RU102938U1 - PLATINUM WIRE FOR THERMOSENSITIVE ELEMENTS, FOR EXAMPLE THERMOCOUPLES AND RESISTANCE THERMOMETERS - Google Patents

Abstract

 1. Platinum wire for heat-sensitive elements, such as thermocouples and resistance thermometers, containing a body made of dispersively hardened barium oxides of high purity platinum, which provides its temperature coefficient of electrical resistance, for example, not lower than 3.830 · 10-3 1 / deg, characterized in that barium oxides are contained in the amount of (0.08-0.15) vol.% and formed by the size of (4-7) 10-8 m by applying a solution of barium salts to the surface of the body and their decomposition during annealing and introduced into the body volume at forged. ! 2. A platinum wire for thermosensitive elements according to claim 1, characterized in that the barium oxides are formed by depositing a solution of barium nitrate on the surface of the body and its decomposition during annealing.

Description

The utility model relates to the metallurgy of noble metals, namely: dispersively hardened platinum in the form of a wire for heat-sensitive elements, such as thermocouples and resistance thermometers.

It is known that platinum, characterized by heat resistance, resistance to erosion and a high thermal coefficient of resistance, in the form of a wire is widely used for working at high temperatures as a material for heat-sensitive elements.

So, platinum wire is known for thermosensitive elements in resistance thermometers: USSR No. 101198, G01K 7/01, s. 11.26.54., A.S. USSR No. 147005, G01K 7/01, s. 07/10/61., A.S. USSR No. 153585, G01K 7/01, s. 01/29/62, A.S. USSR No. 197116, G01K 7/01, s. 05.31.65., Utility model of the Russian Federation No. 78933, G01K 7/18, op. 12/10/08.

Also known is platinum wire for thermosensitive elements in thermocouples: USSR No. 319854, G01K 7/02, s. 05.05.70., A.s. USSR No. 360365, G01K 7/02, s. 11/28/72, A.S. USSR No. 1068736, G01K 7/02, s. 11/17/82.

However, a disadvantage of the known platinum wire for thermally sensitive elements is its low mechanical strength at high temperatures. The high purity of platinum in the known wire reduces its recrystallization temperature, as a result of which relatively low temperatures and efforts in the manufacture and operation of the wire cause its destruction.

High demands are made on the platinum wire for thermosensitive elements over the entire range of properties: strength, both at room and at elevated temperatures, ductility, and temperature coefficient of electrical resistance.

Known platinum wire for heat-sensitive elements, containing a body made of high purity platinum: "Production and operation of products from precious metals and alloys", collection of articles, Sverdlovsk, ed. UC AN USSR, 1983, p. 16, 17; A.S. USSR No. 538753, B21C 1/00, s. 05/29/75., Op. 12.15.76., GOST USSR 18389-73 "Wire made of platinum and its alloys", TU, effective from 01.01.74, as amended on 05.24.2001; GOST USSR 21007-75 "Platinum wire for resistance thermocouples", TU, effective from 01.01.76, as amended on 11.21.97, interstate GOST 10821-2007 "Platinum and platinum-rhodium alloy wire for thermoelectric converters", valid since June 1, 2008

The known wire exhibits thermoelectric properties corresponding to standard values, but has an insufficient level of mechanical characteristics due to a decrease in the temperature threshold of recrystallization due to the high purity of platinum and the absence of any platinum hardening agents.

Also known is platinum wire for thermosensitive elements, the material of which is platinum alloyed with non-ferrous metals such as niobium or tantalum (China Post No. 1067962, G01K 7/02, op. 13.03.96.), One element from a number: copper, aluminum , yttrium, nickel, cobalt, titanium, vanadium, silicon, zirconium, calcium, palladium, rhodium, ruthenium, iridium, gold, silver or osmium (AS Japan No. 1039335, C22C 5/04, op. 09.02.89. ), strontium (Japanese high school No. 2009-287077, C22C 5/04, op. 10.12.09.), platinum rhodium metal (A.S. USSR No. 1362958, G01K 7/18, op. 30.12.87 ., p. US No. 3926681, H01L 35/20, op. 16.12.75.).

