Editing Nitric acid (section)

===Niche uses===

====Metal processing====

Nitric acid can be used to convert metals to oxidized forms, such as converting copper metal to [[cupric nitrate]]. It can also be used in combination with [[hydrochloric acid]] as [[aqua regia]] to dissolve noble metals such as [[gold]] (as [[chloroauric acid]]). These salts can be used to purify gold and other metals beyond 99.9% purity by processes of [[Recrystallization (chemistry)|recrystallization]] and [[Precipitation (chemistry)|selective precipitation]]. Its ability to dissolve certain metals selectively or be a solvent for many metal salts makes it useful in [[gold parting]] processes.

====Analytical reagent====
In [[elemental analysis]] by [[ICP-MS]], [[ICP-AES]], GFAA, and Flame AA, dilute nitric acid (0.5–5.0%) is used as a matrix compound for determining metal traces in solutions.<ref>{{cite book |title=Standard Methods For the Examination of Water and Wastewater |edition=21 |editor-last1=Eaton |editor-first1=Andrew D. |editor-last2=Greenberg |editor-first2=Arnold E. |editor-last3=Rice |editor-first3=Eugene W. |editor-last4=Clesceri |editor-first4=Lenore S. |editor-last5=Franson |editor-first5=Mary Ann H. |year=2005 |publisher=American Public Health Association |isbn=978-0-87553-047-5}} Also available on CD-ROM and [http://www.standardmethods.org/ online] by subscription.{{page needed|date=November 2022}}</ref> Ultrapure trace metal grade acid is required for such determination, because small amounts of metal ions could affect the result of the analysis.

It is also typically used in the digestion process of turbid water samples, sludge samples, solid samples as well as other types of unique samples which require elemental analysis via [[ICP-MS]], [[ICP-OES]], [[ICP-AES]], GFAA and flame [[atomic absorption spectroscopy]]. Typically these digestions use a 50% solution of the purchased {{Chem2|HNO3}} mixed with Type 1 DI Water.

In [[electrochemistry]], nitric acid is used as a chemical doping agent for [[organic semiconductor]]s, and in purification processes for raw [[carbon nanotube]]s.

====Woodworking====
In a low concentration (approximately 10%), nitric acid is often used to artificially age [[pine]] and [[maple]]. The color produced is a grey-gold very much like very old wax- or oil-finished wood ([[wood finishing]]).<ref>{{Cite book|last=Jewitt|first=Jeff|title=Hand-applied finishes|url=https://archive.org/details/handappliedfinis0000jewi|url-access=registration|access-date=2009-05-28|year=1997|publisher=Taunton Press|isbn=978-1-56158-154-2}}</ref>

====Etchant and cleaning agent====
The corrosive effects of nitric acid are exploited for some specialty applications, such as [[etching]] in printmaking, [[Pickling (metal)|pickling stainless steel]] or cleaning silicon wafers in electronics.<ref>Muraoka, Hisashi (1995). "Silicon wafer cleaning fluid with HNO<sub>3</sub>, HF, HCl, surfactant, and water" {{US Patent|5635463}}</ref>

A solution of nitric acid, water and alcohol, [[nital]], is used for etching metals to reveal the microstructure. ISO 14104 is one of the standards detailing this well known procedure.<ref>{{cite ISO standard|csnumber=70396|title=ISO 14104:2017 – Gears – Surface temper etch inspection after grinding, chemical method}}</ref>

Nitric acid is used either in combination with hydrochloric acid or alone to clean glass cover slips and glass slides for high-end microscopy applications.<ref>{{cite journal |last1=Fischer |first1=A. H. |last2=Jacobson |first2=K. A. |last3=Rose |first3=J. |last4=Zeller |first4=R. |title=Preparation of Slides and Coverslips for Microscopy |journal=Cold Spring Harbor Protocols |date=1 May 2008 |volume=2008 |issue=6 |pages=pdb.prot4988 |doi=10.1101/pdb.prot4988 |pmid=21356831 }}</ref> It is also used to clean glass before silvering when making silver mirrors.<ref>{{cite journal |last1=Curtis |first1=Heber D. |title=Methods of Silvering Mirrors |journal=Publications of the Astronomical Society of the Pacific |date=February 1911 |volume=23 |issue=135 |pages=13 |doi=10.1086/122040 |bibcode=1911PASP...23...13C |s2cid=120665136 |url=https://zenodo.org/record/1431273 |doi-access=free |hdl=2027/mdp.39015018047608 |hdl-access=free }}</ref>

Commercially available aqueous blends of 5–30% nitric acid and 15–40% [[phosphoric acid]] are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium and magnesium compounds (either deposited from the process stream or resulting from the use of hard water during production and cleaning). The phosphoric acid content helps to passivate [[iron alloys|ferrous alloys]] against corrosion by the dilute nitric acid.{{Citation needed|date=September 2011}}

Nitric acid can be used as a spot test for [[alkaloid]]s like [[LSD]], giving a variety of colours depending on the alkaloid.<ref name="validation paper">{{cite journal |last1=O’Neal |first1=Carol L |last2=Crouch |first2=Dennis J |last3=Fatah |first3=Alim A |title=Validation of twelve chemical spot tests for the detection of drugs of abuse |journal=Forensic Science International |date=April 2000 |volume=109 |issue=3 |pages=189–201 |doi=10.1016/S0379-0738(99)00235-2 |pmid=10725655 }}</ref>

==== Nuclear fuel reprocessing ====
Nitric acid plays a key role in [[PUREX]] and other [[nuclear fuel reprocessing]] methods, where it can dissolve many different [[actinide]]s. The resulting nitrates are converted to various complexes that can be reacted and extracted selectively in order to separate the metals from each other.