JPS5951336A - Alcohol gas detecting element - Google Patents

Abstract

PURPOSE:To obtain a detecting element having high sensitivity to alcohol gas, good in reproducibility and free from change with the elapse of time, by forming a detecting film by using a composition consisting of NiO, Pd and glass in a specific compositional range as a gas detecting material. CONSTITUTION:70-97wt% of NiO, 0.5-5wt% of Pd and 2.5-59.5wt% of a glass material selected from lead borosilicate glass, zinc borosilicate glass, alkali silicate glass, CaO-ZnO-PbO-TiO2-SiO2 glass or the like are mixed to prepare a paste 4. A heater pattern is printed to the back surface of a base plate 1 comprising Al2O3 by using a Pt-paste while a lower electrode 3 is printed on the surface of the heater pattern after drying to be baked and the surface of the electrode 3 is printed with the aforementioned detecting material paste 4. After drying, the Pt paste is applied to print an upper electrode 5 to be dried. Subsequently, the whole is baked at max. 900 deg.C to obtain a detecting element excellent in sensitivity, a response speed and reproducibility to a alcohol gas.

Description

[Detailed description of the invention] The present invention relates to an alcohol gas detection element.

In particular, the present invention relates to a semiconductor type alcohol gas detection element.

Globskite crystal LnBO1, which is a composite of a rare earth oxide and a transition metal oxide, has been conventionally used as a semiconductor alcohol gas sensor composition. here,
Ln: La, Nd, 8m, Sr, etc., B; CO
, Ni, Fe, etc. These materials have been used as sensor materials because they exhibit high activity against alcohol (which is reducible in nature).

However, materials that are highly sensitive to alcohol have drawbacks such as poor reproducibility of properties and large variations in changes over time, and solving these problems has become an important issue.

An object of the present invention is to overcome these drawbacks and provide a gas sensing element that has high sensitivity to alcohol and excellent reproducibility of characteristics.

In order to achieve all of the above objectives, the present inventors have investigated various composite oxides and materials in which various additives are added to them as gas sensor compositions. As a result, nickel oxide (
Nip) 70-97% by weight, 0.5-97% of mother caries
It has been found that a detection sensor with high sensitivity to alcohol, good response characteristics, and excellent reproducibility can be obtained in a composition containing 5% by weight and 2.5 to 29.5% by weight of glass.

The composition of only nickel oxide (Nip) is a material known as a reducing gas sensing material. However, this material alone has relatively low sensitivity to alcohol! The reproducibility of the characteristics is poor. On the other hand, in the present invention, by completely adding baradium to NiO, the sensitivity to alcohol can be completely increased. The reason why the total amount of baladium added was limited to 0.5 to 5% by weight is that if it is less than 0.5% by weight, the effect of increasing alcohol sensitivity due to addition is small, and if it exceeds 5% by weight, the addition effect will be saturated, and conversely, the characteristics will change. This is because reproduction becomes poor. Furthermore, in the present invention, the reproducibility of characteristics can be improved by adding all of the glass.

The total amount of glass was 2.5 to 29.5% by weight.
If it is less than 29% by weight, the effect of improving characteristic reproducibility is small, and
．． This is because if the amount exceeds 5% by weight, the sensitivity to alcohol becomes low.

As the glass material, various materials can be used, but in particular, lead borosilicate, lead zinc borosilicate, alkali silicate, CaOZnO-PbOT I (%
810 system is suitable. Also, as a glass material, amorphous 5ift + 5nOt * AA! A similar effect can be obtained by using an oxide such as tow. Furthermore, it is also common to add trace amounts of metals or metal oxides for the purpose of changing gas sensitivity, controlling gas response time, or controlling sintering of elements. Even with such addition, the effects of the present invention are not impaired in any way.

Although the sensing element of the present invention has high sensitivity to alcohol,
Other reducing substances (hydrogen, etc.) can also be detected.
Can be used for general purposes.

Hereinafter, the present invention will be explained in detail based on examples. 1st
The figure shows a configuration diagram of one embodiment of the sensing element. As shown in the figure, a heater pattern is printed on the back side of a 96% pure alumina substrate using platinum paste. After this is completely dried, the lower electrode is completely printed on the surface of the alumina substrate using the same platinum paste.

