Zinc oxide powder

In their original form these cements came as a zinc oxide powder and a concentrated solution of poly(acrylic acid) (Wilson, 1975b). Since then they have been subject to a number of chemical modifications. 

Zinc oxide powder 85-2-96-8% ZnO 4-73-10-06% MgO Poly(acrylic acid) solution 32-4-42-9 %... 

Attempts have been made to improve the mechanical properties of these cements by adding reinforcing fillers (Lawrence Smith, 1973 Brown Combe, 1973 Barton et al, 1975). Lawrence Smith (1973) examined alumina, stainless steel fibre, zinc silicate and zinc phosphate. The most effective filler was found to be alumina powder. When added to zinc oxide powder in a 3 2 ratio, compressive strength was increased by 80 % and tensile strength by 100 % (cements were mixed at a powder/liquid ratio of 2 1). Because of the dilution of the zinc oxide, setting time (at 37 °C) was increased by about 100%. As far as is known, this invention has not been exploited commercially. 

Later, better cements appeared based on c. 50% solutions of orthophosphoric acid. But even these were far from satisfactory. As always with dental cements, the problems revolved around the control of the setting reaction the reaction between zinc oxide and orthophosphoric acid was found to be far too fierce. By the time of Fleck s 1902 paper these problems had been solved. The importance of densifying and deactivating the zinc oxide powder to moderate the cement reaction had been recognized. Of equal importance was the realization that satisfactory cements could be produced only if aluminium was incorporated into the orthophosphoric acid solution. The basic science underlying this empirical finding was elucidated only in the 1970s. 

Interesting attempts have been made to formulate water-setting cements by blending solid acid phosphates with the zinc oxide powder. The cement is then prepared by mixing this powder blend with water. These attempts may be considered to have failed. 

A more successful approach was that of Higashi et al. (1969a,b 1972). They blended solid add phosphate salts with zinc oxide powder. One add salt used was a predpitated hydrate of ZnH2P04. The cement was formed by mixing this powder blend with water. Work progressed to the point where three commercial brands of these so-called hydrophosphate cements appeared on the market. None met the spedfication requirements... 

The cementition reaction between zinc oxide powder and aqueous zinc chloride was found to be both rapid and extremely exothermic. Although at least four days equilibration was allowed before examining any of the cements in detail, Sorrell found evidence that reaction was complete within 20 to 30 minutes and occurred without observable development of intermediate phases. He also found that, as the concentration of reactants was increased, so reaction rate increased until, at sufficiently high concentrations, reaction occurred too quickly to allow proper mixing of the reactants. Preheating the zinc oxide at 900 °C for 16 hours was found to slow the reaction down, but only slightly. 

The physical and chemical characteristics of zinc oxide powders are known to affect cement formation (Smith, 1958 Norman et al., 1964 Crisp, Ambersley Wilson, 1980 Prosser Wilson, 1982). The rate of reaction depends on the source, preparation, particle size and surface moisture of the powder. Crystallinity and lattice strain have also been suggested as factors that may change the reactivity of zinc oxide powders towards eugenol (Smith, 1958). 

The heat treatment of zinc oxide powders reduces their reactivity towards eugenol, because of an increase in particle size or a decrease in absorbed water. In the case of zinc oxide powders prepared by the thermal... 

Some materials intended for temporary cementation and cavity lining are formulated as two pastes. One paste is formed by blending the zinc oxide powder with a mineral or vegetable oil and the other by mixing an inert filler into the liquid. These cements are much weaker, with... 

The ZOE impression paste is essentially a two-paste ZOE cement. One paste is formed by plasticizing the zinc oxide powder with 13 % of mineral or vegetable oil. The other paste consists of 12% eugenol or oil of cloves, 50% polymerized rosin, 20% silica filler, 10% resinous balsam (to improve flow) and 5 % calcium chloride (accelerator). 

All cements that contain eugenol inhibit the polymerization of acrylates, and those of EBA-eugenol are no exception. In order to remedy this and other defects, Brauer and his coworkers examined alternatives to eugenol (Figure 9.7). These included the esters of vanillic acid (3-methoxy-4-hydroxybenzoic acid, HV) and syringic acid (3,5-dimethoxy-4-hydroxy-benzoic acid). Both are 3-methoxy-4-hydroxy compounds and are thus chemically related to eugenol and guaiacol. Both are solids and have to be dissolved in EBA where they form satisfactory cements with EBA zinc oxide powder. The vanillate (EBA-HV) cements are the more important. 

