Faculty of Engineering

The adsorption of stearic acid and pyridine and determination of specific surface area of powdered solids

Mon, 01 Jan 1979 00:00:00 GMT

The adsorption of stearic acid and pyridine and determination of specific surface area of powdered solids Ghosh, Ashim Kumar The Bet Gas Adsorption, Flow Micro-Calorimetric And Adsorption From Solution Methods For The Determination Of Surface Areas Of Cupric Oxide, Ferric Oxide And Alumina Pow- Ders Have Been Compared With A View To Examine The Validity Of The Method Of Adsorption From Solution As A Standard. Nitrogen Gas Has Been Chosen For The Bet Method Whereas Stearic Acid, A Commonly Employed Solute, Has Been Used For The Flow Micro-Calorimetric And Adsorption From Solution Measurements. It Has Been Found That Adsorption Of Nitrogen Gas On All The Adsorbents Is Physical In Nature But Stearic Acid Employed In The Flow Micro-Calorimetric And Adsorption From Solution Methods Gives Mostly Chemisorption Of The Mole- Cules On The Adsorbent Powders. Surface Areas Determined By The Flow Micro-Calorimetric And Adsorption From Solutions Have Been Found To Be Identical For The Respective Powders. Despite The Difference In Mechanism Of Adsorption Of Nitro- Gen And Stearic Acid Molecules The Flow Micro-Calorimetric And Adsorption From Solution Surface Areas Agree Fairly Well With The Bet Nitrogen Gas Adsorption Surface Areas Of The Adsorbents If It Is Assumed That The Area Occupied Per Mole- Cule Of Stearic Acid To Be Of The Order Of 60-70 2. The Orientation Of Stearic Acid Molecules On The Solid/Liquid Interface, Therefore, Take Place So That Acid Molecules Lie Neither Completely Perpendicular Nor Completely Parallel To neither completely perpendicular nor completely parallel to the surface. possible orientations of the stearic acid chain on the surface are envisaged. Correspondence of the surface areas of the adsor-bents using nitrogen gas and stearic acid solution reveal that the total sites of the adsorbents are independent of the nature of the solute molecules. To study this hypothesis further pyridine, an orga- nic base, has been chosen as solute and its adsorption on the same adsorbents have been studied. the surface areas obtained by adsorption of pyridine from solution have been found to be identical to the respective areas obtained by bet method and stearic acid adsorption if it is considered that the area occupied by one molecule of pyridine to be around 24.7 2,the molecular area of pyridine. Adsorption of stearic acid on magnesium oxide and silica gel powders gave surface areas to be 90 and 370 m2/g respectively considering area occupied per molecule of stea- ric acid to be 63.3 and 67.5 2. these value agree fairly well with the values quoted in literature. surface areas of these two powders determined by adsorption of pyridine agree fairly well with the above mentioned value if it is consi- dered that one molecule of pyridine occupies 24.8 2. It may, therefore, be concluded that with the appro- priate values of areas occupied per molecule of solute method adsorption of stearic acid and pyridine may be taken as standard for the determination of surface area of the adsor- bents considered. This Thesis is Submitted to the Department of Applied Chemistry and Chemical Engineering, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Master of Philosophy (MPhil)

A Study of Electrical and Optical Properties of Transparent Conducting Sno2 and In203 Thin Films Prepared by Pyrosol Process

