Al2O3 Powder Mixtures Research Articles

Дослідження впливу температури газу процесу холодного газодинамічного напилювання на адгезійну міцність нікелевмісних покриттів

The subject of the research is the influence of low-pressure cold spraying process parameters on the adhesive strength of the coatings. The goal is to ensure the maximum values of the adhesive strength of nickel-based coatings deposited by cold spraying by controlling the gas temperature at the nozzle inlet. The task is to investigate the effect of the temperature mode of the DYMET-405 machine on the adhesive strength of the coatings obtained from the Ni+Zn+Al2O3 powder mixture at constant other spraying parameters. Research methods. The experimental study of the adhesive strength was conducted on the tear using adhesive method in accordance with DSTU 2639-94. The metal-matrix composite powder mixture Ni+Zn+Al2O3 was used as powder material. VT3-1 titanium alloy was chosen as substrate material. Coatings were deposited using DYMET-405 low-pressure cold spraying machine. Temperature regulation at the nozzle inlet was performed by turning on the required temperature mode on the equipment control panel. Other spraying parameters remained constant during coating deposition process. The results. It was established that with an increase in the temperature of the gas in the nozzle, an increase in the adhesive strength of coatings is observed, on average from 9.5 MPa to 28.7 MPa. This can be explained by the fact that an increase in gas temperature leads to an increase in the velocity of the gas flow and, accordingly, of the powder particles in this flow. Higher particle impact velocity has a positive effect on the process of their deforming, filling of pores, densifying of coating layers, and finally increasing the adhesive and cohesive strength. The scientific novelty of the obtained results is that the dependence of the gas temperature at the nozzle inlet during low-pressure cold spraying on the adhesive strength of Ni+Zn+Al2O3 powder mixture coatings deposited on VT3-1 titanium alloy substrates was obtained. Conclusions. The practical value of the obtained results is that the obtained dependences of adhesive strength on gas temperature can be used for the development of cold spraying recommendations for the deposition of restorative coatings on parts made of titanium alloys, in particular in aircraft engines to eliminate operational defects.

Improving the wear resistance of the magnesium alloy WE43 by cold sprayed Ni–Al2O3 and Ni–Zn–Al2O3 coatings

Abstract Lightweight magnesium (Mg) alloys are employed in a wide range of applications due to their high specific strengths. Nevertheless, some applications require improvement of the wear resistance of Mg alloys. The purpose of this study was to investigate the effect of the initial surface conditions, cold spray temperature, and coating material on the wear resistance of the cold sprayed coatings on WE43 Mg substrate. Blasted and sandpapered surfaces were coated with commercial powders of K-32 (Ni and Al2O3) and K-714 (Zn, Ni, and Al2O3). The coating materials were cold sprayed on blasted and sandpapered WE43 Mg surfaces at 500 °C and 600 °C. Surface roughness, thickness and wear resistance of the coatings were examined. Deposition efficiency was improved by raising the N2 gas temperature. The samples with the greatest wear resistance were those that were coated with Zn, Ni, and Al2O3 powder mixture on sandpapered surfaces at temperatures of 600 °C, where deposition efficiency is maximum. Cold spray coatings enhanced the wear resistance of the WE43 Mg substrate.

Boosting the Ceramics with In Situ MOF-Derived Nanocarbons

Metal–organic framework (MOF)-derived nanocarbons have emerged as promising materials for energy and environmental applications owing to their high surface area, structural and chemical tunability, and hierarchical porosity. Although various carbon-based materials such as graphene and carbon nanotubes have been extensively used as secondary sintering additives to develop advanced ceramics with improved mechanical, thermal, and electrical properties, the potential of MOF-derived nanocarbon-based materials has not been explored. Here, we report the first use of MOF-derived nanocarbons as a reinforcement phase in ceramic composites. To this end, Al2O3 and zeolitic imidazolate framework (ZIF-8) are used as the ceramic matrix and nanocarbon source, respectively. The ceramic composites are produced by densifying Al2O3 and ZIF-8 powder mixtures using spark plasma sintering (SPS) at 1550 °C and uniaxial pressure of 50 MPa. The fracture toughness of the composite increases up to 67% in comparison to an alumina monolith as ZIF-derived nanocarbons form interlayers to assist the dissipation of energy during the crack propagation and inhibit grain growth. The room-temperature electrical conductivity of the sintered samples drastically increases with the in situ formed nanocarbon-based fillers, reaching as high as 1410 S/m for 10 wt % ZIF-8 content. These results constitute an excellent initial step toward boosting the mechanical and electrical properties of ceramic matrix composites with in situ MOF-derived nanocarbons.

