NIOSH Manua l of Analytical Methods N MAM Four th Edition SILICA A MORPHOUS  SiO MW

NIOSH Manua l of Analytical Methods N MAM Four th Edition SILICA A MORPHOUS SiO MW - Description

08 C AS Table 1 RTECS Table 1 METHOD 7501 Is sue 3 EV ALU ATI ON P ART IAL Issue 1 15 May 19 85 Issue 3 15 March 2003 OSHA Table 1 NIOSH Table 1 ACGIH Table 1 PROPERT IES solid d 22 g mL MP 1600 C SYNON YMS fumed amorphous silica Aerosil silica ae ID: 35484 Download Pdf

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NIOSH Manua l of Analytical Methods N MAM Four th Edition SILICA A MORPHOUS SiO MW

08 C AS Table 1 RTECS Table 1 METHOD 7501 Is sue 3 EV ALU ATI ON P ART IAL Issue 1 15 May 19 85 Issue 3 15 March 2003 OSHA Table 1 NIOSH Table 1 ACGIH Table 1 PROPERT IES solid d 22 g mL MP 1600 C SYNON YMS fumed amorphous silica Aerosil silica ae

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NIOSH Manua l of Analytical Methods N MAM Four th Edition SILICA A MORPHOUS SiO MW




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NIOSH Manua l of Analytical Methods (N MAM), Four th Edition SILICA, A MORPHOUS 7501 SiO MW: 60.08 C AS: Table 1 RTECS : Table 1 METHOD: 7501, Is sue 3 EV ALU ATI ON : P ART IAL Issue 1: 15 May 19 85 Issue 3: 15 March 2003 OSHA : Table 1 NIOSH: Table 1 ACGIH: Table 1 PROPERT IES: solid; d 2.2 g /mL; MP >1600 C SYNON YMS: fumed amorphous silica (Aerosil, silica aerogel, sili cic anhydrid e); fused amorp hous silica (Ca b-o-sil, collo idal silica, xerogel, diatomac eous earth); hydrated amorphous silic a (Hi-sil). SAMPLING MEASUREMENT SAMPLER: FILTER (Total) or CYCLONE + FILTER

(Respirab le) (10- mm cyclone , nylo n or H iggin s- Dewell + 5-m PVC membrane) FLOW RA TE: Total: 1 to 3 L/min Nylon cyclon e: 1.7 L/min HD cyclone: 2.2 L/min VOL-MIN: 50 L -MA X: 400 L @ 5 mg/m (limit to 2 mg dust on filter). SHIPM ENT: Routine SA MPLE STABILITY: Stable indefin itely BLA NKS: 2 to 10 fiel d blanks per set BULK S AMPL E: High volu me area air sample required TECHN IQUE: X-RAY POWDER DIFFRACTION AN AL YTE: Cristo balite ASH: Llow tempera ture plasma; acid wash; depo sit on PVC filter XRD A NA LYSIS: XRD for quartz, cri stobalite and tridymite befor e and after heating HEAT:

1500 C, 2 h (fumed amorpho us silica) or 11 00 C, 6 h (other amorph ous sil ica); r edepo sit on Ag filter CALIBRA TION: Standard suspe nsions of amorpho us silica in 2- propa nol, co nver ted to cristobalite as fo r samples RA NGE: 0.2 to 2 mg per sample ESTIMATED LOD: 0.005 mg per sample PRECISION ( ): 0.10 @ 0.4 to 5 mg; 0.33 @ 0.2 mg [1] ACCURA CY RANGE STUDIED: Not studied BIA S: Not determined OVERALL PRECISION ( rT ): Not determined ACCURA CY: Not determined APPLICABILITY: This met hod i s specif ic for amorph ous sil ica in crysta lline (e.g. , quar tz) mat rices i n the range 1 to 1

