atomic no. 14, atomic wt. 28.09, non-metal, row 4, col. 4A, val. 4, orbits 2-8-4

{Merck Index - © 1952 by Merck & Co., Inc.}

Silicon. Si; at. wt. 28.09; at. no. 14; valence, 4. Prepared by Gay-Lussac and Thenard in 1811; physical properties determined by Berzelius in 1823. Does not occur free in nature; found as silica (quartz, sandstone, etc.) or as silicates (felspar or orthoclase, kaolinite, anorthite, etc.); constitutes 27.6% of the crust of the earth. Prepn.: Gayler, Nature 142, 478 (1938). Exists in two pseudoallotropic forms, amorphous and crystalline.

Amorphous: Dark-brown powder; m. about 1420°; d2O 2.4. Insoluble in water and most acids. Soluble in hydrofluoric acid. Superficially oxidized on heating in air at 150°. Burns in oxygen at 400°. Attacked by fluorine at room temperature, by chlorine at 450°, by bromine at 500°, by iodine at a red heat. When boiled in alkaline hydroxides, yields alkaline silicates and hydrogen.

Crystalline: Dark-gray, opaque, needle-like crystals or octahedral platelets of cubic system. m. 1420°; d. 2.3. Insoluble in acids; soluble in a mixture of nitric and hydrofluoric acid. Burns when heated in chlorine; catches fire in fluorine. Slightly conducts electricity (the amorphous does not). Chemically resembles the amorphous form, but is less active.

Silicon combines with nitrogen, forming a nitride, and with the metals, forming suicides.

Use: For making alloys: ferrosilicon, stalloy, silicon bronze, silicon copper; as a reducing agent instead of aluminum.

Toxicity: Prolonged exposure: chronic pneumonoconiosis (silicosis) accompanied by shortness of breath, cough, chest pain, lowered capacity for exercise, decreased vital capacity.

Why add silicon to nutrient solutions?

by Bruce Bugbee

Crop Physiology Laboratory, Utah State University, Logan, UT 84322-4820

Although silicon has not been recognized as an essential element for higher plants, its beneficial effects have been shown in many plants. Silicon is abundant in all field grown plants, but it is not present in most hydroponic solutions. Silicon has long been recognized as particularly important to rice growth, but a recent study indicated that it may only be important during pollination in rice (Ma et al. 1989). The beneficial effects of silicon (Si) are twofold: 1) it protects against insect and disease attack (Cherif et al. 1994; Winslow, 1992; Samuels, 1991), and 2) it protects against toxicity of metals (Vlamis and Williams, 1967; Baylis et al. 1994). For these reasons, I recommend adding silicon (about 0.1 mM) to nutrient solutions for all plants unless the added cost outweighs its advantages.

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