ELSEVIER Powder Technology 83 (1995) 35-41 POWDER TECHNOLOGY Surface texture of high-area manganese oxide powders versus compaction A.K.H. Nohman Chemistry Department, Faculty of Science, Minia University, EI-Minia 61519, Egypt Received 15 March 1994; revised 14 October 1994 Abstract Three prepared manganese oxide powders from K+-contaminated NH4MnO4, of high surface area (43-340 m 2 g-X) were investigated for the assessment of the textural consequences of compaction. The powders were compacted in die at various pressures (1-15 ton in -2) encompassing technological conditions. Textural modifications were estimated by applying the f- plots. Results indicated that compaction effects vary depending on the initial physicochemical characteristics of the powder. For industrial applications of pelleted catalysts, it is advisable to choose the appropriate compaction pressure to give optimal textural characteristics. Keywords: Manganese oxide; Surface texture; Compaction 1. Introduction One of the first descriptions of the process of powder compaction was made by Wollaston [1] in 1828 when he produced platinum billets. Compaction for the pur- pose of industrial use is very important, but consequent textural modifications ensue. Several investigations [2-14] have been performed to assess compaction effects on the surface characteristics of finely divided solids. Compaction forces powder particles closer together and can deform or fragment them. Initial textural char- acteristics are altered consequently, sometimes critically. The alterations are often monitored by the analysis of N2 adsorption isotherms at - 196 °C. Changes in surface area and porosity as a function of the compaction pressure applied [6,14-17] can thus be assessed. The importance of such information to powder technology lies in providing a fair estimate of the extent to which the loose powder surface properties can be utilized to account for those of the powder compacts. The com- paction effects can then be traced back to the initial particle properties (size [17], shape, deformability [11,14] and bulk structure [14-17]) of the loose powder. Textural studies on manganese oxide powders are infrequently encountered in the literature, probably due to the generally low surface area of these materials. However, in this laboratory, manganese oxide powders of considerably high surface areas (43--340 m 2 g-l) 0032-5910/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0032-5910(94)02925-E have recently been obtained using novel precursor compounds [18,19]. In view of the industrial importance of manganese oxide catalysts [20--22] and the necessary compaction processing, the present study was under- taken. It aims at following up effects of compaction on the surface texture of these high-area manganese oxide powders. Moreover, the study attempts to explore whether relationships do exist between the initial powder properties and compactability. The experimental tool used was N2 adsorption isotherms at liquid nitrogen temperature (- 196 °C). 2. Experimental 2.1. Materials Manganese oxide powders were prepared by calci- nation of NFLMnO4 (3.6 wt.% K÷-contaminated) at 150, 300 and 600 °C for 5 h. The calcination procedure and precautions are to be found in a previous publication [19]. For simplicity, these powders are respectively denoted by A, B and C. In order to prepare the compacts, a die of 22-mm diameter was charged with the powder at room tem- perature; followed insertion of the plunger and ap- plication of the desired pressure for 3 min. Compaction pressures applied were 1, 5, 10 and 15 ton in -2 (1 ton