Al2O3 Content Research Articles

Al2O3 Concentration Effect on Deep Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over NiWS/Al2O3-ZrO2 Catalysts.

The Al2O3 concentration effect over NiWS/Al x Zr100-x catalysts was investigated for deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The sol-gel method changed the wt % Al2O3 concentrations used to synthesize the Al x Zr100-x supports. The NiWS/Al x Zr100-x catalysts were prepared with ammonium metatungstate hydrate and nickel(II) nitrate hexahydrate by sequential incipient impregnation, calcination, and H2S/H2 activation. The catalytic evaluation data fit a pseudo-first-order trend in the 4,6-DMDBT HDS reactions. In the oxide phase, the catalysts presented Ni and W species in tetrahedral (td) and octahedral (oh) coordination, with the oh species prevailing as a function of the Al2O3 amount. The lower amount of Al2O3 can facilitate the "Type II" NiWS phase formation by weakening the interaction of the W-O-Al bond and promoting W and Ni species sulfidation. In the sulfide phase, catalysts with (oh) coordination and surface WO X species promote the formation of WS2 and NiWS species during the catalyst activation step. This species favors the reaction yield, where the hydrogenation route is predominant, with the highest initial reaction rate using the NiWS/Al25Zr75 catalyst. A direct correlation was found between high hydrogenation/hydrogenolysis ratio values and low Al2O3 concentrations.

Mesoproterozoic depleted spinel peridotites metasomatized by high-K hydrous melt in the Patagonian back-arc

Here we report the first investigation of spinel-bearing mantle xenoliths from Los Gemelos volcano, Canquel Plateau, Patagonia. They are highly-depleted Mesoproterozoic (ReOs model ages of 1.3–0.9 Ga) harzburgites and clinopyroxene-poor lherzolites characterized by typical indicators of partial melt extraction, such as low whole-rock Al2O3 and CaO contents (<1.5 wt%), high Mg# of silicate phases (90–95), and Cr-rich spinel (Cr# 0.20–0.42). Depletion of incompatible highly siderophile elements (Re, Ru, Pd) relative to the primitive upper mantle supports high degrees of melt extraction. The occurrence of phlogopite and K-rich alkaline glass veins with high- and low-SiO2 compositions is clear evidence of modal metasomatism. The light rare earth element (LREE) enrichment in clinopyroxene, as well as the whole-rock U-shaped REE pattern, confirms cryptic metasomatism. This melt-rock interaction is corroborated by major (i.e., Mg# vs. basaltic elements) and trace (i.e., La/YbN vs. Sr/Y and Ti/Eu; and Sr vs. Ti/Eu) element contents of pyroxenes. The calculated compositions of melts in equilibrium with clinopyroxene coexisting with phlogopite suggest interaction with slab-derived materials. This metasomatism has been generated by a chromatographic fractionation-reaction process, from deep to shallow mantle domains. The percolation of a high-K hydrous magma probably is associated with the upwelling of asthenospheric material through a slab-window, which caused partial melting of oceanic crust and overlying sediments during the Paleocene. The varying intensities of metasomatic imprints recorded by mantle xenoliths from Los Gemelos provide valuable insights into the interaction of slab-derived materials near the lithosphere-asthenosphere boundary, at a distance of ∼600 km from the Andean volcanic arc.

Effect of alumina on formation mechanism and structure characteristic of sodium calcium silicate compounds with different stoichiometric coefficients

