摘要:

AbstractA study has been made of the adhesion of chippings to a film of road tar, supported on a base plate, under conditions similar to those encountered in surface dressing, but without interlock of stone particles. Chippings are removed by inertial stresses set up in them when a carefully regulated blow is applied to the base plate.A critical adhesion temperature, above which chippings should be applied to road tar, has been shown to be about 32 deg. c below the equiviscous temperature (e.v.t.) for clean, dry basalt chippings; a lower value is shown to apply in the case of PVC‐modified tar.Results indicate that the unit reasonably simulates service conditions and its use is proposed for additional studie

ISSN:0021-8871    

DOI:10.1002/jctb.5010201101

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractDibarium silicate, Ba2SiO4, was hydrated in two ways: in paste form at 25° using a water/solid weight ratio of 0.7:1, and in a polyethylene bottle rotated on a wheel at 5°, 25° and 50°, using a water/solid weight ratio of 9.0:1. When Ba2SiO4is hydrated in paste form, the stoicheiometry of the reaction at 25° is the same as in bottle‐hydration at 50°: 2BaO.SiO2+2.2H2O = 1.2BaO.SiO2.1.4H2O+0.8Ba(OH)2. The stoicheiometry of bottle‐hydration at 5° and 25° is represented by the equation: 2BaO.SiO2+2.2H2O = BaO.SiO.1.2H2O+Ba(OH)2. Barium silicate hydrate, 1.2BaO.SiO2.1.4H2O, is well crystallised and has a specific surface area of ˜ 3m2/g. The crystals are plate‐like and have a tendency to form clusters. The low‐baria hydrate, BaO.SiO2.1.2H2O, is poorly crystallised and consists of thin platelets. It has a specific surface area of ˜ 35m2/g. The thermal dehydration of fully hydrated barium silicate and of the barium silicate hydrates was investigated by thermogravimetric and differential thermal analysis techniques.The similarities and differences between the barium silicate hydrates obtained in the hydration of barium silicate and the calcium silicate hydrates obtained in the hydration of β‐dicalcium silicate and Ca3SiO5are discussed. A mechanism of hydration of barium silicate is proposed which involves solution, precipitation and c

ISSN:0021-8871    

DOI:10.1002/jctb.5010201102

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe rate of hydration of dibarium silicate (Ba2SiO4) in paste form at room temperature was investigated. The uncombined barium hydroxide produced in the reaction, determined by a modified Franke method, was used as a measure of the extent of hydration. The linear relationship obtained between the uncombined barium hydroxide and the chemically combined water confirms that similar hydration products are formed at all stages of hydration, and either may be used as a measure of the degree of hydration. The rate of hydration of dibarium silicate was found to be lower than that of tricalcium aluminate, but higher than those of alite, tricalcium silicate and β‐dicalcium silicate. The effect of water/solid ratio on the rate of hydration was also investigated. Dibarium silicate was completely hydrated after 30 days when it was mixed with a water/solid weight ratio>0.7

ISSN:0021-8871    

DOI:10.1002/jctb.5010201103

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe kinetics of the isothermal dehydration of sheet and powdered vermiculite were studied bothin vacuoand in the presence of a constant water vapour pressure. Dehydration of the sheet form followed a first‐order mechanism bothin vacuoand in water vapour. The extent of dehydration under constant vapour pressure was greater thanin vacuo, and this is believed to be due to inhibition of the collapse of the fine structure of the dehydration product in a certain direction, thus accelerating the extent of dehydration. The energy of activation was calculated to be comparable to the latent heat of vaporisation of water, and it is suggested that this would measure the ‘heat of desorption’ of water from the surface of the dehydration product.For the dehydration of powdered vermiculitein vacuoand in water vapour, the kinetics may be discussed in conjunction with Mampel's theory of the decomposition of powders. The mechanism is interfacial, and the energy of activation is much lower than for the sheets. Diffusion plays a dominant role for powder dehydration, and in the present case it is an ‘activated diffusion’, being mainly ‘surface diffusion’ along the grain boundaries of the dehydration product. Water vapour also increases the extent of dehydration, and this could be interpreted in the same manner as for t

ISSN:0021-8871    

DOI:10.1002/jctb.5010201104

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

ISSN:0021-8871    

DOI:10.1002/jctb.5010201105

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractTitanium dioxide powders, prepared by the hydrolysis of titanyl sulphate, discolour in a vacuum. The discoloration is stable in dry oxygen or dry air, but it bleaches in the presence of water vapour. Infra‐red and thermogravimetric measurements show that the discoloration and bleaching cycle is associated with the state of adsorption of hydrogen‐bonded water by sulphate impurities on the titanium surf

ISSN:0021-8871    

DOI:10.1002/jctb.5010201106

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractSeveral solvent extraction systems were studied using a cellulose dialysis membrane as an artificial phase boundary separating one solvent phase from the other. Solutes were allowed to come to extraction equilibrium by permeation through the membrane. The rate of permeation depended on the osmotic properties of the solute, such as the molecular size and the presence of colloidal species. The extraction equilibrium was established by the solvent‐extraction properties of the solute in each system, and the equilibrium was approached through the cellulose membrane by a first‐order kinetic process. The method appears to be useful for ‘packaging’ organic solvents in membrane containers to be used for extractions in which time is not a factor. In certain cases, equally well extracted solutes, such as zirconium and aluminium 8‐hydroxyquinolates, can be separated because one solute exists as a partially colloidal material [Zr(IV)] and hence does not pass through the membran

ISSN:0021-8871    

DOI:10.1002/jctb.5010201107

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY