Zirconium oxide, fused

Two common sources of infra-red radiation are the Nernst filament, an element of rare earth oxides, mainly zirconium oxide, fused together in a rod between 1 mm and 2 mm diameter, and the Globar, a larger diameter rod of silicon-carbide. Both elements are heated electrically, and at temperatures between 1,200° and 2,000° emit radiation with a maximum between 1 5// and 2 5// rather like a black body radiator. 

Zirconium oxide is fused with alurnina in electric-arc furnaces to make alumina—zirconia abrasive grains for use in grinding wheels, coated-abrasive disks, and belts (104) (see Abrasives). The addition of zirconia improves the shock resistance of brittle alurnina and toughens the abrasive. Most of the baddeleyite imported is used for this appHcation, as is zirconia produced by burning zirconium carbide nitride. 

The mineral baddeleyite (Zr02) is found in nature only in small quantities. The main raw material for zirconium oxide ceramics is thus zircon (ZrSi04), from which pure Zr02 is produced by fusing with lime and coke to reduce the Si02 and the impurities. 

The range of materials used as refractories is very wide and includes such substances as the fireclays and kaolins, quartzites, bauxites, schist, magnesite, dolomite, graphite, carborundum, fused alumina, chromite, magnesium aluminate, magnesium silicate, zirconium oxide, zirconium silicate, boron nitride, and others. 

Special Refractories.— Under certain conditions refractories of special qualities may be employed such as zirconium oxide, zirconium silicate, chromite, fused silica, boron nitride, aluminum nitride, lime, beryllium oxide, cerium dioxide, thoria, asbestos and various synthetic combinations. 

In the mid-IR several type of sources are used. They are either a lamp filament (Figure 10.13), or a hollow rod, 1-3 mm in diameter and 2 to 4 cm long, made of fused mixtures of zirconium oxide or rare earth oxides (Nernst source) heated by Joule effect by the means of an internal resistor (for example Globar ). These sources are heated to 1500 °C, without a protective shield. They dissipate power of the order of a hundred watts by emitting radiation over a large domain ranging from visible to thermal IR. A maximum is observed for A = 3000/T (A in... 

A. Baraka, A.J. Abdel-Rohman and E.A. El-Taher, The Use of Zirconium/Zirconium Oxide Electrode as an Indicator Electrode in Potentiometric Acid-Base Titration in Fused Potassium Nitrate, Mater. Chem. Phys. 9 (1983) 583-595. 

One of the processes for extracting zirconium from the mineral zircon (ZrSi04) is to fuse the mineral with limestone or dolomite. The reaction product disintegrates on cooling into powdered calcium silicate and coarse crystals of calcium zirconate (equation 12.7). The zirconate is dissolved in acid and converted into zirconium salts or zirconium oxide, much of which are converted into the corrosion-resistant zirconium metal [12.38]. 

Boron nitride Silica, fused Zirconium oxide fiber, high strength Boron nitride... 

Another type of inorganic matrix that is similar to controlled-pore glass but considerably less expensive can be prepared by fusing inorganic compounds such as finely pulverized silica and zirconium oxide to form a porous body. Although the pore distribution is less imiform, the surface composition is almost imiform in the case of silica, the surface is nearly 100% silica. Controlled-pore... 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

An important iadustrial use of NaH involves its in situ formation ia molten NaOH or ia fused eutectic salt baths. At concentrations of 1—2% NaH, these compositions are powerful reducing systems for metal salts and oxides (5). They have been used industrially for descaling metals such as high alloy steels, titanium, zirconium, etc. 

Mixed zircon, coke, iron oxide, and lime reduced together produce zirconium ferrosiUcon [71503-20-3] 15 wt % Zr, which is an alloy agent. Fused zirconia [1314-23-4] has been made from zircon but baddeleyite is now the preferred feed for the production of fused zirconia and fused alumina—zirconia by electric-arc-fumace processing. 

Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

Black body radiators are used as sources of infrared radiation in the range 2-15 yum, e.g. the Nemst glower, which consists of a hollow rod made of the fused oxides of zirconium, yttrium and thorium. For use it is preheated and, when a voltage is applied, it emits intense continuous infrared radiation with very little visible radiation. 

Zirconium may lie removed hy fusing the oxides with KIlFj and extracting with water acidified with UK. The zirconium dissolves, forming K-ZrK, hut both < thorium fluorides are insoluble,... 

CHEMICAL PROPERTIES most zirconium compounds are considered inert zirconium metal can react with hydrofluoric acid, aqua regia, and hot phosphoric acid attacked hy fused potassium hydroxide or potassium nitrate not attacked by cold, concentrated sulfuric or hydrochloric acid resistant to attack by nitric acid very resistant to corrosion oxidizes rapidly at 6°C nitrided slowly at 700°C compact form combines with oxygen, nitrogen, carbon, and the halogens on prolonged heating FP (NA) LFLAJFL (NA) AT (NA) HF (0.0 kJ/mol crystal at 25 C) Hf (21.0 kJ/mol at 2127.85K). 

The reduction of zirconium tetrachloride in a carrier salt with sodium as a reducing agent may be examined next. Again, as described before, complete deoxidation of the bath before reduction is the essential condition for success, if ductile metal is wanted. Zirconium tetrachloride is soluble in sodium chloride or potassium chloride (48) and a salt with about 25% zirconium tetrachloride can be melted without excessive zirconium chloride losses. Such a bath can even be obtained from powdery commercial zirconium silicide and iron dichloride, which react when heated and deliver a stream of zirconium tetrachloride, contaminated with some titanium tetrachloride and silicon tetrachloride. The gas so produced can be condensed in a fused salt bath such as potassium chloride-sodium chloride, in which only the zirconium tetrachloride dissolves (47), To obtain a low oxide metal after reduction with sodium, the conditions for fluo salt deoxidation must be observed. This process of zirconium production has no special interest, except for obtaining powder for getter purposes. A carrier salt, which might introduce oxide, is not wanted, as the reaction itself liberates sodium chloride. 

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