K2O Al2O3 Research Articles

Geochemistry of Weathering Cover and the Main Influencing Factors in Karst Area of Guilin, Southwest China

The chemical weathering of carbonate rocks is the main form of interaction between earth spheres in the karst critical zone. The karst weathering cover, which is composed by residua from carbonate rocks weathering, contains important information about the climate environment and material cycle. We present the chemical composition of weathering covers in karst area of Guilin, Guangxi province, analyze their weathering process and strength, and compare them with the other weathering covers in other karst area in China, including Yunnan, Guizhou, Hunan, and Qinghai Tibet Plateau. The results showed: (1) the chemical composition of Guilin weathering covers were similar to that of carbonate weathering covers in other areas of China, and had the common characteristics of uniform distribution of chemical composition in the profile and obvious enrichment of Fe, Al and trace elements. During the formation of carbonate weathering cover and the residua, the rapid dissolution of Ca and Mg had an important impact on the migration and enrichment of other elements. (2) The chemical index of alteration (CIA) of carbonate weathering covers in Guilin and other karst areas of China was much larger than that in the upper crust (UCC) (60.13), which showed strong chemical weathering characteristics of the humid and hot climate. (3) The weathering process of carbonate rock was different from that of silicate and loess. In the early stage of carbonate rock weathering, soluble components (calcite and dolomite) had been rapidly dissolved and leached. All the carbonate weathering residua was measured to be in the stage of K2O weathering and Al2O3 increasing. Therefore, the weathering degree of carbonate weathering cover was mainly determined by the leaching of K2O and the increase of Al2O3. As a result, there was no correlation between CIA and Na/K (molar ratio), but was a significant negative correlation between CIA and K/Al (molar ratio) in the carbonate weathering cover. (4) The CIA values of weathering residua and carbonate weathering cover in southern China were negatively correlated with latitude, reflecting the influence of climate factors. From the influence of lithology, the chemical compositions of parent rock can affect the CIA of weathering cover, and the content of insoluble matter in carbonate rock was negatively correlated with CIA. From the influence of topography, the CIA value of weathering residua decreased from the high to the low position and from the shallow to the deep part of the profile.

Lithium concentration effect on crystallization kinetics and spectral properties of Cr-doped Li2O–K2O–Al2O3–B2O3 glass-ceramics

Alkali-aluminaborate glass-ceramics doped with Cr ions are synthesized by volume crystallization. According to non-isothermal DSC method three parallel processes occur in material: 2D Avrami-Yerofeev nucleation, 2D and 3D crystallization. During the heat treatment, the LiAl7B4O17 crystalline phase is formed. With Li2O content rising crystallinity of the material increases from 27 to 69% and the crystalline field strength Dq/B of Cr3+ increases from 2.25 to 3.55. The photoluminescence spectra possess intense bands at 685, 700, and 715 nm for glass with 6.8 mol.% Li2O and higher and its decay kinetics is described by the sum of two exponentials. The maximum luminescence QY obtained is 50% at 16.1 mol.% Li2O. The highest conversion efficiency of the 532 nm LED luminescence obtained by glass-ceramics with chromium is 10%. Thus, Cr-doped alkali-alumina-borate glass-ceramics are a promising material for use in the design of radiation sources for the red and NIR spectral regions.

Production and Characterization of ZrO2–Al2O3–K2O Based Ceramic Whitening Agents

Production and Characterization of ZrO2–Al2O3–K2O Based Ceramic Whitening Agents

Paleoceanographic Conditions of Neo-Tethys Deposits in Northeast Iraq (Shiranish Formation) by Geochemical Proxies

