Hull cell

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Understand electrolytes & non-Understand electrolytes & non-electrolyteselectrolytes

Understand how to use Hull CellUnderstand how to use Hull Cell Presented by Selvaraj VenkatesanEmail: [email protected]

Mobile: 0 9843019701

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Water as a SolventWater as a Solvent Many reactions occur in an aqueous Many reactions occur in an aqueous

environment, where water is the environment, where water is the solvent. Water interacts with the solvent. Water interacts with the solute, playing an active role about solute, playing an active role about what goes on in solution.what goes on in solution.

Water creates attractions between Water creates attractions between itself and the substance being itself and the substance being dissolved (both ionic & covalent).dissolved (both ionic & covalent).


Polar Nature of WaterPolar Nature of Water

Water creates a buffer between the Water creates a buffer between the two oppositely charged ions such that two oppositely charged ions such that they do not recombine easily in they do not recombine easily in solution. Water decreases the solution. Water decreases the electrostatic attraction between ions.electrostatic attraction between ions.

Two features of water make it unique:Two features of water make it unique: The distribution of its bonding electrons The distribution of its bonding electrons

as a polar compound & its overall shape.as a polar compound & its overall shape.


Solubility of Ionic CompoundsSolubility of Ionic Compounds Water dissolves ionic compounds into ions. Water dissolves ionic compounds into ions.

When an ionic compound When an ionic compound dissociatesdissociates in in water, it becomes free anions and cations. water, it becomes free anions and cations. These These ionsions allow water to carry an electric allow water to carry an electric current. current.

Electrical conductivityElectrical conductivity is due to the is due to the movement of charged particles (anions & movement of charged particles (anions & cations).cations).

Oppositely charged species separate from Oppositely charged species separate from each other & are “each other & are “solvatedsolvated” by the water.” by the water.


Conductivity of solutionsConductivity of solutions Electrodes are electrical conductors Electrodes are electrical conductors

partially immersed in a solution and partially immersed in a solution and connected to a source of electricity.connected to a source of electricity. AnodeAnode - positive pole of electricity source - positive pole of electricity source CathodeCathode - negative pole of electricity - negative pole of electricity

sourcesource

An An ionion is a carrier of electricity is a carrier of electricity through a solution.through a solution. AnionsAnions are negatively charged particles are negatively charged particles CationsCations are positively charged particles are positively charged particles


Visualization of solution Visualization of solution conductivityconductivity

ANODE CATHODE


What are Electrolytes? What are Electrolytes? A A non-electrolytenon-electrolyte is a solute that is is a solute that is

present in solution almost exclusively as present in solution almost exclusively as molecules. This type of solution does not molecules. This type of solution does not conduct electricity.conduct electricity.

A A strong electrolytestrong electrolyte is a solute that is is a solute that is present in solution almost exclusively as present in solution almost exclusively as ions. This type of solution is a good ions. This type of solution is a good conductor of electricity.conductor of electricity.

A A weak electrolyteweak electrolyte is a solute that is only is a solute that is only partly ionized in solution. This type of partly ionized in solution. This type of solution is a poor conductor of electricity.solution is a poor conductor of electricity.



Ionic Compounds in WaterIonic Compounds in Water Cations are attracted to partial negative Cations are attracted to partial negative

charge on water’s oxygen.charge on water’s oxygen.

Anions in solution are attracted to Anions in solution are attracted to partial positive charge on water’s partial positive charge on water’s hydrogens.hydrogens.

OHH

OH H

O

H

H

O

H

H

Na

OHH

O

H

H

O

H

HO

H HCl


Solubility of ionic compoundsSolubility of ionic compounds An ionic solid has the choice to dissolve or An ionic solid has the choice to dissolve or

not to dissolve. Its solubility is dictated by not to dissolve. Its solubility is dictated by its its energy of solvationenergy of solvation..

When ionic compound dissociate, water When ionic compound dissociate, water makes several temporary bonds makes several temporary bonds (ATTRACTIONS) with the ions.(ATTRACTIONS) with the ions.

Alternatively, the electrostatic forces in the Alternatively, the electrostatic forces in the ionic solid may be so strong (high lattice ionic solid may be so strong (high lattice energy) that water cannot entice the ionic energy) that water cannot entice the ionic solid to dissolve.solid to dissolve.

