Conventional Electric Furnace Research Articles

Microwave-assisted synthesis and sintering of mullite

Mullitization behaviour of a mixture of clay and alumina as the starting materials was examined by microwave heating of (a) mixed powder and (b) compacted powder samples for different soaking times. X-ray diffraction results showed that in compacted samples mullitization process was completed after 20 min heating with a density of about 87%. Densification and microstructure of samples with different green densities heated in a microwave oven and conventional electric furnace were compared. Results showed that the grain growth of mullite was restricted by microwave heating.

Microwave-assisted synthesis of Pr–ZrSiO 4, V–ZrSiO 4 and Cr–YAlO 3 ceramic pigments

An innovative two-step route was successfully applied to the microwave-assisted synthesis of Pr–ZrSiO 4, V–ZrSiO 4 and Cr–YAlO 3 ceramic pigments. It is able to reduce the total synthesis time from many hours down to a few minutes. Industrial batches were pelletized and underwent a short time pre-heating in conventional electric furnace (from 300 up to 1000 °C) prior to dielectric heating in microwave oven (2.45 GHz, 800 W continuous or paused). Pre-heating is necessary to reach a thermal level at which pigment precursors are activated under microwave irradiation (high enough tan δ of dielectric properties). Activation kinetics was followed by measuring (optical pyrometer) the external temperature of crucible during MW irradiation and the internal temperature at the end of heating process. Pigments were characterized by colourimetry (CIE Lab) and XRPD with Rietveld refinement. The V–ZrSiO 4 system is easily activated, already at pre-heating of 300 °C, with good reaction yield and colour performance; nevertheless it is difficult to keep under control, as temperatures exceeding 1200 °C are rapidly reached. The Pr–ZrSiO 4 system is activated after pre-heating over 600 °C and exhibits a slow kinetics, resulting in a low reaction yield and unsatisfactory colour. The Cr–YAlO 3 pigment is formed with colour and reaction yield close to those of the correspondent industrial product, even though after pre-heating at 800 °C or more. A peculiar behaviour of silica phases was observed in zircon systems, particularly after lower pre-heating temperatures. It consists in an early transformation of quartz (present as precursor) into cristobalite and abundant amorphous phase, before the SiO 2 + ZrO 2 → ZrSiO 4 transformation occurred.

Application of Microwave Technique for Dehydration of Sludge Generated in a Stainless Steel Plant

In ironmaking and steelmaking processes, dehydration technology is often recognized to be a key process for the successful operation. That is not an exception in recycling process of valuable elements such as Fe, Ni, Cr and so on by reducing the wasted materials including dust, scales and sludge, generated in each steel works. This investigation basically focused on the availability of microwave technique for dehydration stage of sludge generated in a stainless steel mill. Actually sludge is well-known as a wasted resource difficult to be dehydrated. Unless dehydration of such resource is successful, some problems with slow heating and/or burst of briquettes may arise.In this study, prior to the industrial studies, dehydration experiments of goethite were performed. The results showed that the microwave treatment could heat up the specimen directly from inside of specimen while being heated from the outside by the electric furnace. Thus the dehydration ratio resulted higher in the microwave irradiation, indicating the benefit of the microwave treatment.Thereafter the microwave technique was tried for dehydration of industrial sludge. Consequently, the effectiveness of microwave treatment was confirmed because 34 mass% weight-loss after the microwave treatment corresponded to the complete dehydration while 7 mass% weight-loss after heating in a conventional electric furnace. If application to industrial practice is realized, it is expected that the problems brought by the conventional way will be hopefully solved to prevent burst of agglomerations.

Pb-Free High Temperature Solder Joints for Power Semiconductor Devices

Three types of inexpensive Pb-free solder joints, namely Zn-based and Bi-based solders, and a CuSn alloy were studied for application to the high-temperature operation of wide band-gap power semiconductor devices using GaN or SiC. Zn–Al solder sheets, whose melting point is 380°C were prepared, and then surface oxides were removed by RF plasma etching. Subsequently, Cu thin films were deposited by the DC sputtering method on the solder sheet. After that, joint samples were fabricated using a conventional electrical furnace with H2/N2 gas flow. That the joints were sufficiently dense was confirmed by scanning acoustic microscope. The wettability of the solder was improved due to contact between the pure Zn–Al solder without oxide and the Ni surface of the substrate, and the chemical reaction between the Zn–Al solder and the deposited Cu thin film. Bi with CuAlMn particle solders, whose melting point is 270°C, were fabricated and it was found that the solder has almost double the tensile strength of pure Bi. Excellent wettability was observed with the Ni or Pd thin film deposited on the Cu substrate. It was found that deposited Ni or Pd was not observed in the interface between the substrates after the joint samples were fabricated. CuSn alloy joints were fabricated using Sn thin films deposited and annealed on Cu substrates. The temperature during the annealing was kept at approximately 350°C; therefore, only the Sn film was melted and some chemical reaction occurred between the liquid Sn and solid Cu. Then, Cu3Sn alloy, whose melting point is 640°C, appeared in the joint and the composition was confirmed by X-ray diffraction analysis. Furthermore, it was found that the CuSn alloy is harder than Cu as measured by nano indentation analysis. In addition, the joints showed excellent thermal cycle reliability.Finally, the properties of these joints are summarized.

