Method and apparatus for determining oxide film thickness

Claim 1

A method for determining the thickness of an electrically insulative metal oxide coating on an electrically conductive metal substrate sample which comprises: (a) electrolytically reducing a sample of said oxide coating in an electrochemical cell at relatively constant current density while measuring the cell voltage, (b) defining the relationship between cell voltage rise attributable to electrolytically reducing the oxide coating and the time interval of electrolytic reduction in the form of a mathematical curve, said curve defining the cell voltage rise with time passage from a predetermined threshold voltage value to a final cell voltage value achieved when said oxide coating has been removed by said electrolytic reduction, (c) determining the final time value needed to completely remove said coating on said mathematical curve as the intersection point between a tangent to said curve at the region between said threshold voltage value and said final cell voltage value, and (d) computing the oxide thickness using the total elapsed time of electrolytic reduction as determined by said final time value.

Claim 2

A method for determining the thickness of an electrically insulative metal oxide coating on an electrically conductive metal substrate sample which comprises: (a) electrolytically reducing a sample of said oxide coating in an electrochemical cell at relatively constant current density while measuring the cell voltage, (b) defining the relationship between cell voltage rise attributable to electrolytically reducing the oxide coating and the time interval of electrolytic reduction in the form of a mathematical curve, said curve defining the cell voltage rise with time passage from a predetermined threshold voltage value to a final cell voltage value achieved when said oxide coating has been removed by said electrolytic reduction, (c) determining the final time value needed to completely remove said coating on said mathematical curve as the intersection point between a tangent to said curve at the region between said threshold voltage value and said final cell voltage value, and (d) computing the oxide thickness using the total elapsed time of electrolytic reduction as determined by said final time value.

Claim 12

A method for automatically determining the electrically insulative thickness of a metal oxide coating on an electrically conductive metal substrate sample utilizing a programmed microprocessor which comprises: (a) electrolytically reducing a sample of said oxide coating in an electrochemical cell at relatively constant current density while measuring the cell voltage, (b) computing the cell current by said microprocessor from the sample dimensions, (c) measuring the cell voltage change with respect to the time interval of electrolytic reduction and storing the measurements in said microprocessor, (d) defining the relationship between cell voltage rise attributable to electrolytically reducing the oxide coating and the time interval of electrolytic reduction in the form of a mathematical curve, said curve defining the cell voltage rise with time passage from a predetermined threshold voltage value to a final cell voltage value achieved when said oxide coating has been removed by said electrolytic reduction, (e) determining said threshold voltage which is greater in value by a preselected amount than the cell operation, (f) determining the tangent to said mathematical curve at the region between said threshold voltage value and said final cell voltage value from the stored cell voltage values which are greater by a fixed amount than the minimum cell voltage measured and thereafter determining the final time value to remove said coating by intersection between said tangent and the cell voltage value when said coating has been removed, (g) computing the oxide thickness in said micropressor utilizing the total elapsed time of electrolytic reduction as determined by said final time value according to the following equation: ##EQU2## wherein t=oxide thickness, cm. I D =cell current density, amp./cm 2 T=time value, sec. E=oxide equivalent weight, gms./gm. mole D=oxide density, gm./cc. F C =Faraday's constant, coulombs/gm. mole (h) terminating the steps of said method upon fulfillment of all following conditions: (i) time passage of a said first time interval, (ii) achieving the threshold cell voltage, and (iii) no cell voltage rise above a predetermined value is encountered during a second time interval subsequent to said first time interval.

Claim 13

A method for automatically determining the electrically insulative thickness of a metal oxide coating on an electrically conductive metal substrate sample utilizing a programmed microprocessor which comprises: (a) electrolytically reducing a sample of said oxide coating in an electrochemical cell at relatively constant current density while measuring the cell voltage, (b) computing the cell current by said microprocessor from the sample dimensions, (c) measuring the cell voltage change with respect to the time interval of electrolytic reduction and storing the measurements in said microprocessor, (d) defining the relationship between cell voltage rise attributable to electrolytically reducing the oxide coating and the time interval of electrolytic reduction in the form of a mathematical curve, said curve defining the cell voltage rise with time passage from a predetermined threshold voltage value to a final cell voltage value achieved when said oxide coating has been removed by said electrolytic reduction, (e) determining said threshold voltage which is greater in value by a preselected amount than the cell operation, (f) determining the tangent to said mathematical curve at the region between said threshold voltage value and said final cell voltage value from the stored cell voltage values which are greater by a fixed amount than the minimum cell voltage measured and thereafter determining the final time value to remove said coating by intersection between said tangent and the cell voltage value when said coating has been removed, (g) computing the oxide thickness in said micropressor utilizing the total elapsed time of electrolytic reduction as determined by said final time value according to the following equation: ##EQU2## wherein t=oxide thickness, cm. I D =cell current density, amp./cm 2 T=time value, sec. E=oxide equivalent weight, gms./gm. mole D=oxide density, gm./cc. F C =Faraday's constant, coulombs/gm. mole (h) terminating the steps of said method upon fulfillment of all following conditions: (i) time passage of a said first time interval, (ii) achieving the threshold cell voltage, and (iii) no cell voltage rise above a predetermined value is encountered during a second time interval subsequent to said first time interval.