0 mg/m for a 200- L air sample. Amorp hous silica usual ly contains some cry stalline silica [2]. See also discussio n of crystallin e silica in Chapt er R o f this v olume [3 ]. INTER FERENC ES: Albite, ammonium phosphate and tridy mite interfere w ith the larg est peak of cristo balite. Quar tz and cristob alite are q uanti tated prior to he at tre atment a nd sub tracte d from t he fin al qu antity of cri stobal ite. Al kali a nd al kaline earth oxid e pre vent 100% co nver sion; t hese a re re moved b y acid -was h pri or to heat t reatmen t. X RD sig nal in tensity is pro porti onal to

particle size; similar particle siz e of samples and standards is de sirable. OTHER METHOD S: This method makes improv ements in sample hand ling and q uality assura nce to P&CAM 31 6, which i replaces [4,5]. The XRD analysis steps are sim ilar to those in Method 7500 (Silica, crystalli ne).
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 , Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 2 of 8 NIOSH Manua l of Analytical Methods (N MAM), Four th Edition REAGENTS: 1. Am orphous si li ca standar d appropr iat e to t he air sample, i .e. , one of the f oll owing: a. fumed amo rp ho us si ca gr

ad e C AB- O- SIL M- 5, ava ilable fro Ca bot C orp.; www.cabot -corp. com; b. gell ed amorphous sil ica, grade Bri tesor b D300 xer ogel , av ai la bl e fr om The PQ Corp. , PO Box 8 40, Val le y Fo rge, PA 19482-0840; www.pqcorp. com; c. diatom ace ous earth amorphous sil ica, grade Cel it e 521, av ail able f rom Fisher Scient if ic; www.fi shersci .com; d. preci pit ated amorphous sil ica, grade Zeothi x 265, avai labl e from J.M. Huber Corp.; www.hubermateri als. com. NOT E 1: Som e gell ed or pr ecipi tat ed amorphous sil icas cont ain up to 7% moisture. Dry all amorphous sam ples ove

rnigh t at 115 C [5 ]. NOT E 2: XRD signal int ensit y i s proport ional to par ti cle si ze. Siev e the st andards (10- m sieve ), if nec ess ary, to atc h th e p ar ticle size ex pe cte d in the samples 2. 2-Propanol , r eagent gr ade. 3. ater , dei oniz ed. 4. Sodium chlor ide, reagent grade. 5. Hydrochl ori c acid, 2% (v/v) . Di lut e 20 mL conc. H Cl to 1L with deionized water. 6. De sicc ant. * S ee S PECI AL PR ECAUTI ONS EQUI PMENT: 1. Sam pler: a. Total dust : 37 -mm di ameter, 5.0 -m pore siz e, p ol yv in yl chl ori de fi lt er ( MSA, Ge lm an G LA -500 0, or e quiva lent)

support ed wit h backup pad i n a two- piece, 37-mm cassett e fi lt er hol der (pref erabl y, conducti ve) hel d toget her by tape or cell ulose sh ri nk band. NOTE: Gelman VM-1 and Mil li pore BS filte rs are un ac ce pta ble because of hi gh ash or am orph ous silica co nten t. b. Respirabl e dust: PVC fil ter (1.a . abov e) plus cy clone, 10-mm nyl on or Hi ggins- De well (H D), w ith sam pling h ead holde r. Holder must keep the casset te, cycl one an d c ou ple r to ge the r rig idly s o th at a ir ente rs on ly at the cyc lone inlet. c. Area sample: PVC fil ter (1.a . abov e) at 3 L/min.

2. Personal sampling pu mps 1 to 3 L/min ( tot al or ar ea); 1 .7 L/m in (nylon c yclone ) or 2.2 L/m in (HD cyclone). 3. Fil ter s, PVC, 25-mm diameter , 0. 45-m pore si ze. 4. Filters, silver mem brane, 25-m diame ter, 0.45- m pore si ze, avai labl e from Sterl it ech Corp., 22027 70 th Ave S, Kent , W A 98032- 1911; www. sterl it ech.com. 5. X-ray powder di ffr actometer wi th copper target X-ray tube and scintill ation detector. 6. Glu e or t ape fo r s ecu ri ng A g f te rs t o XRD holder s. 7. Reference speci men (m ica, Arkansas stone or oth er sta ble sta nda rd) fo r data normali

