Estudio de la anisotropía de la dureza

In the present work a study of the variations in the hardness of the minerals has been made in fonction of the crystallographic direction in which it has been measured. Experimental data has been obtained using a Vickers instru- ment. The minerala choosen for study are cinnabar and enargite

Determinación de la dureza de los minerales mediante la medida de micro-huellas

In the prescnt work the nietliod to deterniine the hardiiess by taking measuretrients at microscopical scale is described. The relationship between the Mohs scale of hardness and the VHN is stablished and also the four types of microscope equipment which are used in this method is described

Closed-cycle gas flow system for cooling of high Tc d.c. SQUID magnetometers

A high Tc.d.c SQUID based magnetometer for magnetocardiography is currently under development at the University of Twente. Since such a magnetometer should be simple to use, the cooling of the system can be realized most practically by means of a cryocooler. A closed-cycle gas flow cooling system incorporating such a cooler has been designed, constructed and tested. The aimed resolution of the magnetometer is 0.1 pT Hz−1/2. The required operating temperature for the SQUIDs is 30 to about 77 K with a stability of 2 × 10−4 K Hz−1/2. After a cool-down time of 1–2 h, a stationary cooling power of at least 0.2 W is required. In the design, helium gas is cooled by a Leybold Heraeus RG 210 cryocooler, transported through a gas line, and subsequently passed through a heat exchanger on which SQUIDs can be installed. The lowest obtainable SQUID heat exchanger temperature is 31 ± 2 K. This can be reached in roughly 2–3 h with an optimal mass flow with respect to the cooling power of 6 × 10−6 kg s−1. At this mass flow the cooling power at the SQUID heat exchanger is 0.2 W at 42 K and roughly 1.2 W at 77 K. A temperature stability of 0.05 K was measured at a SQUID heat exchanger temperature of 54 K and a mass flow of 3 × 10kg s−5. The experience gained with this large cooling system will be used in the design of a smaller configuration cooling system, incorporating miniature Stirling cryocoolers. In this paper the design and the construction of the present closed-cycle system are described and test results are presented.\ud \u

Medida de reflectancia de una superficie pulida: estudio microscópico de minerales opacos

After a short historical introduction, we describe the method to study opaque minerals in reflected light quantitati- ve microscopy. Physical properties are calculated: refractive index and coefficient of absortion, from experimental data. Recommendations of the nomenclature for defining the op- tical properties in absorbent crystals are stablished

Descripción de los equipos microfotométricos de reflexión con incidencia normal

We stablish the necessary working conditions for the equipments used in the quantitative methods of reflected light microscopy. The principal characteristics common to al1 the rnicrophotometric equipments of the most prestige in the world are described

Obtención de las secciones pulidas utilizadas en los métodos cuantitativos

The conditions in what one has to perfom the different processes are described in detail: sowing of the sections, bruting or prepolish, polish and final finish, in order to obtain oriented polished sections, in which measurements of reflectance are. The most suitable abrasives and easily ob- tained are mentioned

Determinación y cálculo de las constantes ópticas en un cristal opaco biáxico: enargita

A partir de los valores de reflectancia para longitudes de onda comprendidas entre 440 nm y 660 nm obtenidos por el método microfotométrico con incidencia normal, ernpleanclo dos medios de índice de refracción conocidos, se han calculado el índice de refracción y el coeficiente de absorción en las tres direcciones principales de vibración de la enargita. Las mediciones se han efectuado en las secciones orientadas(001) y (110) de la enargita. El mineral se ha identificado mediante la difracción de rayos X

Estudio óptico del cinabrio

By means of a microphotometer the principal reflectances at normal incidence have been measured, in air and in oil, on oriented sections (OOOl), (1010) and (1120) of cinnabar. Measurements were made at intervals of 10 nm from 400 nm to 850 nm. From 550 nm a Nicol prism was used as the polariser; as monochromator a glass prism was used. Dispersion curves are given for the reflectances (in air and in oil) and also for the values of the refractive index and the absorption coefficien

Aplicaciones de la medida de reflectancia en la identificación de fases metálicas

The phases alpha and beta of the Cu-Zn alloys have been studied by quantitative methods of microscopy in reflected light. The reflectance curves of dispersión are stablished in both phases, finding the value of reflectance depends on the con- tents in weight of Zn

Determinación y cálculo de las constantes ópticas en un cristal opaco uniáxico: zinkenita

Reflectivity data for zinkenite in air and oil on (0001) and (1010) sections were obtained using microphotometric methods under normal incidente. Measurements were made in mo- nochromatic ligth of wavelengths from 4401 to 660' nm. The sefractive indices, the coefficients of absorption indices in the two principal directions of vibration of the crystal were <calculated. Dispersion curves of al1 optical constants are given. The sample were identified by X-ray diffraction and its chemical composition stablished by X-ray fluorescence analysis