摘要:

AbstractBorides, carbides and silicides are reviewed with special reference to newer production methods and fabrication techniques. Crystal structures and types of bonding in binary and ternary compounds are classified and discussed. The scope and limitations of the Pauling‐Rundle theory, molecular orbital treatment and the Ubbelohde‐Samsonov theory are examined critically and appropriate experimental evidence is summarised.Information so far available on the sintering of borides, carbides and silicides is summarised in relation to their chemical reactivity. The sintering is influenced by additives or impurities such as oxides formed by partial hydrolysis and oxidation. Resistance to oxidation is increased by sintering and hot pressing the refractories, but since the affinity of the metals is exclusively higher for oxygen, exchange reactions diminish the quality of the materials. Boride and carbide coatings generally have poor resistance in air or oxygen, but some silicides are more suitable. The kinetics and products of oxidation of borides, carbides and silicides so far studied depend mainly on the intrinsic reactivity of the material and the available surface at which oxidation can oc

ISSN:0021-8871    

DOI:10.1002/jctb.5010190501

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractThe principal methods of boron carbide production are compared and their thermodynamics are examined. Mechanism of carbide formation and sintering of the products are discussed and investigated further. High‐purity stoicheiometric B4C of submicron size was produced on a semi‐technical scale by reduction of diboron trioxide with carbon and magnesium. Rates of sintering were determined from changes in surface areas and average crystallite and aggreagte sizes.Sintering of boron carbide was enhanced by increased temperature and time of calcination. Addition of chromium accelerated sintering at temperatures above 1600° and especially at 1800°. For more extensive sintering, submicron powders from the magnesium reduction process were more suitable than the coarser samples given by the electro‐thermal carbon reduction; the latter required ballmilling to provide suitable grain size composition for effective hot p

ISSN:0021-8871    

DOI:10.1002/jctb.5010190502

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractA proprietary water‐soluble organic polymer (polymeric flocculant) of high molecular weight has been used to remove sediment from cooling water systems; current explanations of the mechanism are inadequate. A new flow‐cell has been designed to study sediment‐flocculant interactions under simulated practical conditions. Quantitative measurements of the conditions required for sediment removal in the flow‐cell together with flocculation tests on the same systems have been made. The effects of an inorganic coagulant on the removal mechanism have also been studied. Sediment removal is interpreted in terms of flocculation theory; flocculation of a dispersed phase is found to be essential to the removal

ISSN:0021-8871    

DOI:10.1002/jctb.5010190503

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractIn the presence of excess air the kinetics of reaction between CaO and PbO to form calcium plumbate are governed by the diffusion process described by Jander's kinetic model. The energy of activation of the process, as calculated from the Arrhenius equation, is 50 kcal/mol. In an air and nitrogen atmosphere (ratio 1:16) the reaction rate is 4–5 times slower.It has been shown that formation of calcium plumbate from pure CaO and PbO takes place between 600–800° without formation of intermediate compounds.From the results obtained it is deduced that the mechanism of formation consists of two main stages–diffusion between the CaO and PbO, substantially due to the more diffusible PbO, and chemical reaction in the presence

ISSN:0021-8871    

DOI:10.1002/jctb.5010190504

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY

摘要:

AbstractIt has been shown thatp‐nitrophenol (PNP) solution is stable only at pH ≥ 9 when PNP is in the completely ionised form. In benzene, PNP exists in a neutral molecular form. These considerations are important in the estimation of surface areas of solids by adsorption of PNP from solut

ISSN:0021-8871    

DOI:10.1002/jctb.5010190505

出版商:John Wiley&Sons, Ltd    

年代:1969

数据来源: WILEY