JPH0429207B2 - - Google Patents
Info
- Publication number
- JPH0429207B2 JPH0429207B2 JP62322992A JP32299287A JPH0429207B2 JP H0429207 B2 JPH0429207 B2 JP H0429207B2 JP 62322992 A JP62322992 A JP 62322992A JP 32299287 A JP32299287 A JP 32299287A JP H0429207 B2 JPH0429207 B2 JP H0429207B2
- Authority
- JP
- Japan
- Prior art keywords
- voltage
- firing
- sintered body
- current
- fired
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000010304 firing Methods 0.000 claims description 60
- 238000000034 method Methods 0.000 claims description 28
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 22
- 238000004519 manufacturing process Methods 0.000 claims description 11
- 239000000126 substance Substances 0.000 claims description 11
- 239000011787 zinc oxide Substances 0.000 claims description 11
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 10
- 239000001301 oxygen Substances 0.000 claims description 10
- 229910052760 oxygen Inorganic materials 0.000 claims description 10
- 239000000654 additive Substances 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 5
- 230000001590 oxidative effect Effects 0.000 claims description 4
- 230000000996 additive effect Effects 0.000 claims description 3
- 238000000465 moulding Methods 0.000 claims description 3
- 238000005245 sintering Methods 0.000 claims 1
- 229910015902 Bi 2 O 3 Inorganic materials 0.000 description 11
- 239000000843 powder Substances 0.000 description 10
- 230000003647 oxidation Effects 0.000 description 9
- 238000007254 oxidation reaction Methods 0.000 description 9
- 230000000694 effects Effects 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 239000008187 granular material Substances 0.000 description 6
- 229910010272 inorganic material Inorganic materials 0.000 description 5
- 239000011147 inorganic material Substances 0.000 description 5
- 230000008646 thermal stress Effects 0.000 description 5
- 239000011800 void material Substances 0.000 description 5
- 230000006378 damage Effects 0.000 description 4
- 239000007791 liquid phase Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 230000008602 contraction Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000013001 point bending Methods 0.000 description 2
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- -1 Sb 2 O 3 Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000006096 absorbing agent Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000011572 manganese Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Landscapes
- Thermistors And Varistors (AREA)
Description
（産業上の利用分野）
本発明は酸化亜鉛を主成分とする電圧非直線抵
抗体に関し、さらに詳しくは、避雷器などの過電
圧保護装置に使用される電圧非直線抵抗体の製造
方法に関するものである。
（従来の技術）
酸化亜鉛を主成分とする電圧非直線抵抗体は、
そのすぐれた非直線電圧−電流特性から電圧安定
化あるいはサージ吸収を目的とした避雷器やサー
ジアブソーバに広く利用されている。この電圧非
直線低抗体は、主成分の酸化亜鉛に電圧非直線性
を発現する少量のビスマス、アンチモン、コバル
ト、マンガン等の酸化物を添加し、混合、造粒、
成形したのち焼成し好ましくは側面高抵抗層を形
成するため無機物質を塗布した後焼成し、その焼
結体に電極を取り付けることにより構成されてい
る。
このようにして得られた電圧非直線抵抗体を大
きなサージ吸収を目的とする避雷器に適用する場
合には、電圧非直線邸抗体の放電耐量は大きいこ
とが望ましい。電圧非直線邸抗体の放電耐量は、
４／１０マイクロ秒の波形のインパルス電流を５分隔
隙で２回印加し、電圧非直線抵抗体が破壊または
沿面閃絡を起こすまで、電流値ステツプアツプし
ていつたときの破壊または沿面閃絡を起こさない
最大電流で表わすことができる。
電圧非直線抵抗体の放電耐量は焼結体中のボイ
ドに依存するものと考えられる。すなわち、4/10
マイクロ秒の波形のインパルス電流を印加したと
きの破壊は熱応力によるものと考えられるので、
ボイドをなくして焼結体の機械的強度を高めれ
ば、放電耐量の向上が期待される。また、ボイド
が存在すると電流方向に直交するボイド先端に電
流が集中し、4/10マイクロ秒のような短時間で
は、まわりへの熱伝導が小さいため局部的な温度
上昇を招く。この温度上昇により熱応力が発生
し、熱応力が焼結体の機械的強度を上回つた場合
は破壊に至る。このため、焼結体の機械的強度を
高めるとともに、電流集中を生じにくくする目的
で、ボイドを除去することが望ましい。焼結体中
からのボイドの除去については、焼成工程の昇温
工程中800℃〜1150℃までを大気圧以下の減圧状
態でで行う方法が、特開昭58−28802号公報にお
いて開示されている。
（発明が解決しようとする問題点）
しかしながら、特開昭58−28802号公報記載の
製造方法においては、ボイド減少の効果は２ミリ
秒の矩形波電流により評価される放電耐量（以
下、２ｍｓ矩形波電流放電耐量と表わす）の向上
が示されているのみで、4/10マイクロ秒の波形の
インパルス電流により評価される放電耐量（以
下、4/10μsインパルス電流放電耐量と表わす）対
しては不明であつた。２ｍｓ矩形波電流放電耐量
と4/10μsインパルス電流放電耐量は、それぞれの
破壊の形態が前者で貫通破壊、後者で裂損破壊と
異なるように、本来、性質の異なるものである。
従つて、ボイドの影響は２ｍｓ矩形波電流放電耐
量と4/10μsインパルス電流放電耐量で異なるもの
と考えられる。ここで、貫通破壊とは、電圧非直
線抵抗体に直径１ミリメートル程度の貫通孔が生
じ、電圧非直線抵抗体の抵抗が1KΩ以下となつ
て非直線電圧−電流特性が失われる破壊をいう。
また、裂損破壊とは、電圧非直線低抗体にクラツ
クが入つたり、電圧非直線抵抗体がばらばらに砕
けて飛散する破壊という。前記したように、裂損
破壊の原因はインパルス電流印加時の熱応力と考
えられている。
また、特開昭58−28802号公報記載の製造方法
においては、1150℃までは減圧下すなわち酸素分
圧の低い状態で焼成しているため、焼成工程の昇
温工程中1150℃を越えてはじめて焼結体の酸化が
開始される。そのため、焼結体寸法がたとえば直
径25mm、厚さ20mmのように直径、厚さともにある
程度以上大きい場合には、数時間の焼成保持では
ボイドは減少するものの、焼結体の酸化が内部ま
で十分行われず、通常の大気中焼結品と同等の非
直線電圧−電流特性が得られない欠点があつた。
また、焼結体の内部まで酸化を進めるために焼成
の保持時間を長くした場合には、Bi2O3成分が蒸
発するため不均一な焼結体しか得られないという
欠点があつた。
さらに、通常の避雷器等の過電圧保護装置にお
いては、沿面閃絡を防止するために電圧非直線抵
抗体の側面に高抵抗層を設ける必要がある。高抵
抗層は、通常、被焼成物の側面に無機物質を塗布
し、この無機物質と被焼成物側面を焼成により反
応させて形成されている。このため側面高抵抗層
の密着性も良い。従つて、側面に塗布した無機物
質は、焼成時に被焼成物が収縮しても剥離しない
ことが重要である。しかし、前記した特開昭58−
28802号公報記載の製造方法では850℃付近の温度
で被焼成物が急激に収縮するため、塗布した無機
物質と被焼成物の収縮に大きな差を生じ、無機物
質が剥離してしまう。このため、電圧非直線抵抗
体の側面に密着性良くかつ一様に高抵抗層を形成
できないという欠点があつた。
本発明の目的は上述した不具合を解消して、高
密度かつ十分な非直線電圧−電流特性をもつた焼
結体を得ることができ、しかも側面高抵抗層の形
成も容易な電圧非直線抵抗体の製造方法を提供し
ようとするものである。
（問題点を解決するための手段）
本発明の電圧非直線抵抗体の製造方法は、主成
分の酸化亜鉛に焼成後に焼結体自身に電圧非直線
性を発現させる添加物の少なくとも１種以上を添
加し、混合、造粒、成形したのち、大気圧より低
い減圧状態でかつ温度850〜1000℃で一次焼成工
程を実施し、次いで被焼成体の少なくとも側面に
焼成後に高抵抗層を形成する無機物質を塗布し、
さらに少なくとも前記一次焼成工程よりも高い酸
素分圧を有する酸化性雰囲気ものとでかつ温度
1050〜1300℃で二次焼成工程を実施することを特
徴とするものである。
（作用）
上述した構成において、減圧下で行う一次焼成
（仮焼）工程と、焼結体の酸化を行う二次焼成
（本焼）工程とが分離されているため、ボイドが
二次焼成工程において除去されるのに十分な下地
を、減圧下の一次焼成工程で作製するとともに、
二次焼成工程においてボイドが除去され、かつ焼
結体の酸化が十分進行するため、高密度であると
同時に十分な非直線電圧−電流特性を有する焼結
体が得られ、放電耐量も向上する。
また、本発明の電圧非直線低抗体の製造方法
は、一次焼成工程で被焼成物の収縮をほぼ完了さ
せたのち、高抵抗層形成のための無機物質を塗布
して二次焼成工程を実施しているので、二次焼成
工程での収縮がほとんどなく、側面塗布物質の剥
離がなくなるため、密着性の良好な側面高抵抗層
を得ることができる。
なお、本発明の製造方法の一次焼成工程は減圧
下で行うため、添加物の１種として例えばBi2O3
のように蒸気圧の高い化合物を用いた場合は、大
気中と比べてBi2O3が蒸発しやすいため、被焼成
物からのBi2O3蒸発を抑制するために、主成分と
しての酸化亜鉛と少なくともBi2O3とを含む粉粒
体に埋め込んで焼成することが好ましい。また、
この粉粒体は被焼成物と同一化学成分を含有して
いるとさらに好ましい。減圧下におけるこのよう
な埋め込み焼成の効果は、以下のように説明でき
る。粉粒体の外側付近では粉粒体中のBi2O3のよ
うな高蒸気圧成分の蒸発がさかんに進むが、被焼
成物の表面付近ではBi2O3蒸気が飽和状態に近く
なるため、被焼成物からのBi2O3蒸発は抑制され
る。一方、被焼成物の収縮により抜け出た空気
は、付近のBi2O3蒸気圧は高いものの、空気を構
成する窒素と酸素の分圧は、減圧により低くなつ
ているので、系外に排出される。通常知られてい
る大気圧下での埋め込み焼成では空気の抜け出し
も抑制されるので、このような効果は得られな
い。このような効果を得るためには、被焼成物を
取り囲む粉粒体の層の厚さは少なくとも10mm以上
必要であり、20mm以上であるとより好ましい。
ここで、一次焼成工程において被焼成物を粉粒
体で埋め込む方法は、被焼成物と粉粒体とが強固
に付着することなく、また被焼成物に化学組成の
不均一を生じない方法であれば、被焼成物を粉粒
体に埋没させる方法に限定されるものではない。
なお、このような一次焼成工程の埋め込み焼成
による効果は、本発明の製造方法のように一次焼
成工程と二次焼成工程とを分離している場合に得
られるものであり、二次焼成工程まで埋め込み焼
成とすると、被焼成物と埋め込みのための粉粒体
とが強固に付着し、滑らかな側面をもつた焼結体
が得られないので好ましくない。
一次焼成の温度は、被焼成物からボイドを十分
除去するため、また高抵抗層形成のために塗布し
た無機物質が剥離しないように被焼成物の収縮を
二次焼成で小さく、一次焼成で大きくするため、
さらに被焼成物と埋め込みのための粉粒体とが強
固に付着することのないようにするため、850〜
1000℃が、また二次焼成の温度は焼結体の内部ま
