silica gel

• シリカゲル

WordNet

1. a white or colorless vitreous insoluble solid (SiO2); various forms occur widely in the earths crust as quartz or cristobalite or tridymite or lechatelierite (同)silicon oxide, silicon_dioxide
2. a colloid in a more solid form than a sol (同)colloidal gel
3. become a gel; "The solid, when heated, gelled"
4. cut off the testicles (of male animals such as horses); "the vet gelded the young horse" (同)cut
5. a unit of force equal to the force exerted by gravity; used to indicate the force to which a body is subjected when it is accelerated (同)gee, g-force

PrepTutorEJDIC

1. 無水ケイ酸,ケイ土
2. ゲル(コロイド溶液の凝固した状態;ゼラチン・寒天など) / =jell
3. 〈動物,特に馬〉‘を'去勢する

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/06/29 20:02:14」(JST)

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Silica gel
Identifiers
CAS number	63231-67-4 Y,
Properties
Molecular formula	SiO2
Molar mass	60.08 g/mol
Appearance	Transparent beads
Odor	Odorless
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Silica gel is a granular, vitreous, porous form of silicon dioxide made synthetically from sodium silicate. Silica gel is tough and hard; it is more solid than common household gels like gelatin or agar. It is a naturally occurring mineral that is purified and processed into either granular or beaded form. As a desiccant, it has an average pore size of 2.4 nanometers and has a strong affinity for water molecules.

Silica gel is most commonly encountered in everyday life as beads in a small (typically 2 x 3 cm) paper packet. In this form, it is used as a desiccant to control local humidity to avoid spoilage or degradation of some goods. Because silica gel can have added chemical indicators (see below) and absorbs moisture very well, silica gel packets usually bear warnings for the user not to eat the contents.

History

Silica gel was in existence as early as the 1640s as a scientific curiosity. It was used in World War I for the adsorption of vapors and gases in gas mask canisters. The synthetic route for producing silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins University, Baltimore, Maryland, USA in 1919.

In World War II, silica gel was indispensable in the war effort for keeping penicillin dry, protecting military equipment from moisture damage, as a fluid cracking catalyst for the production of high octane gasoline, and as a catalyst support for the manufacture of butadiene from ethanol, feedstock for the synthetic rubber program.

Types

Type A - clear pellets, Approximate pore diameter:2.5 nm, drying and moistureproof properties, can be used as catalyst carriers, adsorbents, separators and variable-pressure adsorbent.

Type B - translucent white pellets, pore diameter: 4.5-7.0 nm, Liquid adsorbents, drier and perfume carriers, also may be used as catalyst carriers, cat litter.

Type C - translucent, Micro-pored structure, Raw material for preparation 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, light yellow, Chemically stable，flame-resistant，insoluble except in alkali or hydrofluoric acid．Superficial polarity，thermal stability，performance greater than fine-pored silica gel．

Stabilizing Silica Gel, non-crystalline micro-porous solid powder, nontoxic, flame-resisting, Used in brewery of grains for beer to improve taste, clearness, color and foam, removal of non-micro-organism impurities.

Properties

Silica gel's high surface area (around 800 m²/g) allows it to adsorb water readily, making it useful as a desiccant (drying agent). Silica gel is often described as "absorbing" moisture, which may be appropriate when the gel's microscopic structure is ignored, as in silica gel packs or other products. However, as material silica gel removes moisture by adsorption onto the surface of its numerous pores rather than by absorption into the bulk of the gel.

Regeneration

Once saturated with water, the gel can be regenerated by heating it to 120 °C (250 °F) for two hours. Some types of silica gel will "pop" when exposed to enough water. This is caused by breakage of the silica spheres when contacting the water.

Preparation

A solution of sodium silicate is acidified to produce a gelatinous precipitate that is washed, then dehydrated to produce colorless silica gel. When a visible indication of the moisture content of the silica gel is required, ammonium tetrachlorocobaltate(II) (NH₄)₂CoCl₄ or cobalt chloride CoCl₂ is added. This will cause the gel to be blue when dry and pink when hydrated. An alternative indicator is methyl violet which is orange when dry and green when hydrated.

Applications

Desiccant

Silica gel is a commonly used desiccant as beads packed in a permeable bag

See also: Desiccant

In many items, moisture encourages the growth of mold and spoilage. Condensation may also damage other items like electronics and may speed the decomposition of chemicals, such as those in vitamin pills. Through the inclusion of silica gel packets, these items can be preserved longer.

Silica gel may also be used to keep the relative humidity (RH) inside a high frequency radio or satellite transmission system waveguide as low as possible (see also Humidity buffering). Excessive moisture buildup within a waveguide can cause arcing inside the waveguide itself, damaging the power amplifier feeding it. Also, the beads of water that form and condense inside the waveguide change the characteristic impedance and frequency, degrading the signal. It is common for a small compressed air system (similar to a small home aquarium pump) to be employed to circulate the air inside the waveguide over a jar of silica gel.

