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Octamethylcyclotetrasiloxane
Octamethylcyclotetrasiloxane, also called D4, is an organosilicon compound with the formula . It is a colorless viscous liquid. It is a common cyclomethicone. It is widely used in cosmetics. Production and polymerization Commercially D4 is produced from dimethyldichlorosilane. Hydrolysis of the dichloride produces a mixture of cyclic dimethylsiloxanes and polydimethylsiloxane. From this mixture, the cyclic siloxanes including D4 can be removed by distillation. In the presence of a strong base such as KOH, the polymer/ring mixture is equilibrated, allowing complete conversion to the more volatile cyclic siloxanes: : D4 and D5 are also precursors to the polymer. The catalyst is again KOH. Occurrence It is among the most important of all the cyclic siloxanes, with a global production volume of 136 million kilograms in 1993. 100,000–1,000,000 tonnes per year of D4 is manufactured and/or imported in the European Economic Area. Safety and environmental considerations D4 is of l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclomethicone
A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage. The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)''n''OH and (OSiH2)n. Siloxanes also include branched compounds, the defining feature of which is that each pair of silicon centres is separated by one oxygen (O2-) atom. The siloxane functional group forms the backbone of silicones, the premier example of which is polydimethylsiloxane (PDMS). The functional group R3SiO− (where the three Rs may be different) is called siloxy. Siloxanes are manmade and have many commercial and industrial applications because of the compounds’ hydrophobicity, low thermal conductivity, and high flexibility. Structure Siloxanes generally adopt structures expected for linked tetrahedral ("''sp''3-like") centers. The Silicon-oxygen bond, Si−O bond length is 1.64 Å (vs Si–C distance of 1.92 Å) and the Silicon–oxygen bond#Bond angles, Si-O-Si angl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decamethylcyclopentasiloxane
Decamethylcyclopentasiloxane, also known as D5 and D5, is an organosilicon compound with the formula . It is a colorless and odorless liquid that is slightly volatile. Use The compound is classified as a cyclomethicone. Such fluids are commonly used in cosmetics, such as deodorants, sunblocks, hair sprays and skin care products. It is becoming more common in hair conditioners, as it makes the hair easier to brush without breakage. It is also used as part of silicone-based personal lubricants. D5 is considered an emollient. In Canada, among the volume used in consumer products approximately 70% were for antiperspirants and 20% for hair care products. 10,000–100,000 tonnes per year of D5 is manufactured and/or imported in the European Economic Area. Atmospheric emissions of D5 in the Northern Hemisphere were estimated to 30,000 tonnes per year. Production and polymerization Commercially D5 is produced from dimethyldichlorosilane. Hydrolysis of the dichloride produces a mixt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hexamethylcyclotrisiloxane
Hexamethylcyclotrisiloxane, also known as D3 and D3, is the organosilicon compound with the formula . It is a colorless or white volatile solid. It finds limited use in organic chemistry. The larger tetrameric and pentameric siloxanes, respectively octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane, are of significant industrial interest, whereas 1,000–10,000 tonnes per year of the trimer is manufactured and/or imported in the European Economic Area. Structure and reactions Hexamethylcyclotrisiloxane adopts a planar structure and is considered strained. It reacts with organolithium reagents to give, after hydrolysis, dimethylsilanols: : : Safety and environmental considerations The LD50 for the related pentamer (D5) is >50 g/kg in rats. See also * Octamethylcyclotetrasiloxane (D4) * Decamethylcyclopentasiloxane Decamethylcyclopentasiloxane, also known as D5 and D5, is an organosilicon compound with the formula . It is a colorless and odorless liquid that is sli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrakis(trimethylsilyloxy)silane
Tetrakis(trimethylsilyloxy)silane (TTMS) is an organosilicon compound with the formula Si Si(CH3)3sub>4. This colourless liquid is used as a reagent in organic synthesis. Application TTMS can be used for thin film coating with a nanostructured silicon dioxide prepared by plasma-enhanced chemical vapor deposition Plasma-enhanced chemical vapor deposition (PECVD) is a chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creati ... (PECVD) at atmospheric pressure. References {{Reflist Siloxanes Trimethylsilyl compounds ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parts Per Billion
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million (ppm, ), parts-per-billion (ppb, ), parts-per-trillion (ppt, ) and parts-per-quadrillion (ppq, ). This notation is not part of the International System of Units (SI) system and its meaning is ambiguous. Overview Parts-per notation is often used describing dilute solutions in chemistry, for instance, the relative abundance of dissolved minerals or pollutants in water. The quantity "1 ppm" can be used for a mass fraction if a water-borne pollutant is present at one-millionth of a gram per gram of sample solution. When working with aqueous solutions, it is common to assume that the density of water is 1.00 g/mL. Therefore, it is common to equate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LC50
