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Thermal diffusivity/conductivity of MgAlON-BN Composites
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2006 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 4, 615-621 p.Article in journal (Refereed) Published
Abstract [en]

Thermal diffusivity and heat capacity of MgAlON and MgAlON-BN composites were measured in the temperature range of 25 degrees C to 1300 degrees C using a laser flash technique and a differential scanning calorimeter (DSC) technique, respectively. Based on these measurements, effective thermal conductivity of the composites was calculated using the values measured earlier in the same substance. The experimental effective thermal conductivity results of the composites containing different BN contents were found to show the similar trend, which decreased rapidly with increasing temperature below 900 degrees C followed by a slow decrease with further increasing temperature. This can be explained by the fact that thermal conduction in both components, MgAlON and BN, was dominated by phonons. The phonon mean free path decreased with increasing temperature, limited by the characteristic length between two neighboring atoms. The BN addition has significant influence on the effective thermal conductivity. The effective thermal conductivity of the composites containing BN exhibited a small degree of anisotropy with respect to preferred orientation of the BN phase. The degree of anisotropy of the composites increased with increasing BN content, which is particularly pronounced at the higher BN additions. An equation suitable for the present composites has been derived based on Luo's model. The model was slightly modified in the present article. The predicted values calculated by the model were in good agreement with experimental results.

Place, publisher, year, edition, pages
2006. Vol. 37, no 4, 615-621 p.
Keyword [en]
conductivity, resistance, ceramics
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-5481DOI: 10.1007/s11663-006-0045-4ISI: 000239590300012Scopus ID: 2-s2.0-33747452376OAI: oai:DiVA.org:kth-5481DiVA: diva2:9861
Note
Uppdaterad från "In press" till published: 20100929. QC 20100929Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Synthesis and Characterization of MgA1ON-BN refractories
Open this publication in new window or tab >>Synthesis and Characterization of MgA1ON-BN refractories
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In order to meet the need of metallurgical industry in the world, a new MgAlON-BN composite which can be used for example in special refractory nozzles, tubes and break rings for the continuous casting of steel was studied in the present thesis. The aim was to understand the mechanism of synthesis and their physicochemical properties during the application. Thus, the thermodynamic properties, synthesis process, mechanical properties, thermal shock behaviour, thermal diffusivity/conductivity as well as corrosion resistance to molten iron containing oxygen and molten slag of MgAlON and MgAlON-BN composites have been investigated.

The Gibbs energy of formation of MgAlON was estimated using the method proposed by Kaufman. The phase stability diagram of Mg-Al-O-N-B was investigated, and consequently the synthesis parameters were determined. MgAlON and MgAlON-BN composites were fabricated by hot-pressing method. The composites obtained this way were characterized by XRD, SEM, TEM and HREM analyses. A Matrix-flushing method was employed in the quantitative XRD analysis for the multi-component samples to understand the mechanism of synthesis.

The relationship between mechanical properties and microstructure of the composites was investigated. The experimental results indicated that BN addition has significant influence on the mechanical properties of the composites. These can be explained by the fact that BN has low Young’s modulus, density and non-reactive nature as well as considerable anisotropy of many properties such as thermal expansion, thermal diffusivity/conductivity. Thus, the addition of BN in MgAlON is likely to lead to the presence of microcracks caused by the mismatch of thermal expansion coefficient. The microcracks result in the enhancement of the strength at elevated temperature and thermal shock durability of the composites.

Effective thermal conductivities were evaluated from the present experimental results of thermal diffusivities, heat capacity and density. A model suitable for present composites has been derived based on Luo’s model. The predicted lines calculated by the model were in good agreement with experimental results.

The reactions between the composites and molten iron as well as the slag were investigated by ‘‘finger’’ experiments and sessile drop experiments. Both experimental results indicated that the BN addition has positive influence on the corrosion resistance. These are attributed to the excellent corrosion resistance of BN to molten iron and slag, such as the higher contact angle between BN substrate and liquid iron and molten slag compared with that obtained for pure MgAlON.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xii, 43 p.
Keyword
MgAlON-BN composites, Mechanical properties, Thermal shock durability, Thermal diffusivity/conductivity, Corrosion resistance.
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-3883 (URN)91-7178-271-0 (ISBN)
Public defence
2006-03-31, Salongen, KTHB, Osquars backe 31, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100929Available from: 2006-03-15 Created: 2006-03-15 Last updated: 2010-09-29Bibliographically approved

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