| 1. |
- Antti, Marta-Lena, et al.
(author)
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Phase reactions in a hot pressed TiC/Si powder mixture
- 2012
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 38:3, s. 1999-2003
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Journal article (peer-reviewed)abstract
- This work investigated the possibility of producing dense Ti3SiC2 by hot pressing TiC/Si powders. A hot press with graphite heating elements was used for densification and the phase reactions of some hot pressed samples were further evaluated by pressureless heating in a dilatometer. The density and phase composition of the heat treated samples were evaluated using Archimedes principle and by x-ray diffractometry respectively. Hot pressing resulted in a low Ti3SiC2 yield; the main phases were TiC and TiSi2 regardless of starting powder composition, temperature, holding time or pressure. A second heating without pressure resulted in Ti3SiC2 formation, but only in samples initially hot pressed at 1300 °C or lower. At higher hot pressing temperatures, thin oxide layers on particle surfaces were locked into the structure. Acting as diffusion barriers, they prevented the Ti3SiC2 forming reaction. In hot pressed samples the density was significantly higher than in samples sintered without pressure.
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| 2. |
- Engström, Andreas, et al.
(author)
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Synthesis of a TiCN – SiC polyhedron and elongated crystals nanopowder at low nitrogen concentration
- 2012
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In: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 81, s. 148-150
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Journal article (peer-reviewed)abstract
- At room temperature diluted TiCl4 and CCl4 were reduced by sodium particles and mixed with a polycarbomethylsilane (PCS) solution to yield a precursor. It was dried and subsequently annealed at 1300 °C, 1400 °C and 1450 °C in a tube furnace using argon with 10 ppm N2. After the 1450 °C annealing a nanocrystalline powder of TiC0.5 N0.5–SiC polyhedron and elongated crystals was obtained. At the low nitrogen concentration during annealing a gradual nitration is proposed. It is promoted by carbon gaseous species, precursor oxidation, a sufficient temperature and a summarised nitrogen surplus compared to the titanium and carbon amount.
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| 3. |
- Escalera, Edwin, et al.
(author)
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High temperature phase evolution of Bolivian kaolinitic-illitic clays heated to 1250 degrees C
- 2014
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In: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 101, s. 100-105
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Journal article (peer-reviewed)abstract
- The thermal behaviour of two types of clays collected from different locations in Bolivia has been studied. The clays contain kaolinite, illite, quartz and small amounts of microcline. The phase evolutions have been characterized from room temperature to 1250 degrees C. For both clays, kaolinite is completely transformed into metakaolinite when heated up to 650 degrees C. During further heating to 1050 degrees C, illite undergoes total dehydroxylation. Mullite is formed in the temperature interval of 1050-1150 degrees C and its formation rate is dependent on the amount of K and Fe present in the clays. The clay with higher amounts of K (3.2 mass %) and Fe (5.6 mass%) has an onset temperature for sintering at about 900 degrees C and an onset temperature for liquid formation at 1080 degrees C. This is about 50 degrees C lower onset temperature for sintering and 94 degrees C lower onset temperature for liquid formation when compared with the clay with lower amounts of K (2.3 mass %) and Fe (1.6 mass %).
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| 4. |
- Escalera, Edwin, et al.
(author)
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High temperature phase evolution of Bolivian kaolinitic–illitic clays heated to 1250 °C
- 2014
-
In: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 101, s. 100-105
-
Journal article (peer-reviewed)abstract
- The thermal behaviour of two types of clays collected from different locations in Bolivia has been studied. The clays contain kaolinite, illite, quartz and small amounts of microcline. The phase evolutions have been characterized from room temperature to 1250 °C. For both clays, kaolinite is completely transformed into metakaolinite when heated up to 650 °C. During further heating to 1050 °C, illite undergoes total dehydroxylation. Mullite is formed in the temperature interval of 1050–1150 °C and its formation rate is dependent on the amount of K and Fe present in the clays. The clay with higher amounts of K (3.2 mass %) and Fe (5.6 mass%) has an onset temperature for sintering at about 900 °C and an onset temperature for liquid formation at 1080 °C. This is about 50 °C lower onset temperature for sintering and 94 °C lower onset temperature for liquid formation when compared with the clay with lower amounts of K (2.3 mass %) and Fe (1.6 mass %).
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| 5. |
- Escalera, Edwin, et al.
(author)
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The production of porous brick material from diatomaceous earth and Brazil nut shell ash
- 2015
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 98, s. 257-264
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Journal article (peer-reviewed)abstract
- Diatomaceous earth was mixed with Brazil nut shell ash (BNS ash) in different amounts between 0 and 30 wt% and sintered at temperatures between 750 and 950 °C. The BNS ash contains 33 wt% K2O and 11 wt% CaO mainly in carbonate form. The addition of BNS ash into the diatomaceous earth caused significant changes of the microstructure after sintering. The BNS ash addition produces lightweight porous bricks with acceptable strength at lower sintering temperature. The best combination of strength and porosity was achieved for a mixture of 10 wt% of BNS ash in the diatomaceous earth sintered at 850 °C. The achieved high porosity was 49%, density 1.06 g/cm3, thermal conductivity 0.20 W/(m K) and the compressive strength was 8.5 MPa.
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| 6. |
- Kero, Ida, et al.
