Aluminum Silicate Phase Research Articles

Structural, mechanical, electronic and thermodynamic analysis of calcium aluminum silicate crystalline phases in stone wool insulation materials: A first-principles study

Stone wool materials have gained considerable attention due to their effectiveness as thermal and acoustic insulation solutions. The comprehension of crystal structure properties is pivotal in determining the overall performance of these materials, as it enables us to optimize their composition for enhanced insulating capabilities. Crucial factors such as structural, mechanical, and thermodynamic characteristics of crystalline phases within stone wool are vital for evaluating its thermal and acoustic insulation properties. This study investigates the properties of calcium aluminum silicate crystal phases commonly present in stone wool, including anorthite, svyatoslavite, scolecite, and dehydrated scolecite using density functional theory (DFT) calculations. In comparison to previous works, this study provides a more comprehensive analysis using advanced DFT calculations. Our analysis reveals the complex interplay between the crystal structures and mechanical behavior of these phases. The calculated bulk modulus of the phases varies significantly, ranging from 38 to 83 GPa. We have compared the calculated elastic properties with available experimental data and found excellent agreement, confirming the accuracy of the computational approach. Moreover, we find that polymorphism has a significant impact on the mechanical strength, with anorthite exhibiting higher strength compared to svyatoslavite. Furthermore, dehydration is found to cause a reduction in unit volume and mechanical strength. The thermodynamic properties of dehydrated scolecite, including entropy and heat capacity, are significantly lower due to the absence of water molecules. These findings highlight the importance of understanding the structural and mechanical characteristics of calcium aluminum silicate phases in stone wool materials. Additionally, our findings have broader implications in various industries requiring effective insulation solutions such as to develop new materials or to enhance the energy efficiency of existing insulating products.

The Effect of Superplasticizers on Eco-friendly Low-Energy One-Part Alkali-Activated Slag

One-part alkali-activated materials (OP-AAM) have become a promising binder with low carbon and energy requirements associated with superior mechanical and durability characteristics. This study aims to employ commercial superplasticizers (naphthalene-based “Nb-SP” and polycarboxylate-based “PCb-SP”), as well as laboratory-prepared one (phenol–formaldehyde sulfanilate “PFS-SP”) in enhancing the properties of OP-AAM. The main problem of superplasticizers (SPs) in the AAM is their hydrolysis in the alkaline activator (NaOH) used in the activation reactions. Therefore, the thermo-chemical treatment process was utilized to mitigate the high activator alkalinity by impeding the NaOH in the aluminosilicate precursor matrix. The OP-AAM was fabricated from thermo-chemical treatment powder (TCT-P) resulting from sintering blast furnace slag (GGBFS) with 10 wt% NaOH at 300 and 500 °C. The XRD-pattern showed that NaOH was impeded in the GGBFS via sodium aluminum silicate phase formation after sintering at 500 °C. The results showed that the admixed OP-AAM prepared from TCT-P at 500 °C greatly enhanced the workability and mechanical properties. The PFS-SP proved its efficiency in improving the properties of OP-AAM prepared TCT-P at 300 and 500 °C, referring to its high stability in an alkaline medium. While PCb-SP reinforced the properties of OP-AAM prepared from TCT-P at 500 °C only, proving that PCb-SP promotes high capability in TCT-P-500 as well as in Portland cement.

Deep insight into reactive chemical structures of Class F fly ash

Reactive amorphous aluminum silicates dominate the reactivity of fly ash in alkali cement; however, the quantitative characterization of valid chemical compositions and structures information is highly challenging due to the heterogeneity and complexity of these phases. To acquire this information, in this work, Class F fly ash was treated with 1% hydrofluoric acid, followed by step-by-step analysis using a scanning electron microscope with an energy dispersive spectrometer (SEM-EDS), solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR), and Fourier transform infrared (FT-IR) spectroscopy. Based on the acidolysis method, along with SEM-EDS statistical analysis, four amorphous aluminum silicate phases with relatively higher reactivity were successfully separated and quantitatively showcased, along with their respective average atomic percentage compositions (i.e., Si, Al, Ca, Fe, Na, K, and Mg%). In addition, the use of MAS-NMR and FT-IR analyses allowed for further quantitative insight into the reactive chemical structures and their associations with reactivity. The proposed characterization techniques have unique advantages for acquiring detailed reactive amorphous chemistries, which are difficult to obtain using conventional analysis procedures in alkali systems.

