Alumina Particles Research Articles

Combustion and energy performance of multiple aluminum-based alloy particles

The long ignition delay time, high ignition temperature and agglomeration prevent the aluminum (Al) particles from fully releasing the chemical energy stored within them during combustion. Al-based alloy fuels with high energy density and excellent combustion performance have become a potential candidate for replacement with pure Al. Therefore, understanding the combustion and energy performance of Al-based alloys is beneficial for the development of Al-based energetic materials. Herein, the combustion and energy performance of pure Al and three Al-based alloys were comparatively investigated by means of a thermal analysis system, an ignition and combustion test apparatus, and a variety of physicochemical property characterizations. The results showed that all three Al-based alloys contained at least one intermetallic compound. Al-boron (B) and Al-magnesium (Mg)-B alloys had higher theoretical energy densities than pure Al, while Al-Mg did not. The thermal oxidation properties of all three alloys were significantly better than those of pure Al. Compared with pure Al, the three alloys showed higher burning rate, shorter ignition delays, more vigorous combustion, and higher burnout at room pressure in air. This is still true after adding AP. According to the compositions of the condensed combustion products, the possible chemical reactions during the combustion of the alloys were speculated. Grasping the combustion mechanisms of the alloys is challenging due to the relative lack of thermodynamic data on intermetallic compounds. Finally, a comprehensive comparison of the combustion processes of pure Al and alloys was made. Although the Al-Mg alloy does not have the same theoretical energy density as pure Al, the more outstanding combustion performance and fewer two-phase flow losses may make up for the gap in theoretical energy density.

Combustion and heat release characteristics of micron aluminum with extremely large specific surface area obtained by L-malic acid surface corrosion

Aluminum (Al) particles are widely used in propellants, thermite and pyrotechnics. However, commonly used micro Al has drawbacks such as agglomeration, high ignition temperature and slow burning rate, making its energy potential not fully exploited in applications. Therefore, exploring pathways to enhance the combustion of Al particles has become the focus at present. Herein, L-malic acid (LMA) was used to corrode the surface of Al particles to obtain a sample (named LMAl) with an average specific surface area of 11.456 m2/g (corresponding to Al particles with a diameter of 194 nm). The particle size distribution of LMAl did not change significantly compared to pristine Al. The XPS results showed that a small amount of LMA and corrosion products remained on the surface of the LMAl particles. Thermal analysis tests showed that the thermal oxidation rate and efficiency of LMAl was dramatically higher than that of pristine Al. Compared with the pristine Al, the combustion characterization parameters of LMAl such as combustion intensity, ignition delay time, maximum combustion temperature, mass burning rate and combustion efficiency were all improved. This trend was maintained after blending the ammonium perchlorate (AP). The condensed combustion products (CCPs) of Al revealed a large number of agglomerates and unburned Al particles. While many broken particles and tentacle-like structures were found in the CCPs of LMAl. Overall, compared to Al, the combustion of LMAl is significantly enhanced. The thermal reaction and combustion behaviors of the two are quite different. This study provides new insights into improving the ignition and combustion of Al.

Comparison of Tensile Bond Strength of Soft Denture Liner Material on Denture Base Resins

Aim: This study aims to evaluate the tensile bond strength (TBS) of a silicone-based soft denture liner material on denture bases produced via conventional, subtractive, and additive manufacturing techniques and examine the effect of aluminum oxide particle abrasion (APA) on TBS. Material and Methods: A total of 48 cylindrical denture base resin samples were manufactured using three different techniques: conventional, subtractive, and additive manufacturing. The samples were divided into two groups: control and APA. All samples were separated at the center, and the soft liner was applied to the corresponding surfaces. The specimens then underwent TBS testing. Data were analyzed using Two-way ANOVA and Bonferroni post hoc tests. Results: Two-way ANOVA results indicated a significant difference among the denture base resins, while no significant difference was found between the control and APA groups. The highest TBS was observed in the subtractive-manufactured APA group, while the lowest TBS was in the additive-manufactured APA group. Significant differences were found between the subtractive and additive-manufactured groups (p=0.022). Conclusion: This study demonstrates that TBS varies with the DB's manufacturing technique. While APA increased TBS in subtractive manufacturing, it had no statistically significant effect. Further research should explore different soft lining materials and consider in vivo conditions for more comprehensive insights.

