Preparación y caracterización de un recubrimiento protector autolimpiante de TiO2/caolín

The application of self-cleaning coatings presents one of the most effective ways to protect the surfaces of the building materials. The effect of TiO2/kaolin based coatings applied to three types of substrates: non-porous, porous and highly porous, was investigated. Mechanical activation was applied for the impregnation of the active TiO2 component (in content of 3 and 10 wt. %) into the kaolin support. Surface properties (roughness, hydrophilicity and micro-hardness) and functional properties (photocatalytic activity and self-cleaning efficiency) were studied in order to define the optimal formulation of the applied coatings. The effect of the photocatalytic behavior of the coated substrates in terms of self-cleaning ability was assessed by the photodegradation of Rhodamine B, performed before and after durability tests. The results obtained in this paper showed that photocatalytic activity of the TiO2/kaolin composite coating generally depends on the procedure of TiO2 impregnation into the kaolin clay and the loaded TiO2 content.La aplicación de recubrimientos autolimpiantes presenta una de las maneras más efectivas de proteger las superficies de los materiales de construcción. Se ha investigado el efecto de recubrimientos basados en TiO2/caolín, aplicados sobre tres tipos de sustratos: no poroso, poroso y altamente poroso. Se utilizó activación mecánica para la impregnación del componente de TiO2 activo (en contenido del 3 y 10% en peso) sobre el soporte de caolín. Se han estudiado las propiedades superficiales (rugosidad, hidrofilicidad y microdureza) y las propiedades funcionales (actividad fotocatalítica y eficacia autolimpiante) para definir la formulación óptima de las capas aplicadas. El efecto del comportamiento fotocatalítico de los sustratos revestidos en términos de capacidad de autolimpieza se evaluó mediante la fotodegradación de Rodamina B, realizada antes y después de las pruebas de durabilidad. Los resultados obtenidos en este trabajo mostraron que la actividad fotocatalítica del revestimiento de TiO2/ caolín, dependen en general del procedimiento de impregnación de TiO2 en la capa de caolín y el contenido utilizado de TiO2

Síntesis de un revestimiento nanocompuesto basado en TiO2/ZnAl hidróxidos dobles en capas

The aim of this investigation was the synthesis of nanocomposite coatings based on Zn-Al layered double hydroxides (Zn-Al LDH) and TiO2. The Zn-Al LDH material, which acted as the catalyst support of the active TiO2 component (in the content of 3 and 10 wt. %), was synthesized by a low super saturation co-precipitation method. The interaction between the Zn-Al LDH and the active TiO2 component was accomplished by using vacuum evaporation prior to the mechanical activation and only by mechanical activation. The final suspension based on Zn-Al LDH and 10wt. % TiO2, impregnated only by mechanical activation, showed the optimal characteristics from the aspect of particle size distribution and XRD analysis. These properties had a positive effect on the functional properties of the coatings (photocatalytic activity and self-cleaning efficiency) after the water rinsing procedure.El objetivo de esta investigaci.n fue la preparaci.n de recubrimientos de nanocompuestos basados en Zn-Al hidr.xidos dobles en capas (Zn-Al LDH) y TiO2. El material de LDH Zn-Al, que actuaba como catalizador del componente activo TiO2 (en el contenido de 3 y 10 en peso.%), se sintetiz. por un m.todo de co-precipitaci.n con baja sobresaturaci.n. La interacci.n entre el Zn-Al LDH y el componente activo TiO2 se llev. a cabo mediante el uso de la evaporaci.n al vac.o antes de la activaci.n mec.nica y s.lo por activaci.n mec.nica. La suspensi.n final basada en Zn-Al LDH y 10wt. % TiO2, impregnada solamente por la activaci.n mec.nica, mostr. las caracter.sticas .ptimas desde el aspecto de la distribuci.n de tama.o de part.cula y an.lisis de XRD. Estas propiedades ten.an un efecto positivo sobre las propiedades funcionales de los revestimientos (actividad fotocatal.tica y eficiencia de auto-limpieza) despu.s del procedimiento de aclarado de agua

Uso de cenizas volantes y fosfoyesos en la síntesis de clínkeres belíticos de sulfoaluminatos

Fly ash and phosphogypsum were used as Naturally Occurring Radioactive Materials (NORM) by-products for the synthesis of belite-sulfoaluminate clinkers. The influence of raw mixture composition and firing temperature was investigated. Clinkers and cements were examined by X-ray powder diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The compressive strength of the cements was determined after 28 days. Clinker phases identified included ye’elimite, ß-phase of belite, ternesite and gehlenite, while the main hydration product of the cement pastes was ettringite. The results showed that belite-sulfoaluminate cements can be fabricated with a compressive strength of 45.9 N/mm2 by firing the raw mixture (70 wt.% marl, 10 wt.% bauxite and 20 wt.% phosphogypsum) at a temperature of 1320°C/1h.En este estudio se han utilizado cenizas volantes y fosfoyeso como Naturally Occurring Radioactive Materials (NORM) para la síntesis de clínkeres belíticos de sulfoaluminatos. Se ha investigado la influencia de la composición de la materia prima y de las diferentes temperaturas de cocción. Los clínkeres y cementos se examinaron mediante difracción de rayos X y microscopía electrónica de barrido equipada con espectroscopía de energía dispersiva de rayos X. Los valores de compresión de los cementos se determinaron a la edad de 28 días. Las fases constituyentes de los clínkeres se identificaron como ye’elimita, fase-ß de la belita, ternesita y gehlenita, mientras que el principal producto de hidratación de la pasta de cemento se identificó como ettringita. Los resultados muestran que los cementos belíticos de sulfoaluminatos pueden ser fabricados con una resistencia a compresión de 45.9 N/mm2 mediante una cocción de la materia prima (70 % en peso de marga, 10 % de bauxita y 20 % de fosfoyeso) a una temperatura de 1320°C/1