Ionic compounds are described as either Ionic compounds are described as either soluble, insoluble or sparingly solublesoluble, insoluble or sparingly soluble


Covalent compounds in waterCovalent compounds in water

Sugar dissolves in water, but does not Sugar dissolves in water, but does not create ions since sugar is a molecular create ions since sugar is a molecular compound.compound.

Sugar (a covalent compound) stays as an Sugar (a covalent compound) stays as an intact moleculeintact molecule in water; no bonds are in water; no bonds are broken!broken!

Molecular compounds in water are Molecular compounds in water are considered considered non-electrolytesnon-electrolytes since their since their aqueous solutions do not conduct aqueous solutions do not conduct electricity.electricity.


Acids in waterAcids in water Few molecular compounds do dissociate Few molecular compounds do dissociate

in water, e.g. in water, e.g. acids:acids:HCl (g) HCl (g) H H++ (aq) + Cl (aq) + Cl-- (aq) (aq)

HH++ does not exit in solution alone, and does not exit in solution alone, and reacts with water to produce Hreacts with water to produce H33OO++

HH++ (aq) + H (aq) + H22O (l) O (l) H H33OO++(aq)(aq)

Water can only dissociate molecular Water can only dissociate molecular compounds that contain a removable Hcompounds that contain a removable H++


Strong acids vs. weak acidsStrong acids vs. weak acids Strong acidsStrong acids are acids that are completely are acids that are completely

ionized in water and are good conductors of ionized in water and are good conductors of electricity.electricity.

Weak acidsWeak acids are acids in which only some of are acids in which only some of the molecules are ionized in water; the rest the molecules are ionized in water; the rest remain as intact molecules.remain as intact molecules.

The dissociation of a weak acid in solution is The dissociation of a weak acid in solution is written using a double arrow to indicate that written using a double arrow to indicate that the dissociation does not go to completion.the dissociation does not go to completion.

Some acids have more than one ionizable Some acids have more than one ionizable hydrogen atom. These acids are usually strong hydrogen atom. These acids are usually strong acids for the first ionization and weak acids acids for the first ionization and weak acids for the rest of the ionizations.for the rest of the ionizations.


Acetic acid vs. HClAcetic acid vs. HCl

HCl (g) HCl (g) H H++ (aq) + Cl (aq) + Cl-- (aq) (aq)

0%0% 100% 100%

CHCH33COOH (aq) COOH (aq) H H++ (aq) + (aq) +

CHCH33COOCOO-- (aq) (aq)

99.5 %99.5 % 0.5%0.5%


Strong bases vs. weak basesStrong bases vs. weak bases

Strong basesStrong bases are ionic hydroxides that are ionic hydroxides that completely ionize in water and are good completely ionize in water and are good conductors of electricity.conductors of electricity.

Weak basesWeak bases are substances that act as bases are substances that act as bases but remain mostly molecular at equilibrium in but remain mostly molecular at equilibrium in water.water.

The dissociation of a weak base in solution is The dissociation of a weak base in solution is written using a double arrow to indicate that the written using a double arrow to indicate that the dissociation does not go to completion.dissociation does not go to completion.

Ammonia (NHAmmonia (NH33) is an example of a weak base.) is an example of a weak base.

04/09/23 www.surfinetek.com 16

Hull Cell Apparatus and Hull Cell Apparatus and

Test MethodTest MethodHull Cell is a miniature plating unit Hull Cell is a miniature plating unit

designed to produce cathode deposits designed to produce cathode deposits on a panel that correlates the on a panel that correlates the

characteristics of the plating unit characteristics of the plating unit being evaluated. Interpretation of the being evaluated. Interpretation of the ‘‘as plated’’ cathode panel give rapid ‘‘as plated’’ cathode panel give rapid information about brightness levels, information about brightness levels,

irregular plate deposits, uniformity of irregular plate deposits, uniformity of deposits, coverage, throwing power, deposits, coverage, throwing power,

impurities, and plating bath impurities, and plating bath chemistrychemistry..


Hull Cell Apparatus…Hull Cell Apparatus…

The Hull cell provides a simple and The Hull cell provides a simple and rapid method of visually testing the rapid method of visually testing the

quality of electroplated deposits over quality of electroplated deposits over a wide current density range. It also a wide current density range. It also enables the effect of additions to a enables the effect of additions to a plating solution, or of a purification plating solution, or of a purification treatment, to be readily determined. treatment, to be readily determined.

