# Titanium for rare-event searches: Hydrofluoric acid-free etching

## TL;DR

This paper presents a hydrofluoric acid-free chemical etching method using sulfuric acid for titanium, suitable for rare-event search experiments, reducing health hazards while effectively removing surface contaminants.

## Contribution

It introduces a novel sulfuric acid-based etching process for titanium, offering a safer alternative to hydrofluoric acid in low-background experimental setups.

## Key findings

- Sulfuric acid etches titanium, removing 3.7 μm over 20 hours.
- Surface contaminants are effectively removed after etching.
- The method is a safer alternative for titanium surface preparation.

## Abstract

Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radio-pure forms, titanium is a suitable material for structural elements in rare event searches. To remove surface deposits on materials used, a chemical etching stage is usually performed. However, the chemical resistance of titanium means that, conventionally, such etching is done with hydrofluoric acid. Hydrofluoric acid presents serious health risks to users, and such hazards are compounded in the case of construction in deep underground laboratories. An alternative chemical etching using sulphuric acid is presented. This is demonstrated to etch titanium, removing 3.7 $\mu$m of material from the surface over the course of 20 hours. Scanning electron microscopy with back-scattered electron spectroscopy was used to study the surface and contamination of the titanium, demonstrating the removal of surface contaminants after etching. The proposed method is a potential alternative to those currently employed.