How Much Water Does Silica Gel Absorb
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| Identifiers | |
|---|---|
| CAS Number |
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| ChemSpider |
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| ECHA InfoCard | 100.065.880 |
| UNII |
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| CompTox Dashboard (EPA) |
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| Backdrop | |
| Chemical formula | SiO2 |
| Molar mass | 60.08 g/mol |
| Appearance | Transparent beads |
| Odor | Odorless |
| Except where otherwise noted, data are given for materials in their standard land (at 25 °C [77 °F], 100 kPa). Infobox references | |
Silica gel is an amorphous and porous class of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other liquids, or may be filled by gas or vacuum. In the last case, the material is properly chosen silica xerogel.
Silica xerogel with an boilerplate pore size of 2.4 nanometers has a potent analogousness for water molecules and is widely used as a desiccant. It is difficult and translucent, merely considerably softer than massive silica glass or quartz; and remains hard when saturated with water.
Silica xerogel is usually commercialized as coarse granules or beads, a few millimeters in diameter. Some grains may contain small amounts of indicator substance that changes color when they have absorbed some h2o. Small paper envelopes containing silica xerogel pellets, ordinarily with a "do non eat" alert, are often included in dry out food packages to absorb any humidity that might cause spoilage of the food.
'Wet' silica gel, every bit may be freshly prepared from alkali silicate solutions, may vary in consistency from a soft transparent gel, like to gelatin or agar, to a difficult solid, namely a water-logged xerogel. It is sometimes used in laboratory processes, for example to suppress convection in liquids or prevent settling of suspended particles.[4]
History [edit]
Silica gel was in existence as early on as the 1640s as a scientific marvel.[5] It was used in Globe War I for the adsorption of vapors and gases in gas mask canisters.[6] The synthetic route for producing silica gel was patented in 1918 by Walter A. Patrick, a chemistry professor at Johns Hopkins University.
In Earth War Ii, silica gel was indispensable in the war effort for keeping penicillin dry, protecting armed services equipment from wet damage,[ citation needed ] as a fluid cracking catalyst for the production of high octane gasoline, making carbon disulphide, and as a catalyst back up for the manufacture of butadiene from ethanol (feedstock for synthetic rubber production).
Types [edit]
- Type A – clear pellets, guess pore diameter: 2.five nm, drying and moistureproof backdrop, tin can be used as catalyst carriers, adsorbents, separators and variable-pressure adsorbent.
- Type B – translucent white pellets, pore diameter: 4.5–seven.0 nm, liquid adsorbents, drier and perfume carriers, too may be used as catalyst carriers, cat litter.
- Type C – translucent, micro-pored structure, raw material for grooming of silica gel cat litter. Additionally dried and screened, it forms macro-pored silica gel which is used as drier, adsorbent and catalyst carrier.
Silica alumina gel - lite yellowish, chemically stable, flame-resistant, insoluble except in alkali or hydrofluoric acrid. Superficial polarity, thermal stability, operation greater than fine-pored silica gel.
Stabilizing silica gel - non-crystalline micro-porous solid pulverization, nontoxic, flame-resisting, used in brewery of grains for beer to better sense of taste, clearness, color, and cream and for removal of non-micro-organism impurities.
Backdrop [edit]
Silica gel'south high specific surface area (around 750–800 mtwo/g (230,000–240,000 sq ft/oz))[7] allows it to adsorb h2o readily, making it useful equally a desiccant (drying agent). Silica gel is oftentimes described equally "absorbing" moisture, which may be appropriate when the gel'due south microscopic structure is ignored, every bit in silica gel packs or other products. However, textile silica gel removes moisture by adsorption onto the surface of its numerous pores rather than by absorption into the bulk of the gel.
Regeneration [edit]
Once saturated with water, the gel may be regenerated by heating it to 120 °C (250 °F) for 1–2 hours.[ boosted citation(s) needed ] Some types of silica gel volition "pop" when exposed to enough h2o. This is caused past breakage of the silica spheres when contacting the water.[8]
Training [edit]
An aqueous solution of sodium silicate is acidified to produce a gelatinous precipitate that is washed, then dehydrated to produce colorless silica gel.[7] When a visible indication of the moisture content of the silica gel is required, ammonium tetrachlorocobaltate(Ii) (NHfour)2[CoCliv] or cobalt(Two) chloride CoClii is added.[7] This volition cause the gel to be blue when dry and pink when hydrated.[7] Due to link between the cancer and cobalt chloride, it has been forbidden in Europe for use in silica gel.[9] An alternative indicator is methyl violet which is orange when dry and green when hydrated.
Uses [edit]
Desiccant [edit]
Silica gel, equally chaplet packed in a permeable bag, is a usually used desiccant.
