WO2006123945A1

WO2006123945A1 - Galvanising procedures

Info

Publication number: WO2006123945A1
Application number: PCT/NZ2006/000112
Authority: WO
Inventors: Neal Barr
Original assignee: Fletcher Building Holdings Limited
Priority date: 2005-05-19
Filing date: 2006-05-15
Publication date: 2006-11-23
Also published as: AR057028A1; TW200704821A

Abstract

The procedure involves a novel additive for a hot-dip galvanising zinc or zinc alloy bath. It is pre-prepared nickel powder and flux (optionally also with flammable material) for such both doping. The form of the additive can be as loose powders, a cake involving a flammable binder or a package where the surround is a flammable polymer.

Description

GALVANISING PROCEDURES TECHNICAL FIELD

The use of nickel in galvanising baths is known to give benefits. Nickel levels of zero to 1400 ppm have been used in general galvanising applications. BACKGROUND ART

There are two methods of adding nickel to the molten zinc bath to dose to the required level:

Addition of Ni/Zn alloy.

Addition of nickel powder using a special device to assist in wetting the mixing. (Cominco method).

The first method has disadvantages in baths containing aluminium. The addition of aluminium is common in general galvanising.

The second method requires special hardware in the form of a spinning bucket that gives centrifugal molten zinc flow over the powder. It is an object to provide an alternative to such methods and/or at least a choice of consumable for addition to hot-dip galvanising baths. DISCLOSURE OF INVENTION

The present invention in another aspect comprises the (easy) addition of nickel powder to the hot-dip galvanising bath, the powder preferably being in a pre-prepared form. The invention also consists in the (easy) addition of nickel powder to a hot-dip galvanising together with flux powder or powders. Whilst in some forms close serial addition of flux or the nickel, then the other, is a prospect, preferably the addition is simultaneous or substantially simultaneous. In one option the powders (nickel/flux) can be in mere admixture. Preferably the nickel powder is added together with a flux which facilitates its blending into the zinc bath. Preferably such flux is in addition to any on the top of the bath. Preferably the flux is a galvanising flux.

The addition can be of flux carrying nickel powder, where the flux optionally is encapsulated by and/or encased in [e.g. as if in a matrix] and/or the nickel powder and/or flux is impregnated by or accompanied by or packed in a flammable and/or an organic material [e.g. a wax or polymer such as polyethylene].

Preferably the flux is selected from the group zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these. It may however be any flux that will assist the wetting of a nickel surface by zinc including as part of the "flux" or as all of the "flux": • Any of the commercially available flux mixtures for general hot dip galvanising applications for steel including speciality fluxes and low fume fluxes.

• Zinc chloride.

• Ammonium chloride. • Zinc ammonium chloride.

• Any mixtures of zinc chloride and ammonium chloride including the discrete stoichiometry double salts formed by these mixtures.

• Any mixtures of zinc chloride, ammonium chloride and/or zinc ammonium chloride with potassium chloride The invention in another aspect comprises the use of flux to assist the addition of nickel powder to the zinc bath or zinc alloy bath of a hot-dip galvanising facility. Preferably the flux is galvanising flux.

Preferably the nickel powder has been pre-prepared with the flux. The nickel can be pre-prepared in a number of preferred ways: - The nickel powder can be pre-mixed with a galvanising flux such as zinc ammonium chloride in the weight ratio range of 95% nickel powder to 75% nickel powder.

As above but with a low fume flux powder mixture, such as zinc ammonium chloride and potassium chloride, replacing the zinc ammonium chloride. - The nickel powder can be treated with pre-flux solutions as is known in the industry for the pre-treatment of steel, dried and added to the zinc melt. The nickel powder/flux mixture can be formed into a pellet using compression and/or heat or by the use of a binding material and added to the zinc melt. The pellet containing the nickel powder and the flux can be coated with an organic material such as paraffin wax and this composite pellet added to the zinc bath. The added advantages of organic coating are:

- moisture protection for the pellet allowing storage.

- a reduction in flux decomposition fumes. Preferably the flux can be as defined hereinafter and/or hereinbefore. The flux irrespective of the pre-preparation method used preferably is zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these.