In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the dose required to kill half the members of a tested population after a specified test duration. LD50 figures are frequently used as a general indicator of a substance's acute toxicity. A lower LD50 is indicative of increased toxicity. The test was created by J.W. Trevan in 1927. The term semilethal dose is occasionally used in the same sense, in particular with translations of foreign language text, but can also refer to a sublethal dose. LD50 is usually determined by tests on animals such as laboratory mice. In 2011, the U.S. Food and Drug Administration approved alternative methods to LD50 for testing the cosmetic drug Botox without animal tests. Conventions The LD50 is usually expressed as the mass of substance administered per unit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Persistent, Bioaccumulative And Toxic Substances
Persistent, bioaccumulative and toxic substances (PBTs) are a class of compounds that have high resistance to degradation from abiotic and biotic factors, high mobility in the environment and high toxicity. Because of these factors PBTs have been observed to have a high order of bioaccumulation and biomagnification, very long retention times in various media, and widespread distribution across the globe. Most PBTs in the environment are either created through industry or are unintentional byproducts.Blais J. 2005. Biogeochemistry of persistent bioaccumulative toxicants: processes affecting the transport of contaminants to remote areas. Canadian Journal of Fisheries and Aquatic Sciences 62: 236-243. History Persistent organic pollutants (POPs) were the focal point of the Stockholm Convention 2001 due to their persistence, ability to biomagnify and the threat posed to both human health and the environment. The goal of the Stockholm Convention was to determine the classification of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Substance Of Very High Concern
A substance of very high concern (SVHC) is a chemical substance (or part of a group of chemical substances) concerning which it has been proposed that use within the European Union be subject to authorisation under the REACH Regulation. Indeed, listing of a substance as an SVHC by the European Chemicals Agency (ECHA) is the first step in the procedure for authorisation or restriction of use of a chemical. The first list of SVHCs was published on 28 October 2008 and the list has been updated many times to include new candidates. The most recent update occurred in January 2022 to include a total of 223 SVHC. Criteria The criteria are given in article 57 of the REACH Regulation. A substance ''may'' be proposed as an SVHC if it meets one or more of the following criteria: *it is carcinogenic; *it is mutagenic; *it is toxic for reproduction; *it is persistent, bioaccumulative and toxicAnnex XIII, REACH Regulation, at pp. 383–85. (PBT substances); *it is very persistent and very bio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been described as a '' sui generis'' political entity (without precedent or comparison) combining the characteristics of both a federation and a confederation. Containing 5.8per cent of the world population in 2020, the EU generated a nominal gross domestic product (GDP) of around trillion in 2021, constituting approximately 18per cent of global nominal GDP. Additionally, all EU states but Bulgaria have a very high Human Development Index according to the United Nations Development Programme. Its cornerstone, the Customs Union, paved the way to establishing an internal single market based on standardised legal framework and legislation that applies in all member states in those matters, and only those matters, where the states have agreed to act ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Science Of The Total Environment
''Science of the Total Environment'' is a weekly international peer-reviewed scientific journal covering environmental science. It was established in 1972 and is published by Elsevier. The editors-in-chief are Damià Barceló (Consejo Superior de Investigaciones Científicas), Jay Gan (University of California, Riverside) and Philip Hopke (University of Rochester). According to the ''Journal Citation Reports'', the journal has a 2021 impact factor The impact factor (IF) or journal impact factor (JIF) of an academic journal is a scientometric index calculated by Clarivate that reflects the yearly mean number of citations of articles published in the last two years in a given journal, as i ... of 10.753. Controversies The October 2020 article suggesting that amulets may prevent COVID-19 has been met with skepticism even among the listed coauthors. As of November 2020, the article was under "temporary removal". It was later withdrawn at the request of the authors. References Ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Landfill Gases
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste with daily, intermediate and final covers only began in the 1940s. In the past, refuse was simply left in piles or thrown into pits; in archeology this is known as a midden. Some landfill sites are used for waste management purposes, such as temporary storage, consolidation and transfer, or for various stages of processing waste material, such as sorting, treatment, or recycling. Unless they are stabilized, landfills may undergo severe shaking or soil liquefaction of the ground during an earthquake. Once full, the area over a landfill site may be reclaimed for other uses. Operations Operators of well-run landfills for non-hazardous waste meet predefined specifications by applying techniques to: # confine waste to as small an area a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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