Synthesis of nanostructured zinc silicate from renewable sources

Abstract

A method of making Nanostructured Zinc Silicate from renewable sources comprising preparing powders of husks, preparing powders of ZnO, mixing the powders of husks and the powders of ZnO and forming a homogenous sample powder, pressing the homogenous sample and forming pellets, heating the pellets and forming nanostructured zinc silicate. The nanostructured zinc silicate from renewable sources product of the process of preparing powders of husks, preparing powders of ZnO, mixing the powders of husks and the powders of ZnO and forming a homogenous sample powder, pressing the homogenous sample and forming pellets, heating the pellets and forming nanostructured zinc silicate.

Claims

1. A method of making Nanostructured Zinc Silicate from renewable sources comprising: preparing powders of husks wherein the husks are selected from the group consisting of wheat husk, rice husk, and a combination of wheat husk and rice husk using ball milling including stainless steel milling media; preparing powders of ZnO using ball milling including stainless steel milling media; mixing the powders of husks and the powders of ZnO using ball milling including stainless steel milling media and thereby forming a homogenous sample powder; pressing the homogenous sample powder into disks having a diameter of 1 cm and thickness of 2-3 mm and forming pellets; heating the pellets at a temperature above 1400 C. and forming nanostructured zinc silicate pellets of 50-100 nm; and removing excess carbon by processing the nanostructured zinc silicate pellets in air at a temperature of 650 C.

2. The method of making Nanostructured Zinc Silicate from renewable sources of claim 1 further comprising the steps of washing the husks in distilled water prior to the step of preparing powders of husks wherein the husks are selected from the group consisting of wheat husk, rice husk, and a combination of wheat husk and rice husk using ball milling including stainless steel milling media and utilizing a hydraulic press for the step of pressing the homogenous sample powder into disks.

3. The method of making Nanostructured Zinc Silicate from renewable sources of claim 1 wherein the step of heating the pellets at a temperature above 1400 C. and forming nanostructured zinc silicate pellets of 50-100 nm comprises heat treating in a furnace at temperatures above 1400 C. in an argon atmosphere.

4. The method of making Nanostructured Zinc Silicate from renewable sources of claim 1 wherein the step of heating the pellets at a temperature above 1400 C. and forming nanostructured zinc silicate pellets of 50-100 nm comprises heat treating in a furnace at temperatures above 1400 C. in an argon atmosphere for a period of 2-4 hours.

5. The method of making Nanostructured Zinc Silicate from renewable sources of claim 1 wherein the step of heating the pellets at a temperature above 1400 C. and forming nanostructured zinc silicate pellets comprises temperatures between 1400-1500 C. and comprises an argon atmosphere and using a tube furnace.

6. The method of making Nanostructured Zinc Silicate from renewable sources of claim 1 wherein the step of preparing powders of husks wherein the husks are selected from the group consisting of wheat husk, rice husk, and a combination of wheat husk and rice husk using ball milling including stainless steel milling media comprises 1.54 grams of wheat husk; wherein the step of preparing powders of ZnO using ball milling including stainless steel milling media comprises 0.242 grams of ZnO; and wherein the steps of heating the pellets at a temperature above 1400 C. and forming nanostructured zinc silicate pellets of 50-100 nm comprises forming pellets of 1 gram of homogenous nanostructured Zn.sub.2SiO.sub.4.

7. The method of making Nanostructured Zinc Silicate from renewable sources of claim 1 wherein the step of preparing powders of husks wherein the husks are selected from the group consisting of wheat husk, rice husk, and a combination of wheat husk and rice husk using ball milling including stainless steel milling media comprises 1.54 grams of rice husk; wherein the step of preparing powders of ZnO using ball milling including stainless steel milling media comprises 0.20 grams of ZnO; and wherein the steps of heating the pellets at a temperature above 1400 C. and forming nanostructured zinc silicate pellets of 50-100 nm comprises forming pellets of 1 gram of homogenous nanostructured Zn.sub.2SiO.sub.4.

Description

DESCRIPTION OF THE DRAWINGS

(1) The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrated examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure will be set forth in the following detailed description when considered in conjunction with the drawings.

(2) FIG. 1 illustrates an overlay of X-ray diffraction patterns taken with CuK radiation of as-received wheat husk plus zinc oxide (lower half) and the processed sample showing the diffraction pattern of Zn.sub.2SiO.sub.4 (upper half).

(3) FIG. 2 illustrates X-Ray excited optical spectra of the Zn.sub.2SiO.sub.4 synthesized from wheat husk showing green light emission of 532 nm.

(4) FIG. 3 illustrates room temperature Raman spectra of one RH sample and two WH samples acquired with the 488 nm laser line. Despite the large luminescence background, sharp lines associated to optical phonon modes are observed. Only the phonon lines at 475 and 872 cm.sup.1 are not associated with ZnO nanocrystals.

(5) FIG. 4 illustrates Rietveld Analysis (Phase Purity Observation) Intensity vs. Degrees.

(6) FIG. 5 illustrates room temperature Photo Luminescence spectrum of the Rice Husk sample after thermal treatment, acquired with 10 sec integration time.

(7) FIG. 6 illustrates TEM micrographs of Zn.sub.2SiO.sub.4 samples derived from wheat husks and rice husks showing nanoparticles of 50-100 nm.

DETAILED DESCRIPTION OF THE INVENTION

(8) This invention concerns a new method for the formation of abundant quantities of Zinc Silicate from a thermal treatment of a mixture of aluminum oxide zinc oxide and rice or wheat husks in an argon atmosphere at temperatures in excess of 1450 C.

