–580 K the probability that new Al - nuclears are created significantly decreases due to that amorphous phase is enriched with Ni and Dy atoms and the diffusion controlled growth of Al-nanocrystals is the main contribution into kinetics of transformation.

Injection of enriched lithospheric mantle magmas explains the formation of microgranular enclaves in the Rio Jacaré Batholith, Borborema Province, Brazil

The Rio Jacaré Batholith (RJB; 617 ± 4 Ma) is inserted in the Poço Redondo Domain, Sergipano Orogenic System. This batholith is formed by monzodiorite, quartz monzodiorite, monzonite, and quartz monzonite, with abundant microgranular enclaves (MEs). The MEs vary from black to light gray and exhibit globular to slightly elongated shapes with clear-cut, crenulated, and cuspate, or, more rarely, diffuse contacts. They correspond to diorites, monzodiorites, quartz monzodiorites, and monzonites, and textural features indicate mixing of magmas, such as compositional zoning in plagioclase, inclusion zones in plagioclase phenocrysts, poikilitic alkali feldspar, acicular apatite, and ocellar quartz. Calculations of linear correlations of major elements showed that the smallest fraction of mafic magma involved in the mixing was 0.43. MEs represent the breakdown and cooling of a mafic magma that was injected into a cooler felsic magmatic chamber. Emplacement of this mafic magma occurred at different stages of crystallization of the RJB magmatic chamber. The MEs are magnesian and metaluminous, with affinity to the shoshonitic series. Ratios for Ba/Nb (> 23), Ba/La (> 15), and Nb/La (0.22–0.69) are characteristic of magmas generated from partial melting of an enriched lithospheric mantle source. Batch melting modeling suggests that source melting rates of less than 3% are necessary to generate magmas similar to those of the RJB MEs.

The Zn, S, and Cl isotope compositions of mare basalts: Implications for the effects of eruption style and pressure on volatile element stable isotope fractionation on the Moon

AbstractWe compare the stable isotope compositions of Zn, S, and Cl for Apollo mare basalts to better constrain the sources and timescales of lunar volatile loss. Mare basalts have broadly elevated yet limited ranges in δ66Zn, δ34S, and δ37ClSBC+WSC values of 1.27 ± 0.71, 0.55 ± 0.18, and 4.1 ± 4.0‰, respectively, compared to the silicate Earth at 0.15, –1.28, and 0‰, respectively. We find that the Zn, S, and Cl isotope compositions are similar between the low- and high-Ti mare basalts, providing evidence of a geochemical signature in the mare basalt source region that is inherited from lunar formation and magma ocean crystallization. The uniformity of these compositions implies mixing following mantle overturn, as well as minimal changes associated with subsequent mare magmatism. Degassing of mare magmas and lavas did not contribute to the large variations in Zn, S, and Cl isotope compositions found in some lunar materials (i.e., 15‰ in δ66Zn, 60‰ in δ34S, and 30‰ in δ37Cl). This reflects magma sources that experienced minimal volatile loss due to high confining pressures that generally exceeded their equilibrium saturation pressures. Alternatively, these data indicate effective isotopic fractionation factors were near unity.Our observations of S isotope compositions in mare basalts contrast to those for picritic glasses (Saal and Hauri 2021), which vary widely in S isotope compositions from –14.0 to 1.3‰, explained by extensive degassing of picritic magmas under high-P/PSat values (>0.9) during pyroclastic eruptions. The difference in the isotope compositions of picritic glass beads and mare basalts may result from differences in effusive (mare) and explosive (picritic) eruption styles, wherein the high-gas contents necessary for magma fragmentation would result in large effective isotopic fractionation factors during degassing of picritic magmas. Additionally, in highly vesiculated basalts, the δ34S and δ37Cl values of apatite grains are higher and more variable than the corresponding bulk-rock values. The large isotopic range in the vesiculated samples is explained by late-stage low-pressure “vacuum” degassing (P/PSat ~ 0) of mare lavas wherein vesicle formation and apatite crystallization took place post-eruption. Bulk-rock mare basalts were seemingly unaffected by vacuum degassing. Degassing of mare lavas only became important in the final stages of crystallization recorded in apatite—potentially facilitated by cracks/fractures in the crystallizing flow. We conclude that samples with wide-ranging volatile element isotope compositions are likely explained by localized processes, which do not represent the bulk Moon.

