احیای گندله‌های کوره‌ی بلند اولیوینی

Mineral Reactions and Slag Formation During Reduction

of Olivine Blast Furnace Pellets

واکنش‌های کانی‌ها و تشکیل سرباره در طی احیای گندله‌های کوره‌ی بلند اولیوینی

ABSTRACT

The present work focuses on mineral reactions and slag formation of LKAB olivine iron ore pellets (MPBO) subjected to reducing conditions in the LKAB experimental blast furnace (EBF). The emphasis is on olivine reactions with surrounding iron oxides. Many factors influence the olivine behaviour. The study was performed by use of micro methods; optical microscopy, micro probe analysis, micro Raman and Mössbuer spectroscopy and thremodynamic modeling. During manufacturing, in oxidising atmosphere at high temperature (1350°C), olivine alterations occur through slag formation and rim reactions with iron oxides and other additives. To be able to describe olivine behaviour in the rather complex blast furnace reduction process one has to consider factors such as reactions kinetics, reduction degree of iron oxides, vertical and horizontal position in the furnace and reactions with alkali. Samples were collected from the EBF both from in shaft probing during operation and from excavation following quenching of the EBF.

 

تولید کامپوزیت‌های B4C-TiB2 با پرس گرم

Microstructure and mechanical properties of B4C–TiB2

composites prepared by reaction hot pressing using Ti3SiC2

ریزساختار و خواص مکانیکی کامپوزیت‌های B4C-TiB2 تولیدشده توسط پرس گرم

با استفاده از Ti3SiC2 به عنوان افزودنی

ABSTRACT

B4C–TiB2 composites were fabricated via reaction hot pressing at 2100 °C under a pressure of 25 MPa, using B4C and Ti3SiC2 powders as raw materials. The phase transformations, microstructure and mechanical properties were investigated by XRD, TG–DTA, SEM, TEM and EDS. It is found that the SiC and TiB2 particles are homogenously dispersed in the B4C–TiB2 composites, where nano-sized TiB2 particles are mainly located within the B4C matrix grains, while the large-sized TiB2 particles at the matrix grains boundaries. Due to the pinning effect of SiC and TiB2 particles on B4C grain growth, the grain size of the composite is significantly reduced, leading to a great improvement of the mechanical properties. B4C–TiB2 composite prepared from B4C-10 wt% Ti3SiC2 starting powder shows high flexural strength, fracture toughness and micro-hardness of 592 MPa, 7.01 MPa m1/2 and 3163 kg/mm2, respectively. Crack deflection and crack bridging are most likely the potential toughening mechanisms in the composites. Furthermore, according to the XRD and TG–DTA analysis, the possible reaction mechanisms leading to the in-situ formation of TiB2 were proposed.

رفتار قالب پرکنندگی مذاب های تیتانیوم Mold-filling behavior of titanium melts in vertically rotating molds

Effect of centrifugal and Coriolis forces on

the mold-filling behavior of titanium melts in vertically rotating molds

اثرات نیروهای گریز از مرکز و نیروهای کوریولیس بر رفتار قالب پرکنندگی مذاب های تیتانیوم

در قالب هایی که به صورت عمودی می چرخند

ABSTRACT

The vertical centrifugal-casting technique is widely used in the manufacture of various irregularly-shaped castings of advanced structural alloys with thin walls, complex shapes and/or large sizes. These castings are used in the increasing applications in aero-space/aviation industries, human teeth/bone repairs with near-net shaped components, etc. In a vertically rotating casting system, the mold-filling processes of alloy melts, coupled with solidification-heat transfer, may be much more complicated, because they are driven simultaneously by gravity, centrifugal and Coriolis forces. In the present work, an N-S/VOF-equations-based model, solved using a SOLA-VOF algorithm, under a rotating coordinate system was applied to numerically investigate the impacts of centrifugal and Coriolis forces on metallic melt mold-filling processes in different vertical centrifugal-casting configurations with different mold-rotation rates using an authors' computer-codes system. The computational results show that the Coriolis force may cause remarkable variations in the flow patterns in the casting-part-cavities of a large horizontal-section area and directly connected to the sprue via a short ingate in a vertical centrifugal-casting process. A "turn-back" mold-filling technique, which only takes advantage of the centrifugal force in a transient rotating melt system, has been confirmed to be a rational centrifugal-casting process in order to achieve smooth and layer-by-layer casting-cavities-filling control. The simulated mold-filling processes of Ti-6AI-4V alloy melt, in a vertical centrifugal-casting system with horizontally-connected plate-casting cavities, show reasonable agreement with experimental results from the literature.