In order to illustrate the effects of Al2O3 on silicate structure for synthesizing sodium calcium silicate compounds, the formation characteristics, lattice parameters, molecular structure and element chemical state of sodium calcium silicates with different Al2O3 proportions through solid-state reaction were investigated using XRD, SEM-EDS, Raman spectroscopy and XPS analyses. Increasing the Al2O3 content facilitates the formation of Na2CaSiO4 and converts the polymorph of Na2Ca6Si4O15 from γ-type into β-type. The product particles aggregate to form clumps by increasing the Al2O3 content when the molar ratios of Na2O and CaO to SiO2 are 0.5 and 1.5, and the network orderliness of silicates deteriorates to form glassy phase at the low CaO and Na2O contents. Al2O3 can engage in the bonding process with silicate crystals to produce a finite solid solution. Increasing the Al2O3 porportion is advantageous for facilitating the participation of [AlO6] in the Si-O-Al bonding reaction, which leads to the depolymerization of [Si2O7]6-, [Si3O10]8- and [Si6O18]12− and promotes the formation of silicate chains of [SiO4]4- and [Si2O7]6-. Moreover, increasing the contents of Na2O and CaO promote the formation of [AlO4] and the depolymerization within silicate chains, which increases the bonding number of Si-Oter and Al-Oter and then reduces the binding energies of Si2p and Al2p orbits.

Efficient epoxidation of styrene over single-atomic copper-doped ordered mesoporous alumina (Cu-OMA) composited with carbon nitride

The present study assessed the catalytic performance in epoxidation of styrene using tert‑butyl hydroperoxide (TBHP) as an oxidant over single-atomic copper-doped Ordered mesoporous alumina (Cu-OMA) composited with g-C3N4 (CN). The thermal treatment at three temperatures (300, 500, 700 °C) provided a facile mean to modify the texture and electronic structure of the Cu-OMA@CN composite. The X-Ray absorption spectroscopy proved the single-atomic Cu-O-Al and Cu-O-C in Cu-OMA@CN-500 catalyst. Catalytic reaction parameters, namely temperature (60–80 °C), catalyst amount (10–70 mg), substrate/oxidant ratio (1:1–1:3), and solvents (acetone, ethanol, acetonitrile, N, N-dimethylacetamide) were optimized to obtain high conversion of styrene and selectivity to styrene epoxide. Under the optimized reaction conditions (75 °C, 30 mg of catalyst, 1:2 of styrene/TBHP and acetonitrile as solvent), the conversion decreased in the order of Cu-OMA@CN-500 > Cu-OMA@CN-300 > Cu-OMA@CN-700. This sequence was related to the formation of electron-rich single-atom copper sites, high surface area, medium alkaline environment and high content of graphic nitrogen species in Cu-OMA@CN-500. This structure differed from the blocky structure of C3N4 in Cu-OMA@CN-300 and the destroyed tri-s-triazine ring in Cu-OMA@CN-700. The most active Cu-OMA@CN-500 catalyst displayed a high styrene conversion (87.2 %) and striking selectivity to styrene oxide (90.0 %). Its catalytic activity was retained after five recyclability tests. The possible catalytic mechanism for epoxidation of styrene over this catalyst was tentatively proposed.

Pilot-Scale Aluminothermic Production of Silicon Alloy and Alumina-Rich Slag.

As global demand for silicon (Si) and alumina continues to surge, the significance of developing more sustainable production methods has intensified. The SisAl process represents a path-breaking approach to producing Si and alumina by utilizing side streams from the silicon and aluminum industries. In the present work, a comprehensive series of pilot-scale trials was conducted to assess the scalability and validity of the SisAl process. The influences of reductant raw materials, charging methods, input material ratios, and other processing parameters were also investigated. On coupling between thermodynamic calculations and experimental results, it was demonstrated that the SisAl process is stable and controllable at a pilot scale. The typical composition of the produced Si alloy ranges from 70 to 75 wt % Si, 15-18 wt % Ca, and 8-10 wt % Al. The produced CaO-Al2O3-based slag has a composition of 48-57 wt % Al2O3, 40-45 wt % CaO, and 3-13 wt % SiO2. Furthermore, various reductants, including Al blocks, dross, and scraps, were evaluated in the pilot trials, yielding comparable outcomes, with alloy composition differences only within approximately 3 wt % under the same parameter conditions, demonstrating the versatility of raw materials selection in the SisAl process. Moreover, it was found that acidic slag exhibited better features for future upscaling than the neutral slags, with a 5 wt % higher Si content in the alloy and a 4 wt % increase in Al2O3 content in the slag phase. Additionally, the chemical composition of the products was shown to be controllable by adjusting the stoichiometry of the input materials (Al/SiO2 ratio). As the charged stoichiometry increases from 1 to 1.2, the Si content in the alloy significantly decreases from 73 to 63 wt %, while the Al content correspondingly increases from 9 to 18 wt %. Further investigation into processing parameters, such as charging method, slag prefusion, and stirring methods, has also revealed valuable insights toward the continued upscaling of the SisAl process to a potentially innovative, sustainable, low-carbon industrial process.

