Patent GB-965930-A (GB)
Title: Composite lead oxide-silica particles
Inventor: ORSINO JOSEPH ANTHONY
IPC: C09C1/30
Filed: 1961-12-08
Abstract: A silica-cored lead oxide particle is prepared by forming a slurry of silica and at least one lead oxide selected from litharge and red lead, the lead oxide or oxides being present in amounts from 20-95% by weight and including at least 5% red lead and the silica being present in amounts from 5-80%, grinding the slurry, preferably for at least 4 hours, so that a complete coating of lead oxide or oxides can be formed on the silica surface, removing the liquid, and calcining the solid for 2-8 hours at 450-600 DEG  C. Not more than 0.5% by weight of alkali metal hydroxide may be added to the slurry before grinding.  At calcination temperatures of 470-500 DEG  C. some of the litharge is converted to red lead, and at 500-600 DEG  C. the reverse action occurs. If the higher temperature range is used, quick cooling is necessary to prevent red lead formation on passage through the lower range. The presence of red lead hinders the formation of lead silicate.  For use in paint, the silica and lead oxide should be in approximately equal proportions. In Example 1, equal parts of silica and of a mixture of 25% red lead and 75% litharge are ground in water in a ball mill for 6 hours at room temperature, the liquid is removed, and the dried solid is calcined for 6 hours at 480-490 DEG C. Examples II and III are similar, calcining being effected at 460-480 DEG  C. for 3 hours in Example II and aqueous KOH being incorporated in the slurry in Example III.  In Example IV, 140 grams of silica are used to 2,660 grams of lead oxide mixture and in Example V, 2,240 grams of silica are used to 560 grams lead oxide mixture. In Example VI, the lead oxide mixture of Example I is replaced by one containing 90% red lead and 10% litharge, and in Example VII, the lead oxide mixture may contain 1,300 grams litharge and 100 grams red lead, calcination being effected at 450-460 DEG C., or the same mixture may be used as in Example I and calcination effected at 550-570 DEG  C.  In Example VIII, the same mixture is used as in Example I and calcination effected at 455-465 DEG  C. for 2 hours and then 480-490 DEG  C. for 2 hours. In Example IX, calcination is effected at 530 DEG  C. for 4 hours.ALSO:A silica-cored lead oxide particle is prepared by forming a slurry of silica and at least one lead oxide selected from litharge and red lead, the lead oxide or oxides being present in amounts from 20-95% by weight and including at least 5% red lead and the silica being present in amounts from 5-80%, grinding the slurry, preferably for at least 4 hours, so that a complete coating of lead oxide or oxides can be formed on the silica surface, removing the liquid, and calcining the solid for 2-8 hours at 450-600 DEG  C.  Not more than 0.5% by weight of alkali metal hydroxide may be added to the slurry before grinding.  At calcination temperatures of 470-500 DEG  C. some of the litharge is converted to red lead, and at 500-600 DEG  C. the reverse action occurs.  If the higher temperature range is used, quick cooling is necessary to prevent red lead formation on passage through the lower range.  The presence of red lead hinders the formation of lead silicate.  For use in paint, the silica and lead oxide should be in approximately equal proportions.  In Example 1, equal parts of silica and of a mixture of 25% red lead and 75% litharge are ground in water in a ball mill for 6 hours at room temperature, the liquid is removed, and the dried solid is calcined for 6 hours at 480-490 DEG  C. Examples II and III are similar, calcining being effected at 460-480 DEG  C. for 3 hours in Example II and aqueous KOH being incorporated in the slurry in Example III.  In Example IV, 140 grams of silica are used to 2660 grams of lead oxide mixture and in Example V 2240 grams of silica are used 560 grams lead oxide mixture. In Example VI, the lead oxide mixture of Example I is replaced by one containing 90% red lead and 10% litharge, and in Example VII, the lead oxide mixture may contain 1300 grams litharge and 100 grams red lead, calcination being effected at 450-460 DEG  C., or the same mixture may be used as in Example I and calcination effected at 550-570 DEG  C.  In Example VIII, the same mixture is used as in Example I and calcination effected at 455-465 DEG  C. for 2 hours and then 480-490 DEG  C. for 2 hours.  In Example IX, calcination is effected at 530 DEG  C. for 4 hours.