In known wires, the alloying of platinum, although partially increasing its mechanical characteristics, does not increase their thermoelectric properties, in particular, the thermoelectric coefficient of electrical resistance, and even reduces them. This is due to the fact that the body’s ability to transmit electric current depends on the structure of the metal-platinum, the distortions arising in it due to alloying. During alloying, the dynamics of charge carriers changes, and in the platinum of known wires it changes in such a way that the thermal coefficient of electrical resistance decreases.

Also known is platinum wire for heat-sensitive elements (Japanese high school No. 52-49940, B21F 19/00, op. 21.04.77.), The body of which is made of a core consisting of a heat-resistant fiber of silicon carbide or silica fiber, or of any kind fibrous ceramics with low electrical conductivity, and has a thin coating of platinum.

However, in the known wire, the coating has a very small thickness and already at the beginning of operation of such a wire decreases and disappears, and the wire ceases to work as a thermoelectric.

Also known is a platinum wire for heat-sensitive elements, the body of which is made of fibrous platinum ("Noble Metals", a reference edited by Savitsky EM, Moscow, publ. Metallurgy, 1984, p. 37).

However, the known wire, having thermoelectric properties within the standardized values, does not have sufficient mechanical characteristics due to the heterogeneity of its structure formed from elongated grains along the direction of deformation.

Also known is a platinum wire for thermosensitive elements, the body of which is made of platinum with a fibrous structure, dispersively hardened by internal oxidation by barium oxide particles ("Noble Metals and Their Application", collection of articles. Proceedings of the Institute of Metal Physics, Ufa Scientific Center of the USSR Academy of Sciences, published by UV USSR Academy of Sciences , 1971, issue 28, p. 276).

However, the known wire, having thermoelectric characteristics at the standard level, does not have the required mechanical properties due to distortions introduced by the particles of the hardening phase into the uneven structure of the platinum grains elongated along the deformation.

In terms of technical nature and the achieved result, the closest to the claimed utility model is platinum wire for thermosensitive elements, such as resistance thermometers and thermocouples ("Noble Metals and Their Applications", collection of articles. Proceedings of the Institute of Metal Physics, UC AN USSR, ed. UV USSR Academy of Sciences , 1971, issue 28, pp. 272-273), containing a body made of dispersively hardened platinum barium oxides of high purity, which provides its temperature coefficient of electrical resistance, for example, not lower than 3.830 · 10 ^-3 1 / deg, namely: 3,915 · 10 ^-3 1 / deg.

Known platinum is strengthened in a cermet version due to mechanical alloying (book, E. I. Rytvin, “Heat Resistance of Platinum Alloys”, M., Metallurgy, 1987, p. 179): mixing the powder of the original platinum with the finished oxide powder barium. At the same time, platinum and barium oxide powders from the surface are contaminated with technological materials, for example, lubricant or extraneous metal particles. As a result, the platinum in the dispersion-hardened material of the finished wire is not clean enough, its thermoelectric property - temperature coefficient of electrical resistance, is lower than in the original platinum, although it falls into the range of standardized values according to GOST 21007-75, effective from 01.01.76 g . as amended on 11/21/97. In addition, the mechanical bonds arising at the boundary of barium and platinum oxides are not strong enough, since they are formed only due to the roughness of their combined surfaces, i.e. the nature of the hardening of the wire is mechanical. In this regard, the mechanical properties of the known wire, although slightly increased relative to the clean source platinum, are not high enough. This is also associated with a small amount of oxide component - 0.05 vol.% And its significant fineness - (15-20) · 10 ^-8 m, identified in the experimentally obtained known wire.

The problem to which the claimed utility model is directed is to create a dispersion-strengthened platinum wire for thermosensitive elements with a complex of high mechanical properties and meeting the requirements of standards of thermoelectric characteristics - temperature coefficient of electrical resistance, with values not lower than that of the original, unreinforced platinum.

The technical result is to increase the bond strength of barium and platinum oxides by creating a high chemical-mechanical interaction at their boundary while maintaining the purity of platinum at the initial level.

