Microwave Furnace Research Articles

Fabrication of magnesium-boron carbide metal matrix composite by powder metallurgy route: Comparison between microwave and spark plasma sintering

Microwave and spark plasma sintering processes were used to produce magnesium-B4C metal matrix composites by powder metallurgy route. Magnesium powder with 5 wt% B4C in ethanol media was blended in a high-energy ball mill for 10 min. The sintering process was performed at 500° and 670 °C using spark plasma sintering and microwave furnace, respectively. XRD investigations revealed the crystallization of MgB2 and Mg2C3 compounds during both sintering processes. The mechanical examinations showed higher bending strength (191 ± 15 MPa) and microhardness (92 ± 7 Vickers) of SPS samples rather than microwave samples. FESEM images demonstrated uniform distribution of B4C reinforcements at grain boundaries of metallic matrix. The MAP analysis of SPS samples approved the formation of new compounds as a result of the reaction between magnesium and B4C.

Electrical characterization of La9.33Si2Ge4O26 oxyapatite for prospective intermediate-temperature solid oxide fuel cells

La9.33Si2Ge4O26 materials have been fabricated from La2O3, SiO2 and GeO2 powders by high speed mechanical alloying followed by conventional and microwave hybrid sintering at different temperatures and holding times. XRD data showed that the apatite phase is formed after 1h of mechanical alloying at 850rpm. This phase remained stable after conventional sintering in an electric furnace with density increasing as sintering temperatures and holding times were increased. However, the highest density was achieved for samples sintered in the microwave furnace (5.44gcm−3), corresponding to a relative density of 98%. The electrical conductivity of the samples microwave sintered at 700 and 800ºC are 4.72×10−3 and 1.93×10−2 S.cm−1, respectively, with a correspondent activation energy of 0.952eV.

Synthesis of SiC nanowhiskers from graphite and silica by microwave heating

AbstractSilicon carbide (SiC) is an important ceramics for engineering and industrial applications due to its advantage to withstand in high temperatures. In this article, a demonstration of SiC nanowhiskers synthesis by using microwave heating has been shown. The mixtures of raw materials in the form of pellets were heated, using a laboratory microwave furnace, to 1400 °C for 40 minutes at a heating rate of 20 °C/min. The characterization process proved that the mixture of graphite and silica in the ratio of 1:3 is an ideal composition for synthesizing single phase β-SiC nanowhiskers. Vapor-solid mechanism was suggested to explain the formation of SiC nanowhiskers by the proposed microwave heating.

Experimental Analysis of Hardness and Densification of Microwave Sintered AL/SIC/AL2O3/Flyash Composites

Objectives: Powder metallurgy is one of the best methods to achieve uniform distribution of reinforcement in matrix. In the present study, silicon carbide, alumina and fly ash are reinforced in Aluminium matrix at various proportions through powder metallurgical process using both conventional and microwave sintering and the mechanical properties were evaluated. Methods/Statistical Analysis: The compaction load has varied from 4000 kg to 8000 kg, and it was observed that the maximum densification of 84.04% at 8000 kg was obtained. All the samples were prepared at 8000 kg load and sintering was done using microwave furnace. For comparison purpose, all the samples were sintered conventionally using tubular furnace. Findings: Hardness and densification tests were conducted on both conventional and microwave sintered specimens. Composites, which are, processed through microwave sintering shows a better result than conventionally sintered specimens with saving the process timing and power consumption. It is being observed that the role of SiC in microwave sintering is very vital as it is an absorber of microwaves. Application/Improvements: The working area of a microwave furnace is very less and it restricts the size of the working sample. The role of other absorbers (semiconductors) of microwaves can be studied.

Effect of Heating Method on Microstructure and Mechanical Properties of Zircon Reinforced Aluminum Composites

The mechanical properties and microstructure of aluminum matrix composites containing of zircon (10, 15 and 20 wt.%) as a reinforcement particles and cobalt additive (1, 1.5 and 2 wt.%) were investigated. The aluminum matrix composites were prepared by powder metallurgy technique and sintered in both conventional and microwave furnaces at temperatures higher than the melting point of aluminum. The results revealed that the density and mechanical strength of aluminum were increased by introducing zircon and cobalt particles. The maximum strength was obtained by adding 10 wt.% zircon sintered in microwave furnace at 950oC. The phase analysis and scanning electron microscopy of sintered composites were examined and found some interesting data about intermetallic compounds.

