Mechanical alloying (MA) has been used to obtain the icosahedral phases: i-(Mg-Zn-Al) and i-(Mg-Cu-Al) from metal powders. X-ray diffraction peaks are identical to those of icosahedral obtained by the melt spun technique. SAD patterns from MA samples indicate 2,3,6 and 5-fold symmetry. Annealing of the MA icosahedral phases leads to the formation of related cubic Frank-Kasper phases, that can be transformed into the icosahedral phases by MA. The disclination network which appears in the cubic phase plastically deformed by MA seems to be intrinsic to producing an aperiodic phase with long-range icosahedral order.
{"title":"Mechanochemical synthesis of icosahedral phases in Mg-Zn-Al and Mg-Cu-Al alloys","authors":"E.Yu. Ivanov, I.G. Konstanchuk, B.D. Bokhonov, V.V. Boldyrev","doi":"10.1016/0168-7336(89)80026-9","DOIUrl":"10.1016/0168-7336(89)80026-9","url":null,"abstract":"<div><p>Mechanical alloying (MA) has been used to obtain the icosahedral phases: i-(Mg-Zn-Al) and i-(Mg-Cu-Al) from metal powders. X-ray diffraction peaks are identical to those of icosahedral obtained by the melt spun technique. SAD patterns from MA samples indicate 2,3,6 and 5-fold symmetry. Annealing of the MA icosahedral phases leads to the formation of related cubic Frank-Kasper phases, that can be transformed into the icosahedral phases by MA. The disclination network which appears in the cubic phase plastically deformed by MA seems to be intrinsic to producing an aperiodic phase with long-range icosahedral order.</p></div>","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 2","pages":"Pages 167-172"},"PeriodicalIF":0.0,"publicationDate":"1989-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80026-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87815276","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}
Pub Date : 1989-06-01DOI: 10.1016/0168-7336(89)80023-3
J.E. Sueiras , P. Salagre, J.L.G. Fierro
Substitution of Sr2+ for La3+ in strontium orthovanadates gives materials with interesting bulk and surface properties.
The results indicate that there are correlations between increasing selectivities to formaldehyde and (i) the decreasing crystallinity of the mixed vanadates, (ii) the increasing La migration from the surface towards the bulk, (iii) the decreasing initial temperature of reduction of V5+ in the catalysts.
The migration of the La3+ could leave the oxygen of the crystal structure more accessible to the reducing hydrogen (during TPR measurements) and to the reactants in the catalytic methanol oxidation. This La3+ migration into the bulk may also be the cause of the loss of the crystallinity. In addition the La3+ vacancies in the isostructural mixed vanadate catalysts should be responsible for their selectivities in the oxidation of methanol to formaldehyde.
{"title":"Synthesis and characterization of several La3+ and Sr2+ vanadates, active as methanol oxidation catalysts","authors":"J.E. Sueiras , P. Salagre, J.L.G. Fierro","doi":"10.1016/0168-7336(89)80023-3","DOIUrl":"10.1016/0168-7336(89)80023-3","url":null,"abstract":"<div><p>Substitution of Sr<sup>2+</sup> for La<sup>3+</sup> in strontium orthovanadates gives materials with interesting bulk and surface properties.</p><p>The results indicate that there are correlations between increasing selectivities to formaldehyde and (i) the decreasing crystallinity of the mixed vanadates, (ii) the increasing La migration from the surface towards the bulk, (iii) the decreasing initial temperature of reduction of V<sup>5+</sup> in the catalysts.</p><p>The migration of the La<sup>3+</sup> could leave the oxygen of the crystal structure more accessible to the reducing hydrogen (during TPR measurements) and to the reactants in the catalytic methanol oxidation. This La<sup>3+</sup> migration into the bulk may also be the cause of the loss of the crystallinity. In addition the La<sup>3+</sup> vacancies in the isostructural mixed vanadate catalysts should be responsible for their selectivities in the oxidation of methanol to formaldehyde.</p></div>","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 2","pages":"Pages 131-141"},"PeriodicalIF":0.0,"publicationDate":"1989-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80023-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75631234","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}
Pub Date : 1989-06-01DOI: 10.1016/0168-7336(89)80025-7
M.P.Sridhar Kumar, B. Viswanathan, C.S. Swamy, V. Srinivasan
Impurities in hydrogen affect the storage capacity of intermetallic systems. Carbon monoxide interacts with nickel-containing intermetallics such as CaNi5 to give volatile nickel carbonyl which leads to a fall in the transition metal content, the hydrogen storage capacity and the sorption kinetics. The implications of these effects are investigated here by X-ray Photoelectron Spectroscopy (XPS) and sorption kinetic data.
{"title":"Interaction of carbon monoxide with the hydrogen storage alloy, CaNi5; kinetic and surface studies","authors":"M.P.Sridhar Kumar, B. Viswanathan, C.S. Swamy, V. Srinivasan","doi":"10.1016/0168-7336(89)80025-7","DOIUrl":"10.1016/0168-7336(89)80025-7","url":null,"abstract":"<div><p>Impurities in hydrogen affect the storage capacity of intermetallic systems. Carbon monoxide interacts with nickel-containing intermetallics such as CaNi<sub>5</sub> to give volatile nickel carbonyl which leads to a fall in the transition metal content, the hydrogen storage capacity and the sorption kinetics. The implications of these effects are investigated here by X-ray Photoelectron Spectroscopy (XPS) and sorption kinetic data.</p></div>","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 2","pages":"Pages 157-166"},"PeriodicalIF":0.0,"publicationDate":"1989-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80025-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86150527","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}
Pub Date : 1989-06-01DOI: 10.1016/0168-7336(89)80021-X
Gert Blumenthal ∗, Gerhard Wegner
It has been found that highly reactive amorphous powders are obtained by treatment with concentrated hydrochloric acid of metakaolin or kaolin, followed by removal of the liquid by distillation and calcination of the residue. The result is a porous silica homogeneously mixed with chloride-containing alumina beginning to react with gaseous carbon tetrachloride at 450 K. At temperatures above 700 K aluminium chloride is formed in high yield and high selectivity. The reactivity of these powders is such that they are chlorinated even by gaseous silicon tetrachloride, a compound known to be stable towards metakaolinite up to 1300 K! Some advantages of technological relevance are listed in comparison to leaching and other dissolution processes.
