Material for production of assay stone

FIELD: material for production of assay stone, in particular standard determination.

SUBSTANCE: assay stone is made from oxide ceramic comprising BeO-TiO₂. Material affords the ability to obtain assay stone of regular geometric form with surface, electrical and mechanical properties meeting the requirement for material used in assaying control. Claimed material in useful in standard determination followed by electrochemical recovery of precision metals from solution after assaying control.

EFFECT: material of homogeneous structure; decreased time of precision metal recovery after assaying control.

The invention relates to materials for the manufacture of touchstone and can be used to determine the fineness of precious metals, then getting their electrochemical method from solutions after surgery assay control.

Known material for touchstone when determining the fineness of precious metals from natural siliceous material (Baryshnikov I. Probootborniki and analysis of noble metals. M.: metallurgy, 1986, str-235), which has high hardness, deep blacks and sufficient chemical hardness, the material is suitable for the electrochemical dissolution of metals from their subsequent extraction by electrolysis.

However, due to the heterogeneity of the structure of a natural material, which has inclusions of quartz and cracks, firstly, on some parts of the stone dissolution of metal is difficult due to changes in the chemical composition of the stone under the influence of the electrolyte, which, in turn, increases the duration of the process, and secondly, difficult to manufacture touchstone of regular geometric shape, necessary for carrying out the assay control.

Thus, the authors were quite concerned when determining the fineness of precious stones using touchstone, the material of which the poison with high hardness and chemical resistance has a homogeneous structure.

The problem is solved by applying a ceramic carbide or oxide type as the material for the manufacture touchstone when determining the fineness of precious metals.

Currently, oxide ceramics and carbides of the type widely used in special technique in the manufacture of high temperature nozzles of rocket engines and as a structural material, working in conditions of high temperatures and abrasive wear (Handbook "Refractories for space", M.: metallurgy, 1967, p.46-77; 84-103; 107-162).

The use of ceramic oxide and carbide type as a touchstone when determining the fineness of precious stones became possible after the authors of the studies electrolytic resistance ceramics specified in respect of the electrolytes used for transferring the precious metals in solution after carrying out the assay control. As it was established during the research, oxide ceramics and carbide type along with high hardness (for example, SiC and Al₂O₃have hardness 9-10 on the Mohs scale) and give it any desired geometric shape has high chemical resistance to chemically aggressive electrolyte.

Assay control is carried out for gems by well-known methods Baryshnikov IVAN Probootborniki and analysis of noble metals. M.: metallurgy, 1978, pp. 410-417). For the operation of assay control take 15 pieces assay stones, made of ceramic carbide type SiC composition, and 15 pieces of assay stones, made of ceramic oxide type composition of beryllium oxide - titanium oxide. Carbide SiC ceramics is characterized by the density 3,18 g/cm³has a hardness of 9 units on the Mohs scale and high chemical stability. Oxide ceramic BeO-TiO₂characterized by the density 2,80-2,99 g/cm³has a hardness of 7-9% on the Mohs scale and high chemical stability. Ceramics both types easily sanded and polished 12-14 class. The surface roughness of the stones Ra of 0.5; volume resistivity 2·10²-8·10⁵Ohm·see the Operation of assay control is as follows. On the prepared surface touchstone applied the test object (product, metal, alloy) homogeneous dense strip length of 15-20 mm and a width of 2-3 mm Near the feature causing the same strip assay needle from alloys of gold, silver, platinum or palladium, a suitable composition of the sample and the same color of the alloy. Put strips with a glass rod moistened across the appropriate reagent (a solution of chloride of gold, a solution of nitrate of silver and others), resulting in 15-20 on line spot appears in intensity of colouring which, when compared with the color spots on the strip reference assay needle, judge the fineness of the gold, silver or platinum group metals. If the resulting spots on the strips will be the same intensity, it is considered that the fineness, products or nugget is identical to the sample corresponding number of the probe needle. If the reagent at low sample completely dissolves the test strip of metal, it is considered that the analyzed sample does not contain the appropriate alloy of gold, silver or platinum group metal.

After surgery assay control assay stones subjected to extraction operations with them are precious metals (gold or silver, platinum or palladium) by electrolytic recovery. This assay stones deposited on the surface of gold or silver is placed in a solution containing 50 g of thiourea and 55 g of sulfuric acid in 1 l of water, and is connected to the positive pole of the current source. The cathodes of titanium alloy size 160×140×3 mm is connected to the negative pole of the current source. The dissolution is carried out at an anode current density of 25 a/m²within 4-10 minutes until complete dissolution of the gold or silver from the surface of the stones that is determined visually. Probin the e stones with their surface alloys of platinum and palladium are placed in a solution, containing 20 g/l of hydrochloric acid and is connected to one pole of the AC source frequency of 50 Hz. Protivoelektrodom graphite size 160×140×10 mm is connected to the other pole of the current source. The dissolution is carried out at a current density of 50 a/m²within 15-20 minutes until complete dissolution of the platinum or palladium alloy. The amount of dissolved metal is determined by the difference of mass assay stones before and after surgery assay control. After accumulation in the solution of ions of precious metals in the amount of 0.3 g/l solution served in the cathode chamber of the electrolytic cell flow type in which carry out the extraction of precious metals by electrolysis.

Thus, the use of ceramic oxide or carbide type in the manufacture of touchstone allows to obtain assay stone of regular geometric shape and surface, and electrical and chemical characteristics that satisfy the requirements of materials for carrying out the assay control. In electrochemical dissolution of precious metals assay stones see uniform dissolution of metal across the surface of the stone due to the homogeneity of its structure, which contributes to the reduction in the duration of the extraction of precious metals after surgery assay control.

Assay stone, made of a material based on aluminum oxide ceramics, characterized in that it is made of ceramic oxide composition BeO-TiO₂.