The effect of process temperature and powder composition on microstructure and mechanical characteristics of low-pressure cold spraying aluminum-based coatings

The effect of operating gas temperature and powder type on microstructure and mechanical characteristics of cold spraying coatings deposited on EZ33A-T5 magnesium alloy was studied. Three aluminum-based cold spraying powder mixtures Al + Zn, Al + Al2O3 and Al + Zn + Al2O3 were used for the investigation. Deposition was performed using D423 low-pressure cold spray system at operating gas pressure of 1.0 MPa and different temperatures –300 °C, 450 °C, and 600 °C. The coatings microstructure was investigated with optical and scanning electron microscopy. Mechanical properties of the coatings were characterized through standard test methods for adhesion and cohesion strength, and standard test methods for Vickers hardness of thermal spray coatings. The results demonstrate that with increasing initial gas temperature at spraying nozzle inlet from 300 °C to 600 °C, an increase in the porosity of the coatings of all investigated powder mixtures can be observed. Microstructure characterization showed an increase in porosity from 2.3% to 4.1% for Al + Zn powder mixture, from 2.1% to 3.5% for Al + Al2O3 powder mixture, and from 2.5% to 5.6% for Al + Zn + Al2O3 powder mixture. The minimum porosity was obtained at 450 °C for all investigated powder mixtures. Adhesion and cohesion strength and microhardness of coatings were reach their maximum value at 450 °C. The best performance was obtained for Al + Al2O3 powder mixture: coating adhesion—31.9 MPa (was limited by the bonding strength of the glue), cohesion—93.5 MPa, microhardness—81 HV0.15. The influence of Al2O3 particles in the powder mixture on the above-mentioned parameters was also established. The results show that the presence of ceramic particles in powder mixtures can positively effect porosity level and mechanical characteristics.

DETERMINATION OF ENERGY PARAMETERS OF Ni+Al2O3 POWDER PARTICLES IN A SUPERSONIC NOZZLE DURING COLD GAS-DYNAMIC SPRAYING USING THE ANALYTICAL METHOD

Purpose. To calculate the temperature and velocity of nickel and aluminum oxide particles in the supersonic flow in the low-pressure cold gas-dynamic spraying nozzle. To investigate the effect of gas parameters at the nozzle inlet, in particular temperature and pressure, on the velocity and temperature of particles at the nozzle outlet.
 Research methods. The calculation of the temperature-velocity characteristics of the powder particles is performed after determining the parameters of the gas flow in the supersonic nozzle channel using well known gas-dynamic dependencies. The initial data for the calculation are the following: the geometry of the nozzle, the temperature and pressure of the gas (air) at the nozzle inlet. The density of the material from which particles are obtained, as well as their diameter, were taken into account in the calculation of the energy parameters. Nickel particles with a diameter of 25 µm and aluminum oxide particles with a diameter of 22 µm were used.
 Results. Based on the calculations results, graphs of changes in the velocities and temperatures of the particles of the investigated powders, as well as working gas, in the channel of the low-pressure cold gas-dynamic spraying supersonic nozzle were developed. The dependences of the temperature-velocity parameters of the particles at the nozzle exit in the range of initial values of temperature at the nozzle inlet from 300 to 600 C° and pressure from 0.6 to 1.0 MPa were also developed.
 Scientific novelty. The influence of the initial parameters of the gas at the nozzle inlet in a wide range of values on the temperature and velocity of nickel and aluminum oxide particles during the low-pressure cold gas-dynamic spraying is shown.
 Practical value. The obtained results can be used to determine rational spraying parameters in the development of technological processes of deposition of protective and restorative coatings from Ni+Al2O3 powder mixture.

