Thermal Decomposition-Tsav Sulfur Deposition ntawm Fused Silica
Sodium thiosulfate (Na₂S₂O₃) yog tus txheej txheem kho tus neeg sawv cev hauv kev ua duab thaij duab (kev ua kom tsis muaj nyiaj halides) thiab lwm yam lixiviant rau kub leaching hauv cov txheej txheem uas tsis yog -cyanide. Feem ntau qhov ntau ntawm 10-30% ntawm qhov hnyav, nrog kev ua haujlwm kub ntawm 60-80℃(siab kom nrawm kho lossis leaching tus nqi). Quartz immersion heaters feem ntau siv nyob rau hauv cov kev daws teeb meem thiosulfate vim fused silica muaj kev tiv thaiv zoo rau cov ntsev nruab nrab thiab tsis catalyze thiosulfate decomposition. Txawm li cas los xij, kub concentrated thiosulfate yog thermally tsis ruaj khov thiab decomposes ntawm qhov kub siab: Na₂S₂O₃ + tshav kub → Na₂SO₃ + S (colloidal sulfur). Lub decomposition yog nrawm los ntawm tshav kub, pH tsawg, thiab qee qhov chaw catalytic. Lub generated sulfur precipitates raws li ib tug daj ntseg daj, colloidal deposit rau ntawm quartz nto. Qhov no sulfur deposit yog thermally insulating, tsim kub me ntsis uas ua rau kom ntxiv decomposition. Tsis tas li ntawd, yog tias cov tshuaj ua kua qaub (los ntawm kev nqus ntawm CO₂ lossis los ntawm thiosulfate decomposition mus rau polythionates), tus nqi decomposition nce ntau, thiab hydrogen sulfide (H₂S) roj yuav hloov zuj zus, uas tuaj yeem tua quartz ntawm qhov kub thiab txias. Qhov kev tshuaj ntsuam no ntsuas seb sodium thiosulfate concentration (10-30%), qhov kub thiab txias (60-80 degree), thiab cov tshuaj pH cuam tshuam rau tus nqi ntawm sulfur deposition ntawm fused silica thiab cov hauv paus quartz corrosion. Qhov yuav tsum tau quartz sheath phab ntsa tuab kom ua tiav cov kev pabcuam ua haujlwm (2,000-8,000 teev) hauv cov duab thaij duab thiab kub leaching heaters yog muab los.
Deposition Kinetics ntawm Sulfur rau Quartz Surfaces
Lub degradation ntawm quartz nyob rau hauv sodium thiosulfate cov kev daws teeb meem tsis yog feem ntau chemical corrosion tab sis sulfur deposit tsim. Thiosulfate decomposition ua ntej - xaj kinetics nrog rau thiosulfate concentration thiab nce exponentially nrog kub. Kev ua kom lub zog rau decomposition yog kwv yees li 80-100 kJ / mol. Ntawm 70 degree, ib nrab -lub neej ntawm 20% sodium thiosulfate ntawm nruab nrab pH yog kwv yees li 500-1,000 teev. Ntawm 80 degree, ib nrab -lub neej poob rau 150-300 teev. Thaum 60 degree, nws nce mus rau 2,000-4,000 teev. Lub colloidal sulfur tsim muaj ib tug muaj zog nyiam mus ua raws li rhuab chaw, nrog rau quartz sheaths.
Kev ntsuas dej ntawm fused quartz hauv 20% sodium thiosulfate ntawm 70 degree, pH 7, qhia txog kev loj hlob ntawm sulfur deposit npaum li cas ntawm 0.01-0.05 hli sib npaug thickness ib lub lis piam. Qhov tso nyiaj yog pib muag thiab daj tab sis tuaj yeem tawv dhau sijhawm. Cov deposit yog thermally insulating; 0.1 hli tuab txheej tuaj yeem txo cov cua sov hloov los ntawm 10-20%. Raws li cov deposit thickens, lub quartz hauv qab khiav kub, accelerating lub zos decomposition. Nyob rau hauv cov xwm txheej hnyav, cov sulfur deposits tuaj yeem yaj (sulfur melts ntawm 115 degree) thiab ntws, tsim qhov tsis sib xws. Lub hauv paus quartz nto qhia tias tsis muaj tshuaj tiv thaiv corrosion ntawm nruab nrab pH. Txawm li cas los xij, yog tias cov tshuaj pH poob qis dua 5 (piv txwv li, los ntawm kev nqus ntawm atmospheric CO₂ lossis los ntawm thiosulfate decomposition rau polythionic acids), thiosulfate decomposition nrawm heev, thiab cov kua qaub tuaj yeem maj mam tua quartz (0.0001-0.0005 mm / teev).