Colorful, eco-friendly and scalable passive radiative cooling coatings integrating thermal insulation and self-cleaning properties

Passive radiative cooling can cool space by reflecting sunlight and infrared thermal emission to dissipate heat to the cold outer space without any energy consumption, being one of ideal technologies towards the goals of peak carbon dioxide emission and carbon neutrality. Before the wide application of this technology, however, more efforts are needed to enhance its efficiency and better adapt to different application scenarios. In this work, we have successfully prepared multifunctional color radiative cooling coatings that integrate anti-UV, self-cleaning and heat insulation performances without using any volatile toxic solvents. The optimal coating exhibits exceptional solar reflectivity (R̅Solar% = 92.58 %) and infrared thermal emissivity (ε̅% = 97.96 %). What’s more, the coating achieves a temperature difference of up to 10°C compared to the subambient temperature when applied at a thickness as low as 100 μm under direct sunlight conditions with an intensity of 650 W/m2. Additionally, the hydrophobically modified alumina particles of the top layer not only effectively prevent the absorption of UV light by the bottom layer, but also participate in the construction of micro-nano structures, enabling the coating to exhibit a water contact angle of up to 158° and a low rolling angle (<2°). Furthermore, the coating demonstrates exceptional mechanical robustness and chemical durability. The addition of water-based colorants into the coating allows for a wide range of color options without compromising its properties. These cost-effective and environmentally friendly color radiative cooling coatings possess significant potential in meeting aesthetic requirements while providing efficient cooling for spaces and self-cleaning performance.

Three-dimensional FSI simulation of cell entrapment utilizing acoustic interparticle force in a standing acoustic field

Abstract In recent years, there has been significant development in microfluidic devices for cell separation and sorting using acoustic methods in biomedical applications. The acoustic interparticle force (AIF) arises from particle interactions with the scattered field of other particles, influencing particle motion at close ranges and facilitating optimal trapping and separation. This study analyzes a two-particle system consisting of a fixed particle and a white blood cell (WBC) within a standing acoustic field and creeping flow using fluid-structure interaction (FSI). To reduce computational costs by decoupling the acoustics and FSI, the acoustic pressure equation (AcPr) was solved on the frequency domain to calculate the total acoustic radiation force in each time step. Model accuracy was assessed by evaluating interparticle (AIF) and primary acoustic radiation forces (ARF) on a polystyrene particle and comparing simulation results to analytical and experimental data. Results demonstrate precise ARF performance, with discrepancies in acoustic interparticle force attributed to viscous losses near the particle surface. Moreover, the higher density of the fixed particle compared to WBCs induces significant acoustic interparticle attraction at close distances. Consequently, cell entrapment occurs through strong attraction and collision with fixed aluminum and silicon particles in creeping flow in all three Reynolds numbers 1.4E-3, 2.1E-3, and 3E-3. Increasing Reynolds numbers augment the likelihood of cell separation from the fixed particle. These findings contribute to optimizing cell isolation and entrapment strategies.

Акустические свойства композита алюминий-полистирол

The paper presents the results of experimental studies of the acoustic properties of an aluminum-polystyrene composite with a connectivity of 0-3. The dependences of the speed and attenuation of longitudinal volumetric acoustic waves (BAW) in the composite at a frequency of 17 MHz, as well as its density and acoustic impedance, on the volumetric content of aluminum particles in it, in the range of 0-80%, were obtained. It has been shown that an increase in the volume fraction of filler particles in the aluminum-polystyrene composite leads to significant changes in its physical properties - density and acoustic impedance - almost 2 times, longitudinal wave speed - by 17% and acoustic attenuation - by 25 times. Velocity and attenuation are, respectively, the least and most sensitive parameters to the composition of the composite. The dependences are nonlinear; this is due to the appearance of air inclusions, intergranular interaction of aluminum particles and, as a consequence, deterioration of interphase interaction and structural organization of the composite material.