High-Temperature Synthesis of Mo3Al2C-Based Materials via Combustion of MoO3 + Al + C + Al2O3 Powder Mixtures

High-Temperature Synthesis of Mo3Al2C-Based Materials via Combustion of MoO3 + Al + C + Al2O3 Powder Mixtures

Effect of Addition of Previously-Synthesized Ce-TZP/Al2O3 Submicrometric Powder on the Properties of Al2O3-Based Ceramics

This work investigated the effect of a composite of tetragonal zirconia with alumina-reinforced Ceria (ATZ) previously synthesized, on the properties of alumina-based ceramics (Al2O3). Monolithic alumina powder and Al2O3 powder mixtures containing 5, 10, 15 and 20 wt.% of Ce-TZP/Al2O3 were processed by high energy milling, compacted and then sintered at 1600 °C - 2 h. Sintered pure alumina and composites were characterized by relative density, scanning electron microscopy, X-ray diffraction and surface roughness. Then, the elastic modulus, the Vickers hardness, the fracture toughness and the 4-point flexural strength were evaluated. The results indicated an increase in relative density as a function of the addition of ATZ, with values ​​between 94.3 ± 0.8% and 98.9 ± 0.7%. The observed microstructure after sintering showed tetragonal ZrO2 grains with average sizes of 0.6 μm well dispersed in the Al2O3 matrix, which presents average grain sizes of around 1.5 μm. The crystalline phases identified in the composites were ZrO2-tetragonal and Al2O3 hexagonal. The addition of the composite (ATZ) in the alumina matrix generates a gradual reduction in the elastic modulus (398 ± 15 GPa ~366 ± 34 GPa) and in the hardness (20.5 ± 1 GPa ~17.3 ± 0.7 GPa) of the sintered ceramics. On the other hand, the addition of this same composite (ATZ) in the alumina matrix considerably increases the materials fracture toughness, reaching values of approximately 6.7 ± 0.9 MPa.m1/2. The same trend was observed in the flexural strength results which ranged from 258 MPa (5wt.% Ce-TZP/Al2O3) to 316 MPa (20wt.% Ce,Y-TZP/Al2O3). The Ce-TZP reinforcement acts as a toughening agent of the Al2O3 matrix due to the coupled mechanisms of toughening by zirconia phase transformation, residual stresses due to the difference in thermal expansion of the crystalline phases and differences in microstructural morphologies.

Rapid synthesis of YAG phosphor by facile mechanical method

AbstractIn this study, synthesis of yttrium aluminum garnet (YAG):Ce3+ phosphor powders for white light emitting diodes was investigated by mechanical method using the attrition‐type mill with no external heating and no flux in dry phase. High mechanical energy input to the starting powder mixture of Y2O3, Al2O3 and CeO2 achieved the synthesis of YAG:Ce3+ without any flux materials. X‐ray diffraction patterns of the processed powders after 5 min processing revealed the peaks of YAG were clearly identified. The maximum temperature of the mill chamber during the processing was 240℃. The YAG phosphor obtained by the mechanical method revealed the internal quantum yield of 65% in the case of the sample mechanically processed under a reducing atmosphere. The synthesized powder showed granule structure consisting of submicron size of YAG particles, which is better handling for the fabrication of light emitting diode devices.

Síntesis y caracterización estructural del compuesto de refuerzo de Ti+Ni3Al+Al2O3 a base de Fe producido por aleación mecánica

La mezcla de polvo de Ti+Ni3Al+Al2O3 a base de Fe se alea mecánicamente en un molino de bolas Spex. Los compuestos con adición de Ti+Ni3Al+Al2O3 a base de Fe se produjeron a una temperatura de sinterización de 1000 °C durante un tiempo de 1 h. Las propiedades de estos compuestos se examinaron mediante microscopía electrónica de barrido (SEM), microscopía óptica (OM), espectroscopía de dispersión de energía (EDS), difracción de rayos X (XRD) y análisis de microdureza. El producto final producido por aleación mecánica fue una solución sólida rica en níquel nanocristalina, el tamaño promedio del cristal era de unos pocos nanómetros. El contenido de titanio en el refuerzo aumentó los valores de microdureza del composite. Los compuestos producidos incluían las fases Fe3Al, TiAl, NiAl, Al3Ni2, Al2O3 y Fe3O.

Effect of the additive content on the sintering of pre-sintered Si3N4 composite.