Strong electrically tunable exciton g-factors in an individual quantum dots due to hole orbital angular momentum quenching

Strong electrically tunable exciton g-factors are observed in individual (Ga)InAs self-assembled quantum dots and the microscopic origin of the effect is explained. Realistic eight band k.p simulations quantitatively account for our observations, simultaneously reproducing the exciton transition energy, DC Stark shift, diamagnetic shift and g-factor tunability for model dots with the measured size and a comparatively low In-composition of x(In)~35% near the dot apex. We show that the observed g-factor tunability is dominated by the hole, the electron contributing only weakly. The electric field induced perturbation of the hole wavefunction is shown to impact upon the g-factor via orbital angular momentum quenching, the change of the In:Ga composition inside the envelope function playing only a minor role. Our results provide design rules for growing self-assembled quantum dots for electrical spin manipulation via electrical g-factor modulation

A Charge and Spin Readout Scheme For Single Self-Assembled Quantum Dots

We propose an all optical spin initialization and readout concept for single self assembled quantum dots and demonstrate its feasibility. Our approach is based on a gateable single dot photodiode structure that can be switched between charge and readout mode. After optical electron generation and storage, we propose to employ a spin-conditional absorption of a circularly polarized light pulse tuned to the single negatively charged exciton transition to convert the spin information of the resident electron to charge occupancy. Switching the device to the charge readout mode then allows us to probe the charge state of the quantum dot (1e, 2e) using non-resonant luminescence. The spin orientation of the resident electron is then reflected by the photoluminescence yield of doubly and singly charged transitions in the quantum dot. To verify the feasibility of this spin readout concept, we have applied time gated photoluminescence to confirm that selective optical charging and efficient non perturbative measurement of the charge state can be performed on the same dot. The results show that, by switching the electric field in the vicinity of the quantum dot, the charging rate can be switched between a regime of efficient electron generation and a readout regime, where the charge occupancy and, therefore, the spin state of the dot can be tested via PL over millisecond timescales, without altering it.Comment: 20 Pages, 6 Figures, submitted to Phys. Rev.

Selective Optical Charge Generation, Storage and Readout in a Single Self Assembled Quantum Dot

We report the investigation of a single quantum dot charge storage device. The device allows selective optical charging of a single dot with electrons, storage of these charges over timescales much longer than microseconds and reliable optical readout of the charge occupancy using a time gated photoluminescence technique. This device enables us to directly investigate the electric field dependent tunneling escape dynamics of electrons at high electric fields over timescales up to 4 us. The results demonstrate that such structures and measurement techniques can be used to investigate charge and spin dynamics in single quantum dots over microsecond timescales.Comment: Accepted for publication in AP

Asymmetric optical nuclear spin pumping in a single uncharged quantum dot

A highly asymmetric dynamic nuclear spin pumping is observed in a single self assembled InGaAs quantum dot subject to resonant optical pumping of the neutral exciton transition leading to a large maximum polarization of 54%. This dynamic nuclear polarization is found to be much stronger following pumping of the higher energy Zeeman state. Time-resolved measurements allow us to directly monitor the buildup of the nuclear spin polarization in real time and to quantitatively study the dynamics of the process. A strong dependence of the observed dynamic nuclear polarization on the applied magnetic field is found, with resonances in the pumping efficiency being observed for particular magnetic fields. We develop a model that fully accounts for the observed behaviour, where the pumping of the nuclear spin system is due to hyperfine-mediated spin flip transitions between the states of the neutral exciton manifold.Comment: published version; 4+ pages, 3 figures (eps

Highly Non-linear Excitonic Zeeman Spin-Splitting in Composition-Engineered Artificial Atoms

Non-linear Zeeman splitting of neutral excitons is observed in composition engineered In(x)Ga(1-x)As self-assembled quantum dots and its microscopic origin is explained. Eight-band k.p simulations, performed using realistic dot parameters extracted from cross-sectional scanning tunneling microscopy, reveal that a quadratic contribution to the Zeeman energy originates from a spin dependent mixing of heavy and light hole orbital states in the dot. The dilute In-composition (x<0.35) and large lateral size (40-50 nm) of the quantum dots investigated is shown to strongly enhance the non-linear excitonic Zeeman gap, providing a blueprint to enhance such magnetic non-linearities via growth engineering

PRODUCTION OF GLASS-CERAMICS FROM WASTE MATERIALS AND OPTIMIZATION OF THE MAIN PROCESS PARAMETERS

In this study the 3D surface model was successfully applied in investigating the influence of the process parameters on the physical and mechanical properties of the glass-ceramics. Glassceramics was produced from coal fly ash and waste glass through the sintering method. The raw material was taken from “REK Bitola”, a thermal power plant in the Republic of Macedonia. Glass-ceramics was obtained through the process of consolidation. Compacts with different ratio of fly ash and waste glass were pressed at 45 MPa, sintered in the temperature interval from 1000 to 11000C, and isothermal time at the final temperature from 1h to 5h. The process of optimization was conducted on the process parameters such as quantity of glass, sintering temperature and isothermal time. According to the results of the process of optimization presented by the software package, a final model equations of the density and bending strength dependence were obtained