Electrical Cleaning of Rough Spherical and Bumpy Abrasive Particles Charged by Corona Ions in Post-CMP

This study describes electrostatic methods for effective post-CMP (Chemical Mechanical Polishing) cleaning of contaminated wafers with rough spherical and bumpy abrasive particles. The case when corona ions charged the particles was studied. The extended JKR adhesion model for rough surfaces was used in the analysis. Charges were uniformly distributed across the entire particle surface for the corona charging. Removal of charged rough spherical and bumpy particles was investigated. The electric fields necessary to detach alumina particles with different numbers of bumps, contact asperities, and charges from wafer surfaces with varying roughness levels were evaluated. The present model predictions were compared against experimental data for the detaching polystyrene latex particles from an aluminum oxide substrate. It was shown that the model predictions for the electric detachment fields agree with the corresponding experimental data for the selected range of parameters. The model provides an approach for removing rough spherical and bumpy particles charged by corona ions in diverse applications, including post-CMP cleaning.

Evaluation of vertical marginal discrepancy and load-to-failure of monolithic zirconia and lithium disilicate laminate veneers manufactured in different thicknesses

ObjectivesThis study aimed to evaluate the feasibility of monolithic zirconia laminate veneers (MZLV) compared to lithium disilicate laminate veneers (LDLV).Materials and methodsSixty resin replicas, each prepared with depths of 0.5 mm, 0.7 mm, and 1 mm, were produced using a 3D printer from acrylic teeth. Laminate veneers of these thicknesses were milled from pre-sintered monolithic zirconia (3rd generation) and lithium disilicate blocks. The intaglio surface of MZLV was treated with air abrasion using 110 μm diameter silica-modified aluminium oxide particles and ceramic primer, while LDLV was etched with etchant gel and treated with the ceramic primer before cementation with resin cement. Vertical marginal discrepancy (VMD) was assessed using a stereomicroscope, and a load-to-failure test was conducted using a universal testing machine. Failure modes were evaluated macroscopically on fractured surfaces. Data were analysed statistically using Two-way ANOVA and Bonferroni correction (α = 0.05).ResultsLDLV samples exhibited significantly larger VMD compared to MZLV samples across all thicknesses, especially in cervical, palatal, and mean data. Within the LDLV group, load-to-fracture values for 0.7 mm and 1.0 mm thicknesses were similar, whereas for 0.5 mm thickness, it was significantly lower. In the MZLV group, load-to-fracture values were lower for 0.7 mm and 1.0 mm thicknesses compared to LDLV, but higher for 0.5 mm thickness.ConclusionsMaterial choice and restoration thickness significantly influence laminate veneer restorations’ success. MZLV generally exhibits superior vertical marginal fit compared to LDLV, with varying load-to-failure values across different thicknesses. Clinical management of debonding in MZLV is simpler compared to restoration fracture in LDLV.Clinical relevanceConsidering clinical factors, MZLV may be a preferable option to LDLV for this restoration with the thickness of 0.5 mm.

Effects of Wire-Wrapping Patterns and Low Temperature on Combustion of Propellant Embedded with Metal Wire

Incorporating silver wires into propellant has emerged as a highly effective strategy for enhancing propellant burning rates, a technique extensively deployed in the construction of numerous fielded sounding rockets and tactical missiles. Our research, employing a multi-faceted approach encompassing thermogravimetric-differential scanning calorimetry measurements (TG-DSC), combustion diagnoses, burning rate tests, and meticulous collection of condensed combustion products, sought to elucidate how variations in silver wire quantity and winding configuration impact the combustion properties of propellants. Our findings underscore the remarkable efficacy of double tightly twisted silver wire in significantly boosting propellant burning rates under ambient conditions. Moreover, at lower temperatures, the reduced gap between the propellant and silver wire further magnifies the influence of silver wire on burning rates. However, it is noteworthy that the relationship between burning speed and combustion efficiency is not deterministic. While a smaller cone angle of the burning surface contributes to heightened burning rates, it concurrently exacerbates the polymerization effect of vapor phase aluminum particles, consequently diminishing propellant combustion efficiency. Conversely, propellants configured with sparsely twinned silver wires exhibit notable enhancements in combustion efficiency, despite a less pronounced impact on the burning rate attributed to the larger cone angle of the burning surface. Remarkably, these trends persist at lower temperatures. Based on the principle of heat transfer balance, a theoretical model for the combustion of propellants with wire inserts is developed. The reliability of this theoretical model is validated through a comparison of calculated values with experimental data. Our research outcomes carry significant implications for guiding the application and advancement of the silver wire method in solid propellants for solid rocket motors, offering valuable insights to inform future research and development endeavors in this domain.