zat ion. 8. Low temperatur e plasma asher ( LTA) or muffle fur nace. 9. Fil trat ion ap parat us wit h side- arm vacuum fl ask and 25- and 37- mm fi lt er hol ders. 10. Sieve, 10-m pore siz e, f or wet siev ing. 11. Furnace capabl e of maint aini ng 1100 C for 6 h or 1500 C for 2 h and of tem perature programm ing t o 500 C at 50 C/min. 12. Crucibl es, pl ati num, wit h covers. 13. Analyti cal balance (0.01 m g). 14. Sti rrer , magneti c, wi th t hermall y- insul ated top. 15. Ultr asonic b ath or probe. 16. Pipet s, 2- to 25- mL.
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 ,

Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 3 of 8 NIOSH Manua l of Analytical Methods (N MAM), Four th Edition EQ UIP EN T - c on t.: 17. Volumetri c fl asks, 1-L. 18. Desicca tor. 19. Bottle, 1-L, wi th ground glass s topper. 20. Dryi ng oven. 21. ash bott le, poly ethy lene. 22. Mortar a nd pestl e, agat e. 23. Rubber pol iceman. 24. Beakers, 100- mL, with watchgl ass covers. SPECIA L PRECAUTIONS: 2-Propanol is f lamm able. Hydro chlor ic aci d is co rrosi ve and shoul d be handled in a fume hood. SA MPLI NG: 1. Cali brat e each personal sampling pu mp with a r epresent ati ve sampler i n li

ne. 2. Sam ple at 1 to 3 L/min (t otal and area) , 1. 7 L/min ( nyl on cycl one) or 2.2 L/ min (HD) for a tot al sam ple size of 50 to 40 0 L. NOT E 1: Do not al low t he cycl one to be inv erte d at any ti me. Turning t he cycl one to an yt hing other than a hori zont al or ient ati on may deposi t over -si zed materi al f rom the cycl one body onto the filt er. NOT E 2: A sin gle sa pler/flow rate s hou ld be u sed for a g iven a pplica tion. Sa pling fo r both cry stal li ne sil ica and coal mine dust shoul d be done i n accordance wi th t he ISO /CE N/A CG IH/A ST M r esp irable a eros ol

sam pling c onv ention . Flow rates of 1.7 L/min for the Dorr -Oli ver ny lon cy clone a nd 2.2 L/ min for t he Higgi ns-Dewell cycl one have been f ound to b e opti mal for t his pur pose. Outsi de of coal mine dust sampli ng, the reg ula tor y ag en cie s c ur re ntly u se the se flow rat es with the Do rr- live r c yclo ne in the Uni ted St ates and t he Higgi ns-Dewell sampler i n the Uni ted Ki ngdom. Though the sampling r ecomm endati ons present ed in a NIOSH Criter ia Document have be en form ally acce pted by MS HA for c oal m ine du st sa pling, the Do rr-O liver cyclo ne a t 2.0

L/min wi th 1. 38 conversi on fact or i s current ly used i n the Uni ted St ates f or t he purpose of m atch ing an earlier s am pling c onv ention [6]. In an y cas e, a s ingle s am pler/flow rate should be used i n any giv en appl icat ion so as to el iminat e bias int roduced by differ enc es b etwe en s am pler type s an d sa pler c onv ention s [3]. SA MPLE PREPA RATI ON: 3. As h the sam ple filter in a 100 -m L be ak er in the LT A ac cor ding to m anu fac turer 's instru ctions . After ashing, carefully ( so as to avoid loss of sam ple) add 50 m L 2% HC l to each beake r. 4. Cover t he

beaker wi th a wat chglass. Agit ate i n an ul traso nic bat h for at least 3 min (unt il the agglom erated particles are broken up). W ash the und erside of the watchglass with disti ll ed water, collecti ng the was hings in the sam e beak er. 5. Place a 25-m PVC fil ter in t he filt ration apparatus. Attach the funnel secu rely over the entire fi lt er ci rcumference. it h no vacuum, pour 2 to 3 mL deion iz ed water onto t he fi lt er. Pour t he sample suspensio n from the beaker int o the f unnel, and appl y v acuum. After the t ransfer , r inse the beaker several ti mes with dei oniz ed