COMPARATIVE ANALYSIS OF EFFECTIVENESS OF POLVAK 15/72 AS A COAGULANT FOR DRINKING WATER PRODUCTION

New coagulant Polvak 15/72 consisting of aluminum hydroxychloride with a pure Al2O3 content of at least 15.3 wt % was investigated as a possible highly effective agent for discoloration, clarification, and cleaning the natural freshwater to produce high-quality drinking water. Water was taken from the river of Dnipro during the winter-summer period of 2022. A 20 mg dm-3 coagulant concentration showed sufficient water cleaning effectiveness, and brought its chromaticity, turbidity, permanganate oxidizability, aluminum and iron contents within the sanitary limits. This result has been achieved using a coagulant that does not consist of Fe (for which the toxicity is higher than that of Al) and less Al than in the widely used Polvak-68. The effectiveness of removing trihalomethanes (THM, mostly chloroform) by Polvak 15/72 is insufficient, and additional non-polar adsorbent or the use of a chlorine-free water disinfection technology is required to keep the content of THM within the sanitary limits.

Densification and network structural changes in binary aluminosilicate glass via cold sintering process

Binary aluminosilicate glasses containing 20–50 wt% Al2O3 were successfully densified through a cold sintering process (CSP) using 1–10 M NaOH solutions. The investigation focused on densification and structural unit changes in the cold-sintered binary aluminosilicate glasses. Specifically, the binary aluminosilicate glass with 40 wt% Al2O3, cold-sintered at 180 °C using 1–10 M NaOH solutions, achieved a relative density of up to 90 % at 10 M NaOH. This was attributed to an enhanced dissolution-precipitation process facilitated by an increased concentration of the NaOH solution. In aluminosilicate glasses with 20–50 wt% Al2O3, the relative densities approached 90 % after CSP at 180 °C using a 10 M NaOH solution. Al(OH)3 formation in the cold-sintered glasses was confirmed, particularly at higher concentrations of NaOH solution (>10 M) and higher contents of Al2O3 (>40 wt%). Changes in Si structural units were observed during CSP, with Al-rich Si units becoming dominant as the concentration of the NaOH solution increased. The higher substitution of Si-O-Si bonds by Si-O-Al bonds led to the precipitation of Al(OH)3, as well as an increased Vickers hardness and biaxial flexural strength of the cold-sintered glasses. These findings demonstrate that the Al2O3 content and NaOH concentration play important roles in the densification and enhancement of the mechanical property in the cold-sintered alumina-rich binary aluminosilicate glasses and offer insights into the optimal conditions for obtaining desirable aluminosilicate materials through CSP.

K isotopic fractionation in K-feldspar: Effects of mineral chemistry

Abstract Controlling factors of potassium (K) isotopic fractionation in K-feldspar remain poorly constrained. In this study, we analyzed the K isotopic compositions of 11 K-feldspar samples from diverse lithological compositions. The degree of Al/Si order ranged from 0.22 to 0.94 (1.0 = completely ordered). Analyzed samples are mixtures of K-feldspar (&amp;gt;70 wt%) and coexisting albite. The relative contribution of K2O from the K-feldspar phase of the sample was over 98%, indicating that the K isotopic composition (δ41K) derives mainly from K-feldspar and hence reflects its behavior. The δ41K values of these samples range from –0.710 to –0.075‰, which are slightly correlated with the degree of Al/Si order. The correlations of δ41K with SiO2 and Al2O3 contents and the corresponding Al/Si mole ratios reveal that Al and Si play a significant role in the K isotopic behavior of K-feldspar. The correlations of δ41K with SiO2 and Al2O3 contents are attributed to the difference in K-O bond strengths. Compared to K-feldspar, the K content could be a better proxy for constraining the δ41K of plagioclase. Our results demonstrate that the δ41K of K-feldspar is dependent on its mineral chemistry, and its K isotopic composition may be insensitive to other factors, such as the source heterogeneity. The inference is further confirmed by comparing the δ41K values in this study with published δ41K values of K-feldspar from different sources.

