Borcarbid Chemische Eigenschaften,Einsatz,Produktion Methoden
R-Sätze Betriebsanweisung:
R20:Gesundheitsschädlich beim Einatmen.
S-Sätze Betriebsanweisung:
S22:Staub nicht einatmen.
S36/37/39:Bei der Arbeit geeignete Schutzkleidung,Schutzhandschuhe und Schutzbrille/Gesichtsschutz tragen.
S38:Bei unzureichender Belüftung Atemschutzgerät anlegen.
Beschreibung
Sodium tetraborate decahydrate/borax (anhydrous) is a clear, colorless or pale yellow
hygroscopic substance with a faint odor of detergent. It is stable and is incompatible with
powdered metalsand slightly soluble in water. It is extensively used in the industrial manufacturing
of metallurgical fluxes, fiberglass, ceramics, fertilizers, enamels, heat-resistant
glass (e.g., Pyrex), and other chemicals. It decomposes on heating or on burning producing
toxic fumes including sodium oxide, reacts with strong oxidants, and in fire gives off
irritating or toxic fumes (or gases).
Chemische Eigenschaften
hard, black, shiny crystal(s), -325 mesh with 99.5% purity; rhomb; hardness 9.3 Mohs; less brittle than most ceramics; does not burn in oxygen flame; used as an abrasive; Knoop hardness ~27GPa; produced by reducing B2O3 with carbon at 1400°C–2300°C; used in crucible form as a container for molten salts except molten caustic and as a 99.5% pure sputtering target for producing semiconductor and wear-resistant films [KIR78] [HAW93] [MER06] [CER91]
Physikalische Eigenschaften
Hard black shiny crystals, fourth
hardest material known after
diamond, cubic boron nitride,
and boron oxide. Does not burn
in an O flame if temperature is 2
maintained below 983°C.
Maximum operating
temperature 2000°C (inert,
reducing) or 600°C (oxidizing).
Not attacked by hot HF or
chromic acid. Used as abrasive,
crucible container for molten
salts except molten alkali
hydroxides. In form of molded
shape, used for pressure-blast
nozzles, wire-drawing dies, and
bearing surfaces for gauges. For
grinding and lapping
application available mesh sizes
cover range 240 to 800.
Physikalische Eigenschaften
Black hard crystal; density 2.50 g/cm
3; hardness 9.3 Mohs; melts at 2,350°C; vaporizes above 3,500°C; insoluble in water and acid; inert to most chemicals at ordinary temperatures; rapidly attacked by hot alkalies.
Verwenden
Boron carbide (B4C) is a hard, black crystal that is used as an abrasive powder and as an
additive to strengthen composite parts in aircraft.
synthetische
Boron carbide is prepared by reduction of boric oxide either with carbon or with magnesium in presence of carbon in an electric furnace at a temperature above 1,400°C. When magnesium is used, the reaction may be carried out in a graphite furnace and the magnesium byproducts are removed by treatment with acid.
Definition
boron carbide: A black solid, B
4C,soluble only in fused alkali; it is extremelyhard, over 9? on Mohs’scale; rhombohedral; r.d. 2.52; m.p.2350°C; b.p. >3500°C. Boron carbideis manufactured by the reduction ofboric oxide with petroleum coke inan electric furnace. It is used largelyas an abrasive, but objects can alsobe fabricated using high-temperaturepowder metallurgy. Boron nitride isalso used as a neutron absorber becauseof its high proportion ofboron–10.
Origin
Boron carbide is an artificial abrasive introduced in 1934 by the Norton Company under the name "Norbide." Washington Mills was the only producer of boron carbide in the United States in 2004.
Industrielle Verwendung
Boron carbide (B4C) is produced by the hightemperature(about 1371 to 2482°C) interactionof boric oxide, B2O3, and carbon in an electricalresistance-type furnace. It is a black, lustroussolid. It is used extensively as an abrasive,because its hardness approaches that of the diamond.It is also used as an alloying agent, particularlyin molybdenum steels.
Additionally, it is used in drawing dies andgauges, or into heat-resistant parts such as nozzles.The composition is either B6C or B4C; theformer is the harder but usually contains anexcess of graphite difficult to separate in thepowder. It can be used thus as a deoxidizingagent for casting copper, and also for lapping,since the graphite acts as a lubricant. Borofluxis B4C with flake graphite, used as a casting flux.B4C parts are fabricated by hot pressing,sintering, and sinter-HIPing (HIP = hot-isostaticpress). Industrially, densification is carriedout by hot pressing (2100 to 2200°C, 20to 40 MPa) in argon. The best properties areobtained when pure fine powder is densifiedwithout additives. Pressureless sintering to highdensity is possible using ultrafine powder, withadditives (notably carbon). Less expensive thanhot pressing, sintering also can be used for morecomplex shapes.
Special part formulations include bondingB4C with fused sodium silicate, borate frits,glasses, plastics, or rubbers to lend strength,hardness, or abrasion resistance. B4C-based cermets and MMC (especially Al/B4C, Mg/B4C, Ti/B4C), and CMCs (e.g., TiB2/B4C) haveunique properties, including superior ballisticperformance, that make these materials suitablefor highly specialized applications. Hightemperaturestrength, light weight, corrosionresistance, and hardness make these compositesespecially attractive. B4C shapes can bereaction-bonded using SiC as the bondingphase. B4C–C mixtures are formed, thenreacted with silicon to create the SiC bond. SiCalso can be used as a sintering aid for B4C, andvice versa.
Borcarbid Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