Bi2O3 Vaporization in Microwave‐Sintered ZnO Varistors

Vaporization of Bi2O3 in microwave‐sintered ZnO varistors is discussed in this study. The Bi2O3 vaporization of ZnO varistors sintered by a conventional electric furnace is also studied for comparison. The results show that the Bi2O3 vaporization in microwave‐sintered ZnO varistors is more homogenous from the surface to the inside of the sample, which results from the special thermal gradient inside the microwave‐sintered samples, and we also find out that the Bi2O3 vaporization directly affects the electrical properties of ZnO varistors. Microwave‐sintered samples exhibit more excellent electrical properties than the conventional ones because the homogenous Bi2O3 vaporization leads to more uniform microstructures.

Microwave‐Assisted Reaction Sintering of Bismuth Titanate‐Based Ceramics

Bismuth titanate‐based ceramics, pure and doped with 5 mol% WO3, were prepared by reaction‐sintering using a microwave oven. High densities, ≥96% of theoretical density were achieved with very short thermal treatments, with soaking time ranging from 5 to 15 min. Relatively small platelet‐like grains were formed, and microstructure seemed not to be strongly affected by doping nor soaking time. Electrical measurements were performed and, as expected, a decrease of electrical conductivity was observed in WO3‐doped materials. The results of reaction‐sintered samples, both conventional as well as microwave sintered, are compared with those of samples prepared with previously calcined powders and sintered using microwaves as well as a conventional electric furnace.

BRANCHING STRUCTURE IN BaO-PbO-SrO-P2O5 PHOSPHATE GLASS PREPARED BY MICROWAVE HEATING

Phosphate glass with a composition of 15BaO-10PbO-5SrO-70P2O5 has been prepared by 2.45 GHz microwave heating. In the 31P MAS NMR spectra of this glass, we observed the strong Q3 band corresponding to the branching PO4 group which was not observed in the glass prepared by conventional electric furnace heating. The presence of branching points means that the glass prepared by microwave has three-dimensionally polymerized structure, which gives the higher stability of the glass.

Effect of microwave and conventional regeneration on the microporous and mesoporous network and on the adsorptive capacity of activated carbons

The effect of different heating mechanisms on the porous network of activated carbons (AC) previously exhausted with phenol has been studied. To this end, thermal treatment of the exhausted AC was performed using two experimental devices: a single mode microwave device operating at 2450 MHz and a conventional electric furnace. By employing microwave energy, the regeneration time was considerably shortened compared to conventional thermal heating. Moreover, microwave heating preserved the porous structure of the regenerated AC more efficiently than treatment in a conventional device. In both cases successive regeneration cycles reduced the microporosity of the activated carbons. However, conventional heating shifted the micropore size distribution to pores of narrower sizes. The apparent BET surface areas were also reduced significantly over the regeneration cycles. A loss of the adsorptive capacity of the carbon material was observed after six adsorption–desorption cycles in both systems. The phenol adsorption capacities decreased to a greater extent in the samples regenerated in the electric furnace.

Microwave-induced regeneration of activated carbons polluted with phenol. A comparison with conventional thermal regeneration

Thermal regeneration of activated carbons (AC) was carried out at 1123 K and under N 2 atmosphere. Experiments have been carried out using a single mode microwave device operating at 2450 MHz and a conventional electric furnace (EF) so as to compare the effect of the different heating mechanisms on the adsorptive capacities of the regenerated AC. The adsorbents were saturated with phenol in columns. Adsorptive capacities after subsequent regeneration cycles were evaluated from the breakthrough curves. Additionally, a complete textural and chemical characterization of the regenerated samples was also carried out in order to study the influence of the subsequent regeneration cycles on the texture and the adsorptive capacities of the AC. Textural characterization of the regenerated samples was carried out by means of N 2 adsorption isotherms at 77 K.

