Zinc oxide ceramic powders

Fig. 5. Total reflectance spectra (diffuse and specular components) for three commercial zinc oxide ceramic powders.

Two types of oxidation reactions are of interest in ceramics oxidation of metals and oxidation of sulfides. The oxidation of sulphides is a common extractive metallui cal process, generating an oxide ceramic powder. The oxide product is usually an intermediate product on the way to metal production but if sufficiently pure it can be used directly as a ceramic powder. A common example is the roasting of zinc sulphide to form zinc oxide,... 

Zinc oxide (ZnO) powders are technologically attractive materials due to their inherent characteristics such as dielectric, piezoelectric, pyroelectric and semiconducting properties. To improve the varistor effect and achieve high breakdown fields from ZnO ceramics it is required to have a microstructure with uniformly distributed smaller grains. The grain size for conventional ZnO varistors is larger than 2.0 /rm (Chu, 2000). Note, however, that... 

Zinc oxide is a semiconducting ceramic used to make varistors (variable resistors). Write a balanced equation for the hydrolysis of zinc ethoxide in the sol-gel method for making ZnO powders. 

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. 

Haiyan X, Hao W, Zhang Y, Cai H, Liang W, Mankang Z, et al. Hydrothermal synthesis of zinc oxide powders with controllable morphology. Ceram Int 2004 30 93-7. 

Today, gas-phase processing plays an important role in the commercial production of a number of ceramic powders. These include titanium dioxide, carbon black, zinc oxide, and silicon dioxide. The total annual output of these materials is on the order of 2 million tons. The physical processes involved in gas-phase synthesis are typical of those involved in solution-phase synthesis—chemical reaction kinetics, mass transfer, nucleation, coagulation, and condensation. 

Fused-salt electrolysis of K2NbFy is not an economically feasible process because of the low current efficiency (31). However, electrowinning has been used to obtain niobium from molten alkaU haUde electrolytes (32). The oxide is dissolved in molten alkaU haUde and is deposited in a molten metal cathode, either cadmium or zinc. The reaction is carried out in a ceramic or glass container using a carbon anode the niobium alloys with the cathode metal, from which it is freed by vacuum distillation, and the niobium powder is left behind. 

For the range up to 170 °C, most sensors are based on NTCs. These resistors are made of powder mixtures of metal oxides such as iron, zinc, cobalt, manganese, copper, and nickel. These powder mixtures are formed into discs or wafers and sintered at high temperatures between 1000 and 1400 °C. The cured product is a ceramic material. 

Makovec, D., Drofenik, M., Zthdarsic, A. Hydrothermal synthesis of manganese zinc ferrite powders from oxides. J. Am. Ceram. Soc. 82(5), 1113-1120 (1999)... 

Systems in which two simple oxides react to form a complex oxide are usefiil models for investigating the production of single-phase ceramics by reaction sintering because of the available data on the reaction mechanisms (91) and the relative simplicity of the reactants and product. Two examples are the formation of zinc ferrite by Eq. (11.67) and the formation of zinc aluminate spinel by the reaction between ZnO and AI2O3 powders. 

Ferrite A ceramic material made of powdered and compressed ferric oxide, plus other oxides (mainly cobalt, nickel, zinc, yttrium-iron, and manganese). These materials have low eddy current losses at high frequencies. 

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