CA1308037C

CA1308037C - Chemical filter

Info

Publication number: CA1308037C
Application number: CA000525424A
Authority: CA
Inventors: Carl Girvin Harkins
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1985-12-20
Filing date: 1986-12-16
Publication date: 1992-09-29
Anticipated expiration: 2009-09-29
Also published as: EP0230580A1; DE3664567D1; EP0230580B1; JPS62155917A; US4684510A

Abstract

Abstract Or the Disclosure: A chemical filter is provided for preventing pollu-tants in the atmosphere from contaminating sensitive electronic equipment, such as hard disc drives. The chemical filter comprises a layer of charcoal or char-coal-impregnated foam to remove organic contaminants and at least one layer of a high surface area metal to remove inorganic pollutants, such as SO2, H2S, NO2 and Cl2. In one embodiment, the chemical filter comprises a layer of charcoal, a layer of a copper foam, a layer of a nickel foam and a layer of a particle filter.

Description

~3~ 37 ChEMICAL FILTER

1 ack~round of the Invention:

Thi~ invention relate~ to chemlcal filter~, and, more particularly, to a chemical Pilter Por protecting 5 ele~tronic equipment, sucn aY hard di~ca ~or computers~
from pollutants in the air.
Atmospheric corro~ion of ~rromagnetic ~aterials by pollutant molecule~ such a~ SO~, H2S, NO~ and Cl2 i~ a 3erious problem in many plant environment~ in which computer equipment 13 used5 such a~ Por proce~ control.
Examples of such plant environments include paper mills and oil refinerie~. While the le~el of pollutants at such plants may be within OShA qtandards, nevertheless, even pollution levels in the range of part~ per billion, far below what i~ permis~ible for human~ detrimental to component~ in computer equlpment, such as metals employed in electrical connections on printed circuit boards and in aisc drive3. Importantly~ ferromagnetic materials, 9UCh a~ cobalt, used 1n disc ~rives are a~-v~r~ely af~acted by pollu~ants.
In hard disc drive~ employing cobalt, for exam-ple, th~ chemical reaction of the pollutants with the metal servea to rorm corrosion proauctg such a oxi~e ~ nd chlorides, Which have a larger crystallographic cell ~tructure than the metal itgelf. Thi occur~ as a result of water vapor from the atmogphere, whioh form~ a thin film, about 100 to ~00 ~ngstromg tnick. The pollu-tant~ ~lssolve in the water film, formin~ an a¢i~ elec-trolyte, which corrode9 the metal. AQ a consequence of .

r 3~3~8~ 3 7 the ~ormation of the corrosion pro~ucts, 'chc disc ~rive ~-hea~, which i~ po~itiolled to travel at a hi8h rate of ~peed very cloee to the metal urface, hit~ tne expandea corro3l0n proaucts, called "crashing", with con3equent 5 damage to the hea~ ana possible 109~ of data.
A further problem inclu~es organic ~ontaminants in the atmo~phere, which are readily polymerized by cobalt ;and cobalt oxide, well-known for their catalytio proper-ties. The presence o~ organic polymer~ cau~es a problem 10 termeC ~3tiction", in which the hea~ of the dlsc drive aahere3 to the organic film and i~ ~ubsequently torn off during operation of the aisc ~rive.
Attempts have been made to minimize the corro~ion problem by rormlng a protective film ovor the metal 15 surface. However, the protectlve film hai3 been found to reduce the qignal from the magnetic ~omains in the metal film.
The solution de~cribe~ a~ove ha~ been applied to disc driveY which are primarily ~ealed but nonethele~
Z0 communicate with the out~ide atmosphere. In ~uch units, the flow of air to the hard disc unit i9 on the oraer of 15 to 100 ft3 over the lifetime of the unit. The flow of air is con3idersd necessary for maintainin~ the in-ternal pre33ure the ~ame a~ the amblent barometric pres-;25 ~ure. In many en~ironment , thi~ i~ sufficient to cau~e corroi~ion fallure.

Accordingly, it is an object of an aspect of this invention to provide a filter for pre~enting atmo~pheric pollu~ants from contamlnatin~ metal ~urface~ in electronlc equip-ment.

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~3~3037 It is an object of an aspect of this invention to provide a chemical filter which readily permits passage of air therethrough and thus permits e~ualization of atmospheric pressure in a hard disc drive unit, while removing pollutants from the air.
These and further objects of the invention will become apparent from the hereinafter following commentary taken in conjunction with the drawing.
In accordance with one aspect of the invention, a chemical filter is provided which includes at least one layer of a high surface area metal mesh. Additionally, the chemical filter may include a layer of charcoal and a particle filter. The chemical filter is maintained in a housing, which is provided with an inlet for admitting air and an outlet for exhausting air into an otherwise sealed electronic unit.
Other aspects of the invention are as follows:
A chemical filter for preventing pollutant molecules in the air from contaminating electronic equipment comprising:
ta) a housing having at a first end an inlet means for introducing polluted air into said housing and at a second end a gas outlet means for introducing purified air into said equipment;
(b) a layer of charcoal adjacent said inlet means;
(c) at least one layer of a high surface area metal mesh adjacent said layer of charcoal;
(d) a particle layer between said at least one layer of metal mesh and said outlet means; and (e) an anti-diffusion tube attached to said gas inlet means, said anti-diffusion tube having a length and diameter to reduce water vapor diffusion into a disk drive electronic unit to no more than about 1 g/yr at 30C.

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In combination, an enclosed hard disk drive unit and a chemical filter attached thereto to permit equalization of air pressure therein and to filter pollutant molecules from air introduced into said unit, said chemical filter comprising:
(a) a chamber defined by a housing, said housing provided with an inlet means at a first end for admitting polluted air and an outlet means at a second end for introducing filtered air into said hard disk dri~e unit, said outlet means connected to an air pressurization inlet in said drive unit; and (b) in sequence, the following layers of materials, beginning at said first end;
(1) charcoal, (2) high surface area copper mesh, (3) high surface area nickel mesh, and (4) particle filter.
A method of prevention pollutant molecules in the atmosphere from reacting with electronic equipment comprising:
(a) providing a chemical filter between said electronic equipment and said atmosphere, said chemical filter comprising:
~1) a housing ha~ing a gas inlet means at a first end for admitting polluted air thereinto and a gas outlet means at a second end for introducing filtered air to said electronic equipment, and (2) at least one layer of a high surface area metal mesh within said housing, said at least one layer of metal mesh capable of chemically reacting with said pollutant molecules to form corrosion products which remain in said filter;
(b) introducing said polluted air into said filter;
(c) reacting said pollutant molecules with said at least one layer of metal mesh; and 3a ~`
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~3~ 37 (d) introducing said filtered air to said electronic e~uipment.
Brief Description~of_the Drawing:
FIG. 1 is a schematic of a hard disc drive, including the chemical filter of the invention;
FIG. 2 is an exploded view of a preferred embodiment of the chemical filter of the invention; and FIG. 3 is a three dimansional view of the chemical filter of the invention, partially ~roken away, showing the relationship of the various layers depicted in FIG. 2.
Detailed Description of the Invention:
Referring to the drawing wherein like numerals of reference designate like elements throughout, a piece of electronic equipment which is to be protected from pollutants in the atmosphere is depicted in FIG. 1. In 3b 13~8~3~

1 particular, a hard diso drive 10 iq ~hown, compri~ing a disc 12 mounted on a shaft 14 wnich iQ rotate~ by a motor 1~. The motor 16 i9 controlled by electronic controller 1&.
A housln~ Z0 ~urroun~s the nard diqc 12, formin~ a cham~e~ 21; a seal 22 i~ provided for the shaft 14 to pass throu~h the housin~ ~0. An internal particle filter 24 in the chamber 21 reduceQ particles generated by abra~i~n and the like during operation of th0 diqc drive. A head 26, Qpaced from the top surface of the alsc 12, i9 u~ed to wrlte and read information stored in ma~netic domains formed ~n the ~urface oP the hard disc 12.
The hard disc may comprise any material commonly u~ed l~ the construction of -quch units; for exa~ple, an aluminum qub trate coate~ ~ith co~alt may be employed.
Inasmuch aq the di~c drlve unit is not a part of this invsntion, the ~oregoin~ deQcrlption 13 proYldea merely ~or illustration of one use to which the chemical filter of the inv~ntlon may ~e put.
In accor~ance wlth the invention, a chemical filter 30 i9 provi~ed. The chemical filter co~priseQ a houQin~
32 provided with an inlet mean~ 34 at it~ di~tal en~ ana an outlet ~ans 36 at its proxlmal end. Ths inlet means 34 i3 ooupled to tne hou~ing 32 by coupling means 3~, while the outlet means is couple~ to the housing 3~ by coupling meanq 40. The couplin~ means may comprise any - such mean~ well-known, such aq nuts and the like.
The material of the filter housin~ 32 may compri~e any convenient material, such a~ a plaatic. Alterna~
tively, the housing 32 may comprise a metal, which could be employe~ ag one corroQion cell electrode when using a hi~h surface area metal mesh ag the ~econd electrode.

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~3~ t7 1 The formation of corroqion cells iQ di~cussea more fully below.
The inv~ntion resi~es in means ~or removing multi-ple pollutants Srom the alr entering the inlet means 34.
~he followin~ mean~ for removing pollutants ~rom the air may be employed: a layer of charcoal 42 to remove organ-ic contaminaat3 an~ at least one layer 44 of a high surface area metal mesh to remove inorganio pollutants.
~hile nat essential to the operation of the lnvention, a partlcle rllter 46 i~ suitably employed to prevent par-ticle~ o~ charcoal, metal or corrosion produ¢t (reaction of pollutant with the metal mesh) ~rom entering the interior 21 of th~ disc dri~e unit 10. The particle filter 4~ may oompri~e any material conveniently u~eful for such purpose. Exemplary suitable particlc filter material~ include paper, glasR fiber~ or porous plastic materials suitable for retaining particles larger than about l micrometer.
The charooal employea in layer 42 may comprise any hl~h qurface area charcoal commercially available, but preferably ls a charcoal incorporated in a polyes~er or polyurethane foa~. Such charcoal foam i9 commercially available fro~ Lewcott Chemical~ ~ Plastics, Milbury, Mas3achu~ett3. Ag indicate~ above, the charcoal is used ~5 primarily ~o ad~orD organlc contaminants, although the charcoal is helpful in partially removing inorganic pollutants a well.
At least one metal layer 44 is employe~ to remove inorganic pollutants, such as S02, ~2~ N02 an 2 Prefera~ly, a combinatio~ of two metals is employed, one to remove sulPur~containing and nitrogen-containing pollutants and one to remove chlorine-contain~ng pollu-tants. A metal sultable for the rormer cage i3 copper or lver, whi}e a ~etal ~uitable for tne latter caqe i ~.~, .

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~31~;37 nickel or zinc. Most preferably, two layers, 48 and 50, are employed, layer 48 comprising a high surface area copper mesh and layer 50 comprising a high surface area nickel mesh.
The metal mesh is a high surface area material, typically on the order of 2 to 3 m2/g, with a fine pore size on the order of a few mils. A convenient material to use is a metal foam, which is commercially available as Foametal,~M from Hagen Industries, Willoughby, Ohio.
Alternatively, metal felts are also available which may be advantageously employed in the practice of the invention; metal felts such as Met-L-Mat,TM a product of National-Standard, Corbin, Kentucky, may be used.
It will be appreciated that the use of the term "metal" in the context of the present invention encompasses not only pure metals, such as copper and nickel, but also alloys, which also perform the same function as described above. Examples of suitable alloys include brasses and copper-silver.
For use in a 5-1/4 inch hard disc drive, the chemical filter of the invention conveniently comprises disks of material (charcoal, metal foams and particle filter) about 1 inch in diameter and 1/8 inch thick.
For this low flow application, the inlet and outlet means 34 and 36, respectively, are tubes having an ID of about 1/8 inch or less.
The foam is about 45% dense and thus does not greatly reduce the volume of air flow therethrough.
Consequently, the chemical filter of the invention may also be employed in high flow applications as in con-~unction with cooling fans, ~hich are provided for cooling electronic equipment. In such a configuration, one or more of the metal foams may be placed in a holder between the cooling fan and printed circuit boards of ~3~8~37 1 electronic devices. Even though the circuit boardq are exposed to the atmosphere, the removal of pollutant~
fro~ the flow Or air from the ran, iQ sufficient to retard the corrosion of the metal connectlons on the circuit board.
The chemical fi~ter of tne invention may employ ju~t one metal ~oam or ~elt. ~owever, better results are obtaine~ uqing one metal in eom~ination with the charcoal, and even bctter re~ult3 are obtained u3~ng tWG
metals in com~ination with the chareoal. For ai~e ~rive applicationg, ii; i3 prererred to employ the particle ~ilter at the exit ~rom the ehemlcal ~llter.
Most prereraDly, the two metal~ or a metal and carbon (aeting a8 a noble metal) are eho3en and config-ur~d 90 as to form a galvanie eorroaion eell within thechemical filter. In partieular, a noble metal and an actlve metal are plaeed in electrical contact. The placement of the two metal~, ~or example, copper and nickel, in eleetrioal eontaet potentlate the eorro~ion cell. Water vapor ~rom the air formQ a water film electrolyt~ on the metal ~iqkq and thuq eQtablisheq ~he cell. The eorrosion eell eon~i~uration proviae~ a fa~t-er rate o~ reaetion with ~h~ eontaminant~; the potential differena~ betwean the two ~etals is an additional ariv-ing mechani~m to form corro~ion product~.
As an example, har~ di~e~ followin~ manu~aeture were mapped and founa to evidence abou~ 20 detectabledefects over the surfaoe of the di~c. Exposure to 15 ft3 of polluted air of the type de3eribed above resulte~
in about 3,~00 de~eet~, while use in the same pollu~e~
environme~t of th~ chemieal fllter of the invention, eompri~i~g four layerg (charcoal, eopper, nie~l and the particle filter, eonfigured as a eorro3ion cell), showed no change from the aq-manufae~urea ~i-qe.

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1 It may be de~ireq to al~o reduce the amount o~
water vapor ~ n the a$r Yrom reaching the chamber housing the ~isc arive. ~hile the cobalt fiIm of the hara disc i~ provided with ~ cobalt oxi~e ~ilm for protection, 5 neverthess~ there i3 alway~ the po~sibility of pinhole~
in the oxlde ~ilm, through which water Yapor can pene-trate and react w$th the underlyin~ cobalt to form cobalt oxide and recordin~ ~efect~. The uncontrolled growth of th~ new cobalt oxide resultq in an expan~ion oP the ~ur~acs layer, agaln creating the possibility of crashin~ of th~ hea~ a~a$nst the surface, as ~eqcrl~ed earller.
The trappin~ of water vapor may be accomplished by provi~ing a de3sicant, ~ither associated wlth the che~-15 cal fllter or as a separate unit which communicatesairectly with the di~c drive chambcr. If u~ea ln con-Junctlon wlth the chemical filter of the invention, $t i~ preferrcd that the des~icant be located between the chemical filter an~ the aisc drlve housing. In this mannor, water vapor will ~e avallable to e~taDlish the preferred corrosion cell in the chemical filter, as ~escribed above.
Alternatively, an anti-~iffu~ion tube 5~ may be provided. The anti-di~fusion tube i~ fabricatea ~rom pla~tic tubing havlng an ID and length cho3en in accor-dance with Fick'q law of ~lrfu~Lon. The anti-diffusion tube shoula ~e le39 than abou~ 1/8 inch ID, in order tG
prevent convect~on within the tube. For example, a tu~ing having an ID of 1 mm and a length of 10 cm, attached to the Xnlet mean~ 34 of the chemi¢al filter of the invention, will reduce the maxlmum water vapor dir-fu~ion flux at 30C to about 1 gfyr.
The anti-diffu~lon tube shoul~ be fabricated from a hyarophobic material, such a~ à plagtio. Examples in-~3~8~?37 clude polyethylene, polypropylene and polytetra-fluoroethylene. However, such materials should not include plasticizers, which are sufficiently volatile to act as an additional contaminant. Materials such as stainless steel, which form hydrophilic oxides, should be avoided in constructing the anti-diffusion tube in order to prevent wicking of the water vapor, which defeats the purpose of the tube.
For high flow rate applications, such as in conjunction with cooling fans, a change in color of one of the metals is sufficient to indicate a need to change the filter. For example, copper will turn black, while nickel will turn green. In such applications, the material comprising the housing 32 would conveniently be clear.
For low ~low rate applications, such as in conjunction with disc drives, the chemical filter of the invention is not intended to be removed, but rather is sized to last approximately 10 years in most polluted environments. Dimensions such as given above are adequate for this purpose.