Microwave absorption studies of magnetic sublattices in microwave sintered Cr3+ doped SrFe12O19

The partial substitution of Fe3+ by Cr3+ in strontium hexaferrite has shown to be an effective method to tailor anisotropy for many novel microwave applications. Some basic studies have revealed that this substitution leads to unusual interactions among the magnetic sublattices of the hexaferrite. In order to investigate these interactions, Cr3+ doped SrCrxFe12−xO19 (x=0.0, 0.1, 0.3, 0.5, 0.7 and 0.9) (m-type) hexaferrites were prepared by microwave-hydrothermal (m-H) method and subsequently sintered at 950°C/90min using microwave furnace. The magnetic hysteresis (m-H) loops revealed the ferromagnetic nature of nanoparticles (NPs). The coercive field was increasing from 3291Oe to 7335Oe with increasing chromium content. This resulting compacts exhibited high squareness ratio (Mr/Ms–80%). The intrinsic coercivity (Hci) above 1,20,000Oe and high values of magnetocrystalline anisotropy revealed that all samples are magnetically hard materials. A material with high loss as well as high dielectric constant may be desired in applications such as electromagnetic (EM) wave absorbing coatings. The room temperature complex dielectric and magnetic properties (ε′, ε′′, µ′ and µ′′) of Cr3+ doped SrFe12O19 were measured in X-band region. The frequency dependent dielectric and magnetic losses were increasing to large extent. The reflection coefficient varied from −16 to −33dB at 10.1GHz as Cr3+ concentration increased from x=0.0 to x=0.9. Ferromagnetic resonance spectra (FMR) were measured in the X-band (9.4GHz), linewidth decreases with chromium concentration from 1368 to 752Oe from x=0.0 to x=0.9, which is quite low compared to commercial samples. We also have detailed origins of the FMR linewidth broadenings in terms of some important theoretical models. These results show that chromium doped strontium hexaferrites are useful for microwave absorption in the X-band frequency and also have potential for use in low frequency self-biased microwave/millimeter devices such as circulators and isolators.

Evaluation of superparamagnetic and biocompatible properties of mesoporous silica coated cobalt ferrite nanoparticles synthesized via microwave modified Pechini method

Cobalt ferrite nano particles were synthesized by Pechini sol-gel method and calcined at 700°C in electrical and microwave furnace. The microwave calcined sample was coated with mesoporous silica by hydrothermal method. Characterization was performed by XRD, FESEM, TEM, VSM, BET and FTIR analysis. The cytotoxicity was evaluated by MTT assay with 3T3 fibroblast cells. The XRD and FTIR results confirmed spinal formation in both cases and verified the formation of silica coating on the nanoparticles. For microwave calcination, The XRD and SEM results demonstrated smaller and flat adhesion forms of nanoparticles with the average size of 15nm. The VSM results demonstrated nearly superparamagnetic nanoparticles with significant saturation magnetization equal to 64emu/g. By coating, saturation magnetization was decreased to 36emu/g. Moreover, the BET results confirmed the formation of mesoporous coating with the average pore diameters of 2.8nm and average pore volume of 0.82cm3g−1. Microwave calcined nanoparticles had the best structural and magnetic properties.

Effect of the Addition of Al and Cu on Magnesium Processed by Powder Metallurgy Route

Objectives: Magnesium being HCP structured has the disadvantage of having poor deformation properties at room temperature making it difficult to work below recrystallization temperature. Hence it is necessary to improve the properties of Mg such as hardness and ductility etc. The present work aims to fabricate Mg-3Al-0.3Cu, Mg-3Al-0.6Cu, Mg- 6Al-0.3Cu and Mg-6Al-Cu alloys by powder metallurgy route. Methods/Statistical Analysis: The effect of both Al and Cu on the mechanical properties of pure Mg was evaluated. The elemental metal powders of Mg, Al and Cu are blended to make homogenized mixture and compacted at 300 MPa pressure to a 30mm diameter billets. The compacted samples were sintered using microwave furnace. The sintered samples arethen subjected to microstructural and micro-hardness testing using optical microscope and microhardness tester respectively. Findings: Results of microstructural and mechanical tests suggest that the Al and Cu have significant effect on the hardness of Mg by the formation of Mg2Cu and Mg17Al12 phases. Based on the observations the optimum percentage of Al and Cu was found to be Mg-6Al-0.6Cu for betterhardness. Application/Improvement: The systematic investigation of the effect of Al and Cu on the sintered magnesium alloys is reported for the first time.

