SPECIFICATION
Title of Invention
GLASS-ELECTRODE RESPONSIVE-GLASS CLEANING LIQUID AND
METHOD FOR CLEANING GLASS-ELECTRODE RESPONSIVE-GLASS
Technical Field
[0001]
The present invention relates to a cleaning liquid for a responsive
glass used in a glass electrode, and a method for cleaning the responsive
glass for the glass electrode.
Background Art
[0002]
For a responsive glass used in a glass electrode, depending on a
storage state and a usage state, an impurity (stain) may adhere to a
hydrated layer formed on the surface of the responsive glass. As known, the
responsivity of such glass electrode using the responsive glass lowers due to
inhibition of electrode reaction or the like.
[0003]
An example of a method for recovering the lowering of the
responsivity of the glass electrode is a method for cleaning the responsive
glass described in Patent Literature 1.
In the method described in Patent Literature 1, the responsive glass
is cleaned by immersing the responsive glass in a drug solution (for example,
hydrofluoric acid) fed into a cleaning bath for a predetermined time.
Citation List
Patent Literature
2
[0004]
Patent Literature 1: JPA- 2003-262605
Summary of Invention
Technical Problem
[0005]
In the above-mentioned document, the responsive glass is cleaned by
removing the hydrated layer formed on the surface of the responsive glass by
etching using hydrofluoric acid. The hydrofluoric acid is dissociated in the
solution as follows.
HF ↔ H+ + FHF
+ F- ↔ HF2-
Although ion species that contribute to the etching of the hydrated
layer are HF2- ions, F- ions are hardly dissociated in a hydrofluoric acid
solution and thus, HF2- ions are hardly generated. Accordingly, even when
HF2- ions are consumed by etching, hydrofluoric acid has a low buffering
capacity to generate and supply HF2- ions, which makes control of the
etching rate difficult.
[0006]
This causes a problem that a slight deviation from predetermined
concentration of hydrofluoric acid or etching time disables desired etching.
Further, excessive peeling of the responsive glass by etching causes a
problem that a byproduct such as silicofluoride adheres to the surface of the
responsive glass, lowering the responsivity of the glass electrode.
Moreover, the etching rate of hydrofluoric acid having a low buffering
capacity is affected by environmental factors such as temperature, makes
3
desired etching more difficult.
[0007]
To solve the above-mentioned problems, the present invention
intends to provide a glass-electrode responsive-glass cleaning liquid and a
glass-electrode responsive-glass cleaning method that can easily control the
etching rate to optimally clean the glass electrode.
Solution to Problem
[0008]
That is, the glass-electrode responsive-glass cleaning liquid
according to the present invention for cleaning a responsive glass used in a
glass electrode is a glass-electrode responsive-glass cleaning liquid that is
used with a hydrated-layer forming solution for forming a hydrated layer on
the surface of the responsive glass after cleaning, and contains ammonium
hydrogen fluoride having a predetermined concentration or a salt of a strong
base containing hydrofluoric acid and a fluoride ion.
[0009]
With such configuration, the responsive glass is etched using
ammonium hydrogen fluoride or the salt of the strong base containing the
hydrofluoric acid and the fluoride ion. Ammonium hydrogen fluoride or the
salt of the strong base containing hydrofluoric acid has a high buffering
capacity to generate and supply ions that contribute to etching (HF2- ions)
even when HF2- ions are consumed and therefore, can control the etching
rate more easily than hydrofluoric acid. Thus, even when the
predetermined concentration of hydrofluoric acid and etching time are
strictly controlled, desired etching can be achieved. Moreover, due to the
4
high buffering capacity, the etching rate can be controlled under varying
environmental factors.
[0010]
The hydrated-layer forming solution is preferably neutral or acidic.
When the hydrated-layer forming solution is neutral, for example, pure
water or ion-exchange water, a water-washing step after the hydrated-layer
forming step is unnecessary and can be omitted, simplifying the
responsive-glass cleaning step. When the hydrated-layer forming solution
is acidic, dissociated hydrogen ions generate oxonium ions in the solution,
and promotes formation of the hydrated layer, reducing reaction time.
[0011]
The concentration of ammonium hydrogen fluoride is preferably 4
mass % or less.
This concentration enables easier control of the etching time. In
addition, since ammonium hydrogen fluoride does not need to be handled as
a deleterious substance, handling of the responsive-glass cleaning liquid is
simplified.
[0012]
For the glass-electrode responsive-glass cleaning liquid that serves to
clean the responsive glass containing a metal oxide as a component, metal
ions in the metal oxide forming the responsive glass unite with ununited
oxygen molecules in SiO2 before etching to disturb a network of SiO2, and
etching of the hydrated layer is promoted from this part, reducing the
etching time. Examples of the metal oxide include a lithium oxide.
[0013]
5
A glass-electrode responsive-glass cleaning method according to the
present invention includes a step of cleaning a responsive glass used in a
glass electrode by using a responsive-glass cleaning liquid containing
ammonium hydrogen fluoride, or a salt of a strong base containing
hydrofluoric acid and a fluoride ion.
[0014]
The glass-electrode responsive-glass cleaning method according to
the present invention may further includes a hydrated-layer forming step of
forming a hydrated layer on the surface of the responsive glass by using a
neutral or acidic hydrated-layer forming solution, after the cleaning step of
cleaning the responsive glass.
[0015]
In the cleaning step of the glass-electrode responsive-glass cleaning
method, the temperature of the responsive-glass cleaning liquid is preferably,
kept to be 5 to 40°C.
Advantageous Effects of Invention
[0016]
As described above, according to the present invention, the etching
rate can be easily controlled to optimally clean the glass electrode.
Brief Description of Drawings
[0017]
Fig. 1 is a schematic view showing a glass electrode to be cleaned
with a glass-electrode responsive-glass cleaning liquid in the present
embodiment;
Fig. 2 is a flow chart showing a glass-electrode responsive-glass
6
cleaning method in the present embodiment; and
Fig. 3 is a graph showing a test result of pH electrodes in an example
and a comparison example.
Description of Embodiments
[0018]
An embodiment of a glass-electrode responsive-glass cleaning liquid
according to the present invention will be described below.
[0019]
The glass-electrode responsive-glass cleaning liquid in accordance
with the present embodiment serves to clean a responsive glass 2 used in a
glass electrode 1, is used with a hydrated-layer forming solution for forming
a hydrated layer on the surface of the responsive glass 2 after cleaning, and
contains ammonium hydrogen fluoride having a predetermined
concentration, or a salt of a strong base containing hydrofluoric acid and a
fluoride ion.
[0020]
As shown in Fig. 1, the glass electrode 1 functions to measure pH, is
configured to fill a glass support tube 3 having a front end, to which the
responsive glass 2 is bonded, with an internal solution having a uniform
concentration, such as a potassium chloride solution, and immerse a pH
electrode 5 and a comparison electrode 4 in the internal solution, and has a
composite configuration in which the pH electrode 5 and the comparison
electrode 4 are united.
[0021]
Immersion of the responsive glass 2 in a test solution, pH of which is
7
to be found, generates an electromotive force corresponding to a pH
difference between the internal solution having a known pH and the test
solution, and the pH electrode 5 and the comparison electrode 4 detect the
electromotive force to measure the pH value of the test solution.
[0022]
The responsive-glass cleaning liquid for the glass electrode 1 contains
ammonium hydrogen fluoride of 4 mass % or less, or a salt of a strong base
containing hydrofluoric acid and a fluoride ion such as sodium fluoride or
potassium fluoride.
[0023]
The hydrated-layer forming solution is used after cleaning of the
responsive glass 2 by using the responsive-glass cleaning liquid for the glass
electrode 1, and serves to form a hydrated layer on the surface of the
responsive glass 2. Examples of the hydrated-layer forming solution
include a standard solution having a pH of 2 or 4, an acidic solution such as
hydrochloric acid, nitric acid, or sulfuric acid, a standard solution having a
PH of 7, and a neutral solution such as pure water or ion-exchange water.
However, the acidic solution does not includes hydrofluoric acid.
[0024]
The responsive glass 2 may be lithium glass (lithium-containing
glass).
[0025]
Next, a glass-electrode responsive-glass cleaning method in
accordance with the present embodiment will be described.
[0026]
8
The glass-electrode responsive-glass cleaning method in the present
embodiment, as shown in Fig. 2, includes a cleaning step of cleaning a
responsive glass used in a glass electrode with a responsive-glass cleaning
liquid containing ammonium hydrogen fluoride, a first water-washing step of
performing water-washing after the cleaning step, a hydrated-layer forming
step of forming a hydrated layer on the surface of the responsive glass with a
neutral or acidic hydrated-layer forming solution after the first
water-washing step, and a second water-washing step of performing
water-washing again after the hydrated-layer forming step.
[0027]
The cleaning step will be described in detail.
[0028]
The responsive glass is configured by uniting silicon atoms with
oxygen atoms in the form of a mesh, water molecules enters into the
mesh-like SiO2 to form the hydrated layer, and an impurity (stain) invades
into the hydrated layer, lowering the responsivity of the glass electrode.
[0029]
Thus, the responsive glass is immersed in ammonium hydrogen
fluoride of 4 mass % or less, or a salt of a strong base containing hydrofluoric
acid and a fluoride ion such as sodium fluoride or potassium fluoride for 3
minutes, for example, to etch the hydrated layer.
[0030]
Ammonium hydrogen fluoride is dissociated in the solution as
follows.
NH4(HF2) → NH4+ + HF2-
9
HF2- ↔ HF + FHF
↔ H+ + F-
[0031]
Since ion species that contribute to etching of the hydrated layer are
HF2- ions, SiO2 in the hydrated layer is etched by HF2- ions according to
following reaction.
SiO2 + 3HF2- + H+ → SiF6- + 2H2O
2NH4 + SiF6- → (NH4)2SiF6
[0032]
As apparent from the dissociated state in the solution, ammonium
hydrogen fluoride can easily generate HF2- ions that are ion species
contributing to the etching. Accordingly, even when HF2- ions are consumed
through the etching reaction, ammonium hydrogen fluoride has a high
buffering capacity to generate and supply HF2- ions, and can successively
supply HF2- ions according to the etching reaction.
[0033]
The mixed solution of the salt of the strong base containing the
fluoride ion such as sodium fluoride or potassium fluoride and hydrofluoric
acid is dissociated in the solution as follows. The dissociated state of the
sodium fluoride is described as an example.
NaF → Na+ + FHF
↔ H+ + FHF
+ F- ↔ HF2-
[0034]
In the solution, since completely-dissociated sodium fluoride can
10
supply F-at all times, and hydrofluoric acid is a weak acid having a
dissociation constant of 6.76 × 10-4M and is hardly dissociated, HF2- ions that
are ion species contributing to the etching can be easily generated. Also in
the salt of the strong base containing the fluoride ion, even when HF2- ions
are consumed through the etching reaction, the salt of the strong base has a
high buffering capacity to generate and supply HF2- ions, and can
successively supply HF2- ions according to the etching reaction.
[0035]
As the temperature of the responsive-glass cleaning liquid is higher,
the etching reaction is promoted to reduce the cleaning time. However, the
temperature is too low, the responsive-glass cleaning liquid is frozen to stop
the etching reaction. Thus, the temperature is desirably set to be 0°C or
higher at which the responsive-glass cleaning liquid is never frozen. For
this reason, the temperature of the responsive-glass cleaning liquid may be
set to be 5°C or more and 40°C or less such that the cleaning liquid has a
good operational performance/operability and can be used under room
temperature.
