Abstract:The structural properties of finely divided inorganic materials such as metal and metalloid oxides, silicates or carbonates of both synthetic and natural origin are compared by means of electron microscopy and tomography. The structure of the outer surfaces of various compact or compacted agglomerates may suggest some striking similarities between various amorphous silica on the one hand and crystalline titania and alumina on the other however the details of the interior fine structure are completely different… Show more
“…The branching of carbon black was still pronounced while the silica clusters had a more grape like shape. This finding is in accordance with what Albers et al [40] claimed that carbon black possesses a more open fractal structure in comparison to a denser structure of silica. For a quantitative analysis, approximately 2000 primary particles were evaluated and the average diameters of carbon black and silica were calculated in accordance to ASTM D3849 [41] (Table 5).…”
Section: Structural Differences By Means Of Transmission Electron Micsupporting
Precipitated silica in combination with bifunctional organosilanes almost fully replaces currently the commonly used carbon black fillers in modern passenger car tire tread compounds to improve tire properties such as wet traction (safety) and rolling resistance (fuel consumption). However, it is still challenging to reach a sufficient level of abrasion resistance (service life). An optimum macrodispersion quality of the silica is a fundamental precondition for an optimum abrasion resistance. This goal can be reached by the development of new tailor-made highly dispersible silica grades. In order to achieve this, it is essential to be aware of the analytical silica parameters, which affect the dispersion process. One of these parameters known from carbon black is the structure of the filler. To gain deeper insights into the in-rubber dispersibility of the silica, the structure was investigated by two different methods, the DOA measurement and the void volume measurement. The results were correlated to the in-rubber macrodispersion. In contrast to carbon black filled compounds, no sufficient correlation of the structure with the macrodispersion could be found for the silica-filled compounds. Therefore, it was concluded that the morphology of silica differs from that one that is claimed for carbon black. Additional investigations like TEM, FT-IR and X-ray diffraction measurements were carried out. Carbon black shows a more elastic structure, which can withstand the external forces during the mixing process in a better way. Silica contains a much higher void volume in the structure even after exposed to high forces. These new findings will help to understand the macrodispersion process in rubber in a better way.
“…The branching of carbon black was still pronounced while the silica clusters had a more grape like shape. This finding is in accordance with what Albers et al [40] claimed that carbon black possesses a more open fractal structure in comparison to a denser structure of silica. For a quantitative analysis, approximately 2000 primary particles were evaluated and the average diameters of carbon black and silica were calculated in accordance to ASTM D3849 [41] (Table 5).…”
Section: Structural Differences By Means Of Transmission Electron Micsupporting
Precipitated silica in combination with bifunctional organosilanes almost fully replaces currently the commonly used carbon black fillers in modern passenger car tire tread compounds to improve tire properties such as wet traction (safety) and rolling resistance (fuel consumption). However, it is still challenging to reach a sufficient level of abrasion resistance (service life). An optimum macrodispersion quality of the silica is a fundamental precondition for an optimum abrasion resistance. This goal can be reached by the development of new tailor-made highly dispersible silica grades. In order to achieve this, it is essential to be aware of the analytical silica parameters, which affect the dispersion process. One of these parameters known from carbon black is the structure of the filler. To gain deeper insights into the in-rubber dispersibility of the silica, the structure was investigated by two different methods, the DOA measurement and the void volume measurement. The results were correlated to the in-rubber macrodispersion. In contrast to carbon black filled compounds, no sufficient correlation of the structure with the macrodispersion could be found for the silica-filled compounds. Therefore, it was concluded that the morphology of silica differs from that one that is claimed for carbon black. Additional investigations like TEM, FT-IR and X-ray diffraction measurements were carried out. Carbon black shows a more elastic structure, which can withstand the external forces during the mixing process in a better way. Silica contains a much higher void volume in the structure even after exposed to high forces. These new findings will help to understand the macrodispersion process in rubber in a better way.
“…All primary particles have been fused together to form the three-dimensional aggregates. No inner boundaries are visible within SAS aggregates (Albers et al 2015), see Fig. 2.Fig.…”
Section: E 551 Particle Morphology and Sizementioning
Key messages
Particle sizes of E 551 products are in the micrometre range. The typical external diameters of the constituent particles (aggregates) are greater than 100 nm.
E 551 does not break down under acidic conditions such as in the stomach, but may release dissolved silica in environments with higher pH such as the intestinal tract.
E 551 is one of the toxicologically most intensively studied substances and has not shown any relevant systemic or local toxicity after oral exposure.
AbstractSynthetic amorphous silica (SAS) meeting the specifications for use as a food additive (E 551) is and has always been produced by the same two production methods: the thermal and the wet processes, resulting in E 551 products consisting of particles typically in the micrometre size range. The constituent particles (aggregates) are typically larger than 100 nm and do not contain discernible primary particles. Particle sizes above 100 nm are necessary for E 551 to fulfil its technical function as spacer between food particles, thus avoiding the caking of food particles. Based on an in-depth review of the available toxicological information and intake data, it is concluded that the SAS products specified for use as food additive E 551 do not cause adverse effects in oral repeated-dose studies including doses that exceed current OECD guideline recommendations. In particular, there is no evidence for liver toxicity after oral intake. No adverse effects have been found in oral fertility and developmental toxicity studies, nor are there any indications from in vivo studies for an immunotoxic or neurotoxic effect. SAS is neither mutagenic nor genotoxic in vivo. In intact cells, a direct interaction of unlabelled and unmodified SAS with DNA was never found. Differences in the magnitude of biological responses between pyrogenic and precipitated silica described in some in vitro studies with murine macrophages at exaggerated exposure levels seem to be related to interactions with cell culture proteins and cell membranes. The in vivo studies do not indicate that there is a toxicologically relevant difference between SAS products after oral exposure. It is noted that any silicon dioxide product not meeting established specifications, and/or produced to provide new functionality in food, requires its own specific safety and risk assessment.
“…Coexisting nano-and micro-scale heterogeneities have been achieved in designed nanostructured thermoelectrics [67]. Only in aggregate nanomaterials [68], such as aerogels, xerogels, pyrogenic silica and carbon, structural data [69] indicate a hierarchy of structural organization, named "multilevel structure" over length scales covering about 5 orders of magnitude from ~nm sized "primary particles" to ~100 m sized "agglomerates". Even in this case, however, self-similar, fractal structure spans at most 2 orders of magnitude between the primary particle size (~nm) and the aggregate correlation length (~ 100 nm) [70].…”
Hard form of carbon obtained by collapsing C 60 fullerene molecules at moderate pressure and temperature was investigated using different imaging techniques at spatial resolutions ranging from angstrom to millimeter. Hierarchical granular morphology has been observed from the atomic up to the sample size length scale, revealing scale independent grain size distribution. The unusual fractal-like structure correlates with unique transport and calorimetric properties of this material. Hard carbon can be considered as a bridge between porous and dense amorphous materials.
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