Type K TC

Thermocouple Alloys for Type K Thermocouple and Extension Wires.

 

Nicro + & Nial

 

Scott Precision Wire Nicro and Nial alloys are available in solid wire, strip or tape and flexible bunch or strand constructions. Material can be ordered to all National or International emf standards as well as customer’s own specifications.

 

Physical and Mechanical Properties   (Values stated are nominal or typical.)

 

Units

Nicro +

Nial -

Nominal composition

%

Ni 90

Cr 10

Ni 95

Al,Mn,Si+

Density at 20°C

g/cm³

lb/in³

8.72

0.315

8.60

0.310

Resistivity at 20°C

µWcm

W/cmf

70

420

29

174

Coefficient of thermal expansion

20 – 100°C

68 – 212°F

1/K

1/°F

17 x 10-6

9.4 x 10-6

17 x 10-6

9.4 x 10-6

Thermal conductivity at

20°C

68°F

W/mK

Btu.in/ft².h.°F

19.2

135

29.7

210

Melting point (approx.)

°C

°F

1430

2610

1400

2552

Magnetic properties

 

Non-Magnetic

Magnetic

Tensile strength Rm

(0.5mm annealed wire)

N/mm²

lb/in²

650

95000

590

85000

 

Type K thermocouple wire is recommended for use in oxidising or inert atmospheres.  The larger the diameter the greater the longevity at elevated temperatures. Detrimental effects can occur in the following circumstances where the use of protective sheaths is recommended:

 

·        'Green rot' can develop on the Nicro+ due to the preferential oxidation of Chromium occurring in a reducing or mildly oxidising atmosphere where the partial pressure of oxygen is low.  This causes Chromium Oxide (Cr2O3) to form instead of the protective Nickel-Chromium Oxide (NiO-Cr2O3).  In severe circumstances the Chromium Oxide swells and cracks the surface of the wire, allowing internal oxidation to take place.  The removal of Chromium from the alloy is accompanied by a significant emf drop, especially in the range 816 °C to 1038 °C, and the alloy becomes magnetic. The presence of carbonaceous gases will enhance the attack by the formation of Chromium Carbide along the grain boundaries and oxidation becomes a progressive intercrystalline attack. This effect can also be observed in moist reducing atmospheres where there are no carbonaceous gases.

 

·        Sulphur can act in a similar manner to carbonaceous gases, with the formation of chromium sulphide before oxidation in the Nicro+ and intercrystalline corrosion and cracking in the Nial-.

 

·        In a vacuum the Chromium element will evaporate from Nicro+ causing the emf to drop.

 

Information contained within this technical data sheet is based upon the general experience of Scott Precision Wire Ltd and is believed to be correct at the time of issue. 

No warranty is given or is to be implied from  the details above. 

Customers are advised to carry out independent tests in order to determine the suitability of any Scott Precision Wire Ltd product for an application.

  

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