Gas chromatographic–mass spectrometric study of the oil fractions produced by microwave-assisted pyrolysis of different sewage sludges

The pyrolysis of sewage sludge was studied in a microwave oven using graphite as microwave absorber. The pyrolysis temperature ranged from 800 to 1000 °C depending on the type of sewage sludge. A conventional electrical furnace was also employed in order to compare the results obtained with both methods. The pyrolysis oils were trapped in a series of condensers and their characteristics such as elemental analysis and calorific value were determined and compared with those of the initial sludge. The oil composition was analyzed by GC–MS. The oils from the microwave oven had n-alkanes and 1-alkenes, aromatic compounds, ranging from benzene derivatives to polycyclic aromatic hydrocarbons (PAHs), nitrogenated compounds, long chain aliphatic carboxylic acids, ketones and esters and also monoterpenes and steroids. The oil from the electric oven was composed basically of PAHs such as naphthalene, acenapthylene, phenanthrene, fluoranthene, benzo[ a]anthracene, benzofluoranthenes, benzopyrenes, indenepyrene, benzo[ ghi]perylene, and anthanthrene. In contrast, these compounds were not produced in the case of microwave-assisted pyrolysis.

Study of Metamorphosing Top Si Layer of SOI Wafer into 3C-SiC Using Conventional Electric Furnace

Study of Metamorphosing Top Si Layer of SOI Wafer into 3C-SiC Using Conventional Electric Furnace

선형가열기를 이용한 SillSiO2/Si3N4llSi 이종기판쌍의 직접접합

Direct bonded SOI wafer pairs with <TEX>$Si ll SiO_2/Si_3N_4 ll Si$</TEX> the heterogeneous insulating layers of SiO<TEX>$_2$</TEX>-Si<TEX>$_3$</TEX>N<TEX>$_4$</TEX>are able to apply to the micropumps and MEMS applications. Direct bonding should be executed at low temperature to avoid the warpage of the wafer pairs and inter-diffusion of materials at the interface. 10 cm diameter 2000 <TEX>${\AA}-SiO_2/Si(100}$</TEX> and 560 <TEX>$\AA$</TEX>- <TEX>${\AA}-Si_3N_4/Si(100}$</TEX> wafers were prepared, and wet cleaned to activate the surface as hydrophilic and hydrophobic states, respectively. Cleaned wafers were pre- mated with facing the mirror planes by a specially designed aligner in class-100 clean room immediately. We employed a heat treatment equipment so called fast linear annealing(FLA) with a halogen lamp to enhance the bonding of pre mated wafers We kept the scan velocity of 0.08 mm/sec, which implied bonding process time of 125 sec/wafer pairs, by varying the heat input at the range of 320~550 W. We measured the bonding area by using the infrared camera and the bonding strength by the razor blade clack opening method, respective1y. It was confirmed that the bonding area was between 80% and to 95% as FLA heat input increased. The bonding strength became the equal of <TEX>$1000^{\circ}C$</TEX> heat treated <TEX>$Si ll SiO_2/Si_3N_4 ll Si$</TEX> pair by an electric furnace. Bonding strength increased to 2500 mJ/<TEX>$\textrm{m}^2$</TEX>as heat input increased, which is identical value of annealing at <TEX>$1000^{\circ}C$</TEX>-2 hr with an electric furnace. Our results implies that we obtained the enough bonding strength using the FLA, in less process time of 125 seconds and at lowed annealing temperature of <TEX>$400^{\circ}C$</TEX>, comparing with the conventional electric furnace annealing.

Microwave-induced pyrolysis of sewage sludge

This paper describes a new method for pyrolyzing sewage sludge using a microwave furnace. It was found that if just the raw wet sludge is treated in the microwave, only drying of the sample takes place. However, if the sludge is mixed with a small amount of a suitable microwave absorber (such as the char produced in the pyrolysis itself) temperatures of up to 900°C can be achieved, so that pyrolysis takes place rather than drying. Microwave treatments were also compared with those carried out in a conventional electric furnace, as well as the characteristics of their respective carbonaceous solid residues.

電磁エネルギー焼結 ミリ波加熱を利用した不揮発性メモリー用強誘電体薄膜のアニーリング

SrBi2Ta2O9(SBT) films were prepared on Pt/Ti/SiO2/Si substrates by the spin-coating technique, and they were annealed by 28 GHz millimeter-wave heating method. It was revealed that the annealed films were crystallized at a lower temperature than those by conventional electric furnace heating. For clarifying the difference in the interaction of the radiation with each materials of the substrate, transmission, reflection and absorption properties of various silicon substrates were measured by a low power millimeter-wave radiation. It was found that the carrier density of substrates exceedingly influenced millimeter-wave absorption. In the case of a low carrier density, the substrates were almost transparent for the millimeter-wave, while in the case of a high carrier density the reflection was dominant.