The problem is achieved in that in a platinum wire for thermosensitive elements, such as thermocouples and resistance thermometers, containing a body made of dispersively hardened barium oxides of high purity platinum, which provides its temperature coefficient of electrical resistance, for example, not lower than 3.830 · 10 ^-3 1 / hail, according to the utility model, barium oxides have a size of (4-7) · 10 ^-8 m and are contained in an amount of 0.08-0.15 vol.%, and are formed by applying a solution of barium salts to the surface of the body and decomposing them During subsequent annealing, they are introduced into the body volume during further forging.

In addition, barium oxides can be formed by applying a solution of barium nitrate to the surface of the body and its decomposition during subsequent annealing.

Ensuring the whole complex of high mechanical and thermoelectric properties of the wire is carried out by the presence of new parameters and characteristics of the elements of the device, as well as their relationship.

The essence of the proposed technical solution is as follows.

The presence of barium oxides formed by applying a solution of barium salts to the surface of the wire body and their decomposition during subsequent annealing - chemical alloying (book, E. I. Rytvin “Heat Resistance of Platinum Alloys”, M., “Metallurgy”, 1987, p. 179) indicates a high purity of both the surface of the wire and the surface of the oxide. This is due to the appearance of oxides directly on the surface of the wire as a result of a chemical reaction in the absence of any contaminants. Moreover, the dispersion-hardened platinum matrix has the purity of the original platinum, which corresponds to the coincidence of their temperature coefficients of electrical resistance.

At the boundary of barium oxide with platinum, it is possible that there is a strong adhesion of the phases brought into contact due to intermolecular interaction or chemical bonds, which are combined with their mechanical bonds. This contributes to a particularly strong adhesion of the phases and is characterized as chemical-mechanical hardening.

Moreover, the amount of oxides - (0.08-0.15) vol.% Can be considered insignificant, given that dispersion-hardened materials are, starting from 0.1 vol.% Of the hardening phase (book, D.M. Karpinos, “Composite materials in engineering”, Kiev, 1985, p. 56).

Small size: (4-7) · 10 ^-8 m and a small amount of barium oxides - (0.08-0.15) vol.%, Introduced into the body of the wire during forging, crushed and evenly distributed over the cross section of the wire, is necessary and sufficient to increase the strength and plastic characteristics of the platinum wire.

The physical essence of this dispersion hardening lies in the fact that fine particles of barium oxide impede the movement of the dislocation and stabilize the structure of platinum. At the same time, fixing the dislocation to oxide particles inhibits the formation of recrystallization centers, which develops at temperatures higher than for unstrengthened platinum. All this leads to an increase in the strength of the platinum base and the whole dispersion-strengthened platinum as a whole, especially high-temperature.

Due to the fact that the destruction of dispersion hardened platinum probably occurs along the volume of barium oxides, and not along the boundary of their interaction with platinum, it is possible that the small size of the oxides excludes the propagation of random cracks arising in them, as well as their development in plastic platinum, which increases the strength and ductility of dispersion hardened platinum.

Contrary to the opinion of experts on the dependence of electrical conductivity on defects (“Physical Encyclopedic Dictionary”, chap. Ed. AM Prokhorov, M., Soviet Encyclopedia, 1983, p. 893), the sizes of barium oxides and their quantity are such that they do not change the dynamics charge carriers and do not impair the thermoelectric properties of dispersion hardened platinum compared to the original, not hardened.

So, each element of a platinum wire: with a high level of thermoelectric properties - plastic pure platinum and high-strength barium oxides, affects the performance of the functions of another element, enhancing their inherent properties.

The presence in the platinum wire of finely dispersed barium oxides of a strictly specified size and quantity of high-strength material, formed precisely in the process of chemical-mechanical hardening and inextricably linked with platinum, allows us to create a wire for thermosensitive elements with a complex of high mechanical characteristics and with a predicted thermal coefficient of electrical resistance in magnitude, corresponding to the source material.

The presence of significant features distinctive from the closest analogue allows us to recognize the claimed model as new.

The possibility of manufacturing a utility model and its use in industry allows us to conclude that it meets the criterion of "industrial applicability".

The utility model is illustrated by drawings, which show a General view of the wire and its cross section:

Figure 1 - General view of the wire with a secant plane "A" and with a cross section in isometry, where:

1 - body

2 - barium oxides,

3 - platinum.

Figure 2 - cross section "A" of the wire, rotated, enlarged. The picture shows the microstructure of a thin section:

Figure 3 - microstructure of a platinum wire in cross section of platinum (bright field), dispersively strengthened by barium oxides (dark inclusions), magnification × 20,000.

