Hydroxyl groups on the surface of metal oxides are amphoteric in character. From experiments with anatase, rutile, η-alumina, α-Fe2O3,CeO2, and SnO2, half the OH groups are acidic in character, the other half are mainly basic and may be exchanged for other anions. This behaviour is explained by the structure of the hydroxylated surface. Acidity and basicity depend on the nature of the oxide. Several reactions are described for the determination of total OH content as well as the quantities of acidic and basic OH groups.
{"title":"Acidic and basic properties of hydroxylated metal oxide surfaces","authors":"H. Boehm","doi":"10.1039/DF9715200264","DOIUrl":"https://doi.org/10.1039/DF9715200264","url":null,"abstract":"Hydroxyl groups on the surface of metal oxides are amphoteric in character. From experiments with anatase, rutile, η-alumina, α-Fe2O3,CeO2, and SnO2, half the OH groups are acidic in character, the other half are mainly basic and may be exchanged for other anions. This behaviour is explained by the structure of the hydroxylated surface. Acidity and basicity depend on the nature of the oxide. Several reactions are described for the determination of total OH content as well as the quantities of acidic and basic OH groups.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"377 1","pages":"264-275"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74473765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The mechanisms of current carrier generation involving triplet excitons are studied for anthracene and tetracene samples. The method used is based on the specific dependence of photocurrent and fluorescence on a magnetic field.
{"title":"Paramagnetic excitons and their role in photoconductivity and fluorescence of anthracene and tetracene","authors":"E. Frankevich","doi":"10.1039/DF9715100037","DOIUrl":"https://doi.org/10.1039/DF9715100037","url":null,"abstract":"The mechanisms of current carrier generation involving triplet excitons are studied for anthracene and tetracene samples. The method used is based on the specific dependence of photocurrent and fluorescence on a magnetic field.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"137 1","pages":"37-47"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86281501","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The interaction of water vapour with the surface of rutile (∼4 m2 g–1) has been studied by a combination of three methods: (i) determination of adsorption isotherms, (ii) temperature-programmed desorption (TPD), and (iii) infra-red spectroscopy. A distinction is drawn between dissociative chemisorption of water, which exhibits a TPD peak at 370°C and a heat of desorption of 107kJ mol–1, a strong form of molecular adsorption (with a TPD peak at high coverage at 250°C) and a weak molecular adsorption. It is concluded that the dissociative adsorption occurs heterolytically on Ti—O pairs until ∼50 % of the surface is hydroxylated. Molecular adsorption is considered to occur on isolated titanium ions (strong) and on isolated oxygen ions (weak). Non-dissociatively adsorbed water can be totally removed by evacuation at 325°C, leaving the rutile surface partially hydroxylated. The properties of this surface towards the adsorption of isopropanol and of acetone are described. The vapours are adsorbed to give a type I isotherm, the saturation value being the same in both cases. Desorption has been investigated by TPD. Models are proposed to account for the localized adsorption of the alcohol and ketone on this hydroxylated rutile.The relative strengths of adsorption of water (W), acetone (A) and isopropanol (I) have been further examined by studying the six combinations: W(ads)+A(g); W(ads)+I(g); A(ads)+W(g); A(ads)+I(g); I(ads)+W(g); I(ads)+ A(g). The compositions of the adsorbed and gas phases at equilibrium have been deduced from gas chromatographic analysis. These displacement studies have enabled the pattern for the mutual adsorption characteristics of the three species to be obtained. The results have a particular significance for the rutile-photocatalyzed oxidative dehydrogenation of isopropanol, a process in which the adsorptions of alcohol, ketone and water occur simultaneously.