In another aspect the invention is a nickel powder carrying a flux. Preferably the flux is a galvanising flux (e.g. zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these).

Optionally, yet preferably, the flux carrying nickel powder is encapsulated and/or encased [e.g. as if in a matrix] of a flammable and/or organic material [e.g. a wax or polymer] (e.g. PE or another preferably flammable thermoplastic).

Preferably a doping mass for a zinc or zinc alloy hot-dip galvanising bath, said mass having in a flammable binding matrix both nickel powder and at least one flux powder to effective to improve the interface of the nickel into the bath.

In still a further aspect the invention is, as a doping media for a zinc or zinc alloy hot-dip galvanising bath, a nickel substrate or powder, and a (preferably galvanising) flux.

Preferably said flux is selected from zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these. Preferably said flux is at least substantially in intimate contact (whether by admixture or otherwise) with said nickel.

Preferably said nickel is particulate, i.e. preferably a powder as herein described.

In another aspect the invention is an additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising, the additive being nickel powder [preferably of particle size in the range from 2 to 300 microns maximum dimension], and a flux physically associated with each particle of the powder.

Preferably said flux/particle physical association is by or has involved admixture of powders and/or association of the nickel powder with a flux carrying liquid. Preferably the nickel powder is from 75% to 95% w/w and the flux is from 25% to

5% of the additive (ignoring any optional binder, flux protecting matrix and/or encapsulate).

Preferably the flux is protected by a matrix and/or encapsulant (e.g. a material of no concern to the bath e.g. a flammable or organic material).

In another aspect the invention is an additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising, the additive being nickel powder [preferably of particle size in the range from 2 to 300 microns maximum dimension], and a flux directly affixed to and/or intimate with each particle of the powder. In another aspect the invention is an additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising, the additive being nickel powder [preferably of particle size in the range from 2 to 300 microns maximum dimension], and a flux physically associated via a supporting and/or encapsulating matrix or material with each particle of the powder.

In still another aspect the invention is an additive or media as an additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising comprising or including either as discrete particles or as a cake, nickel powder, flux, and a wax or polymer protecting the flux on the powder.

In still another aspect the invention is a process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining particulate flux powder or powders, and admixing the nickel powder and the flux powder(s).

In another aspect the invention is a process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining a flux containing liquid, and blending the flux containing liquid and the particulate nickel, and drying the blend to form an adherent cake. Preferably said adherent cake is then coated with a wax or with a polymer.

In another aspect the invention consists in a process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining particulate flux powder or powders, admixing the powders, and compressing the powders into a pellet or cake.

Preferably said pellet or cake is encapsulated in a wax, [e.g. by immersion in molten wax and/or spraying of molten wax thereon] and/or a polymer. In yet a further aspect the present invention consists in a process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining particulate flux powder or powders, obtaining an organic material as a powder, admixing the three powder types (i.e. nickel/flux/organic), heating and/or compressing the mixed powders thereby to produce, on cooling and/or removal, a cohesive cake as the additive or media. In another aspect the invention is a vacuum pack of nickel powder and flux or nickel powder, flux and organic material.

Preferably the pack is of the contents in a polymeric surround (e.g. one that allows the pack as a whole or the contents of the pack only to be added to a bath to be doped)..

In another aspect the invention is an additive or media prepared by any such process.

In another aspect the invention is a nickel doped zinc bath or zinc alloy bath doped by an additive of the present invention.

Preferably the doping has been with a doping mass for a zinc or zinc alloy hot-dip galvanising bath, said mass having in a flammable binding matrix both nickel powder and at least one flux powder to effective to improve the interface of the nickel into the bath.

In another aspect the invention is a method of hot-dip galvanising which uses a hot- dip bath doped with an additive of the present invention.

The method of hot-dip galvanising can use a doping mass for a zinc or zinc alloy hot- dip galvanising bath, said mass having in a flammable binding matrix both nickel powder and at least one flux powder to effective to improve the interface of the nickel into the bath prior to hot dip galvanising of an item in the bath.

The method can use the contents of a vacuum or the pack as a whole as the doping additive.

In another aspect the invention is a product of a method of the present invention which is a galvanised steel or other Fe alloy substrate component or fabrication.