Effectiveness and mechanism of uranium adsorption on size-graded red mud

As a type of useful solid waste, red mud (RM) should be reused to achieve waste-to-resource strategies. Additionally, the fast development of nuclear industry requires effective and reliable materials for treating uranium (U)-containing wastewater. This study attempted to remove uranyl ions [U(VI)] from mimic radioactive wastewater by various RM particles with different size fractions (e.g., >75, 45–75, 20–45, 10–20, 5–10, and <5-μm). Sorption data confirmed that the RM with a size fraction of <5-μm exhibited the largest adsorption capacity. The U removal behavior was favorably described by the pseudo-second-order model and Langmuir model. The mineral phases in the RM remarkably influenced U(VI) removal. Cancrinite, katoite, grossular, calcite, and calcium aluminum silicate phases made contributions to U(VI) adsorption. In addition, redox precipitation with iron-bearing minerals on RM surface also led to U(VI) adsorption. The findings of this work offer fundamental knowledge on the potential application of RM for clean-up of U(VI) from contaminated sites.

Aptness of nano alumina (Al2O3) with high range water reducer-incorporated concrete

PurposeThe purpose of this paper is to study the effect of nano alumina (Al2O3) on the properties of fresh concrete, hardened concrete and microstructure of concrete incorporated with high range water reducer (HRWR). This initiative was taken to improve characteristic properties of concrete using nano alumina because nano alumina can be easily be manufactured from a scrap of industrial aluminum products, so its incorporation in concrete will not only reduce industrial aluminum waste but will also change the morphology of concrete at the microstructural level.Design/methodology/approachTo accomplish the objectives of the research, four different concrete mixes with the constant water–cement ratio (W/C) and superplasticizer (SP) content 0.4 and 0.6% by weight of cement, respectively, were prepared, whereas nano alumina content was altered by 0.3% and 0.4% by weight of cement. Fresh property of concrete was analyzed by using slump cone test, whereas hardened properties of concrete were analyzed through compression test and flexural strength test. The interaction of nano alumina with concrete composite was evaluated using an X-ray diffraction test.FindingsIt was observed that 0.6% superplasticizer by weight of cement increased workability by 22% but with the addition of 0.3%, nano alumina by weight of cement workability decreased by 31%. Compressive strength increased by 4.88% with the addition of 0.6% superplasticizer but with the addition of 0.3% nano alumina by weight of cement compressive strength increased by 18.60%. Also, flexural strength increased by 1.21% with the addition of 0.6% superplasticizer by weight of cement but with the addition of 0.3% nano alumina by weight of cement flexural strength increased by 8.76%. With the addition of superplasticizer, alite and belite phases remained un-hydrated but with the addition of nano alumina alite phase was hydrated while belite phase was un-hydrated. The size of belite crystals in mixes having nano alumina was less than that of mix having 0.6% superplasticizer. Also with the addition of nano alumina, a calcium aluminum silicate phase was formed which was responsible for the increment of strength in mixes having nano alumina.Originality/valueIncorporation nano alumina (Al2O3) in concrete will not only reduce industrial aluminum waste but will also reduce CO2 emission. Nano alumina (Al2O3) also changes morphology of concrete at micro structural level.

Transparent Refractory Aerogels for Efficient Spectral Control in High‐Temperature Solar Power Generation

AbstractAlthough spectrally selective materials play a key role in existing and emerging solar thermal technologies, temperature‐related degradation currently limits their use to below 700 °C in vacuum and even lower temperatures in air. Here a solar‐transparent refractory aerogel that offers stable performance up to 800 °C in air is demonstrated, which is significantly greater than its silica counterpart. This improved stability is attributed to the formation of a refractory aluminum silicate phase, which is synthesized using a conformal single cycle of atomic layer deposition within the high‐aspect‐ratio pores of silica aerogels. Based on direct heat loss measurements, the transparent refractory aerogel achieves a receiver efficiency of 75% at 100 suns and an absorber temperature of 700 °C, which is a 5% improvement over the state of the art. Transparent refractory aerogels may find widespread applicability in solar thermal technologies by enabling the use of lower‐cost optical focusing systems and eliminating the need for highly evacuated receivers. In particular, a shift to higher operating temperatures while maintaining a high receiver efficiency can enable the use of advanced supercritical CO2 power cycles and ultimately translate to an ≈10% (absolute) improvement in solar‐to‐electrical conversion efficiency relative to existing linear concentrating systems.

