RU2023751C1 - Liquid for chemical polishing of niobium - Google Patents

Abstract

FIELD: chemical working of metals. SUBSTANCE: liquid for chemical polishing of niobium has, wt.-%: hydrofluoric acid (40%) 5.6-6.2; sulfuric acid (98% ) 56.3-46.9; nitric acid (69%) 25.2-25.7; carbamide 0.5-1.5, and water 20.8-21.3. EFFECT: enhanced quality of liquid. 4 tbl, 4 dwg

Description

 The invention relates to the chemical treatment of metals, in particular to the polishing of niobium, and can find application in the chemical polishing of various parts of particle accelerators in order to impart a mirror surface.

 Electrolytes are known for chemical polishing of niobium surfaces, the basis of which is hydrofluoric acid HF in combination with other acids, for example, with lactic and concentrated sulfuric acid [1] or nitric acid [2]. The disadvantage of these electrolytes is a slight removal of metal from the surface of the workpiece.

As a prototype of the selected electrolyte, consisting of a mixture of hydrofluoric, sulfuric, nitric acids and water [3]. The disadvantage of its use is the need for strict maintenance of technological modes, which in practice is quite difficult. Polishing is recommended at a temperature of from 40 to 70 ^C. At a temperature up to and above ^{70 °} C causes increased loss of volatile components, thereby deteriorating polishing properties of the electrolyte, and therefore is not uniform metal removal, and etching. In addition, the removal rate of deformed surfaces is negligible.

 The aim of the invention is to increase the removal rate of the deformed layer and improve the quality of polishing by increasing the stability of the solution.

The goal is achieved in that the solution containing hydrofluoric, sulfuric, nitric acid and water additionally contains urea in the following ratio of components, wt.%: HF (40%) 5.6-6.2 H ₂ SO ₄ (98%) 46 3-46.9 HNO ₃ (69%) 25.2-25.7 Urea 0.5-1.5 Water 20.8-21.3
The claimed technical solution meets the criterion of "Novelty", since the prototype electrolyte is missing one of the components - urea.

, где Δ h - изменение толщины удаляемого металла с поверхности, см;
S - площадь поверхности металла, см²;
Δ m - изменение массы металла, г;
d - плотность ниобия 8,57 г/см³.Urea is introduced into an aqueous solution of hydrofluoric and nitric acids, and then sulfuric acid is added in small portions, after which the solution is thermostated. The experiments were carried out in a temperature-controlled teflon cell with periodic rise of the polished sample. Lifting frequency 15 s. Full cycle time 15 min. The metal removal was controlled by measuring linear dimensions and weight loss. The calculation of the mass loss was carried out according to the formula
Δh =

where Δ h is the change in the thickness of the removed metal from the surface, cm;
S is the surface area of the metal, cm ² ;
Δ m is the change in mass of the metal, g;
d is the density of niobium 8.57 g / cm ³ .

In all cases, niobium plates (rolled) S = 14 cm ^{2 were} used as samples for polishing. Chemical polishing carried out in the following solutions at 40, 50, 60 and 70 ° ^C.

Solution N 1 (prototype) contains components: ≈ 5.9 wt.% HF, ≈ 25.5 wt. % HNO ₃ , ≈ 47.3 wt.% H ₂ SO ₄ and ≈ 21.3 wt.% H ₂ O.

Solution N 2 contains components, wt.%: HF (40%) 5.9; H ₂ SO ₄ (98%) 46.9; HNO ₃ (69%) 25.5; urea 0.5 and water 21.2.

Solution No. 3 contains components, wt.%: HF (40%) 5.9; H ₂ SO ₄ (98%) 46.6; HNO ₃ (69%) 25.5; urea 1.0 and water 21.0.

Solution No. 4 contains components, wt.%: HF (40%) 5.9; H ₂ SO ₄ (98%) 46.3; HNO ₃ (69%) 25.5; carbamide 1.5 and water 20.8.

 The invention is illustrated by several examples presented in table. 1-4, which shows the results of polishing niobium wafers.

EXAMPLE EXAMPLE 1. A solution of N 1 (prototype) 100 ml thermostated at a temperature (40 ± 0,5) ^C, (50 ± 0,6) ^C, (60 ± 0,8) and ^C (70 ± 1.0) ^о С, then plates for chemical treatment were placed in it for 15, 30, 45, 60 and 75 minutes. The dissolution of niobium depending on the temperature of the electrolyte occurs almost linearly (table. 1). With temperature variation from 40 to ⁷⁰ ° C increased solubility in 1,3-1,75 times. The surface roughness achieved R _a = 0.38-0.22.

PRI me R 2. Solution N 2 tested under the same conditions as solution N 1. In solution N 2 in relation to the prototype (solution N 1), the solubility increased at 40 ^about 1.5 times, at 50 ^about 1.7 times, at 60 ^about 1.7 and at 70 ^about 1.3 times. The surface roughness achieved R _a = 0.35-0.29.

PRI me R 3. Solution N 3, the test conditions are the same. With respect to the prototype niobium increased solubility ^at 40 ° C by 1.2 times ^at 50 ° C by 1.9 times at 60 ° ^C and 2.09 times at ⁷⁰ ° C in 3.2 times. The surface roughness achieved R _a = 0.28-0.20.

PRI me R 4. Solution N 4, the test conditions are the same. With respect to the prototype niobium increased solubility ^at 40 ° C by 1.5 times ^at 50 ° C by 1.8 times at 60 ° ^C and 1.6 times at ⁷⁰ ° C in 1.3 times. The surface roughness achieved R _a = 0.35-0.28.

 In FIG. 1-4 are graphs of the progress of the polishing process for the corresponding temperatures and quantitative content of urea.

The proposed solution is easy to prepare and allows chemical polishing to reduce the surface roughness of niobium. An added urea component is available. The removal of metal compared with the prototype increases by 3.2 times. Advantageously, the electrolyte is that the chemical polishing must be carried out in a 3 N solution, at temperatures of 50-55 ^{° C} instead of 70 ^C, thereby reducing the toxicity of the gas medium due to lower volatility components.

Claims (1)

A solution for the chemical polishing of niobium, containing hydrofluoric, sulfuric and nitric acids and water, characterized in that it additionally contains urea in the following ratio, wt.%:
Hydrofluoric acid (40%) 5.6 - 6.2
Sulfuric acid (98%) 46.3 - 46.9
Nitric acid (69%) 25.2 - 25.7
Urea 0.5 - 1.5
Water 20.8 - 21.3

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