water and add ri nsings t o funnel for a tot al v olume of 20 mL. All ow the suspensi on to set tl e for a few minutes p ri or t o fi lt rati on. Do not wash the chi mney wall s or add dei oniz ed water to t he chimney af ter fi lt rati on has begun. Rinsi ng the chi mney can distur b the thin layer d epo sition. W hen filtration is c om plete, k eep vac uum on u ntil filter is dry. Rem ove th e fi lt er wi th f orceps and at tach i t t o the sample hol der for XRD analysi s.
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 , Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 4 of 8 NIOSH Manua l

of Analytical Methods (N MAM), Four th Edition CALI BRATI ON AND QUALI TY CONTRO L: 6. eigh ca. 1 00 m g drie d am orph ous silica to th e ne ares t 0.01 m g. Q uan titatively trans fer to a 1-L bott le usi ng 1.00 L 2-propa nol. The resul ti ng concentr ati on is 100 g/mL. 7. Su sp en d th e p ow de r in 2 -p ro pa no l us ing an ultr as on ic p ro be or b ath for 20 m in. Im ed iate ly move the 1-L bot tl e to a magneti c sti rrer wit h ther mally -i nsulat ed top an d add a st ir ri ng bar t o the suspension . Al low t he solu ti on to r etur n to r oom tem perat ure befo re wi thdr awing

al iquot s. 8. Prepare a seri es of st andard f il ters, in t ri pli cate, over t he range 0. 005 to 2 mg per sam ple. a. Mount a 37-mm PVC fil ter on the f il trat ion ap parat us. Pl ace several mL 2-propanol on the fi lt er. Turn off t he sti rrer and shake the bott le v igor ously by ha nd. I mm ediat ely remove the stopper and wit hdraw an al iquot (e. g., 2 to 25 mL) by pi pet f rom the center at hal f-hei ght of the suspe nsion. Do not adjust the volum e in the pipet by expelling part of the suspension. If m ore than the d esire d aliqu ot is with draw n, disc ard th e aliqu ot in a b

eak er, rins e an d dry the pipet, and take a new a li quot. Transfer the al iquot from the pi pet t o the f il ter, keeping t he ti p of t he pipet near t he surface but not submerged in t he del ive red suspensi on. b. Rinse t he pip et wi th seve ral mL 2-propanol , dr aini ng the r inse i nto t he funnel . Repeat the r inse several more times. c. All ow the suspensi on to set tl e for a few minutes p ri or t o appl yi ng vacuum. Appl y v acuum and ra pid ly filte r th e s us pe ns ion . D o n ot w as h d ow n th e s ide s o f th e fu nn el a fte r th e d ep os ition is in plac e sinc e

this w ill rearran ge th e m ateria l on the filter. Lea ve va cuu on u ntil the filter is dr y. hen thor oughly dry , mount t he fi lt er i n the XRD sample holder 9. Prepare and analy ze st andard f il ters exactl y l ike samples. a. Ash in LT A; redepos it on 25-mm PVC fil ters (steps 3 through 5). b. Analyze by XRD (s tep 13). c. Heat to conve rt amo rphous s il ica to cristobali te; redeposit on Ag filt ers (steps 14 throu gh 16). d. Analyze by XRD (s tep 17). 10. Prepare c alibrati on graph ( vs. g of standard). NOTE: Po or re pea tability (i.e., S > 0 .1) at a ny g ive n le ve l ind