Structure, thermal and microwave dielectric properties of cold-sintered Li2MoO4-Al2O3 ceramic

Dielectric ceramics are essential components in communication systems that operate within the microwave frequency range. In high-density packages, dielectric substrates ceramics must possess high thermal conductivity to efficiently dissipate heat. However, achieving adequate thermal conductivity (κ) in ceramics sintered at low temperatures is challenging. In this study, we employed the cold sintering process (CSP) to fabricate Li2MoO4-x%Al2O3 (0≤x≤80, in volume) ceramics under 200 MPa pressure at 150 °C. The Li2MoO4-40%Al2O3 composite exhibited significantly enhanced κ of 5.4 W·m–1·K–1, an 80% increase compared to pure Li2MoO4 ceramic with κ of 3 W·m–1·K–1. At 40% Al2O3 content, the Li2MoO4-Al2O3 ceramic demonstrated notable microwave properties (ε ∼ 6.67, Q×f ∼ 17,846 GHz, τf ∼ −105 ×10–6/°C). Additionally, simulation of a microstrip patch antenna for 5 GHz applications using Li2MoO4-20%Al2O3 ceramic as dielectric substrate via Finite Element Simulation software showed excellent performance, with radiation efficiency exceeding 99% and low return loss (S11 < −30 dB) at both 4.9 GHz and 28.0 GHz center frequencies. These findings underscore the suitability of Li2MoO4- Al2O3 ceramics for microwave dielectric substrate. KeynotesMicrowave dielectric ceramic, Thermal conductivity, Cold sintering process, Antenna

Stability performance of an Algerian Ni/purified diatomite catalyst in the dry reforming methane reaction: characterization and properties

AbstractThis work aims to characterize and study the properties of an Algerian diatomaceous earth (Sig-Mascara) as a catalyst carrier. A commercial product of diatomite was characterized by granulometric analysis, X-ray fluorescence, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis/differential scanning calorimetry and scanning electron microscopy/energy-dispersive X-ray spectroscopy methods. To purify the diatomite and remove the impurities (iron oxides, clay minerals, quartz and organic matters), the &lt;63 μm fraction of the diatomite was separated out. The 15Ni/Ds-700 catalyst has lower SiO2, Al2O3 and CaO contents compared with the original diatomite. The NiO content of the catalyst is 15 wt.%, indicating successful impregnation. According to the nitrogen sorption–desorption results, the specific surface area of the purified diatomite particles (&lt;63 μm) increased from 26.47 to 46.33 m2 g–1 compared to crude diatomite. The 15Ni/Ds-700 catalyst was applied in the dry reforming of methane to obtain synthesis gas (CO and H2). The results showed that the catalyst was relatively stable during catalytic measurements for 6 h, although the conversion rate value was low (12%).

Temperature and compositional dependences of H2O solubility in majorite

Abstract We systematically investigated H2O solubility in majorite as a function of temperature from 1670–2270 K under a pressure of 20 GPa using multi-anvil techniques. The H2O solubility in majorite decreases with increasing temperature. In addition, the H2O content is relatively independent of the concentrations of Al2O3 and SiO2 in majorite. Majorite can store more H2O than bridgmanite in the lower mantle. Therefore, when a slab sinks into the lower mantle, hydrous melt could be produced not only by the phase transformation from ringwoodite to bridgmanite + ferropericlase near 660 km depth but also by the majorite to bridgmanite transformation over a wide range of depths from 660 km up to ~800 km, at which majorite dissolves completely in bridgmanite.

