{"id":2956,"date":"2020-08-12T12:14:30","date_gmt":"2020-08-12T16:14:30","guid":{"rendered":"https:\/\/www.guides-sports-loisirs.ca\/aires-glissade\/?page_id=2956"},"modified":"2021-10-08T09:24:32","modified_gmt":"2021-10-08T13:24:32","slug":"principes-physicochimiques","status":"publish","type":"page","link":"https:\/\/www.guides-sports-loisirs.ca\/aires-glissade\/nivologie\/principes-physicochimiques\/","title":{"rendered":"Principes physicochimiques"},"content":{"rendered":"

[vc_row][vc_column width=\u00a0\u00bb1\/1″][vc_column_text]Qu\u2019elle soit naturelle ou de culture (fabriqu\u00e9e), la neige se fonde sur des ph\u00e9nom\u00e8nes physicochimiques inh\u00e9rents aux changements de phases appliqu\u00e9s \u00e0 la mol\u00e9cule d\u2019eau. Les trois principaux ph\u00e9nom\u00e8nes \u00e0 l\u2019\u0153uvre dans la solidification de la vapeur d\u2019eau (nuages) et de l\u2019eau \u00e0 l\u2019\u00e9tat liquide (glace) sont la surfusion<\/strong><\/em>, la nucl\u00e9ation<\/em><\/strong> et la cristallisation<\/strong><\/em>.<\/p>\n

La surfusion<\/strong><\/em> repr\u00e9sente l\u2019\u00e9tat latent du processus de solidification. En th\u00e9orie, l\u2019eau se solidifie \u00e0 0\u00baC. Toutefois, pour passer de l\u2019\u00e9tat liquide \u00e0 l\u2019\u00e9tat solide, les mol\u00e9cules d\u2019eau doivent amorcer leur m\u00e9tamorphose par la nucl\u00e9ation<\/strong><\/em>, processus par lequel les mol\u00e9cules sont soumises \u00e0 une r\u00e9action en cha\u00eene o\u00f9 graduellement elles s\u2019agglutinent les unes aux autres sous une forme polycristalline. Cette derni\u00e8re transformation se nomme cristallisation<\/em><\/strong>.[\/vc_column_text][vc_accordion][vc_accordion_tab title=\u00a0\u00bbSurfusion\u00a0\u00bb tab_id=\u00a0\u00bb1633638332-1-11″][vc_column_text]\u00c0 l\u2019\u00e9tat de surfusion, la temp\u00e9rature de l\u2019eau peut descendre jusqu\u2019\u00e0 -40\u00baC. Le degr\u00e9 de puret\u00e9 influe positivement sur le maintien de l\u2019eau en surfusion. Cela s\u2019explique par une \u00e9nergie interne latente (\u00e9tat de m\u00e9tastabilit\u00e9) ne pouvant amorcer \u00e0 elle seule la r\u00e9action en cha\u00eene de nucl\u00e9ation. Toutefois, la moindre perturbation (ex. : secousse, contact avec un solide) d\u00e9stabilise cet \u00e9tat latent et une solidification presque instantan\u00e9e s\u2019ensuit.<\/p>\n

Graphique illustrant le passage de l\u2019eau de son \u00e9tat liquide \u00e0 l\u2019\u00e9tat solide au contact d\u2019une paroi<\/strong><\/p>\n

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Source : Cdang sur Wikip\u00e9dia fran\u00e7ais<\/figcaption><\/figure>\n

[\/vc_column_text][\/vc_accordion_tab][vc_accordion_tab title=\u00a0\u00bbNucl\u00e9ation\u00a0\u00bb tab_id=\u00a0\u00bb1633638332-2-41″][vc_column_text]\u00c0 ce stade, tout contact de l\u2019eau liquide ou la vapeur avec une surface physique ou toute impuret\u00e9 comme de la poussi\u00e8re, du sable ou des particules de glace devient un germe de nucl\u00e9ation. Attir\u00e9es par ces substances, les mol\u00e9cules d\u2019eau se transforment presque instantan\u00e9ment en cristaux de neige ou glace. Ce type de nucl\u00e9ation est qualifi\u00e9e d\u2019h\u00e9t\u00e9rog\u00e8ne par opposition \u00e0 la nucl\u00e9ation homog\u00e8ne, o\u00f9 les mol\u00e9cules (tr\u00e8s purifi\u00e9es) amorcent leur phase de cristallisation \u00e0 leur temp\u00e9rature de solidification (-40\u00baC) sans apport de germes externes.<\/p>\n