After drying this substrate, it is fired at 1200° C. for 2 hours using an electric furnace to completely form the platinum heater 2 and the lower electrode 3. On the bottom electrode, NiO, Pd and CaO− are used as sensing materials.
A predetermined amount of znO-PbO-TiO2-SiO2 glass is weighed and mixed as shown in Table 1, and the paste is printed. (In the table, materials that fall within the composition of the present invention and materials that deviate from the composition range of the present invention are listed for comparison). After drying this, an upper electrode is printed on it using platinum paste having the same composition as the lower electrode. After drying, it is fired for 10 minutes at a maximum temperature of 900° C. using a belt furnace to form the gas sensing material layer 4 and the upper electrode 5.

The characteristics of the sensor produced as described above are also shown in Table 1.

There are 22 composition points in Table 1, which correspond to the points shown in Figure 2 when shown in a triangular diagram. The O mark in FIG. 2 indicates the composition created. Further, the numbers in Table 1 and the numbers in FIG. 2 correspond. The number of samples for each composition is approximately 10.

The indicated values for resistivity and alcohol sensitivity in Table 1 are average values of about 10 samples. The characteristics shown in Table 1 are as follows:
These are the characteristics when heated to 00°C. The alcohol sensitivity was expressed as the rate of change in resistance when the element was placed in a gas containing 11,000 ppp of alcohol. The larger the rate of change in resistance, the higher the detection sensitivity. Also, is the characteristic reproducibility average for each composition? Alcohol sensitivity characteristics were measured 10 times for each sample, and the variations in sensitivity (resistance change rate) were expressed. The smaller the value of this variation, the higher the characteristic reproducibility. The sample alcohol for each test was ethanol. The composition of the glass is as follows.

ZnO: 5wt%, PbO: 5wt%, CaO
: 16wt%.

8i02: 45wt%lu, o3: 13wt%
, Ti1t: 16wt%.

(vrt% double weight%) No. in Table 1: 1, 2, 3, 7, 11, 12, 13, 1
7°21 and 22 have the drawbacks of low alcohol sensitivity and poor characteristic reproducibility. These are Nol.

2.22 has a NiO composition that is not within the scope of the present invention, and N01
゜7, 11, 12, 13, 17, 2] is Pd
The combination is out of range, No. 1 + 2 + 3,
2] and 22 have glass compositions outside the range, and both are materials that do not fall within the composition range of the present invention. On the other hand, as is clear from Table 1, the detection materials applicable to the present invention, that is, the detection materials with compositions other than those described above falling in the shaded area in Figure 2, have high sensitivity to alcohol and It is clear that the reproducibility of characteristics is also excellent.

Next, T example 2 will be explained.

In Table 1, the composition of No.9 (NiO: 88wt 1%, P
d: 2% by weight, glass = 10% by weight) (1)
Ho: 15% by weight, pbo: 20% by weight, 5iO1:
40% by weight.

B, O,: 15% by weight, AA! , O,: 10% by weight), +31 alkali silicate system (to 81: 62% by weight)
, AA! ,O,: Double view%.

CaO: 6% by weight, MgO: 1% by weight, Na
, O: 3 weight %, 20: 10 weight t%, 810:
8% by weight, BaO: 4%), the entire sensor was fabricated, and its characteristics were investigated.The fabrication method was the same as in Example 1. The measurement results are shown in Table 2. From Table 2, it can be seen that although the specific resistance value differs slightly depending on the type of glass,
It can be seen that there is no essential difference in terms of sensitivity and reproducibility.

Table 2 As mentioned above, the gas sensing element made using the composition of the present invention has high alcohol sensitivity (and excellent reproducibility of characteristics). Significantly more sensitive and reliable gas sensing elements can be achieved compared to the total.

[Brief explanation of the drawing]

FIG. 1 shows a configuration diagram of a gas detection element produced in one embodiment of the present invention. FIG. 2 shows a triangular diagram of the prepared gas sensor composition. 4...Gas detection material. Representative Patent Attorney Masami Akimoto

Claims (1)

[Claims] 1. (a) Nickel oxide (NiO) 70-9
7% by weight, [b) Noya Radium 0.5-5% by weight
, (c) 2.5 to 29.5% by weight of glass, the above (a
An alcohol gas sensing element characterized in that a composition comprising l~(cl?) is used as a sensing material. 2. The composition is made into a sensing material using a thick film method. Claim 1 The alcohol gas detection element described in Section C.