Phase evolution and performance of sodium sulfate-activated slag cement pastes

This study evaluates the reaction kinetics, phase assemblage, and microstructure evolution of Na2SO4-activated slag cements produced with three commercial slags. The main reaction products identified are ettringite and calcium aluminosilicate hydrates, alongside a poorly crystalline SO42- intercalated Mg-Al-layered double hydroxide (LDH) phase. Results revealed that the Al2O3 slag content alone does not correlate with the cement performance. While pastes made with a higher Al2O3 content slag exhibit faster reaction kinetics, those made with a slag with a higher Mg/Al ratio developed superior compressive strength and reduced porosity over extended curing periods. Thermodynamic modelling simulations indicate that sulfate consumption occurs via ettringite and LDH phase formation, influencing the slag reaction degree, pH value, and porosity reduction in these cements. This research highlights the critical role of slag composition in controlling microstructure and, consequently, performance of sodium sulfate activated slag cement pastes.

Effect of Al2O3 coating on the properties of Si3N4 ceramics prepared by vat photopolymerization

The preparation of Si3N4 ceramics by vat photopolymerization (VPP) has motivated increasing research interest. However, it is challenging to prepare Si3N4 ceramics by VPP due to the high UV-light absorbance and refractive index of powder. In this paper, a method for Al2O3-coated Si3N4 powder was proposed. Combined with the boehmite-coated and high-temperature treatment, Al2O3 was successfully coated on the surface of Si3N4 powder. The effect of Al2O3 content on the properties of Si3N4 powders, slurry and the sintered Si3N4 samples were investigated. The Al2O3 coating layer not only improves the curing forming ability of Si3N4 slurries, but also can directly act as one of the sintering aids of Si3N4 ceramics. The bulk density of the samples decreases from 3.04 ± 0.02 g/cm3 to 2.97 ± 0.01 g/cm3 with the increase of coating content, while the porosity increases from 5.38 ± 0.89 % to 7.54 ± 0.63 %. The sample of 5 wt % Al2O3 coating content has the maximum flexural strength of 474.28 ± 16.38 MPa and the highest relative density of 94.62 ± 0.89 %. This work can not only obtain a great modification effect, but also promote the dense sintering of Si3N4 ceramics during subsequent stages, which provides a constructive method for modifying Si3N4 powders to achieve photopolymerization.

Effect of Al2O3 on the sintering process and the metallurgical performance of sinter

ABSTRACT The trend to process iron ore with increasing Al2O3 content has affected the performance of sinter and blast furnace operations. Formation of the primary melts and phase properties such as morphology and reducibility of the iron ore could be easily influenced by the Al2O3 content. In this paper, the effect of the Al2O3 content in the sinter samples, which range from 1.49 to 3.24 wt-% with a basicity of 2.0, MgO/Al2O3 ratio of 1.05, on the sintering process and the metallurgical performance were studied through a sinter pot experiment and a reduction experiment. The results show that an increase in the Al2O3 content deteriorated the sintering index, and the yield and tumble index decreased by 7.61% and 12.02%, respectively. The sintering index was relatively stable when the Al2O3 content was between 2.10 and 2.95 wt-%. Low-reduction columnar silico-ferrite of calcium and aluminum increased with the increasing Al2O3 content, hindered the reduction index of the sinter. The low-temperature reduction degradation index change was only around 2%, due to the higher MgO content of the sinter promoting magnetite formation.

The Genesis of Ultramafic Rock Mass on the Northern Slope of Lüliang Mountain in North Qaidam, China