In many items, wet encourages the growth of mold and spoilage. Condensation may also impairment other items such as electronics and may speed the decomposition of chemicals, such equally those in vitamin pills. Through the inclusion of silica gel packets, these items can be preserved longer. Information technology may aid the drying out of electronic equipment during attempts to restore items that have been exposed to moisture accidentally.
Silica gel may likewise be used to continue the relative humidity inside a high frequency radio or satellite transmission organization waveguide every bit low as possible (see too humidity buffering). Excessive moisture buildup within a waveguide tin can cause arcing inside the waveguide itself, damaging the power amplifier feeding information technology. Also, the beads of water that form and condense inside the waveguide change the feature impedance and frequency, degrading the signal. It is common for a minor compressed air system (similar to a small home aquarium pump) to exist employed to broadcast the air inside the waveguide over a jar of silica gel.
Silica gel is too used to dry the air in industrial compressed air systems. Air from the compressor discharge flows through a bed of silica gel beads. The silica gel adsorbs moisture from the air, preventing impairment at the point of use of the compressed air due to condensation or moisture. The aforementioned system is used to dry the compressed air on railway locomotives, where condensation and ice in the restriction air pipes can lead to restriction failure.
Prior to widespread use of air-conditioning, table salt shakers with caps containing silica gel beads to proceed the salt dry out enough to prevent clumping were marketed in the United states, replacing the practice of including a few grains of rice in salt shakers to effect the same drying.
Silica gel is sometimes used every bit a preservation tool to control relative humidity in museum and library exhibitions and storage.
Other applications include diagnostic test strips, inhalation devices, syringes, drug test kits, and hospital sanitation kits.
Chemistry [edit]
In chemistry, silica gel is used in chromatography as a stationary phase. In column chromatography, the stationary phase is virtually often equanimous of silica gel particles of 40–63 μm. Dissimilar particle sizes are used for dissimilar kinds of column chromatography as the particle size is related to expanse. The differences in particle size dictate if the silica gel should be used for flash or gravity chromatography. In this awarding, due to silica gel's polarity, not-polar components tend to elute before more polar ones, hence the proper name normal phase chromatography. However, when hydrophobic groups (such as Cxviii groups) are attached to the silica gel and so polar components elute showtime and the method is referred to as reverse phase chromatography. Silica gel is also applied to aluminium, glass, or plastic sheets for thin layer chromatography.
The hydroxy (OH) groups on the surface of silica tin can be functionalized to beget specialty silica gels that exhibit unique stationary phase parameters. These so-called functionalized silica gels are also used in organic synthesis and purification as insoluble reagents and scavengers.
Chelating groups take too been covalently bound to silica gel. These materials have the power to remove metal ions selectively from aqueous solutions. Chelating groups tin can be covalently bound to polyamines that have been grafted onto a silica gel surface producing a material of greater mechanical integrity. Silica gel is as well combined with alkali metals to form a One thousand-SG reducing amanuensis. (See SiGNa chemistry)
Silica gel is non expected to biodegrade in either water or soil.[10]
Cat litter [edit]
Silica gel is also used equally true cat litter,[eleven] by itself or in combination with more traditional materials, such as clays including bentonite. It is non-tracking and virtually odorless.
Nutrient additive [edit]
Silica gel, too referred to as silicon dioxide or synthetic amorphous silica (SAS), is listed by the FDA in the United States as more often than not recognized as safe (GRAS), meaning it tin be added to food products without needing approval. Silica is immune to be added to nutrient in the U.s.a. at upwards to 2% as permitted nether 21 CFR 172.480. In the European union, it tin can be in upwards to 5% concentrations.[12] In 2018, a re-evaluation by the EFSA Panel on Food Additives and Nutrient Sources added to Food constitute no indications of toxicity even at the highest estimates of exposure level. [13]
Listed uses include: anticaking agent, defoaming agent, stabilizer, adsorbent, carrier, workout agent, chillproofing agent, filter aid, emulsifying agent, viscosity control agent, and anti-settling amanuensis.[fourteen] Silica can be found commonly in foods including baked goods, spices and herbs, dairy products, cocoa products, and more than. [15]
Water filtration [edit]
Given the water adsorption properties of silica gel, information technology is used in domestic h2o filters.[16] The surface structure of silica gel allows the adsorption of some minerals that are dissolved in the water,[17] or "Ion-substitution" as it is marketed. Due to the lack of regulations for domestic water filtration products, no studies validate the manufacturer claims regarding the effectiveness of the filtration system.
