Anhydrous inorganic halides - chlorides, bromides, iodides - are widely used for growing single crystals for laser and scintillation technology. These compounds have high demands on purity despite the absence of the valid data on the dependence of the optical characteristics of materials obtained from the concentration of certain impurities in them are missing. Specialists in crystal growth for the most part cannot approach the task of content of specific "dangerous" elements, therefore, they formulate common requirements as "material 99,99% of metal (or rare earth) impurities". A separate problem is a difficult purification from carbon impurities, which is not defined in the analysis of the material, but makes the crystals opaque.
Using your own design or using certain specially improved the way we produce halides over 200 titles not in preparative quantities, and kilograms and tens of kilograms. To purify the resulting compounds, especially in cases of separation of pairs of similar properties halides, we use methods of distillation, sublimation, high-temperature distillation, directional solidification, zone melting.
Particular attention is paid to the interaction of inorganic halides with the air moisture. As s rule, the consumers tend to impose very strict requirements on the content of water, hydroxyl groups and oxygen, as the presence of oxyhalide phases are unacceptable. A majority of halides turn to stepped and irreversible hydrolysis in the presence of moisture. In addition, nearly all halides - hygroscopic substances, so besides the problem of obtaining high-purity halides must be addressed as the tasks of delivering these substances to the consumer and the convenience of the practical use.
Now we produce anhydrous halides in the form of nearly monodispersed fused spherical granules (beads). In our view, this type of material has clear benefits for the consumers: halides undergo stages of melting and filtering to prevent the ingress of solid particles of oxyhalide phases in the product, spherical shape minimizes the surface contact with the possible pairs of moisture during further using of the material; monodimension particles may easily and quickly be dosed. In particular, monodisperse granules metal halides can be effectively used in growing single crystals by the Czochralski method with the fueling of the material into the zone melting. We use the author's technique and equipment for granules.
The resulting overall purities of produced halides are between 99.9 and 99.9999%; organic impurities - less than 0,1-1 ppm; сontent of hydrolysis products, OH-group and water in “anhydrous” products is about 0,2-0,3%, in “ultra dry” products - 10-30 ppm. |