Al2O3 Particle Size Research Articles

Influence of Al2O3 particles on the friction and wear behaviors of nitrile rubber against 316L stainless steel

The friction and wear properties of nitrile rubber (NBR) against 316L stainless steel pairs were investigated by using a sphere-on-disc test device. The influence of Al2O3 particle sizes and the normal load on the tribological behaviors of the pairs were primarily evaluated. The damage behaviors of worn surfaces were analyzed using a scanning electric microscopy (SEM) and a surface profilometer. The results show that the friction coefficient decreased because of particles coming into contact pairs, while particles also play an important role in increasing the wear loss of stainless steel with many furrows on the steel ball surface due to the ploughing effect of hard particles. Large-sized particles could accelerate the wear of rubber, and the micro-cutting scratches of the stainless steel induced by the Al2O3 particles embedded in the rubber matrix. However, as the particle’s size decreased, the wear loss of the rubber was gradually mitigated. It is obvious that the normal load affected the wear of the rubber to a larger extent than the stainless steel. Moreover, with large particles, the wear loss of rubber increased sharply with increasing the normal load. In addition, the NBR/stainless steel tribo-pairs presented different wear mechanisms, under different conditions, such as having no particles or varied particle sizes.

New pore structure of nano-alumina (Al2O3) prepared by sol gel method

Nano-porous alumina ceramics were fabricated using a simple and new sol-gel method. Aluminium oxide (Al2O3) nanoporous templates were synthesized by iron (III) nitrate 9-hydrate and aluminium isopropoxide as precursor. The samples were characterized by high resolution transmission electron microscopy (HRTEM), field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and UV-Vis spectrophotometer. XRD technique was used to identify α-alumina and γ-alumina. XRD pattern exhibited gamma-Al2O3 to alphaAl2O3 structural phase transition in nanoporous. The particle size of spherical as-prepared Al2O3 was measured around 20 nm by direct HRTEM observation. The surface morphological studies depicted the samples changed from sphere-like shaped to sponge-like pore structure by increasing annealing temperature. The sharp peaks in FTIR spectrum determined the purity of Al2O3 nanoparticles and absorbance peak of UV-Vis spectrum showed the small bandgap energy of 2.61 ev.

Sintering and Mechanical Properties of Titanium Composites Reinforced Nano Sized Al2O3 Particles

Sintering and Mechanical Properties of Titanium Composites Reinforced Nano Sized Al2O3 Particles

Synthesis and Characterization of In Situ (Al2O3–Si)/Al Composites by Reaction Hot Pressing

In situ (Al2O3–Si)/Al composites with a reinforcement volume fraction of 10% were synthesized from the Al–SiO2 system using low energy ball milling and reaction hot pressing. Differential thermal analysis was used to investigate the reaction mechanisms between SiO2 and Al. X-ray diffraction results revealed that the reaction between Al and SiO2 took place completely at 900 °C with a holding time of 2 h, thereby forming Al2O3 and Si. Scanning electron microscopic, energy dispersive X-ray spectroscopic, and transmission electron microscopic (TEM) results showed that the in situ synthesized Al2O3 and Si particles, whose sizes are less than 2 µm, were polygonal in shape and dispersed uniformly in the matrix. Moreover, Al2O3 particle size showed a tendency to increase from ~2 to ~6 µm when the synthesis temperature was increased. Furthermore, TEM observation showed that the interface between the reinforcements and Al matrix is clean. The yield strength, ultimate tensile strength, and Brinell hardness of the in situ (Al2O3–Si)/Al composite was significantly higher than the aluminum matrix. Mechanisms governing the tensile fracture process are discussed.

Mechanical and Tribological Behaviour of Epoxy Reinforced with Nano Al<sub>2</sub>O<sub>3</sub> Particles

In the present work systematic study has been conducted to investigate the matrix properties by introducing nanosize Al2O3 (particle size 100 nm, 0.5–10 wt %) fillers into an epoxy resin. High shear mixing process was employed to disperse the particles into the resin. The experimental results indicated that frictional coefficient and wear rate of epoxy can be reduced at rather low concentration of nanoAl2O3. The lowest specific wear rate 0.7 x 10-4 mm3/Nm is observed for the composites with 1 wt.% which is decreased by 65% as compared to unfilled epoxy. The reinforcement of Al2O3 particles leads to improved mechanical properties of the epoxy composites. The results have been supplemented with scanning electron micrographs to help understand the possible wear mechanisms.

