SE427552B - Process for the preparation of a metal oxide varistor containing 70-99 mol-% of zinc oxide and other oxides, including barium oxide, diboron trioxide and silicon dioxide - Google Patents

Abstract

Process for the preparation of a metal oxide varistor, in which barium oxide, diboron trioxide and silicon dioxide are added to zinc oxide and to the other oxides, in the form of a reaction product with the composition 3BaO . 3B2O3 . 2SiO2, forming a congruent-melting phase. The process improves the reproducibility of the properties of varistors and reduces the environmental problem.

Description

The present invention relates to a process for preparing a metal oxide variator containing 70-99 mol%, and preferably 85 = 97 mol%, zinc oxide and other oxides comprising barium oxide, dibortrionzide and Idsele dioxide, derived therefrom. , that the barium ozide, g of the diboron trioxide and the silica are added to the zinc oxide and other oxides in the form of a reaction product with the composition SBaO ~ 53205 ~ Ä2SiO2 or with a composition in which the amount of each of the three components not more than 10% by weight of the amount of formula 538.0 513205 ° 2SiO2. the length of said reaction produlite preferably amounts to 0.02-2 percent of the total. the weight of the reaction product and other oxides, including zinc oxide.

The explanation for the favorable results obtained according to the present invention should be. that barium oxide, diborotrioxide and silica form a congruent melting phase 5Ba0 - 318203 ~ 28102. In this, the boron trioxide has a considerably lower tendency to evaporate when heated to sintering temperatures than the boron triocide was used in another. a lower solubility in water, which results in a reduced release of diboron trioxide and barium oxide in the normally occurring wet grinding of the oxides, during the manufacture of the oxide mixture. The addition of the barium oxide, the diborotriide and the silica in the form of a reaction product instead of as individual oxides to the other oxides ensures that the three oxides mentioned. are locally evenly distributed in the varistor.

. In addition to zinc chloride and the onids included in the reaction product, the varistor contains one or more of the initially mentioned oniders. The invention will be explained in more detail by describing the following exemplary embodiments for the manufacture of a variator. 68 parts by weight of BaO having a grain size of not more than 10 microns 27 parts by weight 3205 having a grain size of not more than 10 microns and 15 parts by weight of SiO 2 having a grain size of not more than 10 microns are mixed in a porcelain mortar and transferred seen with lid. The nickel crucible with contents is then heated for 1 hour at 1115 ° C.

Since the melting phase of the congruent melting phase is 100900, the heating is carried out at a temperature exceeding 100900. The reaction product BBaO ° 53203 ~ = 2SiO2 is obtained. This product is crushed and sieved and the fraction below 0.5 mm is ground in a grinding mill with agate particles and water for 1 hour. The

Claims (2)

10 55 7531156 88-3 3 malde. the product is filtered in a mimopor filter with a pore torque: of approx. 5 .mu.m and dried and crushed in a porcelain mortar to a powder. 0.2 parts by weight of the product thus obtained are mixed with a total of 9.8 parts by weight of additional oxides in the proportions 0.5: e-mail percent 31203, 0.5 mole percent 00203, 0.5 mole percent MnO 2, 1.0 mole percent 811205 and 0, 5 mole percent Cr 2 O 5. Mix wet male in a ball mill with water and zirconia for 12 hours. The resulting mass is poured onto plates, dried and leached and sieved through a 50 mesh sieve. Then the powder is calcined at 800 ° C for 2 hours. The resulting product is then wet-milled in Pazlkvramn with water and zirconium dixoid beads for 12 hours. The sludge from the mill with additional oxides is mixed with 90 parts by weight of ZnO with a concentration of less than 10 .mu.m. The stated maximum mixture ZnO corresponds to a molar-processed ZnO of 96.5 of a total of oxides included in the mixture. The mixture diepergerae in water with a stirrer. The diepersion is spray dried, whereby a dried powder is obtained. This powder is formed into cylindrical. tablets and intranet at 1100-150000 for 5 hours. The product thus obtained, which has a lower height than the diameter, is provided on the surfaces perpendicular to the cylinder axis with electrodes in the form of aluminum layers by arc spraying. PATENÉEICTMV A process for preparing a metalloszide veristor containing 70- »99 nzol%, and preferably 85-97 moles of procite, zinc oxide. and other oxides, including barium oxide, diboron trioxide and silica, characterized in that the barium oxide, diboron trioxide and silica dioxide are added to the zinc oxide and other oxides in the form of a reaction product having the composition SBaO - 313203 in any composition, each of the three components barium oxide, diboron trioxide and silica differs by no more than 10% by weight from the amount according to the formula 5Ba0 - 513203 '- 28102. 2. A method according to claim 1, characterized in that the amount of the reaction product constitutes 0.02-2 percent of the total weight of the reaction product and all other oxides. * i xf; a: G32 Summary Method of preparing a metal oxide varistor, in which barium oxide, diboron trioxide and silica are added to the zinc oxide and others. oxides in the form of a reaction product with the composition} Ba.0 - 513205 - 285.02, which forms a congruent phase. The method improves the reproducibility in the properties of varistorerrxa. and reduces environmental problems.