Fri, 01 Dec 1989 00:00:00 GMT

A Study of Electrical and Optical Properties of Transparent Conducting Sno2 and In203 Thin Films Prepared by Pyrosol Process Hakim, Md. Obaidul The design and construction of a simple and low-cost device for the deposition of thin films by the pyrosol process has been described. Doped and undoped films of SnO2 and In203 have been pre- pared on glass substrates. These films were highly conducting and at the same time highly transparent. They were non-stoichiometric but homogeneous and polycrystalline in structure. It is found that an activation energy of about 0.2 eV is associated with the growth process of these films. The sheet resistance of these films shows a size effect below a thickness of about 0.3 um. Doping has been performed by adding autimony (Sb) and fluorine (F) in SnO2 film and higher figure of merit in comparison to other earlier reports has been obtained. In In203 film Sn has been used as doping element to obtain films of higher conductivity and all mobility. The electrical transport properties and the optical transmission coefficients in the UV-VIS range of these films in the carrier concon-tration range~ 6 x 1018 to ~ 1.3 x 1021 cm3 for Sno2 and from ~3x1018 to~ X1020 са-3 for In203 films with thickness about 0.2 μm have been studied in detail to establish a tontative energy band picture of these degenerate samples. The thermoelectric power of the films were measured in the temperature range 27° to 160°C for Sno2 and upto 175°C for In20 films. Using the thermopower and optical transmission data the effective masses of electrons and of holes have res- pectively been determined as a function of the carrier coneen- tration. The optical band gap and the position of the Fermi levels were determined. It has been observed that the Formi levels are pinned near the conduction band edge at decreasing carrier concentrations, and the optical band gap shows an appre- ciable loss-Burstein shift in the investigatod range of carrier concentration. The effect of post-deposition heat treatment on some of the SnO2 and In203 films has been studied. It has been obser- ved that heat treatment in different ambients have remarkable effects on the film resistivity. No appreciable change of carrier concentration was noticed in SnO2 film but it was noticed in the In203 films. Hall mobilities in these films are found thermally activated at temperatures ranging from room temperature upto about 250°c. Oxygen diffusion mechanism at the grain boundaries of these films has been discussed critically to explain the observed mobility data. It is inferred from the heat treatment experiments that the role of oxygen diffusion process in the film is only to modulate the inter-grain boundary potential barrier heights. For SnO thin films two distinct scattering processes viz the grain boundary scattering and the ionized impurity scatte- ring are found to play a predominant role in limiting the Hall mobility in the two different ranges of carrier concentrations at room temperature. For the In203 films however the lattice scattering is found to be the dominant process limiting the carrier mobility. Finally, an attempt has been made to determine the electron affinity and work function of these samples on an empiri- cal basis using the electro negativity concept. The crystal bindings of these samples were also determined and were found to be of fairly ionic in nature. This thesis is Submitted to the Department of Electrical and Electronic Engineering (Former Department of Applied Physics and Electronic Engineering), University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

Synthesis and Characterization of Solid Catalysts

Wed, 01 Dec 2004 00:00:00 GMT

Synthesis and Characterization of Solid Catalysts Azad, Md. Abul Kalam Amorphous silica-alumina catalysts having different silicon aluminum ratios were prepared. The Brönsted surface acidity of these catalyst samples was measured by the base exchange method using aqueous CHCOONH solution and the results were compared with those measured by the base exchange method using NH4OH and KOH as adsorbates from aqueous solution. The amount of NH4' in CH3COONH4 and NH4OH and K in KOH adsorbed was determined by spectrophotometrically and titrimetrically respectively by measuring the concentration of NH4 and K in the solution before and after adsorption. Variation of surface acidity of catalyst samples-A (synthesized without pore regulating agent), sample-B (synthesized with tetramethylammonium bromide as a pore regulating agent) and sample-C (synthesized with pore regulating agent and base exchanged with NILCI solution to obtain H' form by calculation) have been studied using different concentrations of ammonium acetate, ammonium hydroxide and potassium hydroxide solutions. It has been observed that the surface acidity of a given size catalyst increases with the increasing of concentration of CH3COONH, NH4OH and KOH but dilute solutions of CHCOONH, NH4OH and KOH are sufficient to saturate the catalyst surface. It has been observed that the surface acidity of the catalyst samples found by using CHCOONI, is greater than that of NH4OH and KOH: Of the two bases NH4OH gives slightly greater surface acidity than that of given by KOH. At a given concentration of CH3COONH, NH4OH and KOH solutions the surface acidity was more pronounced when ammonium acetate solution was used as an adsorbate. A plausible explanation for this discrepancy is that with the use of NH4OH and KOII as bases considerable dealumination takes place with a consequent decrease of surface acidity of the catalyst samples. In all cases, the surface acidity was found to increase with the decrease of sample size. Surface acidity was also found to increase as the Al content of the catalyst was increased. The surface acidity of the catalyst samples-13 and C are greater than that of sample-A. But this increase of surface acidity is more noticeable in case of sample-C. Iron(III) dispersed on silica was prepared by the incipient wetness method and its surface acidity measured by CH3COONH, solutions was found negligibly small and was comparable to that of chromatographic silica and alumina. Finally, the Brönsted surface acidity of the catalyst sample-A measured by the base exchanged method using ammonium acetate has been found to be well correlated with the equilibrium pH of CH3COONH4 solution. This may therefore, be concluded that surface acidity of silica-alumina catalyst depends on its mode of preparation, sample size, ratio of Si:Al and concentration of titrants although very dilute solutions of titrants are sufficient to saturate the catalyst surface. A weak base like CH3COONH4 gives comparatively high values of surface acidity of all the silica-alumina catalyst samples where dealumination from the silica-alumina catalyst samples are supposed to be negligible. The total surface acidity of the silica-alumina catalyst sample was also determined by the Tamele method (Amine titration method). Considering the carcinogenic effect of benzene and toxicity of n-butylamine substitutes of benzene as a solvent and n- butylamine as a titrant have been sought. With this end in view attempts have been made to modify the Amine titration method by replacing benzene with cyclohexane or n-hexane or n-heptane and replacing n-butylamine by di-n-butylamine or di-iso- butylamine or sec-butylamine. For this parameters varied were concentration of di-n- butylamine, di-iso-butylamine, n-butylamine and sec-butylamine solutions, sample size of catalyst and types of catalyst samples. The results in the present investigation show that surface acidity of catalyst samples tends to increase with the decrease of catalyst sample size. Unlike Brönsted acidity for a given size of sample the total surface acidity tends to increase with the silicon content of the catalyst sample. For bases, the total surface acidity of various catalyst samples increase in the order of di-iso- butylamine