AbstractSintering of Si3N4 compounds requires additives that promote densification through the dissolution-precipitation mechanism in liquid phase sintering. The sintering of the Si3N4 with the SiO2-Y2O3-Al2O3 system has been extensively studied. Nevertheless, because SiO2 depends on the natural amount on the Si3N4 surface, little has been studied about SiO2 control. A pre-sintering treatment can increase the content of SiO2 through controlled oxidation of Si3N4. In this work the effect of the additive content on the densification of Si3N4 composite ceramics was evaluated. For this purpose, powder mixtures of Si3N4, Y2O3 and Al2O3 were prepared. The Y2O3 and Al2O3 ratio were modified in percentages of 4, 8 and 12% by weight. The mixtures were compacted and pre-sintered at 1300°C for 1 hour. Then, these were sintered at 1450°C for two hours. The samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that during pre-sintering, the Y5(SiO4)3N phase is formed; then, it's subsequently oxidized at the sintering stage. A second phase identified as Y3Al5O12 was found in samples with higher proportions of Al2O3. Composition and quantity of the observed phases depend of Y2O3 and Al2O3 proportion in the added additive.

The Inhibiting Effect of Reactive Element Oxides on the Pack Cementation Aluminide Coating Formation

Minor additions of reactive elements (Y, Ce, La, Zr, Hf, etc.) significantly affect the high-temperature oxidation behavior of protective oxide scales. Designing oxidation-resistant aluminide coatings having optimum content of reactive elements is challenging due to the observed hindering effect of these elements on the coating formation. In the current investigation, this effect has been studied by examination of a high activity aluminide coating in powder mixtures of Al, NH4Cl, Y2O3, and Al2O3 with different Y2O3 contents. Oxides of Zr, Ce, and La were also examined for comparison. Cross-sectional microstructure of coatings and weight changes of the specimens were studied at different aluminizing times. The results showed that the inhibition effect applied for all reactive elements under investigation with different strengths and intensifies with more additions of Y2O3 up to a saturation limit. The observed inhibition effect was explained based on the equilibrium amounts of gaseous halides responsible for transfer of coating elements. It was demonstrated that the addition of Y2O3 can decrease the amount of aluminum carrier halide significantly. The mechanism of inhibition was attributed to the large agglomerates rich in aluminum and reactive elements detected in the pack after aluminizing treatment.

Effects of substrate roughness on the surface morphology and corrosion properties of Fe- and Ni-aluminide coatings on martensitic stainless steel

Surface morphology affects several important characteristics of airfoils such as corrosion resistance, fouling and aerodynamic properties. In the current investigation different morphologies were developed on the surface of a martensitic stainless steel used for gas turbine compressor blade applications. A low temperature aluminide diffusion coating was applied on the steel substrates having low, intermediate and high average roughness values. The aluminizing treatment was carried out at 470 °C for 24 h in a powder mixture of Al, AlCl3 and Al2O3. Some of the substrates with intermediate roughness were received a Ni electrodeposition with 5, 10, and 20 μm thicknesses before aluminizing to investigate the resultant influence on the final morphology. Surface morphology and microstructure of the specimens were studied via FE-SEM, XRD and EDS analysis. The surface roughness of the specimens was studied via a stylus profilometer and their corrosion behavior was examined by the potentiodynamic polarization test. The results showed that the surface roughness of the substrate increases after aluminizing treatment but the final roughness can be reduced by applying an appropriate thickness of a Ni interlayer. The raising of the surface roughness reduced the corrosion rate of the uncoated steel specimens but revealed a weak beneficial effect on the aluminized specimens. Thicker Ni interlayers resulted in higher corrosion rates of nickel aluminide coatings.

Ultrafast formation of Al2O3–Y3Al5O12 eutectic ceramic by flash sintering

AbstractIn this study, a dense Al2O3–Y3Al5O12 (YAG) ceramic was synthesized by flash sintering a powder mixture of Al2O3 and Y2O3 in less than 150 seconds at a furnace temperature of 1350°C. The resultant ceramic has a well‐defined eutectic structure consisting of alternating Al2O3 and YAG layers. The hardness and fracture toughness of the ceramic were measured to be 18.5 GPa and 4.3 MPa.m1/2, respectively. These values are comparable to those of similar eutectic ceramics made by directional solidification techniques. The results suggest a new method for making high‐performance eutectic ceramics, which could be applied in other systems.