Humidity indicator (color-irresolute silica gel) [edit]
Silica gel may be doped with a moisture indicator that gradually changes its color when it transitions from the anhydrous (dry) state to the hydrated (moisture) land. Common indicators are cobalt(Two) chloride and methyl violet. Cobalt (2) chloride is deep blue when dry and pinkish when wet, but it is toxic and carcinogenic, and was reclassified by the European Spousal relationship in July 2000 as a toxic material.[xviii] Methyl violet may be formulated to change from orange to dark-green, or orange to colorless. It also is toxic and potentially carcinogenic,[xix] but is safe enough to have medicinal uses. A more ecologically friendly indicator solution is ferric ammonium sulfate, which results in a colour alter from deep orange/amber when dry out to colorless/white when saturated.[20]
Hazards [edit]
Silica gel is non-toxic, non-combustible, and non-reactive and stable with ordinary usage. It will react with hydrogen fluoride, fluorine, oxygen difluoride, chlorine trifluoride, strong acids, strong bases, and oxidizers.[10] Silica gel is irritating to the respiratory tract and may cause irritation of the digestive tract. Dust from the beads may cause irritation to the pare and eyes, so precautions should be taken.[21] Crystalline silica grit can cause silicosis, only synthetic amorphous silica gel is indurated then does not cause silicosis. Additional hazards may occur when doped with a humidity indicator.
References [edit]
- ^ Silica gel, site www.jtbaker.com
- ^ Silica gel, site world wide web.chemcas.org
- ^ Silicon dioxide, site echa.europa.eu
- ^ H.Yard. Henisch (1988): Crystals in Gels and Liesegang Rings. Cambridge Academy Press. ISBN 0521345030
- ^ Maryann Feldman and Pierre Desrochers (March 2003). "Research Universities and Local Economic Development: Lessons from the History of the Johns Hopkins Academy" (PDF). Industry and Innovation. 10 (1): five–24. doi:10.1080/1366271032000068078. S2CID 154423229. Archived from the original (PDF) on 2005-11-12.
- ^ http://hengyeusa.com/customs/desiccants-at-state of war
- ^ a b c d Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN978-0-08-037941-8.
- ^ Spence Konde, "Training of High-Silica Zeolite Beads From Silica Gel," retrieved 2011-09-26
- ^ "Bluish Silicagel & Conclusions: Safety information on bluish silicagel". Archived from the original on 2016-01-05.
- ^ a b Environmental Wellness and Safe (2007-09-x). "Silica Gel". Retrieved 2008-01-12 .
- ^ Andrew Kantor (2004-12-10). "Non-Tech High Tech Litters the Mural". United states Today. Retrieved 2008-03-02 .
- ^ "Notification of the GRAS Decision of Silicon Dioxide When Added Straight or Indirectly to Man Nutrient" (PDF). Archived from the original (PDF) on April xviii, 2013.
- ^ [M. Younes, P. Aggett, F. Aguilar (2018). "Scientific Opinion on the re-evaluation of silicon dioxide (E 551) equally a food additive". EFSA Periodical. 16 (i): 5088, 70pp. doi:x.2903/j.efsa.2018.5088. PMC7009582. PMID 32625658. S2CID 79503431.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ "GRAS Notice (GRN) No. 298" (PDF). Archived from the original (PDF) on April 9, 2011.
- ^ [M. Younes, P. Aggett, F. Aguilar (2018). "Scientific Opinion on the re-evaluation of silicon dioxide (E 551) every bit a food additive". EFSA Journal. 16 (ane): 5088, 70pp. doi:ten.2903/j.efsa.2018.5088. PMC7009582. PMID 32625658. S2CID 79503431.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ ZeroWater
- ^ J. B. Peri , A. Fifty. Hensley Jr. (1968). "The surface structure of silica gel". The Periodical of Concrete Chemistry. 72 (eight): 2926–2933. doi:10.1021/j100854a041.
- ^ "Classifications - CL Inventory".
- ^ "Methyl Violet Prophylactic Information Sheet" (PDF). labchem.
- ^ "SORBSIL CHAMELEON Safety Data Canvass" (PDF). OkerChemie.
- ^ Fisher Scientific (1997-02-09). ""Silica Gel Dessiccant"[sic]". Retrieved 2008-01-12 .
External links [edit]
Wikimedia Commons has media related to Silica gel.
- Record in the Household Products Database of NLM
- United kingdom Cloth Safety Datasheet
- Silica Gel with Moisture indicator: Instructions for Employ Detailed use and re-drying info (broken link?)
- Silica Gel Dehumidifier FAQs Helpful Information on Rechargeable Silica Packs for Abode Usage
- Silica-leap reagents Information on development and Tables illustrating reactivity
- Silica-leap scavengers General notes and Tables that summarize scavenging capacity
How Much Water Does Silica Gel Absorb,
Source: https://en.wikipedia.org/wiki/Silica_gel
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