Electroplating and characterization of Cr–Al2O3 nanocomposite film from a trivalent chromium bath

Purpose – The main aim of this study was to improve current efficiency and to obtain thicker coatings via aluminum oxide (Al2O3) addition to the chromium (Cr) (III) bath. Design/methodology/approach – Pure Cr and nanocomposite Cr–Al2O3 coatings were electrodeposited from Cr (III) bath onto cathode copper substrates by conventional method. Dependence of current efficiency to current density, Al2O3 content and particle size were investigated. Findings – Current efficiency increased with Al2O3 amount and decreased with Al2O3 particle size. Maximum current efficiency was achieved at 25 A/dm2 for pure Cr and 30 A/dm2 for composite coatings. Al2O3 bath content, current density and stirring rate increased the coating Al2O3 weight per cent significantly. Addition of Al3+ bath composition inhibited nanoparticle agglomeration, increasing film homogeneity. Cr–Al2O3 nanocomposites showed higher microhardness and better corrosion resistance than pure Cr layer. Originality/value – Cr (III) is not as toxic and as carcinogenic as Cr (VI) which is widely used for Cr electroplating these days. Low current efficiency and poor product quality are, however, major drawbacks of the former. This paper describes significant improvements obtainable by addition of Al2O3 nanoparticles to the Cr (III) bath for increasing the microhardness, the corrosion resistance and the current efficiency of the deposition.

Process control of particle deposition systems using acoustic and electrical response signals

The implementation of statistical quality control methods for monitoring and control of powder abrasion/deposition is of increasing importance in a manufacturing environment. For the wider adoption of both current and new powder coating technologies, quality control systems need to be developed, which are easily installed, non-invasive and work in real time. This study evaluates the use of a dual electro-acoustic and electrostatic surface-charge measurement technique as means of realising real-time process control. Simultaneous changes in the signals were obtained under both powder flow-on and -off conditions and also for edge detection of the substrate. It was discovered that the most important variables which governed changes in the acoustic response signal were due to variations in the deposition pressure and stand-off distance, whilst those for the electrostatic response signal came from changes in particle size and deposition stand-off distance. A phenomenological predictive equation was developed based on a two-level full factorial design with five variables for both response factors. The coefficients of determination, r2, for the models were 93% and 98%, respectively, with respective χ2 probability values of 99% and 99.5%. This enabled the use of specific limits for any variation of variables amongst those tested to be set up, resulting in the apparatus necessary for the development of a sensitive continuous control system. Examining variations in surface roughness with electrostatic signal was observed to show a linear relationship, decreasing at a rate of 0.19μm per 0.01eV, as the effective particle size of Al2O3 was increased.

Heat transport enhancement of thermal energy storage material using graphene/ceramic composites

Graphene/ceramic composites are proposed by directly depositing graphene on the insulating Al2O3 particles by chemical vapor deposition without any metal catalysts. Carbothermic reduction occurring at the Al2O3 surface is vital during the initial stage of graphene nucleation and the graphene sheet can connect with neighboring sheets to completely cover Al2O3 particles. The quality and layer number of graphene on Al2O3 can be finely tailored by changing the growth temperature and gas ratio. Graphene coated Al2O3 (G-Al2O3) composites are used as effective fillers of stearic acid (SA) to increase the thermal transport property. By the optimization of the layer number of graphene, size of Al2O3 particles and ratio of G-Al2O3/SA in a quantitative, their thermal conductivities significantly increase up to 11 folds from 0.15 to 1.65Wm−1K−1. The great improvement is attributed to the high thermal transfer performance of graphene and excellent wettability between graphene and SA. When the G-Al2O3/SA composites with the graphene coated porous Al2O3 foam, the thermal conductivity further reaches to 2.39Wm−1K−1, and the corresponding latent heat is 38Jg−1. It demonstrates the potential applications of graphene in thermal transport and thermal energy storage devices.

