The proceedings of the 4th International Conference on Sin tering and Related Phenomena, contained in this volume, have been broadened in scope to include the phenomena of sintering and coa lescence of catalytic materials dispersed upon refractory oxides. For it has long been recognized within the circles of chemists and chemical engineers working in the field of catalysis that one of the chief causes of the decline in heterogeneous catalytic activity and/or selectivity is, indeed sintering, or perhaps using a better term, coalescence of the supported catalytic metal and compounds thereof. Essentially catalytic deactivation by sintering is now weIl recognized as Ostwald ripening; which of course is a phenome non familiar to scientists grappling with the problem of sintering of powder compacts. The 4th Conference at Notre Dame marks the first occasion at which scientists and engineers of each discipline were assembled in the same room to exchange views on these phenome na of mutual concern. In the wake of the Conference at Notre Dame, all parties acknowledged the synergistic benefit which issued from this exchange, both at the formal and informal level. All were persuaded that signal benefits will be realized by a continuation of this collab oration in the form of future sintering conferences in which both powder metallurgists and catalytic scientists and engineers would participate.

The Sixth International Conference on Sintering and Related Phenomena took place at the University of Notre Dame, Notre Dame, Indiana June 6-8, 1983. This conference was also the twentieth Conference on Ceramic Sciences organized yearly by a "confederation" of four institutions: North Carolina University at Raleigh, N.C., the University of California at Berkeley, CA, Alfred University at Alfred, NY and the University of Notre Dame, Notre Dame, IN. The papers presented at the last Notre Dame conference collect ed in this volume, reflect the progress in our understanding of the process of sintering achieved in the past four years. It seems that the analysis of the two particle models is finally extended to the analysis of the models of compacts. In these investigations strong emphasis is put on pore-grain boundar ies interaction which appear to be central to this problem. It is to be hoped that in the near future an adequate model of the compact will be developed which may serve as a useful basis of powder tech nology. Also, the effects of atmosphere on the sintering of ceramics after a long period of neglect, seem to attract the attention of more workers in the field.

The Sixth International Conference on Sintering and Related Phenomena took place at the University of Notre Dame, Notre Dame, Indiana June 6-8, 1983. This conference was also the twentieth Conference on Ceramic Sciences organized yearly by a "confederation" of four institutions: North Carolina University at Raleigh, N.C., the University of California at Berkeley, CA, Alfred University at Alfred, NY and the University of Notre Dame, Notre Dame, IN. The papers presented at the last Notre Dame conference collect ed in this volume, reflect the progress in our understanding of the process of sintering achieved in the past four years. It seems that the analysis of the two particle models is finally extended to the analysis of the models of compacts. In these investigations strong emphasis is put on pore-grain boundar ies interaction which appear to be central to this problem. It is to be hoped that in the near future an adequate model of the compact will be developed which may serve as a useful basis of powder tech nology. Also, the effects of atmosphere on the sintering of ceramics after a long period of neglect, seem to attract the attention of more workers in the field.

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Most catalysts used in the chemical and petrochemical indus tries are strongly affected by one or another form of deactivation, leading to poor performances and reduced life. The increasing num ber of scientific communications devoted to the subject in recent years, and culminating with an International Symposium held in Antwerp in October 1980, is a measure of the interest it arouses in both the industrial and academic communities. A stage has been reached whereby it was thought that a NATO Advanced Study Institute on "Catalyst Deactivation" might be fruit ful in establishing the state of the art and in stimulating a more systematic research on the phenomenon. Such a meeting was held ~n Lagos, Portugal, from 18 to 29 May 1981. The purpose of the Institute was to present and discuss in a didatic and systematic way the various processes that lead to cata lyst deactivation, namely coking, poisoning and solid state trans formations, and at the same time to promote the exchange of ideas and experiences among the participants, drawn from industry and uni versity. The lectures presented at the Institute are collected in this volume with the exception of Dr. L.L.Hegedus "Catalyst Poisoning", which has been previously published (Catalysis Reviews, Science md Engineering, 23, 377-476, 1981).

Catalytic oxidation processes are bf central importance to a substantial part of large-scale chemical industry. Indeed, this area of industrial catalysis has an extremely long history which stretches back well into the last century. The development and growth of catalytic oxi dation processes for the manufacture of commodities such as sulfuric acid and nitric acid can be viewed as indicators for the growth of the early and middle years of the entire inorganic chemical industry, and in an analogous fashion the manufacture of products such as phthalic anhydride, maleic anhydride and ethylene oxide has been central to the development of an organic chemical industry. We should all be able" to learn from history, and present-day scientists and technologists will find considerable benefit in following the account of the historical development of catalytic oxidation processes presented in Chapter I by Drs. G. Chinchen, P. Davies and R. J. Sampson. Alkenes are important intermediates in many processes in organic chemical industry. Being mostly petroleum derived, the alkene availability pattern does not necessar ily match consumption requirements and an alkene inter conversion process such as metathesis is clearly of in dustrial importance. In fact alkene metathesis, in addi tion to its industrial significance, poses an interesting mechanistic problem. upon which considerable effort has been expended in recent years and which is now fairly well understood.