Patent Application: US-92368810-A

Abstract:
a process for surface treatment of aluminium foils includes steps of applying an etching solution to chemically etch at least one surface of the foil to form an etched surface , and forming an aluminium oxidized coating on the etched surface . the etching solution comprises an aqueous solution which includes hydrogen peroxide as an oxidant and sulfuric , orthophosphoric or nitric acid .

Description:
a method of surface treating an aluminum foil in accordance with the invention was conducted and includes the following exemplary steps : 1 . the aluminum foil surface was cleaned with acetone , then dried in air and thereafter thoroughly washing with deionized water . 2 . the aluminum foil was then dipped into an oxidizing solution containing a strong acid and a strong oxidant , as more fully detailed below , for a specified time , as more fully detailed below , under ambient conditions . the foil being dipped into the oxidizing solution so that both sides of the foil are uniformly coated and subsequently treated . 3 . the aluminum foil was then removed from the oxidizing solution after the specified time and was washed thoroughly in deionized water and subsequently air drying at room temperature . a scanning electron microscope ( sem ) was used to determine an image of the foil surface . the image of the surface showed that it was covered with nanopores ranging from 100 - 300 nm in diameter . the cross - sectional view showed the existence of nano - tunnel from the surface . the depth of the pores was estimated to be between 150 - 300 nm . the cross - sectional view of the treated aluminum foil showed that 1 micrometer from either surface was affected in the treatment process . the core of the foil was not affected . approximately 15 - 20 % loss of weight of the foil was recorded in the process . energy dispersive x - ray ( edx ) was conducted to determine the extent of oxide coating on the surface of the foil . the edx method showed an association of around 5 % ( by weight ) of oxygen on average on the foil surface . reference may now be made to fig1 a to 1c which show the extent of anodization with different strong acids , fig1 a h 2 so 4 ; fig1 b h 3 po 4 ; and fig1 c hno 3 on an 11 micron aluminum foil with 5 . 4m acid and 15 % h 2 o 2 , treated for 30 minutes . fig1 a to 1b show that under identical conditions , sulphuric acid is most effective in anodizing the aluminum foil among the other strong acids evaluated . oxygen ( o ) content ( by weight ) was approximately 0 . 3 % for foils treated with h 3 po 4 or hno 3 and approximately 2 % for foils treated with h 2 so 4 . atomic force microscopic ( afm ) study showed that the surface substructures were in the order of 50 nm for foil treated with hno 3 , 75 nm for that of h 3 po 4 and over 100 nm in the foil treated with h 2 so 4 . the results rationalize the etching bath constituents , h 2 so 4 and h 2 o 2 . reference may now be made to fig2 a to 2c which show the extent of anodization with different concentration of sulphuric acid h 2 so 4 , fig2 a at 5 . 4m ; fig2 b at 7 . 5m ; and fig2 c at 9 . 4m on 11 micron foil with 12 % h 2 o 2 , treated for 20 minutes . reference may also now be made to fig3 which graphically shows the oxygen - content and weight - loss for foils treated with different molarities of sulphuric acid on 11 micron foil with 12 % h 2 o 2 , treated for 20 minutes . different concentrations of h 2 so 4 at 5 . 4m , 7 . 5m and 9 . 4 m ( moles / 1 ) were examined with respect to the anodization efficiency , the results of which can be see in fig2 a to 2c and 3 respectively . increasing sulphuric acid concentration ( molarity ( m )) did not increase the o - content by a large amount but caused a significant loss of foil - weight , due to pronounce sub - surface etching . due to increasing vigorousness , the reactions at higher h 2 so 4 concentration ( higher than 9 . 4m ) were not controllable . no observable change was observed in samples treated with h 2 so 4 concentration less than 5 . 4m . reference may now be made to fig4 a to 4c which show the extent of anodization with different concentration of hydrogen peroxide h 2 o 2 , fig4 a at 12 %; fig4 b at 15 %; and fig4 c at 18 % on 11 micron foil with 7 . 5m h 2 so 4 , treated for 20 minutes . reference may also now be made to fig5 which graphically shows the oxygen - content and weight - loss for foils treated with different concentration of h 2 o 2 on 11 micron foil with 7 . 5m h 2 so 4 , treated for 20 minutes . similarly , the oxidant ( h 2 o 2 ) content of the anodization bath was optimized against three h 2 o 2 concentrations (%, ( w / v )), 12 %, 15 % and 18 % ( w / v ) under identical experimental conditions shown in fig4 a to 4c . higher o - content and lower weight loss was observed in samples treated with higher concentration of h 2 o 2 as shown in fig5 . more uniformity was observed in surface texture of the samples treated with higher h 2 o 2 concentration . a ratio of 0 . 