ABSTRACT
Pure electrostatically stabilized aqueous alumina suspensions were prepared at various solid loadings in order to study the influence of temperature on the surface charge properties and rheology. Surface charge density at various temperatures was measured through potentiometric titration, and the analysis of the potentiometric data was accomplished using the constant capacitance surface model. Calculations of the pair-wise interaction potential between charged colloidal spheres dispersed in water were then carried out using conventional DLVO theory and a software package Stabil45, taking into account the temperature dependence of surface charge density and dielectric constant. The results showed that increasing temperature leads to a gradual diminution of alumina surface ionization, dielectric constant, and a total energy barrier for coagulation. The enhancement of the coagulation rate with increasing temperature leads to a gradual increase of both relative apparent viscosity and thixotropy. Copyright 2000 Academic Press.
ABSTRACT
The surface charge properties of well and poorly ordered kaolinite and halloysite-7Å, representing three different stages of kaolinite to halloysite-7Å transformation identified in the kaolin deposit of São Vicente de Pereira (Portugal), were studied. Mineralogical (X-ray diffraction, Fourier transformation-infrared) and chemical data (analytic electron microscopy) showed that the gradual transformation from kaolinite to halloysite-7Å minerals was accompanied by an increase in hydration and a decrease in Si/Al ratio. In particular, the replacement of Si(IV) by Al(III) in the tetrahedral layer caused an electrical charge unbalance and a modification of surface charge properties during the kaolinite to halloysite transformation. Accordingly, the cation exchange capacity (CEC) gradually increases when passing from well-ordered kaolinite to halloysite-7Å, attesting the direct correspondence existing among the structural order of the samples, number of tetrahedral substitutions, and CEC. Electrophoretic experiments provided further evidences of the origin of surface charge properties and the variation encountered during kaolinite to halloysite-7Å transformation. The curves of zeta-potential versus pH show the same pH dependency for the three minerals, but a gradual increase of zeta-potential when passing from well ordered kaolinite to halloysite-7Å through the poorly ordered kaolinite. The results can unambiguously be attributed to the increase of permanent charge due to the higher degree of isomorphic substitution, more than to the increase of structural and ionizable water. Copyright 1999 Academic Press.
ABSTRACT
Of 18 operations 16 bone implantations were successful. The mean age of the patients was 13 years. Also the operational technique employed by the authors is described. For bone implantation autotransplantatum taken from the crista iliaca was employed.
Subject(s)
Bone Transplantation , Cleft Palate/surgery , Adolescent , Cleft Lip/surgery , Humans , Male , Surgery, PlasticSubject(s)
Knee Prosthesis/standards , Aged , Female , Follow-Up Studies , Humans , Hungary , Male , Middle Aged , Prosthesis DesignSubject(s)
Knee Prosthesis , Aged , Female , Follow-Up Studies , Humans , Knee Joint/pathology , Knee Prosthesis/adverse effects , Male , Middle Aged , Surveys and QuestionnairesABSTRACT
Authors report on their experiments and observations with knee endoprostheses. On reason of the high price of imported prostheses the home production of implantates is urged. They reported in a preliminary paper in 1977 on the insertion of the first knee prosthesis made in Hungary. Since this time in 36 instances have been inserted without complication their titanium-polyamid and stainless steel-polyamid sledge type prostheses (a total of 42 pairs of 32 patients). After 2 years follow up the results can be classified as "very good". A new improved model of knee prosthesis is under elaboration.
Subject(s)
Knee Prosthesis/methods , Arthritis, Rheumatoid/diagnostic imaging , Arthritis, Rheumatoid/surgery , Humans , Knee Injuries/diagnostic imaging , Knee Injuries/surgery , Knee Prosthesis/instrumentation , RadiographyABSTRACT
The authors introduce the definitive treatment according to the current principles in traumatology by demonstrating the reconstruction of a severe open maxillofacial injury. Attention is drawn to the most frequent mistakes.
Subject(s)
Maxillofacial Injuries/surgery , Surgery, Plastic , Accidents, Traffic , Adult , Anti-Bacterial Agents/administration & dosage , Dentures , Fracture Fixation, Internal , Fractures, Open/surgery , Humans , Male , Suture Techniques , Wound Healing , Wound Infection/prevention & controlABSTRACT
Report on cranioplasty by prefabricated plastic implants, reinforced by stainless steel meshes resp. plates or by glass fibre meshes. In frontal cranioplasties the missing orbital roof was reconstructed by the same technique. To avoid infections the nasal sinuses were sealed by a pedicled mucosal flap resp. a free transplanted flap taken from the periosteum of the tibia. All 39 patients operated on this way during the last 6 years are free of complaints and clinical symptoms.