Academic Reminiscences and Thermodynamics-Kinetics of Thermo-Barometry-Chronology

This article has three major components that include, in addition to the technical aspects, reminiscences of my academic upbringing, my move to the USA from India, and my professional career. I have recounted many stories that I hope convey some sense of time, especially in these two countries with vastly different cultures, my personal journey with its ups and downs and how I made the transition to an academic career path in USA even though that was not in my future plan as a young man. The development of the field of thermobarometry and its integration with diffusion and crystal kinetic modelling of compositional zoning (or lack thereof) and cation ordering in minerals have led to important quantitative constraints on the pressure-temperature-time evolution of terrestrial rocks and meteorites. I review the historical developments in these areas and a segment of my own research spanning the period of 1964-2021. The foundational works of the thermometry of metamorphic rocks and palaeothermometry were laid at the University of Chicago around 1950. Subsequently, the synergetic growth of thermodynamics and experimental studies in petrology in the 1960s and 1970s, along with the introduction of electron microprobe as a nondestructive analytical tool with micron scale resolution, gave a major boost to the field of thermobarometry. There were also significant new developments in the field of thermodynamics of solid solutions in the petrology community and demonstration from observational data, countering strong scepticism, that the principles of classical thermodynamics were applicable to “complex natural systems”. The section on thermodynamic basis of thermobarometry concludes with a discussion of the thermodynamics of trace element and single mineral thermometry. I further deal with the experimental protocols, along with selected examples, for phase equilibrium studies that provide the bedrock foundation for the field of thermobarometry based on elemental compositions of coexisting minerals in a rock. It is followed by an account of the controversies and international meetings relating to the aluminum silicate and peridotite phase diagrams that play crucial roles in the thermobarometry of metamorphic rocks and mantle xenoliths, respectively. The construction of quantitative petrogenetic grids to display stability relations of minerals in multicomponent–multiphase systems came into play in the field of metamorphic petrology in the mid-1960s and early 1970s. Augmented by experimental data, these petrogenetic grids led to important discoveries about the P-T-&lt;em&gt;f&lt;/em&gt;(O&lt;sub&gt;2&lt;/sub&gt;) and bulk compositional controls on the stability of certain “index” minerals that are used to define metamorphic isograds and different types of regional metamorphism; one such grid also opened up a new field that came to be known as ultra-high temperature metamorphism. The construction of petrogenetic grids has now evolved to computer based calculations of complex equilibrium P-T phase diagrams, commonly referred to as “pseudosections”, by minimisation of Gibbs free energy of a system with fixed bulk composition. I discuss these historical developments and modern advancements. Subsequently I highlight some aspects of thermobarometry and diffusion kinetic modelling of selected natural samples along with their broader implications and present a critical discussion of different protocols for thermobarometry of natural assemblages. Following up on the introductory historical perspective of development of palaeothermometry, I discuss the modern advancements using density functional theory (DFT). Examples of DFT based calculations have been shown for hydrogen isotope fractionation in mineral-water/hydrogen systems and “clumped isotope” thermometry. The hydrogen isotope fractionation data led the development of new low temperature palaeothermometers using serpentine-talc/brucite mineral pairs. These results enable simultaneous solutions of both temperature and source of fluid in the serpentinisation process of rocks. The final section is devoted to high temperature thermochronology dealing with the problems of closure temperature of decay systems in minerals and the use of bulk and spatial resetting of mineral age according to a specific decay system to determine cooling rates of the host rocks. Complications arise in the interpretation of mineral ages determined by such decay systems as &lt;sup&gt;176&lt;/sup&gt;Lu-&lt;sup&gt;176&lt;/sup&gt;Hf or the short- lived system &lt;sup&gt;53&lt;/sup&gt;Mn-&lt;sup&gt;53&lt;/sup&gt;Cr in which the parent nuclide has a much lower closure temperature than the corresponding daughter product. Numerical simulations help explain the discrepancy between the &lt;sup&gt;176&lt;/sup&gt;Lu-&lt;sup&gt;176&lt;/sup&gt;Hf and &lt;sup&gt;147&lt;/sup&gt;Sm-&lt;sup&gt;143&lt;/sup&gt;Nd ages of garnets in metamorphic rocks and enable construction of the entire T-t cycle from the discrepant ages and some additional constraints.