EXAMPLES
Printed circuit boards patterned with a bridge circuit for measuring resistance changes induced by corrosion reactions were employed in the test. Metal disks comprising nickel and PermalloyTM (Fe-Ni alloy) were mounted such that one portion was directly exposed to the atmosphere, a second portion was exposed to the atmosphere through a first vented plastic (acrylic) chamber containing a 3 micrometer MilliporeTM particle filter, and a third portion was exposed to the atmo-sphere through a second vented plastic chamber contain-A

-` 13~8~37 1 ing the chemlcal ~llter of the invention. The particle filter in the ~econd chamber wa identical to that u~ed in the firqt ehamberO A similar arran~ement was used ~or comparl on of copper (or gold) conductors on the PC
~oards.
The chemical filter compri~ed a layer of charcoal ~oam, a layer of copper foam, a layer of nickel ~oam, and the particle filter. The charcoal foam wa~ inch thlck. Thc metal foams had a surface area of 2 - 3 m2/g 1~ and were 1/~ lnch thick.
In additlon to tne forsgoing ~ampleq, metal coupon~
(silver, copper and ~lnc) were directly expo3ed to the atmosphere. Th~ metal coupon~ provlded a qualitative mea~ure of the extent of ~ulfur- and chlorine-containing pollutant~ in the environment. While any of the fore-going metal~ will provide a suitable measure of the ~ulfur- and chlorine-containing pollutants, nickel i~
better for chlorine, while copper is better for Yulfur.
The chamber port openlngs were 0.55 cm in diameter anQ 0.32 cm ln le~gth. It was expected tnat for thi~
configura~ion, typical pollutant~ in the range of 10 to 100 pp~ should ~how ~luxe~ of a~out 1 to 10 millimoles per year.
All ~etal ~ample~ were cleaned in ~reon prior to ~5 mountlng on the PC board. Mounting was accomplishe~
u3ing hot-~elt polyethylene aahe~ive. Thi3 adhesive was al~o u~e~ to bond tha pla~tic chamberQ to the PC boards.
The DoarCs were then expoged to the environment at everal inaustrial plant ~ltes, inclu~ing paper mills 3G and oil reflnerie~. Expo9ure wag on the order of sever-al months.
Te~tlng for variou3 gpecieg a9~0ciated wlth common pollutant~ was done using X-ray rluore~cence analysi~
(~hF) ana ion chromatography (IC).
:

, ~3~37 ~xampls 1:

At plant Site A, the environ~ent wa~ high in ~ulfur (both h2S ana S02) and Clx (Cl2 and probabl~ ClO~). A
5 trace of ~ wa~ detected by IC. ~oth the di3k ana Permalloy ~electively reacted to ~orm chloriaeq. The 3 micrometer Millipore filter impeded ~ul~ur aiffu~ion, but wa3 not as effective in reducing C1x attack.
With regard to the chemical filter (~u11 filter;
charcoal, Cu, N~, par~le filter), ~he Goppsr foam trappea chlorine, but wa observed to be more efficlent for sulfur co~pou~d3. Clx 3pecies penetrating the cop-per foam were trapped by the nickel foam. Thi~ order of materials 15 preferred 3ince the nickel ~urface 1~ pro-15 teoted from the ~ulfur an~ remain~ available for chlo-rine scavanging. In long expo-qures, a~ditlonal chlorine react3 with ¢opper ~ulPide at the front copper ~urface.
The diqplacea sulfur then mi~rateq into the unreacte~
copper foam.
~The IC analyses conf'irm ana extend the ~RF re~ult~
: at Site A. Soluble chlorideg domlnate insoluble 9ul-fiaes. Tha 1-year full-filt~red ~alues were below khe limit of aetection even for this meaqurement technique~

~xample_2:

Site ~ was th~ s~cond mo3t aggressive ~ite. The environment at thi~ location tended to be high in ~ulfur .. compoun~s and low in Clx. Thig wa~ rerlected in the data from the Ag and Zn metal foil9. Again, the di~k and Permalloy gample9 in open air reacte~ with both~ but preferably with Clx. The particle ~ilter again impeded sulfur tranqport to the Yample9. The metal foam filter was leag challenged by the Site ~ environment than by : , "'"`
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1 tne Site A environment, qince the copper layer t,raps the sul~ur and the 3mall amount of chlorine without the reaction interface reaching the back side o~ the copper in 12 month~. The nickel foam evidenced little reaction an~ was not required a3 a backup chlorine trap. Thus, at a plant ~ite having the characteri~tic~ a~ Site ~, the chemlcal filter of the invention could include only the copper ~oam a~ the hlgh 3ur~ace area metal me~h.