7 - 0 . 8 mole of h 2 o 2 per mole of acid was identified as the ideal for in - situ chemical anodization of aluminum foil . excess h 2 so 4 was required to initiate the etching process at the initial phase of the anodization , but too much h 2 so 4 results in dissolution of the oxide film from the aluminum surface . reference may now be made to fig6 a to 6c which show the extent of anodization under different contact time , fig6 a at 10 minutes ; fig6 b at 20 minutes ; and fig6 c at 30 minutes on 11 micron foil with 7 . 5m h 2 so 4 , 20 % h 2 o 2 and treated for 20 minutes . reference may now be made to fig7 which graphically shows the oxygen - content and weight - loss for foils treated with a chemical anodization solution and different contact times on 11 micron foil with 21 % h 2 o 2 and 5 . 4m h 2 so 4 . the sem images shown in fig6 a to 6 c reveal the progression of anodization on the aluminum surface . increasing contact time increases the o - content of the film . but the anodization tends to level beyond 20 minutes of contact time ( see fig7 ). a similar trend was noted for the weight loss of the foil . based on the observations of the optimization study , the most effective anodization was reported when aluminum was treated with 7 . 5m h 2 so 4 and 18 % h 2 o 2 for 30 mins . reference may now be made to fig8 which shows an afm 3 - d image of anodized aluminum treated under preferred conditions with 7 . 5m h 2 so 4 , 18 % h 2 o 2 and treated for 30 minutes . the afm image shows that surface substructures in the order of approximately 200 nm . reference may now be made to fig9 a and 9 b which show images of anodized aluminum treated under the following conditions , fig9 a untreated and fig9 b anodized with 7 . 5m h 2 so 4 , 18 % h 2 o 2 and treated for 30 minutes . reference may also now be made to fig1 a and 10b which show images of the cross - section of anodized aluminum treated under the following conditions , fig1 a untreated ; and fig1 b anodized with 7 . 5m h 2 so 4 , 18 % h 2 o 2 and treated for 30 minutes . as shown in fig9 a and 9b and 10 a and 10 b , the surface texture and cross - section of the anodized aluminum was examined and compared with the control ( untreated ) aluminum . a careful examination reveals that in this treatment anodization takes place only within 1 micrometer thickness from either surfaces of the foil . under optimized conditions , anodization results in 5 % weight loss and 5 % oxygen content on the surface layer . thus , this invention demonstrates a new method of chemically anodizing aluminum foil with minimum impact on the aluminum . reference may now be made to fig1 a and 11b which show images of anodized aluminum treated under the following conditions , fig1 a galvanstatically anodized ; and fig1 b method of this work with 7 . 5m h 2 so 4 , 18 % h 2 o 2 and treated for 30 minutes . reference may also now be made to fig1 a to 12 c which show the extent of anodization in different aluminum alloys , fig1 a al : 91 %, c : 5 %, fe : 3 %; fig1 b al : 83 %, c : 1 %, fe : 15 %; and fig1 c al : 72 %, c : 1 %, fe : 26 % with 7 . 5m h 2 so 4 , 18 % h 2 o 2 and treated for 30 minutes . comparison of the anodized foil , anodized by the method described herein method of this work with galvanostatically anodized foil illustrates that the formation of nanometric surface characteristics were much less pronounced in the galvanostatic method in comparison to the method reported in this work ( see fig1 a and 11b ). the anodization was validated for different alloys of aluminum . the effectiveness of anodization was observed to decrease with increasing iron ( fe ) content in the alloy ( see fig1 a to 12c ). the following details a preferred embodiment of the method and apparatus of producing immobilized nanocatalyst of transition metal oxides and their alloys in accordance with the invention . reference may now be made to fig1 which shows an apparatus 100 for nanofiber generation in accordance with this invention . the apparatus includes a pump 106 , a spinning tip / needle 108 , a variable high voltage dc power supply 112 and an enclosure 120 . 1 . polyvinyl acetate ( pvac ) solution ( 45 % w / v ( weight / volume )) was prepared by dissolving pvac of molecular weight 50 , 000 daltons in ( 3 : 2 ) dimethylformamide - tetrahydrofuran mixture ( viscosity : 147 cps at shear rate ≧ 10 , 000 s − 1 ) 2 . tio 2 sol solution was prepared by mixing titanium tetraisopropoxide ( ttip ) in glacial acetate acid ( 1 : 4 ( mole / mole )) 3 . the electrospinning solution was prepared by mixing a prepared pvac solution ( step 1 ) with prepared ttip solution ( step 2 ) at specified ratios of weight to weight . it is to be understood that the present invention is not to be limited to the particular electrospinning oxide solution detailed above , but rather other metal oxides and their alloys as described herein are equally applicable to the present invention . 