Nature and crystallization stages of spherulites within the obsidian: Acıgöl (Cappadocia- Nevşehir, Turkey)

The study area comprises a part of the Central Anatolian Cenozoic volcanism within the Cappadocia Volcanic Province (CVP). Obsidian, perlite rhyolite flows, and volcanic ashes are observed in the study area and the spherulites within the obsidian are the objects of this study. The spherulites occupied within the obsidian in the form of round nodules 0.5-10 cm in diameter. The confocal Raman spectra of feldspar minerals within the spherulites are characterized by T-O-T and M-O lattice modes in the range of 100-250 cm-1, O-T-O deformation and T-O-T lattice modes in the range of 250-350 cm-1, and O-T-O stretch and O-T-O deformation modes in the range of 400-600 cm-1 and cristobalite minerals are remarkable with their weak peaks at the 296.5 cm-1 and 411.1 cm-1 Raman shifts. The geothermometer studies in the plagioclase minerals which are oligoclase and andesine in composition suggest that the spherulites may have 600-650 °C crystallization temperature. The temperature range shows that the spherulites start the first crystallization at the glass transition (Tg) levels and then continue to grow up to below Tg levels and brown rings are associated with Fe-oxidation development at the last stage.

Geothermobarometry and geochemical modeling of Archean charnockites from Carajás Province, Amazonian craton, Brazil

Orthopyroxene-bearing tonalites/trondhjemites with scarce quartz diorites comprise the Café enderbite that crops out in three Neoarchean plutons in the central portion of the Canaã dos Carajás domain, Carajás Province, northern Brazil. Intrinsic parameters based on the mineral chemistry of plagioclase, biotite, amphibole, and pyroxene constrain crystallization conditions to 1150–850°C and 750–600 MPa, moderate water content in the melt (4.8–5.6 wt.%) and relatively oxidizing conditions, between the fayalite–magnetite–quartz (FMQ) and nickel– nickel oxide (NNO) + 1.7 buffers. Geochemical modeling indicates that the Café enderbite evolved via at least two fractional crystallization stages – quartz diorite to orthopyroxene tonalite and orthopyroxene tonalite to orthopyroxene trondhjemite – with high crystal content (45–60%, or even higher). This high crystal content during fractional crystallization was the key factor to the preservation of orthopyroxene in the magmatic system as it left only a relatively small proportion of melt to react with early-formed orthopyroxene.

Non‐isothermal crystallization kinetics of polypropylene/layered double hydroxide composites

AbstractThe crystalline behaviors of polymers have a large impact on their physical and mechanical properties, especially as reinforcing and toughening materials in the construction industry. This work investigates the crystallization behaviors of polypropylene (PP) composites with layered double hydroxide (LDH) by using differential scanning calorimeter and a polarizing optical microscope (POM), and analyzed the non‐isothermal crystallization kinetics of PP composites by Avrami model and Mo's method. The results show that the entire process of non‐isothermal crystallization is appropriate for Mo′s method instead of Avrami model due to the offset of the curves in initial nucleation and secondary crystallization stages. The addition of LDH and modified LDH (SLDH) can increase the crystallinity (Xc) of PP despite decreasing the crystallization rate in the non‐isothermal crystallization process. The migration activation energy (∆E) indicates that LDH acts as a heterogeneous nucleating agent, which is consistent with POM results. The values of ∆E and semi‐crystallization time (t1/2) reveal that the nucleation capacity of PP/LDH is greater than that of PP/SLDH, but the crystallization rate of PP/LDH is slower than that of PP/SLDH, resulting in a decrease in Xc.

Formation of metastable aluminum silicide as intermediate stage of Al-Si alloy crystallization

The mechanism of Al-Si alloy crystallization from an amorphous state is still unclear. Despite the absence of equilibrium compounds for this binary system, there are several experimental evidences confirming the formation of metastable silicide at annealing of amorphous Si mixed with Al. Classification of this metastable structure is a missing puzzle piece in the description of Al-Si alloy crystallization kinetics. Here, we considered the properties of aluminum silicide Al2Si structure, which is a probable candidate for the role of the observed metastable compound. Our investigation was based on the atomistic simulations with the interatomic potential developed recently and DFT approach. All used methods revealed that there are several crystal structures of Al2Si with close geometry and relatively low formation energies. The chemical ordering in such structures is similar to the one in Si-Al melt. We also showed that the combination of these structures allows to form a crystal with different degree of ordering.

