- What to know about silicon dioxide
- silicon dioxide
- Whats the difference between amorphous and crystalline silica?
- about AEROGEL
- silicon dioxide
What to know about silicon dioxideThe presence of silica is crystalline and amorphous. Quartz crystal is crystalline silica, silicon dioxide crystals and oxygen atoms in the atomic ratio of 1: 2 atomic composition of the three-dimensional network of crystals, with different crystal and color. Amorphous refers to the structure of some non-complete crystalline amorphous areas amorphous regions or some amorphous solid amorphous composition. Many of the substances that can constitute crystals are amorphous, and the reactivity is generally greater than that of the same material. Amorphous siliconalso known as amorphous silicon, is a kind of silicon allotropes. Crystalline silicon is usually tetrahedron, and each silicon atom is at the apex of the tetrahedron and is covalently bonded to the other four silicon atoms. This structure can be stretched very large, thus forming a stable lattice structure. And no qualitative silicon does not exist in this extended lattice structure, the lattice network between atoms was disordered. Previous: Hydrochloric acid deposition method of produing silica powder. Next: What affects stability of nano silica suspendcion? Cas Number For Silicon Dioxide. Silicon Dioxide granule Grade. Email: jk jksilica. Product Categories. Previous: Hydrochloric acid deposition method of produing silica powder Next: What affects stability of nano silica suspendcion? Related Industry Knowledge Can silicon dioxide be edible? Can Silicon Dioxide Conduct Electri What is hydrated silica? Differnce Between Silica and Quartz Hydrochloric acid deposition method What affects stability of nano sili What is the difference between sili What is silica powder used for?
Absorption, disposition, elimination: SAS forms [CAS No ] are rapidly eliminated from the lung tissue during and after prolonged inhalation exposure of experimental animals with no disproportionate disposition occurring in the mediastinal lymph nodes, whereas crystalline forms exhibit a marked tendency to accumulate and persist in the lung and lymph nodes. Intestinal absorption of SAS appears to be insignificant in animals and humans. There is evidence of ready renal elimination of bioavailable fractions. Irritation and sensitization: Synthetic amorphous silica and silicates are not irritating to skin and eyes under experimental conditions, but may produce dryness following prolonged and repeated exposure. No sensitization experimental data are available on the synthetic amorphous silicas and silicates. However, there is a long work history with these materials at industrial scales. Data collected from industrial hygiene surveillance over the last 50 years do not indicate any potential for skin sensitization. Given the inherent physico-chemical properties and ubiquitous nature of this class of compounds, there is no structural alert to indicate a sensitizing potential. The US EPA reviewed several toxicity studies for synthetic amorphous silica including four acute toxicity studies acute oral LD50 in the rat, acute inhalation LC50 in the rat, primary eye irritation in the rabbit, and primary dermal irritation in the rabbit ; four mutagenicity studies, and an oral toxicity study. Acute toxicity studies. No mortalities were observed for the oral and inhalation studies. For the primary eye irritation study, there was no corneal opacity or iridial irritation in any of the eyes. For the dermal study, there was no dermal irritation at 72 hours. All studies are toxicity category IV. Mutagenic studies. In all four studies there was no indication of any mutagenic activity associated with exposure to silica, amorphous, fumed crystalline free. Oral toxicity of fumed silica. There were no mortalities or clinical signs. There was no significant difference between the test group and the control group with respect to silica concentration in the carcass. The acute toxicity studies are toxicity category IV. The mutagenicity studies are negative. Silica, amorphous, fumed crystalline free is not classifiable, as to its carcinogenicity however, given its amorphous nature, it is not expected to pose a carcinogenic risk. Silicas are considered to be inert when ingested, and due to the high molecular weight it is unlikely to be absorbed through the skin. There should be no concerns for human health, whether the exposure is acute, subchronic, or chronic by any route. The health effects of synthetic amorphous silica are significantly different from the health effects of crystalline silica. No evidence of silicosis has been found from epidemiological studies of workers with long-term exposure to intentionally manufactured synthetic amorphous silica 4. From a health standpoint, a significant different between crystalline and amorphous silica could be lung clearance. Studies of various animal species have shown that amorphous silica products can be completely cleared from the lungs 5. Excerpts from the OECD SIDS Human Health conclusions are included below 1 : Absorption, disposition, elimination: SAS forms [CAS No ] are rapidly eliminated from the lung tissue during and after prolonged inhalation exposure of experimental animals with no disproportionate disposition occurring in the mediastinal lymph nodes, whereas crystalline forms exhibit a marked tendency to accumulate and persist in the lung and lymph nodes.
Whats the difference between amorphous and crystalline silica?
