There were days when radium inks (radioactive ink) or asbestos were used by the public. And the danger aspects of them came out later.
Something concerns me. Although thermochromic dye like Leuco dyes are well characterized and safe and these can be found in mugs and dozens of other commercial items.. The transition temperature being 87.8 F or 31 C. These comprise the organic thermochormic dyes. But inorganic dyes are not common. I read that "Inorganic thermochromic materials are the main potential substitutes due to their thermal stability and durability in a wide range of temperatures, such as chromium compounds, mercury compounds, and some other metal halides [8]. However, these compounds are either toxic or carcinogenic in many routes of transmission." (see complete reference below)
Can you give other commercial product where the metal changes color to gray at 400 C? Or is the red bucket I bought like radium ink, an experimental product, Remember these are made in china and unregulated. When the bucket burns with fake money, can the chromium content (or sorta) created fumes that can be toxic or carcinogenic? If there is a possibility. I may just throw it away and get regular bucket without this feature. I need to know.
Reference:
https://www.sciencedirect.com/science/article/abs/pii/S0143720817303042
"Introduction
The concept of “inorganic thermochromism” has been found in solids, liquids, solutions and gases for thousands of years, however, the applications of this phenomenon are limited [1]. Thermochromic materials are important family of colour change materials with potential applications in many fields, such as thermometers for cooking tools and hotplates, temperature sensors, laser marks, and thermal warning signals [2], [3]. Compounds that exhibit thermochromism phenomena are mostly found in conjugated organic molecules due to the feasibility for electron transfer excited by external photons [4], such as in liquid crystals [5], dyes [6], and conjugated polymers [7]. However, these organic molecule based materials could only be used under 400 K (127 °C) due to their poor thermal stability. Inorganic thermochromic materials are the main potential substitutes due to their thermal stability and durability in a wide range of temperatures, such as chromium compounds, mercury compounds, and some other metal halides [8]. However, these compounds are either toxic or carcinogenic in many routes of transmission. Besides, most of inorganic thermocrhomic materials are irreversible due to the partially decomposition or phase transition, such as NH4VO3 and Mn(NH4)P2O7 [9]. For example, Co2+-doped Zn3(PO4)2·4H2O shows a color tuneable change of pink → blue → violet due to the thermal-induced H2O release from the compound [10]. Thus, the synthesis and producing safe inorganic thermochromic pigments with reversible color change dependent on temperature is a pressing need in industry. Until now, reversible inorganic thermochromic materials are still limited to two categories: vanadium dioxide (VO2) [11] and tungsten- or molybdenum-based oxides (AW1−xMoxO4, A = Mg, Co, Ni, Cu, or Zn) [12], [13]. SrMnO3 also showed thermochromic behaviour at liquid nitrogen temperature due to the structural distortion of corner-sharing Mn2O9 units [14]. There are two mechanisms for reversible inorganic thermochromic materials: first order phase transition (e.g. vanadium oxides [11]) and charge transfer due to the bond change of ligands and center metal cations (e.g. tungsten and manganite oxides [12], [13], [14]). The ligand field around the chromophore or the crystallographic phase transition occurs in reversible thermochromism in oxides, which gradually reduced the band-gap with increasing temperature."