Donwilhelmsite, [CaAl4Si2O11], a new lunar high-pressure Ca-Al-silicate with relevance for subducted terrestrial sediments

AbstractWe report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001 and discuss the implications of our discovery. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. Transmission electron microscopy based three-dimensional electron diffraction (3D ED) reveals that the CaAl4Si2O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments. The new mineral has a hexagonal structure, with a space group of P63/mmc and lattice parameters of a = 5.42(1) Å; c = 12.70(3) Å; V = 323(4) Å3; Z = 2. This is the first time 3D ED was applied to structure determination of an extraterrestrial mineral. The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” [CaAl4Si2O11], honoring the U.S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events. In the feldspatic lunar meteorite Oued Awlitis 001, needles of donwilhelmsite crystallized in ~200 mm sized shock melt pockets of anorthositic-like chemical composition. These melt pockets quenched within milliseconds during declining shock pressures. Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth's mantle. Donwilhelmsite forms in the Earth's mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite and the Ca-component of clinopyroxene at low pressures and the Al-rich Ca-ferrite phase and Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene. This process may trigger minor partial melting, releasing a range of incompatible minor and trace elements and contributing to the enriched mantle (EM1 and EM2) components associated with subducted sedimentary lithologies.

Effects of using ZSM‐5 and a rock‐reforming mineral as catalysts on liquid fraction collected from polypropylene pyrolysis

AbstractIn this study, a rock‐reforming mineral and zeolite ZSM‐5 were used as catalysts in the pyrolysis of polypropylene (PP) to get liquid products. The structures of catalysts were investigated via XRD and FTIR techniques. The liquid fractions collected from the non‐catalytic and catalytic pyrolysis processes were indicated via GCMS measurement. The results show the rock‐forming mineral has the typical pattern of SiO2 quartz, KAlSi3O8 microcline, and H2KAl3(SiO4)3 muscovite phases, while the zeolite ZSM‐5 has the typical pattern of H0.32Al0.32Si95.68O192 hydrogen aluminum silicate phase. The major products from PP pyrolysis without catalyst was 2,4‐ dimethyl‐1‐heptene (trimer), around 46.43 wt.% and the percentage of branched‐chain alkenes of 90.22 wt.% is significantly high. Whereas, the liquid products, which were formed from the catalytic pyrolysis using the rock‐reforming mineral and ZSM‐5 as catalysts, contain the significantly reduced portions of alkenes.

Prospects and features of microwave sintering in the technology of building ceramics

The results of firing samples from natural aluminum silicates in a microwave oven are considered. The possibility of sintering aluminum silicate raw materials, traditional for the production of building ceramics, is established. The phase compositions of the calcined materials are determined. The influence on the sintering process of the mineral structure of clay raw materials, the composition of the diatomite and the addition of NaCl salt was established. Samples from the mass with the addition of NaCl show high quality and increased strength of the samples. Samples from masses based on brick clay with NaCl salt, annealed in the microwave electromagnetic field, did not show a large increase in strength. For all mass compositions with NaCl, a decrease in the energy of the endothermic process was revealed in the temperature range 400-600 °C. In all mass compositions from clays with NaCl and diatomite with salt and marl, the presence of an aluminum silicate phase with a size of less than 30 nanometers was found. Masses with such a phase structure showed increased strength of the samples.

Raman spectroscopic identification of cookeite in the crystal-rich inclusions in spodumene from the Jiajika lithium pegmatite deposit, China, and its geological implications

Abstract. Cookeite usually occurs as a late alteration product in lithium–cesium–tantalum-type granitic pegmatite. Consequently, cookeite-bearing crystal-rich inclusions (CIs) in pegmatite are considered to be of secondary origin, which constrains our understanding of pegmatite formation. Thus far, no reported cookeite has produced a distinct Raman spectrum. However, the CIs hosted in spodumene in the Jiajika pegmatite deposit, China, contain a cookeite-like hydrous lithium–aluminum–silicate phase, yielding a distinct Raman spectrum. In electron microprobe analysis, focused ion beam scanning electron microscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS), the average composition of this hydrous phase was determined as Li1.005(Al3.997Fe0.018)(Si3.086Al0.914)O10.076OH7.902F0.098, close to the International Mineralogical Association (IMA) formula of cookeite, (Al, Li)3Al2(Si, Al)4O10(OH)8. The distinct Raman peaks at 98, 167, 219, 266, 342, 382, 457, 592, 710, and 3640 cm−1 were consistent with those of natural cookeite recrystallized in a hydrothermal diamond-anvil cell. The peaks were ascribed to the crystallization of cookeite from the liquid trapped in the closed space during the spodumene crystallization, which occurred at relatively high temperature and pressure without incorporating the minor elements commonly present during alteration processes. These minor elements often obscure the Raman signals, primarily by fluorescence effects. This type of cookeite in CIs with distinct Raman signals is unusual and can indicate whether the cookeite crystallized from fluid trapped within the closed space of a primary inclusion. In such a case, the fluid can be considered a flux-rich hydrous melt in pegmatite formation models.