水蒸气与金红石表面(~ 4 m2 g-1)的相互作用已经通过三种方法的组合进行了研究:(i)吸附等温线的测定，(ii)程序升温解吸(TPD)和(iii)红外光谱。水的解离化学吸附在370°C时具有TPD峰，解吸热为107kJ mol-1，强分子吸附(250°C时具有高覆盖的TPD峰)和弱分子吸附之间存在区别。结果表明，解离吸附在Ti-O对上发生异解，直到表面羟基化约50%。分子吸附被认为发生在分离的钛离子(强)和分离的氧离子(弱)上。非解离吸附的水可以通过在325°C的疏散完全除去，留下金红石表面部分羟基化。描述了该表面对异丙醇和丙酮的吸附性能。蒸汽被吸附得到I型等温线，两种情况下的饱和值是相同的。用TPD研究了解吸过程。提出了模型来解释醇和酮在羟基化金红石上的局部吸附。通过研究W(ads)+A(g)这六种组合对水(W)、丙酮(A)和异丙醇(I)的相对吸附强度，进一步考察了它们的吸附强度;W(广告)+ I (g);(广告)+ W (g);(广告)+ I (g);我(广告)+ W (g);我(广告)+ (g)。通过气相色谱分析，推导出了平衡状态下吸附相和气相的组成。这些位移研究使三种物质相互吸附特性的模式得以获得。研究结果对金红石光催化异丙醇氧化脱氢反应具有重要意义，该反应同时吸附醇、酮和水。
{"title":"Adsorption of water and organic vapours on hydroxylated rutile","authors":"G. Munuera, F. Stone","doi":"10.1039/DF9715200205","DOIUrl":"https://doi.org/10.1039/DF9715200205","url":null,"abstract":"The interaction of water vapour with the surface of rutile (∼4 m2 g–1) has been studied by a combination of three methods: (i) determination of adsorption isotherms, (ii) temperature-programmed desorption (TPD), and (iii) infra-red spectroscopy. A distinction is drawn between dissociative chemisorption of water, which exhibits a TPD peak at 370°C and a heat of desorption of 107kJ mol–1, a strong form of molecular adsorption (with a TPD peak at high coverage at 250°C) and a weak molecular adsorption. It is concluded that the dissociative adsorption occurs heterolytically on Ti—O pairs until ∼50 % of the surface is hydroxylated. Molecular adsorption is considered to occur on isolated titanium ions (strong) and on isolated oxygen ions (weak). Non-dissociatively adsorbed water can be totally removed by evacuation at 325°C, leaving the rutile surface partially hydroxylated. The properties of this surface towards the adsorption of isopropanol and of acetone are described. The vapours are adsorbed to give a type I isotherm, the saturation value being the same in both cases. Desorption has been investigated by TPD. Models are proposed to account for the localized adsorption of the alcohol and ketone on this hydroxylated rutile.The relative strengths of adsorption of water (W), acetone (A) and isopropanol (I) have been further examined by studying the six combinations: W(ads)+A(g); W(ads)+I(g); A(ads)+W(g); A(ads)+I(g); I(ads)+W(g); I(ads)+ A(g). The compositions of the adsorbed and gas phases at equilibrium have been deduced from gas chromatographic analysis. These displacement studies have enabled the pattern for the mutual adsorption characteristics of the three species to be obtained. The results have a particular significance for the rutile-photocatalyzed oxidative dehydrogenation of isopropanol, a process in which the adsorptions of alcohol, ketone and water occur simultaneously.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"1 1","pages":"205-214"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90165320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The conductivities of single crystals and compressed samples of isocytosine, pentaerythritol, tetrolic acid and cetyl alcohol, all of which, on the basis of their structural properties, are likely to be protonic semi-conductors, have been measured under a wide range of conditions including inter alia variations in field strength, crystallographic direction, crystal thickness and ambient gas. The bulk conductivity of ultra-dry isocytosine is extremely low even at high temperatures: at 473 K σ[010] is 5.6 × 10–14 and σ[001] less than 8.3 × 10–14 ohm–1 cm–1. The surface conductivity of the ultra-dry solid is, however, significant; for compressed discs the measured conductivity at 473 K is ca. 10–11 ohm–1 cm–1, and there is a reproducible activation energy for conduction of 1.40±0.04 eV. In the presence of water vapour, the conductivity of isocytosine increases markedly, non-ohmic effects being evident and there are strong indications of protonic conductivity.Pentaerythritol, which displays anisotropy as between (101) and (001) faces in its surface conductivity, does not appear to be a protonic conductor even in the vicinity of its first-order transition temperature. Tetrolic acid shows no signs of protonic migration, and neither does cetyl alcohol at room temperature. The conductivity of cetyl alcohol rises sharply (a thousand-fold increase over a few degrees range) beyond 312 K, when rotation within the (001) sheets of hydroxyl group occurs, and the process is almost certainly protonic.