Microstructural evolution of Ti4+-doped calcium hexaaluminate ceramics

Calcium hexaaluminate (CaAl12O19 or CA6) ceramics were fabricated by solid-state reaction sintering of Al2O3 and CaCO3 powder mixtures. The influence of Ti4+ doping on microstructural development of CA6 ceramics was investigated. After doping Ti4+, the lengths and widths of the CA6 grains increased, and the aspect ratios decreased significantly. Al vacancies (VAl) in mirror planes of CA6 are created by substituting Ti4+ for Al3+. As more VAl generates in the mirror planes, vacancy concentration varies considerably between mirror planes and spinel blocks. Combined with the fact that the ionic radius of Ti4+ is larger than that of Al3+, the crystal growth of CA6 along c axis is more promoted than that along basal plane. CaTiO3 and residual Al2O3 were observed in Ti4+-doped samples because of the reactions between CaO and TiO2.

A novel method for Fe-Al2O3 composites prepared from high sulfur Bayan Obo iron concentrate: Effectively eliminate the emission of SO2

Fe-Al2O3 composites with different carbon contents were prepared by reactive sintering from high sulfur iron concentrate, bauxite, Al2O3 powder mixture. The effects of different carbon contents on emission form of sulfur were studied. The thermo gravimetric-infrared radiation results showed there were no gaseous compounds containing sulfur discharged during the sintering except CO2 and H2O. It is indicated that sulfur precipitates around the metal phase in the form of sulfide by the phases and microstructures analysis. And with an increase in carbon contents, sulfide gradually transformed from FeS to MnS. The mechanical properties and acid resistance of materials can be improved by MnS rather than FeS. Samples with higher carbon content had optimal physical and chemical properties with bending strength of 295 MPa, hardness of 13.0 GPa, acid resistance of 94.89 % and alkali-resistance of 98.45 %. This study provides a novel cleaner method for the high sulfur iron concentrate that avoids the emission of sulfur-containing substances while ensuring the performance of the composite.

A research on the surface morphology, microstructure evolution and wear property of selective laser melting Al2O3/P20 composites

The Al2O3/P20 composites were successfully manufactured by selective laser melting (SLM) from powder mixture of Al2O3 and P20 mold steel with different Al2O3 contents (0.5 wt%, 1 wt%, 2 wt%) in this work. The surface morphology analysis indicated that Al2O3 particles were partially or fully melted for agglomerates during the SLM process with segregating between contiguous molten tracks. The model of Al2O3 diffusing during the SLM process was built for illustrating the generated mechanism of Al2O3 agglomerates. Moreover, the densification behavior of specimens became poor (the relative density declined from 99.3% to 94.2%) as the Al2O3 contents increased. The microstructure within samples had some obvious variations including coarsening martensite microstructure, tempering microstructure transformation, reverted austensite and precipitation of fine carbide particles. The result of Rockwll hardness test manifested that 1 wt% obtained the maximum value of 57.6 HRC, while 2 wt% had the minimum value of 45.9 HRC. Tribological test revealed that coefficient of friction (COF) and wear rate significantly declined when the Al2O3 contents were 1 wt% and 2 wt%, which emphasized the superior wear resistance property.

Al and Si diffusion in rutile

Abstract Diffusion of Al and Si has been measured in synthetic and natural rutile under anhydrous conditions. Experiments used Al2O3 or Al2O3-TiO2 powder mixtures for Al diffusant sources, and SiO2-TiO2 powder mixtures or quartz-rutile diffusion couples for Si. Experiments were run in air in crimped Pt capsules, or in sealed silica glass ampoules with solid buffers (to buffer at NNO or IW). Al profiles were measured with Nuclear Reaction Analysis (NRA) using the reaction 27Al(p,γ)28Si. Rutherford Backscattering spectrometry (RBS) was used to measure Si diffusion profiles, with RBS also used in measurements of Al to complement NRA profiles. We determine the following Arrhenius relations from these measurements: For Al diffusion parallel to c, for experiments buffered at NNO, over the temperature range 1100–1400 °C: D Al = 1.21 × 10 − 2 exp ⁡ ( − 531 ± 27 kJ/ mol − 1 / RT ) m 2 s − 1 . For Si diffusion parallel to c, for both unbuffered and NNO-buffered experiments, over the temperature range 1100–1450 °C: D Si = 8.53 × 10 − 13 exp ⁡ ( − 254 ± 31 kJ/ mol − 1 / RT ) m 2 s − 1 . Diffusion normal to (100) is similar to diffusion normal to (001) for both Al and Si, indicating little diffusional anisotropy for these elements. Diffusivities measured for synthetic and natural rutile are in good agreement, indicating that these diffusion parameters can be applied in evaluating diffusivities in rutile in natural systems Diffusivities of Al and Si for experiments buffered at IW are faster (by a half to three-quarters of a log unit) than those buffered at NNO. Si and Al are among the slowest-diffusing species in rutile measured thus far. Diffusivities of Al and Si are significantly slower than the diffusion of Pb and slower than the diffusion of tetravalent Zr and Hf and pentavalent Nb and Ta. These data indicate that Al compositional information will be strongly retained in rutile, providing evidence for the robustness of the recently developed Al in rutile thermobarometer. For example, at 900 °C, Al compositional information would be preserved over ~3 Gyr in the center of 250 μm radius rutile grains, but Zr compositional information would be preserved for only about 300 000 yr at this temperature. Al-in-rutile compositions will also be much better preserved during subsolidus thermal events subsequent to crystallization than those for Ti-in-quartz and Zr-in-titanite crystallization thermometers.