Geochemical proxies provide detailed information on depositional environment and diagenetic processes. The main objectives of the present study are the evaluation of the paleoenvironment and diagenetic conditions of selected three sections of the Shiranish Formation (Late Campanian-Maastrichtian) in Dokan-Sulaymaniyah, Kurdistan Region, northeast of Iraq. The major and some trace elements were analysed by X-Ray Fluoresces. These geochemical results showed a positive correlation of SiO2, Al2O3, Fe2O3, MgO and TiO2 between each other due to the influence of detrital influx from the active oceanic margins and thrust belts of the northeast Arabian Plate. The terrigenous supply of silicates (K-feldspar) and clay minerals (Illite) caused a positive correlation between K2O values and Al2O3. In general, there is a low abundance of SiO2 and Al2O3 contents, referring to the deepening of the Neo-Tythus ocean basin in the formation's lower part. The Mn* factor of the lower and middle part of the formation exhibited anoxic conditions while oxic- suboxic conditions at the upper part. The Mn/Sr ratios were less than one, which means that Shiranish marly limestone was well preserved out of diagenetic processes. The paleoredox proxies {Th/U, V/Cr &V/(V+Ni)} confirmed that the lower part of the Formation was deposited in a relatively anoxic deep-outer shelf environment with a rising in paleoproductivity. In contrast, the upper part was characterised by dyoxic-oxic redox. Due to the inner shelf environment, this redox fluctuation reflects a regression phase of sea level, which is compatible with the closure events of the Neo-Tethys in the Eocene epoch.

Improved optical properties of phosphor-in-glass (PiG) in w-LD through low-temperature and high-pressure technology

How to improve the luminescence efficiency of PiG conversion materials has become a hot topic and challenge in recent years for high-efficiency white LD (w-LD). In this paper, a low-temperature and high-pressure technology is raised, which successfully synthesized the PiG composed of Y3Al5O12: Ce3+ (YAG) phosphor and SiO2–Al2O3–K2O–Na2O glass frit. The hosts possess a relatively perfect and rigorous structure with few pores benefiting from this gentle preparation method. In addition, three configurations of transmission, reflection, and total-emission are adopted in w-LD, which can achieve the highest luminous efficiency of 77.78 lm/W, 178.72 lm/W, and 206.35 lm/W, respectively. Compared with the traditional high-temperature and normal-pressure method, the saturation luminous flux increases by 4.8%, 13.7%, and 14.3% for 10%, 20%, 30% content phosphor PiG, respectively. This technology shows the significant application potential in preparing high-brightness and high-efficiency w-LDs.

Geochemical characteristics and indication of graphite deposits in Xinrong Region, Shanxi, China

The NE–SW-trending graphite belt found in the Xinrong Region, Datong City is one the richest graphite reserves in China, extending for more than 22 km. The ore-bearing layer of the Huangtuyao Formation is a graphite-bearing gneiss. Based on major and trace element analysis data, we determined from three diagrams that the graphite-bearing gneiss is a parametamorphic rock, and this gneiss was formed by the regional metamorphism of carbonaceous argillite. The detritus of this ore deposit originated from an arc region as seen from the K 2 O/Na 2 O–SiO 2 diagram. According to the Ta/Yb, Sr/Yb and K 2 O/Na 2 O ratios as well as the composition of Gehuyao gneiss, we concluded that this gneiss has typical low-potassium adakitic rock characteristics. Combined with the MgO/SiO 2 diagram and the characteristics of low K 2 O and high Al 2 O 3 , the genetic model of Gehuyao gneiss is melted subducted oceanic crust. Based on regional geological data and comparison of samples, we found an inherent relationship in the main composition content between the graphite-bearing gneiss and the Gehuyao gneiss. This indicates that the ore deposit accumulated the weathering products of Gehuyao gneiss during the sedimentary period. This research provides evidence for ore body evolution and makes it possible to establish the sedimentary–metamorphic model of the graphite ore in this region. In light of the range of the ore body, we predict that the potential area for graphite mineralization in the North China Craton was 2 ± 1.5 km away from the boundary. Thematic collection: This article is part of the Applications of Innovations in Geochemical Data Analysis collection available at: https://www.lyellcollection.org/cc/applications-of-innovations-in-geochemical-data-analysis

Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts

Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths > 130 km: minor perturbations of the stable geotherm at >150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases.