1 . a needle 108 containing the prepared electrospinning solution 104 is placed in a pump 106 , capable of delivering at a constant flow rate to the needle 108 . 2 . an aluminum foil support 102 having a thickness of 11 microns or electroless anodized aluminum foil was placed as cathode at a distance from the needle 108 containing the electrospinning solution 104 with the treated surface of the foil facing the needle 104 . 3 . a positive terminal 110 of a variable high voltage dc power supply 112 , capable of delivering a high potential difference ( 0 - 50 kv ), is connected to the metallic needle 108 and a negative or ground terminal 114 is attached to a collector surface 116 ( cathode ) of the aluminium foil 102 . 4 . the electrospinning apparatus 100 is placed inside an enclosure 120 and substantially sealed from external air currents . 5 . the distance between the tip of the needle 108 and the surface of the aluminum foil is set at an optimum separation distance inside the enclosure 120 . 6 . the optimum infusion rate was set and optimum potential difference was applied across terminals 110 and 114 in accordance with the present invention . 7 . discontinuity of fiber formation in the electrospinning was observed below a potential difference of 25 kv and an infusion rate of 0 . 6 ml / h and above separation distance of 32 cm . 8 . dripping of solution was noted beyond the infusion rate of 3 . 2 ml / h . 9 . beyond the potential difference of 40 kv and below separation distance of 12 . 5 cm electrical short circuit ( due to breakage of resistance barrier of air inside the enclosure ) and sparks were observed between the electrodes . 10 . upon applying a high voltage to the solution 104 , with the needle 108 tip being some distance away from the grounded collector surface 116 , a fluid jet 118 is ejected from the needle 108 tip . as the jet 118 accelerates towards the cathode collector surface 116 , the solvent in the solution 104 evaporates and a charged metal / polymer composite fiber is deposited on the collector surface 116 of the aluminum foil support 102 material . 11 . the fine fibers delivered from the tip of the needle 108 is airborne to the target collector surface 116 in a random fashion . 12 . the electrospinning process can be continued until the solution 104 in the syringe is diminished or until till the power supply to the system is turned off . 1 . upon completion of the electrospinning process , the mesh of composite nanofibers , comprising titanium oxide and polymer deposited on the support was collected and subjected to subsequent thermal treatment in accordance with the present invention . 2 . the composite nanofiber is initially subjected to vacuum drying at temperature no less than 105 ° c . for a period of time no less than 2 hours under a vacuum of 600 mm hg . 3 . the polymer is removed and metal oxide fiber formation is facilitated by controlled heating of the vacuum dried specimen in an atmospheric temperature programmable oven up to 300 ° c . and thereafter atmospheric calcining in a muffle furnace to 400 ° c . and holding at temperature between 340 - 550 ° c ., preferably at 400 ° c ., for a period of time no less than 3 hours ( sufficient to pyrolyze the pvac and crystallize the amorphous tio 2 in the nanofibers ). the temperature of the muffle furnace must be kept below melting temperature of the aluminum foil of 600 ° c . or the crystal transformation temperature of the metal catalyst , whichever is lower . 4 . once the polymer is pyrolyzed , the support has pure metal oxide catalyst immobilized as nanofibers . the foil is allowed to cool to ambient temperature . next a gentle blow of clean dry air is applied to remove the loose particles followed by a number of rinses in ultrapure water to remove the remaining polymer ash . the immobilized catalyst on the foil substrate is then dried at 105 ° c . to produce a clean immobilized catalyst . preparation of support : a surface of the supporting scaffolding / material ( treated aluminum sheet in a preferred construction ) 102 is cleaned with acetone , thoroughly washed with deionized water and dried in air . preparation of electrospinning solution : the electrospinning solution 104 is prepared by mixing an organo - metallic salt ( acetate or isopropionate ) of the transition metal in a solvent or solvent mixture ( not limited to dimethylformamide , tetrahydrofuran , methanol , glacial acetic acid ) along with a polymer . the purpose of the polymer is to behave as a carrier for the metal salt and to maintain the viscosity of the electrospinning solution which is needed for fiber formation . it is ideal for the viscosity of the polymer solution to be between about 130 - 160 cp for producing smooth fibres . polyvinyl