{"title":"Carrier injection and related phenomena in molecular crystals. Experimental study of proton injection in hydrogen-bonded organic solids","authors":"J. Thomas, J. Evans, T. Lewis","doi":"10.1039/DF9715100073","DOIUrl":"https://doi.org/10.1039/DF9715100073","url":null,"abstract":"The conductivities of single crystals and compressed samples of isocytosine, pentaerythritol, tetrolic acid and cetyl alcohol, all of which, on the basis of their structural properties, are likely to be protonic semi-conductors, have been measured under a wide range of conditions including inter alia variations in field strength, crystallographic direction, crystal thickness and ambient gas. The bulk conductivity of ultra-dry isocytosine is extremely low even at high temperatures: at 473 K σ[010] is 5.6 × 10–14 and σ[001] less than 8.3 × 10–14 ohm–1 cm–1. The surface conductivity of the ultra-dry solid is, however, significant; for compressed discs the measured conductivity at 473 K is ca. 10–11 ohm–1 cm–1, and there is a reproducible activation energy for conduction of 1.40±0.04 eV. In the presence of water vapour, the conductivity of isocytosine increases markedly, non-ohmic effects being evident and there are strong indications of protonic conductivity.Pentaerythritol, which displays anisotropy as between (101) and (001) faces in its surface conductivity, does not appear to be a protonic conductor even in the vicinity of its first-order transition temperature. Tetrolic acid shows no signs of protonic migration, and neither does cetyl alcohol at room temperature. The conductivity of cetyl alcohol rises sharply (a thousand-fold increase over a few degrees range) beyond 312 K, when rotation within the (001) sheets of hydroxyl group occurs, and the process is almost certainly protonic.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"835 1","pages":"73-84"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82932397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The photo-induced electrical conductivity of a number of arylidene-1,3-indandiones was investigated in order to determine the effect of charge carrier generation on the intramolecular electron shifts. The variation in the polarity of the compounds was achieved by placing electron donor and electron acceptor substituents on the arylidene group. The comparison of dark and photoconductivity of 15 arylidene-1,3-indandiones was obtained on sandwich cells of polycrystalline layers. More detailed experiments with the better photoconductors were carried out with sublimed films and pressed pellets.The photoconductivity of benzylidene derivatives indicated that photoconductivity increases with polarity of the molecule and achieves a maximum value in p-dimethylaminophenyl compound (DMAPID). Photovoltaic cells, giving 1.17–1.24 V open circuit photovoltage, were prepared from DMAPID sublimed film sandwich cells. The spectral response, voltage dependence and temperature dependence of several photoconductors were investigated. Although the generation of light-induced charge carriers is facilitated by increasing the dipole moment, the dark conductivities remained unaffected by such structural modifications.
{"title":"Chromophoric conditioning of photoelectric response in polar molecules","authors":"N. Dimond, T. K. Mukherjee","doi":"10.1039/DF9715100102","DOIUrl":"https://doi.org/10.1039/DF9715100102","url":null,"abstract":"The photo-induced electrical conductivity of a number of arylidene-1,3-indandiones was investigated in order to determine the effect of charge carrier generation on the intramolecular electron shifts. The variation in the polarity of the compounds was achieved by placing electron donor and electron acceptor substituents on the arylidene group. The comparison of dark and photoconductivity of 15 arylidene-1,3-indandiones was obtained on sandwich cells of polycrystalline layers. More detailed experiments with the better photoconductors were carried out with sublimed films and pressed pellets.The photoconductivity of benzylidene derivatives indicated that photoconductivity increases with polarity of the molecule and achieves a maximum value in p-dimethylaminophenyl compound (DMAPID). Photovoltaic cells, giving 1.17–1.24 V open circuit photovoltage, were prepared from DMAPID sublimed film sandwich cells. The spectral response, voltage dependence and temperature dependence of several photoconductors were investigated. Although the generation of light-induced charge carriers is facilitated by increasing the dipole moment, the dark conductivities remained unaffected by such structural modifications.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"1 1","pages":"102-109"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77247802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Electrical conductivity of some organic materials containing metals.","authors":"J R McKellar, J A Weightman, R J Williams","doi":"10.1039/df9715100176","DOIUrl":"https://doi.org/10.1039/df9715100176","url":null,"abstract":"","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"51 ","pages":"176-82"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1039/df9715100176","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"16224382","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Field-induced switching between two impedance states has been observed in both pure and doped organic thin films. Aromatic hydrocarbon films display this phenomenon reproducibly when a mobile electrode material such as gallium-indium alloy is employed. Controlled doping of the hydrocarbons with electron acceptors leads to reproducible switching characteristics which are not electrode dependent. For the doped films, activation energies of conduction typical of bulk charge-transfer complexes characterize the low impedance states whereas the activation energies of the high impedance states are typical of organic insulating films. It is suggested that the switching mechanism involves the formation of conducting filaments.