Lub cheeb tsam meniscus yog qhov uas leej faj deposition hnyav tshaj plaws. Evaporation concentrates thiosulfate, accelerating decomposition. Ib qho daj lossis dawb crust feem ntau tshwm ntawm cov kua kab. Tuav cov kua dej tas li thiab siv lub vapor shield tiv thaiv meniscus crust tsim.
Yuav Ua Li Cas Phab Ntsa Thickness Hloov Kev Pabcuam Lub Neej Hauv Thiosulfate Cov Cua Sov
Vim tias lub tshuab tsis ua haujlwm yog tso nyiaj-vim thermal stress es tsis yog phab ntsa thinning, nce quartz phab ntsa thickness tsis tiv thaiv cov sulfur deposition. Txawm li cas los xij, cov phab ntsa tuab dua muab kev tiv thaiv ntau dua rau thermal shock yog tias kub kub tsim. Rau da dej nrog ceev ceev sulfur deposition (qhov kub thiab txias, pH tsawg), ib tug tuab phab ntsa (2.5-3.0 hli) yog pom zoo kom muab ib tug kev ruaj ntseg npoo tiv thaiv tawg. Rau da dej nrog pH zoo tswj thiab qis kub (60-65 degree), tus qauv 1.5-2.0 hli phab ntsa yog txaus. Tsis tu ncua tu ntawm quartz nto nrog dilute ammonia los yog sodium sulfite tov dissolves sulfur deposits. Ib lub lim tiam lossis txhua hli tu lub voj voog tuaj yeem txuas ntxiv lub neej ntawm lub rhaub dej mus tas li, tsis hais txog ntawm phab ntsa tuab.
Thermal Penalty of Thicker Walls in Thiosulfate Solutions
Sodium thiosulfate daws ntawm 20% concentration thiab 70℃muaj thermal conductivity ntawm kwv yees li 0.50–0.55 W / (m·K)- qis dua dej. Rau phab ntsa 1.5 hli, R_cond=0.00109; rau phab ntsa 3.0 mm, R_cond=0.00217. Nrog h=800 W/(m²·K), R_boundary=0.00125. U poob los ntawm 427 mus rau 292 W/(m²·K), 32% txo. Cov phab ntsa nyias yog nyiam rau kev siv hluav taws xob, tab sis kev tsim tso nyiaj yuav xav tau cov phab ntsa tuab dua rau kev ua haujlwm zoo.
Scenario-Raws li Kev Xaiv Matrix rau Quartz Sheath Phab Ntsa Thickness hauv Kub Sodium Thiosulfate Service
| Daim ntawv thov Scenario & Kev khiav hauj lwm Parameters | Pom zoo Phab ntsa Thickness | Core Rationalale nrog Quantified Trade-Tawm |
|---|---|---|
| Kev kho kev yees duab (20% Na₂S₂O₃, 70 degree, nruam, pH 7, tu txhua lub lim tiam) | 2.0 - 2.5 hli, qib txheem, nplaim taws - polished | Sulfur deposition nruab nrab. Phab ntsa Thicker resists thermal stress los ntawm deposit kub chaw. Nplaim- polish txo adhesion. U ≈ 380 W / (m²·K). |
| Kub leaching (10% Na₂S₂O₃, 65 degree, pH 8, nruam, tu txhua hli) | 2.0 hli, raws li - kos | Qhov kub qis dua slows decomposition. Nyias phab ntsa rau lub zog efficiency. U ≈ 420 W / (m²·K). |
| Siab -kub thiosulfate (80 degree, ib qho) | 2.5-3.0mm, nrog vapor shield | Ceev ceev decomposition. Kev tu kom huv tsis tu ncua. Vapor shield txo meniscus deposit. |
| Acid thiosulfate (pH<5, any temperature) | Tsis yog quartz - siv PTFE | Acid accelerates decomposition thiab tawm tsam quartz. Lwm txoj hlua yuav tsum tau. |
Complementary Design Modifications:Tuav nruab nrab mus rau me ntsis alkaline pH (7-8) txo qis decomposition. Ntxiv sulfite stabilizers (Na₂SO₃) inhibits thiosulfate decomposition. Nitrogen sparging tshem tawm oxygen thiab CO₂. Kev tu ib ntus nrog 5% ammonia lossis sodium sulfite dissolves sulfur deposits. Ib tug polished nto thiaj li deposit adhesion.