ica tes tha t ne w s tan da rd s s ho uld be m ade . Th e da ta sh ould lie along a stra ight line. A weig hted least s qua res (1/S weighi ng) i s prefer able. Curvat ure can be el iminat ed wit h absorpt ion cor recti ons (st ep 20) [7 ]. 11. Se lec t six silv er m em br an e filt er s to be an alyze d a s m ed ia b lan ks . M ak e th e s ele ctio n ra nd om ly from the same box of fi lt ers used f or redep osit ing samples. Mount each media bl ank on the filtration ap para tus a nd a pply vac uum to dra w 5 to 10 m L of 2 -pro pan ol throu gh th e filter. Rem ove, l et dr y and mount on XRD

holders. Determine net normali zed i ntensi ty for t he sil ver pea k, Ag , for ea ch m edia blank . Ob tain an ave rage value fro the six m edia blank s, NOTE: The analy st i s a cri ti cal par t of thi s analy ti cal pr ocedure [ 3]. A high lev el of analy st ex pe rtis e is req uir ed in o rd er to o ptim ize in str um en t pa ra ete rs an d c or re ct f or m atr ix int erfer ences ei ther duri ng the sample pr eparat ion ph ase or t he data a naly sis and interpretati on phas e. XRD analysts should have som e training (universi ty or short course) i n mineral ogy or cry stal logr aphy

i n order to hav e a background i n cry stal structure, diffracti on patterns and m ineral tr ansform ation. I n addition, an int ensive sho rt cou rse in the fu nda enta ls of X -ray diffra ction c an b e us efu l. MEAS UREMENT: 12. Ob tain a qua litati ve X -ray diffraction sc an (e.g., 10 to 80 2 ) of t he bul k (hi gh-vol ume respirabl e) sample to det ermine the presence of free si li ca poly morphs and int erfer ences. The di ffr acti on peaks are: Mineral Peak (2-T heta Deg rees) Prima ry Secon dary Tertiary Quartz 26.66 20.85 50.16 Crist obali te 21.93 36.11 31.46 Tridy mite 21.62

20.50 23.28 Sil ver 38 .12 44.28 77.47
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 , Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 5 of 8 NIOSH Manua l of Analytical Methods (N MAM), Four th Edition NOTE: For quant it ati ve det erminati on of amorphous si li ca in bulk samples, wet-si eve a por ti on of the bulk sam ple thro ugh a 10 -m sieve with 2- prop ano l in an ultra son ic bath . Evaporat e the al cohol a nd dry in a n oven 2 h. W eigh o ut, in t ri pli cate, 2-mg porti ons of the si eved d ust and t ransf er t o beaker s. Ad d 10 mL 2-pr opanol , de posi t on a PVC fi lt er

(st ep 5) and cont inue wi th st eps 13 thr ough 17. 13. Perform the foll owing for each sam ple, working standard an d blank filter. a. Mo unt th e ref eren ce s pec im en. D eterm ine the net inte nsity, I , of the r eference specimen before a nd aft er each f il ter is scanne d. Use a di ffr acti on peak of hi gh int ensit y t hat can be rapidly but reproducibly (S <0.01) measured. b. Mount the sample, worki ng standar d, or blank f il ter. Measure the dif fract ion pe ak area for each sil ica pol ymorph. Scan ti mes m ust be l ong, e. g., 15 min (l onger scan t imes wil l l ower t he li it

of detecti on). c. Measure the backgr ound on each si de of t he peak for o ne-hal f th e ti me used for peak scanning. The sum of these two co unts i s the av erage backgroun d. Det ermine the posit ion of the backgr ound for each sample. d. Ca lculate the n et inten sity, I , ( the di ffer ence between the peak i ntegr ated count and the tot al back ground c ount). e. Ca lculate and reco rd the norm alized inte nsity, , f or e ach p eak: NOTE: Se lect a c onv enie nt no rm alization s cale facto r, N, w hich is app rox im ately eq uivalen t to the n et co unt fo r the re fere nce spe cim

en p eak , and use this va lue of N fo r all ana lyses. Nor mali zi ng t o t he r ef er enc e sp eci men i nt ens ty compe nsa te s f or l ong -t er m dri ft i n X- ray tube i ntensi ty . I f i ntensi ty measurem ents ar e stabl e, t he refer ence speci men m ay be run l ess freque ntl y and the net int ensit ies shou ld be normali zed t o the most re ce ntly- ea su re d re fe re nc e in ten sity. 14. Rem ove th e PVC fil ter from the XRD holder, fol d the f il ter careful ly and pl ace it in a plat inum cru cible in th e fur nac e. Ra ise the tem pera ture o f the fu rnac e slow ly (ca. 50

