<?xml version="1.0" encoding="utf-8"?><!DOCTYPE Zthes SYSTEM "http://zthes.z3950.org/xml/zthes-05.dtd">  <Zthes><term><termId>31320349</termId><termName>hydrogen fluoride</termName><termType>PT</termType><termNote><![CDATA[ A colorless corrosive gas, the hydride of fluorine and an extremely powerful halogen acid, hydrogen fluoride is used as a catalyst and a fluorinating agent. Its chief use is in making fluorine-containing refrigerants such as freons. In a conservation context, hydrogen fluoride is considered as an atmospheric pollutant which damages metal structures, and buildings or monuments made of limestone. ]]></termNote><termCreatedDate>2026-03-30 20:26:20</termCreatedDate><relation><relationType>UF</relationType><termId>31320350</termId><termName>anhydrous hydrofluoric acid</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31320351</termId><termName>fluoride, hydrogen</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31320352</termId><termName>hydrofluoric acid gas</termName><termType>ND</termType></relation><relation><relationType>BT</relationType><termId>31344867</termId><termName>fluoride</termName><termType>PT</termType></relation><relation><relationType>BT</relationType><termId>31306060</termId><termName>acid</termName><termType>PT</termType></relation></term>  </Zthes>