Smoky Plasma in a Dust Flame

The results of experimental investigation of the influence of 0.1÷5.0 mass percent of K2CO3 and KCl additives on the dispersion of combustion products, which were obtained by the combustion of an Al gas suspension in a laminar diffusion flame, are presented. The extreme dependence between the average particle size of Al2O3 and the additive concentration (Ca) was experimentally observed. At the K2CO3 additive concentration over 0.5%, the increase in the average particle size of Al2O3 (d10 ∼50 nm for Ca = 5%) was observed. It is shown that a change in the character of dependence between the Al2O3 average particle size and the concentration of low ionizing additives is due to the interaction between the dust and the ion subsystems of the combustion product plasma in the flame combustion zone. The theoretical calculation of the ion concentration in the system, at which the ion drag force is comparable to the Coulomb force, was done.

Thermochemical synthesis of nanostructured Cu-Al2O3 composite powder

Synthesis of Cu-Al2O3 nanocomposite powder through a thermochemical method from the water solution of copper nitrate (Cu (NO3)2.3H2O) and aluminum nitrate (Al (NO3)6.9H2O) is studied in this research. X-ray diffraction (XRD) technique, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the synthesized powder. XRD results show that γ-Al2O3 phase begins to form at the temperature ≈800°C during the heat treatment process. Studying SEM micrographs proves that the nano sized Al2O3 particles are homogenously dispersed in the copper matrix. XRD results also show that disappearing the reflects of CuO peaks after performing a reduction chemical reaction at the temperatures above 800°C in hydrogen atmosphere indicates that such chemical reaction at the temperatures above 800°C is required in order to achieve Cu-Al2O3 nanocomposite powder.

Transparent and Thermally Conductive Polycarbonate (PC)/Alumina (Al2O3) Nanocomposites: Preparation and Characterizations

We report the preparation and characterization of thermally conductive and transparent polycarbonate (PC)/alumina (Al2O3) composites. First, nano Al2O3 powder was synthesized by flash pyrolysis process and calculated amount of Al2O3 was dispersed into the methylmethacrylate (MMA) followed by bulk polymerization. PC/poly-(methylmethacrylate) (PMMA)-Al2O3 nanocomposites with various amounts of Al2O3 was prepared by mixing bulk polymerized PMMA-Al2O3 composites with PC through melt-mixing. Incorporation of Al2O3 in the bulk polymerized PMMA resulted in good dispersion of the Al2O3 particles in the PC matrix. The effect of particle size of Al2O3 on thermal conductivity, mechanical and optical properties of the composites was investigated.

Effect of Al2O3 particle size on preparation and properties of ZTA ceramics formed by gelcasting

Zirconia-toughened alumina (ZTA) ceramics were prepared using three different kinds of Al2O3 powders (marked PW-A average particle size: 7.53μm, marked PW-B average particle size: 1.76μm, marked PW-C average particle size: 0.61μm) by gelcasting. Effect of Al2O3 particle size on zeta potential, dispersant dosage and solid volume fractions of ZTA suspensions as well as the mechanical properties of ZTA green bodies and ceramics were investigated. The optimum dosages of dispersant for ZTA suspensions prepared by PW-A, PW-B and PW-C are 0.4wt%, 0.5wt% and 0.7wt%, respectively. The highest solid volume fractions of ZTA suspensions can reach 62vol% (SP-A), 60vol% (SP-B) and 52vol% (SP-C), respectively. The green bodies show a bending strength as high as 20MPa, which can meet the requirement of machining. The Al2O3 powder with fine particle size is beneficial to the improvement of mechanical properties. The ZTA ceramics prepared by PW-B Al2O3 powder show the highest bending strength (680MPa) and toughness (7.49MPam1/2).