acetate ( pvac ) is a polymer which degrades at 300 ° c . and chars around 400 ° c . this temperature is below the crystal transformation temperature of transition metal catalyst and the melting temperature of aluminum ( 600 ° c .). thus , pvac of molecular weight ( mw ) 50 , 000 was used to prepare an electrospinning solution ( 45 % pvac ( w / v )) of viscosity 147 cps ( at shear rate ≧ 10 , 000 s − 1 ). electrospinning : in the electrospinning process , the viscous solution 104 , containing the polymer and metal salt in the low boiling solvent , is delivered at a constant flow rate by the pump 106 to the metal capillary needle 108 connected to the positive ( anode ) terminal 110 of the variable high voltage dc power supply 112 , capable of delivering high potential difference ( about 0 - 50 kv ). the negative or ground terminal 114 is attached to a collector surface ( cathode ) 116 of the support material 102 . upon applying a high voltage to the solution 104 and with the needle 108 tip being some distance away from the grounded collector surface 116 , the fluid jet 118 is ejected from the tip of the needle 108 . as the jet 118 accelerates towards the cathode collector surface 116 , the solvent in the solution 104 evaporates and a charged metal / polymer composite fiber is deposited on the collector surface 116 of the support material 102 . the horizontal orientation of electrospinning apparatus 100 was chosen to minimize beading of fibres due to carry - over of excess spinning solution 104 and dripping of solution 104 onto the collector surface 116 . the active section of the apparatus ( capillary to collector ) is enclosed in the sealed enclosure / chamber 120 to mitigate the advective exchange of charged ions with the surrounding air ( produces draught of ionic wind ) and to maintain a stable environment within the enclosure 120 . the applied electrical potential , separation distance of the terminals , solution viscosity and solution flow rate are the major process variables in controlling the diameter of the fabricated nano - composite fiber and subsequently , the diameter of the metal oxide fibres . the electrospinning solution is infused from a metallic capillary under a specific set of parameters — potential difference ( kv ) infusion rate ( ml / h ), and collector - to - ground separation distance ( cm ). the charged jets ejecting from the tip of the capillary moves towards the collector ground and the composite nanofibers comprising of polymer and metallic salt are deposited on the surface of the scaffolding medium . programmed drying in vacuum and then slow calcination in air eliminates the polymer backbone from the nano - composite fiber leaving immobilized metal oxide nanofiber catalyst onto the surface of a support material . fig1 shows a flowchart identifying the steps in the generation of titanium dioxide nanofibers in accordance with this invention . for nickel oxide and cobalt oxide fibres , nickel acetate and cobalt acetate were dissolved in glacial acetic acid in 1 : 100 mol ratio . for zinc oxide fiber , specific amount of zinc acetate was dissolved in dimethylformamide in a 1 : 15 mol ratio . in each case , pvac was added to adjust the viscosity of the electrospinning solution so as to promote fiber formation . experimentally , the optimum levels of electrospinning parameters can be located by a single factor optimization method . however , the minimization of the nanofiber diameter through a single factor optimization is often considered less advantageous than optimization using statistical experimental design . hence , response surface optimization using three factor three levels box - benkhen design ( bbd ) was considered in optimization studies for electrospinning of nanofibers . the factor levels , tabulated in table 1 , were chosen based on preliminary experimentation . discontinuity of fiber formation in the electrospinning was observed below the lowest potential difference ( 25 kv ) and infusion rate ( 0 . 6 ml / h ) and highest level of separation distance ( 32 cm ). dripping of solution was noted beyond the highest level of infusion rate ( 3 . 0 ml / h ). electrical sparks were observed between the electrodes beyond the highest level of potential difference ( 40 kv ) and lowest level of separation distance ( 12 . 