CS208537B1 - Transparent corundum - Google Patents

Description

(54) Transparent corundum

The present invention relates to transparent corundum obtainable from alumina powder by compression and high temperature sintering.

Transparent corundum products are prepared by high-temperature sintering of extruded high purity alumina powders. The desired physical properties of the products, in particular the optical permeability, are achieved by a suitable particle size of the alumina powder and by the addition of impurities which retard the growth of crystalline grains during high temperature sintering. As a dopant is generally used MgO, NiO, Cr ₂ O _2, TiO _3, CeO _z, V ₂ O _5, some rare earth oxides, and optionally also the two component systems such as to Ex. MgO, Y ₂ O _3, MgO, CaO or MgO, TiO ₂ . These impurities improve the optical and possibly mechanical properties of the products even in small concentrations.

However, corundums modified by known additive systems have some drawbacks, in particular insufficient optical transmittance for some applications.

Some of these drawbacks are overcome by the transparent corundum of the present invention, which consists in containing up to 0.5 wt. an admixture system comprising 1 to 10 wt. parts of calcium oxide, 50 to 500 wt. parts of titanium dioxide and 250 to 4000 wt. parts of magnesium oixd. The transparent corundum according to the invention preferably further comprises yttrium or scandium oxide in a weight ratio to magnesium oxide of at most 3: 1, the total amount of magnesium oxide and yttrium oxide or scandium oxide in the admixture system being 250 to 4000 wt. parts. The transparent corundums of the invention exhibit better properties than the prior art corundums. Pre-burnt moldings exhibit greater machining resistance and sintered products have higher optical transmittance (about 91-93%, measured on an Ulbrecht photometer).

Example 1

From powdered Al ₂ O ₃ with an admixture of 0.002 wt. % CaO, 0.01 wt. % TiO ₂ and 0.16 wt. % MgO were produced by corundum transparent tubes by a known process of pressing, preheating, machining and high temperature sintering, which exhibited an average transmittance of 2% / higher in the visible spectrum over the same products with a one- or two-component admixture system prepared by the same manufacturing process. At the same time, the reject rate in the treatment of over-baked products fell by 20 percent.

Example 2

Of powdered Al ₂ O ₃ with an admixture of 0.0008 wt. % CaO, 0.005 wt. % TiO ₂ , 0.12 wt. % MgO and 0.04 wt. % Y ₂ O ₃ were the same procedure as in Example 1 produced a transparent alumina tube, which showed about 3% more throughput than the same products with the two-component system jednoči impurities.

The shrinkage in the machining of the preheated moldings decreased by 20 ° / o.

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Example 3 and 4 Sc ₂ O ₃ had the same characteristics. The products of Example 2 also had the same properties,

The products of Example 2 wherein 0.02 wt. % Y ₂ O ₃ and 0.02 admixture Y ₂ O ₃ replaced by the same amount of wt. % Sc ₂ O ₃ .

Claims (2)

SUBJECT OF THE INVENTION 1. Transparent corundum, characterized in that it contains up to 0.5 wt. an admixture system comprising 1 to 10 wt. parts of calcium oxide, 50 to 500 wt. parts of titanium dioxide and 250 to 4000 wt. parts of magnesium oxide. 2. The transparent corundum of claim 1, further comprising yttrium and / or scandium oxide in a weight ratio to magnesium oxide of not more than 3: 1, the total amount of magnesium oxide and yttrium oxide or scandium oxide in the yttrium or scandium oxide in the admixture system. 250 to 4000 wt. parts.