High-temperature Tube Furnace Research Articles

Formation Mechanism of Soot in Zinc-Bearing Dusts Direct Reduction Process

The high-temperature tube furnace was applied to simulate the rotary hearth furnace (RHF) for the direct reduction of the zinc-bearing dusts from steel plants. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction (XRD), .and scanning electron microscopy (SEM) etc. The results suggested that the main phases of the soot were ZnO, KCl, NaCl and Zn5(OH)8Cl2H2O. Furthermore, the contents of Zn reach to 64.2% which could be used as secondary resources for zinc making. It is concluded that KCl and NaCl resulted from the volatilization from the briquettes at the experimental temperature of 1573K, while the ZnO were produced by the oxidation of the Zn vapor reduced from briquettes.

Direct Detection of NO Produced by High-Temperature Surface-Catalyzed Atom Recombination

The surface-catalytic recombination of oxygen and nitrogen atoms to form nitric oxide was confirmed by the direct detection of product NO molecules, using single-photon laser-induced fluorescence spectroscopy. Experiments were performed from room temperature to 1200 K in a quartz diffusion-tube sidearm reactor enclosed in a high-temperature tube furnace. Atomic nitrogen was generated using a microwave discharge, and atomic oxygen was produced via the rapid gas-phase titration reaction N + NO → O + N 2 . The use of isotopically labeled titration gases 15 N 16 O and 15 N 18 O allowed for the unambiguous identification of nitric oxide produced by the O + N surface reaction. The absolute number densities of surface-produced NO were determined from separate calibration experiments using 14 N 16 O. Observed variations of the NO number density with temperature and varying O/N atomic ratios at the sidearm entrance are generally consistent with the predictions of a simple reaction-diffusion model of the sidearm reactor that includes surface-catalyzed NO production as a species boundary condition.

Analysis of Fracture in High-Temperature Vacuum Tube Furnace

High-temperature vacuum tube furnace (HTVTF) is widely used for processing materials, developing new materials, and sintering various types of material under vacuum or gaseous conditions. A growing concern in engineering research communities and industries is that fracture occurs in the alumina tube after the furnace has run for few hours and this lead to a drainage of huge amount of money when the buyers replace the tube every time. To improve furnace tube longevity and performance in extreme temperature conditions, it is critical to determine the phenomena that take place inside the furnace and cylindrical alumina tube wall. In the present work, mathematical models are developed to understand the effect of stress concentration arising from thermal stresses in tube wall and heat-affected-zones (HAZ) of a HTVTF using multiphysics finite element software Comsol (Stockholm, Sweden). The combination of thermal stress with temperature difference determines the fracture region. Different air flow rates have been considered to find the critical thermal stress region inside the vacuum tube. Analysis suggests that lowering air flow rate and inserting a small copper pipe inside the first block to blow hot air on the second heat-affected zone (HAZ-2) will reduce thermal stress generation inside the tube and prevent the eventual fracture of the vacuum tube. It is expected that this study can lead to a better understanding of the complex phenomena of fracture alumina tube during operation of HTVTF.

Wet route to silicon oxide quantum dots with fixed and strong blue emission

Amorphous silicon oxide quantum dots, with a quantum yield of 0.47 and blue emission fixed at 2.85 eV (433 nm), were obtained via two wet steps: first silicon nanowires reacted with potassium hydroxide at 50 °C, and then the resultants were kept in the dark and exposed to air at 20 °C. The silicon nanowires were synthesized in a high-temperature tube furnace using quartz powder and hydrogen as starting materials, and these products had less oxide outer cover and were ready to react with potassium hydroxide. The transmission electron microscopy was employed in order to characterize the amorphous quantum dots of silicon oxide.

