Sherardising

{{short description|Process of galvanization of ferrous metal surfaces}}

{{Use British English|date=April 2019}}

{{about-distinguish|the galvanisation process|Shepardizing}}

Sherardising or Zinc thermal diffusion is a process of galvanization of ferrous metal surfaces, also called vapour galvanising and dry galvanizing. The process is named after British metallurgist Sherard Osborn Cowper-Coles (son of naval inventor Cowper Phipps Coles) who invented and patented the method c. 1900.{{ cite patent

| country = US

| number = 701298

| status = patent

| title = Process of depositing metals on metallic surfaces and the product thereof

| pubdate = 1902/6/3

| gdate =

| fdate = 1901/7/24

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| inventor =

| invent1 = Sherard

| invent2 = Cowper-Coles

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| class =

}}{{cite web

| url = https://www.google.co.uk/patents/US701298?dq=Sherard+Cowper-Coles+sherardizing&hl=en&sa=X&ei=XZYTU7ThEeiJ0AWW1ID4CA&ved=0CGkQ6AEwBg

| title = Original Patent (Google patents)

| last =

| first =

| website =

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}}{{cite book | url = https://books.google.com/books?id=laACw9i0D_wC | title = Zinc Handbook | first = Frank C. | last = Porter | publisher = CRC Press | year = 1991 | isbn = 978-0-8247-8340-2}}{{cite book|author1=Eric J. Mittemeijer|author2=Marcel A. J. Somers |author3=F. Natrup |author4=W. Graf|title=Thermochemical Surface Engineering of Steels: Improving Materials Performance|chapter-url=https://books.google.com/books?id=8I-uAwAAQBAJ&pg=737|date=21 November 2014|publisher=Elsevier Science|isbn=978-0-85709-652-4|pages=737–|chapter=20 - Sherardizing: corrosion protection of steels by zinc diffusion coatings

}} This process involves heating the steel parts up to 500 °C in a closed rotating drum that contains metallic zinc dust and possibly an inert filler, such as sand.H. G. Arlt, "Finishes on the Metal Parts of Telephone Apparatus", Bell Laboratories Record, Volume 9(4), 175 (December 1932) At temperatures above 300 °C, zinc evaporates and diffuses into the steel substrate forming diffusion bonded Zn-Fe-phases.

Sherardising is ideal for small parts and parts that require coating of inner surfaces, such as batches of small items. Part size is limited by drum size. It is reported that pipes up to 6 m in length for the oil industry are sherardised.{{cn|date=February 2015}} If the metal surface is free of scale or oxides, no pretreatment is needed. The process is hydrogen-free, hence hydrogen embrittlement is prevented.