Synthesis and characterization of newly developed phosphate-based glasses through experimental gamma-ray and neutron spectroscopy methods: Transmission and dose rates

In this study, four new phosphate-based glasses with the compositions of CaO–Na2O–K2O–P2O5 (PN system), CaO–Na2O–K2O–Al2O3–P2O5 (PA system) and CaO–Na2O–K2O–Al2O3–SiO2–P2O5 (PS system) were synthesized and characterized through experimental gamma-ray and neutron spectroscopy methods. Glass densities were then measured experimentally and evaluated theoretically. Next, a high purity Germanium (HPGe) detector was used for determining the fundamental gamma-ray transmission parameters in 35.4–383 keV gamma-ray energies emitted from 133Ba source (Radioactivity: 3Ci). Additionally, the experimental setup was used to determine the equivalent dose (EAD) to get a better knowledge of fast neutron attenuation. Our findings indicate that experimental gamma-ray transmission measurements are consistent with standard theoretical data (EpiXS). Consequently, PA10 was shown to have higher gamma-ray and neutron attenuation capabilities when compared to the other glass samples studied. Our outcomes showed that increasing the molar contribution of Al2O3 to the phosphate-based glasses increased not only their transparency but also their gamma-ray and neutron attenuation capacities. It can be concluded that substituting Al2O3 for P2O5 is a functional and monotonic tool for improving the optical, gamma-ray, and neutron attenuation of phosphate-based glasses, which are being evaluated as prospective shielding materials for medical and industrial radiation facilities.

Spectral characteristics of Tb3+ doped ZnF2–K2O–Al2O3–B2O3 glasses for epoxy free tricolor w-LEDs and visible green laser applications

In the current work, a series of Zinc Potassium Alumino fluoroborate (ZKAlFB) glasses doped with different concentrations of Terbium ions (Tb3+) were synthesized by employing the melt-quench technique. The spectroscopic properties of the as-prepared glass samples were examined using characterization techniques like XRD, FT-IR, DSC, UV–vis–NIR absorption and emission to unlock their utility in photonic devices. Absorption spectral information was used to determine the nature of bonding between Tb3+ ions and its surrounding ligands. FT-IR spectral information recorded for an undoped glass has been used to understand various functional groups present in the as-prepared ZKAlFB glass. The DSC thermogram was used to estimate glass thermal stability (ΔT) and transition temperature (Tg) of the as-prepared ZKAlFB glass. The Judd-Ofelt (J-O) intensity parameters estimated from absorption spectral data are correlated with the emission spectral profiles to estimate radiative properties. The photoluminescence (PL) intensity of the as-prepared ZKAlFBTb glasses is found to be maximum for 1 mol% of Tb3+ ions and beyond decreases showing concentration quenching. Using PL spectral data, the CIE color coordinates, and Correlated Color Temperature (CCT) values were evaluated to understand the suitability of the as-prepared glasses for green color emitting photonic devices. The experimental lifetime values estimated from the decay profiles are decreasing with elevation in Tb3+ ion concentration due to energy transfer through the cross-relaxation process. Quantum efficiency (η), emission cross-section (σse), CIE and CCT values obtained for 1 mol% Tb3+ ions doped ZKAlFB glass demonstrates its superiority in fabricating epoxy free tricolor w-LEDs and visible green lasers.

