Layered ceramic composites via control of electrophoretic deposition kinetics

The article summarises optimisation of electrophoretic deposition of alumina and zirconia from concentrated isopropanolic suspensions stabilised by monochloracetic acid. Method for in situ monitoring of deposited mass was developed and experimentally checked. Prediction of electrophoretic deposition kinetics was based on the voltage drop measurement and electrophoretic mobility estimation from experimental kinetics data. It was shown that voltage change during electrophoretic deposition did not affect relative density of the deposited layers in the laminates prepared. For this purpose a method of the relative density measurement using the microscopic measurement of relative shrinkage of individual layers was developed. Accuracy of the method was confirmed by comparison with shrinkage measurement using high temperature dilatometry. Adopting obtained results the alumina/zirconia laminate with precise control of layers thicknesses and final densities was prepared.     

On the determination of the stress-free temperature for alumina–zirconia multilayer structures

Internal residual stresses can enhance the fracture resistance and mechanical reliability of layered ceramics. The magnitude of the stresses depends on the elastic and thermal properties of the layers and the typically assumed reference (stress-free) temperature, below which internal stresses develop. A novel combined experimental and numerical simulation approach has been developed to determine the reference temperature and experimentally proved in alumina–zirconia ceramic laminates. Dilatometric data of monolithic phases are input for the numerical simulation and experimental data on the laminate properties are used for the stress-free temperature determination. In contrast to typical assumptions, reference temperature very near the sintering temperature (i.e. approx. T_ref≈1470 °C) was found, which should be considered for the estimation of internal (residual) stresses in alumina/zirconia-based layered ceramics.     

Correspondence between DSM-III-R and DSM-IV attention-deficit/hyperactivity disorder

OBJECTIVE: To evaluate the correspondence between DSM-III-R and DSM-IV definitions of attention-deficit/hyperactivity disorder (ADHD) in clinically referred children. Results of the field trials led to the hypothesis that there would be a strong correspondence between DSM-III-R and DSM-IV subtypes. METHOD: The sample consisted of all children and adolescents consecutively referred to a pediatric psychopharmacology clinic (N = 405). Children were comprehensively evaluated with structured diagnostic interviews assessing both DSM-III-R and DSM-IV ADHD. DSM-III-R symptoms were used to approximate DSM-IV subtypes. Kappa statistics and conditional probabilities were used to examine the correspondence between DSM-III-R and DSM-IV ADHD. RESULTS: Ninety-three percent of children who received a DSM-III-R diagnosis of ADHD also received a DSM-IV ADHD diagnosis. The kappa coefficient assessing the agreement between DSM-III-R and DSM-IV ADHD was .73 (z = 14.6, p < .0001). The kappa coefficient assessing the agreement between the DSM-III-R-approximated subtypes and the actual DSM-IV subtypes was .71 (z = 15, p < .0001). CONCLUSION: These results confirm previous findings and indicate that the change from DSM-III-R to DSM-IV results in minimal changes in case identification and provides support for diagnostic continuity between the two classification systems.     

Flow method for study of gas transport in polymers. Application to the study of oxygen,nitrogen, and carbon dioxide permeation through cellulose acetate membranes

Transient permeation of oxygen, nitrogen, and carbon dioxide through certain cellulose acetate (CA) dense membrances made from solutions in dioxane and dioxane-added ethanol were studied by the flow method. In order to explain the overshoots for transient permeation rates in the latter case, a new model is proposed. It postulates a time-dependence solubility coefficient, in the form of a series of exponential terms, which is combined in Fick's second law and solved. The model fits well the obtained permeation kinetics, leading to values of the diffusion, and permeation coefficients, and the structure change-related time. The overshoots are explained by the formation of unstable structure from dioxane-ethanol solvent mixtures, a memory effect of aggregated chains, which undergoes consolidation upon gas penetration. The stable state which results from the consolidation process is the same as that of membrances obtained from pure dioxane solutions. © 1994 John Wiley & Sons, Inc.     

Risk Factors Indoors and Prevalences of Childhood Respiratory Health in Four Countries in Western and Central Europe

Abstract The prevalence of respiratory symptoms and risk factors were gathered in four study centres in Western and Central Europe as part of an EU-funded multi-centre study addressing the use of small area methods in air pollution epidemiology (SAVI-AH). The study was carried out in Prague (CZ), Poznan (PL), Huddersfield (UK) and Amsterdam (NL). Prevalences of respiratory symptoms and risk factors between the centres were compared, and associations between risk factors and respiratory symptoms were calculated. Respiratory health was assessed by a self-administered questionnaire, distributed among parents or guardians of schoolchildren between the age of 7 and 11 years. Life-time wheezing and attacks of shortness of breath showed highest prevalences in Huddersfield (30% and 14%, respectively); usual cough showed highest prevalence in Poznan (27%). Differences in prevalence between the centres were found for the potential determinants “age” (due to different age ranges), “gas cooking” (highest in Amsterdam and Poznan), gas/coal heating (lowest in Central European centres), home dampness (highest in Western European centres), disturbance by traffic (highest in urban centres), maternal smoking (highest in Central European centres), family history (highest in Huddersfield) and education (highest in Huddersfield). The prevalence of pets in the home differed only slightly between the study centres. Of the potential deteminants studied, gender, family history of allergic diseases, dampness of the home and, to a lesser extent, passive smoking were important risk factors for life-time prevalence of respiratory symptoms in schoolchildren.     

The properties of fluorocarbon films prepared by r.f. sputtering and plasma polymerization in inert and active gas

Fluorocarbon films were prepared on glass slides by (i) the r.f. sputtering of PTFE in glow discharges operated in the target emission alone and with argon added and (ii) the plasma polymerization of CF₄ gas on substrates at floating or near plasma potential. Fluorine active groups released during plasma polymerization readily reacted with the soda lime silicate substrates used and polymer growth was prevented on substrates which developed a high negative bias that resulted in sputtering. Scanning electron microscopy showed that films prepared by both techniques were continuous and pinhole free. The coefficient of static friction was measured for glass and steel on the fluorocarbon deposits using the method of detecting movement of a rider on a plane of variable inclination. The friction coefficient for the films was between 2 and 4 times that of the bulk polymer irrespective of the mode of film formation, the rate of growth and the thickness in the range 300–26000 Å. The sputtered PTFE films were yellow tinted and optically absorbing in the UV and blue region of the visible spectrum, indicating fluorine deficiency in their composition. The plasma-polymerized films were neutral in transmission but had a slightly lower transmittance for visible light which could have arisen from scattering by an etched substrate. Measurement of the refractive index (Na_D) of a large number of films gave an average value of 1.35 independent of their thickness or production method. The average index value is approximately 7% less than the value for bulk PTFE derived from the reported dielectric constant. A reduction in index xould arise if the deposited films had a lower density than the bulk polymer.