Brauer, Stansbury Flowers (1986) modified these cements in several ways. The addition of various adds - acetic, propionic, benzoic etc. -accelerated the set. The use of zinc oxide powders coated with propionic add improved mixing, accelerated set, reduced brittleness and increased compressive strength from 63 to a maximum of 72 MPa. The addition of plasticizing agents such as zinc undecenylate yielded flexible materials. Incorporation of metal powders had a deleterious effect and greatly increased the brittleness of these cements. The addition of fluorides was not very successful, for fluoride release was not sustained. 

Although most pharmaceutical colorants in use today are of synthetic origin, a few are obtained from natural mineral and plant sources. For example, red ferric oxide is mixed in small proportions with zinc oxide powder to prepare calamine, giving the latter its characteristic pink color, which is intended to match the skin tone upon application. 

The critical factor in the development of the syndrome is the size of the ultrafine zinc oxide particles produced when zinc is heated to temperatures approaching its boiling point in an oxidizing atmosphere." The particles must be small enough (with formation of larger particles that are deposited in the upper respiratory tract and do not penetrate deeply into the lungs. ... 

Powder for external use e.g. NEBASULF, boric acid powder, zinc oxide powder, talc etc. Tooth powder may also be classified under this group. 

Zinc polycarboxylate, the first polyelectrolyte dental material, was developed and used as early as 1968 [124]. These materials are formed by the reaction of a zinc oxide powder with an aqueous solution of poly(acrylic acid). The zinc ions cross-link the polyacid chains and form a cement. A few years after the development of zinc polycarboxylate cements, Wilson and Kent introduced the first glass-ionomer cement (GIC) [125]. Glass-ionomer cements are formed... 

Morrison and Miller (33) have made some direct measurements on the adsorption of oxygen on zinc oxide powder (Fig. 4), which seem in accord with the conductivity measurements of Bevan and Anderson on sintered zinc oxide. The reversible region of chemisorption was shown to be above about 45O C, corresponding to the reversible region of conductivity versus oxygen pressure found by Bevan and Anderson to be above about 500°C. 

Zinc electrodes for secondary silver-zinc batteries are made by one of three general methods the dry-powder process, the slurry-pasted process, or the electroformed process The active material used in any of the processes for the manufacture of electrodes is a finely divided zinc oxide powder, USP grade 12. 

Fig. 3. Zinc oxide powder particle of 10 5 cm diameter, (a) Dark adapted, (b) light adapted (adapted from Ruppel, Gerritsen and Rose 461)...

This effect of seed addition is illustrated in Fig. 3.8 for the dry granulation of carbon black powder tumbled in a drum [17]. The time required to convert the whole load to granules is reduced as the proportion of recycled agglomerates and their size are increased. For the dry granulation of zinc oxide powders, Meissner et al. [18] found that the initial rate of fines disappearance, (dW/dN)N=0, in the presence of seed granules is given by ... 

For high-temperature applications, sauereisen cement (Omega CC cement) and zinc oxychloride (dental cement) are useful irreversible cements. Sauereisen cement is made by suspending ceramic powders in sodium silicate solution ( water glass ). This cement sets very hard and withstands temperatures up to 1000°C. Zinc oxychloride is made by mixing calcined zinc oxide powder with concentrated zinc chloride solution. One can also use a ceramic putty (Omega CC high-temperature cement), which must be cured at 180°C and is then serviceable up to 850°C. 

Tablets (e.g., quinapril hydrochloride) Capsules (e.g., pancrease) Oral suspensions (e.g., cefuroxime axetil) Injectables (e.g., coumadin) Sterile powders (e.g., cefoxitin) Topicals (e.g., zinc oxide powder) Anti-infectives (e.g., erythromycin ethyl succinate) Anti-coagulants (e.g., warfarin sodium) Anti-asthmatics (e.g., montelukast sodium) Anti-psychotics and anxiolytics Hypnotics and anticonvulsants (e.g., barbiturates) Anti-hypertensives Anti-inflammatories (e.g., indomethacin) Analgesics (e.g., aspirin) Antacids (e.g., aluminum hydroxide) Diuretics Enzymes (e.g., pancreatin) Hormones...

Hazard Zinc oxide fume is harmful by inhalation. Zinc oxide powder reacts violently with chlorinated rubber at 215C. TLV (fume) 5 mg/m3. 

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