 

جوشکاری فولاد زنگ نزن 316 به روش تیگ TIG-welded 316 stainless steel

Acoustic emisson and ultrasonic wave characteristics

in TIG-welded 316 stainless steel

مشخصات انتشار آکوستیک و امواج مافوق صوت در

فولاد ضد زنگ 316 جوش داده شده به روش TIG

ABSTRACT

A TIG welded 316 stainless steel materials will have a large impact on the design and the maintenance of invessel components including pipes used in a nuclear power plant, and it is important to clear the dynamic behavior in the weld part of stainless steel. Therefore, nondestructive techniques of acoustic emission (AE) and ultrasonic wave were applied to investigate the damage behavior of welded stainless steel. The velocity and attenuation ratio of the ultrasonic wave at each zone were measured, and a 10 MHz sensor was used. We investigated the relationship between dynamic behavior and AE parameters analysis and derived the optimum parameters to evaluate the damage degree of the specimen. By measuring the velocity and the attenuation of an ultrasonic wave propagating each zone of the welded stainless steel, the relation of the ultrasonic wave and metal structure at the base metal, heat affected zone (HAZ) metal and weld metal is also discussed. The generating tendency of cumulated counts is similar to that of the load curve. The attenuation ratios from the ultrasonic test results were 0.2 dB/mm at the base zone, and 0.52 dB/mm and 0.61 dB/mm at the HAZ zone and weld zone, respectively.

 

توزیع یونی و مغناطیسی کردن آلومینیوم جانشین فریت های لیتیمی

Ion distribution and saturation magnetization of

aluminum substituted lithium ferrites

توزیع یونی و مغناطیسی کردن آلومینیوم جانشین فریت های لیتیمی 

ABSTRACT

Ion distribution is determined in a series of aluminum substituted lithium ferrites by carefully analyzing the powder X-ray diffraction patterns. A new finding is that Al+3's substitute the Fe+3's in tetrahedral sites as well as in octahedral sites of the spinel structure. The proper formula, then, is (Fe1-a+3Ala+3)[Li0.5 +Fe1.5-(x-a)Alx-a+3]O 4, where a is approximately 0.23x2+0.22x. The saturation magnetizations are calculated and compared with the measured values.

 

مکانیزم نفوذ فلاکس در جوشکاری تیگ برای آلیاژ آلومینیوم

Study of mechanism of activating flux increasing

weld penetration of AC A-TIG welding for aluminum alloy

مطالعه مکانیزم افزایش مکانیزم نفوذ فلاکس فعال ساز جوشکاری AC  A-TIG

برای آلیاژ آلومینیوم

ABSTRACT

When multi-component flux AF305 is used as surface activating flux for an aluminum alloy, the weld penetration of activating flux-tungsten inert-gas (A-TIG) welding is over two times more than that of conventional TIG welding. Using A-TIG welding with the modes of alternating current (AC), direct current electrode negative (DCEN) and direct current electrode positive (DCEP), respectively, the flux differently affects weld penetration when the polarity is different. After studied the effect of compelled arc constriction on weld penetration of AC welding, it is believed that the constriction of the whole arc root is not the main mechanism that flux AF305 dramatically improves weld penetration. The penetration has a relationship with the separate distribution of slag on the weld surface. Then, an observation of scanning electron microscopy (SEM) and an electronic data systems (EDS) analysis of slag were performed respectively. The separate distribution of slag on the weld pool during welding and the great constriction of arc spots were confirmed by TIG welding with helium shielding gas. The relationship between slag distribution and weld penetration was studied by adding aluminum powder into flux AF305 to change the distribution of slag. During welding, the separate distribution of slag on the weld pool results in the great constriction of arc spots, an increase in arc spot force, and an increase in Lorentz force within the arc and weld pool. Finally, the weld penetration is increased.