Enamel Deproteinization or Sandblasting for Enamel Reconditioning Before Acid Etching to Enhance the Shear Bond Strength of Metallic Brackets in a Third Bonding: An In Vitro Study.

Enamel conditioning with 37% phosphoric acid is the most common technique during orthodontic bracket bonding procedures. However, due to the repeated de-bonding of the orthodontic brackets during treatment, other methods were needed to condition the enamel surface and increase the bond strength. This study aimed to compare the effect of conditioning the enamel surface by sandblasting with aluminum oxide particles or 5.25% sodium hypochlorite gel in combination with acid etching compared to acid etching alone on shear bond strength (SBS). One hundred eight extracted upper premolars were randomly divided into three groups according to the conditioning enamel surface method. After the first and second bonding of metal brackets, new metal brackets were bonded with a total-etching adhesive after enamel conditioning using different methods: acid etching only (37% phosphoric acid for 30 seconds) (AE group), sodium hypochlorite associated with acid etching (5.25% NaOCl gel for 60 seconds and then acid etching for 30 seconds) (NaOCl-AE group), and sandblasting associated with acid etching (sandblasting for five seconds and then acid etching for 30 seconds) (SB-AE group). The shear bond strengths of the brackets were tested with a universal testing machine. One-way analysis of variance (ANOVA) and Tukey's honestly significant difference (HSD) tests were used to detect significant differences in shear bond strength among groups at the third bonding. Repeated-measure ANOVA and Bonferroni's tests were used to detect significant differences in shear bond strength among the bonding attempts within each group. 5.25% sodium hypochlorite associated with the acid etching method produced significantly greater shear bond strength than sandblasting associated with acid etching and acid etching only methods at the third bonding (16.40 ± 5.80 MPa, 13.60.47 ± 6.40 MPa, and 9.90 ± 4.40 MPa, respectively; P < 0.001). However, there was no significant difference between the AE and SB-AE groups (P = 0.247). In addition, we found a significant decrease in the shear bond strength within each group after each bonding attempt. Conditioning the enamel surface with 5.25% sodium hypochlorite associated with acid etching produced greater bond strength than conditioning by sandblasting associated with acid etching and acid etching only at the third bonding. The bond strength of the metal bracket decreased with increasing bonding attempts, even with the application of enamel surface conditioning methods.

Micron-sized aluminum particle combustion under elevated gas condition: Equivalence ratio effect

Micron-sized aluminum (Al) particle combustion under elevated gas condition is critical for improving energetic material performance, impacting propulsion and explosives technology. This study utilizes Eulerian-Lagrangian method to investigate Al particle combustion dynamics, encompassing both heterogeneous reaction (HTR) and homogeneous reaction (HMR). It focuses on the critical role of the equivalence ratio in single Al particle combustion, highlighting the interplay between HTR and HMR, aiming to optimize energy release and emission control. Our study identifies four stages in the combustion of a single Al particle, where the highest heat release is attributed to HTR, succeeded by HMR, and the minimal from unburned Al vapor. We observe a decline in the total heat release rate with an increasing equivalence ratio, primarily due to the differential impacts of heterogeneous and homogeneous reactions. The thermal-runaway stage in HTR is governed by the particle temperature, while the subsequent decaying stage is influenced by either the diminishing effective Al droplet diameter or the availability of oxygen, contingent upon the fuel conditions. Utilizing Cantera software to analyze HMR allows us to elucidate the thermal effects of elementary reactions and the key reaction pathways. These findings underscore the complex interactions between Al particles and the surrounding gas, providing insights into optimizing the conditions for Al-containing reaction systems.

