Yuav Ua Li Cas Kub Concentrated Boric Acid (5-8%) ntawm 80-110℃Hloov qhov xav tau Quartz Sheath Phab Ntsa Thickness rau Nuclear Shielding thiab Fiberglass Ntau Cov Cuab Yeej?

Lub siab mos tab sis pheej ua phem ntawm Kub Boric Acid ntawm Fused Silica

Boric acid (H₃BO₃) yog ib qho tsis muaj zog monobasic Lewis acid. Nws yog dav siv los ua ib qho neutron absorber nyob rau hauv lub shielding ntawm nuclear reactors, raws li ib tug flux thiab viscosity modifier nyob rau hauv kev tsim cov fiberglass, nyob rau hauv kev tsim cov iav thiab ceramics, thiab raws li ib tug nplaim hluav taws thiab antiseptic. Feem ntau siv hauv kev lag luam yog 5-8% los ntawm qhov hnyav hauv cov tshuaj aqueous nrog kev ua haujlwm kub ntawm 80-110℃hauv evaporators, dissolvers thiab chemical mixing tanks. Quartz immersion heaters feem ntau tau teev tseg rau boric acid lub luag haujlwm vim tias fused silica yog qhov zoo tshaj plaws purity (tseem ceeb rau cov ntawv thov nuclear qhov twg hlau yuav tsum tau txo qis) thiab muaj kev tiv thaiv zoo rau feem ntau cov acids tsis muaj zog. Boric acid tuaj yeem yog qhov teeb meem me me rau quartz, txawm li cas los xij. Boric acid tsis protonate siloxane daim ntawv cog lus rau txhua qhov loj, tsis zoo li cov ntxhia muaj zog acids, vim nws cov kua qaub nruab nrab (pKa ≈ 9.24 ntawm 25℃-Qhov tseeb boric acid tsis yog tus neeg pub dawb rau hauv qhov kev nkag siab, nws absorbs OH- los tsim B(18ic acid) yog li ntawd, yog li ntawd, cov kua qaub pKa ≈ 9.24. ~5-6 rau 5% tov). Lub tshuab corrosion tsis yog proton tsav tab sis suav nrog kev tsim cov borate-silicate complexes. Nyob rau hauv lub xub ntiag ntawm silanol pawg, boric acid tuaj yeem ua rau muaj kev cuam tshuam los tsim BO-Si daim ntawv cog lus, uas, ntawm qhov kub siab dua, tuaj yeem hloov kho kom muab cov hom borosilicate soluble lossis insoluble. Thaum kub siab, boric acid kuj tuaj yeem dehydrate rau metaboric acid (HBO 2) thiab thaum kawg mus rau boric oxide (B 2 O 3). Ntawm 80-110 degree, lub cev qhuav dej me me. Borate ions kuj tseem tuaj yeem ua rau silica tawg hauv qhov nruab nrab lossis me ntsis alkaline. Qhov kev tshawb nrhiav no ntsuas cov txiaj ntsig ntawm boric acid concentration (5-8%), kub (80-110 degree) thiab tshuaj pH ntawm cov nqi sib txawv ntawm cov fused silica. Kev txiav txim siab quartz sheath phab ntsa tuab kom ua tiav cov kev pabcuam ua tau (5,000-20,000 teev) hauv cov ntawv thov nuclear thiab fiberglass tau muab, nrog rau kev nplua thermal ntawm cov phab ntsa tuab hauv cov khoom siv qis, cov kua nplaum.

Corrosion Kinetics ntawm Fused Silica hauv Kub Boric Acid: Borate Complexation

Kev tawm tsam ntawm quartz los ntawm kub boric acid tsis ua raws li lub tswv yim niaj hnub ntawm acid corrosion. Boric acid yog Lewis acid nyob rau hauv dej: B(OH)3 + H2O ⇌ B(OH)4- + H+. pKa 9.24 ntawm 25℃li no cov tshuaj tsuas yog acidic me ntsis (pH ~ 5.1 rau 0.8 M, ~ 5% boric acid). Lub dissociation tas li nyob ntawm qhov kub thiab txias, thiab ntawm 100℃pH tuaj yeem qis li 4.5-5.0. Ntawm pH 5, txawm li cas los xij, H + concentration tsuas yog 10 -5 M, tsawg dhau los ua rau muaj ntau yam proton- txhawb nqa hydrolysis ntawm silica. Txawm li cas los xij lub ntsiab kev tawm tsam yog cov tshuaj tiv thaiv ntawm tetrahydroxyborate anion B(OH)₄⁻ nrog silanol pawg: Si-OH + B(OH)₄⁻ → Si-O-B(OH)₃⁻ + H₂O. Qhov no tsim ib qho borate - silicate compound rau ntawm qhov chaw. Lub complex tej zaum yuav nyob twj ywm ua ke (passivating) los yog ntxiv hydrolyze, kom tso cov soluble silicon hom. Ntau qhov ntau ntawm boric acid thiab kub ntau dua txhawb kev txhim kho ntawm txoj haujlwm.