The ultramafic rock located on the northern slope of Lüliang Mountain in the northwestern region of North Qaidam Orogen is altered to serpentinite. The occurrence of disseminated chromite within the serpentinite holds significant implications for understanding the petrogenesis of the protolith. This work provides strong evidence of a distinct zonal texture in the chromite found in the ultramafic rock, using petrographic microstructure and electron probe composition analysis. The core of the chromite is characterized by high contents of Cr#, with enrichment in Fe3+# (Fe3+/(Cr + Al + Fe3+)) and depletion in Al2O3 and TiO2. The Cr2O3 content ranges from 51.64% to 53.72%, while the Cr# values range from 0.80 to 0.84. The FeO content varies from 24.9% to 27.8%, while the Fe2O3 content ranges from 5.19% to 8.74%. The Al2O3 content ranges from 6.70% to 9.20%, and the TiO2 content is below the detection limit (&lt;0.1%). Furthermore, the rocks exhibit Mg# values ranging from 0.13 to 0.25 and Fe3+# values ranging from 0.07 to 0.12. The mineral chemistry of the chromite core in the ultramafic rock suggests it to be from an ophiolite. This ophiolite originated from the fore-arc deficit asthenosphere in a supra-subduction zone. The estimated average crystallization temperature and pressure of the chromite are 1306.02 °C and 3.41 GPa, respectively. These values suggest that the chromite formed at a depth of approximately 110 km, which is comparable to that of the asthenosphere. The chromite grains are surrounded by thick rims composed of Cr-rich magnetite characterized by enrichment in Fe3+# contents and depletions in Cr2O3, Al2O3, TiO2, and Cr#. The FeO content ranges from 28.25% to 31.15%, while the Fe2O3 content ranges from 44.94% to 68.92%. The Cr2O3 content ranges from 0.18% to 23.59%, and the Al2O3 and TiO2 contents are below the detection limit (&lt;0.1%). Moreover, the rim of the Cr-rich magnetite exhibits Cr# values ranging from 0.90 to 1.00, Mg# values ranging from 0.01 to 0.06, and Fe3+# values ranging from 0.64 to 1.00, indicating late-stage alteration processes. The LA-ICP-MS zircon U-Pb dating of the ultramafic rock yielded an age of 480.6 ± 2.4 Ma (MSWD = 0.46, n = 18), representing the crystallization age of the ultramafic rock. This evidence suggests that the host rock of chromite is an ultramafic cumulate, which is part of the ophiolite suite. It originated from the fore-arc deficit asthenosphere in a supra-subduction zone during the northward subduction of the North Qaidam Ocean in the Ordovician period. Furthermore, clear evidence of Fe-hydrothermal alteration during the post-uplift-denudation stage is observed.

Design, fabrication, and hydrogen blocking performance of alumina/zirconia functional gradient coatings

When electrophoretic deposition (EPD) is employed for fabricating alumina (Al2O3)-based hydrogen barrier coatings, it becomes customary to enhance the adhesion strength by subjecting the deposited coating to high-temperature annealing. In this study, a functionally-graded Al2O3/ZrO2 coating was designed by using the thermal stress module of Ansys software. The influence of different gradient composition distribution indices, number of layers, and layer thickness on the distribution of thermal stress was systematically investigated by simulation. Based on simulation results, the gradient parameters of the functionally-graded coating were determined as follows: a transition layer with three layers, each with a thickness of 0.13 mm; the first layer consisted of Al2O3 to ZrO2 ratio of 1:3, the second layer with a ratio of 1:1, and the third layer with a ratio of 3:1. Subsequently, the process parameters for EPD of Al2O3 coating were optimized via experimental exploration. Under conditions of deposition time of 120 s, deposition voltage of 60 V, Al2O3 concentration of 8 g L−1 in the electrophoretic solution, and magnesium chloride hexahydrate concentration of 0.6 g L−1, the as-fabricated Al2O3 coating exhibited optimal hydrogen barrier performance. Finally, different proportions of ZrO2 were sequentially incorporated into the prepared Al2O3 coating to form functionally-graded materials (FGM). Thermal cycling experiments showed that the Al2O3 coating with added ZrO2 exhibited better stability at high temperatures. Regarding hydrogen barrier performance, the functionally-graded coating outperformed the non-functionally-graded coating.