で十分酸化し、良好な非直線電圧−電流特性が得
られるようにするため1050〜1300℃がそれぞれ好
ましい。二次焼成工程の気圧は、主成分および添
加物の酸化を十分進行させる程度に酸素分圧を高
くする必要があり、少なくとも一次焼成工程より
も高い酸素分圧を有する酸化性雰囲気が好まし
い。雰囲気制御が容易な点で、大気圧下がさらに
好ましく、酸化性を高めるために空気や酸素を二
次焼成中に加圧することも好ましい。
（実施例）
以下、実際の例について説明する。
所定調合割合の酸化亜鉛と焼成後に焼結体自身
に電圧非直線性を発現させる添加物とを混合、造
粒、成形したのち、成形体を成形体と同一の化学
成分を有する粉粒体に10mm没するように埋め込
み、1Torrの減圧状態下において所定条件の一次
焼成を実施した。次いで、この一次焼結体の外周
側面に、電圧非直線抵抗体の側面抵抗層を形成す
るための無機物質、例えばBi2O3，Sb2O3，SiO2
から成る混合物をペースト状にして塗布し乾燥し
たのち、大気中で所定条件下の二次焼成を実施し
た。
得られた焼結体の一部について、浮力法により
嵩密度を、JIS R1601により４点曲げ強度をそれ
ぞれ測定した。また、焼結体の断面を研磨して、
光学顕微鏡によりボイドの分布状態を観察、評価
した。
別の焼結体について、その両端面を研磨しアル
ミニウムを溶射して電極を形成し、直径28mm、電
極径25mm、厚さ18mmの電圧非直線低抗体を得た。
この電圧非直線抵抗体について、電流１ｍＡにお
ける単位厚さあたりの電圧、VlmA／mm、電流
0.1ｍＡと１ｍＡの間における電圧非曲線指数α
（αは１＝（Ｖ／Ｃ）2で定義される。但し、Ｉは電
流、Ｖは電圧、Ｃは定数である。）および放電耐
量を測定した。放電耐量の測定は、4/10μsの波形
のインパルス電流を５分間隔で２回印加し、電圧
非直線抵抗体が破壊するまで電流値をステツプア
ツプする方法で行つた。電流値は20KAから開始
し、5KAステツプで増加させた。放電耐量は、
試料数ｎ＝30として、各試料が破壊する直前の電
流値の平均で表した。
酸化亜鉛と添加物の調合割合、一次焼成条件お
よび二次焼成条件、および各種特性の測定結果を
第１表に示す。
なお一次焼成を大気中で実施した例、二次焼成
を減圧下で実施した例、および一次焼成に先立つ
て成形体側面に高抵抗層形成のための無機物質を
塗布した例を、他の条件は実施例と同一として焼
結体および電圧非直線抵抗体を得、特性を測定し
た結果をそれぞれ比較例１１，１２，１３として
第１表に合わせて示した。第１表中、ボイド評価
は、直径10μｍ以上のボイドが存在しないものを
○、10μｍ以上のボイドが認められたものを×と
して示した。
(Industrial Application Field) The present invention relates to a voltage nonlinear resistor containing zinc oxide as a main component, and more specifically to a method for manufacturing a voltage nonlinear resistor used in overvoltage protection devices such as lightning arresters. . (Prior art) A voltage nonlinear resistor whose main component is zinc oxide is
Due to its excellent nonlinear voltage-current characteristics, it is widely used in lightning arresters and surge absorbers for voltage stabilization or surge absorption. This voltage nonlinear low antibody is made by adding small amounts of oxides such as bismuth, antimony, cobalt, and manganese that exhibit voltage nonlinearity to the main component zinc oxide, mixing, granulating, and
It is formed by molding and firing, preferably applying an inorganic substance to form a side surface high resistance layer and then firing, and attaching electrodes to the sintered body. When applying the voltage nonlinear resistor thus obtained to a lightning arrester intended for large surge absorption, it is desirable that the voltage nonlinear resistor has a large discharge withstand capacity. The discharge capacity of the voltage nonlinear antibody is
An impulse current with a waveform of 4/10 microseconds was applied twice at 5-minute intervals, and the current value was stepped up until the voltage nonlinear resistor caused destruction or creeping flash. can be expressed in terms of maximum current. It is thought that the discharge capacity of a voltage nonlinear resistor depends on the voids in the sintered body. i.e. 4/10
It is thought that the damage caused by the application of microsecond waveform impulse current is due to thermal stress.
