Study on Mechanical and Tribological Characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiCp Reinforced Aluminum Metal Matrix Composite

In this investigation, an attempt has been made to hardness and wear rate of Al7075 hybrid metal matrix composite reinforced with the hard ceramics like alumina (2, 4, and 6 wt.% of Al2O3) and silicon carbide (3, 6, and 9 wt.% of SiC) is fabricated by using stir casting method. The samples were aging at temperature of 140 ^°C, 160 ^°C and 180 ^°C and monitored by hardness test. Taguchi’s L27 Orthogonal array was used for optimizing the process parameters. The obtained results indicated that hardness increased with increasing reinforcement. A wear test was performed using pin-on disk apparatus at room temperature for constant load of 30N, at a fixed sliding speed of 1.66 m/s and wear resistance increased as the weight percentage of reinforcement increased. Scanning electron microscope (SEM) studies were carried out to evaluate the worn surface. From the analysis of variance (ANOVA), Al₂O₃ is the significant factor that affects the hardness and wear loss of hybrid composites followed by SiCp and heat treatment. Confirmatory test was performed for the optimized parameters and these results were within the acceptable range when compared with the experimental results.     

Studies on Fractures of Friction Stir Welded Al Matrix SiC-B<Subscript>4</Subscript>C Reinforced Metal Composites

Studies pertaining to joining of Al alloy metal matrix composites reinforced with B₄C and SiC by solid state friction stir welding (FSW) are presented in this paper. FSW tool dimensions are designed and fabricated to suit the weld sample dimensions and subsequently, the implications of the tool pin profile on the weldability is investigated. Through experimental recordings, the heat generated during the friction stir joining process of composites is estimated by developing relative equations. Maintaining the tool traverse speed constant, the rate of rotation and its effects on the tensile strength at the joints are investigated which reveals reduced ductility. The study emphasizes that when the speed is maintained between 100–400 mm/min, the tensile strength is at its optimal maximum while speeds higher or lower than the optimal range indicate detrimental effects on the tensile strength. This is followed by fracture studies on samples welding with varying traverse speed and rate of welding. Traverse speed appears to govern the fracture modes while brittle fracture is predominantly noticed indicating the importance of feeding optimal heat input during joining.     

Investigation of Characterization and Mechanical Performances of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and SiC Reinforced PA6 Hybrid Composites

In this study, the influence of different weight percentages of alumina oxide (Al₂O₃) and silicon carbide (SiC) reinforcement on the mechanical properties of Polyamide (PA6) composite is investigated. Test specimens of pure PA6, 85 wt% PA6 + 10 wt% Al₂O₃ + 5 wt% SiC and 85 wt% PA6 +10 wt% SiC + 5 wt% Al₂O₃ are prepared using an injection molding machine. To investigate the mechanical behaviors tensile test, impact test, flexural test, and hardness test were conducted in accordance with ASTM standards. Experimental results indicated that the mechanical properties, such as tensile, impact, hardness, and flexural strength were considerably higher than the pure PA6. The tensile fracture morphology and the characterization of PA6 hybrid composites were observed by scanning electron microscope and Fourier transform infrared spectroscopic method. Further, thermogravimetric analysis confirms the thermal stability of PA6 hybrid composites. The reinforcing effects of Al₂O₃ and SiC on the mechanical properties of PA6 hybrid composites were compared and interpreted in this paper. Improved mechanical and thermal characteristics were observed by the addition of small amount of Al₂O₃ and SiC simultaneously reinforced with the pure PA6.     

Mechanical Properties and Wear Behavior of Zn and MoS<Subscript>2</Subscript> Reinforced Surface Composite Al- Si Alloys Using Friction Stir Processing

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In present investigation, composite reinforced with using Zn/ MoS₂ powder in as-cast alloy were developed at tool rotational speed of 664 rpm and tool transverse speed of 26 mm/min using FSP. Microstructural observation of MoS₂/Zn reinforced composites confirmed the fine and equiaxed grains in the stir zone (SZ) and distribution of fine reinforced particles of MoS₂/Zn in SZ. Moreover, agglomeration of MoS₂/Zn particles were not observed. The ultimate tensile strength was measured to be 113 ± 9 and 82 ± 7 MPa for MoS₂and Zn reinforced Al-Si alloy, respectively. The sliding wear was studied using pin-on-disk tribometer and it was found that FSP enhanced the wear resistance of the as-cast alloy. The MoS₂ reinforced composite showed superior wear resistance than Zn reinforced composite and base material. To understand the acting wear mechanism, the field emission scanning electron microscope (FESEM) of worn out surfaces were performed.     

