The stability of SDAHC has not been systematically stud-The moisture sorption isotherm of amorphous spray-dried aluied. In contrast, the stability of aluminum hydroxycarbonate minum hydroxycarbonate (SDAHC) at 25ะC revealed that moissuspension has been extensively studied (3)(4)(5)(6). This study ture sorption increased sharply when the relative humidity exwas undertaken to investigate the stability of SDAHC when ceeded 80%. The physical and chemical stability of SDAHC was aged under ambient temperature and different relative hustudied for 1 year at 25ะC and 0, 11, 54, 84, or 100% RH. The midities. Emphasis will be placed on understanding the efresults were interpreted to reveal that two mechanisms affect the fect of adsorbed water on the stability of the amorphous properties of SDAHC at 25ะC. The sample stored at 0% RH did solid. Although the results of this study will be directly not exhibit any significant changes during the 1-year study period.
applicable to the manufacture and storage of solid antacid
The surface area and rate of acid neutralization decreased when samples were stored at 11 or 54% RH, but the material remained dosage forms, the adsorption of water by an amorphous solid amorphous. This change is believed to be due to aggregation and is a general phenomena in surface science. It is hoped that cementation of particles. Much larger changes in surface area and the relationship between water adsorption and stability in the rate of acid neutralization occurred in the samples aged at this system can be related to other amorphous solids.
84 or 100% RH. Under these humidity conditions, polymorphic
The moisture sorption isotherm is used to determine a transformations occurred in addition to aggregation and cementasolid's affinity for water at a given temperature. The isotherm tion. X-ray diffraction indicated that microcrystalline boehmite is most frequently expressed as a plot of the moisture content was an intermediate phase. The stable polymorph was bayerite, (%) of the solid versus the relative humidity (%). There which is believed to form due to the high surface pH produced by are two types of moisture sorption isotherms. One is for water sorption at 84 or 100% RH. The moisture sorption isotherm solids which sorb moisture in discrete steps, such as when was useful in identifying the humidity conditions which resulted an anhydrous solid converts to a hydrate (7). The second in high moisture sorption. Polymorphic transformations were only detected when the SDAHC was aged under these humidity condi-type of moisture sorption isotherm occurs when water intertions.