CS253693B1 - Process for the etching of solid substance,containing aluminium ions - Google Patents

Abstract

A method of etching a solid in water insoluble, containing aluminum ions, by a process which avoids the formation of insoluble pollutants adhering to the surface substances that can be easily cleaned surfaces, with the choice of temperature and concentration etching solution can be achieved either high chemical purity and / or optical an etched surface permeability, suitable for example for cleaning products from single crystals corundum or phosphate photoluminescent glass by etching the surface in a solution prepared from 60 to 99% by weight of the acid phosphorous H3PO4 and / or sulfuric H28O4 and 1 to 40 hipot. % of water with such addition boron and lithium compounds to keep in solution during etching, the mass ratio of ions was aluminum, boron and lithium Al3 +: B3 + 3 and Al3 +: Li112, possibly without this formulation when the composition the etched material corresponds to the above weight ratio of aluminum, boron ions and lithium.

Description

The present invention relates to a process for etching a water-insoluble solid containing aluminum ions by a process which avoids the formation of insoluble etch products adhering to the surface of the fabric.

Alumina is used as a starting material for a variety of products, such as monocrystals, ceramics, glass, and the like.

During the preparation or processing of these materials, their surface is contaminated, where the impurities are so strongly bound that the use of simple physical processes is not sufficient to finish the surfaces. This deteriorates not only the utility properties of the products concerned, but in many cases the dimensionally or otherwise unusable parts cannot be used as a raw material for the preparation of a new batch. For this reason, it is necessary to etch the surface of the water-insoluble substances containing aluminum ions. Sulfuric acid and, in the case of chemically particularly resistant materials, phosphoric acid, in particular at elevated temperatures, are preferably used as the etching bath. If, however, the etching bath and / or the etched material contains phosphate ions in higher concentrations, islets generally adhere to the surface of the etched material or thin but continuous aluminate phosphate coatings, which is detrimental both to the purity of the transparent surface and chemical purity because the resulting reaction product prevents the surface layer from being etched.

The aforementioned drawbacks are eliminated by the process of etching a solid containing aluminum ions according to the invention, which consists in that these surfaces are etched in a solution consisting of 60 to 99% by weight of phosphoric acid H 2 PO 4 and / or sulfur253 693

1 to 40% by weight of water and an amount of boron and lithium compounds such that the weight ratio of the ions is in the solution during the etching. AI ♦ B ^ ⁴ 3 & Al ^ ⁴ with Li ⁺ 12.

jl 1

Ions of B and Li fable ionic radius smaller than the ions of Al ^ ⁴ so easily enter the lattice of aluminum phosphate, which then contains defects, which should lead to a slight adhesion to the surface of the etched substance 'against pure aluminum phosphate. The dopant ions, ^B-4, "for example in the form of boric acid and ions of Li ⁴ for example in the form of lithium carbonate is not necessary to the etching solution adding time when boron or a lith microns is present in the etched substance in such a quantity that the weight ratio ^Al-4 to B ⁴ 433 and Al £ ^{4 with} i ⁺

12, also applies to it.

Etching is then released into a solution of ions of ^{Al-4, B-4,} and if at the same relatively ions _R u B * ^, borates or Li ⁺ and prevent the formation of a coherent aluminum phosphate on the surface of the etched material and then etching can be performed at high speeds.

By the method of the invention, the surfaces of the materials containing aluminum ions can be easily cleaned, and by selecting the temperature and the concentration of the etching solution, one can achieve high chemical purity and / or optical permeability of the etched surface.

Example 1

The single crystals grown by the Verneuil method of sapphire had an opaque surface due to the adherence of particulate alumina particles to the crystals during cultivation. Therefore, it was not possible to determine the content of internal defects in single crystals, even by using immersion. Therefore, the single crystals were purified by etching in a mixture consisting of 10 wt% sulfuric acid HgSO 4 98 # and 90 wt% phosphoric acid H 4 PO 4 85 #. The etching was carried out by heating the monocrystals in the acid mixture at 250 DEG C., which was achieved in 1 h and held at this temperature for 1/4 h. After cooling, the monocrystals were rinsed with water and their surface was mostly well transparent but exhibited numerous solids adhering islets of foreign phase whose X-ray analysis showed that it is aluminum phosphate A1P0 / *

-3253 693

The etching mixture used was practically clear. However, if, according to the invention, 8g of boric acid 1.4gB4 ⁺ and 2g of lithium carbonate corresponding to 0.375g of Li were added per 1000 ml of the acid mixture according to the invention, the surface of the single crystals was completely clean after the etching. Analysis of the etching mixture after etching showed that in 1000 ml it contained 4.2 g of Al @ ^{+ +} , corresponding to the weight ratio of Al @ ⁺ : B @ ⁺ = 3 and Al @ ⁺ : Li @ ⁺ = 11.2. Only at a higher content of aluminum ions deposited on the surface of the single crystal.

Example 2

The post-luminescent glass having a composition of 50% by weight of aluminum phosphate Al (PO4), 25% by weight of potassium phosphate (KPO4),% by weight of barium phosphate (BaCPO2), and 5% by weight of silver phosphate AgPO4 was surface-cleaned abrasives after cutting and sanding by etching in phosphoric acid 60% at a temperature of 75 to 85 ° C after a shake time of 60 min. In order to prevent the individual pieces of glass from sticking together, they were placed separately on a Teflon grid. Boric acid H ₃ BO ₄ was added to the phosphoric acid in an amount of 10 g / 1000 ml, ie 1.75 g B ³⁺ / 1000 ml, and lithium carbonate in an amount of 3.2 g / 1000 ml, ie 0.6 g Li ⁺ / 1000 ml. The etching took place even after repeated use of the same etching bath without defects up to the concentration of aluminum ions to approximately

5.3 g of Al2O / 1000 ml, corresponding to a weight ratio of Al2 ⁺ : B4 ⁺ = 3 and Al2 +: Li + 8.8. As the concentration of aluminum ions exceeds this limit, insoluble coatings composed predominantly of the AlPO4 phase were formed on the glass surface even at the first use, even if the aluminum phosphate content in the glass was up to 1/3 lower. Naprotitome of glass, where the potassium phosphate content of KPO ^ was reduced by 10% and this loss was replaced by 10% of the total amount by boron oxide and 5% by lithium phosphate, after etching with regard to the boron and lithium ions, co-infused with aluminum ions, a completely clean surface without any foreign phase particles, since the weight ratio of Al4 and Al4 ⁺ : Li ⁺ was 1.63: 1 and 5.57: 1, respectively. The same results were also obtained for glass using boron oxide replacing barium phosphate and 1-lithium phosphate are substituted for potassium phosphate.

Instead of the above brief heating up to 85 ° C, etching at 20 ° C for 24-36 hours could be used with similar results.

Claims (1)

A process for etching a solid containing aluminum ions, characterized in that its surface is etched in a solution containing 60 to 99 wt% phosphoric acid H 2 PO 4 and / or sulfuric H 2 SO 4 and 1 to 40 wt% water and such an amount of compounds of boron and lithium so that the weight ratio of aluminum, boron and lithium ions is in the grate during the etching process « Al ³ *: B ³⁺ 3 and Al ³⁺ Li Li ⁺ 12.