C/m in) to 50 0 C to as h th e filt er . W he n a sh ing is c om ple te ( ca . 0.5 h), rais e th e te pe ra tur e to 15 00 C an d m ain tain at 1500 C for 2 h ( for f umed am orphous si li ca) or t o 1100 C and maint ain at 1100 C for 6 h (f or ot her amorphous si li cas). Turn the f urnace of f and l et t he cruci bles coo overni ght i n the f urnace. 15. Place ca. 10 mg NaC l i n the cr ucibl e and mix wit h the ash in t he cruci ble. Transfer content s of t he cruci ble t o an agat e mortar and gr ind t o a fi ne powder usi ng an agat e pestl e. Add di sti ll ed water fr om a po et

hy ene squ eez e bo tt e t o t he mor ta r. Use a r ubb er pol ceman to st r. W hen t he Na Cl is di ssolv ed, t ransfer the sol uti on to a 100-mL beaker (hol d the r ubber pol iceman at t he edge of the mortar to gui de the f low i nto t he beaker). Rinse mortar , pest le, cruci ble, and rubber poli ceman, coll ecti ng ri nsings i n the bea ker. Cover the beaker wit h a watchgl ass and pl ace in an ult rasoni c bath f or 2 t o 3 min. NOT E 1: se ex tre e c ar e to av oid air c ur re nts wh en wo rk ing with the dry s am ple , as it is e as ily los t in th e fo rm of a n a er os ol. NOT E 2:

Use unifo rm grindi ng techni ques to pr oduce si milar part icl e siz e in standar ds and samples. 16. ash the un dersi de of t he watchgl ass and col lect ri nsings i n the bea ker. Pl ace a si lve em brane filter i n the fil trati on appa ratus and filter t he contents o f the beake r (step 5). 17. Mount the sil ver mem brane fi lt ers i n the XRD inst rument and: a. Analy ze for the t hree si li ca poly morphs (step 13) ; and b. De term ine the norm alized c oun t, Ag , of an i nter ference- free si lve r peak on t he sample fi lt er fo llow ing the sa e p ro ce du re . U se a s ho rt s

ca n tim e fo r th e s ilve r pe ak (e. g., 5 of s ca n tim for anal yt e peaks) t hroughout the method.
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 , Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 6 of 8 NIOSH Manua l of Analytical Methods (N MAM), Four th Edition CALCULATIONS: 18. Ca lculate the c onc entra tion of am orph ous silica, C (m g/m ), as th e diffe renc e in cr istoba lite conce ntrations me asured b efore and after hea t treatment in the air volume sa pled, V (L): normali zed i ntensi ty for cr ist obali te sample peak on t he Ag fi lt er (st ep 17.a) normali zed i

ntensi ty for cr ist obali te sample peak on t he PVC fil ter before h eati ng (step 13) intercept of calibrati on graph ( vs. g) slope o f cal ibr ati on graph, counts/ f(t) R ln T/( 1 T ) = absor pti on correct ion f actor (Table 2) sin ( Ag )/si n ( Ag /(av erage ) = t ra ns ittan ce of s am ple Ag normali zed si lve r peak i ntensi ty from sample (step 17.b) normali zed si lve r peak i ntensi ty from m edia b lanks ( average of six v alues) NOTE: Com pute t he appl icabl e OSHA standard usi ng the f ormulae i n Table 1 and the % crysta lline silica fo und in the a ir sam ple be fore hea

