Characterisation of the activation and reaction behaviour and determination of the emissivity of reactive nickel-aluminium particles with regenerated fibre Bragg gratings

S Grohmann,J Roths,M F Zaeh,M Lindner,G Langhans

doi:10.1088/1757-899x/480/1/012024

Abstract

Reactive particles represent a customisable heat source for joining applications as each reactive particle is able to undergo an exothermic, self-sustaining reaction. Microwaves are used to homogeneously initiate this reaction and allow the resulting temperature-time profiles to be influenced. The possibility to derive cause-effect relationships between the different particle structures, the activation energy, and the resulting maximum temperatures is essential for developing a resource-efficient, tailored heat source in production engineering. The reaction of reactive nickel and aluminium particles generates heat and thus temperatures up to 1500 K within milliseconds. A promising temperature measurement method despite an unknown emissivity are optical fibre sensors. These feature high frame rates, a compact design, and resistance to high temperatures as well as to electromagnetic waves. In this paper, the investigation of the use of regenerated fibre Bragg gratings (RFBG) as a new, innovative approach to characterise reactive particles is described. Experimental studies with an infrared camera and RFBG demonstrated that RFBG retain their functionality while being exposed to microwaves and high temperatures. The good accordance of the recorded RFBG-based temperature evolutions with infrared thermography data confirmed the suitability of RFBG as a sophisticated characterisation method and for determining the emissivity of reactive metal particles.

Highlights

Established joining technologies like welding, soldering, and adhesive bonding, require a sophisticated heat source, which guarantees an efficient and controllable energy input
It becomes evident that there are missing values for the regenerated fibre Bragg gratings (RFBG)-based fibre sensor. This probably resulted from predominant temperature gradients along the optical fibre sensor, which distorted the spectrum of the RFBG and prevented the calculation of the Bragg wavelength
Reactive particles, which were originally used in the field of combustion synthesis, represent a promising heat source for joining applications, such as welding, soldering, and adhesive bonding

Summary

Introduction

Established joining technologies like welding, soldering, and adhesive bonding, require a sophisticated heat source, which guarantees an efficient and controllable energy input. High-temperature measurement with frame rates in the range of kilohertz and an unknown emissivity is not yet state of the art Optical fibre sensors, such as regenerated fibre Bragg gratings (RFBG), represent a promising solution for investigating reactive particles. Fibre Bragg gratings represent an innovative high-temperature measurement method for reactive particles and enable the determination of the emissivity of powder beds when combined with an infrared camera system. Regenerated fibre Bragg gratings Optical fibre sensors based on Bragg gratings have been successfully used in a wide range of applications, like measuring the temperature gradient during the casting process of an aluminium alloy [23], in gas turbines [24], or in chemical and nuclear reactors [25] Noteworthy are their immunity to electromagnetic fields [26] as well as their small size [27].

Results and discussion

Conclusions