Noyaux de nucl\u00e9ation se formant dans la vapeur d\u2019eau<\/h5>\n
\"\"
Source : Mellon College of Science, Making it Rain : Researchers assess method for predicting ice nucleation properties.<\/a><\/figcaption><\/figure>\n

[\/vc_column_text][\/vc_accordion_tab][vc_accordion_tab title=\u00a0\u00bbCristallisation\u00a0\u00bb tab_id=\u00a0\u00bb1633698273524-2-7″][vc_column_text]Le r\u00e9arrangement des mol\u00e9cules d\u2019eau (devenue glace) ne s\u2019effectue pas de mani\u00e8re al\u00e9atoire. Le processus de cristallisation de l\u2019eau se mat\u00e9rialise selon une structure particuli\u00e8re : polycristalline \u00e0 six facettes. Les cristaux de neige naturelle permettent l\u2019observation tangible de ce ph\u00e9nom\u00e8ne. Cette structure hexagonale est toutefois difficile \u00e0 distinguer \u00e0 l\u2019\u0153il nu dans la neige de culture, se trouvant imbriqu\u00e9e dans les minuscules grains arrondis.<\/p>\n

Formation d\u2019un cristal de glace \u00e0 partir de mol\u00e9cules liquides d\u2019eau<\/h5>\n
\"\"
Source : Heklpiks.org, Water\u2019s States: Gas, Liquid, and Solid<\/a><\/figcaption><\/figure>\n

[\/vc_column_text][\/vc_accordion_tab][\/vc_accordion][\/vc_column][\/vc_row][vc_row][\/vc_row][vc_row row_height_percent=\u00a0\u00bb0″ overlay_alpha=\u00a0\u00bb50″ gutter_size=\u00a0\u00bb3″ shift_y=\u00a0\u00bb0″ css=\u00a0\u00bb.vc_custom_1569108843026{margin-bottom: 50px !important;}\u00a0\u00bb][vc_column width=\u00a0\u00bb1\/1″][vc_button button_color=\u00a0\u00bbaccent\u00a0\u00bb size=\u00a0\u00bbbtn-lg\u00a0\u00bb radius=\u00a0\u00bbbtn-circle\u00a0\u00bb border_width=\u00a0\u00bb0″ link=\u00a0\u00bburl:https%3A%2F%2Fwww.guides-sports-loisirs.ca%2Faires-glissade%2Fwp-content%2Fuploads%2Fsites%2F19%2F2021%2F10%2F6.4_Nivologie_PrincipesPhysicochimiques.pdf||target:%20_blank|\u00a0\u00bb icon=\u00a0\u00bbfa fa-file-o\u00a0\u00bb el_class=\u00a0\u00bbbtn-pdf\u00a0\u00bb]Version PDF[\/vc_button][\/vc_column][\/vc_row]<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

[vc_row][vc_column width=\u00a0\u00bb1\/1″][vc_column_text]Qu\u2019elle soit naturelle ou de culture (fabriqu\u00e9e), la neige se fonde sur des ph\u00e9nom\u00e8nes physicochimiques inh\u00e9rents aux changements de […]<\/p>\n","protected":false},"author":11,"featured_media":0,"parent":2903,"menu_order":4,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"class_list":["post-2956","page","type-page","status-publish","hentry"],"acf":[],"yoast_head":"\nPrincipes physicochimiques - Aires de glissade<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.guides-sports-loisirs.ca\/aires-glissade\/nivologie\/principes-physicochimiques\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Principes physicochimiques - Aires de glissade\" \/>\n<meta property=\"og:description\" content=\"[vc_row][vc_column width=\u00a0\u00bb1\/1″][vc_column_text]Qu\u2019elle soit naturelle ou de culture (fabriqu\u00e9e), la neige se fonde sur des ph\u00e9nom\u00e8nes physicochimiques inh\u00e9rents aux changements de […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.guides-sports-loisirs.ca\/aires-glissade\/nivologie\/principes-physicochimiques\/\" \/>\n<meta property=\"og:site_name\" content=\"Aires de glissade\" \/>\n<meta property=\"article:modified_time\" content=\"2021-10-08T13:24:32+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.guides-sports-loisirs.ca\/aires-glissade\/wp-content\/uploads\/sites\/19\/2021\/10\/6-4_graphique-300x189.jpg\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Dur\u00e9e de lecture estim\u00e9e\" \/>\n\t<meta name=\"twitter:data1\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.guides-sports-loisirs.ca\\\/aires-glissade\\\/nivologie\\\/principes-physicochimiques\\\/\",\"url\":\"https:\\\/\\\/www.guides-sports-loisirs.ca\\\/aires-glissade\\\/nivologie\\\/principes-physicochimiques\\\/\",\"name\":\"Principes physicochimiques - 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