As used herein the term "and/or" means "and" or "or", or both.

As used herein the term "(s)" following a noun includes, as might be appropriate, the singular or plural forms of that noun.

Reference herein to "for" a zinc bath includes "suitable for". As used herein "flux" includes galvanising fluxes such as zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these, but is not restricted thereto. The physical form of the flux can be a powder. Flux particle size has not been found to be critical but preferably the flux powder will pass a 0.5mm sieve. Ideally an effective flux is any flux that will assist the wetting of a nickel surface by zinc including as part of the "flux" or as all of the "flux":

• Any of the commercially available flux mixtures for general hot dip galvanising applications for steel including speciality fluxes and low fume fluxes.

• Zinc chloride. • Ammonium chloride.

• Zinc ammonium chloride.

• Any mixtures of zinc chloride, ammonium chloride and/or zinc ammonium chloride with potassium chloride

Whilst powder flux is preferred, flux liquids, solutions, suspensions, emulsions, pastes, etc. can also be used.

As used herein "nickel" includes pure or near pure nickel. It can also include high nickel percentage nickel alloys. It can also include nickel coupled to material(s) (alloyed or otherwise) suitable for bath addition. Preferably such material(s) do not melt in the galvanising bath i.e. are subject to a dissolution or like process instead.

As used herein "zinc bath" and/or "zinc alloy bath" includes a bath primarily of zinc which may or may not currently have other metal and/or elemental doping additions thereto. Preferably there has been no wet fluxing of the bath (e.g. as would provide a surface carpet of flux).

As used herein "powder" includes consistently and/or inconsistently sized particulate materials.

As a "binder" any suitable non contaminating material or materials may be used. Flammable material(s) is(are) preferred. A wax is such a material. As used herein "wax" is not limited to paraffin wax (e.g. other examples include other natural waxes [such as bees wax, carnauba wax, montan wax, microcrystalline wax, etc] and synthetic waxes [such as Fischer-Tropsch waxes, polyethylene waxes, EAA, etc]. As used herein "organic" includes amongst other materials (preferably all flammable) waxes, paraffin waxes, and polymers such as polyethylene. For example vacuum packed powder in PE. Such a pack preferably includes nickel powder, flux and organic materials to produce wet flux mixtures when melted and fused.

As used herein "polymer" or its derivative words includes any organic material (powder, layer or film) to:

• Protect the powder mixture from moisture, both short and long term.

• Reduce the fume emissions from the flux during use of the additive product.

• Contribute to a molten flux mixture on fusion.

The reference to a size range of 2 to 300 microns is that within which nickel particles can be expected. Below 2 microns nickel powders are more expensive and thus naturally prohibitive. Above 300 will work but such powders are not at all common. A typical powder for use might be:

It is preferable to minimise the binder (or wax) used as just sufficient for its role as binder is all that is required and least compromises the bath and atmosphere. Likewise for the flux inclusion.

By way of example only the amounts of nickel powder should be maximised as seems supported by following Examples. Preferably there is at least 40% w/w nickel powder in the flux containing and optionally binder containing product. More preferably the nickel is greater than 50% w/w and can be up to, say, 98% w/w (more preferably is from 60% w/w to 95% w/w) (better still greater than 75% w/w if there is no binder)..

By way of example only the flux (powder, liquid and/or paste) accounts for preferably no more than 40% w/w of the product. More preferably is from 5% w/w to 35% w/w.

By way of example only the binder and/or encapsulant (if any) is less than 30% w/w of product. More preferably is less than 20% w/w (i.e. 0 to 20% w/w) when as a cake preferably there is from 2% w/w to 25% w/w binder and most preferably from 5% w/w to 15% w/w binder.