Properties of SiO2-Al2O3 refractories based on silica glass binder suspension and investigation of their printability using the Direct Ink Writing method

The SiO2-Al2O3 refractories and corresponding inks for 3D printing were prepared from silica glass binder suspensions and fused alumina with grain sizes of 75 and 240 μm. Phase analysis (XRD) and morphological studies (SEM) were conducted to investigate the influence of sintering temperature and Al2O3 content on the strength, porosity, and density of the refractories. Rheological studies (rotational viscometry) were carried out determine the effect of polyethylene glycol (PEG) and hydroxypropyl methylcellulose (HPMC) content on the flow behavior of the inks. It was established that firing refractories based on fused silica and fused alumina at 1500 and 1600 °C led to the formation of mullite and aluminosilicate melt on the surface of Al2O3 grains, enhancing the strength of the synthesized materials. Addition of PEG and HPMC to the ink composition was found to improve their rheological properties by increasing yield strength and promoting plastic flow. The ink demonstrated high printability and they are suitable for producing refractories using the Direct Ink Writing method.

INFLUENCE OF ALUMINA PARTICLES (AL2O3) ON PHYSICO-MECHANICAL BEHAVIOR OF ADDITIVE MANUFACTURING- DLP RESIN USED FOR RAPID TOOLING

Over the past decade, additive manufacturing (AM) has gained considerable recognition in rapid tool manufacturing owing to its notable advantages. For the rapid injection mold manufacturing by the DLP-AM method, the most important subject that should be focused on is the photopolymer resin, as the 3D printed mold must withstand the stresses and temperatures encountered by the injection pressure and temperature of the molten plastic. This study aimed to investigate the effect of adding alumina (Al2O3) powder on the properties of a DLP-AM photopolymer. For this aim, 2 and 4 wt.% Al2O3 were added to a photopolymer resin, and 3D-printed samples were produced by DLP. Several physico-mechanical properties were studied compared to the pure polymer. The results indicated that as the Al2O3 content increased, the void fraction, volumetric heat capacity, wear resistance, tensile and flexural strength, all decreased. In contrast, as the Al2O3 wt.% increased, so did the flexural strain, impact strength, hardness, and thermal conductivity. This study showed that injection molding cycle times can be shortened considerably due to this benefit, which would be beneficial for quick molding applications. Keywords: Rapid tool manufacturing, polymer composites, 3D printing, alumina, Al2O3, photopolymer, additive manufacturing.

High purity alumina production by leaching-ion exchange process: Design and flowchart proposal

Growing demand for high-purity Al2O3 for the electronic market and green energy production, allied with the need to decrease waste generation and dam use, will impact the future of mining, and new processes should be developed. The present study aimed to develop a hydrometallurgical process to obtain high-purity Al2O3 from bauxite. Among the samples studied, BX03 had the highest Al2O3 (63.8 %) and lowest Fe2O3 content (4.3 %). Different acids were evaluated – H2SO4, HCl, HNO3, and H3PO4 – and the H2SO4 reaction achieved all Al leaching with the best technical–economic analysis (TEA). Purification experiments were carried out with ion exchange resins in batch reactions. The best purification parameters were 4 h of contacting time and mass of resin/volume of solution ratio as 1/10 at 45 °C in two stages. The iminodiacetate resin (Lewatit TP 207) achieved the best results and removed all Fe ions without losses. High-purity Al2O3 was further obtained by precipitation with NH4OH after calcination. Considering the leaching step costs, the proposed process may achieve up to US$ 63,022.91 in profit.

The influence of cyclic creep on the long-term oxidation behavior of a directionally-solidified nickel-based superalloy

This work investigates the effect of cyclic creep on the long-term oxidation of a directionally-solidified nickel-based superalloy DZ445 up to 1800 h. The stress application of cyclic creep refines the oxides, increases the oxidation weight gain, reduces the oxidation rate exponent, and decreases the activation energy. It enhances the content of Al2O3 and TiO2 in the outermost layer and in the sub-outer layer of CrTaO4 in the film. It delays the formation of the continuous innermost layer of Al2O3 and the sub-inner layer that is rich in Al2O3. The change of phase content and type in the oxidation layers could be ascribed to the diffusion kinetic effect of cyclic creep stress in the superalloy.