Study on aluminum recovery from selected aluminum-containing packaging waste by pyrolysis system

Abstract Nowadays, consumers more frequently than not choose packaged food over fast food due to its convenience, high nutrition value, ease of preparation, and health friendliness. This has caused the amount of packaging waste in the world to increase rapidly, becoming one of the major dangers to the global environment. The potential hazard associated with this kind of waste and have been developing more innovative techniques to lessen its negative impacts. This study aims to convert food packaging wastes (FPWs) into raw materials (aluminum and carbon particles) using three combined methods: pyrolysis, mechanical and chemical treatment. This experiment used a furnace used in the laboratory to heat plastic packaging waste to obtain a solid fraction, under pre-set conditions, including temperatures of 500 °C, 600 °C, 700 °C, and 800 °C, and the retention time is 10 min, 20 min, 30 min. Specifically, the highest amount of solid fraction obtained was 20.9% at the condition of 500°C for 10 minutes, while the recovery rate was the lowest at 8.91% at the condition of 800 °C for 30 minutes. According to the references, the retention time condition of 30 minutes is the optimum for aluminum recovery, of which 800°C is the best with 8.11%, along with the ease of separation of aluminum fragments and aluminum particles out of the mixture. Finally, Fourier transform infrared spectroscopy (FTIR) analysis was used to confirm the composition of the solid obtained after the pyrolysis process, the selected wavelength ranged from 650-4000 cm−1. In summary, the experiment was successful when it found the optimal conditions for the pyrolysis method in recovering aluminum from packaging waste. In addition, the recovery of aluminum metal from this type of waste also contributes to solving the very high demand for this metal in recent times.

Effect of aluminum particles on the insulating properties of C4F7N/CO2 mixed gas

The C4F7N/CO2 mixed gas is most expected to replace SF6 in high-voltage power equipment, and the generation of free metal particles in gas-insulated equipment is unavoidable and highly susceptible to inducing insulation failures. In this paper, the effects of flaky, spherical, and mixed shape aluminum particle defects on the breakdown characteristics of C4F7N/CO2 mixed gas are investigated and compared to those of SF6 under the same conditions. The experimental results show that the effect of particle defects on the insulating properties of C4F7N/CO2 gas mixtures is visualized by the fact that particle defects reduce the breakdown voltage of C4F7N/CO2 gas mixtures, increase their stochasticity, and reduce the enhancement of the insulating properties of C4F7N/CO2 gas mixtures by increasing the air pressure. The greater the number of particles, the greater is the degree of influence. Comparison of the SF6 and C4F7N/CO2 gas mixtures reveals that, in the case of flake defects, increasing the air pressure improves the insulation performance of the SF6 gas better than that of the C4F7N/CO2 gas mixture. Under the condition of the same number of particles, the larger the proportion of spherical particles in the hybrid particles, the smaller is the influence of metal particles on the C4F7N/CO2 mixed gas and on SF6 gas.

Mechanical properties of aluminum matrix composite reinforced with titanium carbide

Abstract An original method for the production of metal matrix nanocomposites has been proposed, which consists of depositing carbide structures 4–12 nm thick onto the surface of particles of aluminum powder by molecular layering, mixing the resulting dispersed particles with particles of pure metal in the required concentration, then pressing and sintering the resulting mixture. The resulting workpieces are subjected to intense plastic deformation by high-pressure torsion, which not only significantly reduces porosity, ensures a uniform distribution of reinforcing particles throughout the volume, and destroys carbide shells on the surface of dispersed particles, but also grinds aluminum particles. Experimental stress-strain curves of the synthesized composites were constructed and the contribution of various hardening mechanisms to the final hardening of the metal matrix composite was assessed. In metal matrix composites synthesized by this method, with small fractions of the volume content of reinforcing titanium carbide particles (less than 0.1%), almost twofold hardening and a threefold increase in the yield strength are observed with a slight reduction in plastic deformation before failure.