The Hull cell test is especially The Hull cell test is especially suitable for the visual control of suitable for the visual control of

bright nickel solutions and for the bright nickel solutions and for the detection of metallic impurities. It detection of metallic impurities. It may also be used in other types to may also be used in other types to plating solution such as dull nickel, plating solution such as dull nickel,

chromium, cadmium, zinc and copperchromium, cadmium, zinc and copper


Hull Cell Apparatus….Hull Cell Apparatus….


TheoryTheoryWithin the parameters of recommended operating

characteristics of a particular plating solution, the HULL CELL will

duplicate what is actually occurring in the plating unit proper.

Correlation of the ‘‘as plated’’ panel and the HULL CELL SCALE allows

rapid, nondestructive testing of plating solutions for research,

preventative maintenance, troubleshooting, and quality control.


Test Specimen

Description of Specimen A representative sample from

the plating unit to be evaluated is withdrawn and should be a

composite sampling from various areas in the plating tank and

from various depths within these areas.


Specimen Preparation

The representative sample should be analyzed

chemically for those critical components recommended

by the supplier of the plating bath. Correlation Of Hull Cell panels without the

information on the bath chemistry can be very

misleading.


Operating ConditionsOperating Conditions

Particular attention shall be given to the physical

conditions of the plating unit at the time of sampling and these operating conditions

should be duplicated during Hull Cell testing. If this is

not done, interpretation will be meaningless. Example:

temperature, cathode agitation, air agitation


Hull Cell Apparatus Hull Cell Apparatus and Description of Equipmentand Description of Equipment

A bench or portable miniature plating cell is employed using the following components.

A rectifier (D.C. power source) with variable controls for amperage from 0-10 amps, 0-12 volts. This power source should have less than 5% ripple.

Hull Cell Anode ‘‘+’’ chemistry of the anode the same as is in the plating unit or as recommended by the chemical supplier. Example: zinc anode for zinc plating bath.


Color coded coated cables capable of carrying the current required with an alligator clip soldered to cell end. Color code recognized universally is as follows: anode ‘‘+’’ black; cathode ‘‘–’’ red.

Hull Cell Cathode Panels—two most widely used are zinc plated steel and thin plastic protected brass panels.

Hull Cell—with scribed solution level line, 267 ml, 524 ml, or 1000 ml size. The most commonly used size is the 267 ml. Hull Cells are available in Lucite, Polypropylene, and Porcelain.

Hull Cell Scale—a calibrated ruler for interpretation of 1, 2, 3, and 5 amp panels to determine current densities.


Color Hull Cell Agitator—optional motor driven arm and panel assembly for duplicating solution and/or cathode agitation.

Agitation Hull Cell—specially designed for introducing air into the miniature plating unit to duplicate air agitation operations.

Timer—separate or built into the DC power unit depending upon the sophistication desired.


Hull Cell connections Hull Cell connections


Hull Cell Rectifier


Hull Cell Apparatus Hull Cell Apparatus


Hull Cell Voltage DistrubitionHull Cell Voltage Distrubition

2 Amps / Sq.Dm


Hull Cell Voltage DistrubitionHull Cell Voltage Distrubition

The chart gives the variation in current density along the middle horizontal of the plated portion of the test panel when currents of 1, 2, 3 and 5 amperes are applied. The current distribution is based upon the formula i = I (5.1 - 5.24 log 10 × ). Where i = current density (amp/dm2). I = total current (ampere). ×= distance from high current density end of panel in cm.


Hull Cell Test Procedure Hull Cell Test Procedure

Preparation (It is recommended that panels be handled with tweezers and gloves to prevent misleading results.)

Pre-clean cathode test panel. For zinc plated steel panels: immerse in For zinc plated steel panels: immerse in

50% by volume C.P. Hydrochloric acid to 50% by volume C.P. Hydrochloric acid to strip off protective zinc film.strip off protective zinc film.

Cold water rinse.

Wipe surface with Hull Cell sponge that has been soaked in D.I. water.


Procedure ……Procedure …… Observe panel for water break free

condition. Repeat cleaning processes if necessary.

