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Title: Measuring adhesion between particles
Author: Yang, Jiankai
ISNI:       0000 0004 7428 1829
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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Given that catalyst layer is used to carry automotive catalysts in catalytic converters, the strength of a catalyst layer is important for the durability of catalytic converters. However catalyst layer in service is found to suffer from both cohesive and adhesive failure for which the current literature does not have separate method of strength measurement. This thesis then developed methods to separately measure the cohesive and the adhesive strength of a catalytic layer (made of γ-alumina particles) based on the unit of stress. Measurement of the cohesive strength was based on tensile strength of a tablet made of the same material as the catalyst layer; the adhesive strength was determined from a scraping technique. The cohesive strength obtained was found to vary with particle size, pH of suspension and drying rate of the suspension. A bimodal particle size distribution was found to improve the cohesive strength due to tighter particle packing. A combination of free movement for particles and longer exposure to a drying environment was also found to improve the cohesive strength. The underlying reason was determined to be in close agreement with the DLVO theory. At very high pHs, it was believed that γ-alumina particles can form a more structured material, immobilising them during drying. Furthermore, γ-alumina particles prepared by wet-milling were found to result in stronger cohesive strength compared with those obtained from dry-milling. The adhesive strength of the catalyst layer was found to be influenced by surface roughness profile of substrates, pH of the γ-alumina suspension and porosity of substrates (in the case of alumina substrate). Influence of the pH of the suspension was determined to be related to particle mobility, being similar to the cohesive strength study. A second consideration in granular catalyst support is that the current literature does not determine whether structural failure of the support occurs between primary particles or within primary particles. In this thesis, the primary particles used were micrometre sized boehmite powder (the same powder used for substrate in the adhesive strength study); these primary particles are already agglomerates of nanometre sized crystals and polycrystalline aggregates. A method to directly quantify the strength of such primary agglomerates was developed; strength data obtained were supported by other indirect methods. It was determined that granular catalyst support produced from weak primary agglomerates may have structural failure both within and between primary agglomerates while support produced from strong primary agglomerates tend to have the failure between the agglomerates.
Supervisor: Salman, Agba ; Hounslow, Mike Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available