Titanium Sponge Testing

Titanium sponge inspection mainly conducts scientific testing and analysis on the main element content of the chemical composition, impurity element analysis, Brinell hardness, particle size distribution and apparent density, appearance quality inspection and special chlorine content determination, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Main element content of the chemical composition: Mainly determines the percentage content of the titanium (Ti) in the titanium sponge, usually required to be not lower than 99.5% (first-grade product). It is the basic indicator for evaluating its purity and grade. At the same time, the accurate determination of the main element content is the key premise for calculating the total amount of the impurities and evaluating the product performance.

Impurity element analysis: Systematically detects the impurity elements with the significant influence on the performance of the titanium alloy, including the gaseous impurities (such as the oxygen, nitrogen and hydrogen), metallic impurities (such as the iron, silicon, chlorine, magnesium, sodium and potassium) and carbon. The contents of these elements directly affect the hardness, ductility and subsequent processing performance of the titanium sponge.

Brinell hardness (HB): The hardness of the titanium sponge is an important comprehensive reflection of its metallurgical quality. The indentation diameter is measured under a certain load with a Brinell hardness tester, and the hardness value is converted. The excessively high hardness usually means that the contents of the interstitial impurity elements such as the oxygen and nitrogen exceed the standards, which will deteriorate its processing plasticity.

Particle size distribution and apparent density: Determines the size distribution, average particle size and the mass per unit volume of the titanium sponge particles. These physical indicators directly affect its filling rate, volatilization behaviour and the stability of the electric arc during the melting process, and are crucial for the efficiency of the subsequent melting and ingot casting and the composition uniformity.

Appearance quality inspection: The appearance of the titanium sponge cake or particles is checked through the visual inspection or auxiliary tools, including whether the colour is uniform (should be silver-grey), whether there are the obvious oxidation colours (yellow or blue), whether there are the non-metallic inclusions, foreign metals or excessive chloride residues. The appearance is the most intuitive preliminary judgement of the product quality.

Special chlorine content determination: As the key process residue of the titanium sponge produced by the Kroll process or Hunter process, the chloride ion (Cl⁻) content must be strictly controlled. The high chlorine content will seriously corrode the subsequent melting equipment and may introduce the impurities. The ion chromatography method or potentiometric titration method is usually adopted for the precise determination.

Testing Scope

Raw materials magnesium and titanium tetrachloride: The two main raw materials for producing the titanium sponge — the metallic magnesium and titanium tetrachloride (TiCl₄) — are strictly tested. The purity and impurities of the magnesium are detected, and the purity, colour and key impurities (such as the chlorides of the vanadium, silicon and iron) of the TiCl₄ are analysed, controlling the final product quality from the source.

Reaction product titanium sponge cake: The overall titanium sponge cake obtained after the reduction-distillation process is comprehensively tested, including the sampling at the different parts (top, middle, bottom and edge) for the chemical composition analysis, to evaluate the uniformity of the whole cake product, and its macroscopic structure is checked.

Finished particles after the crushing and screening: The finished titanium sponge particles classified by the particle size (such as 0.83 mm-12.7 mm or 0.83 mm-25.4 mm) after the crushing and screening are tested. This is the main form of the product ex-factory and trade delivery, and the full-item inspection needs to be carried out by the batch sampling.

Products of the different grades and designations: According to the national standards (such as GB/T 2524) or industry agreements, the titanium sponge is divided into the multiple grades (such as the grade 0, grade 1 and grade 2). The testing scope needs to cover all the designations from the high-end aerospace grade to the general industrial grade, ensuring that they meet the corresponding technical conditions.

Process control samples: The samples are taken and tested at the key links of the production process (such as the middle of the distillation and before and after the crushing), used for the real-time monitoring of the process stability, timely adjustment of the parameters and prevention of the batch quality problems. It belongs to the core scope of the internal quality control of the enterprise.

Import and export trade commodities: In the international trade, as a bulk commodity, the testing of the titanium sponge needs to be carried out according to the standards specified in the contracts (such as ASTM B299 and JIS H 2151). The testing report is the only technical basis for the settlement, claims and quality arbitration, and the testing scope needs to fully cover the contract terms.