If voids are eliminated and the mechanical strength of the sintered body is increased, it is expected that the discharge withstand capacity will be improved. Additionally, if a void exists, the current will concentrate at the tip of the void orthogonal to the current direction, and in a short period of time like 4/10 microseconds, heat conduction to the surroundings will be small, causing a local temperature rise. This temperature rise generates thermal stress, and if the thermal stress exceeds the mechanical strength of the sintered body, it will break. Therefore, it is desirable to remove voids in order to increase the mechanical strength of the sintered body and to make current concentration less likely to occur. Regarding the removal of voids from the sintered body, a method is disclosed in JP-A-58-28802 in which the temperature is raised from 800°C to 1150°C during the firing process under reduced pressure below atmospheric pressure. There is. (Problems to be Solved by the Invention) However, in the manufacturing method described in JP-A-58-28802, the effect of reducing voids is limited to the discharge withstand capacity (hereinafter referred to as 2ms rectangular wave current) evaluated by a 2ms rectangular wave current. It has only been shown that the discharge withstand capacity (hereinafter referred to as wave current discharge withstand capacity) has been improved, but the improvement in discharge withstand capacity evaluated by impulse current with a 4/10 microsecond waveform (hereinafter referred to as 4/10 μs impulse current discharge withstand capacity) is unknown. It was hot. The 2 ms rectangular wave current discharge withstand capacity and the 4/10 μs impulse current discharge capacity are inherently different in nature, with the former having different forms of destruction, the former being through-through failure, and the latter being tearing failure.
Therefore, it is considered that the effect of voids is different between the 2 ms rectangular wave current discharge capability and the 4/10 μs impulse current discharge capability. Here, the term "penetrating breakdown" refers to breakdown in which a through hole with a diameter of about 1 millimeter is formed in the voltage nonlinear resistor, the resistance of the voltage nonlinear resistor becomes 1KΩ or less, and the nonlinear voltage-current characteristics are lost.
Furthermore, tearing failure refers to failure in which a crack occurs in a voltage non-linear resistor, or a voltage non-linear resistor is broken into pieces and scattered. As mentioned above, the cause of tearing failure is thought to be thermal stress during application of impulse current. In addition, in the manufacturing method described in JP-A-58-28802, firing is performed under reduced pressure, that is, under a low oxygen partial pressure, up to 1150°C, so it is not until the temperature exceeds 1150°C during the temperature raising step of the firing process. Oxidation of the sintered body begins. Therefore, if the diameter and thickness of the sintered body are larger than a certain amount, such as 25 mm in diameter and 20 mm in thickness, the voids will be reduced by holding the sintered body for several hours, but the oxidation of the sintered body will not reach the inside. This was not carried out, and there was a drawback that non-linear voltage-current characteristics equivalent to those of ordinary air-sintered products could not be obtained.