An investigation about crystallization properties of vermiculite based machinable glass-ceramics

This study investigated the crystallization kinetics of a vermiculite-based glass-ceramic system prepared by the melt-quench technique. Four compositions with different boron content consisting of SiO2–Al2O3–K2O–B2O3–MgF2 components were prepared, and then vermiculite mineral was added to these as 50/50 wt%. Differential scanning calorimetry (DSC), Differential thermal analysis (DTA), X-ray Diffraction (XRD), Scanning electron microscopy (SEM), and field emission scanning electron microscopy (FESEM) were used for characterization. The activation energies for the precipitation of crystalline phases have been evaluated, and DSC results have studied the crystallization mechanisms. Furthermore, a machinability test was performed to understand the machining performance of the samples. Density function theory (DFT) was used to calculate the interactions between SiO4-BO3 and SiO4-BO4. The glass-ceramics exhibited excellent performance in machinability tests without cracking or deforming. While the boron additive had different effects on crystallization, it caused the machinability to be negatively affected.

Phase Equilibrium and Trace-Element Modeling of the Partial Melting of Basaltic Rocks under Low Pressure: Implications for Plagiogranite Generation

AbstractPhase equilibria and trace-element modeling using two previously reported basaltic bulk-rock compositions (samples D11 and 104-16), were carried out in this study, in order to better understand mechanism of low-pressure (LP) partial melting of mafic rocks and associated melt compositions. The T–MH2O pseudosections for both samples at three pressures (i.e. 0.5, 1.0 and 2.0 kbar) display that the H2O-stability field gradually increased with decreasing pressure within the T–MH2O range of 600–1100°C and 0–12 mol.%. The H2O contents of 10, 5.0, and 0.5 mol.% were selected on the basis of the T–MH2O pseudosections to calculate Pressure–Temperature (P–T) pseudosections over a P–T window of 0.1–3 kbar and 600–1100°C, so that the reactions of both the H2O-fluxed and -absent meltings at LP conditions can be investigated. The solidus displays a negative or near-vertical P–T slope, and occurs between 710 and 900°C at pressure between 0.1 and 3.0 kbar. LP melting of metabasites is attributed to the reactions of the hydrous mineral (hornblende and/or biotite) melting and anhydrous mineral (plagioclase, orthopyroxene, and augite) melting. The hydrous mineral melting is gradually replaced by anhydrous mineral melting as pressure decreasing, as the stability of hornblende decreases with falling pressure. With increasing temperature at a given pressure, the modeled melt compositions are expressed as progressions of the granite-granodiorite-gabbroic diorite fields for sample D11and granite-quartz monzonite-monzonite-gabbroic diorite fields for sample 104-16 on the total alkali–silica diagram. The modeled melts produced through the H2O-fluxed melting display higher Al2O3, CaO, MgO, and lower SiO2 and K2O than those formed by H2O-absent melting at the same P–T conditions. Furthermore, the modeled melts formed by H2O-absent melting, become richer in Al2O3, CaO, MgO, FeO, Na2O, but poorer in SiO2 and K2O as increasing water content. The results of trace-element modeling suggest that the nearly flat rare earth elements (REE) patterns of modeled bulk-rock composition are inherited by all the modeled melts, and the negative Eu anomalies and Sr depletion of the modeled melts gradually decrease as melting degree increases. Combined with the geochemical characteristics of natural oceanic plagiogranites, which have low K2O contents and flat or slightly light rare earth (LREE)-depleted REE patterns, our results imply that a bulk-rock composition with low K2O (<0.17 wt.%) and slightly LREEs depletion is the most likely protolith composition (e.g. basalt D11) for plagiogranites, and the compositions of modeled melts formed by LP H2O-absent partial melting of the basalt D11 at relatively high temperatures (1000–1025°C) are coincident with those of 1256D tonalites.