Production of Al-SiC-TiC hybrid composites using pure and 1056 aluminum powders prepared through microwave and conventional heating methods

In the present study aluminum-15 wt% SiC- 7 wt% TiC metal matrix composites containing two different aluminum powders (pure and 1056) as matrix were fabricated through microwave and conventional sintering methods. Sintering process was carried out at 650 and 750 °C in graphite bed in conventional and microwave furnaces for 1 h and without soaking time, respectively. Results indicate that the highest relative density (96.32 ± 0.3), bending strength (340 ± 14 MPa) and microhardness (192 ± 10 Vickers) corresponded to the composite containing 1056 aluminum sintered at 750 °C in microwave furnace. XRD patterns revealed aluminum, SiC and TiC as the only crystalline phases. SEM investigations showed a uniform particle distribution for both reinforcements for all composites containing two different aluminum types as matrix sintered through both conventional and microwave methods.

Effect of ball milling on reactive microwave sintering of MgO-TiO2 System

Abstarct In this paper, effect of mechanical activation on microwave reactive sintering of MgO - TiO2 system was investigated. Mixtures of MgO and TiO2 were milled at different times. Mixed powders along with 10 h milled powders were chosen for microwave sintering between 1000- 1400⁰C. Results showed that increasing of temperature up to 1400C for mixed powders could not give rise to complete formation of Magnesium titanate phases and raw materials were in the products. Also the densities of these samples were about 3 g/Cm3. With milling of reactants up to 10 h, it seems reactions could be completed at 1000⁰C and the density was augmented to 3.58 g/Cm3. The samples were sintered at 1400⁰C in a microwave furnace exhibited good microwave dielectric properties while er and tan δ were 16.3 and 0.0001 respectively.

Development of microwave-assisted sintering of Portland cement raw meal

Typically, using a rotary furnace as a heat generator, a temperature of approximately 1450 °C and a time of 60 min is needed to produce clinker requiring large amounts of energy. Recently, a method of sintering Portland cement by microwave furnace has been developed with the aim to reduce this high consumption of energy in the conventional cement production. In this work, cement raw meal was calcined by a microwave furnace operating at 2.45 GHz with 900 W at 1150 °C at several periods of time but was not completely successful in terms of clinker formation. Therefore, an electric furnace was used at 1300 °C and 1350 °C for 30 min to further heat the material. Chemical compositions of the formed clinker, characterized by XRD, presented C3S, C2S, C3A and C4AF as the main constituents confirming a clinker similar to those of clinker produced by rotary kiln or conventional technique. Loss on ignition and insoluble residue of the resultant clinker were analyzed by chemical analysis and the results were found to pass ASTM C-114. It was found that the raw meal sintering process using a microwave furnace followed by transfer to an electric furnace could reduce not only the temperature by at least 100 °C but also the processing time of the clinker. In addition, there is no grinding cost for clinker preparation in this process. This processing of clinker would decrease energy consumption and carbon dioxide emission to the atmosphere, a major cause of global warming.

Microwave sintering of ceria-doped scandia stabilized zirconia as electrolyte for solid oxide fuel cell

In this work, the effect of microwave sintering on the properties of 1 mol% ceria-doped scandia stabilized zirconia (10Sc1CeSZ) was investigated. The sintering was carried out at temperatures 1300 °C and 1350 °C for 15 min using a 2.45 GHz microwave furnace. The sintering behavior of the microwave sintered ceramics was compared with that obtained via the conventional sintering at temperatures ranging from 1300 °C to 1550 °C with 2 h holding time. It was found that both sintering processes yielded highly dense samples with minimum density of 98% theoretical value. Phase analysis by X-ray diffraction revealed the presences of only cubic phase in all sintered samples. All sintered pellets possessed high Vickers hardness (13–14.6 GPa) and fracture toughness (∼3 MPa m1/2). Microstructural examination by using the scanning electron microscope showed that the grain size varied from 2.9 to 9.8 μm for the conventional sintered samples whereas the grain size of the microwave sintered ceramics was below 2 μm. Electrochemical Impedance Spectroscopy study recorded the maximum ionic conductivity of 0.280 S/cm at 800 °C for the conventional-sintered sample at 1550 °C whereas a high value of 0.314 S/cm was measured for the microwave-sintered sample at 1350 °C.