Furthermore, when the holding time of firing is increased in order to advance the oxidation to the inside of the sintered body, the Bi 2 O 3 component evaporates, resulting in a disadvantage that only a non-uniform sintered body can be obtained. Furthermore, in an ordinary overvoltage protection device such as a lightning arrester, it is necessary to provide a high resistance layer on the side surface of the voltage nonlinear resistor in order to prevent creeping flash. The high-resistance layer is usually formed by applying an inorganic substance to the side surface of the object to be fired, and causing the inorganic material and the side surface of the object to react with each other by firing. Therefore, the adhesion of the side high resistance layer is also good. Therefore, it is important that the inorganic substance applied to the side surface does not peel off even if the object to be fired shrinks during firing. However, the above-mentioned JP-A-58-
In the manufacturing method described in Publication No. 28802, the object to be fired rapidly shrinks at a temperature of around 850°C, resulting in a large difference in shrinkage between the coated inorganic material and the object to be fired, resulting in peeling of the inorganic material. For this reason, there was a drawback that a high resistance layer could not be uniformly formed with good adhesion on the side surface of the voltage nonlinear resistor. The purpose of the present invention is to solve the above-mentioned problems, to obtain a sintered body with high density and sufficient nonlinear voltage-current characteristics, and to provide a voltage nonlinear resistance that can easily form a side high resistance layer. The aim is to provide a method for manufacturing the body. (Means for Solving the Problems) The method for manufacturing a voltage nonlinear resistor of the present invention includes adding at least one kind of additive to zinc oxide, which is the main component, and which causes the sintered body itself to exhibit voltage nonlinearity after firing. After adding, mixing, granulating, and shaping, a primary firing step is performed at a reduced pressure lower than atmospheric pressure and at a temperature of 850 to 1000°C, and then a high-resistance layer is formed on at least the side surface of the object to be fired after firing. Apply an inorganic substance,
Further, at least an oxidizing atmosphere having a higher oxygen partial pressure than that in the primary firing step and at a temperature
It is characterized by performing a secondary firing step at 1050 to 1300°C. (Function) In the above-mentioned configuration, the primary firing (calcination) process performed under reduced pressure and the secondary firing (main firing) process in which the sintered body is oxidized are separated, so that voids are removed from the secondary firing process. In addition to creating a base sufficient to be removed in the primary firing step under reduced pressure,
In the secondary firing process, voids are removed and oxidation of the sintered body progresses sufficiently, so a sintered body with high density and sufficient nonlinear voltage-current characteristics is obtained, and discharge durability is also improved. . In addition, in the method for producing a voltage nonlinear low antibody of the present invention, after the shrinkage of the object to be fired is almost completed in the primary firing step, an inorganic substance for forming a high resistance layer is applied and a secondary firing step is performed. As a result, there is almost no shrinkage in the secondary firing process, and there is no peeling of the side-applied material, making it possible to obtain a side-face high-resistance layer with good adhesion. Note that since the primary firing step of the production method of the present invention is performed under reduced pressure, Bi 2 O 3 is used as one of the additives.