Self-assembly of photonic crystals by controlling the nucleation and growth of DNA-coated colloids

DNA-coated colloids can self-assemble into an incredible diversity of crystal structures, but their applications have been limited by poor understanding and control over the crystallization dynamics. To address this challenge, we use microfluidics to quantify the kinetics of DNA-programmed self-assembly along the entire crystallization pathway, from thermally activated nucleation through reaction-limited and diffusion-limited phases of crystal growth. Our detailed measurements of the temperature and concentration dependence of the kinetics at all stages of crystallization provide a stringent test of classical theories of nucleation and growth. After accounting for the finite rolling and sliding rates of micrometer-sized DNA-coated colloids, we show that modified versions of these classical theories predict the absolute nucleation and growth rates with quantitative accuracy. We conclude by applying our model to design and demonstrate protocols for assembling large single crystals with pronounced structural coloration, an essential step in creating next-generation optical metamaterials from colloids.

Investigating the nodulation mechanism of copper cathode based on microscopic approach: As a punch failure factor

The presence of nodules on the surface of cathode copper plates was the most important reason for the failure of the punch of mechanical clinching of copper cathode sheets. This study demonstrated a comprehensive investigation into the nodulation growth of copper cathodes in the electrorefining plant based on metallographic analysis. More than 15 random samples were selected from the top, middle, and bottom of the cathodes produced in the Khatoon Abad copper refinery, Iran. Studies were carried out based on the determination of growth modes including field oriented isolated crystal (FT), basis-oriented reproduction (BR), field-oriented texture (FT), and unoriented dispersion (UD). A scanning electron microscope equipped with the EDS spectrometer was used to determine the elemental analysis of the origin of each nodule and investigate the effect of entrapped slimes impurities on the nodules' microstructure. The results confirmed that the physical and chemical adsorption of inhibitors including Fe, Ni and Mn as hydrated phases on the preferred active sites restricted the FT growth mode at the first stages of crystallization. Then, it enhanced the local current density and cathodic polarization promoting the UD growth mode. The same mechanisms occurred when as-received-casted anodes replaced the cathode and caused the formation of cavity at the preferred active site and intense nodulation at the border of the sample. Analysis of this site of nodules’ root revealed that the aggregation of inhibitors at the lower preferred active sites, i.e., lower than 5 mm, provided the possibility of large local current density, polarization and encourage the formation of brittle deposition as MeOH. In this case, the formation of the spongy nodule was dominant.

Ferrotorryweiserite, Rh5Fe10S16, a New Mineral Species from the Sisim Placer Zone, Eastern Sayans, Russia, and the Torryweiserite–Ferrotorryweiserite Series