Fabrication of K2O–Al2O3–Gd2O3–P2O5 glasses for photonic and scintillation materials applications

Dysprosium (Dy3+) doped glasses of the potassium aluminum gadolinium phosphate (KAGP) were fabricated by melt-quenching technique. The preparation of glasses was varied the concentrations of Dy2O3 at 0.00, 0.05, 0.10, 0.50, 1.00 and 3.00 mol%. The physical and spectroscopic properties were investigated for white light emitting devices. The absorption spectra were attributed to Dy3+ transitions from the 6H15/2, ground state to the various excited states and found that the intensity of absorption spectra was increased with increasing Dy2O3 concentration. The Judd-Ofelt (JO) intensity parameter Ωλ (λ = 2, 4 and 6) were estimated from the absorption spectra of 0.50 mol% Dy2O3 doped KAGP glass and found to be Ω2 > Ω4 > Ω6. The photoluminescence (PL) spectra were record under 350 nm and showed four intense peaks at 482, 573, 664 and 753 nm which correspond to the excited states (4F9/2) to 6H15/2, 6H13/2, 6H11/2 and 6H9/2 respectively. The intensity of emission spectra increased with content of Dy3+ ions until 0.5 mol% in KAGP glasses and beyond concentration quenching was observed. From the emission spectra have evaluated chromaticity co-ordinates CIE 1931 and observed that the emission of KAGP glasses was in the white region. The results approve that the Dy3+ doped KAGP glasses could be considered for optoelectronic devices such as lasers and white light emitting diode (w-LEDs). The radioluminescence (RL) spectra were measured and show the strongest emission from X-rays excitation at 0.5 mol% of Dy2O3. In evaluation of scintillation property between 0.50 mol% of Dy2O3 doped KAGP glass and BGO crystal, the integral scintillation efficiency was 9% of BGO. It can be potential for integration mode of scintillation such as in medical and industrial X-ray imaging applications.

Understanding the early reaction and structural evolution of alkali activated slag optimized using K-A-S-H nanoparticles with varying K2O/SiO2 ratios

So far, little is known about the manner the synthesized K-A-S-H (K2O–Al2O3–SiO2–H2O) nanoparticles affects the hydration of alkali-activated slag (AAS). To understand the effects of adding K-A-S-H nanoparticles with two distinct K2O/SiO2 ratios on reaction and microstructural development of AAS, heat evolution, TGA, MIP and SEM-BSE analyses were measured. Results revealed that incorporation of synthesized K-A-S-H nanoparticles can not only be used as seeding to induce nucleation, thereby significantly promoting the hydration of slag and manipulating the chemical composition of the hydrate phases, but also as fillers to increase the density of alkali-activated slag pastes; then microstructure analysis found that incorporation of synthetic K-A-S-H nanoparticles in AAS could optimize the pore size distribution, leading to a dense matrix structure. Furthermore, the effect of K-A-S-H particles with varying K2O/SiO2 ratios was mainly related to their specific surface area. These important findings provide possible practical implications for controlling the late-stage performance of alkali-activated binders.

Mechanical, structural, and chemical properties of unmodified and iron-modified phosphate glass fibers based on natural phosphate and kaolin clay

Earlier research has reported that the phosphate glass fibers can be used as fertilizer with slow and controlled release of nutrient ions due to the controllable degradability in aqueous environments. In this study, two series of phosphate glasses were prepared and successfully stretched to continuous monofilaments fibers with a fixed spinning speed. The first series includes four phosphate glass fibers compositions based on natural phosphate and kaolin clay in appropriate amounts. Mechanical properties in terms of tensile strength and tensile modulus were dramatically increased with the progressive addition of kaolin clay. PCA statistical analysis carried out to study the effect of the chemical composition on the mechanical performance of fibers showed a strong correlation between Al2O3, SiO2 and Fe2O3 and K2O oxides and the evolution of tensile strength. The second series is based on the selection of the composition with significant mechanical properties to which increasing amounts of Fe2O3 oxide (3, 3.5 and 4 mol%) were added. The effect of Fe2O3 addition on surface morphology, structure, mechanical properties and dissolution behavior of fibers was studied. The results indicate that the addition of 4 mol% of Fe2O3 increased the tensile strength up to 1612 ± 177 MPa and decreased the dissolution rate of the fibers in distilled water under conditions of temperature, time and pH. These results can be explained by the formation of more covalent P–O–Fe bonds that are more resistant in aqueous media.