Effect of Microwave Roasting on Aluminum Extraction from Diasporic Bauxite-Sodium Carbonate-Calcium Hydroxide Mixtures

The effect of microwave roasting on aluminum extraction from mixtures of diasporic bauxite with sodium carbonate and calcium hydroxide has been studied. The phase constitution and leaching performance of the clinkers were studied under different roasting conditions. Dielectric and thermal investigations on raw slurry obtained from the mix revealed prominent microwave absorption characteristics. X-ray diffraction patterns established significant promotion of NaAlO2 phase. In the microwave field, the aluminum (Al)-bearing minerals, viz. AlOOH and Al2O3, reacted with Ca(OH)2 to form calcium aluminate and calcium aluminum silicate phases at rather low temperature in short time. Furthermore, increasing the temperature and time promoted the reactions of AlOOH and Al2O3 with Na2CO3 to form NaAlO2, resulting in high Al leaching rates. Remarkably, the Al extraction of the clinker microwave roasted at 800°C for 45 min was 82.24%, while the leaching rates of Na and Si were 90.2% and 8.4%, respectively.

Synthesis of open-cell ceramic foam derived from geopolymer precursor via replica technique

This paper describes a facile and effective method for fabrication of open-cell ceramic foam derived from geopolymer precursor through replica technique. The polyurethane sponge method was applied using geopolymer mixture based on powder mixture of metakaolin/precipitated silica, potassium silica solution and fine chamotte filler. Accelerated solidification step at 60°C for 30min was performed to obtain dense structure with a good adhesion to the polymeric sponge. The effect of thermal treatment on mechanical and structural behavior of synthesized foams was investigated. X-ray diffraction (XRD) analysis indicated that no substantial differences in the content of crystalline Leucite – Potassium Aluminum Silicate phases appeared between thermally treated samples at 1100°C, 1200°C and 1300°C. It has been revealed that compression strength of ceramic foams reached 0.85±0.11MPa after the samples had been treated at 1300°C. In addition, scanning electron microscopy (SEM) and X-ray micro computed tomography (µ-CT) confirmed uniform interconnected cellular structure with pore sizes between 1 and 2mm resulting in an open porosity (εo) of 78.88vol%.

Preparation of halloysite-derived mesoporous silica nanotube with enlarged specific surface area for enhanced dye adsorption

The enlargement of specific surface area of halloysite-derived nanotubes could benefit the performance and applications of halloysite mineral. In this work, we propose and demonstrate a novel approach to prepare halloysite-derived mesoporous silica nanotubes with substantial specific surface area. The specific surface area up to 608m2/g is achieved from the natural halloysite (Hal) via a simple process of calcination, alkali-treating and acid-etching. The amorphous Si-O-Al network of the calcined Hal is alkali-treated, becoming an amorphous hydroxyl-enriched sodium aluminum silicate phase. The AlO and NaO compositions are selectively acid-etched to in-situ develop mesopores within the residual silica framework, producing the hydroxyl-enriched mesoporous silica nanotubes. The alkali-treatment is crucial to determine the morphology and porosity of the final nanotubes. The optimized mesoporous silica nanotubes behave favorable monolayer adsorption with capacity of 618mg/g for methylene blue, allowing a promising adsorbent in the future.