Structural and electrical properties of strontium barium niobate thin films crystallized by conventional furnace and rapid-thermal annealing process

Strontium barium niobate (SBN) thin films were crystallized by conventional electric furnace annealing and by rapid-thermal annealing (RTA) at different temperatures. The average grain size of films was 70 nm and thickness around 500 nm. Using x-ray diffraction, we identified the presence of polycrystalline SBN phase for films annealed from 500 to 700 °C in both cases. Phases such as SrNb2O6 and BaNb2O6 were predominantly crystallized in films annealed at 500 °C, disappearing at higher temperatures. Dielectric and ferroelectric parameters obtained from films crystallized by conventional furnace and RTA presented essentially the same values.

Reactive power reduction in three-phase electric arc furnace

A conventional three-phase electric arc furnace causes flicker at the point of common coupling with AC mains. This generally occurs with AC mains having a low short-circuit capacity. The flicker is caused by flucluating reactive power consumption of the furnace. This paper describes a way, through computer simulation, of increasing the dynamic performance of the furnace and keeping reactive power consumption constant. This can be achieved with the addition of a three-phase power controller and a booster transformer to the power source and the introduction of a new control method of regulating the reactive power input. The problem of flicker can thus be minimized. This was experimentally tested on a single-phase model and the results obtained were very satisfying. Due to laboratory facilities, the three-phase testing was not performed.

傾斜機能材料 放電プラズマ法による傾斜機能型インプラントの試作と特性

The titanium (Ti)/hydroxyapatite (HAP) functionally graded materials (FGM) for implant were fabricated by Spark Plasma Sintering (SPS) method. The specimens were sintered at 950°C under 40 MPa. After sintering, the square rods of 1×1×10mm were cut for implant. The various FGM specimens were observed by SEM and evaluated by X-ray scanning analytical microscope. The FGMs with the gradient composition ranging from pure Ti to 100% HAP were implanted into the bone marrow of femora of rats for 2 and 4 weeks. The bone formation around the FGM specimens was histologically observed by optical microscopy. The present study showed that the sintering temperature could be lowered considerably by use of SPS from 1300°C compared to less than 1050°C by conventional electric furnace heating. The Ti/HAP FGM implant showed the biocompatibility and affinity for osteogenesis.

パルス通電加圧焼結法による２Ｎｂ／Ａｌ組成ＭＡ粉末の初期焼結過程

The mechanically alloyed powder of 2Nb/Al composition was sintered in the temperature ranges from 973K to 1173K using either the pulse current pressure sintering (PCPS) apparatus or a conventional electric furnace. X-ray diffraction patterns for the compacts sintered by PCPS showed the weak Al peaks in halo, although the diffraction patterns for the compacts sintered by conventional electric heating did not show the Al peaks. A set of 2Nb/Al powder compact and balls of SUS304 stainless steel were sintered at 973K by PCPS in order to make clear the reason why the Al peaks were detected. Using EDX, Nb were not, but Al were detected in the circumference area in contact with 2Nb/Al compact on the surface of SUS ball. This fact indicates that evaporation and deposition of Al occured during PCPS. It can be estimated that the contact area in the earlier stages of PCPS was heated up to the order of 2000 to 4000K.

Mullitization and densification of (3Al 2O 3 + 2SiO 2) powder compacts by microwave sintering

Reaction sintering of (3Al 2O 3 + 2SiO 2) powder compacts was studied using either a conventional electric furnace or a 2·45 GHz microwave furnace. Special attention was paid to temperature measurement within the microwave furnace. The reality of a microwave effect that accelerates the kinetics and therefore, decreases the temperatures of mullitization and densification, remains uncertain. In any case, such an effect does not exceed ≈ 50 °C, which is in the order of the temperature gradient between the core and the surface of microwave heated specimens.

A comparison of mm-wave Sintering and Fast Conventional Sintering of Nanocrystalline Al2O3

AbstractThe phase transformation and densification behavior under high power millimeter-wave (mm-wave) radiation of a 30 GHz gyrotron and during fast conventional sintering of nanocrystalline γ-A12O3 powder have been investigated and compared. The powder used for compacts was synthesized from aluminum metal by application of the exploding wire technique in an oxidizing atmosphere. The particle size distribution of this powder has a maximum at about 20 nm. Magnetic pulse technique was applied for the compression of samples up to 80% of the theoretical density (TD). Both mm-wave sintering and fast firing in a conventional electrical resistance furnace enable the densification and a complete phase transformation into α-A12O3 already at a temperature of approximately 1150 %C. The average grain size of the sintered ceramic is in the range of 50 to 100 nm. With mm-waves densification starts at about 50 °C lower temperatures compared to conventional techniques and higher final densities were obtained already at 150°C lower temperatures.