{"title":"Bistable switching in organic thin films","authors":"J. Kevorkian, M. Labes, D. Larson, D. Wu","doi":"10.1039/DF9715100139","DOIUrl":"https://doi.org/10.1039/DF9715100139","url":null,"abstract":"Field-induced switching between two impedance states has been observed in both pure and doped organic thin films. Aromatic hydrocarbon films display this phenomenon reproducibly when a mobile electrode material such as gallium-indium alloy is employed. Controlled doping of the hydrocarbons with electron acceptors leads to reproducible switching characteristics which are not electrode dependent. For the doped films, activation energies of conduction typical of bulk charge-transfer complexes characterize the low impedance states whereas the activation energies of the high impedance states are typical of organic insulating films. It is suggested that the switching mechanism involves the formation of conducting filaments.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"18 1","pages":"139-143"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72910621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The surfaces of fine powder samples of MgO, CaO and SrO have been characterized by the diffuse reflectance technique over the wavelength range 200–2000 nm. Spectra due to F+s centres (electron in surface anion vacancy), SH centres (F+s centre with nearby —OH group) and adsorbed O–2 species have been identified. In powders which have been freed from surface contaminants fluorescences exist which can be quenched by O2, H2O or CO2. These fluorescences are interpreted as due to the presence of surface states which create an “effective” band gap at the oxide surfaces at significantly lower energies than the band gaps typical of the bulk oxides.
{"title":"Electronic spectra of the surfaces of alkaline earth oxides","authors":"R. Nelson, J. W. Hale","doi":"10.1039/DF9715200077","DOIUrl":"https://doi.org/10.1039/DF9715200077","url":null,"abstract":"The surfaces of fine powder samples of MgO, CaO and SrO have been characterized by the diffuse reflectance technique over the wavelength range 200–2000 nm. Spectra due to F+s centres (electron in surface anion vacancy), SH centres (F+s centre with nearby —OH group) and adsorbed O–2 species have been identified. In powders which have been freed from surface contaminants fluorescences exist which can be quenched by O2, H2O or CO2. These fluorescences are interpreted as due to the presence of surface states which create an “effective” band gap at the oxide surfaces at significantly lower energies than the band gaps typical of the bulk oxides.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"84 1","pages":"77-88"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74066409","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The chemisorption of water vapour on de-hydroxylated α-Fe2O3 has been investigated by heats of immersion into water at 25°C. The properties of physically adsorbed multilayers on the hydroxylated surface have been studied using dielectric relaxation techniques in conjunction with adsorption isotherms. The heat of immersion of the completely hydroxylated substrate is –367 ergs/cm2 and increases with increased outgassing temperature to –1073 ergs/cm2 for outgassing at 375°C. Differentiation of the integral heat curve gives the initial heat of chemisorption to be at least –50 kcal/mol of water vapour. The electrical capacitance at 70 c/s to 300 kc/s of physically adsorbed water vapour on the hydroxylated substrate is constant within the B.E.T. monolayer, but rises sharply with the onset of the second layer. This behaviour suggests that the first layer of physically adsorbed water is immobile, but that succeeding layers are mobile. Confirming evidence as to the immobile nature of the physisorbed monolayer is given on an entropy basis. The integral entropy of adsorption obtained from multi-temperature isotherms at constant spreading pressure is –33.2 cal/mol K for half a monolayer. This value agrees favourably with the theoretical value of –36.8 cal/mol K calculated from statistical thermodynamics for a localized monolayer, but not with the value –15.9 cal/mol K derived for mobile adsorption. Characteristic relaxation frequencies of adsorbed water vapour were obtained from Cole-Cole are plots of dielectric constant against dielectric loss. The characteristic frequencies increase smoothly with coverage from 10 c/s to a value of 10 kc/s at B.E.T. coverages of three or more, suggesting the development of a hydrogen-bonded ice-like structure for those coverages.