When using a compound with a high vapor pressure such as, Bi 2 O 3 evaporates more easily than in the air, so in order to suppress the evaporation of Bi 2 O 3 from the object to be fired, oxidation as the main component is used. It is preferable to embed it in a powder containing zinc and at least Bi 2 O 3 and then fire it. Also,
It is more preferable that this powder or granular material contains the same chemical components as the material to be fired. The effect of such embedding firing under reduced pressure can be explained as follows. Near the outside of the powder and granules, high vapor pressure components such as Bi 2 O 3 in the powder and granules rapidly evaporate, but near the surface of the object to be fired, Bi 2 O 3 vapor approaches a saturated state. , Bi 2 O 3 evaporation from the object to be fired is suppressed. On the other hand, although the Bi 2 O 3 vapor pressure in the vicinity of the air that escapes due to the contraction of the firing object is high, the partial pressures of nitrogen and oxygen that make up the air have been lowered due to pressure reduction, so the air is not discharged from the system. Ru. Such an effect cannot be obtained in the commonly known embedding firing under atmospheric pressure because the escape of air is also suppressed. In order to obtain such an effect, the thickness of the powder layer surrounding the object to be fired needs to be at least 10 mm or more, and more preferably 20 mm or more. Here, the method of embedding the object to be fired with powder or granules in the primary firing process is a method that does not cause the object to be fired and the granules to adhere firmly and does not cause non-uniformity in the chemical composition of the object to be fired. If there is, the method is not limited to burying the object to be fired in powder or granules. Note that this effect of embedded firing in the primary firing process is obtained when the primary firing process and the secondary firing process are separated as in the manufacturing method of the present invention. Embedding firing is not preferred because the object to be fired and the powder for embedding will firmly adhere to each other, making it impossible to obtain a sintered body with smooth sides. The temperature of the primary firing is set to minimize the shrinkage of the fired object in the secondary firing and increase it in the primary firing in order to sufficiently remove voids from the fired object and to prevent the inorganic material applied to form a high-resistance layer from peeling off. In order to
Furthermore, in order to prevent the object to be fired and the powder for embedding from firmly adhering,
The temperature for the secondary firing is preferably 1050 to 1300°C in order to sufficiently oxidize the inside of the sintered body and obtain good nonlinear voltage-current characteristics. The atmospheric pressure in the secondary firing step must be such that the oxygen partial pressure is high enough to sufficiently progress the oxidation of the main components and additives, and an oxidizing atmosphere having at least a higher oxygen partial pressure than that in the primary firing step is preferable. Atmospheric pressure is more preferable because the atmosphere can be easily controlled, and it is also preferable to pressurize air or oxygen during the secondary firing in order to increase the oxidizing property. (Example) An actual example will be described below. After mixing, granulating, and molding zinc oxide in a predetermined proportion and an additive that causes the sintered body to exhibit voltage nonlinearity after firing, the molded body is transformed into a powder having the same chemical composition as the molded body. It was buried to a depth of 10 mm and primary firing was performed under a reduced pressure of 1 Torr under specified conditions. Next, an inorganic substance such as Bi 2 O 3 , Sb 2 O 3 , SiO 2 for forming a side resistance layer of a voltage nonlinear resistor is applied to the outer peripheral side surface of this primary sintered body.
After applying the mixture in the form of a paste and drying it, secondary firing was performed in the atmosphere under predetermined conditions. A portion of the obtained sintered body was measured for bulk density by the buoyancy method and four-point bending strength according to JIS R1601. Also, by polishing the cross section of the sintered body,
The distribution of voids was observed and evaluated using an optical microscope. For another sintered body, both end faces were polished and aluminum was sprayed to form electrodes to obtain a voltage nonlinear low antibody with a diameter of 28 mm, an electrode diameter of 25 mm, and a thickness of 18 mm.
For this voltage nonlinear resistor, the voltage per unit thickness at a current of 1 mA, VlmA/mm, and the current
Voltage non-curve index α between 0.1mA and 1mA
(α is defined as 1=(V/C) 2 , where I is current, V is voltage, and C is a constant.) and discharge withstand capacity were measured. The discharge withstand capacity was measured by applying an impulse current with a waveform of 4/10 μs twice at an interval of 5 minutes, and stepping up the current value until the voltage nonlinear resistor was destroyed. The current value started at 20 KA and was increased in 5 KA steps. The discharge capacity is
The number of samples was set to n=30, and the value was expressed as the average of the current values immediately before each sample was destroyed. Table 1 shows the blending ratio of zinc oxide and additives, primary firing conditions and secondary firing conditions, and measurement results of various properties. In addition, examples in which the primary firing was carried out in the air, examples in which the secondary firing was carried out under reduced pressure, and examples in which an inorganic substance was applied to the side surface of the molded product to form a high resistance layer prior to the primary firing were performed under other conditions. A sintered body and a voltage nonlinear resistor were obtained as in the example, and the results of measuring the characteristics are shown in Table 1 as Comparative Examples 11, 12, and 13, respectively. In Table 1, the void evaluation is shown as ○ if no voids with a diameter of 10 μm or more were present, and × if voids with a diameter of 10 μm or more were observed.