As previously stated, if there is no binder, or it is ignored, preferably relative to each other, there from 95 to 75% Nickel to 5 to 25% Flux. BRIEF DESCRIPTION OF DRAWINGS

Preferred forms of the present invention will now be described with respect to the accompanying drawings in which

Figure 1 shows a beaker of a simple admixture of nickel powder and flux powders,

Figure 2 shows a pre-fluxed metal powder, Figure 3 shows a nickel powder/flux powder mixture encapsulated and/or impregnated with wax,

Figure 4 shows a wax impregnated powder mixture,

Figure 5 shows a graphic representation of the nickel concentration in a zinc bath following each often doping additions as referred to hereinafter in Example 4, Figure 6 shows a rectangular hot dip bath with the splashes showing the addition pattern,

Figure 7 (with the Xs) shows the sampling points of the bath of Figure 6,

Figure 8 shows addition efficiency % against ppm Nickel for a powder based cake as described in Example 7 hereof, Figure 9 shows efficiency as a plot of ppm Nickel against g of Nickel added, and

Figure 10 shows efficiency for Example 7 as a plot of ppm Nickel against kg of Nickel added.

The additive or media product of the present invention can be used to add nickel to molten zinc baths in both general galvanising and continuous galvanising applications. The product/method is particularly useful in addition of nickel to baths containing aluminium.

General galvanising

The hot dip galvanising of structural and fabricated steel items or the hot dip galvanising of items in a batch processing manner.

Continuous galvanising The continuous automated or semi-automated hot dip galvanising of steel products such as pipe, wire or strip.

Example 1 25Og of -30 micron nickel powder was combined with 2Og of zinc ammonium chloride. The two powders were mixed (as in Figures 5 and/or 6) and added to the zinc bath.

The flux melted, forming a pool of molten flux and the metal powder was transferred to the bulk zinc. Considerable flux fuming was observed. Example 2

25g of ~30 micron nickel powder was placed in a plastic beaker and heated to 95°C. The warm nickel powder was treated with a hot (~70°C) solution of zinc ammonium chloride in water until the powder was fully wetted but not fluid. The mixture was placed in an oven at 95°C and dried to an adherent cake. The dried cake was removed from the container and immersed in molten wax. The fully wax encapsulated cake was allowed to cool (e.g. as in Figure 7) and added to the zinc bath.

The wax melted and ignited, burning with a yellow slightly smoky flame. The flux melted and effected transfer of the metal powder to the bulk zinc bath. Flux fume was minimal. Example 3

25Og of dried ~30 micron nickel powder was mixed with 2Og of dried zinc ammonium chloride and compressed into a pellet. The pellet was encapsulated in paraffin wax and cooled. The pellet was added to the zinc bath.

Example 4

Ten Ig samples of ~30 micron nickel powder were treated as in Example 2 above and the dried cakes encapsulated in wax. The samples were sequentially added to a laboratory molten zinc pot (~35kg) and the nickel concentration in the zinc measured after each addition.

The results of the Example 4 doping additions are summarized in the graph of Figure 5. On addition to the pot the wax ignited and the pre-fluxed powder was transferred to the molten zinc. The analyses confirm transfer of nickel in the zinc.

Example 5 Nickel powder with 8-9μ particle size distribution was made into a cake as follows:

• 100 g nickel powder.

• 5O g zinc ammonium chloride.

• 30 to 35 g of paraffin wax.

• Total weight 180 to 185 g. Stored in zip-lock plastic bags until used.

Note a higher flux ratio used here when compared to Example 6 owing to higher specific surface area of nickel owing to its small particle size.

The preparation of the tablet was as follows:

• 100 g of nickel powder was weighed out (+- 0.5%). • 20 grams ofzinc ammonium chloride (ZnCl₂.3NH₄Cl) was weighed out.

• The two were roughly mixed and the mixed powder poured into an oven proof silicone mould.

• The powder mix was heated to 110⁰C and then infused with molten paraffin wax. It was ensured that all interspatial air was displaced. • The mixture was reheated to 11O⁰C.

• The mixture was left to set at room temperature.

• The solid tablets were removed from the moulds. Example 6

Tablets were made with: 100 g of nickel powder, size range 8-9 micron.

40 g ofzinc ammonium chloride. Approximately 40 g of paraffin wax.

A batch of 20 of these tablets were added to a commercial operating zinc bath and the nickel content analysed before and after addition. The difference on nickel content recorded exceeded 100%. (Please note representative sampling of operating galvanising baths is difficult and the difference in this case was less than 10% of the nickel concentration. See Example 7 for the typical deviation of efficiencies determined over a set of samples by this difference method.)