[0036]
In a first water-washing step, ammonium hydrogen fluoride adhered
to the responsive glass in the cleaning step is removed to stop the etching,
and the responsive glass is cleaned with pure water or ion-exchange water.
[0037]
In a hydrated-layer forming step, a hydrated layer is formed again on
the surface of the responsive glass from which the hydrated layer is removed
in the cleaning step, and the responsive glass is immersed in the 0.01 M of
11
hydrochloric acid for 12 hours, for example. Then, in hydrogen ions-rich
hydrochloric acid, water molecules enter into the mesh of SiO2 on the surface
of the responsive glass to form the hydrated layer.
[0038]
In a second water-washing step, hydrochloric acid adhered to the
responsive glass in the hydrated-layer forming step is removed to make the
glass electrode measurable, the responsive glass is cleaned with pure water
or ion-exchange water, and water droplets adhered to the responsive glass
are wiped off with filter paper or tissue as appropriate.
[0039]
The glass-electrode responsive-glass cleaning liquid thus configured
in the present embodiment has following special effects.
[0040]
That is, the responsive glass is etched using ammonium hydrogen
fluoride. Ammonium hydrogen fluoride has a high buffering capacity to
generate and supply ions that contribute to etching (HF2- ions) even when
HF2- ions are consumed and therefore, can control the etching rate more
easily than hydrofluoric acid. Thus, even when the predetermined
concentration of hydrofluoric acid and etching time are not strictly controlled,
desired etching can be achieved. Moreover, due to the high buffering
capacity, the etching rate can be controlled under varying environmental
factors.
[0041]
Since the concentration of ammonium hydrogen fluoride is 4 mass %
or less, the etching time can be controlled more easily. In addition, since
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ammonium hydrogen fluoride does not need to be handled as a deleterious
substance, handling of the responsive-glass cleaning liquid is simplified.
[0042]
When the hydrated-layer forming solution is neutral, for example,
pure water or ion-exchange water, the water-washing step after the
hydrated-layer forming step is unnecessary and can be omitted, simplifying
the responsive-glass cleaning step.
[0043]
When the acidic solution is used in the hydrated-layer forming step,
hydrogen ions dissociated in the acidic solution unite with water molecules
to form oxonium ions. Then, water molecules and oxonium ions enter into
mesh of SiO2 on the surface of the responsive glass, promoting the formation
of the hydrated layer to reduce the reaction time. In addition, the acidic
solution such as hydrochloric acid, nitric acid, or sulfuric acid can melt metal
to remove a metal-induced stain. Especially, hydrochloric acid can remove
the metal-induced stain, and unlike nitric acid and sulfuric acid, can prevent
a liquid junction potential leading to a measurement error because chloride
ions are initially contained in the internal solution of the glass electrode.
For this reason, hydrochloric acid is less affected by liquid junction and thus,
may have any concentration.
[0044]
For the glass-electrode responsive-glass cleaning liquid that serves to
clean the responsive glass containing a metal oxide as a component, metal
ions in the metal oxide forming the responsive glass unite with ununited
oxygen molecules in SiO2 before etching to disturb a network of SiO2, and
13
etching of the hydrated layer is promoted from this part, reducing the
etching time.
[0045]
The present invention is not limited to the embodiment.
[0046]
Although the responsive glass is lithium glass (lithium-rich glass) in
the embodiment, the responsive glass may be any glass containing metal to
improve performances including electric conductivity of the responsive glass
(for example, calcium, titanium, and zirconia).
[0047]
Although the glass electrode serves to measure pH in the
embodiment, the glass electrode may serve to measure pNa in addition to
pH.
[0048]
The present invention may be variously modified so as not to deviate
from the subject matter.
Example
[0049]
The present invention will be described below in more detail using an
example, but the present invention is not limited to the example.
[0050]

20 pH electrodes as glass electrodes using the responsive glass were
divided into two groups, 95% response time was measured without any
treatment in one group (hereinafter referred to as comparison example), and
14
the 95% response time was measured after performing the cleaning method
of the present invention in the other group (hereinafter referred to as the
example).