 

مقایسه ذرات ریز τ-MnAl تولید شده از طریق راه های مختلف

A comparison of τ-MnAl particulates produced via different routes

مقایسه ذرات ریز τ-MnAl تولید شده از طریق راه های مختلف

ABSTRACT

MnAl alloys are very promising rare-earth-free permanent magnets. Nanocrystalline microstructures can have beneficial effects on the properties of magnetic MnAl alloys. In the present work we examined multiple routes to process MnAl alloys and studied the effects of milling on Mn-46 at.% Al powders. Mn54Al46 was produced via gas atomization, melt spinning, and rapid solidification rate processing. It was then mechanically milled using a water-cooled Union Process attritor for times up to 20 h. X-ray diffraction patterns showed the presence of mostly the high-temperature ε-phase with significant amounts of the equilibrium γ2 and β phases in both the cast and milled particulates. The powders were annealed for various temperatures and times in order to obtain the ferromagnetic τ-phase. Magnetic measurements of the optimally annealed powders showed a coercivity of 3.62 kOe and saturation magnetization of 59.8 emu g(-1) for mechanically milled gas-atomized powder annealed at 500 °C for 30 min.

 

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

Motion of equiaxed grains during directional solidification

under static magnetic field

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

ABSTRACT

The in situ and real time observations of the equiaxed grain motion during directional solidification of Al–10 wt% Cu under static magnetic field has been carried out by means of synchrotron X-ray radiography. It was observed that equiaxed grains moved approximately along the direction perpendicular to both the imposed magnetic field and the temperature gradient. Based on the radiographs, the motion of the solid grains was analyzed for various temperature gradients, and it was shown that the trajectories were imposed by the combination of the Thermo-Electric Magnetic forces, induced by the coupling of thermo-electric currents with the permanent magnetic field and the gravity force. The variations of the velocities and sizes of grains during the equiaxed growth under static magnetic field were measured and compared to a simple analytical model for the Thermo-Electric Magnetic forces and the Stokes law. A good agreement was achieved for the deviation angle as a function of the grain diameter, while a large discrepancy was observed for the velocity intensity when the dimensions of the equiaxed grains increased. In the latter case, it was shown that the corrections for both sample confinement and grain morphology were mandatory to explain the very low values of grain velocities.

 

مکانیزم تشکیل رنگ در نانورنگدانه های سرامیکی

Colour performance of ceramic nano-pigments

مکانیزم تشکیل رنگ در نانورنگدانه های سرامیکی

ABSTRACT

Ceramic nano-pigments have been recently developed for ink-jet decoration of ceramic tiles using quadrichromic technology (cyan, magenta, yellow, and black colours). The colouring mechanisms and performance of CoAl2O4, Au, (Ti,Cr,Sb)O2 and CoFe2O4 nano-pigments were investigated by DRS, XRD and colorimetry. The nano-pigments were dispersed in several ceramic glazes and glassy coatings and their colour performance was compared with that of conventional micro-pigments. Each nano-pigment was characterized in terms of its colour mechanism and chemico-physical stability. Although the micro-pigments provided more saturated hues, intense colours were achievable in nano-pigments despite their very small particle size (<50 nm). Limitations to the use of nano-pigments arose for very high firing temperatures (>1200 °C) due to particle growth (e.g. Au) or dissolution in the glassy phase (e.g. titania).

 

خواص لایه های رسوب نشانی شده CdTe به روش تبخیر باریکه الکترونی

Properties of CdTe films deposited by

electron beam evaporation

خواص لایه های رسوب نشانی شده  CdTe به روش تبخیر باریکه الکترونی 

ABSTRACT

Cadmium telluride thin films were prepared by electron beam evaporation on glass substrates kept at different temperatures in the range 30 - 300 °C. The films were characterized by X-ray diffraction, scanning electron microscopy and optical absorption measurements. The conductivity of the films was measured in the temperature range 100 - 300 K. While the low temperature data (100 - 200 K) could be explained by the variable range hopping process, the high temperature data (200 - 300 K) could be explained on the basis of Seto's model for thermionic emission of the carriers over the grain boundaries. Transmission spectra have indicated a direct band gap around 1.55 eV.