Testing Methods

Inert gas fusion infrared/thermal conductivity method: The standard method for precisely determining the contents of the gaseous impurities such as the oxygen, nitrogen and hydrogen in the titanium sponge. The sample is melted in a high-temperature graphite crucible under the inert gas flow, and the released gases are quantitatively analysed by the infrared detector (measuring CO to obtain the oxygen) and thermal conductivity detector (measuring the nitrogen and hydrogen) respectively, with the high sensitivity.

Inductively coupled plasma atomic emission spectrometry method (ICP-OES): The mainstream method for determining the multiple metallic impurity elements (such as the iron, silicon, manganese, magnesium and sodium) in the titanium sponge. The sample is dissolved in the acid to form a solution, and the ICP-OES is used for the simultaneous or sequential determination of the multiple elements, with the advantages of the wide linear range, low detection limits and good precision.

X-ray fluorescence spectrometry method (XRF): A fast and non-destructive screening and quantitative analysis method, commonly used for the rapid analysis of the main component (Ti) and some constant impurity elements (such as the Fe and Cl) in the titanium sponge at the production sites. It is suitable for the process control and the initial inspection of the batch products.

Ion chromatography method (IC): A high-sensitivity method specially used for determining the chloride ion (Cl⁻) content in the titanium sponge. The chlorine in the sample is converted into the water-soluble ions through the specific combustion absorption or high-temperature steam distillation method, and then enters the ion chromatography system for the separation and conductivity detection. The results are accurate and reliable.

Titration analysis method: A classic chemical analysis method, used to determine the contents of the specific elements in the titanium sponge. For example, the ammonium ferric sulfate titration method is adopted to determine the titanium content; the mercury nitrate or silver nitrate potentiometric titration method is adopted to determine the chlorine content. This method has the simple equipment, but the operation is cumbersome and the requirements for the personnel skills are high.

Screening method and tapped density testing: The physical property testing methods. A standard sieve set is used for the mechanical screening of the titanium sponge particles, calculating the mass percentages of the various particle size ranges. The apparent density and tapped density are measured with the funnels and measuring cups of the standard volumes, measuring the mass per unit volume under the specific conditions.

Testing Standards

Domestic Standards:

1. GB/T 2524, Titanium sponge

International Standards:

1. ASTM B299, Standard specification for titanium sponge

2. JIS H 2151, Titanium sponge

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Oxygen-nitrogen-hydrogen analyser: The core gas analysis equipment, usually integrating the inert gas fusion furnace, infrared detection cells and thermal conductivity detector into one instrument. The instrument needs to be equipped with the high-performance graphite crucibles, high-purity carrier gases (helium or argon) and reference materials, used for the calibration and the assurance of the analysis precision. It is the key equipment for judging the grade of the titanium sponge.

Inductively coupled plasma optical emission spectrometer (ICP-OES): Composed of a radio frequency generator, plasma torch, spectroscopic system and detector. When used for the impurity element analysis of the titanium sponge, it needs to be equipped with the hydrofluoric acid-resistant sample introduction system (such as the platinum or PFA materials), and needs to be operated in an ultra-clean laboratory environment to reduce the background interference.

Wavelength dispersive X-ray fluorescence spectrometer (WD-XRF): Used for the rapid composition analysis. The instrument is equipped with the high-power X-ray tubes, analysing crystals and scintillation counters. When analysing the titanium sponge, the pressed tablets with the flat surfaces or the fused glass bead samples need to be prepared, and the targeted calibration curves need to be established to obtain the accurate results.

Ion chromatograph: Composed of an infusion pump, injection valve, guard/analytical columns, suppressor and conductivity detector. When used for the chlorine content detection, the key is to have the efficient pre-treatment equipment (such as the high-temperature hydrolysis device or combustion furnace) to completely convert the chlorine in the sample into the measurable ionic form.

Brinell hardness tester: Used to measure the hardness of the titanium sponge. The equipment includes a loading mechanism, cemented carbide ball indenter of the specified diameter and microscope measuring system. During the testing, a sufficiently large and flat area on the titanium sponge block needs to be selected, the specified load (such as 306.5 N, F=30D²) is applied, and the indentation diameter is measured after the pressure holding.

Standard test sieves and tapped density instrument: The basic physical testing equipment. The standard sieves are made of the metal wire woven mesh, with the aperture ranges from several tens of meshes to several meshes. The tapped density instrument is usually composed of a measuring cylinder, funnel and mechanical vibration device, and through the specified number of vibrations, the particles reach the close packing state, thereby measuring the tapped density.