Silica gel is also 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 damage at the point of use of the compressed air due to condensation or moisture. The same system is used to dry the compressed air on railway locomotives, where condensation and ice in the brake air pipes can lead to brake failure.

Silica gel is sometimes used as 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

Chromatography column

In chemistry, silica gel is used in chromatography as a stationary phase. In column chromatography, the stationary phase is most often composed of silica gel particles of 40–63 μm. Different particle sizes are used for achieving a desired separation of certain molecular sizes. In this application, due to silica gel's polarity, non-polar components tend to elute before more polar ones, hence the name normal phase chromatography. However, when hydrophobic groups (such as C₁₈ groups) are attached to the silica gel then polar components elute first 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 can be functionalized to afford 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 have also been covalently bound to silica gel. These materials have the ability to remove metal ions selectively from aqueous media. Chelating groups 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 also combined with alkali metals to form a M-SG reducing agent.

Silica gel is not expected to biodegrade in either water or soil.

Cat litter

Silica gel is also used as cat litter, by itself or in combination with more traditional materials, such as clays including bentonite. It is trackless and virtually odorless. Purchasing silica in the form of cat litter can be an easy and cost effective way for retail consumers to purchase silica gel for use in other applications, such as maintaining the desired relative humidity in humidors, keeping tools or other materials rust-free in damp environments or long-term storage, and preserving dried food.

Food additive

Silica gel, also referred to as silica aerogel or hydrated silica, has FDA GRAS (Generally Recognized As Safe) status, meaning it can be added to food products without needing approval. Silica is allowed to be added to food in the US at up to 2% as permitted under 21 CFR 172.480. In the EU it can be in up to 5% concentrations.

Listed uses include: anticaking agent, defoaming agent, stabilizer, adsorbent, carrier, conditioning agent, chillproofing agent, filter aid, emulsifying agent, viscosity control agent, and anti-settling agent.

Hazards

Silica gel is non-toxic, non-flammable, 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. Silica gel is irritating to the respiratory tract and may cause irritation of the digestive tract, and dust from the beads may cause irritation to the skin and eyes, so precautions should be taken. Crystalline silica dust can cause silicosis but synthetic amorphous silica gel is indurated, and so does not cause silicosis.

Humidity indicator

Main article: Humidity indicator

Indicating Silica Gel

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 (wet) state. Common indicators are cobalt(II) chloride and methyl violet. Cobalt (II) chloride is deep blue when dry and pink when wet. It is toxic and carcinogenic, and was reclassified by the European Union in July 2000 as a toxic material.^{[citation needed]} Methyl violet can be formulated to change from orange to green, or orange to colorless. It is also toxic and potentially carcinogenic, but is safe enough to have medicinal uses.

References

External links

• Record in the Household Products Database of NLM
• UK Material Safety Datasheet
• Silica Gel with Moisture indicator: Instructions for Use Detailed use and re-drying info
• Silica Gel Dehumidifier FAQs Helpful Information on Rechargeable Silica Packs for Home Usage
• Silica-bound reagents Information on development and Tables illustrating reactivity
• Silica-bound scavengers General notes and Tables that summarize scavenging capacity
• Education Center

UpToDate Contents

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English Journal

• The ability of retention, drug release and rheological properties of nanogel bioadhesives based on cellulose derivatives.

• Keshavarz M, Kaffashi B.Author information Department of Polymer Engineering, School of Chemical Engineering, University of Tehran , Tehran , Iran.AbstractThe rheological and drug release behavior of biopolymer nanocomposite gels based on the cellulose derivatives, formulated as the bioadhesive drug delivery platforms, were investigated. The bioadhesive gel is composed of the microcrystalline cellulose, sodium carboxymethyl cellulose and phosphate buffered saline (pH = 7.4 at 20 °C) as the dissolution and release medium. The reinforcing nanofillers such as MMT-clay, fumed porous silica and porous starch were used as additives in the nanogel bioadhesive. The constant steady state viscosities of this nanogels upon incorporation of various nanofillers into the systems is the sign of structural stability. Hence, this system is suitable for use in the controlled drug delivery systems in contact with the biological tissues. Based on the rheological measurements, the shear flow properties (i.e. zero shear viscosity and yield stress) were influenced by the concentration of polymers and nanoparticles. The results indicate that the nonlinear rheological data are fitted properly by the Giesekus model. Furthermore, the results showed that the nonlinear viscoelastic parameters (λ and α) are highly affected by the biogel and nanoparticles concentrations. Finally, the drug release was measured, and the results indicated that the biopolymer-clay nanocomposites have appropriate release pattern as the release is better controlled compared to the other nanogel formulations.
• Pharmaceutical development and technology.Pharm Dev Technol.2014 Dec;19(8):952-9. doi: 10.3109/10837450.2013.846371. Epub 2013 Oct 25.
• The rheological and drug release behavior of biopolymer nanocomposite gels based on the cellulose derivatives, formulated as the bioadhesive drug delivery platforms, were investigated. The bioadhesive gel is composed of the microcrystalline cellulose, sodium carboxymethyl cellulose and phosphate buf
• PMID 24160773

• Spectroscopic characterisation of dimeric oxidation products of phytosterols.