For plastic coated brass panels-remove plastic film by peeling it off.

Soak in mild soak cleaner. Reverse current clean at 2 amps for one

minute. Cold water rinse. Acid dip 10% C.P. Hydrochloric Acid for

5 seconds.


Procedure ……Procedure ……

Cold water rinse.

Observe for water break free surface. Repeat cleaning if necessary.

Insert cathode test panel along the slanted side of the Hull Cell (it just fits), which has solution to scribed line.

Hook red cable to anode (+).

Hook black cable to cathode (–).

Set timer to prescribed time


Procedure ……Procedure ……

Turn on power source. Adjust power to described

amperage. Start time. At prescribed time, shut off power. Disconnect cathode cable. Remove cathode panel. Cold water rinse.


Procedure ……Procedure …… Complete desired post plate treatment if any

example: dipping panel in 1/4 to 1/2 of 1% by volume. Nitric Acid (C.P. Grade) for 3-5 seconds enhances the ability to interpret the panel on zinc and cadmium plating solutions.

Warm Water Rinse.

Dry, forced air or even wiping with a water absorbent paper towel.

An alternate method of drying the panels is to water rinse followed by an alcohol rinse to drive off the water. Also, a method of preserving samples is to spray them immediately with a clear lacquer to prevent oxidation.


EvaluationEvaluation Depending upon the bath chemistry

as analyzed, condition of the panel relative to uniformity, burning, cloud patterns skip plate, etc., modification by controlled additions canbe made to the Hull Cell plating solution and procedures can be repeated. Changes caused by addition to the Hull Cell will duplicate results to be expected by the same proportionate additions to the main plating bath.


Evaluation…..Evaluation…..

Correlations of thickness checks in the controlled time, temperature, amperage cathode panel will also tell the optimum plating range to obtain plating thickness desired.


Current and Duration of Current and Duration of Test Test

For the majority of bright plating solutions For the majority of bright plating solutions including nickel, cadmium zinc and including nickel, cadmium zinc and copper, it is usual to use a current of two copper, it is usual to use a current of two amperes and a plating time of 10 minutes. amperes and a plating time of 10 minutes.

When it is wished to emphasize the effect When it is wished to emphasize the effect of impurities at low current densities, e.g. of impurities at low current densities, e.g. in bright nickel solutions, a current of 2 in bright nickel solutions, a current of 2 amperes and a plating time of 10 minutes amperes and a plating time of 10 minutes is usual. However depending on the type is usual. However depending on the type of solution 1 ampere for 20 minutes may of solution 1 ampere for 20 minutes may be used.be used.


Current and Duration of Test…Current and Duration of Test…

To ascertain if burning occurs at To ascertain if burning occurs at high current density, a current of 3 high current density, a current of 3 amperes for 5 minutes is advised.amperes for 5 minutes is advised.

For chromium solutions a current For chromium solutions a current of 5 amperes with a plating time of of 5 amperes with a plating time of 3 minutes is usual but where high 3 minutes is usual but where high current densities are being current densities are being investigated a current of 10 investigated a current of 10 amperes for 1 ½ minutes is amperes for 1 ½ minutes is recommended.recommended.


Current and Duration of Test…Current and Duration of Test…

When using a current of 5 amperes no water When using a current of 5 amperes no water bath is needed but it is best to start plating bath is needed but it is best to start plating with the temperature 0.5 0 C (10F) below the with the temperature 0.5 0 C (10F) below the optimumoptimum, when it will be found that the , when it will be found that the temperature gradually rises to be about 0.5 0 C temperature gradually rises to be about 0.5 0 C (1 0 F) above at the end of the plating test. (1 0 F) above at the end of the plating test. When using 10 amperes the Hull Cell should be When using 10 amperes the Hull Cell should be placed in a cold water bath and the solution placed in a cold water bath and the solution taken to a temperature of 10C (2 0 F) below the taken to a temperature of 10C (2 0 F) below the optimumoptimum at the commencement of plating. In at the commencement of plating. In all cases contact to the cathode should be made all cases contact to the cathode should be made before the warm chromium solution is poured before the warm chromium solution is poured into the Hull Cell. into the Hull Cell.


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Selvaraj VenkatesanSelvaraj Venkatesan

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Hull cell

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