Adsorption–desorption behavior of gaseous formaldehyde on different porous Al2O3 materials

In this work, Al2O3 materials with different pore properties were synthesized using some kinds of surfactant templates including cationic (CTAB), anionic (SDS), nonionic (P123) and blank templates. The gaseous formaldehyde adsorption–desorption behavior was studied using adsorption breakthrough curves and temperature programmed desorption (TPD) methods. The addition of ionic surfactant template (containing anionic and cationic) in synthesized solution resulted in the decrease of the crystalline size of Al2O3 particles compared with Al2O3-Blank. The adsorption capacity for formaldehyde on the Al2O3 samples was as follows: Al2O3-P123>Al2O3-Blank>Al2O3-SDS>Al2O3-CTAB, which was in direct proportion to the surface area and pore volume. A technique based on TPD was used for estimating the desorption activation energy (Ed) of HCHO from different porosity Al2O3 samples. Al2O3-CTAB exhibited the highest deception activation energy for HCHO, which was thought to be related to its narrowest pore size distribution. The presence of abundant surface hydroxyl groups for Al2O3-P123 would be in favor of the chemical adsorption with formaldehyde molecular, and then resulted in higher desorption activation energy even though its broadest pore size distribution.

Effect of Process Parameters and Binder Concentration on Mechanical Properties of Phosphate Bonded Alumina

Alumina and alumina matrix composites typically require sintering temperature in excess of 1550°C. Utilization of aluminium phosphate bonding provides process flexibility and significantly lowers sintering temperature (500° to 1280°C). While phosphate bonded alumina (PBA) may have a lower sintering temperature, its limitations include the presence of porosity in pressure less sintered samples leading to lowered strength and phase instability above approximately 1200°C. The present study describes the effect of processing routes and binder concentration on density, hardness, Young's modulus and transverse rupture strength (TRS) of PBA. In this study, ultra fine Al2O3 (particle size ≈0.5 µm) was reacted with H3PO4 to yield phosphate bond in a matrix of tabular Al2O3 (particle size ≈0.5 µm) after final sintering at 1280°C for 6 h. Green samples were compacted at pressures in the range of 96-290 MPa. The effect of aluminium phosphate binder concentration on mechanical properties of the PBA samples was measured at optimized pressure. The presence of different polymorphs of AlPO4 in the sintered product was confirmed by XRD.

Preparation of Ni-P-Al<sub>2</sub>O<sub>3</sub> Composite Film on Mild Steel with High Resistance to Corrosion and Wear

The Ni-P-Al2O3 composite film was coated on mild steel of SS400 with electroless plating method. In this process, different sizes of Al2O3 particles and different blended amounts of Al2O3 particles into the plating solution were applied. From the surface and cross section observation, it is known that the Al2O3 particles were uniformly dispersed in the Ni-P alloy. The highest corrosion resistance and the highest wear resistance of the Ni-P-Al2O3 composite film were obtained when adding Al2O3 particles with the mean diameter of 0.05μm into the plating solution at the blended amount of 1.0g/L.

Synthesis of Mg–Al2O3 nanocomposites by mechanical alloying

Mg–Al2O3 nanocomposite powders, with Al2O3 particles of 50nm size, were synthesized by mechanical alloying starting from a mixture of 70vol.% pure Mg and 30vol.% Al2O3 powders. A steady-state condition was obtained on milling the powder mix for about 20h, when the crystallite size of the Mg powder was about 10nm. The structural evolution during milling was monitored using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction methods. The results showed that a mixture of Mg, Al2O3, and MgO phases were obtained on mechanical alloying. On annealing the milled powders at 600°C for 30min, a displacement reaction occurred between the Mg and Al2O3 phases, when the formation of a mixture of pure Al and MgO phases was observed. Also, a reaction occurred between the initial Mg powder and Al formed as a result of the displacement reaction, leading to the formation of Mg17Al12, Al0.58Mg0.42, and Al3Mg2 phases. Thus, the powder annealed after milling the Mg+Al2O3 powder mix for 25h consisted of Al, MgO and Al3Mg2 phases.