~xample 3: ' The environment at Site C contalned ClX (primarily HCl) as the major contamlnant, ~ul~ur not being detecta~
on the exposed A~ and Cu coupons. A~ expected, both the ~isk and Permalloy sample~ reacted wlth Clx, even be-neath the particle filter. A variation on the chemical filter was al~o te~ted at this ~ite, compri~ing one or two charcoal layers over the particle ~ilter (omittin~
the metal mesh layer~). The results Qhowsd that the ad~ition of one or two charcoal layers over the particle ~ilter reduced the chloride attack of the ~ample~. The ¢harcoal impedo~ Clx, but it cannot be counted upon as a total barrler. In oomparl~on, th~ full chemical filter trapped ClX that ha~ difru~Qd through the charcoal lay-er.

Example 4:

The enYironment at Site D was the most se~ere 3ite for computer~ an~ wa~ located in ~he ~ame plant a~ SiteA (Exampl~ 1). For the 3ite D computer, room air condi-tionin~ plug an environmental cablnet reduce~ the copper activity over an or~er of magnitu~e. A gimilar reactiv-ity re~uction Yor the film gample3 and filter showed up . . , ,~.

13~8~37 1 in two ways: (1) tne IC ~ata for unprotected di~kq and X~F ~ata indicated that Clx reaction were down an or~er of magnitude, ana (2) tne volume o~ copper foa~ consumed in th~ ~ilter (mo3tly ~ulfide3) was al~o down by an order of magnitude. The XRF re~ult~ indicated that there was no corrosion on protected thin gilm 3amples, althou6h the IC ~ndicated a pos~ible chloriae pre~ence on Permalloy. If thl~ r0prssents enrironmental penetra-tLon through ;:opper ~oam, an ad~itional lay~r of nlckel 10 Poaa~ woult hav~ trapped the C~ x as at Site A.

E;xample 5;

,The environment at Slte E was the ~econd mo3t : 15 severe computer ~ite ~or copper. The high S/Cl ratio wa~ re~lecte~ in an analysl~ of one of the PC boards, whlch showed chloride formation on an unprotected di3k while the first copper ~llter layer qhowed ~ulfide for-mation without Cl. The Clx level at Site ~ wa~ low enough for chloride formation to be un~etectable un~er a particle ~ilter, and ~ulPur removal by the chemical filter i3 readily accompll~hed at this type o~ 3ite.

Almo~t all other siteq (other than onc) tested were much 1~9 r~active than ~hose described above. These other ~ites evldence~ nelther corro~on of the sampleq un~or the chemlcal filter Or the invention nor ~ailure of the chemical rilter. At the one gite mentione~, the . .~ata were div~rse and internally incon~igtentl and thus, the data wsre aigcar~ed from further consideration.

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', 13~C37 1 Example_6:

In or~er to explore the correlation ~etween field exposure and accelerated tests, field ~ample PC boards were exposed in a controlle~ environmental chamber for one week. In thi9 ca~s, the S/Cl ratios ana the amount of co-rsactants (150 ppb S02, 150 ppb ~2S, 40 ppb Cl2 and 300 ppb N02) were exactly known. As in the field, the transition metals reacted preferentially with the chlorin~, while the copp~r (foil and ~oam) ~orm~d 9ul~
~idos. Dlsk and Permalloy sampla~ reacts~ 3llghtly with S2 to rorm trace sulfate.q. There wa-~ minimal nitrate formation from N02, confirmin6 that th~ nitrate/nitrite sourc2 ~or filtered sample was probably not ga~ phase N02, but rather wa~ due to nitrocellulo~e ln the paper particle filter.
The acceleration factor for thi~ laboratory test was 50X for an aYerage industrial environ~ent, 90 the results o~tainea were equivalent to one year in such an ~0 environment.

Tnu~, there ha~ been disclo~ed a chamioal fllter espeoially adapted for use in protecting electronic equipment, ~uch aY har~ c drives an~ printed circuit board COA~O~tion3~ whi¢h preventg pollutant~ in the air from che~ically attackin~ the equipment. Various modi-~ication an~ changes will make themselves available to tho3e o~ ordinary skill in the art, an~ all 3uch changes -. ana variances not ~eviatlng from the splrit and essence of the inv~ntion are inten~e~ to be cover~d by the app en de d ola1m~.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A chemical filter for preventing pollutant molecules in the air from contaminating electronic equipment comprising:
(a) a housing having at a first end an inlet means for introducing polluted air into said housing and at a second end a gas outlet means for introducing purified air into said equipment;
(b) a layer of charcoal adjacent said inlet means;
(c) at least one layer of a high surface area metal mesh adjacent said layer of charcoal;
(d) a particle layer between said at least one layer of metal mesh and said outlet means; and (e) an anti-diffusion tube attached to said gas inlet means, said anti-diffusion tube having a length and diameter to reduce water vapor diffusion into a disk drive electronic unit to no more than about 1 g/yr at 30°C.