[0051]

A test method in the example will be described.
[0052]
· Cleaning method of the present invention
In the cleaning method of the present invention, the responsive
glasses of the pH electrodes in the example were immersed in 0.1 M of
ammonium hydrogen fluoride for 3 minutes, and then, in 0.01 M of HCl for
12 hours.
[0053]
· Method for measuring 95% response time
A method for measuring the 95% response time will be described as
follows.
First, the pH electrodes in the example and the pH electrodes in the
comparison example were immersed in a standard solution of pH4, and
measurement values E0 after an elapse of 3 minutes were checked. Then,
the pH electrodes were cleaned with pure water (ion-exchange water), and
water droplets were wiped off with filter paper or tissue. Then, the pH
electrodes were immersed in tap water for 10 minutes. During this
immersion, the measurement values were recorded, and measurement
values E after an elapse of 10 minutes were checked.
Subsequently, in the recorded measurement values, given that an
15
electromotive force difference between E and E0 is 100%, time required to
reach an electromotive force difference of 95% (95% response time) was
checked. The measurement method was repeated multiple times to find
standard deviations and average values in the comparison example and the
example.
[0054]

Fig. 3 shows a test result. As shown in Fig. 3, an average value of
the 95% response time of the pH electrodes in the comparison example was
90 seconds, while an average value of the 95% response time of the pH
electrodes in the example was 30 seconds.
[0055]
The reason is supposed as follows: in the pH electrodes in the
example, since an impurity of the hydrated layer was removed by cleaning
before the measurement of the 95% response time, the responsivity was
improved to quicken the response time, that is, to make the 95% response
time faster than that in the comparison example.
[0056]
As shown in Fig. 3, upon comparing the example with the comparison
example, the example had a smaller variation in the 95% response time than
the comparison example, and the comparison example had a larger variation
in the 95% response time than the example.
[0057]
Supposedly, the responsive glasses of all pH electrodes used in the
test were cleaned to improve the responsivity in the example, reducing the
16
variation in the response time, while some responsive glasses had an
impurity to lower the responsivity in the comparison example, causing the
variation in the response time.
Reference Signs List
[0058]
1: Glass electrode
2: Responsive glass
17
CLAIMS
1. A glass-electrode responsive-glass cleaning liquid for cleaning a
responsive glass used in a glass electrode, wherein the liquid
is used with a hydrated-layer forming solution for forming a hydrated
layer on the surface of the responsive glass after cleaning, and
contains ammonium hydrogen fluoride having a predetermined
concentration or a salt of a strong base containing hydrofluoric acid and a
fluoride ion.
2. The glass-electrode responsive-glass cleaning liquid according to
claim 1, wherein
the hydrated-layer forming solution is neutral or acidic.
3. The glass-electrode responsive-glass cleaning liquid according to
claim 1, wherein
the responsive-glass cleaning liquid contains ammonium hydrogen
fluoride, and
the concentration of ammonium hydrogen fluoride is 4 mass % or
less.
4. The glass-electrode responsive-glass cleaning liquid according to
claim 1, wherein
the liquid cleans the responsive glass containing a metal oxide as a
component.
18
5. A glass-electrode responsive-glass cleaning method comprising a
step of cleaning a responsive glass used in a glass electrode by using a
responsive-glass cleaning liquid containing ammonium hydrogen fluoride, or
a salt of a strong base containing hydrofluoric acid and a fluoride ion.
6. The glass-electrode responsive-glass cleaning method according to
claim 5, further comprising a hydrated-layer forming step of forming a
hydrated layer on the surface of the responsive glass by using a neutral or
acidic hydrated-layer forming solution after the cleaning step of cleaning the
responsive glass.
7. The glass-electrode responsive-glass cleaning method according to
claim 6, wherein
in the cleaning step, the temperature of the responsive-glass cleaning
liquid is kept to be 5 to 40°C.