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i PREFACE Rocks, various soils, clays and sands are composed almost entirely of silicate minerals and silica. This predominance of sili- cates and alumino silicates is reflected in the abundance of oxygen, silicon and aluminium which are commonest in the Silica has stoichiometric composition presented as S10 includes o tn 2). hydrated species with composition earth I s 2 crust. which sometimes SI0 2 :XH 20 (where X = Tho mlnnrnl AlllcntflA. TlArticulnrly clny minerals 1.e. layer"d silicates also known as "phyllosilicates" (phyllo = leaflike), are essential components of so11, to which we owe our survival. They are also raw materials for some of the mankind I s most ancient and essential artefacts: bricks, social pottery, developments and tiles etc. However, growth,~ the industrial synthetic materials is rising in enormous rate. with continuing need of artificial or The increasing demand of synthetic silica and alumino silicates in the market since last four decades is applications due of to the rapid different changes taking types of amorphous place in the industrial and crystalline silica and alumino silicates. In the present investigations related study the stress has to amorphous silica and been given on the modification of natural Alumino AlllcAtOA pArticularly clay minerals of Amectite group. Properties of amorphous silica such as specific surface and porosity can be varied within a largo range which are attributed ii to ultimate particles of colloid in aggregates. range, of their packing (arrangement) The clay minerals also have particulate matter in colloid the plate like structure and large surface area. mnko tins size and slllcn applications compounding, onel like liquid alumino silicates uniquely surface coa tings, carrier, thickeners, free-flow aid, These proper- suitable for number rubber-reinforcement, beer-stabilizer, toothpaste dessicant adsorbent etc. plastic abrasives, Since these mate- rials are chemically inert and non-toxic they find growing applications in food and pharmaceutical industries. blocking agent in plastic They are also used as anti- industries and matting agent in paint and The clays are widely used in drilling fluid in petroleum varnishes. industry. The dissertation consists of two parts. Part-I includes studies on synthesis of amorphous silica precipitated silica by acldulRtJon of sodJum sJ]jcate. As sillca gels, pyrogenic are industrially important products, synthesis is found pyrogenic much silica silicas and majority of the literature on the in the patent archives. However, silica gels and have been intensively studied academically, but not information is available in literature on the systematic studies of the changes in surface properties of precipitated silica under different conditions with academic interest. efforts silica have varying been the focussed synthetic to In the present investigation, understand parameters the of surface properties of precipitation procedure. iii Part-II silicates i. e. includes clay modification minerals for the studies of preparation natural of alumino pillared inter- lnyered ClAY" (PIl.e). The swelling phyllosilicate are naturally occurring catalysts. minerals, known as smectites Acid mOdified smectites were used as petroleum cracking catalyst until mid 60' s when they were replaced by more thermally stable and shape selective zeolite catalysts. inherent problem with zeolite catalyst/adsorbent crude oil is its relatively small pore size escalation of oil prices in early 70 I S in processing heavy (0.2 to 0.9 nm). having stable structure with The prompted the investigation of catalytic material for processing of heavy crude oils. material The large pores, In search for basic concept of pillared clay gradually emerged and consequently a new class of smectite intercalated compounds was synthesized which makes use of robust poly-hydroxy metal cation as molecular props or pillars between the Rillentn InynrR. The cationic clays hydroxy of smectite groups oligomers of different can metals be intercalated (AI, Si, Zr, with Ti and transition metals) as pillars and thus properties of the products also can be widely varied. been studied The intercalation of clay with Al and Zr has extensively and AI-pillared smectite is thought to be the best understood one. In the present investigation, modification study of Indian bentonite for the preparation of thermally stable PILC has been undertaken by intercalating cationic oligomer of hydroxy aluminium (COHA).