Amorphous silicon a-Si is the non- crystalline form of silicon used for solar cells and thin-film transistors in LCDs. Used as semiconductor material for a-Si solar cellsor thin-film silicon solar cellsit is deposited in thin films onto a variety of flexible substrates, such as glass, metal and plastic. Amorphous silicon cells generally feature low efficiency, but are one of the most environmentally friendly photovoltaic technologies, since they do not use any toxic heavy metals such as cadmium or lead. As a second-generation thin-film solar cell technology, amorphous silicon was once expected to become a major contributor in the fast-growing worldwide photovoltaic market, but has since lost its significance due to strong competition from conventional crystalline silicon cells and other thin-film technologies such as CdTe and CIGS. Amorphous silicon differs from other allotropic variations, such as monocrystalline silicon —a single crystal, and polycrystalline siliconthat consists of small grains, also known as crystallites. Silicon is a fourfold coordinated atom that is normally tetrahedrally bonded to four neighboring silicon atoms. In crystalline silicon c-Si this tetrahedral structure continues over a large range, thus forming a well-ordered crystal lattice. In amorphous silicon this long range order is not present. Rather, the atoms form a continuous random network. Moreover, not all the atoms within amorphous silicon are fourfold coordinated. Due to the disordered nature of the material some atoms have a dangling bond. Physically, these dangling bonds represent defects in the continuous random network and may cause anomalous electrical behavior. The material can be passivated by hydrogen, which bonds to the dangling bonds and can reduce the dangling bond density by several orders of magnitude. Hydrogenated amorphous silicon a-Si:H has a sufficiently low amount of defects to be used within devices such as solar photovoltaic cells, particularly in the protocrystalline growth regime. Introduction of carbon atoms adds extra degrees of freedom for control of the properties of the material. The film could also be made transparent to visible light. Increasing the concentration of carbon in the alloy widens the electronic gap between conduction and valence bands also called "optical gap" and bandgap. This can potentially increase the light efficiency of solar cells made with amorphous silicon carbide layers. On the other hand, the electronic properties as a semiconductor mainly electron mobilityare adversely affected by the increasing content of carbon in the alloy, due to the increased disorder in the atomic network. Several studies are found in the scientific literature, mainly investigating the effects of deposition parameters on electronic quality, but practical applications of amorphous silicon carbide in commercial devices are still lacking. The density of amorphous Si has been calculated as 4. This was done using thin 5 micron strips of amorphous silicon. This density is 1. Unhydrogenated a-Si has a very high defect density which leads to undesirable semiconductor properties such as poor photoconductivity and prevents doping which is critical to engineering semiconductor properties. By introducing hydrogen during the fabrication of amorphous silicon, photoconductivity is significantly improved and doping is made possible. Hydrogenated amorphous silicon, a-Si:H, was first fabricated in by Chittick, Alexander and Sterling by deposition using a silane gas SiH4 precursor. The resulting material showed a lower defect density and increased conductivity due to impurities. Interest in a-Si:H came when inLeComber and Spear discovered the ability for substitutional doping of a-Si:H using phosphine n-type or diborane p-type. While a-Si suffers from lower electronic performance compared to c-Si, it is much more flexible in its applications. For example, a-Si layers can be made thinner than c-Si, which may produce savings on silicon material cost. One further advantage is that a-Si can be deposited at very low temperatures, e. This allows deposition on not only glass, but plastic as well, making it a candidate for a roll-to-roll processing technique. Once deposited, a-Si can be doped in a fashion similar to c-Si, to form p-type or n-type layers and ultimately to form electronic devices.
To save this word, you'll need to log in. Send us feedback. See more words from the same year Dictionary Entries near silica silexite silhouette silic- silica silica aerogel silica brick silica cement. Accessed 9 Apr. Keep scrolling for more More Definitions for silica silica. Please tell us where you read or heard it including the quote, if possible. Test Your Vocabulary Name that Thing: Flower Edition Name that flower chrysanthemum hydrangea hyacinth amaryllis Can you spell these 10 commonly misspelled words? Test Your Knowledge - and learn some interesting things along the way. Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free! What's with his feathered cap? How to Remember 'Affect' and 'Effect' Most of the time. Literally How to use a word that literally drives some people nuts. Is Singular 'They' a Better Choice? One month at a time. Can you spell these 10 commonly misspelled words? Do you know the person or title these quotes describe? Login or Register. Save Word. Log In. Definition of silica. First Known Use of silica circain the meaning defined above. History and Etymology for silica New Latin, from Latin silic- silex hard stone, flint. Keep scrolling for more. Learn More about silica. Time Traveler for silica The first known use of silica was circa See more words from the same year. Dictionary Entries near silica silexite silhouette silic- silica silica aerogel silica brick silica cement See More Nearby Entries. More Definitions for silica. English Language Learners Definition of silica. Comments on silica What made you want to look up silica? Get Word of the Day daily email! Test Your Vocabulary. Love words?