Some Physico-Chemical Properties of Cyanex 272 and Extraction of Some Metal Ions

Mon, 01 May 2006 00:00:00 GMT

Some Physico-Chemical Properties of Cyanex 272 and Extraction of Some Metal Ions Singha, Hari Prosad Using a reported technique for purifying organophosphorous extractants, the as-received Cyanex 272 extractant containing 85% bis-2,4,4-trimethylpentyl- phosphinic acid [BTMPPA] has been purified to a purity of about 99% BTMPPA. The purified reagent has been characterized and compared to the literature values. A technique for the colorimetric estimation of purified Cyanex 272 has been developed. It consists of the digestion of pure sample or its aqueous solution (after evaporating out most of water) with concentrated HNO3 (70%) - HCIO (70%) mixture at 2:1 ratio for 1 h. The oxidizing mixed acid quantitatively converts Cyanex 272 to a clear solution of orthophosphate which can be easily estimated by the molybdenum blue colorimetric method at 830 nm. The method is sensitive with a molar extinction coefficient of 2.6 x 10 and reproducible within ± 2%. Applying this technique of analysis, the dimerization constant (K2), distribution or partition coefficient (K) and the ionization constant (K) of the purified Cyanex 272 ie. BTMPPA have been estimated to be 190, 53 and 5.52 x 10, respectively. Interactions of BTMPPA+ diluent (n-hexane cyclohexane / benzene / toluene / chloroform / carbon tetrachloride / 1,2-dichloroethane (DCE) / 1-heptanol) binary mixtures have been studied in terms of density and viscosity measurements and also in terms of derived properties such as excess molar volumes (V), excess viscosities (n) and excess Gibbs free energy changes of activation of flow (AGE). Variations of these values together with the variations of the Grunberg-Nissan interaction parameter (d) for BTMPPA diluent binary systems show that BTMPPA interacts with the diluents in varying degrees. However, no correlation between d, AGE, nor V and the Cu2+/ Fe3+ - extraction characteristics with BTMPPA could be noticed. - The interfacial adsorption property of Cyanex 272 (purified) at the 0.50 mol/dm3 H2SO4 (pH = 0.8) / BTMPPA - diluent (carbon tetrachloride / cyclohexane/ DCE/ n-hexane / toluene / kerosene / benzene / chloroform / 1-heptanol/ 1-hexanol) interface have been investigated. Applying the Gibbs adsorption isotherm to the y vs. log [BTMPPA] plots for each of the diluent used (y being the interfacial tension, mN/m), the apparent cross-sectional areas (A in A2) of BTMPPA molecules adsorbed at the interfaces have been estimated. A (A3) is found to vary in the order: CCl4 (157 A2)