GB2265717A

GB2265717A - Electrochemical testing of samples

Info

Publication number: GB2265717A
Application number: GB9207116A
Authority: GB
Inventors: David Terence Rickard
Original assignee: University College Cardiff Consultants Ltd; Cardiff University
Current assignee: University College Cardiff Consultants Ltd; Cardiff University
Priority date: 1992-04-01
Filing date: 1992-04-01
Publication date: 1993-10-06
Also published as: GB9207116D0

Abstract

A method of testing or evaluating a sample of material comprises forming a membrane 20 from the sample, bonding the membrane across an opening in a housing (10) which is filled with a reference solution 22, immersing the housing in a selected liquid, and monitoring time- varying changes which occur in the electric potential on an electrode 14 which extends into the reference solution 22. The changes are monitored with respect to a similar, reference electrode immersed in the liquid. The method enables the dissolution behaviour of any sample in any selected liquid or liquid bearing medium (e.g. tissue) to be evaluated. <IMAGE>

Description

Materials Testing This invention relates to a method of testing or evaluating a sample of material.

It is desirable to investigate the manner in which minerals and other materials behave when immersed in specific liquids or liquid-bearing media (e.g. tissue). It is common to observe how samples dissolve in a liquid, but then it is only possible to measure changes which occur in the bulk solution due to dissolution: present techniques do not enable the activity to be monitored which occurs at the surface of a sample as it dissolves in the liquid.

We have now devised a method of testing or evaluating a sample of material which does allow the surface activity of a sample to be measured as it dissolves in a liquid.

In accordance with this invention, there is provided a method of testing or evaluating a sample of material, comprising forming a membrane from the sample, bonding the membrane across an opening in a housing which is filled with a reference solution, immersing the housing in a selected liquid, and monitoring time-varying changes which occur in the electric potential on an electrode which extends into the reference solution within said housing.

The electrode structure of which the sample membrane forms a part resembles P H electrode e.g. of the MacInnes and Dole type. In this type of PK electrode, a thin glass membrane separates the bulk solution from the inner reference electrode.

In accordance with the present invention, preferably the electrode potential which is monitored is compared with a reference potential, for example the potential on a similar electrode also immersed in the same liquid and having a membrane of known properties, e.g. a glass membrane.

The potentials generated across the sample membrane vary as the surface of the sample reacts with the liquid in which it is immersed. As the sample electrode is placed into the liquid, its potential changes continuously until it reaches a constant value. For a membrane of PH quality electrode glass used in PH electrodes, the electrode reaches its constant potential very quickly: however other glasses and mineral materials take considerably longer at e.g. 25"C. The change in potential of the sample electrode with time provides a direct measure of the changes in surface condition of the sample material with time and accordingly provide an indication of the rate of dissolution of the sample material in the particular liquid in which it is immersed.

The invention enables the dissolution behavious to be monitored of any sample in any selected liquid or liquidbearing medium (e.g. tissue).

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawing, the single Figure of which is a longitudinal section through a test electrode having a membrane formed of the sample material.

Referring to the drawing, there is shown a test electrode the structure of which corresponds generally with that of a MacInnes and Dole PH electrode. An insulating glass tube 10 is closed at its upper end by a plug 12 of epoxy. An Ag-Agll electrode 14 projects from the plug 12 along the axis of the glass tube 10 and is connected by a solder joint 16 to the inner conductor of a coaxial cable 18 extending from the exterior of the plug 12. The opposite end of the glass tube 10 is closed by a thin membrane 20 which has been formed from a sample material to be tested, and bonded (e.g. by fusing or by adhesive) to the end of the tube 10. The interior of the tube 10 is filled with a reference solution 22.

The membrane 20 may be formed by sectioning and polishing techniques conventional in geological laboratories, to desired thickness e.g. under O.lmm.

In use, the electrode which is shown may be immersed in any selected liquid or liquid-bearing medium. Then the changes in potential which occur on the inner electrode 14 with time are monitored, to reflect the dissolution behaviour of the sample material in the selected liquid.

Claims

1) A method of testing or evaluating a sample of material, comprising forming a membrane from the sample, bonding the membrane across an opening in a housing which is filled with a reference solution, immersing the housing in a selected liquid, and monitoring time-varying changes which occur in the electric potential on an electode which extends into the reference solution within said housing.

2) A method as claimed in claim 1, in which the electric potential of said electrode is compared with a reference potential.

3) A method as claimed in claim 2, in which the reference potential is the potential on a similar electrode immersed in the same liquid and having a membrane of known properties.

4) A method as claimed in claim 1 and substantially as herein described with reference to the accompanying drawing.