Model and experimental investigations of aluminum oxide slurry transportation and vaporization behavior for nebulization inductively coupled plasma optical emission spectrometry

We analyzed aluminum oxide (Al2O3) by slurry introduction inductively coupled plasma (ICP) optical emission spectrometry through modeling and experimentation. We also studied the relationship between the ICP nebulizer gas flow, the spray chamber geometry, and the particle size of Al2O3 in an attempt to minimize the need for correction factors by ensuring an efficient aerosol mass transport. A cut-off point for the particle size was implemented at approximately 7–10μm for the sample introduction system. Based on modeling using a customized computer model and some experimental evidences, the maximum particle size for complete vaporization is approximately 7μm. For a gas flow of 0.8Lmin−1, particles with a diameter of up to 8μm can be evaporated with an efficiency of 68% and particles as large as 5μm can be evaporated completely within the nebulization gas flow region. The Al2O3 sintering block was ground using a self-made alumina mortar combined with a mixer mill device for particle reduction. The sample slurry was prepared by directly dispersing powdered Al2O3 in an aqueous solution with an addition of 0.5wt% poly (acrylate amine) (NH4PAA) as the dispersant. The accuracy of the results was compared with the data obtained through high-pressure digestion with acid and with the value of a certified reference material, NIST SRM 699 alumina.

Preparation of Graphene Nanosheet/Alumina Composites

Graphene nanosheet (GNS)/ Al2O3 composite powder with homogeneously distributed GNSs has been fabricated from wet ball milled expanded graphite and Al2O3, and then followed by the rotary evaporator at relatively low temperature to dry the mixture and the residual solvent was removed in atmosphere-vacuum pipe-type furnace accessing mixed gases of Argon and Hydrogen at 600 for 6h. During the process, homogeneously dispersed and mixed GNS/ Al2O3 composite powders with quite few damage of GNSs structure and properties have been obtained. The microstructures and grain sizes of GNS/ Al2O3 composite powders have been investigated. The results showed that the addition of GNSs had diminished the size of Al2O3 particles and also the as-prepared GNSs/ Al2O3 composite powders can be dispersed and mixed more homogeneously remarkably with the presence of GNSs.

Effect of precursor particle size distribution on the morphology and low wetting behavior of photocatalytic nanocoatings on glass surfaces

The effect of particle size distribution of coating precursor on the morphology and low wetting character of photocatalytic nanocoatings is investigated in the present work. TiO2–SiO2–Al2O3 nanocomposite coatings containing Al2O3 particles of size in the range 20–200 nm have been prepared on glass substrates by an aqueous sol–gel process. A composite sol of titanium dioxide containing 30 mol% silica comprises the matrix sol to which alumina particles (1–10 mol%) having sizes in the range 20 to 200 nm are introduced as stabilized dispersions and further coated on glass substrates by the dip-coating method followed by annealing of the coatings at 400 °C. A composite coating containing 2 mol% boehmite derived alumina (TS-B-2) has been found to be more photoactive under visible light and was low wetting in nature. The higher photocatalytic activity of the TS-B-2 nanocomposite is attributed to the presence of phase pure anatase with crystallite size of 3.7 nm and high surface area of 315 m2 g−1, while the low wetting character is attributed to the hierarchical morphology resulting in uniform surface roughness. The present study significantly highlights the possibility of designing composite precursors containing desired constituent particle sizes to produce nanocoatings differing in grain sizes, surface roughness and morphology, resulting in increased self-cleaning and low wetting properties.

Effect of addition of potassium carbonate to aluminum powder on the grain size of Al2O3 nanoparticles formed in the laminar dusty flame

Results of studying the effect of K2CO3 additives on the grain size of the products of combustion of a gas suspension of Al particles (with the mean particle diameter of 4.8 µm) in a laminar diffusion flame are reported. An extreme character of the dependence of the mean size of Al2O3 particles on the additive concentration is experimentally observed. For the concentration of the K2CO3 additive equal to 0.5%, the mean diameter of Al2O3 particles is 30 nm; for the additive concentration of 5%, the mean particle size increases to 67 nm. It is demonstrated that the change in the mean size of Al2O3 particles as a function of the concentration of the readily ionized additive is caused by interaction of the dusty and ionic subsystems of the plasma of the combustion products in the reaction zone in the flame. At a high concentration of ions (above 1020 m−3), this interaction increases the rate of coagulation of Al2O3 particles.