Example 7

Nickel addition tablets were prepared by mixing 100 g of broad particle size distribution powder, 5 to 300 micron, 20 g of crystalline commercial grade zinc ammonium chloride, and approximately 15 g of paraffin wax. The quantities of nickel powder and flux crystals were roughly mixed and transferred into silicone moulds. The mixture samples in the moulds were heated to HO⁰C in an oven and molten paraffin wax poured carefully into the mixtures until the mixtures were fully wetted and covered. The prepared tablets were added to an operating hot dip galvanising bath in batches of

20 tablets giving additions of 2000 g of nickel per batch. One occasion of 10 tablets addition was included. The bath contained 231(+-1O) tonnes of molten zinc.

Table 1

Initial GaIv Ni bath added Increased Addition

Ni ppm g Ni ppm Efficency%

48 2000 9.24 106.82

53 2000 5.70 65.88

62 2000 9.99 115.48

69 2000 10.48 121.16

76 2000 9.33 107.86

80 2000 4.86 56.19

89 2000 11.92 137.82

97 2000 12.22 141.31

100 1000 5.42 125.29

102 2000 6.45 74.53

110 2000 4.63 53.48

111 2000 6.07 70.14

119 2000 9.03 104.37

49 2000 8.97 103.72

54 2000 7.49 86.54

62 2000 9.42 108.89

68 2000 7.96 91.97

76 2000 10.58 122.32

82 2000 8.58 99.20

89 2000 11.59 133.95

97 2000 11.98 138.47

99 1000 4.50 104.11

104 2000 7.54 87.19

108 2000 5.20 60.06

112 2000 9.47 109.54

125 2000 10.67 123.36 Average 101.05

The nickel concentration in the bath was measured at 2 sample points and the addition efficiency calculated by concentration difference. The average value 101.05% has an estimated accuracy of +-5%. The data was also analysed on the basis of cumulative bath addition and bath concentration, see Figure 10.

Over the period of addition the operating galvanising bath processed around 400 tonnes of steel and 31 tonnes of fresh zinc was added to the bath. Based on these figures the nickel addition efficiency was 92.5%. 4.07 tonnes of bottom dross was produced at a content of 397 ppm Ni. When corrected for this loss of nickel during processing the nickel addition efficiency was 98.9%.

Other minor components in the zinc melt were: Al, 30 to 45 ppm, average 35 ppm. Pb, 0.94 to 1.05%, average 1.00%. Fe, 170 to 230 ppm, average 210 ppm

Example 8

Nickel powder with 100-200μ particle size distribution was made, in a manner similar to the procedure of Example 5, into a cake as follows:

• 100 g nickel powder. • 2O g zinc ammonium chloride.

• 10 to 15 g of paraffin wax.

• Total weight, 130 to 135 g.

Example 9

9.1 Bath Additions and Analysis Additions were made to an operational general hot dip bath. Bath content was estimated at 230 tonnes of molten zinc.

Tablet addition was done in batches of 20 tablets per addition giving a 2 kg total nickel addition. Tablets were distributed approximately evenly over the bath surface as represented in Figure 6 and the addition of 20 tablets was typically completed in less than a minute. The tablets fused and ignited, flame duration was around 1 minute.

Approximately 8 10O g tablets should be enough daily addition to maintain a bath dipping 10,000 tonnes per year but this will vary with other factors that affect zinc usage. This can be done at one per hour over an 8 hour shift or 8 once a day.

9.2 Sampling and Analysis

Before addition of a batch of tablets the zinc bath was sampled from two points, end and middle, as represented in Figure 7. Sample set 1 (before) was taken at the end of day-shift after the last dip. The plant is running one shift only.

Sample set 2 (after) was taken at the start of dipping after the first two dips.

The sample pellets were themselves sampled by drilling and weighed zinc samples (approximately 5 g) dissolved in 1:1 nitric acid and made up to 100 mis with deionised water. The solutions were analysed by AA (atomic absorption) for nickel concentration and the concentration of nickel in the zinc sample calculated.

After addition and after 2 dips this sampling and analysis practice was repeated.