Effect of YSZ with different Y2O3 contents on toughening behavior of Al2O3/Ba-β-Al2O3/ZrO2 composites

Al2O3 matrix composites containing in-situ formed monoclinic zirconia (m-ZrO2) and BaO·7.3Al2O3 (one of Ba-β-Al2O3 compounds) were prepared via reactive sintering of Al2O3 and BaZrO3 powders. When yttria-stabilized zirconia (YSZ) with Y2O3 contents of 1.5 mol% (1.5YSZ), 2 mol% (2YSZ), and 3 mol% (3YSZ) as well as Y2O3 particles were introduced into Al2O3 and BaZrO3 powder mixtures, the in-situ formed m-ZrO2 was stabilized, resulting from the migration of Y3+ from YSZ or Y2O3 to m-ZrO2 during sintering. The incorporation of YSZ contributed to the refinement of Al2O3 grains, whereas Y2O3-added samples showed larger grain sizes of Al2O3 matrix. The samples with YSZ or Y2O3 addition exhibited high fracture toughness, which is attributed to crack deflection/bridging and transformation toughening of ZrO2. Although the phase transformation is mainly derived from ZrO2 formed during sintering, 1.5YSZ particles added in the composites still showed much higher phase transformability compared to 2YSZ and 3YSZ particles.

Microstructure and mechanical properties of textured TiB2 ceramic fabricated by combination of catalyst and hot–forging

In the present work, the powder mixtures of TiB2 containing 2.0mol.% carbon black with trace La2O3 and Al2O3 are used to fabricate textured TiB2 ceramic using hot–pressing at 1800 °C, and then the TiB2 ceramic is hot–forged. The results of microstructural observation indicated that the addition of the powder mixtures of Al2O3 and La2O3 was favorable to the rearrangement of the anisotropic TiB2 grains, whereas was unfavorable to the improvement of the relative density during hot–pressing and hot–forging. The flexural strength and the fracture toughness of textured TiB2 ceramic fabricated using the combination of oxides and hot–forging were improved significantly, whereas hardness did not show obvious change. The results here pointed to a novel method for fabricating textured TiB2–based ceramics.

Terahertz acoustic phonon detection from a compact surface layer of spherical nanoparticles powder mixture of aluminum, alumina and multi-walled carbon nanotube

We present terahertz spectroscopy study on spherical nanoparticles powder mixture of aluminum, alumina, and MWCNTs induced by surface mechanical attrition treatment (SMAT) of aluminum substrates. Surface alloying of AL, Al2O3 0.95% and MWCNTs 0.05% powder mixture was produced during SMAT process, where a compact surface layer of about 200 μm due to ball bombardment was produced from the mixture. Al2O3 alumina powder played a significant role in MWCNTs distribution on surface, those were held in deformation surface cites of micro-cavities due to SMAT process of Al. The benefits are the effects on resulted optical properties of the surface studied at the terahertz frequency range due to electrical isolation confinement effects and electronic resonance disturbances exerted on Al electronic resonance at the same range of frequencies. THz acoustic phonon around 0.53–0.6THz (17–20cm−1) were observed at ambient conditions for the spherical nanoparticles powder mixture of Al, Al2O3 and MWCNTs. These results suggested that the presence of Al2O3 and MWCNTs during SMAT process leads to the optically detection of such acoustic phonon in the THz frequency range.