Process for growing crystals of a compound with reverse solubility and device for its use

Preparation of crystals with reverse solubility. The process for growing crystals of a compound with reverse solubility from nuclei in a solution enriched in the compound consists in causing a diffusion from a cold zone of the solution containing the parent substance towards a hot zone where it crystallises, by applying to the solution a horizontal temperature gradient of approximately between 5 and 20 DEG C. The device comprises a substantially cylindrical hydrothermal enclosure with a horizontal axis, containing a solution of the compound comprising a cold part containing the parent substance and a hot part containing the crystallisation nuclei, which are connected by a strangulation neck and means for independently heating the hot part and the cold part. Application to the preparation of crystals usable in frequency filters. L'INVENTION CONCERNE LA PREPARATION DE CRISTAUX A SOLUBILITE RETROGRADE.LE PROCEDE DE CROISSANCE DE CRISTAUX DE COMPOSE A SOLUBILITE RETROGRADE A PARTIR DE GERMES DANS UNE SOLUTION ENRICHIE DU COMPOSE, CONSISTE A PROVOQUER UNE DIFFUSION D'UNE ZONE FROIDE DE LA SOLUTION CONTENANT LE CORPS MERE, VERS UNE ZONE CHAUDE OU ELLE CRISTALLISE, EN APPLIQUANT A LA SOLUTION UN GRADIENT DE TEMPERATURE HORIZONTAL COMPRIS ENTRE 5 ET 20C ENVIRON.LE DISPOSITIF COMPREND UNE ENCEINTE HYDROTHERMALE SENSIBLEMENT CYLINDRIQUE D'AXE HORIZONTAL, CONTENANT UNE SOLUTION DU COMPOSE COMPORTANT UNE PARTIE FROIDE CONTENANT LE CORPS MERE ET UNE PARTIE CHAUDE CONTENANT LES GERMES DE CRISTALLISATION RACCORDEES PAR UN GOULOT D'ETRANGLEMENT, AINSI QUE DES MOYENS POUR CHAUFFER INDEPENDAMMENT LA PARTIE CHAUDE ET LA PARTIE FROIDE.APPLICATION A LA PREPARATION DE CRISTAUX UTILISABLES DANS LES FILTRES DE FREQUENCE.