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Experimentation of brazing alloy of gold and silver used in jewelry, manufacturing industry, and in medical purpose.

1. INTRODUCTION

This paper present the first steps in testing of some alloys for pretious metals brazing, in specific environment using this metals. The experiments follow to replace the chemical polishing witch is made at the end of all manufacturing operations, finishing that polishing of articles intended for direct and prolonged contact with skin.

This polish is being made by cathode deposit of ionic decomposition in specific electrolyte for gold and silver, straight on the surface of the pieces, by the interlude of electricity. This metallic cover provided by the series SR EN ISO 27874:2009 is used for design and also to maintain the same colour of the alloy used for brazing, with the brazed metal. Testing: To this purpose gold and silver were chosen as the basis for pasting, materials used nowadays mainly for producing objects that touch the skin directly.

The gold on which the brazing was done has 585 purity, which is 14 karat. This alloy is made of 58.5% fine gold, 20.8% fine silver and 20.9% copper alloy mainly used in the producing industry of the jewels. The silver on which the pasting was done has 925, purity and is made of 92.5% fine silver, 15% copper, also used in the producing industry of the jewels (Feraru et al., 2009).

2. OUTPUT OF TESTS

The tests were being made on gold and silver brazed with an alloy based on gold and silver. Their dimensions were 2mm length on a 2mm width and were brazed with the flame from a lamp with aspiration using butane for the gas. The flux used was borax, and the pickling of the tests was done in a solution of sulphuric acid diluted with distilled water in a proportion of 30% acid, and the rest of 70% water.

For gold, the brazing alloy contains: 40% gold with the same title as the brazing material, 20% silver, 15% zinc and 5% copper; and also gold brazed with an alloy witch contains: 60% silver and 40% zinc. The brazing was done at a 700[degrees]C temperature for the tests brazed with an alloy with a gold basis, and a 600[degrees]C temperature for those tests brazed with an alloy with a silver basis. The tests that were done for the microscopic analysis represent head to head brazing and the overlapping brazing of two golden plates (Feraru et al., 2008). The silver tests were done by brazing the silver brazed with an alloy with silver like base made of 60% silver with the same title as the brazing material, 30% zinc and 10% tin, and for gold brazing was also used in this case. The brazing was done at a 540[degrees]C temperature for the alloy on a silver basis and 700[degrees]C temperature for the alloy on a gold basis (Feraru et al., 2008).

The pickling after the brazing was done in the same solution as the one for the gold.

3. OBSERVATION OF THE BRAZING TESTS

During a visual analysis, at the gold tests brazed with an alloy based on gold, a good quality join can be seen. The alloy used for brazing performs very well all the tasks given for a quality paste. A good fluidity of the alloy and a superior flow of this alloy can be noticed during the brazing like in fig.1, and 2. At the tests pasted with the alloy on a silver basis, during the visual analysis, a good quality join can be seen, while during the brazing there can be seen the nice flow of the alloy that fills very well the joining point.

At a microscopic view there is a good quality join and a nice flow of the alloy that can be noticed, the alloy being able to fill in properly the joining place, it can be seen in fig.3.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

At the silver tests brazed with a silver based alloy, after a visual analysis, there can be seen a good quality join and the brazing alloy fills in very well the place to braze. At the tests brazed with gold basis alloy there is quite a nice join and a quite a nice flow, but the paste of silver and the alloy on a gold basis being very hard to make, unless it was done by a highly experienced operator, because this one is very important to participate due to the high temperature on which the pasting was done, temperature close to the one of silver's melting point.

Under the microscope there can be seen a very nice flow of the adding material and a nice filling of the pasting point, fig.4. At the view of the test pasted with a gold basis alloy, there can be seen a very good quality join, the adding material having a nice flow, fig.5.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

4. PREPARING THE SAMPLES

Preparing the samples to be tested in different solutions specific to the environment where the jewels are worn. In the human body there are numerous biological liquids: blood, urine, digestive secretions, pleural liquid, cephalo-rahydian liquid, synovial liquid, sweat, amniotic liquid etc. These spangles get into direct contact with the skin and has interferes for a long time with the sweat.

To imitate the body sweat a salted solution is being prepared from NaOH and NaHCO3, diluted in water with an addition of CH3-COOH. In this solution the samples previously prepared are being put and after 12 hours a visual analysis is done. There can be noticed very easily that after the gold test, the colour of the brazing alloy on a gold basis did not change comparing to the brase metal, while the microscopic scan shows that this alloy dos not change its colour more than the basis material it can be seen in fig.6. The same thing can be seen after the tests with the samples of silver pasted with a silver basis alloy, except that this one oxidizes in a natural manner when it gets into contact with the skin, just like when it gets into contact with the solution where it was put, this is showed in fig.7 and 8.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

5. CONCLUSION

For all those microscopic analysis, I used a video microscope, tipe: MVM. 100, with a 150 objective.

After the performance and the analysis of the brazed samples there can be seen a pasting highlights quality in both cases of gold brazing with an alloy of a gold basis and the brazing with an alloy of a silver basis and also in the case of brazed silver. These brazing alloys respond well a the flame brazing but also to how they behave in direct contact and long lasting body

In conclusion, the alloys tested in a salted solution have the same behaviour as the basic material, the latter being able to replace the later galvanic covering of the jewels, and the object used for medical purpose. In this maner the price of those articles is one thousand small. Those analysis is the first step in testing the behavior of these alloys in acid solutions. Further, take into consideration the submission of evidence in testing solutions such as strongly acidic and highly oxidizing environments, and subjecting them to a different microscopic analysis with an even stronger, thus determining the degree of deterioration of the alloy used for brazing those samples. These tests aim to having determined the possibility of loose galvanic coatings on noble metals

6. REFERENCES

Feraru V.L; Trif I.N & Galea A, (2009). Metalurgia International Vol.14; No.2 (February 2009); pp 207-210, ISSN 1582-2214

Feraru V.L; Dozescu S.&Trif I.N. (2008). Safety and Reability of Welded Components in Energy and Processing Industry (P.Mayer Institute for Materials Science and Welding Graz

University of Tehnology) pp 725-728. ISBN: 978-3-85125-019-0, Austria, July 2008, Published by Verlang der Technishen Universitat, Graz

Feraru V.L, Baxin A, Lazar C & Trif I.N (2008). Tehnology and Quality for Sustained Development No.8. (October, 2008) pp 417-420, ISSN: 1844 -- 9158

*** (2004) http://www.metaconcept.fr-Brasure Forte Accesed on: 2008-11-16

*** (2006) http://www.lucasmilhaupt.com-Everything About Brazing Accesed on: 2009-03-14

*** (2009) http://www.top-referate.ro-Echilibre Acido-Bazice

In Organismul Uman Accesed on: 2009-06-12 *** (2009) http://www.asro.ro -- Colectii Standarde Accesed on: 2009-06-06
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Author:Feraru, Lucian; Galea, Adrian; Uncu, Ionut; Rosca, Maria Herascu; Trif, Nicolae
Publication:Annals of DAAAM & Proceedings
Article Type:Report
Geographic Code:4EUAU
Date:Jan 1, 2009
Words:1404
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