Ferrotorryweiserite, Rh5Fe10S16, occurs as small grains (≤20 µm) among droplet-like inclusions (up to 50 μm in diameter) of platinum-group minerals (PGM), in association with oberthürite or Rh-bearing pentlandite, laurite, and a Pt-Pd-Fe alloy (likely isoferroplatinum and Fe-Pd-enriched platinum), hosted by placer grains of Os-Ir alloy (≤0.5 mm) in the River Ko deposit. The latter is a part of the Sisim placer zone, which is likely derived from ultramafic units of the Lysanskiy layered complex, southern Krasnoyarskiy kray, Russia. The mineral is opaque, gray to brownish gray in reflected light, very weakly bireflectant, not pleochroic to weakly pleochroic (grayish to light brown tints), and weakly anisotropic. The calculated density is 5.93 g·cm–3. Mean results (and ranges) of four WDS analyses are: Ir 18.68 (15.55–21.96), Rh 18.34 (16.32–20.32), Pt 0.64 (0.19–1.14), Ru 0.03 (0.00–0.13), Os 0.07 (0.02–0.17), Fe 14.14 (13.63–14.64), Ni 13.63 (12.58–14.66), Cu 4.97 (3.42–6.41), Co 0.09 (0.07–0.11), S 29.06 (28.48–29.44), and total 99.66 wt.%. They correspond to the following formula calculated for a total of 31 atoms per formula unit: (Rh3.16Ir1.72Pt0.06Ru0.01Os0.01)Σ4.95(Fe4.48Ni4.11Cu1.38Co0.03)Σ10.00S16.05. The results of synchrotron micro-Laue diffraction studies indicate that ferrotorryweiserite is trigonal; its probable space group is R3¯m (#166) based on its Ni-analog, torryweiserite. The unit-cell parameters refined from 177 reflections are a = 7.069 (2) Å, c = 34.286 (11) Å, V = 1484 (1) Å3, and Z = 3. The c:a ratio is 4.8502. The strongest eight peaks in the X-ray diffraction pattern derived from results of micro-Laue diffraction study [d in Å(hkil)(I)] are 2.7950 (202¯5) (100); 5.7143 (0006) (60); 1.7671 (224¯0) (44.4); 3.0486 (202¯1) (39.4); 5.7650 (101¯2) (38.6); 2.5956 (202¯7) (37.8); 3.0058 (112¯6) (36.5); and 1.5029 (42¯ 2¯12) (35.3). Ferrotorryweiserite and the associated PGM crystallized from microvolumes of residual melt at late stages of crystallization of grains of Os- and Ir-dominant alloys occurred in lode zones of chromitites of the Lysanskiy layered complex. In a particular case, the residual melt is disposed peripherally around a core containing a disequilibrium association of magnesian olivine (Fo72.9–75.6) and albite (Ab81.6–86.4), with the development of skeletal crystals of titaniferous augite: Wo40.8–43.2En26.5–29.3Fs20.3–22.6Aeg6.9–9.5 (2.82–3.12 wt.% TiO2). Ferrotorryweiserite represents the Fe-dominant analog of torryweiserite. We also report occurrences of ferrotorryweiserite in the Marathon deposit, Coldwell Complex, Ontario, Canada, and infer the existence of the torryweiserite–ferrotorryweiserite solid solution in other deposits and complexes.

Experimental study of the factors on solid adsorption vacuum flash evaporation for ice production

The paper based on the solid adsorption vacuum flash ice slurry production device, the process of distilled water flashing was recorded with a high-speed CCD camera, and the vacuum flashing state of distilled water at different pressures and different initial temperatures was analyzed by experimental phenomena. The effect of system pressure, different wall temperatures and solution volumes on the subcooling state of the ice slurry formation process under solid adsorption vacuum flash evaporation was also experimentally investigated. The results show that the lower the pressure the more intense the flashing phenomenon in the vacuum flashing state, and the higher the initial temperature the more likely the solution is to produce bubbles. Within 20 seconds after the start of the experiment, distilled water will appear subcooling phenomenon in solid adsorption vacuum flash evaporation ice making system, due to the vacuum flash action water is constantly disturbed subcooling state duration is very short. The lower the pressure, the lower the subcooling degree, the subcooling degree is about 2 °C - 4 °C. The wall temperature has a greater impact on the ice crystal phase change accumulation stage, the higher the initial wall temperature the greater the fluctuations in the subsequent stages of flashing and the lower the ice content. When the volume of the solution is small, the liquid film is prone to flash formation of solid ice.

Wet Milling, Seeding, and Ultrasound in the Optimization of the Oiling-Out Crystallization Process

Complicated solution environments in oiling-out crystallization can lead to particle agglomeration with wide size distribution and low purity of the products, due to complex interactions among two liquid phases and one solid phase during the oiling-out crystallization. This research mainly focuses on the optimization of size distribution by controlling particle agglomeration during the oiling-out crystallization process in a model system of propyl paraben–ethanol–water. Nucleation control technologies, wet milling, seeding, and ultrasound were used to limit the agglomeration. Further investigations of wet milling were performed before the nucleation or in the crystal growth stages with different geometries, such as coarse, medium, and fine rotor–stator tooth pairs. An integrated process analytical technology tools (PAT) array, including focused beam reflectance measurement (FBRM), particle visual monitoring (PVM), and attenuated total reflectance ultraviolet/visible (ATR-UV/vis), was used to observe the droplet formation of the dispersed phase, size distributions, and particle shapes during the nucleation and crystal growth. The results demonstrate that wet milling, seeding, and ultrasound technologies can help to optimize the particle size distribution in complex solution environments with different levels of efficiencies.