【表】
第１表からわかるように、本発明の方法により
得られた焼結体は10μｍ以上のボイドが存在せ
ず、嵩密度および４点曲げ強度が高い。また、本
発明の方法により得られた電圧非直線抵抗体は、
電圧非直線指数αが大きく、また放電耐量が高
い。一次焼成を減圧状態下で行う本発明の方法
が、一次焼成を大気中で行う比較例11の方法によ
り嵩密度、放電耐量が向上した理由は次のようで
ある。すなわち、電圧非直線低抗体を形成するた
めの成形体は含有成分の一つであるBi2O3が850
℃付近で融解して液相を形成するため、この温度
付近で急激に収縮する。この急激な収縮は液相の
毛管圧力によるものであり、減圧下では液相が粒
子間に浸透しやすくなり、また液相に閉じ込めら
れた気泡が外部に抜け出しやすくなることから収
縮が大きくなる、すなわちボイドが減少し嵩密度
が高くなる。その結果、ボイドの存剤によるボイ
ド先端への電流集中がなくなり、またボイドの減
少により焼結体の機械的強度が増大することか
ら、熱応力による破壊が抑制され、放電耐量が向
上するものと思われる。
比較例12では、嵩密度は比較例11に対し向上す
るものの、二次焼成工程での酸化が十分でないた
め、VlmA／mmおよびαが実施例に比較して劣つ
ている。
比較例13でも嵩密度の向上は認められるが、こ
の例では側面に塗布した無機物が一次焼成におけ
る急激な収縮により剥離してしまう。このため4/
１０マイクロ秒の波形のインパルス電流を印加した
とき沿面閃絡を生じ、放電耐量が低下する。非直
線電圧−電流特性は酸化亜鉛粒子と粒界層との界
面に起因すると考えられているが、焼結体を還元
熱処理すると非直線電圧−電流特性が失われ、こ
れを再び酸化熱処理すると非直線電圧−電流特性
が回復することから（ジヤーナルオブアプライド
フイジクス誌、1983年54巻６号、3466〜3472ペー
ジ）、非直線電圧−電流特性の出現には、酸化亜
鉛粒子と粒界層との界面への酸素の供給が必要と
考えられる。比較例12でVlnA／mm、αが小さいの
は酸化亜鉛粒子と粒界層との界面に十分な酸素が
供給されなかつたためであり、非直線電圧−電流
特性（VlmA／mm，α）のすぐれた電圧非直線抵
抗体を得るためには、焼成時に酸素を十分供給す
る必要があることは、これまでの記述から明らか
である。
なお、上述した本発明の実施例において、いず
れの酸化亜鉛と添加剤の組成についても嵩密度お
よび放電耐量が向上しており、本発明は添加剤の
種類に限定されるものではないことはもちろんで
ある。
（発明の効果）
以上詳細に説明したところから明らかなよう
に、本発明の電圧非直線低抗体の製造方法によれ
ば、減圧下で行う一次焼成工程と焼結体の酸化を
行う二次焼成工程とが分離されているため、焼結
体の酸化が十分進行し、その結果、高密度である
と同時にすぐれた非直線電圧−電流特性をもつた
焼結体が得られ、放電耐量も向上する。
さらに、一次焼成工程後に側面高抵抗層を塗布
形成して二次焼成工程を実施しているので、密着
性が良くはく離のない側面高抵抗層をもつた電圧
非直線低抗体を得ることができる。[Table] As can be seen from Table 1, the sintered body obtained by the method of the present invention has no voids of 10 μm or more, and has high bulk density and four-point bending strength. Furthermore, the voltage nonlinear resistor obtained by the method of the present invention is
The voltage non-linearity index α is large and the discharge withstand capacity is high. The reason why the method of the present invention in which the primary firing is performed under a reduced pressure condition improves the bulk density and discharge durability compared to the method of Comparative Example 11 in which the primary firing is performed in the atmosphere is as follows. In other words, the molded body for forming the voltage nonlinear low antibody contains one of the components, Bi 2 O 3 , at 850
Since it melts and forms a liquid phase around ℃, it contracts rapidly around this temperature. This rapid contraction is due to the capillary pressure of the liquid phase, and under reduced pressure, the liquid phase more easily penetrates between particles, and air bubbles trapped in the liquid phase can more easily escape to the outside, resulting in greater contraction. In other words, voids are reduced and bulk density is increased. As a result, the current concentration at the tip of the void due to the residual material in the void is eliminated, and the mechanical strength of the sintered body is increased due to the reduction of voids, so destruction due to thermal stress is suppressed and the discharge withstand capacity is improved. Seem. In Comparative Example 12, although the bulk density is improved compared to Comparative Example 11, VlmA/mm and α are inferior to those in Examples because oxidation in the secondary firing step is not sufficient. An improvement in bulk density was also observed in Comparative Example 13, but in this example, the inorganic material coated on the side surface peeled off due to rapid shrinkage during primary firing. For this reason 4/
When an impulse current with a waveform of 10 microseconds is applied, creeping flash occurs and the discharge withstand capacity decreases. The non-linear voltage-current characteristics are thought to be caused by the interface between the zinc oxide particles and the grain boundary layer, but when the sintered body is subjected to reduction heat treatment, the non-linear voltage-current characteristics are lost, and when the sintered body is subjected to oxidation heat treatment again, the non-linear voltage-current characteristics become non-linear. Since the linear voltage-current characteristics are restored (Journal of Applied Physics, Vol. 54, No. 6, 1983, pages 3466-3472), the emergence of non-linear voltage-current characteristics is due to the presence of zinc oxide particles and grain boundary layers. It is thought that it is necessary to supply oxygen to the interface with. The reason why VlnA /mm, α is small in Comparative Example 12 is that sufficient oxygen was not supplied to the interface between the zinc oxide particles and