Platinum wire for thermosensitive elements, such as thermocouples and resistance thermometers, contains a body 1 made of dispersively hardened barium oxides 2 of high purity platinum 3, with a temperature coefficient of electrical resistance of 3.830 · 10 ^-3 1 / deg. At the same time, barium 2 oxides have a size of 6-10 ^-8 m and are contained in an amount of 0.12 vol.%, And are formed by applying a solution of barium salt to the surface of body 1, namely, a solution of barium nitrate and its decomposition during subsequent annealing, and introduced into the volume of the body 1 during further forging.

The inventive platinum wire for heat-sensitive elements obtained by technology using known methods and equipment as follows.

Take refined platinum in the form of an ingot. A part weighing 10 g is separated from the ingot, from which a sample of wire with a diameter of 0.5 mm is made by hot forging and cold drawing to establish the initial value of the thermal coefficient of electrical resistance, which amounted to 3.830 · 10 ^-3 1 / deg.

Then the main part of the platinum ingot is hot forged to a bar of size (10 × 10 × 500) mm, followed by cold forging on a НМР URG2-4 + 2VSI rotary forging machine and drawing at room temperature on a SCHUMACHER chain mill and on an eight-time BINGER & WEICHERT drawing mill. Drawing is carried out with intermediate annealing to relieve stresses at the temperature of platinum recrystallization. Temperature control is carried out by a thermometer “Thermoscope-300-1C-VTO”. After drawing, the wire diameter is monitored with a micrometer.

After hot forging, rotary forging and before annealing, the platinum wire is boiled in aqua regia to remove metal and nonmetallic particles and traces of lubricant from the surface of the wire body.

Then a platinum wire in the form of a bay is immersed in an aqueous solution of barium nitrate, removed, allowed to drain the solution and then dried in a cabinet ШСП-025-500 until the moisture evaporates completely.

After that, the platinum wire is annealed in a muffle furnace, in which the barium nitrate salt decomposes to form barium oxide, which creates a thin uniform coating on the surface of the wire.

Next, the wire is compacted and subjected to hot forging. During forging, the oxide shell is crushed and barium oxides are introduced into the body volume of the wire, a monolithic rod is created, from which a wire with a diameter of 0.5 mm is then made.

Then, in accordance with GOST 8461-82 (ST SEV 1058-78), introduced 01.01.83, determine the thermal coefficient of electrical resistance, it amounted to 3,830-10 ^-3 1 / deg.

It should be noted that the value of the thermal coefficient of electrical resistance of 3.830 · 10 ^-3 1 / deg corresponds to its lowest value according to the current GOST 21007-75 (table 2), approved. 1.1.76. as amended on 11.21.97.

In addition, the wire is transferred to a testing laboratory to determine the amount of barium oxides. It amounted to 0.12 vol.%.

The size of barium oxides is determined using a scanning electron microscope at a magnification of × 20,000 using certified microscope software, the size of barium oxides is 6 · 10 ^-8 m.

Mechanical properties of the inventive wire: tensile strength at 20 ° C and 1200 ° C, elongation was measured on a tensile testing machine brand ZWICK / ROELLZ010.

A platinum wire was obtained with the size of the oxides and their content, the values of which lay both within and outside the claimed ranges.

As known, 2 platinum wires are presented. One is the closest analogue of the source material with a thermal coefficient of electrical resistance of 3.922 · 10 ^-3 1 / deg. An experimental sample of such a known wire was made with platinum hardening in a cermet version by mixing powders of platinum and barium oxide, followed by heating of the mixture and its deformation, realizing mechanical hardening. The amount of barium oxides, their size and coefficient of thermal resistance in the final material — dispersion-hardened platinum, amounting to 3.915 · 10 ^-3 1 / deg, were determined in the same way as for the inventive wire.

Another well-known wire is represented by platinum not hardened wire, information about which is taken from GOST-21007-75 (page 3, table 2), approved. 1.1.76 as amended on 11.21.97.