Influence of zircon particle size on conventional and microwave assisted reaction sintering of in-situ mullite–zirconia composites

Mullite–zirconia composites were fabricated by reaction sintering of ZrSiO4 and α-Al2O3 using conventional heating and microwave processing. The powder mixtures were prepared from sub-micron zircon powders with three different particle sizes and CIPed as coin shaped samples. The samples sintered both in a muffle furnace and microwave furnace. The open porosities, bulk and true densities were measured. Phase transformations were characterized by X-ray diffraction and microstructures were evaluated by scanning electron microscopy. The effects of zircon particle size on the in-situ transformation system and mullitization was evaluated for both methods. As a result, decreasing zircon particle size decreases the in-situ transformation temperature for 25°C (1575°C) in conventional heating. Microwave assisted sintering (MAS) lowers the transformation temperature at least 50°C by lowering the activation energy more efficiently and gives better densification than conventional sintering. Furthermore, milling also produces structures having finer mullite grains.

Rapid microwave sintering of carbon nanotube-filled AZ61 magnesium alloy composites

Abstract In this study, a powder metallurgy processing technique combined with rapid microwave sintering was used to synthesise carbon nanotubes (CNTs) filled AZ61 magnesium alloy composites under ambient conditions, without recourse to any secondary process. In order to determine the appropriate amount of CNTs for taking full advantage of the AZ61/CNTs composite, a powder mixture of the CNTs, in varying volume fractions of 1–3%, and the AZ61 alloy was prepared through a mechanical milling process. The optimized milling intensity allowed for reducing the powder size for effective microwave absorption, and thus improved the dispersion of the CNTs in the Mg alloy matrix without reducing the structural integrity of CNTs. In addition to the incorporation of the CNTs with the dual role of mechanical reinforcement and microwave susceptor, microwave sintering was achieved in only 8 min by using a synergetic combination of graphite and silicon carbide as microwave susceptors in a microwave furnace. The sintered samples, whose porosity ranged between 4 and 6%, were characterised for microstructural, hardness, compressive and fracture properties. The results of hardness and compression tests indicated that these properties of all the composites were significantly improved compared to the monolithic samples. The highest microhardness value (∼105% increment) was recorded for the composite with 3.0% volume fraction of CNTs, while the composite sample with 1.0% volume fraction of CNTs had the highest ultimate compressive yield strength and 0.2% offset yield strength with approximate increments of 59% and 127%, respectively. The failure mechanisms of the composites as compared with the monolithic samples were discussed.

Determination of rare earth and concomitant elements in magnesium alloys by inductively coupled plasma optical emission spectrometry

An Inductively Coupled Plasma Optical Emission Spectrometry method for simultaneous determination of Al, Ca, Cu, Fe, In, Mn, Ni, Si, Sr, Y, Zn, Zr and rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in magnesium alloys, including the new rare earth elements-alloyed magnesium, has been developed. Robust conditions have been established as nebulizer argon flow rate of 0.5mLmin−1 and RF incident power of 1500W, in which matrix effects were significantly reduced around 10%. Three acid digestion procedures were performed at 110°C in closed PFA vessels heated in an oven, in closed TFM vessels heated in a microwave furnace, and in open polypropylene tubes with reflux caps heated in a graphite block. The three digestion procedures are suitable to put into solution the magnesium alloys samples. From the most sensitive lines, one analytical line with lack or low spectral interferences has been selected for each element. Mg, Rh and Sc have been studied as internal standards. Among them, Rh was selected as the best one by using Rh I 343.488nm and Rh II 249.078nm lines as a function of the analytical lines. The trueness and precision have been established by using the Certified Reference Material BCS 316, as well as by means of recovery studies. Quantification limits were between 0.1 and 9mgkg−1 for Lu and Pr, respectively, in a 2gL−1 magnesium matrix solution. The method developed has been applied to the commercial alloys AM60, AZ80, ZK30, AJ62, WE54 and AE44.

Microwave heat treatment of natural ruby and its characterization

Natural ruby (in the form of gemstone) collected from Odisha has been heat-treated by microwave (MW). A 3-kW industrial MW furnace with SiC susceptors was used for the heat treatment. The ruby samples showed noticeable improvements (qualitative), may be attributed to account for the improvement in clarity and lustre. Optical absorption in 200–800 nm range and photoluminescence peak at 693 nm (with 400 nm λ ex) clearly show that subtle changes do take place in the ruby after the heat treatment. Further, inorganic compound phases and valence states of elements (impurities) in the ruby were studied by X-ray diffraction, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The valence states of the main impurities such as Cr, Fe, and Ti, in the untreated and MW heat-treated ruby, as revealed from XPS, have been discussed in depth. The overall results demonstrate for the first time the effect of fast heating like MW on the microstructural properties of the gemstone and various oxidation states of impurity elements in the natural ruby.