{"title":"Adsorption of water vapour on α-Fe2O3","authors":"E. Mccafferty, A. Zettlemoyer","doi":"10.1039/DF9715200239","DOIUrl":"https://doi.org/10.1039/DF9715200239","url":null,"abstract":"The chemisorption of water vapour on de-hydroxylated α-Fe2O3 has been investigated by heats of immersion into water at 25°C. The properties of physically adsorbed multilayers on the hydroxylated surface have been studied using dielectric relaxation techniques in conjunction with adsorption isotherms. The heat of immersion of the completely hydroxylated substrate is –367 ergs/cm2 and increases with increased outgassing temperature to –1073 ergs/cm2 for outgassing at 375°C. Differentiation of the integral heat curve gives the initial heat of chemisorption to be at least –50 kcal/mol of water vapour. The electrical capacitance at 70 c/s to 300 kc/s of physically adsorbed water vapour on the hydroxylated substrate is constant within the B.E.T. monolayer, but rises sharply with the onset of the second layer. This behaviour suggests that the first layer of physically adsorbed water is immobile, but that succeeding layers are mobile. Confirming evidence as to the immobile nature of the physisorbed monolayer is given on an entropy basis. The integral entropy of adsorption obtained from multi-temperature isotherms at constant spreading pressure is –33.2 cal/mol K for half a monolayer. This value agrees favourably with the theoretical value of –36.8 cal/mol K calculated from statistical thermodynamics for a localized monolayer, but not with the value –15.9 cal/mol K derived for mobile adsorption. Characteristic relaxation frequencies of adsorbed water vapour were obtained from Cole-Cole are plots of dielectric constant against dielectric loss. The characteristic frequencies increase smoothly with coverage from 10 c/s to a value of 10 kc/s at B.E.T. coverages of three or more, suggesting the development of a hydrogen-bonded ice-like structure for those coverages.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"239 1","pages":"239-254"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78510855","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Heats of immersion of pure and doped magnesia in cyclohexane were measured at 35°C for samples heated at different temperatures in vacuo. For the pure samples, rise in temperature of thermal treatment leads to a gradual decrease in the heats of immersion normalized per unit area (h1, ergs cm–2), till a certain limiting value of 44.5 ergs cm–2 is reached. Pore structure analyses lead to certain correlations between the heat of immersion and the fraction of the total surface located in micropores. Pores which could effectively play a role in altering the heat of immersion were assessed to possess a mean hydraulic radius of 10 A or less. Doping on the surface leads to the same behaviour, except that the decline in the heat of immersion is followed by an increase in the hi values for the high temperature samples heated at or above 560°C. For the doped samples, formation of a solid solution between Li+ and Mg2+, and a spinel between Al3+ and Mg2+ complicates the results obtained.
{"title":"Heats of immersion of pure and doped magnesia in cyclohexane. Effects of micropores","authors":"R. Mikhail, S. Nashed, A. Khalil","doi":"10.1039/DF9715200187","DOIUrl":"https://doi.org/10.1039/DF9715200187","url":null,"abstract":"Heats of immersion of pure and doped magnesia in cyclohexane were measured at 35°C for samples heated at different temperatures in vacuo. For the pure samples, rise in temperature of thermal treatment leads to a gradual decrease in the heats of immersion normalized per unit area (h1, ergs cm–2), till a certain limiting value of 44.5 ergs cm–2 is reached. Pore structure analyses lead to certain correlations between the heat of immersion and the fraction of the total surface located in micropores. Pores which could effectively play a role in altering the heat of immersion were assessed to possess a mean hydraulic radius of 10 A or less. Doping on the surface leads to the same behaviour, except that the decline in the heat of immersion is followed by an increase in the hi values for the high temperature samples heated at or above 560°C. For the doped samples, formation of a solid solution between Li+ and Mg2+, and a spinel between Al3+ and Mg2+ complicates the results obtained.","PeriodicalId":11262,"journal":{"name":"Discussions of The Faraday Society","volume":"45 1","pages":"187-195"},"PeriodicalIF":0.0,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88871453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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