9.3 Efficiency Method 1

The addition efficiencies for the "as received" 5 to 300 micron spread powder based on before and after sampling are summarised in Figure 8. These numbers have been corrected for analytical sensitivity. The efficiency error bars represent the confidence range based on analytical accuracy. It is clear that representative sampling in an operational bath is not easy. The average reading works out at 100.8% (note average line) and the Y spread around the average line reflects the difficulty in sampling. The average value of 100.8% suggests that the transfer of nickel from the tablet to the melt solution is good. The sampling was subject to bath additions other than nickel that were out of the control of the analytical team.

Overall the addition efficiency by this method is 100.8% +_5%.

9.4 Efficiency Method 2 The variation in nickel concentration in ppm is plotted against quantity added in Figure 9 over the period of the test.

The trendline shows a gradient of 0.0032 ppm (after analytical sensitivity correction 0.00358) per added gram of nickel. The weight of zinc over this period must be represented by the weight in the bath plus the weight added over the working period during which approximately 400 tonnes of steel was dipped. 30 tonnes were added during the period so the total weight of zinc dosed was 261 tonnes.

The expected increase in nickel concentration is thus 0.0038 ppm per added gram of nickel.

Addition efficiency by this method is thus (.00358*100/0.00383) or 93.5%.

This figure can be further corrected by estimating the nickel that reported to the dross during the work period. During the period 4.03 tonnes of dross was made and this analysed at a nickel content of 393 ppm or 1,580 g of nickel out of the 25,000 g added. Correcting for the loss of nickel to the dross addition efficiency was 99.8% +-5%.

9.5 Concentrations of Other Components for Reference.

The zinc samples were also analysed for aluminium, lead and iron. The ranges are summarised below:

Al, 30 to 45 ppm, average 35 ppm. Pb, 0.94 to 1.05%, average 1.00%.

Fe, 170 to 230 ppm, average 210 ppm

9.6 Conclusions

The commercially sourced nickel powder of Example 7 with its broad 5 to 300μ particle size spread is the preferred material for preparation of the tablets. The 100-200 μ powder of Example 8 shows no benefits over the powder of Example

7.

The 8 - 9 μ powder of Example 5 or Example 6 is not preferred as it is more difficult to incorporate into the tablet, requires more flux and requires more binding agent. This material nevertheless appears to transfer efficiently from tablet to solution. Transfer of nickel to the molten zinc appears to be effective and efficient for all such powders. The results above refer only to the "as received" 5 to 300 micron powder. With reasonable confidence we can say that the efficiency of transfer is +95%.

Stirring is not necessary, addition to a quiescent bath was done to demonstrate that this is so.

Although sampling in a commercial bath presents some problems the results, the history result particularly as opposed to the single addition analysis supports good transfer.

A limitation imposed was that the bath started at a low level (<50 ppm Ni). This simply reflects past difficulties in obtaining nickel powder. The amounts of nickel powder for the test were insufficient to achieve the ultimate target levels. Previous to the run down of our nickel levels the bath was maintained at approximately 450 ppm Ni by addition of nickel powder by a simpler variation of this method.

Our work suggests that there is no reduction in addition efficiency with increased Ni concentrations, at least up to 450 ppm. The rate of addition was set by the amount of nickel powder available for the trialling, the minimum addition that might lead to reliable analytical results and the need for a statistical sample. There is so far no evident reason to limit addition rate when dosing a bath up to required concentration.

The results suggest that the transfer of nickel to the bath is effective and that little or no nickel reports to the dross on addition but that the nickel in the dross probably originates from work dipped.

Aluminium in the dross analysed at 111 ppm and aluminium usage over the work period did not increase, in fact the addition was reduced but this may or may not be associated with the nickel addition. Comment

Without wishing to be bound by the theory, we believe that the flux in the mixtures melts and assists the wetting of the nickel powder by molten zinc. We believe that the nickel powder being dense falls through the molten flux layer to the flux/zinc interface and then being denser than molten zinc it continues into the molten zinc with the flux assisting the interfacial transport. We further believe that the slow passage of the discrete powder particles through the molten zinc allows dissolution at rates that do not give excessive localized concentrations of nickel. This is particularly important in the case of baths containing higher concentrations of aluminium as aluminium and nickel can react to form floating dross. This feature, we believe, gives advantage over the addition of alloy that melts and gives high nickel concentration at the molten mix zone.