(author)
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Carbon atmosphere effect on on Ti3SiC2 based composites made from TiC/Si powders
- 2010
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 36:4, s. 1259-1263
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Journal article (peer-reviewed)abstract
- The previous termeffect of carbonnext term activity and CO pressure in the furnace previous termatmospherenext term is investigated with respect to the phase reactions during heat treatment of TiC/Si powders. Special attention is given to the production and decomposition of Ti3SiC2. Samples were heated in graphite and alumina furnaces, connected to a dilatometer which enabled the in-situ analysis of the phase reactions. The phase compositions of the heat treated samples were determined by x-ray diffraction. The reducing previous termatmospherenext term of the graphite furnace enhanced the reactivity of the starting powder and enabled phase reactions to take place at a lower temperature than in the alumina furnace. TiSi2 and SiC phases formed at temperatures below the melting point of Si and were continuously consumed at higher temperatures. Ti3SiC2 formed at the melting point of Si regardless of furnace previous termatmosphere.next term No decomposition of the Ti3SiC2 was observed in either furnace.
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| 7. |
- Kero, Ida, et al.
(author)
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Effect of the amounts of silicon on the in situ synthesis of Ti3SiC2 based composites made from TiC/Si powder mixtures
- 2010
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 36:1, s. 375-379
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Journal article (peer-reviewed)abstract
- This paper describes how variations in silicon content and heat treatment influence on the phase composition of TiC/Si powder mixtures during heat treatment. The sintering procedure is investigated with respect to the phases produced with a particular emphasis on maximisation of the Ti3SiC2 content. The heat treated products have been analysed using scanning electron microscopy, energy dispersive spectroscopy and x-ray diffractometry. In the heat treated products Ti3SiC2 and TiC are the dominant phases and SiC and TiSi2 are found in smaller (0-30vol%) amounts. The composition was found to depend on both Si content and heat treatment temperature and time. The silicon content can be optimised with respect to maximum Ti3SiC2 production, but its value changes with different temperature programs. The highest amount (56 vol%) of Ti3SiC2 is achieved by heat treating powder mixtures of initial composition 3TiC/2.2Si at 1350° for 1 h. Heat treatment at lower temperatures (1250-1300 °C) results in an incomplete reaction and production of TiSi2.
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| 8. |
- Kero, Ida, et al.
(author)
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Phase reactions associated with the formation of Ti3SiC2 from TiC/Si powders
- 2011
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 37:7, s. 2615-2619
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Journal article (peer-reviewed)abstract
- The objective of this paper was to investigate the high temperature phase reactions that take place in a 3TiC/2Si powder mixture during heating. Special attention was paid to the formation of Ti3SiC2 and to the evaporation of gases. Differential scanning calorimetry and thermogravimetry were used for in situ analysis of the phase reactions. Samples were heated at a rate of 5 K/min to various temperatures between 890 and 1450 °C and then cooled at a rate of 20 K/min. Heat treated samples were analysed by X-ray diffractometry. The first phase to form was TiSi2, which was consumed in the Ti3SiC2 forming reactions. No decomposition of Ti3SiC2 was observed at temperatures below 1450 °C. Evaporation of CO(g) and small amounts of Si(g) were detected at 1430 °C.
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| 9. |
- Nilsson, Erik A. A., 1986-
(author)
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Degradation Mechanisms of Heat Resistant Steel at Elevated Temperatures : In an Iron Ore Pelletizing Industry
- 2017
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Doctoral thesis (other academic/artistic)abstract
- This thesis focuses on the different degradation mechanisms of the stainless steel in a travelling grate in a Grate-Kiln iron ore pellet indurator. The travelling grate is a conveyor belt that transports green-body pellets to a rotary kiln while the pellets are being dried and pre-heated to a temperature of 900-1100 °C by recycled hot air. After unloading of the pellets to the rotary-kiln for further sintering, the travelling grate is cooled in room temperature while returning to the loading zone of the wet pellets.The steel was tested during thermal cycling in a test-rig, in order to simulate the influence of thermo mechanical fatigue and oxide spallation. The influence of erosion-deposition was investigated in a modified horizontal industrial combustion kiln at 800 °C, with slag and coal from production used as erosive media and combustion fuel, respectively. The influence of minor alloying additions of Mn, Si and Ti on the microstructure was explored by eight different casted alloy compositions. Isothermal heat treatments were performed at 800 °C during 200 hours on steel immersed in deposits recovered from a travelling grate in production.The three main degradation mechanisms found in this work are thermal spallation, erosion-deposition and deposit induced accelerated corrosion (DIAC). Thermal spallation of the oxide layer is caused by the thermal expansion difference between the oxide and the metal during heating and cooling. It has been found that Ti improves the spallation resistance while Si reduces it. Spallation of deposits is another cause believed to increase the degradation. Erosion-deposition appears due to simultaneous erosion and deposition of particles on the travelling grate that causes erosion or deposition depending on the amount of alkali metals in the environment. The velocity of the particles also influences erosion and deposition in the way that higher velocities increase erosion. DIAC is proposed to form on the travelling grate due to the concentration of chloride- and sulphate containing alkali metals in the deposits. Other than these major degrading mechanisms, minor degradation mechanisms such as internal oxidation, sigma formation, carburization and sensitization towards inter-granular attack have been found inside the steel during heating. Thermo mechanical fatigue (TMF) causes intergranular cracks in the material of the travelling grate. Casting issues such as micro-segregation have also been addressed in this thesis.A few different ways to improve degradation resistance have been proposed, such as homogenization heat treatments, optimization of process parameters and inhibitor solutions.
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| 10. |
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