ZnO microcolumns originated from self-assembled nanorods

ZnO microcolumns originating from self-assembled ZnO nanorods have been prepared by thermal evaporation method at 1,160 degrees C in a high-temperature tube furnace. The composition and microstructure of as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It is found that the as-synthesized product consists of ZnO microcolumns with a hexagonal wurtzite structure. The growth direction of the ZnO microcolumns is along the normal direction of (10 (1) over bar2) lattice plane of hexagonal structure, while ZnO nanorods that constitute the former are along [0001] direction. Based on the structures' analysis, the possible growth mechanism of ZnO microcolumns originating from nanorods was discussed. Photoluminescence and Raman studies have also been carried out for the ZnO microcolumns and normal commercial powders at room temperature. The discrepancy between Raman and PL spectra of ZnO microcolumns and commercial powders may attribute more relative defects in the microcolumns.

Analysis of Copper Incorporation into Zinc Oxide Nanowires

ZnO nanowires (NWs) are grown on a bulk copper half-transmission electron microscopy grid by chemical vapor deposition in a high temperature tube furnace. Photoluminescence (PL) microscopy revealed band gap emission at 380 nm and a more intense visible emission around 520 nm due to defect states in these NWs. High-resolution transmission electron microscopy shows that the ZnO NWs are single crystalline with hexagonal structure. Auger electron spectroscopy (AES) and energy dispersive X-ray spectroscopy reveal that copper atoms are present along the length of the NW. AES also found that the surface of the NWs is oxygen rich. The surface concentration of zinc increases moving from the tip toward the base of the NW while the concentration of oxygen decreases. The copper in this system not only remains at the tip of the growing NW but also acts as a dopant along the length of the NW, leading to a decrease in the intensity of the band gap PL of these NWs.

Synthesis of beta silicon carbide powders from biomass gasification residue

The synthesis of beta silicon carbide (β-SiC) powders by carbothermal reduction of silica with carbon in a high temperature tube furnace was investigated. As carbon source, fine carbon-containing char from biomass gasification was used, in order to verify the feasibility of producing a high added value material starting from waste residue, and to promote the gasification processes as alternative route of energy production by the proper by-products exploitation. Starting mixture was prepared by mechanically mixing silica and char in the weight ratio of SiO2:C of 1.514; the mixture then reacted in a tube furnace at temperature of 1,550 °C at different residence times (1, 1.5, 2 and 2.5 h), at a constant flow rate of 0.8 dm3 min−1 of argon. The reaction products were characterised with XRD, FTIR spectroscopy and transmission electron microscopy (TEM). The process turned out to be capable of producing high quality SiC powders, suitable for making ceramic materials and composites; the product shows an uniform spherical shape, a very fine particle size (within the range of 30–100 nm) and a purity degree varying from 70% to 95%, depending on the residence time.

Si nanowires synthesized with Cu catalyst

The metal copper which is a newly developed interconnecting material for integrated circuit (IC) has been used as the catalyst to catalyze the formation of the Si nanowires in high temperature tube furnace. The growth direction of the straight Si nanowires is <111> and the polyhedron η″-Cu 3Si alloy is on the tip of the Si nanowires. The synthesis temperature of the Si nanowires is 500 °C. Such a low temperature implies that the vapor–solid (VS) should be the growth method. The cheap Cu catalyst is favorable for the mass synthesis of Si nanowires.

Single-crystalline ZnS tubular structures: preparation and characterization

Single-crystalline ZnS tubular structures have been successfully synthesized via thermal evaporation of ZnS powders mixed with a small amount of SnO2 at 1180 °C in a high-temperature tube furnace. Structure and microstructure of the ZnS tubes have been characterized by means of scanning electron microscopy and various techniques in a transmission electron microscope. It is found that the as-synthesized ZnS tubes are straight and uniform with lengths of several hundred micrometers. The outer diameters of these tubular structures range from several hundred nanometers to a few micrometers. As a part of the as-synthesized product, ZnS/Zn2SnO4 cables are also observed. A growth mechanism of these novel structures is proposed on the basis of transmission electron microscopy.

