Tungsten trioxide prepared by nanometer tungsten trioxide by the hydrothermal method and calcination treatment, which is characterized by higher non-symmetry axis and the second symmetry axis, the symmetry plane is more complicated. Monoclinic tungsten trioxide has a strong heterogeneity, which has three principal refractive indexes.

Taking Na₂WO₄·2H₂O as raw materials, DL- malice acid as supplement aid, in this context, which can be synthesized in a three-dimensional spherical shape containing precursor (WO_3·xH₂O). It shows that the addition of malice acid dose of WO_3·xH₂O morphology and crystalline phase having a significant impact. Thus gas test shows that the optimum operating temperature of three samples reaches to 250 ℃, and square-shaped monoclinic tungsten trioxide shows the highest sensitivity, which mainly due to its unique and innovative three-dimensional porous structure. At 300 ℃, the optimum operating temperature is the lowest detectable concentration of material, which can reach 0.1ppm, material optimum calcination temperature is determined at500 ℃,the sensitivity of 5ppm acetone sample gas reaches to 7.9; in the relative humidity conditions , the sensitivity of 5ppm acetone resistance remains 5.72.

In tests of different gases (such as acetone, methanol, ethanol, ammonia, etc.) in the gas sensing of different working conditions, monoclinic tungsten trioxide gas shows high selectivity and sensitivity. Taking Na₂WO₄·2H₂O as raw materials, which are used by Na₂C₂O₄, Na₂SO₄ and H₂C₂O₄ supplement. The hydrothermal conditions keep 24 hours at 180 ℃. Experimental results show that the solution plays the role in Na⁺、SO₄^-、C₂O₂^-、HC₂O₄^-  ions and H₂C₂O₄ nano WO₃ crystal nucleation and growth process. The results show that three different adjuvant does not effect on crystal of product system. Subsequent tests show Na₂WO₄ assisting synthesis of WO₃ nimrods at 320 ℃ for certain have concentrations to gas sensing, which mainly due to its high degree of dispersion and crystalline.

Preparation Process:
Preparing various samples at different sintering temperatures after the samples were prepared, than measuring different sets of samples according to voltammeters, impedance spectroscopy and dielectric spectroscopy curves. We can obtain micron tungsten trioxide nonlinear coefficient polyethylene composite samples by calculating the nonlinear coefficients of main sample data. In the composite sample, the tungsten trioxide particles in the sample content has polyethylene nonlinear coefficients, and the nonlinear coefficient of the sintered samples, sintering the other samples at 250 ℃, up to 98%. When the organic matter content of polyethylene is 80%, the sample becomes an insulator; the prepared tungsten trioxide polyethylene material is more stable.

Sample Analysis
The experimental methods commonly is based on varistor methods, and calculating barrier trends, comparing barrier with nonlinear coefficient, typical sample is made by six-phase morphology in the structural analysis. Comparing samples with nonlinear in the function of the body as well as micro particles and nanoparticles composite sample, which shows the trends of barrier are consistent with nonlinear coefficients.

Test results of morphology and electrical properties show that polyethylene resistance and nonlinear crystal polyethylene material are applied in the electric field of tungsten trioxide samples, which resulting shift toward low-resistance crystalline phase, and it has a close relationship. The results of nonlinear of typical sample with impedance spectroscopy show the bias under the grain boundary resistance are not changed significantly. Resistance is low because their low resistances phase structures that are mainly monoclinic.

