Optimizing Shell Strength

Colloidal silica is not a good film former. If it was, one might think that using colloidal silica at maximum would result in the highest strength in the ceramic shell. However, this is not the case. 

As water evaporates from colloidal silica, two things happen  

All colloidal sihcas have a concentration at which they will gel. The smaller the particle size, the lower the gelling concentration. Typically, this gel concentration will be about 35% silica solids for a 7-nm sol, 45% for a 12-nm sol and 55% for a 22-nm sol. Since the silica is more than twice as dense as water, the % volume solids of 

If however, the colloidal silica is used as a thin layer between refractory particles and the refractory particles were in close contact so that, only the thickness of a few particles were needed to bridge the gap between them a better bond should result. 

If you consider how you glue two boards together, the same principles apply  

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Commercial PBT/PC and PET/PC blends contain about 15-20 % of such core-shell mbber impact modifiers for maximum toughness, i.e., notched Izod impact strengths of typically > 700 J/m which is maintained even at low temperature (Tables 15.26 and 15.27). The ratio of PBT/PC or PET/PC is usually kept between 50/50 to 40/60 to optimize the ductility in the blend, while still maintaining a continuous or co-continuous phase of the polyester. A continuous phase of PBT or PET with PC as dispersed phase, would be preferred for solvent resistance. 

Continuous scans of modulus versus temperature utilizing the DuPont Dynamic Mechanical Analyzer (DMA) has provided a comparison of the high temperature service capabilities of radiation-cured experimental formulations of a vinyl-modified epoxy resin. Shell Epocryl-12. These scans were compared to data obtained when the same materials were applied as adhesives on aluminum test panels, radiation-cured with an electron beam, and lap shear strength tested at discrete temperatures. The DMA instrument utilizes a thin rectangular specimen for the analysis, so specimens can be cut from blocks or from flat sheets. In this case the specimens were cured as sheets of resin-saturated graphite-fibers. The same order of high temperature stability was obtained by each method. However, the DMA method provided a more complete characterization of temperature performance in a much shorter test time and thus, it can be very useful for quick analyses of formulation and processing variables in many types of materials optimization studies. The paper will present details of this study with illustrations of the comparisons. 

From about 1950, Shell 205 and similar catalysts based on alkalized iron and chromium oxides were used exclusively for styrene productioa As plant capacities were rapidly expanded, efforts were increased to improve the performance of the catalyst. Higher potash levels were introduced and cement binders were used to increase strength and selectivity. Ethylbenzene conversion, which was still about 30-50% in the 1950 s, was increased to at least 60% by 1960. Better plant designs were developed and reactors with up to three beds were introduced. One of the first higher selectivity catalysts included vanadium pentoxide with the conventional chromium oxide and potash. Improvements often led to different catalysts being used in a single reactor to optimize operation. 

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