Phase Equilibrium in the Ternary System K2O–Al2O3–H2O at 323.15, 333.15, 343.15, and 353.15 K

Phase Equilibrium in the Ternary System K₂O–Al₂O₃–H₂O at 323.15, 333.15, 343.15, and 353.15 K

Effect of V2O5 colorant on the optical properties and crystallization behaviors of lithium disilicate glass-ceramics

To understand the coloration in glass-ceramics for dental application, the effect of V2O5 colorant on the optical properties and crystallization behaviors of lithium disilicate (LS2) glass-ceramics (GCs) has been investigated for two different systems of SiO2-Li2O-P2O5-K2O-ZnO and SiO2-Li2O-P2O5-K2O-Al2O3. For this study, the amount of V2O5, SiO2 + Li2O, and P2O5 were fixed to have 0.5, 93.5, and 1.5 mol%, respectively, while the ratios of both ZnO/K2O (Zn/K) and Al2O3/K2O (Al/K) were varied from 0.5 to 2. The GC samples were prepared by two-stage heat treatments of 500 °C for 1 h as a nucleation stage and 600, 700, and 800 °C for 2 h as a growth stage in air. The light green glass samples having only V5+ ion continuously changed to violet, blue, green, and brown for GC samples due to its reduction into V4+ and V3+ ions with progressing crystallization. TEM-EDS analyses revealed that a small amount of V5+ ion was incorporated into both LS2 and SiO2 crystalline phases, causing greenish fluorescence, while most of vanadium ions remained in a residual glassy matrix. At the growth temperature of 800 °C, while the growth rate of LS2 was increased by lowering the viscosity of the glass matrix, and thus the LS2 crystal size of the GVZ1.5 and GVZ3 samples became larger (∼1 μm) compared with its size below 500 nm for the samples without V2O5 colorant. The GVAl1.5 and GVAl3 samples exhibited the smaller size (<1 μm) than GVZ1.5 and GVZ3 samples because of higher nucleation rate and lower growth rate, leading to undesirable high translucency for the dental application.

A simple and clean method to prepare SiC-containing vitreous ceramics for solar thermal storage in the clay-feldspar system

A simple and clean in-situ method was designed to prepare SiC whisker-reinforced vitreous ceramics for solar thermal storage. SiC whiskers were in-situ synthesized in the clay-feldspar system via a carbon-buried sintering process to improve the thermal properties of vitreous ceramics. The synthesis mechanism and the optimized processing procedure of SiC-containing vitreous ceramics from the clay-feldspar system were obtained. Results indicated that the in-situ SiC whiskers were synthesized inside the pores of vitreous ceramic matrix through the vapor-solid mechanism and covered by the liquid of K2O–Al2O3–SiO2 system. SiC whiskers with a diameter of 9–23 nm decreased the thermal expansion coefficients of the vitreous ceramics significantly from 6.59 × 10−6 °C−1 to 4.23 × 10−6 °C−1 (room temperature∼1000 °C). Meanwhile, the thermal conductivity increases to 4.78 W·(m·k)−1, 2.6 times higher than that of the original products. The increased porosity was found to improve the amount of SiC whiskers by providing space for their growth. SiC whiskers also enhanced the mechanical properties of the products and the sample with the largest content of SiC exhibited the highest bending strength of 75.7 MPa. The introduction of SiC whiskers through the in-situ synthesis method makes vitreous ceramics more competent for solar thermal storage applications. The in-situ method can save the energy and costs needed for separately producing SiC whiskers and prevent the inhalation toxicity of SiC whiskers.