Microstructure and Mechanical Properties of Friction Stir Welded SiC/TiB2 Reinforced Aluminum Hybrid Composites

Silicon - In the recent decades, the use of aluminum alloy has significantly enhanced especially in engineering applications extensively used in shipbuilding, aircraft, structural and automobile...     

Tribological Characterization of Stir-cast Aluminium-TiB<Subscript>2</Subscript> Metal Matrix Composites

The present study considers friction and wear of aluminium matrix composites reinforced with TiB₂ micro particles processed through the stir casting method rather than in-situ techniques adopted by earlier studies. Different weight percentages of TiB₂ powders having average sizes of 5 - 40 micron were incorporated into molten LM4 aluminium matrix by stir casting method. The friction and wear behavior were studied for Al-TiB₂ composites prepared according to specific dimensions by using a block-on-roller type multi-tribotester at room temperature. Normal loads of 25 - 75 N and rotational speed of 400 – 600 rpm were used for determination of friction and wear behavior. It is found that friction and wear decrease with increase in percentage of TiB₂ reinforcement in the composite, while friction and wear increase with applied load and speed. Scanning electron microscopy studies the reveal presence of both abrasive and adhesive wear mechanisms with abrasive wear being predominant.     

纤维增强树脂基复合材料的搅拌摩擦焊研究

利用搅拌摩擦焊实现了纤维增强树脂基复合材料的焊接,获得了焊接接头力学性能并分析了接头形成和断裂机制。结果表明,由于搅拌摩擦焊过程中搅拌针的摩擦剪切及对塑化材料的挤压作用,使树脂基体发生塑化并带动碳纤维迁移形成焊接接头,在搅拌头旋转速度950 r/min,焊接速度38 mm/min时,接头拉伸强度可以达到52.43 MPa,接近母材强度的51%,焊接接头的断裂机制主要为基体剪切断裂和纤维-基体界面脱粘。     

Optical Properties of CeO<Subscript>2</Subscript> Doped SiO<Subscript>2</Subscript>-Na<Subscript>2</Subscript>O-CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glasses

Cerium oxide is one of the most important rare earth elements that is introduced into glass compositions due to its great effects on the optical properties. CeO₂ was introduced in Hench’s patented SiO₂-Na₂O-CaO-P₂O₅ glasses with different concentrations in order to study its effect on the optical behavior of this glass including optical band gap, transmittance, reflectance and refractive index and to give a complete view for the optical properties on cerium oxide-doped silicate glasses.     

Effect of Annealing Temperature and Alumina Particles on Mechanical and Tribological Properties of Ni-P-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Coatings

In this study, the effect of annealing temperature and alumina particles on micro-hardness, corrosion, wear, and friction of Ni-P-Al₂O₃ composites coating is studied. The electroless nickel composite coating with various alumina particle content is deposited on a mild steel substrate. The corrosion behaviour and tribological behaviour (wear and friction) of the composite coated samples are investigated and compared with Ni-P coated samples. The micro-hardness, wear resistance, and corrosion resistance of the composite coating improved significantly after heat treatment (400 °C) and in the presence of alumina particles. The composite coating deposited with alumina particle concentration of 10 g/L in an electroless bath and heat treated at 400 °C shows excellent results compared to Ni-P, as-deposited Ni-P-Al₂O₃ coating and coatings heat treated at different annealing temperature (200 °C, 300 °C, and 500 °C). Microstructure changes and composition of the composite coatings due to incorporation of alumina particles and heat treatment are studied with the help of SEM (scanning electron microscopy), EDX (energy dispersive X-ray analysis and XRD (X-ray diffraction analysis).     

On the Role of Tool Tilt Angle on Friction Stir Welding of Aluminum Matrix Composites

Silicon - The current study investigates the influence of tool tilt angle (TTA) on the mechanical strength of friction stir welded aluminum matrix composite (AMC). Aerospace-grade AA6092/ 17.5...     

