DD288505A7 - PROCESS FOR PREPARING HIGH-PURITY CALCIUM TITANICILATE CATISIO DEEP 5 (CTS) - Google Patents

Abstract

The invention relates to a process for the preparation of the ceramic compound calcium titanosilicate (CaTiSiO5, titanite, sphene) in a synthetic manner in a highly pure crystalline form. The compound represents an important component for the production of electrical functional ceramics, in particular capacitors. The object and the object of the invention is to synthetically produce CTS by a process which proceeds at the lowest possible temperatures and leads reproducibly to a high-purity, crystalline product. This object is achieved according to the invention in that a thermally easily decomposable Ca component (preferably Ca (OH) 2) is ground with TiO 2 and an amorphous SiO 2 raw material (preferably Suprasil), dried and heat-treated for 0.5-2 hours 1 323 K to 1 423 K. {electric functional ceramics; capacitors; Titanium compounds; Calcium titanium silicate; Synthesis; calcination}

Description

Characteristic of the known solutions There are two principal ways of producing calcium titanosilicate (CTS). The first possibility is the calcination of

amorphous starting compounds prepared by chemical fumigation reactions. So in the patent

SU 623829 the CTS by alkaline precipitation of dissolved and mixed Ca, Ti and Si compounds at a pH of

10-12.5 and subsequent calcination at 1023-1073K.

Vance describes in Mater. Res. Bull. 21 (1986) 321 -9 the preparation of the CTS via a Ca-Ti-Si-GeI, which via intermediate CaTiOj leads to calcination at 1573 K to the final product. The patent US 3,695,836 sheds the synthesis of pure CTS, wherein an aqueous mixture of CaO, TiO ₂ and SiO _{2 is} subjected to a 12-hour hydrothermal treatment (T473K; ρ 1.45 MPa) with the addition of mineralizers. Especially this way requires a high expenditure in terms of equipment and time as well as selected basic chemicals. The second way is based on a classic, ceramic technology with the steps mixing / grinding the solid Starting materials, calcination, fine grinding and then repeated heat treatment. Belous et al. (Ukr. Khim. Zh 53 (1987) 129-132) investigated in this connection the systems CaO / anatase / SiO ₂ , CaCO ₃ / Anatase / SiO ₂ , CaCO ₃ / rutile / SiO ₂ in the temperature range up to 1633 K. It has been found that independently of the Starting materials CTS via the intermediates CaTiOj and 0-CaSiO _{3 is} formed, with a narrow temperature interval close

of the melting point (1643K) must be selected.

DD-WP 254934 protects a two-step process of CTS production, where the first step is the formation of CaTiO ₃ ,

followed by the reaction with mechanically activated quartz flour bui a temperature of 1493-1533 K for a period of 1 hour.

According to WP 263747, CTS is produced in which CaO, TiO ₂ or CaTiO ₃ or mixtures of these components and a SiO ₂ raw material,

which consists of at least 45% by weight of cristobalite, is mixed and subjected to a temperature treatment of 1453-1533K for 0.5-8 hours. Characteristic of this synthesis pathway are the high calcination temperatures of 1473 K.

Object of the invention

The aim of the invention is to apply a simple ancestor for the production of high purity, synthetic CTS according to the ceramic technology, wherein the formation temperatures for the CTS should be <1423K. The CTS produced by the process according to the invention must be usable on the basis of its properties as an essential component of electrical functional ceramics.

Representation dos essence of the invention

The object of the invention is the production of high purity CTS according to the ceramic technology at low calcination temperatures of T <1423 K.

The object is achieved in that a Ca compound is used as starting material, which converts at temperatures <773 K in reactive CaO. This Ca compound is wet-ground with an amorphous SiO ₂ raw material and TiO ₂ and, after drying, this powder mixture is subjected to a heat treatment of 1323-1423K for 0.5-2 hours. CaSiO ₃ preferably occurs as an intermediate over CaTiO ₃ . The Ca compound can be Ca (OH) ₂ ; the amorphous SiO _{2 is} a precipitated silica (Suprasil).

Ausführungsbeisplel

15 g Ca (OH) ₂ , 15.98 g TiO ₂ and 12 g SiO _{2 ;} , (Suprasil) are made with 45g agate balls and 200ml dist. H ₂ O mixed for 24 hours in a PVC drum, then filtered with suction, dried at 12O ⁰ C. The resulting powder mixture is calcined at 1373 K for 2 hours. The X-ray diffractogram indicates high-purity, crystalline CTS.

Claims (1)

Process for the preparation of calcium titanosilicate (CaTiSiO ₆ ) by a ceramic technology at low calcination temperatures using a Ca component which converts to reactive CaO at temperatures of <773 K and which is wet mixed with an amorphous SiO ₂ raw material and TiO ₂ and after drying the mixture is subjected to a temperature treatment for 0.5-2 h, characterized in that the temperature treatment of the powder mixture at 1323 bjs 1423 K. Field of application of the invention The invention relates to a method m for producing the compound calcium titanosilicate in a highly pure, crystalline form by a synthetic route. The compound is an important component for the production of electrical functional ceramics, in particular ceramic capacitors.