• Sosińska E1, Przybylski R2, Aladedunye F3, Hazendonk P2.Author information 1Institute of Biochemistry and Biophysics Polish Academy of Sciences, 02-106 Warsaw, Poland. Electronic address: esosinska@ibb.waw.pl.2Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada.3Max Rubner-Institut (MRI), Federal Research Institute for Nutrition and Food, D-32756 Detmold, Germany.AbstractSterol dimers are the main oxidation products formed during sterols degradation at elevated temperatures. An investigation was carried out to decipher the structure of dimers differing in polarity, formed during β-sitosterol thermo-oxidation. The oxidation products were fractionated using silica gel into non-polar (NP), mid-polar (MP) and polar fractions (P). Oligomers were further separated by size-exclusion chromatography (SEC). Tentative chemical structures of non-polar, mid-polar and polar dimers were identified using Ag(+)/CIS-MS and APCI-MS procedures after on-line RP-HPLC separation. Further structures were verified by NMR and FT-IR spectroscopies.
• Food chemistry.Food Chem.2014 May 15;151:404-14. doi: 10.1016/j.foodchem.2013.11.079. Epub 2013 Nov 22.
• Sterol dimers are the main oxidation products formed during sterols degradation at elevated temperatures. An investigation was carried out to decipher the structure of dimers differing in polarity, formed during β-sitosterol thermo-oxidation. The oxidation products were fractionated using silica ge
• PMID 24423550

• A simplified procedure for the determination of organochlorine pesticides and polychlorobiphenyls in edible vegetable oils.

• Li J1, Liu D1, Wu T1, Zhao W1, Zhou Z1, Wang P2.Author information 1Department of Applied Chemistry, China Agricultural University, Beijing 100193, PR China.2Department of Applied Chemistry, China Agricultural University, Beijing 100193, PR China. Electronic address: wangpeng@cau.edu.cn.AbstractA one-step extraction-purification multiresidue method for the determination of 14 organochlorine pesticides (OCPs) and 7 polychlorinated biphenyls (PCBs) in edible vegetable oils based on matrix solid-phase dispersion (MSPD) has been developed. The experimental parameters affecting the recoveries and the efficiency of the cleanup procedure were thoroughly evaluated. Under an optimised condition, 0.5g of oil sample was blended with 3.5g of sulfuric acid-impregnated silica and 0.8g of silica gel was used as co-column absorbent. The PCBs and OCPs were eluted by 10mL of n-hexane/dichloromethane (70:30, v/v) and determined by gas chromatography equipped with an electron capture detector (GC-ECD). Good recoveries were obtained in the range of 69.6-105.3% with relative standard deviations (RSD) values below 15% in most cases. The limits of detection (LOD), based on a signal-to-noise ratio (S/N) of 3, were in the range of 0.04-0.74ng/g.
• Food chemistry.Food Chem.2014 May 15;151:47-52. doi: 10.1016/j.foodchem.2013.11.047. Epub 2013 Nov 19.
• A one-step extraction-purification multiresidue method for the determination of 14 organochlorine pesticides (OCPs) and 7 polychlorinated biphenyls (PCBs) in edible vegetable oils based on matrix solid-phase dispersion (MSPD) has been developed. The experimental parameters affecting the recoveries a
• PMID 24423500

Japanese Journal

• Recent Progress of Research and Development of Adsorption Desalination (Special Issue for Sustainable Environmental Technologies)

• LI Yuanyuan,HU Eric,WU Jun W. [他]
• Journal of chemical engineering of Japan 47(4-7), 303-308, 2014-07
• NAID 40020131766

• BCSJ Award Article : Cosolvent-Free Sol–Gel Synthesis and Optical Characterization of Silica Glasses Containing LaF₃ and (La,Er)F₃ Nanocrystals

• Suzuki Kotomi,Kajihara Koichi,Kanamura Kiyoshi
• Bulletin of the Chemical Society of Japan 87(7), 765-772, 2014-07
• NAID 40020119031

• ＜解説＞　無機テンプレート法によるシリカナノ中空粒子の迅速合成

• 高井 千加,石野 尊拡,白井 孝,藤 正督,タカイ チカ,イシノ タカヒロ,シライ タカシ,フジ マサノリ,Takai Chika,Ishino Takahiro,Shirai Takashi,Fuji Masayoshi,Rapid synthesis
• 名古屋工業大学先進セラミックス研究センター年報 = Annual report Advanced Ceramics Research Center Nagoya Institute of Technology 2, 25-28, 2014-06-30
• … This article in Japanese reviews our recent paper,"Rapid and high yield synthesis of hollow silica nanoparticles using an NH 4 F catalyst", published in Colloids and Surfaces A: Physicochemical and Engineering Aspects 446, 46-49, (2014) by C. … The rapid synthesis of hollow silica nanoparticles based on the CaCO 3 template method is proposed. …
• NAID 120005467132

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