Precursor formation and crystal nucleation in stretched polyethylene/carbon nanotube nanocomposites

Based on molecular dynamics simulations, we focused on the stretch-induced precursor formation and nucleation process in carbon nanotube (CNT) filled polyethylene. During stretching, in addition to polymer segments, CNTs can also orient along the stretching direction. In this condition, the segments in interfacial regions are subject to two orientation effects: CNT-induced segment orientation and stretch-induced segment orientation, which then can exhibit higher degree of orientation and higher content of segments with trans-conformation, compared with the segments in non-interfacial regions. Finally, these interfacial segments are easier to evolve into precursors and oriented crystallites. Based on the theoretical analysis, it was demonstrated that the crystallization rate at the early stage of crystallization is codetermined by the difference in the nucleation modes (homogeneous nucleation or heterogeneous nucleation), the stretch-induced conformational entropy reduction and the orientation entropy reduction.

The influence of temperature and arsenic molecular form at crystallization stage on the InAs nanostructure growth during droplet epitaxy

In this work, experimental studies of the influence of the arsenic molecular form (di-or tetramers) and substrate temperature on the crystallization of In/GaAs droplet nanostructures during droplet epitaxy have been carried out. We have shown the critical influence of the temperature and arsenic molecular form on the reproducibility of the characteristics of an array of self-organizing InAs nanostructures during crystallization. We also showed that a decrease in the initial In droplet size has a positive effect on the reproducibility of the parameters of the InAs nanostructures arrays. Our work also showed important role of substrate temperature at the crystallization stage.

Investigation of the structure glass-ceramic materials according to data of IR spectroscopy

The efficiency of the use of IR spectroscopy in studying the structure of magnesium-aluminosilicate glass-ceramic materials was analyzed. It was established that the formation of the structure of these glass-ceramic materials during the heat treatment is associated with a distortion of the cordierite structure. The presence of solid solutions, high and low cordierite in the structure of the materials under study was detected according to the systems of bands F2, E2, C2 and D2, depending on the temperature of their heat treatment. The mechanism of phase formation in magnesium-aluminosilicate glass-ceramic materials has been determined, which consists in the formation of future crystals of -cordierite and spinel at the initial stages of nucleation, and crystals of -cordierite and mullite at the stage of crystallization. Formation of a finely dispersed glass-ceramic structure with a predominant content of -cordierite or mullite under conditions of low-temperature heat treatment is a decisive factor in ensuring high thermal and mechanical properties of glass-ceramic materials. This allows them to be used as structural elements of devices and equipment under thermal and mechanical loads.

Modern authigenic amorphous and crystalline iron oxyhydroxides in subsurface Ordovician dolostones (Jinan, North China Block): Biomineralization and crystal morphology

Iron oxide/oxyhydroxide precipitation in nature can involve various mechanisms that are associated with environmental conditions. Amorphous and crystalline Fe oxyhydroxides associated with extracellular polymeric substances (EPS) are common in some of the pores and fractures of subsurface Ordovician dolostone (Jinan, North China Block). These precipitates, dominated by ferrihydrite nanogranules (20–30 nm), acicular goethite nanorods and nanofibers (>200 nm), and various twinned goethite polymorphs (~1–3 mm), record a series of crystallization stages that reflect the mechanisms of iron mineralization. For Fe oxyhydroxide formation this involved: (1) biogenic ferrihydrite and goethite nanoparticle formation, (2) ferrihydrite–goethite transformation and development of nanogranule-attached goethite, (3) goethite twin development, and (4) multi-generation overgrowths on twined goethite. This process shows that the Fe was fixed biogenically with crystallization taking place via a nonclassical nanogranule-aggregation pathway. As such, it highlights the complex mechanisms of crystal growth and morphological development involved with Fe oxyhydroxide mineralization in nature. The distribution of the precipitates, concentrated in larger voids ~11 m below ground surface, demonstrates their sensitivity to ambient conditions such as redox and Fe supply.