Influences of High Calcination Temperature on Densification and Magnetic Properties of Low-Temperature-Fired NiCuZn Ferrites
Traditional low-temperature-fired NiCuZn ferrites (900 °C sintered) were generally prepared at relatively low calcination temperatures to increase the activity of the calcined powders and promote sintering. However, in this study, we changed the calcination temperature from 700 °C to 1000 °C to investigate the influences of high calcination temperature on the densification characteristic and magnetic properties of the low-temperature-fired NiCuZn ferrites. It was found that although a high calcination temperature decreased the activity of the calcined powder, the NiCuZn ferrite could attain a higher sintered density with an adequate sintering aid. Furthermore, a uniform microstructure with small average grain size was obtained for the sample calcined at 1000 °C with 1 wt% Bi2O3 sintering aid. It also displayed high performances on Q-factor and permeability. Hence, choosing a high calcination temperature and adding more sintering aid was also an option for obtaining high performance and low-temperature-fired NiCuZn ferrites.
Effects of  ${\hbox {Nb}}_{2}{\hbox {O}}_{5}$ on DC-Bias-Superposition Characteristic of the Low-Temperature-Fired NiCuZn Ferrites
The influences of Nb2O5 addition on the microstructure and magnetic properties, especially DC-bias-superposition characteristic of the low-temperature-fired NiCuZn ferrites, were investigated. It was found that Nb ions entered into the lattice when Nb2O5 content was less than 0.3 wt%, after that, a second phase, bismuth iron (zinc or nickel) niobium oxide appeared. The second phase consumed some sintering aid Bi2O3 and had obvious influences on sintered density, grain size and magnetic properties, such as permeability of the ferrites. All of the sintered density, saturation magnetic flux density and average grain size gradually decreased with Nb2O5 content. Initial permeability first increased, and then continuously decreased with Nb2O5 content. The sample with 0.1 wt% Nb2O5 displayed the highest initial permeability, which was mainly due to the decrease of magnetocrystalline anisotropy constant. Under relatively low superposition magnetic field H ≤ 375 A/m, a higher initial permeability favored to obtain a higher incremental permeability. However, when the superposition magnetic field continued to increase, some samples with a lower initial permeability displayed a higher incremental permeability. The normalized incremental permeability was mainly determined by the coercivity of the samples. A higher coercivity favored the attainment of a better DC-bias-superposition characteristic on normalized permeability. So the sample with 0.5 wt% Nb2O5, which displayed the largest coercivity, had the best performance. Possible mechanisms contributing to the above results were discussed in detail.
Rethinking Health: Healthy or Healthier than?
Theorists of health have, to this point, focused exclusively on trying to define a state—health—that an organism might be in. I argue that they have overlooked the possibility of a comparativist theory of health, which would begin by defining a relation—healthier than—that holds between two organisms or two possible states of the same organism. I show that a comparativist approach to health has a number of attractive features, and has important implications for philosophers of medicine, bioethicists, health economists, and policy makers. 1 Introduction 2 Comparative and Non-comparative Concepts 3 Traditional Theories of Health 4 An Argument for Comparativism: Intergenerational Assessments of Health 5 Another Reason to be a Comparativist: Functionalist Theories of Health 6 A Non-comparative Alternative? 7 An Objection to Comparativism? 8 Why this Matters: The Consequences of Comparativism 1 Introduction 2 Comparative and Non-comparative Concepts 3 Traditional Theories of Health 4 An Argument for Comparativism: Intergenerational Assessments of Health 5 Another Reason to be a Comparativist: Functionalist Theories of Health 6 A Non-comparative Alternative? 7 An Objection to Comparativism? 8 Why this Matters: The Consequences of Comparativism