Also without wishing to be bound by theory, we believe that the use of fluxed powder is superior to the addition of neat nickel powder as the neat nickel powder is unable to penetrate the surface layer due to surface tension effects and requires special equipment to overcome this. A nickel powder added without flux or mechanical assistance remains predominantly on the surface of the molten zinc and the molten zinc wicks into the interstitial space in the bulk powder. This allows prolonged contact of nickel with relatively small proportions of zinc and insoluble Ni/Zn alloys (dross) can form. The availability of oxygen on the surface allows oxidation of the zinc that has wicked into the powder further inhibiting the transfer of the nickel into the bulk melt.

The wax or organic component protects the hygroscopic fluxes from water during storage but also, without wishing to be bound by theory, we believe it has two further functions:

• The burning wax burns with a reducing flame and forms some carbon soot. The net effect of this is to surround the molten flux/nickel powder mixture by a reducing atmosphere.

• The flux fumes must travel through the molten wax to escape and are inhibited. The fume escaping is mixed with the soot from the burning wax and coagulated. The net effect is a marked reduction in fume emission as compared with a composite sample without wax.

In summary our nickel addition tablet technique is as follows:

• A simple addition method for general hot dip baths. • A composite, nickel powder, flux and binder system is used.

• The binder has the secondary functions of: i. Providing viscosity in the melted flux layer after addition, ii. Burning on the zinc bath surface to provide a reducing environment, iii. Burning with a smoky flame that reduces flux fume. iv. Reducing the rate of flux decomposition as is typical in wet flux mixtures. Within reasonable and practical limits the tablets can be made in any size. Tablets so far have been made in 1 gram to 2 kilo sizes in terms of nickel content.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

Claims

WHAT WE CLAIM IS:

1. The addition of nickel powder to a hot-dip galvanising both together with flux powder or flux powders.

2. The addition of claim 1 wherein the nickel and flux powder(s) are added as close serial additions.

3. The addition of claim 1 wherein the nickel and flux powder(s) are added simultaneously.

4. The addition of claim 3 wherein the powders are in admixture.

5. The addition of claim 3 or 4 wherein the powders are in a cake.

6. The addition of any one of the preceding claims wherein the at least one flux is a galvanising flux.

7. The addition of claim 3 wherein both the nickel and flux powders are encapsulated by, encased in or impregnated by a flammable and/or an organic material or the nickel powder and flux is accompanied by or packed in a material or materials that is or are at least one of flammable, organic or a polymer.

8. The addition of claim 7 wherein the flammable and/or organic material is a wax or polymer.

9. The addition of claim 6 wherein the flux is selected from the group zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these.

10. The use of flux to assist the addition of nickel powder to the zinc bath or zinc alloy bath of a hot-dip galvanising facility.

11. The use of claim 10 wherein the flux is galvanising flux.

12. The use of claim 10 or 11 wherein the nickel powder has been pre-prepared with the flux.

13. The use of claim 12 wherein the nickel powder has been pre-mixed with a galvanising flux in the weight ratio range of 95% nickel powder to 75% nickel powder to 5% to 25% flux.

14. The use of claim 13 wherein the flux is zinc ammonium chloride zinc ammonium chloride and potassium chloride.

15. The use of claim 12 wherein the nickel powder/flux mixture has been formed into a pellet or cake using compression and/or heat or by the use of a binding material and that pellet or cake is or has been added to the zinc or zinc alloy melt.

16. The use of claim 15 wherein there is an organic material.

17. The use of claim 16 wherein the organic material is paraffin wax.

18. The use of claim 12 wherein the flux is zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these.

19. A nickel powder carrying a flux.

20. A powder of claim 19 wherein the flux is a galvanising flux.

21. A powder of claim 20 wherein the flux is zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these.

22. A cake or pellet for hot dip galvanising both addition that includes a powder of claim 19.

23. A doping mass for a zinc or zinc alloy hot-dip galvanising bath, said mass having in a flammable binding matrix both nickel powder and at least one flux powder to effective to improve the interface of the nickel into the bath.

