Plasma sprayed alumina coatings for radiation detector development

Abstract

Conventional design of radiation detectors uses sintered ceramic insulating modules. The major drawback of these ceramic components is their inherent brittleness. Ion chambers, in which these ceramic spacers are replaced by metallic components with plasma spray coated alumina, have been developed in our Research Centre. These components act as thin spacers that have good mechanical strength as well as high electrical insulation and replace alumina insulators with the same dimensions. As a result, the design of the beam loss monitor ion chamber for CAT could be simplified by coating the outer surface of the HT electrode with alumina. One of the chambers developed for isotope calibrator for brachytherapy gamma sources has its outer aluminium electrode (60 mm dia ¢ 220 mm long) coated with 250 thick alumina (97%) · titania (3%).In view of potential applications in neutron-sensitive ion chambers used in reactor control instrumentation, studies were carried out on alumina 100 to 500 thick coatings on copper, aluminium and SS components. The electrical insulation varied from 10 ohms to 10 ½¾ ohms for coating thicknesses above 200 . The porosity in the coating resulted in some fall in electrical insulation due to moisture absorption. An improvement could be achieved by providing the ceramic surface with moisture-repellent silicone oil coating. Irradiation at Apsara reactor core location showed that the coating on aluminium was found to be unaffected after exposure to 10 ½ nvt fluence.

Plasma-sprayed alumina coating on Inconel 600 for fast reactor neutron detector application

“…McPherson [12,13] reported that during solidification of molten droplets at higher cooling rates, the formation of γ-Al 2 O 3 is more favoured than α-Al 2 O 3 as the free energy barrier to nucleation was low for the formation of γ-Al 2 O 3 . Alex et al [1] evaluated the coating characteristics of plasma-sprayed alumina coatings on copper, aluminium and stainless steel components for neutron and gamma detector applications. However, the adhesion strength and thermal cycling studies were not reported.…”

“…The monolithic ceramic insulating discs/spacers used in nuclear reactors are prone to failure during seismic vibration and shock. Therefore, the feasibility of using metallic parts coated with high-purity alumina by plasma spraying was explored and was found to be useful [1]. There is a need for using such ceramic insulated neutron detectors in the prototype fast breeder reactor, under construction in Kalpakkam.…”

Emission characteristics of ultrafine particles from bare and Al2O3 coated graphite for high temperature applications

“…In general, a higher thickness of coating (increased volume fraction) may affect the neutronic balance and thermal diffusivity while lesser thickness impacts the oxidation shielding. Lesser electrical insulation resistance was also linked to lesser thickness of plasma sprayed Al 2 O 3 coating 49 . A typical picture of both types of specimens i.e.…”

Intermediate temperature tribological behavior of carbon nanotube reinforced plasma sprayed aluminum oxide coating

“…Carbon nanotubes (CNTs) have attracted much attention as a potential reinforcement for the enhancement of toughness [1][2][3][4][5][6] and wear resistance [7][8][9][10] of the ceramic matrix due to their remarkable mechanical [11][12][13][14][15] and thermal properties [16,17]. In the past, researchers have addressed the tribological behavior of CNT reinforced aluminum oxide (Al 2 O 3 ) composite [7][8][9][10].…”