K-Based Geopolymer from metakaolin: roles of K/Al ratio and water or steam Curing at different temperatures

K-based geopolymer binder was prepared by reacting metakaolin with alkaline solutions having different potassium contents and by water curing at room temperature and 80 °C as well as steam curing at 150 and 180 °C. The phase formation, microstructure and Al and Si nearest neighbor environments were studied using XRD, TEM and 27Al and 29Si MAS NMR spectroscopy, respectively. The results revealed that amorphous alumino-silicates were predominant in geopolymer prepared by curing up to 28 days at room temperature or at 80 °C. The amorphous alumino-silicates persisted after hydrothermal treatment at 150 °C/48 hrs and even at 180 °C/30 hrs. However, the samples cured hydrothermally at 180 °C/48 hrs revealed formation of crystalline potassium aluminum silicate and chabazite phases. The Al nearest neighbor environments was not significantly affected by increasing the K/Al ratio up to 1.55 or by the curing temperatures. On the other hand, the geopolymer reaction appears to have increased when cured at 80 °C or steam cured at 150° and 180 °C and crystalline aluminosilicates resulted when the geopolymer sample was hydrothermally treated at 180 °C/48 hrs.

Development of Machinable Glass-Ceramic without Nucleating Agents

Mica containing glass-ceramic is prepared by crystallizing magnesium alumino silicate glass between 600°C and 1100°C without the use of any additives or nucleating agents. Effects of ceramization heat treatment conditions on phase constitution and microstructures are analyzed using XRD and HRSEM respectively. Developed glass-ceramics have been analyzed for its microhardness and machinability. Optimum heat treatment condition for achieving uniformly distributed fluorophlogopite phase essential for machinability, and at the same time, magnesium aluminum silicate phase for increasing the hardness, is presented.

Structural and chemical changes in kaolinite caused by flash calcination: Formation of spherical particles

To understand the morphological changes of three commercial kaolins during flash calcination and to compare them with those obtained during traditional heat treatments in the laboratory (an electric furnace at 700°C for 5h), this paper presents the physical and chemical characteristics of metakaolins obtained from an industrial flash calciner. In the metakaolin products, kaolinite was not completed dehydroxylated during calcination, and the proportion of untransformed kaolinite was greater in flashed metakaolins than in traditional rotary-calcined metakaolins. Several particle morphologies were discernible in the metakaolins, including spherical particles that were formed in flash calcinations. These spherical particles were cut with a focused ion beam (FIB) and were revealed to contain a vitrified aluminum silicate phase with traces of mullite and various gases. These spherical particles were produced from the direct calcination of several submicron kaolinites near the flame of the calciner.

Changes to the Triaxial Composition of the Hydrated Phases (CaO/Al2O3/SiO2) in the Metakaolin/Lime System

This study examines the composition of certain hydrates (calcium silicate, aluminum silicate, and related phases) produced by the pozzolanic reaction of waste‐paper sludge that had previously been activated at different temperatures. It summarizes and compares the evolution of the oxide compounds, and records their stability intervals. Changes to their mineralogical composition were analyzed using X‐Ray Diffraction, scanning electron microscopy, and energy dispersive X‐ray spectroscopy. The hydration products from 1 to 360 days of curing time were CSH gels, hydrotalcite‐type compounds (LDH), and stratlingite (C2ASH8). CSH gels were employed as substrates for growing other materials and their morphologies were modified from fibrous to hexagonal layers. The composition of the LDH‐type compounds observed in the carbonate group varied with changes in curing time. Two LDH‐type compound types were identified: (a) with and (b) without magnesium. Stratlingite was the only stable material after long‐curing times.

The quantity of oxygen radicals occluded in a new aluminum silicate phase, Ca12Al14O33 - Ca12Al10Si4O35 solid solutions

The quantity of oxygen radicals occluded in a new aluminum silicate phase, Ca12Al14O33 - Ca12Al10Si4O35 solid solutions

In situ formation of Al 2O 3–SiC–mullite from Al-matrix composites

Five composite batches (M1–M5) containing Al 2O 3–SiC–mullite–Al were designed and prepared in situ from different proportion mixtures of alumina, silicon carbide and aluminum alloy. The phase composition and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Sinterability in terms of bulk density, apparent porosity and compressive strength were also measured. All samples exhibit XRD reflections characteristic of alumina, SiC, and mullite. The amount of these phases depended on starting batch compositions, oxidation of Al-alloy, oxidation of SiC, and reaction of starting and oxidized materials together to form mullite. In the composites-containing lower mullite content, new silica-rich phase (aluminum silicate phase, i.e. Al 2Si 4O 10) and/or cristobalite appeared. The formed mullite or silica rich phase prevents further oxidation of SiC or Al–metal. These phase compositions reflect the higher density, lower porosity and good mechanical properties of such composites. The presence of low melting silicate phases was found to increase the bulk density and consequently to decrease the apparent porosity.