Search results for "Zinc phosphate"
showing 10 items of 12 documents
A study of thin surface layers by multilayer Mössbauer spectroscopy /MMS/
1990
A stacking Mossbauer technique, MMS has been applied for studying thin surface layers. The surface layers formed on the57Fe film in aqueous solutions of corrosion inhibitors, such as zinc phosphate and barium metaborate, and in distilled water was studied by this method. It has been found that the corrosion is much slower in the presence of zinc phosphate and barium metaborate. XPS analysis suggests the formation of a mixed iron zinc phosphate on the surface of the57Fe film after corrosion in a zinc phosphate solution.
Sealing ability of five different retrograde filling materials.
1996
The sealing ability of Amalgam, Harvard-Cement, Diaket, gold-leaf, and Ketac-Endo as retrofilling materials was investigated. Paper cones were fixed with Harvard-Cement in the instrumented roots of 100 extracted human incisors. Apicectomy was performed and a 2-mm-deep retrograde cavity was prepared. Teeth were assigned to five groups (n = 20); each group received a different filling material. Surfaces of the roots were isolated with nail polish. Teeth, were stored in 1% methylene blue dye for 72 h. Roots were sectioned, and the depth of dye penetration was evaluated through a stereomicroscope. Retrofills with Ketac-Endo showed significantly less leakage compared with amalgam. There was no s…
Applications of conduction calorimetry to the setting reaction of zinc phosphate dental cement
1999
The kinetics of the exothermic setting reaction of zinc phosphate dental cement can be successfully investigated by conduction calorimetry. The primary objective of this study is to examine the effects arising from the addition of various additives to the liquid and calcination of cement powder. The rate of heat evolution versus time shows the occurrence of merely one maximum. In the case of unmodified orthophosphoric acid a sharp peak occurs early after onset of mixing due to the formation of crystalline α-hopeite. Commercial cement liquids contain aluminum and zinc. From the calorimetric curves it has been found that these cations act as a setting retarders, and ensure sufficient working …
Thermally highly stable amorphous zinc phosphate intermediates during the formation of zinc phosphate hydrate.
2015
The mechanisms by which amorphous intermediates transform into crystalline materials are still poorly understood. Here we attempt to illuminate the formation of an amorphous precursor by investigating the crystallization process of zinc phosphate hydrate. This work shows that amorphous zinc phosphate (AZP) nanoparticles precipitate from aqueous solutions prior to the crystalline hopeite phase at low concentrations and in the absence of additives at room temperature. AZP nanoparticles are thermally stable against crystallization even at 400 °C (resulting in a high temperature AZP), but they crystallize rapidly in the presence of water if the reaction is not interrupted. X-ray powder diffract…
Corrosion protection of Nd–Fe–B type permanent magnets by zinc phosphate surface conversion coatings
2001
Abstract The use of protective zinc phosphate top coatings to protect Nd–Fe–B type permanent magnets against corrosion is discussed. The progress of the phosphatisation process has been tested by simultaneous measurement of pH near surface, corrosion potential, substrate mass loss and phosphate coating mass gain. The corrosion behaviour of the magnet in phosphate solution was analyzed by the anodic polarization technique and the general resistance of the magnet to corrosion was evaluated by the Akimov drop test. It is shown that immersion of the magnet in the acidified (pH=2) phosphating solution containing Zn(II), nitrate and fluoride ions resulted in the formation of well adhered, thin an…
Vibrational analysis of iron and zinc phosphate conversion coating constituents
2001
Abstract The FT-MIR/FT-FIR and NIR-FT-Raman spectra of orthorhombic α -Zn 3 (PO 4 ) 2 ·4H 2 O (α-hopeite) and monoclinic Zn 2 Fe(PO 4 ) 2 ·4H 2 O (phosphophyllite), including deuterated samples, have been measured in the polycrystalline state at room temperature and below. The distribution of vibrational levels was related to the results of complete unit-cell group analyses. The number of uncoupled OD stretching modes of α-hopeite (isotopically dilute samples) strongly exceeds that expected from the number of hydrogen positions of the structure reported. In contrast, unequivocal assignment of the four hydrogen bonds of phosphophyllite has been performed. The distortion of the phosphate tetr…
In-Situ DRIFT Spectroscopic Investigation on the Chemical Evolution of Zinc Phosphate Acid−Base Cement
2000
Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been used to follow the chemical evolution of zinc phosphate acid−base cement (ZPC), which has been prepared from unmodified, as well as from aluminum- and zinc-modified orthophosphoric acid. For the first time, amorphous dizinc cyclotetraphosphate octahydrate, Zn2P4O12·8H2O, although hydrolytically instable, has been observed as precursor phase prior to crystallization of α-hopeite, α-Zn3(PO4)2·4H2O, in both systems. Within minutes from onset of mixing the infrared spectrum of unmodified ZPC is dominated by the characteristic vibrations of α-hopeite, due to matrix crystallization. Setting of modified ZPC is strongly af…
Synthesis and characterization of α-hopeite, Zn3(PO4)2·4H2O
1999
Orthorhombic α-Zn3(PO4)2·4H2O, α-hopeite, was synthesized from an aqueous solution of zinc acetate and orthophosphoric acid. The synthesis from these starting materials yielded best results with respect to purity and crystallinity. Structural characteristics of the compound were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA). Supplemental data came from surface area, particle size distribution, and density measurements. The obtained compound proved to be highly crystalline and stoichiometric. Dehydration of α-hopeite is accompanied by at least two endothermic effect…
Effect of thermocycling with or without 1 year of water storage on retentive strengths of luting cements for zirconia crowns
2015
Abstract Statement of problem Bond stability between zirconia crowns and luting cement and between cement and dentin is a main concern; however, only limited evidence is available as to its longevity. Purpose The purpose of this in vitro study was to measure the retentive strengths of 7 self-adhesive cements (RelyX Unicem Aplicap, RelyX Unicem Clicker, RelyX Unicem 2 Automix, iCEM, Maxcem Elite, Bifix SE, SpeedCem), 2 adhesive cements with self-etch primers (Panavia 21, SEcure), 1 glass ionomer cement (Ketac Cem), 1 resin-modified glass ionomer cement (Meron Plus), and 1 zinc phosphate cement for luting zirconia crowns (LAVA) to extracted teeth after thermocycling with or without 1 year of …
Vertical root fracture in endodontically treated teeth: A review of 25 cases
2001
Abstract Objective: We sought to examine the clinical conditions under which 25 endodontically treated teeth underwent vertical root fracture (VRF) and to relate this condition to the time elapsed from endodontic treatment to fracture. Study Design: This was a retrospective study in which we reviewed 25 case histories of patients with postendodontic VRF and studied the effect of various pretreatment and posttreatment factors as they related to VRF. Results And Conclusions: The mean time to VRF was 54 months; this was not significantly influenced by the presence or absence of prior restoration or by the presence or absence of a crown fitting. The use of a prefabricated, cylindrical, cemented…