t treatm ent. EVA LUATI ON OF METHOD: his m eth od is b as ed on NI SH P& AM 31 6 [4 ,5] w hic h w as fur the r ev alu ate d w ith f ield sa ple s in Ju ly, 1982 [1] . The rel ati ve stan dard devi ati on was deter mined to be r elat ed to t he ty pe of amorphous si li ca; gell ed, f umed, and preci pit ated amorphous si li ca yi elded 4.4%, 8. 2%, and 4.7%, r especti vel y, over t he range of 0.5 t o 5 mg. The m ethod was f urth er eval uated usi ng 11 di ffer ent t ypes of gell ed, pr ecipi tat ed, and fumed am orphous si li cas and di atomaceous earth [8] , wi th t he fol lowi ng concl

usions: 1. Not al l f umed sili cas convert ed to cr ist obali te at 1100 C. A highe r t emperature ( 1500 C) was neede to conv ert all the f umed sili cas to cr ist obali te. 2. The m oist ure cont ent of the gel led an d preci pit ated si li cas was ca. 7%; of diat omaceous earth, ca. 4%; an d o f ume d, f om 0 5 t o 3 %. 3. The cali brat ion cur ves fr om the four di ffer ent t ypes of amorphous sil icas i ndicat ed very simil ar sl opes (S = 6.6% ). 4. Com pari ng the f our sl opes to a slope o f a pure respi rabl e cri stobal it e material , t hey wer e runni ng approxi mately 30%

lower i n slope val ue. Theref ore, fi eld samples o f amorphous sil icas must be compared only to st andards pr epared f rom am orphous si li cas. 5. Preci sion st udies a t 0. 2-, 1-, and 2.5- mg level s (si x samples per l evel ) of gel led, preci pit ated, diatom ace ous earth , and fum ed s ilicas ind icated a po oled prec ision, r, of 8. 8, 10 5, 5. 6, an d 2 1. 5%, respect ive ly , fo r t he above si li cas. 6. Recovery studi es of t he same sili cas and concent rati on lev els i ndicat ed average recover ies of 82, 115, 95, and 1 11%, respect ive ly , wi th pool ed equal to 18. 2, 13.

1, 12. 9, and 15 .3%, resp ecti vel y, for t he gell ed, pr ecipi tat ed, and f umed sili cas, and di atomaceous earth
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 , Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 7 of 8 NIOSH Manua l of Analytical Methods (N MAM), Four th Edition REFERENCES: [1] Pa lass is J [19 82]. N IOS H In terna l Rep ort. C incinn ati, OH : Na tional Ins titute for O ccu pation al Sa fety and H ealth, (unpublished, August). [2] IO SH [19 81 ]. N IO SH /O SH A O cc up atio na l He alth G uid elin es for Ch em ica l Ha zar ds . C inc inn ati, OH: U.S. Depart ment of

Healt h and Human Services, Publi c Healt h Servi ce, Cent ers for Disease Control , Nati onal I nsti tut e for Occupat ional Safety and Healt h. DHHS (NIOSH) Publi cati on No. 81- 123. Av ail able a s GPO Stock #017-0 33-00337- 8 from Superi ntendent of Documents, W ashingt on, DC 20402. [3] Key- Schwartz RJ, Baron PA, Bartl ey DL, Rice FL, Schlecht PC [2003] . Chapt er R, Det erminati on of airbo rne c rystalline s ilica. In: NIO SH Ma nua l of An alytical M etho ds, 4 th ed., 3 rd Su pp l. Cin cin na ti, OH: U.S. Depart ment of Healt h and Human Services, Publi c Healt h Servi ce, Cent ers

for Disease Control , Nati onal I nsti tut e for Occupat ional Safety and Healt h, DHHS (NIOSH) Publi cati on No. 2003- 154. [4] NIOSH [1980]. Amorphous Sil ica: Method P&CAM 316. In: Tayl or DG, ed., NIOSH M anual of Analy ti cal Met hods, 2nd ed., Vol. 6. Ci ncinnat i, OH: U.S. Depart ment of Healt h and Human Servi ces, Publ ic Heal th Serv ice, Centers f or Disea se Control , Nati onal I nsti tut e for Occupat ional Safety and Healt h, DHHS (NIOSH) Publi cati on No. 80- 125. [5] Lange BA, Haart z JC, Horn ung RW [1981] . Det erminati on of sy nthet ic amorphous si li ca on indust ri al ai