24. As a doping media for a zinc or zinc alloy hot-dip galvanising bath, a nickel substrate or powder, and a flux.

25. A media of claim 24 wherein said flux is selected from zinc chloride, ammonium chloride, zinc ammonium chloride, potassium chloride or any combination of these.

26. A media of claim 24 or 25 wherein said flux is at least substantially in intimate contact (whether by admixture or otherwise) with said nickel.

27. A media of claim 26 wherein said nickel is particulate.

28. An additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising, the additive being nickel powder, and a flux.

29. An additive of claim 28 wherein the particle size in the range from 2 to 300 microns maximum dimension

30. An additive of claim 28 or 29 wherein said flux/particle physical association is by or has involved admixture of powders and/or association of the nickel powder with a flux carrying liquid.

31. An additive of the nickel powder is from 75% to 95% w/w and the flux is from 25% to 5% w/w of the additive (ignoring any optional flux protecting matrix and/or encapsulate).

32. An additive of claim 28 wherein the flux is protected by a matrix and/or encapsulant

(e.g. a material of no concern to the bath e.g. a flammable or organic material).

33. An additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising, the additive being nickel powder, and a flux directly affixed to and/or intimate with each particle of the powder.

34. An additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising of particle size in the range from 2 to 300 microns maximum dimension.

35. An additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising, the additive being nickel powder and a flux physically associated via a supporting and/or encapsulating matrix or material with each particle of the powder.

36. An additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising of particle size in the range from 2 to 300 microns maximum dimension,

37. An additive or media as an additive for the zinc bath or zinc alloy bath to be used for hot-dip galvanising comprising or including either as discrete particles or as a cake, nickel powder, flux, and a wax or polymer protecting the flux on the powder.

38. A vacuum pack of nickel powder and flux or nickel powder, flux and organic material.

39. A pack of claim 38 wherein the pack is of the contents in a polymeric surround.

40. A process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining particulate flux powder or powders, and admixing the nickel powder and the flux powder(s).

41. A process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining a flux containing liquid, and blending the flux containing liquid and the particulate nickel, and drying the blend to form an adherent cake.

42. A process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining particulate flux powder or powders, admixing the powders, and compressing the powders into a pellet or cake.

43. A process for preparing an additive or media as an additive for a hot-dip galvanising bath, said process comprising or including obtaining particulate nickel, obtaining particulate flux powder or powders, obtaining an organic material as a powder, admixing the three powder types (i.e. nickel/flux/organic), heating and/or compressing the mixed powders thereby to produce, on cooling and/or removal, a cohesive cake as the additive or media.

44. A process for preparing an additive or media as an additive for a hot-dip galvanising bath as in any one of claims 40 to 43 wherein said pellet or cake is encapsulated in a wax,

[e.g. by immersion in molten wax and/or spraying of molten wax thereon] and/or a polymer.

45. A process for preparing an additive for a hot-dip galvanising bath, said process comprising or including obtaining either (i) particulate nickel and a galvanising flux, or (ii) particulate nickel, a galvanising flux and organic material, and vacuum packing (i) or (ii).

46. A process of claim 44 wherein the pack material is a polymer.

47. An additive or media prepared by a process of any one of claims 38 to 46.

48. A nickel doped zinc bath or zinc alloy bath doped by an additive of both nickel powder and a flux.

49. A nickel doped bath of claim 48 wherein the doping has been with a doping mass for a zinc or zinc alloy hot-dip galvanising bath, said mass having, in a flammable binding matrix, both nickel powder and at least one flux powder to effective to improve the interface of the nickel into the bath.

50. A method of hot-dip galvanising which uses a hot-dip bath doped with an additive of both nickel powder and a flux.

51. A method of hot-dip galvanising which uses a doping mass for a zinc or zinc alloy hot-dip galvanising bath, said mass having in a flammable binding matrix both nickel powder and at least one flux powder to effective to improve the interface of the nickel into the bath prior to hot dip galvanising of an item in the bath.

52. A method of claim 48, 49 or 50 wherein said doping has been with the contents of a pack of claim 38 or 39 or the whole pack of claim 39.

53. A product of a method of claim 50 to 52 which is a galvanised steel or other Fe alloy substrate component or fabrication.