High purity fused quartz yog immersion kuaj nyob rau hauv 5% boric acid ntawm 95 degree. Tus nqi corrosion yog ib yam thiab tshwj xeeb tsawg, 0.00005-0.0001 mm / teev. Ntawm 110 degree, qhov kub thiab txias feem ntau pom nyob rau hauv boric acid evaporators, tus nqi nce mus rau 0.0001-0.0002 mm / teev. Tus nqi ntawm 80℃yog<0.00003 mm/hour. For comparison 5% HCl at 95C corroded quartz at 0.005-0.010 mm/hr-two orders of magnitude higher. Life at 95 o C would be about 25,000 hours (close to 3 years) since a 2.0 mm quartz sheath in 5% boric acid would lose 0.00008 mm/hr x 25,000 hours = 2.0 mm. 1.5 mm wall = 18,750 hours (2.1 years) Quartz is therefore quite resistant to hot boric acid and uniform corrosion is seldom a life-limiting problem. The corrosion rate is relatively low, so that very thin walls (1.0-1.5 mm) will last for decades in most applications.

Lwm cov ions (xws li sodium, calcium lossis chloride) kuj tuaj yeem cuam tshuam tus nqi ntawm corrosion. Boric acid cov ntsiab lus feem ntau muaj sodium hydroxide los tswj corrosion ntawm stainless hlau Cheebtsam nyob rau hauv nuclear shielding daim ntaub ntawv los ntawm kev kho cov pH mus rau 7-9 . Cov concentration ntawm B(OH)4- yog siab dua ntawm pH 8-9 thiab quartz corrosion tus nqi yuav yog 0.0002-0.0005 mm/hour- tseem tsawg heev. Txawm li cas los xij, ntawm pH tshaj 10 qhov kev daws teeb meem dhau los ua alkaline thiab cov txheej txheem corrosion hloov mus rau hydroxide nres nrog cov nqi nce ntxiv (0.005-0.010 mm / teev). Rau lub neej ntawm quartz, boric acid tov yuav tsum tau khaws cia ntawm pH ze nruab nrab (5-7).

Localized crystallization thiab pitting ntawm boric acid

Boric acid crystallizes readily on evaporation, leaving hard glassy coatings on heated surfaces. In evaporators or tanks where the liquid level changes, boric acid crystals may develop on the quartz sheath above the liquid level. These crystals are not corrosive to quartz but they are thermal insulators. A thick covering of crystal slows heat conduction and causes the underlying quartz to run hotter. At high temperature (>130 degree) cov crystals yuav plam lawv cov dej crystallization rau boric oxide (B2O3) uas muaj qhov qis melting point (450 degree) thiab tej zaum yuav ntub lub quartz nto, ua rau lub zos kev nyuaj siab rau txias. Qhov tseem ceeb tshaj, cov rwb thaiv tsev thermal tuaj yeem tsim cov chaw kub uas tuaj yeem ua kom muaj kev cuam tshuam hauv qab, txawm tias nyob ntawm qhov qis heev. Qhov kev txhawj xeeb loj tshaj plaws yog kev puas tsuaj los ntawm kev sib txawv thermal expansion ntawm boric acid nplai thiab quartz. Lub tshuab cua sov yog ib ntus ntxuav nrog dej kub los yog dilute acid, uas dissolves cov muaju thiab rov hloov cov cua sov.

Crystallization yog tshwj xeeb tshaj yog hais nyob rau hauv cheeb tsam ntawm meniscus. evaporation ntawm dej concentrates boric acid, ua rau nws ua supersaturated thiab tsim muaju. Kev tsim cov meniscus crust yog tiv thaiv los ntawm kev ua kom cov kua theem tsis tu ncua lossis los ntawm kev siv lub vapor shield. Quartz nto yog polished, uas minimizes siv lead ua adhesion thiab ua kom yooj yim los ntxuav.