r samples, Anal Chem 53 (9): 1479-84. [6] Inh al ed Par ti cle s and Vap ours [19 61] . Pe rgamon Pre ss, Oxford, U.K. [7] Leroux, J, Powers C [1969] . Di rect X-ray dif fract ion qu anti tat ive analy sis of quart z i n indu stri al dust film s de pos ited on silver m em bran e filters, L uft 29 (5): 26. [8] Palassi s, J [ 1984]. Amorphous sil ica ana ly sis by X-ray powder di ffr acti on. Paper present ed to t he Am Ind Hyg Con ference. De troit , MI (May 1984). METHOD REVI SED BY: Rosa Key -Sc hwa rt z, Ph. D., NI OSH/ DART TA BLE 1. CA S N umb er s, RTE CS Nu mbe s, an d E xp os ur e L mi

s f or A mor ph or ou s S ca Fo ms Amorph ous For ms CAS# RTECS OSHA PEL (mg/m NIOSH PEL (mg/m ACGIH T LV (mg/m diatomaceous earth, <1% crystalline SiO 61790-53-2 HL8600000 80/% SiO 10 (total) precipitated, and gel 7699-41-4, 112926-00-8 VV8850000 80/% SiO 10 (total) fumed 69012-64-2 112945-52-5 VV310000 80/% SiO 2 (respir) fused 60676-86-0 VV7328000 0.1 (respir)
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SIL ICA , AM ORP HOU S: M ETH OD 7 501 , Is sue 3, dat ed 15 Ma rch 20 03 - Pa ge 8 of 8 NIOSH Manua l of Analytical Methods (N MAM), Four th Edition Table 2. MATRI X A BSORP TI ON CORRE CTI ON FA CTORS F OR CRI STOBA

LI TE ( HEA T- CONVERT ED AMOR PHOUS SILICA) AND SILVER PEA KS. Degrees 2- Cris toba lite Sil ver 21.93 38.12 21.93 44.28 21.93 38.12 21.93 44.28 f( T) f( T) f( T) f( T) 1.00 1.0000 1.0000 0.74 1.2806 1.3278 0.99 1.0087 1.0100 0.73 1.2944 1.3440 0.98 1.0174 1.0201 0.72 1.3084 1.3605 0.97 1.0264 1.0305 0.71 1.3226 1.3774 0.96 1.0355 1.0410 0.70 1.3372 1.3946 0.95 1.0447 1.0517 0.69 1.3521 1.4122 0.94 1.0541 1.0625 0.68 1.3673 1.4303 0.93 1.0636 1.0736 0.67 1.3829 1.4487 0.92 1.0733 1.0849 0.66 1.3987 1.4675 0.91 1.0831 1.0963 0.65 1.4150 1.4868 0.90 1.0932 1.1080 0.64 1.4316 1.5064 0.89 1.1034

1.1199 0.63 1.4485 1.5266 0.88 1.1137 1.1320 0.62 1.4659 1.5472 0.87 1.1243 1.1443 0.61 1.4836 1.5684 0.86 1.1350 1.1568 0.60 1.5018 1.5900 0.85 1.1460 1.1696 0.59 1.5204 1.6122 0.84 1.1571 1.1827 0.58 1.5394 1.6349 0.83 1.1685 1.1959 0.57 1.5590 1.6582 0.82 1.1800 1.2095 0.56 1.5790 1.6820 0.81 1.1918 1.2232 0.55 1.5995 1.7065 0.80 1.2038 1.2373 0.54 1.6205 1.7317 0.79 1.2160 1.2516 0.53 1.6421 1.7575 0.78 1.2284 1.2663 0.52 1.6642 1.7840 0.77 1.2411 1.2812 0.51 1.6870 1.8112 0.76 1.2540 1.2964 0.50 1.7103 1.8391 0.75 1.2672 1.3199