The range of industrial applications for precious metal wires is wide and varied.
In certain areas, such as resistance thermometry and combustible gas detection, there is a specific requirement for wires at very small diameters (<0.025 mm) with tightly controlled material properties. Through on-going development and investment, Johnson Matthey are now able to produce a range of ultrafine wires with diameters as low as 0.01 mm, combined with very specific material properties such as temperature coefficient of resistance (alpha value), actual resistance, diameter and tensile requirements.
1) Platinum wire for resistance thermometry (Alpha Platinum Wire)
The measurement of temperature by means of the resistance thermometer is based on the fact that a change in the temperature of a conductor produces a measurable change in resistance. The magnitude of this change per unit increase in temperature depends on the temperature coefficient of resistance of the conductor (the alpha value).
Platinum is a conductor of high melting point and exceptional chemical inertness, combined with extremely stable electrical properties. This combination of properties makes it the best available material for resistance thermometer elements.
For the production of wire wound platinumresistance thermometers (PRT’s), the consistent supply of high quality, specific alpha value platinum wires at diameters of around 0.018 mm is essential. Johnson Matthey can supply a wide range of alpha platinum wires, to meet the specific needs of PRT manufacturers throughout the world. Wires are available with alpha values ranging from 0.003800 to 0.003925, with a tolerance on alpha value that can be as tight as +/- 3ppm. Commonly required wires are available as overleaf:-
| ALPHA VALUE | COMMENTS |
| >= 0.003925 | Very pure platinum wire for high precision PRTD’s (standards). Typical wire diameter = 0.07 mm. |
| 0.003850 | For the Pt100 detector. This alpha value is the industry standard for the majority of sensors outside the USA and Japan (as per IEC Publication 751, 1983). The reduced alpha value is achieved by very accurate doping of pure platinum with other platinum group metals. Typical wire diameter is 0.018 mm. |
| 0.003916 | Alpha value requirement that is common in the USA and Japan, where it is the accepted standard (as per JIS C1604, 1981 and US standard curve). |
| 0.003900 | Alpha value originally specified for the British Aircraft Industry (as per BS 2G 148). |
ADDITIONAL NOTES:-
– As indicated, Johnson Matthey can supply alpha platinum wire with a tolerance on alpha value as tight as +/- 3ppm. Through our expertise in wire drawing techniques and diamond die maintenance, we are also able to tightly control the wire diameter (measured by resistance) and eliminate contamination (typical resistance tolerance at ultrafine wire sizes is +/-3%).
– Through batch selection and careful doping, tailor-made ingots can be produced to specific
customer requirements. Once batch selections have been made, Johnson Matthey will hold
dedicated material in stock for our customer’s requirements.
2) PLATINUM WIRE FOR COMBUSTIBLE GAS DETECTION (SENSORS)
Combustible gas sensors are based on an established catalytic bead technology. They are supplied in pairs, a detector and compensator, with the detector element consisting of a catalytic bead supported on a very fine diameter platinum wire. In the presence of combustible gas, a catalytic oxidation reaction takes place, producing heat and changing the resistance of the platinum wire. This produces a signal from the bridge circuit proportional to the concentration of gas.
Within our dedicated production area in the UK, Johnson Matthey manufacture a range of ultrafine platinum wires for the gas detection industry, where there are increasing demands to supply smaller and smaller diameter wires, which draw less current and therefore extend the
battery life of portable sensors. Typical wire diameters and capabilities are as follows:-
| NOMINAL DIAMETER | MEASURED RESISTANCE (AND TOLERANCE) |
| 0.025 mm | 220 ohms/m (+/- 3%) |
| 0.015 mm | 600 ohms/m (+/- 5%) |
| 0.0125 mm | 865 ohms/m (+/- 5%) |
| 0.010 mm | 1347 ohms/m (+/- 5%) |
NOTES:-
– Wire can be supplied as drawn, or stress relieved to give straightness to the wire.
– Wire diameters, resistances, tensile properties and reeling requirements (eg. wire length per reel) can be tailored to meet individual customer requirements. For diameters <=0.0125 mm, maximum wire length per reel is approx. 25-50 metres.
– Actual wire resistances are measured and recorded for each individual reel.
Johnson Matthey work to the highest quality standards and have BS EN 9002 Part 2, UKAS, CAA, Ford Q1 and Rolls Royce approval, ensuring a high level of control in our processes and consistent product quality.
For more information regarding the supply of ultrafine precious metal wires (for resistance thermometry, gas detection or other applications) please contact us at the address given below.