Cov nyhuv ntawm Phab Ntsa Thickness ntawm Kev Pabcuam Lub Neej hauv Kub Boric Acid Heaters

Vim tias cov nqi tsis sib xws yog qeeb heev (0.00005-0.0002 mm / teev), qhov kev tiv thaiv corrosion xav tau thaum 5-10 xyoo ntawm cov khoom siv lub neej tsuas yog 0.005-0.02 hli. Yog li ntawd, cov phab ntsa tuab yog xaiv los ntawm lub hauv paus ntawm txhua yam muaj zog, lub siab ntim (yog tias muaj) thiab tiv thaiv thermal shock thiab tuav kev puas tsuaj, es tsis yog kev tiv thaiv corrosion. Standard quartz rhaub phab ntsa thicknesses ntawm 1.5-2.0 hli yog ntau tshaj li haum rau boric acid siv. Phab ntsa Thicker (3.0–4.0 mm) muab cov txiaj ntsig corrosion me ntsis thiab tsuas yog ntxiv cov thermal kuj thiab qhov hnyav ntxiv. Thaum lub sij hawm ntxuav cov kua qaub yog ua hauj lwm kom tshem tawm boric acid nplai, cov tshuaj ntxuav (xws li HCl tsis muaj zog los yog dej) yuav corrosive ntau tshaj li boric acid nws tus kheej. Nyob rau hauv xws li cov phab ntsa thickness yuav tsum tau xaiv nyob rau hauv xws li ib tug txoj kev uas ib tug corrosion pub rau lub tu mus ncig.

The corrosion rate for pH adjusted solutions of boric acid (e.g., pH 8-9 with NaOH) is still very low (0.0002-0.0005 mm/hour), and walls of 1.5-2.0 mm are still sufficient for multi-year operation. Only if the pH control were poor and the solution alkaline (pH >10) yuav tsum muaj phab ntsa tuab, txawm tias lwm cov ntaub ntawv xav tau.

Thermal Penalty of Thicker Walls nyob rau hauv Boric Acid Solutions

Thermal conductivity of boric acid solutions at concentration 5% and temperature 95°C is ~0.60-0.65 W/(m.K) and is close to that of pure water. Viscosity is close to water (0.5-0.8 cP) Density is 1.01-1.02 g/cm³ The convective heat transfer coefficients in the agitated tanks are in the range 800-1500 W/(m2K). The conducting resistance of quartz is R cond = t/1.38. For 1.5 mm wall, R_cond = 0.00109 m 2 K/W. For 3.0 mm wall, R_cond = 0.00217 m 2 K/W. With h = 1000 W/m 2 K , R boundary = 0.00100 . Total resistance for 1.5 mm = 0.00209 -> U = 478 W/(m2K); for 3.0 mm = 0.00317 ->U=315 W/(m2K), txo 34%. Kev rau txim yog qhov tseem ceeb heev. Hauv boric acid tsis txhob siv cov phab ntsa tuab; tsis muaj cov txiaj ntsig corrosion. Qhov zoo tshaj plaws phab ntsa thickness yog qhov tsawg kawg nkaus thickness uas muab ib feem ntawm cov neeg kho tshuab lub zog kom ciaj sia tuav thiab installation. Feem ntau qhov no yog 1.5 txog 2.0 hli.

Quartz Sheath Phab Ntsa Thickness Xaiv Matrix Raws li Scenario rau Kub Boric Acid Service