Microwave assisted synthesis, sintering of lead-free ferroelectric CaBi4Ti4O15 ceramics

Calcium Bismuth Titanate (CBTi) ceramics were prepared by solid state reaction method and sintered in microwave heating process from 1050°C – 1200°C for 20 min. The formation of single phase with Orthorhombic structure was verified by X-Ray diffraction and Raman spectroscopy. The orthorhombic distortion present in the CBTi ceramic sintered at 1150°C was found to be maximum. The plate like morphology of the surface of the samples is observed in FE-SEM. The dielectric properties were measured at room temperature with Impedance Analyser. The ceramics sintered at 1150°C for 20 min. in microwave furnace show superior dielectric properties than 1200°C in conventional furnace for 2 hrs. The dielectric constants varies from 125-212 at 3KHz and losses are minimum. The presence of large orthorhombic distortion in the CBTi ceramics sintered at 1150°C results in high dielectric constant and low dielectric loss. The observed results indicate the importance of orthorhombic distortion and microwave sintering in enhancing the dielectric properties of a ferroelectric material.

Optimization of Holding Time on Microwave Irradiation of the Composite Iron-Chromium Reinforced with Alumina Particle

In this study, the effect of holding time on the microwave sintered 84Fe-11Cr-5Al2O3 metal matrix composite (MMC) was investigated. Sintering was carried out in a tubular microwave furnace HAMiLab-V3 under N2 atmosphere. The holding time was selected between 0 to 75 minutes with increment of 15 minutes respectively. A study of microstructure and physical properties was carried out on sintered samples. It was discovered that, when the samples sintered at 1400oC with 20oC/min heating rate, the hardness was significantly increased from 110Hv to 160 Hv for holding time ranging from 30 to 45oC/min. Further increment until 75 minutes of holding time, no significant changes were obtained and hardness values were at steady state. The enhancement of bulk density and reduction of porosity were observed commences at 30 minutes until 45 minutes holding time. However, the results showed that the optimum holding time was at 45 minutes where the micro hardness is at the highest point which is about 160Hv.

Effect of short milling time and microwave heating on phase evolution, microstructure and mechanical properties of alumina–mullite–zirconia composites

Abstract Alumina–mullite–zirconia composites were prepared using alumina and zircon powders pressed uniaxially at 250 MPa and sintered in a microwave furnace held at 1 550 °C for 90 min. The effects of short milling and sintering time on the density, phase evaluation and mechanical strength of the sintered composites were analyzed and compared with composites sintered in a conventional furnace. The goal was to decrease sintering time and temperature over that for conventional heating. The results showed that, although the densities were similar for both methods, the hardness, mechanical strength and fraction of the tetragonal zirconia phase of the microwave-sintered composites were much higher. The milling time yielded better densification and higher mechanical properties. It was found that the shorter sintering time in a microwave furnace requires longer milling time of the powders to obtain the same composite properties.

Microwave-Assisted Hydrothermal Synthesis of Ni-Mg Layered Silicate Clays

The synthesis of Ni-containing layered silicate clays from the lizardite-nepouite series (1:1) and kerolite-pimelite series (2:1) with random distribution of octahedral cations was feasible with the microwave-assisted hydrothermal synthesis method. These series were obtained from co-precipitated gels with Si 2 Mg 3-x Ni x O 7 .nH 2 O and Si 4 Mg 3-x Ni x O 11 .nH 2 O (x = 0, 0.5, 1, 1.5, 2, 2.5, and 3) compositions. Syntheses were performed at 220°C during 48 hours under equilibrium water pressure using microwave furnace. X-ray diffraction revealed pure 1:1 and 2:1 synthesized phyllosilicates for the lizardite and the kerolite series, respectively. Fourier transform infrared spectroscopy in both near and mid infrared regions revealed a random distribution of Ni cations in the octahedral sheet of 1:1 and 2:1 silicate clays, that is a good requirement for material applications, especially for the synthesis of metallic catalysts.