(9) Here, the inventors discovered the formation of pure Zn.sub.2SiO.sub.4 by carbothermal reduction of ZnO with rice and wheat husks in the presence of an Ar atmosphere to produce nano-tubes and nanoparticles in a graphite boat then purified in an O.sub.2 atmosphere in an Al.sub.2O.sub.3 crucible.

(10) No additives/dopants were added to enhance the scintillating properties. The product was naturally scintillating.

Example 1

(11) It was determined that the presence of crystalline phases of SiO.sub.2 was found to have a weight percentage of 16% for the rice husk and 14% for the wheat husks. The appropriate ratios were weighed out and the ZnO and wheat or rice husks mixtures were thoroughly mixed and pulverized using ball milling which produced a very homogenous fine powder.

(12) The fine powder was pressed into disks having diameter of 1 cms and 2-3 mm thickness using the hydraulic press.

(13) The pellets were heat treated in a conventional furnace at temperatures above 1400 C. in an argon atmosphere for a period of 2-4 hours and subsequently treated in air at 650 C. to remove the excess carbon.

Example 2

(14) Samples were made from raw wheat and rice husks after thoroughly washing in distilled water and mixed with ZnO powder in the appropriate weight ratios to produce 1 gm of zinc silicate.

(15) By weighing the wheat and rice samples before and after heat treatment in air and using x-ray diffraction scans, the presence of crystalline phases of SiO.sub.2 was found to have a weight percentage of 16% for the rice husk and 14% for the wheat husks.

(16) It took 0.242 gm of ZnO and 1.54 gms of wheat husk to produce 1 gram of Zn.sub.2SiO.sub.4, whereas it took only 0.20 grams of ZnO and 1.54 grams of rice husks to produce 1 gram of Zn.sub.2SiO.sub.4.

Example 3

(17) The ZnO and wheat or rice husks mixtures were thoroughly mixed and pulverized using ball milling which produced a very homogenous fine powder.

(18) The fine powder was pressed into disks having diameter of 1 cms and 2-3 mm thickness using the hydraulic press.

(19) The pellets were heat treated in conventional furnace at temperatures above 1400 C. in an argon atmosphere for a period of 2-4 hours and subsequently treated in air at 650 C. to remove the excess carbon.

(20) The mixed samples were then pulverized into powder using a SPEX 8000M high energy mill with stainless steel milling media.

(21) Pellet samples of 1 cm diameter were prepared again from the reaction product.

Example 4

(22) The samples in the form of pellets were heated in an argon atmosphere using a conventional tube furnace to a temperature between 1400-1500 C.

(23) The processed samples were characterized using x-ray diffraction, Raman scattering and photoluminescence spectroscopy, and electron microscopy techniques.

(24) X-ray diffraction profiles were collected using a Rigaku 18 kW generator and a high resolution powder diffractometer. Monochromatic CuK radiation was used for all x-ray diffraction scans.

Example 5

(25) Optical emission spectra were collected during X-ray irradiation using a USB2000 Ocean Optics spectrometer equipped with a fiber optic probe with a 1000 m core. The fiber optic probe was positioned perpendicularly 2 mm from the sample surface while the X-ray incident angle was 45 degrees.

Example 6

(26) For TEM analysis, the pyrolyzed sample was added to ethyl alcohol and the mixture was placed in the ultrasonic cleaner for a period of time. A carbon coated 200 mesh copper grid was immersed in the mixture to pick up the Zn.sub.2SiO.sub.4 powder samples. The specimens were examined in a FEI Tecnai G2 TEM operated at 300 kV.

(27) A home-built confocal micro-Raman spectrometer, comprised of a single-mode 488 nm and 532 nm lasers, a half meter Acton spectrometer with an 1800 groove/mm holographic grating, and a Princeton Instruments back-thinned, deep depleted, Nitrogen cooled CCD (1340400 pixel array) was employed to verify the samples structural and composition properties. The spectral resolution of this configuration of the system is 2.5 cm.sup.1, and the repeatability with which a line position can be determined is within 0.1 cm.sup.1. Neutral density filters were employed to control the laser power. Samples were mounted on a precision, computer-controlled Aerotech XYZ translator having a bi-directional position accuracy of better than 0.1 m. Raman spectra and the incident and reflected laser power were measured and stored for each position in each spatial map.

(28) The room temperature PL spectra were acquired with a small UV-enhanced CCD fiber optical spectrometer covering the UV-NIR spectral region. The samples were excited with the 325 nm line of a HeCd laser, and low power density (only 64 mW/cm.sup.2) was employed to prevent sample heating and luminescence bleaching and/or saturation. Real color and monochromatic luminescence imaging of the samples, under 325 nm laser line excitation, were acquired with a home built luminescence imaging set up.

(29) There are many advantages with the current invention.

(30) These include No additives/dopants are added to enhance the scintillating properties and the product is naturally scintillating, unlike conventional methods of producing zinc silicate.

(31) This process can also be used to make other silicates that can be used for scintillators and other detectors.

(32) This invention will serve to protect Navy vessels operating in salt water due to its anticorrosion properties. The Navy can reduce costs by using this invention to create low-cost high value zinc silicate.

(33) Scintillators are used by DHS radiation detectors. Scintillators can also be used in particle detectors, new energy resource exploration, X-ray security, nuclear cameras, computed tomography and gas exploration. Other applications of scintillators include CT scanners and gamma cameras in medical diagnostics, and screens in older style CRT computer monitors and television sets.

(34) This invention described here is a single step process without any additives to enhance scintillating properties.

(35) This invention pushes the Navy to more environmentally greener processes.

(36) This new process should become the standard processing route for Zinc Silicate.

(37) The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In addition, although a particular feature of the disclosure may have been illustrated and/or described with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms including, includes, having, has, with, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term comprising.