For the experiment, we also took the initial platinum wire of high purity with a thermal coefficient of electrical resistance from the range of standardized values, with the same coefficient as that of the closest analogue in the initial state, namely: 3.922 · 10 ^-3 1 / deg. The amount and size of barium oxides were also selected from the claimed intervals. After obtaining dispersion-strengthened platinum by the above method, its thermal coefficient of electrical resistance was also measured.

All received data were listed in the table.

The table shows that the hardening of the proposed wire does not lead to a change in its thermal coefficient of electrical resistance relative to the source material.

So, the thermal coefficient of electrical resistance of 3.830 · 10 ^-3 1 / deg (examples 2, 3, 4) of the source material is stored for the final dispersion-strengthened material.

Also, the thermal coefficient of electrical resistance 3.922 · 10 ^-3 1 / deg (examples 7, 8, 9) of the source material does not change for the final dispersion-strengthened platinum.

This allows you to get a wire with a previously set, meeting the requirements of standards, thermal coefficient of electrical resistance.

In addition, from a comparison of the proposed wire (examples 7, 8, 9) with a wire - the closest analogue (example 11), with the same thermal coefficient of electrical resistance in the starting material for both wires, it can be seen that the proposed dispersion-strengthened wire has a higher complex mechanical characteristics and thermal coefficient of electrical resistance.

The inventive utility model allows to obtain high-strength platinum wire of high purity for thermosensitive elements, such as thermocouples and resistance thermometers, with predicted thermoelectric properties.

Characterization and properties of the claimed and known wires
Table No. p / p Platinum wire for thermosensitive elements such as thermocouples and resistance thermometers Wire characteristic Wire properties Thermal coefficient of electrical resistance of the starting material, 10 ^-3 , 1 / degree The basis The composition of the reinforcing particles The number of hardening particles, vol.% The size of the reinforcing particles, 10 ^-8 , m Nature of hardening Strength at 20 ° C, kgf / mm ² Strength at 1200 ° C, kgf / mm ³ Elongation at 20 ° С,% Thermal coefficient of electrical resistance of hardened platinum, 10 ^-3 , 1 / degree one 3,830 platinum Bao 0.04 8 chemical mechanical 19.7 6.0 28 3,830 2 Proposed 3,830 platinum Wow 0.08 7 chemical mechanical 21.0 7.2 29th 3,830 3 3,830 platinum Wow 0.12 6 chemical mechanical 21.5 7.6 28 3,830 four 3,830 platinum Wow 0.15 four chemical mechanical 22.1 8.2 26 3,830 5 3,830 platinum Wow 0.20 3 chemical mechanical 23.5 8.8 7 3,810 6 3,922 platinum Wow 0.04 8 chemical mechanical 19.3 5.9 29th 3,922 7 Proposed 3,922 platinum Wow 0.08 7 chemical mechanical 20.6 7.0 thirty 3,922 8 3,922 platinum Wow 0.12 6 chemical mechanical 21.1 7.3 thirty 3,922 9 3,922 platinum Wow 0.15 four chemical mechanical 21.8 7.8 25 3,922 10 3,922 platinum Wow 0.20 3 chemical mechanical 23.0 8.5 8 3,919 eleven Famous 3,922 platinum Wow 0.05 twenty mechanical 21.1 6.1 28 3,915 12 Famous 3,915 platinum - - - - 12.0 1,2 - - Note: examples No.: 2, 3, 4 and 7, 8, 9 - the proposed wire with the declared range of values 1, 5 and 6, 10 - wire with outrageous values of ranges 11 is the closest analogue 12 - wire according to GOST 21007-75 1-12 - for wire diameters of 0.5 mm

Claims (2)

1. Platinum wire for temperature-sensitive elements, such as thermocouples and resistance thermometers, containing a body made of dispersively hardened barium oxides of high purity platinum, which provides its temperature coefficient of electrical resistance, for example, not lower than 3.830 · 10 ^-3 1 / deg, characterized in that barium oxides are contained in the amount of (0.08-0.15) vol.% and are formed by the size of (4-7) 10 ^-8 m by applying a solution of barium salts to the surface of the body and their decomposition during annealing and introduced into the body volume at forged. 2. A platinum wire for heat-sensitive elements according to claim 1, characterized in that the barium oxides are formed by applying a solution of barium nitrate to the surface of the body and its decomposition during annealing.