New experimental method for the simultaneous determination of concentration and size profiles of condensed combustion products around a burning aluminum droplet

When an aluminum particle burns in the diffusive regime, a cloud of nanometric particles of its primary oxide, alumina, is formed around the droplet. Characterizing this oxide smoke surrounding a burning aluminum droplet is essential. The original contribution of this paper is to introduce an experimental approach that allows for simultaneous size and concentration measurement of the particles composing the oxide smoke. This paper employs an electrodynamic levitator to facilitate the self-sustained combustion of an isolated aluminum particle, with a radius of 35μm, in atmospheric air. This levitation apparatus is paired with an optical setup that allows for a multi-spectral light extinction method. This technique is specifically designed to measure the size and concentration of alumina particles below the micrometric scale, which is scarcely documented in existing literature. Consequently, spatially resolved concentration and size profiles of the nanometric alumina particles are measured and compared to simulated data from the literature. The radii of alumina particles in the cloud are found to evolve closely around 80 nm. Volume fractions are evaluated from 2.8⋅10−4 near the particle surface to 3⋅10−5 further in the cloud. Therefore, significant concentrations of alumina particles are revealed during the short (15 to 20 ms) combustion process at distances of the order of magnitude of a few initial particle diameters. Such characterization could then lead to a better assessment of the interaction distance among aluminum particles as they burn collectively.Novelty and significance statementThis article introduces the first experimentally determined profiles of alumina concentration and size distribution surrounding a single burning aluminum droplet. The uniqueness of our experimental setup lies in its ability to study of the most fundamental case of the autonomous combustion of a single levitating particle, without any convective effects. A new non-intrusive method specifically designed provides unprecedented results in the field of metallic particle combustion. Data provided in the paper are crucial as they serve as the first reference case for future simulation and experiments. The results introduced in this paper highlight the inability of current simulation methods to accurately account for nucleation and condensation processes, and emphasize the need for a non-invasive characterization method.

Effects of aluminum particle size on metal acceleration for CL-20-based aluminized explosives

The addition of aluminum (Al) powder to CL-20 significantly enhances the overall energy of mixed explosives. Nonetheless, the metal acceleration ability of explosion after Al addition shows unpredictable behavior due to the unclear reaction characteristics of Al in CL-20 detonation products. This study utilizes a plate push test employing CL-20-based aluminized explosives to acquire the reaction degree formulation for Al powder with varying particle sizes in a CL-20 detonation environment. Moreover, it elucidates the reaction mechanism of microsized Al particles during the initial phase of afterburning. Additionally, this reaction formulation enhances the equation of state (EOS) for CL-20-based aluminized explosives. Subsequently, the new EOS is implemented in LS-DYNA to simulate the metal flyer acceleration process. Consequently, the impact of Al particle size on the metal acceleration capability of aluminized CL-20 is examined. The results indicate that for CL-20-based aluminized explosives with 15 % Al content, an optimal Al particle size of 34.12 μm exists when the particle size exceeds 10 μm. This optimum increases the speed of the driving metal plate by 7.4 % compared to CL-20/LiF explosives.

Measurement of the temperature of burning aluminum particles using multi-spectral pyrometry

ABSTRACT Aluminum is used in the composition of many high explosives and contributes to their blast effect. This work focuses on the study of the combustion of a single isolated particle of size between 30 and 100 µm in an arbitrary atmosphere, whose pressure and composition are chosen to be close to those encountered in a high-explosive fireball. This gaseous atmosphere is still largely unreferenced, and this work aims to provide a better understanding of combustion in this environment. The use of an electrostatic levitator coupled with multi-spectral pyrometric diagnostics enables us to select a single particle and measure its temperature during combustion. Photomultipliers (PMs) are used to follow the temporal evolution of the particle’s light emission during combustion. In this work, we also used PMs as pyrometric devices to measure temperature. The diagnostic allows us to determine the temporal evolution of the integrated temperature of the condensed phase during combustion of the aluminum particle. By way of example, a temperature of 3300K was obtained for the combustion of Al in air at 1 bar. The data collected will also be used to verify the assumptions made in the combustion models (e.g. temperature stability during combustion).