{"title":"Preferential formation of aluminium chloride by chlorination of a highly reactive powder obtained from metakaolin or kaolin by hydrochloric acid treatment","authors":"Gert Blumenthal ∗, Gerhard Wegner","doi":"10.1016/0168-7336(89)80021-X","DOIUrl":"10.1016/0168-7336(89)80021-X","url":null,"abstract":"<div><p>It has been found that highly reactive amorphous powders are obtained by treatment with concentrated hydrochloric acid of metakaolin or kaolin, followed by removal of the liquid by distillation and calcination of the residue. The result is a porous silica homogeneously mixed with chloride-containing alumina beginning to react with gaseous carbon tetrachloride at 450 K. At temperatures above 700 K aluminium chloride is formed in high yield and high selectivity. The reactivity of these powders is such that they are chlorinated even by gaseous silicon tetrachloride, a compound known to be stable towards metakaolinite up to 1300 K! Some advantages of technological relevance are listed in comparison to leaching and other dissolution processes.</p></div>","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 2","pages":"Pages 105-113"},"PeriodicalIF":0.0,"publicationDate":"1989-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80021-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88229541","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}
Pub Date : 1989-04-01DOI: 10.1016/0168-7336(89)80010-5
J. Słoczyński
{"title":"Autocatalytic effect in MoO3 reduction in hydrogen","authors":"J. Słoczyński","doi":"10.1016/0168-7336(89)80010-5","DOIUrl":"10.1016/0168-7336(89)80010-5","url":null,"abstract":"","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 1","pages":"Pages 83-88"},"PeriodicalIF":0.0,"publicationDate":"1989-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80010-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81591535","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}
Pub Date : 1989-04-01DOI: 10.1016/0168-7336(89)80007-5
C. Vinckier ∗, S. De Jaegere
Some mechanistic aspects of the atomization processes in the afterglow of microwave-induced plasmas are reconsidered. Besides lattice atomization, where only heterogeneous interactions between radicals and the solid occur, a pure gas-phase atomization process also has to be taken into account. The latter mechanism becomes dominant with the chlorides or organic salts of transition metals.
The role of charged species in the overall atomization process is found to be negligible, indicating that an electrochemical mechanism is not important in most cases.
{"title":"Mechanistic aspects of atomization processes in microwave-induced plasma afterglows","authors":"C. Vinckier ∗, S. De Jaegere","doi":"10.1016/0168-7336(89)80007-5","DOIUrl":"10.1016/0168-7336(89)80007-5","url":null,"abstract":"<div><p>Some mechanistic aspects of the atomization processes in the afterglow of microwave-induced plasmas are reconsidered. Besides lattice atomization, where only heterogeneous interactions between radicals and the solid occur, a pure gas-phase atomization process also has to be taken into account. The latter mechanism becomes dominant with the chlorides or organic salts of transition metals.</p><p>The role of charged species in the overall atomization process is found to be negligible, indicating that an electrochemical mechanism is not important in most cases.</p></div>","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 1","pages":"Pages 61-65"},"PeriodicalIF":0.0,"publicationDate":"1989-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80007-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77319272","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 kinetics of the interaction of oxygen and nitrous oxide with the (100) silicon surface within the temperature range 20–830°C has been studied. At temperatures between 20 and 600°C, irreversible supermonolayer gas chemisorption occurs. At temperatures between 700 and 830°C, the character of the interaction of N2O and O2 with the silicon surface is determined by the ratio of the oxidizer pressure and the surface temperature of the sample. This results in either etching of the sample surface with relief formation or growth of a silicon dioxide layer on the surface. Reversible adsorption of the oxidizer molecules on the initially formed oxide layer experimentally observed here for the first time plays a key role in the mechanism of SiO2 formation.
{"title":"Initial stages of the interaction of nitrous oxide and oxygen with the (100) silicon surface under low pressures","authors":"M.R. Baklanov, V.N. Kruchinin, S.M. Repinsky, A.A. Shklyaev","doi":"10.1016/0168-7336(89)80002-6","DOIUrl":"10.1016/0168-7336(89)80002-6","url":null,"abstract":"<div><p>The kinetics of the interaction of oxygen and nitrous oxide with the (100) silicon surface within the temperature range 20–830°C has been studied. At temperatures between 20 and 600°C, irreversible supermonolayer gas chemisorption occurs. At temperatures between 700 and 830°C, the character of the interaction of N<sub>2</sub>O and O<sub>2</sub> with the silicon surface is determined by the ratio of the oxidizer pressure and the surface temperature of the sample. This results in either etching of the sample surface with relief formation or growth of a silicon dioxide layer on the surface. Reversible adsorption of the oxidizer molecules on the initially formed oxide layer experimentally observed here for the first time plays a key role in the mechanism of SiO<sub>2</sub> formation.</p></div>","PeriodicalId":101061,"journal":{"name":"Reactivity of Solids","volume":"7 1","pages":"Pages 1-18"},"PeriodicalIF":0.0,"publicationDate":"1989-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0168-7336(89)80002-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74527786","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}