High-temperature furnace for dynamic neutron radiography

An easy-to-build and comparatively inexpensive high-temperature graphite tube furnace has been designed, fabricated, and tested for measuring physical properties of silicate melts with dynamic neutron radiography up to temperatures of 2300 K. This furnace allows in situ and real-time observations of large melt volumes at these high temperatures. The furnace has been used for the visualization of the interaction of two chemically distinct melts and for a determination of melt viscosities of silicates with the falling sphere method.

00/02172 Combined thermal analysis and gas-analysis methods and software simulations for the investigation of the potential endangerment to the environ

The high-temperature tube furnace was applied to simulate the rotary hearth furnace (RHF) for the direct reduction of zinc-bearing dusts from steel plants. The removal mechanism of Zn, Pb and alkalis from cold bonded briquettes made by mixing metallurgical wastes, such as dust from bag house filter, OG sludge, fine converter ash and dust from the third electric field precipitator of the sinter strand, in various proportions was investigated. More than 70% of metallization rate, more than 95% of zinc removal rate, 80% of lead removal, as well as more than 80% of K and Na removal rates were achieved for the briquettes kept at 1473–1603 K for 15 min during the direct reduction process respectively. The soot generated in the direct reduction process was studied by chromatography, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results suggested that the main phases of the soot were ZnO, KCl, NaCl and 4ZnO · ZnCl2 · 5H2O. Furthermore, the content of Zn reached 64.2%, which could be used as secondary resources for zinc making. It was concluded that KCl and NaCl in secondary dust resulted from the volatilization from the briquettes, whilst ZnO and PbO were produced by the oxidation of Zn or lead vapour from briquettes by direct reduction.

Bulk-quantity Si nanowires synthesized by SiO sublimation

High-purity Si nanowires in bulk-quantity have been grown from SiO in a high-temperature tube furnace. Thermal sublimation of SiO powders produced SiO vapor, which was transported and deposited on the inner wall of the tube at ∼930 oC. We proposed that the SiO deposit underwent a disproportionation reaction to form nanowires containing Si and SiO 2. Each wire consisted of a single crystalline Si core and an oxide sheath, 6–28 nm in diameter and up to 1 mm in length. This work gave strong support to the recently proposed oxide-assisted growth mechanism. The yield of Si nanowires increased with sublimation temperature and pressure. Under suitable deposition conditions, Si nanowire growth rate of more than 10 mg/h could be routinely obtained.

Gold nanoparticles : Production, reshaping, and thermal charging

Gold nanoparticles are of great interest for various nanoelectronic applications, e.g., for making single electron transistors or very fine leads to molecular size entities. For this and other applications, it is important that all particles have controllable size and shape. In this paper, we describe the production of size-selected gold aerosol particles in the 20 nm range made by evaporation in a high-temperature tube furnace and subsequent size selection. To obtain spherical particles, it was necessary to reshape the particles at high temperature, which was investigated for temperatures between 25°C and 1200°C. High-resolution transmission electron microscopy showed that the degree of crystallinity became higher for higher reshaping temperature. During reshaping at high temperature, an anomalous charging behavior was discovered, whereby negatively as well as positively charged particles became multiply negatively charged. Possible mechanisms for explaining this thermally activated phenomenon are discussed.

Analysis on SiO2 particle generation and deposition using tube furnace reactor

The combined phenomena of SiO2 particle generation and deposition were analyzed theoretically and experimentally in a tubular flow reactor. The deposition tube was directly connected to a high-temperature tube furnace reactor by a flange and the deposition characteristics of SiO2 particles were measured. The SiCl4 conversion and deposition efficiencies were calculated, solving the mass and energy balance equations and the aerosol dynamic equation in the tubular flow reactor. Effects of process variables such as furnace set temperature, inlet SiCl4 concentration and total gas-flow rate were examined. Experimental results agreed closely with theoretical prediction. Effects of natural convection are significant at low gas-flow rate. Tube wall temperature profiles inside the deposition tube were proposed for uniform coating of SiO2 particles. The study shows that the tube furnace reactor can be used to coat the inside wall of the deposition tube with ultrafine particles uniformly by adjusting tube wall temperature profiles.