3. Use pressure type spray gun to spray ammonia lanthanum acid solution to blue tungsten oxide in the form of atomizing with stirring, then dry to generate blue tungsten oxide doped with ammonia lanthanum acid;
4. Put the blue tungsten oxide into a reduction furnace, and reduced in the high purity hydrogen atmosphere to obtain lanthanum & tungsten alloy powder;
5. Wash the alloy powder with quantitative hydrochloric and hydrofluoric acid, thus to remove the excess dopant and other impurities;
6. Pressed to form tungsten strip with uniform density;
7. Pre-sintering tungsten strip at 1200~400℃ for 30~50 minutes under the protective of hydrogen to obtain the pre-sintered bars;
8. Vertical sintering the pre-sintered bars in the hydrogen atmosphere to get vertical sintered strips, and then hammering the strips to generate tungsten rods;
9. Annealing the tungsten rods;
10. Hammered again to get tungsten rods with diameter 3.7mm;
11. Use big wheel to rough drawing the tungsten rods to obtain coarse tungsten wires;
12. Oxidation annealing the coarse tungsten wires in the air, and coating with graphite, and then stretching by single-mode to eliminate work hardening and reduce the tensile strength of tungsten wires;
Note: Oxidation annealing is to eliminate the innerstress in tungsten wire doped with micro lanthanum, thus to make tungsten wire has good seismic performance.
13. Get the fine tungsten wire doping lanthanum needed.

At present, production of tungsten wire is usually using ammonium paratungstate (APT) as raw material, and tungsten wire used in the bulb almost contained with potassium, aluminum, and silicon. Different impurity elements play their own roles, which are as follows:
1. Potassium (K) will hinder the lateral growth of the crystal and generate the structure of coarse long lap joint, thus significantly reduce the low temperature brittleness and splitting, and then tungsten wire with excellent anti-seismic is obtained.
2 Aluminum (Al) can greatly improve the content of K in the reduction process, thus to obtain high-quality anti-seismic tungsten wire;
3. Silicon (Si) exists at the tungsten powder surface in the form of silicate, thus to keep the sponginess of oxide coating and permeability of water in reducing process, therefore benefit for uniform doping, as well as obtaining K which is necessary.



Lanthanum (La), the number 57 atomic, which the weight of atomic is 138.9055, belongs to the lanthanides, is the most active metal in the rare earth metal. It is easily to oxidized in the air, and can be used in producing alloy, as well as the catalyst. La has two natural isotopes: NO.139 and 138 with radioactivity. A small amount of lanthanum added in tungsten production can change the components and the grain size in doped tungsten wire, thereby improving the physical properties that cold and heating resistance of tungsten wire. A method to produce micro lanthanum doped tungsten wire from ammonium paratungstate is proposed in this paper, the steps show as follows:
1. Ammonium paratungstate (APT) pre-reduced into blue tungsten oxide in the atmosphere of high purity hydrogen in a furnace;
2. Use wet-process and stirring to dope potassium, silicon, aluminum in blue tungsten oxide, then dried to generate doped blue tungsten oxide;

Europium is silver and white metallic element, it is used as color TV phosphors, and europium has important applications in laser materials and atomic energy industry. Europium content in the crust is 0.000106%, it is the rarest of rare earth elements. There are two isotopes of europium in the monazite in nature: Europium Eu 151 and 153. Europium oxide is also used in recent years of new X-ray medical diagnostic system stimulated emission phosphor. Europium oxide can also be used in the manufacture of colored lenses and optical filters for magnetic bubble storage devices. It is used in atomic reactor for neutron absorbing materials because its atoms can absorb more neutrons than any other element. In addition, it can be used as color TV phosphors, which emits bright red phosphor to make television screen.

The preparation method of europium surface-modified tungsten oxide photoelectrode including following steps:
1) The preparation of amorphous tungsten oxide thin film: adding H₂O₂ in Na₂WO₄ solution to obtain clarification W₂0n₂_ containing electrolyte; and Electrodeposition was carried out to obtain an amorphous tungsten trioxide thin film;
2) The dropwise europium surface modification method: the surface of the thin film orphous tungsten oxide europium nitrate was added solution of Step I), drying to obtain surface-modified tungsten oxide europium thin film;
3) Calcining: the Step 2) surface modification europium obtained tungsten oxide thin film in high-temperature about 450 ° C, cooling and taking out at room temperature to obtain surface-modified tungsten trioxide europium photoelectrode. Its photoelectric performance significantly improved, and the test equipment is simple, it has easy operation, mild conditions, and environmentally friendliness.