Properties of unsupported MoS<Subscript>2</Subscript> species produced in the preparation of MoS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> using a sonochemical method

Unsupported MoS₂ particles, which were produced in the preparation of MoS₂/Al₂O₃ using a sonochemical method, were successfully separated from the prepared sample catalyst by adding oleylamine as an agent for dispersing the unsupported particles. The fraction of the unsupported MoS₂, which was estimated based on Mo balance, varied between 0.03 and 0.4, independent of the Mo loading levels investigated (6–54 wt% of Mo). The activity of the unsupported MoS₂ for the hydrodesulfurization of dibenzothiophene was nearly the same as that of the Al₂O₃-supported MoS₂, indicating that the activity of the prepared catalyst was not affected by the presence of the unsupported MoS₂ particles.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

氢氧化铝增强PPC复合材料的力学性能与热稳定性研究

用氢氧化铝(ATH)对聚碳酸亚丙酯(PPC)进行改性,研究了ATH用量对PPC/ATH复合材料力学性能、热稳定性、阻燃性能和断面形貌的影响。结果表明:随着ATH用量的增加,复合材料的拉伸强度、弯曲强度和弯曲模量均逐渐提高,冲击强度呈先提高后降低的趋势;ATH在PPC基体中能够均匀分散,其界面具有良好的相容性;PPC/ATH的维卡软化温度和热变形温度均随着ATH用量的增加而逐渐提高;ATH还能明显改善PPC的阻燃性能,将PPC从易燃材料变为阻燃材料。总之,ATH可显著提高PPC的力学性能、热稳定性能和阻燃性能,拓宽了PPC的应用范围。     

Electrical conductivity and structure of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na₂O-P₂O₅-Na₂S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na₂O-P₂O₅ system has shown their fair coincidence. The introduction of sodium sulfide into the Na₂O-P₂O₅ system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm³, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.     

Low-temperature anti-icing reagents in the Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O system and their properties

The polytherms of ice melting in sections of the Ca(NO₃)₂-Mg(NO₃)₂-CO(NH₂)₂-H₂O system with different component ratios were studied in the temperature interval from 0 to −40°C. A series of nitrate and nitrate-carbonate reagents that are promising for the creation of anti-acing reagents were found, which form eutectics with ice at temperatures from −25 to −39°C. Their properties, viz., melting properties with respect to ice and corrosiveness on metals and alloys, were determined. An effective corrosion inhibitor was selected.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Unexpected Support Effect in Hydrotreating: Evidence of a Metallic Character for ReS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ReS<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Catalysts

Abstract  

Rhenium sulfide based catalysts were prepared by the incipient wetness impregnation method over alumina and silica supports and evaluated for 4,6-dimethyldibenzothiophene hydrodesulfurization in a high-pressure stirred-tank reactor. The catalyst prepared over silica was about six times more active for hydrodesulfurization than the corresponding catalyst prepared over alumina and a NiMo/Al₂O₃ industrial reference catalyst. This surprising and positive SiO₂ support effect was explained by a metallic character of the supported sulfide, which was demonstrated using a kinetic approach of competitive hydrogenations and by XPS characterization.     

Synthesis and Thermoelectric Properties of Ceramics Based on Bi<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Co<Subscript>1.7</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Oxide

Layered ceramics based on bismuth–calcium cobaltite with varied cobalt oxide contents is synthesized by the solid-phase method, the ceramics phase composition is determined, and the microstructure, thermal expansion, electroconductivity, and thermal electromotive force are investigated. The formation of just one compound, ternary oxide composed of Bi₂Ca₂Co_1.7O _y , is established within the quasi-binary Bi₂Ca₂O₅–CoO _z system. The effect of the cobalt oxide content on the Bi₂Ca₂Co _x O _y ceramics’ microstructure and physicochemical properties is analyzed. The single-phased ceramic sample Bi₂Ca₂Co_1.7O _y demonstrated the highest power factor value among all the investigated samples—26.0 μW/(m K²) at a temperature of 300 K. This sample showed the lowest value of the thermal linear expansion coefficient of 9.72 × 10^–6 K^–1.     

Preparation and Properties of Hyperbranched Polyurethanes via Oligomeric A<Subscript>2</Subscript>+bB<Subscript>2</Subscript> Approach

Hyperbranched polyurethanes (HPUs) were synthesized from isocyanate end-capped poly(1,4-butylene adipate glycol) and diethanolamine via oligomeric A₂ + bB₂ approach. The structures of the resulting polymers were characterized by FT-IR, ¹³C NMR. The degree of branching (DB) was calculated according to the ¹³C NMR spectra. The properties of HPUs were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), adhesion strength tests. It was found that the thermal stability of the HPU decreased with the increase of hard segment content. The HPU could be used as hot melt adhesive, and the maximum lap shear strength was up to 6.84 MPa.