2. The chemical filter of Claim 1 wherein said at least one layer of metal mesh comprises at least two layers of high surface area metal mesh between said layer of charcoal and said particle filter.

3. The chemical filter of Claim 2 wherein said at least two layers of metal mesh, comprises one layer of a first metal mesh adjacent said layer of charcoal and a second layer of a second metal mesh adjacent said particle filter.

4. The chemical filter of Claim 3 in which said first metal mesh consists essentially of a metal selected from the group consisting of copper and silver.

5. The chemical filter of Claim 4 in which said first metal mesh consists essentially of copper.

6. The chemical filter of Claim 3 in which said second metal mesh consists essentially of a metal selected from the group consisting of nickel and zinc.

7. The chemical filter of Claim 6 in which said second metal mesh consists essentially of nickel.

8. The chemical filter of Claim 1 in which said anti-diffusion tube comprises a hydrophobic material and has a diameter less than about 1/8 inch.

9. In combination, an enclosed hard disk drive unit and a chemical filter attached thereto to permit equalization of air pressure therein and to filter pollutant molecules from air introduced into said unit, said chemical filter comprising:
(a) a chamber defined by a housing, said housing provided with an inlet means at a first end for admitting polluted air and an outlet means at a second end for introducing filtered air into said hard disk drive unit, said outlet means connected to an air pressurization inlet in said drive unit; and (b) in sequence, the following layers of materials, beginning at said first end;
(1) charcoal, (2) high surface area copper mesh, (3) high surface area nickel mesh, and (4) particle filter.

10. The combination of Claim 9 in which the metal meshes comprise metal foams or metal felts.

11. A method of prevention pollutant molecules in the atmosphere from reacting with electronic equipment comprising:
(a) providing a chemical filter between said electronic equipment and said atmosphere, said chemical filter comprising:
(1) a housing having a gas inlet means at a first end for admitting polluted air thereinto and a gas outlet means at a second end for introducing filtered air to said electronic equipment, and (2) at least one layer of a high surface area metal mesh within said housing, said at least one layer of metal mesh capable of chemically reacting with said pollutant molecules to form corrosion products which remain in said filter;
(b) introducing said polluted air into said filter;
(c) reacting said pollutant molecules with said at least one layer of metal mesh; and (d) introducing said filtered air to said electronic equipment.

12. The method of Claim 11 wherein said filter additionally comprises a layer of charcoal adjacent said gas inlet means.

13. The method of Claim 11 wherein said filter additionally comprises a particle filter adjacent said gas outlet means.

14. The method of Claim 11 wherein said at least one layer of metal mesh comprises at least two layers of a high surface area metal mesh within said housing.

15. The method of Claim 14 in which said metal mesh is selected from the group consisting of metal foam and metal felt.

16. The method of Claim 14 wherein said at least one layer of metal mesh comprises two layers of metal mesh, a first of said layers comprises a noble metal and a second of said layers comprises an active metal.

17. The method of Claim 16 wherein said first layer comprises a first metal mesh consisting essentially of a metal selected from the group consisting of copper and silver.

18. The method of Claim 17 in which said first metal mesh consists essentially of copper.

19. The method of Claim 16 wherein said second layer comprises a second metal mesh consisting essentially of a metal selected from the group consisting of nickel and zinc.

20. The method of Claim 19 in which said second metal mesh consists essentially of nickel.

21. The method of Claim 11 wherein said filter additionally comprises an anti-diffusion tube attached to said gas inlet means, said anti-diffusion tube having a length and diameter to reduce water vapor diffusion into said electronic equipment to no more than about 1 g/yr at 30C.

22. The method of Claim 21 in which said anti-diffusion tube comprises a hydrophobic material and has a diameter less than about 1/8 inch.

23. The process of Claim 11 in which said pollutant molecules comprise members selected from the group consisting of SO2, H2S, NO2, Cl2 and HCl.