Daim ntawv thov scenario thiab kev khiav hauj lwm parametersCore Rationale nrog Quantified Trade-Tawm pom zoo phab ntsa Thickness
Siab -purity quartz (tsawg hlau) Nuclear reactor shielding (5% H 3 BO 3, 90 degree, pH 5, nruam, 5-xyoo tu) 1.5 - 2.0 mmCorrosion Rate<0.00008 mm/hr -> 2.0 mm would take >25,000 teev (2.8 xyoo) Neutron pob tshab xav tau siab purity. U ~ 450 W / (m²K).
Boric acid dissolver for fiberglass manufacture (8% H3BO3, 105C, continuous, pH 6) 1.5 - 2.0 mm, standard, flame-polished Rate ~0.00015 mm/hour → 2.0 mm gives >13,000 teev (1.5 xyoo). Flame polished rau qis siv lead ua adhesion. U ~ 400 W / (m2·K)
Boric acid evaporator (6% H3BO3, 110 degree, crystallization, nquag tu) 2.0 hli, raws li - kos Corrosion insignificant. Phab ntsa thickness tau xaiv rau txhua yam robustness nyob rau hauv tu cycles. U ~ 380 W / (m2.K).
Boric acid (pH adjusted, pH 8.5, NaOH, 95°C, nuclear waste treatment)2.0 mm, monitor pH Rate ~0.0003 mm/hour → 2.0 mm gives >6,600 teev (9 lub hlis) OK yog pH<9 controlled. Alkaline boric acid (pH>10, any temp) Not quartz - use PTFE or titanium Hydroxide attack prevails. >0.005 hli / teev hauv quartz corrosion. Xav tau lwm txoj.
Complementary tsim hloov pauv rau kub boric acid cua sov

Cov phab ntsa tuab yog qhov tseem ceeb heev, tab sis peb txoj hauv kev tuaj yeem ua haujlwm kom ntev lub neej ntawm quartz rhaub. Ua ntej, kev tu ncua sij hawm: Lub rhaub dej yog muab tso rau hauv dej kub deionized los yog dilute hydrochloric acid (5%) kom yaj cov boric acid crystals thiab rov ua kom cov cua sov hloov mus. Lub voj voog tu txhua hli txhawm rau tiv thaiv kev loj hlob. Qhov thib ob, cua sov ntawm qhov chaw vapor: ib qho chaw tso cua sov tso rau ntawm lub quartz sheath saum cov kua kab tsis tu ncua ntawm thaj tsam ntawd, tiv thaiv crystallization ntawm boric acid nyob rau sab sauv sheath. Thib peb, cov qib ua kua tsis tu ncua: kev siv cov tswj qib kom ua kom cov qib ua kua tsis tu ncua kom tsis txhob meniscus crystallization, qhov loj tshaj plaws ntawm kev tsim cov nplai. Plaub, polished nto: qhia cov nplaim taws- polished los yog mechanically polished quartz nto txo ​​cov crystal adhesion, ua rau cov nplai yooj yim tshem tawm thaum ntxuav.

Cov ntsiab lus: Yuav ua li cas kom ntseeg tau tias Quartz Phab Ntsa Thickness rau Kub Boric Acid Corrosion Resistance

Quartz immersion heaters yog tshwj xeeb tshaj yog zoo- haum rau kub concentrated boric acid kev pab cuam ntawm 80-110 degree, nrog uniform corrosion tus nqi qis dua 0.0002 mm / teev nyob rau hauv nruab nrab rau me ntsis acidic daws (pH 5-7). Standard phab ntsa thicknesses ntawm 1.5-2.0 hli muab kev pab lub neej ntawm 10,000-25,000 teev (1-3 xyoo) nyob ntawm qhov kub thiab txias pH, nrog corrosion ua lub luag hauj lwm nyob rau hauv tsis ua hauj lwm. Hauv kev saib xyuas, qhov kev txhawj xeeb tshaj plaws tsis yog corrosion tab sis cov boric acid crystals yog tsim rau ntawm quartz nto thiab qhov no tuaj yeem txwv qhov ua tau zoo ntawm kev hloov hluav taws xob. Txoj hauv kev zoo tshaj plaws los tswj cov crystallization yog ntxuav nws, ua kom sov qhov chaw vapor, thiab tswj cov kua dej kom ruaj khov. Cov phab ntsa tuab (3.0-4.0 hli) tsis muaj txiaj ntsig corrosion thiab ua rau 30-35% thermal nplua, yog li lawv tsis pom zoo. Rau pH- kho boric acid daws txog pH 9, quartz tseem nyob ruaj (tus nqi<0.0005 mm/hour); above pH 10, alternative sheath materials are required. When requesting quotations for boric acid heaters, specify the concentration, operating temperature, pH range, expected crystallization frequency, and cleaning protocol. This enables the manufacturer to recommend the optimal wall thickness-typically 1.5–2.0 mm-ensuring energy-efficient, long-term performance in nuclear shielding, fiberglass production, and other boric acid processing applications.