5 cm ), due to breakage of resistance barrier of air inside the enclosure . reference may now be made to fig1 a to 15b which show the effect of bbd design factors on the response variable ( mean fiber diameter ( nm )). fig1 a showing a 3d surface plot of response for infusion rate and potential difference ; fig1 b showing a 3d surface plot of response for potential difference and separation distance ; and fig1 c showing a 3d surface plot of response for infusion rate and separation distance . three dimensional ( 3d ) surface plots of the response variable ( diameter of nanofibers ( nm )) for the experimental factors ( two - factor - at - a - time ) are presented in fig1 a to 15c . the surface in the figures is formed by connecting the points of equal response ( equal mean fibre diameter ). the 3d plots shows that at higher potential difference , higher separation distance is highly conducive for producing smaller diameter nanofibers . further optimization analysis was performed to locate the region of minimum response . the numerical optimization function in the minitab software , based on the d - optimality index , was used to locate the maximum response within the factor - space under evaluation . the d - optimality index varied between zero ( worst case ) and one ( ideal case ) for all the factors . the software searches for all possible factor settings and computes a value for the largest d - optimality value . a minimum response ( mean fibre diameter ) was recorded for 40 kv potential distance , 1 . 2 ml / h infusion rate and 32 cm separation distance . an analysis of variance ( anova ) and multiple regression analysis were performed to derive a response surface model for the mean fiber diameter ( nm ) involving all three experimental factors , potential difference , infusion rate and separation distance ( eqn . 1 ). reference may now be made to fig1 which graphically represents a comparison of the model output against experimental values . the model prediction was validated with the experimental values . the model prediction closely matches the experimental values at all levels of factor settings shown in fig1 . reference may now be made to fig1 a to 17c which show images of immobilized nanofibers , fig1 a showing sem images of tio 2 nanofibres before calcinations ; fig1 b showing sem images of tio 2 nanofibres after calcinations ; and fig1 c showing afm surface images of tio 2 nanofibers - sintered crystal . reference may also now be made to fig1 a to 18c which show sem images of immobilized nanofibers before calcinations , fig1 a coo ; fig1 b nio ; and fig1 c zno . a scanning electron microscope ( sem ) and atomic force microscope was used to image the nanofibers . scandium image processing software was used to measure the diameter of the nanofibers . the sem images revealed uniform nanofiber dimension under optimum electrospinning parameter settings . reference may now be made to fig1 which shows a histogram of tio 2 nanofibers for different fibre diameters . reference may also now be made to fig2 which shows a graphical representation of the effect on increasing ti - content on specific surface area and diameter of nanofibers . fig1 shows the distribution of fiber diameter produced under optimum parameter setting in electrospinning process . the histogram of fiber diameter shows normal distribution . the fiber diameter ranged from 16 to 80 nm with an average of 44 nm ( with standard deviation of 14 nm ). minimum fiber diameter registered was 16 nm . the reported fiber diameter is the smallest produced in any electrospinning process ; particularly knowing that the minimum diameter of the available tio 2 nanoparticles is approximately 5 nm ( manufactured by alfa aesar , wardhill , mass .). fig2 shows that increasing specific surface area was associated with the smallest diameter nanofibers . the maximum specific surface area recorded was 259 ± 22 m 2 / g . the reported specific surface area is the highest reported surface area for any immobilized nanofiber catalyst . the figure also shows that increasing metal content increases the fiber diameter and thereby decreases the specific surface area of the immobilized catalyst . the following publications describe various processes and apparatus , as related to aspects of the invention hertofor described , and the disclosures of which are hereby incorporated herein by reference : 1 . wegman . r . f . 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( 2008 ). fabrication of zirconium carbide ( zrc ) ultra - thin fibers by electrospinning . materials letters , 62 , 12 - 13 , 1961 - 1964 . 34 . tappmeyer , w . p ., davidson , a . w . ( 1963 ). cobalt and nickel acetates in anhydrous acetic acid . inorganic chemistry , 2 , 4 , 823 - 825 . 35 . u . s . pat . no . 5 , 106 , 653 36 . rodriguez - gattarno , g ., oskam , g . ( 2006 ). forced hydrolysis vs . self - hydrolysis of zinc acetate in ethanol and isobutanol . ecs transactions , 3 , 9 , 23 - 28 . 37 . myer , r . h ., montogomery , d . c . ( 2002 ). response surface methodology : process and product optimization using designed experiment , second ed ., john wiley and sons , new york , 343 - 350 . 38 . ray , s . rsm : a statistical tool for process optimization . indian textile journal 117 , ( 2006 ) 24 - 30 . although this disclosure has described and illustrated certain preferred embodiments of the present invention , it is also to be understood that the invention is not restricted to these particular embodiments .