Optimization of mechanical and tribological properties of a dental SiO2–Al2O3–K2O–CaO–P2O5 glass-ceramic

Dental glass-ceramics with main crystal of fluorapatite are usually employed as veneering porcelain. However, failure of the porcelain happens clinically in the form of fracture or excessive wear. The aims of the study were to evaluate the influence of microstructures of a SiO2–Al2O3–K2O–CaO–P2O5 fluorapatite glass-ceramic on its mechanical properties and tribological behaviors, and to improve the comprehensive performance by adjusting content and sintering process. The glass-ceramics were fabricated by sintering method with different CaO contents and heat treatment regimes. Phase compositions and crystal length of specimens were characterized by X-ray diffractometer and scanning electron microscope. Combined with mechanical properties, friction and wear behaviors in both dry and artificial saliva lubrication conditions were investigated. The results show that different content of CaO and heat treatment temperature could change crystallinity of main fluorapatite crystal. Larger crystallinity improves the mechanical properties, significantly influencing friction and wear behaviors. The specimens with 6.0 wt % CaO and sintered at 1100 °C have the best comprehensive performance, which show excellent mechanical properties and wear resistance.

Lateral cracks during sliding indentation on various optical materials

AbstractA series of static and sliding indentation (ie, scratching) was performed and characterized on a wide range of optical workpiece materials [single crystals of Al2O3 (sapphire), SiC, Y3Al5O12 (YAG), CaF2, and LiB3O5 (LBO); a SiO2–Al2O3–P2O5–Li2O glass ceramic (Zerodur); and glasses of SiO2:TiO2 (ULE), SiO2 (fused silica), and P2O5–Al2O3–K2O–BaO (Phosphate)] at various applied loads using various indenters (Vickers, 10 µm conical, and 200 µm conical). Despite having different load dependencies, the lateral crack depth formed during sliding indentation quantitatively scales with that formed during static indentation, explaining why static indentation has been historically effective in describing various grinding parameters. Depending on the indenter geometry, the amount of residual trench damage (plastic deformation and local fracturing) during sliding indentation was often enhanced by more than an order of magnitude compared with static indentation. A simple ploughing scratch model, which considers both tangential and normal stresses (where the tangential stress is amplified by relatively small tangential contact area), explains this enhancement and other observed trends. Accounting for the high correlation between residual trench depth and volumetric fracturing, the model is extended to estimate the amount of fracture damage as a function of the material properties of the workpiece, indenter geometry, and applied load. Such a model has utility in the design of optimized grinding processes, particularly the abrasive geometry. Finally, at higher loads (&gt;1 N), lateral cracks were often observed to preferentially propagate in the forward scratching direction, as opposed to perpendicular to the scratch as typically observed. High‐speed imaging of the scratch process confirms that these cracks propagate ahead of the sliding indenter during the scratching event. Finite element stress analysis suggests the ploughing frictional forces increase the mode I tensile stresses at the leading edge of the sliding indenter explaining the direction of crack propagation of such cracks.

Современное физико-химическое описание равновесий в системе Na2O–Al2O3–H2O и ее аналогах

Equilibrium and non-equilibrium states of systems Na2O–Al2O3–H2O and K2O–Al2O3–H2O are crucial for establishing key technological parameters in alumina production and their optimization. Due to a noticeable discrepancy between experimental results and thermodynamic calculations based on materials of individual researchers the necessity of systematization and statistical processing of equilibrium data in these systems to create a reliable base of their physicochemical state, analysis and mathematical modeling of phase equilibria is substantiated. The tendency to a decrease of the hydration degree of solid sodium aluminates with increasing temperature and the transition of systems from the steady state of gibbsite to equilibrium with boehmite is revealed. The paper contains approximating functions that provide high-precision description of equilibrium isotherms in technologically significant area of Na2O–Al2O3–H2O and K2O–Al2O3–H2O concentrations. Approximating function can be simplified by dividing the isotherm into two sections with the intervals of alkaline content 0-0.25 and 0.25-0.4 mole/100 g of solution. The differences in solubility isotherms for Na2O–Al2O3–H2O and K2O–Al2O3–H2O systems provide are associated with changes in the ionic composition solutions that depends on concentration and temperature, as well as differences connecting with alkali cation hydration, which is crucially important for thermodynamic modeling of equilibria under consideration.