Performance investigation of the artificial aggregate by integrally recycling incineration bottom ash and fly ash

The potential expansion risks caused by the reaction of metallic aluminum and glass particles in incineration bottom ash (IBA) in high-alkalinity environments limit its use as an aggregate in concrete applications. This study aims to develop artificial aggregates (AAs) by integrating IBA with a low-alkalinity binder comprising incineration fly ash (IFA) and blast furnace slag (GGBS). The synergetic effects of using IBA with IFA-GGBS binders in AAs are investigated and compared to integrating IBA with IFA-OPC binders. The impacts of IFA and IBA contents on physico-mechanical properties and mineralogical characteristics of AAs are also assessed. The results show that AAs achieve a loose bulk density ranging from 890 to 1072 kg/m3, with the highest strength of 5.7 MPa recorded for GGBS-based aggregates with 40 % IBA. The pozzolanic reaction of GGBS-IFA contributes to a robust binder that facilitates interlocking within the system. The relatively low alkalinity associated with the pozzolanic reaction between GGBS and IFA suppresses the potential expansion reaction, ensuring the safe application of AAs in concrete. Moreover, the internal curing of GGBS-based AAs and their interaction with the cement matrix densify the microstructure of the interface transition zone, resulting in excellent compressive strength of AAs-contained concrete (>45 MPa), which surpasses that of conventional concrete.

Thermal Conductivity of AlSi12/Al2O3-Graded Composites Consolidated by Hot Pressing and Spark Plasma Sintering: Experimental Evaluation and Numerical Modeling

Functionally graded metal matrix composites have attracted the attention of various industries as materials with tailorable properties due to spatially varying composition of constituents. This research work was inspired by an application, such as automotive brake disks, which requires advanced materials with improved wear resistance on the outer surface as combined with effective heat flux dissipation of the graded system. To this end, graded AlSi12/Al2O3 composites (FGMs) with a stepwise gradient in the volume fraction of alumina reinforcement were produced by hot pressing and spark plasma sintering techniques. The thermal conductivities of the individual composite layers and the FGMs were evaluated experimentally and simulated numerically using 3D finite element (FE) models based on micro-computed X-ray tomography (micro-XCT) images of actual AlSi12/Al2O3 microstructures. The numerical models incorporated the effects of porosity of the fabricated AlSi12/Al2O3 composites, thermal resistance, and imperfect interfaces between the AlSi12 matrix and the alumina particles. The obtained experimental data and the results of the numerical models are in good agreement, the relative error being in the range of 4 to 6 pct for different compositions and FGM structure. The predictive capability of the proposed micro-XCT-based FE model suggests that this model can be applied to similar types of composites and different composition gradients.

Roughness affects the response of human fibroblasts and macrophages to sandblasted abutments

BackgroundA strong seal of soft-tissue around dental implants is essential to block pathogens from entering the peri-implant interface and prevent infections. Therefore, the integration of soft-tissue poses a challenge in implant-prosthetic procedures, prompting a focus on the interface between peri-implant soft-tissues and the transmucosal component. The aim of this study was to analyse the effects of sandblasted roughness levels on in vitro soft-tissue healing around dental implant abutments. In parallel, proteomic techniques were applied to study the interaction of these surfaces with human serum proteins to evaluate their potential to promote soft-tissue regeneration.ResultsGrade-5 machined titanium discs (MC) underwent sandblasting with alumina particles of two sizes (4 and 8 μm), resulting in two different surface types: MC04 and MC08. Surface morphology and roughness were characterised employing scanning electron microscopy and optical profilometry. Cell adhesion and collagen synthesis, as well as immune responses, were assessed using human gingival fibroblasts (hGF) and macrophages (THP-1), respectively. The profiles of protein adsorption to the surfaces were characterised using proteomics; samples were incubated with human serum, and the adsorbed proteins analysed employing nLC–MS/MS. hGFs exposed to MC04 showed decreased cell area compared to MC, while no differences were found for MC08. hGF collagen synthesis increased after 7 days for MC08. THP-1 macrophages cultured on MC04 and MC08 showed a reduced TNF-α and increased IL-4 secretion. Thus, the sandblasted topography led a reduction in the immune/inflammatory response. One hundred seventy-six distinct proteins adsorbed on the surfaces were identified. Differentially adsorbed proteins were associated with immune response, blood coagulation, angiogenesis, fibrinolysis and tissue regeneration.ConclusionsIncreased roughness through MC08 treatment resulted in increased collagen synthesis in hGF and resulted in a reduction in the surface immune response in human macrophages. These results correlate with the changes in protein adsorption on the surfaces observed through proteomics.