During my undergraduate, I worked on a process in lab to make alumina sol-gel starting with hydrous aluminium nitrate which was dissolved in water and precipitated using ammonium hydroxide. Precipitated alumina (/boehmite) was magnetically stirred in acidic solution (pH ~2). There was a critical value of pH which gave sol, if pH was lowered further it converted into gel. 65% HNO3 solution was used drop by drop to achieve appropriate pH for making sol. This sol was homogenized and used fro some coating purpose.