the grain boundary layer, and the nonlinear voltage-current characteristics (VlmA/mm, α) were small. It is clear from the above description that in order to obtain an excellent voltage nonlinear resistor, it is necessary to supply a sufficient amount of oxygen during firing. In addition, in the above-mentioned examples of the present invention, the bulk density and discharge capacity were improved for all compositions of zinc oxide and additives, and the present invention is of course not limited to the types of additives. It is. (Effects of the Invention) As is clear from the detailed explanation above, according to the method for producing a voltage nonlinear low antibody of the present invention, the primary firing step is performed under reduced pressure, and the secondary firing step is performed in which the sintered body is oxidized. Because the process is separated, oxidation of the sintered body progresses sufficiently, resulting in a sintered body with high density and excellent nonlinear voltage-current characteristics, and improved discharge durability. do. Furthermore, since the secondary firing process is performed after applying and forming the side high resistance layer after the primary firing process, it is possible to obtain a low voltage nonlinear antibody with a side high resistance layer that has good adhesion and does not peel off. .
Claims (1)
電圧非直線性を発現させる添加物の少なくとも１
種以上を添加し、混合、造粒、成形したのち、大
気圧より低い減圧状態でかつ温度850〜1000℃で
一次焼成工程を実施し、次いで被焼成体の少なく
とも側面に焼成後に高低抗層を形成する無機物質
を塗布し、さらに少なくとも前記一次焼成工程よ
りも高い酸素分圧を有する酸化性雰囲気ものとで
かつ温度1050〜1300℃で二次焼成工程を実施する
ことを特徴とする電圧非直線抵抗体の製造方法。1 At least one additive that causes the sintered body to develop voltage nonlinearity after sintering is added to the main component, zinc oxide.
After adding seeds or more, mixing, granulating, and molding, a primary firing step is carried out at a reduced pressure lower than atmospheric pressure and at a temperature of 850 to 1000°C, and then a high-low anti-layer is formed on at least the side surface of the object to be fired after firing. Voltage non-linearity characterized by applying an inorganic substance to be formed and further performing a secondary firing process at a temperature of 1050 to 1300°C in an oxidizing atmosphere having a higher oxygen partial pressure than at least the primary firing process. Method of manufacturing a resistor.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62322992A JPH01165102A (en) | 1987-12-22 | 1987-12-22 | Manufacture of voltage nonlinear resistor |
| US07/285,528 US4940960A (en) | 1987-12-22 | 1988-12-16 | Highly densified voltage non-linear resistor and method of manufacturing the same |
| EP88312114A EP0322211B1 (en) | 1987-12-22 | 1988-12-21 | Highly densified voltage non-linear resistor and method of manufacturing the same |
| DE3888328T DE3888328T2 (en) | 1987-12-22 | 1988-12-21 | Highly compressed nonlinear voltage dependent resistor and manufacturing process. |
| CA000586564A CA1315093C (en) | 1987-12-22 | 1988-12-21 | Highly densified voltage non-linear resistor and method of manufacturing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62322992A JPH01165102A (en) | 1987-12-22 | 1987-12-22 | Manufacture of voltage nonlinear resistor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH01165102A JPH01165102A (en) | 1989-06-29 |
| JPH0429207B2 true JPH0429207B2 (en) | 1992-05-18 |
Family
ID=18149936
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP62322992A Granted JPH01165102A (en) | 1987-12-22 | 1987-12-22 | Manufacture of voltage nonlinear resistor |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH01165102A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0667626A3 (en) * | 1994-02-10 | 1996-04-17 | Hitachi Ltd | Voltage non-linear resistor and fabricating method thereof. |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5021297A (en) * | 1973-06-28 | 1975-03-06 | ||
| JPS5828802A (en) * | 1981-08-13 | 1983-02-19 | 株式会社東芝 | Method of producing voltage non-linear resistor |
-
1987
- 1987-12-22 JP JP62322992A patent/JPH01165102A/en active Granted
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5021297A (en) * | 1973-06-28 | 1975-03-06 | ||
| JPS5828802A (en) * | 1981-08-13 | 1983-02-19 | 株式会社東芝 | Method of producing voltage non-linear resistor |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH01165102A (en) | 1989-06-29 |
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